A high-nickel positive electrode material and a preparation method and application thereof

Abstract

The application provides a high-nickel positive electrode material and a preparation method and application thereof. The high-nickel positive electrode material is a secondary particle formed by primary grains gathering, and a crystal boundary is included between adjacent primary grains; the mass ratio of cobalt elements to nickel elements at the crystal boundary of a surface layer of the secondary particle is A, the mass ratio of cobalt elements to nickel elements at the crystal boundary of a core of the secondary particle is B, and the mass ratio of cobalt elements to nickel elements of a primary grain of the surface layer of the secondary particle is C, wherein A is greater than B, and A is greater than C. The high-nickel positive electrode material has a secondary particle surface layer crystal boundary cobalt-rich structure, can enhance the structural stability of the material, reduces the side reaction between the material and an electrolyte, and thus makes the battery have excellent discharge capacity, coulomb efficiency and capacity retention rate.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium ion batteries, and relates to a high-nickel positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Under the promotion of national new energy policy, the new energy related industries in China have developed rapidly and vigorously. Lithium ion batteries are widely used due to the advantages of high working voltage, high energy density and long cycle life.

[0003] The positive electrode material is an important component of a lithium ion battery and is a key factor determining the performance and cost of the lithium ion battery. The ternary positive electrode material is a lithium metal oxide containing at least nickel and cobalt, has a good ternary synergistic effect, and has the advantages of high specific capacity, good cycle performance, low cost and low toxicity, and is a positive electrode material with great application value. In the ternary positive electrode material, nickel is the main redox reaction element, and the specific capacity of the ternary material can be effectively improved by increasing the content of nickel. 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 ternary positive electrode materials is becoming more and more obvious. However, with the increase of nickel content and the decrease of cobalt content, the stability of the positive electrode material becomes poor, and the side reaction with the electrolyte is more serious, resulting in poor capacity, cycle performance and coulomb efficiency of the lithium ion battery. SUMMARY

[0004] The application provides a high-nickel positive electrode material, which has a cobalt-rich structure at the surface layer grain boundary of secondary particles, can enhance the structural stability of the material, reduce the side reaction with the electrolyte, and thus make the battery have excellent discharge capacity, coulomb efficiency and capacity retention rate.

[0005] The application also provides a preparation method of the high-nickel positive electrode material. The method pre-sinters a mixed system of a high-nickel positive electrode material precursor, a lithium source and a cobalt source, forms lithium cobaltate on the surface of the precursor particles, and injects the lithium cobaltate into the grain boundary under the fluxing of the lithium source. By controlling the subsequent sintering conditions, the diffusion of cobalt elements into the inner core of secondary particles and the interior of the crystal grains is avoided, so as to prepare the high-nickel positive electrode material with cobalt-rich structure at the surface layer grain boundary of secondary particles.

[0006] The application also provides a positive electrode sheet. Since the positive electrode sheet comprises the above high-nickel positive electrode material, the positive electrode sheet has good stability and is not prone to side reaction with the electrolyte.

[0007] The application also provides a lithium ion battery. Since the lithium ion battery comprises the above positive electrode sheet, the lithium ion battery has excellent discharge capacity, coulomb efficiency and capacity retention rate.

[0008] The first aspect of the present application provides a high-nickel positive electrode material, the high-nickel positive electrode material is a secondary particle formed by aggregation of primary grains, and a crystal boundary is included between adjacent primary grains;

[0009] The mass ratio of cobalt element to nickel element at the crystal boundary of the surface layer of the secondary particle is A, the mass ratio of cobalt element to nickel element at the crystal boundary of the core of the secondary particle is B, and the mass ratio of cobalt element to nickel element of the primary grain of the surface layer of the secondary particle is C, wherein A is greater than B, and A is greater than C.

[0010] The high-nickel positive electrode material as described above, wherein the first doping element is selected from at least one of metal elements capable of reaching a valence of +5 and above.

[0011] The high-nickel positive electrode material as described above, wherein the first doping element is selected from at least one of Ta, Nb, Mo, and W.

[0012] The high-nickel positive electrode material as described above, wherein the concentration of the first doping element at the crystal boundary of the surface layer of the secondary particle is greater than the concentration of the first doping element in the primary grain of the surface layer.

[0013] The high-nickel positive electrode material as described above, wherein the secondary particle includes 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.

[0014] The high-nickel positive electrode material as described above, wherein the surface of the secondary particle is coated with a coating layer, and the coating layer includes at least one element of B, Al, Ce, Zr, Ti, and Si.

[0015] The high-nickel positive electrode material as described above, wherein the chemical composition of the high-nickel positive electrode 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, and 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, and Sc; and N is selected from at least one of Ta, Nb, Mo, W, Sb, Bi, and V.

[0016] The second aspect of the present application provides a preparation method of the high-nickel positive electrode material as described above, comprising the following steps:

[0017] 1) pre-sintering a mixed system comprising a high-nickel positive electrode material precursor, a lithium source and a cobalt source under an oxygen-containing atmosphere to obtain a pre-sintered material;

[0018] The pre-sintering temperature is 400-600℃, and the time is 4-10h;

[0019] 2) primary sintering a mixed system comprising the pre-sintered material and a compound of a first doping element under an oxygen-containing atmosphere to obtain a primary sintered material;

[0020] The first doping element is selected from at least one of metal elements with a valence of +5 or above;

[0021] The primary sintering temperature is 650-800℃, and the time is 8-16h;

[0022] 3) secondary sintering the first sintered product under an oxygen-containing atmosphere to obtain the high-nickel positive electrode material.

[0023] The preparation method as described above, wherein in step 2), the mixed system further comprises a compound of a second doping element selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr and B.

[0024] The preparation method as described above, wherein in step 3), the secondary sintering comprises sintering a mixed system of the first sintered product and a coating agent at 200-500℃ for 8-16h;

[0025] The coating agent is selected from a compound containing a coating element selected from at least one of B, Al, Ce, Zr, Ti and Si.

[0026] The third aspect of the present application provides a positive electrode sheet comprising the high-nickel positive electrode material as described above.

[0027] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode sheet as described above.

[0028] The implementation of the present application has at least the following advantages:

[0029] 1) The high-nickel positive electrode material of the present application, the secondary particles of which are formed by aggregation of a plurality of primary grains, and the grain boundaries of the surface layer of the secondary particles are rich in cobalt, specifically, the mass ratio of cobalt element to nickel element at the grain boundaries of the surface layer of the secondary particles is A, which is greater than the mass ratio C of cobalt element to nickel element of the primary grains of the surface layer of the secondary particles and the mass ratio B of cobalt element to nickel element at the grain boundaries of the core of the secondary particles, 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 charging and discharging process to ensure the lithium ion transmission channel and improve the rate performance. Moreover, the cobalt enrichment at the grain boundaries of the surface layer of the secondary particles can effectively reduce the overall cobalt content of the secondary particles and thus avoid the excessive cobalt element concentration of the overall secondary particles, thereby reducing the capacity of the positive electrode material and improving the energy density of the positive electrode material.

[0030] 2) The preparation method of the high-nickel positive electrode material provided by the present application, which comprises pre-sintering the mixed system of the high-nickel positive electrode material precursor, lithium source and cobalt source, can ensure that the cobalt source and lithium source are in full contact and reaction to form lithium cobaltate on the surface of the precursor particles, and the lithium cobaltate is injected into the grain boundaries under the fluxing of the lithium source. During the primary sintering process, high-valence metal elements are added to be doped into the surface layer grain boundaries. The stronger metal-oxygen bond of the high-valence metal inhibits the diffusion of Co element from the grain boundaries to the primary grains and the diffusion between the primary grains, thereby maintaining the structure of the surface layer grain boundaries rich in cobalt during high-temperature process, and the cobalt concentration at the surface layer grain boundaries is greater than the cobalt concentration in the surface layer primary grains. In addition, the doped high-valence elements in the surface layer of the secondary particles can also inhibit the oxygen evolution and improve the storage performance of the positive electrode material and reduce the gas production.

[0031] 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 application of the high-nickel positive electrode material to the positive electrode sheet and then to the lithium ion battery can make the lithium ion battery have excellent discharge capacity, coulomb efficiency and capacity retention rate. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows, and it is easy to understand that the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0033] Figure 1 SEM image of the high-nickel positive electrode material of Example 1 of the present application. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions and advantages of the present application clearer, the following will combine the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0035] The first aspect of the present application provides a high-nickel positive electrode material, which is a secondary particle formed by aggregation of primary grains, and a crystal boundary is included between adjacent primary grains;

[0036] The mass ratio of cobalt element to nickel element at the crystal boundary of the surface layer of the secondary particle is A, the mass ratio of cobalt element to nickel element at the crystal boundary of the core of the secondary particle is B, and the mass ratio of cobalt element to nickel element of the primary grain in the surface layer of the secondary particle is C, wherein A is greater than B, and A is greater than C.

[0037] When A, B and C satisfy the above relationship, the high-nickel positive electrode material has a surface cobalt-rich structure, especially the crystal boundary of the surface layer of the secondary particle is rich in cobalt, 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 the cycle life, and maintain the layered structure during the charging and discharging process to ensure the lithium ion transmission channel and improve the rate performance. Cobalt enrichment at the crystal boundary of the surface layer of the secondary particle can effectively reduce the overall cobalt content of the secondary particle and avoid the excessive cobalt element concentration of the overall secondary particle, thereby reducing the capacity of the positive electrode material and improving the energy density of the positive electrode material.

[0038] In an optional embodiment, the surface layer of the secondary particle further includes a first doping element, and the first doping element is selected from at least one of metal elements with a valence of +5 or more. For example, the doping element N can be selected from Ta, Nb, Mo, W, Bi, Sb, V and the like. Doping of high-valence metal elements in the surface layer of the secondary particle can avoid the diffusion of cobalt elements on the surface of the secondary particle to the inside of the material and the diffusion of cobalt elements at the crystal boundary to the primary grain, thereby retaining the cobalt-rich structure at the crystal boundary of the surface layer of the secondary particle and further ensuring the stability of the high-nickel positive electrode material.

[0039] Further, the first doping element is selected from at least one of Ta, Nb, Mo and W, and the doping of the above elements can further improve the structural stability of the high-nickel positive electrode material.

[0040] Further, the concentration of the first doping element at the crystal boundary of the surface layer of the secondary particle is greater than the concentration of the first doping element in the primary grain in the surface layer. The enrichment of the first doping element at the crystal boundary of the surface layer can effectively prevent the diffusion of cobalt elements during sintering.

[0041] In the present application, the mass content of cobalt and nickel elements at the grain boundaries of the surface layer 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 of the primary grains of the surface layer of the secondary particles, the mass content of the first doping element at the grain boundaries of the surface layer of the secondary particles, and the mass content of the first doping element in the primary grains of the surface layer of the secondary particles can be determined by using EDS (X-ray spectrometer) to take samples from the corresponding regions.

[0042] In an alternative embodiment, the secondary particles further comprise a second doping element selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, B, and the specific capacity, stability and rate performance of the positive electrode material can be further improved by doping the second doping element.

[0043] The high-nickel positive electrode material of the present application can be directly composed of secondary particles, or a coating layer can be further coated on the surface of the secondary particles to obtain the high-nickel positive electrode material, wherein the coating layer comprises at least one element selected from B, Al, Ce, Zr, Ti and Si. Coating the surface of the secondary particles with the above-mentioned elements can further avoid the contact between the positive electrode material and the electrolyte, thereby reducing the side reaction between the positive electrode active material and the electrolyte.

[0044] In an alternative embodiment, the chemical composition of the high-nickel positive electrode 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 and Sc; and N is selected from at least one of Ta, Nb, Mo, W, Sb, Bi and V.

[0045] The second aspect of the present application provides a preparation method of the above-mentioned high-nickel positive electrode material, comprising the following steps:

[0046] 1) Pre-sintering a mixed system comprising a high-nickel positive electrode material precursor, a lithium source and a cobalt source under an oxygen-containing atmosphere to obtain a pre-sintered material;

[0047] wherein the pre-sintering temperature is 400-600℃, and the time is 4-10h;

[0048] 2) One-step sintering a mixed system comprising the pre-sintered material and a compound of a first doping element under an oxygen-containing atmosphere to obtain a one-step sintered material;

[0049] The first doping element is selected from at least one of metal elements with a valence of +5 or more; the temperature of the first sintering is 650-800℃, and the time is 8-16h.

[0050] 3) performing secondary sintering on the first sintering product in an oxygen-containing atmosphere to obtain the high-nickel positive electrode material.

[0051] In step 1), by pre-sintering the mixed system including the high-nickel positive electrode material precursor, the lithium source and the cobalt source at a lower temperature, lithium cobaltate can be formed on the surface of the precursor under the condition of lithium enrichment, and the lithium cobaltate is injected into the grain boundary under the fluxing of the lithium source, and the lower temperature can avoid the diffusion of cobalt elements into the interior of the particles, and maintain the cobalt-rich structure on the surface of the secondary particles.

[0052] In step 2), by performing the first sintering on the mixed system including the pre-sintered material and the compound of the first doping element, 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 particles and the core of the particles, on the other hand, the time of the first sintering can be relatively shortened after pre-sintering, and thus the high-nickel positive electrode material with cobalt-rich grain boundaries on the surface of the secondary particles is obtained.

[0053] The first doping element includes but is not limited to Ta, Nb, Mo, W, Bi, Sb, V and other metal elements with a valence of +5 or more; 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 and the like of the first doping element.

[0054] In the above preparation method, the high-nickel positive electrode material precursor can be in the form of hydroxide, oxide or carbonate, for example, when the high-nickel positive electrode material is a nickel-cobalt-manganese ternary material, the precursor thereof can be a nickel-cobalt-manganese hydroxide, oxide or carbonate. The present application does not limit the source of the high-nickel positive electrode material precursor, which can be obtained by commercial purchase or prepared by conventional methods in the art.

[0055] Further, in step 1), the lithium source is selected from LiOH, and the melting effect of lithium hydroxide helps to smoothly and uniformly coat the lithium cobaltate on the surface of the secondary particles, thereby improving the structural stability of the material.

[0056] The present application does not specifically limit the type of cobalt source, which can be selected from the commonly used cobalt sources 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.

[0057] In step 1), the oxygen-containing atmosphere refers to an atmosphere containing oxygen, which can be a pure oxygen atmosphere or an air atmosphere, and is preferably a pure oxygen atmosphere.

[0058] In step 2), after obtaining the primary sintered material, a process of washing and drying the primary sintered material is further included, wherein the washing can remove residual alkali on the surface of the primary sintered material, and the drying can remove water. The present application does not particularly limit the conditions of washing and drying, and the conditions commonly used in the art can be used.

[0059] In step 3), the primary sintered material is subjected to secondary sintering to remove the combined water and internal water combined with the surface of the material, thereby avoiding swelling of the battery during use. The secondary sintering can be completed at 200-500°C for 8-16h.

[0060] In an alternative embodiment, when the high-nickel positive electrode material further includes a second doping element, a compound of the second doping element is further added to the mixed system in step 2) before secondary sintering, so as 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, and carbonates of the second doping element.

[0061] In an alternative embodiment, when the secondary particles of the high-nickel positive electrode material are further coated with a coating layer, a coating agent is further added to the mixed system in step 3) before secondary sintering, so as 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, and carbonates of the coating element.

[0062] The third aspect of the present application provides a positive electrode sheet comprising the high-nickel positive electrode material described above. It can be understood that the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer arranged 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.

[0063] The present application does not particularly limit the positive electrode current collector, and the current collector commonly used in the art, such as an aluminum foil, can be used, which can be obtained by commercial purchase.

[0064] The positive electrode active layer of the present application comprises the high-nickel positive electrode material as described above, which means that the high-nickel positive electrode material as described above is used as the positive electrode active material in the positive electrode active layer. In addition to the positive electrode active material, the positive electrode active layer can further comprise a conductive agent, a binder and the like. The conductive agent and the binder can both be the conventional conductive agent and binder used in the art, which will not be described here in detail.

[0065] The fourth aspect of the present application provides a lithium ion battery comprising the positive electrode sheet as described above. Since the positive electrode sheet comprises the high-nickel positive electrode material provided by the present application, which has the advantages of good stability and less side reactions with electrolyte, the battery has good discharge capacity, coulombic efficiency and capacity retention rate.

[0066] The lithium ion battery of the present application comprises a separator, a negative electrode sheet and an electrolyte in addition to the positive electrode sheet. The composition of the negative electrode sheet can refer to the conventional negative electrode sheet in the art, which will not be described here in detail. The separator can also be the conventional separator used in the art, such as a PP film, a PE film and the like.

[0067] The lithium ion battery of the present application can be prepared by the conventional method in the art, for example, the positive electrode sheet, the separator and the negative electrode sheet can be sequentially stacked and placed, and then the electrode core can be obtained by lamination or winding process, and then the above-mentioned lithium ion battery can be obtained through processes such as baking, liquid injection, formation, packaging and the like.

[0068] Hereinafter, the high-nickel positive electrode material provided by the present application and the preparation method thereof will be further described in detail through specific examples.

[0069] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, conventional materials and conventional instruments in the art, which can be obtained by commercial purchase, and the reagents involved can also be synthesized by the conventional method in the art.

[0070] Example 1

[0071] The chemical composition of the high-nickel positive electrode material of the present example 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, and the preparation method thereof comprises the following steps:

[0072] 1) The hydroxide precursor of NCM9253, LiOH, Co2O3 were mixed at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, and then heated to 550°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0073] 2) The pre-sintered material was mixed with ammonium molybdate, ZrO2, SrO, Y2O3 at a molar ratio of 1:0.002:0.002:0.001:0.0005 at 800 rpm, and then heated to 750°C at a rate of 5°C / min in an oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0074] 3) The primary sintered material was washed with deionized water and vacuum dried at 120°C to obtain a water-washed and dried material;

[0075] 4) The water-washed and dried material was mixed with coating agent H3BO3, Al2O3, TiO2 at a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 min, and then heated to 300°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 10 h to obtain a high-nickel positive electrode material.

[0076] Example 2

[0077] The chemical composition of the high-nickel positive electrode material of this example 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, and the preparation method comprises the following steps:

[0078] 1) The hydroxide precursor of NCM9442, LiOH, Co(OH)2 were mixed at a molar ratio of 1:1.05:0.01 at 800 rpm for 30 min, and then heated to 500°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0079] 2) The pre-sintered material was mixed with WO3, ZrO2, Al(OH)3, MgCO3, Y2O3 at a molar ratio of 1:0.001:0.002:0.003:0.002:0.0005 at 800 rpm, and then heated to 750°C at a rate of 5°C / min in an oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0080] 3) The primary sintered material was washed with deionized water and vacuum dried at 120°C to obtain a water-washed and dried material;

[0081] 4) The water-washed dried material is mixed with the coating agent B2O3, Al2O3, TiO2 at a molar ratio of 1:0.01:0.0015:0.001 at 800 rpm for 30 min, and then heated to 400°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 12 h to obtain the high-nickel positive electrode material.

[0082] Example 3

[0083] The high-nickel positive electrode material of this example has a chemical composition of 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, and the preparation method comprises the following steps:

[0084] 1) The hydroxide precursor of NCM9343, LiOH, and cobalt acetate are mixed at a molar ratio of 1:1.05:0.01 at 800 rpm for 30 min, and then heated to 450°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0085] 2) The pre-sintered material is mixed with Ta2O5, ZrO2, TiO2, MgO, Y2O3 at a molar ratio of 1:0.001:0.002:0.001:0.001:0.0005 at 800 rpm, and then heated to 740°C at a rate of 5°C / min in an oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0086] 3) The primary sintered material is washed with deionized water, and then dried in a vacuum at 120°C to obtain a water-washed dried material;

[0087] 4) The water-washed dried material is mixed with the coating agent H3BO3, Al2O3 at a molar ratio of 1:0.01:0.002 at 800 rpm for 30 min, and then heated to 350°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 8 h to obtain the high-nickel positive electrode material.

[0088] Example 4

[0089] The high-nickel positive electrode material of this example has a chemical composition of 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 comprising the following steps:

[0090] 1) the NCM9145 precursor, LiOH, CoSO4, CoCO3 are mixed at 800 rpm for 30 min in a molar ratio of 1:1.05:0.004:0.004, then heated to 500 DEG C at 2 DEG C / min under oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0091] 2) the pre-sintered material is mixed with MoO3, Nb2O5 and ZrO2 at 800 rpm in a molar ratio of 1:0.0005:0.0005:0.002, then heated to 750 DEG C at 5 DEG C / min under oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0092] 3) the primary sintered material is washed with deionized water, then vacuum dried at 120 DEG C to obtain a water-washed and dried material;

[0093] 4) the water-washed and dried material is mixed with B2O3, Al2O3 and TiO2 at 800 rpm for 30 min in a molar ratio of 1:0.01:0.0015:0.001, heated to 400 DEG C at 2 DEG C / min under oxygen atmosphere, and kept for 12 h to obtain a high-nickel positive electrode material.

[0094] Example 5

[0095] The chemical composition of the high-nickel positive electrode material of the present example 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 comprising the following steps:

[0096] 1) the NCM9145 precursor, LiOH, CoSO4, CoCO3 are mixed at 800 rpm for 30 min in a molar ratio of 1:1.05:0.004:0.004, then heated to 500 DEG C at 2 DEG C / min under oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0097] 2) the pre-sintered material is mixed with MoO3, Nb2O5 and ZrO2 at 800 rpm in a molar ratio of 1:0.0005:0.0005:0.002, then heated to 750 DEG C at 5 DEG C / min under oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0098] 3) The primary sintered material is washed with deionized water and vacuum dried at 120°C to obtain a water-washed and dried material;

[0099] 4) The water-washed and dried material is mixed with the coating agent H3BO3, TiO2 at a molar ratio of 1:0.01:0.002 at 800 rpm for 30 min, heated to 300°C at 2°C / min in an oxygen atmosphere, and kept for 10 h to obtain a high-nickel positive electrode material.

[0100] Example 6

[0101] The chemical composition of the high-nickel positive electrode material of this example 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, and the preparation method comprises the following steps:

[0102] 1) The hydroxide precursor of NCM9253, LiOH, and Co2O3 are mixed at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, then heated to 550°C at 2°C / min in an oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0103] 2) The pre-sintered material is mixed with Sb2O5, ZrO2, SrO, and Y2O3 at a molar ratio of 1:0.001:0.002:0.001:0.0005 at 800 rpm, then heated to 750°C at 5°C / min in an oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0104] 3) The primary sintered material is washed with deionized water and vacuum dried at 120°C to obtain a water-washed and dried material;

[0105] 4) The water-washed and dried material is mixed with the coating agent H3BO3, Al2O3, and TiO2 at a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 min, heated to 300°C at 2°C / min in an oxygen atmosphere, and kept for 10 h to obtain a high-nickel positive electrode material.

[0106] Comparative Example 1

[0107] The chemical composition of the high-nickel positive electrode material of this example is consistent with that of Example 1, and the preparation method comprises the following steps:

[0108] 1) The NCM9253 precursor, LiOH, Co2O3, ammonium molybdate, ZrO2, SrO, 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 then heated to 750°C at a rate of 5°C / min in an oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0109] 2) The primary sintered material was washed with deionized water and then vacuum dried at 120°C to obtain a water-washed and dried material;

[0110] 3) The water-washed and dried material was mixed with the coating agent H3BO3, Al2O3, TiO2 at a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 min, and then heated to 300°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 10 h to obtain a high-nickel positive electrode material.

[0111] Comparative Example 2

[0112] The chemical composition of the high-nickel positive electrode material of the present comparative example is Li 1.01 Ni 0.915 Co 0.056 Mn 0.029 Zr 0.002 Sr 0.00 1Y 0.001 B 0.01 Al 0.004 Ti 0.002 O2, and the preparation method comprises the following steps:

[0113] 1) The hydroxide precursor of NCM9253, LiOH, Co2O3 were mixed at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, and then heated to 550°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0114] 2) The pre-sintered material was mixed with ZrO2, SrO, Y2O3 at a molar ratio of 1:0.002:0.001:0.0005 at 800 rpm, and then heated to 750°C at a rate of 5°C / min in an oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0115] 3) The primary sintered material was washed with deionized water and then vacuum dried at 120°C to obtain a water-washed and dried material;

[0116] 4) The water-washed and dried material was mixed with the coating agent H3BO3, Al2O3, TiO2 at a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 min, and then heated to 300°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 10 h to obtain a high-nickel positive electrode material.

[0117] Comparative Example 3

[0118] The high-nickel positive electrode material of the present comparative example has the same chemical composition as Example 1, and its preparation method comprises the following steps:

[0119] 1) The hydroxide precursor of NCM9253, LiOH, and Co2O3 were mixed at a molar ratio of 1:1.05:0.004 at 800 rpm for 30 min, and then heated to 750°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 8 h to obtain a pre-sintered material;

[0120] 2) The pre-sintered material was mixed with ammonium molybdate, ZrO2, SrO, and Y2O3 at a molar ratio of 1:0.002:0.002:0.001:0.0005 at 800 rpm, and then heated to 750°C at a rate of 5°C / min in an oxygen atmosphere, and kept for 12 h to obtain a primary sintered material;

[0121] 3) The water-washed and dried material was mixed with coating agent H3BO3, Al2O3, and TiO2 at a molar ratio of 1:0.01:0.002:0.002 at 800 rpm for 30 min, and then heated to 300°C at a rate of 2°C / min in an oxygen atmosphere, and kept for 10 h to obtain a high-nickel positive electrode material.

[0122] Test Example

[0123] 1. The high-nickel positive electrode material of Example 1 was subjected to SEM characterization, Figure 1 which is the SEM image of the high-nickel positive electrode material of Example 1, from Figure 1 which can be seen that the high-nickel positive electrode material of Example 1 is a secondary spherical particle formed by aggregation of primary grains.

[0124] 2. The high-nickel positive electrode materials obtained in the above examples and comparative examples were subjected to the following parameter determination:

[0125] 1) The mass ratio A of cobalt element to nickel element and the content of the first doping element at the surface layer grain boundary of the secondary particle

[0126] The determination method is as follows: the surface morphology of the sample is observed using SEM, and then EDS test is performed at the grain boundary to obtain the contents of cobalt, nickel, and the first doping element, and the mass ratio A of cobalt / nickel is calculated.

[0127] 2) The mass ratio C of cobalt element to nickel element and the content of the first doping element of the primary grain at the surface layer of the secondary particle

[0128] The determination method is as follows: the surface morphology of the sample is observed using SEM, and then EDS test is performed at the center of the primary grain to obtain the contents of cobalt, nickel, and the first doping element, and the mass ratio C of cobalt / nickel is calculated.

[0129] 3) mass ratio B of cobalt to nickel at the grain boundary of the secondary particle core

[0130] The test method is: using argon ion beam to ion mill the sample to obtain the positive electrode particles of the section. Using SEM to observe the sample section, selecting the grain boundary of the secondary particle core for EDS test to obtain the contents of cobalt, nickel and the first doping element, and calculating the mass ratio B of cobalt to nickel.

[0131] The test results of the above parameters are listed in Table 1.

[0132] 3. The high-nickel positive electrode material, the conductive agent Super-P, and the binder PVDF are mixed in a mass ratio of 96.5:1.5:2, added into an NMP solvent, and uniformly mixed to obtain a positive electrode slurry with a solid content of 30-40%. The positive electrode slurry is coated on the positive electrode current collector aluminum foil at a surface density of about 20 mg / cm 2 , and sequentially subjected to drying, punching, and rolling to obtain a positive electrode sheet;

[0133] The above positive electrode sheet, PP separator, and metal lithium sheet are sequentially stacked, 1.0M LiPF6 electrolyte is added, and an LR2430 type button cell is assembled. The performance of the obtained button cell is measured as follows:

[0134] 1) Discharge capacity

[0135] The measurement method is: at room temperature, the button cell is charged at 0.2C constant current to 4.25V, and then charged at 4.25V constant voltage until the cutoff current is equal to 0.05C. After standing for 5min, the battery is discharged at 0.2C constant current to 2.5V, and the discharge capacity of the battery is recorded. Wherein, 1C=200mA / g.

[0136] 2) First coulombic efficiency

[0137] The measurement method is: at room temperature, the button cell is charged at 0.2C constant current to 4.25V, and then charged at 4.25V constant voltage until the cutoff current is equal to 0.05C. After standing for 5min, the battery is discharged at 0.2C constant current to 2.5V, and the discharge capacity of the battery is recorded. Wherein, 1C=200mA / g.

[0138] The above positive electrode sheet, PP separator, and graphite negative electrode sheet are sequentially stacked, wound to obtain a battery cell, and then packaged in an aluminum plastic film and injected with 1.0M LiPF6 electrolyte. After packaging and standing, the battery cell is formed to obtain a full battery. The performance of the obtained full battery is tested as follows:

[0139] 3) Capacity retention rate after 300 cycles

[0140] Determination method: the full battery was placed in a 45℃ constant temperature box, first charged to 4.25V at 0.2C constant current, then charged to 4.25V constant voltage until the cutoff current was 0.05C, and then discharged to 2.8V at 0.2C constant current after 5 minutes of standing, the initial capacity a1 of the battery was recorded, then the charge-discharge cycle of 0.2C charge / 0.2C discharge was carried out, and the capacity a2 of the battery was recorded after 300 cycles, and the capacity retention rate was a2 / a1 x 100%. Wherein, 1C = 200mA / g.

[0141] The determination results of the above performances are listed in Table 1.

[0142] Table 1

[0143]

[0144]

[0145] From the data in Table 1, it can be seen that:

[0146] 1) The A value of the high-nickel positive electrode material of Example 1 to Example 6 is greater than the B value and the C value, and the first doping element has a higher concentration at the grain boundary, and the material can make the battery have higher discharge capacity, first coulombic efficiency and capacity retention rate.

[0147] 2) By comparing Example 1 with Comparative Example 1 and Comparative Example 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 carried out or the pre-sintering temperature is too high, the distribution of cobalt and nickel elements of the secondary particle surface layer and the core, the grain boundary and the primary grain is close, and the discharge capacity, the first coulombic efficiency and the capacity retention rate of the battery obtained by using the high-nickel positive electrode material of Comparative Example 1 and Comparative Example 3 are all poor.

[0148] 3) By comparing Example 1 with Comparative Example 2, it can be seen that when no high-valence metal element with valence higher than positive five is added for doping in the primary sintering, the concentration distribution of cobalt and nickel elements of the secondary particle surface layer and the core, the grain boundary and the primary grain is close, and the discharge capacity, the first coulombic efficiency and the capacity retention rate of the battery obtained by using the high-nickel positive electrode material of Comparative Example 2 are obviously poorer than those of the battery obtained by using the high-nickel positive electrode material of Example 1.

[0149] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high-nickel cathode material, characterized in that, The high-nickel cathode material is a secondary particle formed by the aggregation of primary grains, and there are grain boundaries between adjacent primary grains. The mass ratio of cobalt to nickel at the grain boundary of the secondary particle surface is A, the mass ratio of cobalt to nickel at the grain boundary of the secondary particle core is B, and the mass ratio of cobalt to nickel at the primary grain of the secondary particle surface is C, wherein A is greater than B and A is greater than C. The secondary particle surface layer includes a first doping element N, which is selected from at least one of the metallic elements whose valence can reach positive pentavalent or higher. 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 ≤ 0.05, 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.

2. The high-nickel cathode material according to claim 1, characterized in that, The first dopant element N is selected from at least one of Ta, Nb, Mo, and W.

3. The high-nickel cathode material according to claim 2, characterized in that, The concentration of the first doped element N at the grain boundary of the secondary grain is greater than the concentration of the first doped element N in the primary grain.

4. The high-nickel cathode material according to claim 1, characterized in that, The secondary particles include a second doping element, which is selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B.

5. The high-nickel cathode material according to any one of claims 1-4, characterized in that, The surface of the secondary particles is coated with a coating layer, which includes at least one element selected from B, Al, Ce, Zr, Ti, and Si.

6. A method for preparing the high-nickel cathode material according to any one of claims 1-5, characterized in that, Includes the following steps: 1) A mixed system including a high-nickel cathode material precursor, a lithium source, and a cobalt source is pre-sintered in an oxygen-containing atmosphere to obtain a pre-sintered material; The pre-sintering temperature is 400~600℃, and the time is 4~10h; 2) The mixture system comprising the pre-sintered material and the compound containing the first dopant element N is sintered once in an oxygen-containing atmosphere to obtain a primary sintered material; The first dopant element N is selected from at least one metallic element whose valence can reach +5 or higher. The temperature of the first sintering is 650~800℃, and the time is 8~16h; 3) The primary sintering material is subjected to secondary sintering in an oxygen-containing atmosphere to obtain the high-nickel cathode material.

7. The preparation method according to claim 6, characterized in that, In step 2), the mixed system further includes a compound of a second dopant element, wherein the second dopant element is selected from at least one of Zr, Al, Ti, Mg, Sc, Y, La, Sr, and B.

8. The preparation method according to claim 6, characterized in that, In step 3), the secondary sintering includes: sintering the mixture of primary sintering material and coating agent at 200~500℃ for 8~16h; 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.

9. A positive electrode plate, characterized in that, Includes the high-nickel cathode material as described in any one of claims 1-5.

10. A lithium-ion battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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