Pyrochlore‐Type Iron Hydroxy Fluorides as Low‐Cost Lithium‐Ion Cathode Materials for Stationary Energy Storage

Abstract

Pyrochlore‐type iron (III) hydroxy fluorides (Pyr‐IHF) are appealing low‐cost stationary energy storage materials due to the virtually unlimited supply of their constituent elements, their high energy densities and fast Li‐ion diffusion. However, the prohibitively high cost of synthesis and cathode architecture currently prevent their commercial use in low‐cost Li‐ion batteries. Herein, we present a facile and cost‐effective dissolution‐precipitation synthesis of Pyr‐IHF from soluble iron (III) fluoride precursors. High capacity retention by synthesized Pyr‐IHF of > 80% after 600 cycles at a high current density of 1 A g‐1 was obtained, without elaborate electrode engineering. Operando synchrotron X‐ray diffraction guided the selective synthesis of Pyr‐IHF such that different water contents could be tested for their effect on the rate capability. Li‐ion diffusion was found to occur in the 3D hexagonal channels of Pyr‐IHF, formed by corner‐sharing FeF6‐x(OH)x octahedra.This article is protected by copyright. All rights reserved