High-nickel ternary positive electrode material, preparation method thereof and electrochemical device

Abstract

The application provides a high-nickel ternary positive electrode material, a preparation method thereof and an electrochemical device. The method comprises the following steps: mixing a high-nickel ternary precursor and a lithium source and performing primary sintering to obtain a base material; adding the base material into water to perform first stirring and mixing, then adding a phosphate to perform second stirring and mixing and drying, so that the phosphate is coated on the surface of the base material, and a dried material is obtained, wherein the phosphate is a phosphate compound containing at least one of Co, Mn, Ti, Mg, Al, Ni and Nb elements; and performing secondary sintering on the dried material to form a phosphate coating layer on the surface of the base material, so that the high-nickel ternary positive electrode material is obtained. The preparation method has the advantages of simplifying the preparation process, reducing the residual lithium content on the surface of the material, reducing the interface side reaction, improving the structural stability of the material in a high-temperature environment, and improving the cycle performance and safety performance of the battery.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to a high-nickel ternary cathode material, its preparation method and electrochemical device. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles and energy storage, higher requirements have been placed on the performance and cost of lithium-ion batteries. As an important component of lithium-ion batteries, cathode materials affect the battery's energy density, cycle stability, and manufacturing cost. Among them, high-nickel ternary cathode materials have become a research hotspot in the power battery industry due to their high capacity and high energy density characteristics.

[0003] However, existing high-nickel ternary cathode materials still face many challenges in their preparation and application. High-nickel ternary cathode materials suffer from irreversible capacity loss and severe interfacial side reactions during lithium cycling, leading to the depletion of effective electrolyte components, increased interfacial impedance, and consequently reduced battery cycle life and rate performance. Simultaneously, the high residual lithium content on the material surface can trigger severe gas expansion at high temperatures, increasing the internal pressure of the cell and affecting battery safety. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above-mentioned technical problems, this application needs to provide a method for preparing a high-nickel ternary cathode material.

[0005] In addition, this application also provides a high-nickel ternary cathode material prepared by the aforementioned preparation method and an electrochemical device using the cathode material.

[0006] In a first aspect, this application provides a method for preparing a high-nickel ternary cathode material, comprising: mixing a lithium source with a high-nickel ternary precursor, stirring, and sintering once to obtain a matrix material; adding the matrix material to water for a first stirring and mixing, then adding phosphate for a second stirring and mixing and drying, so that the phosphate coats the surface of the matrix material to obtain a dried material; wherein the phosphate is a phosphate compound containing at least one of the following metal elements: Co, Mn, Ti, Mg, Al, Ni, and Nb; and sintering the dried material a second time to obtain the high-nickel ternary cathode material.

[0007] Based on the first aspect, in some embodiments of this application, the phosphate includes at least one of AlPO4 and Mg3(PO4)2.

[0008] Based on the first aspect, in some embodiments of this application, the mass ratio of the matrix material to the phosphate is 1:(0.0003~0.005); and / or, the molar ratio of the total molar amount of lithium element in the lithium source to the total molar amount of metal element in the precursor is 1.0~1.16:1.

[0009] Based on the first aspect, in some embodiments of this application, the atmosphere of the primary sintering is oxygen, the sintering temperature is 700℃~900℃, and the sintering time is 10h~15h; and / or, the atmosphere of the secondary sintering is air or oxygen, the sintering temperature is 500℃~750℃, and the sintering time is 6h~14h.

[0010] Based on the first aspect, in some embodiments of this application, before the step of adding the matrix material to water for the first stirring and mixing, the method further includes: mechanically pulverizing the matrix material to make the median particle size of the matrix material 9μm~11μm.

[0011] Based on the first aspect, in some embodiments of this application, the stirring time for the first stirring and mixing is 1 min to 3 min, and the stirring frequency is 10 Hz to 30 Hz; the stirring time for the second stirring and mixing is 1 min to 5 min, and the stirring frequency is 10 Hz to 30 Hz; the drying conditions are: drying in a vacuum at 120 to 150 ℃ for 5 to 10 hours.

[0012] Based on the first aspect, in some embodiments of this application, the chemical formula of the high-nickel ternary precursor is Ni. x Co y Mn 1-x-y (OH)2, where 0.7≤x≤0.9, 0.05≤y≤0.15.

[0013] Based on the first aspect, in some embodiments of this application, the median particle size D50 of the high-nickel ternary cathode material is 9 μm to 11 μm; and / or, the Span value of the high-nickel ternary cathode material is 1.3 to 1.5; and / or, the compaction density of the high-nickel ternary cathode material is 2.5 g / cm³. 3 ~2.9g / cm 3 .

[0014] Secondly, this application provides a high-nickel ternary cathode material, which is prepared by the aforementioned preparation method.

[0015] Thirdly, this application provides an electrochemical device, the electrochemical device including a positive electrode sheet, the positive electrode sheet including a positive electrode material, the positive electrode material being a positive electrode material prepared by the aforementioned high-nickel ternary positive electrode material preparation method or the aforementioned high-nickel ternary positive electrode material.

[0016] The method for preparing high-nickel ternary cathode material provided in this application involves mixing a high-nickel cobalt-manganese precursor and a lithium source and performing a first sintering to obtain the matrix material. Subsequent processes include water washing and a second sintering, thereby reducing interfacial side reactions. The water washing and drying processes remove residual lithium from the material surface, reducing interfacial impedance and improving the battery's cycle life and rate performance. Simultaneously, the addition of phosphate during the water washing stage forms a uniform coating layer on the matrix material surface. This coating layer not only improves the material's structural stability but also enhances its stability under high-temperature conditions, reducing the cell's internal pressure and thus improving battery safety. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the high-nickel ternary cathode material preparation method of this application.

[0018] Figure 2 This is a powder morphology diagram of the high-nickel ternary cathode material from Example 1.

[0019] Figure 3 The image shows the powder morphology of the high-nickel ternary cathode material in Comparative Example 1.

[0020] Figure 4 The image shows the powder morphology of the high-nickel ternary cathode material in Comparative Example 2.

[0021] Figure 5 The image shows the powder morphology of the high-nickel ternary cathode material in Comparative Example 3.

[0022] Figure 6 This is a comparison diagram of the particle size distribution of high-nickel ternary cathode material powders in Examples 1 to 3 of this application and Comparative Examples 1 to 3. Detailed Implementation

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this application pertain. The terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the embodiments of this application. 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.

[0024] The following describes some embodiments of this application in detail. Unless otherwise specified, the embodiments and features described below can be combined with each other.

[0025] Please see Figure 1 As shown, this application provides a method for preparing a high-nickel ternary cathode material, specifically including the following steps: Step S1 involves mixing the lithium source with a high-nickel ternary precursor, stirring, and sintering in one step to obtain the matrix material. This single sintering process allows lithium elements to initially embed into the precursor lattice, forming an electrochemically active matrix material.

[0026] In some embodiments, the atmosphere for the primary sintering is oxygen, the sintering temperature is 700℃~900℃, and the sintering time is 10h~15h. This temperature and time range is conducive to the full diffusion of lithium into the precursor lattice and to obtaining suitable particle morphology and crystal structure. Indicative sintering temperatures may be 700℃, 750℃, 800℃, 850℃, 900℃, or any value within the range of any two of the above values. Indicative sintering times may be 10h, 11h, 12h, 13h, 14h, 15h, or any value within the range of any two of the above values.

[0027] In some embodiments, the chemical formula of the high-nickel ternary precursor is Ni x Co y Mn 1-x-y (OH)₂, where 0.7 ≤ x ≤ 0.9 and 0.05 ≤ y ≤ 0.15. This composition range is beneficial for ensuring a high nickel content in the material to achieve high capacity, while maintaining structural stability through the appropriate addition of cobalt and manganese. Exemplary values ​​for x can be 0.7, 0.75, 0.8, 0.85, 0.9, or any value within the range of any two of the above values; exemplary values ​​for y can be 0.05, 0.1, 0.15, or any value within the range of any two of the above values.

[0028] In some embodiments, the molar ratio of lithium to the total molar amount of metal elements in the lithium source is 1.0 to 1.16. This molar ratio range is advantageous for providing sufficient lithium to form a complete crystal lattice, while also helping to control the residual lithium on the surface of the cathode material at a low level. Exemplary molar ratios may be 1.00, 1.02, 1.05, 1.08, 1.10, 1.12, 1.16, or any value within the range of any two of the above values.

[0029] Step S2: The matrix material is added to water for the first stirring and mixing, followed by the addition of phosphate for the second stirring and mixing and drying, so that the phosphate coats the surface of the matrix material, and then a dried material is obtained; wherein, the phosphate is a phosphate compound containing at least one of the following metal elements: Co, Mn, Ti, Mg, Al, Ni and Nb.

[0030] This step involves directly washing the substrate material with water, which helps remove residual lithium compounds from the material surface and reduces interfacial impedance. Simultaneously, the addition of phosphates during the washing process promotes uniform phosphate adhesion to the material surface, facilitating the subsequent formation of a uniform phosphate coating layer. Furthermore, achieving uniform phosphate adhesion while removing residual lithium simplifies the process. In addition, phosphates containing the aforementioned elements can form a stable coating layer on the substrate material surface, suppressing interfacial side reactions, improving the material's structural stability, and enhancing ionic and electronic conductivity. This, in turn, improves the cycle performance, rate performance, and high-temperature safety of the high-nickel ternary cathode material.

[0031] In some embodiments, the phosphate includes at least one of AlPO4 and Mg3(PO4)2. The coating layer formed using phosphates derived from elements such as Al and Mg exhibits higher structural stability and ionic conductivity, further improving the material's cycling performance and high-temperature stability.

[0032] In some embodiments, the mass ratio of the matrix material to the phosphate is 1:(0.0003~0.005). This mass ratio range is beneficial for providing sufficient phosphate to form a moderately thick and continuous coating layer, while also helping to maintain the material's capacity and coating uniformity. Exemplary mass ratios can be 1:0.0003, 1:0.0005, 1:0.001, 1:0.002, 1:0.003, 1:0.004, 1:0.005, or any value within the range of any two of the above ratios. A further ratio of 1:(0.0005~0.001) can further optimize the density and uniformity of the coating layer, reducing the impact of excessive phosphate on the material's capacity while ensuring interface protection, thereby achieving a better balance between cycle stability and specific capacity.

[0033] Prior to water washing, the preparation method further includes mechanically pulverizing the matrix material, resulting in a median particle size of 9 μm-11 μm. Pulverization disperses large particles or agglomerates generated during the first sintering process into the target particle size range, which is beneficial for improving particle dispersibility and surface contact uniformity during subsequent water washing and coating processes. This results in more uniform adhesion of phosphate to the particle surface and facilitates the acquisition of high-nickel ternary cathode materials with suitable particle size distribution and good processing performance.

[0034] The pulverization method can employ mechanical pulverization or air jet pulverization methods known in the art, to achieve a median particle size D50 of 9μm to 11μm in the pulverized product. Those skilled in the art can select appropriate pulverization parameters (such as air pressure, classifier speed, feed rate, etc.) according to the type of equipment used and the target particle size range, which will not be listed in detail here.

[0035] In some embodiments, the stirring time for the first mixing step is 1-3 minutes, and the stirring frequency is 10-30 Hz. These stirring conditions facilitate uniform dispersion of the matrix material in water, improving the efficiency of lithium removal through washing, while avoiding excessive particle refinement or surface damage caused by excessively long stirring times or frequencies. Exemplary stirring times may be 1 minute, 2 minutes, or 3 minutes, or any value within the range of any two of the above values; exemplary stirring frequencies may be 10 Hz, 15 Hz, 20 Hz, 25 Hz, or 30 Hz, or any value within the range of any two of the above values.

[0036] In some embodiments, the stirring time for the second mixing is 1-5 minutes, and the stirring frequency is 10-30 Hz. These stirring conditions facilitate the uniform dispersion of phosphates in the slurry and their full adhesion to the surface of the matrix material, improving the uniformity and consistency of the coating, while preventing the coating layer from detaching or the particles from breaking due to over-stirring. Exemplary stirring times can be 1 minute, 2 minutes, 3 minutes, 4 minutes, or 5 minutes, or any value within the range of any two of the above values; exemplary stirring frequencies can be 10 Hz, 15 Hz, 20 Hz, 25 Hz, or 30 Hz, or any value within the range of any two of the above values.

[0037] In some embodiments, the drying conditions are: drying in a vacuum at 120°C to 150°C for 5 to 10 hours. These drying conditions are beneficial for thoroughly removing moisture from the washed material, preventing residual moisture from reacting with the material during subsequent secondary sintering, and also for maintaining the structural integrity of the material and the initial state of the coating layer. Exemplary drying temperatures can be 120°C, 130°C, 140°C, 150°C, or any value within the range of any two of the above values; exemplary drying times can be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, or any value within the range of any two of the above values.

[0038] Step S3: The dried material is sintered a second time to obtain a high-nickel ternary cathode material.

[0039] In this step, under the action of the secondary sintering temperature, the phosphates adhering to the material surface are transformed into a stable coating layer, which helps to reduce the interfacial side reactions generated by contact with the electrolyte, thereby improving the structural stability of the material in a high-temperature environment.

[0040] In some embodiments, the atmosphere for secondary sintering is air or oxygen, the sintering temperature is 500℃~750℃, and the sintering time is 6h~14h. Secondary sintering under these conditions enables a stable chemical bond to form between the phosphate and the matrix material, resulting in a denser and more uniform coating layer, thereby improving the structural stability and electrochemical performance of the material. Simultaneously, this sintering temperature range is beneficial in promoting the bonding between the coating layer and the matrix while avoiding abnormal grain growth or structural damage caused by excessively high temperatures, thus helping to maintain the structural integrity of the matrix material. Exemplary sintering temperatures can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, or any value within the range of any two of the above values. Exemplary sintering times can be 6h, 8h, 10h, 12h, 14h, or any value within the range of any two of the above values.

[0041] In some embodiments, the median particle size D50 of the high-nickel ternary cathode material is 9 μm to 11 μm. This particle size range is beneficial for improving slurry dispersibility and coating uniformity, enhancing particle packing effect and electrode density during rolling, thereby balancing processing performance and compaction density. It also helps to shorten the lithium-ion diffusion path and improve rate performance. Furthermore, this particle size is largely inherited after subsequent coating and sintering. Exemplary D50 values ​​can be 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, or any value within the range of any two of the above values.

[0042] It should be noted that during the washing and coating processes, the phosphate additives are uniformly adhered to the surface of the particles in the primary sintering product in the form of nano-sized particles. The coating layer formed after secondary sintering is typically only a few nanometers to tens of nanometers thick. This coating layer thickness is negligible relative to the bulk particle size (micrometers). Therefore, the median particle size D50 and particle size distribution Span remain essentially unchanged before and after coating and secondary sintering. In other words, the particle size of the final high-nickel ternary cathode material has good inheritance with the particle size of the pulverized matrix material. Therefore, by controlling the median particle size D50 of the matrix material in the pulverization step to 9~11 μm, the final product can have the same particle size range.

[0043] In some embodiments, the Span value of the high-nickel ternary cathode material is 1.3 to 1.5. This Span value range is beneficial for uniform particle distribution and improves battery consistency. Exemplary Span values ​​can be 1.3, 1.35, 1.4, 1.45, 1.5, or any value within the range of any two of the above values.

[0044] In some embodiments, the compaction density of the high-nickel ternary cathode material is 2.5 g / cm³. 3 ~2.9g / cm 3This compaction density range is beneficial for dense material packing, thereby increasing the volumetric energy density of the electrode. An exemplary compaction density could be 2.5 g / cm³. 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 , or any value within the range formed by any two of the above values.

[0045] This application also provides a high-nickel ternary cathode material, which is prepared by the aforementioned method. This high-nickel ternary cathode material has advantages such as low surface residual lithium content, mild interfacial side reactions, and good high-temperature stability, which are beneficial for improving the cycle performance and safety performance of lithium-ion batteries.

[0046] Compared with related technologies, the preparation method of the high-nickel ternary cathode material and the cathode material provided in this application have the following technical advantages: 1. In this application, the product obtained after one sintering is directly added to water for washing, and phosphate is added during the washing process to make the phosphate uniformly adhere to the material surface. At the same time, residual lithium compounds on the material surface are removed by water washing. The removal of residual lithium and the adhesion of phosphate are carried out in a combined manner, which simplifies the preparation process.

[0047] 2. This application removes residual lithium compounds from the surface of the material by washing with water, which helps to reduce interfacial impedance and improve the cycle life and rate performance of the battery.

[0048] 3. This application adds phosphate during the water washing stage and forms a stable coating layer after secondary sintering. This coating layer is beneficial to improving the structural stability of the material, reducing interfacial side reactions, improving the stability of the electrolyte, and enhancing the stability of the material under high temperature environment, thereby improving the cycle performance and safety performance of lithium-ion batteries.

[0049] 4. By optimizing process parameters such as the mixing ratio of nickel-cobalt-manganese precursors and lithium sources, sintering temperature and time, the preparation efficiency and quality stability of materials were improved, ensuring product consistency and controllability.

[0050] 5. This application adopts a process route that combines primary sintering and secondary sintering, which simplifies the preparation process, helps to reduce equipment investment and production costs, and is easy to industrialize.

[0051] This application also provides an electrochemical device, which includes a positive electrode sheet and a positive electrode material, wherein the positive electrode material is the aforementioned high-nickel ternary positive electrode material. Because this positive electrode material has the characteristics of low surface residual lithium content, mild interfacial side reactions, and good high-temperature stability, the electrochemical device has advantages such as long cycle life, good rate performance, and high high-temperature safety.

[0052] The present application will be further described below with reference to specific embodiments and comparative examples.

[0053] Example 1 Step 1, Dry mixing: Mix lithium hydroxide with high-nickel Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor was mixed with lithium in a molar ratio of 1.08:1 to the metal element in the precursor, and the mixture was stirred evenly using a plow mixer for 20 minutes at a stirring frequency of 40 Hz.

[0054] Step 2, First sintering: The dry mixture obtained in Step 1 is sintered once in an oxygen atmosphere at a temperature of 800℃ for 15 hours to obtain the matrix material.

[0055] Step 3, Crushing: The matrix material is mechanically crushed, and the median particle size D50 is controlled to be 10μm to obtain the crushed product.

[0056] Step 4, Washing and Coating: The pulverized product obtained in Step 3 is added to pure water and stirred for 3 minutes at a stirring frequency of 20 Hz. Then, AlPO4 auxiliary material is added to the slurry at a mass ratio of pulverized product to AlPO4 of 1:0.001. The mixture is stirred for 2 minutes at a stirring frequency of 20 Hz. Then, it is filtered by pressure (extrusion pressure 0.4±0.1 MPa, extrusion time 20 minutes) and vacuum dried at a drying temperature of 150℃ for 6 hours. After natural cooling to room temperature, the dried material is obtained.

[0057] Step 5, Secondary sintering: The dried material obtained in step 4 is subjected to secondary sintering (the temperature of secondary sintering is 500℃ and the time is 10h), and after sieving (double-layer 400 mesh screen), high-nickel ternary cathode material is obtained.

[0058] Example 2 The difference from Example 1 is that the molar ratio of lithium to the metal element in the precursor is adjusted to 1.00:1 in step 1. The remaining steps and parameters are the same as in Example 1.

[0059] Example 3 The difference from Example 1 is that the excipient added in step 4 is Mg3(PO4)2, and the mass ratio of the pulverized product to Mg3(PO4)2 is 1:0.001. The remaining steps and parameters are the same as in Example 1.

[0060] Comparative Example 1 The difference between this comparative example and Example 1 is that AlPO4 was not added during the water washing in step 4. Instead, AlPO4 was added to the dried material after vacuum drying in step 4 via a high-speed mixer. The amount of AlPO4 added was the same as in Example 1. The specific steps are as follows: Step 1, Dry mixing: Mix lithium hydroxide with high-nickel Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor was mixed with lithium in a molar ratio of 1.08:1 to the metal element in the precursor, and the mixture was stirred evenly using a plow mixer for 20 minutes at a stirring frequency of 40 Hz.

[0061] Step 2, primary sintering: The dry mixture obtained in Step 1 is sintered once in an oxygen atmosphere at a temperature of 800℃ for 15 hours to obtain the matrix material.

[0062] Step 3, Crushing: The matrix material is mechanically crushed (the median particle size D50 is controlled to be 10μm) to obtain the crushed product.

[0063] Step 4, Water Washing: The pulverized product obtained in Step 3 is added to pure water and stirred for 3-10 minutes at a stirring frequency of 20 Hz. Then, it is filtered by pressure and vacuum dried at 150℃ for 6 hours. After natural cooling to room temperature, the dried material is obtained. Once cooled, the dried material is dry-mixed with AlPO4 additive using a high-speed mixer until homogeneous. The AlPO4 additive is added at a mass ratio of 1:0.001 (pulverized product to AlPO4).

[0064] Step 5, Secondary sintering: The mixture obtained in step 4 is sintered a second time and then sieved to obtain high-nickel ternary cathode material.

[0065] Comparative Example 2 The difference between this comparative example and Example 1 is that no phosphate excipient was added in step 4. The specific steps are as follows: Step 1, Dry mixing: Mix lithium hydroxide with high-nickel Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor was mixed with lithium in a molar ratio of 1.08:1 to the metal element in the precursor, and the mixture was stirred evenly using a plow mixer for 20 minutes at a stirring frequency of 40 Hz.

[0066] Step 2, primary sintering: The dry mixture obtained in Step 1 is sintered once in an oxygen atmosphere at a temperature of 800℃ for 15 hours to obtain the matrix material.

[0067] Step 3, Crushing: The matrix material is mechanically crushed to obtain the crushed product.

[0068] Step 4, Water Washing: The pulverized product obtained in Step 3 is added to pure water and stirred for 3 minutes. Then, it is filtered by pressure and vacuum dried at 150°C for 6 hours. After natural cooling to room temperature, the dried material is obtained. No phosphate additives are added in this step.

[0069] Step 5, Secondary sintering: The dried material obtained in step 4 is subjected to secondary sintering (temperature 300℃, duration 10h), and after sieving, high-nickel ternary cathode material is obtained.

[0070] Comparative Example 3 The difference from Example 1 is that the sintering temperature in step 2 is 900°C and the sintering time is 16 hours. The remaining steps and parameters are the same as in Example 1.

[0071] Test method: Particle size testing: The particle size distribution of the high-nickel ternary cathode material was tested using a Malvern 3000 particle size analyzer after internal ultrasonic dispersion for 5 minutes.

[0072] Compacted density: The density of high-nickel ternary cathode material powder under 200MPa pressure was tested using a compaction density meter.

[0073] Span value test: Based on the particle size test results, it is calculated using the formula Span=(D90-D10) / D50.

[0074] Button cell testing: A half-cell was prepared by mixing high-nickel ternary cathode material, conductive carbon, and PVDF binder in a mass ratio of 90:5:5. Constant current charge-discharge testing was performed using the Blue Battery Testing System.

[0075] The initial discharge capacity test voltage range is 2.8V~4.3V, the charge / discharge rate is +1C / -1C, and the CV cutoff current is 0.01C.

[0076] The high-temperature cycling test temperature is 45℃, the voltage range is 2.8V~4.3V, the charge / discharge rate is +1C / 1C, and the CV cutoff current is 0.01C.

[0077] Free lithium test: The potentiometric titration method is used. A certain volume of water is used to dissolve the residual alkali (lithium hydroxide and lithium carbonate) on the surface of a certain mass of sample. After filtration, the filtrate is taken and titrated with a standard hydrochloric acid solution (both lithium hydroxide and lithium carbonate can be titrated with a standard hydrochloric acid solution, and two obvious equivalence points appear during potentiometric titration). The titration endpoint is determined by the point jump during the reaction (generally, at pH≈8.5, the lithium hydroxide reaction is complete; at pH≈4.5, the lithium carbonate reaction is complete). The amount used is calculated, and the weight ratio of lithium hydroxide and lithium carbonate is obtained by conversion. Free lithium is the sum of the lithium content in these two.

[0078] The test results for the examples and comparative examples are shown in Table 1 below.

[0079] Table 1 Note: D50 in Table 1 refers to the particle size of the final high-nickel ternary cathode material.

[0080] The span values ​​in Table 1 are also calculated based on the particle size of the final high-nickel ternary cathode material.

[0081] Results analysis: Combining Figures 2 to 5 As shown in Table 1, Example 1 added AlPO4 additive during the water washing stage, while Comparative Example 1 added AlPO4 additive through dry mixing after drying. Firstly, a comparison of particle morphology shows that Example 1, with additive added during water washing, exhibits better uniformity in polycrystalline particle coating, while Comparative Example 1, with dry coating after drying, shows some uneven coating with additive on the surface. Secondly, Example 1 shows higher initial discharge capacity, initial efficiency, and cycle retention rate than Comparative Example 1. Therefore, the coating layer formed by adding phosphate additive during the water washing stage in this application's examples is beneficial for obtaining better electrochemical performance, and the wet adhesion method is more conducive to coating uniformity than dry mixing.

[0082] A comparison of Example 1 and Comparative Example 2 shows that Comparative Example 2, which did not add any phosphate additives during the water washing stage, had a higher free lithium content than Example 1, and its first discharge capacity, first efficiency, and cycle retention were all lower than those of Example 1. Therefore, the present application's embodiment adds phosphate additives during the water washing process. The phosphates can react with residual lithium compounds on the material surface (or neutralize some residual alkali), which is beneficial for further reducing surface residual lithium and improving capacity and cycle performance.

[0083] A comparison of Example 1 and Comparative Example 3 shows that Comparative Example 3, by increasing the primary sintering temperature and extending the sintering time, resulted in abnormally large sintered particles and decreased cycle performance. Its initial discharge capacity, initial efficiency, and cycle retention rate were all lower than those of Example 1. The embodiments of this application, by controlling the primary sintering temperature within the range of 700℃ to 900℃ and the sintering time within the range of 10h to 15h, are beneficial for obtaining suitable particle morphology and crystal structure. The primary sintering temperature is not too high, and the time is not too long, effectively reducing over-burning and preventing abnormal particle growth, thereby ensuring the electrochemical performance of the material.

[0084] A comparison of Examples 1, 2, and 3 shows that the preparation method of this application can obtain high-nickel ternary cathode materials with low free lithium content and high cycle retention rate under conditions of a wide range of lithium ratios and the use of different phosphate additives (AlPO4, Mg3(PO4)2), and has good process adaptability.

[0085] In summary, the preparation method of the high-nickel ternary cathode material provided in this application involves directly washing the obtained product with water after a first sintering process, adding phosphate additives during the washing process to ensure uniform adhesion of phosphate to the material surface, and simultaneously removing residual lithium compounds from the surface. This combined process of removing residual lithium and attaching phosphate simplifies the preparation process. Secondary sintering transforms the phosphate adhering to the material surface into a stable coating layer, which helps reduce interfacial side reactions and improves the structural stability of the material at high temperatures. Furthermore, water washing to remove residual lithium compounds helps reduce interfacial impedance and improves the cycle life and rate performance of the battery.

[0086] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A method for preparing a high-nickel ternary cathode material, characterized in that, include: The high-nickel ternary precursor is mixed with a lithium source and sintered once to obtain the matrix material; The matrix material is first stirred and mixed in water, followed by the addition of phosphate for a second stirring and mixing, and then dried to coat the surface of the matrix material with the phosphate, resulting in a dried material. The phosphate is a phosphate compound containing at least one of the following metal elements: Co, Mn, Ti, Mg, Al, Ni, and Nb. The dried material is sintered a second time to form a phosphate coating layer on the surface of the matrix material, thereby obtaining the high-nickel ternary cathode material.

2. The preparation method according to claim 1, characterized in that, The phosphate includes at least one of AlPO4 and Mg3(PO4)2.

3. The preparation method according to claim 1, characterized in that, The mass ratio of the matrix material to the phosphate is 1:(0.0003~0.005); and / or, The molar ratio of lithium element in the lithium source to the total molar amount of metal elements in the high-nickel ternary precursor is 1.0~1.16:

1.

4. The preparation method according to claim 1, characterized in that, The sintering atmosphere is oxygen, the sintering temperature is 700℃~900℃, and the sintering time is 10h~15h; and / or, The atmosphere for the secondary sintering is air or oxygen, the sintering temperature is 500℃~750℃, and the sintering time is 6h~14h.

5. The preparation method according to claim 1, characterized in that, Before the step of adding the matrix material to water for the first stirring and mixing, the method further includes: The matrix material is mechanically pulverized to achieve a median particle size of 9μm-11μm.

6. The preparation method according to claim 1, characterized in that, The stirring time for the first mixing is 1 min to 3 min, and the stirring frequency is 10 Hz to 30 Hz. The stirring time for the second mixing is 1 min to 5 min, and the stirring frequency is 10 Hz to 30 Hz. The drying conditions are: drying in a vacuum at 120~150℃ for 5~10 hours.

7. The preparation method according to claim 1, characterized in that, The chemical formula of the high-nickel ternary precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.7≤x≤0.9, 0.05≤y≤0.

15.

8. The preparation method according to claim 1, characterized in that, The median particle size D50 of the high-nickel ternary cathode material is 9 μm to 11 μm; and / or, The Span value of the high-nickel ternary cathode material is 1.3~1.5; and / or, The compaction density of the high-nickel ternary cathode material is 2.5 g / cm³. 3 ~2.9g / cm 3 .

9. A high-nickel ternary cathode material, characterized in that, The high-nickel ternary cathode material is prepared by the preparation method as described in any one of claims 1 to 8.

10. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, and the positive electrode material is the high-nickel ternary positive electrode material as described in claim 9.

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