Prediction of State-of-Health for Nickel-Metal Hydride Batteries by a Curve Model Based on Charge-Discharge Tests

Abstract

Based on charge-discharge cycle tests for commercial nickel-metal hydride (Ni-MH) batteries, a nonlinear relationship is found between the discharging capacity (Cdischarge, Ah) and the voltage changes in 1 s occurring at the start of the charging process (ΔVcharge, mV). This nonlinear relationship between Cdischarge and ΔVcharge is described with a curve equation, which can be determined using a nonlinear least-squares method. Based on the curve equation, a curve model for the state-of-health (SOH) prediction is constructed without battery models and cycle numbers. The validity of the curve model is verified using (Cdischarge, ΔVcharge) data groups obtained from the charge-discharge cycle tests at different rates. The results indicate that the curve model can be effectively applied to predict the SOH of the Ni-MH batteries and the best prediction root-mean-square error (RMSE) can reach upto 1.2%. Further research is needed to confirm the application of this empirical curve model in practical fields.

Keywords

• nickel-metal hydride (Ni-MH) battery
• state-of-health (SOH)
• curve fitting
• nonlinear least-squares method
• prediction