When the lithium battery is overcharged to a voltage higher than 4.2V, it will start to cause side effects. The higher the overcharge voltage, the higher the risk. When the lithium battery voltage is higher than 4.2V, the amount of lithium atoms remaining in the positive electrode material is less than half. At this time, the storage cell often collapses, causing a permanent drop in battery capacity. If the charging continues, since the cell of the negative electrode is already filled with lithium atoms, the subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms grow dendrites from the surface of the negative electrode toward the lithium ions. These lithium metal crystals pass through the separator paper, shorting 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 generate gas, causing the battery casing or pressure valve to bulge and rupture, allowing oxygen to enter and react with the lithium atoms deposited on the surface of the negative electrode. Then exploded.