1. Causes of reversible capacity loss: Reversible capacity loss is caused by a reversible discharge reaction, the principle of which is the same as the normal discharge reaction of a battery. The difference is that the electron path in normal discharge is the external circuit and the reaction speed is very fast; the electron path in self-discharge is the electrolyte and the reaction speed is very slow.
2. Causes of irreversible capacity loss: When an irreversible reaction occurs inside a lithium iron ion battery, the resulting capacity loss is called irreversible capacity loss.
There are two main reasons for excessive self-discharge in lithium-ion batteries: physical micro-short circuits and chemical reactions.
1. Physical micro short circuit
Physical micro-short circuits are the direct cause of low voltage in lithium-ion batteries. This manifests as the battery voltage falling below the normal cutoff voltage after storage at room temperature or high temperature for a period of time. Unlike self-discharge caused by chemical reactions, self-discharge caused by physical micro-short circuits does not result in irreversible capacity loss in lithium-ion batteries.
2. Chemical reaction
During storage, the temperature in the warehouse can cause the SEI film to peel off and re-react, leading to battery swelling and low pressure. Over-sealing at the tabs may cause tab corrosion, resulting in low pressure due to lithium source depletion. Over-sealing at other locations may allow electrolyte to penetrate the CPP layer and corrode the aluminum foil, causing perforation of the aluminum-plastic film, allowing moisture to enter and causing low pressure and swelling.
3. Battery level
With the same power and capacity loss efficiency, the longer the time, the more power and capacity are lost. However, self-discharge performance is generally used as an indicator to compare different cells, and comparisons are made based on self-discharge rate, that is, under the same conditions and the same time. Therefore, the use of time can only be said to affect the amount of self-discharge.
