Positive electrode material precursor and preparation method and application thereof

Abstract

The invention provides a positive electrode material precursor and a preparation method and application thereof. The preparation method comprises the following steps: a first stage: introducing a ternary metal salt solution, a complexing agent and a precipitator into a first reaction kettle, and carrying out nucleation growth to obtain a core solution; in the second stage, the core solution is transferred into a second reaction kettle, and a ternary metal salt solution, a complexing agent and a precipitator are introduced for a growth reaction until the particles grow to the target particle size in the second stage; and a third stage: keeping the introduction of each raw material solution in the second stage, and introducing the doped metal salt solution to continue the growth reaction until the growth particle size of the particles reaches the target particle size in the third stage, thereby obtaining the positive electrode material precursor. According to the invention, a reaction container transfer means is utilized, so that the doping elements are intensively doped into the shell layer of the particles in the coprecipitation process, the maximized doping effect is realized in the most efficient mode and at the lowest cost, and the electrochemical performance of the positive electrode material is remarkably improved.

Description

Technical Field

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

[0002] Nickel-rich layered cathode materials are considered to be the most promising candidate materials that can meet the needs of new energy vehicles and energy storage systems. In particular, LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) layered materials have become a hot topic in the research and commercialization of lithium-ion batteries (LIBs) due to their high energy density and environmentally friendly properties. However, NCM811 materials still have some problems during the cycle process, such as Li + / Ni 2+ Problems such as cation disorder, irreversible structural degradation, lithium residue and oxygen release can lead to severe capacity fading, poor rate performance, thermal instability, structural instability and a series of safety issues.

[0003] To address these issues, researchers have proposed improvements such as surface coatings and bulk doping. For surface coatings, these typically consist of lithium ion conductors (such as Li3VO4, Li3PO4, LaPO4, LiAIO2, Li2ZrO3, Li2SiO3, or Li2TiO3), electronically conductive materials (such as PPy or PANI), and thermally or structurally stable materials (such as SiO2, AlPO4, AlF3, Al2O3, LiF, or V2O5). For bulk doping, the dopant typically consists of non-metallic anions (such as F) and metal cations (such as Al, Mg, Cr, Ti, or La).

[0004] Specifically, there are two ways to introduce dopants: one is dry doping, which involves mixing the dopant with the precursor and lithium source, and diffusing it into the cathode during heat treatment to achieve doping; the other is wet doping, which involves incorporating the dopant during the co-precipitation process of the precursor synthesis to achieve doping. Due to their respective process differences, there are significant differences between the two doping methods. In the case of dry doping, the dopant diffuses from the outside to the inside at high temperatures, which makes it challenging to concentrate the dopant in specific areas where its effect can be maximized. In contrast, wet doping can distribute the dopant throughout the particle, but due to its process characteristics, it also allows the dopant to be concentrated in the desired location, i.e., the core or shell region of the particle. Since most dopants are electrochemically inactive, their presence in places where they cannot produce a doping effect can actually worsen the electrochemical performance of the cathode material.

[0005] Therefore, how to maximize the doping effect in the most efficient way and at the lowest cost to improve the electrochemical performance of the positive electrode material is a technical problem that needs to be solved urgently. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a positive electrode material precursor and its preparation method and application. The present invention fully utilizes the advantages of the wet doping process, and utilizes the means of transferring the reaction vessel in the process of growing the shell layer, so that the doping elements are concentratedly incorporated into the shell layer of the particles during the co-precipitation process. The process is simple, and the maximum doping effect is achieved in the most efficient way and at the lowest cost. It not only helps to grow precursor particles with uniform radial distribution and better sphericity, but also the content of doping elements in the shell layer can be gradiently changed along the thickness direction of the shell, which is beneficial to improve the transmission rate of lithium ions. After sintering, the positive electrode material precursor prepared by this method forms a LiM2O4-type spinel crystal structure on the surface of the shell, and the primary particles in the positive electrode material are radially arranged rod-shaped particles, which helps to dissipate the stress caused by the anisotropic volume expansion during the cycle of the positive electrode material, significantly inhibits the formation of microcracks, and is also beneficial to Li + The shell can effectively prevent the penetration of electrolyte, inhibit the occurrence of side reactions, and improve its cycle performance.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a cathode material precursor, the preparation method comprising the following steps:

[0009] The first stage: the ternary metal salt solution, the complexing agent and the precipitant are introduced into the first reaction kettle to carry out nucleation growth to obtain a core solution.

[0010] The second stage: the core solution is transferred to a second reactor, and a ternary metal salt solution, a complexing agent and a precipitant are introduced to carry out a growth reaction until the particles grow to the target particle size of the second stage.

[0011] The third stage: keep introducing the raw material solutions in the second stage, and then introduce the doping metal salt solution to continue the growth reaction until the growth particle size of the particles reaches the target particle size of the third stage, thereby obtaining the positive electrode material precursor.

[0012] The present invention fully utilizes the advantages of the wet doping process, and utilizes the means of transferring the reaction vessel in the process of growing the shell layer, so that the doping elements are concentratedly incorporated into the shell layer of the particles during the co-precipitation process. The process is simple, and the maximum doping effect is achieved in the most efficient way and at the lowest cost. It not only helps to grow precursor particles with uniform radial distribution and better sphericity, but also the content of the doping elements in the shell layer can be gradiently varied along the thickness direction of the shell, which is beneficial to improving the transmission rate of lithium ions. After sintering, the positive electrode material precursor prepared based on this method forms a LiM2O4 type spinel crystal structure on the surface of the shell, and the primary particles in the positive electrode material are radially arranged rod-shaped particles, which helps to dissipate the stress caused by the anisotropic volume expansion during the cycle of the positive electrode material, significantly inhibits the formation of microcracks, and is also beneficial to Li + The shell can effectively prevent the penetration of electrolyte, inhibit the occurrence of side reactions, and improve its cycle performance.

[0013] Preferably, the ternary metal salt solution is a nickel-cobalt-manganese mixed salt solution.

[0014] Preferably, the preparation method of the nickel-cobalt-manganese mixed salt solution comprises:

[0015] A nickel-containing salt solution, a cobalt-containing salt solution, and a manganese-containing salt solution are mixed to obtain a nickel-containing salt solution.

[0016] Preferably, the nickel-containing salt solution includes any one of nickel sulfate, nickel nitrate, nickel acetate or nickel chloride, or a combination of at least two thereof, preferably nickel sulfate.

[0017] Preferably, the cobalt-containing salt solution comprises any one of cobalt sulfate, cobalt nitrate, cobalt acetate or cobalt chloride, or a combination of at least two thereof, preferably cobalt sulfate.

[0018] Preferably, the manganese-containing salt solution comprises any one of manganese sulfate, manganese nitrate, manganese acetate or manganese chloride, or a combination of at least two thereof, preferably manganese sulfate.

[0019] Preferably, the total concentration of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution is 50-200 g / L, for example, 50 g / L, 100 g / L, 150 g / L or 200 g / L.

[0020] Preferably, in the nickel-cobalt-manganese mixed salt solution, the molar ratio of nickel element, cobalt element and manganese element is (50-90):(1-25):(1-25), wherein the selection range of nickel element "50-90" can be, for example, 50, 60, 70, 80 or 90, etc., the selection range of cobalt element "1-25" can be, for example, 1, 5, 10, 15, 20 or 25, etc., and the selection range of manganese element "1-25" can be, for example, 1, 5, 10, 15, 20 or 25, etc.

[0021] Preferably, the precipitant comprises any one of sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution, or a combination of at least two of them.

[0022] Preferably, the complexing agent comprises any one or a combination of at least two of ammonia, oxalic acid or citric acid.

[0023] Preferably, the doping element in the doped metal salt solution includes any one or a combination of at least two of aluminum, titanium, niobium, zirconium, tungsten, vanadium, strontium, gallium, cerium, yttrium, lanthanum, antimony or boron, preferably yttrium.

[0024] Since yttrium oxide can react with lithium residues on the surface of the positive electrode material to form LiYO2, the LiYO2 residing on the particle surface acts as an electrode protective film and is also a lithium ion conductor. 3+ Can significantly expand Li + The diffusion channel of YO is enhanced and the structural stability is enhanced because the binding energy of YO is stronger than that of Ni, Co, Mn and oxygen. 3+ Doping can promote the formation of lithium-rich layered oxides Li[Li 0.2 Ni 0.534 Co 0.133 Mn 0.133 ]O2 and LiNi 0.33 Co 0.33 Mn 0.33 The cycling stability, electronic conductivity and initial Coulombic efficiency of O2 materials. Based on the above analysis, it can be seen that yttrium modification plays a significant positive role in improving the comprehensive performance of lithium-ion battery cathode materials.

[0025] Preferably, the anions in the doping metal salt solution include chloride ions.

[0026] Preferably, the concentration of the doped metal salt solution is 20-50 g / L, for example, 20 g / L, 30 g / L, 40 g / L or 50 g / L.

[0027] Preferably, in the first stage, the feed flow rate of the ternary metal salt solution is 2-4 L / h, for example, it can be 2 L / h, 2.5 L / h, 3 L / h, 3.5 L / h or 4 L / h, etc., the feed flow rate of the complexing agent is 200-400 mL / h, for example, it can be 200 mL / h, 250 mL / h, 300 mL / h, 350 mL / h or 400 mL / h, etc., and the feed flow rate of the precipitant is 1-2 L / h, for example, it can be 1 L / h, 1.2 L / h, 1.4 L / h, 1.6 L / h, 1.8 L / h or 2 L / h, etc.

[0028] Preferably, in the first stage, the pH of the reaction system is controlled in the range of 11.5-12, for example, 11.5, 11.6, 11.7, 11.8, 11.9 or 12.

[0029] In the first stage of the present invention, the pH of the reaction system can be stabilized by adjusting the flow rates of the ternary liquid and the precipitant.

[0030] Preferably, in the first stage, the concentration of the complexing agent in the reaction system is controlled at 7-9 g / L, for example, 7 g / L, 7.5 g / L, 8 g / L, 8.5 g / L or 9 g / L.

[0031] In the first stage of the present invention, the concentration of the complexing agent in the reaction system can be adjusted by changing the flow rate of the complexing agent during the reaction.

[0032] In the first stage of the present invention, the pH of the reaction system is controlled within a range of 11.5-12, and the concentration of the complexing agent is controlled within a range of 7-9 g / L, which can maintain the stability of the system, promote uniform nucleation, and enable orderly growth of crystal nuclei.

[0033] Preferably, the nucleation and growth process is accompanied by stirring, and the stirring rate is 300-400 rpm, for example, 300 rpm, 350 rpm or 400 rpm.

[0034] Preferably, the growth temperature of the nucleation growth is 40-80°C, for example, 40°C, 50°C, 60°C, 70°C or 80°C.

[0035] Preferably, in the core solution, the particle size D50 of the core particles is 3.5-4 μm, for example, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm or 4 μm.

[0036] Preferably, a bottom liquid is further provided in the first reaction kettle.

[0037] Preferably, the method for preparing the base liquid includes:

[0038] The precipitant, the complexing agent and water are mixed to obtain the base solution.

[0039] Preferably, before the nucleation growth, the pH value of the base liquid is 11.2-12, for example, it can be 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9 or 12, etc., the concentration of the complexing agent is 4-8 g / L, for example, it can be 4 g / L, 5 g / L, 6 g / L, 7 g / L or 8 g / L, etc., and the temperature is controlled at 40-60°C, for example, it can be 40°C, 50°C or 60°C, etc.

[0040] Preferably, nitrogen is introduced during the mixing process, and the nitrogen flow rate is 0.5-2m 3 / h, for example, it can be 0.5m 3 / h、1m 3 / h、1.5m 3 / h or 2m 3 / h, etc.

[0041] In the present invention, nitrogen is introduced during the mixing process to maintain a low-oxygen environment inside the system and inhibit oxidation of materials during the reaction.

[0042] Preferably, the feed flow rates of the ternary metal salt solution, the complexing agent and the precipitant in the second stage are all greater than the feed flow rates of the ternary metal salt solution, the complexing agent and the precipitant in the first stage.

[0043] In the present invention, after replacing the reactor, the feed flow rates of the ternary metal salt solution, the complexing agent and the precipitant in the second stage are adjusted to be greater than the feed flow rates of the ternary metal salt solution, the complexing agent and the precipitant in the first stage, which serves to maintain the stability of the growth over time during the reaction process.

[0044] Preferably, in the second stage, the feed flow rate of the ternary metal salt solution is 4-8 L / h, for example, it can be 4 L / h, 5 L / h, 6 L / h, 7 L / h or 8 L / h, etc., the feed flow rate of the complexing agent is 600-1000 mL / h, for example, it can be 600 mL / h, 700 mL / h, 800 mL / h, 900 mL / h or 1000 mL / h, etc., and the feed flow rate of the precipitant is 2.5-4 L / h, for example, it can be 2.5 L / h, 3 L / h, 3.5 L / h or 4 L / h, etc.

[0045] Preferably, in the second stage, the pH of the reaction system is controlled in the range of 9.5-10, for example, 9.5, 9.6, 9.7, 9.8, 9.9 or 10.

[0046] Preferably, there is no bottom liquid in the second reaction kettle.

[0047] Preferably, in the second stage, water is introduced into the core solution for dilution during the process of adding the core solution into the second reactor, so as to control the reaction rate of the second stage and regulate the pH of the reaction system.

[0048] Preferably, in the second stage, the concentration of the complexing agent in the reaction system is controlled at 3-5 g / L, for example, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L or 5 g / L.

[0049] The present invention defines that in the second stage, the pH control range of the reaction system is reduced to 9.5-10, and the concentration of the complexing agent is controlled at 3-5g / L, which controls the reaction rate so that the overall reaction speed remains consistent and obtains primary particles with more uniform growth.

[0050] Preferably, in the second stage, the growth temperature of the growth reaction is 40-80°C, for example, 40°C, 50°C, 60°C, 70°C or 80°C.

[0051] Preferably, in the second stage, the growth reaction is accompanied by stirring, and the stirring rate is 200-300 rpm, for example, 200 rpm, 250 rpm or 300 rpm.

[0052] Preferably, the target particle size in the second stage refers to a particle size D50 reaching 8-11 μm, for example, 8 μm, 9 μm, 10 μm or 11 μm.

[0053] Preferably, in the third stage, the feed flow rate of the doping metal salt solution is 100-500 mL / h, for example, 100 mL / h, 200 mL / h, 300 mL / h, 400 mL / h or 500 mL / h.

[0054] In the present invention, the feed flow rate of the doping metal salt solution is limited to a stable value and is selected within the range of 100-500 mL / h, which helps to improve the distribution uniformity and concentration of the doping metal elements in the shell layer and optimize the electrochemical properties of the material.

[0055] Preferably, in the third stage, the pH of the reaction system is controlled in the range of 10-10.5, for example, 10, 10.1, 10.2, 10.3, 10.4 or 10.5.

[0056] In the present invention, the pH of the reaction system is controlled within the range of 10-10.5 in the third stage, so that the morphology of the primary particles is more compact, which helps to obtain a shell layer with better compactness.

[0057] Preferably, in the third stage, the concentration of the complexing agent in the reaction system is controlled at 3-5 g / L, for example, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L or 5 g / L.

[0058] The present invention defines that in the second stage, the pH control range of the reaction system is 10-10.5, and the concentration of the complexing agent is controlled at 3-5g / L, which controls the reaction rate so that the overall reaction speed remains consistent and obtains primary particles with more uniform growth.

[0059] Preferably, in the third stage, the reaction temperature of the growth reaction is 40-80°C, for example, 40°C, 50°C, 60°C, 70°C or 80°C.

[0060] Preferably, in the third stage, the growth reaction is accompanied by stirring, and the stirring rate is 100-200 rpm, for example, 100 rpm, 150 rpm or 200 rpm.

[0061] In the present invention, regulating the stirring rate of the growth reaction in the third stage within a reasonable range helps to improve the distribution of the doping elements in the shell, enhance the morphological consistency of the particles, and improve the cyclic stability of the material.

[0062] Preferably, the target particle size in the third stage refers to a particle size D50 reaching 11-14 μm, for example, 11 μm, 12 μm, 12.5 μm, 13 μm or 14 μm.

[0063] It should be noted that the thickness of the shell layer grown in the third stage is the thickness of the layer containing the doping element.

[0064] Preferably, the preparation method comprises the following steps:

[0065] (1) preparing a nickel-cobalt-manganese mixed salt solution, a doping metal salt solution, a complexing agent, a precipitant, and a base solution respectively; in the nickel-cobalt-manganese mixed salt solution, the total concentration of nickel, cobalt, and manganese is 50-200 g / L, and the molar ratio of nickel, cobalt, and manganese is (50-90):(0-25):(0-25); the concentration of the doping metal salt solution is 20-50 g / L; the mass concentration of the complexing agent is 5-15% (for example, 5%, 10%, or 15%), and the mass concentration of the precipitant is 15-25% (for example, 15%, 20%, or 25%); the preparation method of the base solution comprises:

[0066] The precipitant, complexing agent and water are stirred and mixed at a speed of 100-200 rpm, and then the temperature is raised to 40-60°C, and the pH value is controlled to be 11.2-12 to obtain the base liquid; the concentration of the complexing agent in the base liquid is 4-8 g / L, and nitrogen is also introduced during the stirring and mixing process, and the nitrogen introduction flow rate is 0.5-2 m 3 / h.

[0067] (2) The first stage: a nickel-cobalt-manganese mixed salt solution, a complexing agent, and a precipitant are simultaneously introduced into a first reactor containing the base liquid, the pH of the reaction system is controlled to be 11.5-12, the concentration of the complexing agent is controlled to be 7-9 g / L, and nucleation growth is carried out at a rate of 300-400 rpm and a growth temperature of 40-80°C to obtain a core solution with a particle size D50 of 3.5-4 μm.

[0068] In the first stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 2-4 L / h, the feed flow rate of the complexing agent is 200-400 mL / h, and the feed flow rate of the precipitant is 1-2 L / h.

[0069] (3) Second stage: The core solution is transferred to a second reactor without bottom liquid, and a nickel-cobalt-manganese mixed salt solution, a chelating agent, and a precipitant are introduced in parallel to carry out a growth reaction. The pH of the reaction system is controlled in the range of 9.5-10, and the concentration of the chelating agent in the reaction system is controlled in the range of 3-5 g / L until the particles grow to the target particle size of the second stage.

[0070] In the second stage, the feed rate of the nickel-cobalt-manganese mixed salt solution is 4-8 L / h, the feed rate of the complexing agent is 600-1000 mL / h, and the feed rate of the precipitant is 2.5-4 L / h; the reaction temperature of the growth reaction is 60-100°C; the growth reaction is accompanied by stirring, and the stirring rate is 200-300 rpm; the target particle size in the second stage refers to a particle size D50 reaching 8-11 μm.

[0071] (4) Maintain the flow of the raw material solutions in the second stage, and then introduce the doped metal salt solution to continue the growth reaction. The pH of the reaction system is controlled in the range of 10-10.5, and the concentration of the complexing agent in the reaction system is controlled in the range of 3-5 g / L until the growth particle size of the particles reaches the target particle size of the third stage, thereby obtaining a precursor precipitate.

[0072] In the third stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 4-8 L / h, the feed flow rate of the complexing agent is 600-1000 mL / h, the feed flow rate of the precipitant is 2.5-4 L / h, and the feed flow rate of the doped metal salt solution is 100-500 mL / h; the reaction temperature of the growth reaction is 40-80°C; the growth reaction is accompanied by stirring, and the stirring rate is 100-200 rpm; the target particle size in the third stage refers to a particle size D50 reaching 11-14 μm.

[0073] (5) Aging and washing the precursor precipitate, and then drying it at 100-200° C. (for example, 100° C., 150° C., or 200° C.) to obtain the positive electrode material precursor.

[0074] In a second aspect, the present invention provides a cathode material precursor, which is prepared using the preparation method described in the first aspect.

[0075] The chemical formula of the positive electrode material precursor is Ni a Co b Mn c M d (OH)2, wherein 0.5<a<0.9, 0<b<0.25, 0<c<0.25, 0<d<0.1, a+b+c+d=1, and M is a doping element.

[0076] The positive electrode material precursor comprises a core and a shell covering the surface of the core, and the content of the doping element in the shell changes gradiently in the thickness direction of the shell.

[0077] In the present invention, 0.5<a<0.9, for example, it can be 0.6, 0.7 or 0.8, etc., 0<b<0.25, for example, it can be 0.05, 0.1, 0.15 or 0.2, etc., 0<c<0.25, for example, it can be 0.05, 0.1, 0.15 or 0.2, etc., 0<d<0.1, for example, it can be 0.02, 0.04, 0.06 or 0.08, etc.

[0078] Preferably, based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor as 100%, the doping amount of the doping element is 0.05-5%, for example, it can be 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%.

[0079] In the present invention, an appropriate doping amount is helpful to change the morphology of the primary particles, and the formed uniform loose porous primary particles can effectively dissipate the stress caused by the anisotropic volume expansion during the cycle, significantly inhibiting the formation of microcracks.

[0080] In a third aspect, the present invention provides a positive electrode material, which is obtained by mixing and sintering the positive electrode material precursor described in the second aspect with a lithium source.

[0081] The positive electrode material has a core-shell structure, wherein the core is nickel-cobalt-manganese oxide and the surface of the shell forms a LiM2O4 spinel crystal structure, where M is the doping element; in the positive electrode material, the primary particles are rod-shaped particles arranged radially.

[0082] In the present invention, the radially arranged rod-shaped particles can effectively dissipate the stress caused by the anisotropic volume expansion of the material during the cycle, significantly inhibiting the formation of microcracks, and at the same time, a LiM2O4 type spinel crystal structure is formed on the surface of the rod-shaped particles, which is beneficial to the Li + embedding and ejecting, improving the rate performance of the material.

[0083] Preferably, in the positive electrode material precursor, the ratio of the total molar amount of Ni, Co, Mn and M to the molar amount of lithium in the lithium source is 1:(1.1-1.2), for example, it can be 1:1.1, 1:1.15 or 1:1.2.

[0084] Preferably, the mixed sintering includes a first sintering and a second sintering, and the temperature of the first sintering is lower than the temperature of the second sintering.

[0085] Preferably, the temperature of the first sintering is 400-600°C, for example, 400°C, 500°C or 600°C, etc., the time is 4-6h, for example, 4h, 5h or 6h, etc., and the heating rate is 2-5°C / min, for example, 2°C / min, 3°C / min, 4°C / min or 5°C / min, etc.

[0086] Preferably, the temperature of the second sintering is 800-1100°C, for example, it can be 800°C, 900°C, 1000°C or 1100°C, etc., the time is 8-15h, for example, it can be 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, etc., and the heating rate is 4-8°C / min, for example, it can be 4°C / min, 5°C / min, 6°C / min, 7°C / min, etc. or 8°C / min, etc.

[0087] It should be noted that the present invention does not limit the type of lithium source. For example, it can be lithium carbonate, lithium hydroxide, lithium nitrate or lithium acetate.

[0088] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the positive electrode material as described in the third aspect.

[0089] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0090] Compared with the prior art, the present invention has the following beneficial effects:

[0091] The present invention fully utilizes the advantages of the wet doping process, and utilizes the means of transferring the reaction vessel in the process of growing the shell layer, so that the doping elements are concentratedly incorporated into the shell layer of the particles during the co-precipitation process. The process is simple, and the maximum doping effect is achieved in the most efficient way and at the lowest cost. It not only helps to grow precursor particles with uniform radial distribution and better sphericity, but also the content of the doping elements in the shell layer can be gradiently varied along the thickness direction of the shell, which is beneficial to improving the transmission rate of lithium ions. After sintering, the positive electrode material precursor prepared based on this method forms a LiM2O4 type spinel crystal structure on the surface of the shell, and the primary particles in the positive electrode material are radially arranged rod-shaped particles, which helps to dissipate the stress caused by the anisotropic volume expansion during the cycle of the positive electrode material, significantly inhibits the formation of microcracks, and is also beneficial to Li + The shell can effectively prevent the penetration of electrolyte, inhibit the occurrence of side reactions, and improve its cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 This is a surface SEM image of the positive electrode material precursor prepared in Example 1 of the present invention.

[0093] Figure 2 This is a cross-sectional SEM image of the positive electrode material precursor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0094] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0095] Example 1

[0096] This embodiment provides a method for preparing a positive electrode material precursor, the preparation method comprising the following steps:

[0097] (1) preparing a nickel-cobalt-manganese mixed salt solution, a yttrium chloride solution, a complexing agent, a precipitant and a base solution respectively; the nickel-cobalt-manganese mixed salt solution includes nickel sulfate, cobalt sulfate and manganese sulfate, the total concentration of nickel, cobalt and manganese is 150 g / L, and the molar ratio of nickel, cobalt and manganese is 80:10:10; the concentration of the yttrium chloride solution is 30 g / L; the mass concentration of the complexing agent is 5-15%, and the complexing agent is ammonia water; the mass concentration of the precipitant is 20%, and the precipitant is sodium hydroxide solution; the preparation method of the base solution comprises:

[0098] Sodium hydroxide solution, ammonia water and 500L water were stirred and mixed at a speed of 150rpm, and then heated to 60°C and the pH value was controlled to be 11.6 to obtain the base liquid; the concentration of ammonia water in the base liquid was 7g / L, and nitrogen was also introduced during the stirring and mixing process, and the nitrogen introduction flow rate was 2m 3 / h.

[0099] (2) The first stage: nickel-cobalt-manganese mixed salt solution, ammonia water and sodium hydroxide solution are introduced into the first reactor containing the base liquid in parallel, the pH of the reaction system is controlled to 11.6, the concentration of ammonia water is controlled to 8 g / L, and nucleation growth is carried out at a rate of 350 rpm and a growth temperature of 80°C to obtain a core solution with a particle size D50 of 4 μm.

[0100] In the first stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 3 L / h, the feed flow rate of the ammonia water is 400 mL / h, and the feed flow rate of the sodium hydroxide solution is 1.5 L / h.

[0101] (3) Second stage: The core solution is diluted with water and then transferred to a second reactor without bottom liquid, and nickel-cobalt-manganese mixed salt solution, ammonia water and sodium hydroxide solution are introduced in parallel to carry out growth reaction. The pH of the reaction system is controlled at 9.6, and the concentration of ammonia water in the reaction system is controlled at 4.5 g / L until the particles grow to the target particle size of the second stage.

[0102] In the second stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 6 L / h, the feed flow rate of the ammonia water is 800 mL / h, and the feed flow rate of the sodium hydroxide solution is 3.5 L / h; the reaction temperature of the growth reaction is 80°C; the growth reaction is accompanied by stirring, and the stirring rate is 250 rpm; the target particle size of the second stage refers to the particle size D50 reaching 10 μm.

[0103] (4) Maintain the flow of the raw material solutions in the second stage, and then introduce yttrium chloride solution to continue the growth reaction. The pH of the reaction system is controlled at 10.1, and the concentration of ammonia water in the reaction system is controlled at 3.5 g / L until the growth particle size of the particles reaches the target particle size of the third stage, thereby obtaining a precursor precipitate.

[0104] In the third stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 6 L / h, the feed flow rate of the ammonia water is 800 mL / h, the feed flow rate of the sodium hydroxide solution is 3.5 L / h, and the feed flow rate of the yttrium chloride solution is 300 mL / h; the reaction temperature of the growth reaction is 80°C; the growth reaction is accompanied by stirring, and the stirring rate is 150 rpm; the target particle size of the third stage refers to the particle size D50 reaching 12 μm.

[0105] (5) The precursor precipitate is aged and washed, wherein the washing is performed by alkali washing twice and water washing three times, and then dried at 200° C. to obtain a positive electrode material precursor.

[0106] This embodiment also provides a positive electrode material precursor, the chemical formula of which is Ni a Co b Mn c Y d (OH)2, wherein a=0.7984, b=0.0998, c=0.0998, d=0.002, a+b+c+d=1.

[0107] The positive electrode material precursor comprises a core and a shell covering the surface of the core, and the content of the doping element in the shell changes gradiently in the thickness direction of the shell.

[0108] Based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%, the doping amount of Y is 0.2%.

[0109] This embodiment also provides a positive electrode material, which is obtained by mixing and sintering the positive electrode material precursor as described above and lithium carbonate; the positive electrode material has a core-shell structure, the core is nickel-cobalt-manganese oxide, and the surface of the shell has a LiY2O4-type spinel crystal structure; in the positive electrode material, the primary particles are rod-shaped particles arranged radially.

[0110] In the positive electrode material precursor, the ratio of the total molar amount of Ni, Co, Mn and M to the molar amount of the lithium element in the lithium carbonate is 1:1.15; the mixed sintering includes a first sintering and a second sintering, the temperature of the first sintering is 550°C, the time is 5h, and the heating rate is 3°C / min; the temperature of the second sintering is 1100°C, the time is 9h, and the heating rate is 6°C / min.

[0111] Figure 1 The surface SEM image of the cathode material precursor prepared in this embodiment is shown. It can be seen from the image that the particles of the cathode material precursor are relatively loose and present a flaky structure.

[0112] Figure 2 A cross-sectional SEM image of the cathode material precursor prepared in this embodiment is shown, from which obvious radial distribution characteristics can be observed, which is beneficial for improving the electrochemical performance of the cathode material.

[0113] Example 2

[0114] This embodiment provides a method for preparing a positive electrode material precursor, the preparation method comprising the following steps:

[0115] (1) preparing a nickel-cobalt-manganese mixed salt solution, a yttrium chloride solution, a complexing agent, a precipitant and a base solution respectively; the nickel-cobalt-manganese mixed salt solution includes nickel sulfate, cobalt sulfate and manganese sulfate, the total concentration of nickel, cobalt and manganese is 50 g / L, and the molar ratio of nickel, cobalt and manganese is 80:10:10; the concentration of the yttrium chloride solution is 20 g / L; the mass concentration of the complexing agent is 5%, and the complexing agent is ammonia water; the mass concentration of the precipitant is 15%, and the precipitant is sodium hydroxide solution; the preparation method of the base solution comprises:

[0116] Sodium hydroxide solution, ammonia water and 500L water were stirred and mixed at a speed of 100rpm, and then heated to 50°C and the pH value was controlled to be 11.2 to obtain the base liquid; the concentration of ammonia water in the base liquid was 4g / L, and nitrogen was also introduced during the stirring and mixing process, and the nitrogen introduction flow rate was 0.5m 3 / h.

[0117] (2) The first stage: nickel-cobalt-manganese mixed salt solution, ammonia water and sodium hydroxide solution are introduced into the first reactor containing the base liquid in parallel, the pH of the reaction system is controlled to 11.5, the concentration of ammonia water is controlled to 7 g / L, and nucleation growth is carried out at a rate of 300 rpm and a growth temperature of 60°C to obtain a core solution with a particle size D50 of 3.5 μm.

[0118] In the first stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 2 L / h, the feed flow rate of the ammonia water is 200 mL / h, and the feed flow rate of the sodium hydroxide solution is 1 L / h.

[0119] (3) Second stage: The core solution is transferred to a second reactor, and a nickel-cobalt-manganese mixed salt solution, ammonia water, and sodium hydroxide solution are introduced in parallel to carry out a growth reaction. The pH of the reaction system is controlled within a range of 9.7, and the concentration of ammonia water in the reaction system is controlled at 4.5 g / L until the particles grow to the target particle size of the second stage.

[0120] In the second stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 4 L / h, the feed flow rate of the ammonia water is 600 mL / h, and the feed flow rate of the sodium hydroxide solution is 2.5 L / h; the reaction temperature of the growth reaction is 60°C; the growth reaction is accompanied by stirring, and the stirring rate is 250 rpm; the target particle size of the second stage refers to the particle size D50 reaching 11 μm.

[0121] (4) The introduction of each raw material liquid in the second stage is maintained, and yttrium chloride solution is introduced to continue the growth reaction. The pH of the reaction system is controlled within a range of 10.2, and the concentration of ammonia water in the reaction system is controlled at 4 g / L until the growth particle size of the particles reaches the target particle size of the third stage, thereby obtaining a precursor precipitate.

[0122] In the third stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 4 L / h, the feed flow rate of the ammonia water is 600 mL / h, the feed flow rate of the sodium hydroxide solution is 2.5 L / h, and the feed flow rate of the yttrium chloride solution is 100 mL / h; the reaction temperature of the growth reaction is 60°C; the growth reaction is accompanied by stirring, and the stirring rate is 150 rpm; the target particle size of the third stage refers to the particle size D50 reaching 14 μm.

[0123] (5) The precursor precipitate is aged and washed, wherein the washing is performed by alkali washing twice and water washing three times, and then dried at 200° C. to obtain a positive electrode material precursor.

[0124] This embodiment also provides a positive electrode material precursor, the chemical formula of which is Ni a Co b Mn c Y d (OH)2, wherein a=0.7984, b=0.0998, c=0.0998, d=0.002, a+b+c+d=1.

[0125] The positive electrode material precursor comprises a core and a shell covering the surface of the core, and the content of the doping element in the shell changes gradiently in the thickness direction of the shell.

[0126] Based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%, the doping amount of Y is 0.2%.

[0127] This embodiment also provides a positive electrode material, which is obtained by mixing and sintering the positive electrode material precursor as described above and lithium carbonate; the positive electrode material has a core-shell structure, the core is nickel-cobalt-manganese oxide, and the surface of the shell has a LiY2O4-type spinel crystal structure; in the positive electrode material, the primary particles are rod-shaped particles arranged radially.

[0128] In the positive electrode material precursor, the ratio of the total molar amount of Ni, Co, Mn and M to the molar amount of lithium element in the lithium carbonate is 1:1.1; the mixed sintering includes a first sintering and a second sintering, the temperature of the first sintering is 400°C, the time is 6 hours, and the heating rate is 2°C / min; the temperature of the second sintering is 900°C, the time is 12 hours, and the heating rate is 4°C / min.

[0129] Example 3

[0130] This embodiment provides a method for preparing a positive electrode material precursor, the preparation method comprising the following steps:

[0131] (1) preparing a nickel-cobalt-manganese mixed salt solution, a yttrium chloride solution, a complexing agent, a precipitant and a base solution respectively; the nickel-cobalt-manganese mixed salt solution includes nickel sulfate, cobalt sulfate and manganese sulfate, the total concentration of nickel element, cobalt element and manganese element is 200 g / L, and the molar ratio of nickel element, cobalt element and manganese element is 80:10:10; the concentration of the yttrium chloride solution is 50 g / L; the mass concentration of the complexing agent is 15%, and the complexing agent is ammonia water; the mass concentration of the precipitant is 25%, and the precipitant is sodium hydroxide solution; the preparation method of the base solution comprises:

[0132] Sodium hydroxide solution, ammonia water and 500L water were stirred and mixed at a speed of 200rpm, and then heated to 40°C and the pH value was controlled to be 12 to obtain the base liquid; the concentration of ammonia water in the base liquid was 8g / L, and nitrogen was also introduced during the stirring and mixing process, and the nitrogen introduction flow rate was 1m 3 / h.

[0133] (2) The first stage: nickel-cobalt-manganese mixed salt solution, ammonia water and sodium hydroxide solution are introduced into the first reactor containing the base liquid in parallel, the pH of the reaction system is controlled to 11.8, the concentration of ammonia water is controlled to 9 g / L, and nucleation growth is carried out at a rate of 40 rpm and a growth temperature of 100°C to obtain a core solution with a particle size D50 of 4 μm.

[0134] In the first stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 4 L / h, the feed flow rate of the ammonia water is 300 mL / h, and the feed flow rate of the sodium hydroxide solution is 2 L / h.

[0135] (3) Second stage: The core solution is transferred to a second reactor, and a nickel-cobalt-manganese mixed salt solution, ammonia water, and sodium hydroxide solution are introduced in parallel to carry out a growth reaction. The pH of the reaction system is controlled within a range of 9.8, and the concentration of ammonia water in the reaction system is controlled at 5 g / L until the particles grow to the target particle size of the second stage.

[0136] In the second stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 8 L / h, the feed flow rate of the ammonia water is 1000 mL / h, and the feed flow rate of the sodium hydroxide solution is 4 L / h; the reaction temperature of the growth reaction is 40°C; the growth reaction is accompanied by stirring, and the stirring rate is 250 rpm; the target particle size of the second stage refers to the particle size D50 reaching 8 μm.

[0137] (4) Maintaining the introduction of each raw material solution in the second stage, and then introducing yttrium chloride solution to continue the growth reaction, the pH control range of the reaction system is 10, and the concentration of ammonia water in the reaction system is controlled at 3 g / L until the growth particle size of the particles reaches the target particle size of the third stage, thereby obtaining a precursor precipitate.

[0138] In the third stage, the feed flow rate of the nickel-cobalt-manganese mixed salt solution is 8 L / h, the feed flow rate of the ammonia water is 1000 mL / h, the feed flow rate of the sodium hydroxide solution is 4 L / h, and the feed flow rate of the yttrium chloride solution is 500 mL / h; the reaction temperature of the growth reaction is 40°C; the growth reaction is accompanied by stirring, and the stirring rate is 150 rpm; the target particle size of the third stage refers to the particle size D50 reaching 11 μm.

[0139] (5) The precursor precipitate is aged and washed, wherein the washing is performed by alkali washing twice and water washing three times, and then dried at 200° C. to obtain a positive electrode material precursor.

[0140] This embodiment also provides a positive electrode material precursor, the chemical formula of which is Ni a Co b Mn c Y d (OH)2, wherein a=0.7984, b=0.0998, c=0.0998, d=0.002, a+b+c+d=1.

[0141] The positive electrode material precursor comprises a core and a shell covering the surface of the core, and the content of the doping element in the shell changes gradiently in the thickness direction of the shell.

[0142] Based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%, the doping amount of Y is 0.2%.

[0143] This embodiment also provides a positive electrode material, which is obtained by mixing and sintering the positive electrode material precursor as described above and lithium carbonate; the positive electrode material has a core-shell structure, the core is nickel-cobalt-manganese oxide, and the surface of the shell has a LiY2O4-type spinel crystal structure; in the positive electrode material, the primary particles are rod-shaped particles arranged radially.

[0144] In the positive electrode material precursor, the ratio of the total molar amount of Ni, Co, Mn and M to the molar amount of lithium element in the lithium carbonate is 1:1.2; the mixed sintering includes a first sintering and a second sintering, the temperature of the first sintering is 600°C, the time is 4h, and the heating rate is 5°C / min; the temperature of the second sintering is 800°C, the time is 15h, and the heating rate is 8°C / min.

[0145] Example 4

[0146] The difference between this embodiment and embodiment 1 is that the feed flow rate of the yttrium chloride solution in the third stage reaction is adjusted so that the doping amount of Y in the positive electrode material precursor is 0.05% (based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%).

[0147] The rest of the preparation methods and parameters remained the same as in Example 1.

[0148] Example 5

[0149] The difference between this embodiment and embodiment 1 is that the feed flow rate of the yttrium chloride solution in the third stage reaction is adjusted so that the doping amount of Y in the positive electrode material precursor is 0.5% (based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%).

[0150] The rest of the preparation methods and parameters remained the same as in Example 1.

[0151] Example 6

[0152] The difference between this embodiment and Example 1 is that the feed flow rate of the yttrium chloride solution in the third stage reaction is adjusted so that the doping amount of Y in the positive electrode material precursor is 2% (based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor as 100%).

[0153] The rest of the preparation methods and parameters remained the same as in Example 1.

[0154] Example 7

[0155] The difference between this embodiment and embodiment 1 is that the target particle size in the third stage refers to a particle size D50 reaching 11 μm.

[0156] The rest of the preparation methods and parameters remained the same as in Example 1.

[0157] Example 8

[0158] The difference between this embodiment and embodiment 1 is that the target particle size in the third stage refers to a particle size D50 reaching 14 μm.

[0159] The rest of the preparation methods and parameters remained the same as in Example 1.

[0160] Example 9

[0161] The difference between this embodiment and Example 1 is that the feed flow rate of the yttrium chloride solution in the third stage reaction is adjusted so that the doping amount of Y in the positive electrode material precursor is 0.02% (based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%).

[0162] The rest of the preparation methods and parameters remained the same as in Example 1.

[0163] Example 10

[0164] The difference between this embodiment and Example 1 is that the feed flow rate of the yttrium chloride solution in the third stage reaction is adjusted so that the doping amount of Y in the positive electrode material precursor is 6% (based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%).

[0165] The rest of the preparation methods and parameters remained the same as in Example 1.

[0166] Example 11

[0167] The difference between this embodiment and embodiment 1 is that nitrogen is not introduced during the preparation of the base liquid.

[0168] The rest of the preparation methods and parameters remained the same as in Example 1.

[0169] Example 12

[0170] The difference between this embodiment and embodiment 1 is that the pH of the reaction system in step (4) is 9.5.

[0171] The rest of the preparation methods and parameters remained the same as in Example 1.

[0172] Example 13

[0173] The difference between this embodiment and embodiment 1 is that the pH of the reaction system in step (4) is 11.

[0174] The rest of the preparation methods and parameters remained the same as in Example 1.

[0175] Comparative Example 1

[0176] The difference between this comparative example and Example 1 is that the step of transferring to the second reactor in step (3) is omitted, and the second stage is directly continued in the first reactor.

[0177] The rest of the preparation methods and parameters remained the same as in Example 1.

[0178] Performance Testing

[0179] The positive electrode material obtained in the above embodiments and comparative examples was used as the positive electrode active material, and was mixed with conductive carbon and PVDF in a mass ratio of 97:1.5:1.5. The obtained mixture was then dispersed in a solvent, methyl pyrrolidone, to obtain a positive electrode slurry, which was then coated on an aluminum foil. After coating, the current collector was punched to obtain a coin-shaped electrode, which was vacuum-dried at 120°C overnight to obtain a positive electrode sheet. Metallic lithium was selected as the negative electrode. LiPF6 was dissolved in EC and DMC solvents (volume ratio of 3:7) to obtain an electrolyte with a concentration of 1 mol / L. The diaphragm was a polypropylene diaphragm. The positive electrode, negative electrode and diaphragm were wound to prepare a battery cell, which was then assembled into a lithium-ion battery through packaging, liquid injection, formation, and volume separation.

[0180] The prepared lithium-ion battery was subjected to electrochemical performance tests: at 0.2C, the + ) and measured the initial discharge capacity and efficiency, as well as the capacity retention after 100 cycles.

[0181] The test results are shown in Table 1.

[0182] Table 1

[0183]

[0184]

[0185] analyze:

[0186] As shown in Table 1, the present invention fully utilizes the advantages of the wet doping process and utilizes the transfer of the reaction vessel during the shell growth process to centrally incorporate the doping element into the particle shell during the coprecipitation process. This simple process achieves the maximum doping effect in the most efficient manner at the lowest cost. The cathode material prepared based on this method exhibits excellent electrochemical performance.

[0187] By comparing Example 1 with Examples 9-10, it can be seen that if the doping amount of Y in the positive electrode material precursor is too small, the improvement of the transition metal ion interlayer spacing is limited, and the doping effect is not achieved, and the material performance is poor; if the doping amount of Y in the positive electrode material precursor is too large, more transition metal ion sites will be occupied, the discharge capacity of the material will be limited, and the lattice distortion effect will also deteriorate the electrochemical performance.

[0188] From the comparison between Example 1 and Example 11, it can be seen that if nitrogen is not introduced when preparing the base solution, the material will be severely oxidized when the reaction is started, the growth rate will be accelerated and difficult to control, and the primary particle morphology will also be uneven, thereby deteriorating the electrochemical performance.

[0189] By comparing Example 1 with Examples 12-13, it can be seen that if the pH of the reaction system in step (4) is too low, uneven primary particle morphology will be formed, and the risk of particle agglomeration will be increased; if the pH of the reaction system in step (4) is too high, the instability of the reaction system will be increased, and the degree of supersaturation of the reaction will be easily reduced, thereby generating a large number of small particles, which is not conducive to improving material properties.

[0190] By comparing Example 1 with Comparative Example 1, it can be seen that if the step of transferring to the second reactor in step (3) is omitted and the second stage is continued directly in the first reactor, the growth rate of the primary particles will fluctuate over time, and the morphology of the primary particles will be uneven, which is not conducive to improving the electrochemical properties of the positive electrode material, and the first discharge capacity, first coulomb efficiency and cycle performance of the positive electrode material will all be significantly deteriorated.

[0191] It should be noted that while the present invention illustrates the process method through the above-described embodiments, the present invention is not limited to the above-described process steps, and does not necessarily rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent replacements for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a cathode material precursor, characterized in that: The preparation method comprises the following steps: The first stage: introducing the ternary metal salt solution, the complexing agent and the precipitant into the first reactor to carry out nucleation growth to obtain a core solution; The second stage: transferring the core solution to a second reactor, and introducing a ternary metal salt solution, a complexing agent, and a precipitant to carry out a growth reaction until the particles grow to the target particle size of the second stage; The third stage: keep introducing the raw material solutions in the second stage, and then introduce the doping metal salt solution to continue the growth reaction until the growth particle size of the particles reaches the target particle size of the third stage, thereby obtaining the positive electrode material precursor.

2. The preparation method according to claim 1, characterized in that The ternary metal salt solution is a nickel-cobalt-manganese mixed salt solution; Preferably, the total concentration of nickel, cobalt and manganese in the nickel-cobalt-manganese mixed salt solution is 50-200 g / L; Preferably, in the nickel-cobalt-manganese mixed salt solution, the molar ratio of nickel element, cobalt element and manganese element is (50-90):(1-25):(1-25); Preferably, the precipitant comprises any one of sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution, or a combination of at least two thereof; Preferably, the complexing agent comprises any one of ammonia, oxalic acid or citric acid, or a combination of at least two thereof; Preferably, the doping element in the doped metal salt solution includes any one or a combination of at least two of aluminum, titanium, niobium, zirconium, tungsten, vanadium, strontium, gallium, cerium, yttrium, lanthanum, antimony or boron, preferably yttrium; Preferably, the concentration of the doped metal salt solution is 20-50 g / L.

3. The preparation method according to claim 1 or 2, characterized in that In the first stage, the feed rate of the ternary metal salt solution is 2-4 L / h, the feed rate of the complexing agent is 200-400 mL / h, and the feed rate of the precipitant is 1-2 L / h; Preferably, in the first stage, the pH of the reaction system is controlled in the range of 11.5-12; Preferably, in the first stage, the concentration of the complexing agent in the reaction system is controlled at 7-9 g / L; Preferably, the nucleation and growth process is accompanied by stirring, and the stirring rate is 300-400 rpm; Preferably, the growth temperature of the nucleation growth is 40-80°C; Preferably, in the core solution, the particle size D50 of the core particles is 3.5-4 μm.

4. The preparation method according to any one of claims 1 to 3, characterized in that The first reactor is also provided with a bottom liquid; Preferably, the method for preparing the base liquid includes: mixing a precipitant, a complexing agent and water to obtain the base solution; Preferably, before the nucleation growth, the pH value of the base solution is 11.2-12, the concentration of the complexing agent is 4-8 g / L, and the temperature is controlled at 40-60°C; Preferably, nitrogen is introduced during the mixing process, and the nitrogen flow rate is 0.5-2m 3 / h.

5. The preparation method according to any one of claims 1 to 4, characterized in that The feed flow rates of the ternary metal salt solution, the complexing agent, and the precipitant in the second stage are all greater than the feed flow rates of the ternary metal salt solution, the complexing agent, and the precipitant in the first stage; Preferably, in the second stage, the feed rate of the ternary metal salt solution is 4-8 L / h, the feed rate of the complexing agent is 600-1000 mL / h, and the feed rate of the precipitant is 2.5-4 L / h; Preferably, in the second stage, the pH of the reaction system is controlled in the range of 9.5-10; Preferably, in the second stage, the concentration of the complexing agent in the reaction system is controlled at 3-5 g / L; Preferably, in the second stage, the reaction temperature of the growth reaction is 40-80°C; Preferably, in the second stage, the growth reaction is accompanied by stirring at a rate of 200-300 rpm; Preferably, the target particle size in the second stage refers to a particle size D50 reaching 8-11 μm.

6. The preparation method according to any one of claims 1 to 5, characterized in that In the third stage, the feed flow rate of the doping metal salt solution is 100-500 mL / h; Preferably, in the third stage, the pH of the reaction system is controlled in the range of 10-10.5; Preferably, in the third stage, the concentration of the complexing agent in the reaction system is controlled at 3-5 g / L; Preferably, in the third stage, the reaction temperature of the growth reaction is 40-80°C; Preferably, in the third stage, the growth reaction is accompanied by stirring at a rate of 100-200 rpm; Preferably, the target particle size in the third stage refers to a particle size D50 reaching 11-14 μm.

7. The preparation method according to any one of claims 1 to 6, characterized in that The preparation method comprises the following steps: (1) preparing a nickel-cobalt-manganese mixed salt solution, a doping metal salt solution, a complexing agent, a precipitant, and a base solution respectively; in the nickel-cobalt-manganese mixed salt solution, the total concentration of nickel, cobalt, and manganese is 50-200 g / L, and the molar ratio of nickel, cobalt, and manganese is (50-90):(0-25):(0-25); the concentration of the doping metal salt solution is 20-50 g / L; the mass concentration of the complexing agent is 5-15%, and the mass concentration of the precipitant is 15-25%; the preparation method of the base solution comprises: The precipitant, complexing agent and water are stirred and mixed at a speed of 100-200 rpm, and then the temperature is raised to 40-60°C, and the pH value is controlled to be 11.2-12 to obtain the base liquid; the concentration of the complexing agent in the base liquid is 4-8 g / L, and nitrogen is also introduced during the stirring and mixing process, and the nitrogen introduction flow rate is 0.5-2 m 3 / h; (2) The first stage: a nickel-cobalt-manganese mixed salt solution, a complexing agent, and a precipitant are simultaneously introduced into a first reactor containing the base solution, the pH of the reaction system is controlled to be 11.5-12, the concentration of the complexing agent is controlled to be 7-9 g / L, and nucleation growth is carried out at a rate of 300-400 rpm and a growth temperature of 40-80° C. to obtain a core solution with a particle size D50 of 3.5-4 μm; In the first stage, the feed rate of the nickel-cobalt-manganese mixed salt solution is 2-4 L / h, the feed rate of the complexing agent is 200-400 mL / h, and the feed rate of the precipitant is 1-2 L / h; (3) Second stage: the core solution is transferred to a second reactor without bottom liquid, and a nickel-cobalt-manganese mixed salt solution, a complexing agent, and a precipitant are introduced in parallel to carry out a growth reaction. The pH of the reaction system is controlled in the range of 9.5-10, and the concentration of the complexing agent in the reaction system is controlled in the range of 3-5 g / L until the particles grow to the target particle size of the second stage; In the second stage, the feed rate of the nickel-cobalt-manganese mixed salt solution is 4-8 L / h, the feed rate of the complexing agent is 600-1000 mL / h, and the feed rate of the precipitant is 2.5-4 L / h; the reaction temperature of the growth reaction is 40-80° C.; the growth reaction is accompanied by stirring at a rate of 200-300 rpm; the target particle size in the second stage is a particle size D50 of 8-11 μm; (4) maintaining the introduction of the raw material solutions in the second stage, and then introducing the doping metal salt solution to continue the growth reaction, the pH of the reaction system is controlled in the range of 10-10.5, and the concentration of the complexing agent in the reaction system is controlled in the range of 3-5 g / L, until the growth particle size of the particles reaches the target particle size of the third stage, thereby obtaining a precursor precipitate; In the third stage, the feed rate of the nickel-cobalt-manganese mixed salt solution is 4-8 L / h, the feed rate of the complexing agent is 600-1000 mL / h, the feed rate of the precipitant is 2.5-4 L / h, and the feed rate of the doping metal salt solution is 100-500 mL / h; the reaction temperature of the growth reaction is 40-80° C.; the growth reaction is accompanied by stirring at a rate of 100-200 rpm; the target particle size in the third stage refers to a particle size D50 of 11-14 μm; (5) Aging and washing the precursor precipitate, and then drying it at 100-200° C. to obtain the positive electrode material precursor.

8. A cathode material precursor, characterized in that: The positive electrode material precursor is prepared by the preparation method according to any one of claims 1 to 7; The chemical formula of the positive electrode material precursor is Ni a Co b Mn c M d (OH)2, wherein 0.5<a<0.9, 0<b<0.25, 0<c<0.25, 0<d<0.1, a+b+c+d=1, and M is a doping element; The positive electrode material precursor includes a core and a shell covering the surface of the core, and the content of the doping element in the shell changes gradiently in the thickness direction of the shell; Preferably, based on the total molar amount of Ni, Co and Mn in the positive electrode material precursor being 100%, the doping amount of the doping element is 0.05-5%.

9. A positive electrode material, characterized in that The positive electrode material is obtained by mixing and sintering the positive electrode material precursor according to claim 8 and a lithium source; The positive electrode material has a core-shell structure, wherein the core is nickel-cobalt-manganese oxide and the surface of the shell forms a LiM2O4 spinel crystal structure, where M is the doping element; in the positive electrode material, the primary particles are rod-shaped particles arranged radially.

10. A lithium ion battery, characterized in that: The positive electrode of the lithium-ion battery includes the positive electrode material according to claim 9.

Images