Positive electrode material for high-power lithium ion battery and preparation method thereof

Abstract

Disclosed is a positive electrode material for a high-power lithium ion battery. The positive electrode material is in form of secondary particles with a hollow microsphere structure, and a shell of the secondary particles is formed by aggregating a plurality of primary particles. The secondary particles have a uniform particle size, a loose and porous surface, and a large specific surface area. The obtained particles are regular in shape, stable in material structure, so that the positive electrode material has high rate performance and excellent cycle performance. The disclosure also provides a preparation method for the positive electrode material comprising (1) synthesizing a Ni.sub.xCo.sub.yM.sub.z(OH).sub.2 precursor by a co-precipitation method, such that the precursor has a central portion consisted by fine particles and a shell portion consisted by large particles having a larger particle size than that of the fine particles; (2) mixing the precursor and a lithium salt uniformly, and adding an oxide of a doping element during the mixing, and then sintering the mixture to provide a Li.sub.aNi.sub.xCo.sub.yM.sub.zO.sub.2 positive electrode material. The preparation method is simple and low cost, and can be industrialized.

Claims

1. A preparation method of a positive electrode material for a lithium ion battery, wherein the positive electrode material is represented by Li.sub.aNi.sub.xCo.sub.yM.sub.zO.sub.2, wherein 0.96a1.35, 0.3x1, 0y0.4, 0z0.4, x+y+z=1, M is one or more selected from Mn, Al, Zr, Mg, W, Ti, Y, La, B and Sr; the positive electrode material is secondary particles with a hollow microsphere structure, and a shell of the secondary particles is formed by aggregating a plurality of primary particles, wherein the preparation method comprises the steps of: (1) synthesizing a Ni.sub.xCo.sub.yM.sub.z(OH).sub.2 precursor by a co-precipitation method comprising a nucleation and inner core growth stage and a shell growth stage; and wherein the obtained precursor has a central portion consisting of fine particles with a particle size of <0.3 m and a shell portion consisting of large particles having a particle size larger than that of the fine particles; (2) mixing the precursor obtained in step (1) with a lithium salt uniformly, and then sintering the mixture to obtain the Li.sub.aNi.sub.xCo.sub.yM.sub.zO.sub.2 positive electrode material; wherein in step (1), synthesizing the Ni.sub.xCo.sub.yM.sub.2(OH).sub.2 precursor by the co-precipitation method comprises the steps of: adding a metal salt solution of Ni, Co and M, an alkaline solution and an aqueous ammonia solution to a reaction kettle containing a base solution for reaction, during which a reaction temperature is 40 C.-60 C., a stirring speed is 100 r/min-1000 r/min, pH of a reaction system is controlled from 8-13, and nitrogen is continuously introduced into the reaction kettle; controlling an ammonium concentration of the reaction system in a range of 7 g/L-15 g/L at the nucleation and inner core growth stage, and in a range of 30 g/L-40 g/L at the shell growth stage for synthesizing the precursor, providing that the ammonium concentration of the reaction system at the shell growth stage is higher than that at the nucleation and inner core growth stage; and subjecting a precipitate obtained from the reaction to solid-liquid separating, aging, washing and drying to obtain the Ni.sub.xCo.sub.yM.sub.2(OH).sub.2 precursor.

2. The preparation method according to claim 1, wherein the metal salt solution is one or more selected from sulfate solution, a nitrate solution, a chloride solution, an acetate solution and a meta-aluminate solution, a total concentration of metal ions in the metal salt solution is 0.05 mol/L-3 mol/L; the alkaline solution is a sodium hydroxide solution and has a concentration of 1 mol/L-10 mol/L; and the ammonium concentration of the aqueous ammonia solution is 3 mol/L-6 mol/L.

3. The preparation method according to claim 1, wherein in step (2), adding the lithium salt in an amount such that a molar ratio of Li to Ni+Co+M is 0.96-1.35, and the lithium salt is one or more selected from lithium carbonate, lithium hydroxide, lithium oxalate and lithium acetate; when mixing the precursor with the lithium salt, an oxide of a doping element which is one or more selected from Al, Zr, Mg, W, Ti, Y, La, B and Sr is additionally added, and the doping element is presented in the positive electrode material in a mass percentage of 0.01 wt %-2 wt %.

4. The preparation method according to claim 1, wherein in step (2), the sintering is performed under a temperature of 500 C.-1000 C. for 6-24 hours with an atmosphere of air or oxygen or a mixture of oxygen and air.

5. The preparation method according to claim 4, wherein a multi-stage temperature-controlled sintering method is used in the sintering, wherein firstly a temperature of 500 C.-700 C. is held for 5-6 hours, secondly the temperature is elevated to 810 C.-1000 C. and held for 8-10 hours, and lastly the temperature is lowered to 700 C.-750 C. and held for 5-8 hours.

6. A preparation method of a positive electrode material for a lithium ion battery, wherein the positive electrode material is represented by Li.sub.aNi.sub.xCo.sub.yM.sub.zO.sub.2, wherein 0.96a1.35, 0.3x1, 0y0.4, 0z0.4, x+y+z=1, M is one or more selected from Mn, Al, Zr, Mg, W, Ti, Y, La, B and Sr; the positive electrode material is secondary particles with a hollow microsphere structure, and a shell of the secondary particles is formed by aggregating a plurality of primary particles; the secondary particles have an average particle size of 0.1 m-40 m and a specific surface area of 0.1 m2/g-15.0 m2/g; the primary particles have a particle size of 0.1 m-3.5 m; and a ratio of a thickness of the shell of the secondary particles to the particle size of the secondary particles is 1%-49%, wherein the preparation method comprises the steps of: (1) synthesizing a Ni.sub.xCo.sub.yM.sub.z(OH).sub.2 precursor by a co-precipitation method comprising a nucleation and inner core growth stage and a shell growth stage; and wherein the obtained precursor has a central portion consisting of fine particles with a particle size of <0.3 m and a shell portion consisting of large particles having a particle size larger than that of the fine particles; (2) mixing the precursor obtained in step (1) with a lithium salt uniformly, and then sintering the mixture to obtain the Li.sub.aNi.sub.xCo.sub.yM.sub.zO.sub.2 positive electrode material; wherein in step (1), synthesizing the Ni.sub.xCo.sub.yM.sub.2(OH).sub.2 precursor by the co-precipitation method comprises the steps of: adding a metal salt solution of Ni, Co and M, an alkaline solution and an aqueous ammonia solution to a reaction kettle containing a base solution for reaction, during which a reaction temperature is 40 C.-60 C., a stirring speed is 100 r/min-1000 r/min, pH of a reaction system is controlled from 8-13, and nitrogen is continuously introduced into the reaction kettle; controlling an ammonium concentration of the reaction system in a range of 7 g/L-15 g/L at the nucleation and inner core growth stage, and in a range of 30 g/L-40 g/L at the shell growth stage for synthesizing the precursor, providing that the ammonium concentration of the reaction system at the shell growth stage is higher than that at the nucleation and inner core growth stage; and subjecting a precipitate obtained from the reaction to solid-liquid separating, aging, washing and drying to obtain the Ni.sub.xCo.sub.yM.sub.2(OH).sub.2 precursor.

7. The preparation method according to claim 6, wherein the metal salt solution is one or more selected from sulfate solution, a nitrate solution, a chloride solution, an acetate solution and a meta-aluminate solution, a total concentration of metal ions in the metal salt solution is 0.05 mol/L-3 mol/L; the alkaline solution is a sodium hydroxide solution and has a concentration of 1_mol/L-10 mol/L; and the ammonium concentration of the aqueous ammonia solution is 3 mol/L-6 mol/L.

8. The preparation method according to claim 6, wherein in step (2), adding the lithium salt in an amount such that a molar ratio of Li to Ni+Co+M is 0.96-1.35, and the lithium salt is one or more selected from lithium carbonate, lithium hydroxide, lithium oxalate and lithium acetate; when mixing the precursor with the lithium salt, an oxide of a doping element which is one or more selected from Al, Zr, Mg, W, Ti, Y, La, B and Sr is additionally added, and the doping element is presented in the positive electrode material in a mass percentage of 0.01 wt %-2 wt %.

9. The preparation method according to claim 6, wherein in step (2), the sintering is performed under a temperature of 500 C.-1000 C. for 6-24 hours with an atmosphere of air or oxygen or a mixture of oxygen and air.

10. The preparation method according to claim 9, wherein a multi-stage temperature-controlled sintering method is used in the sintering, wherein firstly a temperature of 500 C.-700 C. is held for 5-6 hours, secondly the temperature is elevated to 810 C.-1000 C. and held for 8-10 hours, and lastly the temperature is lowered to 700 C.-750 C. and held for 5-8 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference will now be made briefly to the accompanying drawings required in the examples or the description of the prior art to describe the examples of the disclosure or the technical solutions in the prior art more clearly. It will be apparent that the accompanying drawings in the following description illustrate some examples of the disclosure, and other drawings may be obtained according to these drawings to those skilled in the art without involving any inventive effort.

(2) FIG. 1 is a schematic cross-sectional view of a positive electrode material according to the disclosure (A is the thickness of the shell portion and D is the secondary particle size);

(3) FIG. 2 is an electron microscopy picture of a sectional view of the positive electrode material obtained in Example 2;

(4) FIG. 3 is an electron microscopy picture of the positive electrode material obtained in Comparative Example 3;

(5) FIG. 4 is an electron microscopy picture of a sectional view of the positive electrode material obtained in Comparative Example 3;

(6) FIG. 5 is a graph showing the discharge specific capacity of the positive electrode material obtained in Comparative Example 3 at different rates.

DETAILED DESCRIPTION

(7) In order to facilitate understanding of the disclosure, the disclosure will now be described more comprehensively and in detail with reference to the accompanying drawings and the preferred examples thereof, however the scope of the disclosure is not limited to the following specific examples.

(8) Unless defined otherwise, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific examples only and are not intended to limit the scope of the disclosure.

(9) Unless specifically stated otherwise, the various raw materials, reagents, instruments and equipment used in the disclosure are commercially available or can be prepared by existing methods.

Example 1

(10) A positive electrode material for a lithium ion battery according to the disclosure having the chemical formula of Li.sub.1.2Ni.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2, as shown in FIG. 1, is in form of secondary particles with a hollow microsphere structure and a shell formed by aggregated primary particles.

(11) The positive electrode material was prepared with the following steps.

(12) (1) Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 precursor was synthesized by a co-precipitation method including a nucleation and inner core growth stage and a shell growth stage. Specifically the method included the following steps. First, a mixed metal salt solution having a total metal ion concentration of 2 mol/L was prepared by using sulfates of Ni, Co and Mn with the molar ratio of Ni:Co:Mn=6:2:2. Then, 2 mol/L of sodium hydroxide solution and an aqueous ammonia solution with an ammonium concentration of 6 mol/L were prepared. Pure water was used as the base solution of the reaction kettle, and pH of the base solution in the reaction kettle was adjusted to 12.0 with sodium hydroxide. By controlling the ammonium concentration at 7 g/L, the mixed metal salt solution, the sodium hydroxide solution and the aqueous ammonia solution were added into the reaction kettle via metering pumps for reaction. The reaction temperature was 55 C., the stirring speed was 500 r/min, pH of the reaction system in the reaction kettle was controlled at 10.512.0, and nitrogen was continuously introduced into the reaction kettle during the reaction. The ammonium concentration of the reaction system was controlled at 7 g/L at the nucleation and inner core growth stage until the particle size of the material increased to 1.5 m, and then the ammonium concentration of the reaction system was adjusted to 35 g/L to allow the shell growing until the particle size increased to 5.5 m. The precipitate from the reaction was obtained by solid-liquid separating, and the precipitate was subjected to aging, washing and drying to provide Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 precursor with the average particle size of 5.5 m and the thickness of shell portion of about 2 m. The precursor was constituted by a central portion consisted of fine particles and a shell portion consisted of large particles with a particle size larger than that of the fine particles.

(13) (2) An appropriate amount of the above said precursor and lithium carbonate were weighed with a lithium to metal ratio (i.e., a molar ratio of Li to Ni+Co+Mn) of 1.20, an appropriate amount of MgO was weighed based on 0.1 wt % of Mg in the positive electrode material, and an appropriate amount of TiO.sub.2 was weighed based on 0.08 wt % of Ti in the positive electrode material. The above feeds were uniformly mixed and then sintered at a high temperature under a sintering atmosphere of a mixture of oxygen and air, in which the material was sintered at 700 C. for 6 hours firstly and then at an elevated temperature of 850 C. for 10 hours. After the sintering and cooling to room temperature, the material was sieved to obtain the positive electrode material, Li.sub.1.2Ni.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2, with a hollow structure and doped with Mg and Ti.

(14) The physical and chemical properties of the positive electrode material Li.sub.1.2Ni.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 were measured. The positive electrode material had the specific surface area of 1.08 m.sup.2/g and the average particle size of 5.5 m. The material was subjected to SEM and cross-sectional SEM observations. The SEM result showed that the material had a secondary spherical structure and the particle size was uniform. The cross-sectional SEM result showed that the positive electrode material was in a form of hollow microsphere secondary particles which had a shell formed by primary particles aggregated by sintering and having a thickness of about 2.0 m.

(15) The electrical performance of the positive electrode material was evaluated by using a 2032-type button cell. The positive electrode material had an initial discharge specific capacity of 165 mAh/g at 1 C and had a relatively good rate performance which was 97.81% at 2 C/1 C, 93.44% at 5 C/1 C and 90.65% at 10 C/1 C.

Example 2

(16) A positive electrode material for a lithium ion battery according to the disclosure having the chemical formula of Li.sub.1.08Ni.sub.0.9Co.sub.0.08Al.sub.0.02O.sub.2, as shown in FIG. 1, is in form of secondary particles with a hollow microsphere structure and a shell formed by aggregated primary particles.

(17) The positive electrode material was prepared with the following steps.

(18) (1) Ni.sub.0.9Co.sub.0.08Al.sub.0.02(OH).sub.2 precursor was synthesized by a co-precipitation method including a nucleation and inner core growth stage and a shell growth stage. Specifically the method included the following steps. First, a mixed metal salt solution having a total metal ion concentration of 2 mol/L was prepared by using sulfates of Ni and Co with the molar ratio of Ni:Co=90:8. Then, a meta-aluminate solution containing 0.1 mol/L of aluminum was prepared by using an aluminum sulfate and an excess of sodium hydroxide. Next, 2 mol/L of sodium hydroxide solution and an aqueous ammonia solution with an ammonium concentration of 5 mol/L were prepared. Pure water was used as the base solution of the reaction kettle, and pH of the base solution in the reaction kettle was adjusted to 11.5 with sodium hydroxide. By adjusting the ammonium concentration to 10 g/L, the mixed metal salt solution, the meta-aluminate solution, the sodium hydroxide solution and the aqueous ammonia solution were added into the reaction kettle via metering pumps for reaction. The reaction temperature was 55 C., the stirring speed was 450 r/min, pH of the reaction system in the reaction kettle was controlled at 10.011.5, and nitrogen was continuously introduced into the reaction kettle during the reaction. The flowing ratio of the mixed metal salt solution to the meta-aluminate solution was controlled so that the metal molar ratio of Ni:Co:Al was 90:8:2. The ammonium concentration of the reaction system was controlled at 10 g/L at the nucleation and inner core growth stage until the particle size of the material increased to 2 m, and then the ammonium concentration of the reaction system was adjusted to 30 g/L to allow the shell growing until the particle size increased to 9.0 m. The precipitate from the reaction was obtained by solid-liquid separating, and the precipitate was subjected to aging, washing and drying to provide Ni.sub.0.9Co.sub.0.08Al.sub.0.02(OH).sub.2 precursor with the average particle size of 9.0 m and thickness of shell portion of about 3.5 m. The precursor was constituted by a central portion consisted of fine particles and a shell portion consisted of large particles with a particle size larger than that of the fine particles.

(19) (2) An appropriate amount of the above said precursor and lithium hydroxide were weighed with a lithium to metal ratio (i.e., a molar ratio of Li to Ni+Co+Mn) of 1.08, and an appropriate amount of SrCO.sub.3 was weighed based on 0.2 wt % of Sr in the positive electrode material. The above feeds were uniformly mixed and then sintered at a high temperature under a sintering atmosphere of a mixture of oxygen and air, in which the temperature was elevated to 710 C. directly and held for 12 hours. After the sintering and cooling to room temperature, the material was sieved to obtain the positive electrode material, Li.sub.0.08Ni.sub.0.9Co.sub.0.08Al.sub.0.02O.sub.2, with a hollow structure and doped with Sr.

(20) The physical and chemical properties of the positive electrode material Li.sub.1.08Ni.sub.0.9Co.sub.0.08Al.sub.0.02O.sub.2 were measured. The positive electrode material had the specific surface area of 0.76 m.sup.2/g and the average particle size of 9.0 m. The material was subjected to SEM and cross-sectional SEM observations. The SEM result showed that the material had a secondary spherical structure and the particle size was uniform. The cross-sectional SEM result (see FIG. 2) showed that the positive electrode material was in a form of hollow microsphere secondary particles which had a shell formed by primary particles aggregated by sintering and having a thickness of about 3.5 m.

(21) The electrical performance of the positive electrode material was evaluated by using a 2032-type button cell. The positive electrode material had an initial discharge specific capacity of 192 mAh/g at 1 C and had a relatively good rate performance which was 97.09% at 2 C/1 C, 92.68% at 5 C/1 C and 90.00% at 10 C/1 C.

Comparative Example 3

(22) A positive electrode material for a lithium ion battery according to the disclosure having the chemical formula of Ni.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2, as shown in FIG. 1, is in form of secondary particles with a hollow microsphere structure and a shell formed by aggregated primary particles.

(23) The positive electrode material was prepared with the following steps.

(24) (1) Ni.sub.1/3Co.sub.1/3Mn.sub.1/3(OH).sub.2 precursor was synthesized by a co-precipitation method including a nucleation and inner core growth stage and a shell growth stage. Specifically the method included the following steps. First, a mixed metal salt solution having a total metal ion concentration of 2 mol/L was prepared by using sulfates of Ni, Co and Mn with the molar ratio of Ni:Co:Mn=1:1:1. Then, 2 mol/L of sodium hydroxide solution and an aqueous ammonia solution with an ammonium concentration of 5 mol/L were prepared. Pure water was used as the base solution of the reaction kettle, and pH of the base solution in the reaction kettle was adjusted to 11.0 with sodium hydroxide. The aqueous ammonium solution was not added (ensuring the ammonium concentration was 0). The mixed metal salt solution and the sodium hydroxide solution were added into the reaction kettle via metering pumps for reaction. The reaction temperature was 50 C., the stirring speed was 500 r/min, pH of the reaction system in the reaction kettle was controlled at 9.511.0, and nitrogen was continuously introduced into the reaction kettle during the reaction. The aqueous ammonium solution was not added at the nucleation and inner core growth stage until the particle size of the material increased to 1.6 m, and then the aqueous ammonium solution was added and the ammonium concentration of the reaction system was controlled at 10 g/L to allow the shell growing until the particle size increased to 4.0 m. The precipitate from the reaction was obtained by solid-liquid separating, and the precipitate was subjected to aging, washing and drying to provide Ni.sub.1/3Co.sub.1/3Mn.sub.1/3(OH).sub.2 precursor with the average particle size of 4 m and thickness of shell portion of about 1.2 m. The precursor was constituted by a central portion consisted of fine particles and a shell portion consisted of large particles with a particle size larger than that of the fine particles.

(25) (2) An appropriate amount of the above said precursor and lithium carbonate were weighed with a lithium to metal ratio (i.e., a molar ratio of Li to Ni+Co+Mn) of 1.25, and an appropriate amount of ZrO.sub.2 was weighed based on 0.5 wt % of Zr in the positive electrode material. The above feeds were uniformly mixed and then sintered at a high temperature under a sintering atmosphere of a mixture of oxygen and air, in which the sintering process included a heating platform, a high-temperature platform and a cooling platform, i.e., sintering at 600 C. for 6 hours firstly, then increasing the temperature to 900 C. and holding for 8 hours, last cooling the temperature to 700 C. and holding for 5 hours. After the sintering and cooling to room temperature, the material was sieved to obtain the positive electrode material, Li.sub.1.25Ni.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2, with a hollow structure and doped with Mg and Zr.

(26) The physical and chemical properties of the positive electrode material Li.sub.1.25Ni.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 were measured. The positive electrode material had the specific surface area of 2.13 m.sup.2/g, the average particle size of secondary particles of 4.5 m and the average particle size of primary particles of 0.1 m to 2 m. The material was subjected to SEM and cross-sectional SEM observations (see FIG. 3 and FIG. 4).

(27) FIG. 3 shows that the material has a secondary spherical structure and the particle size is uniform. FIG. 4 shows that the positive electrode material is in a form of hollow microsphere secondary particles which had a shell formed by primary particles aggregated by sintering and having a thickness of about 1.2 m.

(28) The electrical performance of the positive electrode material was evaluated by using a 2032-type button cell. The result is shown in FIG. 5. The positive electrode material had an initial discharge specific capacity of 147.7 mAh/g at 1 C and had a relatively good rate performance which was 98.24% at 2 C/1 C, 94.85% at 5 C/1 C and 90.66% at 10 C/1 C.

Comparative Example 4

(29) A positive electrode material for a lithium ion battery according to the disclosure having the chemical formula of Li.sub.1.1Ni.sub.0.4Co.sub.0.3Mn.sub.0.3O.sub.2, as shown in FIG. 1, is in form of secondary particles with a hollow microsphere structure and a shell formed by aggregated primary particles.

(30) The positive electrode material was prepared with the following steps.

(31) (1) Ni.sub.0.4Co.sub.0.3Mn.sub.0.3 (OH).sub.2 precursor was synthesized by a co-precipitation method including a nucleation and inner core growth stage and a shell growth stage. Specifically the method included the following steps. First, a mixed metal salt solution having a total metal ion concentration of 2 mol/L was prepared by using sulfates of Ni, Co and Mn with the molar ratio of Ni:Co:Mn=4:3:3. Then, 4 mol/L of sodium hydroxide solution and an aqueous ammonia solution with an ammonium concentration of 5 mol/L were prepared. Pure water was used as the base solution of the reaction kettle, and pH of the base solution in the reaction kettle was adjusted to 13.0 with sodium hydroxide. The aqueous ammonium solution was not added (ensuring the ammonium concentration was 0). The mixed metal salt solution and the sodium hydroxide solution were added into the reaction kettle via metering pumps for reaction. The reaction temperature was 45 C., the stirring speed was 600 r/min, pH of the reaction system in the reaction kettle was controlled at 9.513.0, and nitrogen was continuously introduced into the reaction kettle during reaction. The aqueous ammonium solution was not added at the nucleation and inner core growth stage until the particle size of the material increased to 0.8 m, and then the ammonium concentration of the reaction system was adjusted to 15 g/L to allow the shell growing until the particle size increased to 3.8 m. The precipitate from the reaction was obtained by solid-liquid separating, and the precipitate was subjected to aging, washing and drying to provide Ni.sub.0.4Co.sub.0.3Mn.sub.0.3(OH).sub.2 precursor with the average particle size of 3.8 m and thickness of shell portion of about 1.5 m. The precursor was constituted by a central portion consisted of fine particles and a shell portion consisted of large particles with a particle size larger than that of the fine particles.

(32) (2) An appropriate amount of the above said precursor and lithium carbonate were weighed with a lithium to metal ratio (i.e., a molar ratio of Li to Ni+Co+Mn) of 1.10, and an appropriate amount of ZrO.sub.2 was weighed based on 0.3 wt % of Zr in the positive electrode material, and an appropriate amount of boric acid was weighed based on 0.1 wt % of B in the positive electrode material. The above feeds were uniformly mixed and then sintered at a high temperature under a sintering atmosphere of a mixture of oxygen and air, in which the sintering process included a heating platform, a high-temperature platform and a cooling platform, i.e., sintering at 660 C. for 5 hours firstly, then increasing the temperature to 810 C. and holding for 8 hours, last cooling the temperature to 700 C. and holding for 8 hours. After the sintering and cooling to room temperature, the material was sieved to obtain the positive electrode material, Li.sub.1.1Ni.sub.0.4Co.sub.0.3Mn.sub.0.3O.sub.2, with a hollow structure and doped with Zr and B.

(33) The physical and chemical properties of the positive electrode material Li.sub.1.1Ni.sub.0.4Co.sub.0.3Mn.sub.0.3O.sub.2 were measured. The positive electrode material had the specific surface area of 0.65 m.sup.2/g, the average particle size of 4.0 m. The material was subjected to SEM and cross-sectional SEM observations. The SEM result showed that the material had a secondary spherical structure and the particle size was uniform. The cross-sectional SEM result showed that the positive electrode material was in a form of hollow microsphere secondary particles which had a shell formed by primary particles aggregated by sintering and having a thickness of about 1.5 m.

(34) The electrical performance of the positive electrode material was evaluated by using a 2032-type button cell. The positive electrode material had an initial discharge specific capacity of 152 mAh/g at 1 C and had a relatively good rate performance which was 98.00% at 2 C/1 C, 94.24% at 5 C/1 C and 91.37% at 10 C/1 C.

Comparative Example 5

(35) A positive electrode material for a lithium ion battery according to the disclosure having the chemical formula of Li.sub.1.2Ni.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2, as shown in FIG. 1, is in form of secondary particles with a hollow microsphere structure and a shell formed by aggregated primary particles.

(36) The positive electrode material was prepared with the following steps.

(37) (1) Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 precursor was synthesized by a co-precipitation method including a nucleation and inner core growth stage and a shell growth stage. Specifically the method included the following steps. First, a mixed metal salt solution having a total metal ion concentration of 2 mol/L was prepared by using sulfates of Ni, Co and Mn with the molar ratio of Ni:Co:Mn=6:2:2. Then, 2 mol/L of sodium hydroxide solution and an aqueous ammonia solution with an ammonium concentration of 6 mol/L were prepared. Pure water was used as the base solution of the reaction kettle, and pH of the base solution in the reaction kettle was adjusted to 12.0 with sodium hydroxide. By adjusting the ammonium concentration to 0 g/L, the mixed metal salt solution, the sodium hydroxide solution and the aqueous ammonia solution were added into the reaction kettle via metering pumps for reaction. The reaction temperature was 55 C., the stirring speed was 500 r/min, pH of the reaction system in the reaction kettle was controlled at 10.512.0, and nitrogen was continuously introduced into the reaction kettle during the reaction. Waiting until the particle size of the material increased to 1.5 m, then the ammonium concentration of the reaction system was adjusted to 25 g/L to allow the shell growing until the particle size increased to 5.5 m. The precipitate from the reaction was obtained by solid-liquid separating, and the precipitate was subjected to aging, washing and drying to provide Ni.sub.0.6Co.sub.0.2Mn.sub.0.2(OH).sub.2 precursor with the average particle size of 5.5 m and thickness of shell portion of about 2 m. The precursor was constituted by a central portion consisted of fine particles and a shell portion consisted of large particles with a particle size larger than that of the fine particles.

(38) (2) An appropriate amount of the above said precursor and lithium carbonate were weighed with a lithium to metal ratio (i.e., a molar ratio of Li to Ni+Co+Mn) of 1.20, an appropriate amount of MgO was weighed based on 0.1 wt % of Mg in the positive electrode material, and an appropriate amount of TiO.sub.2 was weighed based on 0.08 wt % of Ti in the positive electrode material. The above feeds were uniformly mixed and then sintered at a high temperature under a sintering atmosphere of a mixture of oxygen and air, in which the materials were sintered at 700 C. for 6 hours firstly and then at an elevated temperature of 850 C. for 10 hours. After the sintering and cooling to room temperature, the material was sieved to obtain the positive electrode material, Li.sub.1.2Ni.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2, with a hollow structure and doped with Mg and Ti.

(39) The physical and chemical properties of the positive electrode material Li.sub.1.2Ni.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2 were measured. The positive electrode material had the specific surface area of 0.88 m.sup.2/g and the average particle size of 6.0 m. The material was subjected to SEM and cross-sectional SEM observations. The SEM result showed that the material had a secondary spherical structure and the particle size was uniform. The cross-sectional SEM result showed that the positive electrode material was in a form of hollow microsphere secondary particles which had a shell formed by primary particles aggregated by sintering and having a thickness of about 2.5 m.

(40) The electrical performance of the positive electrode material was evaluated by using a 2032-type button cell. The positive electrode material had an initial discharge specific capacity of 163 mAh/g at 1 C and had a relatively good rate performance which was 92.16% at 2 C/1 C, 88.06% at 5 C/1 C and 86.42% at 10 C/1 C.

Comparative Example 6

(41) A positive electrode material for a lithium ion battery according to the disclosure having the chemical formula of Li.sub.1.08Ni.sub.0.9C.sub.0.08Al.sub.0.02O.sub.2, as shown in FIG. 1, is in form of secondary particles with a hollow microsphere structure and a shell formed by aggregated primary particles.

(42) The positive electrode material was prepared with the following steps.

(43) (1) Ni.sub.0.9Co.sub.0.08Al.sub.0.02(OH).sub.2 precursor was synthesized by a co-precipitation method including a nucleation and inner core growth stage and a shell growth stage. Specifically the method included the following steps. First, a mixed metal salt solution having a total metal ion concentration of 2 mol/L was prepared by using sulfates of Ni and Co with the molar ratio of Ni:Co=90:8. Then, 0.1 mol/L of a meta-aluminate solution was prepared by using an aluminum sulfate and an excess of sodium hydroxide. Next, 2 mol/L of sodium hydroxide solution and an aqueous ammonia solution with an ammonium concentration of 5 mol/L were prepared. Pure water was used as the base solution of the reaction kettle, and pH of the base solution in the reaction kettle was adjusted to 11.5 with sodium hydroxide. By adjusting the ammonium concentration to 0 g/L, the mixed metal salt solution, the meta-aluminate solution, the sodium hydroxide solution and the aqueous ammonia solution were added into the reaction kettle via metering pumps for reaction. The reaction temperature was 55 C., the stirring speed was 450 r/min, pH of the reaction system in the reaction kettle was controlled at 10.011.5, and nitrogen was continuously introduced into the reaction kettle during the reaction. The flowing ratio of the mixed metal salt solution to the meta-aluminate solution was controlled so that the metal molar ratio of Ni:Co:Al was 90:8:2. Waiting until the particle size of the material increased to 2 m, then the ammonium concentration of the reaction system was adjusted to 25 g/L to allow the shell growing until the particle size increased to 9.0 m. The precipitate from the reaction was obtained by solid-liquid separating, and the precipitate was subjected to aging, washing and drying to provide Ni.sub.0.9Co.sub.0.08Al.sub.0.02(OH).sub.2 precursor with the average particle size of 9.0 m and thickness of shell portion of about 3.5 m. The precursor was constituted by a central portion consisted of fine particles and a shell portion consisted of large particles with a particle size larger than that of the fine particles.

(44) (2) An appropriate amount of the above said precursor and lithium hydroxide were weighed with a lithium to metal ratio (i.e., a molar ratio of Li to Ni+Co+Mn) of 1.08, and an appropriate amount of SrCO.sub.3 was weighed based on 0.2 wt % of Sr in the positive electrode material. The above feeds were uniformly mixed and then sintered at a high temperature under a sintering atmosphere of a mixture of oxygen and air, in which the temperature was elevated to 710 C. directly and held for 12 hours. After the sintering and cooling to room temperature, the material was sieved to obtain the positive electrode material, Li.sub.1.08Ni.sub.0.9Co.sub.0.08Al.sub.0.02O.sub.2, with a hollow structure and doped with Sr.

(45) The physical and chemical properties of the positive electrode material Li.sub.1.08Ni.sub.0.9Co.sub.0.08Al.sub.0.02O.sub.2 were measured. The positive electrode material had the specific surface area of 0.5 m.sup.2/g and the average particle size of 9.0 m. The material was subjected to SEM and cross-sectional SEM observations. The SEM result showed that the material had a secondary spherical structure and the particle size was uniform. The cross-sectional SEM result showed that the positive electrode material was in a form of hollow microsphere secondary particles which had a shell formed by primary particles aggregated by sintering and having a thickness of about 4 m.

(46) The electrical performance of the positive electrode material was evaluated by using a 2032-type button cell. The positive electrode material had an initial discharge specific capacity of 188 mAh/g at 1 C and had a relatively good rate performance which was 90.89% at 2 C/1 C, 87.43% at 5 C/1 C and 85.24% at 10 C/1 C.

Comparative Example 7

(47) A positive electrode material for a lithium ion battery according to the disclosure having the chemical formula of Li.sub.1.1Ni.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2, as shown in FIG. 1, is in form of secondary particles with a hollow microsphere structure and a shell formed by aggregated primary particles.

(48) The positive electrode material was prepared with the following steps.

(49) (1) Ni.sub.0.5Co.sub.0.3Mn.sub.0.2(OH).sub.2 precursor was synthesized by a co-precipitation method including a nucleation and inner core growth stage and a shell growth stage. Specifically the method included the following steps. First, a mixed metal salt solution having a total metal ion concentration of 2 mol/L was prepared by using sulfates of Ni, Co and Mn with the molar ratio of Ni:Co:Mn=5:3:2. Then, 2 mol/L of sodium hydroxide solution and an aqueous ammonia solution with an ammonium concentration of 5 mol/L were prepared. Pure water was used as the base solution of the reaction kettle, and pH of the base solution in the reaction kettle was adjusted to 12.0 with sodium hydroxide. By adjusting the ammonium concentration to 3 g/L, the mixed metal salt solution, the sodium hydroxide solution and the aqueous ammonia solution were added into the reaction kettle via metering pumps for reaction. The reaction temperature was 55 C., the stirring speed was 400 r/min, pH of the reaction system in the reaction kettle was controlled at 10.012.0, and nitrogen was continuously introduced into the reaction kettle during the reaction. The ammonium concentration of the reaction system was controlled at 3 g/L at the nucleation and inner core growth stage until the particle size of the material increased to 2.5 m, and then the ammonium concentration of the reaction system was adjusted to 25 g/L to allow the shell growing until the particle size increased to 4.5 m. The precipitate from the reaction was obtained by solid-liquid separating, and the precipitate was subjected to aging, washing and drying to provide Ni.sub.0.5Co.sub.0.3Mn.sub.0.2(OH).sub.2 precursor with the average particle size of 4.5 m and thickness of shell portion of about 1 m. The precursor was constituted by a central portion consisted of fine particles and a shell portion consisted of large particles with a particle size larger than that of the fine particles.

(50) (2) An appropriate amount of the above said precursor and lithium carbonate were weighed with a lithium to metal ratio (i.e., a molar ratio of Li to Ni+Co+Mn) of 1.10, and an appropriate amount of WO.sub.3 was weighed based on 0.1 wt % of W in the positive electrode material. The above feeds were uniformly mixed and then sintered at a high temperature under a sintering atmosphere of a mixture of oxygen and air, in which the sintering process included a heating platform, a high-temperature platform and a cooling platform, i.e., sintering at 700 C. for 6 hours firstly, then increasing the temperature to 880 C. and holding for 10 hours, last cooling the temperature to 750 C. and holding for 5 hours. After the sintering and cooling to room temperature, the material was sieved to obtain the positive electrode material, Li.sub.1.1Ni.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2, with a hollow structure and doped with W.

(51) The physical and chemical properties of the positive electrode material Li.sub.1.1Ni.sub.0.5Co.sub.0.3Mn.sub.0.2O.sub.2 were measured. The positive electrode material had the specific surface area of 1.89 m.sup.2/g and the average particle size of 4.5 m. The material was subjected to SEM and cross-sectional SEM observations. The SEM result showed that the material had a secondary spherical structure and the particle size was uniform. The cross-sectional SEM result showed that the positive electrode material was in a form of hollow microsphere secondary particles which had a shell formed by primary particles aggregated by sintering and having a thickness of about 1 m.

(52) The electrical performance of the positive electrode material was evaluated by using a 2032-type button cell. The positive electrode material had an initial discharge specific capacity of 158.6 mAh/g at 1 C and had a relatively good rate performance which was 99.02% at 2 C/1 C, 95.66% at 5 C/1 C and 92.13% at 10 C/1 C.