Lithiation of V2O3(SO4)2 – a flexible insertion host

Abstract

Materials that display strong capabilities for lithium insertion without significant change in unit cell size on cycling are of considerable importance for electrochemical applications. Here, we present V₂O₃(SO₄)₂ as a host for lithium-ion batteries. Electrochemically, 2.0 Li⁺ ions can be inserted, giving Li₂V₂O₃(SO₄)₂ with an oxidation state of V⁴⁺, as determined by X-ray absorption spectroscopy. The capacity of V₂O₃(SO₄)₂ can be increased from 157 mA h g⁻¹ to 313 mA h g⁻¹ with the insertion of two additional Li⁺ ions which would drastically improve the energy density of this material, but this would be over a wider potential range. Chemical lithiation using n-butyllithium was performed and characterisation using a range of techniques showed that a composition of Li₄V₂O₃(SO₄)₂ can be obtained with an oxidation state of V³⁺. Structural studies of the lithiated materials by X-ray diffraction showed that up to 4.0 Li⁺ ions can be inserted into V₂O₃(SO₄)₂ whilst maintaining its framework structure.