Meaning
Physical expansion of a lithium-ion cell occurs due to the insertion of lithium ions into the anode during charging and the gas generation from electrolyte decomposition over time. This volumetric cell swelling applies significant mechanical force to the surrounding module structure. It is a primary design consideration for battery containment and thermal systems.
Structural Pressure
Swelling forces can deform module housings and crush internal cooling plate channels if the structure is too rigid. Designers must calculate the maximum expansion force to size the module endplates and tie rods correctly. This calculation ensures that the mechanical structure can contain the forces without yielding.
Electrical Performance
Maintaining a consistent compressive force on the cell surfaces improves the cycle life by keeping the active electrode layers in close contact. When cells are allowed to swell without constraint, the distance between the anode and cathode increases, which raises internal resistance and reduces capacity. A balance must be maintained to optimize performance.
Module Integration
Flexible foam pads and spring elements are placed between the cells to absorb the expansion during cycling while maintaining a steady force. These compressible materials deform during charging and rebound during discharging to ensure that the cells remain within the optimal pressure range. This design increases the safety and durability of the battery pack.
It prevents the internal layers from delaminating, which reduces the risk of lithium plating and the associated risks of internal short circuits during high-rate charging.
