Lithium iron phosphate battery and its development status
Release Time: 2022-05-26
Ferrous lithium phosphate (LiFePO4, abbreviated as LFP) is a kind of cathode material for lithium ion batteries, which has the ability to intercalate and intercalate lithium ions into lithium ion batteries. Its theoretical specific capacity is 170mAh/g, and the actual specific capacity of mass-produced materials at present is about 140 -145mAh/g(1C, full battery, 2.5-3.65V).
When LFP material is applied to lithium ion battery, it has the following characteristics:
1. Good theoretical safety:
The lattice structure of Ferrous lithium phosphate is as follows:
It is called "zero phase change material" together with lithium titanate because of its small volume change in the process of intercalation and intercalation of lithium ions. This also determines that Ferrous lithium phosphate materials have excellent cycle performance in theory.
2. Good theoretical security:
The decomposition temperature of Ferrous lithium phosphate is about 750℃, which is much higher than that of ternary materials (200-300℃), and no oxygen precipitates during decomposition, which makes it have good theoretical safety. Together with lithium manganate, it is called the safest two cathode materials.
3. Low energy density
Compared with NCM ternary materials, the energy density of LFP is relatively low, which is mainly determined by three factors:
1) the capacity of 1)LFP material is 140mAh/g, which is lower than that of ternary material (currently the capacity of NCM523 is 155-180mah/g);
2) The compaction density of LFP material is relatively low. At present, the compaction density of LFP material is 2.2-2.6g/cm3, while that of NCM523 material is 3.4-3.6g/cm3. This parameter determines that under the same coating weight, NCM material can crush the pole piece thinner;
3) The rated voltage of 3)LFP battery is generally 3.2V, while that of NCM ternary battery is generally 3.6-3.7V
4. Poor conductivity/power performance/low temperature performance
LFP materials are generally considered to have poor power performance and low-temperature performance because of their high resistance to lithium ion removal (lattice binding force, which can be called impedance) and poor electronic conductivity. However, at present, the mass production of LFP materials has basically avoided this problem through particle nanocrystallization, carbon coating technology and carbon-coated aluminum foil technology.
In view of the above characteristics, lithium iron phosphate batteries are generally used in areas such as pure electric buses/energy storage, which require low energy density, high cycle life and safety.
However, it should be noted that good safety and cycle performance are only the theoretical characteristics of LFP materials, while the cycle performance, safety performance and reliability of batteries are not only determined by positive materials, but also by other matching materials (negative electrode, electrolyte, separator, etc.), and the processing process of batteries has a great influence on cycle performance and reliability. After being processed into a battery system, the design and processing of the battery pack also have a decisive influence. Therefore, we can't simply say that LFP batteries have good safety and cycle performance, which is the wrong guidance of some media that don't understand technology.
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