soldering-materials-dat

soldering wire

Nickel, Copper, and Sandwich (For 18650/21700)

Material	Best Use Case	Pros	Cons
Pure Nickel	Standard DIY packs (5A-15A)	Easiest to spot weld; corrosion resistant.	Higher resistance than copper; heats up at high current.
Pure Copper	High-performance (30A+)	Lowest resistance; minimal heat generation.	Extremely difficult to spot weld (requires laser/ultrasonic).
Sandwich	High-current DIY (Nickel + Copper)	Better conductivity than pure nickel; weldable with high-power spot welders.	Hard to tune welding parameters; risk of "cold" welds or blow-through.

Material	Conductivity	Weldability	Best Used For...
Pure Nickel	Good (~25% of Cu)	Excellent	Standard DIY packs, Robotics (Rover V2), Electric bikes.
Pure Copper	Best (100%)	Very Poor	Ultra-high performance racing drones or EV modules.
Sandwich	High	Difficult	High-current DIY builds (Copper strip under a Nickel strip).

High Resistance (Ideal for Welding): Spot welding relies on electrical resistance to generate heat. Nickel resists current just enough to melt instantly at the contact point, creating a strong bond.
Thermal Control: Copper is a "heat sink"—it pulls heat away so fast that the weld point never gets hot enough to melt, but the battery cell underneath gets dangerously hot.
Corrosion Resistance: Nickel does not rust or oxidize easily. Copper turns green (oxidizes) over time, which increases resistance and creates "hot spots."
Tool Compatibility: Most hobbyist spot welders (Sunkko, Malectrics, Kweld) are designed specifically for the physics of nickel.

Primary Purpose: Transitioning between dissimilar metals.

When to use: Specifically for Pouch Cells or Prismatic Cells where the positive terminal (tab) is made of Aluminum.
Why: Aluminum and Nickel do not bond well through standard spot welding.
How it works: The strip is bi-metallic (half Al, half Ni).
- Al side is welded to the battery's Aluminum tab.
- Ni side provides a weldable surface for standard nickel busbars or wires.
Summary: It is a "bridge" material, not for 18650s (which use steel/nickel caps), but for batteries with raw aluminum electrodes.

examples: