Electrochemo‐Mechanical Effects on Structural Integrity of Ni‐Rich Cathodes with Different Microstructures in All Solid‐State Batteries

Abstract The electrochemo‐mechanical effects on the structural integrity of electrode materials during cycling is a non‐negligible factor that affects the cyclability and rate performance of all solid‐state batteries (ASSBs). Herein, combined with in situ electrochemical impedance spectroscopy (EIS), focused ion beam (FIB)–scanning electron microscope (SEM), and solid state nuclear magnetic resonance (ssNMR) techniques, the electrochemical performance and electrochemo‐mechanical behavior are compared of conventional polycrystalline NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ), small‐size polycrystalline NCM811 and single‐crystal (S‐) NCM811 in Li 10 SnP 2 S 12 based ASSBs during long charge–discharge cycles. The results show that the deteriorating performance of both large and small polycrystalline NCM811 originates from their inherent structural instability at >4.15 V, induced by the visible voids between the randomly oriented grains and microcracks due to the electrode pressing process and severe anisotropic volume change during cycling, rather than lithium ion transport in the primary particle. In contrast, S‐NCM811 with good microstructural integrity show remarkably high capacity (187 mAh g −1 , 18 mA g −1 ), stable cyclability (100 cycles, retention of 64.5%), and exceptional rate capability (102 mAh g −1 at 180 mA g −1 ) in ASSBs even without surface modification. Moreover, 1 wt% LiNbO 3 @S‐NCM811 further demonstrates excellent initial discharge capacity and capacity retention. This work highlights the critical role of electrochemo‐mechanical integrity and offers an promising path towards mechanically‐reliable cathode materials for ASSBs.