Lithium-ion battery life is limited, with the use of the number of times, the lithium battery capacity is also depleted. Until eventually is lost use value. So why does the lithium battery capacity decay?
1) Structural changes in the cathode material
The cathode material is the main source of electricity for lithium-ion batteries, when the lithium ion from the cathode, in order to maintain the electrically neutral state of the material, the metal elements will be oxidized to a high oxidation state, here accompanied by the transformation of the components. The transformation of components can easily lead to phase transfer and changes in the bulk phase structure. The phase transition of the electrode material can cause changes in lattice parameters and lattice mismatch, and the resulting induced stress causes grain fragmentation and crack propagation, resulting in mechanical damage to the material structure, thus causing the electrochemical performance of the lithium battery to decay.
2）Anode material structure
Li-ion battery commonly used anode materials are carbon materials, lithium titanate, etc. This paper analyzes the typical anode graphite. The decay of lithium battery capacity occurs for the first time in the chemistry stage, in which SEI will be formed on the surface of the cathode, consuming part of the lithium ion. With the use of Li-ion battery, the change of graphite structure also causes the decrease of battery capacity. Although the morphological structure of graphite is maintained, the half-height width of its crystalline surface 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 cathode surface and promotes the repair of the SEI film, and the overgrowth of the SEI film consumes active lithium, thus causing irreversible capacity decay of Li-ion batteries.
3) Oxidation decomposition of electrolyte and interfacial reaction
The nature of electrolyte significantly affects the specific capacity, lifetime, multiplier charge/discharge performance, operating temperature range and safety performance of Li-ion batteries. Electrolyte mainly includes solvent, electrolyte and additives. The decomposition of solvent and electrolyte will lead to the loss of lithium battery capacity. The decomposition of electrolyte and side reactions are the main factors of lithium battery capacity decay. Regardless of the positive and negative electrode materials and process, with the recycling of lithium batteries, the decomposition of electrolyte and the interfacial reaction between positive and negative electrode materials will cause the decay of capacity.
4）Anodic overcharge reaction
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 positive electrode overcharge of Li-ion battery is mainly due to the generation of electrochemical inert substances (such as Co3O4, Mn2O3, etc.), which disrupts the capacity balance between electrodes, and its capacity loss is irreversible.
5) Electrode instability
Unstable cathode active material during charging will react with electrolyte to cause capacity reduction. Factors affecting the instability of the cathode material include structural defects of the cathode material, carbon black content, and high charging potential, of which structural defects of the cathode material are the most important of the influencing factors.
Li-ion battery capacity refers to the size of the battery storage power. We now design electronic products, many times also use lithium battery power supply, the same as cell phones or tablet computers with lithium battery power supply, familiar with the understanding of lithium battery capacity learning, perhaps the use and design of lithium battery power supply, including the design of battery chargers, it is necessary.
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