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

In this study, Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 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% Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (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 LiFePO 4 ) 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.