Dynamic lithium-ion battery thermal loss control method

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

Due to the rapid development of new energy vehicles, the dynamic lithium-ion battery industry also has received attention. The power lithium-ion battery is a power source for power supply from the tool, and is a battery that is electric vehicle, electric train, electric bicycle, golf cart. The first national lithium-ion battery safety technology seminar hosted by Tsinghua University was held in Beijing.

This meeting surrounds the thermal loss of power (high temperature thermal out of control), discussing various factors affecting battery safety, and how to further enhance the technical means and technical measures for lithium-ion battery safety. Professor Ouyang Minggao, Tsinghua University decided three kinds of causes of dynamic lithium-ion battery thermal out-of-control, and proposed some treatment methods and proposals. In terms of thermally, the so-called thermally incentives are external high temperature environments, including external fire, poor battery heat dissipation, etc.

At high temperatures in the external, due to the characteristics of the lithium ion battery structure, the SEI film, the electrolyte, the et al, the analyte of the electrolyte also reacts with the positive electrode, the negative electrode, and the electrical core diaphragm will melt analysis, and a number of reactions lead to a large amount. The emergence of heat. The melting of the diaphragm causes the internal short circuit and the release of electric energy and increases heat.

This cumulative mutually strengthened destruction is used, which causes the electrical core explosion-proof membrane to break, the electrolyte spray, the burning fire. The experimental data shows that when the battery monomer temperature reaches 135 ¡ã C, the diaphragm begins to melt, the voltage drops; 150 ¡ã C battery voltage is lowered; when the temperature is as high as 245 ¡ã C, the diaphragm is completely collapsed, and the battery will appear a fire explosion. In this regard, the manufacturer can handle two aspects of battery design and BMS battery management system.

From the battery design angle, you can develop a hot-outable material, block the reaction of thermal out-of control; from battery management perspectives, you can predict different temperature ranges to mean different security levels, thus grading alarm. The powerful lithium-ion battery of electric vehicles on the market contains thermal management systems, using air-cooled or water-cooled approach to heat dissipation. Related users, to eliminate thermally from usage habits, such as alert sunlight direct vehicle, do not place flammable objects in the car, while always prepares the car fire extinguisher to eliminate spontaneous combustion factors.

In addition, always pay attention to the battery temperature information on the instrument panel or medium control, generally, between the operating temperature of the battery cells is between 40 ¡ã C to 50 ¡ã C, which is not conducive to the battery. Electrochemical induce battery manufacturing impurities, metal particles, charge and discharge of electric expansion, the lithium lithium is likely to cause internal short circuit. This intramine short circuit is slow, and the time is very long, and I don't know when it will have a thermal out of control.

If you experiment, you cannot repeat the verification. At present, the world experts have not found the process of short-circuit caused by impurities, both in research. To handle this problem, first improve the manufacturing process to reduce impurities in battery manufacturing.

This should choose a battery manufacturer of product quality, followed by safe prediction in the internal short circuit, and find a single single body before the heat is out of control. This means that it is necessary to find the characteristics of the monomer, you can start from the consistency. The battery is inconsistent, the internal resistance is inconsistent, as long as it finds the monomer with variation in the middle, you can distinguish it.

For example, the equivalent circuit of the normal battery and the equivalent circuit of the micro-short circuit, the form of the equation is actually the same, but only the normal monomer, the parameters of the micro-short cells have changed. It can be studied for these parameters to see some of their characteristics in the short-circuit changes. The battery negative electrode is embedded in a large amount of lithium ions, after the charge, the lithium phenomenon appears on the negative electrode, and the needle lithium metal crystallization is present.

In the BMS battery management system, there will be an over-charge protection policy. When the system is tested to the battery voltage reaches the threshold, the charging circuit will be turned off to protect the battery. Although in front of the factory, the manufacturer conducts some of the transformer performance detection, but in order to prevent it, it is still not proposed to charge the electric vehicle for a long time, and the regular charging equipment is selected, eliminating the overfrontation.

Mechanical electrical convinced collision is a way of typical mechanical triggering heat loss, that is, car collision accidents and causing battery damage. When the battery is damaged, there will be a short circuit and a heat loss caused by the short circuit, but this short circuit is different from the electrochemical cause, and the mechanical damage is generally occurring. It corresponds to an emergency in actual life, strong impact, turn into the car , Extrusion can cause the battery to be active damage within a short period of time.

The method of treating collision (mechanical) triggering thermal out-of control is to do the structural security design of the battery. To this end, Professor Ouyang Ming Gao gives four design routes: 1 assembly structure design: plastic frame support + steel strip pre-tightening assembly structure and high strength skeleton; 2 reliability design: use battery pack vibration isolation connector to reduce vibration Wear; elastic floating board guarantees connection reliability; IP67 method dust-proof design; 3 anti-collision light quantization design: anti-collision CAE structure optimization; satisfying battery module is lightweight, square shell system quality is 90%; 4 Battery group positioning locking technology: Exactly position the battery pack using limited self-locking and single locking mechanism, locking. Participants believe that electric vehicle batteries should meet performance and security related requirements, safety detection is verified to meet thermal detection (high temperature hazard, thermal stability, no heat management cycle, thermal impact cycle, passive communication resistance), electrical detection (short circuit, Safety requirements for overcharge and over-discharge) and mechanical detection (impact, drop, puncture, rolling, immersion, crushing).

However, this does not mean that the power lithium-ion battery company can be high enough. Safe, there is no endurance, improve electric vehicle safety, and also have a joint effort to multiply, the country, research institutions, and dynamic lithium-ion batteries. In a hundred years of history in the development of fuel cars, there have been incurred accidents.

It encounters setbacks and the law of anything. Therefore, there is no such thing as a variety of accidents, electric vehicles should not stop, and should be examined and perfecting their own problems and deficiencies. At the same time, it should also be aware that consumers have endless requirements, so that security has become the primary condition to meet all funct.

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