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Termal kaçak lityum iyon pili anlamak - nedenleri, mekanizması ve önlenmesi
Termal kaçak lityum iyon pil modern enerji depolama teknolojisinde önemli bir güvenlik sorunudur. Lityum pilin termal kaçak mekanizmasını ve önleyici tedbirlerini anlamak, pil sisteminin güvenliğini ve güvenilirliğini sağlamak için çok önemlidir.
Bu makale bize termal kaçak lityum iyon pilin nedenlerini, mekanizmasını ve önlenmesini anlatacaktır.
What is thermal runaway in lithium ion batteries?
Lithium battery thermal runaway refers to the phenomenon that lithium battery current and internal temperature rise occur a cumulative mutually reinforcing use, resulting in lithium battery damage. The main body of thermal runaway in a narrow sense refers to a single cell. Generalized thermal runaway, the subject of which refers to PACK.
Simply put, thermal runaway is a positive energy feedback loop process: rising temperatures cause the system to heat up, which in turn causes the system to heat up, which in turn makes the system even hotter, and ultimately causes a fire or explosion.
What causes thermal runaway in lithium ion batteries?
External short circuit
External high temperature
The melting of the diaphragm leads to an dahili kısa devre, and the release of electrical energy increases heat production.
The result of this cumulative and mutually reinforcing destructive use is that the explosion proof film of the battery cell is broken, the electrolyte is ejected, and the fire occurs.
Dahili kısa devre
Due to the wrong use of lithium-ion batteries or lithium battery quality defects, such as the branch crystals caused by overcharge and overdischarge, impurities in the battery production process dust, etc., will deteriorate the growth and puncture the diaphragm, there is a micro short circuit, the release of electrical energy leads to temperature rise, and the chemical reaction of the material brought by temperature rise expands the short circuit path, forming a larger short circuit current. A cumulative, mutually reinforcing destruction is formed, leading to thermal runaway.
In the cases of fire caused by thermal runaway of lithium batteries in recent years, most of them are first caused by internal short circuits, and its heat and temperature form an external high temperature environment for adjacent batteries, triggering thermal runaway of adjacent batteries, which leads to a chain reaction of the whole PACK.
Mechanism of Thermal runaway lithium ion battery
Lithium batteries are lithium ions embedded in carbon (petroleum coke and graphite) to form a negative electrode.
The cathode material is usually LixCoO2, LixNiO2 and LixMnO4, and the electrolyte is LiPF6+ diethylene carbonate (EC)+ dimethyl carbonate (DMC).
The main inducing factors of thermal runaway are mechanical damage, akü aşırı şarjı, internal short circuit , etc. Under the influence of various factors, the active material inside the lithium-ion battery has a violent exothermic reaction, and the internal temperature of the battery exceeds the controllable range, which ultimately leads to thermal runaway.
The exothermic chemical reaction in lithium ion batteries comprises the decomposition of SEI solid electrolyte interface film, the reaction of negative active material and electrolyte, the reaction of negative active material and binder, and the oxidation decomposition reaction of electrolyte.
How to prevent thermal runaway in lithium ion batteries?
External protection
PTC (positive temperature coefficient) components
Explosion-proof valve
Improved cooling system
The thermal management system is mainly responsible for controlling the temperature to ensure that the battery is always at a reasonable operating temperature. Usually, the thermal management system is controlled by the vehicle controller. When the temperature of the lithium battery is abnormal, heat dissipation or heating is carried out in time by the air conditioning system to ensure the safety and life of the battery.
Aerogel battery insulation sheet
The aerogel insulation pad can be assembled between the power battery cell and the module. When thermal control of the battery cell occurs, the aerogel with low thermal conductivity can play a heat insulation role, delaying or blocking the accident.
When the battery cell overheats and burns, the aerogel insulation sheet reaches class. A non-combustible performance can also effectively block or delay the spread of the fire, and can ensure that the battery pack does not burn or explode within 5 minutes, providing enough time for escape.
Internal improvement
Improve the electrolytic liquid system
As the blood of lithium-ion batteries, the lityum iyon pil elektroliti directly determines the akü performansi, and plays an important role in the battery’s capacity, operating temperature range, cycling performance and safety performance .
At present, the most widely used components in the electrolytic liquid system of commercial lithium-ion batteries are LiPF6, vinyl carbonate and linear carbonate. A large number of carbonate solvents with low boiling points and low flash points in the electrolyte will flash at a low temperature, which has great safety risks.
Therefore, many researchers try to improve the electrolytic liquid system to improve the safety performance of the electrolyte. If the main material of the battery does not undergo subversive changes in a short time, improving the stability of the electrolyte is an important way to enhance the safety of the battery.
Positive electrode material
Lithium-ion battery cathode material is unstable when the charging state lityum iyon pil voltajı is higher than 4V, and it is easy to thermal decomposition at high temperatures to release oxygen, and oxygen continues to react with organic solvents to produce a large amount of heat and other gases, reducing the safety of the battery. Therefore, the reaction between lityum iyon pil anotu and electrolyte is considered to be the main cause of thermal runaway.
For positive electrode materials, coating modification is a common method to improve their safety. Such as MgO, A12O3, SiO2, TiO2, ZnO, SnO2, ZrO2 and other substances on the surface of the positive electrode material, can reduce the reaction between the positive electrode and the electrolyte after Li+ removal, while reducing the oxygen release of the positive electrode, inhibit the phase change of the positive electrode material, improve its structural stability, reduce the disorder of the cation in the lattice, and reduce the positive electrode material. This reduces heat generation from side reactions during the cycle.
Separator
At present, the most widely used separator in commercial lithium-ion batteries is still polyolefin materials, whose main disadvantages are heat shrinkage at high temperatures and poor electrolyte wetting.
In order to overcome these defects, researchers have tried many methods, such as finding a heat-stable material instead, or adding a small amount of Al2O3 or SiO2 nanoparticle powder to the diaphragm, which not only uses ordinary diaphragm, but also improves the thermal stability of the positive electrode material.
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