Effect of annealing on electrochemical stability of chemically preintercalated bilayered vanadium oxide cathodes in batteries

Abstract

Bilayered vanadium oxide, δ-V2O5·nH2O, is a promising electrode material for Na-ion batteries due to its large interlayer spacing, 11.5 A, that allows for insertion of many charge-carrying ions. Previously, δ-V2O5·nH2O electrodes have shown high capacities in Na-ion batteries1-3. However, capacity fade is common when synthesized via cost effective, sol-gel routes. Poor cycling stability is attributed to the loss of V-O layers’ stacking order upon cycling1. Therefore, methods to improve the structural stability of the δ-V2O5·nH2O phase are necessary for its utilization as Na-ion cathodes. A synthesis approach known as chemical pre-intercalation allows for the insertion of inorganic cations into the structure of electrode materials prior to electrochemical cycling. Previously, we have demonstrated that chemical pre-intercalation of Na-ions into the bilayered phase results in high initial capacities above 350 mAh g-1 in Na-ion cells3. In this study, we focus on the incorporation of low-temperature annealing to increase structural and electrochemical stability of the bilayered phase in Na-ion batteries. We demonstrate that annealing can lead to increased crystallinity leading to increased cycling stability. This result shows how synthesis approaches affect the structure of the bilayered vanadium oxide phase and can lead to increased electrochemical stability in Na-ion cells.