The present disclosure relates to mixed ionically and electronically conducting solid-state phases for their application in electrochemical devices, such as lithium-metal or lithium ion batteries. The solid-state mixed phase comprises of active cathode and carbon-based structures functionalized by a heteropolyacid (HPA) or a metal salt of a heteropolyacid (Me-HPA) to form a solid-state architecture with incorporated ceramic or glass-ceramic electrolyte for enhanced ionic and electronic conductivity pathways. Combining the solid-state phase components in melted solid-state electrolyte results in perfect distribution, improved adhesion between particles, and improved characteristics of the electrochemical device, such as high charge rates, long-term performance, and broad voltage window.