An electrochemical capacitor includes a positive electrode, a negative electrode disposed proximally to the positive electrode, and a non-aqueous electrolyte, wherein the positive electrode and the negative electrode are immersed in the non-aqueous electrolyte, and a case is presented in the energy storage system to accommodate the non-aqueous electrolyte, the positive electrode, and the negative electrode. The positive electrode has a porous matrix having a plurality of micrometer sized pores and nanostructured metal oxides, wherein the porous matrix is a 3-dimensional (3D) mesoporous metal or a 3D open-structured carbonaceous material, and the nanostructured metal oxides are coated inside the plurality of pores of the porous matrix. The non-aqueous electrolyte includes organic compounds having at least one acylamino group and lithium salts characterized as LiX, wherein Li is lithium and X comprises SCN−; the organic compounds are cyclic compounds; and the cyclic compounds comprise 2-oxazolidinone, ethyleneurea, or the combination thereof.