WO2010051749A1

WO2010051749A1 - Method of preparing cathode active material and method of forming lithium secondary battery

Info

Publication number: WO2010051749A1
Application number: PCT/CN2009/074774
Authority: WO
Inventors: Ye Tian; Tangli Cheng; Xiaobing Xi
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2008-11-05
Filing date: 2009-11-03
Publication date: 2010-05-14
Anticipated expiration: 2011-05-05
Also published as: WO2010051746A1

Abstract

A method of preparing a cathode active material comprising a mixed crystal is provided. The method comprises the following steps: (1) providing a first crystalline substance having one or more members with general formulas Li_xM’_y(XO₄)_z, LiM’_XO₅, LiM’XO₆ and LiM’X₂O₇; (2) providing a second crystalline substance having one or more members with a general formula A_aM_bN_cO_d; and sintering the two crystalline substances to provide the mixed crystal. Further, a method of preparing a lithium secondary battery is provided. According to the cathode active material prepared by the method, the electrical property is superior, which enhances the duration and performance of a lithium secondary battery.

Description

METHOD OF PREPARING CATHODE ACTIVE MATERIAL AND METHOD OF FORMING LITHIUM SECONDARY BATTGERY

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Patent Application No. 200810173652.X, filed on November 5, 2008, which is hereby incorporated by reference in its entirety.

This application claims priority to Chinese Patent Application No. 200810175243.3, filed on November 6, 2008, which is hereby incorporated by reference in its entirety.

This application claims priority to Chinese Patent Application No. 200810189238.8, filed on December 26, 2008, which is hereby incorporated by reference in its entirety. This application claims priority to Chinese Patent Application No.

200810189233.5, filed on December 26, 2008, which is hereby incorporated by reference in its entirety.

This application claims priority to Chinese Patent Application No. 200810189235.4, filed on December 26, 2008, which is hereby incorporated by reference in its entirety.

This application claims priority to U.S. Patent Application No. 12/316,180, filed on December 9, 2008, which is hereby incorporated by reference in its entirety.

This application claims to U.S. Patent Application No. 12/316,165, filed on December 9, 2008, which is hereby incorporated by reference in its entirety. FIELD OF THE INVENTION

The present invention relates to rechargeable batteries, more specifically, to a composite compound having a mixed crystalline structure that can be used as a cathode material for lithium secondary batteries.

BACKGROUND OF THE RELATED ART

Lithium secondary batteries are widely used in various devices such as laptop computers, cameras, camcorders, PDAs, cell phones, iPods and other portable electronic devices. These batteries are also growing in popularity for defense, automotive and aerospace applications because of high energy density thereof.

Presently, to enhance the electrical properties of lithium secondary batteries, the high valence metal is used for coating and doping. A cathode material for lithium battery is disclosed in U.S. Pat. Application No. 2007/0207385A1 including a first compound and a second compound. The first compound has a formula of A_3xMl_2y(Pθ₄)₃ . The second compound is at least one compound selected from the group consisting of SiC, BN and metal oxide having a formula of M2_aO_b, coating on the first compound. And A is at least one element selected from the group consisting of Groups IA, HA and IIIA. Each of the Ml and M2 is selected from at least one element from Groups HA, IIIA, IVA and VA and transition metal elements, respectively. More specifically, each of the Ml and M2 is at least one element selected from the group consisting Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Be, Mg, Ca, Sr, B, Al, Sn, Ga, In, Si and Ge. And the material of LiFePO₄/ZnO/C, LiFeP0₄/ZnA10₂/C, LiFePO₄/CuO/C and LiFePO₄/ZnAlO/C are disclosed in the examples of the application. The electrical properties of the coated cathode material have been enhanced, but the electrical conductivity is still too low, approximately at about 10^~5 S/cm, and the battery prepared by using such cathode material has poor specific capacity and cycle performance. SUMMARY OF THE INVENTION

In viewing thereof, the present invention needs to provide a method of forming a cathode active material, which has a novel crystal structure that may enhance electrical properties of the battery significantly. Further, the present invention needs to provide a method of providing a lithium ion secondary battery having a cathode made therefrom.

According to an embodiment of the invention, a method of preparing a cathode active material comprising a mixed crystal is provided. The method may comprise the following steps: (1) providing a first crystalline substance having one or more members with general formulas Li_xM'_y(Xθ₄)_z, LiM'XOs, LiM'XO_ό and LiM⁵X₂O₇, in which 0<x/z<l and 0<y/z<l . l; M' may be an element selected from a group consisting of Na, Mn, Fe, Co, Ni, Ti, V, Y, Mg, Ca, Nb and Zn; X may be an element selected from a group consisting of P, S, As, Mo and W; (2) providing a second crystalline substance having one or more members with a general formula A_aM_bN_cO_d, in which A, M and N may be different metals selected from groups HA,

IIIA, IVA, VA, IB, HB, IIIB, IVB, VB, VIB, VIIB and VIII in the periodic table, and 0<a<6, 0<b<6, 0<c<6 and 0<d<12, in which a and b cannot be zero at the same time; and (3) sintering the two crystalline substances to provide the mixed crystal.

According to another embodiment of the invention, a method of preparing a cathode active material comprising a mixed crystal is provided. The method may comprise the following steps: (1) providing a first material having a combination of lithium, iron and phosphorous sources; (2) providing a second material having one or more members with a general formula A_aM_bN_cO_d, in which A, M and N may be different metals selected from groups HA, IIIA, IVA, VA, IB, HB, IIIB, IVB, VB, VIB, VIIB and VIII of the periodic table; and 0<a<6, 0<b<6, 0<c<6 and 0<d<12; a and b cannot both be zero at the same time; and (3) sintering the two materials to provide the mixed crystal.

According to still another embodiment of the invention, a method of forming a lithium secondary battery is provided. The method comprises the following steps: (1) providing electrodes having a cathode, an anode and a divider film which are wounded or stacked, the cathode comprising the cathode active material by the method as described above; and (2) providing a battery shell and electrolyte, the electrodes and the electrolyte being sealed within the battery shell. The present invention, for the first time, successfully provides preparing a lithium metal intercalation compound with a mixed crystal. With the mixed crystalline structure, the novel cathode material disclosed in the present invention significantly improves electrical properties of lithium batteries.

Other variations, embodiments and features of the present invention will become evident from the following detailed description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the invention will become apparent and more readily appreciated from the following descriptions taken in conjunction with the drawings in which:

Fig. 1 shows a XRD pattern of a composite compound according to Example i;

Fig. 2 shows a XRD pattern of a composite compound according to Example 2; Fig. 3 shows a XRD pattern of a composite compound according to Example

3;

Fig. 4 shows a XRD pattern of a composite compound according to Example

4;

Fig. 5 shows a XRD pattern of a composite compound according to Example 5; and

Fig. 6 shows a XRD pattern of a composite compound according to Example 6. DETAILED DESCRIPTION OF THE INVENTION

It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive.

Generally, a mixed crystal can be referred to as a solid solution. It is a crystal containing a second constituent, which fits into and is distributed in the lattice of the host crystal. See_ IUPAC Compendium of Chemical Terminology 2nd Edition (1997) . Mixed crystals have been used in semiconductors for enhancing light output in light emitting diodes (LEDs). They have also been used to produce sodium-based electrolyte for galvanic elements.

The current invention is the first time that a mixed crystal has been successfully prepared for lithium metal intercalation compounds. It is also the first time that a mixed crystalline structure has been used as a cathode material for lithium secondary batteries. The new cathode material disclosed in the present invention has significantly better electrical properties than traditional cathode materials.

The description thereof will be described in detail with reference to accompanying figures. A cathode active material can be provided having a mixed crystal structure.

The mixed crystal structure may have: a first crystalline substance having one or more members with the general formulas Li_xM'_y(X0₄)_z, LiM⁵XO₅, LiM⁵XO₆ and LiM⁵X₂O₇, in which:

0<x/z<l and O≤y/z≤l . l ; M⁵ may be an element selected from the group of Na, Mn, Fe, Co, Ni, Ti, V, Y,

Mg, Ca, Nb and Zn;

X may be an element selected from the group of P, S, As, Mo and W; and a second crystalline substance having one or more members with the general formula A_aM_bN_c0d, in which: A, M and N are different metals selected from groups HA, IIIA, IVA, VA, IB, HB, IIIB, IVB, VB, VIB, VIIB and VIII in the periodic table; and

0<a<6, 0<b<6, 0<c<6 and 0<d<12 excepting for a = b = zero, i.e., a and b cannot both be zero at the same time. And the cathode active material may have electrical conductivity of about 0.01

S/cm to about 10 S/cm at about 25 ⁰C.

The mixed crystal structure can be formed by sintering two or more compounds, the intermediary mixture having oxygen vacancies or metallic crystalline structures. The two or more compounds do not exhibit any major chemical reactions when mixed together. However, upon sintering, a large number of crystalline defects can be formed, thereby altering the electronic states of the compounds creating a large number of oxygen vacancies. These oxygen vacancies provide the needed carriers, thus greatly enhancing the electrical conductivity of the mixed crystal. Accordingly, the cathode active material can achieve electrical conductivity of about 0.1 S/cm to 2S/cm at about 25°C with a Simens per centimeter, which is larger than traditional lithium iron phosphate cathode active materials. According to an embodiment of the invention, the first crystalline substance and the second crystalline substance may have a molar ratio of about 1 : 0.01-0.05. The first crystalline substance can have a mixed crystalline structure with the general formula Li_xM'_y(XO₄)_z including one or more members selected from the group consisting of LiFeO₄, LiMnPO₄ and LiCoPO₄ etc. In other embodiments, single-crystalline structures including Li₃Fe₂(PO₄)_S, LiTi₂(PO₄)₃, Li₃V₂(PO₄)₃ and Li₂Na V₂(PO₄)₃ may be incorporated. For the general formula LiM'XOs, the first crystalline substance can be LiTiPOs. For the general formula LiM'XO_ό, the first crystalline substance can include LiVMoOo and LiVWOό respectively. For the general formula LiM⁵X₂O₇, the first crystalline substance can include LiVP₂O₇ and LiFeAs₂O₇. In the mixed crystalline structure with the general formula Li_xM'_y(Xθ₄)_z, M' may include element Fe and one or more members selected form the group consisting of Mn, Co, Ni, Ti, Y, Mg, Ca and Zn, and the amount of Fe is from 90 % to 100 % by molar. Then the first crystalline substance can include one or more members selected from LiFePO₄, Li_{0 99}Y_{0 01}FePO₄ and LiR₁Fe_I-1PO₄, in which 0<i<0.1, R may be one or more members selected from Mn, Co, Ni, Ti, Mg, Ca and Zn.

The second crystalline substance can include one or more members selected from the group consisting of Bi₄Ti₃Oi₂, CuNb₂O₆, MnTaO₄, FeWO₄, ZnZrNb₂O₈, NiNb₂O₆, NiZrNb₂O₈, FeTiNb₂O₈, MnTiNb₂O₈, MgSnNb₂O₈, ZnTa₂O₆, Cu₀ S₅Zn₀ 15Nb₂O₆, YBa₃Ti₂O₈5, Zr₀75Ti₀75Sn₀5O4, HfTiO₄ and MgNb₂O₆.

The mixed crystal structure can further include carbon, which is about 1-5 % of the mixed crystal structure by weight. The carbon can further enhance the electrical conductivity of the mixed crystal. According to an embodiment of the invention, a method of preparing a cathode active material for lithium secondary batteries is provided, comprising the following steps:

Providing a first material having one or more members with the general formulas Li_xM'_y(X0₄)_z, LiM⁵XO₅, LiM⁵XO₆ and LiM⁵X₂O₇, in which: 0<x/z<l and 0<y/z<l .l; M⁵ is selected from elements Na, Mn, Fe, Co, Ni, Ti, V, Y, Mg, Ca, Nb and Zn; X is selected from elements P, S, As, Mo and W;

Providing a second material having one or more members with the general formulas A_aM_bN_cO_d, in which: A, M and N are different metals selected from groups IIA, IIIA, IVA, VA, IB, HB, IIIB, IVB, VB, VIB, VIIB and VIII in the periodic table; 0<a<6, 0<b<6, 0<c<6 and 0<d<12; a and b cannot both be O at the same time; and

Sintering the two materials to provide a mixed crystal.

The first material and the second material may have a molar ratio of about 1 to 0.01-0.05. In one embodiment, the second material can be formed by heating oxide compounds of A, M and N with a molar ratio of a : b : c at about 400 to 1000 ⁰C for about 8 to 15 hours. The sintered product can be measured with a Rigaku D/MAX-2200/PC x-ray diffraction (XRD) instrument to acquire an XRD pattern thereof, which can subsequently be compared with known chemical standards provided by the system. The oxide compound or oxygen-containing compound of A can be oxides of A and/or sintered products of oxides of A and other compounds, the oxides of A and other compounds include hydroxides of A, carbonates of A, and bicarbonates of A. Likewise, the oxide compound or oxygen-containing compound of M can be oxides of M and/or sintered products of oxides of M and other compounds, the oxides of M and other compounds include hydroxides of M, carbonates of M, and bicarbonates of M. Similarly, the oxide compound or oxygen-containing compound of N can be oxides of N and/or sintered products of oxides of N and other compounds, the oxides of N and other compounds include hydroxides of N, carbonates of N, and bicarbonates of N.

In some embodiments, the first material may include one or more members selected from the group consisting of LiFePO₄, LiMnPO₄, LiCoPO₄, Li₃Fe₂(PO₄)₃, LiTi₂(PO₄)₃, Li₃V₂(PO₄),, Li₂NaV₂(PO₄),, Li_{0 99}Yo OiFePO₄, LiR₁FeJ_-1PO₄, LiTiPO₅, LiVMoO₆, LiVWO₆, LiVP₂O₇ and LiFeAs₂O₇ in which 0<i<0.1, R is one or more members selected from elements Mn, Co, Ni, Ti, Mg, Ca and Zn. In other embodiments, the first material may include one or more members selected from LiFePO₄, Li_{0 99}Y₀01FePO₄ and LiR₁FeI_-1PO₄.

The second material can include one or more members selected from the group consisting of Bi₄Ti₃Oi₂, CuNb₂O₆, MnTaO₄, FeWO₄, ZnZrNb₂Og, NiNb₂O₆, NiZrNb₂O₈, FeTiNb₂O₈, MnTiNb₂O₈, MgSnNb₂O₈, ZnTa₂O₆, Cu_{0 85}Zn_{0 I5}Nb₂O₆, YBa₃Ti₂O_{8 5}, Zr_{0 75}Ti_{0 75}Sn_{0 5}O₄, HfTiO₄ and MgNb₂O₆.

In some embodiments, the method may further comprise sintering a carbon additive into the two crystalline substances, the carbon additive capable of providing the mixed crystal with about 1-5 % of carbon by weight. The carbon additive includes one or more members selected from the group consisting of carbon black, acetylene black, graphite, glucose, sucrose, citric acid, starch, dextrin, polyethylene glycol, and other organic and inorganic sources. However, it should be noted that the examples are for illustration purpose rather than for limitation. A person skilled in the art can use equivalents thereof to achieve the same as described herein.

And a heating rate of the sintering step ranges from about 5⁰C to 20 ⁰C per minute, a sintering temperature thereof from about 500 ⁰C to 800 ⁰C, and a sintering time thereof from about 5 hours to 32 hours. The sintering atmosphere is chose according the selected materials. For example, when the first or second material is easily oxidized, the sintering atmosphere may be inert atmosphere or reduction atmosphere; and when the first or second material is not easily oxidized, the sintering atmosphere may be any atmosphere.

In another embodiment, a method of preparing a cathode active material for a lithium secondary battery is provided. However, the method thereof is not limited for use in a lithium secondary battery. A person normally skilled in the art can apply the solution in the present invention to other rechargeable batteries, thus the description hereinafter is for illustrative purpose rather than for limitation. The method thereof may comprise: Providing a first material having a combination of lithium, iron and phosphorous sources;

Providing a second material having one or more members with the general formulas A_aM_bN_cO_d, in which A, M and N may be different metals selected from groups HA, IIIA, IVA, VA, IB, HB, IIIB, IVB, VB, VIB, VIIB and VIII of the periodic table; 0<a<6, 0<b<6, 0<c<6 and 0<d<12 except for the case where a and b equal to zero at the same time, i.e., a and b cannot both be zero at the same time; and

Sintering the two materials to provide a mixed crystal. The lithium, iron and phosphorous (Li : Fe : P) sources may have a molar ratio of about 0.95-1.1 : 1 : 0.95-1.1, and the first material and the second material may have a molar ratio of about 1 to 0.01-0.05.

In some embodiments, the lithium source may include one or more members selected from the group consisting of lithium carbonate, lithium hydroxide, lithium oxalate and lithium acetate; the iron source may include one or more members selected from the group consisting of ferrous oxalate, ferrous carbonate, iron acetate, iron oxide, iron phosphate, iron pyrophosphate and iron nitrate; and the phosphate source may include one or more members selected from the group consisting of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, phosphoric acid and lithium dihydrogen phosphate.

In one embodiment, the second material may be formed by heating oxide compounds of A, M and N at a molar ratio of a : b : c at about 400⁰C to 1000 ⁰C for about 8 hours to 15 hours. The sintered product can be measured with a Rigaku D/MAX-2200/PC x-ray diffraction (XRD) instrument to acquire an XRD pattern, which can subsequently be compared with known chemical standards provided by the instrument. The oxide compound or oxygen-containing compound of A can be oxides of A and/or sintered products of oxides of A and other compounds, the oxides of A and other compounds include hydroxides of A, carbonates of A, and bicarbonates of A. Likewise, the oxide compound or oxygen-containing compound of M can be oxides of M and/or sintered products of oxides of M and other compounds, the oxides of M and other compounds include hydroxides of M, carbonates of M, and bicarbonates of M. Similarly, the oxide compound or oxygen-containing compound of N can be oxides of N and/or sintered products of oxides of N and other compounds, the oxides of N and other compounds include hydroxides of N, carbonates of N, and bicarbonates of N.

The second material can include one or more members selected from a group consisting of Bi₄Ti₃Oj₂, CuNb₂O₆, MnTaO₄, FeWO₄, ZnZrNb₂O₈, NiNb₂O₆, NiZrNb₂O₈, FeTiNb₂O₈, MnTiNb₂O₈, MgSnNb₂O₈, ZnTa₂O₆, Cu_{0 85}Zn₀ I₅Nb₂O₆, YBa₃Ti₂O_{8 5}, Zr_{0 75}Ti_{0 75}Sn_{0 5}O₄, HfTiO₄ and MgNb₂O₆.

In some embodiments, the method further comprises sintering a carbon additive with the two crystalline substances, the carbon additive capable of providing the mixed crystal with about 1-5 % carbon by weight. The carbon additive may include one or more members selected from the group consisting of carbon black, acetylene black, graphite, glucose, sucrose, citric acid, starch, dextrin, polyethylene glycol, and other organic and inorganic sources.

And the sintering step may have a heating rate of from about 5⁰C to 20 ⁰C per minute, a sintering temperature of from about 500 ⁰C to 800 ⁰C, and a sintering time of from about 5 hours to 32 hours. The sintering atmosphere is selected according to the chosen different materials. For example, when the first or second material is easily oxidized, the sintering atmosphere may be an inert or reducing one. When the first or second material is not easily oxidized, the sintering atmosphere may be any atmosphere known in the art.

According to another embodiment of the invention, a lithium ion secondary battery may be provided, the lithium ion secondary battery having a battery shell, electrodes and electrolyte, the electrodes and electrolyte being sealed within the battery shell, the electrodes having wounded or stacked cathode, anode and divider film, the cathode further including the cathode active materials described above.

The cathode may include cathode components such as the cathode active materials described above with adhesives. The adhesives can be hydrophobic or hydrophilic binding additives without any specific binder ratio restrictions. In one instance, the hydrophilic to hydrophobic adhesive binder can have weight ratios of about 0.3 : 1 to about 1 : 1. The adhesive can be solid, aqueous or as an emulsion. The concentration can be adjusted accordingly based on methods of preparing the cathode, anode and the slurry viscosity and coating. In one example, the hydrophilic adhesive solution has a concentration of about 0.5 to 4 weight percent while the hydrophobic latex binder has a concentration of about 10 to 80 weight percent.

Hydrophobic adhesives can include PTFE, styrene butadiene rubber, or mixtures thereof. Hydrophilic adhesives can include HPMC, CMC, hydroxyethyl cellulose, polyvinyl alcohol, or mixtures thereof. The binder content can be about 0.01% to 8 % by weight of the total cathode active material.

In addition, conductive agents may be incorporated or added in the cathode active material, the conductive agents include, but without limitation, graphite, carbon fiber, carbon black, metal powders and fibers as well as any suitable material understood by one skilled in the art. The conductive agent can be about 0.1% to 20 % by weight of the total cathode active material.

The method of preparing the cathode include using solvents to dissolve the cathode active material and mixing with adhesives and conductive agents to form a cathode slurry. The cathode slurry can be applied onto cathode collectors, dried, rolled or compressed, and sliced into pieces to produce the cathode. In one example, the slurry can be dried at about 100 ⁰C to 150 ⁰C for about 2 hours to 10 hours. The cathode collectors include aluminum foil, copper foil, nickel-plated steel or punched stainless steel. The types of solvent to use include N-methyl pyrrolidone (NMP), dimethylformamide (DMF), diethyl formamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, alcohol and mixtures thereof. The amount of solvent to use can be adjusted accordingly to provide the proper slurry coating and viscosity, hi one instance, the amount of solvent can be about 40% to 90 % by weight of the cathode active material. The method of preparing the cathode and types of solvents, adhesives, conductive agents and cathode collectors can also incorporate other techniques understood by one skilled in the art.

As discussed above, the lithium secondary battery includes a battery shell, electrodes and electrolyte, the electrodes and electrolyte capable of being sealed within the battery shell. The electrodes may include wounded or stacked cathode, anode and divider film with the cathode utilizing the cathode active material of the presently disclosed embodiments.

The divider film can be situated between the cathode and anode for preventing electrical shortcuts and for maintaining the electrolytic solution. In one instance, the divider film can include any membrane including, but without limitation, micro-porous membrane polyolefin, polyethylene fibers, ultra-fine glass fibers and fiber paper.

The anode can incorporate any anode active materials and known methods of forming such materials as known in the arts. The anode active material can be provided in slurry form and coated onto anode collectors similar to the cathode collectors above. Additionally, the anode active material may include carbon additives such as non-carbon graphite, graphite, and polymers having undergone high-temperature carbon oxidation. The carbon additive can also include pyrolytic coal, coke, organic polymer sintered materials and activated carbons. The organic polymer sintered materials include phenolic resin, epoxy resin, and carbonized products obtained by sintering.

Adhesives can utilize traditional adhesives for lithium secondary batteries including polyvinyl alcohol, PTFE, carboxymethyl cellulose (CMC), hydroxymethyl cellulose (HMC), and styrene butadiene rubber (SBR). The adhesive binder can be about 0.5 to 8 weight percent of the total anode active material.

The anode active material can further include conductive agents, the conductive agent capable of increasing electrical conductivity and reducing internal resistance of the battery. The conductive agent may include, but without limitation to, carbon black, nickel powder and copper powder etc. Other conductive agents known by one skilled in the art may also be utilized and can be about 0.1 to 12 weight percent of the anode active material.

The method of preparing the anode includes: using solvents to dissolve the anode active material and mixing with adhesives and conductive agents to form anode slurry. The anode slurry can be applied onto the anode collectors similar to that of the cathode slurry described above, dried, rolled or compressed, and sliced into pieces to produce the anode. In one example, the slurry can be dried at about 100⁰C to 150 ⁰C for about 2 hours to 10 hours. The types of solvent for dissolving the anode active material include N-methyl pyrrolidone (NMP), dimethylformamide (DMF), diethyl formamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, alcohol and mixtures thereof. The amount and concentration of solvents to use can be adjusted accordingly to provide the proper slurry coating and viscosity. Like the cathode slurry, the amount of anode slurry applied to the anode collector can be about 40 to 90 weight percent of the anode active material.

The electrolyte for the lithium secondary battery can be a non-aqueous electrolyte, which can be formed by dissolving lithium salt in a non-aqueous solvent. The lithium salt electrolyte can include one or more members selected from lithium hexafluorophosphate (LiPF₆), lithium perchlorate (LiClO₄), lithium tetrafluoroborate (LiBF₄), lithium hexafluoroarsenate (LiAsF₆), lithium hexafluorosilicate (LiSiF₆), lithium tetraphenylborate (LiB(C₆H₅)₄), lithium chloride (LiCl), lithium bromide (LiBr), lithium aluminum tetrachloride (LiAlCl₄), LiC(So₂CF₃)₃, LiCH₃SO₃, and LiN(SO₂CF₃)₂. The non-aqueous solvent can be chain ester and ester ring mixed solution, the chain ester being one or more members of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), dimethylpropyl carbonate (DPC) and other fluoride or sulfur-containing unsaturated key chain organic esters, with the ester ring being one or more members of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), gamma-butyrolactone (γ-BL), sodium fluoride and other lactone-containing or unsaturated organic ester rings. In one instance, the lithium salt electrolyte has a concentration of about 0.1 to 2 mole per liter. The presently disclosed lithium secondary batteries can be provided by processes known by one skilled in the art. The preparation method may include winding or stacking cathode, anode and divider films into the battery core, and placing the battery core into the battery shell, adding the electrolyte, and sealing the battery accordingly. The winding, stacking and sealing of the batteries can utilize traditional techniques as understood by one skilled in the art. Furthermore, other known steps of manufacturing the lithium secondary battery can be incorporated.

The following will describe various embodiments of mixed-crystal cathode active materials according to the presently disclosed invention. EXAMPLE 1

Firstly, Mix MnCO₃, TiO₂ and Nb₂Os with a molar ratio of 1 : 1 : 1, grind the mixture in a ball mill for 5 hours, heat in a nitrogen atmosphere at 10 ⁰C per minute to 500 ⁰C and continue sintering the product for 10 hours. With a Rigaku D/MAX-2200/PC, an XRD pattern is obtained on the resulting product. In comparison with the standard XRD pattern for MnTiNb₂Og, it is determined that the sintered product is MnTiNb₂O₈.

Mix LiFePO₄ with the resulting MnTiNb₂Os from above in a molar ratio of 1 : 0.04, add starch as a source of carbon (amount of carbon capable of providing 5 wt% of carbon content in the final product). In one example, the LiFePO₄ can be prepared by mixing lithium carbonate, ferrous oxalate, and ammonium dihydrogen phosphate in a Li : Fe : P molar ratio of 1 : 1 : 1. Alternatively, the LiFePO₄ can be prepared by other lithium, iron and phosphate sources or by a third party.

Grind the mixture in a ball mill for 10 hours, remove and dry at 80 ⁰C. Heat the resulting powder in a nitrogen or argon atmosphere at 10 ⁰C per minute to 600 ⁰C, continue sintering the product for 20 hours to provide a LiFePO₄ / MnTiNb₂Og / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material as shown in Fig. 1. Looking at diffraction peaks of the sintered product, except for peaks corresponding to LiFePO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiFePO₄ and MnTiNb₂Og exist in two phases and that no new compound is created. Accordingly, this pattern demonstrates that the process described above provides a cathode active material having LiFePO₄ / MnTiNb₂Og / C in a mixed crystalline form. EXAMPLE 2

Mix ZnO and Ta₂O₅ in a molar ratio of 1 : 1, grind the mixture in a ball mill for 5 hours, heat in an oxygen atmosphere at 15 ⁰C per minute to 800 ⁰C and continue sintering the product for 8 hours. With the Rigaku D/MAX-2200/PC, an XRD pattern can be carried out on the resulting product. And it is determined that the sintered product is ZnTa₂O₆ by comparing it with a standard XRD pattern for ZnTa₂O₆

Mix LiFePO₄ with the resulting ZnTa₂O₆ from above in a molar ratio of 1 : 0.03 with acetylene black as a source of carbon (amount of carbon capable of providing O % by weight of carbon content in the final product). The LiFePO₄ can be prepared by mixing lithium oxalate, iron oxide and diammonium hydrogen phosphate in a Li : Fe : P molar ratio of 0.95 : 1 : 1, which can be added to the ZnTa₂O₆ at a diammonium hydrogen phosphate to ZnTa₂O₆ molar ratio of 1 : 0.03 (taking into account the phosphorous components in the mixture). Alternatively, the LiFePO₄ can be prepared by other lithium, iron and phosphate sources or by a third party.

Grind the mixture in a ball mill for 10 hours, remove and dry at 80 ⁰C. Heat the resulting powder in a nitrogen or argon atmosphere at a heating rate of 5 ⁰C per minute to 500 ⁰C, continue sintering the product for 30 hours to provide a LiFePO₄ / ZnTa₂O₆ mixed crystal cathode active material. With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material as shown in Fig. 2. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiFePO₄ and ZnTa₂O₆, there is no new peak or feature which indicates that the LiFePO₄ and ZnTa₂O₆ exist in two phases and that no new compound is created. Accordingly, it is determined that the process described above provides a cathode active material having LiFePO₄ / ZnTa₂Oo in a mixed crystal form. EXAMPLE 3

Mix Y₂O₃, BaCO₃ and TiO₂ in a molar ratio of 0.5 : 3 : 2, grind the mixture in a ball mill for 5 hours, heat it in a nitrogen atmosphere at a heating rate of 7 ⁰C per minute to 1000 ⁰C and continue sintering the product for 15 hours. With the Rigaku D/MAX-2200/PC, an XRD pattern can be carried out on the resulting product. And it is determined that the sintered product is YBa₃Ti₂O_{8 S} by comparing it with a standard XRD pattern Of YBa₃Ti₂O_{8 5}. Mix LiFePO₄ with the resulting YBa₃Ti₂O_{8 5} from above in a molar ratio of 1 :

0.02 with carbon black as a source of carbon (amount of carbon capable of providing 2 wt% of carbon content in the final product). The LiFePO₄ can be prepared by mixing lithium hydroxide, ferrous carbonate and phosphoric acid in a Li : Fe : P molar ratio of 1.05 : 1 :1.05, which can be added to the YBa₃Ti₂O_{8 5} at a phosphoric acid to YBa₃Ti₂O_{8 S} molar ratio of 1 : 0.02 (taking into account the phosphorous components in the mixture). Alternatively, the LiFePO₄ can be prepared by other lithium, iron and phosphate sources or by a third party.

Grind the mixture in a ball mill for 10 hours, remove and dry at 80 ⁰C. Heat the resulting powder in a nitrogen or argon atmosphere at a heating rate of 20 ⁰C per minute to 800 ⁰C, continue sintering the product for 8 hours to provide a LiFePO₄ / YBa₃Ti₂O_{8 5} / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material as shown in Fig. 3. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiFePO₄ and YBa₃Ti₂O_{8 5}, there is no new peak or feature which indicates that the LiFePO₄ and YBa₃Ti₂O_{8 5} exist in two phases and that no new compound is created. Accordingly, it is determined that the process described above provides a cathode active material having LiFePO₄ / YBa₃Ti₂O_{8 5} / C in a mixed crystal form. EXAMPLE 4 Mix CuO, ZnO and Nb₂O₅ with a molar ratio of 0.85 : 0.15 : 1, grind the mixture in a ball mill for 5 hours, heat in a nitrogen atmosphere at a heating rate of 7 ⁰C per minute to 1000 ⁰C and continue sintering the product for 15 hours. With the Rigaku D/MAX-2200/PC, an XRD pattern can be carried out on the resulting product. And it is determined that the sintered product is Cu_{0 85}Zn_{0 15}Nb₂O₆ in comparison with the standard XRD pattern of Cu_{0 85}Zn_{0 15}Nb₂O₆.

The remaining steps incorporate those used in Example 1, with the difference being that the Cu_{0 85}Zn_{0 15}Nb₂O₆ substitutes the MnTiNb₂O₈ to provide a LiFePO₄ / Cu_{0 85}Zn_{0 15}Nb₂O₆ / C mixed crystal cathode active material. With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material as shown in Fig. 4. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiFePO₄ and Cuo ₈₅Zn_{0 15}Nb₂O₆, there is no new peak or feature, which indicates that the LiFePO₄ and Cuo ₈₅Zn_{0 15}Nb₂O₆ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiFePO₄ / Cu_{0 85}Z11_{0 I5}Nb₂O₆ / C in a mixed crystal form. EXAMPLE 5

Mix ZrO₂, TiO₂ and SnO₂ in a molar ratio of 0.75 : 0.75 : 0.5, grind the mixture in a ball mill for 5 hours, heat in a nitrogen atmosphere at a heating rate of 7 ⁰C per minute to 1000 ⁰C and continue sintering the product for 15 hours. With the Rigaku D/MAX-2200/PC, an XRD pattern can be carried out on the resulting product. In comparison with the standard XRD pattern Of Zr_{O 75}Ti_{0 75}Sn_{0 5}O₄, it is determined that the sintered product is Zr_{0 75}Ti_{0 75}Sn_{0 5}O₄.

The remaining steps are the same as those used in Example 1, with the difference being that the Zr_{0 75}Ti_{0 75}Sn_{0 5}O₄ substitutes the MnTiNb₂Os to provide a LiFePO₄ / Zr_{0 75}Ti_{0 75}Sn_{0 5}O₄ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material as shown in Fig. 5. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiFePO₄ and Zr_{0 75}Ti_{0 75}Sn_{0 5}O₄, there is no new peak or feature which indicates that the LiFePO₄ and Zr_{0 75}Tio ₇₅Sn_{0 5}θ₄ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiFePO₄ / Zr_{0 75}Tio ₇₅Sn_{0 5}O₄ / C in a mixed crystal form. EXAMPLE 6

Mix FeO and WO₃ in a molar ratio of 1 : 1 , grind the mixture in a ball mill for 5 hours, heat in an oxygen atmosphere at a heating rate of 15 ⁰C per minute to 800 ⁰C and continue sintering the product for 8 hours. With the Rigaku D/MAX-2200/PC, an XRD pattern can be carried out on the resulting product. In comparison with the standard XRD pattern for FeWO₄, it is determined that the sintered product is FeWO₄.

The remaining steps are the same as those used in Example 1, with the difference being that the FeWO₄ substitutes the MnTiNb₂Og to provide a LiFePO₄ / FeWO₄ / C mixed crystal cathode active material. With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material as shown in Fig. 6. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiFePO₄ and FeWO₄, there is no new peak or feature which indicates that the LiFePO₄ and FeWO₄ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiFePO₄ / FeWO₄ / C in a mixed crystal form. EXAMPLE 7

Mix ZnO and Al₂O₃ in a molar ratio of 2 : 1 , grind the mixture in a ball mill for 5 hours, heat in an oxygen atmosphere at 15 ⁰C per minute to 800 ⁰C and continue sintering the product for 8 hours. With the Rigaku D/MAX-2200/PC, an XRD pattern can be carried out on the resulting product. And, it is determined that the sintered product is ZnAlO₂ in comparison with the standard XRD pattern for ZnAlO₂. The remaining steps are the same as those used in Example 1, with the difference being that the ZnAlO₂ substitutes the MnTiNb₂Og to provide a LiFePO₄ / ZnAlO₂ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Upon examination of the diffraction peaks of the sintered product, except for peaks corresponding to LiFePO₄ and ZnAlO₂, there is no new peak or feature which indicates that the LiFePO₄ and ZnAlO₂ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiFePO₄ / ZnAlO₂ / C in a mixed crystal form.

EXAMPLE 8

According to the disclosed method of "A Method of Preparing Lithium Battery Cathode Active Material Li_{0 99} Yo ₀₁FePO₄" (JOURNAL OF FUNCTIONAL MATERIALS, VOLUME 36, ISSUE 5 (2005)) to prepare Li₀99 Yo 0₁FePO₄. The steps are similar to those used in Example 1, with the difference being that the Li_{0 99} Yo ₀₁FePO₄ substitutes the LiFePO₄ to provide a Li_{0 99} YQ ₀₁FePO₄ / MnTiNb₂O₈ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to Li_{0 99} Yo ₀₁FePO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the Li_{0 99} Yo ₀₁FePO₄ and MnTiNb₂O₈ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having Li_{0 99} Yo ₀₁FePO₄ / MnTiNb₂O₈ / C in a mixed crystal form. EXAMPLE 9

According to the disclosed method of "The Preparation and Performance of Lithium Battery Cathode Active Material LiNi_{0 I}Fe_{0 9}PO₄" (THE CHINESE JOURNAL OF NONFERROUS METALS, VOLUME 16, ISSUE 4 (Apr. 2006)) to prepare LiTi_{0 05}Fe_{0 95}PO₄. Mix Li₂CO₃, FeC₂O₄-2H₂O, NH₄H₂PO₄ and TiO₂ in a molar ratio to the stoichiometry of LiTi_{0 05}Fe_O QsPO₄. Grind the mixture in a ball mill with ethanol for 5 hours, remove and dry at room temperature. And then heat in an argon atmosphere at 320 ⁰C for 7 hours; continue sintering the product for 24 hours at 700 ⁰C to provide LiTi_{0 05}Fe_{0 95}PO₄. The steps are similar to those used in Example 1, with the difference being that the LiTi_{0 05}Fe_{0 95}PO₄ substitutes the LiFePO₄ to provide a LiTi_{0 05}Fe_{0 95}PO₄ / MnTiNb₂O₈ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiTi_{0 05}Fe_{0 95}PO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiTi_{0 05}Fe_{0 95}PO₄ and MnTiNb₂O₈ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiTi_{0 05}Fe_{0 95}PO₄ / MnTiNb₂O₈ / C in a mixed crystal form. EXAMPLE 10

According to the disclosed method of "The Preparation and Performance of Lithium Battery Cathode Active Material LiNi_{0 1}Fe_{0 9}PO₄" (THE CHINESE JOURNAL OF NONFERROUS METALS, VOLUME 16, ISSUE 4 (Apr. 2006)) to prepare LiNi₀ 1Fe_{0 9}PO₄. Mix Li₂CO₃, FeC₂O₄-2H₂O, NH₄H₂PO₄ and Ni(CH₃COO)₂-4H₂O in a molar ratio to the stoichiometry of LiNi_{0 1}Fe_{0 9}PO₄.

Grind the mixture in a ball mill with ethanol for 5 hours, remove and dry at room temperature. And then heat in an argon atmosphere at 320 ⁰C for 7 hours; continue sintering the product for 24 hours at 700 ⁰C to provide LiNi_{0 1}Fe_{0 9}PO₄.

The steps are similar to those used in Example 1, with the difference being that the LiNi_{0 1}Fe_{0 9}PO₄ substitutes the LiFePO₄ to provide a LiNi_{0 1}Fe_{0 9}PO₄ / MnTiNb₂O₈ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiNi_{0 1}Fe_{0 9}PO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiNio iFeo 9PO₄ and MnTiNb₂Og exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiNio iFeo 9PO₄ / MnTiNb₂Og / C in a mixed crystal form. EXAMPLE I l

According to the disclosed method of "The Preparation and Performance of Lithium Battery Cathode Active Material LiNi_{0 I}Fe_{0 9}PO₄" (THE CHINESE JOURNAL OF NONFERROUS METALS, VOLUME 16, ISSUE 4 (Apr. 2006)) to prepare LiCo_{0 O}iFe_{o 99}PO₄. Mix Li₂CO₃, FeC₂O₄-2H₂O, NH₄H₂PO₄ and CoO in a molar ratio to the stoichiometry of LiCo_{0 O}iFe_{o 99}PO₄. Grind the mixture in a ball mill with ethanol for 5 hours, remove and dry at room temperature. And then heat in an argon atmosphere at 320 ⁰C for 7 hours; continue sintering the product for 24 hours at 700 ⁰C to provide LiCo_{0 O}iFe_{o 99}PO₄.

The steps are similar to those used in Example 1, with the difference being that the LiCo_{0 O}iFe_{o 99}PO₄ substitutes the LiFePO₄ to provide a LiCo_{0 O}iFe_{o 99}PO₄ / MnTiNb₂O₈ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiCo_{0 O}iFe_{o 99}PO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiCo_{0 O}iFe_{o 99}PO₄ and MnTiNb₂O₈ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiCo_{0 O}iFe_{o 99}PO₄ / MnTiNb₂O₈ / C in a mixed crystal form. EXAMPLE 12 According to the disclosed method of "The Preparation and Performance of

Lithium Battery Cathode Active Material LiNi_{0 1}Fe_{0 9}PO₄" (THE CHINESE JOURNAL OF NONFERROUS METALS, VOLUME 16, ISSUE 4 (Apr. 2006)) to prepare LiMn_{0 02}Fe_{0 98}PO₄. Mix Li₂CO₃, FeC₂O₄-2H₂O, NH₄H₂PO₄ and MnCO₃ in a molar ratio to the stoichiometry of LiMn_{0 02}Fe_{0 98}PO₄. Grind the mixture in a ball mill with ethanol for 5 hours, remove and dry at room temperature. And then heat in an argon atmosphere at 320 ⁰C for 7 hours; continue sintering the product for 24 hours at 700 ⁰C to provide LiMn₀02Fe₀98PO4.

The steps are similar to those used in Example 1, with the difference being that the LiMn_{0 02}Fe_{0 98}PO₄ substitutes the LiFePO₄ to provide a LiMn_{0 02}Fe_{0 98}PO₄ / MnTiNb₂O₈ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiMn_{0 02}Fe_{0 98}PO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiMn_{0 02}Fe_{0 98}PO₄ and MnTiNb₂O₈ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiMn_{0 02}Fe_{0 98}PO₄ / MnTiNb₂O₈ / C in a mixed crystal form.

EXAMPLE 13 According to the disclosed method of "The Preparation and Performance of

Lithium Battery Cathode Active Material LiNi_{0 I}Fe_{0 9}PO₄" (THE CHINESE JOURNAL OF NONFERROUS METALS, VOLUME 16, ISSUE 4 (Apr. 2006)) to prepare LiMg_{0 03}Fe_{0 97}PO₄. Mix Li₂CO₃, FeC₂O₄-2H₂O, NH₄H₂PO₄ and MgO in a molar ratio to the stoichiometry of LiMg_{0 03}Fe_{0 97}PO₄. Grind the mixture in a ball mill with ethanol for 5 hours, remove and dry at room temperature. And then heat in an argon atmosphere at 320 ⁰C for 7 hours; continue sintering the product for 24 hours at 700 ⁰C to provide LiMg_{0 03}Fe_{0 97}PO₄.

The steps are similar to those used in Example 1, with the difference being that the LiMg_{0 03}Fe_{0 97}PO₄ substitutes the LiFePO₄ to provide a LiNi_{0 1}Fe_{0 9}PO₄ / MnTiNb₂O₈ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiMg_{0 03}Fe_{0 97}PO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiMg_{0 03}Fe_{0 97}PO₄ and MnTiNb₂O₈ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiMg₀03Fe₀97PO4 / MnTiNb₂Og / C in a mixed crystal form.

EXAMPLE 14 According to the disclosed method of "The Preparation and Performance of

Lithium Battery Cathode Active Material LiNi₀ IFe_{0 9}PO₄" (THE CHINESE JOURNAL OF NONFERROUS METALS, VOLUME 16, ISSUE 4 (Apr. 2006)) to prepare LiCa_{0 05}Fe₀95PO4. Mix Li₂CO₃, FeC₂O₄-2H₂O, NH₄H₂PO₄ and CaO in a molar ratio to the stoichiometry of LiCa_{0 05}Fe₀ ^PO₄. Grind the mixture in a ball mill with ethanol for 5 hours, remove and dry at room temperature. And then heat in an argon atmosphere at 320 ⁰C for 7 hours; continue sintering the product for 24 hours at 700 ⁰C to provide LiCa_{0 05}Fe_{0 95}PO₄.

The steps are similar to those used in Example 1, with the difference being that the LiCa_{0 05}Fe₀ ^PO₄ substitutes the LiFePO₄ to provide a LiCa_{0 05}Fe₀ ^PO₄ / MnTiNb₂Os / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiCa_{0 05}Fe₀ ^PO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiCa_{0 05}Fe₀ ^PO₄ and MnTiNb₂O₈ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiCa_{0 05}Fe₀ ^PO₄ / MnTiNb₂O₈ / C in a mixed crystal form. EXAMPLE 15

According to the disclosed method of "The Preparation and Performance of Lithium Battery Cathode Active Material LiNi_{0 1}Fe_{0 9}PO₄" (THE CHINESE JOURNAL OF NONFERROUS METALS, VOLUME 16, ISSUE 4 (Apr. 2006)) to prepare LiZn_{0 07}Fe_{0 93}PO₄. Mix Li₂CO₃, FeC₂O₄-2H₂O, NH₄H₂PO₄ and ZnCO₃ in a molar ratio to the stoichiometry Of LiZn_{0 07}Fe_{0 93}PO₄. Grind the mixture in a ball mill with ethanol for 5 hours, remove and dry at room temperature. And then heat in an argon atmosphere at 320 ⁰C for 7 hours; continue sintering the product for 24 hours at 700 ⁰C to provide LiZn_{0 07}Fe_{0 93}PO₄.

The steps are similar to those used in Example 1, with the difference being that the LiZn_{0 07}Fe_{0 93}PO₄ substitutes the LiFePO₄ to provide a LiZn_{0 07}Fe_{0 93}PO₄ / MnTiNb₂O₈ / C mixed crystal cathode active material.

With the Rigaku D/MAX-2200/PC, an XRD pattern is carried out on the cathode active material. Looking at the diffraction peaks of the sintered product, except for peaks corresponding to LiZn_{0 07}Fe_{0 93}PO₄ and MnTiNb₂O₈, there is no new peak or feature which indicates that the LiZn_{0 07}Fe_{0 93}PO₄ and MnTiNb₂O₈ exist in two phases and that no new compound is created. Accordingly, this demonstrates that the process described above provides a cathode active material having LiZn_{0 07}Fe_{0 93}PO₄ / MnTiNb₂O₈ / C in a mixed crystal form. COMPARATIVE EXAMPLE Rl

Example B of U.S. Patent Application No. 2007/0207385 provides a cathode material with LiFePO₄ to ZnAlO₂ with a molar ratio of 1 : 0.04 and carbon additive to provide a total carbon content of 5 % by weight in the final product. The

ZnAlO₂ and carbon additive are coated on the exterior surfaces of the LiFePO₄ to provide a cathode active material having LiFePO₄ / ZnAlO₂ / C.

CONDUCTIVITIES OF EXAMPLES 1-15 AND COMPARATIVE EXAMPLE Rl

At 25 ⁰C, separately take each cathode active materials of Examples 1-15 and Comparative example Rl, apply 30 MPa of pressure to provide a cylinder. Measure the height (V), diameter (d) and resistance (R) of each cylinder. Use the following formula to calculate the electrical conductivity (σ) for each sample: Electrical conductivity σ = 4 x 1 1 (π R x d²)

The electrical conductivities of Examples 1-15 and Comparative example Rl are shown in Table 1.

Table 1. Electrical conductivities of samples at 25 ⁰C. From Table 1, it can be observed that the cathode active materials of the present embodiments can achieve electrical conductivity up to 1.8 S / cm measured by a Siemens per Centimeter. By contrast, the cathode active material of Comparative example Rl, obtained by known publication having ZnAlO₂ and carbon additives coated on the surfaces of LiFePO₄, achieves electrical conductivity of 2.6 x 10^"6 S / cm while the cathode active material of Example A7, having similar composition to that of Comparative example Rl but provides by the presently disclosed method, achieves electrical conductivity of 0.5 S / cm, the latter being 19,000 times more electrically conductive. TESTINGS OF EXAMPLES 1-15 AND COMPARATIVE EXAMPLE Rl (1) Battery preparation

(a) Cathode active material

Separately combine 90 grams of each of the composite cathode materials from Examples 1-15 and Comparative example Rl with 5 grams of polyvinylidene fluoride (PVDF) binder and 5 grams of acetylene black to 50 grams of

N-methylpyrrolidone (NMP). Place in a vacuum mixer to mix into uniform slurry.

Apply a coating with a thickness of about 20 microns on both sides of an aluminum foil, dry at 150⁰C, roll and cut into a size of 540 x 43.5 mm to provide about 5.2 grams of cathode active material.

(b) Anode active material

Combine 90 grams of natural graphite with 5 grams of polyvinylidene fluoride (PVDF) binder and 5 grams of conductive carbon black to 100 grams of N-methylpyrrolidone (NMP). Place in a vacuum mixer to mix into uniform slurry. Apply a coating of about 12 microns thick to both sides of a copper foil, dry at 90⁰C, roll and crop to a size of 500 x 44 mm² to provide about 3.8 grams of anode active material.

(c) Battery assembly

Separately wind each of the cathode and anode active materials with polypropylene film into a lithium secondary battery core, followed by dissolving one mole of LiPF₆ in a mixture of non-aqueous electrolyte solvent EC/EMC/DEC to provide a ratio of 1 : 1 : 1, inject and seal the electrolyte having a capacity of 3.8 g/Ah into the battery to provide separate lithium secondary batteries Al -Al 5 (Examplesl-15) and ACl (Comparative example Rl) for testing. PERFORMANCE TESTINGS OF BATTERIES Al -Al 5 and ACl

Separately place each of batteries Al -Al 5 and ACl on the testing cabinet. At 25 ⁰C, charge each battery at a current of 0.5 C with a voltage limit of 3.8 V and set the battery aside for 20 minutes. Using a current of 0.5 C, discharge the battery from 3.8 V to 2.5 V and record the discharge capacity as the battery's initial discharge capacity. The following equation is used to calculate the battery's specific discharge capacity. The test results for batteries Al -Al 5 and ACl are shown in Table 2.

Specific discharge capacity = Initial discharge capacity (milliampere hour) / weight of cathode active material (grams)

The process as described above is repeated: charge the battery, set it aside, and discharge each battery for 500 cycles. Record the battery's discharge capacity and use the following equation to calculate the battery's ability to maintain discharge capacity after 500 cycles. The higher the maintenance rate, the better the performance of the battery in maintaining its discharge capacity. The test results for batteries Al -Al 5 and ACl are shown in Table 2.

Capacity maintenance rate = (Discharge capacity after n^th cycle / initial discharge capacity ) x 100 %

TABLE 2. Electrical testing results for batteries A1-A15 and ACl . From Table 2, it can be observed that the cathode active materials according to Examples 1-15 of the presently disclosed invention are able to achieve better electrical performance than Comparative example Rl . Specifically, the cathode active materials of batteries Al -Al 5 are able to achieve specific discharge capacity of at least 123mAh/g at 0.5 C and maintain greater than 95 % discharge capacity after 500 cycles.

Additionally, the cathode active material of Comparative example Rl achieved specific discharge capacity of 112 mAh/g and maintained 90.12 % discharge capacity after 500 cycles while cathode active material of Example 7, having similar composition to that of Comparative example Rl but provided by the presently disclosed method, achieved specific discharge capacity of 126 mAh/g and maintained 96.44 % discharge capacity after 500 cycles. Accordingly, the cathode active materials for lithium secondary batteries and methods of manufacturing the same according to the presently disclosed embodiments are able to provide superior electrical performance, e.g., higher electrical conductivity, discharge capacity and discharge capacity maintenance or retention rate.

Although the invention has been described in detail with reference to several embodiments, additional variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of preparing a cathode active material comprising a mixed crystal comprising the following steps: providing a first crystalline substance having one or more members with general formulas Li_xM'_y(XO₄)_z, LiM⁵XO₅, LiM⁵XO₆ and LiM⁵X₂O₇, wherein: 0<x/z<l and O≤y/z≤l .l;

M⁵ is an element selected from a group consisting of Na, Mn, Fe, Co, Ni, Ti, V, Y, Mg, Ca, Nb and Zn;

X is an element selected from a group consisting of P, S, As, Mo and W; providing a second crystalline substance having one or more members with a general formula A_aMbN_cOd, wherein:

A, M and N are different metals selected from groups of HA, IIIA, IVA, VA, IB, HB, IIIB, IVB, VB, VIB, VIIB and VIII in the periodic table, and wherein

0<a<6, 0<b<6, 0<c<6 and 0<d<12, in which a and b cannot be zero at the same time; and sintering the two crystalline substances to provide the mixed crystal.

2. The method of claim 1, wherein the first crystalline substance and the second crystalline substance has a molar ratio of about 1 to 0.01-0.05.

3. The method of claim 1, wherein the second crystalline substance is prepared by heating the oxide compounds of A, M and N at a molar ratio of a : b : c at about 400 ^°C to 1000 ^°C for about 8 hours to 15 hours.

4. The method of claim 1, wherein M⁵ includes element Fe and one or more members selected form the group consisting of Mn, Co, Ni, Ti, Y, Mg, Ca and Zn, and wherein the amount of Fe is from 90 % to 100 % by molar.

5. The method of claim 1, wherein the first crystalline substance includes one or more members selected from a group consisting of LiFePO₄, LiMnPO₄, LiCoPO₄, Li₃Fe₂(PO₄)₃, LiTi₂(PO₄),, Li₃V₂(PO₄),, Li₂NaV₂(PO₄),, Li_{0 99}Yo _OiFePO₄, LiR₁FeI_-1PO₄, LiTiPO₅, LiVMoO₆, LiVWO₆, LiVP₂O₇ and LiFeAs₂O₇ ,wherein 0<i<0.1, R is one or more members selected from elements Mn, Co, Ni, Ti, Mg, Ca and Zn; and wherein the second crystalline substance includes one or more members selected from a group consisting of Bi₄Ti₃Oi₂, CuNb₂O₆, MnTaO₄, FeWO₄, ZnZrNb₂O₈, NiNb₂O₆, NiZrNb₂O₈, FeTiNb₂O₈, MnTiNb₂O₈, MgSnNb₂O₈, ZnTa₂O₆, Cu_{0 85}Zn_{0 I5}Nb₂O₆, YBa₃Ti₂O_{8 5}, Zr_{0 75}Ti_{0 75}Sn_{0 5}O₄, HfTiO₄ and MgNb₂O₆.

6. The method of claim 5, wherein the first crystalline substance includes one or more members selected from a group consisting of LiFePO₄, Li_{0 99}Y_{0 0}iFePO₄ and LiR₁Fe_I-1PO₄ wherein 0<i<0.1, R is one or more members selected from elements Mn, Co, Ni, Ti, Mg, Ca and Zn.

7. The method of claim 1, further comprising sintering a carbon additive with the two crystalline substances to provide the mixed crystal with about l%-5 % carbon by weight.

8. The method of claim 7, wherein the carbon additive includes one or more members selected from a group consisting of carbon black, acetylene black, graphite, glucose, sucrose, citric acid, starch, dextrin and polyethylene glycol.

9. The method of claim 1, wherein the sintering step has a heating rate of from 5 to 20 °C/min with a sintering temperature from 500 to 800 ⁰C and a sintering time from 5 to 32 hours.

10. A method of preparing a cathode active material comprising a mixed crystal, comprising the following steps: providing a first material having a combination of lithium, iron and phosphorous sources; providing a second material having one or more members with a general formula A_aMbN_c0d, wherein:

A, M and N are different metals selected from groups HA, IIIA, IVA, VA, IB, HB, IIIB, IVB, VB, VIB, VIIB and VIII of the periodic table; and 0<a<6, 0<b<6, 0<c<6 and 0<d<12; wherein a and b cannot both be zero at the same time; and sintering the two materials to provide the mixed crystal.

11. The method of claim 10, wherein the lithium, iron and phosphorous (Li : Fe : P) sources have a molar ratio of about 0.95-1.1 : 1 : 0.95-1.1, and wherein the first material and the second material has a molar ratio of about 1 to 0.01-0.05.

12. The method of claim 10, wherein the second crystalline substance is prepared by heating the oxide compounds of A, M and N at a molar ratio of a : b : c at about 400 ⁰C to 1000 ⁰C for about 8 to 15 hours.

13. The method of claim 10, wherein the second crystalline substance includes one or more members selected from a group consisting of Bi₄Ti₃Oi₂,

CuNb₂O₆, MnTaO₄, FeWO₄, ZnZrNb₂O₈, NiNb₂O₆, NiZrNb₂O₈, FeTiNb₂O₈, MnTiNb₂O₈, MgSnNb₂O₈, ZnTa₂O₆, Cu_{0 85}Zn_{0 I5}Nb₂O₆, YBa₃Ti₂O_{8 5}, Zr_{0 75}Ti_{0 75} Sn_{0 5}O₄, HfTiO₄ and MgNb₂O₆.

14. The method of claim 10, wherein the lithium source includes one or more members selected from a group consisting of lithium carbonate, lithium hydroxide, lithium oxalate and lithium acetate; the iron source includes one or more members selected from a group consisting of ferrous oxalate, ferrous carbonate, iron acetate, iron oxide, iron phosphate, iron pyrophosphate and iron nitrate; and the phosphate source includes one or more members selected from a group consisting of ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, phosphoric acid and lithium dihydrogen phosphate.

15. The method of claim 10, wherein the first material further includes a carbon source.

16. The method of claim 15, wherein the carbon source provides the mixed crystal with about 1-5 % carbon by weight, and wherein the carbon source includes one or more members selected from a group consisting of carbon black, acetylene black, graphite, glucose, sucrose, citric acid, starch, dextrin and polyethylene glycol.

17. The method of claim 10, wherein the sintering step has a heating rate of from 5 to 20 °C/min, a sintering temperature of from 500 to 800 ⁰C, and a sintering time of from 5 to 32 hours.

18. A method of forming a lithium secondary battery comprising the following steps: providing electrodes having a cathode, an anode and a divider film which are wounded or stacked, the cathode comprising the cathode active material by the method according to claim 1 or 10; and providing a battery shell and electrolyte, the electrodes and the electrolyte being sealed within the battery shell.