Abstract
Lithium-ion batteries are an attractive power source in many scenarios. In some particular cases, including providing backup power for drones, frequency modulation, and powering electric tools, lithium-ion batteries are required to discharge at a high rate (2~20 C). In this work, we present a method to estimate the state of health (SOH) of lithium-ion batteries with a high discharge rate using the battery’s impedance at three characteristic frequencies. Firstly, a battery model is used to fit the impedance spectrum of twelve LiFePO4 batteries. Secondly, a basic estimation model is built to estimate the SOH of the batteries via the parameters of the battery model. The model is trained using the data of six batteries and is tested on another six. The RMS of relative error of the model is lower than 4.2% at 10 C and lower than 2.8% at 15 C, even when the low-frequency feature of the impedance spectrum is ignored. Thirdly, we adapt the basic model so that the SOH estimation can be performed only using the battery’s impedance at three characteristic frequencies without having to measure the entire impedance spectrum. The RMS of relative error of this adapted model at 10 C and 15 C is 3.11% and 4.25%, respectively.
Highlights
Lithium-ion batteries (LIBs) are widely used in portable terminals, electric vehicles (EVs), hybrid electric vehicles (HEVs), aerospace, and other fields [1,2]
Seeking to link the parameters of the battery model and the battery’s state of health (SOH), we took battery 2 and battery 11 as an example, and drew Figure 5 to visualize the relationship between the SOH and the normalized battery parameters
In consideration of the time and money involved, it is of merit to find an alternative way to estimate the SOH that can still achieve a high accuracy without measuring the whole impedance spectrum of the battery
Summary
Lithium-ion batteries (LIBs) are widely used in portable terminals, electric vehicles (EVs), hybrid electric vehicles (HEVs), aerospace, and other fields [1,2]. In this paper, based on the battery impedance at different frequencies, two methods are proposed to estimate the SOH of lithium-ion batteries under high-rate discharge. The first method is the traditional EIS method, which uses the battery’s impedance spectrum to determine the values of the parameters of the battery equivalent model and uses these values to estimate the SOH. The relationship between these points and the parameters in the battery model is illustrated, which lends support to the accuracy of this second model and the fact that it is more accessible.
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