Why do batteries bulge after excessive use?

Batteries bulge after excessive use due to a process called outgassing, where gases build up inside the battery casing.

Outgassing is a common phenomenon in batteries, particularly in lithium-ion batteries, which are widely used in many electronic devices. This process occurs when the battery is overcharged, overheated, or used excessively, causing the electrolyte inside the battery to break down and produce gas. This gas builds up inside the sealed battery casing, causing it to expand or 'bulge'.

The electrolyte in a battery is a medium that allows for the flow of electrical charge between the cathode and anode. In a lithium-ion battery, the electrolyte is typically a mixture of organic solvents and lithium salts. When the battery is overcharged or overheated, these solvents can decompose, releasing gases such as carbon dioxide, oxygen, and in some cases, even flammable gases like hydrogen.

The battery casing is designed to be airtight to prevent leakage of the electrolyte. However, it is not designed to withstand the pressure build-up from the gases produced during outgassing. As a result, the casing begins to expand or 'bulge' to accommodate the increased pressure. In extreme cases, this can lead to the battery casing rupturing or even exploding.

It's important to note that battery bulging is a sign of a failing battery and can pose a safety risk. The gases produced during outgassing are not only potentially flammable, but they can also cause the battery to fail, leading to loss of power. Furthermore, a bulging battery can cause physical damage to the device it's in, as the expanding casing can warp or break the device's components. Therefore, if you notice a battery starting to bulge, it's recommended to stop using it immediately and dispose of it properly.

In conclusion, battery bulging is a result of outgassing, a process where gases are produced inside the battery due to overcharging, overheating, or excessive use. This is a sign of a failing battery and can pose a safety risk.