Surficial Regulation of LLZO for High Performance Composite Solid Electrolyte

Composite solid electrolytes (CSEs) based on inorganic oxide electrolyte and organic polymer electrolyte are recognized as promising candidates to realize high-performance solid state Li metal battery. Although the ionic conductivity of CSEs is limited, the usage of a plasticizer can make a great difference. Due to the high conductivity and extraordinary resistance to electrochemical oxidation, succinonitrile (SN) is widely used as a plasticizer in CSEs. However, the influence of the compatibility between SN and conductive oxide ceramics is underrated. In this work, we solve the catalytic decomposition effect of Li₇La₃Zr₂O₁₂ (LLZO) toward SN by silane coupling agent coating. Due to good affinity and chemical bonding toward the organic phase, the coating layer can promote the Li⁺ exchange rate through the heterogeneous interface between the organic/inorganic phase and improve the ionic conductivity of CSEs. Besides, surficial carbonyl groups of LLZO introduced by a coating can regulate the Li⁺ coordination structure and accelerate the ion transport. Our design realizes a high conductivity of 5.9 × 10^–4 S cm^–1 at 30 °C and enables the cyclability of Li symmetric cell over 480 h at 0.1 mA cm^–2. Besides, the full cell with LiFePO₄ (LFP) as the cathode delivers a capacity of 137.6 mAh g^–1 with a capacity retention of 96.1% after 150 cycles. Our work demonstrates the regulation effect of interfacial structure on the electrochemical performance of SN-based CSEs, which contributes to realizing a practical solid state Li metal battery.