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

Abstract

A modified ternary cathode material, its preparation method, and a secondary battery are disclosed. The preparation method of the modified ternary cathode material includes: mixing the ternary cathode material and coating additives through sand milling to obtain a slurry; drying the slurry by spray drying; the coating additives include one or more of aluminum hydroxide, alumina, aluminum phosphate, titanium oxide, cobalt hydroxyl oxide, cobalt nitrate, and strontium carbonate to obtain a mixture; and sintering the mixture to obtain the modified ternary cathode material. This preparation method reduces the residual alkali content of the obtained modified ternary cathode material by improving the mixing process. The process is relatively simple, reduces the need for water washing, and helps save process costs. The modified ternary cathode material obtained by the above preparation method has a low residual alkali content and good cycle performance. When used in processing, such as manufacturing secondary batteries, the modified ternary cathode material can maintain good uniformity during the homogenization and coating processes, providing good electrochemical performance for the secondary battery.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage, specifically to a modified ternary cathode material and its preparation method, and a secondary battery. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, are the core power source for new energy vehicles, and the energy density, cycle performance, and safety performance of their cathode materials are crucial. However, existing cathode materials, especially high-nickel ternary cathode materials, are prone to high residual alkali content. Residual alkali is easily involved in side reactions with the electrolyte and can also decompose to produce a large amount of gas, causing capacity decay and posing safety risks to the secondary battery. Moreover, excessively high residual alkali content can lead to uneven slurry and coating during secondary battery manufacturing (such as the appearance of a "jelly-like" phenomenon during the process), increasing the processing difficulty of the electrode sheets. Summary of the Invention

[0003] In view of this, this application provides a method for preparing a modified ternary cathode material, solving at least one of the above-mentioned technical problems. Furthermore, this application also provides a modified ternary cathode material and a secondary battery.

[0004] To achieve the above objectives, in a first aspect, this application provides a method for preparing a cathode material, the method comprising: mixing a ternary cathode material with a coating additive by sand milling, wherein the coating additive includes one or more of aluminum hydroxide, aluminum oxide, aluminum phosphate, titanium oxide, cobalt hydroxyl oxide, 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 employs a sand milling process for mixing, which improves the uniformity of coating excipients on the surface of the ternary cathode material and achieves good interfacial consistency. Furthermore, during the sand milling process, residual alkali in the ternary cathode material can combine and react with the aforementioned coating excipients, thereby reducing the residual alkali content of the resulting modified ternary cathode material. In addition, the uniform coating of the coating excipients on the surface of the ternary cathode material and the good interfacial consistency also help reduce side reactions between the resulting modified ternary cathode material and the electrolyte. This application also incorporates a spray drying process to dry the slurry after sand milling, which synergistically improves the uniformity of coating excipients on the surface of the ternary cathode material and achieves good interfacial consistency. Furthermore, during spray drying, the residual alkali in the ternary cathode material can combine with the liquid medium in the slurry and be carried out with the liquid medium during drying, thereby further reducing the residual alkali content of the obtained modified ternary cathode material. This not only helps reduce 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 helps improve the homogenization and coating uniformity of the obtained modified ternary cathode material, reducing processing difficulty. This application reduces the residual alkali content of the obtained modified ternary cathode material by improving the mixing process, which simplifies the preparation process and reduces the need for water washing, thus saving process costs.

[0006] Based on the first aspect, in some possible implementations, the ternary cathode material and coating excipients are milled and then mixed with a liquid medium to obtain a slurry, wherein the mass ratio of the liquid medium to the milled mixture is 0.4 to 1. This application finds that controlling the mass ratio of the liquid medium to the milled mixture within the above range is beneficial for further improving the uniformity of the spray-dried mixture and simultaneously further promoting the full combination of residual alkali and the liquid medium. Therefore, more residual alkali can react with the coating excipients or be carried out with the liquid medium, which is beneficial for further reducing the residual alkali content of the obtained modified ternary cathode material.

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

[0008] Based on the first aspect, in some possible implementations, before mixing the ternary cathode material with the coating additives, the preparation method further includes: pulverizing the ternary cathode material. Pulverization helps improve the mixing uniformity of the ternary cathode material and the coating additives, allowing them to come into more complete contact and increasing the possibility of bonding and reaction.

[0009] Based on the first aspect, in some possible implementations, before mixing the ternary cathode material with the coating additives, the preparation method further includes: mixing lithium salt with the ternary cathode material precursor to obtain a dry mixture, and sintering the dry mixture to obtain the ternary cathode material. This application prepares modified ternary cathode materials through segmented mixing and segmented sintering, which helps reduce lithium-nickel mixing, thereby improving the structural stability and cycle performance of the obtained modified ternary cathode material.

[0010] Based on the first aspect, in some possible implementations, the general chemical 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 higher nickel content are more prone to residual alkali problems and lithium-nickel mixing problems. Therefore, this application effectively improves the above-mentioned problems caused by high nickel content while utilizing the advantages of high nickel (such as higher energy density, excellent rate performance and good cycle performance).

[0011] Based on the first aspect, in some possible implementations, the dry mix further includes a dopant, which includes one or more of Sr, Mg, Al, and Zr sources. The presence of these dopants in the dry mix is ​​beneficial for improving the mixing uniformity of the dry mix, thereby improving the uniformity of lithium distribution in the resulting ternary cathode material.

[0012] Based on the first aspect, in some possible implementations, the sintering temperature of the dry mixture is 700 ℃ to 900 ℃, and the time is 8 h to 15 h. When sintering the dry mixture, controlling the temperature and time within the above range is beneficial to controlling the particle morphology and size of the sintered product, thereby further improving the electrochemical performance of the obtained modified ternary cathode material.

[0013] Secondly, this application provides a modified ternary cathode material, which is prepared by the above-described preparation method. The modified ternary cathode material of this application has a low residual alkali content and good cycle performance. When used in processing, such as manufacturing secondary batteries, the modified ternary cathode material can maintain good uniformity during homogenization and coating processes, thus providing good electrochemical performance for secondary batteries.

[0014] Thirdly, this application provides a secondary battery comprising the aforementioned modified ternary cathode material. The secondary battery of this application exhibits high capacity, initial coulombic efficiency, and good cycle performance. Attached Figure Description

[0015] Figure 1A process flow diagram of the preparation method of the modified ternary cathode material provided in one embodiment of this application.

[0016] Figure 2 A process flow diagram of another preparation method of the modified ternary cathode material provided in one embodiment of this 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 this 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 this application. Detailed Implementation

[0019] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, 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 this application belongs; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0020] To address the problem of excessively high residual alkali content in cathode materials, related technologies typically employ additional water washing processes or multiple sintering methods to reduce the residual alkali content. However, these methods can easily lead to lithium loss from the cathode material surface, resulting in a decline in the electrochemical performance of the cathode material. Furthermore, adding extra processes or increasing process complexity usually increases process costs. Therefore, this application aims to reduce the residual alkali content of cathode materials and better control process costs by improving the preparation method of cathode materials.

[0021] Based on this, please refer to Figure 1 One embodiment of this application provides a method for preparing a modified ternary cathode material, the method comprising: S10: The ternary cathode material and the coating additives are mixed by sand milling. The coating additives include one or more of aluminum hydroxide, aluminum oxide, aluminum phosphate, titanium oxide, cobalt hydroxyl oxide, cobalt nitrate and strontium carbonate to obtain a slurry.

[0022] This application employs a sand milling process for mixing, which improves the uniformity of coating excipients on the surface of the ternary cathode material and achieves good interfacial consistency. Furthermore, during the sand milling process, residual alkali in the ternary cathode material can combine and react with the aforementioned coating excipients, thereby reducing the residual alkali content of the resulting modified ternary cathode material. In addition, the uniform coating of the excipients on the surface of the ternary cathode material and the good interfacial consistency also help reduce side reactions between the resulting modified ternary cathode material and the electrolyte.

[0023] In some embodiments, in S10, the ternary cathode material and the coating excipients are milled and then mixed with a liquid medium to obtain a slurry. The mass ratio of the liquid medium to the milled mixture is 0.4 to 1. For example, the mass ratio of the liquid medium to the milled 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 of any two of the above values. This application has found that controlling the mass ratio of the liquid medium to the milled mixture within the above range is beneficial to further improve the uniformity of the spray-dried mixture and at the same time further promotes the full combination of residual alkali and the liquid medium. Therefore, more residual alkali can react with the coating excipients or be carried out with the liquid medium, which is beneficial to further reduce the residual alkali content of the obtained modified ternary cathode material.

[0024] In some embodiments, before mixing the ternary cathode material with the coating additives in S10, the preparation method further includes pulverizing the ternary cathode material. Pulverization helps improve the mixing uniformity of the ternary cathode material and the coating additives, allowing them to come into more complete contact and increasing the possibility of bonding and reaction.

[0025] S20: The slurry is dried by spray drying to obtain a mixture.

[0026] This application also incorporates a spray drying process to dry the slurry after sand milling and mixing, which synergistically improves the uniformity of coating excipients on the surface of the ternary cathode material and achieves good interfacial consistency. Furthermore, during spray drying, residual alkali in the ternary cathode material can combine with the liquid medium in the slurry and be carried out with the liquid medium during drying, thereby further reducing the residual alkali content of the resulting modified ternary cathode material. This not only helps reduce 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 helps improve the homogenization and coating uniformity of the resulting modified ternary cathode material, reducing processing difficulty. This application reduces the residual alkali content of the resulting modified ternary cathode material by improving the mixing process, simplifying the preparation process and reducing the need for water washing, which helps save process costs.

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

[0028] In some embodiments, the sintering temperature of the mixture is from 500 °C to 750 °C, and the time is from 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 of 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 of any two of the above values. Controlling the temperature and time within the above ranges when sintering the mixture is beneficial for controlling the particle morphology and size of the sintered product, thereby further improving the electrochemical performance of the obtained modified ternary cathode material.

[0029] In related technologies, ternary cathode materials often suffer from insufficient structural stability. As the nickel content in ternary cathode materials increases, such as high-nickel ternary cathode materials, structural stability decreases, and lithium-nickel mixing is prone to occur, affecting the electrochemical performance of ternary cathode materials and limiting the advantages of high-nickel materials.

[0030] Based on this, please refer to Figure 2 Based on the above preparation methods (S10, S20 and S30), one embodiment of this application also provides a method for preparing a positive electrode material, the method comprising: S100: Lithium salt is mixed with ternary cathode material precursor to obtain dry mixture, and the dry mixture is sintered to obtain ternary cathode material.

[0031] This application prepares modified ternary cathode materials through segmented mixing and sintering, which helps to reduce lithium-nickel mixing and thus improves the structural stability and cycle performance of the obtained modified ternary cathode materials.

[0032] In some embodiments, the general chemical 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, and 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 of 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 of 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 of 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 higher nickel content are more prone to residual alkali problems and lithium-nickel mixing problems. Therefore, this application effectively improves the above-mentioned problems caused by high nickel content while utilizing the advantages of high nickel (such as higher energy density, excellent rate performance and good cycle performance).

[0033] In some embodiments, the dry mix further includes a dopant, which includes one or more of Sr, Mg, Al, and Zr sources. 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-mentioned dopant in the dry mix is ​​beneficial to improving the mixing uniformity of the dry mix, thereby improving the uniformity of lithium distribution in the resulting ternary cathode material.

[0034] In some embodiments, the sintering temperature of the dry mix is ​​700 °C to 900 °C, and the time is 8 h to 15 h. For example, when sintering the dry mix, 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 of 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 of any two of the above values. When sintering the dry mixture, controlling the temperature and time within the above range is beneficial to controlling the particle morphology and size of the sintered products, thereby further improving the electrochemical performance of the obtained modified ternary cathode material.

[0035] S200: Same as S10.

[0036] S300: Same as S20.

[0037] S400: Same as S30.

[0038] An embodiment of this application also provides a modified ternary cathode material, which is prepared by the above-described preparation method.

[0039] The modified ternary cathode material of this application has a low residual alkali content and good cycle performance. When used in processing, such as manufacturing secondary batteries, the modified ternary cathode material can maintain good uniformity during the homogenization and coating process, and can provide good electrochemical performance for secondary batteries.

[0040] One embodiment of this application also provides a secondary battery comprising the modified ternary cathode material described above.

[0041] The secondary battery of this application has high capacity, initial coulombic efficiency and good cycle performance.

[0042] In some embodiments, the secondary battery includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing. The casing can be a packaging bag encapsulated with a film (such as an aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased 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 and negative electrode sheets and can be disposed between the positive and negative electrode sheets. In some embodiments, the electrode assembly can be a stacked structure, for example, it is formed by alternately stacking a positive electrode sheet, a separator, and a negative electrode sheet. 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 after they are stacked in sequence. The positive electrode sheet includes a positive current collector and a positive electrode material active layer disposed on at least one surface of the positive current collector. The positive electrode material active layer includes the aforementioned positive electrode material.

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

[0044] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.

[0045] Example 1: A method for preparing a modified ternary cathode material, comprising: Step 1: React lithium hydroxide with Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor was mixed at a molar ratio of 1.05 (i.e., lithium metal ratio Li / Me), and SrCO3 and ZrO2 were added as dopants. The mixture was stirred evenly using a plow mixer for 20 minutes to obtain a dry mixture. The dry mixture was then sintered in an oxygen atmosphere at a sintering temperature of 850 °C for 12 h in the main sintering zone to obtain the ternary cathode material.

[0046] Step 2: The ternary cathode material is subjected to air jet milling to obtain the pulverized product. The pulverized product and the coating auxiliary material Al2O3 are then sand-milled to obtain a sand-milled mixture. Water and the sand-milled mixture are mixed at a mass ratio of 0.6 (i.e., water / sand-milled mixture) to obtain a slurry.

[0047] Step 3: The slurry is dried using a spray drying device to obtain a mixture.

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

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

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

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

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

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

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

[0055] Example 8: The difference from Example 1 is that in the fourth step, the sintering temperature is 850 ℃ and the main temperature zone duration is 15h.

[0056] Example 9: The difference from Example 1 is that in the fourth step, the sintering temperature is 400 ℃ and the main temperature zone duration is 9h.

[0057] Comparative Example 1: The difference from Example 1 is that the second step does not involve sand milling, nor does the third step involve spray drying. Instead, the pulverized product and the coating excipient Al2O3 are mixed evenly using a pear-shaped 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 and 300 ℃ low-temperature calcination process were added to reduce the residual alkali content.

[0059] Taking Example 1 and Comparative Example 1 as examples, the particle morphology of the cathode materials obtained by the corresponding preparation methods was tested using a scanning electron microscope (model: JSM-6510, manufacturer: NEC). Please refer to... Figure 3 Using the same coating additives and sintering conditions, Example 1, which employed a combination of sand milling and spray drying to mix the modified ternary cathode material, exhibited better polycrystalline particle coating uniformity. This demonstrates that during the mixing process, the ternary cathode material and the coating additives achieved sufficient contact, indicating that residual alkali also fully combined with the coating additives or liquid medium, effectively reacting or being carried away. For comparison, please refer to [link to relevant documentation]. Figure 4 In Comparative Example 1 (Step 2), the materials were mixed using a dry mixing method. The resulting cathode material had only localized coatings on its surface, and some of the coatings were present on the surface. After sintering, they were not completely coated onto the cathode material, indicating that the coating uniformity was relatively poor. During the mixing process, the contact between the residual alkali and the coatings may not have been sufficient, and the residual alkali could not be carried out by the liquid medium. The removal effect of residual alkali from the cathode material during the preparation process may have been poor.

[0060] This application also conducted 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. Testing of free lithium content to characterize the residual alkali content of each cathode material. The testing methods for free lithium content include: potentiometric titration, in which a certain volume of water is used to dissolve the residual alkali on the surface of a certain mass of sample, the filtrate is filtered and titrated with a standard hydrochloric acid titration solution, the titration endpoint is determined by the point jump during the reaction process, the content is calculated, and the residual alkali content is obtained by conversion.

[0061] 2. Particle size test: After the positive electrode material is internally ultrasonically dispersed for 5 min, the particle sizes Dv10, Dv50 and Dv90 are measured using a Malvern 3000 particle size analyzer. The particle size span is calculated as span=(Dv90-Dv10) / Dv50.

[0062] 3. Compacted density test: The positive electrode material is pressed into powder under a pressure of 200 MPa, and the compacted density is measured using a compacted density meter (model: PRCD-1100, equipment manufacturer: Yuaneng Technology).

[0063] 4. Preparation of half-cell: The positive electrode material, conductive carbon and binder PVDF are mixed evenly in a mass ratio of 90:5:5.

[0064] 5. Electrochemical performance testing: The obtained half-cells were subjected to constant current charge-discharge tests using the Blue Battery testing system. The initial charge capacity test had an operating voltage range of 2.8 V to 4.3 V, a charge-discharge rate of +1C / -1C, and a CV cutoff current of 0.01 C. The high-temperature cycling test had an operating voltage range of 2.8 V to 4.3 V, a temperature of 45 ℃, a charge-discharge rate of +1C / 1C, and a CV cutoff current of 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 modified ternary cathode material preparation methods of Examples 1-9 of this application, a sand milling process is used for mixing, which can improve the uniformity of coating of the excipients on the surface of the ternary cathode material and achieve good interface consistency. Furthermore, during the sand milling process, the residual alkali in the ternary cathode material can combine and react with the aforementioned coating excipients, thereby reducing the residual alkali content of the obtained modified ternary cathode material. In addition, the uniform coating of the excipients on the surface of the ternary cathode material and the good interface consistency also help reduce side reactions between the obtained modified ternary cathode material and the electrolyte. The above preparation method also incorporates a spray drying process to dry the slurry after sand milling, which can synergistically improve the uniformity of coating of the excipients on the surface of the ternary cathode material and achieve good interface consistency. Furthermore, during spray drying, the residual alkali in the ternary cathode material can combine with the liquid medium in the slurry and be carried out with the liquid medium during drying, thereby further reducing the residual alkali content of the obtained modified ternary cathode material. This not only helps reduce 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 helps improve the homogenization and coating uniformity of the obtained modified ternary cathode material, reducing processing difficulty. The modified ternary cathode material preparation method of Examples 1-9 of this application reduces the residual alkali content of the obtained modified ternary cathode material by improving the mixing process. The preparation process is simpler and can reduce the water washing process, which is beneficial to saving process costs.

[0066] In addition to Examples 4-5, Examples 1-3 further controlled the mass ratio of the liquid medium to the milled mixture within a preset range, which further improved the uniformity of the spray-dried mixture and simultaneously promoted the full combination of residual alkali and the liquid medium. Therefore, more residual alkali could react with the coating additives or be carried out with the liquid medium, further reducing the residual alkali content of the obtained modified ternary cathode material. In addition to Examples 6-7, Examples 1-3 further controlled the sintering conditions of the dry mixture within a preset range. Similarly, in Examples 8-9, Examples 1-3 further controlled the sintering conditions of the mixture within a preset range. All of these measures are beneficial for controlling the particle morphology and size of the sintered products, thereby further improving the electrochemical performance of the obtained modified ternary cathode material.

[0067] Compared to Example 1, Comparative Example 1 uses a dry mixing method (replacing sand milling and spray drying) for mixing. During the preparation process, there are fewer ways to remove residual alkali, and the contact between the residual alkali and the coating additives may be insufficient. This results in the modified ternary cathode material obtained in Comparative Example 1 having a free lithium content approximately 500 ppm higher (significantly higher than other examples). In other words, the modified ternary cathode material obtained in Comparative Example 1 has a higher residual alkali content (consistent with the results predicted during the morphology test above), indicating that the preparation method in Comparative Example 1 has a poor effect on removing residual alkali. Combined with Comparative Example 2, the modified ternary cathode material obtained in Comparative Example 1 requires additional water washing and low-temperature calcination processes to reduce the residual alkali content to a level close to that of the embodiments of this application. This also demonstrates that the preparation method of the embodiments of this 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 calcination treatment, significantly saving process costs.

[0068] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A method for preparing a modified ternary cathode material, characterized in that, The preparation method includes: The ternary cathode material and coating additives are mixed by sand milling. The coating additives include one or more of aluminum hydroxide, aluminum oxide, aluminum phosphate, titanium oxide, cobalt hydroxyl oxide, cobalt nitrate and strontium carbonate to obtain a slurry. The slurry was dried by spray drying to obtain a mixture; The mixture is sintered 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 additives are mixed with a liquid medium after being milled to obtain the slurry. The mass ratio of the liquid medium to the milled mixture is 0.4 to 1.

3. The preparation method according to claim 1, characterized in that, The mixture is sintered at a temperature of 500°C to 750°C for 10 h to 14 h.

4. The preparation method according to claim 1, characterized in that, Before mixing the ternary cathode material with the coating excipient, the preparation method further includes: The ternary cathode material is pulverized.

5. The preparation method according to claim 1, characterized in that, Before mixing the ternary cathode material with the coating excipient, the preparation method further includes: Lithium salt is mixed with a ternary cathode material precursor to obtain a dry mixture, which is then sintered to obtain the ternary cathode material.

6. The preparation method according to claim 5, characterized in that, The general chemical 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, and 0.05≤y≤0.

15.

7. The preparation method according to claim 5, characterized in that, The dry mix also includes a dopant, which includes one or more of Sr, Mg, Al and Zr sources.

8. The preparation method according to claim 5, characterized in that, The dry mixture is sintered at a temperature of 700°C to 900°C for 8 to 15 hours.

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 as described in claim 9.

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