The authoritative magazine IEEE Spectrum is carrying a report about Korean scientists who have succeeded in weaving Li-Ion batteries into fabric, and charging them with solar cells similarly woven:
They came up with a fabric-based battery comprising a nickel-coated polyester yarn as the current collector, polyurethane as a binder holding materials together, and a polyurethane separator. The resulting battery can withstand repeated folding and unfolding and still function, a requirement for any tech that’s actually going to wrap around the wrist or be worn in other ways.
If this is replicable at decent cost, this could be a significant breakthrough…