Studying the thermal loss of the charging lithium battery is out of control, what are we very powerful?

Studying the thermal loss of the charging lithium battery is out of control, what are we very powerful?

About lithium-ion batteries, thermal out of control is the most serious safety accident. Lithium-ion battery thermal out of control is much higher than the heat dissipation rate, and a large amount of heat accumulates inside the lithium ion battery, causing the rapid increase in temperature of the lithium ion battery, resulting in shorthane shrinkage, melting, positive and negative active material decomposition. Exhaust reactions, causing lithium ion batteries to fire and explod.

Preventing thermal out-of control is the ultimate goal of countless lithium-ion battery designers, but to achieve this goal, first, there is a clear and comprehensive understanding of the reaction history of lithium-ion battery thermal out-of control, but the seal of lithium-ion batteries The structure is very difficult to hinder our first level, the full seal structure design makes the observation of the internal reaction of the lithium ion battery.. Second, the high temperature in thermal out-of control is to hinder our second level, thousands of high temperatures will be burned.

Finally, the high speed of thermal out-of control is hindering our third level, and the time in the thermal out of control is often less than 0.01s, which also makes it particularly difficult to track the reaction process..

First level: Sealed first, let’s see the first level, lithium-ion battery generally use square, cylindrical hard shell sealing structure or soft bag sealing structure, and the common feature is that the external detection equipment is difficult to enter the inside of the lithium ion battery. Therefore, it is necessary to implement tracking of the internal reaction of lithium ion batteries in thermal out-of control, first solving this problem..

There are two ideas to solve this problem: 1. Internal implantation. We can place a thermocouple in the lithium ion battery, in real time tracking the internal temperature of the lithium ion battery in the thermal out of control, and we can also use the FBG fiber detector in the lithium ion battery in the heat loss of control.

Temperature and pressure change tracking analysis, this is also a wide range of ways. Second, Perspective Technology. Although the sealing structure of the lithium-ion battery can block visible light, it cannot be blocked with high-energy ray techniques, so it is also a very effective method for tracking the behavior of lithium ion batteries in thermal out of control.

For example, we have The Donalp.finegan et al. To the London City Academy has been fully tracked by the high-speed X-ray photographic device for the internal reaction process of the lithium ion battery in thermal out-of-control, revealing the explosion-proof valve of 18650 battery during thermal out-of control.

Working principle. Neutrons do not charge, so the penetration capacity is very strong. In recent years, it has also been used for research on the internal reaction mechanism of lithium-ion batteries.

For example, the engineers of Germany Bosch will use neutron diffraction technology to electrolyte in lithium-ion batteries. The internal infiltration process has been tracked and studied. Through neutron diffraction technology, we “directly see” the infiltration process of the electrolyte in the lithium-ion battery cell, so neutron diffraction technology is also very potential to use in lithium ion batteries.

In the study of thermal out of control. Second level: When the high temperature lithium ion battery is completely out of control, the chemical energy stored inside the lithium ion battery is released in a short period of time, which is much higher than the heat dissipation rate of lithium ion batteries, so that the lithium ion battery is caused. The temperature rapidly in a short period of time, the study shows that the temperature of the lithium-ion battery can reach 1000 ° C in the thermal out of control, which even melts the copper foil inside the lithium ion battery (1085 ° C of Cu), extreme high temperature will all The evidence that may be retained is all torched, so we are difficult to infer the cause of heat loss from the lithium-ion battery wreckage from the heat-lost.

. Speed ​​cooling can effectively solve this problem. For example, we have reported that Ouyang Minggao, Ouyang Minggao, Tsinghua University, put the battery in the heat out-of-control into liquid nitrogen, and quickly cool down for lithium ion batteries, thus achieving “first The evidence of the case is fixed, which also helps Ouyang Professor discovered that the lithium ion battery still passed the “shuttle” between the positive and negative poles even in the case where the diaphragm did not melt and shrink.

This also opened a new door for the study of thermal out of control.. Third level: High-speed lithium-ion battery in thermal out-of-control is very fast, especially when the thermal out-of control explosion occurs, the reaction time is often less than 0.

01s, which also leads to most of the means often cause observations due to the lack of time accuracy. Accurately, in order to solve this problem, X-ray high-speed photography technology is grandly played, and Donalp.finegan et al.

In order to study the reaction process inside the lithium-ion battery in the acupuncture experiment, the frame rate of X-ray high-speed photography technology has reached 2000 FPS. (Resolution 10UM) and 5130FPS (Resolution 20UM), we can basically clear all the reaction history of thermal out-of-control under such high frame rate, but even such a high frame rate is still difficult to capture lithium ion batteries The reaction process in the explosion (time is often less than 0.01 s), which is to be on the ground.

. The intensity of synchronous radiation light is much higher than that of ordinary X-rays, so it can achieve shorter exposure time, the European synchronous radiation center passes the exposure frame rate to 10,000 frames per second by synchronous radiation light source, thereby implementing Observation on the process of breaking, arcing, etc..

With the help of synchronous radiation technology, Donalp.finegan successfully observed 18650 battery explosion. X-ray shooting speed reached 20,272 frames / sec, and successfully observed the explosion-proof valve of 18650 battery during the explosion.

work. Lithium-ion battery thermal out of control, seriously threatens the lives and property safety of users, so the research on thermal out-of-control mechanism is particularly important, and in the past, due to the limitations of experimental conditions, we can only pass through the case temperature and battery voltage. Inference some reaction inside the lithium ion battery.

The advancement of technology not only allows us to detect the temperature and pressure of the lithium-ion battery, but the blessing of high-speed photography techniques is to visually observe the high-speed response process inside the lithium-ion battery in the thermal out-of-control. We recognize the reaction mechanism of lithium-ion batteries is very important, and also supply guidance for more secure lithium-ion battery design.

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