Lacunary Strategy Facilitates Catalytic Conversion of Polysulfides by Polyoxometalates for High-Performance Quasi-Solid-State Li-S Batteries Based on LLZTO Electrolyte

Abstract

Solid-state lithium-sulfur (Li-S) batteries are deemed next-generation energy storage systems based on their high theoretical energy density and enhanced safety. However, challenges such as sluggish sulfur conversion kinetics and the polysulfides shuttle effect remain critical obstacles to their practical deployment. Herein, we propose a functional modification strategy for garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid-state electrolytes (SSEs) using a lacunary polyoxometalate, tetrabutylammonium 11-tungstophosphate (PW11), to address these issues. The optimized PW11-LLZTO composite electrolyte exhibits uniform surface morphology and improved interfacial stability with lithium metal. Symmetric Li/PW11-LLZTO/Li cells achieve a critical current density of 0.9 mA cm -2 and stable cycling over 800 h with low polarization. When applied in quasi-solid-state Li-S batteries, the PW11-LLZTO SSE significantly suppresses polysulfides shuttling, enhances sulfur redox kinetics, and delivers a superior reversible capacity of 619.4 mAh g -1 after 200 cycles at 1 C. Density functional theory calculation reveals that the lacunary introduction can alter the distribution of electronic environments within the saturated 12-tungstophosphate, thereby promoting greater electron accumulation and showing the stronger nucleophilicity.Therefore, the lacunary PW11 exhibits efficient Lewis acid-base interactions between oxygen atoms of polyoxoanions and Li moieties in polysulfides, thereby facilitating the conversion kinetics of polysulfides. This work demonstrates the great potential of lacunary strategy of polyoxometalates in designing high-performance SSEs for advanced quasi-solid-state Li-