Songfeng
Liang
and
Xiaoyu
Wu
*
School of Automobile and Transportation, Shenzhen Polytechnic University, Shenzhen 518055, China. E-mail: wuxiaoyu@szpu.edu.cn
First published on 1st July 2025
Solid-state batteries (SSBs) are considered the core of the next generation of energy storage technology due to their high safety and energy density. However, the commercialization of SSBs still faces challenges such as low ionic conductivity of solid electrolytes, poor electrode/electrolyte interface stability, and high material cost. In recent years, biomass-derived materials have attracted much attention for use in the key components of SSBs such as electrolytes and electrodes due to their renewability, low cost and unique chemical structure. In this paper, the latest research progress of biomass-derived materials in SSBs is systematically reviewed, focusing on their component and structural design, performance optimization mechanism and scale application potential, and the future development direction is proposed.
Solid-state batteries (SSBs), as a revolutionary battery technology, are considered a key breakthrough to address these challenges.7 By using solid-state electrolytes instead of traditional liquid electrolytes, SSBs fundamentally solve safety issues related to flammability, volatility, and leakage, significantly improving battery safety.8–10 They also offer higher energy density, allowing compatibility with high-capacity electrode materials like lithium metal anodes and silicon anodes, which can substantially extend the battery range and meet the urgent demand for long-range capabilities in electric vehicles.11 Moreover, SSBs exhibit superior cycle stability and broader operating temperature ranges, maintaining reliable performance even in extreme environments.12 Despite these advantages, the commercialization of SSBs still faces several challenges. Solid-state electrolytes generally have lower ionic conductivity, especially at room temperature, which hinders fast charging and discharging. Poor interfacial compatibility between electrodes and solid-state electrolytes leads to high interfacial impedance, degrading battery performance.13 Additionally, the high manufacturing costs of SSBs limit their large-scale adoption.14 Therefore, developing high-performance, low-cost solid-state electrolytes and improving electrode–electrolyte interfacial properties are crucial for advancing SSB technology.
Biomass-derived materials, sourced from renewable biological resources such as plants, animals, and microorganisms, are abundant, renewable, environmentally friendly, biodegradable, and low-cost.15–18 These materials are rich in functional groups (e.g., hydroxyl, amino, and carboxyl groups), which can interact with metal ions to enhance ionic conductivity.19,20 They also have excellent mechanical properties, biocompatibility, and processability. Their utilization in SSBs not only provides a new way to address the issues of resource shortage and environmental pollution, but also has the potential to reduce the production cost of batteries, which is conducive to the large-scale application and popularization of SSBs.21 For example, some biomass-derived materials can be used as solid-state electrolytes or electrolyte additives to improve the ionic transport efficiency of SSBs;22–26 some can enhance the structural stability of the electrodes in SSBs and improve the interfacial compatibility between the electrodes and the electrolyte, thereby enhancing the overall performance of the battery.27Table 1 compares the performance and properties of typical biomass materials with conventional solid-state electrolytes, which shows that biomass materials are not inferior to conventional materials in core performance metrics such as ionic conductivity, while additionally possessing unique advantages of ultra-low cost, environmental degradability, and renewability.
Types | Materials | Ionic conductivity (S cm−1) | Mechanical strength (MPa) | Cycle life and durability | Cost | Biodegradability and renewability | Ref. |
---|---|---|---|---|---|---|---|
Biomass | Cellulose-based electrolyte | 1.09 × 10−3 | 12 | >1000 cycles | <$10 per kg | Completely | 28 |
Conventional materials | Polymer electrolyte (PEO, PBO) | 10−4 (60 °C) | 0.1–74.4 (PEO: 5.3) | 1200–1600 cycles | <$100 per kWh, PEO ∼$50 per kg | Partly | 29 and 30 |
Oxide electrolyte (LATP, LLZO) | 10−4 | 5–15 | ≤500 cycles | ∼$300–600 per kg | No | 31 | |
Sulfide electrolyte (Li2S, Li6PS5Cl) | 10−3–10−2 | 50–100 | >2500 cycles | ∼$800 per kg | No | 32 |
Researching biomass-derived materials in the field of SSBs can provide new material options and solutions for breakthroughs in SSB technology, promote the sustainable development of the new energy industry, and facilitate the efficient utilization of biomass resources, achieving resource recycling and environmental protection, which has important research significance and broad application prospects. Despite the proliferation of review articles addressing biomass materials in electrochemical energy storage systems, comprehensive analyses focusing specifically on their applications in SSBs remain conspicuously scarce. This review specifically addresses this research gap by methodically examining recent advancements in biomass-derived materials for SSB technologies. By systematically categorizing and critically evaluating pertinent scientific literature, the work provides an in-depth assessment of the types, characteristics, and application scenarios of biomass-derived materials in SSBs. Furthermore, the analysis elucidates fundamental mechanisms through which these sustainable materials enhance ionic conductivity, interfacial stability, and electrochemical performance in solid-state systems. These insights establish critical theoretical frameworks to guide future innovations in eco-friendly energy storage technologies.
In detail, cathode materials are important components for storing lithium ions in SSBs, and their performance directly affects key performance indicators of the battery, such as energy density, charge–discharge voltage, and cycle life. Common cathode materials for SSBs include transition metal oxides (such as lithium cobalt oxide (LiCoO2 or LCO), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), and ternary composite materials such as LiNixCoyMn1−x−yO2 (NCM) and LiNixCoyAl1−x−yO2 (NCA), etc.), polyanionic compounds (such as lithium iron phosphate (LiFePO4 or LFP), lithium vanadium phosphate (Li3V2(PO4)3), etc.), and lithium-rich manganese-based materials.7 In addition to these lithium-metal oxides, lithium-based sulfides such as Li2S and Li3PS4 have also been used as cathode alternatives for high-performance SSBs.7 Spinel oxides like LiMn2O4 (LMO) also serve as a complementary option for cathode materials. Different cathode materials have different crystal structures and electrochemical properties. For example, LCO has a high theoretical specific capacity and operating voltage, but it has a high cost and limited resources; LFP has good safety, cycle stability, and a low cost, but its energy density is relatively low. It should be noted that cathode materials in SSBs need to have good compatibility with solid-state electrolytes to ensure the rapid transmission of lithium ions at the interface and reduce the interfacial impedance.
Anode materials also undertake the important function of storing and releasing lithium ions. The main anode material of traditional LIBs is graphite, which has advantages such as low cost and good cycle performance, but its theoretical specific capacity is relatively low (about 372 mAh g−1), making it difficult to meet the requirements of future high-energy-density batteries. In order to increase the energy density of the battery, some new anode materials, such as silicon-based materials, lithium metal, and tin-based materials, have been gradually introduced in SSBs. Silicon-based materials have an extremely high theoretical specific capacity (up to 4200 mAh g−1), but they will undergo huge volume changes (up to 300%) during the charging and discharging processes, resulting in material pulverization and electrode structure damage, thus affecting the cycle life of the battery.34,35 Lithium metal has an extremely high theoretical specific capacity (3860 mAh g−1) and the lowest electrochemical potential (−3.04 V relative to the standard hydrogen electrode) and is one of the most promising anode materials.36,37 Besides, anode materials that alloy with lithium, such as silicon, tin, and aluminum, offer high capacity that can yield high-energy battery cells. The use of alloy anodes in SSBs potentially offers major mechanistic benefits compared to other anode contenders and battery systems, such as lithium metal in solid-state architectures or alloys in liquid-electrolyte batteries.38 However, during the charging and discharging processes, it is easy to form lithium dendrites that can pierce the separator and cause safety problems such as short-circuits. Therefore, developing technologies and methods to inhibit the growth of lithium dendrites and improve the stability of silicon-based materials and finding a suitable matching system of anode materials and solid-state electrolytes are among the current research focuses of SSBs.
Solid-state electrolytes are the core components of SSBs.39 They not only play a role in conducting lithium ions but also separate the positive and anodes to prevent direct electron conduction and avoid internal short-circuits of the battery. High ionic conductivity in electrolytes is crucial for achieving effective charge-transfer reactions in SSBs.13,14 Compared with traditional liquid electrolytes, solid-state electrolytes have advantages such as non-flammability, no risk of liquid leakage, and good thermal stability, which can significantly improve the safety of the battery. Solid-state electrolytes mainly include three categories: polymer solid-state electrolytes, inorganic solid-state electrolytes, and composite solid-state electrolytes.10 Polymer solid-state electrolytes are usually composed of a polymer matrix (such as polyethylene oxide (PEO), polyacrylonitrile (PAN), etc.) and lithium salts.40,41 They have good flexibility and processability, but their room-temperature ionic conductivity is relatively low, generally in the range of 10−6–10−4 S cm−1. Inorganic solid-state electrolytes can be further divided into oxide solid-state electrolytes (such as garnet-type Li7La3Zr2O12 (LLZO), NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATO), etc.) and sulfide solid-state electrolytes (such as Li10GeP2S12, Li6PS5Cl, etc.).39,42,43 They have high ionic conductivity, and the room-temperature ionic conductivity of some sulfide solid-state electrolytes can reach more than 10−3 S cm−1, but they have problems such as complex preparation processes and poor interfacial compatibility with electrodes. Composite solid-state electrolytes combine the advantages of polymers and inorganic materials.44,45 By adding inorganic fillers to the polymer matrix or introducing a polymer phase into the inorganic solid-state electrolyte, the ionic conductivity, mechanical properties, and interfacial compatibility can be improved.
The function of current collectors is to collect and conduct electrons, transfer the electrons generated by the electrode materials to the external circuit, or receive electrons from the external circuit and transfer them to the electrode materials. For the cathode current collector, aluminum foil is usually used because aluminum has good chemical stability at high potentials and is not easily oxidized. The anode current collector generally uses copper foil. Copper has good electrical conductivity and a low potential and will not react chemically with the anode materials. The electrical conductivity, thickness, and mechanical properties of the current collector will all affect the performance of the battery. Besides, since the solid-state electrolyte itself has the function of separating the cathode and anode, the role of the separator in conventional batteries is relatively weakened and can even be omitted.7 However, for some composite SSB systems, the separator is still a necessary component to further improve the safety and stability of the battery.46
The working principle of SSBs is similar to that of traditional LIBs; it involves the reversible insertion and extraction of lithium ions between the cathodes and anodes to achieve the mutual conversion of electrical energy and chemical energy. During the charging process, an external power source supplies energy to the battery. Lithium ions in the positive electrode material are extracted from the crystal lattice and migrate to the anode through the solid-state electrolyte. At the same time, electrons flow from the positive electrode to the anode through the external circuit to maintain charge balance. On the surface of the anode, lithium ions combine with electrons and are inserted into the crystal lattice of the anode material, realizing the storage of chemical energy. During the discharging process, the battery acts as a power source to output electrical energy. Lithium ions in the anode are extracted from the crystal lattice, migrate to the positive electrode through the solid-state electrolyte, and electrons flow from the anode to the positive electrode through the external circuit. On the surface of the positive electrode, they combine with lithium ions and are re-inserted into the crystal lattice of the cathode material. At this time, chemical energy is converted into electrical energy to power external devices. Accommodation of lithium in the host structure needs to be without restrictive forces; therefore it demands anode and cathode materials to be chosen correspondingly. The anode and cathode's Fermi potential difference determines the cell voltage and the number of Li ions that enter the electrodes increases the current delivered.33 Throughout the charging and discharging processes, the solid-state electrolyte plays a crucial role in conducting lithium ions, and its ionic conductivity and stability directly affect the performance of the battery. Different from traditional liquid LIBs, the solid-state electrolyte in SSBs has no fluidity, and the transmission mechanism of lithium ions in it mainly occurs through methods such as vacancy diffusion and interstitial diffusion in the crystal lattice.47 This transmission method gives SSBs potential advantages in terms of safety and energy density, which will be discussed in detail below.
Compared with traditional liquid LIBs, SSBs exhibit significant performance advantages in terms of energy density, safety, cycle life, and operating temperature range, making them an important direction for the future development of battery technology. Importantly, SSBs have the potential to achieve higher energy density.7,11 On the one hand, solid-state electrolytes can be adapted to high-capacity electrode materials, such as lithium-metal anodes and silicon-based anodes. For example, lithium-metal anodes have an extremely high theoretical specific capacity and the lowest electrochemical potential as mentioned before. Using lithium-metal anodes can significantly increase the energy density of the battery. However, in traditional liquid LIBs, lithium-metal anodes will react violently with the liquid electrolyte, and lithium dendrites are easily formed during the charging and discharging processes, leading to battery short-circuits and safety hazards. The use of solid-state electrolytes can effectively inhibit the growth of lithium dendrites and improve the stability of lithium-metal anodes, thus realizing a high-energy-density battery system. On the other hand, solid-state electrolytes usually have a high electrochemical window and can be matched with high-voltage positive-electrode materials to further enhance the energy density of the battery. Typically, the electrochemical window of some oxide solid-state electrolytes can reach more than 5 V, which makes it possible to use high-voltage cathode materials (such as high-nickel ternary materials, lithium-rich manganese-based materials, etc.), thereby increasing the output voltage and energy density of the battery.
The organic liquid electrolytes used in traditional liquid LIBs are flammable. In case of battery overheating, overcharging, short-circuits, etc., the electrolyte is likely to catch fire or even explode, posing serious safety hazards. SSBs use solid-state electrolytes instead of liquid electrolytes, fundamentally solving problems such as flammability, volatility, and liquid leakage of the electrolyte.11 Solid-state electrolytes usually have good thermal stability and chemical stability and are not easy to decompose and react under extreme conditions such as high temperature and high pressure, which can effectively prevent the occurrence of battery thermal runaway. In addition, solid-state electrolytes can also inhibit the growth of lithium dendrites, reduce the risk of short-circuits caused by lithium dendrites piercing the separator, and further improve the safety of the battery.48 SSBs also perform well in terms of cycle life. Due to the good interfacial stability between the solid-state electrolyte and the electrode materials, during the charging and discharging processes, the increase in interfacial impedance is relatively slow, which can effectively reduce the capacity fade of the battery. At the same time, the solid-state electrolyte can inhibit the volume change of the electrode materials, reduce material pulverization and structural damage, and thus extend the cycle life of the battery. For example, for silicon-based anode materials, huge volume expansion and contraction will occur during the charging and discharging processes, leading to electrode structure damage and a short cycle life. In SSBs, the solid-state electrolyte can play a certain restrictive role in the silicon-based anode, relieve its volume change, and improve the stability of the electrode, thereby extending the cycle life of the battery.34 Additionally, SSBs have a wider operating temperature range and can maintain good performance under extreme temperature conditions. Traditional liquid LIBs face increased electrolyte viscosity and decreased ion diffusion at low temperatures, leading to higher internal resistance and significant performance loss during charging/discharging. On the other hand, at high temperatures, liquid electrolytes are prone to volatilization and decomposition, accelerating battery aging and capacity degradation. In contrast, the physical and chemical properties of solid-state electrolytes are relatively stable and are less affected by temperature.12,49,50 This makes SSBs have broader application prospects in fields with high requirements for the operating temperature range, such as aerospace and electric vehicles.
Despite these advantages, the development of SSBs also faces some challenges. The interface impedance between the solid-state electrolyte and the electrode material is one of the key factors restricting the performance improvement of SSBs.8,13,33 Due to the large differences in physical and chemical properties between the solid-state electrolyte and the electrode material, a large impedance is easily formed at the interface, hindering the transmission of lithium ions and thus affecting the battery's charge–discharge performance. In addition, the manufacturing process of SSBs is complex, and the production cost is high, which also limits their large-scale commercial application.14,51 Currently, the preparation of SSBs requires high-precision equipment and complex processes, resulting in a much higher production cost compared to that of traditional liquid LIBs. Therefore, reducing the manufacturing cost of SSBs and improving their production efficiency are important tasks to promote the commercialization of SSBs.
Chitin and chitosan are other important animal-based materials. Chitin is the second-most abundant polysaccharide in nature after cellulose and is mainly found in the exoskeletons of crustaceans (such as crabs and shrimps) and the cell walls of fungi.78 Chitosan is a deacetylated derivative of chitin. Both chitin and chitosan have unique properties, such as antibacterial activity and good film-forming ability.79 In SSBs, they can be used in the modification of electrode surfaces to improve the interface stability between the electrode and the electrolyte. Furthermore, as typical animal-based waste, eggshells are mainly composed of calcium carbonate, with a small amount of proteins and organic matter.80 Eggshell powder can be used as a calcium source additive in the feed and food industries, and to prepare adsorbents and catalyst carriers after high-temperature calcination. Livestock and poultry manure contains a large amount of organic matter and microorganisms. Through specific treatment processes, the organic matter in livestock and poultry manure can also be converted into biomass-based materials.81
Some biomass-derived materials, especially those obtained through pyrolysis or other thermal-chemical treatments, often have high porosity and large surface areas. Typically, bio-carbon materials derived from biomass sources like wood or agricultural waste always exhibit a hierarchical porous structure. This porous structure can increase the contact area between the electrode materials and the electrolyte of SSBs, facilitating the diffusion of ions during the charging and discharging processes. The large surface area can provide more active sites for electrochemical reactions, enhancing the battery's capacity and rate performance. Moreover, the porosity can also buffer the volume changes of the electrode materials during cycling, improving the cycle stability of the battery. Besides, certain biomass-derived polymers, such as some types of cellulose-based materials and silk fibroin, possess both flexibility and good mechanical strength. These properties are highly desirable for the development of flexible SSBs, which are experiencing an increasing demand in the fields of wearable devices and flexible electronics. Exceptional biocompatibility is another important property of biomass-derived materials owing to their natural origin and non-cytotoxic properties. This trait is critical for integrating SSBs into biomedical implants or wearable electronics, where direct interaction with biological tissues necessitates minimal immune response. The inherent tissue compatibility of these materials ensures safe, reliable operation of SSBs in physiological environments, eliminating risks of inflammation or rejection while enabling long-term functional stability in human-centric applications.
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Fig. 4 Cellulose-derived solid-state electrolytes. (a) Self-standing, transparent, flexible, and twistable solid polymer electrolyte membranes. Reprinted with permission from ref. 88. Copyright 2021 American Chemical Society. (b) Schematic illustration of the fabrication procedure of a cellulose-based eutectogel with flame resistance. Reprinted with permission from ref. 90. Copyright © 2024 Elsevier. (c) Preparation of electrolyte films from cellulose derivatives derived from cotton and sugarcane. Reprinted with permission from ref. 23. Copyright © 2022 Elsevier. (d) SEM images of bacterial cellulose (BC), grafted bacterial cellulose (BCD), and PPy@BCD membranes. Reprinted with permission from ref. 91. Copyright © 2024 Elsevier. (e) Performance including stress–strain curves, ionic conductivity and lithium transference number of bacterial cellulose supported LAGP. Reprinted with permission from ref. 92. Copyright © 2023 Elsevier. |
Cellulose-based solid-state electrolytes also show applications in solid-state zinc-ion batteries,93–95 supercapacitors,96–101 lithium–sulfur batteries,102 sodium-ion batteries, and electrochemical transistors.103 Recent research has focused on further optimizing the structure of cellulose-based solid-state electrolytes. For example, some studies have introduced nanotechnology to fabricate cellulose-nanofiber-reinforced solid-state electrolytes.104 The high-aspect-ratio cellulose nanofibers can form a continuous network within the electrolyte matrix, not only enhancing the mechanical strength but also providing fast ion-transport channels. In order to optimize the Li+ transport, Jicheng Shan et al. incorporated 1-ethyl-3-methylimidazolium LiTFSI to plasticize both cellulose and polyethylene oxide (PEO).45 By leveraging the synergistic effects of cellulose and PEO, an ion-conducting network is established, which allows Li+ to form multiple Li–O coordination simultaneously with the hydroxyl group of cellulose and the ether group of PEO, thereby enabling Li+ to transport between the two polymers in a decoupled manner. The electrolyte demonstrated an ionic conductivity of 4 × 10−4 mS cm−1 (at room temperature) and a Li+ transference number of 0.43, significantly exceeding traditional PEO-based values of 10−5 mS cm−1 and 0.1–0.2.45 Similarly, metal–organic frameworks were in situ grown on the cellulose skeleton surfaces which are rich in hydroxyl groups, and combined with PEO-based electrolytes to form composite solid electrolytes for enhancing the Li+ transfer efficiency and strength of PEO-based composite solid electrolytes.105Table 2 compares the key performance metrics of typical cellulose-based solid electrolytes. These advanced cellulose-based electrolytes have shown great potential in improving the overall performance of SSBs.
Electyrolyte | Ionic conductivity (S cm−1) | Li+ transfer number | Application scenario | Ref. |
---|---|---|---|---|
CA-PVA (gel), OCMC-PVA (solid) | ∼10−2 | ∼0.8 | High-performance lithium-ion batteries | 23 |
Poly(cyclocarbonate-ether)/cellulose | 3.60 × 10−4 | N/A | Solid-state lithium batteries | 24 |
Cellulose/PEO/EMITFSI | 4 × 10−7 | 0.43 | High-performance solid-state Li batteries | 45 |
Cellulose phthalate (CP) | 1.09 × 10−3 | 0.81 | Lithium metal batteries (LFP, LCO, etc.) | 28 |
Cellulose triacetate- polymer composite IL | 5.24 × 10−3 (25 °C) | 0.43 | Lithium-ion batteries (EVs, smart grids) | 88 |
CSE (cellulose solid electrolyte) | 6.5 × 10−3 (25 °C) | N/A | Electrochromic displays | 89 |
CETG10 (cellulose-based eutectogel) | 2.04 × 10−3 (30 °C) | 0.64 | Solid-state lithium-ion batteries | 90 |
LAGP@BC-PEO (Li1.5Al0.5Ge1.5(PO4)3) | 1.01 × 10−4 | 0.45 | Lithium metal batteries | 92 |
PPC-based hydrogel (ZnSO4 infused) | 2.4 × 10−2 | N/A | Flexible Zn-ion batteries | 93 |
Polyacrylamide/hemp cellulose nanofibers (CNFs) | 5.96 × 10−2 (for 1.0 wt% CNFs) | N/A | Flexible rechargeable zinc-ion batteries | 94 |
Bacterial cellulose-based gel polymer electrolyte | 1.3 × 10−2 | N/A | Quasi-solid-state supercapacitors | 98 |
Cellulose eutectic gel electrolytes based on ethylene glycol/zinc chloride deep eutectic solvent (DES) | 5.0 × 10−2 (RT), 1.57 × 10−2 (−40 °C) | 0.30 | Flexible solid-state supercapacitors | 100 |
LiClO4-sulfonated methyl cellulose | 1.5 × 10−3 (RT) | N/A | Solid-state electrochromic devices | 101 |
TFSI-modified cationic cellulose/PEO | 2.07 × 10−4 (60 °C) | 0.42 | Lithium–sulfur batteries | 102 |
EO-co-EPI/CNF/LiTFSI | 6 × 10−5 (25 °C), 7 × 10−3 (95 °C) | N/A | Lithium-metal batteries | 104 |
Lignin, a complex aromatic polymer with abundant functional groups and good thermal stability, has also attracted attention in the field of solid-state electrolytes. Lignin has a high carbon content and a unique chemical structure, which endows it with certain electrochemical properties. Some research has focused on preparing lignin-based carbon materials through pyrolysis and using them as components in solid-state electrolytes. Qiang Li et al. reported the molecular engineering of biorefining lignin waste for solid-state electrolytes.60 In their studies, lignin was grafted with polyethylene glycol (PEG), then mixed with poly(vinylidene fluoride)-co-hexafluoropropylene and PEG-g-lignin-based LiTFSI to prepare a solid polymer electrolyte, which has an ionic conductivity of 2.5 × 10−5 S cm−1 at 25 °C. Lignin-derived carbon materials often have a porous structure, which can provide channels for ion diffusion. However, lignin-based solid-state electrolytes also face problems such as low ionic conductivity at room temperature and complex preparation processes. The abundance of benzene rings in lignin leads to strong π–π interaction forces, resulting in a large steric hindrance that impedes ion transport.106 The complex chemical structure of lignin makes it difficult to precisely control the reaction during the preparation of electrolytes, resulting in inconsistent performance. Moreover, the interface compatibility between lignin-based materials and electrodes needs to be further improved. To overcome these challenges, researchers are exploring new preparation methods and surface modification techniques. For instance, some studies have used chemical modification to introduce functional groups to lignin to improve its ion-conducting ability and interface compatibility.107 Hailing Liu et al. studied the synthesis of lignin-graft-PEG, including functionalization of natural lignin's hydroxyl groups to create alkene groups, followed by graft-copolymerization of PEG thiol to the lignin.108 With the addition of LiTFSI, the obtained polymer graft electrolytes exhibit ionic conductivity up to 1.4 × 10−4 S cm−1 at 35 °C. Recently, Xuliang Lin et al. developed a strategy that maximizes the utilization of the negative potential created by the repeated functional groups in lignin, which facilitates Na-ion transport while minimizing the unfavorable steric hindrance. As a result, a naturally superionic polymer electrolyte of macromolecular lignin for sodium-ion SSBs was obtained, which demonstrated an enhanced ionic conductivity of 3.4 × 10−4 S cm−1 at room temperature, with a Na-ion transfer number as high as 0.53.106 For potassium batteries, Sabrina Trano et al. designed a lignin-based electrolyte membrane by crosslinking a pre-oxidized Kraft lignin matrix with an ethoxylated difunctional oligomer, realizing an ionic conductivity exceeding 10−3 S cm−1 at ambient temperature.109
Chitosan is a kind of natural polysaccharide obtained from the deacetylation of chitin.110 It has good biocompatibility, biodegradability and ion exchange ability. M. Leo Edward et al. prepared a chitosan based solid electrolyte by combining chitosan with lithium salt.111 They prepared the membrane by mixing the chitosan with LiClO4 by solution casting. In the electrolyte system, the amino and hydroxyl groups on the chitosan molecular chain can interact with lithium ions and promote the transport of lithium ions. The experimental results show that the chitosan solid electrolyte has a certain ionic conductivity of 4.56 × 10−4 S cm−1 at room temperature, and can achieve a certain charge–discharge performance after being assembled into a battery. However, the ionic conductivity of chitosan based solid electrolytes is relatively low at present, and their properties need to be further improved by chemical modification, addition of plasticizers or composite formation with other high ionic conductivity materials.112 Yinfeng Huang et al. synthesized a novel protonated nanostructure through the reaction between PEO and chitosan (Chi) and applied it as a filler to form PEO/Chi composite solid-state electrolytes.113 The fillers play an important role in promoting Li+ transport properties, due to the protonated amino groups improving the dissociation of LiTFSI and the nanoscale size and high dispersity of the nanostructure. Interestingly, Md. Mehadi Hassan et al. reported a nanoarchitecture strategy by utilizing a cellulose derivative and a chitosan biopolymer to fabricate a nanoporous electrospun composite electrolyte for flexible and wearable sodium-ion SSBs. The resulting electrolyte exhibited a sodium-ion conductivity of 1.04 × 10−4 S cm−1 and a sodium ion transference number of 0.48 at room temperature.114
Starch, a polysaccharide widely found in plants, has been investigated as a potential material for solid-state electrolytes due to its abundance, low cost, and biodegradability.115 Starch-based solid-state electrolytes are usually prepared by blending starch with lithium salts and other additives. The hydroxyl groups in starch can interact with lithium ions, which is beneficial for the conduction of lithium ions to a certain extent. However, the ionic conductivity of starch-based solid-state electrolytes at room temperature is generally still relatively low, usually in the range of 10−7–10−5 S cm−1. This is mainly because the crystalline structure of starch restricts the movement of lithium ions. In addition, the poor mechanical strength of starch-based materials also limits their application in SSBs. To address these issues, researchers have tried various modification methods, such as chemical cross-linking, copolymerization, and the addition of nanofillers. For example, some studies have introduced conductive nanofillers like carbon nanotubes into starch-based electrolytes to enhance their ionic conductivity and mechanical properties. A. S. Mohamed et al. explored the ion conduction in a chitosan–starch blend based polymer electrolyte with ammonium thiocyanate as a charge provider, achieving the highest room temperature conductivity of 1.30 ± 0.34 × 10−4 S cm−1.116 As reported by Saeed Hadad et al. in 2022, carboxymethyl starch (CMS) and starch acetate (SA) were synthesized as amorphous starch derivatives from corn starch, and then crosslinked by poly(vinyl alcohol) (PVA) to form a polymer network.117 At room temperature, the ionic conductivity of solid CMS and gel SA electrolytes reached 9.2 × 10−3 S cm−1 and 1.13 × 10−2 S cm−1, respectively. Among all types, IL doped starch-based electrolytes demonstrated appreciable room temperature Li-ion conductivity.115 Although these modification methods have shown certain positive effects, there are still challenges in achieving a good balance between ionic conductivity, mechanical strength, and long-term stability.
In addition, there are also studies on the application of biomass materials such as agar and silk protein to the preparation of solid electrolytes. Agar is a polysaccharide extracted from seaweed and has good gel-forming ability.118 The dispersion of ILs into agar-based polymer matrices allows the development of solid polymer electrolytes with high ionic conductivity. By modulating the content of 1-ethyl-3-methylimidazolium thiocyanate ([Emim][SCN]) in agar-based electrolytes, the highest conductivity value is obtained for the sample with 40 wt% [Emim][SCN], with the value being 2.9 × 10−3 S cm−1 at 30 °C and 5.6 × 10−3 S cm−1 at 90 °C.119 Silk protein is a kind of natural protein with excellent mechanical properties and biocompatibility. By modifying the silk protein, it can be made ionically conductive and used to prepare solid electrolytes. K. Suvarnna et al. prepared a solid-state biopolymer electrolyte from the biomaterial corn silk extract by blending with PVA and different concentrations of MgCl2, and the maximum ionic conductivity of 1.28 × 10−3 S cm−1 for the biopolymer electrolyte was obtained.120 However, these biomass-based solid electrolytes are still in the research stage, and there are still some problems in ionic conductivity, mechanical properties, and compatibility with electrode materials, which need to be further studied and optimized. New types of biomass-composite electrolytes are also emerging. For instance, the use of chitosan-based composite electrolytes with inorganic nanoparticles, such as titanium dioxide (TiO2), has been explored.121 The addition of TiO2 can improve the ionic conductivity and electrochemical stability of the chitosan-based electrolyte by interacting with lithium ions and reducing the crystallinity of the polymer matrix.
In the specific realm of SSB anodes, biomass-derived carbon materials also exhibit remarkable potential owing to their distinct structural and performance merits. The ideal anode material for solid-state lithium batteries is considered to be Li metal due to its high specific capacity (3860 mAh g−1) and low electrochemical potential (−3.04 V vs. standard hydrogen electrode). However, Li metal anodes face significant challenges that limit their practical application, including the formation of lithium dendrites during cycling, which can lead to internal short circuits, capacity degradation, and safety risks. The tendency of Li metal to undergo volume expansion upon cycling exacerbates these issues, reducing cycle life and affecting the structural integrity of the anode. Additionally, Li metal anodes suffer from low coulombic efficiency, which further impacts battery performance over repeated cycles. Overpotential rise and capacity fading due to these factors are significant hurdles in enhancing the long-term stability of Li-metal-based SSBs.7 In this case, biomass-derived carbon materials are considered ideal host materials for Li metal because of their high mechanical strength, high conductivity, high surface area, and good chemical stability.123 For example, as shown in Fig. 5a, Yunbo Zhang et al. fabricated a lightweight 3D carbon current collector composed of ultra-fine nanofibers derived from bacterial cellulose.124 As reported, the high surface area, good mechanical strength, and high conductivity of these 3D porous skeletons could effectively reduce the current density and increase the number of oxygen-containing sites, promoting the uniform nucleation of Li metal and suppressing Li dendrite growth. Besides, 2D bio-carbon materials like sulfur/nitrogen co-doped porous carbon nanosheets derived from chitosan and gelatin (Fig. 5b),125 as well as 3D bio-carbon frameworks with well-aligned channels for Li metal deposition derived from wood,126 are used as carbon skeletons for Li metal anodes. Recently, Gangyi Xiong et al. reported an ideal framework composed of carbonized bacterial cellulose nanofibers, which shows intrinsic lithiophilicity to molten lithium without any lithiophilic surface modification.127 The wetting behavior of molten lithium can be enhanced through two synergistic mechanisms: (i) thermodynamically, the presence of stable fluorinated functional groups on the substrate reduces the interfacial energy, and (ii) kinetically, the hierarchical surface roughness originating from nanocracks accelerates capillary-driven infusion. The hybrid anode exhibits long cycle life up to 2000 h and excellent deep stripping-plating capacity up to 20 mAh cm−2. When further assembled with a LiFePO4 cathode, the full cell maintains stable cycling over 700 cycles. Besides, Dongdong Li et al. utilized the biological characteristics of Aspergillus niger to synthesize one-dimensional (1D) Sb2S3 nanoparticle composite N-doped C ribbons, and then assembled them with Ti3C2Tx nanosheets into a free-standing flexible anode for quasi-solid sodium-ion batteries (Fig. 5c).128 The strategy of filling 1D biomass-derived carbon fiber into the MXene layer can stabilize the sulfide and the assembled free-standing electrodes can effectively improve the energy density of the battery, providing valuable solution for the design of high-energy-density flexible batteries.
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Fig. 5 Biomass-derived electrode materials for SSBs. (a) Fabrication of the 3D interconnected carbon fibers from bacterial cellulose, and the cycling performance comparison between 3D Li-BC and Li metal in symmetric cells.124 (b) Schematic of the synthesis of biomass-derived sulfur–nitrogen co-doped porous carbon nanosheets and the SEM images.125 (c) Schematic illustration of biomass-derived N-doped carbon ribbons (NCRs), Ti3C2Tx and Sb2S3@NCR/MXene, and the electrochemical performances of free-standing quasi-solid-state sodium full-batteries. Reprinted with permission from ref. 128. Copyright © 2023 Elsevier. (d) Schematic of the preparation process of LFP@NFPC (a biomass carbon source derived from microbial residue was used to modify LiFePO4). Reprinted with permission from ref. 129. Copyright © 2024 Elsevier. (e) Cycling performance and SEM images of soybean flour carbon as a conductive agent for electrochemically stable cathodes of all-solid-state lithium–sulfur batteries. Reprinted with permission from ref. 130. Copyright © 2023 Elsevier. |
Nevertheless, biomass-derived carbon materials encounter several challenges in SSB anode applications. Firstly, some materials have a relatively low initial coulombic efficiency. Abundant surface defects and functional groups trigger side reactions with the electrolyte during the first charge–discharge, leading to irreversible capacity loss. Secondly, due to variations in raw materials and preparation processes, the performance reproducibility of these materials is poor, hampering large-scale industrial production. To tackle these issues, researchers are exploring strategies such as optimizing preparation processes and surface modification. Surface coating can reduce surface defects, mitigate side reactions, and improve the initial coulombic efficiency. Meanwhile, developing standardized preparation processes and strictly controlling raw materials and conditions can enhance performance reproducibility and promote the industrial application of biomass-derived carbon materials in anodes. Further development of nanostructured biomass-derived anode materials, such as nanoporous carbon, carbon nanotubes (CNTs), and graphene-like carbon nanosheets derived from biomass precursors, seems to be a key research direction.52,55,131,132 By precisely controlling the pyrolysis process and post-treatment methods, high-value CNTs and graphene-like 2D materials with a uniform porous structure can be obtained.54,133 The well-designed structure can provide more active sites for lithium-ion storage and buffer the volume changes during cycling. These anode materials have a high theoretical specific capacity, fast ion-diffusion rates, and good cycling stability.
On the other hand, biomass-derived cathode materials are attracting increasing attention. In battery assembly, the cathode is essential not only for enhancing electrochemical performance but also for improving the durability of the battery. Biomass-derived carbon materials with high specific surface area, porosity, and conductivity are suitable for use in battery cathodes, especially in lithium–sulfur battery cathodes. Biomass wastes like pistachio shells, almond shells, coconut shells, argan shells, soybean dregs, tea waste, and bamboo leaves have been employed to derive carbon to fabricate cathodes.134–141 For application in LIB cathodes, carbon coating is one of the most important techniques used to improve the specific capacity, rate performance and cycling life of LiFePO4 cathode materials. The main roles of carbon coating include enhancing the surface electronic conductivity of LiFePO4 particles so that the active materials can be fully utilized at high current rates, reducing the particle size of LiFePO4 by inhibiting particle growth during sintering, and acting as a reducing agent to suppress the oxidation of Fe2+ to Fe3+ during sintering and thus simplifying the atmosphere requirement in synthesis.142–144 As shown in Fig. 5d, Jian Liu et al. introduced a biomass carbon source derived from microbial residue to modify LiFePO4 (LFP@NFPC), and synthesized the LFP@NFPC composite with a three-dimensional (3D) porous structure via facile wet ball milling and high-temperature calcination.129 The high conductive 3D network structure is achieved by coating the surface of LiFePO4 with a carbon layer doped with N, F, and P, facilitating fast electron transport and rapid reaction kinetics between intercrystalline regions, and improving the accessibility of Li+ over a protracted cycle. Gyu Sang Sim et al. utilized sericin, one of the components of silk cocoon which is abundant in carbon and nitrogen and readily available, to fabricate nitrogen-doped carbon coating of LiFePO4. The cathode exhibited excellent discharge capacity delivering 113.51 mAh g−1 at 1 C rate, whereas bare LiFePO4 with no coating achieved only 94.27 mAh g−1, confirming approximately 20% improvement of the discharge capacity compared to that of bare LFP with no coating.145 Since LiFePO4 is also one of the key cathode materials for SSBs, the application of biomass-derived materials could potentially extend to SSBs. However, current research in this area remains limited. From the perspectives of economic feasibility and environmental sustainability, this direction holds significant potential as a priority for exploration. Nonetheless, material performance requires further optimization to meet the high energy density requirements of SSB applications. Moreover, Hong Jin Son et al. developed flexible, compressible, versatile biomass-derived freestanding carbon monoliths, which show great performance as membrane-type air cathodes for solid-state zinc-air batteries.17 As shown in Fig. 5e, S. Jin et al. reported an efficient electron transfer skeleton fabricated from biomass material as a conductive agent for the electrochemically stable cathode of lithium–sulfur all-SSBs.130 The introduction of the N-doped carbon skeleton improves the electronic conductivity of the composite cathode and the sulfur on this skeleton reduces direct contact between the electronic conductor and the sulfide electrolyte, thus effectively promoting rapid electron transfer and inhibiting electron aggregation on the surface of the electrolyte.130
It should be noted that mechanistic analysis or structure–function relationships could guide future biomass-derived material design or engineering, especially for biomass-derived carbon materials with ever-changing structures and morphologies. Ruizi Li et al. reviewed the structural engineering of biomass-derived carbon materials for electrochemical energy storage. In this review, they systematically summarized the controllable design of biomass-derived carbon structures boosting their storage sites and diffusion kinetics for energy storage devices, including pseudographic structure, hierarchical pore structure, surface functional groups, and heteroatom doping, as well as the composite structure.146 Yu Sun et al. comprehensively summarized activated carbon methods and the structural classification of BDC materials from zero, one, two to three dimension for developing high-performance batteries.147 Besides, the need to elucidate the kinetics and reaction barriers at the electrolyte–electrode interface and the modalities of electron/proton transfers cannot be exaggerated.148 Typically, the results of the theoretical simulations based on density functional theory (DFT) performed by Mei Chen et al. confirmed that the synergistic effect of S, N co-doping strongly influenced the effectiveness of biomass-derived carbon nanosheets in controlling lithium growth for stable lithium metal anodes.125 Furthermore, advancing biomass-derived carbon materials requires a systematic understanding of how distinct biomass structures influence their properties and functionality. Understanding the composition and structure of biomass materials is the basis for biomass-derived material/active mass composite design.147 According to the research by Wenjie Tian et al., biomass-derived key active site interactions governing electron transfer have been identified. This research not only underscores the significance of carefully selecting plant biomass for the development of carbon-based catalysts but also offers crucial guidelines for augmenting active sites and refining selective catalytic pathways in both amorphous and graphitic forms of carbon.149 These results also have reference significance for the field of biomass-derived carbon materials used as electrode materials in solid-state batteries.
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Fig. 6 Physicochemical properties of sericin and PVDF binders. (a) Schematic illustration of the composition of a single silk fiber originated from the cocoon. The silk fiber is composed of fibroin protein (internal) and sericin protein (outer, gold yellow), possessing glue-like characteristics. (b) Primary structure of silk sericin, which is linked together through peptide bond by a dehydration condensation process of amino acids. The four major amino acids of sericin are shown in the bottom of (b). The secondary structure is formed via a hydrogen bond between amino acids. (c) FTIR spectra for the PVDF powder, sericin powder, PVDF electrode, and sericin electrode. High-resolution XPS spectra of (d) C1s and (e) N1s peaks for sericin, respectively. (f) Viscosities of PVDF in NMP solvent and sericin binder with a molecular weight of 2k (S2k), 25k (S25k), 100k Da (S100k) in aqueous solution (2 wt%). The insets are their corresponding digital images of PVDF and sericin solution. (g) Elastic modulus and hardness of PVDF and sericin films at dry state. Reprinted with permission from ref. 154. Copyright © 2017 The Authors. Advanced Materials published by Wiley-VCH GmbH. |
Biomass-derived materials can have a significant impact on the ionic conductivity of SSBs. In cellulose-based solid-state electrolytes, the modification of cellulose can change the electrolyte's structure and the mobility of ions within the electrolyte. As mentioned in the study of CP-SSE,28 the introduction of phthalic acid groups broadens the spacing of the polymer backbone segments, which is beneficial for the diffusion of Li+. The carboxyl groups in the phthalic acid groups can coordinate with Li+, promoting the dissociation of lithium salts and providing key sites for the hopping transfer of Li+, resulting in an ionic conductivity of 1.09 × 10−3 S cm−1. These mechanisms have been verified by electrochemical impedance spectroscopy (EIS), nuclear magnetic resonance (NMR), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) analysis. Given that the ionic conductivity of traditional polymer-based solid electrolytes is generally between 10−8 and 10−5 S cm−1, while the ionic conductivity of CP-SSE is improved by several orders of magnitude, it is clear that cellulose based materials have a significant improvement effect on ionic conductivity through structure and functional group design.28
In addition to cellulose, other biomass-derived materials such as lignin and chitosan also affect ionic conductivity through their unique structures and functional groups.106,155 Lignin consists of rich functional groups such as phenolic hydroxyl groups and methoxy groups. In the lignin-based solid electrolyte, these functional groups can interact with lithium salts and affect the dissociation and ion transport. The phenolic hydroxyl group can provide protons, participate in exchange reactions with Li+, and promote the conduction of Li+.156 The methoxy group can affect the arrangement of polymer chain segments through the steric hindrance effect, and then change the ion conduction path. Besides, according to the research results reported by Zitong Liu et al., lignin derivatives as fillers can also improve the ionic conductivity of polymer-based electrolytes.157 Chitosan is a kind of natural polysaccharide obtained by deacetylation of chitin.158,159 Its molecular chain contains a lot of amino (–NH2) and hydroxyl groups. The amino group has strong alkalinity and can interact with the anion in lithium salt to promote the dissociation of lithium salt. At the same time, amino and hydroxyl groups can also form hydrogen bonds with lithium ions, stabilize the transport environment of lithium ions, and improve the ion migration rate. Some studies have shown that the solid electrolyte prepared by combining chitosan with lithium salt can improve the ionic conductivity to a certain extent.111,113 However, compared with cellulose-based solid electrolytes, lignin-based and chitosan-based solid electrolytes have relatively weak ionic conductivity enhancement effects.
Furthermore, it should be noted that some biomass-based materials still face challenges in terms of ion conductivity. For instance, starch-based solid-state electrolytes usually have relatively low ionic conductivity at room temperature, typically in the range of 10−7–10−5 S cm−1.115 This is mainly due to the crystalline structure of starch, which restricts the movement of Li+. Therefore, adding plasticizers such as glycerin to reduce the crystallinity of the starch matrix can improve the ionic conductivity. Typically, for starch, IL doped starch-based electrolytes demonstrated appreciable room temperature Li-ion conductivity among all types.115 Generally speaking, to enhance the ion conductivity of biomass-derived materials, it is necessary to coordinate the regulation from multiple perspectives such as molecular structure design, material composite strategy, and interface optimization. One effective approach involves the targeted chemical modification of these materials to introduce polar or ionisable functional groups. For example, sulfonic (–SO3H) or carboxylic (–COOH) groups can act as strong proton donors, significantly enhancing the dissociation of lithium salts like LiTFSI and increasing the concentration of free Li+. Structural engineering at multiple scales plays a pivotal role in optimizing ion transport pathways. Biomass materials can be processed into 3D porous networks using techniques such as freeze-drying or templating, which shorten lithium ion diffusion distances. Oriented alignment of polymer chains through electrospinning or shear forces creates anisotropic ion channels. Bioinspired architectures mimicking biological ion channels enable confined or gradient-driven transport. Hybridizing biomass materials with functional additives further addresses performance limitations.101,160 Combining organic biomass polymers with inorganic ceramic fillers leverages interfacial effects to enhance ion transport; ILs can also be incorporated as plasticizers to lower glass transition temperatures and improve chain mobility; and blending biomass materials with conductive polymers such as PEO or PVDF further reduces crystallinity and enhances ion mobility. However, balancing functional group density with material stability remains critical, as excessive modification may compromise mechanical integrity. Crosslinking and plasticization strategies may balance mechanical stability with ion mobility. The PEG modified cellulose electrolytes achieved a room-temperature conductivity of 3.31 × 10−3 S cm−1, and possessed superior tensile strength ranging from 33.92 MPa to 211.06 MPa and excellent bending resistance.161
For example, Meng Lei et al. innovatively used sericin to solve the interface problem of NASICON ceramic-based SSBs.163 Among many solid electrolyte materials, NASICON electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) has become one of the research hotspots of SSB electrolytes due to its high ionic conductivity (10−3–10−4 S cm−1) and good humid air stability. However, when the LATP is in direct contact with the lithium metal anode, the lithium metal will reduce the Ti4+ in the LATP lattice to form an intermediate phase with electronic conductivity. This process can accelerate the reduction and decomposition of the LATP ceramic electrolyte, which can cause serious interface problems and lead to battery failure, as illustrated in Fig. 7. In order to solve this problem, Meng Lei et al. proposed a strategy to construct a conformal interface layer of Li-LATP using natural macromolecule sericin, which is composed of various amino acids connected by peptide bonds, and possesses intrinsic electrochemical stability and electronic insulation properties. During the preparation of the sericin membrane, solvent evaporation induces uniform cavity formation. These cavities and Li-/anion-philic functional groups on molecular polar side chains efficiently trap IL via TFSI− interactions. According to scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis results, as well as DFT calculations, IL disperses uniformly within the membrane, suppressing Li-LATP interface decomposition, passivation, and cracking via fluidity, maintaining conformal/compact interfaces post long-term cycling. The IL-sericin modification layer reduces Li-LATP impedance, enabling NASICON-based solid-state Li–Fe–F batteries to achieve an initial capacity of 524.3 mAh g−1, a capacity of 346.3 mAh g−1 after 100 cycles, and a coulombic efficiency of 97–98%.163
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Fig. 7 Schematic diagram of the LATP failure mechanism and the sericin film protection mechanism. (a) LATP pellet is reduced after touching with Li metal, and the interface is constituted by reduction products of LATP such as Li5AlO4 and Li2O. Inset: scenario of reduction from Ti4+ to Ti3+ and resultant fragmentation of LATP grains stemming from inner stress. (b) Artificial SPF layer is tightly adhered on LATP surface, which is chemically and mechanically robust against Li. SPF is an electronic insulator separating LATP from Li metal but still allowing Li+ transport across interface. (c) PDOS of bulk Li, sericin-chain and LTP aligned based on their vacuum levels, which are obtained from work function calculated from corresponding surface structure: Li (001), sericin (001) and LTP (012). (d) Scheme showing the positions of band energies of bulk LTP, sericin-chain and Li with respect to vacuum level as well as electron migration situation. Reprinted with permission from ref. 163. Copyright © 2022 Elsevier. |
In addition to sericin, other biomass-derived materials such as polysaccharides and proteins have also been studied and applied in battery interface modification. Cellulose-based materials such as cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) possess a high specific surface area and abundant hydroxyl functional groups.84,164 This endows them with the ability to undergo specific interactions with the surfaces of electrodes and electrolytes, thereby effectively optimizing the interfacial properties. Taking the solid-state electrolyte system with PEO as the matrix as an example, after the addition of CNC, the interfacial impedance of the battery is significantly reduced, and the cycle performance is remarkably improved, demonstrating promising application prospects.165 Besides, chitosan, rich in amino and hydroxyl groups, exhibits excellent film-forming properties and biocompatibility, showing potential application value in the field of battery interface modification.158 The amino and hydroxyl functional groups in the chitosan molecule can undergo complexation reactions with lithium ions, facilitating the rapid transport of lithium ions at the interface through an ion exchange mechanism. Furthermore, the chitosan film can also inhibit the dissolution and volume change of the electrode material during the charging and discharging processes, thereby significantly improving the stability of the electrode. Lignin has a complex and rich aromatic structure and various functional groups, which enable it to closely bind to electrodes and electrolytes through non-covalent interactions such as π–π stacking and hydrogen bonding, thereby significantly improving the interfacial compatibility. In the research of SSBs, introducing lignin-based carbon materials as an interface modification layer into the battery system can effectively reduce the interfacial impedance and significantly improve the rate performance of the battery.
Biomass-derived materials can stabilize the electrode/electrolyte interface through multiple mechanisms including a combination of molecular interactions, structural adaptations, and intrinsic material properties. At the molecular level, functional groups inherent to biomass materials play a pivotal role in passivating reactive interfaces. For instance, phenolic hydroxyl (–OH) groups in lignin exhibit strong reductive properties, enabling them to react preferentially with lithium metal to form a stable interface, which effectively blocks continuous electrolyte decomposition while maintaining low interfacial impedance.166 Sulfonic acid (–SO3H) groups in modified cellulose can electrostatically anchor anions such as TFSI−, mitigating concentration polarization and suppressing lithium dendrite growth.167 The hierarchical structures of biomass materials further contribute to interfacial stability by optimizing physical contact and mitigating mechanical stress. CNFs, as mentioned above, can be engineered into 3D interpenetrating networks via electrospinning, creating seamless interfaces with electrodes.168 Blending rigid lignin backbones with flexible polymers like PEO to create gradient modulus interfaces is another structural strategy. Besides, biomass materials impart macroscopic stability through their intrinsic electrochemical and thermal resilience. For example, lignin's polyphenolic structures can act as radical scavengers to neutralize reactive oxygen species generated at high-voltage cathodes, thus reducing the accumulation of deleterious byproducts at interfaces.169 However, the long-term durability of these functional groups under oxidative or protonation conditions remains a concern, necessitating strategies like covalent grafting of stable moieties to enhance chemical robustness. Moreover, scalable fabrication methods must be refined to ensure uniform interfacial layer deposition across large-area electrodes for commercial applications.
The design of composite materials by combining biomass-derived materials with other materials has emerged as a prominent research hotspot in the field of SSBs. By integrating biomass-derived materials with various other substances, researchers aim to synergistically optimize the performance of SSBs, addressing multiple challenges simultaneously. One of the key directions is the combination of biomass-derived materials with nanomaterials. For example, the incorporation of CNTs or graphene into biomass-based solid-state electrolytes has been extensively studied. Typically, graphene, with its large specific surface area and high electron-transfer ability, also shows great potential in composite materials for SSBs.170,171 When graphene is introduced into biomass-derived electrode materials, it can enhance the electrode's electrical conductivity and structural stability.172 In addition to carbon-based nanomaterials, metal nanoparticles and metal-oxide nanoparticles, as well as metal salts, have also been explored for composite material design.160,173 Furthermore, the combination of biomass-derived materials with other polymers is another important aspect of composite material design. Blending biomass-based polymers with synthetic polymers can combine the advantages of both. As reported, blending cellulose with PEO in solid-state electrolytes can improve the ionic conductivity of the electrolyte.174 PEO has good ion-conduction properties, and when combined with cellulose, it can disrupt the crystalline structure of cellulose, increasing the mobility of lithium ions.105 At the same time, the mechanical strength and flexibility of the composite electrolyte can also be adjusted by controlling the ratio of cellulose and PEO.
The application of new preparation technologies in biomass-derived material-based SSBs has become a crucial research area, aiming to fabricate battery components with unique structures and enhanced properties. 3D printing technology has shown great potential in the manufacturing of SSBs. It allows for the precise control of the structure and morphology of battery components at the micro- and nano-scales.175,176 Recently, lignocellulosic biomass and its derivatives have been used in 3D printing due to their renewable nature and sustainability.177,178 Therefore, a 3D-printed biomass-derived carbon-based anode can be designed with a hierarchical porous structure. This structure can provide a large surface area for electrochemical reactions, facilitating the diffusion of lithium ions and electrons. The 3D-printed anode can also have a more uniform distribution of active materials, reducing the internal resistance of the battery and improving its rate performance. Furthermore, 3D printing can be used to fabricate solid-state electrolytes with precise architectures. By precisely controlling the deposition of materials, 3D-printed electrolytes can have a more uniform distribution of ionic-conductive pathways, which enhances the ionic conductivity of the electrolyte. In addition, 3D printing enables the customization of battery components according to specific application requirements, such as the design of flexible or curved batteries for wearable devices. Electrospinning is another emerging technology with significant applications in SSBs. It is mainly used to prepare nanofibrous materials, which can be applied to various components of SSBs.179 In the context of biomass-derived materials, electrospinning can be used to produce nanofibers from biomass-based polymers, such as cellulose and silk fibroin.180 These nanofibers can be used as components in composite electrolytes. Besides, electrospinning can be used to prepare composite nanofibers by co-electrospinning biomass-based polymers with other functional materials. For example, co-electrospinning cellulose with lithium-ion-conductive polymers can produce composite nanofibers with enhanced ionic-conductive properties.181 These composite nanofibers can be used as a novel electrolyte material in SSBs, combining the advantages of biomass-derived materials and lithium-ion-conductive polymers to improve the overall performance of the battery.
Although certain progress has been made in the research of biomass-derived materials in the field of SSBs, there are still many challenges in practical applications. Typically, some biomass-derived materials show good performance in laboratory research, but there is still a gap compared with commercial requirements. Taking biomass-based solid electrolytes as an example, although their ionic conductivity at room temperature has been improved, they still lag behind traditional liquid electrolytes in terms of conductivity. This limits the use of SSBs in high-power application scenarios, such as fast charging of electric vehicles. In addition, the capacity retention rate and rate performance of biomass-based electrode materials also need further optimization. Some biomass-based anode materials experience rapid capacity decay during charging and discharging at high current densities, and hence cannot meet the requirements for fast charging and long cycle life of batteries in practical applications.
Currently, most of the preparation processes for biomass-derived materials are relatively complex, making it difficult to achieve large-scale industrial production. For example, during the preparation of cellulose-based solid electrolytes, the homogeneous esterification reaction requires precise control of reaction conditions, including temperature, reaction time, and reactant ratio, which increases the difficulty and cost of the production process. As to chitosan, its solubility in acidic solutions limits its processing in a way that is compatible with current industrial battery manufacturing processes. The poor mechanical strength and relatively low ionic conductivity also make it challenging to integrate it into existing battery production lines without significant modifications.110 Moreover, the source and quality of biomass raw materials vary to some extent, which poses challenges in maintaining consistency and stability of product quality in large-scale preparation. Biomass raw materials collected from different regions and seasons may have different chemical composition and structures, which can lead to unstable performance of the prepared biomass-derived materials and affect product quality. Cost control is also an important challenge in the application of biomass-derived materials in SSBs. Although biomass raw materials themselves have the advantage of low cost, a large amount of chemical reagents and complex equipment are often required in the preparation process, which significantly increases the production cost. The preparation of some biomass-based solid electrolytes requires the use of expensive lithium salts and special organic solvents, and the energy consumption during the preparation process is high, resulting in high final product costs. This makes biomass-derived materials lack price competitiveness compared with traditional battery materials to some extent, hindering their large-scale commercial application.
In response to the challenges, researchers have proposed a series of solutions, but these solutions still have certain limitations in practical applications. For example, researchers have adopted methods such as chemical modification to improve the performance of biomass-derived materials. In chemical modification, the functional groups of biomass-derived materials are modified to improve their performance; for example, esterifying cellulose and introducing phthalic acid functional groups has been shown to enhance the ionic conductivity of cellulose-based solid electrolytes. This method can change the molecular structure of the material and enhance its interaction with ions, thereby promoting ion transport. However, the chemical modification process often requires a large amount of chemical reagents, which not only increases the production cost but may also cause certain pollution to the environment. Moreover, the reaction conditions for chemical modification are relatively harsh, requiring precise control of parameters such as reaction temperature, time, and reactant ratio, which places high requirements on the production process and increases the difficulty of large-scale production. Besides, compounding biomass-derived materials with other high-performance materials, such as compounding lignin with quaternized chitosan and polyvinyl alcohol to prepare hydrogel electrolytes, can integrate the advantages of each material and improve the material's performance. This compounding method can utilize the synergistic effect between different materials to improve the ionic conductivity and mechanical properties of the material. However, there may be problems of poor compatibility between materials, resulting in unstable performance. Moreover, the reaction process is also relatively complex, and appropriate compounding methods and process parameters need to be explored to ensure that the performance of the composite material meets expectations.
To overcome the complexity of the preparation process, researchers have attempted to develop new preparation technologies and processes. For example, Jiying Yang et al. used dry processing with hard CNC as the skeleton and soft polyacrylonitrile as the filler to develop a solid polymer electrolyte with a 3D network through in situ graft polymerization.182 This method only requires a very small amount of solvent and has the advantage of easy processing, providing a new idea for large-scale preparation. However, research and development of new preparation technologies and processes often require a large amount of cost and time, and in actual production, problems such as equipment modification and process optimization may be encountered, resulting in slow progress in large-scale production. In addition, the problem of fluctuations in the source and quality of biomass raw materials still exists, and even with new preparation processes, it is difficult to fully ensure the consistency and stability of product quality.
In order to further reduce cost, on the one hand, researchers are trying to find cheaper biomass raw materials and chemical reagents to reduce production costs. For example, using discarded biomass such as discarded bagasse, straw and bamboo sawdust as raw materials not only reduces the raw material cost but also realizes the resource utilization of waste. However, in practical applications, certain costs are also incurred in the collection, transportation, and pretreatment of discarded biomass, and the uncertainty of its quality and composition may affect the performance and quality stability of the product. On the other hand, optimizing the preparation process, improving production efficiency, and reducing energy consumption are also important ways to reduce costs. However, the current optimization measures still face difficulties in achieving the ideal cost control effect in actual production. The high energy consumption and complex process in the preparation of biomass-derived materials are still the main factors leading to high costs.
In addition to the above issues, the real-world scalability, material purity concerns, and compatibility with current industrial processing lines are of great importance for the commercial promotion and application of biomass materials in the field of SSBs, and they are also key issues that need to be considered and addressed in the research process. For example, the production of bacterial cellulose primarily relies on microbial fermentation processes, which are time-consuming processes with limited throughput. Additionally, the fermentation process is highly sensitive to environmental factors, including temperature, pH, nutrient composition, and oxygen availability. Any deviation can lead to inconsistent quality and yield. To address these issues, researchers have been exploring dynamic fermentation systems, such as stirred-tank reactors and membrane bioreactors.183 These systems can increase the growth rate of bacteria by enhancing nutrient and oxygen transfer, potentially reducing the production time by up to 50%. Moreover, genetic engineering of Gluconacetobacter xylinus to improve the growth characteristics and producing efficiency is an emerging area of research.184 During the fermentation process, bacterial cellulose can be contaminated with residual culture media components, such as unconsumed sugars, proteins, and salts. These impurities can disrupt the ionic conductivity of bacterial cellulose-based solid-state electrolytes and may also react with lithium metal, leading to safety issues. Superior purification methods need to be developed to address these material purity issues.
For electrode materials, the future research focus may be on developing biomass-based electrode materials with higher specific capacity, better rate performance, and cycle stability. For biomass-based anode materials, new biomass raw materials and preparation methods can be further explored to obtain materials with more ideal microstructures and properties. For instance, researchers can focus on extracting biomass raw materials from special plants or microorganisms and preparing anode materials with ultra-high specific capacity and good cycle stability through unique pyrolysis and carbonization processes. For biomass-based cathode materials, in addition to optimizing the compounding methods with traditional cathode active substances, new biomass-based cathode material systems can be explored. Through deep processing and modification of biomass, it can be made to have cathode activity itself, or new biomass-based composite materials can be developed as cathode materials to improve the energy density and charge–discharge performance of batteries.
For battery interface modification materials, it is crucial to develop biomass-derived materials with better interface compatibility, lower interface impedance, and stronger ability to inhibit lithium dendrite growth. The structure and function of existing biomass-derived interface modification materials such as silk sericin and chitosan can be optimized and enhanced to improve their stability and effectiveness at the battery interface. New biomass-derived materials can also be sought to develop interface modification layers with unique structures and properties. Biomass materials with special functional groups can be used to design and synthesize interface modification layers that can form chemical bonds at the electrode/electrolyte interface, thereby significantly reducing interface impedance and improving the cycle life and safety of batteries.
In materials science, it is necessary to study in-depth the relationship between the microstructure and properties of biomass-derived materials to provide a theoretical basis for material design, synthesis and optimization.146 Through advanced material characterization techniques such as high-resolution transmission electron microscopy (HRTEM), XPS, and NMR, the crystal structure, elemental composition, and functional group distribution of biomass-derived materials can be analysed in depth to reveal their mechanism of action in SSBs. Theoretical calculation methods such as first-principles calculations and molecular dynamics simulations can be used to study the electronic structure, ion transport paths, and interface interactions of materials at the atomic and molecular levels, predict material properties, and provide guidance for material design and modification.125 When studying cellulose-based solid electrolytes, HRTEM can be used to observe the arrangement and microstructure of molecular chains, XPS to confirm the chemical state of functional groups, and molecular dynamics simulations to study the lithium-ion transport mechanism in the electrolyte, so as to understand the relationship between the ionic conductivity and microstructure of cellulose-based solid electrolytes.
The field of chemical engineering focuses on developing efficient preparation processes and modification methods to achieve large-scale preparation and performance optimization of biomass-derived materials. New synthesis methods and processes such as electrospinning, 3D printing, and chemical vapour deposition can be studied to achieve precise preparation and structure control of biomass-derived materials. Green and environmentally friendly chemical modification methods can be developed to reduce the use of chemical reagents, minimize environmental pollution and improve material performance. Electrospinning technology can be used to prepare biomass-based nanofibers, and by controlling spinning parameters, the diameter, morphology, and structure of nanofibers can be precisely regulated to meet the requirements of SSBs for material microstructures. In chemical modification, green chemical reagents and mild reaction conditions can be explored to modify the functional groups of biomass-derived materials and improve their ionic conductivity and interface compatibility.
The bioengineering discipline can provide new raw materials and preparation methods for the development of biomass-derived materials. Through technologies such as genetic engineering and cell engineering, biomass raw materials can be modified to have more excellent performance. Microbial fermentation technology can be used to synthesize biomass-derived materials with specific structures and functions. Through gene editing technology, plants can be genetically modified to synthesize cellulose with a more regular molecular structure and higher crystallinity, thereby improving the performance of cellulose-based solid electrolytes. Microbial fermentation technology can be used to synthesize polysaccharide biomass-derived materials with high ionic conductivity as candidates for solid electrolytes.
In addition, interdisciplinary integration can also promote the collaborative optimization between biomass-derived materials and other components of SSBs. Researchers from materials science, chemical engineering, bioengineering, and artificial intelligence can cooperate to study the interface compatibility and interaction mechanism between biomass-derived materials, electrode materials, and solid electrolytes, and develop effective interface modification methods to improve the overall performance of batteries. Through interdisciplinary collaborative innovation, it is expected to develop SSBs with high energy density, long cycle life, high safety, and low cost, promoting the development of the new energy industry.
In the field of electric vehicles, the application of biomass-derived materials in SSBs is expected to drive the innovation of electric vehicle technology. Currently, the driving range and safety of electric vehicles are the key concerns of consumers. SSBs have the characteristics of high energy density and high safety, which can effectively improve the driving range and safety of electric vehicles. The application of biomass-derived materials in solid electrolytes and electrode materials can further optimize the performance of SSBs and reduce battery costs. Applying biomass-based solid electrolytes to electric vehicle batteries can improve the ionic conductivity and interface stability of batteries, thereby enhancing the charge–discharge efficiency and cycle life of batteries. Using biomass-based anode materials can increase the energy density of batteries and extend the driving range of electric vehicles. As the application technology of biomass-derived materials in SSBs matures, electric vehicles are expected to achieve longer driving ranges, faster charging speeds, and higher safety, promoting the rapid development of the electric vehicle industry.
As to energy storage, the application of biomass-derived materials in SSBs also has great potential. With the wide application of renewable energy such as solar and wind energy, the importance of energy storage systems is becoming increasingly prominent. SSBs have the characteristics of long cycle life and high safety, which make them very suitable for application in energy storage systems. The application of biomass-derived materials can reduce the cost of SSBs and improve the economic efficiency of energy storage systems. In large-scale energy storage power stations, using SSBs prepared from biomass-derived materials can reduce the construction and operation costs of energy storage systems and improve their stability and reliability. The application of biomass-derived materials in the energy storage field can also promote the consumption of renewable energy and drive the optimization and transformation of the energy structure.
In addition, the application of biomass-derived materials in SSBs can also be expanded to other fields such as consumer electronics and aerospace. In the field of consumer electronics, the high energy density and thinness of SSBs can meet the requirements of smartphones, tablets, and other devices for battery endurance and thinness. The application of biomass-derived materials can further reduce battery costs and improve the cost–performance ratio of consumer electronic products. In the aerospace field, the high energy density and high safety of SSBs can meet the strict requirements of aircraft for battery performance. The lightweight characteristics of biomass-derived materials can also reduce the weight of aircraft and improve their performance and efficiency.
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