Electro-Chemo-Mechanical Study of Cathode-Interface-Engineered All-Solid-State Lithium Batteries
Authors: Wang Longlong 
Published: February 2024

All-solid-state lithium batteries (ASSLBs) have been regarded as one of the most promising next-generation batteries in terms of their superior safety and great potential to meet the requirements of high energy and power density.1 However, the performance of ASSLBs based on even state-of-the-art solid electrolytes (SEs) with a high room-temperature ion conductivity of 10−2 S·cm−1 is still inferior to that of commercially available LIBs, because fast solid electrode/electrolyte interfacial lithium-ion transport remains a vital challenge in ASSLBs.2 The sluggish lithium-ion transport across the solid electrode/electrolyte interface mainly results from the electro-chemo-mechanical degradation, such as the space charge layer (SCL), interface reaction generating ionically resistive products, and poor physical contact.3,4 On the cathode side, coating high-voltage cathodes with chemically compatible and stable buffering layers with high ionic conductivity but low electronic conductivity has been widely confirmed to be an effective approach to overcome these problems.However, a mechanistic understanding of the coating functionality remains unresolved, and there is still much room for improvement regarding the methodology and associated material properties.5

Here, from electro-chemo-mechanical perspectives, we have fully studied the improvement mechanism of cathode interface engineering for ASSLBs based on the complementary analyses including calculations (e.g., first-principles, finite element methods), in-situ (e.g., differential phase contrast scanning transmission electron microscopy (DPC-STEM), Raman, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT)) and ex-situ (X-ray absorption spectra (XAS), X-ray photoelectron spectroscopy (XPS), focused-ion beam scanning electron microscopy (FIB-SEM)) characterizations. We find that discontinuous ferroelectric BaTiO3 coating can effectively suppress the SCL formation and lead to fast continuous interfacial lithium-ion conduction pathways, thus significantly improving the interfacial migration kinetics between cathode materials and the sulfide SEs.6 The bidirectionally compatible NASICON-type LixZr2(PO4)3 (LZPO) buffering layer enables the high-voltage cathode interface (4.5 V LiCoO2/Li6PS5Cl) with high chemical/electrochemical stability and fast Li-ion transport dynamics.7 Additionally, the high Young’s modulus of the coating layer (e.g., LZPO) can remarkably decrease stress inside cathodes and prevent cathode/SE interface separation, which is beneficial to mitigate microcracks in cathodes and cathode/SE interface contact loss, respectively.8 We believe these findings will help advance the fundamental scientific understanding of the coating functionality and the interfacial lithium-ion transport mechanism in ASSLBs, thus shed light on rational electrode/electrolyte interface design for high-rate performance ASSLBs.
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