The lithium battery exploded again! Who will solve the pain points in the industry?

At noon on April 16, a fire broke out in a lithium battery energy storage power station in a home market in South Fourth Ring Road, Fengtai District, Beijing. It was not until the early morning of April 17 that the open flame was completely extinguished. According to the report, the fire caused two firefighters to die, 1 fireman was injured (in stable condition), and 1 employee in the power station lost contact.

On the evening of April 17, local time in Texas, USA, a Tesla Model S car hit a tree while driving on the road and caused a fire, resulting in the death of two men in the car. The fire lasted for four hours. When the fire went out, there was only one main frame left in the whole Tesla car.

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With the temperature rising, all kinds of lithium battery equipment seem to become restless, and fire/explosion incidents occur one after another. However, the fire of lithium battery equipment is different from other fire events, and its huge energy density makes it explode very violently. The combustion temperature of the battery is very high, and the fire extinguishing water will be evaporated or electrolyzed at high temperature in an instant, which is also the reason why the fire in the energy storage power station is difficult to put out.

Since the explosion of lithium battery equipment is so dangerous, how to prevent it?

The anode and cathode of lithium battery are located at the corresponding two ends, and lithium ions move between the two electrodes with the help of electrolyte. However, the positive and negative electrodes of the battery cannot be in direct contact, because this will redirect energy to the electrolyte. Moreover, the electrolyte itself is an extremely unstable chemical substance. When it bears a lot of energy, it will produce a lot of heat, react with other chemicals to produce gas, and release heat at an increasing speed. This uncontrollable heating process is called "thermal runaway" and is the chief culprit of battery fire/explosion. So in order to avoid this situation, the battery factory will place a diaphragm between the two poles. However, when lithium batteries are charged at high rate (that is, fast charge), especially in cold winter, serious lithium precipitation is easy to occur. Lithium ions can't move normally between the anode and cathode of the battery, but can only be deposited in the electrolyte, which may lead to the decrease of the life of the lithium battery, or the accumulated lithium ions may form lithium dendrites and puncture the separator, resulting in the short circuit between the anode and cathode of the battery and the instantaneous explosion of the battery.

The existing electrochemical/thermodynamic detection methods for lithium batteries have serious signal lag, and the obvious alarm signal will only appear at the end of the battery life cycle, that is, when the battery is about to be in danger, which greatly limits the time for us to take countermeasures against the danger; Moreover, these traditional detection methods are often accompanied by destruction and disassembly, which means that the battery in the production line cannot be comprehensively detected, which is also one of the dilemmas of battery product quality control.

In view of the current severe battery safety problems, Tsinghua University Battery Safety Laboratory cooperated with Shuode (Beijing) Technology Co., Ltd. to develop a set of ultrasonic nondestructive testing system for lithium batteries, which uses ultrasonic to test batteries, providing a brand-new battery testing idea different from the previous visual nondestructive testing.

"Academician Gao introduced the ultrasonic testing system for lithium batteries"

This battery monitoring system can detect/real-time monitor all kinds of adverse reactions generated in the battery, such as gas generation, lithium evolution and SOC, as well as the state of electrolyte penetration and solid-state battery solidification during battery production, and can predict the SOH health state and life span of the detected object. The physical changes inside these batteries will be recorded by ultrasonic signals in real time, and form a C-scan image, which can let us directly see the location, size and degree of problems inside the batteries.

C-scan image of battery

The appearance of this ultrasonic testing system for lithium battery greatly shortens the experimental period, replaces most dangerous disassembly work in the past, and ensures the safety of the experiment while improving efficiency.

We can imagine that when the ultrasonic nondestructive testing technology for lithium batteries is mature, it can be used not only in the research and development process of batteries, but also in the battery production line outside the laboratory, so that every produced battery has a test report and the problem batteries are strictly screened, which is helpful to establish battery quality control standards and grasp the first line of defense for battery safety. It can even establish a battery safety detection ecology for the whole life cycle of the battery, carry out health monitoring during the use of the battery, and call the police immediately if there is a danger signal, so as to minimize the threat to people's lives and property.