Synergistic approach toward developing highly compatible garnet-liquid electrolyte interphase in hybrid solid-state lithium-metal batteries

The hybrid solid-liquid electrolyte concept is one of the best approaches for counteracting the interface problems between solid electrolytes and Li anodes/cathodes. However, a solid-liquid electrolyte layer forming at the interfaces degrades battery capacity and power during a longer cycle due to highly reactive chemical and electrochemical reactions. To solve this problem in the present study, a synthetic approach is demonstrated by combining AlCl₃ Lewis acid and fluoroethylene carbonate as additives in a conventional LiPF₆-containing carbonate-based electrolyte. This electrolyte design triggers the fluoroethylene carbonate polymerization by AlCl₃ addition and can also form a mechanically robust and ionically conductive Al-rich interphase on the surface of Li₇La_2.75Ba_0.25Zr_1.75Ta_0.25O₁₂ garnet-type structured solid electrolytes, Li anodes and LiNi_0.6Mn_0.2Co_0.2O₂ cathodes. Benefitting from this approach, the assembled Li symmetric cell exhibits a remarkably high critical current density of 4.2 mA cm⁻², and stable long-term cycling over 3000 h at 0.5 mA cm⁻² at 25 °C. The assembled hybrid full cell shows an impressive specific capacity retention of 92.2% at 1 C till 200 cycles. This work opens a new direction in developing safe, long-lasting, and high-energy hybrid solid-state lithium-metal batteries.