Thin film all-solid-state power sources, including pseudocapacitors having solid inorganic Li+-ion conductive electrolyte, for IoT, microsensors, MEMS, RFID TAGs, medical devices, elements of microfluidic chips Micro Electro Harvesting and ultra-light energy storage. An electrochemical power source includes a substrate; a first current collector layer on the substrate; a first buffer/cache layer on the first current collector layer; a solid-state electrolyte layer on the first buffer/cache layer; a second buffer/cache layer on the solid-state electrolyte layer; a second current collector layer on the second buffer/cache layer. Each buffer/cache layer is formed of LiXMYO3, where M is Nb, Ta, Ti, V, X is 0.8-1.4, and Y is 1.2-0.6. The buffer/cache layer is 15-1000 nm. At least one Faradaic layer is between the first collector layer and the first buffer layer and/or between the second collector layer and the second buffer layer.