Asymmetric Solid-State Lithium-Metal-Battery Electrolytes Featuring Na Superionic Conductor-Type Ceramic and Garnet-Type Ceramic Filled Composite Polymer

Abstract In this study, Li1.3Al0.3Ti1.7(PO4)3 (LATP)-based lithium metal battery (LMB) cells are prepared using two different protection layers against Li metal: a solid polymer electrolyte (SPE) containing polyethylene oxide and lithium bis(fluorosulfonyl)imide (LiTFSI), and a composite polymer electrolyte (CPE) filled with a 14 wt% Li6.4La3Zr1.4Ta0.6O12 (LLZTO). The CPE-containing symmetric cell exhibits a smaller overvoltage than that of its SPE-containing counterpart, which is maintained for ~1000 h at 0.1 mA·cm-2 at 60 °C, owing to enhanced Li-ion transport in the CPE and at the LATP–CPE interface as well as the uniform Li deposition induced by the CPE with a higher Li+ transference number. Post-material analyses reveal that the CPE imparts long-term (~1000 h) protection to the LATP against Li metal, whereas the SPE is effective over a shorter period (~100 h). The CPE-based full cell exhibits a higher capacity (~141 mAh·g-1; with a LiFePO4) and capacity retention (~95%) than those of the SPE-based full cell (~130 mAh·g-1 and ~ 55%, respectively), for 310 cycles at 60 °C. This study recommends utilizing asymmetric solid electrolytes containing a ceramic (LATP at the cathode) and composite polymer (PEO + LLZTO at the anode) to improve cyclability and suppress Li dendrite growth in solid-state LMBs.