Explain the necessary precautions for lithium batteries

Lithium is the lightest of the alkali metals, with an atomic number of 3 and an atomic weight of 6,941. To improve safety and voltage, scientists have developed materials such as graphite and lithium cobalt oxide to store lithium atoms. The molecular structure of these materials forms tiny nanoscale storage cells that can be used to store lithium atoms. In this way, even if the battery case breaks and oxygen enters, the oxygen molecules are too large to fit into the tiny battery, preventing the lithium atoms from coming into contact with the oxygen and exploding.

When the charge voltage exceeds 4.2V, the Lithium Iron Phosphate Battery begins to appear secondary. The higher the pressure, the greater the risk. When the LiFePO4 Battery voltage exceeds 4.2V, less than half of the lithium atoms remain in the positive material and the battery often crashes, permanently reducing the battery capacity. When the battery is recharged, the subsequent lithium metal accumulates on the surface of the material because the negative battery is already full of lithium atoms. These lithium atoms grow dendritic crystals from the cathode surface towards the lithium ions. These lithium crystals will pass through the membrane paper, short-circuiting the anode and cathode. Sometimes batteries explode before a short circuit can occur. This is because overcharging causes substances such as the electrolyte to decompose the gas, causing the battery case or pressure valve to expand and burst, allowing oxygen to enter and react with the lithium atoms that have accumulated on the surface of the negative electrode, causing the negative electrode to explode.

Therefore, when charging the Li-ion battery, the upper voltage limit must be set to take into account the life, capacity and safety of the battery. The optimum upper limit of the charging voltage is 4.2V. The discharge of the Li-ion battery must also have a lower voltage limit. If the battery voltage is lower than 2.4V, some of the material begins to deteriorate. And because the battery will self-discharge the longer the voltage is lower, it is best not to stop discharging at 2.4V. During a 3.0-2.4V discharge, lithium-ion batteries can only release about 3% of their capacity. Therefore, 3.0V is the ideal discharge cut-off voltage. When charging and discharging, it is necessary to limit the current as well as the voltage. If the current is too high, lithium ions will not have time to enter the battery and will accumulate on the surface of the material.

When these ions gain electrons, they crystallise lithium atoms on the surface of the material, which is the same danger as overcharging. If the battery casing is broken, it will explode. Therefore, the protection of lithium-ion batteries should include at least three parts: the upper limit of the charge voltage, the lower limit of the discharge voltage and the upper limit of the current. The general Li-ion battery pack, in addition to the Li-ion battery cell, will also have a protection plate, the protection plate is important to provide these three protections. However, the protection of the three plates is obviously not enough, and Li-ion battery explosion accidents still occur frequently around the world. In order to ensure the safety of the battery system, the cause of the battery explosion must be analysed more carefully.