What do SOC and SOH mean for lithium batteries? The impact of SOC status on lithium batteries?

What is the meaning of lithium-ion battery SOC and SOH? The effect of SOC status on lithium-ion batteries. Lithium-ion battery status includes battery temperature, SOC, SOH, SOS, SOF, and SOE. In order to give full play to the power performance of the battery system, improve the safety of its use, prevent the battery from overcharging and overdischarging, extend the service life of the battery, optimize driving and improve the performance of electric vehicles, the BMS system needs to accurately estimate the state of charge, or SOC, of the lithium-ion battery. SOC is an important parameter used to describe the capacity that can be charged in and out of a battery during use.

What is the meaning of lithium-ion battery SOC and SOH?

SOC refers to the state of charge, also known as the remaining power, which represents the ratio of the remaining capacity of the battery after use for a period of time or long-term use to the capacity of the fully charged state, commonly expressed as a percentage. The value ranges from 0 to 1. SOC=0 indicates that the battery is fully discharged. SOC=1 indicates that the battery is fully charged. Lithium-ion battery SOC cannot be measured directly, and can only be estimated by battery terminal voltage, charge and discharge current and internal resistance. These parameters will also be affected by a variety of uncertain factors such as battery aging, ambient temperature change and vehicle driving state, so accurate SOC estimation has become an urgent problem to be solved in the development of electric vehicles.

SOH refers to the battery capacity, health, performance status, simply said that the battery after a period of time after the performance parameters and nominal parameters of the ratio, the new factory battery is 100%, completely scrapped 0%. It is the ratio of the capacity released by the battery from a certain rate of discharge to the cut-off voltage under full charge to the corresponding nominal capacity, which is simply understood as the limit capacity of the battery. There is a certain relationship between the internal resistance of the battery and SOH. The lower the SOH, the greater the internal resistance of the lithium-ion battery, through the detection of voltage, current, temperature and other data, the internal resistance of the battery is calculated indirectly, and then the SOH is calculated according to the relationship between SOH and the internal resistance of the battery. However, the internal resistance of the battery does not change significantly when the SOH variation range is small, and the resistance value changes greatly when the battery is seriously aged. Therefore, the measurement error of this method will be larger when the SOH variation is small.

The effect of SOC status on lithium-ion batteries

1. The cycle life of lithium-ion batteries and the change law of SOC are consistent with expectations, and the cycle life is significantly increased with the reduction of SOC.

2, SOC is the most important parameter in BMS, involving all other BMS operation work, so the accuracy and robustness of SOC is extremely important. Without a precise SOC, the BMS will not work properly, the battery will often be in a protected state, and the battery life will be shortened. The higher the accuracy of the battery with the same capacity, the higher the range can be.

3, lithium-ion battery in the process of thermal runaway has a considerable part of the heat from the battery storage of electrical energy, usually high SOC state will lead to positive and negative material reactivity increased and thermal stability decreased, so the lithium-ion battery SOC state on the lithium-ion battery in the abuse of the conditions of safety has a crucial impact.

4, different temperatures and different SoCs have different effects on the storage of lithium-ion batteries, 55℃ has the greatest impact on the capacity attenuation of lithium-ion batteries, and 0% and 100% SOCs are not the best state of charge for the most favorable battery performance. The best storage conditions for lithium-ion iron phosphate batteries were investigated by combining various factors.

The above is the meaning of lithium-ion battery SOC and SOH and the impact of SOC state on lithium-ion batteries. The aging of lithium-ion batteries is a long-term gradual process, and the health status of batteries is affected by many factors such as temperature, current ratio, cut-off voltage, and so on. Battery health status assessment has guiding significance for battery use, maintenance and economic analysis, but the battery health status assessment lacks targeted sorting and summary.