High-nickel positive electrode material, and preparation method therefor and use thereof

Abstract

Provided in the present application are a high-nickel positive electrode material, and a preparation method therefor and the use thereof. The high-nickel positive electrode material of the present application is secondary particles formed by gathering primary crystal grains, and there is a crystal boundary between adjacent primary crystal grains. The mass ratio of cobalt to nickel at the grain boundary of a surface layer of the secondary particles is A, the mass ratio of cobalt to nickel at the grain boundary of an inner core of the secondary particles is B, and the mass ratio of cobalt to nickel of the primary crystal grains of the surface layer of the secondary particles is C, wherein A is larger than B and is also larger than C. The high-nickel positive electrode material of the present application has a crystal boundary cobalt-rich structure on the surface layer of the secondary particle, and can enhance the structural stability of the material and reduce side reactions with an electrolyte, such that the battery has an excellent discharge capacity, coulombic efficiency and capacity retention rate.

Description

A high-nickel cathode material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 29, 2023, with application number 202311870331.6 and application name “A high-nickel positive electrode material, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the field of lithium-ion batteries and relates to a high-nickel cathode material and its preparation method and application. Background Art

[0003] Driven by the national new energy policy, my country's new energy-related industries have developed rapidly. Lithium-ion batteries have been widely used due to their advantages such as high operating voltage, high energy density and long cycle life.

[0004] Positive electrode materials are an important component of lithium-ion batteries and a key factor in determining the performance and cost of lithium-ion batteries. Ternary positive electrode materials are lithium metal oxides containing at least two elements, nickel and cobalt. They have good ternary synergistic effects, and exhibit advantages such as high specific capacity, good cycle performance, low cost, and low toxicity. They are positive electrode materials with great application value. In ternary positive electrode materials, nickel is the main redox reaction element. By increasing the nickel content, the specific capacity of the ternary material can be effectively improved. The cobalt element can stabilize the layered structure of the material, reduce cation mixing, and facilitate the transmission of lithium ions and electrons. With the scarcity of cobalt resources, the trend of high nickel and low cobalt in ternary positive electrode materials is becoming more and more obvious. However, as the nickel content increases and the cobalt content decreases, the stability of the positive electrode material deteriorates, and the side reactions with the electrolyte become more serious, resulting in the deterioration of the capacity, cycle performance and coulombic efficiency of the lithium-ion battery. Summary of the Invention

[0005] The present application provides a high-nickel positive electrode material having a cobalt-rich structure at the surface grain boundaries of secondary particles, which can enhance the structural stability of the material and reduce side reactions with the electrolyte, thereby enabling the battery to have excellent discharge capacity, coulombic efficiency and capacity retention rate.

[0006] The present application also provides a method for preparing a high-nickel positive electrode material, which pre-sinters a mixed system of a high-nickel positive electrode material precursor, a lithium source and a cobalt source to form lithium cobalt oxide on the surface of the precursor particles, and injects the lithium cobalt oxide into the grain boundaries with the help of lithium source flux. By controlling the subsequent sintering conditions, the diffusion of cobalt elements into the cores of the secondary particles and the interior of the grains is avoided, thereby preparing a high-nickel positive electrode material with cobalt-rich grain boundaries on the surface of the secondary particles.

[0007] The present application also provides a positive electrode sheet. Since the positive electrode sheet includes the above-mentioned high-nickel positive electrode material, the positive electrode sheet has good stability and is not prone to side reactions with the electrolyte.

[0008] The present application also provides a lithium-ion battery. Since the lithium-ion battery includes the above-mentioned positive electrode sheet, the lithium-ion battery has excellent discharge capacity, coulombic efficiency and capacity retention rate.

[0009] In a first aspect, the present application provides a high-nickel positive electrode material, wherein the high-nickel positive electrode material is a secondary particle formed by aggregation of primary crystal grains, and adjacent primary crystal grains include grain boundaries;

[0010] The mass ratio of cobalt to nickel at the grain boundaries of the secondary particle surface is A, the mass ratio of cobalt to nickel at the grain boundaries of the secondary particle core is B, and the mass ratio of cobalt to nickel in the primary grains of the secondary particle surface is C, wherein A is greater than B, and A is greater than C.

[0011] The high-nickel positive electrode material as described above, wherein the surface layer of the secondary particles includes a first doping element, and the first doping element is selected from at least one metal element with a valence of positive pentavalent or higher.

[0012] In the high-nickel positive electrode material as described above, the first doping element is selected from at least one of Ta, Nb, Mo, and W.

[0013] In the high-nickel positive electrode material as described above, the concentration of the first doping element at the surface grain boundaries of the secondary particles is greater than the concentration of the first doping element in the surface primary grains.

[0014] The high-nickel positive electrode material as described above, wherein the secondary particles include a second doping element, and the second doping element is selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B.

[0015] In the high-nickel positive electrode material as described above, the surface of the secondary particles is coated with a coating layer, and the coating layer includes at least one element selected from the group consisting of B, Al, Ce, Zr, Ti, and Si.

[0016] The high nickel cathode material as described above, wherein the chemical composition of the high nickel cathode material is Li n Ni x Co y K z M a N bO2, wherein 0.95<n<1.1, 0.85≤Ni<1, 0<y≤0.15, 0≤z≤0.15, 0<a≤0.15, 0<b≤0.05; K is selected from Mn or Al; M is selected from at least one of Al, Zr, Y, Ti, Sr, Ce, La, Mg, B, Si, Sc; N is selected from at least one of Ta, Nb, Mo, W, Sb, Bi, V.

[0017] A second aspect of the present application provides a method for preparing the high-nickel positive electrode material as described above, comprising the following steps:

[0018] 1) pre-sintering a mixed system including a high-nickel cathode material precursor, a lithium source, and a cobalt source in an oxygen-containing atmosphere to obtain a pre-sintered material;

[0019] The pre-sintering temperature is 400-600°C and the time is 4-10 hours;

[0020] 2) sintering the mixed system including the pre-sintered material and the compound of the first doping element in an oxygen-containing atmosphere to obtain the primary sintered material;

[0021] The first doping element is selected from at least one metal element having a valence of positive pentavalent or higher;

[0022] The primary sintering temperature is 650-800°C and the time is 8-16 hours;

[0023] 3) performing secondary sintering on the first sintered product in an oxygen-containing atmosphere to obtain the high-nickel positive electrode material.

[0024] As described above, in the preparation method, in step 2), the mixed system further includes a compound of a second doping element, and the second doping element is selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B.

[0025] The preparation method as described above, wherein in step 3), the secondary sintering comprises: sintering the mixed system of the first sintered product and the coating agent at 200-500° C. for 8-16 hours;

[0026] The coating agent is selected from a compound containing a coating element, and the coating element is selected from at least one of B, Al, Ce, Zr, Ti, and Si.

[0027] A third aspect of the present application provides a positive electrode sheet comprising the high-nickel positive electrode material as described above.

[0028] A fourth aspect of the present application provides a lithium-ion battery comprising the positive electrode sheet as described above.

[0029] The implementation of this application has at least the following advantages:

[0030] 1) The high-nickel positive electrode material of the present application has secondary particles formed by the aggregation of multiple primary grains, and the grain boundaries of the secondary particles are cobalt-rich, which is specifically reflected in that the mass ratio of cobalt to nickel at the grain boundaries of the secondary particles is A, which is greater than the mass ratio C of cobalt to nickel in the primary grains on the surface of the secondary particles, and the mass ratio of cobalt to nickel at the grain boundaries of the secondary particle core is B. It can significantly improve the structural stability of the material, reduce the side reactions between the material and the electrolyte, improve the coulomb efficiency and cycle life, and maintain the layered structure during the charge and discharge process to ensure the lithium ion transmission channel, thereby improving the rate performance. The cobalt enrichment at the grain boundaries of the secondary particles can effectively reduce the overall cobalt content of the secondary particles, thereby avoiding the excessively high cobalt concentration of the secondary particles as a whole, which reduces the capacity of the positive electrode material and improves the energy density of the positive electrode material.

[0031] 2) The preparation method of the high-nickel positive electrode material provided in the present application is to pre-sinter the mixed system of the high-nickel positive electrode material precursor, lithium source and cobalt source, which can ensure that the cobalt source and the lithium source are fully contacted to react to form lithium cobaltate on the surface of the precursor particles, and the lithium cobaltate is injected into the grain boundary under the flux of the lithium source. During the primary sintering process, high-valent metal elements are added to the surface grain boundaries. The stronger metal-oxygen bond of the high-valent metal inhibits the diffusion of the Co element from the grain boundary to the primary grains and the diffusion between the primary grains, thereby maintaining the surface grain boundary cobalt-rich during the high temperature process, and the cobalt concentration at the surface grain boundary is greater than the cobalt concentration in the surface primary grains. In addition, the high-valent elements doped on the surface of the secondary particles can also inhibit oxygen precipitation, improve the storage performance of the positive electrode material, and reduce gas production.

[0032] 3) Since the high nickel positive electrode material of the present application has good structural stability and can reduce the side reactions between the material and the electrolyte, the high nickel positive electrode material is applied to the positive electrode sheet and then applied to the lithium ion battery, which can enable the lithium ion battery to have excellent discharge capacity, coulombic efficiency and capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. It is obvious that the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0034] FIG1 is a SEM image of the high nickel positive electrode material of Example 1 of the present application. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0036] In a first aspect, the present application provides a high-nickel positive electrode material, wherein the high-nickel positive electrode material is a secondary particle formed by aggregation of primary crystal grains, and adjacent primary crystal grains include grain boundaries;

[0037] The mass ratio of cobalt to nickel at the grain boundaries of the secondary particle surface is A, the mass ratio of cobalt to nickel at the grain boundaries of the secondary particle core is B, and the mass ratio of cobalt to nickel in the primary grains of the secondary particle surface is C, where A is greater than B and A is greater than C.

[0038] When A, B, and C satisfy the above relationship, the high-nickel positive electrode material has a surface cobalt-rich structure, especially the grain boundaries of the secondary particles are cobalt-rich, which can significantly improve the structural stability of the material, reduce the side reactions between the material and the electrolyte, improve the coulombic efficiency and cycle life, and maintain the layered structure during the charge and discharge process to ensure the lithium ion transmission channel and improve the rate performance. The cobalt enrichment at the grain boundaries of the secondary particles can effectively reduce the overall cobalt content of the secondary particles, thereby avoiding the overall cobalt concentration of the secondary particles being too high to reduce the capacity of the positive electrode material and improve the energy density of the positive electrode material.

[0039] In an optional embodiment, the surface layer of the secondary particles further includes a first doping element, which is selected from at least one metal element with a valence of positive pentavalent or higher. For example, the doping element N can be selected from metal elements such as Ta, Nb, Mo, W, Bi, Sb, and V. Doping the surface layer of the secondary particles with a high-valence metal element can prevent the cobalt element on the surface of the secondary particles from diffusing into the material and the cobalt element at the grain boundaries from diffusing into the primary grains, thereby preserving the cobalt-rich structure of the grain boundaries of the secondary particles and further ensuring the stability of the high-nickel positive electrode material.

[0040] Furthermore, the first doping element is selected from at least one of Ta, Nb, Mo, and W. Doping with the above elements can further improve the structural stability of the high-nickel positive electrode material.

[0041] Furthermore, the concentration of the first doping element at the surface grain boundaries of the secondary particles is greater than that in the surface primary grains. The enrichment of the first doping element at the surface grain boundaries can effectively prevent the diffusion of cobalt during the sintering process.

[0042] In the present application, the mass content of cobalt and nickel elements at the grain boundaries of the surface of the secondary particles, the mass content of cobalt and nickel elements at the grain boundaries of the core of the secondary particles, the mass content of cobalt and nickel elements in the primary grains on the surface of the secondary particles, the mass content of the first doping element at the grain boundaries of the surface of the secondary particles, and the mass content of the first doping element in the primary grains on the surface of the secondary particles can all be measured by taking samples from the corresponding areas using EDS (X-ray energy spectrometer).

[0043] In an optional embodiment, the secondary particles also include a second doping element, and the second doping element is selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B. By doping the second doping element, the specific capacity, stability, and rate performance of the positive electrode material can be further improved.

[0044] The high-nickel cathode material of the present application can be directly composed of secondary particles, or the secondary particles can be further coated with a coating layer to obtain a high-nickel cathode material, wherein the coating layer includes at least one element selected from B, Al, Ce, Zr, Ti, and Si. Coating the surface of the secondary particles with the aforementioned elements can further prevent the positive electrode material from contacting the electrolyte, thereby reducing side reactions between the positive electrode active material and the electrolyte.

[0045] In an optional embodiment, the chemical composition of the high nickel cathode material is Li n Ni x Co y K z M a N b O2, wherein 0.95<n<1.1, 0.85≤Ni<1, 0<y≤0.15, 0≤z≤0.15, 0<a≤0.15, 0<b≤0.05; K is selected from Mn or Al; M is selected from at least one of Al, Zr, Y, Ti, Sr, Ce, La, Mg, B, Si, Sc; N is selected from at least one of Ta, Nb, Mo, W, Sb, Bi, V.

[0046] A second aspect of the present application provides a method for preparing the above-mentioned high-nickel positive electrode material, comprising the following steps:

[0047] 1) pre-sintering a mixed system including a high-nickel cathode material precursor, a lithium source, and a cobalt source in an oxygen-containing atmosphere to obtain a pre-sintered material;

[0048] The pre-sintering temperature is 400-600°C and the time is 4-10 hours;

[0049] 2) sintering the mixed system including the pre-sintered material and the compound of the first doping element in an oxygen-containing atmosphere to obtain a primary sintered material;

[0050] The first doping element is selected from at least one metal element with a valence of pentavalent or higher; the primary sintering temperature is 650-800° C., and the sintering time is 8-16 hours;

[0051] 3) The first sintered product is subjected to a secondary sintering in an oxygen-containing atmosphere to obtain a high-nickel positive electrode material.

[0052] In step 1), by pre-sintering the mixed system including the high-nickel positive electrode material precursor, lithium source and cobalt source at a relatively low temperature, lithium cobalt oxide can be formed on the surface of the precursor under lithium-rich conditions, and the lithium cobalt oxide is injected into the grain boundaries with the help of lithium source flux. The relatively low temperature can avoid the diffusion of cobalt elements into the interior of the particles, thereby maintaining the cobalt-rich structure on the surface of the secondary particles.

[0053] In step 2), a mixed system including a pre-sintered material and a compound of a first doping element is sintered once. On the one hand, the first doping element with a high valence can form a protective layer between the grain boundaries, and the stronger metal-oxygen bond of the high-valence metal inhibits the diffusion of cobalt elements from the grain boundaries to the interior of the primary grains and the core of the particles. On the other hand, after pre-sintering, the time of the primary sintering can be relatively shortened, thereby obtaining a high-nickel positive electrode material with cobalt-rich grain boundaries on the surface of the secondary particles.

[0054] The first doping element includes but is not limited to metal elements such as Ta, Nb, Mo, W, Bi, Sb, and V whose valence can reach positive pentavalent or above; the compound of the first doping element refers to a compound containing the first doping element, including but not limited to oxides, hydroxides, chlorides, sulfates, nitrates, acetates, carbonates, etc. of the first doping element.

[0055] In the above preparation method, the high-nickel cathode material precursor can be in the form of a hydroxide, an oxide, or a carbonate. For example, when the high-nickel cathode material is a nickel-cobalt-manganese ternary material, its precursor can be a hydroxide, an oxide, or a carbonate of nickel-cobalt-manganese. This application does not limit the source of the high-nickel cathode material precursor, which can be obtained commercially or prepared using conventional methods in the art.

[0056] Furthermore, in step 1), the lithium source is selected from LiOH, and the melting effect of lithium hydroxide helps to smoothly and evenly coat the surface of the secondary particles with lithium cobalt oxide, thereby improving the structural stability of the material.

[0057] The present application does not specifically limit the type of cobalt source, which can be selected from cobalt sources commonly used in the art, including but not limited to at least one of CoO, Co2O3, Co3O4, Co(OH)2, CoOOH, CoCO3, CoSO4, Co(NO3)2, and cobalt acetate.

[0058] In step 1), the oxygen-containing atmosphere refers to an atmosphere containing oxygen, which can be either a pure oxygen atmosphere or an air atmosphere, preferably a pure oxygen atmosphere.

[0059] In step 2), after obtaining the primary sintered material, the primary sintered material is further subjected to water washing and drying. The water washing can remove residual alkali on the surface of the primary sintered material, and the drying can remove moisture. The present application does not particularly limit the conditions for water washing and drying, and conditions commonly used in the art can be used.

[0060] In step 3), the primary sintered material is subjected to a secondary sintering process to remove bound water and internal moisture formed on the material surface, thereby preventing swelling of the battery during use. The secondary sintering process can be completed at 200-500°C for 8-16 hours.

[0061] In an optional embodiment, when the high-nickel positive electrode material further includes a second doping element, in step 2), a compound of the second doping element is further added to the mixed system, and sintering is performed again to complete the doping of the second doping element. The second doping element can be selected from one or more of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B, and the compound containing the second doping element can be selected from oxides, hydroxides, chlorides, sulfates, nitrates, acetates, carbonates, and the like of the second doping element.

[0062] In an optional embodiment, when the surface of the secondary particles of the high-nickel positive electrode material is also coated with a coating layer, in step 3), a coating agent is further added to the mixed system, and then a secondary sintering is performed to complete the coating of the surface of the secondary particles. The coating agent is a compound containing a coating element, and the coating element is selected from at least one of B, Al, Ce, Zr, Ti, and Si. The compound containing the coating element can be selected from oxides, hydroxides, chlorides, sulfates, nitrates, acetates, carbonates, and the like of the coating element.

[0063] A third aspect of the present application provides a positive electrode sheet comprising the high-nickel positive electrode material described above. It is understood that the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer disposed on at least one functional surface of the positive electrode current collector, wherein the positive electrode active layer comprises the high-nickel positive electrode material described above.

[0064] The present application does not impose any particular limitation on the positive electrode current collector, and current collectors commonly used in the art, such as aluminum foil, can be used, which can be commercially available.

[0065] The positive electrode active layer of the present application includes the high-nickel positive electrode material as described above, which means that the positive electrode active layer contains the high-nickel positive electrode material as described above as the positive electrode active material. In addition to the positive electrode active material, the positive electrode active layer may also include components such as a conductive agent and a binder. Among them, the conductive agent and the binder can be conventionally used in the field and will not be described in detail here.

[0066] A fourth aspect of the present application provides a lithium-ion battery comprising the above-described positive electrode sheet. Because the above-described positive electrode sheet comprises the high-nickel positive electrode material provided herein, which has the advantages of good stability and a low tendency to undergo side reactions with the electrolyte, the battery has good discharge capacity, coulombic efficiency, and capacity retention.

[0067] The lithium-ion battery of the present application includes, in addition to a positive electrode, a separator, a negative electrode, and an electrolyte. The composition of the negative electrode can refer to conventional negative electrode sheets in the art and will not be further described here. The separator can also be a conventional separator in the art, such as PP film or PE film.

[0068] The lithium-ion battery of the present application can be prepared by conventional methods in the field. For example, the positive electrode sheet, the separator and the negative electrode sheet can be stacked in sequence, and then the battery cell can be obtained by a lamination or winding process. Then, the above-mentioned lithium-ion battery can be obtained through baking, liquid injection, formation, packaging and other processes.

[0069] Hereinafter, the high nickel cathode material and the preparation method thereof provided by the present application will be further described in detail through specific examples.

[0070] Unless otherwise specified, the reagents, materials, and instruments used in the following examples are conventional reagents, conventional materials, and conventional instruments in the art and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0071] Example 1

[0072] The chemical composition of the high nickel cathode material of this embodiment is Li 1.01 Ni 0.915 Co 0.056 Mn 0.029 Mo 0.002 Zr 0.002 Sr 0.001 Y 0.001 B 0.01 Al 0.004 Ti 0.002 O2, the preparation method thereof comprises the following steps:

[0073] 1) Mixing the hydroxide precursor of NCM9253, LiOH, and Co2O3 at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, then heating to 550°C at 2°C / min in an oxygen atmosphere and holding for 8 h to obtain a pre-sintered material;

[0074] 2) mixing the pre-sintered material with ammonium molybdate, ZrO2, SrO, and Y2O3 in a molar ratio of 1:0.002:0.002:0.001:0.0005 at 800 rpm, heating to 750°C at 5°C / min in an oxygen atmosphere, and holding for 12 hours to obtain a primary sintered material;

[0075] 3) washing the primary sintered material with deionized water and then drying it in vacuum at 120° C. to obtain a washed and dried material;

[0076] 4) The washed and dried material was mixed with the coating agent H3BO3, Al2O3, and TiO2 in a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 minutes, and the temperature was raised to 300°C at 2°C / min under an oxygen atmosphere and maintained for 10 hours to obtain a high-nickel positive electrode material.

[0077] Example 2

[0078] The chemical composition of the high nickel cathode material of this embodiment is Li 1.015 Ni 0.933 Co 0.048 Mn 0.019 W 0.001 Zr 0.002 Al 0.005 Mg 0.002 Y 0.001 B 0.02 Ti 0.001 O2, the preparation method thereof comprises the following steps:

[0079] 1) Mixing the hydroxide precursor of NCM9442, LiOH, and Co(OH)2 at a molar ratio of 1:1.05:0.01 at 800 rpm for 30 min, then heating to 500°C at 2°C / min in an oxygen atmosphere and holding for 8 h to obtain a pre-sintered material;

[0080] 2) The pre-sintered material was mixed with WO3, ZrO2, Al(OH)3, MgCO3, and Y2O3 in a molar ratio of 1:0.001:0.002:0.003:0.002:0.0005 at 800 rpm, and the temperature was raised to 750°C at 5°C / min in an oxygen atmosphere and maintained for 12 hours to obtain a primary sintered material;

[0081] 3) washing the primary sintered material with deionized water and then drying it in vacuum at 120°C to obtain a washed and dried material;

[0082] 4) The washed and dried material was mixed with the coating agent B2O3, Al2O3, and TiO2 in a molar ratio of 1:0.01:0.0015:0.001 at 800 rpm for 30 min, and the temperature was raised to 400°C at 2°C / min in an oxygen atmosphere and maintained for 12 h to obtain a high-nickel positive electrode material.

[0083] Example 3

[0084] The chemical composition of the high nickel cathode material of this embodiment is Li 1.01 Ni 0.923 Co 0.048 Mn 0.029 Ta 0.002 Zr 0.002 Ti 0.001 Mg 0.001 Y 0.001 B 0.01 Al 0.004 O2, the preparation method thereof comprises the following steps:

[0085] 1) Mixing the hydroxide precursor of NCM9343, LiOH, and cobalt acetate at a molar ratio of 1:1.05:0.01 at 800 rpm for 30 minutes, heating to 450°C at 2°C / min in an oxygen atmosphere, and holding for 8 hours to obtain a pre-sintered material;

[0086] 2) mixing the pre-sintered material with Ta2O5, ZrO2, TiO2, MgO, and Y2O3 in a molar ratio of 1:0.001:0.002:0.001:0.001:0.0005 at 800 rpm, heating to 740°C at 5°C / min in an oxygen atmosphere, and holding for 12 hours to obtain a primary sintered material;

[0087] 3) washing the primary sintered material with deionized water and then drying it in vacuum at 120°C to obtain a washed and dried material;

[0088] 4) The washed and dried material was mixed with the coating agent H3BO3 and Al2O3 in a molar ratio of 1:0.01:0.002 at 800 rpm for 30 minutes, and the temperature was raised to 350°C at 2°C / min in an oxygen atmosphere and maintained for 8 hours to obtain a high-nickel positive electrode material.

[0089] Example 4

[0090] The chemical composition of the high nickel cathode material of this embodiment is Li 1.015 Ni 0.905 Co 0.046 Mn 0.019 Mo 0.001 Nb 0.001 Zr 0.002 Al 0.005 Mg 0.002Y 0.001 B 0.02 Ti 0.001 O2, the preparation method thereof comprises the following steps:

[0091] 1) NCM9145 precursor, LiOH, CoSO4, and CoCO3 were mixed at a molar ratio of 1:1.05:0.004:0.004 at 800 rpm for 30 min, and then heated to 500°C at 2°C / min in an oxygen atmosphere and maintained for 8 h to obtain a pre-sintered material;

[0092] 2) mixing the pre-sintered material with MoO3, Nb2O5, and ZrO2 in a molar ratio of 1:0.0005:0.0005:0.002 at 800 rpm, heating to 750°C at 5°C / min in an oxygen atmosphere, and maintaining the temperature for 12 hours to obtain a primary sintered material;

[0093] 3) washing the primary sintered material with deionized water and then drying it in vacuum at 120°C to obtain a washed and dried material;

[0094] 4) The washed and dried material was mixed with B2O3, Al2O3, and TiO2 in a molar ratio of 1:0.01:0.0015:0.001 at 800 rpm for 30 min, and the temperature was raised to 400°C at 2°C / min under an oxygen atmosphere and maintained for 12 h to obtain a high-nickel positive electrode material.

[0095] Example 5

[0096] The chemical composition of the high nickel cathode material of this embodiment is Li 1.01 Ni 0.906 Co 0.0477 Al 0.038 Mo 0.002 Zr 0.002 Sr 0.001 Y 0.001 B 0.01 Ti 0.002 O2, the preparation method thereof comprises the following steps:

[0097] 1) Mixing the hydroxide precursor of NC9505, Al(OH)3, LiOH, and Co2O3 at a molar ratio of 1:0.04:1.05:0.004 at 800 rpm for 30 min, heating to 550°C at 2°C / min in an oxygen atmosphere, and holding for 8 h to obtain a pre-sintered material;

[0098] 2) mixing the pre-sintered material with ammonium molybdate, ZrO2, SrO, and Y2O3 in a molar ratio of 1:0.002:0.002:0.001:0.0005 at 800 rpm, heating to 750°C at 5°C / min in an oxygen atmosphere, and holding for 12 hours to obtain a primary sintered material;

[0099] 3) washing the primary sintered material with deionized water and then drying it in vacuum at 120° C. to obtain a washed and dried material;

[0100] 4) The washed and dried material was mixed with the coating agent H3BO3 and TiO2 in a molar ratio of 1:0.01:0.002 at 800 rpm for 30 minutes, and the temperature was raised to 300°C at 2°C / min under an oxygen atmosphere and maintained for 10 hours to obtain a high-nickel positive electrode material.

[0101] Example 6

[0102] The chemical composition of the high nickel cathode material of this embodiment is Li 1.01 Ni 0.915 Co 0.056 Mn 0.029 Sb 0.002 Zr 0.002 Sr 0.001 Y 0.001 B 0.01 Al 0.004 Ti 0.002 O2, the preparation method thereof comprises the following steps:

[0103] 1) Mixing the hydroxide precursor of NCM9253, LiOH, and Co2O3 at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, then heating to 550°C at 2°C / min in an oxygen atmosphere and holding for 8 h to obtain a pre-sintered material;

[0104] 2) mixing the pre-sintered material with Sb2O5, ZrO2, SrO, and Y2O3 in a molar ratio of 1:0.001:0.002:0.001:0.0005 at 800 rpm, heating to 750°C at 5°C / min in an oxygen atmosphere, and holding for 12 hours to obtain a primary sintered material;

[0105] 3) washing the primary sintered material with deionized water and then drying it in vacuum at 120° C. to obtain a washed and dried material;

[0106] 4) The washed and dried material was mixed with the coating agent H3BO3, Al2O3, and TiO2 in a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 minutes, and the temperature was raised to 300°C at 2°C / min under an oxygen atmosphere and maintained for 10 hours to obtain a high-nickel positive electrode material.

[0107] Comparative Example 1

[0108] The chemical composition of the high nickel positive electrode material of this comparative example is consistent with that of Example 1, and its preparation method comprises the following steps:

[0109] 1) NCM9253 precursor, LiOH, Co2O3, ammonium molybdate, ZrO2, SrO, and Y2O3 were mixed at a molar ratio of 1:1.05:0.004:0.002:0.002:0.001:0.0005 at 800 rpm, and the mixture was heated to 750°C at 5°C / min in an oxygen atmosphere and maintained for 12 h to obtain a primary sintered material;

[0110] 2) washing the primary sintered material with deionized water and then drying it in a vacuum oven at 120° C. to obtain a washed and dried material;

[0111] 3) The washed and dried material was mixed with the coating agent H3BO3, Al2O3, and TiO2 in a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 minutes, and the temperature was raised to 300°C at 2°C / min in an oxygen atmosphere and maintained for 10 hours to obtain a high-nickel positive electrode material.

[0112] Comparative Example 2

[0113] The chemical composition of the high nickel cathode material of this comparative example is Li 1.01 Ni 0.915 Co 0.056 Mn 0.029 Zr 0.002 Sr 0.001 Y 0.001 B 0.01 Al 0.004 Ti 0.002 O2, the preparation method thereof comprises the following steps:

[0114] 1) Mixing the hydroxide precursor of NCM9253, LiOH, and Co2O3 at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, then heating to 550°C at 2°C / min in an oxygen atmosphere and holding for 8 h to obtain a pre-sintered material;

[0115] 2) mixing the pre-sintered material with ZrO2, SrO, and Y2O3 in a molar ratio of 1:0.002:0.001:0.0005 at 800 rpm, heating to 750°C at 5°C / min in an oxygen atmosphere, and holding for 12 hours to obtain a primary sintered material;

[0116] 3) washing the primary sintered material with deionized water and then drying it in vacuum at 120° C. to obtain a washed and dried material;

[0117] 4) The washed and dried material was mixed with the coating agent H3BO3, Al2O3, and TiO2 in a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 minutes, and the temperature was raised to 300°C at 2°C / min in an oxygen atmosphere and maintained for 10 hours to obtain a high-nickel positive electrode material.

[0118] Comparative Example 3

[0119] The chemical composition of the high nickel positive electrode material of this comparative example is consistent with that of Example 1, and its preparation method comprises the following steps:

[0120] 1) Mixing the hydroxide precursor of NCM9253, LiOH, and Co2O3 at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, heating to 750°C at 2°C / min in an oxygen atmosphere, and maintaining the temperature for 8 h to obtain a pre-sintered material;

[0121] 2) mixing the pre-sintered material with ammonium molybdate, ZrO2, SrO, and Y2O3 in a molar ratio of 1:0.002:0.002:0.001:0.0005 at 800 rpm, heating to 750°C at 5°C / min in an oxygen atmosphere, and holding for 12 hours to obtain a primary sintered material;

[0122] 3) The washed and dried material was mixed with the coating agent H3BO3, Al2O3, and TiO2 in a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 minutes, and the temperature was raised to 300°C at 2°C / min in an oxygen atmosphere and maintained for 10 hours to obtain a high-nickel positive electrode material.

[0123] Test Case

[0124] 1. The high nickel positive electrode material of Example 1 was characterized by SEM. FIG1 is an SEM image of the high nickel positive electrode material of Example 1 of the present application. It can be seen from FIG1 that the high nickel positive electrode material of Example 1 is a secondary spherical particle formed by the aggregation of primary grains.

[0125] 2. The following parameters were measured for the high nickel cathode materials obtained in the above examples and comparative examples:

[0126] 1) The mass ratio A of cobalt to nickel at the grain boundary of the secondary particle surface and the content of the first doping element

[0127] The determination method is: using SEM to observe the surface morphology of the sample, then selecting the grain boundary for EDS testing to obtain the contents of cobalt, nickel, and the first doping element, and calculating the cobalt / nickel mass ratio A.

[0128] 2) The mass ratio C of cobalt and nickel in the primary grains of the secondary particle surface layer and the content of the first doping element

[0129] The determination method is: using SEM to observe the surface morphology of the sample, then selecting the center of a grain for EDS testing to obtain the contents of cobalt, nickel, and the first doping element, and calculating the cobalt / nickel mass ratio C.

[0130] 3) Mass ratio of cobalt to nickel at the grain boundary of the secondary particle core B

[0131] The testing method involves ion milling the sample using an argon ion beam to obtain sliced ​​cathode particles. The sample cross-section is observed using a scanning electron microscope (SEM). EDS analysis is performed on the grain boundaries of the secondary particle cores to determine the cobalt, nickel, and primary doping element contents, and to calculate the cobalt / nickel mass ratio, B.

[0132] The test results of the above parameters are listed in Table 1.

[0133] 3. Mix high nickel cathode material, conductive agent Super-P, and binder PVDF in a mass ratio of 96.5:1.5:2 and add them into NMP solvent to mix evenly to obtain a cathode slurry with a solid content of 30-40%. 2 The surface density of the positive electrode is coated on the positive electrode collector aluminum foil, and the positive electrode sheet is obtained by drying, punching and rolling.

[0134] The above-mentioned positive electrode sheet, PP separator, and metal lithium sheet were stacked in sequence, and 1.0M LiPF6 electrolyte was added to assemble into LR2430 button cells. The following performance of the obtained button cells was measured:

[0135] 1) Discharge capacity

[0136] Determination method: At room temperature, charge the button cell at a constant current of 0.2C to 4.25V, then charge at a constant voltage of 4.25V to a cutoff current of 0.05C. After standing for 5 minutes, discharge at a constant current of 0.2C to 2.5V, and record the discharge capacity of the battery. 1C = 200mA / g.

[0137] 2) First Coulombic efficiency

[0138] Determination method: At room temperature, charge the button cell at a constant current of 0.2C to 4.25V. Then, charge at a constant voltage of 4.25V to a cutoff current of 0.05C. Record the charge capacity. After 5 minutes of rest, discharge at a constant current of 0.2C to 2.5V. Record the discharge capacity. The initial coulombic efficiency is calculated as: discharge capacity / charge capacity × 100%. 1C = 200mA / g.

[0139] The positive electrode sheet, PP separator, and graphite negative electrode sheet were stacked in sequence and wound to obtain a battery cell. The battery cell was encapsulated in an aluminum plastic film, injected with 1.0M LiPF6 electrolyte, and the encapsulated cell was allowed to stand for formation to obtain a full battery. The following performance tests were performed on the obtained full battery:

[0140] 3) Capacity retention after 300 cycles

[0141] Measurement method: Place the full battery in a 45°C constant temperature chamber. First, charge it at a constant current of 0.2C to 4.25V. Then, charge it at a constant voltage of 4.25V to a cutoff current of 0.05C. After standing for 5 minutes, discharge it at a constant current of 0.2C to 2.8V. Record the initial capacity a1 of the battery. Then, perform a charge-discharge cycle of 0.2C charge / 0.2C discharge. After 300 cycles, record the capacity a2 of the battery. The capacity retention rate is a2 / a1×100%. Where 1C = 200mA / g.

[0142] The test results of the above properties are listed in Table 1.

[0143] Table 1

[0144] From the data in Table 1 we can see that:

[0145] 1) The A values ​​of the high-nickel positive electrode materials of Examples 1 to 6 are all greater than the B and C values, and the concentration of the first doping element is higher at the grain boundaries. These materials can enable the battery to have a higher discharge capacity, first coulombic efficiency and capacity retention rate.

[0146] 2) By comparing Example 1 with Comparative Examples 1 and 3, it can be seen that when the chemical composition of the high-nickel positive electrode material is the same, but the pre-sintering step is not performed or the pre-sintering temperature is too high, the distribution of cobalt and nickel elements in the surface and inner core of the secondary particles, grain boundaries and primary grains is close, and the discharge capacity, first coulombic efficiency and capacity retention rate of the batteries obtained using the high-nickel positive electrode materials of Comparative Examples 1 and 3 are all poor.

[0147] 3) By comparing Example 1 with Comparative Example 2, it can be seen that when high-valent metal elements with a valence higher than positive pentavalent are not added for doping in the primary sintering, the concentration distributions of cobalt and nickel elements in the surface and inner core of the secondary particles, grain boundaries and primary grains are close. The battery obtained using the high-nickel positive electrode material of Comparative Example 2 has a discharge capacity, first coulombic efficiency and capacity retention rate significantly worse than the battery obtained using the high-nickel positive electrode material of Example 1.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high-nickel cathode material, wherein, The high-nickel cathode material is secondary particles formed by aggregation of primary grains, and grain boundaries are included between adjacent primary grains; The mass ratio of cobalt element to nickel element at the grain boundaries on the surface layer of the secondary particles is A, the mass ratio of cobalt element to nickel element at the grain boundaries in the core of the secondary particles is B, and the mass ratio of cobalt element to nickel element of the primary grains on the surface layer of the secondary particles is C, wherein A is greater than B and A is greater than C.

2. The high-nickel cathode material according to claim 1, wherein, The surface layer of the secondary particles includes a first doping element, and the first doping element is selected from at least one of metal elements whose valence can reach +5 or higher.

3. The high-nickel cathode material according to claim 2, wherein, The first doping element is selected from at least one of Ta, Nb, Mo, and W.

4. The high-nickel cathode material according to claim 2 or 3, wherein, The concentration of the first doping element at the grain boundaries on the surface layer of the secondary particles is greater than the concentration of the first doping element in the primary grains on the surface layer.

5. The high-nickel cathode material according to any one of claims 1-4, wherein, The secondary particles include a second doping element, and the second doping element is selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B.

6. The high-nickel cathode material according to any one of claims 1-5, wherein, The surface of the secondary particles is coated with a coating layer, and the coating layer includes at least one element selected from B, Al, Ce, Zr, Ti, and Si.

7. The high-nickel cathode material according to any one of claims 1-6, wherein, The chemical composition of the high-nickel cathode material is Li n Ni x Co y K z M a N b O2, where 0.95 < n < 1.1, 0.85 ≤ Ni < 1, 0 < y ≤ 0.15, 0 ≤ z ≤ 0.15, 0 < a ≤ 0.05, 0 < b ≤ 0.05; K is selected from Mn or Al; M is selected from at least one of Al, Zr, Y, Ti, Sr, Ce, La, Mg, B, Si, Sc; N is selected from at least one of Ta, Nb, Mo, W, Sb, Bi, V.

8. A method for preparing the high-nickel cathode material according to any one of claims 1-7, wherein, It includes the following steps: 1) Pre-sinter a mixed system including a high-nickel cathode material precursor, a lithium source, and a cobalt source in an oxygen-containing atmosphere to obtain a pre-sintered material; The temperature of the pre-sintering is 400-600 °C, and the time is 4-10 h; 2) Perform primary sintering on a mixed system including the pre-sintered material and a compound of the first doping element in an oxygen-containing atmosphere to obtain the primary sintered material; The first doping element is selected from at least one of metal elements whose valence can reach +5 or higher; The temperature of the primary sintering is 650-800 °C, and the time is 8-16 h; 3) Perform secondary sintering on the first sintered product in an oxygen-containing atmosphere to obtain the high-nickel cathode material.

9. The preparation method according to claim 8, wherein, In step 2), the mixed system further includes a compound of a second doping element, and the second doping element is selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B.

10. The preparation method according to claim 8 or 9, wherein In step 3), the secondary sintering includes: sintering a mixed system of the first sintered product and a coating agent at 200-500 °C for 8-16 h; The coating agent is selected from compounds containing coating elements, and the coating elements are selected from at least one of B, Al, Ce, Zr, Ti, and Si.

11. A positive electrode sheet, wherein, It includes the high-nickel cathode material according to any one of claims 1-7.

12. A lithium-ion battery, wherein, It includes the positive electrode sheet according to claim 11.

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