The root cause of gas production in lithium batteries is essentially the result of a series of unwanted chemical and electrochemical side reactions inside the battery. These reactions consume the active ingredients in the battery and generate gaseous products, leading to a decrease in battery performance and even causing safety issues.

  The gas production of lithium batteries mainly comes from the following aspects:

1. Electrolyte decomposition

When used improperly at high temperatures or voltages (such as overcharging), organic solvents in the electrolyte can undergo oxidation or reduction reactions and decompose. 

The main gases are:

Carbon dioxide (CO ₂), carbon monoxide (CO), methane (CH ₄), ethylene (C ₂ H ₄), etc. two SEI film damage and recombination.

2. SEI film damage and recombination

If the SEI protective film on the negative electrode surface ruptures due to overcharging, overdischarging, or high temperature, the electrolyte will directly react with the negative electrode material in an attempt to repair the SEI film, and this process will continuously generate gas.

The main gases are:

Hydrogen (H ₂), ethylene (C ₂ H ₄), ethane (C ₂ H ₆), etc.

3. Excessive moisture content

Even trace amounts of water (ppm level) can react with lithium salts (such as lithium hexafluorophosphate LiPF ₆) in the electrolyte, generating corrosive hydrofluoric acid (HF) and further triggering side reactions to produce gas. 

The main gases are:

Hydrogen (H ₂), hydrogen fluoride (HF), carbon monoxide (CO), carbon dioxide (CO ₂).

4. Side reactions of positive electrode materials

Under overcharging or high temperature, the structure of positive electrode materials (especially high nickel ternary materials) may collapse, releasing oxygen. The released oxygen will oxidize the electrolyte, producing more gas. 

The main gases are:

Oxygen (O ₂), carbon dioxide (CO ₂).

5. Negative electrode material side reactions

For materials such as silicon anodes, significant volume changes during charge and discharge can repeatedly damage the SEI film, leading to sustained side reactions and gas production. Under excessive discharge or high temperature, the graphite negative electrode will also react with the electrolyte. 

The main gases are:

Hydrogen (H ₂), Ethylene (C ₂ H ₄), Ethane (C ₂ H ₆).