W-CONTAINING HIGH-NICKEL TERNARY CATHODE MATERIAL AND PREPARATION METHOD THEREOF

Abstract

The present disclosure discloses a W-containing high-nickel ternary cathode material, including both spherical secondary particles and single-crystal particles. There is basically no W inside the single-crystal particles, and the spherical secondary particles are doped with W. A preparation method of the W-containing high-nickel ternary cathode material includes: mixing a nickel salt, a cobalt salt, and a manganese salt according to a specified molar ratio, and adding an ammonia solution and a sodium hydroxide solution for co-precipitation to prepare a precursor A; mixing a nickel salt, a cobalt salt, a manganese salt, and a tungsten salt, and adding an ammonia solution and a sodium hydroxide solution for co-precipitation to prepare a W-containing precursor B; and mixing the precursor A, the precursor B, a lithium source, and a doping element M-containing compound, and subjecting a resulting mixture to high-temperature sintering in an oxygen atmosphere to obtain the high-nickel ternary cathode material including both spherical secondary particles and single-crystal particles. While increasing the capacity, the spherical secondary particles in the product of the present disclosure can ensure that a crystal structure will not undergo obvious phase transition when lithium ions are deintercalated during a cycling process, which helps to improve the cycling performance.

Claims

1. A W-containing high-nickel ternary cathode material, with a chemical formula of Li.sub.aNi.sub.xCo.sub.yMn.sub.1-x-yW.sub.bM.sub.cO.sub.2, wherein the high-nickel ternary cathode material comprises both spherical secondary particles and single-crystal particles; there is basically no W inside the single-crystal particles; and the spherical secondary particles are doped with W.

2. The W-containing high-nickel ternary cathode material according to claim 1, wherein the spherical secondary particles have a particle size of 2.4 μm to 5.5 μm; the single-crystal particles have a particle size of 1.0 μm to 5.5 μm; and the high-nickel ternary cathode material has a median diameter of 3.0 μm to 5.5 μm.

3. The W-containing high-nickel ternary cathode material according to claim 1, wherein a mass ratio of the spherical secondary particles to the single-crystal particles in the high-nickel ternary cathode material is determined by a ratio of a W-containing precursor B to a W-free precursor A in a raw material.

4. The W-containing high-nickel ternary cathode material according to claim 3, wherein a mass ratio of the precursor B to the precursor A is (0.05-19):1.

5. The W-containing high-nickel ternary cathode material according to claim 4, wherein a mass ratio of the precursor B to the precursor A is (0.4-1.5):1.

6. The W-containing high-nickel ternary cathode material according to claim 1, wherein a surface of the high-nickel ternary cathode material is at least partly or completely coated with a lithium tungstate layer.

7. The W-containing high-nickel ternary cathode material according to claim 2, wherein a surface of the high-nickel ternary cathode material is at least partly or completely coated with a lithium tungstate layer.

8. The W-containing high-nickel ternary cathode material according to claim 1, wherein in the molecular formula of Li.sub.aNi.sub.xCo.sub.yMn.sub.1-x-yW.sub.bM.sub.cO.sub.2, 1.00≤a≤1.16, 0.7<x<1, 0<y<0.3, 0.002<b+c<0.01, and the M is one or more from the group consisting of Zr, Mg, Ti, Al, Si, La, Ba, Sr, Nb, Cr, Mo, Ca, Y, In, Sn, and F; and the high-nickel ternary cathode material has a specific surface area (SSA) of 0.8±0.3 m.sup.2/g.

9. The W-containing high-nickel ternary cathode material according to claim 2, wherein in the molecular formula of Li.sub.aNi.sub.xCo.sub.yMn.sub.1-x-yW.sub.bM.sub.cO.sub.2, 1.00≤a≤1.16, 0.7<x<1, 0<y<0.3, 0.002<b+c<0.01, and the M is one or more from the group consisting of Zr, Mg, Ti, Al, Si, La, Ba, Sr, Nb, Cr, Mo, Ca, Y, In, Sn, and F; and the high-nickel ternary cathode material has a specific surface area (SSA) of 0.8±0.3 m.sup.2/g.

10. The W-containing high-nickel ternary cathode material according to claim 1, wherein on the premise of ignoring element loss during a preparation process, a Ni—Co—Mn molar ratio in the spherical secondary particles is consistent with a Ni—Co—Mn molar ratio in the single-crystal particles.

11. W-containing high-nickel ternary cathode material according to claim 2, wherein on the premise of ignoring element loss during a preparation process, a Ni—Co—Mn molar ratio in the spherical secondary particles is consistent with a Ni—Co—Mn molar ratio in the single-crystal particles.

12. A preparation method of a W-containing high-nickel ternary cathode material, comprising the following steps: (1) mixing and dissolving a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt in deionized water according to a nickel-cobalt-manganese molar ratio in a molecular formula of the product, continuously stirring a resulting solution in a reactor, and adding an ammonia solution and a sodium hydroxide solution for co-precipitation to prepare a precursor A; (2) mixing and dissolving a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt in deionized water according to a nickel-cobalt-manganese molar ratio in the molecular formula of the product, adding a soluble tungsten salt, and after the tungsten salt is completely dissolved, transferring a resulting solution to a reactor; and continuously stirring the solution, and adding an ammonia solution and a sodium hydroxide solution for co-precipitation to prepare a W-containing precursor B; and (3) thoroughly mixing the precursor A, the precursor B, a lithium source, and a doping element M-containing compound, subjecting a resulting mixed material to high-temperature sintering in an oxygen atmosphere, and crushing a sintered material to a median diameter of 3.0 μm to 5.5 μm to obtain the W-containing high-nickel ternary cathode material, which has a molecular formula of Li.sub.aNi.sub.xCo.sub.yMn.sub.1-x-yW.sub.bM.sub.cO.sub.2 and comprises both spherical secondary particles and single-crystal particles.

13. The preparation method according to claim 12, wherein in step (2), the soluble tungsten salt comprises one or more from the group consisting of ammonium metatungstate (AMT), phosphotungstic acid (PTA), sodium tungstate, and ammonium paratungstate (APT); and a molar ratio of tungsten in the soluble tungsten salt to a sum of nickel, cobalt, and manganese in the precursor B is (0.00025-0.00550):1.

14. The preparation method according to claim 12, wherein in step (3), the lithium source is one or more from the group consisting of lithium carbonate, lithium hydroxide, lithium acetate, and lithium oxalate; and a molar ratio of lithium in the lithium source to a sum of main metal elements in the precursor B, the precursor A, and the doping element M-containing compound is (0.95-1.1):1.

15. The preparation method according to claim 12, wherein in step (3), the doping element M-containing compound is an oxide of the M element, and the oxide of the M element is at least one from the group consisting of ZrO.sub.2, MgO, TiO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, La.sub.2O.sub.3, BaO, SrO, Nb.sub.2O.sub.5, Cr.sub.2O.sub.3, MoO.sub.3, CaO, Y.sub.2O.sub.3, In.sub.2O.sub.3, and SnO.sub.2.

16. The preparation method according to claim 12, wherein in step (3), the high-temperature sintering is conducted for 8 h to 18 h at a temperature of 750° C. to 980° C. and an oxygen flow rate of 20 L/min to 60 L/min.

17. The preparation method according to claim 14, wherein in step (3), the high-temperature sintering is conducted for 8 h to 18 h at a temperature of 750° C. to 980° C. and an oxygen flow rate of 20 L/min to 60 L/min.

18. The preparation method according to claim 12, wherein in step (3), the high-temperature sintering is conducted once.

19. The preparation method according to claim 14, wherein in step (3), the high-temperature sintering is conducted once.

20. The preparation method according to claim 15, wherein in step (3), the high-temperature sintering is conducted once.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To describe the technical solutions in examples of the present disclosure or in the prior art more clearly, the accompanying drawings required for describing the examples or the prior art will be briefly described below. Apparently, the accompanying drawings in the following description show some examples of the present disclosure, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

[0034] FIG. 1 is a scanning electron microscopy (SEM) image of the high-nickel ternary cathode material prepared in Example 1 of the present disclosure;

[0035] FIG. 2 shows the particle size distribution of the high-nickel ternary cathode material prepared in Example 1 of the present disclosure;

[0036] FIG. 3 is an energy dispersive spectroscopy (EDS) spectrum of the W element on a selected area of the surface of single-crystal particles in the high-nickel ternary cathode material obtained in Example 1 of the present disclosure;

[0037] FIG. 4 is a Rietveld refined X-ray diffraction (XRD) pattern of the high-nickel ternary cathode material prepared in Example 1 of the present disclosure;

[0038] FIG. 5 is an SEM image of the spherical-secondary-particle high-nickel ternary cathode material prepared in Comparative Example 1;

[0039] FIG. 6 shows the comparison of pH titration curves of the high-nickel ternary cathode material prepared in Example 1 and the high-nickel ternary cathode material prepared in Comparative Example 1 of the present disclosure;

[0040] FIG. 7 is an SEM image of the single-crystal-particle high-nickel ternary cathode material prepared in Comparative Example 2;

[0041] FIG. 8 is an SEM image of the single-crystal-particle high-nickel ternary cathode material prepared in Comparative Example 3;

[0042] FIG. 9 is an EDS spectrum of the W element on a selected area of the surface of single-crystal particles in the high-nickel ternary cathode material prepared through physical blending in Comparative Example 4;

[0043] FIG. 10 is a particle size distribution diagram obtained from the SEM image of Comparative Example 1 according to a legend scale;

[0044] FIG. 11 is a particle size distribution diagram obtained from the SEM image of Comparative Example 2 according to a legend scale; and

[0045] FIG. 12 is a Rietveld refined XRD pattern of the high-nickel ternary cathode material prepared in Example 2 of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] In order to facilitate the understanding of the present disclosure, the present disclosure is described in detail below in conjunction with the accompanying drawings of the specification and the preferred examples, but the protection scope of the present disclosure is not limited to the following specific examples.

[0047] Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are merely for the purpose of describing specific examples, and are not intended to limit the protection scope of the present disclosure.

[0048] Unless otherwise specified, various raw materials, reagents, instruments, equipment, and the like used in the present disclosure can be purchased from the market or can be prepared by existing methods.

Example 1

[0049] A W-containing high-nickel ternary cathode material of the present disclosure was provided, with a chemical formula of Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1W.sub.0.0008Al.sub.0.006O.sub.2. The high-nickel ternary cathode material included both spherical secondary particles and single-crystal particles, where there was basically no W inside the single-crystal particles and the spherical secondary particles were doped with W; and the high-nickel ternary cathode material had a median diameter of 4.5 μm and an SSA of 0.68 m.sup.2/g.

[0050] A preparation method of the W-containing high-nickel ternary cathode material in this example was as follows:

[0051] (1) A mixed solution of 0.8 mol/L nickel sulfate, 0.1 mol/L cobalt sulfate, and 0.1 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 80 ml/min, during which a pH of the reaction system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a precursor A.

[0052] (2) A mixed solution of 0.8 mol/L nickel sulfate, 0.1 mol/L cobalt sulfate, and 0.1 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1, and then AMT was added to the mixed solution, where a molar ratio of tungsten to a sum of nickel, cobalt, and manganese in the mixed solution was 0.0008:1 and W had a concentration of 0.004 mol/L in the mixed solution; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 80 ml/min, during which a pH of the system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a W-doped precursor B.

[0053] (3) The precursor B, the precursor A, LiOH, and Al.sub.2O.sub.3 were mixed, and a resulting mixed material was stirred for 25 min at a speed of 3,000 r/min, where a mass ratio of the precursor B to the precursor A was 1:4, a molar ratio of Al to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.6%, and a molar ratio of Li to other main metal elements was about 1:1; the mixed material was subjected to one-time high-temperature sintering for 10 h at a temperature of 890° C. and an oxygen flow rate of 40 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 4.5 μm to obtain the high-nickel ternary cathode material Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1W.sub.0.0008Al.sub.0.006O.sub.2 in which a theoretical mass ratio of spherical secondary particles to single-crystal particles was 1:4.

[0054] The product prepared in Example 1 was subjected to field emission-scanning electron microscopy (FE-SEM), and a resulting image in FIG. 1 showed that, in the high-nickel cathode material prepared in this example, there were both spherical secondary particles and single-crystal particles, and the spherical secondary particles had uniform sphericity and were uniformly distributed. A mass ratio of the spherical secondary particles to the single-crystal particles in the high-nickel ternary cathode material was adjusted by adjusting a ratio of the W-containing precursor B to the W-free precursor A in the raw material, and was about 1:4. A powder of the cathode material had a compacted density of 3.58 g/cm.sup.3, a median particle size of 4.5 μm (as shown in FIG. 2), an SSA of 0.68 m.sup.2/g, and a pH of 11.0. The spherical secondary particles had a particle size range of 2.4 μm to 5.5 μm (as shown in FIG. 10), and the single-crystal particles had a particle size range of 1.0 μm to 5.5 μm (as shown in FIG. 11). Through the EDS analysis shown in FIG. 3 in combination with the subsequent test of comparative examples, it can be seen that W was mainly distributed in the spherical secondary particles (which was not only internally doped, but also coated on the surface of the spherical secondary particles); and for the single-crystal particles, only the surface was covered with a W-containing coating layer, and there was almost no W inside, indicating that the W was only distributed on the surface. According to Gibbs free energy, lithium tungstate was easily formed, and thus a lithium tungstate layer was preferentially formed on a surface with W and Li. Al was uniformly distributed on the surface of single-crystal and spherical secondary particles, resulting in uniform doping. The Rietveld refinement was conducted on XRD data, and a resulting pattern was shown in FIG. 4, with a c value of 14.1966 and an a value of 2.8727. The c value and the c/a value were both significantly increased, indicating that W effectively increased the c value. On the premise of ignoring element loss during the preparation process, a Ni—Co—Mn molar ratio in the spherical secondary particles was consistent with a Ni—Co—Mn molar ratio in the single-crystal particles, and the particles of the two morphologies had the same crystal structure and lattice parameters.

[0055] The high-nickel ternary cathode material with two morphologies prepared in this example was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0056] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 205 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 93.2% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 98.6%. IL indicates that the high-nickel cathode material with two morphologies can effectively improve the capacity, cycling performance, and rate performance. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 97.3%. It indicates that the high-nickel ternary cathode material with two morphologies has excellent high-temperature cycling performance.

Example 2

[0057] A W-containing high-nickel ternary cathode material of the present disclosure was provided, with a chemical formula of Li.sub.1.004Ni.sub.0.88Co.sub.0.09Mn.sub.0.03W.sub.0.001Zr.sub.0.003O.sub.2. The high-nickel ternary cathode material included both spherical secondary particles and single-crystal particles, where there was basically no W inside the single-crystal particles and the spherical secondary particles were doped with W; and the high-nickel ternary cathode material had a median diameter of 4.2 μm and an SSA of 0.72 m.sup.2/g.

[0058] A preparation method of the W-containing high-nickel ternary cathode material in this example was as follows:

[0059] (1) A mixed solution of 0.88 mol/L nickel sulfate, 0.09 mol/L cobalt sulfate, and 0.03 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.88:0.09:0.03; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.8 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3.5 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 70 ml/min, during which a pH of the system was controlled at 11.8 (with an ammonia value of 3.5 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a precursor A.

[0060] (2) A mixed solution of 0.88 mol/L nickel sulfate, 0.09 mol/L cobalt sulfate, and 0.03 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.88:0.09:0.03, and then AMT was added to the mixed solution, where a molar ratio of tungsten to a sum of nickel, cobalt, and manganese in the mixed solution was 0.001:1 and W had a concentration of 0.002 mol/L in the mixed solution; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.8 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3.5 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 70 ml/min, during which a pH of the system was controlled at 11.8 (with an ammonia value of 3.5 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.6 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a W-doped precursor B.

[0061] (3) The precursor B, the precursor A, LiOH, and ZrO.sub.2 were mixed, and a resulting mixed material was stirred for 30 min at a speed of 2,000 r/min, where a mass ratio of the precursor B to the precursor A was 1:1, a molar ratio of Zr to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.3%, and a molar ratio of Li to other main metal elements was about 1:1; the mixed material was subjected to one-time high-temperature sintering for 14 h at a temperature of 870° C. and an oxygen flow rate of 45 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 4.2 μm to obtain the high-nickel ternary cathode material Li.sub.1.004Ni.sub.0.88Co.sub.0.09Mn.sub.0.03W.sub.0.001Zr.sub.0.003O.sub.2 in which a theoretical mass ratio of spherical secondary particles to single-crystal particles was 1:1.

[0062] The product prepared in this example was subjected to FE-SEM, and a resulting image showed that, in the high-nickel cathode material prepared in this example, there were both spherical secondary particles and single-crystal particles, and the spherical secondary particles had uniform sphericity and were uniformly distributed. A mass ratio of the spherical secondary particles to the single-crystal particles in the high-nickel ternary cathode material was adjusted by adjusting a ratio of the W-containing precursor B to the W-free precursor A in the raw material, and was about 1:1. A powder of the cathode material had a compacted density of 3.62 g/cm.sup.3, a median particle size of 4.2 μm, an SSA of 0.72 m.sup.2/g, and a pH of 11.2. The spherical secondary particles had a particle size range of 2.4 μm to 5.5 μm, and the single-crystal particles had a particle size range of 1.0 μm to 5.5 μm. Through the EDS analysis in combination with the subsequent test of comparative examples, it can be seen that W was mainly distributed in the spherical secondary particles (which was not only internally doped, but also coated on the surface of the spherical secondary particles); and for the single-crystal particles, only the surface was covered with a W-containing coating layer, and there was almost no W inside, indicating that the W was only distributed on the surface. According to Gibbs free energy, lithium tungstate was easily formed, and thus a lithium tungstate layer was preferentially formed on a surface with W and Li. Zr was uniformly distributed on the surface of single-crystal and spherical secondary particles, resulting in uniform doping. The Rietveld refinement was conducted on XRD data, and a resulting pattern was shown in FIG. 12, with a c value of 14.1968 and an a value of 2.8726. The c value and the c/a value were both significantly increased, indicating that W effectively increased the c value. On the premise of ignoring element loss during the preparation process, a Ni—Co—Mn molar ratio in the spherical secondary particles was consistent with a Ni—Co—Mn molar ratio in the single-crystal particles, and the particles of the two morphologies had the same crystal structure and lattice parameters.

[0063] The high-nickel ternary cathode material with two morphologies prepared in this example was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0064] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 218 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 93.6% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 98.1%. It indicates that the high-nickel cathode material with two morphologies can effectively improve the capacity, cycling performance, and rate performance. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 97.0%. It indicates that the high-nickel ternary cathode material with two morphologies has excellent high-temperature cycling performance.

Example 3

[0065] A W-containing high-nickel ternary cathode material of the present disclosure was provided, with a chemical formula of Li.sub.1.0029Ni.sub.0.83Co.sub.0.11Mn.sub.0.06W.sub.0.0009La.sub.0.002O.sub.2. The high-nickel ternary cathode material included both spherical secondary particles and single-crystal particles, where there was basically no W inside the single-crystal particles and the spherical secondary particles were doped with W; and the high-nickel ternary cathode material had a median diameter of 5.0 μm and an SSA of 0.80 m.sup.2/g.

[0066] A preparation method of the W-containing high-nickel ternary cathode material in this example was as follows:

[0067] (1) A mixed solution of 0.83 mol/L nickel sulfate, 0.11 mol/L cobalt sulfate, and 0.06 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.83:0.11:0.06; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.5 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3.5 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 75 ml/min, during which a pH of the system was controlled at 11.5 (with an ammonia value of 3.5 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.5 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a precursor A.

[0068] (2) A mixed solution of 0.83 mol/L nickel sulfate, 0.11 mol/L cobalt sulfate, and 0.06 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.83:0.11:0.06, and then AMT was added to the mixed solution, where a molar ratio of tungsten to a sum of nickel, cobalt, and manganese in the mixed solution was 0.0009:1 and W had a concentration of 0.003 mol/L in the mixed solution; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.5 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3.5 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 75 ml/min, during which a pH of the system was controlled at 11.5 (with an ammonia value of 3.5 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.6 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a W-doped precursor B.

[0069] (3) The precursor B, the precursor A, LiOH, and La.sub.2O.sub.3 were mixed, and a resulting mixed material was stirred for 30 min at a speed of 2,000 r/min, where a mass ratio of the precursor B to the precursor A was 3:7, a molar ratio of La to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.2%, and a molar ratio of Li to other main metal elements was about 1:1; the mixed material was subjected to one-time high-temperature sintering for 14 h at a temperature of 880° C. and an oxygen flow rate of 40 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 5.0 μm to obtain the high-nickel ternary cathode material Li.sub.1.0029Ni.sub.0.83Co.sub.0.11Mn.sub.0.06W.sub.0.0009La.sub.0.002O.sub.2 in which a theoretical mass ratio of spherical secondary particles to single-crystal particles was 3:7.

[0070] According to FE-SEM, in the high-nickel ternary cathode material prepared, there were both spherical secondary particles and single-crystal particles, and the spherical secondary particles had uniform sphericity and were uniformly distributed. A mass ratio of the spherical secondary particles to the single-crystal particles in the high-nickel ternary cathode material was about 3:7. A powder of the cathode material had a compacted density of 3.62 g/cm.sup.3, a median particle size of 5.0 μm, an SSA of 0.80 m.sup.2/g, and a pH of 11.1. The spherical secondary particles had a particle size range of 2.4 μm to 5.5 μm, and the single-crystal particles had a particle size range of 1.0 μm to 5.5 μm. Through the EDS analysis in combination with the subsequent test of comparative examples, it can be seen that W was mainly distributed in the spherical secondary particles (which was not only internally doped, but also coated on the surface of the spherical secondary particles); and for the single-crystal particles, only the surface was covered with a W-containing coating layer, and there was almost no W inside, indicating that the W was only distributed on the surface. According to Gibbs free energy, lithium tungstate was easily formed, and thus a lithium tungstate layer was preferentially formed on a surface with W and Li. La was uniformly distributed on the surface of single-crystal and spherical secondary particles, resulting in uniform doping. The Rietveld refinement was conducted on XRD data, and it can be known that a c value was 14.1972 and an a value was 2.8725. The c value and the c/a value were both significantly increased, indicating that W effectively increased the c value. On the premise of ignoring element loss during the preparation process, a Ni—Co—Mn molar ratio in the spherical secondary particles was consistent with a Ni—Co—Mn molar ratio in the single-crystal particles, and the particles of the two morphologies had the same crystal structure and lattice parameters.

[0071] The high-nickel ternary cathode material with two morphologies was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0072] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 213 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 94.6% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 98.2%. It indicates that the high-nickel cathode material with two morphologies can effectively improve the capacity, cycling performance, and rate performance. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 97.2%. It indicates that the high-nickel ternary cathode material with two morphologies has excellent high-temperature cycling performance.

Example 4

[0073] A W-containing high-nickel ternary cathode material of the present disclosure was provided, with a chemical formula of Li.sub.1.0042Ni.sub.0.92Co.sub.0.06Mn.sub.0.02W.sub.0.0012Ti.sub.0.003O.sub.2. The high-nickel ternary cathode material included both spherical secondary particles and single-crystal particles, where there was basically no W inside the single-crystal particles and the spherical secondary particles were doped with W; and the high-nickel ternary cathode material had a median diameter of 3.8 μm and an SSA of 0.81 m.sup.2/g.

[0074] A preparation method of the W-containing high-nickel ternary cathode material in this example was as follows:

[0075] (1) A mixed solution of 0.92 mol/L nickel sulfate, 0.06 mol/L cobalt sulfate, and 0.02 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.92:0.06:0.02; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.9 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 4 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 60 ml/min, during which a pH of the system was controlled at 11.9 (with an ammonia value of 4 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a precursor A.

[0076] (2) A mixed solution of 0.92 mol/L nickel sulfate, 0.06 mol/L cobalt sulfate, and 0.02 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.92:0.06:0.02, and then AMT was added to the mixed solution, where a molar ratio of tungsten to a sum of nickel, cobalt, and manganese in the mixed solution was 0.0012:1 and W had a concentration of 0.003 mol/L in the mixed solution; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.9 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 4 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 60 ml/min, during which a pH of the system was controlled at 11.9 (with an ammonia value of 4 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a W-doped precursor B.

[0077] (3) The precursor B, the precursor A, LiOH, and TiO.sub.2 were mixed, and a resulting mixed material was stirred for 30 min at a speed of 2,500 r/min, where a mass ratio of the precursor B to the precursor A was 2:3, a molar ratio of Ti to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.3%, and a molar ratio of Li to other main metal elements was about 1:1; the mixed material was subjected to one-time high-temperature sintering for 12 h at a temperature of 860° C. and an oxygen flow rate of 50 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 3.8 μm to obtain the high-nickel ternary cathode material Li.sub.1.0042Ni.sub.0.92Co.sub.0.06Mn.sub.0.02W.sub.0.0012Ti.sub.0.003O.sub.2 in which a theoretical mass ratio of spherical secondary particles to single-crystal particles was 2:3.

[0078] According to FE-SEM, in the high-nickel ternary cathode material prepared, there were both spherical secondary particles and single-crystal particles, and the spherical secondary particles had uniform sphericity and were uniformly distributed. A mass ratio of the spherical secondary particles to the single-crystal particles in the high-nickel ternary cathode material was about 2:3. A powder of the cathode material had a compacted density of 3.63 g/cm.sup.3, a median particle size of 3.8 μm, an SSA of 0.81 m.sup.2/g, and a pH of 11.6. The spherical secondary particles had a particle size range of 2.4 μm to 5.5 μm, and the single-crystal particles had a particle size range of 1.0 μm to 5.5 μm. Through the EDS analysis in combination with the subsequent test of comparative examples, it can be seen that W was mainly distributed in the spherical secondary particles (which was not only internally doped, but also coated on the surface of the spherical secondary particles); and for the single-crystal particles, only the surface was covered with a W-containing coating layer, and there was almost no W inside, indicating that the W was only distributed on the surface. According to Gibbs free energy, lithium tungstate was easily formed, and thus a lithium tungstate layer was preferentially formed on a surface with W and Li. Ti was uniformly distributed on the surface of single-crystal and spherical secondary particles, resulting in uniform doping. The Rietveld refinement was conducted on XRD data, and it can be known that a c value was 14.1952 and an a value was 2.8726. The c value and the c/a value were both increased, indicating that W effectively increased the c value. On the premise of ignoring element loss during the preparation process, a Ni—Co—Mn molar ratio in the spherical secondary particles was consistent with a Ni—Co—Mn molar ratio in the single-crystal particles, and the particles of the two morphologies had the same crystal structure and lattice parameters.

[0079] The high-nickel ternary cathode material with two morphologies was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0080] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 223 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 93.2% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 97.9%. It indicates that the high-nickel cathode material with two morphologies can effectively improve the capacity, cycling performance, and rate performance. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 96.5%. It indicates that the high-nickel ternary cathode material with two morphologies has excellent high-temperature cycling performance.

Comparative Example 1

[0081] A high-nickel spherical-secondary-particle ternary cathode material was prepared using only a tungsten-doped precursor in Comparative Example 1, which was formed by doping LNMCO with W and Al and had a molecular formula of Li.sub.1.006Ni.sub.0.8Co.sub.0.1Mn.sub.0.1W.sub.0.0008Al.sub.0.006O.sub.2. A preparation method of the ternary cathode material included the following steps:

[0082] (1) A mixed solution of 0.8 mol/L nickel sulfate, 0.1 mol/L cobalt sulfate, and 0.1 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1, and then AMT was added to the mixed solution, where W had a concentration of 0.0008 mol/L in the mixed solution; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 900 rpm and fed into a reactor at a flow rate of 75 ml/min, during which a pH of the system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a W-doped precursor B.

[0083] (2) The precursor B. LiOH, and Al.sub.2O.sub.3 were mixed, and a resulting mixed material was stirred for 25 min at a speed of 2,500 r/min, where a molar ratio of Al to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.6% and a molar ratio of Li to other metal elements was about 1:1; the mixed material was subjected to sintering for 12 h at a temperature of 890° C. and an oxygen flow rate of 50 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 4.5 μm to obtain the high-nickel spherical-secondary-particle ternary cathode material Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1W.sub.0.0008Al.sub.0.006O.sub.2.

[0084] The composition of Comparative Example 1 was basically the same as that of Example 1, but only the W-doped precursor B was used for the preparation through sintering. It can be seen from FE-SEM images in FIG. 1 and FIG. 5 that the high-nickel ternary cathode material prepared in Comparative Example 1 only included uniform spherical secondary particles, which was different from the co-existence of single-crystal particles and spherical secondary particles in Example 1. A powder of the cathode material in this comparative example had a compacted density of 3.36 g/cm.sup.3 (which was lower than that of Example 1 due to the lack of a combination of two morphologies), a median particle size of 4.5 μm, an SSA of 0.62 m.sup.2/g, and a pH of 11.3. According to EDS analysis, W was uniformly distributed in the spherical secondary particles. The Rietveld refinement was conducted on XRD data, and it can be known that a c value was 14.1982 and an a value was 2.8725. The c value and the c/a value were both increased, indicating that W effectively increased the c value.

[0085] The high-nickel ternary cathode materials obtained in Example 1 and Comparative Example 1 were subjected to pH titration, and titration curves were shown in FIG. 6. It can be seen that the spherical-secondary-particle high-nickel ternary cathode material of Comparative Example 1 that was prepared by sintering only a W-doped precursor consumed a larger volume of hydrochloric acid than example 1 during the titration, indicating that a residual Li content in the material of Comparative Example 1 was higher than a residual Li content in the material of Example 1.

[0086] The spherical-secondary-particle high-nickel ternary cathode material was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0087] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 208 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 95.8% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 93.8%. It indicates that the tungsten-doped spherical secondary particles have prominent rate performance and high capacity compared with Example 1 (which is one of the characteristics of small-particle secondary spheres), but show poor room-temperature cycling performance. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 90.6%. Compared with the data of Example 1, it shows that the pure spherical secondary particle morphology leads to unsatisfactory high-temperature cycling performance.

Comparative Example 2

[0088] A W-free cathode material was prepared in Comparative Example 2, with a molecular formula of Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1Al.sub.0.006O.sub.2. A preparation method of the cathode material included the following steps:

[0089] (1) A mixed solution of 0.8 mol/L nickel sulfate, 0.1 mol/L cobalt sulfate, and 0.1 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 900 rpm and fed into a reactor at a flow rate of 75 ml/min, during which a pH of the system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a precursor A.

[0090] (2) The precursor A, LiOH, and Al.sub.2O.sub.3 were mixed, and a resulting mixed material was stirred for 25 min at a speed of 2,500 r/min, where a molar ratio of Al to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.6% and a molar ratio of Li to other main metal elements was about 1:1; the mixed material was subjected to sintering for 12 h at a temperature of 890° C. and an oxygen flow rate of 50 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 4.5 μm to obtain the single-crystal-particle high-nickel ternary cathode material Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1Al.sub.0.006O.sub.2.

[0091] The chemical formula of the product of Comparative Example 2 was the same as the chemical formula of the product of Example 1 except that there was no W. It can be seen from the FE-SEM image shown in FIG. 7 that the high-nickel ternary cathode material prepared in Comparative Example 2 only included uniform single-crystal particles, which was different from the co-existence of single-crystal particles and spherical secondary particles in Example 1, indicating the key role of W in the formation of spherical secondary particles. A powder of the cathode material in this comparative example had a compacted density of 3.68 g/cm.sup.3 (pure single-crystal particles led to a high compacted density, and thus would help improve the compacted density of spherical secondary particles when used in combination with the spherical secondary particles), a median particle size of 4.5 μm, an SSA of 0.75 m.sup.2/g, and a pH of 11. According to EDS analysis, Al was uniformly distributed in the single-crystal particles. Rietveld refinement was conducted on XRD data, and it can be known that a c value was 14.1941 and an a value was 2.8726. The c value and the c/a value were both reduced compared with that in Example 1, indicating that the c value could not be effectively increased without W.

[0092] The single-crystal-particle high-nickel ternary cathode material was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0093] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 203 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 92.3% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 95.8%. The rate performance is not significantly improved, and the capacity is low, but the room-temperature cycling performance is prominent and better than that of the spherical secondary particles in Comparative Example 1, which is consistent with the characteristics of a high-nickel single-crystal cathode material. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 94.1%. The high-temperature cycling performance is prominent and better than that of the spherical secondary particles in Comparative Example 1, which is consistent with the characteristics of a high-nickel single-crystal cathode material. However, the high-temperature cycling performance is inferior to that of Example 1, indicating that the W coating layer formed on the surface from co-sintering of two precursors in Example 1 also plays a key role.

Comparative Example 3

[0094] A high-nickel ternary cathode material was prepared in Comparative Example 3, which was formed by doping LNMCO with Mo and Al and had a molecular formula approximately of Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1Mo.sub.0.0008Al.sub.0.006O.sub.2. A preparation method of the ternary cathode material included the following steps:

[0095] (1) A mixed solution of 0.8 mol/L nickel, 0.1 mol/L cobalt, and 0.1 mol/L manganese was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 80 ml/min, during which a pH of the system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a precursor A.

[0096] (2) A mixed solution of 0.8 mol/L nickel sulfate, 0.1 mol/L cobalt sulfate, and 0.1 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1, and then ammonium molybdate was added to the mixed solution, where Mo had a concentration of 0.004 mol/L in the mixed solution; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 80 ml/min, during which a pH of the system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a Mo-doped precursor B.

[0097] (3) The precursor B, the precursor A, LiOH, and Al.sub.2O.sub.3 were mixed, and a resulting mixed material was stirred for 25 min at a speed of 3,000 r/min, where a mass ratio of the precursor B to the precursor A was 1:4, a molar ratio of Al to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.6%, and a molar ratio of Li to other metal elements was about 1:1; the mixed material was subjected to sintering for 10 h at a temperature of 890° C. and an oxygen flow rate of 40 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 4.5 μm to obtain the single-crystal-particle high-nickel ternary cathode material Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1Mo.sub.0.0008Al.sub.0.006O.sub.2.

[0098] In Comparative Example 3, Mo of the same subgroup and a similar ionic radius was used to replace W in Example 1. It can be seen from the FE-SEM image shown in FIG. 8 that the high-nickel ternary cathode material prepared in Comparative Example 3 only included uniform single-crystal particles, which was different from the co-existence of single-crystal particles and spherical secondary particles in Example 1. It can be seen that W played a key role in the formation of spherical secondary particles, and another element could not lead to the formation of the cathode material with the two morphologies. A powder of the cathode material in this comparative example had a compacted density of 3.65 g/cm.sup.3, a median particle size of 4.5 μm, an SSA of 0.78 m.sup.2/g, and a pH of 11. According to EDS analysis, Al was uniformly distributed in the single-crystal particles. Rietveld refinement was conducted on XRD data, and it can be known that a c value was 14.1944 and an a value was 2.8725. The c value and the c/a value were both reduced compared with that in Example 1, indicating that the c value could not be effectively increased without W. It showed that, after the W in the precursor B was replaced, the cathode material with the two morphologies could not be formed, but a pure single-crystal morphology was formed.

[0099] The single-crystal-particle high-nickel ternary cathode material was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0100] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 202.5 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 92.1% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 95.6%. The rate performance is not significantly improved, and the capacity is low, but the room-temperature cycling performance is excellent, which is consistent with the characteristics of a high-nickel single-crystal cathode material. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 93.6%. It shows that, after the W is replaced by another element, the electrochemical performance of a product is also consistent with the characteristics of a single-crystal material.

Comparative Example 4

[0101] A high-nickel ternary cathode material was prepared in this comparative example, which was formed by doping LNMCO with W and Al and had a molecular formula approximately of Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1W.sub.0.0008Al.sub.0.006O.sub.2. A preparation method of the ternary cathode material included the following steps:

[0102] (1) A mixed solution of 0.8 mol/L nickel sulfate, 0.1 mol/L cobalt sulfate, and 0.1 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 80 ml/min, during which a pH of the system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a precursor A.

[0103] (2) A mixed solution of 0.8 mol/L nickel sulfate, 0.1 mol/L cobalt sulfate, and 0.1 mol/L manganese sulfate was prepared according to a Ni—Co—Mn molar ratio of 0.8:0.1:0.1, and then AMT was added to the mixed solution, where W had a concentration of 0.004 mol/L in the mixed solution; a 3 mol/L sodium hydroxide solution and a 1 mol/L ammonia solution were prepared; a pH of the mixed solution was controlled at 11.6 using the sodium hydroxide solution and the ammonia solution (with an ammonia value of 3 g/L), and then the mixed solution was continuously stirred at a rotational speed of 800 rpm and fed into a reactor at a flow rate of 80 ml/min, during which a pH of the system was controlled at 11.6 (with an ammonia value of 3 g/L) by the sodium hydroxide solution and the ammonia solution, a median particle size was controlled at 3.8 μm during crystallization, and the flow rate was controlled through cocurrent flow; and an obtained precursor was washed, centrifuged, and dried to obtain a W-doped precursor B.

[0104] (3) The precursor A. LiOH, and Al.sub.2O.sub.3 were mixed, and a resulting mixed material was stirred for 25 min at a speed of 3,000 r/min, where a molar ratio of Al to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.6% and a molar ratio of Li to other metal elements was 1:1; the mixed material was subjected to sintering for 10 h at a temperature of 890° C. and an oxygen flow rate of 40 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 4.5 μm to obtain a single-crystal-particle cathode material A-1.

[0105] (4) The precursor B, LiOH, and Al.sub.2O.sub.3 were mixed, and a resulting mixed material was stirred for 25 min at a speed of 3,000 r/min, where a molar ratio of Al to a sum of Ni, Co, and Mn in a theoretical cathode material was 0.6% and a molar ratio of Li to other metal elements was 1:1; the mixed material was subjected to sintering for 10 h at a temperature of 890° C. and an oxygen flow rate of 40 L/min in an oxygen furnace; and after the sintering was completed, a sintering product was naturally cooled under the protection of an oxygen atmosphere, then taken out from the furnace, and crushed with a crusher in a constant-temperature and constant-humidity environment to a particle size of 4.5 μm to obtain a spherical-secondary-particle cathode material B-1.

[0106] (5) The cathode materials of the two morphologies were physically mixed thoroughly according to a B-1:A-1 mass ratio of 1:4 to obtain the high-nickel ternary cathode material with the molecular formula of Li.sub.1.0068Ni.sub.0.8Co.sub.0.1Mn.sub.0.1W.sub.0.0008Al.sub.0.006O.sub.2.

[0107] An area was selected from the surface of the single-crystal particles in the mixed material of this comparative example to conduct EDS spectrum mapping, and as shown in FIG. 9, no W was found on the single-crystal particles. An area was selected from the surface of the single-crystal particles in Example 1 to conduct EDS spectrum mapping, and as shown in FIG. 3, there was a peak of W, indicating that, due to the blending and sintering in the precursor stage, W diffused from the interior of the spherical secondary particles and formed a uniform tungsten-containing coating layer on the single-crystal particles. The tungsten-containing coating layer facilitated the improvement of the cycling performance of the material, which could be proved from the following electrochemical performance analysis.

[0108] The ternary cathode material obtained from physical mixing was made into a coin-type cell with a lithium sheet as a negative electrode for evaluation test:

[0109] (1) The coin-type cell was charged at 0.1 C and 25° C. in a voltage range of 3.0 V to 4.3 V, and a capacity of 204 mAh/g was obtained; then the coin-type cell was discharged at 0.2 C/0.5 C/1.0 C/2.0 C, and results showed that a discharge capacity retention rate was 92.2% at 2.0 C/0.2 C; and 60 cycles were further conducted at 1 C, and a capacity retention rate was 93.6%. (2) 60 cycles were conducted at 50° C. in a voltage range of 3.0 V to 4.3 V, and a capacity retention rate was 92.1%. It shows that, in the material of this comparative example, W fails to coat and modify the surface of the single-crystal particles; and although the capacity is not much different from that of Example 1, the rate performance is reduced and the cycling performance is significantly worse than that of Example 1.