Electrochemical lithium intercalation in VO2(B) in aqueous electrolytes

Electrochemical lithium intercalation in VO2(B) electrodes in aqueous electrolytes has been studied by means of electrochemical methods (such as cyclic voltammetry and constant current discharge and charge) as well as atomic absorption spectrophotometry, Experiments were conducted in various buffer electrolytes having a range of pH from 6.0 to 11.3. Voltammetry clearly reveals current peaks related to lithium intercalation and deintercalation in the whole pH range investigated. Electrolyte pH plays a very important role in the performance of VO2(B) electrodes. When pH is higher than about 10, the capacity involved in the lithium intercalation in VO2(B) electrodes shows a rapid decline with repetitive cycling, which is suggested to be the result of the dissolution of the VO2(B) electrodes into the bulk electrolytes. Decreasing the pH tends to reduce the dissolution of VO2(B) and thereby gives better cycling behavior of VO2(B) electrodes. On the other hand, it also leads to increased hydrogen evolution that might affect the lithium intercalation reaction. Thus, the optimum pH range for the lithium intercalation reaction is found to be between 8 and 10. VO2(B) electrodes cycled in this pH range demonstrate very good capacity retention.