Technical introduction of iron lithium ion battery and ternary lithium ion battery pack



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Lithium iron phosphate batteries are characterized by high safety, high rate charge and discharge characteristics and long cycle life. The literature shows that when the charging condition is 1C rate charging to 3.65V, then the constant voltage is changed until the current drops to 0.02C, and then the 1C rate is discharged to a cut-off voltage of 2.0V. After 1600 cycles, the battery capacity still has 80% of the initial capacity. Lithium iron phosphate batteries also have good fast charging characteristics. Under the condition of 3C rate charging, they can be charged 55% in 15 minutes, and the capacity can exceed 95% in 30 minutes.

The biggest advantage of lithium iron phosphate battery is its safety. The chemical properties of lithium iron phosphate are stable, and the high temperature stability is good. It will start to decompose at 700-800℃, and it will not be exposed to impact, needle stick, short circuit, etc. It will release oxygen molecules, will not burn violently, and have high safety performance.

However, the disadvantage of lithium iron phosphate batteries is that their performance is greatly affected by temperature, especially in low-temperature environments, the discharge capacity and capacity will be greatly reduced. In addition, the energy density of lithium iron phosphate is relatively low. The weight energy density of the battery is only 120Wh/kg. If the energy density of the entire stack, including the battery management system, heat dissipation and other components is calculated, it is even lower.

In the field of small passenger cars, ternary lithium-ion battery packs have completely replaced lithium iron phosphate batteries. The ternary lithium ion battery pack has high energy density and better cycle performance than normal lithium cobalt oxide. At present, with the continuous improvement of the formula and the perfect structure, the nominal voltage of the battery has reached 3.7V, and the capacity has reached or exceeded the level of lithium cobalt oxide batteries.

Ternary lithium-ion battery refers to a lithium-ion battery that uses lithium nickel cobalt manganate as the positive electrode material and graphite as the negative electrode material. Unlike lithium iron phosphate, the ternary lithium-ion battery has a high voltage platform, which means that under the same volume or weight, the ternary lithium-ion battery pack has a greater specific energy and specific power. In addition, ternary lithium-ion batteries also have great advantages in terms of high-rate charging and low-temperature resistance.

The dispute over the ternary lithium-ion battery pack and lithium iron phosphate technical route seems huge, but for users and vehicle companies, the two technical routes actually have their own merits. In the final analysis, choosing different batteries for different models is the root of the problem.

The thermal stability of the ternary lithium-ion battery pack is poor, and it will decompose at 250-300℃. It will stop after encountering the combustible electrolyte and carbon materials in the battery. The heat that appears will further aggravate the decomposition of the positive electrode in a very short time. It will deflagrate inside. Although there are safety concerns, ternary lithium-ion battery packs have shown a trend to replace lithium iron phosphate batteries and become the mainstream of passenger cars because of the policy's energy density regulations.


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