Modified ternary positive electrode material, preparation method thereof and secondary battery

Abstract

The invention discloses a modified ternary positive electrode material, a preparation method thereof and a secondary battery. The preparation method of the modified ternary positive electrode material comprises the following steps: mixing the ternary positive electrode material and a coating auxiliary material through sanding to obtain slurry; the slurry is dried through spray drying, the coating auxiliary materials comprise one or more of aluminum hydroxide, aluminum oxide, aluminum phosphate, titanium oxide, hydroxyl cobalt oxide, cobalt nitrate and strontium carbonate, and a mixture is obtained; and sintering the mixture to obtain the modified ternary positive electrode material. According to the preparation method, the residual alkali content of the obtained modified ternary positive electrode material is reduced by improving a material mixing process, the process is relatively simple and convenient, a water washing process can be reduced, and the process cost is saved. The modified ternary positive electrode material is prepared by the preparation method, has low residual alkali content and good cycle performance, can maintain good uniformity in the homogenizing and coating process when being used for processing, such as manufacturing a secondary battery, and can provide good electrochemical performance for the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and particularly to a modified ternary cathode material, a preparation method thereof, and a secondary battery. Background Art

[0002] For secondary batteries, such as lithium-ion batteries, as the core power source of new energy vehicles, the energy density, cycle performance, and safety performance of the cathode material are crucial. However, for existing cathode materials, especially high-nickel ternary cathode materials, there is a problem of relatively high residual alkali content. The residual alkali is prone to side reactions with the electrolyte and is also prone to decompose to generate a large amount of gas, resulting in capacity attenuation of the secondary battery and triggering safety risks. Moreover, too high a residual alkali content will cause uneven homogenization and coating during the production of secondary batteries (such as the appearance of a "jelly-like" phenomenon during the process), increasing the processing difficulty of the electrode sheet. Summary of the Invention

[0003] In view of this, the present application provides a preparation method of a modified ternary cathode material to solve at least one of the above technical problems. In addition, the present application also provides a modified ternary cathode material and a secondary battery.

[0004] To achieve the above object, in a first aspect, the present application provides a preparation method of a cathode material, the preparation method comprising: mixing a ternary cathode material with a coating auxiliary material by sand grinding, the coating auxiliary material comprising one or more of aluminum hydroxide, aluminum oxide, aluminum phosphate, titanium oxide, cobalt oxyhydroxide, cobalt nitrate, and strontium carbonate, to obtain a slurry; drying the slurry by spray drying to obtain a mixture; and sintering the mixture to obtain a modified ternary cathode material.

[0005] This application uses a sanding process for mixing materials, which can improve the coating uniformity of the coating auxiliary on the surface of the ternary cathode material and achieve good interfacial consistency. Moreover, during the sanding process, the residual alkali in the ternary cathode material can combine and react with the above-mentioned coating auxiliary, thereby reducing the residual alkali content of the obtained modified ternary cathode material. In addition, the uniform coating of the coating auxiliary on the surface of the ternary cathode material and good interfacial consistency are also beneficial to reducing the side reactions between the obtained modified ternary cathode material and the electrolyte. This application also combines the process of spray drying to dry the slurry after sanding and mixing, which can synergistically improve the coating uniformity of the coating auxiliary on the surface of the ternary cathode material and achieve good interfacial consistency. Moreover, during the spray drying process, the residual alkali in the ternary cathode material can also combine with the liquid medium in the slurry and be carried out with the liquid medium during the drying process, thereby further reducing the residual alkali content of the obtained modified ternary cathode material. This not only helps to reduce the side reactions between the modified ternary cathode material and the electrolyte, thus improving the cycle performance and safety of the modified ternary cathode material, but also contributes to improving the slurry homogenization and coating uniformity of the obtained modified ternary cathode material and reducing the processing difficulty. This application reduces the residual alkali content of the obtained modified ternary cathode material by improving the mixing process, the preparation process is relatively simple, and the water washing process can be reduced, which is beneficial to saving the process cost.

[0006] Based on the first aspect, in some possible implementation manners, the ternary cathode material and the coating auxiliary are mixed with a liquid medium after sanding to obtain a slurry, and the mass ratio of the liquid medium to the sanding mixture is 0.4 to 1. This application finds that controlling the mass ratio of the liquid medium to the sanding mixture within the above range is beneficial to further improving the mixing uniformity of spray drying and mixing, and at the same time further promoting the full combination of the residual alkali and the liquid medium. Therefore, more residual alkali can react with the coating auxiliary or be carried out with the liquid medium, which is beneficial to further reducing the residual alkali content of the obtained modified ternary cathode material.

[0007] Based on the first aspect, in some possible implementation manners, the temperature for sintering the mixture is 500 °C to 750 °C, and the time is 10 h to 14 h. When sintering the mixture, controlling the temperature and time within the above range is beneficial to controlling the particle morphology and size of the sintering product, thereby being beneficial to further improving the electrochemical performance of the obtained modified ternary cathode material.

[0008] Based on the first aspect, in some possible implementation manners, before mixing the ternary cathode material and the coating auxiliary, the preparation method further includes: crushing the ternary cathode material. Crushing helps to improve the mixing uniformity of the ternary cathode material and the coating auxiliary, enables the two to contact more fully, and increases the possibility of combination and reaction.

[0009] Based on the first aspect, in some possible implementation manners, before mixing the ternary cathode material with the coating auxiliary material, the preparation method further includes: mixing a lithium salt with a ternary cathode material precursor to obtain a dry mixture, and sintering the dry mixture to obtain the ternary cathode material. By mixing materials in stages and sintering in stages to prepare the modified ternary cathode material, it is beneficial to reduce the mixing of lithium and nickel, thereby improving the structural stability and cycling performance of the obtained modified ternary cathode material.

[0010] Based on the first aspect, in some possible implementation manners, the chemical general formula of the ternary cathode material is: Li a Ni x Co y Mn 1-x-y O2, where 1.0 ≤ a ≤ 1.08, 0.7 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.15. Ternary materials with a higher nickel content are more likely to have problems such as residual alkali and lithium-nickel mixing. Therefore, while taking advantage of the high nickel (such as higher energy density, excellent rate performance, and good cycling performance), this application effectively improves the above problems caused by high nickel.

[0011] Based on the first aspect, in some possible implementation manners, the dry mixture further includes a dopant, and the dopant includes one or more of an Sr source, a Mg source, an Al source, and a Zr source. The presence of the above dopant in the dry mixture is beneficial to improve the mixing uniformity of the dry mixture, thereby being beneficial to improve the distribution uniformity of lithium in the obtained ternary cathode material.

[0012] Based on the first aspect, in some possible implementation manners, the temperature for sintering the dry mixture is 700 °C to 900 °C, and the time is 8 h to 15 h. When sintering the dry mixture, controlling the temperature and time within the above ranges is beneficial to control the particle morphology and size of the sintered product, thereby being beneficial to further improve the electrochemical performance of the obtained modified ternary cathode material.

[0013] In the second aspect, this application provides a modified ternary cathode material, which is prepared by the above preparation method. The modified ternary cathode material of this application has a low residual alkali content and good cycling performance. When used for processing, such as making secondary batteries, the modified ternary cathode material can maintain good uniformity during the slurry mixing and coating processes, and can provide good electrochemical performance for secondary batteries.

[0014] In the third aspect, this application provides a secondary battery, which includes the above modified ternary cathode material. The secondary battery of this application has a high capacity, a high first Coulombic efficiency, and good cycling performance. Description of the Drawings

[0015] Figure 1Process flow chart of the preparation method of the modified ternary cathode material provided by an embodiment of the present application.

[0016] Figure 2 Process flow chart of another preparation method of the modified ternary cathode material provided by an embodiment of the present application.

[0017] Figure 3 Scanning electron microscope image of the modified ternary cathode material particles obtained by the preparation method provided in Example 1 of the present application.

[0018] Figure 4 Scanning electron microscope image of the modified ternary cathode material particles obtained by the preparation method provided in Comparative Example 1 of the present application. Detailed description of specific embodiments

[0019] The embodiments of the present application will be described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and should not be construed as a limitation of the present application; it should be noted that unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs; in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other; a lot of specific details are set forth in the following description in order to fully understand the present application, and the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0020] To solve the problem of too high residual alkali content in the cathode material, the related art usually adds a water washing process or adopts the method of multiple sintering to reduce the residual alkali content of the cathode material. However, these means are all likely to cause lithium loss on the surface of the cathode material, resulting in a decline in the electrochemical performance of the cathode material, and additionally adding a process or increasing the process complexity usually increases the process cost. Therefore, the present application improves the preparation method of the cathode material to achieve the purpose of reducing the residual alkali content of the cathode material and better controlling the process cost.

[0021] Based on this, please refer to Figure 1 , an embodiment of the present application provides a preparation method of a modified ternary cathode material, and the preparation method includes: S10: Mix the ternary cathode material and the coating auxiliary material by sand grinding. The coating auxiliary material includes one or more of aluminum hydroxide, aluminum oxide, aluminum phosphate, titanium oxide, cobalt oxyhydroxide, cobalt nitrate, and strontium carbonate to obtain a slurry.

[0022] This application uses a sanding process for mixing materials, which can improve the coating uniformity of the coating auxiliary on the surface of the ternary cathode material and achieve good interface consistency. Moreover, during the sanding process, the residual alkali in the ternary cathode material can combine and react with the above-mentioned coating auxiliary, thereby reducing the residual alkali content of the obtained modified ternary cathode material. In addition, the uniform coating of the coating auxiliary on the surface of the ternary cathode material and good interface consistency are also beneficial to reducing the side reactions between the obtained modified ternary cathode material and the electrolyte.

[0023] In some embodiments, after the ternary cathode material and the coating auxiliary are sanded in S10, they are mixed with a liquid medium to obtain a slurry. The mass ratio of the liquid medium to the sanded mixture is 0.4 to 1. For example, the mass ratio of the liquid medium to the sanded mixture is 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or any value within the range composed of any two of the above values. This application finds that controlling the mass ratio of the liquid medium to the sanded mixture within the above range is beneficial to further improving the mixing uniformity of spray drying and at the same time further promoting the full combination of the residual alkali and the liquid medium. Therefore, more residual alkali can react with the coating auxiliary or be carried out with the liquid medium, which is beneficial to further reducing the residual alkali content of the obtained modified ternary cathode material.

[0024] In some embodiments, before mixing the ternary cathode material and the coating auxiliary in S10, the preparation method further includes: crushing the ternary cathode material. Crushing helps to improve the mixing uniformity of the ternary cathode material and the coating auxiliary, enables the two to contact more fully, and increases the possibility of combination and reaction.

[0025] S20: Dry the slurry by spray drying to obtain a mixture.

[0026] This application also combines a spray drying process to dry the slurry after sanding and mixing, which can synergistically improve the coating uniformity of the coating auxiliary on the surface of the ternary cathode material and achieve good interface consistency. Moreover, during the spray drying process, the residual alkali in the ternary cathode material can also combine with the liquid medium in the slurry and be carried out with the liquid medium during the drying process, thereby further reducing the residual alkali content of the obtained modified ternary cathode material. This not only helps to reduce the side reactions between the modified ternary cathode material and the electrolyte, thereby improving the cycling performance and safety of the modified ternary cathode material, but also contributes to improving the slurry and coating uniformity of the obtained modified ternary cathode material and reducing the processing difficulty. This application reduces the residual alkali content of the obtained modified ternary cathode material by improving the mixing process. The preparation process is relatively simple and can reduce the water washing process, which is beneficial to saving process costs.

[0027] S30: Sinter the mixture to obtain a modified ternary cathode material.

[0028] In some embodiments, the temperature for sintering the mixture is 500 °C to 750 °C, and the time is 10 h to 14 h. For example, when sintering the mixture, the temperature can be 500 °C, 525 °C, 550 °C, 575 °C, 600 °C, 625 °C, 650 °C, 675 °C, 700 °C, 725 °C, 750 °C or any value within the range formed by any two of the above values, and the time can be 10 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h, 14 h or any value within the range formed by any two of the above values. When sintering the mixture, controlling the temperature and time within the above ranges is beneficial to controlling the particle morphology and size of the sintered product, thereby being beneficial to further improving the electrochemical performance of the obtained modified ternary cathode material.

[0029] In the related art, there is usually also a problem of insufficient structural stability in the ternary cathode material. As the nickel content in the ternary cathode material increases, such as in high-nickel ternary cathode materials, the structural stability decreases, and lithium-nickel mixing phenomenon is likely to occur, which affects the electrochemical performance of the ternary cathode material and limits the advantages of high-nickel materials from being exerted.

[0030] Based on this, please refer to Figure 2 , on the basis of the above preparation methods (S10, S20 and S30), an embodiment of the present application further provides a preparation method of a cathode material, and this preparation method includes: S100: Mix a lithium salt with a ternary cathode material precursor to obtain a dry mixture, and sinter the dry mixture to obtain a ternary cathode material.

[0031] The present application prepares the modified ternary cathode material by mixing in segments and sintering in segments, which is beneficial to reducing lithium-nickel mixing, thereby improving the structural stability and cycling performance of the obtained modified ternary cathode material.

[0032] In some embodiments, the chemical general formula of the ternary cathode material is: Li a Ni x Co y Mn 1-x-yO2, where 1.0 ≤ a ≤ 1.08, 0.7 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.15. For example, a can be 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08 or any value within the range formed by any two of the above values. x can be 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9 or any value within the range formed by any two of the above values. Y can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15 or any value within the range formed by any two of the above values. For example, the chemical formula of the ternary cathode material can be Li 1.05 Ni 0.8 Co 0.1 Mn 0.1 O2. Ternary materials with a higher nickel content are more likely to have problems such as residual alkali and lithium-nickel mixing. Therefore, while taking advantage of the high nickel advantages (such as higher energy density, excellent rate performance, and good cycling performance), this application effectively improves the above problems caused by high nickel.

[0033] In some embodiments, the dry blend further includes a dopant, and the dopant includes one or more of an Sr source, an Mg source, an Al source, and a Zr source. For example, the Sr source can be SrCO3, SrO, SrTiO3, etc., the Mg source can be Mg(OH)2, MgCO3, MgO, etc., the Al source can be Al(OH)3, Al2O3, etc., and the Zr source can be ZrO2. The presence of the above dopants in the dry blend is beneficial to improving the mixing uniformity of the dry blend, and thus beneficial to improving the distribution uniformity of lithium in the obtained ternary cathode material.

[0034] In some embodiments, the temperature for sintering the dry blend is 700 °C to 900 °C, and the time is 8 h to 15 h. For example, when sintering the dry blend, the temperature can be 700 °C, 720 °C, 740 °C, 760 °C, 780 °C, 800 °C, 820 °C, 840 °C, 860 °C, 880 °C, 900 °C or any value within the range formed by any two of the above values, and the time can be 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h, 14 h, 14.5 h, 15 h or any value within the range formed by any two of the above values. When sintering the dry blend, controlling the temperature and time within the above ranges is beneficial to controlling the particle morphology and size of the sintered product, and thus beneficial to further improving the electrochemical performance of the obtained modified ternary cathode material.

[0035] S200: The same as S10.

[0036] S300: The same as S20.

[0037] S400: The same as S30.

[0038] One embodiment of the present application further provides a modified ternary cathode material, which is prepared by the above - mentioned preparation method.

[0039] The modified ternary cathode material of the present application has a low residual alkali content and good cycle performance. When used for processing, such as manufacturing a secondary battery, the modified ternary cathode material can maintain good uniformity during the slurry mixing and coating processes, and can provide good electrochemical performance for the secondary battery.

[0040] One embodiment of the present application further provides a secondary battery, which includes the above - mentioned modified ternary cathode material.

[0041] The secondary battery of the present application has a high capacity, a high initial Coulomb efficiency, and good cycle performance.

[0042] In some embodiments, the secondary battery includes a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located inside the housing. The housing can be a packaging bag encapsulated with a packaging film (such as an aluminum - plastic film), for example, a soft - pack battery. In other embodiments, it can also be a steel - shell battery, an aluminum - shell battery, etc. The electrode assembly includes electrode sheets and a separator. The electrode sheets include a positive electrode sheet and a negative electrode sheet. The separator is used to separate the positive electrode sheet from the negative electrode sheet and can be disposed between the positive electrode sheet and the negative electrode sheet. In some embodiments, the electrode assembly can be a stacked - sheet structure, for example, it is formed by alternately stacking a positive electrode sheet, a separator, and a negative electrode sheet in sequence. In other embodiments, the electrode assembly can also be a wound structure, for example, it is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet stacked in sequence. The positive electrode sheet includes a positive electrode current collector and a positive electrode material active layer disposed on at least one surface of the positive electrode current collector. The positive electrode material active layer includes the above - mentioned positive electrode material.

[0043] In some embodiments, the secondary battery can be a lithium - ion battery, a sodium - ion battery, or a potassium - ion battery.

[0044] The solutions of the present application will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following examples are only for explaining the present application and should not be construed as limiting the present application. Unless otherwise specified, the reagents, software, and instruments involved in the following embodiments that are not specifically described are all commercially available products or open - source.

[0045] Example 1: A preparation method of a modified ternary cathode material, comprising: Step 1: Mix lithium hydroxide with Ni 0.8 Co 0.1 Mn 0.1 (OH)2 precursor in a molar ratio of 1.05 (i.e., lithium metal ratio Li / Me), and add SrCO3 and ZrO2, etc. as dopants. Mix and stir evenly using a plow mixer for 20 min to obtain a dry mixture. Sinter the dry mixture in an oxygen atmosphere at a sintering temperature of 850 °C and a main temperature zone duration of 12 h to obtain a ternary cathode material.

[0046] Step 2: Subject the ternary cathode material to air flow pulverization to obtain a pulverized product. Grind the pulverized product and coating auxiliary material Al2O3 to obtain a ground mixture. Mix water and the ground mixture in a mass ratio of 0.6 (i.e., water / ground mixture) to obtain a slurry.

[0047] Step 3: Dry the slurry through a spray drying device to obtain a mixture.

[0048] Step 4: Sinter the mixture in an oxygen atmosphere at a sintering temperature of 650 °C and a main temperature zone duration of 10 h to obtain a cathode material.

[0049] Example 2: The difference from Example 1 is that in Step 2, the water-to-material ratio is 0.4.

[0050] Example 3: The difference from Example 1 is that in Step 2, the water-to-material ratio is 1.

[0051] Example 4: The difference from Example 1 is that in Step 2, the water-to-material ratio is 0.2.

[0052] Example 5: The difference from Example 1 is that in Step 2, the water-to-material ratio is 1.2.

[0053] Example 6: The difference from Example 1 is that in Step 1, the sintering temperature is 1000 °C and the main temperature zone duration is 16 h.

[0054] Example 7: The difference from Example 1 is that in Step 1, the sintering temperature is 600 °C and the main temperature zone duration is 7 h.

[0055] Example 8: The difference from Example 1 is that in Step 4, the sintering temperature is 850 °C and the main temperature zone duration is 15 h.

[0056] Example 9: The difference from Example 1 is that in Step 4, the sintering temperature is 400 °C and the main temperature zone duration is 9 h.

[0057] Comparative Example 1: The difference from Example 1 is that in the second step, sanding is not carried out, and spray drying in the third step is not carried out either. The pulverized product and the coating auxiliary material Al2O3 are mixed evenly by a pear-shaped blade mixer to obtain a mixture.

[0058] Comparative Example 2: The difference from Comparative Example 1 is that after obtaining the modified ternary cathode material, a water washing process and a low-temperature sintering process at 300 °C are added to reduce the residual alkali content.

[0059] Taking Example 1 and Comparative Example 1 as examples, in this application, the particle morphology of the cathode material obtained by the corresponding preparation method was tested by a scanning electron microscope (model: JSM-6510, equipment manufacturer: JEOL Ltd., Japan). Please refer to Figure 3 , on the basis of using the same coating auxiliary material and sintering conditions, the polycrystalline particle coating uniformity of the modified ternary cathode material obtained by sanding combined with spray drying in Example 1 is better, indicating that during the mixing process, the ternary cathode material and the coating auxiliary material are in full contact, and further indicating that the residual alkali also fully combines with the coating auxiliary material or the liquid medium during this process, and can be effectively reacted or carried out. In contrast, please refer to Figure 4 , in Comparative Example 1 (the second step), dry mixing is used for mixing. Only locally on the surface of the obtained cathode material is there the coating auxiliary material, and some of the auxiliary materials are on the surface and are not completely coated on the cathode material after sintering, indicating that the coating uniformity is relatively poor. During the mixing process, the contact between the residual alkali and the coating auxiliary material may not be sufficient, and the residual alkali cannot be carried out through the liquid medium either. The effect of removing the residual alkali from the cathode material during the preparation process may not be good.

[0060] This application also carried out the following processing and performance tests on the modified ternary cathode materials obtained in Examples 1-9 and Comparative Examples 1-2. The test results are shown in Table 1: 1. Test of free lithium content to characterize the residual alkali content of each cathode material. The test method for free lithium content includes: potentiometric titration method. A certain volume of water is used to dissolve the residual alkali on the surface of a certain mass of the sample, and after filtration, the filtrate is taken and titrated with a standard hydrochloric acid titration solution. The titration end point is determined by the potential jump during the reaction process, and its content is calculated, and the residual alkali content is obtained through conversion.

[0061] 2. Particle size test: After ultrasonic dispersion of the cathode material for 5 min, the particle sizes Dv10, Dv50, and Dv90 are measured by a Malvern 3000 particle size analyzer, and the particle size span (span) is calculated, span = (Dv90 - Dv10) / Dv50.

[0062] 3. Compaction density test: The cathode material is pressed into powder under a pressure of 200 MPa, and the compaction density is measured by a compaction density meter (model: PRCD-1100, equipment manufacturer: Yuaneng Technology).

[0063] 4. Preparation of half-cell: The cathode material, conductive carbon, and binder PVDF were uniformly mixed at a mass ratio of 90:5:5.

[0064] 5. Electrochemical performance test: The obtained half-cell was subjected to constant current charge and discharge test using a Blue Power battery test system. The working voltage range for the first charge capacity test was 2.8 V - 4.3 V, the charge and discharge rate was +1C / -1C, and the CV cut-off current was 0.01 C. For the high-temperature cycle test, the working voltage range was 2.8 V - 4.3 V, the temperature was 45 °C, the charge and discharge rate was +1C / 1C, and the CV cut-off current was 0.01 C.

[0065] Table 1. Performance test results of the modified ternary cathode materials obtained in Examples 1 - 9 and Comparative Examples 1 - 2 of this application In the preparation method of the modified ternary cathode materials of Examples 1 - 9 of this application, the sanding process was used for mixing, which could improve the coating uniformity of the coating auxiliary on the surface of the ternary cathode material and achieve good interface consistency. Moreover, during the sanding process, the residual alkali in the ternary cathode material could combine and react with the above-mentioned coating auxiliary, thereby reducing the residual alkali content of the obtained modified ternary cathode material. In addition, the uniform coating of the coating auxiliary on the surface of the ternary cathode material and the good interface consistency were also beneficial to reducing the side reaction between the obtained modified ternary cathode material and the electrolyte. The above preparation method also combined the spray drying process to dry the slurry after sanding and mixing, which could synergistically improve the coating uniformity of the coating auxiliary on the surface of the ternary cathode material and achieve good interface consistency. And during the spray drying process, the residual alkali in the ternary cathode material could also combine with the liquid medium in the slurry and be carried out with the liquid medium during the drying process, thereby further reducing the residual alkali content of the obtained modified ternary cathode material. This not only was beneficial to reducing the side reaction between the modified ternary cathode material and the electrolyte, thereby improving the cycle performance and safety of the modified ternary cathode material, but also helped to improve the slurry and coating uniformity of the obtained modified ternary cathode material and reduce the processing difficulty. The preparation method of the modified ternary cathode materials of Examples 1 - 9 of this application reduced the residual alkali content of the obtained modified ternary cathode material by improving the mixing process, the preparation process was relatively simple, and the water washing process could be reduced, which was beneficial to saving the process cost.

[0066] Among them, based on Examples 4-5, Examples 1-3 further control the mass ratio of the liquid medium to the sanding mixture within a preset range, which can further improve the uniformity of the spray-dried mixture, and at the same time further promote the full combination of the residual alkali and the liquid medium. Therefore, more residual alkali can react with the coating auxiliary or be carried out with the liquid medium, further reducing the residual alkali content of the obtained modified ternary cathode material. Based on Examples 6-7, Examples 1-3 further control the sintering conditions of the dry mixture within a preset range. Based on Examples 8-9, Examples 1-3 further control the sintering conditions of the mixture within a preset range, which are all beneficial to controlling the particle morphology and size of the sintered product, thereby being beneficial to further improving the electrochemical performance of the obtained modified ternary cathode material.

[0067] Compared with Example 1, Comparative Example 1 uses dry mixing (instead of sanding and spray drying) for mixing. During the preparation process, the removal path of the residual alkali becomes less, and the contact between the residual alkali and the coating auxiliary may be insufficient, resulting in the free lithium content of the modified ternary cathode material obtained in Comparative Example 1 being about 500 ppm higher (also significantly higher than other examples), that is, the residual alkali content in the modified ternary cathode material obtained in Comparative Example 1 is relatively high (consistent with the result speculated during the above morphology test), indicating that the preparation method of Comparative Example 1 has a poor effect on removing the residual alkali. Combining with Comparative Example 2, the modified ternary cathode material obtained in Comparative Example 1 needs to add an additional water washing process and a low-temperature sintering process to reduce the residual alkali content to a level close to that of the examples of the present application. This also shows that the preparation method of the examples of the present application can effectively reduce the residual alkali content during the preparation process, can reduce or even replace the water washing process, and does not require additional firing treatment, significantly saving the process cost.

[0068] The above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A preparation method of a modified ternary cathode material, characterized in that, The preparation method includes: Mixing the ternary cathode material and the coating auxiliary materials by sand milling, where the coating auxiliary materials include one or more of aluminum hydroxide, aluminum oxide, aluminum phosphate, titanium oxide, cobalt oxyhydroxide, cobalt nitrate, and strontium carbonate, to obtain a slurry; Drying the slurry by spray drying to obtain a mixture; Sintering the mixture to obtain the modified ternary cathode material.

2. The preparation method according to claim 1, characterized in that, The ternary cathode material and the coating auxiliary materials are mixed with a liquid medium after the sand milling to obtain the slurry, and the mass ratio of the liquid medium to the sand milling mixture is 0.4 to 1.

3. The preparation method according to claim 1, characterized in that, The temperature for sintering the mixture is 500°C to 750°C, and the time is 10 h to 14 h.

4. The preparation method according to claim 1, wherein Before mixing the ternary cathode material and the coating auxiliary materials, the preparation method further includes: Crushing the ternary cathode material.

5. The preparation method according to claim 1, characterized in that, Before mixing the ternary cathode material and the coating auxiliary materials, the preparation method further includes: Mixing a lithium salt with a ternary cathode material precursor to obtain a dry mixture, and sintering the dry mixture to obtain the ternary cathode material.

6. The preparation method according to claim 5, characterized in that, The chemical general formula of the ternary cathode material is: Li a Ni x Co y Mn 1-x-y O2, where 1.0 ≤ a ≤ 1.08, 0.7 ≤ x ≤ 0.9, 0.05 ≤ y ≤ 0.

15.

7. The preparation method according to claim 5, characterized in that The dry mixture further includes a dopant, and the dopant includes one or more of an Sr source, an Mg source, an Al source, and a Zr source.

8. The preparation method according to claim 5, characterized in that, The temperature for sintering the dry mixture is 700°C to 900°C, and the time is 8 h to 15 h.

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

10. A secondary battery, characterized in that, The secondary battery includes the modified ternary cathode material according to claim 9.

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