Analysis of Electrochemical Reaction in Positive and Negative Electrodes during Capacity Recovery of Lithium Ion Battery Employing Recovery Electrodes

Abstract

Electrochemical reactions in positive and negative electrodes during recovery from capacity fades in lithium ion battery cells were evaluated for the purpose of revealing the recovery mechanisms. We fabricated laminated type cells with recovery electrodes, which sandwich the assemblies of negative electrodes, separators, and positive electrodes. The positive electrodes were replenished with Li⁺ by applying current between the recovery and the positive electrodes. A discharge curve analysis revealed that Li⁺ replenishment enabled the cells to recover from the capacity fade originating from capacity slippage between the positive and the negative electrodes. However, an issue is low recovery efficiency, which is defined as the ratio of recovery capacity of capacity slippage to the electric charge between the recovery and the positive electrodes. The cause of low recovery efficiency was elucidated by evaluating the positive and the negative electrodes after replenishment. It was found that the following mechanisms are involved in the replenishment of the positive electrodes: (a) Li⁺ are intercalated into the positive electrodes as they are released from the recovery electrodes, which significantly contributes to recovery from capacity slippage; however, (b) some amount of Li⁺ is released from the planes of the negative electrodes facing the positive electrodes as they are intercalated into the planes of the negative electrodes facing the recovery electrodes, which does not significantly contribute to recovery. Consequently, the recovery efficiencies were less than 50 %. We conclude that, to increase recovery efficiency, process (b) should be suppressed.