Explore the cause of the thermal out of control of lithium ion batteries

　　Author ：Iflowpower – Portable Power Station Supplier

About lithium-ion batteries, thermal out-of control is the most severe safety accident, which will cause lithium-ion batteries to fire and even explosion, straight custom users. The thermal loss of lithium ion batteries is due to the internal production of heat than the heat dissipation rate, and a large amount of heat is accumulated in the inside of the lithium ion battery, and then the chain reaction causes the battery to fire and explode. There are many factors that cause heat out of control, and in general, it is divided into two categories, internal elements and external elements.

The internal elements are tightly: battery production defects lead to internal short circuits; improper battery use, causing lithium delegra to cause positive and negative short circuits internally. The external element is tightly: kneading and acupuncture and other external elements cause a short circuit in the lithium ion battery; the external short circuit forming the battery is too fast in the internal heat of the battery; the external temperature is too high, resulting in an analysis of the SEI film and positive electrode material. Krishnashah, University of Texas, Arlington, decomposed the thermal out-of control phenomenon of lithium-ion battery, and established a set of conjecture in lithium-ion battery thermal out-of control, and the safety plan for lithium-ion batteries has a tight reference significance.

Related Discussion Flashing, lithium-ion battery thermal out-control process is tightly consisting of a reaction: SEI membrane analysis, electrolyte and adhesive reactions, electrolyte and positive electrode active substances. Elements affecting the thermal out of the lithium ion battery can be divided into two, one is the heat generating rate inside the battery, the other one is the heat dissipation rate of the lithium ion battery. Traditional thermal decomposition, generally assuming that the heat of the lithium-ion battery is averaged throughout the volume, so these things decomposes that the thermal out of control is independent of the thermal conductivity of the battery, which is different from the status of lithium ion batteries in practice.

Therefore, the conjecture effect is not accurate. The discussion is flashing, even in the 26650 battery, there is also a large thermal gradient, so traditional approaches and things can't come to accurately guess the internal and external thermal status of the battery. In order to solve the above problem, Krishnashah adds thermal conductivity parameters on a conventional lithium electrical decomposition model, and then there is a number of dimensionless parameters (TRN).

The primary Krishnashah establishes a battery temperature between the temperature and heat generation and heat dissipation, as shown below, the heat generating function Q (t) in the formula is turned to Taylor at the temperature of T0, ignoring the high order Get the following formula and then the requirements of the formula pass through the chaotic mathematical solution process, Xiaobian does not understand, do not give us a resolution, let us look straight. After all, the following effects have been obtained throughout the operation plan, which is not satisfied with the above formula to ensure that no thermal failure occurs. The formula combines the internal heat transfer KR in the battery, and the battery is dissipated.

μ1, battery heat rate parametersβAnd the battery radius and other parameters. Battery heat quality parametersβAnd battery heat dissipation and thermal conductivity coefficients are key parameters for controlling the thermal out of control of lithium ion battery, by increasingβValue, TRN value also echoes increases. When TRN1, the battery will generate thermal out of control, and TRN <1 is that the battery will not occur, and the demand is concerned.

βIt is not a fixed value, but the increase of temperature is increasing, so TRN will increase. The heat dissipation of the battery is composed of two steps, and the thermal conductivity of the battery and the external heat of the battery are outside.βUnder the premise, adjust the thermal conductivity KR and surface heat dissipation parameters of the battery in demandμ1 To ensure TRN <1, then make sure the battery is safe.