The charging and discharging capacity of the battery system and the life of the battery system follow the barrel principle and are determined by the worst battery in the system.
A good thermal management system must make the temperature distribution of the battery system uniform and make the battery temperature have good consistency. Because temperature has a great influence on the capacity, charging and discharging power and safety of lithium-ion batteries.
1. Capacity decay
The chemical reactions and physical changes inside lithium-ion batteries are not completely reversible reactions. As the number of charge and discharge times increases, the available capacity of lithium-ion batteries will decay at different rates. Capacity is an important indicator of the basic characteristics of the reaction battery, and temperature is a key factor affecting the capacity decay rate of lithium-ion batteries.
The higher the temperature, the faster the occurrence of side reactions, the faster the capacity of lithium-ion batteries decays. The lower the temperature, the more active lithium will be deposited on the electrode surface. The mutual influence of temperature and capacity decay aggravates the aging of the battery and shortens the service life of the battery.
The optimal operating temperature of energy storage batteries is 15 to 35°C.
2. Thermal runaway
The thermal runaway of lithium-ion batteries is mainly divided into three ways: thermal abuse, mechanical abuse and electrical abuse.
Thermal abuse refers to the exothermic chemical reaction of the active materials inside the battery due to excessive external temperature, which in turn causes thermal runaway; mechanical abuse refers to thermal runaway caused by harsh conditions such as external extrusion and collision; electrical abuse refers to thermal runaway caused by harsh conditions such as overcharging, overdischarging and short circuit.
3. Low temperature damage
When the temperature decreases, the capacity of lithium-ion batteries will decrease with the decrease in temperature, and this phenomenon becomes more obvious below 0℃. This is due to the significant decrease in the transmission performance of the electrolyte and the diffusion rate of lithium in graphite at low temperatures.
Under low temperature conditions, the charging performance of lithium-ion batteries is worse than the discharging performance, which is caused by poor charge transfer at the interface between the electrode and the electrolyte.
Yorumlar