Oxygen substitution at the unbonded S site for excellent wet-air stability and lithium compatibility of Br-rich Li-argyrodite solid-state electrolytes

Abstract

Sulfide solid-state electrolytes (SSEs) are one of the best candidates for all-solid-state Li metal batteries (ASSLMBs) due to their advantages such as ultra-high ionic conductivity. However, the stability of SSEs under wet-air conditions and the poor compatibility of the Li anode have hindered their commercial application. In this paper, a variety of novel moisture tolerant Br-rich Li-argyrodite SSEs Li_5.6PS_4.6−xO_xBr_1.4 (0 ≤ x ≤ 0.3) with high Li compatibility have been synthesized by O doping. Neutron diffraction results with the Rietveld refinement confirm the successful substitution of O for the unbonded S(4d) site in the Li_5.6PS_4.6Br_1.4 structure, which will facilitate ionic transport and contribute to the stability of the electrolyte under wet-air conditions. The optimized best composition of the Li_5.6PS_4.45O_0.15Br_1.4 electrolyte exhibits a high ionic conductivity of 5.8 mS cm⁻¹ at room temperature. Notably, the O-substituted Br-rich Li_5.6PS_4.45O_0.15Br_1.4 electrolyte significantly improves the interfacial compatibility with the Li metal anode and exhibits an ultra-high critical current density (1.55 mA cm⁻²) that is superior to that of the original electrolyte (0.8 mA cm⁻²). Excellent Li plating/stripping performance is demonstrated at current densities of 0.1 mA cm⁻² and 0.5 mA cm⁻². Furthermore, the Li_5.6PS_4.45O_0.15Br_1.4 electrolyte exhibits a small increment in total resistance and maintains favorable structural stability when exposed to wet air. The assembled LiNbO₃@LiCoO₂/Li_5.6PS_4.45O_0.15Br_1.4/Li ASSLMB exhibits a high initial discharge capacity of 120.6 mA h g⁻¹ at 0.1C and more stable capacity during 100 cycles. This study provides a simple and effective method for the practical design of high-performance Li-argyrodite SSEs.