Positive electrode active material and preparation method therefor, and lithium ion battery

Abstract

A positive electrode active material and a preparation method therefor, and a lithium ion battery. In a first aspect, the positive electrode active material is provided, the chemical composition thereof being Li1+a[NixCoyM1zM2b]O2±cAd, wherein 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. Controlling the Ni content in secondary particles having different particle sizes can avoid the problem of inconsistent attenuation of the secondary particles having different particle sizes during a battery cycle process, thus improving the cycle stability of lithium ion batteries.

Description

Positive electrode active material, preparation method thereof, and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 15, 2023, with application number 202311197498.0 and application name “A positive electrode active material, its preparation method and lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to a positive electrode active material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries. Background Art

[0003] Lithium-ion batteries are secondary batteries that primarily rely on the movement of lithium ions between the positive and negative electrodes. The positive electrode active material is a crucial 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 hot topic in positive electrode active material research. However, the cycling stability of existing ternary positive electrode active materials remains to be improved.

[0004] Summary of the Invention

[0005] The present application provides a positive electrode active material and a preparation method thereof, which are used to improve the structural stability of the ternary positive electrode active material and improve the cycle performance of lithium-ion batteries.

[0006] The present application also provides a lithium-ion battery comprising the above-mentioned positive electrode active material, which has good cycle performance.

[0007] The first aspect of the present application provides a positive electrode active material, the chemical composition of which 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;

[0008] 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; A is one of F, Cl, and S;

[0009] The X value corresponding to the Ni element in the chemical composition of the first particle is X1, the X value of the Ni element in the chemical composition of the second particle is X2, and 0.005≤(X1-X2)≤0.07;

[0010] The first particles are particles having a particle size equal to that of the positive electrode active material D10, and the second particles are particles having a particle size equal to that of the positive electrode active material D90.

[0011] In a specific embodiment, the Y value corresponding to the Co element in the chemical composition of the first particle is Y1, the Y value corresponding to the Co element in the chemical composition of the second particle is Y2, and Y2>Y1.

[0012] In one embodiment, (X1-X2)>(Y2-Y1).

[0013] In a specific embodiment, the Z value corresponding to the M1 element in the chemical composition of the first particle is Z1, the Z value corresponding to the M1 element in the chemical composition of the second particle is Z2, and Z2>Z1.

[0014] In one embodiment, (X1-X2)>(Z2-Z1).

[0015] In a specific embodiment, the b value corresponding to the M2 element in the chemical composition of the first particle is b1, the b value corresponding to the M2 element in the chemical composition of the second particle is b2, and b1=b2.

[0016] In a specific embodiment, the size of the primary particles constituting the first particles is R1, the size of the primary particles constituting the second particles is R2, and R1<R2.

[0017] In one embodiment, R1 ≥ 0.85R2.

[0018] A second aspect of the present application provides a method for preparing any of the above-mentioned positive electrode active materials, comprising the following steps:

[0019] Mixing a nickel source, a cobalt source, and an M1 source to prepare a positive electrode active material precursor; the positive electrode active material precursor includes a first positive electrode active material precursor and a second positive electrode active material precursor;

[0020] The size of the first positive electrode active material precursor is smaller than that of the second positive electrode active material precursor, the molar content of Ni in the chemical composition of the first positive electrode active material precursor is W1, the molar content of Ni in the chemical composition of the second positive electrode active material precursor is W2, and W1-W2≥0.005;

[0021] Mixing the positive electrode active material precursor, lithium source, and M2 source to form a mixed material;

[0022] The mixed material is sintered in an oxygen or air atmosphere to obtain a positive electrode active material.

[0023] A third aspect of the present application provides a lithium-ion battery comprising any of the above-mentioned positive electrode active materials.

[0024] The present application provides a positive electrode active material, which can avoid the problem of inconsistent attenuation of secondary particles of different particle sizes during battery cycling by controlling the Ni content in particles of different particle sizes, thereby improving the cycling stability of lithium-ion batteries. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0026] The first aspect of the present application provides a positive electrode active material, the chemical composition of which 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;

[0027] 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; A is one of F, Cl, and S.

[0028] The positive electrode active material provided in the present application is a ternary material of lithium nickel cobalt manganese oxide (NCM) or lithium nickel cobalt aluminum oxide (NCA). In addition, it may further include a doping element M2 and an element A. M2 can be specifically 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.

[0029] Furthermore, M2 is selected from one or more of Zr, Mg, Ti, Al, Sr, Mo, Ce, and Y.

[0030] Further, A is F.

[0031] This application does not impose too many restrictions on x, y, z, a, b, c, and d within the above-defined ranges, as long as they are within the corresponding ranges.

[0032] The positive electrode active material provided in the present application is obtained by mixing a plurality of secondary particles, and the particle size of the secondary particles is normally distributed in the positive electrode active material. The secondary particles are divided according to the distribution of the secondary particles in the positive electrode active material, wherein 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 when the particle size distribution number reaches 10%, and D90 refers to the particle size corresponding to when the particle size distribution number reaches 90%. The specific determination can be carried out according to the conventional particle size testing method in this field and sieving.

[0033] Since the first particles have a smaller particle size, their structural stability during the lithium-ion battery cycle is significantly better than that of the second particles with a larger particle size. However, as the Ni content in the particles increases, their structural stability during the lithium-ion battery cycle decreases. Therefore, the present application increases the Ni content on the surface of the first particles to be higher than the Ni content on the surface of the second particles, so that the structural stability of secondary particles of different particle sizes is basically the same, thereby avoiding the problem of rapid battery capacity decay caused by different structural stabilities of secondary particles of different particle sizes. Specifically, the X value corresponding to the Ni element in the chemical composition of the first particles is X1, the X value of the Ni element in the chemical composition of the second particles is X2, and (X1-X2)≥0.005.

[0034] As the Ni content in the secondary particles increases, the battery cycle performance will decrease. Therefore, the difference between (X1-X2) should not be higher than 0.07, that is, 0.005≤(X1-X2)≤0.07, otherwise it will lead to the attenuation of the lithium-ion battery capacity.

[0035] Further, 0.005≤(X1-X2)≤0.06, and further, 0.01≤(X1-X2)≤0.05.

[0036] In a 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, Y2>Y1. By increasing the content of the Co element in the second particle, it helps 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)>(Y2-Y1), that is, the difference in the content of the Co element in the first particle and the second particle is smaller than the difference in the content of the Ni element, which helps to reduce the use of the Co element and reduce the preparation cost of the positive electrode active material.

[0038] In a specific embodiment, the Z value corresponding to the M1 element in the chemical composition of the first particle is Z1, and the Z value corresponding to the M1 element in the chemical composition of the second particle is Z2, Z2>Z1. By increasing the content of the M1 element in the second particle, it helps 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.

[0039] Furthermore, (X1-X2)>(Z2-Z1), that is, the difference in the content of the M1 element in the first particle and the second particle is less than the difference in the content of the Ni element. When the difference in the content of the Ni element in the first particle and the second particle is less than or equal to the difference in the content of the M1 element, 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.

[0040] In a 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, b1=b2, that is, X1+Y1+Z1=X2+Y2+Z2, and the M2 element can cause a large performance change based on a smaller 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.

[0041] In a specific embodiment, secondary particles are formed by agglomeration of primary particles, the size of the primary particles constituting the first particles is R1, and the size of the primary particles constituting the second particles is R2, R1<R2, the size of the primary particles of the first particles is relatively low, which helps to improve the capacity of the lithium-ion battery, and the particle size of the primary particles of the second particles is relatively high, which helps to reduce the particle composition, improve the strength of the particles, and ensure the stability of the positive electrode active material; the size of the primary particles can be measured by scanning electron microscopy.

[0042] Furthermore, R1≥0.85R2.

[0043] A second aspect of the present application provides a method for preparing any of the above-mentioned positive electrode active materials, comprising the following steps:

[0044] Mixing a nickel source, a cobalt source, and an M1 source to prepare a positive electrode active material precursor; the positive electrode active material precursor includes a first positive electrode active material precursor and a second positive electrode active material precursor;

[0045] The size of the first positive electrode active material precursor is smaller than that of the second positive electrode active material precursor, the molar content of Ni in the chemical composition of the first positive electrode active material precursor is W1, the molar content of Ni in the chemical composition of the second positive electrode active material precursor is W2, and W1-W2≥0.005;

[0046] Mixing a positive electrode active material precursor, a lithium source, and an M2 source to form a mixed material;

[0047] The mixed material is sintered in an oxygen or air atmosphere to obtain a positive electrode active material.

[0048] In one embodiment, the method for preparing the positive electrode active material comprises the following steps:

[0049] Step 1: Mix the nickel source, cobalt source, and M1 source to prepare a positive electrode active material precursor.

[0050] First, a co-precipitation method is used to prepare a positive electrode active material precursor. Specifically, a nickel source, a cobalt source, and an M1 source are configured into a soluble mixed solution, and then a precipitant or a complexing agent is added. By controlling the reaction conditions, a spherical positive electrode active material precursor is formed.

[0051] The M1 source may be a manganese salt and / or an aluminum salt, and the present application does not impose any further restrictions on the types of the nickel source, cobalt source, and M1 source, which may be conventional materials in the art.

[0052] In order to achieve the different Ni element content in the first particle and the second particle, two positive electrode active material precursors of different sizes can be mixed, and the Ni element content in the two sizes of positive electrode active material precursors is different, so that 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 the Ni element in the chemical composition of the first positive electrode active material precursor is W1, the molar content of the Ni element in the chemical composition of the second positive electrode active material precursor is W2, and W1-W2≥0.005.

[0053] Step 2: Mix the positive electrode active material precursor, lithium source, and M2 source to form a mixed material.

[0054] This application does not specifically limit the lithium source and M2 source, which can be conventional materials 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, for example, ZrO2, MgO, Mg(OH)2, TiO2, Al2O3, SrO, MoO3, CeO2, Y2O3, etc.

[0055] The positive electrode active material precursor, lithium source and M2 source are mixed according to a certain molar ratio, and the mixture is fully mixed. The mixing process can be carried out in high-speed mixing equipment, sand milling equipment, ball milling equipment, plowshare mixing equipment, inclined mixing equipment and other equipment to fully mix and crush the mixture.

[0056] Step 3: sintering the mixed material in an oxygen or air atmosphere to obtain a positive electrode active material.

[0057] The mixed material is sintered according to conventional technical means in the art. The sintering process is carried out in a high-temperature sintering equipment such as a muffle furnace, a tunnel furnace, a roller kiln, or a tubular furnace. During the sintering process, oxygen or air is introduced to control the sintering temperature to be not less than 750°C. After sintering for 12-20 hours, the positive electrode active material is obtained by cooling.

[0058] A third aspect of the present application provides a lithium-ion battery comprising any of the above-mentioned positive electrode active materials.

[0059] Based on the positive electrode active material provided in the first aspect of the present application, the lithium-ion battery provided in the present application has good cycle performance.

[0060] In a specific embodiment, the present application does not limit the specific structure of the lithium-ion battery, for example, it can be a square shell battery, a cylindrical battery, etc.

[0061] The lithium-ion battery provided in the present application includes an electrode assembly, a casing and an electrolyte, wherein the electrode assembly includes a positive electrode plate, a separator and a negative electrode plate, the positive electrode plate includes a positive electrode collector and a positive electrode active material layer arranged on the surface of the positive electrode collector, and the positive electrode active material layer includes the aforementioned positive electrode active material.

[0062] In addition to the aforementioned positive electrode active material, the positive electrode active material layer further includes a conductive agent and a binder. The selection of the conductive agent and the binder is not special and can be conventionally selected in the art. 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 polyacrylate lithium (PAALi).

[0063] The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent and a binder. The negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microbeads, lithium titanate, silicon carbon, and silicon oxide.

[0064] The diaphragm, shell and electrolyte are all conventional materials in this field.

[0065] Hereinafter, the positive electrode active material of the present application will be introduced through specific examples.

[0066] Example 1

[0067] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0068] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 83.2:7.4:9.4, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 4.5 μm;

[0069] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 80.6:9.6:9.8, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.1 μm.

[0070] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol ZrO2 (where 1% is the Zr:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0071] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 765° C. for 14 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0072] Example 2

[0073] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0074] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 81.9:7.2:10.9, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 4.1 μm;

[0075] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 81.4:7.4:11.2, and a precipitant or complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.5 μm.

[0076] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol ZrO2 (where 1% is the Zr:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0077] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 775° C. for 18 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0078] Example 3

[0079] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0080] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 83.6:7.9:8.5, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.9 μm;

[0081] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 77.6:11.8:11.2, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 15.1 μm.

[0082] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol ZrO2 (where 1% is the Zr:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0083] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 775° C. for 14 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0084] Example 4

[0085] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0086] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 82.7:7.7:9.6, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.6 μm;

[0087] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 81.7:8.5:9.8, and a precipitant or complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14 μm.

[0088] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol SrO (where 1% is the Sr:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0089] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 775° C. for 14 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0090] Example 5

[0091] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0092] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 82.5:8:9.5, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.9 μm;

[0093] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 77.5:12.6:9.9, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.9 μm.

[0094] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol TiO2 (wherein 1% is the Ti:TM value) is added; a high-speed mixer is used for mixing for 15 minutes at 800 rpm to obtain a mixed material;

[0095] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 770° C. for 14 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0096] Example 6

[0097] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0098] Step 1: nickel salt, cobalt salt, and aluminum salt are mixed and dissolved in a ratio of 91.2:6:2.8%, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 4.1 μm;

[0099] Nickel salt, cobalt salt and aluminum salt are mixed and dissolved in a ratio of 87.3:9.5:3.2, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.8 μm.

[0100] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol Al2O3 (wherein 1% is the Al:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0101] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 780° C. for 20 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0102] Example 7

[0103] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0104] Step 1: nickel salt, cobalt salt, and aluminum salt are mixed and dissolved in a ratio of 91.5:6.2:2.3, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.5 μm;

[0105] Nickel salt, cobalt salt and aluminum salt are mixed and dissolved in a ratio of 87:10.4:2.6, and a precipitant or complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 10.3 μm.

[0106] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol Y2O3 (where 1% is the Y:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0107] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 750° C. for 12 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0108] Example 8

[0109] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0110] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 82.5:7.9:9.6, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.5 μm;

[0111] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 77.2:9.4:13.4, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.3 μm.

[0112] Step 2: The first cathode active material precursor, the second cathode active material precursor and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 0.5% mol SrO and 0.5% mol MoO3 (wherein 0.5% is the Sr:TM value and Mo:TM value) are added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0113] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 760° C. for 18 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0114] Example 9

[0115] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0116] Step 1: nickel salt, cobalt salt, and aluminum salt are mixed and dissolved in a ratio of 82.9:15.2:1.9, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.9 μm;

[0117] Nickel salt, cobalt salt and aluminum salt are mixed and dissolved in a ratio of 79.2:17.1:2.7, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.2 μm.

[0118] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 0.5% mol Al2O3 and 0.5% mol CeO2 (wherein 0.5% is the Al:TM value and Ce:TM value) are added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0119] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 760° C. for 17 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0120] Example 10

[0121] This embodiment provides a method for preparing a positive electrode active material, comprising the following steps:

[0122] Step 1: nickel salt, cobalt salt, and aluminum salt are mixed and dissolved in a ratio of 61:10.8:28.2, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.8 μm;

[0123] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 58.9:11.5:29.6, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.2 μm.

[0124] Step 2: Mix the first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide in 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 for 15 minutes to obtain a mixed material;

[0125] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 890° C. for 15 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0126] Comparative Example 1

[0127] This comparative example provides a method for preparing a positive electrode active material, comprising the following steps:

[0128] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 82.1:7.4:10.5, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 4 μm;

[0129] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 82.1:7.4:10.5, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.4 μm.

[0130] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol ZrO2 (where 1% is the Zr:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0131] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 770° C. for 16 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0132] Comparative Example 2

[0133] This comparative example provides a method for preparing a positive electrode active material, comprising the following steps:

[0134] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 82.4:7.3:10.3, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 3.9 μm;

[0135] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 75.1:11.9:13, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.3 μm.

[0136] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol ZrO2 (where 1% is the Zr:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0137] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 790° C. for 18 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0138] Comparative Example 3

[0139] This comparative example provides a method for preparing a positive electrode active material, comprising the following steps:

[0140] Step 1: nickel salt, cobalt salt, and manganese salt are mixed and dissolved in a ratio of 82.1:7.7:10.2, and a precipitant or complexing agent is added to control the reaction conditions to form a first positive electrode active material precursor with a spherical particle size of 4.3 μm;

[0141] Nickel salt, cobalt salt and manganese salt are mixed and dissolved in a ratio of 77.7:7.7:14.6, and a precipitant or a complexing agent is added to control the reaction conditions to form a spherical second positive electrode active material precursor with a particle size of 14.2 μm.

[0142] Step 2: The first cathode active material precursor, the second cathode active material precursor, and lithium hydroxide are mixed in a total Li:TM ratio of 1.05, and 1% mol SrO (where 1% is the Sr:TM value) is added; a high-speed mixer is used to mix the materials for 15 minutes at 800 rpm to obtain a mixed material;

[0143] Step 3: The mixed material was loaded into a 2.5 kg boat using a sagger and sintered in an oxygen atmosphere in a box furnace at 785° C. for 17 h. The mixed sintered sample was mechanically crushed to obtain the positive electrode active material.

[0144] Test example

[0145] 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 tester, and D10 and D90 were calculated. The molar content of Ni, Co, M1, and M2 elements in the particles meeting D10 and D90 was tested using an ICP tester. The test results are shown in Table 1.

[0146] The positive electrode active materials prepared in Examples 1-10 and Comparative Examples 1-3 were tested using an ultramicrodynamic hardness tester with a 50 μm flat indenter. Pressure tests were performed on secondary particles of different particle sizes. At least five points were tested, and the average data was recorded as the strength of the corresponding particles. The test results are shown in Table 1.

[0147] Table 1

[0148] The positive electrode active materials prepared in Examples 1-10 and Comparative Examples 1-3 were made into positive electrode sheets, and were assembled with lithium sheets, polyethylene diaphragms, and electrolytes (the electrolyte was LiPF6 and the solvent was EC / DMC) to obtain button batteries. Under the charge and discharge conditions of 0.2C, the first-cycle discharge capacity of the button batteries was tested and recorded as the button capacity. The gram capacity (mAh / g) was calculated according to the button capacity / battery weight. The calculation results are shown in Table 2.

[0149] The positive electrode active materials prepared in Examples 1-10 and Comparative Examples 1-3 were made into positive electrode sheets, and a full battery was assembled with a graphite negative electrode, a polyethylene separator, and an electrolyte (the electrolyte was LiPF6 and the solvent was EC / DMC). The capacity retention rate (%) of the full battery after 500 cycles was tested at 45°C and 1C. The test results are shown in Table 2.

[0150] Table 2

[0151] According to the data provided in Table 2, the lithium-ion batteries provided in Examples 1-3 have a higher capacity retention rate than those in Comparative Examples 1-2, indicating that the difference in the molar content of the Ni element in the first particles and the second particles should be maintained in the range of 0.005-0.07. At the same time, changes in the nickel content in the positive electrode active materials provided in Examples 1-3 will not affect the gram 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 is greater than 6%, the capacity retention rate of the lithium-ion battery actually decreases, indicating that the preferred range of X1-X2 is 0.01-0.05. According to Comparative Example 3, the difference in the content of the Mn element in the first particles and the second particles should be less than the difference in the content of the Ni element. When the difference in the content of the Ni element in the first particles and the second particles is equal to the difference in the content of the Mn element, it is not conducive to improving the gram capacity and capacity retention rate of the lithium-ion battery.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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, 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; 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; A is one of F, Cl, and S; The X value corresponding to the Ni element in the chemical composition of the first particle is X1, the X value of the Ni element in the chemical composition of the second particle is X2, and 0.005≤(X1-X2)≤0.07; The first particles refer to particles having a particle size equal to that of the positive electrode active material D10, and the second particles refer to particles having a particle size equal to that of the positive electrode active material D90.

2. The positive electrode active material according to claim 1, wherein 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, and Y2>Y1.

3. The positive electrode active material according to claim 2, wherein (X1-X2)>(Y2-Y1).

4. The positive electrode active material according to claim 1, wherein The Z value corresponding to the M1 element in the chemical composition of the first particle is Z1, the Z value corresponding to the M1 element in the chemical composition of the second particle is Z2, and Z2>Z1.

5. The positive electrode active material according to claim 4, wherein (X1-X2)>(Z2-Z1).

6. The positive electrode active material according to claim 1, wherein 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, and b1=b2.

7. The positive electrode active material according to claim 1, wherein The size of the primary particles constituting the first particles is R1, and the size of the primary particles constituting the second particles is R2, and R1<R2.

8. The positive electrode active material according to claim 7, wherein R1≥0.85R2.

9. A method for preparing a positive electrode active material according to any one of claims 1 to 8, wherein: The steps include: Mixing a nickel source, a cobalt source, and an M1 source to prepare a positive electrode active material precursor; 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 in the chemical composition of the first positive electrode active material precursor is W1, the molar content of Ni in the chemical composition of the second positive electrode active material precursor is W2, and W1-W2≥0.005; Mixing the positive electrode active material precursor, the lithium source, and the M2 source to form a mixed material; The mixed material is sintered in an oxygen or air atmosphere to obtain a positive electrode active material.

10. A lithium ion battery, wherein: The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 8.

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