Self-discharge refers to the phenomenon that the battery is automatically reduced after being stored for a period of time. For the battery, it is also called the charge retention capability.
In Thermodynamically, the primary cause of self-discharge is due to the instability of the electrode active material in the electrolyte. Since most of the negative electrode active material is an active metal, its reduction potential in an aqueous solution is lower than that of the hydrogen electrode, and thus a self-dissolution of the metal and a conjugation reaction of hydrogen deposition are formed, so that the negative electrode active material is continuously consumed. The positive electrode active material also acts on the electrolyte or the impurities in the electrode to be reduced to cause self-discharge.
- A micro short circuit between the positive and negative electrodes or dissolution of the positive electrode active material is transferred to the negative electrode. It must be solved with a good diaphragm. The original function of the diaphragm is to isolate the positive and negative electrodes so that only lithium ions pass through and electrons cannot pass. If there is a problem with the quality of the diaphragm, the effect of the barrier will not function properly. A small defect will also have a significant impact on the self-discharge rate.
- The battery is not tightly sealed, so it is self-discharged by entering moisture, air and other substances.
Factors affecting self-discharge rate
- Temperature The higher the ambient temperature, the higher the activity of the electrochemical material, and the side reaction of the positive electrode material, the negative electrode material, and the electrolyte of the battery is more intense, causing more capacity loss in the same period of time.
- External short circuit The external short circuit of the battery placed in the open circuit is mainly affected by the degree of air pollution and the humidity of the air. Regular battery self-discharge characteristics test experiments, strict requirements of the laboratory environment and humidity range, is the reason. High air humidity can cause the conductivity to rise. Air pollution mainly means that conductive particles may be contained in the pollutants, and the conductivity of the air will increase.
- Electricity The higher the charge, the higher the positive potential and the lower the negative potential. Thus, the stronger the positive electrode oxidizability, the stronger the negative electrode selectivity and the more intense the side reaction.
- Time With the same power and capacity loss efficiency, the longer the time, the more power and capacity are lost. However, the self-discharge performance is generally used as an indicator for comparison of different batteries. It will be compared with the “self-discharge rate”, that is, the same precondition, at the same time, so the effect of time can only be said to affect the “self-discharge amount”.