Li-ion battery protection mechanism let me tell you

Since incorrect use will reduce the life span and may even cause an explosion, a variety of protection mechanisms have been added to the design of lithium-ion batteries.

protect the circuit

Prevent overcharge, overdischarge, overload, and overheating.

Vent

Because of its anti-explosion function, people in the battery industry are also called explosion-proof holes or explosion-proof lines. The principle is very simple. A line or hole is drawn on the surface of the shell that is slightly thinner than the surface of the shell. When the battery core is short-circuited, a large amount of gas will be generated inside the battery in a short time and the pressure will increase rapidly. When the pressure is overloaded, Because the explosion-proof hole is thinner than the rest of the shell, the gas will leak at the explosion-proof hole, so as to avoid the danger of the whole battery explosion.

Diaphragm

Isolate the positive and negative plates of the battery core to prevent direct contact between the positive and negative plates inside the winding core and cause a short circuit; from a microscopic point of view, the surface of the diaphragm is a mesh structure, usually divided into PP and PE, and there are also PE and PP composites. .

The separator is usually divided by thickness and width. The thickness of the separator used in aluminum-shell lithium-ion batteries is usually 16um, 18um, 20um, etc., and the thickness of the separator used in power batteries is more than 30um as the mainstream.

If distinguished by shape, there are rolls and strips. The rolled diaphragm is to roll the cut-width diaphragm on a paper tube for the customer to cut the length of the single diaphragm (the shape is similar to the transparent glue). The strip diaphragm is directly cut into strip diaphragms by the supplier according to the length, width, thickness and other parameters provided by the customer. The advantage of the rolled diaphragm is that it has strong versatility, but requires more manpower for cutting. The advantage of the strip diaphragm is that it can be used without manual cutting, but the versatility is not strong.

The diaphragm can melt when the internal temperature of the battery is too high to prevent the battery from exploding. When the internal temperature of the battery reaches 130℃ (the national standard for lithium ion batteries GB18287-2000), the mesh holes of the diaphragm will be closed to prevent lithium ions from passing through and increase the internal resistance (to 2kΩ) to prevent the internal temperature of the battery from continuing to rise High function, thereby protecting the battery from the danger of explosion.

Once the vent and diaphragm are activated, the battery will permanently fail.

Lithium battery drum shell

Lithium is the smallest and most active metal on the chemical periodic table. Because of its small size and high capacity density, it is widely welcomed by consumers and engineers. However, the chemical properties are too active, which brings extremely high risks. When lithium metal is exposed to the air, it will react violently with oxygen and explode. In order to improve safety and voltage, scientists invented materials such as graphite and lithium cobalt oxide to store lithium atoms. The molecular structure of these materials forms a small nano-scale storage grid that can be used to store lithium atoms. In this way, even if the battery shell ruptures and oxygen enters, the oxygen molecules will be too large to enter these small storage cells, so that lithium atoms will not come into contact with oxygen and avoid explosion.

This principle of lithium-ion battery enables people to achieve the goal of safety while obtaining its high capacity density. When a lithium-ion battery is charged, the lithium atoms in the positive electrode lose electrons and are oxidized to lithium ions. Lithium ions swim to the negative electrode through the electrolyte, enter the storage cell of the negative electrode, and obtain an electron, which is reduced to lithium atoms. When discharging, the whole procedure is reversed. In order to prevent the battery's positive and negative electrodes from directly touching and short-circuiting, a diaphragm paper with many pores is added to the battery to prevent short-circuiting. A good diaphragm paper can also automatically close the pores when the battery temperature is too high, so that lithium ions cannot pass through, so as to waste martial arts and prevent danger.