Ultra-stable high voltage lithium metal batteries enabled by solid garnet electrolyte surface-engineered with a grafted aromatics layer

The instability and Li2CO3 contaminants of garnet-type electrolytes exposed to air could lead to in its poor interfacial contact with the lithium metal. Generally, the thermal treatment temperature of garnet should overpass 700 & DEG;C to remove surface contaminants. Herein, we report a low temperature method in which con-taminants are converted to the aromatics lithiophilic interface via a simple azo reaction at 60 & DEG;C. The free radicals formed by the decomposition of the azo compound are grafted onto garnet, thereby the garnet compatibility in lithium metal batteries (LMBs) are improved effectively. The reaction mechanism is confirmed by density functional theory calculations, comprehensive electrochemical characterizations, and applying designed azo compounds. The modified garnet membrane shows a high mechanical property and reduced interfacial impedance, high Young's modulus of 169.99 GPa and ionic conductivity of 0.457 mS/cm at 20?. Subsequently, combined XPS depth etching and TOF-SIMS characterizations show that the interfacial layer is composed of a rich C-F bond surface layer and a rich-LiF bottom layer, enabling rapid transport and uniform deposition of lithium ions. Moreover, the superior cycling stability facilitated by modified composite electrolyte is demonstrated in Li/LiFePO4 and Li/LiNi0.5Co0.2Mn0.3O2 full batteries. This new conversion chemistry via azo compound provides a practical solution for achieving high-energy solid-state LMBs.