Positive electrode material precursor, preparation method thereof and positive electrode material

Abstract

The invention discloses a positive electrode material precursor, a preparation method thereof and a positive electrode material, the positive electrode material precursor provided by the invention comprises a secondary particle formed by aggregating a plurality of primary particles, and the secondary particle comprises a loose core and a compact shell formed on the surface of the loose core; and the porosity of the loose core is 5-15% and is uniformly distributed. The positive electrode material precursor has a relatively large internal ion transmission channel, and the sintering performance of the precursor is improved, so that the positive electrode material with obvious advantages in capacity and stability is obtained.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a cathode material precursor, its preparation method, and the cathode material. Background Technology

[0002] Lithium-ion batteries using ternary cathode materials have been widely used in the new energy vehicle field due to their significant advantages in energy density and cycle life. In recent years, the rapid development of applications such as intelligent robots and low-altitude aircraft has placed higher demands on the performance of lithium batteries, and ternary cathode materials are among the most promising and high-potential cathode materials currently in mass production.

[0003] As the core raw material of ternary cathode materials, ternary precursors inherit most of their structural characteristics, playing a decisive role in the latter's electrical and safety performance. Therefore, improving the performance of ternary precursors is also one of the important means to improve the performance of lithium-ion batteries. Co-precipitation is currently the most widely used route for the controllable production of high-quality ternary precursors. Controlling the internal structure of ternary precursor particles during co-precipitation is of great significance for improving their processability, thereby enhancing the capacity and structural stability of the cathode material.

[0004] To facilitate lithium-ion transport and ensure strong physical and chemical stability, the ternary precursor must have certain interconnected pores and as uniform an internal and external crystal structure as possible to avoid stress concentration and cracking due to differences in crystal structure during growth.

[0005] Patent CN114590846 increases the internal porosity by using a nickel-cobalt-manganese oxide core to precipitate nickel-cobalt-manganese hydroxide, which can suppress microcracks in the cathode material. However, it requires the synthesis and sintering of the core, which makes the production process complex. In addition, the lattice parameters of the internal oxide and the external hydroxide are quite different, which can easily lead to mismatch during growth and abnormal precipitation.

[0006] Patent CN112624213A describes a method of creating pores in the core of a ternary precursor by adding an organic solvent during the precipitation process, resulting in a precursor with a regular arrangement and loose, porous structure. However, the use of an organic solvent requires additional recycling of the mother liquor, which increases production costs and places higher demands on the control of the production environment.

[0007] The above-mentioned solutions involve complex production processes, high production costs, or introduce impurities such as organic solvents into the production system that require additional treatment, making them unsuitable for actual production. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned deficiencies of the prior art and provide a cathode material precursor, its preparation method, and the cathode material.

[0009] The technical problem solved by this invention is achieved by the following technical solution.

[0010] The present invention provides a cathode material precursor, the cathode material precursor comprising secondary particles formed by the agglomeration of multiple primary particles, the secondary particles comprising a loose core and a dense shell formed on the surface of the loose core; the porosity of the loose core is 5-15% and is uniformly distributed.

[0011] This invention provides a method for preparing the above-mentioned cathode material precursor, comprising: using an aqueous solution of potassium hydroxide as a precipitant during the precipitation of the precursor core, and subjecting the byproducts generated in the reaction system to a supersaturated state; using an aqueous solution of sodium hydroxide as a precipitant during the precipitation of the precursor shell, gradually reducing the content of byproducts, and gradually dissolving the byproducts attached to the precursor core, thereby obtaining a cathode material precursor with a loose and porous interior and a tightly packed exterior.

[0012] The present invention provides a cathode material, which is formed by sintering the above-mentioned cathode material precursor with lithium salt.

[0013] The present invention has the following beneficial effects: This invention provides a cathode material precursor, its preparation method, and the cathode material itself. The cathode material precursor provided by this invention comprises secondary particles formed by the agglomeration of multiple primary particles. Each secondary particle includes a loose core and a dense outer shell formed on the surface of the loose core. The porosity of the loose core is 5-15% and uniformly distributed. The aforementioned cathode material precursor has a large internal ion transport channel, which is beneficial to improving the sintering performance of the precursor, thereby obtaining a cathode material with significant advantages in capacity and stability. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 Solubility curves of sodium sulfate and potassium sulfate; Figure 2 This is a cross-sectional view of the precursor obtained in Example 1; Figure 3 This is a cross-sectional view of the precursor prepared in Comparative Example 1. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0017] The following is a detailed description of a cathode material precursor, its preparation method, and the cathode material provided by embodiments of the present invention.

[0018] In a first aspect, embodiments of the present invention provide a cathode material precursor, the cathode material precursor comprising secondary particles formed by the agglomeration of multiple primary particles, the secondary particles comprising a loose core and a dense shell formed on the surface of the loose core; the porosity of the loose core is 5-15% and is uniformly distributed.

[0019] This invention provides a cathode material precursor, which is a secondary particle formed by the agglomeration of primary particles. The secondary particle includes a loose and porous core and a shell in which the primary particles are radially arranged and tightly packed. This structure is beneficial for lithium ion transport and has high stability to the electrolyte, which is beneficial for improving the sintering activity of the precursor, thereby obtaining a cathode material with significant advantages in capacity and stability.

[0020] In some alternative embodiments, the cathode material precursor satisfies one or more of the following conditions: a. The primary particles include sheet-like primary particles and strip-like primary particles. The sheet-like primary particles are interlaced to form the honeycomb structure, and the strip-like primary particles form the radial structure. b. The loose core has a honeycomb structure, and the dense outer shell has a radial structure; c. The tap density of the cathode material precursor is 1.3-2.2 g / cm³. 3 ; d. The specific surface area of ​​the cathode material precursor is 5-30 m². 2 / g; e. The particle size D50 of the cathode material precursor is 3-15 μm; f. The span value of the cathode material precursor is 0.3-1.3; g. The chemical formula of the cathode material precursor is Ni x Co y Mn (1-x-y) (OH)2, where 0≤x≤1, 0≤y<1.

[0021] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned cathode material precursor, comprising: using an aqueous solution of potassium hydroxide as a precipitant during the precipitation of the precursor core, and subjecting the byproducts generated in the reaction system to a supersaturated state; using an aqueous solution of sodium hydroxide as a precipitant during the precipitation of the precursor shell, gradually reducing the content of byproducts, and gradually dissolving the byproducts attached to the precursor core, thereby obtaining a cathode material precursor with a loose and porous interior and a tightly packed exterior.

[0022] This invention provides a method for preparing the aforementioned cathode material precursor. Utilizing the significant differences in solubility of different byproducts at different temperatures, the reaction temperature and reactant concentration are controlled during the first precipitation stage to create a supersaturated environment for the byproducts. This causes byproduct crystals to precipitate in situ, adhering to the precursor crystals and controlling and isolating the growth of primary precursor particles. This increases the spacing between primary particles in the precursor core, improves the integrity of the precursor core crystallization, and strengthens the core framework. In the second precipitation stage, potassium hydroxide solution is replaced with sodium hydroxide solution, and the reaction temperature and reactant concentration are controlled. During the outer shell precipitation process, the byproduct content is gradually reduced, causing the byproduct crystals adhering to the precursor core to gradually dissolve. This preserves the porosity of the precursor core and the internal-to-external connectivity pathways, facilitating lithium-ion transport and resulting in a cathode material with excellent capacity and cycle performance.

[0023] In some alternative implementations, the following steps are included: Step 1: The metal sulfate solution, complexing agent solution, and potassium hydroxide solution are fed into the reactor in a parallel flow to obtain the first slurry. During the growth of the precursor core, the byproduct potassium sulfate produced in the reaction system is in a supersaturated state. Step 2: After the reaction product grows to the target median particle size, the potassium hydroxide solution is replaced with sodium hydroxide solution to continue the reaction. While the precursor shell is rapidly generated on the surface of the precursor core, the potassium sulfate content is gradually reduced so that the potassium sulfate slowly dissolves in the precursor core to form a loose and porous structure, thus obtaining the second slurry. Step 3: Aging, washing and drying the second slurry to obtain the cathode material precursor.

[0024] This invention provides a method for preparing the above-mentioned cathode material precursor. During the core precipitation of the precursor, an aqueous solution of potassium hydroxide is used as a precipitant. The content of potassium sulfate, a reaction product, in the first precursor slurry is controlled to be greater than that in the saturated potassium sulfate solution. This allows the generated byproduct potassium sulfate to easily precipitate and adhere to the precursor precipitate in the reaction environment. By adjusting the temperature to control the crystallization rate and crystal size, the growth of precursor crystals can be limited to a certain extent, and the adhesion between primary hydroxide precursor particles can be controlled, resulting in a precursor core with a complete primary particle crystal structure and wide spacing. During the outer layer precipitation of the precursor, an aqueous solution of sodium hydroxide is used as a precipitant. The solubility of the generated byproduct sodium sulfate is several times that of potassium sulfate. Sodium hydroxide is used to rapidly grow the outer shell on the surface of the precursor core. Simultaneously, as the sodium hydroxide solution enters the system, the concentration of potassium hydroxide in the system begins to decrease. The potassium sulfate crystals that precipitate along with the precursor in the core slowly dissolve, thereby forming a precursor core framework with larger internal pores, achieving in-situ pore creation. The solubility curves of potassium sulfate and sodium sulfate at different temperatures are shown below. Figure 1 As shown.

[0025] During subsequent growth, the primary particles continue to grow along the morphology of the core, resulting in a uniform crystal structure both inside and out. By controlling the slow dissolution of potassium sulfate in the core, the interconnected pathways from the inside out are preserved, which is beneficial for improving the sintering activity of the precursor and yielding a cathode material with significant advantages in capacity and stability. The above preparation method does not change the existing production process, does not introduce harmful substances that cannot be treated by existing wastewater treatment systems, and the prepared cathode material exhibits excellent electrochemical performance.

[0026] In some optional embodiments, the metal sulfate solution is a sulfate of nickel, cobalt, or manganese, the total molar concentration of metal ions in the metal sulfate solution is 1.2-2.5 mol / L, the complexing agent is an aqueous ammonia solution with a mass concentration of 10-20%, the potassium hydroxide solution is an aqueous potassium hydroxide solution with a mass concentration of 10-40%, and the sodium hydroxide solution is an aqueous sodium hydroxide solution with a mass concentration of 20-40%.

[0027] In some optional embodiments, in step 1, the temperature is adjusted to 20-60℃, the pH to 9-13, the ammonia concentration to 0-17 g / L, and the stirring speed to 100-600 rpm. In step 1, if the pH of the system is higher than 13, the product D50 will never reach 2 μm after a long precipitation reaction, resulting in amorphous fragments. If the pH is lower than 9, metal ion precipitation will be incomplete, and the metal ions will not precipitate according to the set ratio, leading to abnormal material composition and structure. Some incompletely precipitated metal ions will also enter the mother liquor and be lost with it, causing waste and pollution. Furthermore, excessively high ammonia concentration in the reaction system will excessively inhibit metal ion precipitation, leading to uncontrolled particle growth and the formation of large, uneven particles. Simultaneously, the complexation effect will also carry away a large amount of metal ions, again causing waste.

[0028] In some alternative embodiments, in step 2, the temperature is adjusted to 40-80°C, the pH to 9-12, the ammonia concentration to 0-17 g / L, and the stirring speed to 100-600 rpm.

[0029] In some optional embodiments, in step 3, the aging temperature is 30-80°C and the time is 2-12 hours; the detergent used for washing is a sodium hydroxide aqueous solution with a mass fraction of 3-5% at 50-80°C and pure water at 50-80°C; the drying temperature is 80-200°C.

[0030] Thirdly, embodiments of the present invention provide a cathode material, which is formed by sintering the above-mentioned cathode material precursor with lithium salt.

[0031] In some alternative embodiments, the cathode material precursor is mixed with a lithium salt at a molar ratio of 1:(1.01-1.10) and sintered at 650-980°C for 6-20 hours to produce the cathode material.

[0032] The following detailed description, in conjunction with embodiments, illustrates a cathode material precursor, its preparation method, and the cathode material provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0033] Example 1 A cathode material precursor with the molecular formula Ni 0.6 Co 0.2 Mn 0.2 (OH)2, its preparation method includes the following steps: Step 1: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in pure water at a ratio of 6:2:2 to prepare a 2 mol / L mixed metal sulfate solution. Simultaneously introduce the mixed metal sulfate solution, 16% ammonia solution, and 40% potassium hydroxide solution into the reaction vessel using a metering pump. Start stirring at 300 rpm, maintain the temperature at 40℃, pH 12, and ammonia concentration at 8 g / L. Proof of solidification is achieved using nitrogen gas. A thickener is then used for further solidification.

[0034] Step 2: When the solid particle D50 reaches 2μm, stop the flow of potassium hydroxide solution and switch to 32% sodium hydroxide solution. That is, continue to use a metering pump to simultaneously flow the mixed metal sulfate solution, 16% ammonia water, and 32% sodium hydroxide solution into the reactor. Adjust the temperature to 60℃, maintain pH 12, and ammonia concentration of 8g / L. Nitrogen gas is introduced for protection during the process. Use a thickener to solidify until the particles grow to a D50 of 3.5μm.

[0035] Step 3: Wash the precursor slurry in a centrifuge, using a 3% sodium hydroxide solution at 70℃ and pure water at 70℃, and then spin dry; put the filter cake into an oven and dry it at 120℃ for 8 hours to obtain the finished precursor product.

[0036] The preparation process of a positive electrode material includes the following steps: Lithium carbonate was mixed with the above precursor at a molar ratio of 1.05:1 and sintered in a muffle furnace at 860°C for 12 hours in an air atmosphere. The sintered material was then crushed and sieved to obtain the finished cathode material.

[0037] Example 2 A cathode material precursor with the molecular formula Ni 0.6 Co 0.2 Mn 0.2 (OH)2, its preparation method includes the following steps: Step 1: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in pure water at a ratio of 6:2:2 to prepare a 2 mol / L mixed metal sulfate solution. Simultaneously introduce the mixed metal sulfate solution, 16% ammonia, and 40% potassium hydroxide solution into the reaction vessel using a metering pump. Start stirring at 300 rpm, maintain the temperature at 30°C, pH at 12, and the ammonia concentration at 10 g / L. Proof the process with nitrogen gas. Use a thickener for solidification.

[0038] Step 2: When the solid particle D50 reaches 2μm, stop the flow of potassium hydroxide solution and switch to 32% sodium hydroxide solution. That is, continue to use a metering pump to simultaneously flow the mixed metal sulfate solution, 16% ammonia water, and 32% sodium hydroxide solution into the reactor. Adjust the temperature to 65℃, maintain pH 12, and ammonia concentration of 10g / L. Nitrogen gas is introduced for protection during the process. Use a thickener to solidify the particles until the particle D50 reaches 3.5μm.

[0039] Step 3: Wash the precursor slurry in a centrifuge, using a 3% sodium hydroxide solution at 70℃ and pure water at 70℃, and then spin dry; put the filter cake into an oven and dry it at 120℃ for 8 hours to obtain the finished precursor product.

[0040] The preparation process of a positive electrode material includes the following steps: Lithium carbonate was mixed with the above precursor at a molar ratio of 1.05:1 and sintered in a muffle furnace at 860°C for 12 hours in an air atmosphere. The sintered material was then crushed and sieved to obtain the finished cathode material.

[0041] Example 3 A cathode material precursor with the molecular formula Ni 0.5 Co 0.2 Mn 0.3 (OH)2, its preparation method includes the following steps: Step 1: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in pure water at a ratio of 5:2:3 to prepare a 2 mol / L mixed metal sulfate solution. Simultaneously introduce the mixed metal sulfate solution, 16% ammonia, and 25% potassium hydroxide solution into the reaction vessel using a metering pump. Start stirring at 300 rpm, maintain the temperature at 40℃, pH 12, and ammonia concentration at 6 g / L. Proof the process with nitrogen gas. Use a thickener for solidification.

[0042] Step 2: When the solid particle D50 reaches 2μm, stop the flow of potassium hydroxide solution and switch to 32% sodium hydroxide solution. That is, continue to use a metering pump to simultaneously flow the mixed metal sulfate solution, 16% ammonia water, and 32% sodium hydroxide solution into the reactor. Adjust the temperature to 55℃, maintain pH 12, and ammonia concentration of 6g / L. Nitrogen gas is introduced for protection during the process. Use a thickener to solidify until the particles grow to a D50 of 3.5μm.

[0043] Step 3: Wash the precursor slurry in a centrifuge, using a 3% sodium hydroxide solution at 70℃ and pure water at 70℃, and then spin dry; put the filter cake into an oven and dry it at 120℃ for 8 hours to obtain the finished precursor product.

[0044] The preparation process of a positive electrode material includes the following steps: Lithium carbonate was mixed with the above precursor at a molar ratio of 1.05:1 and sintered in a muffle furnace at 860°C for 12 hours in an air atmosphere. The sintered material was then crushed and sieved to obtain the finished cathode material.

[0045] Comparative Example 1 A cathode material precursor with the molecular formula Ni 0.6 Co 0.2 Mn 0.2 (OH)2, its preparation method includes the following steps: Step 1: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in pure water at a ratio of 6:2:2 to prepare a 2 mol / L mixed metal sulfate solution. Simultaneously introduce the mixed metal sulfate solution, 16% ammonia, and 32% sodium hydroxide into the reaction vessel using a metering pump. Start stirring at 300 rpm, maintain the temperature at 40℃, pH 12, and ammonia concentration at 8 g / L. Proof of solidification is achieved using nitrogen gas. A thickener is then used for further solidification.

[0046] Step 2: When the solid particle D50 reaches 2μm, adjust the temperature to 60℃, and continue to use a metering pump to simultaneously introduce a mixed metal sulfate solution, 16% ammonia water, and 32% sodium hydroxide solution into the reactor, maintaining pH 12 and ammonia concentration of 8g / L. Nitrogen gas is introduced for protection during the process, and a thickener is used for consolidation until the particles grow to a D50 of 3.5μm.

[0047] Step 3: Wash the precursor slurry in a centrifuge, using a 3% sodium hydroxide solution at 70℃ and pure water at 70℃, and then spin dry; put the filter cake into an oven and dry it at 120℃ for 8 hours to obtain the finished precursor product.

[0048] The preparation process of a positive electrode material includes the following steps: Lithium carbonate was mixed with the above precursor at a molar ratio of 1.05:1 and sintered in a muffle furnace at 860°C for 12 hours in an air atmosphere. The sintered material was then crushed and sieved to obtain the finished cathode material.

[0049] Comparative Example 2 A cathode material precursor with the molecular formula Ni 0.6 Co 0.2 Mn 0.2 (OH)2, its preparation method includes the following steps: Step 1: Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate in pure water at a ratio of 6:2:2 to prepare a 2 mol / L mixed metal sulfate solution. Simultaneously introduce the mixed metal sulfate solution, 16% ammonia, and 32% sodium hydroxide into the reaction vessel using a metering pump. Start stirring at 300 rpm, maintain the temperature at 40℃, pH 12, and ammonia concentration at 8 g / L. During the process, introduce air at a rate of 100 L / h and use a thickener for solidification.

[0050] Step 2: When the solid particle D50 reaches 2μm, adjust the temperature to 60℃, and continue to use a metering pump to simultaneously introduce a mixed metal sulfate solution, 16% ammonia water, and 32% sodium hydroxide solution into the reactor, maintaining pH 12 and ammonia concentration of 8g / L. Nitrogen gas is introduced for protection during the process, and a thickener is used for consolidation until the particles grow to a D50 of 3.5μm.

[0051] Step 3: Wash the precursor slurry in a centrifuge, using a 3% sodium hydroxide solution at 70℃ and pure water at 70℃, and then spin dry; put the filter cake into an oven and dry it at 120℃ for 8 hours to obtain the finished precursor product.

[0052] The preparation process of a positive electrode material includes the following steps: Lithium carbonate was mixed with the above precursor at a molar ratio of 1.05:1 and sintered in a muffle furnace at 860°C for 12 hours in an air atmosphere. The sintered material was then crushed and sieved to obtain the finished cathode material.

[0053] The tap density, specific surface area, and internal and external porosity of the precursors obtained from Examples 1-3 and Comparative Examples 1-2 were tested, and the statistical results are shown in the table below: Table 1 Physical properties of precursors prepared in the examples and comparative examples

[0054] As can be seen from the table above, compared to Comparative Example 1, the method in this embodiment creates a larger porosity inside the precursor particles while retaining approximately the same external porosity, thus achieving a more ideal tap density and specific surface area. Comparative Example 2, through controlled oxidation of the core, also creates a relatively large internal porosity, but the tap density is lower.

[0055] The cathode materials obtained in Examples 1-2 and Comparative Examples 1-2 were subjected to electrochemical performance testing according to the following methods: The positive electrode material, conductive agent (acetylene black), and binder (PVDF) were mixed and dispersed in an organic solvent NMP at a ratio of 90:5:5. After stirring evenly, the mixture was coated onto aluminum foil to form a positive electrode sheet. A lithium sheet was used as the negative electrode. A button cell was fabricated in a glove box under a protective atmosphere. The electrical performance was tested on a battery testing system, and the test results are shown in Table 2. Table 2 Electrical properties of cathode materials

[0056] As can be seen from the table above, due to the large lithium-ion transport channels retained internally, the example exhibits higher discharge capacity and higher initial charge-discharge efficiency under the same sintering process. Furthermore, the overall structural stability of the cathode material is improved due to the support of the core framework, resulting in better cycle performance. The cathode material obtained in Comparative Example 2 also has advantages in capacity and initial efficiency due to the presence of internal channels; however, the oxidation process damages the crystal structure of the precursor, leading to defects in the cathode material's crystal structure and thus poorer cycle performance.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cathode material precursor, characterized in that, The cathode material precursor includes secondary particles formed by the aggregation of multiple primary particles. The secondary particles include a loose core and a dense shell formed on the surface of the loose core. The porosity of the loose core is 5-15% and it is uniformly distributed.

2. The cathode material precursor according to claim 1, characterized in that, The cathode material precursor satisfies one or more of the following conditions: a. The primary particles include sheet-like primary particles and strip-like primary particles. The sheet-like primary particles are interlaced to form the honeycomb structure, and the strip-like primary particles form the radial structure. b. The loose core has a honeycomb structure, and the dense outer shell has a radial structure; c. The tap density of the cathode material precursor is 1.6-2.2 g / cm³. 3 ; d. The specific surface area of ​​the cathode material precursor is 5-30 m². 2 / g; e. The particle size D50 of the cathode material precursor is 3-15 μm; f. The span value of the cathode material precursor is 0.3-1.1; g. The chemical formula of the cathode material precursor is Ni x Co y Mn (1-x-y) (OH)2, where 0≤x≤1, 0≤y<1.

3. A method for preparing a cathode material precursor according to claim 1 or 2, characterized in that, It includes: using potassium hydroxide aqueous solution as a precipitant during the precipitation of the precursor core, and keeping the byproducts generated in the reaction system in a supersaturated state; using sodium hydroxide aqueous solution as a precipitant during the precipitation of the precursor shell, gradually reducing the content of byproducts, and gradually dissolving the byproducts attached to the precursor core, thereby obtaining a positive electrode material precursor with a loose and porous interior and a tightly packed exterior.

4. The preparation method according to claim 3, characterized in that, Includes the following steps: Step 1: The metal sulfate solution, complexing agent solution, and potassium hydroxide solution are fed into the reactor in a parallel flow to obtain the first slurry. During the growth of the precursor core, the byproduct potassium sulfate produced in the reaction system is in a supersaturated state. Step 2: After the reaction product grows to the target median particle size, the potassium hydroxide solution is replaced with sodium hydroxide solution to continue the reaction. While the precursor shell is rapidly generated on the surface of the precursor core, the potassium sulfate content is gradually reduced so that the potassium sulfate slowly dissolves in the precursor core to form a loose and porous structure, thus obtaining the second slurry. Step 3: Aging, washing and drying the second slurry to obtain the cathode material precursor.

5. The preparation method according to claim 4, characterized in that, The metal sulfate solution is a sulfate of nickel, cobalt, or manganese, and the total molar concentration of metal ions in the metal sulfate solution is 1.2-2.5 mol / L. The complexing agent solution is ammonia water with a mass concentration of 10-20%. The potassium hydroxide solution is an aqueous solution of potassium hydroxide with a mass concentration of 10-40%. The sodium hydroxide solution is an aqueous solution of sodium hydroxide with a mass concentration of 20-40%.

6. The preparation method according to claim 4, characterized in that, In step 1, adjust the temperature to 20-60℃, pH to 9-13, ammonia concentration to 0-17g / L, and stirring speed to 100-600rpm.

7. The preparation method according to claim 4, characterized in that, In step 2, adjust the temperature to 40-80℃, pH to 9-12, ammonia concentration to 0-17g / L, and stirring speed to 100-600rpm.

8. The preparation method according to claim 4, characterized in that, In step 3, the aging temperature is 30-80℃ and the time is 2-12 hours; the detergent used for washing is a sodium hydroxide aqueous solution with a mass fraction of 3-5% at 50-80℃ and pure water at 50-80℃; the drying temperature is 80-200℃.

9. A positive electrode material, characterized in that, The cathode material is formed by sintering a cathode material precursor with a lithium salt, wherein the cathode material precursor is prepared by the cathode material precursor according to any one of claims 1-2 or by the preparation method according to any one of claims 3-8.

10. The cathode material according to claim 9, characterized in that, The cathode material precursor is mixed with lithium salt at a molar ratio of 1:(1.01-1.10) and sintered at 650-980℃ for 6-20h to produce the cathode material.

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