A 2D–3D co-conduction effect in PEO-based all-solid-state batteries for long term cycle stability

Abstract

The insufficient ionic conductivity and serious interface problems of oxide-based solid electrolytes greatly limit the performance of all solid-state lithium rechargeable batteries. Herein, a new type of lithium-ion conductor oxide Li₁₉La₃₆Ga₇O₇₄ (LLGO) with a high bulk conductivity of 1.4 × 10⁻³ S cm⁻¹ which is higher than that of Li₇La₃Zr₂O₁₂ (LLZO, 7 × 10⁻⁴ S cm⁻¹) is synthesized to solve the poor ionic conductivity problem. Based on density functional theory (DFT), LLGO has a two-dimensional and three-dimensional (2D–3D) co-conduction lithium ion migration path. Using LLGO as a conductor filler, the polyethylene oxide (PEO)/LiTFSI/LLGO (PLG) composite prepared by solution casting served as solid electrolyte to improve the interface compatibility between the solid electrolyte and electrode. The lithium ion migration number (t⁺) of the PLG electrolyte membrane is as high as 0.69. At a current density of 200 μA cm⁻², the Li|PLG|Li battery can circulate stably for more than 4000 hours. Remarkably, in the LiFePO₄|PLG|Li full battery, good compatibility of the PLG with the electrode can ensure the batteries not only a reversible capacity of 80 mA h g⁻¹ at 25 °C, but also stable cycling of more than 110 days at a rate of 0.5C at 60 °C. Therefore, the addition of LLGO has greatly improved the electrochemical performance of solid-state batteries.