Surface Oxygen Vacancy Inducing Li‐Ion‐Conducting Percolation Network in Composite Solid Electrolytes for All‐Solid‐State Lithium‐Metal Batteries

Composite solid electrolytes (CSEs) are newly emerging components for all-solid-state Li-metal batteries owing to their excellent processability and compatibility with the electrodes. Moreover, the ionic conductivity of the CSEs is one order of magnitude higher than the solid polymer electrolytes (SPEs) by incorporation of inorganic fillers into SPEs. However, their advancement has come to a standstill owing to unclear Li-ion conduction mechanism and pathway. Herein, the dominating effect of the oxygen vacancy (O_vac ) in the inorganic filler on the ionic conductivity of CSEs is demonstrated via Li-ion-conducting percolation network model. Based on density functional theory, indium tin oxide nanoparticles (ITO NPs) are selected as inorganic filler to determine the effect of O_vac on the ionic conductivity of the CSEs. Owing to the fast Li-ion conduction through the O_vac inducing percolation network on ITO NP-polymer interface, LiFePO₄ /CSE/Li cells using CSEs exhibit a remarkable capacity in long-term cycling (154 mAh g^-1 at 0.5C after 700 cycles). Moreover, by modifying the O_vac concentration of ITO NPs via UV-ozone oxygen-vacancy modification, the ionic conductivity dependence of the CSEs on the surface O_vac from the inorganic filler is directly verified.