Unveiling the Impact of Interface Modulation on the Behavior of the Cathode in All-Solid-State Battery System

Abstract

All-solid-state batteries (ASSBs) are increasingly being investigated as next-generation battery systems, owing to their inherent thermal stability and the theoretical potential for higher energy density compared to conventional lithium-ion batteries. However, several challenges persist, particularly in achieving prominent cell performance at high current density and long-term cyclability, primarily due to kinetic limitations and interfacial degradation at the cathode interface. To address these issues, this work focuses on enhancing the cathode kinetics and cathode–solid electrolyte interface stability through the application of an ionically conductive coating layer. In this study, we introduce a halide solid electrolyte, Li₃InCl₆ (LIC), as a coating material for Ni-rich layered oxide cathodes using a mechano-fusion method. LIC coating on NCM cathode contributes to improved rate capability and cyclability. Beyond the electrochemical performance enhancement, the underlying mechanisms were systematically investigated from both microstructural and intraparticle perspectives. From a microstructural viewpoint, we observe reduced ionic tortuosity and enhanced active surface area within the cathode composite. From the intraparticle perspective, in-situ XRD and TXM analyses reveal that the coated cathode exhibits a more homogeneous state-of-charge distribution and lower degree of intraparticle heterogeneity, which contributes to the cyclability of ASSB system. Ultimately, this study proposes critical design criteria for cathode coatings in ASSBs, highlighting that an ideal coating layer must not only suppress chemical degradation but also actively facilitate lithium- ion transport in perspective of interparticle and intraparticle both. This dual functionality of the coating layer offers a holistic strategy to improve both the interfacial stability and kinetic of cathode composites, thereby advancing the practical implementation of high-performance ASSBs.