Doped positive electrode precursor and preparation method and application thereof

Abstract

The invention provides a doped positive electrode precursor and a preparation method and application thereof.The doped positive electrode precursor sequentially comprises an inner layer, a middle layer and an outer layer from inside to outside in the radial direction, the porosity of the inner layer is larger than that of the middle layer, and the porosity of the middle layer is smaller than or equal to that of the outer layer; and the outer layer comprises a radial channel. The doped positive electrode precursor provided by the invention is helpful for improving the cycle performance and the capacity of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of positive electrode precursors, and in particular to a doped positive electrode precursor and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and energy storage systems due to their high energy density, long cycle life, and low self-discharge rate. Among the many components of lithium-ion batteries, the performance of the positive electrode active material plays a vital role in the overall performance of the battery. In recent years, ternary positive electrode materials, such as lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA), have attracted widespread attention due to their excellent electrochemical properties and high energy density. An appropriate amount of doping elements can help improve the electrochemical properties of ternary positive electrode materials. For example, an appropriate amount of zirconium (Zr) doping can reduce the degree of cation mixing inside the ternary positive electrode material, which is beneficial to Li + Diffusion increases the migration rate, while improving the stability of the overall structure of the ternary positive electrode material and enhancing the cycle performance of the ternary positive electrode material.

[0003] However, due to the limitations of existing production processes, most doped ternary positive electrode materials are doped during the sintering process, which makes the doped ternary positive electrode materials prone to uneven distribution of doping elements (such as Zr). The uneven distribution of doping elements may lead to differences in electrochemical activity in local areas, thereby affecting the battery's cycle performance and capacity.

[0004] Therefore, achieving doped positive electrode precursors that have both excellent cycle performance and capacity is a research focus in this field. Summary of the invention

[0005] The present invention provides a doped positive electrode precursor and a preparation method and application thereof, which are helpful to improve the capacity and cycle performance of a battery and effectively solve the problems existing in the existing doped positive electrode precursor.

[0006] The present invention provides a doped positive electrode precursor, which includes an inner layer, a middle layer and an outer layer in the radial direction from the inside to the outside, the porosity of the inner layer is greater than the porosity of the middle layer, the porosity of the middle layer is less than or equal to the porosity of the outer layer, and the outer layer includes a radial channel.

[0007] Optionally, the porosity of the inner layer is 10% to 15%, the porosity of the middle layer is 1% to 5%, and the porosity of the outer layer is 5% to 10%.

[0008] Optionally, the porosity of the doped positive electrode precursor is 2% to 8%; and / or the radial dimensions of the inner layer, the middle layer and the outer layer are R 1 , R2 , R 3 , R 1 is 0.6 to 1.3 μm, R 2 is 0.4 to 0.8 μm, R 3 is 0.3 to 0.8 μm.

[0009] Optionally, the thickness of the primary particles in the inner layer is 10 - 50 nm, the thickness of the primary particles in the intermediate layer is 400 - 600 nm, and the thickness of the primary particles in the outer layer is 300 - 400 nm.

[0010] Optionally, the chemical formula of the doped cathode precursor is: (Ni a Co b Mn c )M d (OH) 2 , where 0.8 ≤ a < 1.0, 0 < b ≤ 0.1, 0 < c ≤ 0.1, a + b + c + d = 1, 0 < d ≤ 0.05, M includes one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, Mo; and / or, the mass percentage content of the doping element in the doped cathode precursor is 1000 - 8000 ppm; and / or, the tap density of the doped cathode precursor is 1.7 - 2.0 g / cm 3 ; and / or, the specific surface area of the doped cathode precursor is greater than or equal to 4 m 2 / g and less than 10 m 2 / g; and / or, the D50 of the doped cathode precursor is 3.0 - 4.0 μm, and SPAN is 0.6 - 1.2; and / or, the length of the radial channel is 90 - 220 nm; and / or, the sphericity of the doped cathode precursor is greater than or equal to 0.9 and less than 1.0.

[0011] The present invention also provides a method for preparing the doped cathode precursor as described above, including: introducing a raw material system including ammonia water, an alkali solution, and a metal salt solution into a bottom liquid, so that the reaction system undergoes a first coprecipitation reaction at an ammonia value of A 1 , a pH of B 1 , and a flow rate of the metal salt solution of C 1 to obtain a first product; after the D50 of the first product reaches the expected particle size, gradually increase the ammonia value of the reaction system, decrease the pH of the reaction system, and control the flow rate of the metal salt solution to be C 2 , so that the reaction system undergoes a second coprecipitation reaction to obtain a second product; after the D50 of the second product reaches the expected particle size, make the reaction system at an ammonia value of A 3 , a pH of B 3 , and a flow rate of the metal salt solution of C 3Perform a third coprecipitation reaction to obtain the doped cathode precursor; wherein, A 1 < A 3 , B 1 > B 3 , C 1 < C 2 < C 3 .

[0012] Optionally, A 1 is 2.5 to 3.5 g / L, A 3 is 5.5 to 6.5 g / L; and / or, B 1 is 11.60 to 11.80, B 3 is 11.40 to 11.50; and / or, C 1 is 1.0 to 2.0 g / L, C 2 is 3.5 to 4.5 g / L, C 3 is 7.0 to 8.0 g / L.

[0013] Optionally, the ammonia value of the bottom liquid is 1 to 4 g / L, the pH is 11.6 to 12.0; and / or, the temperature of the reaction system is 40 to 70 °C; and / or, the metal salt solution includes a mixed solution of nickel, cobalt, and manganese with a total molar concentration of 1.0 to 2.5 mol / L, and the molar ratio of nickel, cobalt, and manganese is a:b:c, 0.8 ≤ a < 1.0, 0 < b ≤ 0.1, 0 < c ≤ 0.1, and a + b + c = 1; and / or, the metal salt solution includes doping elements, and the doping elements include one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, Mo.

[0014] The present invention also provides a cathode active material, the cathode active material is a doped cathode active material, and in the radial direction from the inside to the outside of the cathode active material, it sequentially includes an inner layer, a middle layer, and an outer layer. The porosity of the inner layer is greater than the porosity of the middle layer, the porosity of the middle layer is less than or equal to the porosity of the outer layer, and the outer layer includes radial channels.

[0015] Optionally, the cathode active material is formed from the doped cathode precursor as described above or the doped cathode precursor prepared according to the preparation method as described above.

[0016] The present invention also provides a cathode sheet, and the cathode sheet includes the cathode active material as described above.

[0017] The present invention also provides a lithium-ion battery, and the lithium-ion battery includes the cathode sheet as described above.

[0018] The present invention provides a doped cathode precursor, a preparation method thereof and an application. In the three-layer structure of the doped cathode precursor, the inner layer has the highest porosity and a relatively loose structure, which is beneficial to the absorption and storage of lithium ions. The cathode active material can inherit the morphology of the doped cathode precursor, so it helps to alleviate the volume expansion of the cathode active material during the charge and discharge process. The middle layer has a lower porosity and a relatively dense structure, which can play a role in stabilizing the structure of the doped cathode precursor and preventing particle breakage during the sintering process. The outer layer has a moderate porosity and a relatively dense structure, and the outer layer includes radial channels, forming longitudinal lithium ion channels, which helps lithium ions to diffuse into the interior of the precursor along the channels during the sintering of the cathode, increasing the amount of combined lithium salt and making the lithium salt distribution more uniform, which helps to improve the sintering uniformity of the doped cathode precursor and helps to improve the cycle performance and capacity of the cathode active material of the battery, thus effectively overcoming the problems existing in the doped cathode precursor in the prior art. Description of the Drawings

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0020] Figure 1 Cross-sectional view of the doped cathode precursor for Example 1;

[0021] Figure 2 SEM image of the inner layer of the doped cathode precursor for Example 1;

[0022] Figure 3 SEM image of the middle layer of the doped cathode precursor for Example 1;

[0023] Figure 4 SEM image of the outer layer of the doped cathode precursor for Example 1;

[0024] Figure 5 SEM image of the outer layer of the doped cathode precursor for Example 1;

[0025] Figure 6 SEM image of the outer layer of the doped cathode precursor for Example 1;

[0026] Figure 7 Energy spectrum mapping diagram of nickel element in the doped cathode precursor for Example 1;

[0027] Figure 8 Energy spectrum mapping diagram of cobalt element in the doped cathode precursor for Example 1;

[0028] Figure 9 Energy spectrum mapping diagram of manganese element in the doped cathode precursor of Example 1;

[0029] Figure 10 Energy spectrum mapping diagram of doped zirconium element in the doped cathode precursor of Example 1;

[0030] Figure 11 Scanning electron microscope image of the cathode precursor of Comparative Example 1;

[0031] Figure 12 Scanning electron microscope image of the cathode precursor of Comparative Example 1;

[0032] Figure 13 Scanning electron microscope image of the doped cathode precursor of Comparative Example 2;

[0033] Figure 14 Scanning electron microscope image of the doped cathode precursor of Comparative Example 2;

[0034] Figure 15 Scanning electron microscope image of the doped cathode precursor of Comparative Example 4;

[0035] Figure 16 Cross-sectional view of the cathode active material of Example 1.

[0036] Explanation of reference numerals:

[0037] 01 - Inner layer, 02 - Intermediate layer, 03 - Outer layer, 04 - Radial channel, R 1 - Radial dimension of the inner layer, R 2 - Radial dimension of the intermediate layer, R 3 - Radial dimension of the outer layer. Detailed implementation manners

[0038] To enable those skilled in the art to better understand the solution of the present invention, the present invention will be further described in detail below. The following specific implementation manners are only used to describe the principles and features of the present invention, and the examples given are only used to explain the present invention, not to limit the scope of the present invention. Based on the embodiments of the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0039] In the prior art, doped cathode active materials are mostly prepared by a sintering process. These doped cathode active materials are prone to the problem of uneven distribution of doped elements, which in turn leads to deterioration of the cycle performance and capacity of the battery. The inventors found in their research that the distribution of doped elements in the doped cathode precursor prepared by the coprecipitation reaction is relatively uniform, but there is a problem of large size differences in the lithium element diffusion paths, which affects the sintering uniformity and has an adverse effect on the battery performance.

[0040] To overcome the defects in the prior art, an embodiment of the present invention provides a doped cathode precursor. In the radial direction from the inside to the outside of the doped cathode precursor, it sequentially includes an inner layer, an intermediate layer, and an outer layer. The porosity of the inner layer is greater than that of the intermediate layer, the porosity of the intermediate layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

[0041] Figure 1 It is a cross-sectional view of the doped cathode precursor according to an embodiment of the present invention. To better understand the distribution of the inner layer, intermediate layer, and outer layer in the doped cathode precursor, the following will be used Figure 1 as an example for explanation.

[0042] As Figure 1 shown, in the radial direction from the inside to the outside of the doped cathode precursor, it sequentially includes an inner layer (01), an intermediate layer (02), and an outer layer (03). The inner layer (01) is located inside the doped cathode precursor, the intermediate layer (02) surrounds the outside of the inner layer (01), and the outer layer (03) surrounds the outside of the intermediate layer (02).

[0043] More specifically, the doped cathode precursor can be assumed to be a sphere. The inner layer (01) is a small sphere located inside the sphere, the intermediate layer (02) is an annular region surrounding the outside of the small sphere, and the outer layer (03) is an annular region surrounding the outside of the intermediate layer (02).

[0044] It can be understood that the doped cathode precursor according to an embodiment of the present invention is a secondary particle formed by agglomeration of primary particles, and it has a porous structure.

[0045] In the three-layer structure of the above-mentioned doped cathode precursor, the inner layer (01) has the highest porosity and a relatively loose structure, which is beneficial to the absorption and storage of lithium ions, and alleviates the volume expansion of the cathode active material during charge and discharge. The intermediate layer (02) has a lower porosity and a relatively dense structure, which can play a role in stabilizing the structure of the doped cathode precursor and prevent particle breakage during the sintering process. The outer layer (03) has a moderate porosity and a relatively dense structure, and the outer layer (03) includes radial channels (04). The radial channels (04) are hollow channels distributed along the radial direction. These radial channels form longitudinal lithium ion channels, which help lithium ions to diffuse into the interior of the precursor along the channels during the sintering of the cathode, increasing the amount of combined lithium salt, making the lithium salt distribution more uniform, helping to improve the sintering uniformity of the doped cathode precursor, helping to improve the cycle performance and capacity of the cathode active material of the battery, and thus effectively overcoming the problems existing in the doped cathode precursor in the prior art.

[0046] Therefore, the doped cathode precursor according to an embodiment of the present invention can have good cycle performance and capacity, and effectively overcome the problems existing in the doped ternary cathode active material in the prior art.

[0047] In some embodiments, the porosity of the inner layer is 10% - 15%, the porosity of the middle layer is 1% - 5%, and the porosity of the outer layer is 5% - 10%. By further controlling the porosities of the inner layer, the middle layer, and the outer layer within the above ranges, it helps to better improve the structural stability of the doped cathode precursor and the absorption and storage performance of lithium ions, and is more conducive to improving the cycling performance and capacity of the cathode active material of the lithium-ion battery, thereby effectively solving the problems existing in the doped cathode precursor.

[0048] Exemplarily, the porosity of the above-mentioned inner layer can be 10%, 11%, 12%, 13%, 14%, 15% or the range composed of any two of them, the porosity of the middle layer can be 1%, 2%, 3%, 4%, 5% or the range composed of any two of them, and the porosity of the outer layer can be 5%, 6%, 7%, 8%, 9%, 10% or the range composed of any two of them.

[0049] In some embodiments, the thickness of the primary particles in the inner layer is 10 - 50 nm, the thickness of the primary particles in the middle layer is 400 - 600 nm, and the thickness of the primary particles in the outer layer is 300 - 400 nm. The primary particles in the inner layer are thinner, and the primary particles are intertwined with each other, leaving more voids, making the inner layer have a loose and porous honeycomb-like structure, which is beneficial to the absorption and storage of lithium ions and alleviates the volume expansion of the cathode active material during charge and discharge. The primary particles in the middle layer are thicker, and the primary particles are arranged staggered and closely packed without obvious voids. The structure of the middle layer is relatively dense, which can play a role in stabilizing the structure of the doped cathode precursor and prevent particle breakage during the sintering process. The thickness of the primary particles in the outer layer is moderate, the structure of the outer layer is relatively dense, and the primary particles are arranged directionally to form a hollow channel distributed radially, that is, a radial channel, and then form a longitudinal lithium-ion channel, which helps lithium ions to diffuse into the precursor interior along the channel during cathode sintering, increasing the amount of combined lithium salt, and the lithium salt is more evenly distributed, which helps to improve the sintering uniformity of the doped cathode precursor and helps to improve the cycling performance and capacity of the cathode active material of the battery, thereby effectively overcoming the problems existing in the doped cathode precursor in the prior art.

[0050] Furthermore, the primary particles in the inner layer may include 2 to 10 nanosheets, that is, they are stacked by 2 to 10 nanosheets; the primary particles in the middle layer may include 80 to 120 nanosheets, that is, they are stacked by 80 to 120 nanosheets; the primary particles in the outer layer may include 60 to 80 nanosheets, that is, they are formed by stacking 60 - 80 nanosheets. The number of nanosheet layers in the primary particles of the inner layer is small, the primary particles are intertwined with each other, and there are many voids left, making the inner layer have a loose and porous honeycomb-like structure, which is beneficial to the absorption and storage of lithium ions, alleviates the volume expansion of the positive electrode active material during the charge and discharge process. The number of nanosheet layers in the primary particles of the middle layer is large, the primary particles are staggered and arranged tightly, without obvious voids. The structure of the middle layer is relatively dense, which can play a role in stabilizing the structure of the doped positive electrode precursor and prevent particle breakage during the sintering process. The number of nanosheet layers in the primary particles of the outer layer is moderate, the structure of the outer layer is relatively dense, and the primary particles are arranged directionally, forming a hollow channel distributed radially, that is, a radial channel, and further forming a longitudinal lithium ion channel. This helps lithium ions to diffuse into the precursor along the channel during the sintering of the positive electrode, increasing the amount of combined lithium salt, and the lithium salt is more evenly distributed, which helps to improve the sintering uniformity of the doped positive electrode precursor, helps to improve the cycle performance and capacity of the positive electrode active material of the battery, thus effectively overcoming the problems existing in the doped positive electrode precursor in the prior art.

[0051] In some embodiments, the porosity of the doped positive electrode precursor first decreases and then increases from the inside to the outside. The inner layer has a higher porosity, fewer nanosheets (layers), thinner primary particles, and the primary particles are intertwined to form a loose and porous honeycomb-like structure, which is beneficial to the absorption and storage of lithium ions and alleviates the volume expansion during the charge and discharge process. The middle layer has a lower porosity, more nanosheets (layers), thicker primary particles, and the main function of the middle layer is to stabilize the structure and prevent particle breakage during the sintering process. The outer layer region is relatively dense, the number of nanosheets (layers) is in the middle, the thickness of the primary particles is in the middle, and the primary particles are arranged directionally, forming a hollow channel distributed radially, that is, a radial channel, and forming a longitudinal lithium ion channel. When the positive electrode is sintered, lithium ions can diffuse into the precursor along the channel, and the amount of combined lithium salt is more and the distribution is more uniform, significantly improving the cycle performance and capacity of the positive electrode active material of the lithium ion battery.

[0052] In some embodiments, the length of the radial channel in the above-mentioned outer layer, that is, the lithium ion channel, can be 90 to 220 nm, which helps lithium ions to diffuse into the precursor along the channel during the sintering of the positive electrode, increasing the amount of combined lithium salt, and the lithium salt is more evenly distributed, which helps to improve the sintering uniformity of the doped positive electrode precursor, helps to improve the cycle performance and capacity of the positive electrode active material of the battery, thus effectively overcoming the problems existing in the doped positive electrode precursor in the prior art.

[0053] In some embodiments, the porosity of the above-doped cathode precursor is 2% - 8%. Since the cathode active material can inherit the morphology of the doped cathode precursor, it helps to improve the cycling performance and capacity of the cathode active material.

[0054] Exemplarily, the porosity of the above-doped cathode precursor can be 2%, 3%, 4%, 5%, 6%, 7%, 8% or a range composed of any two of them.

[0055] The inner layer, the middle layer and the outer layer have dimensions in the radial direction of R 1 , R 2 , R 3 . Taking Figure 1 as an example, it can be seen that the dimension R 1 of the inner layer in the radial direction is its diameter, the dimension R 2 of the middle layer in the radial direction is its width in the radial direction, and the dimension R 3 of the outer layer in the radial direction is its width in the radial direction.

[0056] Specifically, R 1 can be 0.6 - 1.3 μm, such as 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.3 μm or a range composed of any two of them, R 2 can be 0.4 - 0.8 μm, such as 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or a range composed of any two of them, R 3 can be 0.3 - 0.8 μm, such as 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or a range composed of any two of them. By controlling the dimensions of the inner layer, the middle layer and the outer layer in the radial direction to meet the above range, it helps to better improve the structural stability of the doped cathode precursor and the absorption and storage performance of lithium ions, and is more helpful to improve the cycling performance and capacity of the cathode active material of the lithium-ion battery, thus effectively solving the problems existing in the doped cathode precursor.

[0057] The doping elements in the doped cathode precursor of the present invention can include one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, Mo.

[0058] The above doping element is preferably Zr. After the Zr element is doped into the doped cathode precursor through bulk doping, it can reduce the surface energy of the primary particles, relieve the nucleation agglomeration phenomenon, improve the sphericity, reduce the particle size distribution width SPAN. At the same time, the ionic radius of Zr 4+ is slightly larger than that of nickel cobalt manganese. The Zr 4+ incorporated into the unit cell will increase the crystal layer spacing and expand the lithium ion transport channels, thereby helping to improve the cycling performance and capacity of the battery.

[0059] In some embodiments, the sphericity of the doped cathode precursor is greater than or equal to 0.9 and less than 1.0.

[0060] In some embodiments, the doped elements in the doped cathode precursor are uniformly distributed from the inside to the outside, which helps to improve the cycle performance and capacity of the battery.

[0061] In some embodiments, the mass percentage content of the doped elements in the doped cathode precursor is 1000 - 8000 ppm, which helps to improve the cycle performance and capacity of the battery.

[0062] In addition, the chemical formula of the above-mentioned doped cathode precursor can be: (Ni a Co b Mn c )M d (OH) 2 , where 0.8 ≤ a < 1.0, 0 < b ≤ 0.1, 0 < c ≤ 0.1, a + b + c + d = 1, 0 < d ≤ 0.05, and M includes one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, Mo.

[0063] That is to say, M is the doped element.

[0064] The tap density of the above-mentioned doped cathode precursor can be 1.7 - 2.0 g / cm 3 , which helps to improve the capacity of the battery.

[0065] The specific surface area of the above-mentioned doped cathode precursor can be greater than or equal to 4 m 2 / g and less than 10 m 2 / g. The smaller specific surface area of this doped cathode precursor helps to reduce side reactions and improve the cycle performance.

[0066] The D50 of the above-mentioned doped cathode precursor can be 3.0 - 4.0 μm, which is suitable for sintering single-crystal cathode active materials.

[0067] The doped cathode precursor is prone to the problem of wide particle size distribution. Taking zirconium element doping as an example, compared with nickel-cobalt-manganese hydroxide, the solubility product (Ksp) of Zr(OH) 4 is too low, only 6.30*10 -49 , which makes Zr(OH) 4 more likely to precipitate and nucleate separately in the doping reaction system of the cathode precursor, generating small particles, thus resulting in too wide a particle size distribution of the cathode precursor doped with zirconium.

[0068] The SPAN of the doped cathode precursor in the embodiments of the present invention is relatively narrow, which can be 0.6 - 1.2, helping to improve the uniformity of the lithium element diffusion path, improving the sintering uniformity, and helping to improve the cycle performance and capacity of the battery.

[0069] In the embodiments of the present invention, the above-mentioned SPAN is equal to (D90 - D10) / D50.

[0070] In most of the existing doping techniques, doping is carried out during the sintering process of the positive electrode. However, due to reasons such as the atomic size of the doping element (for example, the size of zirconium atoms is relatively large), it is difficult for the doping element to enter the interior of the positive electrode active material during the sintering process. The doping element is unevenly distributed inside and outside the positive electrode active material, and the doping amount cannot be controlled, making it difficult to achieve atomic-level doping. In addition, as mentioned above, the low solubility product (Ksp) of the doping element (such as zirconium) will cause the doping element to be more likely to precipitate and nucleate separately in the doping reaction system of the positive electrode precursor, generating small particles. As a result, the particle size distribution of the doped positive electrode precursor is too wide, which cannot meet the capacity and cycle requirements of the positive electrode active material, and will also cause the morphology of the doped positive electrode precursor to be irregular and the sphericity to be poor. During the sintering process of using the above-mentioned doped precursor to prepare the positive electrode active material (such as single-crystal positive electrode active material), the size difference of the lithium element diffusion path is relatively large, and the sintering uniformity is poor, which will have an adverse impact on the battery performance.

[0071] Based on this, the embodiments of the present invention further provide a method for preparing the above-mentioned doped positive electrode precursor, including: introducing a raw material system including ammonia water, an alkali solution, and a metal salt solution into the bottom liquid, and making the reaction system carry out a first coprecipitation reaction at an ammonia value of A 1 and a pH of B 1 with the flow rate of the metal salt solution being C 1 to obtain a first product; after the D50 of the first product reaches the expected particle size, gradually increase the ammonia value of the reaction system, decrease the pH of the reaction system, and control the flow rate of the metal salt solution to be C 2 to make the reaction system carry out a second coprecipitation reaction to obtain a second product; after the D50 of the second product reaches the expected particle size, make the reaction system carry out a third coprecipitation reaction at an ammonia value of A 3 and a pH of B 3 with the flow rate of the metal salt solution being C 3 to obtain the doped positive electrode precursor; wherein, A 1 < A 3 , B 1 > B 3 , C 1 < C 2 < C 3 .

[0072] The above preparation method can be divided into a first stage, a second stage, and a third stage. Among them, the first stage is the process of the first coprecipitation reaction, the second stage is the process of the second coprecipitation reaction, and the third stage is the process of the third coprecipitation reaction.

[0073] In the first stage, the first coprecipitation reaction is carried out in the reaction system under the conditions of a relatively low ammonia value (low ammonia), a relatively high pH, and a relatively low flow rate of the metal salt solution. At this time, the supersaturation of ions (including doped element ions) in the reaction system is relatively high, and the doped element ions mainly undergo precipitation reactions, generating a certain number of crystal nuclei in the reaction system, and the nucleation rate is relatively high, which helps to form primary particles with fewer lamellae and loose packing, thus forming a loose inner layer (the first product).

[0074] In the second stage, the second coprecipitation reaction is carried out in the reaction system under the conditions of a moderate flow rate of the metal salt solution (medium), a gradually increasing ammonia value, and a gradually decreasing pH. During the process of the second coprecipitation reaction, the ammonia value and pH of the reaction system change dynamically, the growth rate gradually increases, and the nucleation rate gradually decreases, which helps to form an intermediate layer with an increasing number of lamellae and dense packing of the primary particles, thus obtaining a second product including an inner layer and an intermediate layer.

[0075] It should be noted that during the process of the above second coprecipitation reaction, both the ammonia value (ammonia concentration) and pH are in a dynamic change state. Among them, the ammonia value gradually increases (gradient increase), for example, from A 1 gradually increases to A 3 , and the pH gradually decreases (gradient decrease), for example, from B 1 gradually decreases to B 3 , and the metal salt flow rate remains C 2 unchanged.

[0076] In the third stage, the third coprecipitation reaction is carried out in the reaction system under the conditions of a relatively high flow rate of the metal salt solution, a relatively high ammonia value (high ammonia), and a relatively low pH. The growth rate further increases, the nucleation rate further decreases, and the particles undergo oriented attachment ripening, thus forming a hollow radial channel (radial lithium ion channel) formed by the oriented arrangement of primary particles and a relatively dense outer layer, obtaining a doped cathode precursor including an inner layer, an intermediate layer, and an outer layer.

[0077] Since the complexation reaction and the precipitation reaction are in a competitive relationship, in the second and third stages, the ammonia value is increased, and under conditions such as a gradually increasing ammonia value, more doped element ions (such as Zr 4+ ) in the reaction system can complex with ammonia water, so that the doped element ions mainly undergo complexation reactions in the reaction system. The supersaturation of the doped element ions in the reaction system is relatively low, and a small amount of free doped element ions preferentially coprecipitate with nickel, cobalt, and manganese on the surface of the precursor, rather than reacting with OH - in the system, so that they will not nucleate alone to form fine powder. Therefore, the problem that the doped cathode precursor is prone to generate small particles and has a wide SPAN during the synthesis process can be effectively solved.

[0078] The above preparation method prepares a doped cathode precursor with three different hierarchical structures including an inner layer, an intermediate layer, and an outer layer by dynamically adjusting the flow rate of the metal salt solution, the ammonia value (the amount of ammonia water introduced), and the pH (the amount of alkali solution introduced) during the reaction process. The process includes operations such as low ammonia value in the early stage, high ammonia value in the later stage, high pH in the early stage, low pH in the later stage, low metal salt flow rate in the early stage, and high metal salt flow rate in the later stage, which helps to improve the cycle performance and capacity of the battery. In addition, the SPAN and doping content of the doped precursor are controllable, the morphology is regular, the sphericity is high, and the distribution of the doped elements is relatively uniform, overcoming the defects of the prior art.

[0079] The preparation method is simple to operate and suitable for industrial promotion.

[0080] The reaction site of the above preparation method is not limited in the embodiments of the present invention. For example, it can be carried out in a reaction kettle (such as a reaction kettle with a volume of 100 L).

[0081] During specific implementation, an inert gas, such as high-purity nitrogen, can be introduced below the liquid level of the reaction system to ensure that the reaction system is in an inert atmosphere and avoid the occurrence of oxidation reactions.

[0082] The flow rate of the above inert gas (such as nitrogen) can be 0.1 - 1.0 m 3 / h.

[0083] The ammonia value of the above bottom liquid can be 1 - 4 g / L, and the pH can be 11.6 - 12.0.

[0084] The bottom liquid can be prepared through the following process: Under the stirring state with a rotation speed of 300 - 900 rpm, ammonia water is added to water (such as deionized water), and its ammonia value is controlled to be 1 - 4 g / L. Then, the alkali solution is introduced into it to adjust its pH to 11.6 - 12.0, obtaining the bottom liquid.

[0085] In some embodiments, the ammonia value A 1 in the first stage is 2.5 - 3.5 g / L, the ammonia value A 3 in the third stage is 5.5 - 6.5 g / L, and the ammonia value in the second stage gradually increases from A 1 to A 3 , which helps to further control the porosity of the inner layer, intermediate layer, and outer layer within a suitable range, and further helps to improve the cycle performance and capacity of the battery.

[0086] In some embodiments, the pH value B 1 in the first stage is 11.60 - 11.80, the pH value B 3 in the third stage is 11.40 - 11.50, and the pH value in the second stage gradually increases from B 1 to B 3, which helps to further control the porosity of the inner layer, middle layer and outer layer within a suitable range, and further helps to improve the cycling performance and capacity of the battery.

[0087] In the embodiment of the present invention, doping is carried out during the synthesis of the doped cathode precursor. Specifically, by adjusting the flow rate of the metal salt solution (feed flow rate), the doping amount can be precisely controlled to achieve atomic-level doping.

[0088] In some embodiments, the flow rate C of the metal salt solution in the first stage 1 is 1.0 - 2.0 g / L, the flow rate C of the metal salt solution in the second stage 2 is 3.5 - 4.5 g / L, and the flow rate C of the metal salt solution in the third stage 3 is 7.0 - 8.0 g / L, which helps to further control the porosity of the inner layer, middle layer and outer layer within a suitable range, and further helps to improve the cycling performance and capacity of the battery.

[0089] It can be understood that the above metal salt solution further includes doping elements, and the doping elements may include one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, Mo, and preferably Zr.

[0090] The concentration of the doping element in the metal salt solution can be 0.05 - 2.5 mol / L.

[0091] For example, the above metal salt solution may include a mixed solution of nickel, cobalt, and manganese with a total molar concentration of 0.05 - 2.5 mol / L, such as 0.05, 0.1, 1.0, 2, 2.5 mol / L or a range composed of any two of them. The molar ratio of nickel, cobalt, and manganese is a:b:c, 0.8 ≤ a < 1.0, 0 < b ≤ 0.1, 0 < c ≤ 0.1, and a + b + c = 1.

[0092] During specific implementation, a nickel source, a cobalt source, a manganese source, a doping substance, and water (such as deionized water) can be mixed to prepare the above metal salt solution. Among them, the nickel source may include nickel sulfate, the cobalt source may include cobalt sulfate, the manganese source may include manganese sulfate, and the doping substance may include zirconium sulfate (such as anhydrous zirconium sulfate).

[0093] The function of the above ammonia water is a complexing agent, and its concentration can be 5 - 12 mol / L. Specifically, it can be prepared by mixing ammonia water with a mass percentage of ammonia of 25% and water.

[0094] The above alkali solution may include an aqueous sodium hydroxide solution, and its concentration can be 5 - 12 mol / L.

[0095] In specific implementation, in the first co-precipitation reaction, after the reaction solution in the reaction system overflows for a period of time (such as 4 h), the thickener can be started to increase its solid content.

[0096] In the third co-precipitation reaction, after the particle size of the doped cathode precursor reaches 3.0 - 4.0 μm, the third co-precipitation reaction can be terminated to obtain the doped cathode precursor, which can be used for the sintering preparation of the single-crystal cathode active material.

[0097] In addition, after the third co-precipitation reaction ends, the obtained mixed slurry can be aged, centrifugally washed, dried, sieved, and iron-removed, and then the doped cathode precursor (such as a zirconium-doped nickel cobalt manganese precursor) can be obtained.

[0098] Specifically, the above aging process can be carried out in an aging kettle, the centrifugal washing can be carried out in a centrifuge, and the drying can be carried out in a blast drying oven.

[0099] In the above centrifugal washing process, a hot alkali solution (such as a concentration of 10 mol / L) or hot water can be used as the washing liquid, and the washing can be carried out for 20 - 40 min. Among them, the temperature of the hot alkali solution or hot water can be 50 - 70 °C, and the hot alkali in the hot alkali solution can include at least one of sodium hydroxide and potassium hydroxide.

[0100] In the above drying process, the temperature can be 110 - 130 °C, and the drying time can be 15 - 20 h.

[0101] In specific implementation, a 325-mesh sieve can be used for sieving.

[0102] In some embodiments, the expected particle size (D50) of the first product can be 0.6 - 1.3 μm, the expected particle size (D50) of the second product can be 1.0 - 2.2 μm, and the expected particle size (D50) of the doped cathode precursor can be 3.0 - 4.0 μm.

[0103] In practical applications, the temperature of the above reaction system can be 40 - 70 °C.

[0104] Based on the same inventive concept, an embodiment of the present invention further provides a cathode active material, which is a doped cathode active material. In the radial direction from the inside to the outside of the cathode active material, it sequentially includes an inner layer, an intermediate layer, and an outer layer. The porosity of the inner layer is greater than the porosity of the intermediate layer, the porosity of the intermediate layer is less than or equal to the porosity of the outer layer, and the outer layer includes radial channels.

[0105] Based on the previous description, this cathode active material helps to improve the cycle performance and capacity of the battery, which will not be elaborated here.

[0106] The positive electrode active material is formed from the above-doped positive electrode precursor or the doped positive electrode precursor prepared according to the above preparation method. Based on this doped positive electrode precursor, the positive electrode active material helps to improve the cycle performance and capacity of the battery, which will not be elaborated here.

[0107] In some embodiments, the above positive electrode active material is obtained by sintering a mixture of the above-doped positive electrode precursor and a lithium salt.

[0108] Specifically, the above lithium salt may include at least one of lithium carbonate and lithium hydroxide.

[0109] Based on the same inventive concept, an embodiment of the present invention further provides a positive electrode sheet, which includes the above positive electrode active material.

[0110] The positive electrode sheet of the embodiment of the present invention specifically includes a positive electrode current collector and a positive electrode active layer formed on the surface of the positive electrode current collector and composed of the above positive electrode active material.

[0111] When specifically preparing the positive electrode sheet, for example, the above positive electrode active material of the present invention, a conductive agent, and a binder can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and sufficiently stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling, and slitting, a positive electrode sheet is obtained. For example, the positive electrode active layer includes 70-99 wt% of the positive electrode active material, 0.5-15 wt% of the conductive agent, and 0.5-15 wt% of the binder by mass percentage. Further, it includes 80-98 wt% of the positive electrode active material, 1-10 wt% of the conductive agent, and 1-10 wt% of the binder.

[0112] The material of the above positive electrode current collector can be at least one of aluminum foil and nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, a polymer containing ethylene oxide, polyvinylpyrrolidone, and polyurethane.

[0113] The battery prepared using this positive electrode sheet has a high capacity and excellent cycle performance.

[0114] Based on the same inventive concept, an embodiment of the present invention provides a lithium-ion battery, which includes the above positive electrode sheet.

[0115] It can be conceived that in addition to the above positive electrode sheet, the lithium-ion battery of the embodiment of the present invention further includes a negative electrode sheet, an electrolyte, and a separator.

[0116] The embodiments of the present invention do not strictly limit the anode active material in the anode sheet, which can be the anode active materials commonly used in current lithium-ion batteries, such as at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based anode materials (mainly including silicon monoxide and silicon-carbon anodes), tin-based anode materials (mainly including tin and tin alloys), etc.

[0117] The embodiments of the present invention do not strictly limit the selection of the electrolyte, which can include one or more of the solvents commonly used in current lithium-ion battery electrolytes, as well as the electrolyte lithium salts commonly used in current lithium-ion electrolytes. For example, the solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salts can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0118] The embodiments of the present invention do not strictly limit the material selection of the separator, which can be the separator materials commonly used in current lithium-ion batteries, such as one of polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite film (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene three-layer composite film (PP / PE / PP), cellulose non-woven separator, and separator with ceramic coating.

[0119] When preparing a lithium-ion battery, the positive electrode sheet, the separator, and the negative electrode sheet are wound or laminated to obtain a bare battery cell, and the bare battery cell is encapsulated into a pre-stamped aluminum-plastic film bag. After the encapsulated battery is dried at 85°C to remove moisture, the electrolyte is injected into the dried battery, and the battery is completed after standing, formation, and secondary sealing.

[0120] This lithium-ion battery has a high capacity and excellent cycling performance.

[0121] The present invention will be further described below through specific examples and comparative examples. Unless otherwise specified, the reagents, materials, and instruments used below are all conventional reagents, conventional materials, and conventional instruments, which can be obtained commercially, and the reagents and materials involved can also be obtained by conventional synthesis methods.

[0122] Example 1

[0123] This example provides a preparation method of a doped cathode precursor, including:

[0124] Mix nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate and deionized water to prepare a metal salt solution with a total ion concentration of 1.5 mol / L. Among them, the molar ratio of metal ions satisfies Ni:Co:Mn = 88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; prepare ammonia water with an ammonia concentration of 9.8 mol / L and an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 11 mol / L.

[0125] Under the stirring state with a rotation speed of 600 rpm, add the above ammonia water into deionized water at 60 °C, control its ammonia value to be 3.0 g / L, then introduce the aqueous sodium hydroxide solution with a concentration of 11 mol / L into it, adjust its pH to 11.6 - 11.80, and introduce high-purity nitrogen gas below the liquid surface. The flow rate of high-purity nitrogen gas is 0.3 m 3 / h to obtain the bottom liquid;

[0126] Introduce a raw material system including the above ammonia water, the above aqueous sodium hydroxide solution, and the metal salt solution into the bottom liquid, so that the reaction system reacts under the conditions that the ammonia value A 1 is 3.0 g / L, the pH value B 1 is 11.6 - 11.80, and the flow rate C 1 of the metal salt solution is 1.5 L / h to carry out the first coprecipitation reaction to obtain the first product;

[0127] After the D50 of the first product reaches 1.2 μm, gradually increase the ammonia value of the reaction system to 6.0 g / L, gradually decrease the pH of the reaction system to 11.40 - 11.50, and control the flow rate C 2 of the metal salt solution to be 4.0 L / h, so that the reaction system carries out the second coprecipitation reaction to obtain the second product;

[0128] After the D50 of the second product reaches 2.2 μm, make the reaction system react under the conditions that the ammonia value A 3 is 6.0 g / L, the pH value B 3 is 11.40 - 11.50, and the flow rate C 3 of the metal salt solution is 7.5 L / h to carry out the third coprecipitation reaction. After the particle size of the product reaches 3.8 μm, stop the third coprecipitation reaction;

[0129] Then, after aging the reaction solution of the third coprecipitation, first centrifuge and wash it with a 10 mol / L hot alkali solution for 20 min, then centrifuge and wash it with hot water for 40 min, then dry it at 130 °C for 20 h, and then sieve it through a 325-mesh sieve. After removing iron, the doped cathode precursor of this example is obtained.

[0130] Example 2

[0131] This example is basically the same as Example 1, the difference is:

[0132] The concentration of Zr in the metal salt solution is 0.1 mol / L; other conditions remain unchanged.

[0133] Example 3

[0134] This example is basically the same as Example 1, except that:

[0135] The concentration of Zr in the metal salt solution is 0.15 mol / L; other conditions remain unchanged.

[0136] Example 4

[0137] This example is basically the same as Example 1, except that:

[0138] The concentration of Zr in the metal salt solution is 0.25 mol / L; other conditions remain unchanged.

[0139] Example 5

[0140] This example is basically the same as Example 1, except that:

[0141] The ammonia value of the bottom solution is 2.5 g / L and the pH is 11.60;

[0142] In the first coprecipitation reaction, A 1 is 2.5 g / L, B 1 is 11.60, C 1 is 1.0 g / L;

[0143] In the second coprecipitation reaction, the ammonia value of the reaction system is gradually increased to 5.5 g / L, the pH of the reaction system is gradually decreased to 11.40, and C 2 is 3.5 g / L;

[0144] In the third coprecipitation reaction, A 3 is 5.5 g / L, B 3 is 11.40, C 3 is 7.0 g / L;

[0145] The reaction temperature is 40 °C;

[0146] Other conditions remain unchanged.

[0147] Example 6

[0148] This example is basically the same as Example 1, except that:

[0149] The ammonia value of the bottom solution is 3.5 g / L and the pH is 11.80;

[0150] In the first coprecipitation reaction, A 1 is 3.5 g / L, B 1 is 11.80, C1 is 2.0 g / L;

[0151] In the second coprecipitation reaction, gradually increase the ammonia value of the reaction system to 6.5 g / L, and gradually decrease the pH of the reaction system to 11.50. C 2 is 4.5 g / L;

[0152] In the third coprecipitation reaction, A 3 is 6.5 g / L, B 3 is 11.50, C 3 is 8.0 g / L;

[0153] The temperature of the reaction is 70 °C;

[0154] Other conditions remain unchanged.

[0155] Example 7

[0156] This example is basically the same as Example 1, except that:

[0157] The ammonia value of the bottom solution is 3.5 g / L, and the pH is 11.80;

[0158] In the first coprecipitation reaction, A 1 is 3.0 g / L, B 1 is 11.70, C 1 is 1.5 g / L;

[0159] In the second coprecipitation reaction, gradually increase the ammonia value of the reaction system to 6.0 g / L, and gradually decrease the pH of the reaction system to 11.45. C 2 is 4.5 g / L;

[0160] In the third coprecipitation reaction, A 3 is 6.0 g / L, B 3 is 11.45, C 3 is 7.5 g / L;

[0161] Other conditions remain unchanged.

[0162] Example 8

[0163] This example is basically the same as Example 1, except that:

[0164] The ammonia value of the bottom solution is 1.0 g / L, and the pH is 11.90;

[0165] In the first coprecipitation reaction, A 1 is 1.0 g / L, B 1 is 11.70, C 1 is 1.5 g / L;

[0166] In the second coprecipitation reaction, gradually increase the ammonia value of the reaction system to 6.0 g / L, gradually decrease the pH of the reaction system to 11.45, and C 2 is 4.5 g / L;

[0167] In the third coprecipitation reaction, A 3 is 6.0 g / L, B 3 is 11.45, and C 3 is 7.5 g / L;

[0168] Keep other conditions unchanged.

[0169] Example 9

[0170] This example is basically the same as Example 1, except that:

[0171] After the D50 of the first product reaches 0.6 μm, carry out the second precipitation reaction;

[0172] After the D50 of the second product reaches 2.2 μm, carry out the third precipitation reaction;

[0173] After the D50 of the product of the third precipitation reaction reaches 3.8 μm, stop the third precipitation reaction;

[0174] Keep other conditions unchanged.

[0175] Example 10

[0176] This example is basically the same as Example 1, except that:

[0177] After the D50 of the first product reaches 1.5 μm, carry out the second precipitation reaction;

[0178] After the D50 of the second product reaches 2.1 μm, carry out the third precipitation reaction;

[0179] After the D50 of the product of the third precipitation reaction reaches 2.9 μm, stop the third precipitation reaction;

[0180] Keep other conditions unchanged.

[0181] Example 11

[0182] This example is basically the same as Example 1, except that:

[0183] After the D50 of the first product reaches 0.4 μm, carry out the second precipitation reaction;

[0184] After the D50 of the second product reaches 2.4 μm, carry out the third precipitation reaction;

[0185] After the D50 of the product of the third precipitation reaction reaches 2.8 μm, stop the third precipitation reaction;

[0186] Other conditions remain unchanged.

[0187] Example 12

[0188] This example is basically the same as Example 1, except that:

[0189] Lanthanum chloride hexahydrate is used to replace zirconium sulfate anhydrous, and other conditions remain unchanged.

[0190] Comparative Example 1

[0191] This comparative example is basically the same as Example 1, except that:

[0192] The metal salt solution does not include zirconium sulfate, that is, the positive electrode precursor of Comparative Example 1 is not doped; other conditions remain unchanged.

[0193] Comparative Example 2

[0194] This comparative example provides a method for preparing a doped positive electrode precursor, including:

[0195] Mix nickel sulfate, cobalt sulfate, manganese sulfate, zirconium sulfate anhydrous and deionized water to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn = 88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; prepare ammonia water with an ammonia concentration of 9.8 mol / L and an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 11 mol / L;

[0196] Under the stirring state with a rotation speed of 600 rpm, add the above ammonia water into deionized water, control its ammonia value to be 3.0 g / L, then introduce the aqueous sodium hydroxide solution with a concentration of 11 mol / L into it, adjust its pH to 11.6 - 11.80, and introduce high-purity nitrogen gas below the liquid surface, and the flow rate of high-purity nitrogen gas is 0.3 m 3 / h to obtain the bottom liquid;

[0197] Introduce a raw material system including the above ammonia water, the above aqueous sodium hydroxide solution, and the metal salt solution into the bottom liquid, so that the reaction system reacts under the conditions that the ammonia value A 1 is 3.0 g / L, the pH value B 1 is 11.6 - 11.80, and the flow rate C 1 of the metal salt solution is 1.5 L / h to carry out the first coprecipitation reaction to obtain the first product;

[0198] After the particle size of the first product reaches 3.5 μm, stop the first coprecipitation reaction. Then, after aging the reaction solution of the first coprecipitation, first centrifuge and wash it with a 10 mol / L hot alkali solution for 20 min, then centrifuge and wash it with hot water for 40 min, then dry it at 130 °C for 20 h, and then screen it through a 325-mesh sieve. After removing iron, the doped cathode precursor of this comparative example is obtained.

[0199] That is to say, in Comparative Example 2, only the first coprecipitation reaction is carried out, and other conditions remain unchanged as in Example 1.

[0200] Comparative Example 3

[0201] This comparative example provides a method for preparing a doped cathode precursor, including:

[0202] Mix nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate and deionized water to prepare a metal salt solution with a total ion concentration of 1.5 mol / L. Among them, the molar ratio of metal ions satisfies Ni:Co:Mn = 88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; prepare ammonia water with an ammonia concentration of 9.8 mol / L and an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 11 mol / L.

[0203] Under the stirring state with a rotation speed of 600 rpm, add the above ammonia water to deionized water, control its ammonia value to 3.0 g / L, then introduce the 11 mol / L aqueous sodium hydroxide solution into it, adjust its pH to 11.6 - 11.80, and introduce high-purity nitrogen gas below the liquid surface. The flow rate of high-purity nitrogen gas is 0.3 m 3 / h to obtain the bottom liquid;

[0204] Introduce the raw material system including the above ammonia water, the above aqueous sodium hydroxide solution, and the metal salt solution into the bottom liquid, gradually increase the ammonia value of the reaction system to 6.0 g / L, gradually decrease the pH of the reaction system to 11.40 - 11.50, control the flow rate of the metal salt solution to 4.0 L / h, and make the reaction system carry out the second coprecipitation reaction to obtain the second product;

[0205] After the D50 of the second product reaches 3.5 μm, stop the second coprecipitation reaction;

[0206] Then, after aging the reaction solution of the second coprecipitation, first centrifuge and wash it with a 10 mol / L hot alkali solution for 20 min, then centrifuge and wash it with hot water for 40 min, then dry it at 130 °C for 20 h, and then screen it through a 325-mesh sieve. After removing iron, the doped cathode precursor of this comparative example is obtained.

[0207] That is to say, in Comparative Example 3, only the second coprecipitation reaction is carried out, and other conditions remain unchanged as in Example 1.

[0208] Comparative Example 4

[0209] This comparative example provides a method for preparing a doped cathode precursor, including:

[0210] Mix nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate and deionized water to prepare a metal salt solution with a total ion concentration of 1.5 mol / L. Among them, the molar ratio of metal ions satisfies Ni:Co:Mn = 88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; prepare ammonia water with an ammonia concentration of 9.8 mol / L and an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 11 mol / L;

[0211] Under the stirring state with a rotation speed of 600 rpm, add the above ammonia water into deionized water, control its ammonia value to be 3.0 g / L, then introduce the aqueous sodium hydroxide solution with a concentration of 11 mol / L into it, adjust its pH to 11.6 - 11.80, and introduce high-purity nitrogen gas below the liquid surface. The flow rate of the high-purity nitrogen gas is 0.3 m 3 / h to obtain the bottom liquid;

[0212] Introduce a raw material system including the above ammonia water, the above aqueous sodium hydroxide solution, and the metal salt solution into the bottom liquid, so that the reaction system reacts under the conditions of ammonia value A 3 being 6.0 g / L, pH value B 3 being 11.40 - 11.50, and the flow rate C 3 of the metal salt solution being 7.5 L / h to carry out the third coprecipitation reaction;

[0213] Then, after aging the reaction solution of the third coprecipitation, first centrifuge and wash it with a 10 mol / L hot alkali solution for 20 min, then centrifuge and wash it with hot water for 40 min, then dry it at 130 °C for 20 h, and then sieve it through a 325-mesh sieve. After removing iron, the doped cathode precursor of this comparative example is obtained.

[0214] That is to say, Comparative Example 4 only conducts the third coprecipitation reaction, and other conditions remain the same as those in Example 1.

[0215] Comparative Example 5

[0216] This comparative example provides a method for preparing a doped cathode precursor, including:

[0217] Mix nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate and deionized water to prepare a metal salt solution with a total ion concentration of 1.5 mol / L. Among them, the molar ratio of metal ions satisfies Ni:Co:Mn = 88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; prepare ammonia water with an ammonia concentration of 9.8 mol / L and an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 11 mol / L;

[0218] Under the stirring condition at a rotational speed of 600 rpm, add the above-mentioned ammonia water into deionized water at 60 °C, control its ammonia value to be 3.0 g / L, then introduce an aqueous sodium hydroxide solution with a concentration of 11 mol / L into it, adjust its pH to 11.70, and introduce high-purity nitrogen gas below the liquid surface. The flow rate of the high-purity nitrogen gas is 0.3 m 3 / h to obtain the bottom liquid;

[0219] Introduce a raw material system including the above-mentioned ammonia water, the above-mentioned aqueous sodium hydroxide solution, and a metal salt solution into the bottom liquid, so that the reaction system has an ammonia value A 1 of 3.0 g / L, a pH value B 1 of 11.70, and the flow rate C 1 of the metal salt solution is 1.5 L / h to carry out the first coprecipitation reaction to obtain the first product;

[0220] After the D50 of the first product reaches 1.2 μm, gradually increase the ammonia value of the reaction system to 6.0 g / L, gradually decrease the pH of the reaction system to 11.45, and control the flow rate C 2 of the metal salt solution to be 4.0 L / h, so that the reaction system undergoes a second coprecipitation reaction to obtain the second product;

[0221] After the D50 of the second product reaches 3.0 μm, stop the second coprecipitation reaction;

[0222] Then, after aging the reaction solution of the second coprecipitation, first centrifuge and wash it with a 10 mol / L hot alkali solution for 20 min, then centrifuge and wash it with hot water for 40 min, then dry it at 130 °C for 20 h, and then sieve it through a 325-mesh sieve. After removing iron, the doped cathode precursor of this example is obtained.

[0223] That is to say, Comparative Example 5 only performs the first coprecipitation reaction and the second coprecipitation reaction, and other conditions remain the same as those in Example 1.

[0224] Comparative Example 6

[0225] This comparative example provides a method for preparing a doped cathode precursor, including:

[0226] Mix nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate and deionized water to prepare a metal salt solution with a total ion concentration of 1.5 mol / L. Among them, the molar ratio of metal ions satisfies Ni:Co:Mn = 88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; prepare ammonia water with an ammonia concentration of 9.8 mol / L and an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 11 mol / L;

[0227] Under the stirring condition at a rotational speed of 600 rpm, add the above ammonia water into deionized water at 60 °C, control its ammonia value to be 3.0 g / L, then introduce an aqueous sodium hydroxide solution with a concentration of 11 mol / L into it, adjust its pH to 11.70, and introduce high-purity nitrogen gas below the liquid surface. The flow rate of the high-purity nitrogen gas is 0.3 m 3 / h to obtain the bottom liquid;

[0228] Introduce a raw material system including the above ammonia water, the above aqueous sodium hydroxide solution, and a metal salt solution into the bottom liquid, so that the reaction system has an ammonia value A 1 of 3.0 g / L, a pH value B 1 of 11.70, and a flow rate C 1 of the metal salt solution of 1.5 L / h to carry out the first coprecipitation reaction to obtain the first product;

[0229] After the D50 of the first product reaches 1.2 μm, make the reaction system have an ammonia value A 3 of 6.0 g / L, a pH value B 3 of 11.45, and a flow rate C 3 of the metal salt solution of 7.5 L / h to carry out the third coprecipitation reaction. After the particle size of the product reaches 3.4 μm, stop the third coprecipitation reaction;

[0230] Then, after aging the reaction solution of the third coprecipitation, first centrifuge and wash it with a 10 mol / L hot alkali solution for 20 min, then centrifuge and wash it with hot water for 40 min, then dry it at 130 °C for 20 h, and then sieve it through a 325-mesh sieve. After removing iron, the doped cathode precursor of this example is obtained.

[0231] That is to say, Comparative Example 6 only carries out the first coprecipitation reaction and the third coprecipitation reaction, and other conditions remain the same as those in Example 1.

[0232] Comparative Example 7

[0233] This comparative example provides a method for preparing a doped cathode precursor, including:

[0234] Mix nickel sulfate, cobalt sulfate, manganese sulfate, anhydrous zirconium sulfate and deionized water to prepare a metal salt solution with a total ion concentration of 1.5 mol / L, wherein the molar ratio of metal ions satisfies Ni:Co:Mn = 88.5:9:2.5, and the concentration of Zr is 0.05 mol / L; prepare ammonia water with an ammonia concentration of 9.8 mol / L and an aqueous sodium hydroxide solution with a sodium hydroxide concentration of 11 mol / L;

[0235] Under the stirring state with a rotational speed of 500 - 700 rpm, add the above ammonia water into deionized water at 60 °C, control its ammonia value to be 2.5 - 3.5 g / L, then introduce an aqueous sodium hydroxide solution with a concentration of 11 mol / L into it, adjust its pH to 11.6 - 11.80, and introduce high-purity nitrogen gas below the liquid surface. The flow rate of the high-purity nitrogen gas is 0.3 m 3 / h to obtain the bottom liquid;

[0236] Introduce a raw material system including the above ammonia water, the above aqueous sodium hydroxide solution, and a metal salt solution into the bottom liquid, gradually increase the ammonia value of the reaction system to 6.0 g / L, gradually decrease the pH of the reaction system to 11.45, and control the flow rate C 2 of the metal salt solution to be 4.0 L / h to cause the reaction system to undergo a second coprecipitation reaction to obtain a second product;

[0237] After the D50 of the second product reaches 1.5 μm, make the reaction system have an ammonia value A 3 of 6.0 g / L, a pH value B 3 of 11.45, and a flow rate C 3 of the metal salt solution of 7.5 L / h to carry out a third coprecipitation reaction. After the particle size of the product reaches 3.1 μm, stop the third coprecipitation reaction;

[0238] Then, after aging the reaction solution of the third coprecipitation, first centrifuge and wash it with a 10 mol / L hot alkali solution for 20 min, then centrifuge and wash it with hot water for 40 min, then dry it at 130 °C for 20 h, and then sieve it through a 325-mesh sieve. After removing iron, the doped cathode precursor of this example is obtained.

[0239] That is to say, Comparative Example 7 only conducts the second coprecipitation reaction and the third coprecipitation reaction, and other conditions remain the same as those in Example 1.

[0240] Test Example 1

[0241] Test the following parameters of the doped cathode precursors of each example and comparative example:

[0242] 1) Morphology characteristics: Conduct electron microscopy scans on the cross-section, inner layer, middle layer, and outer layer of the doped cathode precursor of Example 1. As Figures 1 - 6 shown, conduct energy spectrum mapping analysis on the doped cathode precursor of Example 1, and the results are shown in Figures 7 - 10 ; The scanning electron microscope images of the cathode precursor of Comparative Example 1 are shown in Figure 11 and Figure 12 ; The scanning electron microscope images of the doped cathode precursor of Comparative Example 2 are shown in Figure 13 and Figure 14 ; The scanning electron microscope images of the doped cathode precursor of Comparative Example 4 are shown in Figure 15 .

[0243] 2) D50 and SPAN: Test D90, D10, and D50 using a Malvern 3000 particle size analyzer, and then calculate SPAN according to the following formula: SPAN = (D90 - D10) / D50.

[0244] 3) Tap density (TD): Test using a tap density tester.

[0245] 4) Specific surface area: Test using a Micromeritics specific surface area analyzer.

[0246] 5) Doping amount (in ppm): Test using an inductively coupled plasma atomic emission spectrometer (ICP).

[0247] 6) Porosity of the inner layer, middle layer, and outer layer, and porosity of the doped cathode precursor (cathode precursor):

[0248] Take a cross-sectional view of the prepared precursor sample by SEM, process it using Metis software to separately obtain the sum of the pore areas of the inner layer, the sum of the pore areas of the middle layer, the sum of the pore areas of the outer layer, the sum of the pore areas of the precursor cross-section, and the cross-sectional area of this cross-section. Calculate the porosity of the inner layer, middle layer, and outer layer, and the porosity of the doped cathode precursor (cathode precursor) according to the formula: porosity = sum of pore areas / cross-sectional area × 100%.

[0249] 7) Thickness of primary particles, number of nanosheet layers in the inner layer, middle layer, and outer layer, and radial dimensions R 1 、R 2 、R 3 in the inner layer, middle layer, and outer layer, and length of the radial channel in the outer layer:

[0250] According to the scanning electron microscope images, use the measurement software Nano Measurer 1.2 to measure the above indicators;

[0251] 8) Sphericity of the doped cathode precursor: Scan the precursor particles in the SEM using Metis software to obtain the projected area S and perimeter L. The sphericity R calculation formula is: R = 4πS / (L×2).

[0252] Test results

[0253] Table 1 Porosity (%), length of radial channel (nm), and sphericity of the inner layer, middle layer, outer layer, and doped cathode precursor

[0254]

[0255] As can be seen from Table 1, the doped cathode precursor of the embodiment of the present invention has a three-layer structure, and the porosity satisfies that the porosity of the inner layer is greater than that of the intermediate layer, the porosity of the intermediate layer is less than or equal to that of the outer layer, and the outer layer includes radial channels.

[0256] Table 2

[0257]

[0258] Table 2 gives data such as SPAN, tap density TD, specific surface area, D50, and doping amount of each example and comparative example.

[0259] Table 3

[0260]

[0261] As can be seen from Table 3, the doped cathode precursors of each example are divided into an inner layer, an intermediate layer, and an outer layer. The inner layer has a loose and porous honeycomb structure, and the primary particles in the intermediate layer are most densely packed; the primary particles in the outer layer are arranged in an oriented manner to form longitudinal lithium ion channels, and the outer layer region is relatively dense. In addition, in the doped cathode precursor of the above embodiment, the radial dimension R of the inner layer 1 can be 0.4 - 1.5 μm, preferably 0.6 - 1.3 μm, and the ratio of the radial dimension R of the inner layer 1 to the diameter of the doped cathode precursor particle can be 25 - 50%.

[0262] Figure 1 is a cross-sectional view of the doped cathode precursor of Example 1. It can be clearly seen that the doped cathode precursor is divided into an inner layer, an intermediate layer, and an outer layer. The inner layer has a loose and porous honeycomb structure, and the primary particles in the intermediate layer are most densely packed; the primary particles in the outer layer are arranged in an oriented manner to form longitudinal lithium ion channels, and the outer layer region is relatively dense.

[0263] Figure 2 is a scanning electron micrograph of the inner layer of the doped cathode precursor of Example 1. The primary particles in the inner layer region are relatively thin, with a thickness of about 10 - 50 nm. The primary particles are formed by stacking 2 - 10 nanosheets. The primary particles are intertwined with each other and have many voids.

[0264] Figure 3 is a scanning electron micrograph of the intermediate layer of the doped cathode precursor of Example 1. The primary particles in the intermediate layer are relatively thick, with a thickness of about 400 - 600 nm. The primary particles are formed by stacking 80 - 120 nanosheets. The primary particles are arranged in a staggered manner and are densely packed without obvious voids. The structure of the intermediate layer is the densest.

[0265] Figures 4 - 6SEM image of the outer layer of the doped cathode precursor in Example 1. The thickness of the primary particles in the outer layer is about 300 - 400 nm. The primary particles are formed by stacking 60 - 80 nanosheets. The primary particles have good consistency and are arranged directionally, forming a directional channel. The particle size distribution of the secondary spherical particles is uniform and the sphericity is good.

[0266] Figures 7 - 10 EDS mapping diagram (cross-sectional EDS-mapping spectrum) of nickel, cobalt, manganese, and zirconium elements in the doped cathode precursor of Example 1. It can be seen from Figure 10 that the doped zirconium element is evenly distributed without obvious regional differences.

[0267] Figure 11 and Figure 12 SEM image of the cathode precursor of Comparative Example 1. Compared with Example 1, although there are no obvious small particles in the cathode precursor of Comparative Example 1 without Zr doping, the whisker consistency is poor, the sphericity is poor, and the multi-head phenomenon is obvious, indicating that Zr doping can significantly improve the whisker consistency and improve the problem of particle agglomeration.

[0268] Figure 13 and Figure 14 SEM image of the doped cathode precursor of Comparative Example 2. Compared with Example 1, the doped precursor prepared under the condition of low ammonia throughout the process has more small particles, which will lead to differences in the diffusion path size of lithium elements during the sintering process of the cathode active material, affecting the sintering uniformity and having an adverse effect on the battery performance. The whiskers of the precursor prepared under the low ammonia condition are thinner, about 160 nm.

[0269] Figure 15 SEM image of the doped cathode precursor of Comparative Example 4. Compared with Example 1, the precursor prepared with a high salt solution concentration in the early stage has serious agglomeration, many small particles, poor sphericity, and obvious multi-head phenomenon. The doped cathode precursor of Example 1 prepared by the gradient lift feed flow process has significantly better sphericity, indicating that the gradient lift feed flow process is beneficial to the improvement of sphericity.

[0270] Test Example 2

[0271] The cathode active material was prepared using the doped cathode precursors of the above examples and comparative examples, which specifically included the following steps: The above doped cathode precursor and lithium carbonate were mixed in a certain proportion and then sintered once to obtain the cathode active material.

[0272] 1) Morphological characteristics: The cross-section, inner layer, middle layer, and outer layer of the cathode active material of Example 1 were scanned by electron microscopy. As Figure 16 shown,

[0273] 2) Porosities of the inner layer, middle layer, and outer layer, and porosity of the positive electrode active material: Take a cross-sectional SEM image of the prepared positive electrode active material, and use Metis software to process it to separately obtain the sum of the pore areas of the inner layer, the sum of the pore areas of the middle layer, the sum of the pore areas of the outer layer, the sum of the pore areas of the precursor on the cross-section, and the cross-sectional area of this cross-section. Calculate the porosities of the inner layer, middle layer, and outer layer, and the porosity of the positive electrode active material according to the formula: porosity = sum of pore areas / cross-sectional area × 100%. The results are shown in Table 4;

[0274] 3) Length of the radial channel: According to the scanning electron microscope image, use the measurement software Nano Measurer 1.2 to measure the above indicators.

[0275] Table 4

[0276]

[0277] From Figure 16 As can be seen from the above table, the positive electrode active material of the embodiment of the present invention has a three-layer structure, and the porosity satisfies: the porosity of the inner layer is greater than the porosity of the middle layer, the porosity of the middle layer is less than or equal to the porosity of the outer layer, and the outer layer includes radial channels.

[0278] Test Example 3

[0279] Prepare the positive electrode active materials corresponding to the examples and comparative examples in Test Example 2 into positive electrode sheets, and assemble them with negative electrode sheets, electrolytes, and separators into button cells according to the following method. The method includes:

[0280] Mix each positive electrode active material with conductive carbon black (SP) and PVDF in a weight ratio of 80%:10%:10% respectively, and obtain a positive electrode slurry through dispersion. Coating the slurry on an aluminum foil current collector, roll-pressing to prepare a positive electrode sheet, then punching the positive electrode sheet with a mold into small round pieces with a diameter of 12 mm, after drying and weighing, in a glove box under an Ar protection atmosphere, using a 2025 button cell case, using a Li metal round sheet as the negative electrode, the electrolyte includes LiPF 6 and a solvent. Among them, the concentration of LiPF 6 in the electrolyte is 1.0 M, and the solvent includes EC and DMC with a volume ratio of 1:1. Assemble the above positive electrode sheet (the small round piece after drying and weighing), negative electrode, electrolyte, and a 2025 button cell case together into a button cell.

[0281] 1) After standing the obtained button cells in a conventional environment for 4 h, perform battery charge-discharge capacity tests according to the following steps:

[0282] Charge at 0.2C to 4.55V, charge at constant voltage until cutoff at 0.025C, let it stand for 3 min, then discharge at 0.2C to 3.0V, obtain the charge-discharge curve, and record the initial charge capacity per gram C0 and the initial discharge capacity per gram D0.

[0283] 2) Test the cycle performance of the battery according to the following steps:

[0284] At 25°C, charge at a constant current of 1C to 4.50V, then charge at a constant voltage of 0.05C to 4.50V, and then discharge at a discharge rate of 1C to 3.0V. Repeat this charge-discharge cycle 200 times, and measure the discharge capacity Q at the first cycle 1 and the discharge capacity Q at the 200th cycle 200 .

[0285] Calculate the capacity retention rate Q after 200 cycles according to the following formula.

[0286] Capacity retention rate Q = Q 200 / Q 1 *100%

[0287] The relevant data is shown in Table 5.

[0288] Table 5 Test results of coin cells

[0289]

[0290] It can be seen from the analysis results of the electrochemical performance of each example and comparative example that the doped cathode precursor of the embodiment of the present invention can have good cycle performance and capacity at the same time.

[0291] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and 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 doped positive electrode precursor, characterized in that: The doped positive electrode precursor includes an inner layer, a middle layer and an outer layer in the radial direction from the inside to the outside, the porosity of the inner layer is greater than the porosity of the middle layer, the porosity of the middle layer is less than or equal to the porosity of the outer layer, and the outer layer includes a radial channel.

2. The doped positive electrode precursor according to claim 1, characterized in that: The porosity of the inner layer is 10% to 15%, the porosity of the middle layer is 1% to 5%, and the porosity of the outer layer is 5% to 10%.

3. The doped positive electrode precursor according to claim 1 or 2, characterized in that The porosity of the doped positive electrode precursor is 2% to 8%; And / or, radial dimensions of the inner layer, the middle layer and the outer layer are R1, R2 and R3 respectively, R1 is 0.6-1.3 μm, R2 is 0.4-0.8 μm, and R3 is 0.3-0.8 μm.

4. The doped positive electrode precursor according to any one of claims 1 to 3, characterized in that: The thickness of the primary particles in the inner layer is 10-50 nm, the thickness of the primary particles in the middle layer is 400-600 nm, and the thickness of the primary particles in the outer layer is 300-400 nm.

5. The doped positive electrode precursor according to any one of claims 1 to 4, characterized in that: The chemical formula of the doped positive electrode precursor is: (Ni a Co b Mn c )M d (OH)2, wherein 0.8≤a<1.0, 0<b≤0.1, 0<c≤0.1, a+b+c+d=1, 0<d≤0.05, and M includes one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo; And / or, the mass percentage of the doping element in the doped positive electrode precursor is 1000-8000 ppm; And / or, the tap density of the doped positive electrode precursor is 1.7-2.0 g / cm 3 ; And / or, the specific surface area of ​​the doped positive electrode precursor is greater than or equal to 4m 2 / g and less than 10m 2 / g; And / or, the D50 of the doped positive electrode precursor is 3.0-4.0 μm, and the SPAN is 0.6-1.2; And / or, the length of the radial channel is 90-220 nm; And / or, the sphericity of the doped positive electrode precursor is greater than or equal to 0.9 and less than 1.

0.

6. A method for preparing a doped positive electrode precursor according to any one of claims 1 to 5, characterized in that: include: A raw material system including ammonia water, an alkaline solution, and a metal salt solution is introduced into the bottom liquid, and the reaction system is subjected to a first coprecipitation reaction at an ammonia value of A1, a pH of B1, and a flow rate of the metal salt solution of C1 to obtain a first product; After the D50 of the first product reaches the expected particle size, gradually increasing the ammonia value of the reaction system, lowering the pH of the reaction system, controlling the flow rate of the metal salt solution to C2, and allowing the reaction system to undergo a second coprecipitation reaction to obtain a second product; After the D50 of the second product reaches the expected particle size, the reaction system is subjected to a third coprecipitation reaction at an ammonia value of A3, a pH of B3, and a flow rate of the metal salt solution of C3 to obtain the doped positive electrode precursor; Among them, A1<A3, B1>B3, C1<C2<C3.

7. The method for preparing a doped positive electrode precursor according to claim 6, characterized in that: A1 is 2.5~3.5g / L, A3 is 5.5~6.5g / L; and / or, B1 is 11.60-11.80, B3 is 11.40-11.50; And / or, C1 is 1.0~2.0g / L, C2 is 3.5~4.5g / L, and C3 is 7.0~8.0g / L.

8. The method for preparing a doped positive electrode precursor according to claim 6 or 7, characterized in that: The base liquid has an ammonia value of 1-4 g / L and a pH of 11.6-12.0; and / or, the temperature of the reaction system is 40-70°C; And / or, the metal salt solution comprises a mixed solution of nickel, cobalt and manganese with a total molar concentration of 1.0 to 2.5 mol / L, the molar ratio of nickel, cobalt and manganese is a:b:c, 0.8≤a<1.0, 0<b≤0.1, 0<c≤0.1, and a+b+c=1; And / or, the metal salt solution includes doping elements, and the doping elements include one or more of Zr, La, Al, Ce, Ta, Ti, Y, Sr, W, and Mo.

9. A positive electrode active material, characterized in that: The positive electrode active material is a doped positive electrode active material, and the positive electrode active material includes an inner layer, a middle layer and an outer layer in the radial direction from the inside to the outside, the porosity of the inner layer is greater than the porosity of the middle layer, the porosity of the middle layer is less than or equal to the porosity of the outer layer, and the outer layer includes a radial channel.

10. The positive electrode active material according to claim 9, characterized in that The positive electrode active material is formed by the doped positive electrode precursor according to any one of claims 1 to 5 or the doped positive electrode precursor prepared by the preparation method according to any one of claims 6 to 8.

11. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the positive electrode active material according to claim 9 or 10.

12. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 11.

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