It is essential to know the behavior of the battery at all relevant internal and external conditions when the battery cell is in the new and the aging state. 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, in order to investigate the state of charge effects on the LIBs, three types of commercial LIB cells were used, and the EIS measurements were performed under 100%, 80%, 50%, 20% and 0% SOC, respectively. An equivalent circuit model (ECM) including two constant phase angle elements in parallel with resistor elements is established to study the impedance characteristics for LIBs. The influence of the state of charge on the parameters of the ECM was analyzed. Based on the results we think EIS combined with ECM simulation tool can be used to derive useful information for improving battery design and state of health prediction.
Electrochemical impedance spectroscopy (EIS) is one of the most effective methods that can be used to study the cycling decay behavior of lithium ion batteries (LIBs) without destruction of the battery. In this paper, in order to understand and to analyse the impedance response of the Lithium iron phosphate (LFP) batteries during various cycling rates, an equivalent circuit model (ECM) is established to investigate the cycling influence on the ECM parameters of LIBs. The influence of the discharging process on the patterns of the ECM was also analysed. The results indicate that the sum ohmic resistance and the Li+ diffusion through the SEI layer resistance keep increasing and the charge transfer resistance drop during the cycling when the retention capacities are higher than 90%. While the LFP batteries cycle under 1 C, the charge transfer resistance of them drop at first and then increase significantly after around 200 cycles when the retention capacities are lower than 80%. The results also show that when the LFP batteries are discharged during one single cycle, the sum ohmic resistance, the Li+ diffusion through the SEI layer resistance and the charge transfer resistance keep increasing. The results in this study indicate that EIS is a useful tool to obtain information for monitoring the state of health of LIBs.
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.
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