TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The composite cathode active material comprises the overlithiated metal oxide (5-95, preferably 40-60 wt.%). The material having an olivine structure is doped with nitrogen atoms, and a region doped with nitrogen atoms in the material having an olivine structure exists in a crystalline phase. The material having an olivine structure includes a metal with an oxidation number of +2 and a metal with an oxidation number of +3, and a content of the metal with an oxidation number of +3 in the material having an olivine structure is less than or equal to 5 wt.% of a total content of the metal with an oxidation number of +2 and the metal with an oxidation number of +3 in the material having an olivine structure. The material having an olivine structure exhibits a nitrogen peak having a binding energy range of 398-400 eV and an oxygen peak having a binding energy of 530-534 eV in an X-ray photoelectron spectrum, and a ratio of an area of the nitrogen peak to an area of the oxygen peak is greater than or equal to 1:100 (preferably 1:100 to 20:100); exhibits a nitrogen peak having a binding energy range of 398-400 eV and a phosphorus peak having a binding energy of 132-136 eV in an X-ray photoelectron spectrum, and a ratio of an area of the nitrogen peak to an area of the phosphorus peak is greater than or equal to 1:100 (preferably 1:100 to 30:100); or exhibits a nitrogen peak having a binding energy of 396-398 eV. The composite cathode active material further comprises a coating layer including conductive carbon formed on the material having an olivine structure. Preferred Components: The inorganic material includes: a nitride or carbide of at least one element selected from group 2, group 13, group 14, and group 15 of the Periodic Table (preferably nitride or carbide of metalloid element, especially boron nitride (BN), boron carbide (B4C), silicon nitride (Si3N4), or silicon carbide (SiC)); boron; at least one amorphous boron nitride, boron nitride having a cubic crystal structure, boron nitride having a hexagonal crystal structure, or boron nitride having a wurtzite crystal structure. The inorganic material has at least one form of a nanoparticle, a nanofiber, a nanomesh, or a nanotube; has a Mohs hardness higher than a Mohs hardness of the material having an olivine structure (preferably greater than or equal to 1); and has an electrical conductivity lower than an electrical conductivity of amorphous carbon (preferably less than or equal to 10-1 S/cm). The overlithiated metal oxide is a compound of formula Li(LixMey)O2+d (I), Li(LixNiaCobMnc)O2+d (II). The material having an olivine structure includes a lithium metal oxide of formula Lix'My'M'z'PO4-d'Xd' (III) (preferably LiFePO4, LiFe1-aMnaPO4, or LiMnPO4).Me=Mn, V, Cr, Fe, Co, Ni, Zr, Re, Al, B, Ge, Ru, Sn, Ti, Nb, Mo, or Pt;a-c and x=0-1;d=0-0.1;orx+y and x+a+b+c=1;x'=0.9-1.1;y' and z'=0-1;orx'+y'+z'=1.9-2.1;d'=0-0.2;M=Fe, Mn, Ni, or Co;M'=Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, or Si;X=S or F. EXAMPLE - LiFePO4 (300 mg) having an average particle diameter of about 200 nm and a carbon-coating layer formed on its surface was put into a silica tube furnace at room temperature and pressure inside the furnace was made into a vacuum state. Subsequently, the furnace in a vacuum state was heated from room temperature to 300 degrees C for 10 minutes and ammonia gas (99.98%) was then supplied at a flow rate of 500 standard cubic centimeters per minutes (sccm) for 10 minutes while the inside of the furnace was maintained at 300 degrees C and a pressure of 760 Torn Thereafter, the flow rate was decreased and ammonia gas was supplied at a flow rate of 100 sccm for 20 minutes to perform nitrogen doping for a total of 30 minutes. The nitrogen doping was terminated by stopping the flow of ammonia gas and then the pressure inside the furnace was again made into a vacuum state. Nitrogen-doped LiFePO4 was obtained by cooling to room temperature. A composite cathode active material was prepared by mixing overlithiated metal oxide Li1.04Ni0.45Co0.16Mn0.35O2 (20 wt.%) and the nitrogen-doped material having an olivine structure (80 wt.%). The mixing was performed at 150 revolutions per minute (rpm) for 30 minutes by using a ball mill and subsequently performed by using a mortar.