Designable air-stable and dendrite-free Li metal anode via the oligomer layer for in-situ gel polymer batteries

Lithium (Li) metal anode has been an indispensable electrode material in the development of the future battery system, especially in the pursuit of energy density of the solid state battery. However, the poor air stability and dendrite problems are stumbling blocks to the practical application of Li metal anode. Herein, we design the poly (methyl methacrylate) (PMMA) oligomer coating layer for the surface of Li metal anode (Li-PMMA). The LiPMMA anode can obtain hydrophobic oxygen resistance ability and maintain air stability for 48h in the environment of 70% relative humidity. When applied to the liquid battery, the PMMA oligomer can open the double bond by the catalysis of Li+ and repolymerize into the PMMA gel polymer electrolyte (GPE). As a result, the cathode and anode are cohered together by GPE to become an in-situ GPE battery. The GPE displays high ionic conductivity (7.92 mS cm-1) and perfect interfacial contact with various electrodes. The newly designed in-situ GPE is employed to Li||Li symmetric battery without separator, which can run up to 2000 h with the overpotential of only 2.8 mV. Applications of the in-situ GPE in Li-S battery and 5000mAh LiNi0.5Co0.2Mn0.3O2/Li pouch cell both obtain excellent electrochemical performance. Our strategy may provide a versatile and practical approach to promote the large-scale application for solid state Li metal batteries.