In lithium-ion battery packs, the small metal links that join cells carry a big responsibility. Pure nickel strips are widely used to connect cylindrical cells—18650, 21700, and 32650—because they offer a dependable mix of electrical conductivity, weldability, and corrosion resistance. This guide focuses on how these strips are specified, processed, and selected in real production settings.
Why Pure Nickel (and not plated steel)?
For interconnections, material choice directly affects performance:
- Stable conductivity: Pure nickel provides consistent current flow across parallel groups.
- Reliable spot welding: It forms strong weld nuggets with common battery welders.
- Corrosion resistance: Useful in humid or mildly corrosive environments.
By contrast, nickel-plated steel is cheaper but behaves differently in welding and can limit current capacity. In critical packs, verifying true nickel composition is standard practice.
Common Cell Formats & Strip Layouts
- 18650 (18×65 mm): Mature ecosystem, compact layouts.
- 21700 (21×70 mm): Higher capacity per cell; wider spacing and thicker tabs are common.
- 32650 (32×65 mm): Larger diameter; requires broader, often thicker strips.
Strips are supplied as straight bands (cut to length) or pre-patterned tabs (including multi-cell patterns) to speed up assembly and keep spacing consistent.
Material Basics (What actually matters)
- High nickel purity (~99%): Preferred for predictable electrical and welding behavior.
- Low carbon content: Supports ductility and helps avoid brittleness during processing.
- Ductility & formability: Important for bending, shaping, and consistent welds.
Industry specifications for pure nickel products are commonly aligned with ASTM B162 / ASME SB-162 (for plate, sheet, and strip) and UNS N02201 for low-carbon nickel grades used at higher temperatures.
Thickness Selection vs Current
Thickness is the quickest way to match a strip to current demand:
- Thin strips (≈0.10–0.15 mm): Low to moderate current packs, compact designs.
- Medium (≈0.15–0.20 mm): General-purpose builds and 21700 packs.
- Thicker (≈0.20–0.30 mm+): Higher current paths or longer bus runs.
Practical tip: instead of one very thick strip, many builders use multiple parallel strips to spread current and improve weld consistency.
Surface Finish & Edges
- Bright annealed (BA): Clean surface, consistent welding.
- Matte/2B: Slightly different appearance, still suitable for welding.
- Edge condition: Slit edges should be smooth to avoid tearing separators or insulating parts during assembly.
Processing Route (from coil to tabs)
- Cold rolling to reach final thickness and tight tolerances
- Annealing to restore ductility
- Slitting into narrow widths
- Stamping / punching for tabs or multi-cell patterns
- Final inspection (thickness, flatness, surface condition)
This sequence is standard across nickel strip production and ensures repeatable quality for battery applications.
Welding Considerations
- Spot welding is the dominant method for cylindrical cells.
- Use clean surfaces (both cell terminals and strip).
- Dial in pulse energy and pressure for your thickness; too low → weak joints, too high → burn-through.
- Keep consistent overlap and alignment to avoid uneven current paths.
Quality Checks Before You Buy
- Material certification (chemical composition aligned to standards)
- Dimensional tolerance (thickness, width, camber)
- Surface cleanliness (oil, oxidation)
- Lot traceability for production consistency
For critical builds, many teams also perform a simple magnet and resistance check to distinguish pure nickel from plated alternatives (plated steel is strongly magnetic; pure nickel is only weakly magnetic at room temperature).
Typical Applications
- E-bikes & EV modules
- Power tools
- Energy storage systems (ESS)
- Consumer electronics packs
Across these uses, the goal is the same: low-resistance connections, durable welds, and long service life.
Nickel 200 vs Nickel 201 in Strips
Both are commercially pure nickel grades. Nickel 201 has lower carbon, which improves stability at elevated temperatures. For most battery strip applications, either can be used, but 201 is often preferred where thermal exposure during processing is higher.
Conclusion
Pure nickel strips remain the industry standard for connecting cylindrical lithium-ion cells because they balance conductivity, weldability, and durability. Choosing the right thickness, finish, and pattern, along with verified material quality, has a direct impact on pack performance and safety.
