Why LiFePO4 battery safe?

Why is it that among all lithium battery packs, the LFP(LiFePO4) batteries provide the most environmental protection, the highest service life, the highest safety, and the largest discharge rate? Why is the thermal stability of LFP(lithium iron phosphate) battery the best in the current automotive lithium battery?

The working principle of the lithium iron phosphate battery pack is the same as that of the lithium battery pack. It is a process of charging and discharging through lithium-ion moving back and forth through electrolytes at the positive and negative poles of the battery. In terms of capacity, lithium iron phosphate battery packs can be divided into three categories: small, medium, and large. In terms of parameters, similar parameters of different types of batteries are also different. GMB mainly provides lithium iron phosphate battery packs for low-speed vehicles.

Why does a lithium iron phosphate battery pack have high safety?

It is difficult to form a stable P-O bond even if it is charged with lithium or iron phosphate at a high temperature. Therefore, it is not as safe as lithium-o-o bond. It is reported that in the actual operation, a small number of samples were found to burn in the acupuncture or short-circuit experiment, but there was no explosion.

The stability of the lithium iron phosphate battery pack under high temperatures can reach more than 390 ℃, which ensures the internal high safety of the lithium battery pack. It will not explode or burn due to overcharge, high temperature, short circuit and impact. It can easily pass the needle test. This safety feature is the most appropriate for China's new energy vehicle industry, which is still in its infancy.

The combustion of lithium iron phosphate battery requires external oxygen. Once the oxygen source is cut off, the fire can be extinguished. In extreme cases, the combustion of lithium iron phosphate is not intense, the fire expands slowly, and the fire is easier to be extinguished.

Compared with a single lithium iron phosphate battery, a lithium iron phosphate battery pack has many advantages, but it also inevitably has disadvantages. In terms of advantages, lithium iron phosphate battery pack has high safety performance, high service life, good high-temperature performance, large capacity, lightweight, and good environmental protection. However, in terms of disadvantages, the service life of a single lithium iron phosphate battery is much higher than that of the battery pack. In addition, the low-temperature performance of the lithium iron phosphate battery pack is not very good, and the conductivity needs to be further developed and improved.

The deoxidation temperature of the ternary material is 200 ℃, and the exothermic energy exceeds 800j / g. the ternary lithium battery cannot pass the needle puncture experiment, which shows that the ternary battery is easy causes safety accidents in the case of internal short circuit.

The absolute advantages of lithium iron phosphate battery over ternary lithium battery in safety and cycle life are the key elements and development needs of China's new energy vehicles

When the battery temperature is at 500-600 ℃, its internal chemical composition begins to decompose, while the internal chemical composition of lithium cobaltate battery, which belongs to lithium battery, is already in an unstable state at 180-250 ℃. In other words, the safety of lithium iron phosphate battery packs is second to none among lithium batteries. Therefore, it has also become one of the main categories of electric vehicle batteries.

Safety and reliability test items of lithium iron phosphate battery

General lithium iron phosphate battery test items include internal short circuit test, continuous charging test, overcharge, high current charging, forced discharge, falling test, falling test from height, penetration test, plane crushing test, cutting test, low pressure internal shelving test, thermal abuse test, immersion test, burning test, high voltage test, baking test, electronic furnace test, etc.

1. Extrusion test: put the fully charged lithium iron phosphate battery on a plane, apply an extrusion force of 13 ± 1kn by the oil cylinder, and squeeze the battery from the plane of the steel rod with a diameter of 32mm. Once the extrusion pressure reaches the maximum, stop extrusion, and the battery will not catch fire or explode.

2. Impact test: after the battery is fully charged, place it on a plane, place the steel column with a diameter of 15.8mm vertically in the center of the battery, and freely drop the weight of 9.1kg from the height of 610mm onto the steel column above the battery. Lithium batteries do not fire or explode.

3. Overcharge test: fully charge the lithium iron phosphate battery with 1c and conduct the overcharge test according to 3C overcharge 10V. When the battery is overcharged, the voltage rises to a certain voltage and stabilizes for a period of time. When it approaches a certain time, the battery voltage rises rapidly. When it rises to a certain limit, the high cap of the battery is pulled off, the voltage drops to 0V, and the lithium battery can not catch fire or explode.

4. Short circuit test: after the battery is fully charged, short circuit the positive and negative electrodes of the battery with a wire with a resistance of no more than 50m Ω, test the surface temperature change of the battery, the maximum temperature of the battery surface is 140 ℃, the battery cover is opened, and the battery will not catch fire and explode.

5. Needle test: place the fully charged battery on a flat surface and pierce the battery radially with a 3mm diameter steel needle. Test the lithium battery pack without fire and explosion.

6. Temperature cycle test: the temperature cycle test of lithium iron phosphate battery is used to simulate the safety of lithium-ion battery under repeated exposure to low temperature and high temperature during transportation or storage. The test is carried out by using rapid and extreme temperature changes. After the test, the sample shall be free from fire, explosion and liquid leakage.

Lithium iron phosphate battery is relatively stable under high-temperature conditions, so in terms of safety, the lithium iron phosphate battery pack has naturally become the best choice.