NICKEL LITHIUM ION BATTERY POSITIVE ELECTRODE MATERIAL HAVING CONCENTRATION GRADIENT, AND PREPARATION METHOD THEREFOR

Abstract

A nickel lithium ion battery positive electrode material having a concentration gradient, and a preparation method therefor. The material is a core-shell material having a concentration gradient, the core material is a material having a high content of nickel, and the shell material is a ternary material having a low content of nickel. The method comprises: synthesizing a material precursor having a high content of nickel by means of co-precipitation, co-precipitating a ternary material solution having a low content of nickel outside the material precursor having a high content of nickel, aging, washing, and drying to form a composite precursor in which the low nickel material coats the high nickel material, adding a lithium source, grinding, mixing, calcining, and cooling to prepare a high nickel lithium ion battery positive electrode material. The obtained material has regular morphology, uniform coating, narrow particle size distribution range, gradient distribution of the concentration of the nickel element, high content of the nickel element in the core, and low content of the nickel element in the shell; the nickel element in the core guarantees the specific capacity of the material, and the shell coating material maintains the stability of the structure of the material, so as to improve the safety of the material in the charge and discharge process, and improve the cycle and rate performance of the material.

Claims

1. A cathode material for nickel lithium ion battery with a concentration gradient, characterized in that the material is a core-shell material with a concentration gradient, wherein the core material has the structural formula of LiNi.sub.xM.sub.yO.sub.2, wherein 0.5≦x≦1, 0≦y≦0.5, x+y=1, M=Co.sub.αMn.sub.β, 0≦α≦1, 0≦β≦1, α+β=y, and/or the structural formula of LiNi.sub.xM.sub.yO.sub.2, wherein 0.5≦x≦1, 0≦y≦0.5, x+y=1, M=Co.sub.αAl.sub.β, 0≦α≦1, 0≦β≦1, α+β=y; the shell material is a nickel-containing ternary material having the structural formula of LiNi.sub.xCo.sub.yMn.sub.zO.sub.2, wherein 0<x≦0.5, 0<y≦1, 0<z≦1, x+y+z=1, and/or the structural formula of LiNi.sub.xCo.sub.yAl.sub.zO.sub.2, wherein 0<x≦0.5, 0<y≦1, 0<z≦1, x+y+z=1.

2. The cathode material for nickel lithium ion battery according to claim 1, characterized in that the core material has an average particle size of 5-15 μm; the shell material has an average thickness of 1-5 μm.

3. A process for preparing the cathode material for nickel lithium ion battery according to claim 1, characterized in that the process comprises the steps of: (1) synthesizing a precursor of the core material by co-precipitation, then co-precipitating a shell material solution outside the core material precursor, aging, washing and drying to obtain a composite precursor in which the core material is coated with the shell material; and (2) adding a lithium source into the composite precursor, grinding and mixing, calcining and cooling to prepare a cathode material for nickel lithium ion battery.

4. The process according to claim 3, characterized in that the co-precipitation of the core material precursor comprises the following steps: (1) weighing in turn nickel salt, cobalt salt and manganese salt to formulate a solution after mixing; (2) weighing a precipitator to formulate of a precipitator solution having a concentration of 1-3 mol/L, adding an ammonia as a complexing agent to formulate a mixed solution; (3) pumping into a reaction still the solution in step (1) and the mixed solution in step (2) via a constant flow pump; (4) controlling the flow of the two solutions in step (3) and adjusting the pH, stirring under constant temperature conditions till the completion of adding dropwise the solution; or the co-precipitation of the core material precursor comprises the following steps: (1′) weighing in turn nickel salt, cobalt salt and aluminium salt to formulate a solution after mixing; (2) weighing a precipitator to formulate a precipitator solution having a concentration of 1-3 mol/L, adding an ammonia as a complexing agent to formulate a mixed solution; (3) pumping into a reaction still the solution in step (1′) and the mixed solution in step (2) via a constant flow pump; (4) controlling the flow of the two solutions in step (3) and adjusting the pH, stirring under constant temperature conditions till the completion of adding dropwise the solution.

5. The process according to claim 4, characterized in that, the nickel salt in the co-precipitation of the core material precursor is anyone selected from the group consisting of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate, nickel acetate, nickel phosphate and nickel oxalate, or a combination of at least two selected therefrom; the cobalt salt in the co-precipitation of the core material precursor is anyone selected from the group consisting of cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt acetate, cobalt phosphate and cobalt oxalate, or a combination of at least two selected therefrom; the manganese salt in the co-precipitation of the core material precursor is anyone selected from the group consisting of manganese chloride, manganese sulfate, manganese acetate, manganese nitrate, manganese carbonate and manganese oxalate, or a combination of at least two selected therefrom; the aluminium salt in the co-precipitation of the core material precursor is anyone selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum acetate, aluminum nitrate, aluminum carbonate and aluminum oxalate, or a combination of at least two selected therefrom;

6. The process according to claim 4, characterized in that, the nickel salt, cobalt salt and manganese salt in step (1) of the co-precipitation of the core material precursor have a metal element molar ratio of 6-9:0-2.5:0-2.5, including 0; the nickel salt, cobalt salt and aluminium salt in step (1′) of the co-precipitation of the core material precursor have a metal element molar ratio of 6-9:0-2.5:0-2.5, including 0; each component of the solution(s) formulated in step (1) and/or step (1′) of the co-precipitation of the core material precursor has a concentration of 1-3 mol/L.

7. The process according to claim 4, characterized in that, the precipitator in step (2) of the co-precipitation of the core material precursor is anyone selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate, or a combination of at least two selected therefrom; the ammonia in step (2) of the co-precipitation of the core material precursor is added in an amount of making the ammonia concentration in the mixed solution be 0.2-0.5 mol/L.

8. The process according to claim 4, characterized in that, the solution is pumped into the reaction still in step (3) of the co-precipitation of the core material precursor using a hydroxide precipitator at a flow rate which makes the pH of the solution in step (4) be 9-11; the solution is pumped into the reaction still in step (3) of the co-precipitation of the core material precursor using a carbonate precipitator at a flow rate which makes the pH of the solution in step (4) be 7.5-8.5; the constant temperature in step (4) of the co-precipitation of the core material precursor ranges from 45-55° C.; the stirring rate in step (4) of the co-precipitation of the core material precursor ranges from 800-1000 r/min.

9. The process according to claim 3, characterized in that the co-precipitation of the shell material solution outside the core material precursor comprises the following steps: (1) weighing in turn nickel salt, cobalt salt and manganese salt to formulate a solution; (2) weighing a precipitator to formulate a precipitator solution having a concentration of 1-3 mol/L, adding an ammonia as a complexing agent to formulate a mixed solution; (3) pumping into a reaction still the solution in step (1) and the mixed solution in step (2) via a constant flow pump at the same time after the completion of adding dropwise the solution during the synthesis of the core material precursor by co-precipitation; (4) controlling the flow of the two solutions in step (3) and adjusting the pH till the completion of adding dropwise the solution; or the co-precipitation of the shell material solution outside the core material precursor comprises the following steps: (1′) weighing in turn nickel salt, cobalt salt and aluminium salt to formulate a solution; (2) weighing a precipitator to formulate a precipitator solution having a concentration of 1-3 mol/L, adding an ammonia as a complexing agent to formulate a mixed solution; (3) pumping into a reaction still the solution in step (1′) and the mixed solution in step (2) via a constant flow pump after the completion of adding dropwise the solution during the synthesis of the core material precursor by co-precipitation; (4) controlling the flow of the two solutions in step (3) and adjusting the pH till the completion of adding dropwise the solution.

10. The process according to claim 9, characterized in that, the nickel salt in the co-precipitation of the shell material solution is anyone selected from the group consisting of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate, nickel acetate, nickel phosphate and nickel oxalate, or a combination of at least two selected therefrom; the cobalt salt in the co-precipitation of the shell material solution is anyone selected from the group consisting of cobalt chloride, cobalt sulfate, cobalt nitrate, cobalt carbonate, cobalt acetate, cobalt phosphate and cobalt oxalate, or a combination of at least two selected therefrom; the manganese salt in the co-precipitation of the shell material solution is anyone selected from the group consisting of manganese chloride, manganese sulfate, manganese acetate, manganese nitrate, manganese carbonate and manganese oxalate, or a combination of at least two selected therefrom; the aluminum salt in the co-precipitation of the shell material solution is anyone selected from the group consisting of aluminum chloride, aluminum sulfate, aluminum acetate, aluminum nitrate, aluminum carbonate and aluminum oxalate, or a combination of at least two selected therefrom;

11. The process according to claim 9, characterized in that, the nickel salt, cobalt salt and manganese salt in step (1) of the co-precipitation of the shell material solution have a metal element molar ratio of 1:0-1:0-1; the nickel salt, cobalt salt and aluminum salt in step (1′) of the co-precipitation of the shell material solution have a metal element molar ratio of 1:0-1:0-1; the solution(s) formulated in step (1) and/or step (1′) of the co-precipitation of the shell material solution independently has a concentration of 1-3 mol/L.

12. The process according to claim 9, characterized in that, the precipitator in step (2) of the co-precipitation of the shell material solution is anyone selected from the group consisting of sodium hydroxide, sodium carbonate, sodium bicarbonate, ammonium carbonate or ammonium bicarbonate, or a combination of at least two selected therefrom; the ammonia in step (2) of the co-precipitation of the shell material solution is added in an amount of making the ammonia concentration in the mixed solution be 0.2-0.5 mol/L.

13. The process according to claim 9, characterized in that, the solution is pumped into the reaction still in step (3) of the co-precipitation of the shell material solution using a hydroxide precipitator at a flow rate which makes the pH of the solution in step (4) be 9-11; the solution is pumped into the reaction still in step (3) of the co-precipitation of the shell material solution using a carbonate precipitator at a flow rate which makes the pH of the solution in step (4) be 7.5-8.5; the temperature, stirring rate and pH during the process of adding dropwise the solution in step (4) of the co-precipitation of the shell material solution are the same as those during the process of the co-precipitation of the core material precursor.

14. The process according to claim 3, characterized in that the aging in step (1) lasts for 12-15 h; the aging temperature in step (1) ranges from 45-55° C.

15. The process according to claim 3, characterized in that, the lithium source in step (2) is anyone selected from the group consisting of lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium formate, lithium bromide, lithium citrate and lithium chloride, or a combination of at least two selected therefrom; the lithium source and all the metal elements in the composite precursor in step (2) of the process for preparing the cathode material for nickel lithium ion battery have a molar ratio of 1-1.1:1.

16. The process according to claim 3, characterized in that the grinding in step (2) is carried out by ball grinding; the grinding in step (2) of the process for preparing the cathode material for nickel lithium ion battery lasts for 10-15 h.

17. The process according to claim 3, characterized in that the calcination in step (2) is carried out under oxygen atmosphere.

18. The process according to claim 3, characterized in that the calcination in step (2) comprises two steps of pre-calcination and calcination; the pre-calcination is heated at an increasing rate of 5° C./min from room temperature to 400-500° C.; the pre-calcination lasts for 4-6 h; the calcination is heated at an increasing rate of 5° C./min from 500° C. to 750-950° C.; the calcination lasts for 10-20 h.

19. Use of the cathode material for nickel lithium ion battery prepared according to the process claimed in claim 3 in the field of battery manufacturing.

Description

DESCRIPTION OF THE FIGURES

[0085] FIG. 1 shows the scanning electron microscopy image of the precursor with a concentration gradient obtained in Example 1 of the present invention.

[0086] FIG. 2 shows the scanning electron microscopy image of the precursor with a concentration gradient obtained in Example 1 of the present invention.

[0087] FIG. 3 shows the XRD image of the cathode material for lithium battery with a concentration gradient obtained in Example 1 of the present invention.

[0088] FIG. 4 shows the electrochemical performance test image of the cathode material for lithium battery with a concentration gradient obtained in Example 1 of the present invention.

[0089] FIG. 5 shows the electrochemical cycle performance test image of the cathode material for lithium battery with a concentration gradient obtained in Example 2 of the present invention.

EMBODIMENTS

[0090] In order to better illustrate the present invention and to better understand the technical solutions of the present invention, the typical and non-limiting examples of the present invention are described below.

Example 1

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0091] (1) weighing in turn NiSO.sub.4, CoSO.sub.4 and MnSO.sub.4 according to a metal element molar ratio of 8:1:1 to formulate 200 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 200 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 8 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0092] (1) weighing in turn NiSO.sub.4, CoSO.sub.4 and MnSO.sub.4 according to a metal element molar ratio of 1:1:1 to formulate 50 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 50 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 8 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 50° C., aging for 12 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium carbonate and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1.02:1, mixing and ball grinding for 10 h, then heating under oxygen atmosphere from room temperature to 500° C. at an increasing rate of 5° C./min, pre-calcining for 5 h, then heating to 800° C. at the same rate, calcining for 15 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient (as shown in FIGS. 1-3).

[0093] The obtained material was coated and assembled into a button battery for electrochemical test (shown in FIG. 4). The obtained material had a specific capacity of 180 mAh/g and a specific energy of 720 Wh/kg at 0.1 C, and a reversible capacity of 170 mAh/g after 100 cycles, and good cycle performance.

Example 2

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0094] (1) weighing in turn NiSO.sub.4, CoSO.sub.4 and Al.sub.2(SO.sub.4).sub.3 according to a metal element molar ratio of 8:1:1 to formulate 200 ml of a solution having a concentration of 2 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 200 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 11 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0095] (1) weighing in turn NiSO.sub.4, CoSO.sub.4 and Al.sub.2(SO.sub.4).sub.3 according to a metal element molar ratio of 1:1:1 to formulate 20 ml of a solution having a concentration of 2 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 20 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 11 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 50° C., aging for 12 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium hydroxide and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1.02:1, mixing and ball grinding for 10 h, then heating under oxygen atmosphere from room temperature to 500° C. at an increasing rate of 5° C./min, pre-calcining for 5 h, then heating to 850° C. at the same rate, calcining for 15 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0096] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 190 mAh/g and a specific energy of 760 Wh/kg at 0.1 C, and good cycle performance (as shown in FIG. 5).

Example 3

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0097] (1) weighing in turn NiCl.sub.2, CoCl.sub.2, MnCl.sub.2 according to a metal element molar ratio of 6:2:2 to formulate 200 ml of a solution having a concentration of 2 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 200 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.4 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 11 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0098] (1) weighing in turn NiSO.sub.4, CoSO.sub.4 and Al.sub.2(SO.sub.4).sub.3 according to a metal element molar ratio of 1:1:1 to formulate 40 ml of a solution having a concentration of 2 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 40 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 11 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 50° C., aging for 12 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium nitrate and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1.02:1, mixing and ball grinding for 10 h, then heating under oxygen atmosphere from room temperature to 500° C. at an increasing rate of 5° C./min, pre-calcining for 5 h, then heating to 900° C. at the same rate, calcining for 12 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0099] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 175 mAh/g and a specific energy of 685 Wh/kg at 0.1 C.

Example 4

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0100] (1) weighing NiSO.sub.4 to formulate 200 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 200 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 8 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0101] (1) weighing in turn NiSO.sub.4, CoSO.sub.4, MnSO.sub.4 according to a metal element molar ratio of 1:1:1 to formulate 100 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 100 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 8 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 50° C., aging for 15 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium carbonate and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1.02:1, mixing and ball grinding for 10 h, then heating under oxygen atmosphere from room temperature to 500° C. at an increasing rate of 5° C./min, pre-calcining for 5 h, then heating to 800° C. at the same rate, calcining for 12 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0102] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 210 mAh/g and a specific energy of 824 Wh/kg at 0.1 C.

Example 5 this Example is an Enlarge Test

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0103] (1) weighing in turn NiSO.sub.4, CoSO.sub.4, MnSO.sub.4 according to a metal element molar ratio of 9:0.5:0.5 to formulate 2 L of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 2 L of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.4 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 8 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0104] (1) weighing in turn NiSO.sub.4, CoSO.sub.4, MnSO.sub.4 according to a metal element molar ratio of 1:1:1 to formulate 100 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 100 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.4 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 8 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 1000 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 50° C., aging for 12 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium nitrate and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1.05:1, mixing and ball grinding for 12 h, then heating under oxygen atmosphere from room temperature to 500° C. at an increasing rate of 5° C./min, pre-calcining for 5 h, then heating to 850° C. at the same rate, calcining for 15 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0105] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 195 mAh/g and a specific energy of 775 Wh/kg at 0.1 C.

Example 6

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0106] (1) weighing in turn Ni.sub.3(PO.sub.4).sub.2, Co.sub.3(PO.sub.4).sub.2, Mn.sub.3(PO.sub.4).sub.2 according to a metal element molar ratio of 5:2.5:2.5 to formulate 230 ml of a solution having a concentration of 2.5 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 230 ml of a solution having a concentration of 2.5 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.5 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 9 by controlling the flow of the two solutions, stirring at a constant temperature of 55° C. and a rate of 900 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0107] (1) weighing in turn Ni.sub.3(PO.sub.4).sub.2, Co.sub.3(PO.sub.4).sub.2, Mn.sub.3 (PO.sub.4).sub.2 according to a metal element molar ratio of 1:1:1 to formulate 60 ml of a solution having a concentration of 2.5 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 60 ml of a solution having a concentration of 2.5 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.5 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 9 by controlling the flow of the two solutions, stirring at a constant temperature of 55° C. and a rate of 900 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 55° C., aging for 13 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium citrate and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1.07:1, mixing and ball grinding for 15 h, then heating under oxygen atmosphere from room temperature to 450° C. at an increasing rate of 5° C./min, pre-calcining for 4 h, then heating to 950° C. at the same rate, calcining for 10 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0108] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 173 mAh/g and a specific energy of 658 Wh/kg at 0.1 C.

Example 7

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0109] (1) weighing in turn nickel acetate, cobalt acetate and aluminum acetate according to a metal element molar ratio of 7:1.5:1.5 to formulate 250 ml of a solution having a concentration of 3 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 250 ml of a solution having a concentration of 3 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.3 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 10 by controlling the flow of the two solutions, stirring at a constant temperature of 45° C. and a rate of 800 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0110] (1) weighing in turn nickel acetate, cobalt acetate and aluminum acetate according to a metal element molar ratio of 1:1:1 to formulate 50 ml of a solution having a concentration of 3 mol/L;
(2) weighing a hydroxide precipitator NaOH to formulate 50 ml of a solution having a concentration of 3 mol/L, and adding NH.sub.3.H.sub.2O into the NaOH solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.3 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 10 by controlling the flow of the two solutions, stirring at a constant temperature of 45° C. and a rate of 800 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 45° C., aging for 12 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium bromide and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1.1:1, mixing and ball grinding for 15 h, then heating under oxygen atmosphere from room temperature to 400° C. at an increasing rate of 5° C./min, pre-calcining for 6 h, then heating to 750° C. at the same rate, calcining for 20 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0111] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 180 mAh/g and a specific energy of 703 Wh/kg at 0.1 C.

Example 8

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0112] (1) weighing in turn nickel oxalate, cobalt oxalate and aluminum oxalate according to a metal element molar ratio of 8:1:1 to formulate 200 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 200 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 8.5 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 850 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0113] (1) weighing in turn nickel oxalate, cobalt oxalate and aluminum oxalate according to a metal element molar ratio of 1:1:1 to formulate 30 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 30 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 8.5 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 850 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 50° C., aging for 13 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium formate and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1:1, mixing and ball grinding for 13 h, then heating under oxygen atmosphere from room temperature to 500° C. at an increasing rate of 5° C./min, pre-calcining for 6 h, then heating to 850° C. at the same rate, calcining for 14 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0114] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 180 mAh/g and a specific energy of 720 Wh/kg at 0.1 C.

Example 9

1. Synthesizing a Core Material Precursor by Co-Precipitation

[0115] (1) weighing in turn nickel oxalate and cobalt oxalate according to a metal element molar ratio of 7:2 to formulate 200 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 200 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the two solutions in steps (1) and (2) into a reaction still via a constant flow pump;
(4) adjusting the pH to 7.5 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 850 r/min till the completion of adding dropwise the solution.

2. Co-Precipitating a Shell Material Solution Outside the Core Material Precursor

[0116] (1) weighing in turn nickel oxalate, cobalt oxalate and manganese oxalate according to a metal element molar ratio of 1:1:1 to formulate 30 ml of a solution having a concentration of 2 mol/L;
(2) weighing a carbonate precipitator Na.sub.2CO.sub.3 to formulate 30 ml of a solution having a concentration of 2 mol/L, and adding NH.sub.3.H.sub.2O into the Na.sub.2CO.sub.3 solution to formulate a mixed solution, wherein NH.sub.3.H.sub.2O had a molar concentration of 0.2 mol/L;
(3) simultaneously pumping the solution in step (1) and the mixed solution in step (2) into a reaction still via a constant flow pump after the completion of adding dropwise the solution in the process of synthesizing the core material precursor by co-precipitation;
(4) adjusting the pH to 7.5 by controlling the flow of the two solutions, stirring at a constant temperature of 50° C. and a rate of 850 r/min till the completion of adding dropwise the solution, maintaining a constant temperature of 50° C., aging for 13 hours, filtering, washing and drying to obtain a composite precursor having a concentration gradient;
3. Weighing lithium formate, lithium bromide and the composite precursor according to a molar ratio of lithium to all the metal elements in the composite precursor of 1:1, mixing and ball grinding for 13 h, then heating under oxygen atmosphere from room temperature to 500° C. at an increasing rate of 5° C./min, pre-calcining for 5 h, then heating to 850° C. at the same rate, calcining for 14 h and naturally cooling to obtain a cathode material for lithium battery having a concentration gradient.

[0117] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 176 mAh/g and a specific energy of 680 Wh/kg at 0.1 C.

Example 10

[0118] Except for weighing nickel oxalate and manganese oxalate according to a metal element molar ratio of 7:2 in the process of synthesizing a core material precursor by co-precipitation, other steps were the same as those in Example 1.

[0119] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 176 mAh/g and a specific energy of 680 Wh/kg at 0.1 C.

Comparison Example 1

[0120] Except for not carrying out the process of co-precipitating low-nickel ternary material solution outside the core material precursor, other steps were the same as those in Example 1.

[0121] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 186 mAh/g at 0.1 C, and a reversible capacity of 140 mAh/g after 100 cycles which showed a poor cycle performance.

Comparison Example 2

[0122] Except for synthesizing a low-nickel ternary material precursor directly by precipitation, rather than synthesizing a core material precursor by co-precipitation, other steps were the same as those in Example 1.

[0123] The obtained material was coated and assembled into a button battery for electrochemical test. The obtained material had a specific capacity of 105 mAh/g and a specific energy of 405 Wh/kg at 0.1 C.

[0124] The performance test results of the materials prepared in Examples 1-10 and Comparison Examples 1-2 are listed in Table 1 below.

TABLE-US-00001 TABLE 1 The performance test results of the materials prepared in Examples 1-10 and Comparison Examples 1-2 Comparison Examples Examples 0.1 C 1 2 3 4 5 6 7 8 9 10 1 2 Specific 180 190 175 210 195 173 180 180 176 176 186 105 capacity mAh/g Specific 720 760 685 824 775 658 703 720 680 680 727 405 energy Wh/kg

[0125] The results in Examples 1 to 10 and Comparison Examples 1-2 show that the prepared material has a specific capacity of more than 170 mAh/g and a specific energy of 700 Wh/kg or more at 0.1 C. The synthesis of the composite precursor in which the core material is coated with the shell material by one-step method makes the nickel element in the obtained material show a concentration gradient distribution, wherein the content of the nickel element in the core is high, and the content of the nickel element in the shell is less. The inner nickel element ensures the specific capacity of the material, and the outer coating material maintains the stability of the structure of the material, which solves the problems of insufficient high-nickel-lithium battery materials, safety, electrochemical cycle and magnification, increases the safety of the material in the charge and discharge process and improves the cycle and rate capability of the material.

[0126] The applicant claims that the present invention describes the process of the present invention in details, but the present invention is not limited to the above detailed process. That is to say, it does not means that the present invention shall be carried out with respect to the above-described process. Those skilled in the art shall know that any improvements to the present invention, equivalent replacements of the raw materials of the present invention, additions of auxiliary ingredients, selections of specific ways and the like all fall within the protection scope and disclosure scope of the present invention.