A lithium-polymer (LiPo) battery can swell due to a variety of factors, most of which involve issues with the battery’s internal chemistry or physical integrity. Here are the primary causes of swelling in LiPo batteries:

1. Overcharging:

• Cause: Charging a LiPo battery beyond its maximum voltage (typically 4.2V per cell) can lead to excessive gas generation inside the battery.
• Effect: Overcharging causes the electrolyte to decompose, creating gas that causes the battery to swell. This can also lead to overheating and potentially dangerous situations like fires or explosions.

2. Overdischarging:

• Cause: Discharging a LiPo battery below its minimum voltage threshold (usually around 3.0V per cell) can lead to chemical instability.
• Effect: Overdischarging can damage the battery’s internal structure, leading to swelling as the battery struggles to recover or reassemble its internal components.

3. Physical Damage:

• Cause: Punctures, dents, or other physical impacts can damage the internal layers of a LiPo battery.
• Effect: Physical damage can cause the electrolyte to leak or the internal layers to short-circuit, generating gas and causing swelling. This can also lead to a risk of thermal runaway.

4. Excessive Heat:

• Cause: Operating or charging a LiPo battery at high temperatures or in direct sunlight can cause thermal stress.
• Effect: Excessive heat accelerates chemical reactions inside the battery and can lead to the decomposition of the electrolyte, generating gas and causing swelling.

5. Manufacturing Defects:

• Cause: Poor quality control during the manufacturing process can result in defects such as improper sealing or incorrect electrolyte formulation.
• Effect: Defects can lead to chemical imbalances or leakage, causing the battery to swell over time.

6. Improper Charging Equipment:

• Cause: Using a charger that is not designed for LiPo batteries or that provides incorrect voltage or current levels.
• Effect: Incorrect charging parameters can lead to overcharging or overheating, both of which can cause swelling.

7. Aging and Wear:

• Cause: Over time, the performance of a LiPo battery degrades due to normal wear and tear.
• Effect: As the battery ages, its internal components can become unstable or break down, leading to gas generation and swelling.

8. Battery Chemistry Issues:

• Cause: Issues with the battery’s electrolyte or electrode materials can also cause problems.
• Effect: Chemical reactions or breakdowns in the battery’s internal materials can create gas and lead to swelling.

Conclusion:

Swelling in LiPo batteries is usually a sign of an issue such as overcharging, overheating, physical damage, or a manufacturing defect. It’s important to handle LiPo batteries with care, use proper charging equipment, and avoid exposing them to extreme conditions. If a LiPo battery begins to swell, it should be handled carefully, kept away from flammable materials, and disposed of properly according to local regulations.