TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The composite cathode active material is a compound of formula (1-r)LixMe'yM'zPO4-dXd-r(M'q)bC1-aNa (V), (1-r)LixMe'yM'zPO4-dXd-rC1-aNa (VI), (1-r)LixMn1-z'(M'1)z'PO4-dXd-rM'qC1-aNa (VII) or (1-r)LixMn1-z'(M'1)z'PO4-dXd-rC1-aNa (VIII). The composite cathode active material further includes a carbonaceous material (0.1-30 wt.%).a and b=0-1;x=0.6-1.4;y and z=0-1;d=0-0.2;Me'=iron, manganese, nickel, and cobalt;M'=magnesium, calcium, copper, neodymium, strontium, barium, titanium, zirconium, niobium, molybdenum, tungsten, zinc, aluminum, or silicon;X=S or F;M'q=titanium, calcium, magnesium, zinc, nickel, cobalt, aluminum, zirconium, iron, copper, boron, tantalum, niobium, vanadium, tungsten, molybdenum, silicon, uranium, or thorium;r=0-1 (preferably 0.0001-0.3);M'1=Fe, Ni, Co, Mg, Ca, Cu, Nd, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, or Si;z'=0-0.2.Preferred Method: In the method (P1), the precursor of the compound with the olivine crystal structure includes a lithium precursor, a phosphate precursor, or a transition metal precursor, where the sintering is performed at 400-900 degrees C under an inert gas atmosphere for 2-48 hours. Preferred Components: The inorganic material includes the metal carbonitride of formula M''bC1-aNa (I). The inorganic material includes the metal carbonitride including titanium carbonitride, calcium carbonitride, magnesium carbonitride, molybdenum carbonitride, zinc carbonitride, nickel carbonitride, cobalt carbonitride, aluminum carbonitride, zirconium carbonitride, iron carbonitride, copper carbonitride, or boron carbonitride. The inorganic material includes the carbonitride of formula C1-aNa (II). The inorganic material includes the carbonitride including at least one selected from C3N4, CN, or C3N. The compound having the olivine crystal structure is a compound of formula LixMe'yM'zPO4-dXd (III) or LixMn1-z(M'1)zPO4-dXd (IV). The compound with the olivine crystal structure includes LiFePO4, LiFe1-aMnaPO4 or LiMnPO4. The inorganic material is in the form of nanoparticle, nanofiber, nanomesh, or nanotube. The inorganic material has a Mohs hardness that is greater than a Mohs hardness of the compound with the olivine crystal structure. The inorganic material has a Mohs hardness of greater than or equal to 1. The inorganic material has an electrical conductivity higher than that of amorphous carbon. The inorganic material has an electrical conductivity of greater than or equal to 10 S/cm.M''=metal or metalloid selected from Group 2 to Group 14 elements in the periodic table of elements (preferably titanium, calcium, magnesium, zinc, nickel, cobalt, aluminum, zirconium, iron, copper, boron, tantalum, niobium, vanadium, tungsten, molybdenum, silicon, uranium, or thorium). EXAMPLE - Preparation of a composite cathode active material was carried as follows: Li2CO3, MnCO3, FeC2O4, and NH4H2PO4 were mixed together in a mole ratio of 0.5:0.9:0.1:1, and Ketjen Black 600JD (RTM: carbon powder) (4.8 wt.%) and titanium carbonitride (0.2 wt.%) were added to the mixture, based on a total weight of the mixture. Then, the mixture was sintered under an inert atmosphere (nitrogen atmosphere) at 600 degrees C for 6 hours to prepare the composite cathode active material. The composite cathode active material included a compound with an olivine crystal structure of formula LiMn0.9Fe0.1PO4.