Nickel can be resistance welded. The question here is: can foil be handled and equipment sized to process it? The answer is - probably, yes. Equipment referred to as “Micro Resistance Welders” is used in industry to process very small intricate parts for medical, electronics, electrical and many other applications. The best place to find an answer to the above question will be on the web. Search for suppliers or users of micro resistance welders.
MICRO DC RESISTANCE WELDER
Reference: RWMA – Resistance Welding Manual 4th Edition