In recent years, there have been many domestic and foreign documents studying the ageing mechanism and law of the lipo battery. It is generally believed that li-ion deposition, thickening of SEI film and loss of active materials are the main causes of battery ageing and capacity degradation. The overuse of the lipo battery will accelerate the ageing of the battery. Also, the normal charging and discharging of the battery will also affect the battery health and accelerate the ageing.
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1. The influence of temperature on the SOH of the lipo battery
In general, the temperature is considered the main factor affecting battery health. The temperature has a dual effect on the performance of the lipo battery. On the one hand, high temperature will speed up the chemical reaction in the battery and improve its efficiency and performance. On the other hand, high temperature will accelerate the occurrence of some irreversible chemical reactions, which will result in the reduction of active material in the battery and cause the ageing and capacity degradation of the battery. There are experimental data showing that high temperatures will accelerate the growth of the SEI film of the battery electrode. Also, it will increase the difficulty for li ion penetrating the SEI film, which is equivalent to the increase in the internal resistance of the battery.
2. The influence of charge and discharge current rate on the SOH of the lipo battery
The charge and discharge rate will affect the battery life. The Sony lithium ion 18650 battery was tested for 300 cycles with three different discharge rates, the battery capacity decreased by 9.5%, 13.2%, and 16.9%, and the internal resistance of the battery respectively increased by 12.4%, 18.3%, and 27.7%. At the same time, the high discharge rate will generate more heat inside the battery and accelerate the ageing of the battery. The SEI film on the electrode surface of high rate battery discharge under an electron microscope is thicker than that of low rate battery discharge.
3. The influence of discharge depth on SOH of the lipo battery
The charge and discharge depth of the battery has an impact on battery health and ageing. It is believed that the battery has accumulated total transferred energy, and the capacity attenuation and aging analysis of the battery are based on the total transferred energy. Technicians analyze the relationship between the cumulative transferred energy and capacity attenuation of the lipo battery by conducting cycling tests on different discharge depths. They concluded that the cumulative amount of energy transferred between the deep charge and the shallow charge is about the same before the battery capacity attenuation to 85%. When the battery capacity reduces to 85%~75%, the accumulated energy transferred by the battery and the energy efficiency of the deep charge and deep discharge mode are better than the shallow charge and shallow discharge mode.
4. The influence of cycle interval on the SOH of the lipo battery
The charge and discharge cycle interval will also affect the battery ageing process, and the internal resistance of the charge and discharge battery varies with the cycle intervals. Therefore, the heating and reaction of the battery during the cycle process are slightly different, which will affect the health and aging of the battery in the long term. Therefore, some experts suggest that the battery SOC range should be 20% to 80%, which is conducive to the health and cycle life of li ion batteries.
5. The influence of charge and discharge cutoff voltage on SOH of the lipo battery
Both overcharge and overdischarge of the battery will have an impact on battery health, and improper upper and lower voltage also affect the battery. The lower the discharge cutoff voltage, the greater the internal resistance of the battery. And it will cause internal heating of the battery and increase side reactions. The active material of the battery will decrease and the cathode graphite layer will collapse, and there is an acceleration of ageing and capacity attenuation of the battery. The high changing cutoff voltage causes the increase of internal resistance and internal heat. Overcharging will lead to the "lithium precipitation" phenomenon in the cathode and the corresponding increase in side reactions, which affects the capacity and ageing of the battery.
In summary, the operating temperature, charge and discharge rate, discharge depth, cycle interval, charge and discharge cutoff voltage of the battery will all have an impact on the health and life of the battery. Currently, the research on the factors affecting the health of li ion batteries is in the qualitative research stage. The quantitative analysis of these influencing factors on battery ageing and the coupling relationship of various factors are difficult to study, and it is also a hot spot for researching battery health and life.
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