Laser-induced breakdown spectroscopy to obtain quantitative three-dimensional hydrogen mapping in a nickel–metal-hydride battery cathode for interpreting its reaction distribution

Abstract

We present a method for obtaining a three-dimensional quantitative hydrogen distribution in a Ni–MH battery cathode using laser-induced breakdown spectroscopy (LIBS) and demonstrate that the reaction distribution in the cathode can be interpreted based on a state-of-charge (SOC) distribution converted from the hydrogen distribution. In this method, we measured the hydrogen emission-line intensities at 656.28 nm for a model cathode cycled five times at 2.3 mA cm⁻² and a commercial Ni–MH battery cathode cycled 1000 times at 1C under a 3000 Pa helium atmosphere. Our results show that the average SOC in the SOC distributions of the cathodes agreed with those evaluated from X-ray diffraction and charge–discharge curves and that the overcharged areas exhibited SOC values above 100%. The present LIBS method will allow us to understand the deterioration mechanism of a Ni–MH battery and improve its cycle life and capacity.