Lithium battery internal short circuit test

As the most popular new energy source, lithium ion battery has been increasingly connected with our life. Whether it is smart phones, watches, electric toothbrushes, or new energy vehicles, lithium batteries are the most economical and reliable energy source at present, and have experienced long-term market verification. With a case of battery caused by fire, explosion and other accidents, the safety of lithium battery is more and more attention.

A preliminary analysis of battery safety incidents that occur around the world each year shows that most of them are caused by short circuits inside batteries. Since 2004, a Japanese company laptop batteries after a fire, after detailed investigation, the fire is because internal battery in the process of production with the tiny metal particles, the particles on the outside of the battery charge and discharge, temperature change and impact in the process of piercing the anode diaphragm, which can lead to internal short circuit happens, resulting in thermal runaway, so that a fire. However, such accidental mixing cannot be completely avoided, so we put forward new testing requirements for lithium batteries, that is, batteries should still be safe to use even if they are mixed with tiny particles, and testing the performance of batteries mixed with tiny particles is the forced internal short circuit test of lithium ion batteries.

Forced internal short circuit test for lithium ion batteries

The forced internal short circuit test can be applied to both cylindrical batteries such as 18650 and 21700, as well as square flexible pack batteries. Gloves are required in the specified environment before testingThe battery is disassembled in the box and packaged with a standard metal nickel sheet that simulates tiny metal particles. After reaching the specified temperature and time conditions, the battery was placed in the forced internal short circuit test system at the speed of 0.1mm/s to put pressure on the position of the nickel plate, and the change of the pressure and surface temperature of the lithium battery was monitored in real time at the same time of reaching the specified pressure at a uniform speed. When a 50mV drop in voltage is observed or when the pressure load reaches 400N (square cell) or 800N (cylindrical cell), stop pressurization and hold for 30 seconds, then withdraw the voltage.

If a voltage drop of 50mV occurs before reaching the specified pressure, the battery does not meet the safety standards for mandatory internal short circuit test. If the voltage drop occurs when the pressure reaches 400N or 800N, it indicates that the battery can greatly avoid internal short circuit caused by external particles. A high-precision forced internal short circuit test system requires a high-precision, high-sampling rate load application system. This system needs to monitor and record the voltage and temperature changes of lithium batteries at the same time, and can flexibly set test conditions to meet more stringent testing and research and development needs.

Forced internal short circuit test system

In terms of load application and recording, the LLOYD LD system can achieve load accuracy of 0.5% reading level and record load changes at 1000Hz sampling rate. This system uses 32 bit A/D conversion, with extremely high force resolution. While achieving load accuracy and resolution, its voltage and temperature record can also be up to 250Hz, which is the highest accuracy and the highest sampling rate of the test system in the industry.

This system is equipped with explosion-proof high and low temperature environment box, which can meet the temperature requirements of standard forced internal short circuit test, and can simulate the mechanical properties of batteries at different temperatures by changing the temperature. The temperature chamber itself to explosion-proof level, even in the case of violent combustion, explosion of the battery can still ensure the safety of the test personnel and the system, and with active exhaust system, can be tested in the battery flue gas discharge, effectively ensure the laboratory environment.