American scientists improve the design of lithium batteries to solve internal short-circuit problems

Recently, research scholars at the National Renewable Energy Laboratory of the US Department of Energy said that they have developed an internal short-circuit device and successfully applied for patent protection. The circuit breaker can simulate the internal defects that may cause the temperature of lithium-ion batteries to rise and eventually lead to heat loss. The main purpose of the research and development of the internal short-circuit breaker is to determine the root cause of the temperature increase and heat loss of the lithium ion battery by simulating the internal defects of the lithium ion battery, and finally improve the design of the lithium ion battery.

In the process of research and development, the National Renewable Energy Laboratory of the United States has cooperated with NASA in the project. The main content of the cooperation is to develop a new and more accurate internal short-circuit breaker through joint efforts, so as to predict the follow-up behavior after the battery is short-circuited. Finally, a corresponding security mechanism can be established when designing a single battery or battery stack. So far, the first products of the above internal short-circuit breaker project have been successfully applied to the National Renewable Energy Laboratory, NASA, and lithium battery manufacturers. Through the above internal short circuit breaker products can effectively help the above users to learn the impact of internal defects of the battery and corresponding solutions.

The short circuit problem in lithium batteries is usually caused by many factors, the most fundamental of which is caused by some small internal defects. For example, if a small amount of foreign material is accidentally added to the battery during the manufacturing process, the battery will have some internal defects.

The internal circuit breaker of the National Renewable Energy Laboratory in the United States can not only predict the performance of the battery, but also prevent the surrounding environment from affecting the battery and causing heat loss. If a short circuit problem does occur inside the cell, limiting the heat loss to one cell will effectively reduce the damage to the entire battery. The use of internal circuit breakers can help lithium battery manufacturers optimize their battery structures to minimize the heat loss of the entire battery. Among the measures commonly used to optimize the design of battery structures include adding protective barriers between cell units, ensuring the limitations of cell loss, and establishing a special preventive mechanism between cell power connections.

The new internal circuit breaker is a revolutionary design for the current internal short-circuit measures. At present, measures that can actively promote the internal short-circuit of the battery mainly include nail puncture, hard rod puncture, impact battery, adding reverse voltage to the battery, and increasing the temperature of the battery. As a structure built into the inner part of the battery, it is found that the internal short-circuit device can effectively simulate the internal defect of the battery. At the same time, through the application of the internal circuit breaker, the internal short circuit of the battery can be experimentally studied without damaging the external structure of the battery.

Compared with the traditional internal short-circuit measures, the internal short-circuit device is a kind of heat management switch that is completely built into the inside of the battery. Its working process is quite reliable and it is also quite controllable. It can also be placed in any position inside the battery, and it can also simulate all four short-circuit methods, including electrode-electrode short circuit, electrode-cathode short circuit, electrode-anode short circuit, and cathode-anode short circuit. Different short-circuit methods correspond to different reactions.

The internal structure of the new internal short-circuit device consists of a small copper aluminum disc, a copper ball, polyethylene or polypropylene separator, and a layer of wax film(the thickness of the wax film is equivalent to the diameter of a hair WIRE). After the internal short circuit breaker is placed in the battery, the wax film on the surface of the internal short circuit breaker can be melted by heating the internal short circuit breaker, so that the metal parts inside the short circuit can contact each other and eventually trigger the short circuit. After a short circuit occurs inside the battery, the sensors arranged inside and outside the battery begin to work to record the subsequent reaction of the battery.

The wax film problem is the further research on the internal short circuit breaker. The paraffin melting temperature is 30 °C -150 °C, but the researchers found that the paraffin material used in the above internal short circuit breakers is not flexible enough to break, and may be broken for this reason during embedding into the battery. In the end, the researchers chose to use microcrystalline paraffin, which is more resilient and widely used in non-industrial applications such as cosmetics and hairspray. By mixing the above microcrystalline paraffin with ordinary paraffin, we can obtain paraffin materials that meet the requirements of internal short-circuit breaker for adhesion, flexibility and hardness.

So far, Keyser and his team have conducted research on internal short-circuit breaker technology for more than five years. Now it is negotiating with various battery manufacturers on specific commercial cooperation issues whose ultimate goal is to promote the wide range of applications of its internal short-circuit breakers.

The National Renewable Energy Laboratory of the United States stated that it will continue to maintain cooperation with NASA on the safety ofspecial batteries. At the same time, more and more battery manufacturers have begun to accept the use of the above new internal short-circuit breakers. In addition to the internal circuit breakers, researchers at the National Renewable Energy Laboratory in the United States have also adopted various models and various simulation tools to comprehensively study the safety of batteries at multiple physical levels. At the molecular level, the optimum design of the battery electrode surface can effectively reduce the electrode decomposition and the corresponding gas generation problems. At the battery level, the trend of internal pressure change is obtained by simulation.

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