Dual-salt effect on polyethylene oxide/Li_6.4La₃Zr_1.4Ta_0.6O₁₂ composite electrolyte for solid-state lithium metal batteries with superior electrochemical performance

The polymer composite electrolytes, especially garnet ceramic Li_6.4La₃Zr_1.4Ta_0.6O₁₂ 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/Li_6.4La₃Zr_1.4Ta_0.6O₁₂ 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 [email protected] can steadily cycle for 1700 h without short circuit. An 80% capacity retention is achieved for LiFePO₄| [email protected] |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 LiNi_0.8Co_0.1Mn_0.1O₂ cathode. This study proposed a promising polymer composite electrolyte for solid-state lithium metal batteries with superior performance.