5 V-Class 35.3 mAh cm-2 All-Solid-State Li Batteries

The advancement of battery technology has been impeded by the voltage constraints of electrolytes. Here, we present a high-energy all-solid-state battery (ASSB) design that achieves both a >5 V operation and an ultrahigh areal capacity of 35.3 mAh cm-2; these attributes were enabled by a new, highly conductive and ultrahigh voltage stable fluoride solid electrolyte (SE), LiCl–4Li2TiF6 (1.7 x 10-5 S cm-1 at 30 °C). This material provides over 100 times higher Li+ conductivity than Li2TiF6, attributable to the enlarged Li+ channels and increased Li+ concentration at the nanocrystallite interfaces, as proved by combined experimental and theoretical investigations. LiCl–4Li2TiF6 shields high-voltage spinel oxide cathodes, achieving excellent performance (e.g., 106 mAh g-1 at 2C and 30 °C with 75.2% retention after 500 cycles for LiNi0.5Mn1.5O4), sharply contrasting with the conventional LiNbO3 counterpart, which decomposes and fails to prevent detrimental interfacial degradation. The efficacy of LiCl–4Li2TiF6 is validated across various systems, including higher-voltage LiCoMnO4, cost-effective LiFe0.5Mn1.5O4, pouch-type LiNi0.5Mn1.5O4//Li ASSBs, operability down to 2.3 V with 258 mAh g-1, and 1.8 mm ultrathick electrodes. This newly proposed SE with over 5 V stability introduces a new design paradigm by revisiting the previously forbidden high-voltage cathodes for high-energy ASSBs.