Protective measures for electric vehicle batteries

Shell protection: In order to prevent air from entering, lithium batteries are sealed in sealed containers and usually equipped with stainless steel and aluminum alloy shells to prevent external damage. For example, Tesla's electric vehicles even use titanium alloy protective plates to prevent damage to battery containers during vehicle use, especially in traffic accidents.

Diaphragm blocking protection not only prevents external damage, but also prevents damage from inside the battery.

Usually, in order to prevent short circuits caused by direct contact between the positive and negative poles of a battery, there is a layer of separator inside the battery, which separates the positive and negative poles and allows charged ions to pass through.

However, in lithium batteries, the separator also serves another protective function. When the battery temperature is too high, the diaphragm gap will automatically close, preventing lithium ions from passing through and thus terminating the entire battery reaction. This prevents the problem of high voltage generated by the gasification of the electrolyte in the battery due to high temperature, which can damage the sealing structure of the battery.

Overcharge voltage protection not only blocks the air, but also prevents the leakage of metallic lithium from the electrode.

Scientists store and lock the metallic lithium formed during charging and discharging through the nanopores and lattice mechanisms of electrode materials.

In this way, even if the battery casing ruptures and oxygen enters, the oxygen molecules are too large to enter these small storage cells, thus avoiding the occurrence of spontaneous combustion.

However, using too high voltage or continuing to charge for too long after being fully charged can cause very dangerous damage to lithium batteries.

After the charging voltage of a lithium battery exceeds the rated voltage (usually 4.2V), if it continues to charge, the negative electrode storage cell will be filled with lithium atoms, and subsequent lithium ions will accumulate on the surface of the negative electrode material. These lithium ions undergo electron transfer due to polarization, forming metallic lithium and growing dendritic crystals from the negative electrode surface towards the direction of lithium ions.

These metal lithium without electrode protection are extremely reactive and prone to oxidation reactions and explosions. On the other hand, the formed metallic lithium crystals will penetrate the diaphragm, causing a short circuit between the positive and negative electrodes, thereby causing a short circuit and generating high temperature. At high temperatures, materials such as electrolytes will crack to produce gas, causing the battery casing or pressure valve to bulge and rupture, allowing oxygen to enter and react with lithium atoms stacked on the negative electrode surface, resulting in an explosion.

When charging lithium batteries, it is necessary to set the upper voltage limit and overcharge protection. Lithium batteries produced by legitimate battery manufacturers are equipped with such protective circuits. Automatically power off when the voltage exceeds the limit or the battery is fully charged.