Cathode performance of novel γ-Li<inf>x</inf>V<inf>2</inf>O<inf>5</inf>/carbon composite in organic and aqueous electrolyte

Abstract

Preparation of in-situ composites with carbon by pyrolysis of an organic precursor is an effective strategy to improve performances of insulating and semiconducting cathode materials. However, due to the property of organic precursor to act as a strong reductive agent during carbonization process, the in-situ synthesis of LiV2O5/C composite cathode material is delicate and presents a challenge for researchers, since vanadium in LiV2O5 coexists in two oxidation states, V4+ and V5+. In our research, we utilized an adopted conventional solid state method for the in-situ preparation of LixV2O5/C composite (x ≈ 0.86). By using methylcellulose polymer as a carbon source, LixV2O5/C was synthesized via two-step solid state reaction at elevated temperatures. LixV2O5 crystallized as gamma polymorph phase, and the amount of in-situ formed carbon does not exceed 3wt%. The electrochemical characteristics of the as-prepared LixV2O5/C were investigated in aqueous and non-aqueous electrolyte via cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) tests and electrochemical impedance spectroscopy (EIS). On lithium insertion/removal, the LixV2O5/C composite exhibits stable cycling performance and achieves significant storage capacity enhancement when compared to pristine LixV2O5 obtained under similar conditions. Under current densities of 0.1, 0.2, 0.3 and 1 A/g, the specific capacity enhancement is around 112, 91, 80 and 62 %, respectively. Replacing the organic electrolyte with the aqueous one has a negligible effect on the mechanism and efficiency of lithium intercalation within the LixV2O5/C, which opens up the possibility of using this material in aqueous as well as in organic-electrolyte batteries. The decay of cathode's activity evidenced during electrochemical exchange of lithium with sodium in aqueous environment comes as a result of the formation of electrochemically inactive β-NaxV2O5.