The influence of hydrogen intercalation on inner pressure of Ni/MH battery during fast charge

Gaseous hydrogen is confirmed to be the main component and primarily responsible for the inner pressure rise inside the 8-Ah Ni/MH batteries during fast charge. Based on a temperature-dependent pressure model proposed in this work, the kinetic characteristics of the hydrogen evolution were investigated. The overpotential and exchange current density were obtained by fitting the presented equation to the experimental data. Moreover, the profiles of hydrogen concentration during fast charge was further modeled and calculated according to the proposed mathematical model of hydrogen intercalation. It is indicated that diffusion step controls the fast charge performances and the higher the charge rate is, the more quickly the negative electrode attains to the maximum surface intercalation fraction, and however, the calculated results also show that further charge can reduce the difference of charge efficiency among the various rate during fast charge. Numerical investigations also reveal that the increase of diffusion coefficient and decrease of the particle size can efficiently improve the characteristics of fast charge, respectively.