High-Capacity Li⁺ Storage through Multielectron Redox in the Fast-Charging Wadsley–Roth Phase (W_0.2V_0.8)₃O₇

Abstract

The Wadsley–Roth phase (W0.2V0.8)3O7, crystallizing in a structure obtained through crystallographic shear of 3 × 3 × ∞ ReO3 blocks, is a somewhat rare exemplar for this class of compounds in that it contains a relatively small amount of 4d and/or 5d transition elements. Here, we demonstrate that it functions as a high-rate, high-capacity material for lithium-ion batteries. Electrochemical insertion and deinsertion in micron-sized particles made by conventional solid-state preparation and in sub-100 nm particles made by combining sol–gel precursors with freeze-drying methods indicate good rate capabilities. The materials display high capacity—close to 300 mA h g–1 at low rates—corresponding to the insertion of up to 1.3 Li per transition metal at voltages above 1 V. Li insertion is associated with multielectron redox for both V and W observed from ex situ X-ray photoelectron spectroscopy. The replacement of 4d and 5d elements with vanadium results in a higher voltage than seen in other, usually niobium-containing shear-structured electrode materials, and points to new opportunities for tuning voltage, electrical conductivity, and capacity in compounds in this structural class.