Causes and countermeasures of thermal runaway of power lithium batteries

It mainly occurs in a car collision. Due to the influence of external forces, the lithium battery cell and battery pack are deformed, and the relative displacement of each part itself causes the battery membrane to be torn and internal short-circuit; the leakage of flammable electrolyte eventually causes a fire. In mechanical abuse, puncture damage is the most serious, and the conductor may be inserted into the battery body, causing a direct positive and negative short circuit. In contrast, collisions, extrusions, etc. are only probabilistic internal short circuits, and the heat that occurs during breakdown is stronger, leading to a higher probability of heat escape. (2) Abuse of electricity The abuse of electricity is mainly caused by improper use of batteries, including external short circuits, overcharge, and overdischarge. Among them, the over-discharge is the least harmful, but the copper dendrite growth caused by over-discharge will reduce the safety of the battery and increase the possibility of thermal runaway. The external short circuit is the result of the connection of two conductors with differential voltage on the outside of the battery. Overcharging is the most harmful form of electricity abuse. Lithium dendrites grow on the anode surface due to excessive lithium insertion. Secondly, excessive de-embedding of lithium will cause the cathode structure to collapse due to the release of heat and oxygen (oxygen release from the NCA cathode). (3) Heat abuse Heat abuse mainly refers to the partial overheating inside the battery. This phenomenon rarely exists independently, and often develops through mechanical abuse and electrical abuse. It is a situation that eventually directly leads to accidents such as thermal runaway. . Thermal abuse is usually caused by the temperature control system not working due to the high external environment or the overheating of the battery, resulting in a short circuit and thermal runaway. In terms of causes, the causes of heat abuse are the most complicated. The collision and damage of the battery pack, the internal structure and performance of the battery, or the failure of other thermal management systems and air conditioning systems may all lead to heat abuse. (4) Internal short circuit The internal short circuit is caused by the direct contact between the positive and negative electrodes of the battery. Of course, the degree of contact is different, and the subsequent response is also very different. Large-scale internal short circuits usually caused by mechanical and thermal abuse can directly lead to thermal abuse. The cause of the internal short circuit is also very complicated. If the lithium battery is overcharged, the dendrites will accumulate to a certain extent, causing the battery membrane to be broken down, leading to an internal short circuit, or direct contact between the positive and negative electrodes after collision or breakdown damage, leading to thermal runaway. Compared with the internal short circuit caused by external factors, the internal short circuit caused by spontaneous defects in the battery manufacturing process is relatively small. The inherent internal short circuit generates less heat and does not immediately cause thermal runaway. It takes some time for this internal defect to develop into a milder internal short circuit. Regarding the thermal runaway of lithium batteries, the important domestic solution is to protect it from the outside and improve it from the inside. External protection is important to upgrade and improvement of the system, and internal improvement is important to the improvement of the battery itself. (1) Promote cooling methods. The thermal management system is responsible for controlling the temperature to ensure that the battery is always at a reasonable working temperature. The thermal management system is usually controlled by the vehicle controller. When the battery temperature is abnormal, the air conditioning system can be cooled or heated in time to ensure the safety and service life of the battery. The battery's heat dissipation methods are divided into four types according to the heat conduction method and the medium: air cooling (air cooling), liquid cooling (water cooling), phase change material (solid), and composite cooling (water cooling + solid). (2) Improvement of internal materials and structure The internal improvement is to transform the internal material structure of the battery to make the battery have better heat resistance and heat dissipation performance. As far as the current research focus is concerned, the development of solid electrolytes; the positive and negative electrodes are reconstructed. The use of safer diaphragm materials is one of the important ways to improve the thermal performance of the battery from the inside. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: Comparative analysis of the advantages and disadvantages of solid-state lithium batteries and hydrogen fuel power batteries