The over discharge and over charge of lithium batteries refer to the normal discharge of the battery to the cut-off voltage before continuing to discharge. Due to the need to maintain a certain amount of lithium ions in the negative electrode to maintain structural stability, excessive discharge causes more lithium ions to migrate out, damaging the stable structure of the negative electrode and causing irreversible damage to the negative electrode.
Under an electron microscope, the negative electrode of a lithium battery cell has a layered structure, while the positive electrode is a pile of angular crystals with different shapes depending on the anode material.
The important consequence of over discharge is the layered collapse of the negative electrode plate. When recharging, the number and convenience of lithium ions embedded in the negative electrode plate are limited. A decrease in capacity, an increase in internal resistance, and a shortened lifespan cannot be restored.
The battery has reached a fully charged state. The negative electrode undergoes the intercalation reaction of lithium ions into the deposition of lithium metal on the surface of the negative electrode, and the solvent is oxidized. As the battery temperature increases, the reactions between metal lithium and the solvent, as well as between intercalated carbon and the solvent, occur one after another, causing the battery to ignite and explode. As the electrolyte decomposes, the bonding agent can also react with lithium metal.
After overcharging, needle like lithium metal crystals are everywhere on the electrode, which can cause micro short circuits when puncturing the diaphragm. Mild, exacerbating self discharge; The short-circuit current of the crystal branch causes a sharp increase in battery temperature, and the electrolyte decomposes and gasifies. This situation, whether it is due to excessive temperature causing material combustion and explosion, or the shell being first broken, causing air to enter and undergo intense oxidation with lithium metal, all end in combustion and explosion.
In summary, the dead end of lithium batteries is over discharge and over charging. The solution is to provide each single core with a protective board.