X-ray absorption spectroscopy study of the structural and electronic changes upon cycling of LiNiVO4 as a battery electrode

LiNiVO4 is among the transition metal oxides which are candidates as negative electrode materials in lithium-ion batteries. This study describes the cycling behavior of LiNiVO4 synthesized by a soft chemistry method, X-ray absorption spectroscopy has been used to characterize the structural and electronic modifications induced in the first cycle of a LiNiVO4/Li battery. The experiments were performed at both vanadium and nickel K edges. During the first discharge, the vanadium atoms shift from their pristine tetrahedral sites to distorted octahedra, and a short Ni-Ni distance occurs. During the recharge, the vanadium comes back to a tetrahedral environment. At the same time, the short Ni-Ni distance is always observed. Changes in the edge indicate that both vanadium and nickel are reduced upon lithiation. Vanadium is reduced reversibly at oxidation state two. Nickel reaches a very low oxidation state close to zero and does not recover the pristine oxidation state two upon charging.