What are the reasons for the reduction of lithium battery capacity? Users who have used it should know that the capacity of lithium batteries will decrease after a period of use. The usage time of the lithium battery mainly depends on the capacity of the lithium battery. The higher the voltage of the lithium battery, the greater the capacity, that is, the stronger the load capacity. So, what are the factors that affect the capacity attenuation of lithium batteries? Let's take a look together.
The positive electrode material is an important source of lithium 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 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.
Commonly used anode materials for lithium batteries include carbon materials, lithium titanate, etc., and the typical 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 width at half maximum of its (002) crystal plane becomes larger, resulting in a smaller grain size in the c-axis direction. The change in crystal structure leads to cracks in the carbon material, which in turn destroys the SEI film on the negative surface and promotes the repair of SEI film, the excessive growth of SEI film consumes active lithium, thus causing irreversible capacity fading of lithium batteries.
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 additive. 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 attenuation of lithium-ion batteries. No matter what kind of positive and negative materials and processes are used, with the recycling of lithium batteries, the decomposition of electrolyte and the interface reaction with positive and negative materials will cause the attenuation of capacity.
When the ratio of positive electrode active material to negative electrode active material is too low, positive electrode overcharge is likely to occur. The capacity loss caused by overcharge of the positive electrode of lithium batteries is mainly due to the initiation of electrochemically inert substances (such as Co3O4, Mn2O3, etc.), which destroys the capacity balance between electrodes, and the capacity loss is irreversible.
The positive active material is unstable during charging and reacts with the electrolyte to reduce the capacity. The factors affecting the instability of the positive electrode material are the structural defects of the positive electrode material, the content of carbon black, and the high charging potential, among which the structural defects of the positive electrode material are the most important factors.
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