Cause of the Memory Effect Observed in Alkaline Secondary Batteries and Its Measures

使用镍电极对碱性二次电池进行浅放电和过充电，在放电曲线上观察到工作电压的降低，这被称为记忆效应。正常镍电极荷电状态的X射线衍射图只包含β-NiOH的衍射峰。荷电状态的镍电极表现出较低的放电电压，除了γ-NiOH的衍射峰外，还有β-NiOOH的衍射峰。γ-NiOOH的形成可以归因于在碱性二次电池中常见的记忆效应的主要原因，如镍镉和镍氢电池。通过X射线衍射分析和交流阻抗研究发现，γ-NiOH型化合物最初形成于集电侧，在浅放电-充电循环过程中逐渐扩展到溶液侧。因此，如果形成的γ-NiOH量很小，即使在观察到记忆效应的情况下，也只能检测到[β-NiOOH]。在这种情况下，可以通过使用一张砂纸刮掉电极表面的γ-NiOH来检测到β-NiOH。这种γ-NiOOH在正常的充放电循环的几个循环内消失，导致记忆效应的消除。由此可以得出结论，记忆效应的产生主要是由于γ-NiOOH的形成。

By repeating shallow discharging and overcharging of alkaline secondary batteries using nickel electrode, a lowering of working voltage is observed on the discharge curve, which is called a memory effect. The X-ray diffraction pattern of the charged-state of the normal nickel electrode contained only diffraction peaks due to β-NiOOH.A charged-state nickel electrode showing lowered discharge voltage had diffraction peaks due to γ -NiOOH in addition to those due to β-NiOOH.The formation of γ -NiOOH can be attributed to be the main cause for the memory effect commonly observed in alkaline secondary batteries such as nickel cadmium and nickel hydrogen batteries. By XRD analysis and AC impedance study, γ -NiOOH was found to be initially formed at the current collector side ; it grows to the solution side in the course of shallow discharge-charge cycling. Therefore, if the amount of γ -NiOOH formed is small, only [β-NiOOH can be detected, even when the memory effect is observed. In this case, γ -NiOOH can be detected by shaving the surface of the electrode using a piece of emery paper to remove covering β-NiOOH.This γ -NiOOH disappears within a few cycles of the normal charge-discharge cycling, resulting in the elimination of the memory effect. It may be concluded that the cause of the memory effect is mainly due to the formation of γ-NiOOH.