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Simulation Thermal Analysis of Lithium Ion 18650
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Simulation Thermal Analysis of Lithium Ion 18650

Li ion batteries are considered one of the most important energy storage technologies. With the continuous promotion of li ion batteries, its safety has attracted more attention. In this article, the simulation thermal analysis of lithium ion 18650 was carried out. The user subroutine DFLUX was used to set the battery heat source during the analysis. Li ion batteries are widely used in 3C digital products, mobile power supplies, and electric vehicles.

1. Thermal runaway process of li ion batteries

In recent years, fire cases caused by the thermal runaway of li ion batteries are all caused by the fact that the heat generation rate of the battery is much higher than the heat dissipation rate, and a large amount of heat is accumulated and not released in time.

(1) The first stage: the internal thermal runaway stage of the battery

The lithium-ion 18650 is safe at 80~90℃. When the temperature rises to between 90 and 120°C, the SEI film begins to decompose, release heat, and raise the temperature. However, when the temperature reaches 120-130°C, the protective SEI film will be destroyed, the anode electrode will react with the solvent and the binder. Also, the temperature will rise, and the separator will melt and shut down. After the temperature continues to rise above 150°C, the internal electrolyte will begin to decompose and continue to release heat to further heat the battery.

(2) The second stage: the swollen battery stage

When the battery temperature reaches above 200°C, the cathode material will decompose and release a large amount of heat and gas, and the temperature will continue to rise. At 250-350°C, the lithium anode will begin to react with the electrolyte.

(3) The third stage: the battery thermal runaway and explosion failure stage

During the reaction, the electrolyte reacts violently with the oxygen produced by the cathode electrode reaction and further makes thermal runaway of the battery. PLS Battery provides good quality li ion battery wholesale, contact us for more information! We are one of the top li ion battery suppliers in China whose products go through strict test before they leave the factory.

2. Reasons of thermal runaway of li ion batteries

In fact, the probability of an internal short circuit in a battery in an electronic product is one in ten million, which means the safety of a single battery used in daily life is relatively high. However, in electric vehicles, the battery pack of an electric vehicle consists of thousands of cells, and the probability of thermal runaway increases from one in ten million to one in a thousand. In addition, dangerous batteries of electric vehicles will cause very serious consequences. Therefore, it is particularly important to study the causes of battery thermal runaway.

(1) Cathode material

The safety performance of the cathode electrode material mainly includes overcharge safety and thermal stability. In the oxidized state, the cathode material will have an exothermic decomposition reaction and release oxygen.

(2) Anode material

Although the anode material is relatively stable, the carbon anode in the lithium state will firstly react with the electrolyte at a high temperature.

(3) Electrolyte

The electrolyte includes an inorganic conductive agent and an organic solvent. The flammability of the organic solvent will affect the safety performance of the battery.

(4) Production process

The production process of li ion batteries is very complicated. Metal impurities or burrs generated in the production process cannot be completely avoided even under strict control. If there are impurities, burrs or dendrites in the battery, the amplification and deterioration will cause the increase of conductivity and temperature, and the heat generated by the chemical reaction and discharge heating will continue to accumulate, which may eventually lead to the thermal runaway of the battery.    

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