SurficialRegulationof LLZO for High PerformanceComposite 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.