The Electrochemical Impedance Spectroscopy Features of the Lithium Nickel Manganese Cobalt Oxide Based Lithium Ion Batteries During Cycling

Abstract

Electrochemical impedance spectroscopy (EIS) is a viable approach that can be used in lithium ion batteries (LIBs) to investigate the electrochemical behavior. In this paper, Lithium Nickel Manganese Cobalt Oxide (NMC) type lithium ion batteries were divided into four groups. They were charged and discharged under various currents. The results showed that the higher the charging or discharging currents were, the faster the NMC batteries capacities fading were. In order to investigate the electrochemical behavior of the NMC batteries during cycling, we established an equivalent circuit model including one capacitor element in parallel with resistor and one constant phase angle element in parallel with resistor elements to study the impedance characteristics of the NMC batteries. The simulated results indicate that when the capacities of the batteries are dropping, the sum ohmic resistance of them will go up, and the resistance of Li+ diffusion through the SEI layer keeps increasing during cycling. The charge transfer resistance of the NMC batteries decreased at first and then kept increasing after 100 cycles. Among the three parameters, the charge transfer resistance values are the most sensitive factors that are corresponding to the state of charge of the NMC batteries during one single discharging process. We think that the internal ohmic resistance values can be used to predict the state of health (SOH) of the batteries and the charge transfer resistance can be used to predict the state of charge of the NMC batteries.