Why do lithium-ion batteries for electric vehicles explode?
1. Overcharge causes too much lithium to be released, and the capacity of the negative electrode is insufficient. The lithium that appears during charging cannot be inserted into the interlayer structure of the negative electrode graphite, and metallic lithium will be formed on the surface of the negative electrode. Over time, these lithium atoms will grow dendrites from the surface of the negative electrode toward the direction of the lithium ions. These lithium metal crystals will pass through the diaphragm paper and short-circuit the positive and negative electrodes. Sometimes the battery explodes before the short circuit occurs. This is because during the overcharging process, the electrolyte and other materials will crack and produce gas, causing the battery shell or pressure valve to swell and break, allowing oxygen to enter and react with the lithium atoms accumulated on the surface of the negative electrode. And then exploded.
2. Current limitation is also necessary when charging and discharging. When the current is too large, lithium ions will not have time to enter the interlayer structure and will also collect on the surface of the negative electrode material. After these lithium ions obtain electrons, lithium atom crystals will appear on the surface of the material, which is the same as overcharging and can cause danger.
Therefore, in the lithium-ion battery pack, in addition to the lithium-ion battery core, there will be a protective board, which is what we often call BMS (BATTERYMANAGEMENTSYSTEM), the Chinese name is battery management system. It can monitor the voltage, current and temperature of the lithium-ion battery, and intervene when necessary according to the state of the lithium-ion battery.
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