Meaning
Internal electrode tension occurs when the spirally wound components of a lithium ion battery expand or contract under thermal and electrochemical loads. This jellyroll mechanical stress originates from the lithium intercalation process where active materials shift in volume, pushing against the separator and the outer casing. Excessive force leads to internal short circuits or the delamination of the active coating from the current collector foil.
Uniformity in the wind tension during initial assembly governs the capacity of the cell to withstand these cyclical pressures over a long service life.
Physical Expansion
Operational limits depend on the elasticity of the containment vessel and the core winding density. High winding speeds create tight coils that suffer from restricted lithium ion diffusion paths and localized heating. Lowering the initial wrap tension reduces the risk of separator perforation as the electrodes move during charging cycles.
Material Integrity
Electrode longevity hinges on the adhesion strength between the current collector and the active chemical paste. Fatigue arises when the jellyroll mechanical stress exceeds the binding energy of the composite layer, causing particles to detach. Failure patterns show that degraded cells exhibit a rise in internal resistance as the contact pathways break down.
Structural Performance
Geometric constraints dictate the maximum allowable volume change before the cell geometry alters permanently. Cylindrical housings offer high resistance to deformation but focus the pressure on the central mandrel and the outer tab connections. Rigid packaging designs mitigate displacement by constraining the jellyroll mechanical stress into a preloaded state.
Stable contact pressure maintains low ohmic impedance throughout the discharge cycles.
