A positive electrode active material, a method for preparing the same, and a lithium ion battery

Abstract

The application provides a positive electrode active material, a preparation method thereof and a lithium ion battery. The first aspect of the application provides a positive electrode active material, which has a chemical composition of Li 1+a [Ni x Co y M1 z M2 b ]O 2± c A d , M1 is one or both of Mn and Al, M2 is one or more of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce and Y, and A is one of F, Cl and S. By controlling the content of Ni in the secondary particles with different particle sizes, the application can avoid the problem that the secondary particles with different particle sizes are inconsistent in attenuation during battery cycling, and improve the cycle stability of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to a positive electrode active material, its preparation method, and a lithium-ion battery, and relates to the field of lithium-ion battery technology. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that primarily function by the movement of lithium ions between the positive and negative electrodes. The positive electrode active material is the decisive factor in the performance of lithium-ion batteries, directly determining their overall performance. Ternary positive electrode active materials, such as lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA), are currently a research hotspot. However, among existing materials, the cycle stability of ternary positive electrode active materials still needs improvement. Summary of the Invention

[0003] This invention provides a positive electrode active material and its preparation method, which can improve the structural stability of ternary positive electrode active materials and improve the cycle performance of lithium-ion batteries.

[0004] The present invention also provides a lithium-ion battery comprising the above-mentioned positive electrode active material, which has good cycle performance.

[0005] The first aspect of this invention provides a positive electrode active material, wherein the chemical composition of the positive electrode active material is Li. 1+a [Ni x Co y M1 z M2 b ]O 2±c A d , 0<a<0.2, 0.5≤x<1, 0<y<0.3, 0<z<0.3, 0<b<0.2, c<0.02, 0≤d≤0.05, x+y+z+b=1;

[0006] M1 is one or two of Mn and Al; M2 is one or more of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y; and A is one of F, Cl, and S.

[0007] The first particle has a Ni element with an X value of X1, and the second particle has a Ni element with an X value of X2, where 0.005 ≤ (X1 - X2) ≤ 0.07.

[0008] The first particle refers to a particle with a particle size equal to D10 of the positive electrode active material, and the second particle refers to a particle with a particle size equal to D90 of the positive electrode active material.

[0009] In one specific embodiment, the Y value corresponding to the Co element in the chemical composition of the first particle is Y1, and the Y value corresponding to the Co element in the chemical composition of the second particle is Y2, where Y2 > Y1.

[0010] In one specific implementation, (X1-X2) > (Y2-Y1).

[0011] In one specific embodiment, the Z value corresponding to element M1 in the chemical composition of the first particle is Z1, and the Z value corresponding to element M1 in the chemical composition of the second particle is Z2, where Z2 > Z1.

[0012] In one specific implementation, (X1-X2) > (Z2-Z1).

[0013] In one specific embodiment, the b value corresponding to the M2 element in the chemical composition of the first particle is b1, and the b value corresponding to the M2 element in the chemical composition of the second particle is b2, where b1 = b2.

[0014] In one specific embodiment, the size of the primary particles constituting the first particle is R1, and the size of the primary particles constituting the second particle is R2, where R1 < R2.

[0015] In one specific implementation, R1 ≥ 0.85R2.

[0016] A second aspect of the present invention provides a method for preparing any of the above-described positive electrode active materials, comprising the following steps:

[0017] A positive electrode active material precursor is prepared by mixing a nickel source, a cobalt source, and an M1 source; the positive electrode active material precursor includes a first positive electrode active material precursor and a second positive electrode active material precursor.

[0018] The size of the first positive electrode active material precursor is smaller than the size of the second positive electrode active material precursor. The molar content of Ni element in the chemical composition of the first positive electrode active material precursor is W1, and the molar content of Ni element in the chemical composition of the second positive electrode active material precursor is W2, where W1-W2≥0.005.

[0019] The positive electrode active material precursor, lithium source, and M2 source are mixed to form a mixture.

[0020] The mixture is sintered in an oxygen or air atmosphere to obtain a positive electrode active material.

[0021] A third aspect of the present invention provides a lithium-ion battery comprising any of the above-described positive electrode active materials.

[0022] This invention provides a positive electrode active material that, by controlling the Ni content in particles of different sizes, can avoid the problem of inconsistent degradation of secondary particles of different sizes during battery cycling, thereby improving the cycle stability of lithium-ion batteries. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] The first aspect of this invention provides a positive electrode active material with a chemical composition of Li. 1+a [Ni x Co y M1 z M2 b ]O 2± c A d , 0<a<0.2, 0.5≤x<1, 0<y<0.3, 0<z<0.3, 0<b<0.2, c<0.02, 0≤d≤0.05, x+y+z+b=1;

[0025] M1 is one or both of Mn and Al; M2 is one or more of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y; and A is one of F, Cl, and S.

[0026] The positive electrode active material provided by the present invention is a ternary material of lithium nickel cobalt manganese oxide (NCM) or lithium nickel cobalt aluminum oxide (NCA). In addition, it may further include doping element M2 and element A. M2 can be selected from one or more of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y, and A is one of F, Cl, and S.

[0027] Furthermore, M2 is selected from one or more of Zr, Mg, Ti, Al, Sr, Mo, Ce, and Y.

[0028] Furthermore, A is F.

[0029] This invention does not impose excessive restrictions on x, y, z, a, b, c, and d within the above-mentioned limits; they are acceptable as long as they fall within the corresponding ranges.

[0030] The positive electrode active material provided by this invention is obtained by mixing several secondary particles. The particle size of the secondary particles is normally distributed in the positive electrode active material. According to the distribution of the secondary particles in the positive electrode active material, the secondary particles are divided. The first particle refers to the particle with a particle size equal to D10 of the positive electrode active material, and the second particle refers to the particle with a particle size equal to D90 of the positive electrode active material. D10 refers to the particle size corresponding to 10% of the particle size distribution, and D90 refers to the particle size corresponding to 90% of the particle size distribution. The specific particle size distribution can be determined and obtained by conventional particle size testing methods in the art.

[0031] Because the first particle has a smaller particle size, its structural stability during lithium-ion battery cycling is significantly better than that of the second particle, which has a larger particle size. However, as the Ni content in the particle increases, its structural stability during lithium-ion battery cycling decreases. Therefore, this invention increases the Ni content on the surface of the first particle, making it higher than the Ni content on the surface of the second particle. This ensures that the structural stability of secondary particles of different sizes is basically the same, avoiding the problem of excessively rapid battery capacity decay caused by the different structural stability of secondary particles of different sizes. Specifically, the X value of Ni in the chemical composition of the first particle is X1, and the X value of Ni in the chemical composition of the second particle is X2, and (X1-X2)≥0.005.

[0032] As the Ni content in the secondary particles increases, the battery cycle performance will actually decrease. Therefore, the difference between (X1-X2) should not be higher than 0.07, i.e., 0.005≤(X1-X2)≤0.07, otherwise it will lead to the degradation of lithium-ion battery capacity.

[0033] Furthermore, 0.005≤(X1-X2)≤0.06, and even further, 0.01≤(X1-X2)≤0.05.

[0034] In one specific embodiment, the Y value corresponding to the Co element in the chemical composition of the first particle is Y1, and the Y value corresponding to the Co element in the chemical composition of the second particle is Y2, where Y2 > Y1. By increasing the Co element content in the second particle, it is helpful to improve the structural stability of the second particle, reduce the gap in structural stability between the first particle and the second particle, and improve the cycle performance of the lithium-ion battery.

[0035] Furthermore, (X1-X2) > (Y2-Y1), meaning the difference in Co content between the first and second particles is less than the difference in Ni content, which helps to reduce the amount of Co used and lower the preparation cost of the positive electrode active material.

[0036] In one specific embodiment, the Z value corresponding to element M1 in the chemical composition of the first particle is Z1, and the Z value corresponding to element M1 in the chemical composition of the second particle is Z2, where Z2 > Z1. By increasing the content of element M1 in the second particle, it is helpful to improve the structural stability of the second particle, reduce the gap in structural stability between the first particle and the second particle, and improve the cycle performance of the lithium-ion battery.

[0037] Furthermore, (X1-X2) > (Z2-Z1), meaning that the difference in the content of element M1 between the first and second particles is less than the difference in the content of element Ni. When the difference in the content of element Ni between the first and second particles is less than or equal to the difference in the content of element M1, it is not conducive to improving the stability of the secondary particle structure and will affect the cycle stability and capacity of the lithium-ion battery.

[0038] In one specific embodiment, the b value corresponding to the M2 element in the chemical composition of the first particle is b1, and the b value corresponding to the M2 element in the chemical composition of the second particle is b2, where b1=b2, that is, X1+Y1+Z1=X2+Y2+Z2. The M2 element can cause a large performance change with a small doping amount. Therefore, this application does not adjust the doping amount of the M2 element in the first particle and the second particle, and the two can be the same.

[0039] In one specific embodiment, the secondary particles are formed by the agglomeration of primary particles. The size of the primary particles constituting the first particle is R1, and the size of the primary particles constituting the second particle is R2, where R1 < R2. The smaller size of the primary particles in the first particle helps to increase the capacity of the lithium-ion battery, while the larger size of the primary particles in the second particle helps to reduce particle composition, increase particle strength, and ensure the stability of the positive electrode active material. The size of the primary particles can be measured by scanning electron microscopy.

[0040] Furthermore, R1 ≥ 0.85R2.

[0041] A second aspect of the present invention provides a method for preparing any of the above-described positive electrode active materials, comprising the following steps:

[0042] A positive electrode active material precursor is prepared by mixing a nickel source, a cobalt source, and an M1 source; the positive electrode active material precursor includes a first positive electrode active material precursor and a second positive electrode active material precursor.

[0043] The size of the first positive electrode active material precursor is smaller than the size of the second positive electrode active material precursor. The molar content of Ni element in the chemical composition of the first positive electrode active material precursor is W1, and the molar content of Ni element in the chemical composition of the second positive electrode active material precursor is W2, where W1-W2≥0.005.

[0044] The positive electrode active material precursor, lithium source, and M2 source are mixed to form a mixture.

[0045] The mixture is sintered in an oxygen or air atmosphere to obtain a positive electrode active material.

[0046] In one specific embodiment, the preparation method of the above-mentioned positive electrode active material specifically includes the following steps:

[0047] Step 1: Mix the nickel source, cobalt source and M1 source to prepare the positive electrode active material precursor.

[0048] First, a precursor for the positive electrode active material is prepared by co-precipitation. Specifically, a nickel source, a cobalt source, and an M1 source are prepared into a soluble mixed solution, and then a precipitant or a complexing agent is added. By controlling the reaction conditions, a spherical precursor for the positive electrode active material is formed.

[0049] The M1 source can be a manganese salt and / or an aluminum salt, and the present invention does not further limit the types of nickel source, cobalt source, and M1 source, which can be conventional materials in the field.

[0050] To achieve a difference in Ni content between the first and second particles, two cathode active material precursors of different sizes can be mixed, with different Ni content in the two sizes of cathode active material precursors. This results in the cathode active material precursors comprising a first cathode active material precursor and a second cathode active material precursor, with the size of the first cathode active material precursor being smaller than that of the second cathode active material precursor. The molar content of Ni in the chemical composition of the first cathode active material precursor is W1, and the molar content of Ni in the chemical composition of the second cathode active material precursor is W2, where W1-W2≥0.005.

[0051] Step 2: Mix the positive electrode active material precursor, lithium source, and M2 source to form a mixture.

[0052] This invention does not specifically limit the lithium source and M2 source, and can be any conventional material in the field. For example, the lithium source can be lithium hydroxide, lithium carbonate, lithium oxide, etc.; the M2 source can be any oxide or hydroxide containing M2, such as ZrO2, MgO, Mg(OH)2, TiO2, Al2O3, SrO, MoO3, CeO2, Y2O3, etc.

[0053] The positive electrode active material precursor, lithium source, and M2 source are mixed in a certain molar ratio, and the mixture is thoroughly mixed. The mixing process can be carried out in equipment such as high-speed mixing equipment, sand milling equipment, ball milling equipment, plow mixing equipment, and inclined mixing equipment to ensure that the mixture is fully mixed.

[0054] Step 3: Sinter the mixture in an oxygen or air atmosphere to obtain the positive electrode active material.

[0055] According to conventional technical methods in this field, the mixture is sintered in a high-temperature sintering equipment such as a muffle furnace, tunnel furnace, roller kiln, or tube furnace. During the sintering process, oxygen or air is introduced and the sintering temperature is controlled to be no less than 750°C. After sintering for 12-20 hours, the mixture is cooled to obtain the positive electrode active material.

[0056] A third aspect of the present invention provides a lithium-ion battery comprising any of the above-described positive electrode active materials.

[0057] Based on the positive electrode active material provided in the first aspect of the present invention, the lithium-ion battery provided by the present invention has good cycle performance.

[0058] In one specific embodiment, the present invention does not limit the specific structure of the lithium-ion battery, for example, it can be a square-shell battery, a cylindrical battery, etc.

[0059] The lithium-ion battery provided by the present invention includes an electrode assembly, a casing, and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive active material layer includes the aforementioned positive active material.

[0060] In addition to the aforementioned positive electrode active material, the positive electrode active material layer also includes a conductive agent and a binder. The selection of the conductive agent and binder is not special and can be conventional in the field. For example, the conductive agent is selected from one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, single-walled carbon nanotubes, multi-arm carbon nanotubes, and carbon fibers, and the binder is selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium polyacrylate (PAALi).

[0061] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The negative active material layer includes a negative active material, a conductive agent, and a binder. The negative active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbide, and silicon suboxide.

[0062] The diaphragm, shell, and electrolyte are all conventional materials in this field.

[0063] The positive electrode active material of the present invention will be described below through specific embodiments.

[0064] Example 1

[0065] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0066] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 83.2:7.4:9.4. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 4.5μm and near-spherical shape.

[0067] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 80.6:9.6:9.8. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.1 μm and near-spherical shape was formed.

[0068] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol ZrO2 (where 1% is the Zr:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0069] Step 3: Load the mixture into a 2.5kg crucible and sinter it in an oxygen atmosphere in a box furnace at 765℃ for 14 hours. Then, mechanically crush the sintered mixture to obtain the positive electrode active material.

[0070] Example 2

[0071] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0072] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 81.9:7.2:10.9. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 4.1 μm and near-spherical shape.

[0073] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 81.4:7.4:11.2. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.5 μm and near-spherical shape was formed.

[0074] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol ZrO2 (where 1% is the Zr:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0075] Step 3: Load the mixture into a 2.5kg crucible and sinter it in an oxygen atmosphere in a box furnace at 775℃ for 18 hours. Then, mechanically crush the sintered mixture to obtain the positive electrode active material.

[0076] Example 3

[0077] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0078] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 83.6:7.9:8.5. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 3.9μm and near-spherical shape.

[0079] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 77.6:11.2:11.2. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 15.1 μm and near-spherical shape was formed.

[0080] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol ZrO2 (where 1% is the Zr:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0081] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 775℃ for 14 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0082] Example 4

[0083] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0084] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 82.7:7.7:9.6. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 3.6μm and near-spherical shape.

[0085] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 81.7:8.5:9.8. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14 μm and near-spherical shape was formed.

[0086] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol SrO (where 1% is the Sr:TM value); use a high-speed mixer at 800 rpm to mix for 15 min to obtain the mixture.

[0087] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 775℃ for 14 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0088] Example 5

[0089] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0090] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 82.5:8:9.5. By adding a precipitant or complexing agent and controlling the reaction conditions, a first positive electrode active material precursor with a particle size of 3.9 μm and near-spherical shape is formed.

[0091] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 77.5:12.6:9.9. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.9 μm and near-spherical shape was formed.

[0092] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol TiO2 (where 1% is the Ti:TM value); use a high-speed mixer at 800 rpm to mix for 15 min to obtain the mixture.

[0093] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 770℃ for 14 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0094] Example 6

[0095] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0096] Step 1: Mix and dissolve nickel salt, cobalt salt, and aluminum salt in a ratio of 91.2:6:2.8. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 4.1 μm and near-spherical shape.

[0097] Nickel salt, cobalt salt, and aluminum salt were mixed and dissolved in a ratio of 87.3:9.5:3.2. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.8 μm and near-spherical shape was formed.

[0098] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol Al2O3 (where 1% is the Al:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0099] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in a box furnace under an oxygen atmosphere at 780℃ for 20 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0100] Example 7

[0101] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0102] Step 1: Mix and dissolve nickel salt, cobalt salt, and aluminum salt in a ratio of 91.5:6.2:2.3. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 3.5μm and near-spherical shape.

[0103] Nickel salt, cobalt salt, and aluminum salt were mixed and dissolved in a ratio of 87:10.4:2.6. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 10.3 μm and near-spherical shape was formed.

[0104] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol Y2O3 (where 1% is the Y:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0105] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 750℃ for 12 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0106] Example 8

[0107] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0108] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 82.5:7.9:9.6. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 3.5μm and near-spherical shape.

[0109] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 77.2:9.4:13.4. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.3 μm and near-spherical shape was formed.

[0110] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 0.5% mol SrO and 0.5% mol MoO3 (where 0.5% represents the Sr:TM value and Mo:TM value); mix the mixture at 800 rpm for 15 min using a high-speed mixer to obtain the mixture.

[0111] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 760℃ for 18 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0112] Example 9

[0113] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0114] Step 1: Mix and dissolve nickel salt, cobalt salt, and aluminum salt in a ratio of 82.9:15.2:1.9. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 3.9μm and near-spherical shape.

[0115] Nickel salt, cobalt salt, and aluminum salt were mixed and dissolved in a ratio of 79.2:17.1:2.7. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.2 μm and near-spherical shape was formed.

[0116] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 0.5% mol Al2O3 and 0.5% mol CeO2 (where 0.5% represents the Al:TM value and Ce:TM value); mix using a high-speed mixer at 800 rpm for 15 min to obtain the mixture.

[0117] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 760℃ for 17 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0118] Example 10

[0119] This embodiment provides a method for preparing a positive electrode active material, including the following steps:

[0120] Step 1: Mix and dissolve nickel salt, cobalt salt, and aluminum salt in a ratio of 61:10.8:28.2. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 3.8μm and near-spherical shape.

[0121] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 58.9:11.5:29.6. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.2 μm and near-spherical shape was formed.

[0122] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol MgO (where 1% is the Mg:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0123] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 890℃ for 15 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0124] Comparative Example 1

[0125] This comparative example provides a method for preparing a positive electrode active material, including the following steps:

[0126] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 82.1:7.4:10.5%, and control the reaction conditions by adding a precipitant or complexing agent to form a first positive electrode active material precursor with a particle size of 4μm spherical.

[0127] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 82.1:7.4:10.5. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.4 μm and near-spherical shape was formed.

[0128] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol ZrO2 (where 1% is the Zr:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0129] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 770℃ for 16 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0130] Comparative Example 2

[0131] This comparative example provides a method for preparing a positive electrode active material, including the following steps:

[0132] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 82.4:7.3:10.3. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 3.9μm and near-spherical shape.

[0133] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 75.1:11.9:13. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.3 μm and near-spherical shape was formed.

[0134] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol ZrO2 (where 1% is the Zr:TM value); use a high-speed mixer at 800 rpm and mix for 15 min to obtain the mixture.

[0135] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 790℃ for 18 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0136] Comparative Example 3

[0137] This comparative example provides a method for preparing a positive electrode active material, including the following steps:

[0138] Step 1: Mix and dissolve nickel salt, cobalt salt, and manganese salt in a ratio of 82.1:7.7:10.2. By adding a precipitant or complexing agent, control the reaction conditions to form a first positive electrode active material precursor with a particle size of 4.3 μm and near-spherical shape.

[0139] Nickel salt, cobalt salt, and manganese salt were mixed and dissolved in a ratio of 77.7:7.7:14.6. By adding a precipitant or complexing agent and controlling the reaction conditions, a second positive electrode active material precursor with a particle size of 14.2 μm and near-spherical shape was formed.

[0140] Step 2: Mix the first positive electrode active material precursor, the second positive electrode active material precursor, and lithium hydroxide at a total Li:TM ratio of 1.05, and add 1% mol SrO (where 1% is the Sr:TM value); use a high-speed mixer at 800 rpm to mix for 15 min to obtain the mixture.

[0141] Step 3: The mixture is loaded into a boat using a 2.5kg sagger and sintered in an oxygen atmosphere in a box furnace at 785℃ for 17 hours. The sintered mixture is then mechanically crushed to obtain the positive electrode active material.

[0142] The particle size of the positive electrode active materials prepared in Examples 1-10 and Comparative Examples 1-3 was tested using a particle size analyzer. D10 and D90 were statistically analyzed. The molar content of Ni, Co, M1 and M2 elements in particles that meet D10 and D90 was tested using an ICP analyzer. The test results are shown in Table 1.

[0143] The positive electrode active materials prepared in Examples 1-10 and Comparative Examples 1-3 were used to perform pressure tests on secondary particles of different sizes using an ultra-micro dynamic hardness tester with a 50 μm flat indenter. At least five points were tested, and the average data was recorded as the strength of the corresponding particle. The test results are shown in Table 1.

[0144] Table 1

[0145]

[0146] The positive electrode active materials prepared in Examples 1-10 and Comparative Examples 1-3 were used to make positive electrode sheets, and then assembled with lithium sheets, polyethylene separators and electrolyte (LiPF6 electrolyte, EC / DMC solvent) to obtain coin cells. The first discharge capacity of the coin cells was tested under 0.2C charge and discharge conditions and recorded as the coin cell capacity. The specific capacity (mAh / g) was calculated according to the coin cell capacity / battery weight. The calculation results are shown in Table 2.

[0147] The positive electrode active materials prepared in Examples 1-10 and Comparative Examples 1-3 were used to make positive electrode sheets, which were then combined with graphite negative electrodes, polyethylene separators, and electrolytes (LiPF6 electrolyte, EC / DMC solvent) to assemble a full cell. The capacity retention rate (%) of the full cell after 500 cycles was tested at 45°C and 1C. The test results are shown in Table 2.

[0148] Table 2

[0149]

[0150] According to the data provided in Table 2, the lithium-ion batteries provided in Examples 1-3 have a higher capacity retention rate compared to Comparative Examples 1-2. This indicates that the difference in the molar content of Ni in the first and second particles should be maintained within the range of 0.005-0.07. Furthermore, changes in the nickel content in the positive electrode active material provided in Examples 1-3 do not affect the specific capacity of the lithium-ion battery. According to the data provided in Examples 1-3, as the difference between X1 and X2 increases, the capacity retention rate of the lithium-ion battery increases. However, when the difference between X1 and X2 exceeds 6%, the capacity retention rate of the lithium-ion battery initially decreases, indicating that the preferred range for X1-X2 is 0.01-0.05. According to Comparative Example 3, the difference in Mn content between the first and second particles should be less than the difference in Ni content. When the difference in Ni content between the first and second particles equals the difference in Mn content, it is detrimental to improving the specific capacity and capacity retention rate of the lithium-ion battery.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized in that, The chemical composition of the positive electrode active material is Li 1+a [Ni x Co y M1 z M2 b O 2±c A d , 0<a<0.2, 0.5≤x<1, 0<y<0.3, 0<z<0.3, 0<b<0.2, c<0.02, 0≤d≤0.05, x+y+z+b=1; M1 is one or two of Mn and Al; M2 is one or more of Zr, Mg, Ti, Te, Al, Ca, Sr, Sb, Nb, Pb, V, Ge, Se, W, Mo, Zn, Ce, and Y; and A is one of F, Cl, and S. The first particle has a Ni element with an X value of X1, and the second particle has a Ni element with an X value of X2, where 0.01 ≤ (X1 - X2) ≤ 0.05; the first particle has a M2 element with a b value of b1, and the second particle has a M2 element with a b value of b2, where b1 = b2. In the chemical composition of the first particle, the Y value corresponding to the Co element is Y1, and in the chemical composition of the second particle, the Y value corresponding to the Co element is Y2, where Y2 > Y1; (X1-X2) > (Y2-Y1). In the chemical composition of the first particle, the Z value corresponding to element M1 is Z1, and in the chemical composition of the second particle, the Z value corresponding to element M1 is Z2, Z2 > Z1; (X1-X2) > (Z2-Z1). The first particle refers to a particle with a particle size equal to D10 of the positive electrode active material, and the second particle refers to a particle with a particle size equal to D90 of the positive electrode active material.

2. The positive electrode active material according to claim 1, characterized in that, The size of the primary particles that make up the first particle is R1, and the size of the primary particles that make up the second particle is R2, where R1 < R2.

3. The positive electrode active material according to claim 2, characterized in that, R1≥0.85R2.

4. A method for preparing the positive electrode active material according to any one of claims 1-3, characterized in that, Includes the following steps: A positive electrode active material precursor is prepared by mixing a nickel source, a cobalt source, and an M1 source; the positive electrode active material precursor includes a first positive electrode active material precursor and a second positive electrode active material precursor. The size of the first positive electrode active material precursor is smaller than the size of the second positive electrode active material precursor. The molar content of Ni element in the chemical composition of the first positive electrode active material precursor is W1, and the molar content of Ni element in the chemical composition of the second positive electrode active material precursor is W2, where W1-W2≥0.

005. The positive electrode active material precursor, lithium source, and M2 source are mixed to form a mixture. The mixture is sintered in an oxygen or air atmosphere, and the sintered sample is mechanically crushed to obtain the positive electrode active material.

5. A lithium-ion battery, characterized in that, Includes the positive electrode active material as described in any one of claims 1-3.

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