Self-discharge mechanism of Ni-MH battery by using acrylic acid grafted polypropylene separator

The deposition of corrosion products of MmNi3.55Co0.75Al0.2Mn0.5 alloy in the positive electrodes of nickel-metal-hydride (Ni-MH) battery is tested by using inductively coupled plasma spectroscopy. The deposition amounts of Al and Mn are markedly reduced by using an acrylic acid (AA) grafted polypropylene (PP) separator. The detrimental effect of Mn on self-discharge performance of Ni-MH battery is indirectly demonstrated by using nickel-cadmium (Ni-Cd) battery with a deliberate addition of Mn element into the KOH electrolyte. The shuttle reactions between Mn(III) and Mn(II) in the electrolyte are confirmed by cyclic voltammetry tests. Based on these results, a possible mechanism of AA grafted PP separator is proposed that it can trap Mn ion in the electrolyte, thus suppressing the detrimental shuttle reactions, and thereby reducing the self-discharge rate of the batteries.