TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method (M1) further involves sintering a carbon additive with the two crystalline substances, the carbon additive capable of providing the mixed crystal with carbon (1-5 wt.%). In the method (M1), the second crystalline substance is produced by heating the oxide compounds of A, M and N at molar ratio of a:b:c at 400-1000 degrees C for 8-15 hours. The method (M1) involves providing a first crystalline substance having a combination of lithium, iron and phosphorus sources, where the lithium, iron and phosphorus (Li:Fe:P) sources have molar ratios of 0.95-1.1:1:0.95-1.1. Preferred Components: The first crystalline substance and the second crystalline substance have molar ratios of 1 to 0.01-0.05. The carbon additive includes at least one members selected from carbon black, acetylene black, graphite, glucose, sucrose, citric acid, starch, dextrin and polyethylene glycol. The first crystalline substance includes at least one members selected from lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), Li3Fe2(PO4)3, LiTi2(PO4)3, Li3V2(PO4)3, Li2NaV2(PO4)3, LiTiPO5, LiVMoO6, LiVWO6, LiVP2O7 and LiFeAs2O7 and the second crystalline substance includes at least one members selected from Bi4Ti3O12, CuNb2O6, MnTaO4, FeWO4, ZnZrNb2O8, NiNb2O6, NiZrNb2O8, FeTiNb2O8, MnTiNb2O8, MgSnNb2O8, ZnTa2O6, Cu0.85Zn0.15Nb2O6, YBa3Ti2O8.5, Zr0.75Ti0.75Sn0.5O4, HfTiO4 and MgNb2O6. The phosphorus source and the second crystalline substance have molar ratios of 1 to 0.01-0.05, taking only the phosphorus source in the material into consideration. The lithium source includes at least one members selected from lithium carbonate, lithium hydroxide, lithium oxalate and lithium acetate; the iron source includes at least one members selected from ferrous oxalate, ferrous carbonate, iron acetate, iron oxide, iron phosphate, iron pyrophosphate and iron nitrate; and the phosphate source includes at least one members selected from ammonium phosphate, ammonium dihydrogen phosphate, ammonium, iron phosphate, phosphoric acid and lithium dihydrogen phosphate. EXAMPLE - A manganese carbonate (MnCO3), titanium dioxide (TiO2) and niobium pentaoxide (Nb2O5) was mixed in a molar ratio of 1:1:1, grounded in a ball mill for 5 hours, heated in a nitrogen atmosphere at 10-500 degrees C and continued sintering the product for 10 hours. An X-ray diffraction (XRD) pattern was carried out on the resulting product and determined that the sintered product was manganese titanium niobium oxide (MnTiNb2O8). The lithium iron phosphate (LiFePO4) was mixed with the MnTiNb2O8 in a molar ratio of 1:0.04, and starch was added as a source of carbon. The LiFePO4 was prepared by mixing lithium carbonate, ferrous oxalate, and ammonium dihydrogen phosphate in a Li:Fe:P molar ratio of 1:1:1. The mixture was grounded in a ball mill for 10 hours, removed and dried at 80 degrees C. The powder was heated in a nitrogen or argon atmosphere at 10-600 degrees C, continued sintering for 20 hours to give a LiFePO4/MnTiNb2O8/C mixed crystal form of a cathode active material.