How To Correctly Select Thickness & Width of Copper-Nickel Clad Strip for Your Battery Module

Introduction

Copper-nickel clad strips combine copper’s conductivity with nickel’s weldability and corrosion resistance. Incorrect sizing leads to overheating, energy loss, poor welds, or mechanical failure. This guide covers current-carrying capability, temperature-rise limits, mechanical stiffness, weld-process compatibility, surface finish, and provides practical selection examples.

1. Current-carrying capacity

• Rule of thumb: continuous current density for copper-clad strips is typically 3–5 A/mm² (adjust for cooling and installation).
• Area A (mm²) = Current I (A) / Current density J (A/mm²).
• Example: For 200 A at J = 4 A/mm² → A = 50 mm². If width = 20 mm → thickness ≈ 50/20 = 2.5 mm. In practice, use wider strips or multiple parallel strips rather than extremely thick single layers.
• Use copper effective area if nickel layer is significant.

1. Temperature rise constraint

• Target: module interior ΔT ≤ 20–30 °C.
• Approximate heating: ΔT ≈ I⊃2;·R·θ_th, with R = ρ·L/A and θ_th the thermal resistance to ambient.
• Solve for A under given ΔT: A_min ≥ I·sqrt(ρ·L·θ_th / ΔT) (approximate). Apply safety factor 1.2–1.5 to account for contact resistance and pulses.

1. Mechanical strength and vibration/impact

• Thin wide strips may meet electrical needs but lack stiffness. Consider:
  • Increase thickness or add mechanical supports for rigidity.
  • Multiple fixation points and short free spans to improve vibration resistance.
• For harsh environments, raise thickness by 10–30% or validate with vibration/drop testing.

1. Weldability and process matching

• Thicker strips require higher welding energy/time.
• Welding considerations:
  • Ultrasonic welding: sensitive to thickness and surface cleanliness; typically effective up to ~0.5–1.0 mm copper depending on equipment.
  • Laser welding: affected by reflectivity differences between Ni and Cu; may require higher power or multiple passes for thick strips.
  • Resistance/spot welding: suitable for thicker parts but watch heat transfer to cells.
• Always validate thickness vs. your welding equipment’s process window (energy, time, pressure).

1. Surface roughness & cleanliness

• Contamination or oxides reduce ultrasonic and laser weld yield and increase contact resistance.
• Control surface roughness (slight roughness can aid mechanical interlock for ultrasonic), implement cleaning (solvent, plasma), and use protective packaging pre-weld.

1. Typical selection cases

• 50 Ah prismatic module:
  • Example: 0.2 mm × 20 mm Cu-Ni (Cu ~0.18 mm, Ni ~0.02 mm). Area 4 mm²; at 4 A/mm² supports ~16 A per strip—use multiple strips/short paths as needed.
• 100 Ah+ modules:
  • Example: 0.3 mm × 30 mm (Cu ~0.28 mm, Ni ~0.02 mm). Area 9 mm²; at 4 A/mm² supports ~36 A per strip; use parallels or larger sizes for hundreds of amps.
• High-current busbars (≥200 A): use much thicker (≥1.0–2.5 mm) or wider structures with mechanical support and nickel finish for weldability/corrosion protection.

1. Practical recommendations

• Balance electrical loss, hotspots, manufacturability and cost.
• Prototype with thermal imaging and vibration/thermal cycle testing.
• Confirm material specs (Ni thickness, resistivity, bonding quality) with suppliers and get samples & datasheets.

Conclusion

Start from required current and use 3–5 A/mm² to size area, then apply temperature-rise limits, mechanical and welding constraints, and verify through prototyping and testing.