NOVELTY - Preparing (M1) cathode active material comprising a mixed crystal involves providing a first crystalline substance; providing a second crystalline substance; and sintering the two crystalline substances to provide the mixed crystal.    USE - For preparing cathode active material used in lithium secondary battery (claimed) which is used in various devices such as laptop computers, cameras, camcorders, cell phones, and other portable electronic devices.    ADVANTAGE - The method produces cathode active material that enhances the electrical properties of lithium secondary batteries. The method uses the step of sintering, upon sintering, a large number of crystalline defects can be formed, thus alters the electronic states of the compounds creating a large number of oxygen vacancies, these oxygen vacancies provide the needed carriers, thus greatly enhances the electrical conductivity of the mixed crystal. The cathode active material achieves electrical conductivity of 0.1 to 2 S/cm at 25 degrees C with a Simens per centimeter, which is larger than traditional lithium iron phosphate cathode active materials.    DETAILED DESCRIPTION - Preparing (M1) cathode active material comprising a mixed crystal involves providing a first crystalline substance having at least one member having formulae LixM'y(XO4)z, LiM'5XO5, LiM'5XO6 and LiM'5X2O7; providing a second crystalline substance having at least one member having A'aB'bN'cOd; and sintering the two crystalline substances to provide the mixed crystal.    x/z=0-1;    y/z=0-1.1;    M'=element selected from Na, Mn, Fe, Co, Ni, Ti, V, Y, Mg, Ca, Nb or Zn;    X=element selected from P, S, As, Mo and W;    A', B' and N'=different metals selected from IIA, IIIA, IVA, VA, IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIII in the periodic table;    a-c=0-6;    d=0-12.    Provided that a and b, cannot be zero at the same time. INDEPENDENT CLAIMS are included for the following:    (1) preparing (M2) cathode active material comprising mixed crystal involving providing a first material having a combination of lithium, iron and phosphorus sources; providing a second material having at least one member with formula A'aB'bN'cOd; and sintering the two materials to provide the mixed crystal; and    (2) forming a lithium secondary battery involving providing electrodes having a cathode, an anode and a divider film which are wounded or stacked, where the cathode contains the cathode active material prepared by the method (M1) or (M2); and providing a battery shell and electrolyte, the electrodes and the electrolyte being sealed within the battery shell.