In the production process of pouch cell battery, there are many factors that can lead to abnormal gas production, which can be divided into several categories:

First, the film formation of the cell itself is unstable. In the subsequent cycle process, the SEI film on the surface of the negative electrode may fall off or become loose, and the SEI film(SEI Formation Machine) is reconstructed, accompanied by gas generation;

The second is that the water content inside the battery exceeds the standard;

The third is the abnormal gas production caused by the short circuit in the battery;

Fourth, gas production during high temperature storage;

Fifth, overcharge and over-release gas.

2. Analysis of the causes of abnormal gas production

1. Abnormal water content flatulence

Due to the sensitivity of the entire battery system to moisture, although a large number of studies believe that LiF produced by the presence of trace moisture makes the SEI film more stable, but when there is excess moisture, not only the consumption of lithium salt increases, but the battery performance is reduced.

In addition, it will also be accompanied by a large amount of gas, which will cause the battery to swell and cause the battery to fail. When lithium is precipitated in the negative electrode, it will react violently with water and generate heat, which will cause more serious safety problems.

2. Internal short-circuit flatulence

During the production process of the battery, when there is an internal short-circuit point, the local temperature rises sharply, resulting in the decomposition of the electrolyte.

This is because the electrolyte reacts with the decomposition product PF5 of LiPF6 in the presence of high temperature and trace water, resulting in a significant increase in the amount of CO2 and gas swelling.

When the internal short circuit occurs, the temperature can reach more than 200 ℃, and the battery separator is burned and carbonized. Generally, the burning short-circuit point can be found when the cell is disassembled.

3. High temperature storage and overcharge and over discharge gas production

During high temperature storage and overcharge and overdischarge, LiCoO2 is in a metastable state and is extremely unstable.

In addition, when the stability of the SEI film is low, the organic layer of the outer layer of the film in contact with the electrolyte will dissolve with the increase of temperature,

For example, (CH2OCO2Li)2 is the main component of the alkyl ester lithium layer of the SEI film, which is very unstable, generates gas, and swells the cell;

3. Measures to suppress abnormal gas production

Suppressing abnormal gas production requires both material design and manufacturing process.

First of all, it is necessary to design and optimize the material and electrolyte system to ensure the formation of a dense and stable SEI film, improve the stability of the cathode material, and inhibit the occurrence of abnormal gas production. Secondly, it is necessary to strictly control the parameters of the manufacturing process to ensure the reliability of the packaging and prevent the flatulence caused by excessive moisture inside the battery. The control method is as follows:

(1) After the battery core is wound, it is fully dried to prevent the moisture content in the diaphragm from exceeding the standard;

(2) Strictly control the time from the cell to liquid injection and the humidity of the drying room after vacuum baking;

(3) Ensure the tightness of the glove box for injection;

(4) Control the content of moisture and free acid in the electrolyte;

(5) Standardize the electrolyte storage environment and sealing conditions to prevent the electrolyte from entering excessive moisture during use and storage;

(6) Use closed-mouth pressurized formation or external airbag formation and then vacuum and seal the exhaust;

(7) Adopt multi-step formation and high temperature shelving process to ensure complete gas production;

(8) Improve package reliability.