1. Structural changes of cathode materials:
The positive electrode material is an important source of lithium-ion batteries. When the lithium-ion battery is removed from the positive electrode, in order to maintain the neutral state of the material, the metal element will inevitably be oxidized to a high oxidation state, which is accompanied by the change of composition. The transition of components easily leads to phase transition and change of bulk phase structure. The phase transition of the electrode material can cause changes in lattice parameters and lattice mismatch. The induced stress caused by the induced stress causes the breakage of the grains and the propagation of cracks, resulting in mechanical damage to the structure of the material, resulting in the degradation of electrochemical performance.
3. Negative electrode material structure:
Commonly used anode materials for lithium-ion batteries include carbon materials, lithium titanate, etc., and the anode graphite is used for analysis. The capacity attenuation of lithium-ion batteries first occurs in the formation stage, in which SEI is formed on the surface of the negative electrode, consuming part of the lithium ions. As lithium-ion batteries are used, changes in the graphite structure can also cause battery capacity to drop.
Although the morphology and structure of graphite is maintained, the half-height width of its crystal plane becomes larger, resulting in a smaller grain size in the c-axis direction, and the change of crystal structure leads to cracks in the carbon material, which in turn destroys the SEI film on the surface of the negative electrode and promotes Repair of SEI film, excessive growth of SEI film consumes active lithium, thus causing irreversible capacity fading of Li-ion batteries.
3. Oxidative decomposition and interface reaction of electrolyte:
The properties of the electrolyte significantly affect the specific capacity, life, rate charge-discharge performance, operating temperature range, and safety performance of lithium-ion batteries. The electrolyte mainly includes three parts: solvent, electrolyte and additives. The decomposition of the solvent and the decomposition of the electrolyte will lead to the loss of the capacity of the lithium-ion battery. The decomposition and side reactions of the electrolyte are important factors for the capacity decay of lithium-ion batteries. No matter what kind of positive and negative materials and processes are used, with the recycling of lithium-ion batteries, the decomposition of the electrolyte and the occurrence of the interaction with the positive and negative materials The interfacial reaction will cause the capacity decay.
4. Positive electrode overcharge reaction:
When the ratio of the positive electrode active material to the negative electrode active material is too low, overcharging of the positive electrode is likely to occur. The capacity loss caused by overcharge of the positive electrode of lithium-ion batteries is mainly due to the appearance of electrochemically inert substances (such as Co3O4, Mn2O3, etc.), which destroys the capacity balance between electrodes, and the capacity loss is irreversible.
