Construction of a self-sacrificing selenium interfacial coating and its performance in all-solid-state lithium-ion batteries

Abstract

All-solid-state lithium-ion batteries (ASSLIBs) are considered a crucial direction for the development of next-generation energy technologies, owing to their high energy density and superior safety performance. However, the incompatibility between high-voltage cathode materials, such as LiCoO₂ (LCO), and sulfide solid electrolytes (sulfide SEs) presents a bottleneck that limits overall performance. To address this issue, we have proposed an in situ selenium-induced thermal reduction strategy to form a selenium-containing interfacial layer. Within this layer, Co(III) from LCO is reduced to the less oxidative Co(II), effectively suppressing the parasitic reactions between LCO and sulfide SEs. Employing this interface engineering approach, the Se-LCO/Li₆PS₅Cl/Li–In ASSLIB cell achieves a high initial specific capacity of 157.2 mAh g⁻¹ at 0.2 C, significantly enhanced Li⁺ diffusivity with a D_Li of 10⁻⁹ cm² s⁻¹ (approximately one order of magnitude higher than the original sample), and excellent cycling stability with a capacity retention of 90.1% after 100 cycles at 0.5 C. The experimental results confirm the effectiveness of the selenium coating strategy in enhancing interface compatibility and optimising electrochemical cycling performance. This study introduces a self-sacrificing in situ coating method for selenium-reduced cathode materials, offering innovative insights into the design of high-performance ASSLIBs with stable cathode/sulfide SE interfaces.

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1. Introduction

The urgency to control carbon emissions has driven a rapid advancement in new energy technologies, particularly in the development of electric vehicles (EVs).^1–3 However, current EV battery technologies struggle to strike a balance between energy density and safety. In this context, solid-state batteries (SSBs) that leverage solid electrolytes (SEs) have emerged as a promising solution, raising significant attention due to their potential advantages in safety, cost, and energy density. SEs can be compatibly paired with high-voltage cathodes as well as with lithium metal anodes, offering theoretical capacities up to 3860 mAh g⁻¹ and 2061 mAh cm⁻³. This compatibility enables batteries with gravimetric and volumetric energy densities surpassing 400 Wh kg⁻¹ and 1,000 Wh L⁻¹, respectively.^4,5 Also, the all-solid-state processing enables battery stacking using bipolar electrodes within a single package, resulting in reduced packaging size and enhanced energy density.⁶ Moreover, SSBs benefit from the inherent safety of solid electrolytes. The use of thermally stable solid electrolytes⁷ instead of flammable liquid electrolytes mitigates the risks of electrolyte leakage and battery combustion,^5,8–11 effectively addressing the critical safety concerns of EV batteries in urban environments.^12–14 In recent years, researchers have made a series of breakthroughs in the field of SSBs through various approaches such as the design of new electrolytes, interface control strategies, and structural innovations.^15,16 Notably, recent research has demonstrated lithium batteries achieving energy densities exceeding 600 Wh kg⁻¹, representing substantial progress in overcoming energy density limitations.¹⁷ These developments establish all-solid-state batteries as one of the most promising next-generation energy storage systems.

Inorganic solid electrolytes (ISEs) are typically single-ion cationic conductors, possessing higher migration numbers than traditional liquid electrolytes, and thus more efficient in charge transport.¹⁸ Among inorganic solid electrolytes, sulfide solid electrolytes represented by Li₁₀Ge₂S₁₂ (ref. 19) and Li₆PS₅Cl (LPSCl)²⁰ exhibit not only high migration numbers but also outstanding ionic conductivities comparable to that of liquid electrolytes (>1 mS cm⁻¹), effectively overcoming the limitations associated with the ionic conductivity of traditional SEs. Additionally, the good mechanical softness of sulfide solid electrolytes contributes to their processability, offering a promising candidate for all-solid-state lithium-ion batteries (ASSLIBs).^21–23 However, the narrow electrochemical potential window of sulfide SEs (<2.1 V vs. Li/Li⁺) poses thermodynamic compatibility challenges with most cathode materials, such as layered oxides,^10,24,25 leading to severe parasitic reactions at the interface. The ionic insulating products generated at the cathode/SE interface hinder ion diffusion, consequently diminishing battery performance.^26,27 Therefore, addressing the interfacial instability issue becomes a primary concern for advancing the development of ASSLIBs.

The interfacial instability between oxide cathodes and sulfide SEs arises from the high surface valence state of Co(III) and even higher surface oxidation states in LCO that spontaneously oxidize sulfide SEs.^23,28–30 Traditional methods, such as physically isolating the interface using heterogeneous coating technology, are challenged by complex synthesis processes,^16,31 difficulty in controlling the thickness, and the potential for interface separation, rendering them unsuitable for practical applications.^32–37 To address this, we speculate that reconstructing the interface in situ could create a stable reduction layer on the cathode surface with good interface affinity, thereby minimising the parasitic reaction and phase separation. This approach aims to achieve long-term interface stability, offering a promising strategy for developing high-performance ASSLIBs.

In this work, we propose a low-cost, straightforward in situ interface reconstruction strategy to suppress the parasitic reaction at the cathode/sulfide SE interfaces. By utilising the self-sacrificing reducing intermediate phase, a selenium coating was in situ constructed on the surface of LCO. The concept of self-sacrifice in this context refers to the oxide cathode employing itself as one of the reactants in the reaction that facilitates the formation of a coating layer. The interfacial high-valence Co(III) was reduced to low-valence Co(II) by selenium, weakening the surface oxidative ability of LCO. This in situ phase-transition-induced coating displays a thin and uniform CoO/selenate interphase, the lattice of which matches well with that of the maternal LCO substrate. The structural compatibility between LCO/sulfide SEs is thereby enhanced, which leads to the assembled ASSLIBs demonstrating improved interface stability during cycling. The LCO-based ASSLIB with selenium-coated LCO (Se-LCO) has a high initial capacity of 157.2 mAh g⁻¹ at 0.2 C and a capacity retention rate of 89.2% after 100 cycles (140.2 mAh g⁻¹). The cell delivers an initial discharge capacity of 136.7 mAh g⁻¹ at 0.5 C and maintains a high capacity retention of 90.1% after 100 cycles. The performance of the Se-LCO cathode material demonstrates a significant improvement over that of the initial cobalt oxide bare material (bare-LCO) cathode, which delivers a discharge capacity of 110.9 mAh g⁻¹ at 0.2 C and 30.1 mAh g⁻¹ at 0.5 C after 100 cycles. The outstanding electrochemical performance confirms the feasibility and effectiveness of the in situ coating strategy.

2. Experiments and characterisation

2.1 Preparation of Se-LCO samples

The cathode material LiCoO₂ (LCO, purchased from Tianjin Bamo Corporation) and selenium reagent (99.9%) were ground together in an agate mortar for 20–40 minutes to achieve a homogeneous mixture. The thoroughly mixed precursor was then transferred into a quartz tube, which was subsequently sealed under vacuum using a vacuum sealing apparatus. The sealed quartz tube was introduced into a muffle furnace, where it was calcined at 800 °C for 5 hours with a heating rate of 5 °C min⁻¹. After calcination, the sample was allowed to cool to room temperature. The calcined material was then retrieved from the quartz tube and reground in an agate mortar for an additional 4–6 minutes to obtain the final Se-LCO composite.

2.2 ASSLIB assembling

To prepare the composite cathode material, the active material Se-LCO, Li₆PS₅Cl solid-state electrolyte (LPSCl, >99%), and conductive agent (Super P) were first weighed in a mass ratio of 150 : 100 : 5, respectively. Subsequently, these components were mixed and ground in sequence until a uniform dispersion was achieved, with the grinding process lasting 10–15 minutes. The uniformly mixed cathode material was then used to assemble ASSLIBs with lithium–indium alloy as the anode. The assembly of the ASSLIBs was completed in a glovebox filled with argon gas. The mass loading of the LCO active material was 3.5 mg cm⁻², and the mass of the LPSCl solid electrolyte used in each cell was 240–270 mg.

2.3 Material characterisation

The morphological characteristics of the materials were examined using a field-emission scanning electron microscope (FESEM, Hitachi S-4800), while elemental distribution was mapped via energy-dispersive X-ray spectroscopy (EDS). The structural analysis of the samples was conducted using powder X-ray diffraction (XRD, Rigaku Ultima IV) with Cu-Kα radiation (λ = 1.5418 Å) as the incident beam. The samples were scanned at a rate of 1° min⁻¹ over a 2θ range of 5° to 80°. X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha, USA) was employed to determine the valence states of elements and the corresponding bonds. The binding energy calibration was primarily based on the C 1s peak, with the non-graphitic carbon layer referenced at 284.8 eV. Data fitting and analysis were performed using Avantage software. The compositional distribution at different depths of the samples was investigated using XPS etching technology (Shimadzu/Kratos AXIS Ultra DLD). Raman spectroscopy measurements were performed using a Renishaw/InVia Qontor instrument. Hard X-ray absorption spectroscopy (hXAS) was performed at the Shanghai Synchrotron Radiation Facility (BL14W1, SSRF) to characterize the Co K-edge. The sample was prepared with a dual-beam focused ion beam (FIB) micro/nano fabrication system (Quanta 3D FEG, USA) to expose the cross-section of the Se-LCO samples. The interface structure was then observed by transmission electron microscopy (TEM, A9L3ZD11160).

2.4 Electrochemical measurement

The electrochemical cycling performance of the all-solid-state lithium-ion battery (ASSLIB) was evaluated using a battery testing system (CT-4008T, Neware, Shenzhen, China), with 1 C defined as 150 mA g⁻¹. The LCO was tested at an upper cutoff voltage of 4.3 V (vs. Li⁺/Li), while the ASSLIB was cycled within a voltage range of 2.0–3.7 V (vs. Li⁺/Li–In alloy). Electrochemical impedance spectroscopy (EIS) was performed using a CHI 760E electrochemical workstation (Shanghai, China) over a frequency range of 10⁻⁶ Hz to 10⁻² Hz. The galvanostatic intermittent titration technique (GITT) was employed to conduct discharge tests at a rate of 15 mA g⁻¹ for 10 minutes, followed by a relaxation period of 30 minutes, with this sequence repeated to complete the charge–discharge process.

3. Results and discussion

3.1 Synthesis of LCO cathode material bearing a self-sacrificing selenium coating

As depicted in Fig. 1, the Se-LCO cathode material was prepared via a solid-phase method. First, bare-LCO and selenium (Se₈) were intimately mixed through grinding. The mixture was then heated to 800 °C under vacuum to induce a thermal reduction reaction. As represented in eqn (1), the treatment of LCO with Se₈ yielded CoO, whereby Co(III) underwent reduction to Co(II). Concurrently, selenium was oxidised to the selenate anion (SeO₄²⁻), which reacted with Li⁺ to give Li₂SeO₄. A series of Se-LCO samples with varied selenium contents were prepared. The label Se-LCO-X% (in which X represents Se mass ratios of 0.2%, 0.5%, and 1.0%, respectively) was used to designate the samples treated with varying Se mass ratios.

48LiCoO₂ + Se₈ → 48CoO + 16Li₂O + 8Li₂SeO₄ (1)

Fig. 1 Schematic synthesis procedure of Se-LCO.

3.2 Phase composition and structural identification of the selenium coating and LCO interphase

As shown in the X-ray diffraction (XRD) spectra (Fig. 2a), both the Se-LCO and bare-LCO samples exhibit high crystallinity, and their crystal structures are generally consistent with each other. This indicates that the formation of the selenium coating has minimal impact on the bulky crystal structure of LCO. Notably, for Se-LCO, the emergence of additional diffraction peaks at 2θ angles of 36.5°, 42.5°, and 61.6°, in accordance with the CoO phase (JCPDS No. 48-1719), suggests the reduction of Co(III) on the LCO surface. The intensity of these peaks corresponding to CoO is amplified with the increase of Se content. The presence of the interfacial coating layer is further confirmed by Raman spectroscopy. As shown in Fig. 2b, bare-LCO displays two distinct Raman peaks at 477.1 and 587.3 cm⁻¹, which are attributed to the E_g and A_1g^38,39 modes of LCO, respectively. For Se-LCO, in addition to retaining the LCO E_g and A_1g modes, an additional Raman peak is observed at 673 cm⁻¹, attributable to CoO.⁴⁰

Fig. 2 (a) XRD patterns of Se-LCO and bare-LCO; (b) Raman spectra of Se-LCO and bare-LCO; (c) SEM images of the Se-LCO particle and the corresponding Co, O, and Se SEM-EDS mapping; (d) XPS spectra of O 1s; (e) XPS spectra of Se 3d; (f) XPS spectra of Se 3d at different depths in the Se-LCO particle; (g) the HR-TEM image of the cross-section of Se-LCO-0.2% and the corresponding fast Fourier transform (FFT) results in region 1 and region 2; (h) the TEM-EDS mapping of the cross-section of Se-LCO-0.2% showing Co, O, and Se elements.

The morphological features of bare-LCO (Fig. S2a) and Se-LCO particles (Fig. S1 and 2b–d) were unveiled by the scanning electron microscopy (SEM) images. Both bare-LCO and Se-LCO particles display a nearly spherical shape with an approximate diameter of 15 µm; notably, the Se-LCO particles feature a discernible coating layer. The Se-LCO-0.2% particles (Fig. S2b) demonstrate surface smoothness comparable to that of bare-LCO, which underscores the uniformity of the phase interface for this self-sacrificing selenide coating. As the selenium mass fraction increases, the surface roughness and granularity of LCO also increase (Fig. S2b–d). Energy-dispersive X-ray spectroscopy (SEM-EDS) (Fig. 2c) confirms the uniform distribution of cobalt (Co), oxygen (O), and selenium (Se) across the surface of the Se-LCO material.

To investigate the oxidation state evolution of cobalt on the LCO surface, X-ray photoelectron spectroscopy (XPS) was utilised to analyse the surface composition and valence states. The XPS Co, O, and Se spectra of Se-LCO-0.2%, displayed in Fig. 2e and S3–6, respectively, confirm the presence of Co, O, and Se elements on the sample surface. As shown in Fig. S3, two distinct cobalt species in different valence states are identified in the high-resolution Co 2p spectra of both bare-LCO (a) and Se-LCO (b). The peaks at 779.1 eV/794.2 eV correspond to the Co(III) signal of LCO, while a stronger Co(II) signal at 781.6 eV/796.8 eV in Se-LCO (41%) compared to bare-LCO (31%) indicates the formation of CoO.⁴¹ The conclusion is corroborated by the Co K-edge X-ray absorption near edge structure (XANES) spectra (Fig. 2d).^42,43 The Co K-edge X-ray absorption spectra (XAS) of Co, CoO and Co₃O₄ (Fig. S7) provide additional evidence for this conclusion, revealing distinct differences in their electronic structures. Compared with bare-LCO, Se-LCO exhibits a negative shift, signalling a decrease in the oxidation state of cobalt. In the O 1s XPS spectrum (Fig. S4), oxygen signals at binding energies of 529.7, 531.6, and 532.8 eV originate from the LCO lattice oxygen, C=O or CO₃²⁻, or the surface oxygen on LCO, and species related to C–O, respectively.^44–46

Bare-LCO and Se-LCO show a noticeable difference at 531.6 eV, which may be related to the formation of Li₂CO₃ on the surface during the selenium reduction process. The Se 3d high-resolution XPS spectrum for Se-LCO exhibits the peaks at 58.4 eV attributed to selenates, with additional peaks at 55.9 and 56.7 eV corresponding to Se 3d_5/2 and Se 3d_3/2, respectively (Fig. 2e).^44,47 The XPS etching profile of Se-LCO, as illustrated in Fig. S5 and 6, demonstrates that, with increasing etching depth, the signal peak for Se-Ox in the Se-LCO material gradually diminishes, confirming that the selenium coating is established on the surface of LCO.

To study and understand the microstructure of the in situ formed selenium coating interface on LCO, Se-LCO-0.2% particles were sectioned using focused ion beam (FIB) technology to reveal their cross-sections, which were then examined with high-resolution transmission electron microscopy (HR-TEM). As shown in Fig. 2g, a distinct interface layer is visible on the surface of Se-LCO, along with a uniform and continuous coating covering the LCO surface.

Upon conducting a fast Fourier transform (FFT) on the selected regions 1 and 2 (the dashed boxes 1 and 2 in Fig. 2g, respectively), the FFT of region 1 is identified as bulk LCO crystals with an R3̄M space group. Moreover, the FFT of region 2 reveals the crystal planes (111), (200), and (220) of CoO, demonstrating good orientation and confirming the presence of CoO. Both regions 1 and 2 exhibit well-oriented planes without any apparent cracks. The seamless transition from the bulky LCO to the surface CoO, featured by the absence of a phase boundary and minimal damage to the bulky structure, underscores the excellent lattice coherence between them, ensuring smooth lithium-ion transport at the LCO/LPSCl interface. Additionally, the superior interface affinity between LCO and CoO enables good coverage and durable protection. The mapping analysis of the TEM-EDS spectra (Fig. 2h) indicates that the Se is concentrated on the surface, while Co and O are uniformly distributed throughout the cross-section. These observations are consistent with the results of XRD, Raman spectroscopy, and XPS analyses, offering valuable insights into the structure of the self-sacrificing selenium coating interphase.

3.3 Electrochemical tests of bare-LCO and Se-LCO

To evaluate the effectiveness of the in situ formed selenium coating in reducing parasitic interfacial reactions between LCO and sulfide SEs, ASSLIBs were assembled using LPSCl and Li–In alloy anodes. The electrochemical performance of Se-LCO was tested at different rates under room temperature conditions. Fig. S8 and 9 illustrate the cycling performance of Se-LCO-X% (X = 0.2, 0.5, 1.0) at a current density of 0.2 C. Notably, the cyclic capacity results of Se-LCO-0.2% surpass those of the other two groups, with an initial capacity of 157.2 mAh g⁻¹ and a capacity retention rate of 89.2% after 100 cycles (140.2 mAh g⁻¹).

As depicted in Fig. 3b, under identical testing conditions, the bare-LCO demonstrates a capacity retention of merely 49.8% after 100 cycles, whereas Se-LCO-0.2% achieves a significantly higher capacity retention. As shown in Fig. 3d and S10, when cycling at 0.5 C, the bare-LCO exhibits the most significant capacity loss of 55.5% in its first cycle, suggesting its poor cycling performance. In contrast, Se-LCO-0.2% maintains a high specific capacity with a retention rate of 90.1% (123.2 mAh g⁻¹) after 100 cycles. Given that the CoO component in the sacrificial layer of Se-LCO does not contribute to capacity (Fig. S11), the improved performance of Se-LCO is attributable to the stabilisation of the LCO/LPSCl interface by the selenium coating.

Fig. 3 (a) Charge and discharge curves of Se-LCO-0.2% at 0.2 C; (b) cycling performance of Se-LCO and bare-LCO at 0.2 C; (c) rate properties of bare-LCO and Se-LCO; (d) cycling performance of Se-LCO and bare-LCO at 0.5 C; (e) GITT curve and polarization of Se-LCO and bare-LCO. (f) Nyquist plots of Se-LCO and bare-LCO after 10 cycles at 0.2 C; (g and h) Nyquist plots of Se-LCO after different cycles.

The rate performances of Se-LCO (0.2%, 0.5%, and 1.0%) and bare-LCO were examined under varying current conditions. As plotted in Fig. 3c, S12 and 13, Se-LCO-0.2% shows superior capacity and capacity retention compared to other cathodes. Specifically, Se-LCO-0.2% delivers reversible capacities of 161.1 mAh g⁻¹, 149.2 mAh g⁻¹, 118.9 mAh g⁻¹, and 59.0 mAh g⁻¹ at current densities of 0.1 C, 0.2 C, 0.5 C, and 1.0 C, respectively.

Its capacity loss remains below 1% at lower rates (0.1–0.5 C). Furthermore, it maintains over 80.0% of its capacity at higher rates of 1 C. Notably, when the current density is restored to 0.1 C, the capacity recovers to 160.2 mAh g⁻¹, demonstrating excellent rate capability and reversibility. In contrast, bare-LCO exhibits a much lower initial capacity of 73.5 mAh g⁻¹ at 0.1 C and the performance decays rapidly as the current density increased. The enhancement of rate performance demonstrates the effectiveness of the self-sacrificing selenium coating in facilitating Li⁺ transport kinetics.

Battery polarization and Li⁺ diffusion coefficients (D_Li) were measured for bare-LCO and Se-LCO using the galvanostatic intermittent titration technique (GITT). The results are plotted in Fig. 2e, S14 and 15. As shown, bare-LCO exhibits severe polarization of 0.11 V at the discharge plateau. In contrast, Se-LCO, with its sacrificial selenium coating that facilitates interfacial charge transfer, reduces the initial polarization potential to 0.04 V. Based on formula (2), the calculated Li⁺ diffusion coefficient of Se-LCO (≈10⁻¹⁰ cm² s⁻¹) is one order of magnitude larger than that of bare-LCO (≈10⁻¹¹ cm² s⁻¹) (Fig. S14b).^48,49 Based on these results, it can be concluded that Se-LCO exhibits superior kinetic properties, reduced electrochemical polarization, and enhanced reversibility.

Electrochemical impedance spectroscopy (EIS) tests were conducted on cells with bare-LCO and Se-LCO after 10 cycles at 0.2 C, to examine interface stability.^50,51 The fitting results of the Nyquist plots in Fig. 3f, S16 and 17 reveal that the electrolyte impedance (R_s) and cathode interface impedance (R_CI) of bare-LCO and Se-LCO are comparable after cycling. However, the charge transfer impedance (R_ct) of bare-LCO is significantly larger, amounting to 2104 Ω, compared to 487.1 Ω for Se-LCO-0.2%. This discrepancy is likely attributable to parasitic reactions that impede ion diffusion at the LCO/LPSCI interface. The observation suggests that the construction of a self-sacrificing coating is more effective in reducing impedance and enhancing the stability of the LCO/LPSCI interface. Furthermore, to study the impedance evolution of the cathode interface in Se-LCO, EIS tests were performed during cycling. As depicted in Fig. 3g and h, the charge transfer impedance (R_ct) increases from 384.6 Ω at the first cycle to 827.8 Ω after 50 cycles. The rise in impedance can be attributed to the minor degradation of the cathode material during prolonged cycling.

The mechanical degradation effects, such as the formation of microcracks, can significantly contribute to the decline in battery performance.⁵² The surface morphology of Se-LCO and bare-LCO after 100 cycles at 0.2 C was examined using SEM. As shown in Fig. 4a, numerous microcracks appear on the surface of bare-LCO particles after cycling. This is due to the continuous buildup of interfacial by-products, which substantially impede Li⁺ diffusion at the interface. Hindered diffusion obstructs the rapid transport of Li⁺ within the LCO bulk, creating a concentration gradient and lattice stress. The ongoing accumulation of stress eventually leads to structural degradation and the propagation of cracks.^53,54 In contrast, the SEM image of Se-LCO after cycling (Fig. 4b) reveals relatively undamaged particle surfaces with minimal mechanical cracking. This suggests that the selenium coating effectively maintains the integrity of the bulk LCO structure by reducing interfacial parasitic reactions, which is crucial for achieving better cycling stability.

Fig. 4 SEM images of bare-LCO (a) and Se-LCO (b) after 100 cycles at 0.2 C.

4. Conclusions

In summary, this work demonstrates an effective strategy involving the in situ formation of a self-sacrificing selenium coating on the LCO surface. This coating effectively reduces interfacial parasitic reactions between LCO and LPSCI, improves interfacial stability, and enhances the fast charging/discharging capability of ASSLIBs. The selenium coating is prepared through in situ thermal reduction of LCO with Se₈, where high-valence Co(III) on the surface is reduced to low-valence Co(II) in the form of CoO. This process alleviates the detrimental effects of the highly oxidative cathode on sulfide SE. It fundamentally suppresses interfacial reactions, thereby enabling excellent compatibility between cathode materials and electrolytes. As a result of this strategy, the electrochemical performance of the Se-LCO/LPSCl/Li–In ASSLIB cell has been significantly improved. The cell shows a high initial capacity of 157.2 mAh g⁻¹ at 0.2 C and retains 89.2% of its capacity after 100 cycles. It also performed well at 0.5 C, with a capacity retention of 90.1% after 100 cycles. Furthermore, the Se-LCO exhibits superior rate performance (delivering over 80.0% capacity at 1.0 C) and reduces charge transfer impedance. This study highlights the potential of in situ constructed selenium coatings to stabilise the cathode/sulfide SE interface and offers a new approach to enhancing ASSLIB performance. More importantly, the in situ interface reconstruction strategy based on “self-sacrifice” proposed in this work exhibits significant universality and practical application potential. The core advantage of this approach stems from its foundation in universal chemical principles and a streamlined preparation process. First, the strategy does not require complex vacuum deposition techniques or costly heterogeneous precursors; instead, it employs a simple heat treatment to induce spontaneous chemical reactions on the cathode material surface, thereby facilitating seamless integration with conventional electrode manufacturing processes and enabling scalability. Second, the conceptual design, which involves using reducing media to reconstruct the cathode surface and form a stable protective coating, can potentially be extended to other high-voltage layered oxide cathodes, such as NCM and lithium-rich manganese-based materials, as well as to the interfaces of other oxygen-sensitive functional electrolytes. This offers a promising pathway for addressing the prevalent issue of interfacial incompatibility in solid-state batteries.

Author contributions

Simin You: conceptualization, synthesis, characterization, original draft writing. Minghao Zhang: synthesis, characterization. Jingting Yang: conceptualization, synchrotron radiation characterization. Zeheng Li: funding acquisition, review and editing of writing. Zhan Lin: funding acquisition, project management. Jun Lu: project supervision, writing, review and editing. All authors participated in the manuscript review.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Supplementary information: structural characterization data and electrochemical performance data. See DOI: https://doi.org/10.1039/d5ta07592k.

Acknowledgements

This work was supported by the Major Research Plan of the National Natural Science Foundation of China (grant no. 92372207), the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang (grant no. 2023R01007), the National Natural Science Foundation of China (grant no. 52172190 and 52402315), and the Zhejiang Provincial Natural Science Foundation of China under grant no. LQN25B030004. We thank Wei Wang at the State Key Laboratory of Extreme Photonics and Instrumentation, Zhejiang University for assistance with FIB.

Notes and references

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