Provided is an internal hybrid electrochemical cell comprising: (A) a pseudocapacitance cathode comprising a cathode active material that contains a conductive carbon material and a porphyrin compound, wherein the porphyrin compound is bonded to or supported by the carbon material to form a redox pair for pseudocapacitance, wherein the carbon material is selected from activated carbon, activated carbon black, expanded graphite flakes, exfoliated graphite worms, carbon nanotube, carbon nanofiber, carbon fiber, a combination thereof; (B) a battery-like anode comprising lithium metal, lithium metal alloy, or a prelithiated anode active material (e.g. prelithiated Si, SiO, Sn, SnO.sub.2, etc.), and (C) a lithium-containing electrolyte in physical contact with the anode and the cathode; wherein the cathode active material has a specific surface area no less than 100 m.sup.2/g which is in direct physical contact with the electrolyte.

Provided is an internal hybrid electrochemical cell comprising: (A) a pseudocapacitance cathode comprising a cathode active material that contains a conductive carbon material and a porphyrin compound, wherein the porphyrin compound is bonded to or supported by the carbon material to form a redox pair for pseudocapacitance, wherein the carbon material is selected from activated carbon, activated carbon black, expanded graphite flakes, exfoliated graphite worms, carbon nanotube, carbon nanofiber, carbon fiber, a combination thereof; (B) a battery-like anode comprising lithium metal, lithium metal alloy, or a prelithiated anode active material (e.g. prelithiated Si, SiO, Sn, SnO.sub.2, etc.), and (C) a lithium-containing electrolyte in physical contact with the anode and the cathode; wherein the cathode active material has a specific surface area no less than 100 m.sup.2/g which is in direct physical contact with the electrolyte.

The invention relates to an oxygen and nitrogen co-doped polyacrylonitrile-based carbon fiber and a preparation method thereof. The oxygen and nitrogen co-doped polyacrylonitrile-based carbon fiber is prepared by electrochemical modification of a raw-material polyacrylonitrile-based carbon fiber, such that the surface thereof has an active layer formed by oxygen-containing active functional groups and nitrogen-containing active functional groups, wherein the nitrogen-containing active functional groups are obtained by activation of the doped nitrogen inherently contained in the raw-material polyacrylonitrile-based carbon fiber by means of electrochemical modification. The method for preparing the oxygen and nitrogen co-doped polyacrylonitrile-based carbon fiber comprises the following steps: placing the raw-material polyacrylonitrile-based carbon fiber in an electrolyte solution, subjecting it to cyclic treatment between electrochemical oxidation and electrochemical reduction, and thus obtaining the oxygen and nitrogen co-doped polyacrylonitrile-based carbon fiber. The oxygen and nitrogen co doped polyacrylonitrile based carbon fiber of the present invention has both the pseudo capacitive properties for oxidation reduction reactions and electrocatalytic properties for the cathodic oxygen reduction reaction.