Grain‐Boundary Engineered Co‐Crystal Electrolytes for Dendrite‐Free High‐Voltage Solid‐State Li‐Metal Batteries

ABSTRACT Solid‐state lithium‐metal batteries (SSLBs) are considered as promising next‐generation energy storage systems due to their high energy density and substantially improved safety. However, the poor interfacial contact between electrodes and solid electrolytes leads to high internal impedance, low coulombic efficiency, and rapid capacity degradation. Herein, a novel organic co‐crystal (LiDFOB‐SN) containing lithium difluoro(oxalato)borate (LiDFOB) and succinonitrile (SN) is developed to establish cohesive contact at the electrode/electrolyte interface. The designed LiDFOB 0.5 ‐SN electrolyte shows a wide electrochemical window (anodic reduction potential >5.2 V) and high conductivity (0.56 mS·cm −1 at 30°C). Assembled with this electrolyte, lithium cobalt oxide (LiCoO 2 , LCO) || Li batteries cycled between 3.0 and 4.5 V exhibit a high‐capacity retention of over 87% after 500 cycles. The improved high‐voltage cycling performance originates from the designed solid electrolytes, which reduce irreversible phase transformation in cathode materials and suppress Li dendrite growth. Furthermore, operando Raman measurements and molecular dynamics simulations are combined to explore the Li‐ion transport mechanism, suggesting that Li‐ions tend to transport along the highly conductive grain boundaries of the polycrystalline LiDFOB‐SN. This work provides a comprehensive insight into the operation mechanisms of organic co‐crystal electrolytes, which can further enable high‐performance solid‐state Li‐metal batteries and promote their practical applications.