Meaning
Resistance to electrical or thermal flow at the physical interface between two mating surfaces under pressure. Contact impedance governs the voltage drop and heat generation at terminal-to-busbar junctions and electrode-to-collector interfaces. The value decreases as contact pressure increases, which deforms surface asperities.
Surface Interaction
Microscopic peaks and valleys on the metal surfaces limit actual contact to a fraction of the apparent area. Microscopic electrical paths are formed only at these mating points, restricting current flow. Chemical oxidation or surface contamination further restricts these conduction zones, raising the resistance value.
Mechanical Force
Clamping force must be carefully calibrated to ensure sufficient deformation without damaging the delicate cell terminals. Engineers specify torque values for bolted joints or clamping pressures for sandwiched interfaces to hit targeted impedance limits. Inadequate force results in high resistance, which leads to localized heating during high-rate operation.
Excessive force risks crushing the terminal threads or causing structural fatigue in the busbar assembly.
Material Selection
Plating the terminal surfaces with softer metals like tin or silver facilitates greater contact area at lower pressures. Sourcing contracts dictate the surface finish and plating thickness to guarantee long-term electrical performance. These specifications prevent galvanic corrosion and preserve interface integrity over the pack lifetime.
