Raising the Intrinsic Safety of Layered Oxide Cathodes by Surface Re-Lithiation with LLZTO Garnet-Type Solid Electrolytes

Battery safety concerns are becoming more and more prominent with the increasing demands of lithium-ion batteries (LIBs) with higher energy density. The greatest threat to battery safety derives from the easy release of oxygen from the high-capacity layered oxide cathodes at highly delithiated states and subsequent exothermic reactions with reductive agents in batteries. Herein, it is demonstrated that solid electrolyte Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) can supply lithium ions to re-lithiate the charged LiCoO₂ at elevated temperatures. Such a re-lithiation process can lower the state-of-charge of LiCoO₂, and thus, inherently postpones its structural decomposition and the associated release of oxygen during the heating process. The LiCoO₂/graphite full cell with 1 wt% addition of LLZTO demonstrates remarkably enhanced safety performances. This work proposes a strategy that through the adoption of solid electrolytes to solve safety issues raised from both flammable liquid electrolytes and high capacity cathodes, to achieve intrinsically safe LIBs or solid-state batteries.