Lithium metal anode with lithium borate layer for enhanced cycling stability of lithium metal batteries

Lithium metal is one of the most promising next generation anode materials to make a leap of the energy density of conventional lithium-ion batteries. However, lithium metal has fatal problems to overcome in cycling stability and safety. In this study, lithium metal is pre-treated to form a lithium borate layer (LBL) on the surface to suppress dendritic growth of lithium and stabilize the interface between the carbonate-based electrolyte and anode. The pre-treated lithium metal greatly enhances the cycling stability of the cells (Li parallel to Li symmetric and LiMn2O4 (LMO) parallel to Li cells). Especially, cycling test with the LMO parallel to Li cell reveals the pre-treatment with boric acid is more effective approach than addition of boric acid in the electrolyte because water is continuously generated during charge/discharge in the latter case and it causes side reactions and degrades the cycling performance. The LBL along with LiF stabilizes the solid electrolyte interface (SEI) layer and suppresses the dendritic growth of lithium. Due to the lithium-ion conducting ability of lithium borate, the pre-treated lithium anode also shows lower interfacial resistance than the pristine lithium and enhances rate capability.