Analysis of the Causes of Lithium Battery Charging Explosion.Nickel Hydride No. 5

　　When a lithium-ion battery is charged, the lithium atoms in the positive electrode will lose electrons and oxidize into lithium ions. Lithium ions swim to the negative electrode through the electrolyte, enter the storage cell of the negative electrode, and obtain an electron, which is reduced to lithium atoms. When discharging, the entire program is reversed. In order to prevent short circuits caused by direct contact between the positive and negative poles of the battery, a separator paper with numerous small holes is added inside the battery to prevent short circuits. A good separator paper can also automatically close the pores when the battery temperature is too high, making it impossible for lithium ions to pass through, thereby self defeating martial arts skills and preventing danger from happening. Protective measures: After overcharging the lithium battery cell to a voltage higher than 4.2V, it will begin to have side effects. The higher the overcharging voltage, the higher the danger. When the voltage of a lithium battery cell exceeds 4.2V, less than half of the lithium atoms remain in the positive electrode material. At this time, the storage cell often collapses, causing a permanent decrease in battery capacity. If charging continues, as the storage cell of the negative electrode is already filled with lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendritic crystals from the negative electrode surface towards the direction of lithium ions. These lithium metal crystals will pass through the diaphragm paper, causing a short circuit between the positive and negative poles. Sometimes, before a short circuit occurs, the battery explodes first. This is because during overcharging, materials such as electrolyte will crack and produce gas, causing the battery casing or pressure valve to swell and rupture, allowing oxygen to enter and react with lithium atoms accumulated on the negative electrode surface, leading to an explosion. Therefore, when charging lithium-ion batteries, it is necessary to set a voltage limit in order to simultaneously consider the battery's lifespan, capacity, and safety. The optimal charging voltage limit is 4.2V.

　　When discharging lithium batteries, there should also be a lower voltage limit. When the voltage of the battery cell is below 2.4V, some materials will begin to be damaged. Also, due to the self discharge of the battery, the voltage will decrease as it is discharged for a long time. Therefore, it is best not to stop discharging at 2.4V. During the period of discharging from 3.0V to 2.4V, the energy released by lithium batteries only accounts for about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cutoff voltage.

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