Lithium battery performance test

1. Cycle life

The number of cycles of lithium batteries reflects how many times the battery can be repeatedly charged and discharged. According to the different environments in which lithium batteries are used, the cycle life can test how much the battery can reach at low temperature, room temperature and high temperature. Usually, the battery disposal standard is selected according to the purpose of the battery. If the battery is used for power batteries (electric vehicles, electric forklifts), etc., the discharge capacity retention rate is generally selected as 80% as the standard parameter for disposal, while if the battery is used for energy storage, power storage, etc., it can be relaxed to 60%. The batteries we often come into contact with are useless if the discharge capacity/initial discharge capacity is less than 60%, and they will not last for half a day.

2. Rate

Nowadays, lithium batteries are not only used in 3C, but also in more and more power batteries. Electric vehicles need to change current when driving under different working conditions. In the current fast-paced life, the shortage of electric vehicle charging piles has also increased the requirements for fast charging of lithium batteries. Therefore, it is necessary to test the rate performance of lithium batteries. It can be tested according to the national standard for power batteries. Now domestic and foreign battery factories are producing special high-rate batteries to meet market needs. The design of high-rate batteries can start from the type of active material, the surface density of the pole piece, the compaction density, the selection of the pole ear, the welding process and the assembly process. Interested friends can learn about it themselves.

3. Safety test

Safety can be said to be a very concerned issue for battery users. Whether it is the explosion of mobile phone batteries or the fire of electric vehicles, it is enough to make people terrified. The safety of lithium batteries must be inspected. The safety inspection contents include overcharging, over-discharging, short circuit, falling, heating, vibration, extrusion, puncture, etc. However, according to the lithium battery faction, these safety tests are passive safety tests, which means taking a battery and letting foreign objects actively destroy the battery to test whether the battery is safe enough. When submitting for inspection, the battery and module need to be designed accordingly for safety testing. However, in actual use, for example, an electric vehicle loses control and hits another car or object. It is an irregular collision and may face more complicated situations. However, in this way, the cost of testing is higher, and only relatively reliable test contents can be selected.

4. Discharge at low temperature and discharge at high temperature

The effect of temperature on the discharge performance of the battery is directly reflected in the discharge capacity and discharge voltage. When the temperature decreases, the internal resistance of the battery increases, the electrochemical reaction speed slows down, the polarization internal resistance increases rapidly, and the battery discharge capacity and discharge platform decrease, affecting the output of battery power and energy.

For lithium-ion batteries, the discharge capacity drops sharply under low temperature conditions, but the discharge capacity under high temperature conditions is not lower than that at room temperature, and sometimes it is slightly higher than the capacity at room temperature. This is mainly because the lithium ion migration speed is accelerated under high temperature conditions, and the lithium electrode does not decompose or form hydrogen at high temperatures like the nickel electrode and the hydrogen storage electrode to reduce the capacity.

When the battery module is discharged at low temperature, as the discharge proceeds, heat is generated due to resistance and other reasons, causing the battery temperature to rise, which is manifested as a voltage increase. As the discharge proceeds, the voltage gradually decreases.

At present, the batteries on the market are mainly ternary batteries and lithium iron phosphate batteries. The ternary battery is much less safe than the lithium iron phosphate battery because the material collapses at high temperatures and is unstable, but its energy density is higher than that of lithium iron phosphate, so the two systems coexist and develop.