An electrochromic (EC) device and method, the EC device including: an optically transparent first substrate; a working electrode disposed on the first substrate and including electrochromic nanoparticles and a flux material having a melting point ranging from about 25° C. to about 500° C.; and an electrolyte disposed on the working electrode. The flux material is configured to prevent or reduce sintering of the nanoparticles at a temperature of up to about 700° C.