Even in an open circuit state, the battery's charge can still decrease, which is mainly attributed to the self-discharge phenomenon of the battery. Self-discharge can cause the battery's charge to be lost, hurting its performance and service life. Next, we will delve into the various reasons that cause battery self-discharge.
| Internal electron leakage Internal electron leakage occurs because of local electron conduction within the electrolyte or because of other internal short circuit issues. The electrolyte in a battery functions to transmit ions throughout the system. The electrolyte exhibits local electron conduction which results in internal electron leakage when specific conditions occur. An internal short circuit within the battery causes electrons to move away from their regular path thus leading to charge loss. |
| External electron leakage External electron leakage is usually caused by poor insulation of the battery's sealing ring or gasket or insufficient resistance between the external lead shells. If the insulation performance of the battery's sealing ring or gasket is not ideal, it is like providing electrons with a "shortcut", allowing them to leak out easily. Moreover, when the resistance between the external lead shells is not large enough due to external conductors, humidity, and other factors, external electron leakage can also occur. For example, in a humid environment, a thin layer of water film may form on the battery surface, which has a certain degree of conductivity and may cause electron leakage. |
| Electrode/electrolyte reaction The reaction between the electrode and the electrolyte can also cause self-discharge. Corrosion of the anode and reduction of the cathode due to impurities in the electrolyte are common situations. The anode undergoes an oxidation reaction during the battery's operation. However, under some abnormal conditions, the anode may corrode excessively, resulting in the loss of electrode material and concurrent charge consumption. Meanwhile, if the cathode comes into contact with impurities in the electrolyte, these impurities may act as oxidants and reduce the cathode, thereby causing self-discharge. |
| Partial decomposition of electrode active materials Sometimes the materials that make up the electrodes, in a battery can break down a bit in situations as the battery is used and goes through charging and discharging cycles. The active materials in experience pressures and chemical changes, during this process. As time goes by the electrode's active materials might start to break down. This does not change how the electrode works and performs. Also leads to higher self-discharge rates. |
| Electrode passivation Decomposition products, such as insoluble substances and adsorbed gases, can cause electrode passivation. When chemical reactions occur inside the battery and produce insoluble substances, or when gases are adsorbed on the electrode surface, a layer of obstructive material forms on the electrode surface. This layer hinders the normal reaction between the electrode and the electrolyte, increasing the battery's internal resistance and thereby causing self-discharge. |
| Mechanical wear of the electrode or increased resistance between the electrode and the current collector Mechanical wear of the electrode or increased resistance between the electrode and the current collector can also lead to self-discharge. During the battery's usage, it may be subjected to mechanical forces such as vibration and compression, which can cause mechanical wear of the electrode. After the electrode wears, its contact with the current collector may no longer be tight, and the resistance increases. Increased resistance means that electrons encounter more obstacles during transmission, generating more heat and accelerating the self-discharge process. |
Understanding these causes of battery self-discharge is of great significance for better usage and maintenance of batteries, helping to extend their service life and improve their performance.
