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Advantages and disadvantages of lithium iron phosphate batteries

by:dcfpower     2021-03-15

The working principle of lithium iron phosphate battery:

When the external power supply charges the battery, the electron e on the positive electrode runs from the external circuit to the negative electrode, and the lithium ion worker i+ jumps in from the positive electrode. In the electrolyte, 'climbing' through the small winding holes in the diaphragm, 'swimming' to the negative electrode, and combining with the electrons that have run over long ago. When the battery is discharged, the mechanism and charging are just the opposite. Taking LiFePO4 as an example, the chemical reaction equation is:

Charging: LiFePO4 – xLi﹢ – xe- → xFePO4 +(1-x)LiFePO4

Discharge: FePO4 + xLi﹢ + xe- → xLiFePO4+(lx)LiFePO4

First, the advantages of lithium iron phosphate batteries

1. The nominal voltage of LiFePO4 battery is 3.2V (stable discharge platform), the final charging voltage is 3.6V, and the final discharge voltage is 2.0V;

2. Large specific capacity, high efficiency output: Standard discharge is 2~5C, continuous high current discharge can reach 10C, instant pulse discharge (10S) can reach 20C;

3, wide operating temperature range (-20℃—+75℃), high temperature Good performance: when the external temperature is 65℃, the internal temperature is as high as 95℃, and when the battery is discharged, the temperature can reach 160℃. The internal structure of the battery is safe and intact;

4. Even if the battery is damaged internally or externally, the battery No combustion, no explosion, and the best safety;

5. Excellent cycle life, under the condition of 100% DOD, it can be charged and discharged more than 2000 times; (reason: the stability of lithium iron phosphate lattice Good, the insertion and extraction of lithium ions have little effect on the crystal lattice, so it has good reversibility. The disadvantages are that the transmission rate of electron ions is poor, it is not suitable for high current charging and discharging, and it is hindered in application. Solution: The electrode surface is coated with conductive material and doped to modify the electrode.

6. There is no damage to zero volts after overdischarge. The battery has no leakage after 7 days of zero voltage storage, with good performance and 100% capacity; After 30 days of storage, there is no leakage, good performance, and the capacity is 98%; after 30 days of storage, the battery is charged and discharged for 3 times, and the capacity is restored to 100%.

7. Fast charging and self-discharging Less, no memory effect: high current 2C fast charge and discharge, under the special charger, 1.5C charge can make the battery full within 40 minutes, the starting current can reach 2C;

8, high energy density : Its theoretical specific capacity is 170mAh/g, and the actual specific capacity of the product can exceed 140mAh/g (0.2C, 25℃);

9. Safety: It is currently the safest cathode material for lithium-ion batteries; Does not contain any heavy metal elements harmful to the human body;

10, no memory effect;

11, charging performance: lithium iron phosphate cathode material lithium battery pack can be charged at a high rate, The battery can be fully charged within 1 hour at the fastest.

The raw materials are rich in sources, inexpensive, environmentally friendly, and do not contain any heavy metal elements harmful to the human body.

12, good thermal stability :Lithium iron phosphate has good thermal stability, FePO4 only emits heat in the temperature range of 210~410C 210j/g;

LiCoO2 charge state (CoO2) begins to decompose to produce oxygen at a temperature of 240℃, and the heat release is about 1000j/g

13, good cycle performance: due to LiFePO4 and The structure of FePO4 is similar. After lithium ions are extracted/intercalated, the crystal structure of LiFePO4 hardly undergoes rearrangement.

8, low cost;

9, no pollution to the environment.

II. Disadvantages of lithium iron phosphate batteries

1. Poor conductivity: At present, in the actual production process, the precursor is combined with an organic carbon source and high-valent metal ions. To improve the conductivity of the material (A123, Yantai Zhuoneng is using this method), studies have shown that the conductivity of lithium iron phosphate has increased by 7 orders of magnitude, so that lithium iron phosphate has similar electrical conductivity characteristics to lithium sulphate.

2. Lithium ion diffusion rate is slow. The current solutions are mainly nano-sized LiFePO crystal grains to reduce the diffusion distance of lithium ions in the crystal grains, and the other is doping to improve the diffusion channels of lithium ions. The latter method does not seem to be effective. There has been a lot of research on nanometerization, but it is difficult to apply it to actual industrial production. At present, only A123 claims to have mastered the nanometerization industry technology of LiFePO.

3. The tap density is lower. Generally, it can only reach 0.8-1.3, and the low tap density can be said to be the biggest disadvantage of lithium iron phosphate. But this shortcoming will not be prominent in the power battery. Therefore, lithium iron phosphate is mainly used to make power batteries.

4. The low temperature performance of lithium iron phosphate battery is poor. The capacity retention rate at 0℃ is about 60~70%,

40~55% at -10℃, and 20~40% at -20℃. Obviously, such low temperature performance cannot meet the requirements of power supply. At present, some manufacturers have improved the low-temperature performance of lithium iron phosphate by improving the electrolyte system, improving the positive electrode formula, improving the material performance and improving the cell structure design.

Low electronic conductivity, low ion diffusion coefficient, low tap density, slightly higher synthesis cost

Three, lithium iron phosphate shortcomings compensation method

phosphoric acid The shortcomings of lithium iron can be compensated by: carbon coating to improve electronic conductivity, adding metal particles, conductive organic coating, doping metal ions to improve electronic conductivity, synthesizing small particle size materials to reduce diffusion distance, and synthesizing spherical particles with controllable particle size.

1. Carbon coating technology

Mixed addition of raw materials

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