Palygorskite-Derived Ternary Fluoride with 2D Ion Transport Channels for Ampere Hour-Scale Li-S Pouch Cell with High Energy Density.

Abstract

Although various excellent electrocatalysts/adsorbents have made notable progress as sulfur cathode hosts on the lithium-sulfur (Li-S) coin-cell level, high energy density (W_G ) of the practical Li-S pouch cells is still limited by inefficient Li-ion transport in the thick sulfur cathode under low electrolyte/sulfur (E/S) and negative/positive (N/P) ratios, which aggravates the shuttle effect and sluggish redox kinetics. Here a new ternary fluoride MgAlF₅ ·2H₂ O with ultrafast ion conduction-strong polysulfides capture integration is developed. MgAlF₅ ·2H₂ O has an inverse Weberite-type crystal framework, in which the corner-sharing [AlF₆ ]-[MgF₄ (H₂ O)₂ ] octahedra units extend to form two-dimensional Li-ion transport channels along the [100] and [010] directions, respectively. Applied as the cathode sulfur host, the MgAlF₅ ·2H₂ O lithiated by LiTFSI (lithium salt in Li-S electrolyte) acts as a fast ionic conductor to ensure efficient Li-ion transport to accelerate the redox kinetics under high S loadings and low E/S and N/P. Meanwhile, the strong polar MgAlF₅ ·2H₂ O captures polysulfides by chemisorption to suppress the shuttle effect. Therefore, a 1.97 A h-level Li-S pouch cell achieves a high W_G of 386 Wh kg^-1 . This work develops a new-type ionic conductor, and provides unique insights and new hosts for designing practical Li-S pouch cells.