LiFePO4 battery and ternary lithium battery capacity attenuation reasons

LiFePO4 battery and ternary lithium battery capacity attenuation reasons. With the continuous improvement of the energy density of the power battery, the power battery of the terpolymer material has attracted more and more attention, and as the LiFePO4 material that has been widely used, many parts have been retired or are close to retirement. The in-depth analysis of the recycled LiFePO4 battery and ternary lithium battery to find out the reason of capacity attenuation has important guiding significance for the improvement of battery performance in the future.

LiFePO4 battery capacity attenuation reasons

1, The internal resistance of lithium battery, especially the inconsistency of the internal resistance of polarization, makes the voltage of individual batteries change dramatically in the process of charging and discharging, resulting in drastic changes in the entire battery pack.

2, The inconsistency of the voltage of the single ultra-thin battery will affect the peak load capacity of the battery, making the energy released by the overall LiFePO4 battery reduced.

3, Due to the ultra-thin battery work in the process of heat release and heat absorption, the battery temperature will continue to change, when overheated, it will bring performance degradation and safety risks, it has been proved that in recent years, the electric vehicle operation and test fire fuse is due to over-temperature protection is not in place caused by the battery heat fire, the battery type not only lithium manganese acid, LiFePO4 battery is also the same.

4, Capacity is the most serious factor in the dispersion, capacity inconsistency mainly causes two aspects of performance problems, one is that part of the LiFePO4 battery will be in the overcharge and overdischarge state, resulting in combustion, explosion and other unsafe factors, the second is low capacity single battery because of early completion of work, affecting the entire ultra-thin battery pack in the other single battery energy can not be fully released. This causes the life of the entire LiFePO4 battery to decay.

5, Electrolyte oxidation decomposition and interface reaction

The properties of electrolyte significantly affect the specific capacity, life, rate charge-discharge performance, operating temperature range and safety performance of lithium-ion battery. The electrolyte mainly includes three parts: solvent, electrolyte and additive. The decomposition of solvents and the decomposition of electrolytes will lead to the loss of battery capacity.

6, Temperature is definitely one of the key factors affecting the life of LiFePO4 battery, too high temperature or too low temperature will cause the reduction of active lithium ion content, thereby reducing the life of lithium battery.

Ternary lithium battery capacity attenuation reasons

First, the structural change of the positive electrode material

The positive electrode material is the main source of lithium ions, when lithium ions from the positive electrode, in order to maintain the material's electric neutral state, the metal element will inevitably be oxidized to a high oxidation state, which is accompanied by a change in composition. The transformation of components easily leads to phase transfer and the change of bulk phase structure. The phase transformation of electrode materials can cause the change of lattice parameters and lattice mismatch, and the induced stress caused by the resulting breakage of grains, and the propagation of cracks, resulting in mechanical damage to the structure of the material, resulting in the attenuation of electrochemical performance.

Second, the negative electrode material structure

The negative electrode materials commonly used in commercial lithium batteries are carbon materials, lithium titanate, etc. In this paper, the typical negative electrode graphite is analyzed. The attenuation of lithium battery capacity first occurs in the formation stage, at which SEI is formed on the negative surface, consuming some lithium ions.

With the use of lithium batteries, changes in the graphite structure will also cause a decrease in battery capacity. LIU et al. studied the capacity attenuation mechanism of LiFePO4/C batteries, which is also applicable to ternary lithium batteries. The study found that although the carbon material maintained the morphology and structure of graphite after cycling, the half-height and width of its crystal face increased, resulting in smaller grain size in the C-axis direction, and the change of crystal structure led to cracks in the carbon material. The SEI film on the surface of the negative electrode is destroyed and the repair of the SEI film is promoted. The excessive growth of the SEI film consumes active lithium, thus causing irreversible capacity attenuation of the battery.

Third, the oxidation decomposition and interface reaction of the electrolyte

The properties of electrolyte significantly affect the specific capacity, life, rate charge-discharge performance, operating temperature range and safety performance of lithium-ion battery. The electrolyte mainly includes three parts: solvent, electrolyte and additive. The decomposition of solvents and the decomposition of electrolytes will lead to the loss of battery capacity. The decomposition and side reaction of the electrolyte is the main factor of the capacity attenuation of the lithium battery, no matter what kind of positive and negative electrode materials and what kind of process are used, with the recycling of the lithium battery, the decomposition of the electrolyte and the interface reaction between the positive and negative electrode materials will cause the capacity attenuation.

By introducing Co to reduce the cationic mixing occupying situation, effectively stabilize the layered structure of the material, the introduction of Mn can reduce the cost and improve the safety and stability of the material. Ternary materials with better electrochemical performance and stability, has been accepted by the world's mainstream lithium manufacturers, used in electric vehicles, 3C and other fields. Fourth, lithium battery conditions

It has to be mentioned that the use of lithium battery environment and conditions on its capacity damage: (1) lithium battery abuse; (2) Temperature factor.

The essence of affecting the capacity attenuation of lithium batteries is the reduction of the content of removable lithium ions, the main factors are the structural damage or inactivation of positive and negative electrode materials, the decomposition of electrolyte, the abuse of lithium batteries, and so on. The charge and discharge process of the battery is a complex electrochemical process, and the factors that lead to the attenuation of the battery capacity are not single, and the deterioration of one aspect may cause other factors to jointly affect the capacity of the battery, cycle performance, energy density, etc. Through the analysis of the above factors, we can take targeted programs to reduce the loss of capacity and extend the service life of lithium batteries.