Lithium ion protection mechanism

Since misuse will reduce life span and may even lead to explosion, lithium-ion batteries are designed with various protection mechanisms.
1. Protection circuit
Prevent overcharging, over-discharging, overloading and overheating.
2. Vent
Because of its explosion-proof function, people in the battery industry are also called explosion-proof holes or explosion-proof lines. The principle is very simple. Draw a line or hole on the surface of the shell that is slightly thinner than the surface of the shell. When the battery 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 be deflated at the explosion-proof hole, thereby avoiding the danger of the overall explosion of the battery cell.
3. Diaphragm
Isolate the positive and negative pole pieces of the battery core to prevent short circuit caused by direct contact between the positive and negative pole pieces inside the winding core; from a microscopic point of view, the surface of the separator is a mesh structure, usually divided into PP and PE, and also PE and PP compounded together .
Separators are usually divided by thickness and width. The thickness of separators used in aluminum shell lithium-ion batteries is usually 16um, 18um, 20um, etc., and the thickness of separators used in power batteries is more than 30um.
If distinguished by shape, there are rolls and strips. The roll-shaped diaphragm is to roll the cut-to-width diaphragm on a paper tube for customers to cut a single length of the diaphragm (similar in shape to transparent glue). The strip diaphragm is directly cut into a strip diaphragm by the supplier according to the length, width, thickness and other parameters provided by the customer. The advantage of the roll-shaped diaphragm is that it has strong versatility, but it requires more manpower for cutting. The advantage of the strip-shaped diaphragm is that it can be used without manpower cutting, but its versatility is not strong.
The separator can also 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°C (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), so as to prevent the internal temperature of the battery from continuing to rise. High effect, so as to protect the battery from the danger of explosion.
Once the vent, diaphragm is activated, the battery will permanently fail.
4. Lithium battery drum shell
Lithium is the smallest and most active metal on the periodic table. Due to its small size and high capacity density, it is widely welcomed by consumers and engineers. However, the chemical properties are too active, which brings a very high risk. When lithium metal is exposed to air, it will explode due to a violent oxidation reaction with oxygen. In order to improve safety and voltage, scientists have invented materials such as graphite and lithium cobalt oxide to store lithium atoms. The molecular structures of these materials form tiny storage lattices at the nanometer level, which can be used to store lithium atoms. In this way, even if the battery casing is broken and oxygen enters, the oxygen molecules are too large to enter these tiny storage cells, so that the lithium atoms will not come into contact with oxygen to avoid explosion.
This principle of lithium-ion batteries enables people to achieve the purpose of safety while obtaining its high capacity density. When a lithium-ion battery is charged, the lithium atoms at the positive electrode will lose electrons and be oxidized to lithium ions. The lithium ion swims to the negative electrode through the electrolyte, enters the storage cell of the negative electrode, and obtains an electron, which is reduced to a lithium atom. When discharging, the whole procedure is reversed. In order to prevent the positive and negative poles of the battery from directly touching and short-circuiting, a separator paper with many pores is added inside the battery to prevent short-circuiting. A good separator paper can also automatically close the pores when the battery temperature is too high, so that lithium ions cannot pass through, so as to abolish martial arts and prevent danger.