Effect of local cell reaction at cathode on the performance of nickel metal-hydride battery

It has been widely known that nickel metal-hydride battery would degrade the capacity after shallow charge-discharge cycles. Whereas the formation of γ-NiOOH has been reported to degrade the capacity, its formation mechanism has not been clarified yet. We thought that local cell reaction between the cathode active material (β-NiOOH) and current collector (CC) results in the formation of γ-NiOOH to degrade the capacity. In the present study, we employed three types of CCs, i.e. gold, platinum and nickel meshes, to compare the phase change and capacity loss in terms of the local cell reaction. Only for nickel mesh CC, additional XRD peak around 13° in 2θ occurs accompanied by capacity degradation during charge-discharge cycles, while such phenomena do not for other CCs. This local cell reaction reduces β-NiOOH to transform into a γ-derivative which degrades the battery performance.