What are the reasons for the decline of lithium battery capacity
Back
2022/10/10 10:00:27
Cause 1: Overcharging
1, graphite anode overcharging reaction:
When the battery is overcharged, lithium ions are easy to reduce and deposit on the surface of the negative electrode:
The deposited lithium coated the surface of the negative electrode, blocking the lithium embedment. The discharge efficiency is reduced and capacity loss is caused by:
① the amount of recyclable lithium is reduced;
② The deposited lithium metal reacts with solvent or supporting electrolyte to form Li2CO3, LiF or other products;
(3) Lithium metal is usually formed between the negative electrode and the diaphragm, which may block the pores of the diaphragm and increase the internal resistance of the battery;
④ Due to the nature of lithium is very active, easy to react with electrolyte and consume electrolyte. As a result, the discharge efficiency is reduced and the capacity is lost.
Fast charging, excessive current density, negative polarization, lithium deposition will be more obvious. This situation tends to occur when the positive active material is related to the excess of the negative active material. However, in the case of high charging rate, the deposition of lithium metal may occur even if the ratio of positive and negative active substances is normal.
2. Positive electrode overcharge reaction
When the ratio of positive active material to negative active material is too low, it is easy to have positive overcharging.
The capacity loss caused by positive electrode overcharging is mainly due to the appearance of electrochemical inert substances (such as Co3O4, Mn2O3, etc.), which destroy the capacity balance between electrodes, and the capacity loss is irreversible.
(1) LiyCoO2
LiyCoO2→ (1 -) y / 3 [Co3O4 + O2 (g)] + yLiCoO2y & lt; 0.4
At the same time, the oxygen produced by the decomposition of the positive electrode material in the sealed lithium ion battery is accumulated at the same time because there is no recombination reaction (such as the formation of H2O) and the combustible gas produced by the decomposition of the electrolyte, and the consequences will be unimaginable.
(2) & lambda; -MnO2
Lithium manganese reaction occurs when lithium manganese oxide is completely delithium: λ -MnO2→ Mn2O3+O2(g)
3, electrolyte oxidation reaction in the overcharge
When the pressure is higher than 4.5, the electrolyte will oxidize to form insoluble substances (such as Li2Co3) and gases, which will block the migration of lithium ions in the micropores of the electrode and cause capacity loss during the cycle.
Previous
