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All-solid-state batteries (ASSBs), combining high energy density with outstanding safety, are considered the ideal next-generation battery system. However, in the process of replacing liquid electrolytes with solid electrolytes to achieve solid-state batteries, a key challenge is enabling fast lithium-ion transport inside the battery, which is crucial for practical application.

Recent studies have shown that sulfide-based solid electrolytes (such as Li₁₀GeP₂S₁₂, Li₆PS₅Cl, Li₃PS₄, etc.) possess room-temperature lithium-ion conductivities comparable to conventional liquid electrolytes (>1×10⁻³ S cm⁻¹). Moreover, their relatively soft nature allows the formation of good interfacial contact with electrode materials via simple cold pressing, enabling rapid lithium-ion transport. Currently, one of the major research hotspots and challenges in ASSBs based on these electrolytes is improving the interfacial compatibility between sulfide electrolytes and high-specific-energy ternary cathode materials (NCM).

On the cathode side, the mechanisms by which interfacial chemical/electrochemical stability, interface creep, and space-charge layer effects influence lithium-ion transport are not yet fully understood. This severely restricts the development of novel, stable cathode interfaces and the commercialization of ASSB technology.

Recently, the Secondary Battery Research Team at College of Smart Energy, Shanghai Jiao Tong University, precisely constructed a stable interfacial layer on ternary cathodes through fluidized-bed coating and sintering processes. The lithium niobate-coated ternary cathode (NCM@LNO) achieved intimate contact with the argyrodite-type sulfide electrolyte and effectively suppressed chemical/electrochemical side reactions and interface creep at the cathode side. This work lays a solid foundation for further investigations into the influence of space-charge layer effects on lithium-ion transport kinetics.

By combining ex-situ characterization techniques (such as transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy) with density functional theory (DFT) calculations, the formation and evolution mechanisms of the space-charge layer were comprehensively studied, and effective suppression of the space-charge layer was achieved. In addition, the team pioneered the use of an in-situ Raman peak-shift/stress-decoupling method to elucidate the structure–function relationship between space-charge layer configuration at the cathode interface and lithium-ion electrochemical behavior patterns.

As a result, ASSBs assembled with the NCM@LNO cathode maintained 85.2% of their discharge specific capacity (136.2 mAh g−1) after 800 cycles at 0.2C. In summary, this study systematically investigated the formation and evolution mechanisms of the space-charge layer at the ASSB cathode interface, providing important theoretical foundations for efficient interface optimization and design. The related work was published in the internationally renowned energy journal Advanced Energy Materials under the title "Elucidating and Minimizing the Space-Charge Layer Effect between NCM Cathode and Li₆PS₅Cl for Sulfide-Based Solid-State Lithium Batteries."

Dr. Chen Yawei, postdoctoral researcher at College of Smart Energy, Shanghai Jiao Tong University, is the first author of the paper, with Professor Cui Lifeng as the corresponding author. This work was supported by the National Natural Science Foundation of China, the Shanghai International Science and Technology Cooperation Project, the Guangdong Basic and Applied Basic Research Foundation, and the Shanghai Super Postdoctoral Incentive Program.