Regulating the anionic environment of the COF@CNT composite for kinetics-boosted and wide-temperature lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries offer high theoretical energy density but are limited by issues such as polysulfide shuttling and poor performance across a wide temperature range. To overcome these challenges, we developed ionized COF@CNT composites and studied how their anionic centers influence polysulfide adsorption and conversion. By replacing Br⁻ in EB-COF-Br with LiTFSI and LiOTF, we tailored the COF interface to improve ion conductivity and the Li⁺ transference number. This demonstrated that the OTF anion was more effective in reducing charge transfer resistance and promoting lithium sulfide formation. In situ Raman spectroscopy confirmed that the COF-OTF@CNT-modified separator effectively suppressed polysulfide shuttling. Electrochemical tests showed excellent cycling stability and rate performance, with the modified cell achieving 800 cycles at 1C with only 0.058% capacity loss per cycle, and 89.3% capacity retention after 200 cycles at 0 °C. These findings highlight chemical tuning of the COF@CNT anionic centers as a promising strategy to enhance Li–S battery performance, particularly in extreme temperature environments.

---

Jie Xu

Jie Xu received his PhD degree in Chemical Engineering from East China University of Science and Technology (ECUST) in 2020. After being a postdoctoral fellow for two years (2020–2022) at Fudan University under the supervision of Prof. Yongyao Xia and Prof. Yonggang Wang, he joined the School of Materials Science and Engineering of Anhui University of Technology (AHUT). His current research interests focus on organic-derived energy storage materials for wide-temperature secondary batteries, including Li–S batteries, Li/Na/Zn-ion batteries, and full-organic energy storage devices.

---

Introduction

Lithium–sulfur (Li–S) batteries have been recognized as a promising next-generation energy storage technology due to their high energy density (approaching 800 Wh kg⁻¹), cost-effectiveness, and the natural abundance of sulfur.^1–5 These advantages make Li–S systems attractive candidates for replacing traditional lithium-ion batteries.^6–10 However, their practical implementation is limited by several critical issues, including the shuttle effect caused by lithium polysulfides (LiPSs), incomplete sulfur redox reactions, and the formation of lithium dendrites at the anode.^11–15 These challenges are further exacerbated at extreme temperatures.^16–19 At low temperatures, sluggish LiPS conversion leads to poor sulfur utilization and large polarization behavior.^20,21 At high temperatures, increased polysulfide solubility and diffusion in ether-based electrolytes aggravate the shuttle effect, compromising cycling stability.^22,23 Therefore, achieving stable cycling performance across a broad temperature range is vital for the practical deployment of Li–S batteries under real-world conditions.

Efforts to improve Li–S batteries have largely focused on cathodic strategies, such as electrocatalyst design and polysulfide confinement using porous hosts and functional separator coatings.^24–29 Metal-based electrocatalysts could enhance sulfur redox kinetics across temperatures but show less effectiveness at high temperatures due to polysulfide oversaturation.^30–32 Alternatively, covalent organic frameworks (COFs) offer strong chemical affinity and distinct structural confinement for LiPSs, functioning as sulfur hosts or separator coatings.^33–37 Recent developments highlight heteroatom doping and covalent sulfur anchoring to enhance polysulfide immobilization.^38–41 Furthermore, adding ionic groups to COFs creates ionic frameworks, where the charged sites strongly bind with polysulfides through Lewis acid–base interactions, helping to prevent their dissolution and movement.^42–45 Despite these advantages, COFs suffer from low electronic conductivity, which limits their performance. They effectively suppress the shuttle effect at high temperatures, but their weak catalytic activity at low temperatures hinders polysulfide conversion, reducing battery performance in cold environments.

Targeting the challenges, combining COFs with conductive carbon nanotubes (CNTs) greatly enhances the electrical conductivity of the resulting composite. This hybrid structure makes COF@CNT materials highly desirable in the applications of electrocatalysis and organic electrodes.^46–49 In Li–S batteries, research on COF@CNT composites mainly focuses on adjusting the CNT content and using the porous structure of COFs to reduce the polysulfide shuttle effect.^50,51 During battery cycling, Li⁺ transport and its interaction with polysulfides are also influenced by the electrolyte and surrounding anions. Recently, Sun et al. investigated a cationic COF containing TFSI⁻ anions and demonstrated enhanced battery performance due to strong electrostatic interactions between TFSI⁻ and LiPSs.⁵² Similarly, ionic COFs containing pyridinium groups have shown strong binding to LiPSs, thereby limiting their dissolution and migration when used as sulfur hosts.⁵³ However, the mechanisms by which ionizable sites in COFs regulate these interactions and their catalytic behavior remain poorly understood. In addition, the application of ionic COF@CNT composites with favorable conductivity for supporting stable Li–S battery operation across a wide temperature range remains largely unexplored.

In this work, we developed ionized COF@CNT composites and studied how changing the anions at the COF interface affects polysulfide adsorption and conversion in Li–S batteries. By replacing Br⁻ in EB-COF-Br with TFSI⁻ and OTF⁻, we found that these anions improved ionic conductivity and Li⁺ transport due to their delocalized charge and polar functional groups. Among them, OTF⁻ showed the best performance by lowering charge transfer resistance and accelerating Li₂S formation. In situ Raman spectroscopy confirmed that COF@CNT-modified separators effectively blocked polysulfide shuttling. Electrochemical tests showed that the COF-OTF@CNT-modified cell had excellent rate performance and long-term cycling stability, with only 0.058% capacity loss per cycle over 800 cycles at 1C. It also maintained stable operation from 0 °C to 60 °C, delivering 766 mAh g⁻¹ at 60 °C and 5C, and retaining 89.3% capacity after 200 cycles at 0 °C and 0.5C. These results demonstrate the strong potential of ionized COF@CNT composites for high-performance Li–S batteries across a wide temperature range.

Results and discussion

A covalent organic framework (COF) was synthesized via a Schiff-base condensation reaction between the monomers TP and EB.⁵³ To enhance conductivity and structural integration, 50 wt% CNTs were incorporated during synthesis, enabling the COF to grow in situ on the CNT surface and form a conformal coating. The resulting COF-Br@CNT composite was subsequently subjected to anion exchange by immersion in LiTFSI or LiOTF electrolyte solutions for three days, producing two COF@CNT materials with distinct anionic environments, referred to as COF-TFSI@CNT and COF-OTF@CNT, respectively (Fig. 1a). In the engineered COF@CNT composites, Li⁺ transport was facilitated not only by the intrinsic pore channels of the COF but also finely tuned by the anionic microenvironment introduced through the EB monomer. These modified composites were subsequently applied as a functional coating on Celgard separators, with the purpose of suppressing the polysulfide shuttle effect and enhancing reaction kinetics over a wide temperature range (Fig. 1b).

Fig. 1 (a) Schematic illustration of synthesis of COF@CNTs with a tunable chemically anionic environment; (b) application of the COF@CNT modified separator using in kinetics-boosted and wide-temperature LSBs.

To characterize the synthesized materials, Fourier-transform infrared spectroscopy (FTIR) was first performed to identify key functional groups. As shown in Fig. 2a, the successful formation of imine-linked COFs was confirmed by the characteristic imine stretching band and the disappearance of the functional group of NH₂, indicating completion of the Schiff-base condensation between TP and EB-Br. Powder X-ray diffraction (XRD) analysis revealed a distinct peak at 3.5°, corresponding to the (100) plane of the crystalline COF, along with a broad feature near 27°, associated with π–π stacking in partially amorphous regions (Fig. 2b). After in situ growth of the COF on CNTs and subsequent anion exchange, the XRD patterns showed that the COF's crystallinity was preserved. Additionally, a peak near 25.6°, characteristic of CNTs, confirmed their successful incorporation without disrupting the ordered COF structure. The Brunauer–Emmett–Teller surface areas of COF-Br@CNT, COF-TFSI@CNT, and COF-OTF@CNT were measured to be 364.2, 237.8, and 280.8 m² g⁻¹, respectively (Fig. S1†). The reduced surface areas for COF-TFSI@CNT and COF-OTF@CNT suggest that the replacement of Br⁻ with larger TFSI⁻ and OTF⁻ anions results in partial pore occupation. The relatively higher surface area of COF-OTF@CNT compared to COF-TFSI@CNT may be attributed to the larger ionic radius of TFSI⁻, which causes more significant steric hindrance within the COF channels.

Fig. 2 (a) FT-IR spectral measurement. (b) Powder XRD test. (c) N 1s and (d) S 2p fine spectra of the XPS test. (e) SEM image of COF-Br. (f) SEM image of COF-Br@CNT with an inset TEM image.

X-ray photoelectron spectroscopy (XPS) was employed to investigate the ionic environments within the COF@CNT composites. As shown in Fig. 2c, the N 1s spectra exhibited four distinct peaks at 399.0, 400.2, ∼402, and ∼405 eV, corresponding to C=N, N–H, C–N⁺, and π–π* interactions, respectively. Notably, the binding energy of the C–N⁺ peak varied with the incorporated anion, indicating differences in electron-donating ability. Among the samples, COF-Br displayed the lowest C–N⁺ binding energy (401.6 eV), while COF-TFSI exhibited the highest, followed by COF-OTF. This trend is attributed to the larger molecular size and symmetric structure of the TFSI anion, which promote electron delocalization and decrease its electron-donating strength. Supporting this observation, the S 2p spectra showed that TFSI⁻containing samples had higher binding energies than those with OTF (Fig. 2d), further confirming the more delocalized electron distribution of TFSI due to its symmetrical configuration, in contrast to the asymmetric nature of OTF.

Scanning electron microscopy (SEM) images revealed that the COF-Br sample consisted of aggregated, layered bulk structures (Fig. 2e). In contrast, the COF@CNT composite exhibited a uniform and conformal COF coating on the CNT surfaces (Fig. 2f and S2†), indicating successful integration of the conductive CNT network with the polar functional groups of the COF, which are known for their strong chemical adsorption capability. Notably, the morphology of the COF@CNT composites remained intact following anion exchange with TFSI and OTF (Fig. S3†). This indicates that modulation of the anionic environment can tailor the interfacial properties of COF@CNT materials, with potential implications for enhancing polysulfide adsorption and controlling redox kinetics in Li–S batteries.

Subsequently, a separator modification strategy was then implemented by uniformly coating the three COF@CNT composites onto commercial Celgard separators at a controlled loading to produce functionalized separators. This approach aimed to mitigate the polysulfide shuttle effect and improve the cycling stability of sulfur cathodes in Li–S batteries. The intrinsic physicochemical properties of the modified separators were first assessed, with a focus on ionic conductivity and Li⁺ transference number (Fig. 3a). Compared to the COF-Br@CNT-modified separator, the COF-TFSI and COF-OTF variants exhibited enhanced ionic conductivity and higher Li⁺ transference numbers. In particular, the COF-OTF-modified separator demonstrated an ionic conductivity of 1.71 mS cm⁻¹ (Fig. S4†) and a Li⁺ transference number of 0.85 (Fig. S5†), indicating that OTF⁻ effectively participates in the Li⁺ solvation sheath, resulting in a weaker Li⁺–anion binding and faster Li⁺ hopping between coordination sites.

Fig. 3 (a) Physicochemical properties including ionic conductivity and transference number. (b) EIS plots for three COF@CNTs modified cells. Nucleation test of Li₂S for (c) COF-Br@CNT, (d) COF-TFSI@CNT, and (e) COF-OTF@CNT, respectively. (f) CV tests of three modified cells.

Electrochemical impedance spectroscopy (EIS) was carried out on Li–S cells equipped with each type of modified separator (Fig. 3b). Among them, the COF-OTF@CNT-modified cell exhibited the lowest charge-transfer resistance, indicating enhanced electrolyte wettability and accelerated interfacial charge-transfer kinetics. This enhancement is attributed to the high polarity of OTF⁻, which strengthens the local electric field and promotes ion dissociation and mobility. The practical energy density of Li–S batteries is often constrained by sluggish Li₂S conversion kinetics at the cathode. To elucidate the role of the modified separators in this process, Li₂S deposition experiments were conducted using a catholyte containing 0.2 M Li₂S₈.⁵⁴ The COF-Br@CNT-modified separator yielded a Li₂S deposition capacity of 63.2 mAh g⁻¹ (Fig. 3c), which increased to 69.5 mAh g⁻¹ with the COF-TFSI@CNT-modified separator (Fig. 3d). Notably, the COF-OTF@CNT-modified separator achieved a significantly higher capacity of 136.1 mAh g⁻¹ (Fig. 3e).

These results highlight the critical influence of the tailored anionic microenvironment within the COF@CNT framework on promoting Li₂S nucleation and growth, thereby enhancing sulfur utilization and overall reaction kinetics in Li–S batteries.

Cyclic voltammetry (CV) measurements were further carried out to examine the redox behavior of the three modified Li–S cells. All cells exhibited two reduction peaks at approximately 2.3 V and 2.05 V, and a single oxidation peak at around 2.45 V (Fig. 3f), consistent with typical sulfur redox reactions.⁵⁵ While the COF-Br@CNT and COF-TFSI@CNT-modified cells showed comparable current response intensities, the COF-OTF@CNT-modified cell exhibited the highest peak currents for both reduction and oxidation processes. This further confirms the superior sulfur utilization and enhanced redox kinetics enabled by the COF-OTF@CNT modification strategy.

Comprehensive electrochemical measurements were performed to evaluate the performance of Li–S cells assembled with COF@CNT-modified separators. Rate capability tests revealed that the COF-OTF@CNT-modified cell exhibited superior high-rate performance compared to its COF-Br@CNT and COF-TFSI@CNT counterparts (Fig. 4a). Specifically, it delivered a high specific capacity of 810 mAh g⁻¹ at a current density of 5C, significantly outperforming the COF-Br@CNT and COF-TFSI@CNT cells, which achieved capacities of 436 and 668 mAh g⁻¹, respectively. As shown in Fig. 4b, the COF-OTF@CNT-modified cell also maintained a low polarization voltage of 0.37 V under 5C cycling, whereas the other two cells exhibited noticeably higher polarization (Fig. S6†), indicating enhanced reaction kinetics and reduced internal resistance.

Fig. 4 (a) Rate capabilities. (b) Galvanostatic charge–discharge profiles. (c) Cycling performance at 0.2C. (d) Polarization voltage comparison. (e) Rate performance under a high sulfur load of 5.0 mg cm⁻². (f) High-sulfur-load cycling in lean electrolyte. (g) Long-term cycling at 1.0C current.

The cycling stability of the three COF@CNT-modified Li–S cells was evaluated at a current rate of 0.2C (Fig. 4c). Following initial activation, the COF-Br@CNT, COF-TFSI@CNT, and COF-OTF@CNT cells delivered specific capacities of 1047, 1322, and 1367 mAh g⁻¹, respectively. Among them, the COF-OTF@CNT-modified cell maintained the highest reversible capacity over 100 cycles, demonstrating superior low-rate cycling stability. Comparative charge–discharge profiles at 0.2C showed that both the COF-TFSI and COF-OTF separators enabled enhanced discharge capacities at both the high-voltage (2.3 V) and low-voltage (2.1 V) plateaus relative to COF-Br, with the COF-OTF@CNT cell exhibiting the lowest voltage polarization of only 154 mV (Fig. 4d). These findings suggest that the integration of TFSI⁻ and OTF⁻ anions into the COF@CNT framework effectively promotes sulfur redox reactions by improving sulfur utilization and lowering the activation barriers for polysulfide conversion.

To further assess the practical applicability of the COF-OTF@CNT-modified separator, its electrochemical performance was tested using high-loading sulfur cathodes (5 mg cm⁻²) under lean electrolyte conditions (5 μL mg⁻¹). At a low current density of 0.05C, the cell delivered an initial discharge capacity of 1191 mAh g⁻¹. As the current density increased to 0.1, 0.2, 0.3, 0.5, and 1C, the capacity gradually declined but remained substantial, reaching 590 and 360 mAh g⁻¹ at 0.5C and 1C, respectively (Fig. S7†). Notably, upon reverting the current back to 0.05C, the discharge capacity recovered to 798 mAh g⁻¹ and exhibited stable cycling behavior without significant capacity fading (Fig. 4e).

The cycling stability of the COF-OTF@CNT separator was evaluated under practical operating conditions, including lean electrolyte usage (5 μL mg⁻¹), high sulfur loading (5 mg cm⁻²), and ambient temperature (25 °C), as shown in Fig. 4f. Following three initial activation cycles at 0.05C, the high-loading Li–S cell exhibited an initial specific capacity of 1015 mAh g⁻¹ at 0.1C, which stabilized at 883 mAh g⁻¹ after 100 cycles. This corresponds to an areal capacity of 4.42 mAh cm⁻² and a high capacity retention of 87%, outperforming the state-of-the-art lithium-ion battery systems.

To evaluate the long-term durability of the modified separators, cycling performance at 1C was systematically investigated (Fig. 4g). After two initial low-rate activation cycles, the COF-OTF@CNT-modified cell delivered an initial discharge capacity of 1220 mAh g⁻¹ at 1C, surpassing those of its COF-TFSI (1178 mAh g⁻¹) and COF-Br (998 mAh g⁻¹) counterparts. While the COF-Br-modified cell exhibited rapid capacity degradation within the first 200 cycles, both the COF-TFSI and COF-OTF@CNT cells demonstrated significantly enhanced cycling stability. Notably, the COF-OTF@CNT cell retained a high discharge capacity of 652 mAh g⁻¹ after 800 cycles, corresponding to an ultralow capacity decay rate of just 0.058% per cycle (Fig. S8†). Additionally, the average coulombic efficiency remained consistently high at 99.8% over the entire cycling period, indicating effective suppression of the polysulfide shuttle. Overall, the COF-OTF@CNT-modified cell exhibits superior electrochemical performance compared to most previously reported COF-based Li–S battery systems (Table S1†).

To further investigate the mechanism by which the COF-OTF@CNT-modified separator suppresses the polysulfide shuttle effect, a visualized polysulfide diffusion test was conducted. A headspace bottle containing a Li₂S₆ solution was sealed with the test separator placed over a hole in the bottle cap and then inverted into a larger bottle filled with blank electrolyte. Compared to the COF-OTF@CNT-modified separator, the bottle with the Celgard separator showed a light yellow color after standing still for 24 h (Fig. S9†), indicating the shuttling of Li₂S₆. Additionally, in situ Raman spectroscopy was further conducted to study the polysulfide migration behavior. A Li metal anode with a precisely machined aperture was used to monitor the migration of polysulfide species from the cathode to the anode, enabling a direct assessment of the separator's polysulfide-blocking capability.⁵¹ As shown in Fig. 5a, the unmodified Celgard-based cell exhibited distinct Raman signals on the anode side after 2 h of resting, corresponding to various lithium polysulfide species. Specifically, characteristic peaks at 180, 285, 402, and 455 cm⁻¹ were assigned to Li₂S₈, Li₂S₄, Li₂S₆, and Li₂S₅, respectively. Additionally, a pronounced peak at 488 cm⁻¹, attributable to the ether-based liquid electrolyte (LE), was observed (Fig. 5b).^20,56

Fig. 5 (a) Contour map and (b) selected curves of the in situ Raman spectral test with a Celgard separator. (c) Contour map and (d) selected curves of the in situ Raman spectral test with a COF-OTF@CNT modified separator in the discharging process.

In sharp contrast, no Raman signatures corresponding to lithium polysulfides were detected on the anode side of the cell equipped with the COF-OTF@CNT-modified separator during discharge; only the related LE peak at 488 cm⁻¹ was observed (Fig. 5c and d). This result clearly indicates that the COF-OTF@CNT separator effectively suppresses polysulfide migration. Upon subsequent charging, the Celgard-based cell continued to display strong polysulfide signals on the anode side, suggesting irreversible polysulfide accumulation and poor redox reversibility (Fig. S10†). In contrast, the modified separator exhibited the absence of polysulfide peaks, further confirming its ability to block shuttle effects. These findings highlight the crucial role of the COF-OTF@CNT separator in stabilizing Li–S batteries by physically confining polysulfides within the cathode compartment.

Given that the anion-regulated environment of COF@CNT enhances lithium polysulfide adsorption and conversion kinetics, this material is expected to deliver robust electrochemical performance across a broad temperature range. To validate this, we systematically investigated the temperature-dependent behavior of COF-OTF@CNT-modified Li–S batteries under both elevated and sub-ambient conditions.^57,58 As shown in Fig. 6a, the electrochemical performance was first evaluated at elevated temperatures ranging from 30 to 60 °C. With increasing temperature, a progressive reduction in polarization voltage was observed, indicating that elevated temperatures promote the redox kinetics of polysulfide species. Remarkably, the modified cell retained a high specific capacity of 1150 mAh g⁻¹ at 60 °C. Furthermore, under continuous cycling at 0.5C, a stable capacity of 677 mAh g⁻¹ was maintained after 150 cycles at this elevated temperature (Fig. 6b). In contrast, the cell with the unmodified separator exhibited rapid capacity decay, retaining only 450 mAh g⁻¹ after 150 cycles (Fig. S11†).

Fig. 6 Wide-temperature test of COF-OTF@CNT modified cells. (a) High-temperature test curves at 0.5C and temperatures ranging from 30 to 60 °C. (b) Cycling performance and (c) rate capability at 60 °C. (d) Low-temperature test curves at 0.5C and temperatures ranging from 30 to 0 °C. (e) Cycling performance and (f) rate capability at 0 °C. (g) Low-temperature cycling at 1.0C. (h) Wide-temperature performance comparison.

To assess the high-rate capability at elevated temperatures, rate performance at 60 °C was further examined (Fig. 6c). Impressively, the COF-OTF@CNT-modified cell delivered a discharge capacity of 766 mAh g⁻¹ at a high current density of 5C (Fig. S12†). Although some irreversible capacity loss was noted upon returning to lower current densities, this is likely attributable to temperature-induced polysulfide over-dissolution or electrolyte degradation. Subsequently, the low-temperature performance was investigated by gradually cooling the system from 30 °C to 0 °C. As illustrated in Fig. 6d, the cell still delivered an initial discharge capacity of 832 mAh g⁻¹ at 0 °C. During long-term cycling at 0.5C over 200 cycles, the capacity declined slightly from 825 to 737 mAh g⁻¹, corresponding to a high retention of 89.3% (Fig. 6e). Moreover, the high-sulfur loading cell (5.0 mg cm⁻²) demonstrates stable cycling performance at 0 °C under lean electrolyte conditions (Fig. S13†).

Rate capability at 0 °C revealed a capacity of 623 mAh g⁻¹ at 3C, which decreased to 367 mAh g⁻¹ at 5C (Fig. S14†), reflecting the persistent kinetic limitations under sub-zero conditions (Fig. 6f). However, when the current density was reduced stepwise back to 0.1C, the capacity substantially recovered, confirming that sluggish polysulfide conversion at low temperatures can be mitigated by slower cycling rates. In addition to 0.5C cycling, we also explored long-term cycling stability at a more demanding current density of 1C under both high and low temperature conditions. At 60 °C, the cell retained a reversible capacity of 595 mA h g⁻¹ after 400 cycles (Fig. S15†), while at 0 °C, the capacity decreased from 898 to 555 mAh g⁻¹ over 500 cycles, corresponding to a retention of 62% (Fig. 6g). Collectively, these results highlight the outstanding thermal adaptability of the COF-OTF@CNT-modified system, which maintains excellent electrochemical performance across a wide temperature window, outperforming many reported systems under comparable conditions (Fig. 6h and Table S2†).

Conclusions

In summary, we investigated an anionic center tuning strategy for ionized COF@CNT composites to address critical challenges in Li–S batteries, including polysulfide shuttling and limited performance across a wide temperature range. By replacing Br⁻ with LiTFSI and LiOTF, the interfacial properties of the COF were effectively optimized, resulting in enhanced ionic conductivity and Li⁺ transport. Comparative studies revealed that the OTF⁻ anion was more effective than TFSI⁻ in reducing charge transfer resistance and promoting Li₂S nucleation. As a result, the modified Li–S cells exhibited excellent cycling stability, with minimal capacity decay over 800 cycles at 1C and high capacity retention even at 0 °C.

This work highlights the potential of using anion-engineered COF@CNT composites as a viable strategy for developing high-performance Li–S batteries. Based on the results, the design of optimal anionic sites should consider key characteristics, including (1) high molecular polarity to promote ion dissociation and Li⁺ interaction; (2) asymmetric charge distribution to enable dynamic solvation and electrostatic coordination; (3) functional groups (e.g., –SO₃⁻ and –SO₂⁻) capable of LiPS adsorption and Li₂S anchoring; and (4) suitable molecular size and flexibility to minimize steric hindrance while preserving channel accessibility within the COF (e.g., FSI⁻).

Data availability

The data supporting this article have been included as part of the ESI.†

Author contributions

Z. Zheng: experiments, methodology, formal analysis, data curation, writing – original draft; W. Zhang: visualization, formal analysis; Q. Dai: visualization, formal analysis; H. Wu: formal analysis, funding acquisition, writing – review & editing; Z. Huang: visualization, formal analysis; Y. Zhang: visualization, formal analysis, supervision, writing – review & editing; B. Peng: investigation, visualization; L. Ma: investigation, supervision; J. Xu: project administration, funding acquisition, methodology, supervision, writing – review & editing.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

The authors acknowledge funding support from the National Natural Science Foundation of China (22309003) and the Natural Science Research Project of Anhui Province Education Department (2023AH051119), and the open funding from Shanghai Key Laboratory of Multi phase Materials Chemical Engineering (MMCE2024001). Dr Wu acknowledges funding support from the Natural Science Foundation of Anhui Province (2308085QE132). The authors also acknowledge the Shiyanjia Lab (https://www.shiyanjia.com) for the XPS and TEM measurements.

Notes and references

1. Q. Cheng, Z.-X. Chen, X.-Y. Li, L.-P. Hou, C.-X. Bi, X.-Q. Zhang, J.-Q. Huang and B.-Q. Li, J. Energy Chem., 2023, 76, 181–186.
2. W. Yao, J. Xu, L. Ma, X. Lu, D. Luo, J. Qian, L. Zhan, I. Manke, C. Yang, P. Adelhelm and R. Chen, Adv. Mater., 2023, 35, 2212116.
3. J. Wang, J. Zhang, Y. Zhang, H. Li, P. Chen, C. You, M. Liu, H. Lin and S. Passerini, Adv. Mater., 2024, 36, 2402792.
4. Z. Zheng, X. Qian, D. Bin, Y. Wang and J. Xu, Chem. Commun., 2025, 61, 6486–6489.
5. K. Chen, Y. Zhang, Z. Fan, J. Zhu, Q. Xu and J. Xu, Adv. Funct. Mater., 2025 DOI:10.1002/adfm.202500574.
6. J. Pu, Y. Tan, J. Yin, Z. Shen, S. Liu, K. Zhang, L. Zhou and Y. Yao, J. Energy Chem., 2025, 104, 740–748.
7. L. Ma, Y. Wang, Z. Wang, J. Wang, Y. Cheng, J. Wu, B. Peng, J. Xu, W. Zhang and Z. Jin, ACS Nano, 2023, 17, 11527–11536.
8. Y. Song, W. Cai, L. Kong, J. Cai, Q. Zhang and J. Sun, Adv. Energy Mater., 2020, 10, 1901075.
9. Y. Zhuang, H. Yang, Y. Li, Y. Zhao, H. Min, S. Cui, X. Shen, H.-Y. Chen, Y. Wang and J. Wang, ACS Nano, 2025, 19, 11058–11074.
10. K. Chen, Y. Zhu, Z. Huang, B. Han, Q. Xu, X. Fang and J. Xu, ACS Nano, 2024, 18, 34791–34802.
11. H. Yuan, H.-J. Peng, B.-Q. Li, J. Xie, L. Kong, M. Zhao, X. Chen, J.-Q. Huang and Q. Zhang, Adv. Energy Mater., 2019, 9, 1802768.
12. H. Yang, Y. Qiao, Z. Chang, P. He and H. Zhou, Angew. Chem., Int. Ed., 2021, 60, 17726–17734.
13. H. Yang, J. Chen, J. Yang and J. Wang, Angew. Chem., Int. Ed., 2020, 132, 7374–7386.
14. J. Wang, Y. Xu, Y. Zhuang, Y. Li, H.-H. Chang, H. Min, X. Shen, H.-Y. Chen, H. Yang and J. Wang, Adv. Energy Mater., 2024, 14, 2410630.
15. B. Han, X. Cao, X. Liu, K. Chen, L. Xiao, Q. Xu, S. Wu and J. Xu, Adv. Funct. Mater., 2025, 35, 2415782.
16. H. Zhang, J. Chen, Z. Li, Y. Peng, J. Xu and Y. Wang, Adv. Funct. Mater., 2023, 33, 2304433.
17. J. Xu, H. Zhang, F. Yu, Y. Cao, M. Liao, X. Dong and Y. Wang, Angew. Chem., Int. Ed., 2022, 134, e202211933.
18. D.-R. Deng, F. Xue, C.-D. Bai, J. Lei, R. Yuan, M.-S. Zheng and Q.-F. Dong, ACS Nano, 2018, 12, 11120–11129.
19. F.-Y. Lan, H.-Y. Zhang, J. Fan, Q. Xu, H. Li and Y.-L. Min, ACS Appl. Mater. Interfaces, 2021, 13, 2734–2744.
20. Y. Lin, J. Wang, X. Zhang, X. Cheng, Q. Zhuang, J. Zhang, Q. Guan, Y. Wang, C. Shen, H. Lin, L. Zhan, L. Ling and Y. Zhang, Adv. Funct. Mater., 2025, 35, 2501496.
21. F. Na, X. Li, J. Wang, X. Cheng, J. Zhang, Y. Wang, H. Lin, L. Zhan, L. Ling and Y. Zhang, Energy Stor. Mater., 2025, 78, 104228.
22. Y. He, S. Wu, Q. Li and H. Zhou, Small, 2019, 15, 1904332.
23. Y. Li, Q. Zhang, S. Shen, S. Wang, L. Shi, D. Liu, Y. Fu and D. He, Chem. Eng. J., 2023, 468, 143562.
24. R.-B. LingHu, J.-X. Chen, J.-H. Zhang, B.-Q. Li, Q.-S. Fu, G. Kalimuldina, G.-Z. Sun, Y.-H. Han and L. Kong, J. Energy Chem., 2024, 93, 663–668.
25. S. Han, B. Hu, Z. Zheng, K. Huang, Z. Fan, D. Luo, T. Xu, T. Zhu and J. Xu, J. Power Sources, 2025, 636, 236575.
26. Y. He, D. Xiong, Y. Luo, W. Zhang, S. Liu, Y. Ye, M. Wang, Y. Chen, H. Liu, J. Wang, H. Lin, J. Su, X. Wang, H. Shu and M. Chen, Adv. Funct. Mater., 2024, 35, 2410899.
27. R. Yan, Z. Zhao, M. Cheng, Z. Yang, C. Cheng, X. Liu, B. Yin and S. Li, Angew. Chem., Int. Ed., 2023, 62, e202215414.
28. J. Pu, S. Fan, Z. Shen, J. Yin, Y. Tan, K. Zhang, B. Wu, G. Hong and Y. Yao, Adv. Funct. Mater., 2025, 2424215.
29. Y. Jiang, P. Liang, M. Tang, S. Sun, H. Min, J. Han, X. Shen, H. Yang, D. Chao and J. Wang, J. Mater. Chem. A, 2022, 10, 22080–22092.
30. L. Peng, Z. Wei, C. Wan, J. Li, Z. Chen, D. Zhu, D. Baumann, H. Liu, C.-S. Allen, X. Xu, A.-I. Kirkland, I. Shakir, Z. Almutairi, S. Tolbert, B. Dunn, Y. Huang, P. Sautet and X. Duan, Nat. Catal., 2020, 3, 762–770.
31. W. Hua, T. Shang, H. Li, Y. Sun, Y. Guo, J. Xia, C. Geng, Z. Hu, L. Peng, Z. Han, C. Zhang, W. Lv and Y. Wan, Nat. Catal., 2023, 6, 174–184.
32. W. Hua, H. Li, C. Pei, J. Xia, Y. Sun, C. Zhang, W. Lv, Y. Tao, Y. Jiao, B. Zhang, S.-Z. Qiao, Y. Wan and Q. Yang, Adv. Mater., 2021, 33, 2101006.
33. B. Hu, J. Xu, Z. Fan, C. Xu, S. Han, J. Zhang, L. Ma, B. Ding, Z. Zhuang, Q. Kang and X. Zhang, Adv. Energy Mater., 2023, 13, 2203540.
34. B. Hu, S. Han, T. Xu, D. Luo, T. Zhu and J. Xu, J. Energy Storage, 2024, 93, 112374.
35. D. Han, L. Sun, Z. Li, W. Qin, L. Zhai, Y. Sun, S. Tang and Y. Fu, Energy Stor. Mater., 2024, 65, 103143.
36. Y. Cao, Y. Zhang, C. Han, S. Liu, S. Zhang, X. Liu, B. Zhang, F. Pan and J. Sun, ACS Nano, 2023, 17, 22632–22641.
37. L. Bi, J. Xiao, Y. Song, T. Sun, M. Luo, Y. Wang, P. Dong, Y. Zhang, Y. Yao, J. Liao, S. Wang and S. Chou, Carbon Energy, 2024, 6, e544.
38. D. Chen, S. Huang, L. Zhong, S. Wang, M. Xiao, D. Han and Y. Meng, Adv. Funct. Mater., 2020, 30, 1907717.
39. S. Haldar, M. Wang, P. Bhauriyal, A. Hazra, A. Khan, V. Bon, M. Isaacs, A. De, L. Shupletsov, T. Boenke, J. Grothe, T. Heine, E. Brunner, X. Feng, R. Dong, A. Schneemann and S. Kaskel, J. Am. Chem. Soc., 2022, 144, 9101–9112.
40. R. Yan, B. Mishra, M. Traxler, J. Roeser, N. Chaoui, B. Kumbhakar, J. Schmidt, S. Li, A. Thomas and P. Pachfule, Angew. Chem., Int. Ed., 2023, 62, e202302276.
41. X. Liu, X. Sun, R. Yan, J. Yang, M. Wu, R. Zhu, S. Li and B. Yin, Adv. Funct. Mater., 2025 DOI:10.1002/adfm.202505986.
42. S. Lv, X. Ma, S. Ke, Y. Wang, T. Ma, S. Yuan, Z. Jin and J.-L. Zuo, J. Am. Chem. Soc., 2024, 146, 9385–9394.
43. J. Liu, H. Li, J. Wang, Y. Zhang, D. Luo, Y. Zhao, Y. Li, A. Yu, X. Wang and Z. Chen, Adv. Energy Mater., 2021, 11, 2101926.
44. B. Sun, B. Jia, H. Yu, C. Yao, W. Xie and Y. Xu, J. Power Sources, 2025, 632, 236325.
45. J. Xu, S. An, X. Song, Y. Cao, N. Wang, X. Qiu, Y. Zhang, J. Chen, X. Duan, J. Huang, W. Li and Y. Wang, Adv. Mater., 2021, 33, 2105178.
46. B. Sun, J. Liu, A. Cao, W. Song and D. Wang, Chem. Commun., 2017, 53, 6303–6306.
47. H. Dong, M. Lu, Y. Wang, H.-L. Tang, D. Wu, X. Sun and F.-M. Zhang, Appl. Catal., B, 2022, 303, 120897.
48. D. Yan, L. Song, F. Kang, X. Mo, Y. Lv, J. Sun, H. Tang, X. Zhou and Q. Zhang, Angew. Chem., Int. Ed., 2025, e202422851.
49. F. Xu, S. Jin, H. Zhong, D. Wu, X. Yang, X. Chen, H. Wei, R. Fu and D. Jiang, Sci. Rep., 2015, 5, 8225.
50. R. Gomes and A. Bhattacharyya, ACS Sustainable Chem. Eng., 2020, 8, 5946–5953.
51. J. Xu, W. Tang, C. Yang, I. Manke, N. Chen, F. Lai, T. Xu, S. An, H. Liu, Z. Zhang, Y. Cao, N. Wang, S. Zhao, D. Niu and R. Chen, ACS Energy Lett., 2021, 6, 3053–3062.
52. L. Sun, Z. Li, L. Zhai, H. Moon, C. Song, K.-S. Oh, X. Kong, D. Han, Z. Zhu, Y. Wu, S.-Y. Lee and L. Mi, Energy Stor. Mater., 2024, 66, 103222.
53. X.-F. Liu, H. Chen, R. Wang, S.-Q. Zang and T. Mak, Small, 2020, 16, 2002932.
54. J. Xu, F. Yu, J. Hua, W. Tang, C. Yang, S. Hu, S. Zhao, X. Zhang, Z. Xin and D. Niu, Chem. Eng. J., 2020, 392, 123694.
55. J. Xu, W. Tang, F. Yu, S. Zhao, D. Niu, X. Zhang, Z. Xin and R. Chen, J. Mater. Chem. A, 2020, 8, 19001–19010.
56. X. Zhang, X. Li, Y. Zhang, X. Li, Q. Guan, J. Wang, Z. Zhuang, Q. Zhuang, X. Cheng, H. Liu, J. Zhang, C. Shen, H. Lin, Y. Wang, L. Zhan and L. Ling, Adv. Funct. Mater., 2023, 33, 2302624.
57. A. Zhu, S. Li, Y. Yang, B. Peng, Y. Cheng, Q. Kang, Z. Zhuang, L. Ma and J. Xu, Small, 2024, 20, 2305494.
58. J. Xu, A. Zhu, Z. Zheng, Y. Qi, Y. Cheng, Y. Cao, B. Peng, L. Ma and Y. Wang, J. Energy Chem., 2025, 101, 702–712.

---

Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5ta03689e

---