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

Abstract

AbstractAlthough 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 MgAlF5·2H2O with ultrafast ion conduction–strong polysulfides capture integration is developed. MgAlF5·2H2O 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 MgAlF5·2H2O 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 MgAlF5·2H2O 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.