Ternary Positive Electrode Material and Method for Preparing Same, Positive Electrode Sheet and Lithium Ion Battery

Abstract

A ternary positive electrode material, a method for preparing the same, a positive electrode sheet and a lithium ion battery in which the ternary positive electrode material has a chemical composition of Li.sub.a(Ni.sub.xCo.sub.yM.sub.1-x-y).sub.1-bM′bO.sub.2-cA.sub.c, wherein 0.75≤a≤1.2, 0.5≤x<1, 0<y≤0.1, 0≤b≤0.01, 0≤c≤0.2; M is at least one selected from the group consisting of Mn and Al; M′ is at least one selected from the group consisting of Al, Zr, Ti, Y, Sr, W and Mg; A is at least one selected from the group consisting of S, F and N; and 2%≤C.sub.Col−C.sub.Co, 5%≤C.sub.Al−C.sub.All. The lithium ion battery shows better short-term kinetic performances and long-term kinetic performances, and it also exhibits excellent stability in long-term cycles.

Claims

1. A ternary positive electrode material, wherein the ternary positive electrode material has a chemical composition of Li.sub.a(Ni.sub.xCo.sub.yM.sub.1-x-y).sub.1-bM′.sub.bO.sub.2-cA.sub.c, wherein 0.75≤a≤1.2, 0.5≤x<1, 0<y≤0.1, 0<b≤0.01, 0≤c≤0.2; M is at least one selected from the group consisting of Mn and Al; M′ includes Al and optionally one or more selected from the group consisting of Zr, Ti, Y, Sr, W and Mg; and A is one or more selected from the group consisting of S, F and N; wherein 2%≤C.sub.Col−C.sub.Co, wherein C.sub.Col is an atomic percentage of Co element with respect to all metal elements except Li element measured by XPS after etching of the positive electrode material, and C.sub.Co is an atomic percentage of Co element with respect to all metal elements except Li element obtained by analyzing the positive electrode material with ICP; 5%≤C.sub.Al−C.sub.All, wherein C.sub.Al is an atomic percentage of Al element with respect to all metal elements except Li element obtained by analyzing the positive electrode material directly with XPS, and C.sub.All is an atomic percentage of Al element with respect to all metal elements except Li element measured by XPS after etching of the positive electrode material.

2. The ternary positive electrode material according to claim 1, wherein C.sub.Col is an atomic percentage of Co element with respect to all metal elements except Li element measured by XPS at a depth of 20-60 nm from a surface of the positive electrode material after etching of the positive electrode material; C.sub.All is an atomic percentage of Al element with respect to all metal elements except Li element measured by XPS at a depth of 20-60 nm from a surface of the positive electrode material after etching of the positive electrode material.

3. The ternary positive electrode material according to claim 1, wherein 5.3%≤C.sub.Al−C.sub.All.

4. The ternary positive electrode material according to claim 1, wherein 10%≤C.sub.Al−C.sub.All.

5. The ternary positive electrode material according to claim 1, wherein 2.7%≤C.sub.Col−C.sub.Co.

6. The ternary positive electrode material according to claim 1, wherein 5%≤C.sub.Col−C.sub.Co.

7. The ternary positive electrode material according to claim 1, wherein conditions for the etching are: Ar.sup.+ ion etching, 2,500 eV≤E≤3,500 eV, 90s≤t≤100s, wherein E is energy used for the etching, and t is etching time.

8. The ternary positive electrode material according to claim 1, wherein in the chemical composition Li.sub.a(Ni.sub.xCo.sub.yM.sub.1-x-y).sub.1-bM′.sub.bO.sub.2-cA.sub.c of the ternary positive electrode material, M′ includes Al and one or more selected from the group consisting of Zr, Ti, Y, Sr, W and Mg.

9. The ternary positive electrode material according to claim 1, wherein in the chemical composition Li.sub.a(Ni.sub.xCo.sub.yM.sub.1-x-y).sub.1-bM′.sub.bO.sub.2-cA.sub.c of the ternary positive electrode material, M′ includes Al and Zr.

10. The ternary positive electrode material according to claim 1, wherein in the chemical composition Li.sub.a(Ni.sub.xCo.sub.yM.sub.1-x-y).sub.1-bM′.sub.bO.sub.2-cA.sub.c of the ternary positive electrode material, c=0.

11. The ternary positive electrode material according to claim 1, wherein a particle size D.sub.v50 corresponding to a cumulative particle volume distribution at 50% for the ternary positive electrode material satisfies 2 μm≤D.sub.v50≤5 μm.

12. A method for preparing the ternary positive electrode material of claim 1, comprising the following steps: Step S1: mixing a ternary positive electrode precursor containing Ni, Co, Mn or Ni, Co, Al with a lithium source fully to form a mixture I; Step S2: heating the mixture I in an air or oxygen atmosphere, wherein the mixture I needs to be held at 700-1,100° C. for 4-15 hours, followed by rolling and pulverization to obtain an intermediate product II; Step S3: mixing the intermediate product II with an Al-containing solid powder and a Co-containing solid powder fully to form a mixture III; Step S4: heating the mixture III in an air or oxygen atmosphere, wherein the mixture III needs to be held at 700-1,000° C. for 4-15 hours, followed by rolling and pulverization to obtain a ternary positive electrode material having an α-NaFeO.sub.2 structure; wherein if M′ element in the ternary positive electrode material includes one or more elements selected from the group consisting of Zr, Ti, Y, Sr, W and Mg, a compound comprising the one or more elements selected from the group consisting of Zr, Ti, Y, Sr, W and Mg is added in a process of forming the mixture I and/or a process of forming the mixture III; wherein if the ternary positive electrode material comprises A element, a compound containing the A element is added in a process of forming the mixture I and/or a process of forming the mixture III.

13. The method for preparing the ternary positive electrode material according to claim 12, wherein in Step S1, the lithium source is one or more selected from the group consisting of lithium carbonate and lithium hydroxide.

14. The method for preparing the ternary positive electrode material according to claim 12, wherein in Step S1, the M′ element in the ternary positive electrode material comprises Zr element, and a Zr-containing compound is added in the process of forming the mixture I.

15. The method for preparing the ternary positive electrode material according to claim 12, wherein in Step S3, the Al-containing solid powder is an alumina powder having a particle size in the range of 100 nm≤D.sub.alumina≤1,000 nm.

16. The method for preparing the ternary positive electrode material according to claim 12, wherein in Step S3, the Co-containing solid powder is any one or more selected from the group consisting of Co.sub.3O.sub.4, CoO, Co(OH).sub.2, CoOOH and CoCO.sub.3.

17. The method for preparing the ternary positive electrode material according to claim 12, wherein in Step S3, a molar ratio of Co element in the Co-containing solid powder to the intermediate product II is (1-3):100; and/or a mass ratio of Al element in the Al-containing solid powder to the intermediate product II is (0.02-1.5):100.

18. A positive electrode sheet comprising the ternary positive electrode material of claim 1.

19. A lithium ion battery comprising the positive electrode sheet of claim 18.

Description

DETAILED DESCRIPTION

[0056] The present disclosure will be illustrated in detail with reference to the following specific Examples. The following Examples will help those skilled in the art to further understand the present disclosure, but do not limit the present disclosure in any way. It should be noted that, for those skilled in the art, variations and modifications can be made without departing from the concept of the present disclosure. They all fall in the protection scope of the present disclosure.

Example 1

[0057] A Ni.sub.0.66Co.sub.0.06Mn.sub.0.28(OH).sub.2 precursor was selected for mixing with lithium carbonate. A molar ratio of the precursor:lithium was 1:1.05. A 0.12 wt % (with respect to the precursor) nano-sized ZrO.sub.2 powder was added and mixed uniformly in a high-speed mixer to obtain a mixture I. The mixture I was loaded into a sagger which was then placed in a roller kiln. Then, the temperature in the roller kiln was raised to 940° C. at a rate of 5° C./min and held for 8 hours. After the resulting block material was cooled, it was subjected to rolling and fed into a jet mill for pulverization to obtain a primarily sintered product (an intermediate product II). The primarily sintered product was mixed with Co(OH).sub.2 at a molar ratio of 2.0% and Al.sub.2O.sub.3 powder (having a primary particle size of about 150 nm) at a mass ratio of 0.25 wt % uniformly in a high-speed mixer to obtain a mixture (mixture III). The mixture III was loaded into a sagger which was then placed in the roller kiln. Then, the temperature in the roller kiln was raised to 850° C. at a rate of 10° C./min and held for 5 hours to perform the secondary sintering. After cooling, the powder was a positive electrode material product. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.3 μm.

[0058] The composition of the material was Li.sub.0.99(Ni.sub.0.65Co.sub.0.08Mn.sub.0.27).sub.0.998Zr.sub.0.001Al.sub.0.001O.sub.2 as determined by ICP, that is, C.sub.Co=7.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 20.2% Al, 14.1% Co, 29.1% Mn, 33.7% Ni, 2.9% Zr, that is, C.sub.Al=20.2%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 10.2% Al, 17.5% Co, 30.7% Mn, 40.1% Ni, 1.5% Zr, that is, C.sub.Col=17.5%, C.sub.All=10.2%.

Example 2

[0059] A Ni.sub.0.66Co.sub.0.06Mn.sub.0.28(OH).sub.2 precursor was selected for mixing with lithium carbonate. A molar ratio of the precursor:lithium was 1:1.05. A 0.12 wt % (with respect to the precursor) nano-sized ZrO.sub.2 powder was added and mixed uniformly in a high-speed mixer to obtain a mixture I. The mixture I was loaded into a sagger which was then placed in a roller kiln. Then, the temperature in the roller kiln was raised to 940° C. at a rate of 5° C./min and held for 8 hours. After the resulting block material was cooled, it was subjected to rolling and fed into a jet mill for pulverization to obtain a primarily sintered product (an intermediate product II). The primarily sintered product was mixed with Co(OH).sub.2 at a molar ratio of 1.0% and Al.sub.2O.sub.3 powder (having a primary particle size of about 110 nm) at a mass ratio of 0.20 wt % uniformly in a high-speed mixer to obtain a mixture (mixture III). The mixture III was loaded into a sagger which was then placed in the roller kiln. Then, the temperature in the roller kiln was raised to 820° C. at a rate of 10° C./min and held for 5 hours to perform the secondary sintering. After cooling, the powder was a positive electrode material product. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.5 μm.

[0060] The composition of the material was Li.sub.1.01(Ni.sub.0.65Co.sub.0.07Mn.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 as determined by ICP, that is, C.sub.Co=6.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 25.7% Al, 7.8% Co, 31.0% Mn, 33.1% Ni, 2.4% Zr, that is, C.sub.Al=25.7%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 2,700 eV, duration 95s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 9.4% Al, 9.7% Co, 38.7% Mn, 41.0% Ni, 1.2% Zr, that is, C.sub.Col=9.7%, C.sub.All=9.4%.

Example 3

[0061] A Ni.sub.0.64Co.sub.0.06Mn.sub.0.30(OH).sub.2 precursor was selected for mixing with lithium carbonate. A molar ratio of the precursor:lithium was 1:1.05. A 0.12 wt % (with respect to the precursor) nano-sized ZrO.sub.2 powder was added and mixed uniformly in a high-speed mixer to obtain a mixture I. The mixture I was loaded into a sagger which was then placed in a roller kiln. Then, the temperature in the roller kiln was raised to 940° C. at a rate of 5° C./min and held for 8 hours. After the resulting block material was cooled, it was subjected to rolling and fed into a jet mill for pulverization to obtain a primarily sintered product (an intermediate product II). The primarily sintered product was mixed with Co(OH).sub.2 at a molar ratio of 2.5% and Al.sub.2O.sub.3 powder (having a primary particle size of about 200 nm) at a mass ratio of 0.15 wt % uniformly in a high-speed mixer to obtain a mixture (mixture III). The mixture III was loaded into a sagger which was then placed in the roller kiln. Then, the temperature in the roller kiln was raised to 840° C. at a rate of 10° C./min and held for 5 hours to perform the secondary sintering. After cooling, the powder was a positive electrode material product. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.7 μm.

[0062] The composition of the material was Li.sub.1.03(Ni.sub.0.63Co.sub.0.08Mn.sub.0.29).sub.0.9978Zr.sub.0.001Al.sub.0.0012O.sub.2 as determined by ICP, that is, C.sub.Co=7.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 19.7% Al, 13.0% Co, 29.1% Mn, 33.7% Ni, 4.5% Zr, that is, C.sub.Al=19.7%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3300 eV, duration 90 s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 12.2% Al, 18.5% Co, 29.7% Mn, 38.6% Ni, 1.0% Zr, that is, C.sub.Col=18.5%, C.sub.All=12.2%.

Example 4

[0063] A Ni.sub.0.61Co.sub.0.07Mn.sub.0.32(OH).sub.2 precursor was selected for mixing with lithium carbonate. A molar ratio of the precursor:lithium was 1:1.05. A 0.12 wt % (with respect to the precursor) nano-sized ZrO.sub.2 powder was added and mixed uniformly in a high-speed mixer to obtain a mixture I. The mixture I was loaded into a sagger which was then placed in a roller kiln. Then, the temperature in the roller kiln was raised to 930° C. at a rate of 5° C./min and held for 8 hours. After the resulting block material was cooled, it was subjected to rolling and fed into a jet mill for pulverization to obtain a primarily sintered product (an intermediate product II). The primarily sintered product was mixed with Co(OH).sub.2 at a molar ratio of 1.5% and Al.sub.2O.sub.3 powder (having a primary particle size of about 300 nm) at a mass ratio of 0.20 wt % uniformly in a high-speed mixer to obtain a mixture. The mixture was loaded into a sagger which was then placed in the roller kiln. Then, the temperature in the roller kiln was raised to 840° C. at a rate of 10° C./min and held for 5 hours to perform the secondary sintering. After cooling, the powder was a positive electrode material product. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.5 μm.

[0064] The composition of the material was Li.sub.1.03(Ni.sub.0.60Co.sub.0.09Mn.sub.0.31).sub.0.9979Zr.sub.0.001Al.sub.0.0011O.sub.2 as determined by ICP, that is, C.sub.Co=8.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 27.3% Al, 10.5% Co, 27.8% Mn, 31.9% Ni, 2.5% Zr, that is, C.sub.Al=27.3%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,400 eV, duration 90s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 8.0% Al, 14.4% Co, 35.7% Mn, 39.9% Ni, 2.0% Zr, that is, C.sub.Col=14.4%, C.sub.All=8.0%.

Example 5

[0065] A Ni.sub.0.61Co.sub.0.07Mn.sub.0.32(OH).sub.2 precursor was selected for mixing with lithium carbonate. A molar ratio of the precursor:lithium was 1:1.05. A 0.12 wt % (with respect to the precursor) nano-sized ZrO.sub.2 powder was added and mixed uniformly in a high-speed mixer to obtain a mixture I. The mixture I was loaded into a sagger which was then placed in a roller kiln. Then, the temperature in the roller kiln was raised to 930° C. at a rate of 5° C./min and held for 8 hours. After the resulting block material was cooled, it was subjected to rolling and fed into a jet mill for pulverization to obtain a primarily sintered product (an intermediate product II). The primarily sintered product was mixed with Co(OH).sub.2 at a molar ratio of 2.0% and Al.sub.2O.sub.3 powder (having a primary particle size of about 150 nm) at a mass ratio of 0.16 wt % uniformly in a high-speed mixer to obtain a mixture. The mixture was loaded into a sagger which was then placed in the roller kiln. Then, the temperature in the roller kiln was raised to 850° C. at a rate of 10° C./min and held for 5 hours to perform the secondary sintering. After cooling, the powder was a positive electrode material product. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 3.1 μm.

[0066] The composition of the material was Li.sub.1.03(Ni.sub.0.60Co.sub.0.09Mn.sub.0.31).sub.0.998Zr.sub.0.001Al.sub.0.001O.sub.2 as determined by ICP, that is, C.sub.Co=8.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 22.1% Al, 12.5% Co, 29.0% Mn, 34.7% Ni, 1.7% Zr, that is, C.sub.al=22.1%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 2,600 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 10.8% Al, 16.6% Co, 31.7% Mn, 38.6% Ni, 2.3% Zr, that is, C.sub.Col=16.6%, C.sub.All=10.8%.

Example 6

[0067] A Ni.sub.0.61Co.sub.0.07Mn.sub.0.32(OH).sub.2 precursor was selected for mixing with lithium carbonate. A molar ratio of the precursor:lithium was 1:1.05. A 0.12 wt % (with respect to the precursor) nano-sized ZrO.sub.2 powder was added and mixed uniformly in a high-speed mixer to obtain a mixture I. The mixture I was loaded into a sagger which was then placed in a roller kiln. Then, the temperature in the roller kiln was raised to 930° C. at a rate of 5° C./min and held for 8 hours. After the resulting block material was cooled, it was subjected to rolling and fed into a jet mill for pulverization to obtain a primarily sintered product (an intermediate product II). The primarily sintered product was mixed with Co(OH).sub.2 at a molar ratio of 2.5% and Al.sub.2O.sub.3 powder (having a primary particle size of about 150 nm) at a mass ratio of 0.12 wt % uniformly in a high-speed mixer to obtain a mixture. The mixture was loaded into a sagger which was then placed in the roller kiln. Then, the temperature in the roller kiln was raised to 860° C. at a rate of 10° C./min and held for 5 hours to perform the secondary sintering. After cooling, the powder was a positive electrode material product. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 3.6 μm.

[0068] The composition of the material was Li.sub.1.03(Ni.sub.0.60Co.sub.0.09Mn.sub.0.31).sub.0.998Zr.sub.0.001Al.sub.0.001O.sub.2 as determined by ICP, that is, C.sub.Co=8.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 18.8% Al, 14.2% Co, 28.6% Mn, 35.9% Ni, 2.5% Zr, that is, C.sub.Al=18.8%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 13.5% Al, 17.4% Co, 30.3% Mn, 36.7% Ni, 2.1% Zr, that is, C.sub.Col=17.4%, C.sub.All=13.5%.

Example 7

[0069] The difference between this Example and Example 1 lies in that no ZrO.sub.2 powder was added after the precursor and lithium carbonate were mixed. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 3.6 μm.

[0070] The composition of the material was Li.sub.0.99(Ni.sub.0.65Co.sub.0.08Mn.sub.0.27).sub.0.999Al.sub.0.001O.sub.2 as determined by ICP, that is, C.sub.Co=7.99%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 20.7% Al, 14.9% Co, 30.1% Mn, 34.3% Ni, that is, C.sub.Al=20.7%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 10.5% Al, 18.0% Co, 31.2% Mn, 40.3% Ni, that is, C.sub.Col=18.0%, C.sub.All=10.5%.

Example 8

[0071] A Ni.sub.0.77Co.sub.0.04Al.sub.0.19(OH).sub.2 precursor was selected for mixing with lithium carbonate. A molar ratio of the precursor:lithium was 1:1.05. A 0.12 wt % (with respect to the precursor) nano-sized ZrO.sub.2 powder was added and mixed uniformly in a high-speed mixer to obtain a mixture I. The mixture I was loaded into a sagger which was then placed in a roller kiln. Then, the temperature in the roller kiln was raised to 930° C. at a rate of 5° C./min and held for 8 hours. After the resulting block material was cooled, it was subjected to rolling and fed into a jet mill for pulverization to obtain a primarily sintered product (an intermediate product II). The primarily sintered product was mixed with Co(OH).sub.2 at a molar ratio of 2.5% and Al.sub.2O.sub.3 powder (having a primary particle size of about 150 nm) at a mass ratio of 0.12 wt % uniformly in a high-speed mixer to obtain a mixture. The mixture was loaded into a sagger which was then placed in the roller kiln. Then, the temperature in the roller kiln was raised to 840° C. at a rate of 10° C./min and held for 5 hours to perform the secondary sintering. After cooling, the powder was a positive electrode material product. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.6 μm.

[0072] The composition of the material was Li.sub.1.02(Ni.sub.0.76Co.sub.0.06Al.sub.0.18).sub.0.999Zr.sub.0.001O.sub.2 as determined by ICP, that is, C.sub.Co=5.99%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 26.8% Al, 11.2% Co, 59.1% Ni, 2.9% Zr, that is, C.sub.Al=26.8%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 16.5% Al, 9.2% Co, 71.6% Ni, 2.7% Zr, that is, C.sub.Col=9.2%, C.sub.All=16.5%.

Comparative Example 1

[0073] The difference between this Comparative Example and Example 1 lies in that no Al.sub.2O.sub.3 powder was added for the secondary sintering. The rest conditions and processes for preparing the material are consistent with Example 1. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.3 μm.

[0074] The composition of the material was Li.sub.1.01(Ni.sub.0.65Co.sub.0.07Mn.sub.0.28).sub.0.999Zr.sub.0.001O.sub.2 as determined by ICP, that is, C.sub.Co=6.99%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 0% Al (N.D), 10.9% Co, 40.4% Mn, 44.1% Ni, 4.6% Zr, that is, C.sub.Al=0%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 0% Al (N.D), 9.5% Co, 42.7% Mn, 45.4% Ni, 2.4% Zr, that is, C.sub.Col=9.5%, C.sub.All=0%.

Comparative Example 2

[0075] The difference between this Comparative Example and Example 1 lies in that Co(OH).sub.2 was not added for the secondary sintering. The rest conditions and processes for preparing the material are consistent with Example 1. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.3 μm.

[0076] The composition of the material was Li.sub.1.01(Ni.sub.0.66Co.sub.0.06Mn.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 as determined by ICP, that is, C.sub.Co=5.99%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 27.3% Al, 4.1% Co, 32.3% Mn, 34.9% Ni, 1.4% Zr, that is, C.sub.Al=27.3%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 8.2% Al, 6.3% Co, 39.6% Mn, 43.0% Ni, 2.9% Zr, that is, C.sub.Col=6.3%, C.sub.All=8.2%.

Comparative Example 3

[0077] The difference between this Comparative Example and Example 1 lies in that neither Al.sub.2O.sub.3 powder nor Co(OH).sub.2 was added for the secondary sintering. The rest conditions and processes for preparing the material are consistent with Example 1. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.3 μm.

[0078] The composition of the material was Li.sub.1.01(Ni.sub.0.66Co.sub.0.06Mn.sub.0.28).sub.0.999Zr.sub.0.001O.sub.2 as determined by ICP, that is, C.sub.Co=5.99%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 0% Al (N.D), 6.7% Co, 39.8% Mn, 51.3% Ni, 2.2% Zr, that is, C.sub.Al=0%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 0% Al (N.D), 7.1% Co, 37.3% Mn, 52.9% Ni, 2.7% Zr, that is, C.sub.Col=7.1%, C.sub.All=0%.

Comparative Example 4

[0079] The difference between this Comparative Example and Example 1 lies in that Al.sub.2O.sub.3 added for the secondary sintering in this Comparative Example had a primary particle size of 10 nm. The rest conditions and processes for preparing the material are consistent with Example 1. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.3 μm.

[0080] The composition of the material was Li.sub.1.01(Ni.sub.0.65Co.sub.0.07Mn.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 as determined by ICP, that is, C.sub.Co=6.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 19.3% Al, 9.2% Co, 28.7% Mn, 40.3% Ni, 2.5% Zr, that is, C.sub.Al=19.3%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 18.2% Al, 10.1% Co, 30.3% Mn, 39.6% Ni, 1.8% Zr, that is, C.sub.Col=10.1%, C.sub.All=18.2%.

Comparative Example 5

[0081] The difference between this Comparative Example and Example 1 lies in that the temperature chosen for the secondary sintering in this Comparative Example was 550° C. The rest conditions and processes for preparing the material are consistent with Example 1. The positive electrode material product had a single-crystal morphology, and its particle size D.sub.v50 corresponding to a cumulative particle volume distribution of 50% was 2.1 μm.

[0082] The composition of the material was Li.sub.0.01(Ni.sub.0.65Co.sub.0.07Mn.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 as determined by ICP, that is, C.sub.Co=6.98%; the percentages of the metal elements except Li on the surface were determined by XPS as follows: 23.1% Al, 15.6% Co, 24.4% Mn, 34.8% Ni, 2.1% Zr, that is, C.sub.Al=23.1%. Ar.sup.+ ions were used to etch the material, and the conditions were chosen as follows: spot width 1.5 mm, energy 3,000 eV, duration 100s. After the material was treated by etching, the percentages of the metal elements except Li on the surface were determined by XPS as follows: 15.5% Al, 8.3% Co, 33.2% Mn, 40.3% Ni, 2.7% Zr, that is, C.sub.Col=8.3%, C.sub.All=15.5%.

[0083] The positive electrode material products prepared in the above Examples and Comparative Examples were used to prepare batteries according to the following method:

[0084] The positive electrode active material was mixed with carbon black as a conductive agent and polyvinylidene fluoride (PVDF) as a binder at a mass ratio of 97:1.7:1.3, added into N-methyl pyrrolidone (NMP) as an organic solvent, and stirred at a high speed to form a uniform dispersion. After the high-speed stirring was completed, the dispersion was defoamed in the stirring tank under negative pressure to obtain a positive electrode slurry suitable for coating. The resulting positive electrode slurry was coated on an aluminum foil with a transfer coating machine. After drying, cold pressing and slitting, a positive electrode sheet in a desired shape was made. In the cold pressing process, the compact density of the area coated with the positive electrode active material was controlled within 3.2 g/cm.sup.3-3.6 g/cm.sup.3.

[0085] A negative electrode active material was mixed with carbon black as a conductive agent, a binder and sodium carboxymethylcellulose (CMC-Na) at a mass ratio of 96.8:1.2:1.2:0.8, added into deionized water, and stirred at a high speed to form a uniform dispersion. After the high-speed stirring was completed, the dispersion was defoamed in the stirring tank under negative pressure to obtain a negative electrode slurry suitable for coating. The resulting negative electrode slurry was coated on a copper foil with a transfer coating machine. After drying, cold pressing and slitting, a negative electrode sheet in a desired shape was made. In the cold pressing process, the compact density of the area coated with the negative electrode active material was controlled within 1.5 g/cm.sup.3-1.8 g/cm.sup.3.

[0086] The positive and negative electrode sheets were disposed on two sides of a 9 μm thick PE separator respectively, and rolled up to form a roll core. An uncoated area of each of the electrode sheets was reserved and connected to a nickel tab by ultrasonic welding. The roll core was wrapped with an aluminum-plastic film and heat-sealed, and one side was reserved for liquid infusion.

[0087] To make an electrolyte, a mixed solvent of EC:EMC:DEC at a mass ratio of 3:5:2 were added with 13 wt % (based on the total mass of the electrolyte) of LiPF.sub.6 as a lithium salt, and, as additives, 1 wt % (based on the total mass of the electrolyte) of vinylene carbonate and 2 wt % (based on the total mass of the electrolyte) of ethylene sulfate (DTD). The electrolyte was infused into the aluminum plastic film wrapping the roll core. Lithium ion batteries were obtained by further processes of vacuum packaging, standing and forming.

[0088] The positive electrode materials and the resulting batteries were tested for their performances. The results are shown in Table 1. The test methods are as follows:

[0089] Particle size D.sub.v50 test: 5 g of a ternary positive electrode material sample was weighed and put in a 100 mL beaker to which 50 mL deionized water and 1 mL sodium hexametaphosphate solution (concentration: 1 wt %) were then added. The resulting mixture was ultrasonicated for 1 min, and then transferred to an injection system of Malvern 3000 Laser Particle Size Analyzer. The total volume of the sample and deionized water was kept at 500 mL. The agitator speed was set to 2,800 rpm. The particle refractive index was 1.8, the particle absorptivity was 1.0, and the solvent refractive index was 1.33. The particle size distribution was determined under these conditions, and D.sub.v50 in the volume distribution data was read.

[0090] ICP test: 0.4 g of a positive electrode material sample was weighed and put in a 250 ml beaker to which 10 ml HCl (1:1 by volume of HCl: water) was then added. The sample was dissolved by heating at 180° C. The heated liquid was transferred to a volumetric flask, and pure water was added to its constant volume. The liquid was diluted to a measurable range, and tested using an ICP instrument. In the chemical formula Li.sub.a(Ni.sub.xCo.sub.yM.sub.1-x-y).sub.1-bM′.sub.bO.sub.2-cA.sub.c of the positive electrode material, the x and y values were calculated by comparing the relative contents of the Ni, Co, and Mn elements determined by the ICP test, and a, b, and c were determined by ICP directly. If M′ and A each included more than one element, b and c each were equal to a sum of the contents of different elements.

[0091] XPS test: A positive electrode material powder sample was spread on an aluminum foil to which a double-sided adhesive tape was adhered. The sample was flattened using a tablet press, and then the material was tested using an XPS instrument. In the test process, a full-spectrum scan might be performed first to determine possible elements, and then a narrow-spectrum scan was performed for the existing elements. The relative atomic content of each element was calculated based on the area of the signal peak in view of the sensitivity factor of the element.

[0092] Etching: Ar.sup.+ ion etching was utilized: spot width 1.5 mm, 2,500 eV≤E≤3,500 eV, 90s≤t≤100s. E was the energy used for etching, and t was the etching time. The material was treated. After the treatment, the material was tested using the XPS instrument. See the Examples and Comparative Examples for the specific etching parameters. The relative atomic content of an element determined by the XPS test after the positive electrode material was etched under the above conditions (Ar.sup.t ion etching, spot width 1.5 mm, 2,500 eV≤E≤3,500 eV, 90s≤t≤100s) was a relative atomic content of the element at a depth of 20-60 nm from the surface.

[0093] Direct current internal resistance (DCR) test: The DCR of a battery could serve as an indicator of the kinetic performance of the cathode material when other design and materials are fixed, especially at low state of charge (SOC), when the cathode lattice is nearly fully inserted with Li ions. The SOC of a battery was adjusted to 10% (i.e. charging the battery from a fully discharged state to 10% of its rated capacity) at a rate of 0.33 C (i.e. at a current set to 0.33 time the rated capacity of the battery in ampere hours) using a charge/discharge device. After standing for 30 minutes, the battery was discharged at a 3 C constant current A, and the voltage change ΔV during the discharge process was recorded. Then, DCR=ΔV/A.

[0094] Cycle life: The battery was subjected to charge/discharge cycles at a rate of 1 C using the charge/discharge device, and the capacity retention rate after 1,000 cycles was recorded.

[0095] DCR growth rate test: For the battery obtained after 1,000 cycles, the state of charge (SOC) of the battery was adjusted to 50% (i.e. charging the battery from a fully discharged state to 50% of its rated capacity) at a rate of 0.33 C (i.e. at a current set to 0.33 time the rated capacity of the battery in ampere hours) using the charge/discharge device. After standing for 30 minutes, the battery was discharged at a 3 C constant current A, and the voltage change ΔV during the discharge process was recorded. Then, DCR1000=ΔV/A. DCR growth rate=(DCR1000/DCR)−1.

TABLE-US-00001 TABLE 1 Test results of the Examples and Comparative Examples Capacity DCR retention growth 10% SOC rate after rate after C.sub.Co1- C.sub.A1-C.sub.A11 DCR 1,000 1,000 Chemical formula C.sub.Co % % (mQ) cycles % cycles % Ex.1 Li.sub.0.99(Ni.sub.0.65Co.sub.0.08M.sub.0.27).sub.0.998Zr.sub.0.001Al.sub.0.001O.sub.2 9.52 10.0 15.3 96.2 7.3 Ex.2 Li.sub.1.01(Ni.sub.0.65Co.sub.0.07M.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 2.72 16.3 17.3 97.0 7.5 Ex.3 Li.sub.1.03(Ni.sub.0.63Co.sub.0.08M.sub.0.29).sub.0.9978Zr.sub.0.001Al.sub.0.0012O.sub.2 10.52 7.5 13.1 95.5 8.9 Ex.4 Li.sub.1.03(Ni.sub.0.60Co.sub.0.09M.sub.0.31).sub.0.9979Zr.sub.0.001Al.sub.0.0011O.sub.2 5.42 19.3 14.5 97.3 6.8 Ex.5 Li.sub.1.03(Ni.sub.0.60Co.sub.0.09M.sub.0.31).sub.0.998Zr.sub.0.001Al.sub.0.001O.sub.2 7.62 11.3 11.7 96.4 7.3 Ex.6 Li.sub.1.03(Ni.sub.0.60Co.sub.0.09M.sub.0.31).sub.0.998Zr.sub.0.001Al.sub.0.001O.sub.2 8.42 5.3 10.2 95.1 7.7 Ex.7 Li.sub.0.99(Ni.sub.0.65Co.sub.0.08M.sub.0.27).sub.0.999Al.sub.0.001O.sub.2 10.01 10.2 14.2 93.5 8.9 Ex.8 Li.sub.1.02(Ni.sub.0.76Co.sub.0.06Al.sub.0.18).sub.0.999Zr.sub.0.001O.sub.2 3.21 10.3 13.7 92.9 6.9 Comp. Li.sub.1.01(Ni.sub.0.65Co.sub.0.07M.sub.0.28).sub.0.999Zr.sub.0.001O.sub.2 2.51 0.0 14.9 87.3 18.2 Ex.1 Comp. Li.sub.1.01(Ni.sub.0.66Co.sub.0.06M.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 0.31 19.1 21.3 95.2 15.4 Ex.2 Comp. Li.sub.1.01(Ni.sub.0.66Co.sub.0.06M.sub.0.28).sub.0.999Zr.sub.0.001O.sub.2 1.11 0.0 19.4 85.7 31.1 Ex.3 Comp. Li.sub.1.01(Ni.sub.0.65Co.sub.0.07M.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 3.12 1.1 16.2 89.9 16.9 Ex.4 Comp. Li.sub.1.01(Ni.sub.0.65Co.sub.0.07M.sub.0.28).sub.0.9975Zr.sub.0.001Al.sub.0.0015O.sub.2 1.32 7.6 16.7 93.7 13.6 Ex.5

[0096] The technical features of the materials described in Examples 1 to 8 all reside within the preferred ranges described in the present disclosure, and the batteries made using the corresponding materials have a lower initial direct current internal resistance (DCR), a better cyclic capacity retention rate and a better cyclic direct current internal resistance (DCR) growth rate. C.sub.Col−C.sub.Co is the difference between the percentage of Co atoms near the surface of the material and the average Co atom content in the material. When the difference is ≥2%, it means that there is more Co near the surface of the material, which enables promotion of both electron conduction and ion transfer of the material. C.sub.Al−C.sub.All is the difference between the percentage of Al atoms on the surface of the material and the percentage of Al atoms near the surface. When the difference is ≥5%, it means that the surface of the material has an Al coating, and Al atoms have not penetrated into the material. As it can be seen from a comparison of the data of Example 1 and Comparative Example 1, when the surface of the material is not coated with Al, C.sub.Al−C.sub.All<5%, which is outside the preferred range, and the cyclic capacity retention rate of the material is apparently reduced. As it can be seen from a comparison of the data of Example 1 and Comparative Example 2, when the surface of the material is not coated with Co, C.sub.Col−C.sub.Co<2%, which is outside the preferred range. Although the capacity retention rate of the material can be maintained at a high level, the direct current impedance is high. As it can be seen from a comparison of the data of Example 1 and Comparative Example 3, when the surface of the material has neither of these two coatings, CA1−C.sub.All and C.sub.Col−C.sub.Co are both outside the preferred ranges, and the direct current impedance, cyclic capacity retention rate and cyclic direct current internal resistance (DCR) growth rate of the material are all poor. As it can be seen from a comparison of the data of Example 1 and Comparative Example 4, when the coating process is carried out with a coating agent of smaller particles, the Al element will penetrate into the region near the surface and the inside of the material, such that C.sub.Al−C.sub.All<5%. In such a case, the coating cannot function to protect the material in a long-term cycling process on the one hand, and on the other hand, it also hinders migration of electrons and ions, and thus increases the direct current internal resistance of the material. As it can be seen from a comparison of the data of Example 1 and Comparative Example 5, when the secondary sintering temperature selected is not high enough, such that the Co element fails to enter the region near the surface of the material, and C.sub.Col−C.sub.Co<2% will also be resulted. In such a case, although the direct current impedance and cyclic capacity retention rate of the material are still good, it cannot be guaranteed that the direct current impedance of the battery will be maintained at a low level during a long-term cycling process.

[0097] Specific embodiments according to the present disclosure have been described above. It should be appreciated that the present disclosure is not limited to the above specific embodiments. Those skilled in the art can make various changes or modifications within the scope defined by the claims, and the substantive matter of the present disclosure is not affected. Where there is no conflict, the Examples and the features in the Examples in the present disclosure can be combined with each other freely.