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

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 (WG) 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 center dot 2H2O with ultrafast ion conduction-strong polysulfides capture integration is developed. MgAlF5 center dot 2H2O has an inverse Weberite-type crystal framework, in which the corner-sharing [AlF6]-[MgF4 (H2O)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 center dot 2H2O 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 center dot 2H2O captures polysulfides by chemisorption to suppress the shuttle effect. Therefore, a 1.97 A h-level Li-S pouch cell achieves a high WG 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. MgAlF5 center dot 2H2O provides 2D ion channels owing to its inverse Weberite-type crystal framework, to ensure efficient Li-ion transport under harsh conditions, thereby accelerating Li2S redox kinetics. MgAlF5 center dot 2H2O simultaneously captures polysulfides by chemisorption to suppress shuttle effect. MgAlF5 center dot 2H2O-based cathode achieves a 1.97 A h-level Li-S pouch cell with high gravimetric energy density and cycle stability.image