Prussian Blue Analog Batteries on Thread Substrates for Wearable Electronic Applications

Flexible, wearable electronics are starting to reach mass consumer markets but an adequate solution to power these devices remains a challenge. The size constraints in traditional mobile devices impose a premium on high energy density batteries to capitalize on limited space. These energetically dense systems often require bulky, rigid casings for robust protection against fire and chemical hazards. Thus we target energy storage in textiles, where size constraints are less stringent, battery real estate is scalable to requirements, and safer materials may be used.

We demonstrate a zinc/Prussian blue analog battery on a thread/fiber architecture that can be woven into clothing/textiles. First, we show a cell that consists of a copper hexacyanoferrate (CuHcf) cathode dyed or coated on to conductive carbon fibers and a counter zinc electrode, suspended in a sodium-rich agarose hydrogel electrolyte at neutral pH. Agarose is a seaweed based gel known to conduct ions such as Na+. We introduce sodium salt loaded agarose gels as a potential high rate battery electrolyte.  Preliminary charge/discharge tests of the 1.7 V cells in a flooded 2 cell setup show an initial specific discharge capacity of 51 mAhr/g of CuHcf, and 43 mAhr/g after 25 cycles. Further optimization is likely to improve cycle life significantly.

Next, we demonstrate simple woven structures with CuHcf and Zn coated threads with Agarose/Na+ electrolyte as a proof of concept towards realizing wearable and washable electronics. We characterize the physical properties of the fiber electrodes and gel electrolyte with SEM, stress loading, and washing with sodium salt based laundry detergents. A range of electrochemical characterization is performed on the woven structures to analyze their cycle life, energy and coulombic efficiencies and specific capacities.