Dual-salt effect on polyethylene oxide/Li6.4La3Zr1.4Ta0.6O12 composite electrolyte for solid-state lithium metal batteries with superior electrochemical performance

Abstract The polymer composite electrolytes, especially garnet ceramic Li6.4La3Zr1.4Ta0.6O12 reinforced polyethylene oxide (PEO), are expected to be the most promising substitute for commercial liquid electrolytes in lithium metal batteries due to their good safety, easy-manufacturing and flexibility. However, their insufficient ionic conductivity and instability towards reductive Li anode at room temperature are the long-standing issues. In this work, a dual-salt solid composite electrolyte with superior ambient-temperature electrochemical performance is designed by regulating polyethylene oxide/lithium perchlorate/Li6.4La3Zr1.4Ta0.6O12 composite electrolyte with additive lithium tetrafluoroborate (LL@PL). The stable solid electrolyte interphase with LiF, B–F, and Li–B–O formed on lithium metal effectively induces even Li deposition and strengthens the compatibility of electrolyte/Li anode interface. The combined action of each composition in the electrolyte guarantees the efficient ion immigration kinetic and suppresses the lithium dendrite growth of solid-state batteries. The Li symmetric cells using LL@PL-0.1 can steadily cycle for 1700 h without short circuit. An 80% capacity retention is achieved for LiFePO4| LL@PL-0.1 |Li cell after 350 cycles at 25 °C. The electrochemical stability of the composite electrolyte is extended to 4.6 V and the assembled cell works well with LiNi0.8Co0.1Mn0.1O2 cathode. This study proposed a promising polymer composite electrolyte for solid-state lithium metal batteries with superior performance.