Pre-impregnated protective layer for high energy density Li metal batteries using aqueous electrolyte

Aqueous electrolytes have been considered as alternatives for solving thermal safety issues of batteries caused by the high flammability of non-aqueous electrolytes. However, the use of low-potential anodes for high energy density batteries using aqueous electrolytes is limited by the narrow electrochemical stability window of water (1.23 V). Therefore, an artificial protective layer is required to compensate for the potential difference between the electrolyte and anode: however, using selectively conducting Li ions while suppressing water penetration during cycling tests in batteries is a key problem that has not yet been solved. In this study, a pre-impregnated protective layer using a Li ion conductive high concentration solution in a hydrophobic polymer framework (PIPL-H) was developed for the reversible use of Li metal in batteries using aqueous electrolyte. PIPL-H minimizes hydrogen evolution reactions by preventing direct contact between the water molecules and the Li metal. PIPL-H enabled a Li symmetric cell without increasing polarization for 1000 h, as well as a full cell using LiMn2O4 with 88.2 % capacity retention for up to 60 cycles. These results provide a new perspective into protective layers that enable stable operation without being constrained by the limited cathodic stability of aqueous electrolytes.