Enabling non-flammable Li-metal batteries via electrolyte functionalization and interface engineering

Abstract

Li-metal batteries (LMBs) with composite polymer electrolytes (CPEs) have attracted considerable attention compared with conventional Li-ion batteries. However, the uncontrolled Li deposition and the flammability of CPEs are still pressing issues. In this article, a non-flammable CPE is fabricated. The CPE consists of a poly(vinylidene fluoride) matrix, Li_6.4La₃Zr_1.4Ta_0.6O₁₂ fillers, a flame-retardant trimethyl phosphate as the solvent, and a LiClO₄ salt. It exhibits unique characteristics, including non-flammability, high ionic conductivity, flexibility, and good thermal stability. A fluoroethylene carbonate (FEC) additive is used on the surface of Li metal to facilitate the formation of a LiF-rich solid electrolyte interphase layer. The FEC-coated Li|CPE|LiFePO₄ battery exhibits excellent cycling stability (at room temperature) with a discharge capacity of 152 mA h g⁻¹ and nearly 100% coulombic efficiency over 500 cycles at 0.2C. The non-flammable CPE has a high rate capability of 109 mA h g⁻¹ at 4C. To improve the energy density of the LMB, the LiFePO₄ cathode is replaced with a high-voltage material LiNi_1/3Mn_1/3Co_1/3O₂. The obtained Li|CPE|LiNi_1/3Mn_1/3Co_1/3O₂ cell exhibits a discharge capacity of 109 mA h g⁻¹ after 100 cycles at 0.2C. Consequently, the strategy offers guidelines for the future development of safe batteries with high energy density.