Atomic-scale insight into the lattice volume plunge of Li_xCoO₂ upon deep delithiation

Abstract

The practical capacity utilization of LiCoO₂ is limited to 50–70% due to the dramatic volume shrinkage induced cracks and subsequent interface parasitic reactions at high voltage. However, the fundamental understanding of the dramatic lattice volume shrinkage remains unclear. In this work, we discover that the delithiation paths have an impact on the lattice volume turning point of Li_xCoO₂, where the corresponding capacity utilization can be as low as 62.5% or as high as 75% consequently. In addition, the O ↔ O interlayer distance across the Li layer (O_(d3)) mainly contributes to the volume increase before 62.5–75% delithiation, and the O ↔ O interlayer distance across the Co layer (O_(d2)) is the dominant factor for the dramatic volume decrease after the volume turning point. The electron localization function (ELF) around O keeps increasing during delithiation and it increases significantly after more than 62.5% delithiation, indicating that the lattice oxygen participates in charge compensation during the whole delithiation process and it becomes the main contributor to the charge compensation at a high delithiated state compared with Co. This work unravels the fundamental reason for the dramatic volume shrinkage of Li_xCoO₂ at high voltage. It claims that the antisite defects (Co_Li) of LiCoO₂ should be designed carefully owing to the weaker Co–O bond strength and further oxygen release, which accelerate the degradation of LiCoO₂, although it can increase the voltage of LiCoO₂. More importantly, LiCoO₂ material design with elemental doping, oxygen defects (V_O), Li defects (V_Li), and Co defects (V_Co) will contribute to the capacity utilization of LiCoO₂.

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Introduction

LiCoO₂ was the first commercialized cathode material for lithium-ion batteries (LIBs) by the Sony Corporation in 1991 and it remains one of the most heavily used cathodes for consumer electronics owing to its high tap density, high initial coulombic efficiency, and high volumetric energy density.^1–5 For a long time, only about half of the Li was utilized in the LiCoO₂ cathode material. Researchers try to achieve more capacity while maintaining the stability of the LiCoO₂ cathode material to fully utilize the energy density, such as doping and coating, which enables reversible Li-utilization up to 0.7 at high voltage,⁴ and little or no oxygen release from the bulk.⁶ However, deeper delithiation would lead to oxygen release or particle breakage, leading to capacity fading because of prominent parasitic reactions at the Li_xCoO₂/electrolyte interface and material loss.^4,7–9 These indicate that keeping the particle integrity during deep lithiation is important to achieve LiCoO₂ with high capacity.

Previous studies showed that the lattice volume of LiCoO₂ experiences a dramatic decrease at high voltage and the volume turning points differ depending on different LiCoO₂ samples.^4,9–13 The existence of the sample difference results in the variation of capacity utilization of LiCoO₂. The reported dramatic volume turning point of Li_xCoO₂ ranges between 50% and 70% delithiation rates. Dahn et al. reported that the volume of LiCoO₂ decreases around 4.2 V and the corresponding Li utilization is around 50%.¹² Besides, the volume change of LiCoO₂ is thought to be dominated by lattice c, and Tarascon et al. proposed that the lattice c parameter stably increased owing to the increasing electrostatic repulsion of O ↔ O interactions of adjacent CoO₆ layers during delithiation. Then, the c parameter underwent a dramatic decrease when the delithiation ratio was 54%, stemming from a transformation from monoclinic distortion to a hexagonal structure.^10,14 Van der Ven et al. also demonstrated that the lattice c parameter increases and then decreases dramatically when delithiation was over 60% Li.¹¹ Liu et al. claimed that the reversible Li utilization of La- and Al-co-doped LiCoO₂ was increased to 70% with the cut-off voltage increasing to 4.5 V.⁴ Barker et al. showed that the Li utilization in LiCoO₂ reached up to 64% with 100% coulombic efficiency.¹³ It is well accepted that the dramatic volume change of Li_xCoO₂ at high voltage is closely related to the O ↔ O interaction environments in LiCoO₂, including O ↔ O interaction environments in the CoO₆ layer and O ↔ O interaction environment across the Li layer. Recently, the oxygen redox reaction is regarded as the predominant factor for the electrochemical performance of transition metal oxide cathodes at high voltage,^15–20 where O contributes much more to charge compensation than Co.⁶ The oxygen redox reaction at high voltage has an impact on the volume change of Li_xCoO₂. However, there is no clear understanding of the variation of the dramatic volume turning point of Li_xCoO₂ at high voltage, as well as the explicit perception regarding the change of O ↔ O interaction environment.

In this work, the fundamental reasons for the lattice volume shrinkage of LiCoO₂ during delithiation are investigated via theoretical calculations, especially at high voltage. We found that there exists a relationship between delithiation paths and the lattice volume plunging point during charging, which determines the reversible capabilities of the LiCoO₂ cathode. Four different random delithiation paths are considered. The O ↔ O distances with three different O ↔ O interaction environments in Li_xCoO₂ along delithiation path 1 are further investigated, which are O ↔ O intralayer distance (O_(d1)), O ↔ O interlayer distance across the Co layer (O_(d2)), and O ↔ O interlayer distance across the Li layer (O_(d3)). To further identify the electronic properties, the electron localization function (ELF) of Li_xCoO₂ is calculated. There is peroxo-like O–O formation during delithiation. The analysis of the total density of states (TDOS) of Li_xCoO₂ and the projected density of states (PDOS) of O and Co uncovers that the oxygen oxidation and the dramatic volume shrinkage point of Li_xCoO₂ are correlated. In addition, the phase transition of Li_xCoO₂ is examined for the reliability of these simulation results. This work provides theoretical guidance for reasonable materials design and synthesis to achieve a higher capacity utilization of LiCoO₂ cathode.

Methods

The lattice volume plunge of Li_xCoO₂ during delithiation is crucial for the energy density of LIBs. To study the fundamental reason for the lattice volume shrinkage of Li_xCoO₂ during delithiation, density functional theory (DFT) calculations are performed by using the Vienna Ab initio Simulation Package (VASP) code.²¹ The Perdew–Burke–Ernzerhof (PBE) functional is employed to approximate the exchange–correlation function. The projector augmented wave (PAW) method^22–24 is used for electron and core interactions. A Hubbard U parameter of 4.91 eV is applied to the delocalization correction of the Co d-orbital.²⁵ The cutoff energy is set at 520 eV. The convergence criterion in the electronic self-consistent iteration is 10⁻⁴ eV and the convergence criterion for ionic relaxation is set at 0.03 eV Å⁻¹. The layered LiCoO₂ (space group: R3m) structure is used for calculations, which consists of 48 Li, 48 Co, and 96 O. The cell volume is allowed to change²⁶ and the delithiated Li_xCoO₂ structure is fully relaxed during structure optimization. The volume calculation of Li_xCoO₂ is performed by considering four different delithiation paths. The electron localization function (ELF) of Li_xCoO₂ at different delithiation states is examined²⁷ to further study the valence states and bonding states of Co and O. The ELF and the phase transformation of Li_xCoO₂ is visualized with the aid of VESTA software.²⁸ The density of states (DOS)²⁹ of Li_xCoO₂ is examined via executing the ‘split_dos’ script from the VASP output. Besides, the Bader charge analysis^30–33 is performed to calculate the charge states of Co and O in Li_xCoO₂ during the delithiation process. In addition, the volume change of the Li_xCoO₂ cathode during delithiation is characterized using in situ X-ray diffraction (XRD).³⁴

Results and discussion

To reveal the fundamental reason for the volume change of Li_xCoO₂ during Li extraction, the lattice volumes of Li_xCoO₂ at different delithiation states are first calculated. The layered LiCoO₂ structure with the R3m space group used for density functional theory (DFT) calculations is shown in Fig. 1(a) and Fig. S1a (ESI†). Fig. 1(a) also demonstrates that the lattice volume of LiCoO₂ is closely related to the intralayer O ↔ O distance O_(d1), the O ↔ O interlayer distance across the Co layer O_(d2), and the O ↔ O interlayer distance across the Li layer O_(d3). As shown in Fig. 1(b), the volume of Li_xCoO₂ with four different delithiation paths stably increases and then decreases dramatically when 62.5–75% Li is removed from the host, which has the same trend as the volume change of Li_xCoO₂ measured with the in situ XRD experiment (Fig. S1b, ESI†). The simulation results are different from the experimental results because the simulation results are based on an ideal model, assuming that the LiCoO₂ particles are uniform and pure single crystals. However, in reality, it is challenging to reach the theoretical value. In addition, the practical LiCoO₂ particles in experiments possess different kinds of defects. There are four types of defects in LiCoO₂, including antisite cation (Co_Li), Li-ion vacancy (V_Li), Co-ion vacancy (V_Co), and O-ion vacancy (V_O).³⁵ The antisite defects and V_O defects lead to an increase in intercalation potential. A higher intercalation potential of LiCoO₂versus Li/Li⁺ indicates a higher discharge voltage.³⁶ Meanwhile, the LiCoO₂ with antisite defects (Co_Li) contributes to weaker Co–O bond strength and further oxygen release,^37,38 which might be responsible for the variation of the dramatic volume change point of LiCoO₂. Whilst the V_Li and V_Co defects are responsible for the electron conductivity and charge compensation during delithiation. It is also reported that oxygen defects can ensure a high degree of oxygen redox.³⁹ Furthermore, it is claimed that the phase transitions and volume variation are very sensitive to the impurity levels of LiCoO₂ particles and it can be used as a quality check for the synthetic LiCoO₂ material.^13,40 Fig. S1c (ESI†) shows that the lattice c parameter of Li_xCoO₂ increases with delithiation and then decreases after more than 62.5–75% delithiation, which shows the same trend as the volume change of Li_xCoO₂. Meanwhile, the lattice a parameter of Li_xCoO₂ decreases and then increases after more than 62.5–75% removal of Li (Fig. S1d, ESI†), which is consistent with reported experimental results.⁴¹ It also shows that the volume change of Li_xCoO₂ is influenced by the lattice c parameter of Li_xCoO₂, which is consistent with reported work.¹¹ More importantly, it is reported that the ordering of lithium and vacancy has a profound effect on the electrochemical performance of Li-ion batteries.⁴² The lattice volume of Li_xCoO₂ shrinks at different delithiation capacities by considering four different delithiation paths. Fig. 1(b) clearly shows that different delithiation paths in Li_xCoO₂ produce different volume turning points, where it is between 62.5% and 75%, explaining why there exists a dramatic volume turning point difference between different experimental works. The difference in delithiation paths during the charging process may come from material defects and synthesis process of LiCoO₂. To improve the delithiation performance of LiCoO₂, the antisite defects of LiCoO₂ should be designed carefully because although it contributes to the increase of the voltage of LiCoO₂, it will cause a weaker Co–O bond strength and further oxygen release as well. More crucially, LiCoO₂ material design with V_O, V_Li and V_Co will contribute to the improvement of voltage, electron conductivity, and charge compensation during the delithiation process.

Fig. 1 (a) The three different O ↔ O interactions including the O ↔ O distances O_(d1), O_(d2) and O_(d3), and schematic of four different random delithiation paths in Li_xCoO₂ considered during volume calculations using DFT; (b) the volume change of Li_xCoO₂ along four different random delithiation paths. It demonstrates that the volume of Li_xCoO₂ stably increases and then decreases dramatically when 62.5–75% Li is removed from the host, which has the same tendency as the volume change of Li_xCoO₂ measured with the XRD experiment.

To further identify the fundamental reason for the volume changes of Li_xCoO₂, one of the four delithiation paths is chosen to analyze the change of O ↔ O interactions and the Co ↔ O interaction during delithiation. The initial delithiation structure of Li_xCoO₂ along four different delithiation paths is shown in Fig. 2(a) and the Li vacancy formation energy of the four different delithiation paths is demonstrated in Fig. 2(b). The Li formation energy can measure how easily for Li to be extracted from the host, where a lower Li formation energy indicates the easier formation of Li vacancy. It shows that Li prefers to be extracted from the host during the whole delithiation owing to the negative value of Li vacancy formation energy. Besides, the Li vacancy formation energy of the four delithiation paths is almost the same when delithiation is less than 75%, except that there is a small difference when 12.5% Li is extracted. The Li vacancy formation energy of path 3 becomes the lowest and that of path 4 becomes the highest when delithiation is more than 75%. Based on the Li vacancy formation energy of the four delithiation paths, path 1 is selected for further analysis because the Li vacancy formation energy values of path 1 are located in the middle of the four paths during delithiation process. Fig. 2(c) shows that the Co ↔ O distance keeps decreasing from 1.93 Å to 1.88 Å, coinciding with the increasing charge state of Co attributed to the charge compensation delithiation. Besides, the O ↔ O intralayer distance O_(d1) decreases slightly from 2.83 Å to 2.79 Å before delithiation reaching 62.5% and then increases rapidly to 2.86 Å between 62.5% and 100% delithiation (Fig. 2(c)). Meanwhile, the O ↔ O distance across the Co layer O_(d2) is almost unchanged until 37.5% delithiation and the O ↔ O distance across the Co layer O_(d2) decreases dramatically from 2.62 Å to 2.46 Å after the delithiation is more than 62.5%. In contrast, the O ↔ O interlayer distance across the Li layer O_(d3) increases slightly and then increases dramatically after 62.5% Li is removed (Fig. 2(c)). The lowest O ↔ O distance is around 2.46 Å, which is almost the same as the reported results.⁶ The O ↔ O interlayer distance across the Co layer and Li layer dominates the volume change of LiCoO₂ during delithiation. The O ↔ O interlayer distance across the Li layer O_(d3) dominates the volume change of Li_xCoO₂ when delithiation is less than 62.5% due to the electrostatic repulsion interaction between negatively charged O (Fig. 2(d)). More importantly, the O ↔ O interlayer distance across the Co layer O_(d2) is mainly responsible for the dramatic volume turning point of Li_xCoO₂ when delithiation is more than 62.5% owing to the oxygen oxidation at high voltage.

Fig. 2 The Li_xCoO₂ structure during initial delithiation with four different delithiation paths (a); the Li vacancy formation energy of Li_xCoO₂ along four different delithiation paths (b); the Co ↔ O distance, the O ↔ O intralayer distance O_(d1), the O ↔ O interlayer distance across the Co layer O_(d2), and the O ↔ O interlayer distance across the Li layer O_(d3) along delithiation path 1 (c); the schematic illustrating the mechanism of O ↔ O interaction induced volume change at different delithiation states. The O ↔ O interlayer distance across the Li layer O_(d3) mainly contributes to the increasing volume of Li_xCoO₂ when delithiation is less than 62.5% due to the electrostatic repulsion interaction between negatively charged O (d).

To further investigate the electronic structure of the three O ↔ O interaction environments that induced the dramatic volume change of Li_xCoO₂, the electron localization function (ELF) of Li_xCoO₂ is calculated.⁴³ The ELF results show the bonding type and lone pair electrons of Li_xCoO₂, where the red color means fully localized and the blue color represents fully delocalized electrons. The fully localized electrons indicate the existence of a lone-pair electron, while the delocalized electrons imply the bonding state. Fig. 3(a) and Fig. S2a (ESI†) illustrate that the ELF around O keeps increasing during delithiation, implying that there exist more lone-pair electrons and the valence state of oxygen gradually changes from O²⁻ to (O₂)ⁿ⁻ (1 ≤ n ≤ 3), which indicates that the oxygen contributes to the charge compensation and there is O–O bond formation during the delithiation process. But Yang et al. claimed that there is no O–O bond formation via COOP analysis.⁶ We believe the ELF calculation is more comprehensive and reasonable because the electron localization function is calculated by considering the entire Li_xCoO₂, whereas the COOP analysis is conducted only checking a specific O–O bonding state in Li_xCoO₂, which is not sufficient to represent the whole Li_xCoO₂ structure during delithiation. The 2D electron localization function of Li_xCoO₂ shown in Fig. 3(b) and Fig. S2b (ESI†) is sliced with half of lattice b and the Miller index is (010), and it clearly shows that the ELF around O increases significantly after more than 62.5% delithiation. Therefore, the lattice oxygen in Li_xCoO₂ participates in charge compensation during the whole delithiation process and it becomes the main contributor to the charge compensation at a highly delithiated state compared with Co, where the oxygen redox reaction occurs.

Fig. 3 The 3D (a) and 2D (b) electron localization function of Li_xCoO₂ during delithiation (the red color means electron localization, indicating the existence of lone pair electrons, while the blue color means electron delocalization showing that there is a bonding state). The electrons localized around O increase during delithiation and the ELF increases dramatically after delithiation is more than 62.5%, implying that O oxidation occurs and the lattice oxygen mainly contributes to the charge compensation at a high delithiation state.

To further reveal the electronic properties of Li_xCoO₂ during delithiation, the total density of states (TDOS) and the projected density of states (PDOS) of O and Co in Li_xCoO₂ are calculated. Fig. 4(a) and Fig. S3a (ESI†) display that the highest energy peak of TDOS shifts to a lower energy level during delithiation. The lower energy state of TDOS suggests that the electrons in an atomic orbital are more difficult to escape. Therefore, it becomes harder for Li and electrons to escape from the Li_xCoO₂ host during delithiation, which is reasonable due to the limited reversibility of LiCoO₂ cathode materials. Then, the electronic properties of O in Li_xCoO₂ are analyzed and the lattice oxygen atoms with and without surrounded Li extracted are considered. The O_number 30 and O_number 76 are in the oxygen sites with and without surrounded Li extracted respectively. The atomic environments of O_number 30 and O_number 76 are shown in Fig. S3b (ESI†). As illustrated in Fig. 4(b) and Fig. S3c (ESI†), the energy level of the PDOS peak of O_number 30 initially increases and then decreases when delithiation is around 62.5%, which indicates that oxygen oxidation occurs more easily when delithiation increases to 62.5%. However, after the dramatic volume change turning point, the energy level of the PDOS peak decreases, implying that it becomes more difficult for oxygen oxidation to occur when the dramatic volume change of Li_xCoO₂ starts. It agrees well with the volume change and the O ↔ O distance calculation. It further provides the fundamental reason for the dramatic volume change occurring after more than 62.5% delithiation, corresponding to the reported experimental results that the reversible capacity of Li_xCoO₂ is around 50–70%.^12,13 Therefore, the oxygen oxidation and the dramatic volume change point of Li_xCoO₂ are correlated. The energy level of the PDOS peak of O_number 76 also increases and then decreases, demonstrating that the oxygen oxidation capability is influenced by the whole delithiation state instead of the local atomic environment (Fig. 4(c) and Fig. S3d, ESI†). In addition, the PDOS of Co is checked and the atomic environments of Co_number 20 and Co_number 38 are demonstrated in Fig. S3b (ESI†). As shown in Fig. 4(d) and Fig. S3e (ESI†), the energy level of the PDOS peak of Co_number 20 increases with delithiation and then decreases because the dramatic volume change of Li_xCoO₂ starts. The energy level of the PDOS of Co_number 38 shows the same trend as Co_number 20 (Fig. 4(e) and Fig. S3f, ESI†), which suggests that the Co oxidation is also mainly related to the whole delithiation state of Li_xCoO₂ instead of the local atomic environment.

Fig. 4 The TDOS of Li_xCoO₂ during delithiation (a), the PDOS of O_number 30 with surrounded Li extracted (b), the PDOS of O_number 76 without surrounded Li extracted (c), and the PDOS of Co_number 20 (d) and Co_number 38 (e) during delithiation. The energy level of the PDOS peak of O keeps increasing until 62.5% Li is extracted from Li_xCoO₂, implying that it becomes easier for O oxidation to occur with increasing delithiation, while the energy level of the PDOS peak shifts to a lower energy level when delithiation is more than 62.5%, indicating that there is a correlation between O oxidation and the dramatic volume change of Li_xCoO₂.

To uncover the effect of oxygen charge compensation for delithiation on the dramatic volume change of Li_xCoO₂, the average charge states of all O and Co, and the charge states of O_number 30, O_number 76, Co_number 20, and Co_number 38 are calculated via Bader analysis.^30–33 The average charge state of O increases from −1.05 to −0.67 (Fig. 5(a)) and the average charge state of Co keeps increasing from +1.25 to +1.33 (Fig. 5(b)), which is close to previously calculated results.^6,11 This reveals that both Co and O participate in the charge compensation during the delithiation process but for different stages. The charge compensation for delithiation is predominated by Co via changing Co³⁺ to Co⁴⁺ when less than 62.5% Li is removed and the charge compensation for delithiation is dominated by O at a high delithiation state through changing from O²⁻ to (O₂)ⁿ⁻. Besides, the charge states of individual O_number 30, O_number 76, Co_number 38, and O_number 76 in Li_xCoO₂ are calculated (Fig. 5(a) and (b)), which show that there exists a slight difference between the average charge state and individual Co and O in Li_xCoO₂. The charge states of Co and O are almost linear with the delithiation state, while the charge states of individual Co and O change dramatically around 62.5% delithiation. This reveals that the charge compensation of Co and O in Li_xCoO₂ for delithiation is not uniform. A reasonable elemental doping, such as La and Al, can mitigate this non-uniformity and stabilize the crystalline structure of L_xCoO₂ at a high delithiation state.^4,44–47

Fig. 5 The average charge states of all O, individual O_number 30 with surrounded Li extracted, and individual O_number 76 without surrounded Li extracted in Li_xCoO₂ during delithiation (a); the average charge states of all Co, individual Co_number 20, and individual Co_number 38 in Li_xCoO₂ during delithiation (b).

In addition, the change of O ↔ O interaction environments in the presence of CoO₆ slab migration during delithiation, which is correlated with the phase transformation of the Li_xCoO₂ structure. The phase transformation of Li_xCoO₂ directly influences the volume change of Li_xCoO₂. Fig. 6 demonstrates that the Co layer has a slight glide when 12.5% and 25% Li are extracted from LiCoO₂. The Co layer undergoes a huge displacement when the delithiation is more than 62.5%. The CoO₆ slab continues to glide, and the gradual angle, defined as the Co stacking in the LiCoO₂ along the 001 direction, decreases with further delithiation, which is consistent with recently reported in situ XRD and ex situ STEM.⁴⁸ This also indicates that the Li_xCoO₂ evolves from the O3 phase to the O1 phase, which also agrees well with reported observation.⁴⁸ More notably, this demonstrates that there is an accumulation of vacancy phenomenon, which is one of the main factors causing the phase transformation of LiCoO₂. The accumulation of Li vacancies becomes more severe with delithiation, accompanied by the rich-vacancy phase formation owing to the lower energy state. Therefore, this theoretically confirms that the CoO₆ slab glides continuously and is an intelligent dynamic response to the delithiation process, disclosing the existence of the accumulation of vacancy phenomenon in Li_xCoO₂ cathode materials during delithiation.

Fig. 6 The phase transformation of Li_xCoO₂ during delithiation: the Li_xCoO₂ evolves from the O3 phase to the O1 phase and the gradual angle keeps decreasing during delithiation.⁴⁸

Conclusion

In this work, it reveals that the different delithiation paths have an impact on the initiation of volume shrinkage of Li_xCoO₂, which ranges between 62.5% and 75% delithiation. This means that the available capacity of the LiCoO₂ cathode is tunable by manipulating Li extraction sites and LiCoO₂ with poor reversible capacity can be improved via materials synthesis. In addition, the O ↔ O interlayer distance across the Li Layer (O_(d3)) mainly contributes to the volume increase when less than 62.5–75% removal of Li and the O ↔ O interlayer distance across the Co layer (O_(d2)) dominates the dramatic volume shrinkage of Li_xCoO₂ when delithiation is more than 62.5%. The ELF calculation shows that there is peroxo-like O ↔ O formation during delithiation, which is more reasonable than the reported COOP analysis for only specific O–O bonding state. Furthermore, the oxygen oxidation and the dramatic volume change point of Li_xCoO₂ are correlated. The delithiation state of Li_xCoO₂ will influence oxygen oxidation, which will induce dramatic volume changes in Li_xCoO₂. The volume shrinkage of Li_xCoO₂ has an impact on the oxygen oxidation in return. Moreover, the volume shrinkage of Li_xCoO₂ stems from the oxygen charge compensation, and the charge compensation of Co and O in Li_xCoO₂ for delithiation is not uniform, which can be remitted by implementing a doping strategy. This provides new insight into the fundamental reason for the dramatic volume change of Li_xCoO₂ from the electronic and atomic levels. We propose that the antisite defects of LiCoO₂ should be designed carefully, which lead to weaker Co–O bond strength and further oxygen release, although they enable a higher intercalation potential of LiCoO₂. More importantly, LiCoO₂ material design with elemental doping, oxygen defects, Li defects, and Co defects contributes to the improvement of the reversible capacity of LiCoO₂.

Data availability

The Li_xCoO₂ structures at different delithiation states are provided in the ESI.† All structures used for simulations and other data supporting the findings of this work are available upon request.

Author contributions

Yufang He conducted the simulations and wrote the manuscript; Xiangming He and Li Wang provided guidance and suggestions for this work; Jonghyun Park and Hiep Pham provided suggestions and modified the manuscript; Bo Zhang and Hong Xu provided suggestions for the calculations and manuscript.

Conflicts of interest

The authors declare no competing interests.

Acknowledgements

This work was sponsored by the National Natural Science Foundation of China (No. U21A20170), the National Science and Technology Major Project (No. 2019YFE0100200) and China Postdoctoral Science Foundation (No. 2022M711791 and 2021M701873). We also appreciate the Joint Work Plan for Research Projects under the Clean Vehicles Consortium at U.S. and China – Clean Energy Research Center (CERC-CVC) and the Tsinghua University – Zhangjiagang Joint Institute for Hydrogen Energy and Lithium-Ion Battery Technology.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d2ya00278g

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