Ternary positive electrode material, preparation method thereof and electrochemical device

Abstract

The invention discloses a ternary positive electrode material, a preparation method thereof and an electrochemical device. The preparation method comprises the steps that a carbonate ternary precursor and a first lithium source are mixed and sintered for the first time, a first sintered product is obtained, the carbonate ternary precursor contains transition metal elements, and the ratio of the total molar weight M1 of the transition metal elements in the carbonate ternary precursor to the molar weight L1 of lithium elements in the first lithium source is 1: (0.8-1.1); the primary sintering product and a second lithium source are mixed and subjected to secondary sintering, a base material is obtained, and the ratio of the total molar weight M1 of transition metal elements in the primary sintering product to the molar weight L2 of lithium elements in the second lithium source is 1: (0.06-0.5); and mixing the base material and the coating material, and carrying out third sintering, so that the coating material forms a coating layer on the surface of the base material, thereby obtaining the ternary positive electrode material. The carbonate ternary precursor is combined with step-by-step lithium supplement and sintering, so that the ternary positive electrode material with high single crystallization and uniform lithium distribution is prepared at low cost.

Description

Technical Field

[0001] This application relates to the field of new energy technology, specifically to a ternary cathode material and its preparation method, and an electrochemical device. Background Technology

[0002] In recent years, with the rapid development of new energy vehicles and electronic products, consumer demand for lithium-ion batteries has been increasing. As a key component of lithium-ion batteries, the performance of cathode materials directly affects the battery's energy density, cycle life, and safety. Currently, ternary cathode materials occupy a mainstream position among lithium-ion battery cathode materials due to their advantages such as high energy density, good cycle performance, and structural stability.

[0003] However, existing ternary cathode materials still suffer from problems such as high preparation costs, particle agglomeration, and uneven sintering during the preparation process, which limit the large-scale production of ternary cathode materials. Summary of the Invention

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

[0005] In addition, embodiments of this application also provide a ternary cathode material and an electrochemical device.

[0006] In a first aspect, embodiments of this application provide a method for preparing a ternary cathode material. The method includes the following steps: mixing a ternary carbonate precursor and a first lithium source and performing a first sintering to obtain a sintered product, wherein the ternary carbonate precursor contains a transition metal element, and the ratio of the total molar amount M1 of the transition metal element in the ternary carbonate precursor to the molar amount L1 of lithium element in the first lithium source is 1:(0.8~1.1); mixing the sintered product and a second lithium source and performing a second sintering to obtain a matrix material, wherein the ratio of the total molar amount M1 of the transition metal element in the ternary carbonate precursor to the molar amount L2 of lithium element in the second lithium source is 1:(0.06~0.5); and mixing the matrix material and a coating material and performing a third sintering to form a coating layer on the surface of the matrix material, thereby obtaining the ternary cathode material.

[0007] Based on the first aspect, in some possible embodiments, M1, L1 and L2 satisfy: M1 / (L1+L2)=1: (1.02~1.35).

[0008] Based on the first aspect, in some possible embodiments, the chemical formula of the carbonate ternary precursor is Ni. x Co y Mn 1-x-yCO3, where 0.5 ≤ x < 0.9, 0.05 <y≤0.25,0.05<1-x-y≤0.3。

[0009] Based on the first aspect, in some possible embodiments, the temperature of the first sintering is 600℃~800℃, and the time of the first sintering is 5h~10h.

[0010] Based on the first aspect, in some possible embodiments, the temperature of the second sintering is 800℃~950℃, and the time of the second sintering is 5h~10h.

[0011] Based on the first aspect, in some possible embodiments, the third sintering includes a first sintering stage and a second sintering stage performed sequentially, wherein the temperature of the first sintering stage is 300℃~600℃ and the time of the first sintering stage is 6h~10h, the temperature of the second sintering stage is 150℃~250℃ and the time of the second sintering stage is 2h~4h.

[0012] Based on the first aspect, in some possible embodiments, the sintering atmosphere for both the first sintering and the second sintering is an oxygen atmosphere, and the gas flow rate of the oxygen atmosphere is 100 mL / min to 200 mL / min.

[0013] Based on the first aspect, in some possible embodiments, the first lithium source and the second lithium source are respectively selected from at least one of lithium carbonate and lithium hydroxide; and / or the coating material includes at least one of alumina, aluminum phosphate and zirconium oxide.

[0014] Secondly, this application provides a ternary cathode material, which is prepared by the aforementioned preparation method. The ternary cathode material includes a matrix material containing a ternary cathode active substance and a coating layer located on the surface of the matrix material.

[0015] Thirdly, embodiments of this application also provide 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 the aforementioned ternary positive electrode material.

[0016] Compared to existing technologies, the ternary cathode material preparation method provided in this application uses inexpensive carbonate ternary precursors as raw materials, reducing costs. Simultaneously, the combination of stepwise and quantitative lithium replenishment and multi-step sintering allows lithium to fully penetrate the interior of the carbonate ternary precursor and improves the uniformity of lithium dispersion in the ternary cathode material. Specifically, the first lithium source acts as a flux in the first sintering, effectively reducing the temperature and time of the first sintering and decreasing the crystallinity of the first-sintering product. This allows the second lithium source to fully and uniformly penetrate the carbonate ternary precursor during the second sintering, forming a matrix material with high monocrystalline degree and uniform lithium distribution. Furthermore, the stepwise and quantitative lithium replenishment and multi-step sintering also reduce the agglomeration of carbonate ternary precursor particles and improve reaction uniformity, thereby enabling the low-cost preparation of ternary cathode materials with high monocrystalline degree, uniform lithium distribution, uniform particle size, and good dispersion. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of a method for preparing a ternary cathode material according to an embodiment of this application.

[0018] Figure 2 These are scanning electron microscope (SEM) images of the ternary cathode materials in Example 1 and Comparative Examples 1-3 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] The applicant's research found that traditional methods for preparing ternary cathode materials typically employ co-precipitation of hydroxide ternary precursors. This method requires real-time monitoring and control of the reaction pH and ammonia concentration, leading to both high production costs and lengthy preparation times. Furthermore, during sintering, severe particle agglomeration occurs (especially in single-crystal ternary cathode materials), necessitating robust crushing and separation post-processing, which can easily damage particles and negatively impact the performance of the ternary cathode material. In addition, incomplete sintering may occur during the sintering process, resulting in smaller particle sizes or agglomeration into polyspherical particles, which also severely affects the performance of the ternary cathode material.

[0021] For this purpose, please refer to Figure 1 As shown in Figure 1 , an embodiment of the present application provides a method for preparing a ternary cathode material with low cost, which specifically includes the following steps: Step S1: Mix a carbonate ternary precursor and a first lithium source and perform the first sintering to obtain a first sintered product. Among them, the carbonate ternary precursor contains transition metal elements, and the ratio of the total molar amount M1 of the transition metal elements in the carbonate ternary precursor to the molar amount L1 of lithium elements in the first lithium source is 1:(0.8~1.1).

[0022] Controlling the ratio of the total molar amount M1 of the transition metal elements in the carbonate ternary precursor to the molar amount L1 of lithium elements in the first lithium source to be 1:(0.8~1.1) can, while ensuring that a certain amount of lithium ions participate in the phase change reaction during the first sintering to occupy the lattice sites, facilitate the full dispersion of the first lithium source into the carbonate ternary precursor. Exemplarily, M1 / L1 can be any value within the range composed of 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1.0, 1:1.05, 1:1.1 or any two of the above values.

[0023] In some embodiments, the chemical formula of the carbonate ternary precursor can be Ni x Co y Mn 1-x-y CO3, where 0.5≤x<0.9, 0.05<y≤0.25, 0.05<1-x-y≤0.3, and the nickel content in the carbonate ternary precursor is 50%~90%, which is beneficial to improving the energy density of the ternary cathode material, reducing the cobalt consumption, and further reducing the manufacturing cost of the ternary cathode material. Exemplarily, the chemical formula of the carbonate ternary precursor can be Ni 0.6 Co 0.1 Mn 0.3 CO3, Ni 0.65 Co 0.15 Mn 0.2 CO3, or Ni 0.75 Co 0.1 Mn 0.15 CO3.

[0024] In some embodiments, the carbonate ternary precursor and the first lithium source can be stirred and mixed for 30 min to 60 min using a plowshare mixer.

[0025] In some embodiments, the temperature of the first sintering is 600℃~800℃, and the time of the first sintering is 5h~10h. Due to the addition of an appropriate amount of the first lithium salt, the temperature and time of the first sintering are reduced, allowing the carbonate ternary precursor and the first lithium source to undergo a preliminary solid-phase reaction at the lower temperature and shorter time. The first lithium source fully penetrates into the interior of the carbonate ternary precursor particles. The temperature of the first sintering can, exemplarily, be 600℃, 650℃, 700℃, 750℃, 800℃, or any value within the range of any two of the above values. The temperature of the first sintering can further be 650℃~750℃. The time of the first sintering can, exemplarily, be 5h, 6h, 7h, 8h, 9h, 10h, or any value within the range of any two of the above values. The time of the first sintering can further be 7h~9h.

[0026] In some embodiments, the sintering atmosphere for the first sintering can be an oxygen atmosphere, with a gas flow rate of 100 mL / min to 200 mL / min. An oxygen atmosphere facilitates the full oxidation of transition metal elements in the carbonate ternary precursor, reduces cation mixing, reduces lithium volatilization, and reduces oxygen vacancy formation. The gas flow rate within the aforementioned range provides sufficient oxygen to further oxidize the transition metal elements and suppress cation mixing and lithium volatilization.

[0027] In some embodiments, the first lithium source is selected from at least one of lithium carbonate and lithium hydroxide.

[0028] Step S2: The first sintering product and the second lithium source are mixed and sintered for the second time to obtain the matrix material, wherein the ratio of the total molar amount of transition metal elements M1 in the carbonate ternary precursor to the molar amount of lithium elements L2 in the second lithium source is 1:(0.06~0.5).

[0029] By controlling the total molar amount of transition metal elements M1 in the ternary carbonate precursor and the molar amount of lithium L2 in the second lithium source to be 1:(0.06~0.5), the local shift in the molar ratio of lithium to nickel, cobalt, and manganese elements caused by prolonged mixing and dispersion when the first lithium source is added can be balanced. For example, M1 / L2 can be 1:0.06, 1:0.08, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, or any value within the range of any two of the above values.

[0030] Furthermore, the ratio of the total molar amount of transition metal elements M1 in the carbonate ternary precursor to the total molar amount of lithium elements (the sum of L1 and L2) in the first and second lithium sources is controlled to be 1:(1.02~1.35), that is, M1, L1 and L2 satisfy: M1 / (L1+L2)=1:(1.02~1.35, which is beneficial to provide sufficient lithium ions, prevent their high-temperature volatilization from causing insufficient lithiation, and at the same time suppress Li / Ni mixing.

[0031] In some embodiments, the temperature of the second sintering is 800℃~950℃, and the time of the second sintering is 5h~10h. The higher temperature of the second sintering is beneficial for promoting grain growth, improving the crystallinity of the matrix material, and repairing minor crystal defects caused by the low-temperature first sintering, thereby promoting the formation of a single and stable layered structure in the matrix material. The temperature of the second sintering can, exemplarily, be 800℃, 850℃, 900℃, 950℃, or any value within the range of any two of the above values, and the temperature of the second sintering can further be 850℃~900℃. The time of the second sintering can, exemplarily, be 5h, 6h, 7h, 8h, 9h, 10h, or any value within the range of any two of the above values, and the time of the second sintering can further be 7h~9h.

[0032] In some embodiments, the sintering atmosphere for the second sintering can be an oxygen atmosphere, with a gas flow rate of 100 mL / min to 200 mL / min. An oxygen atmosphere is beneficial for maintaining the oxidizing properties of transition metal elements in the matrix material, reducing cation mixing, reducing lithium volatilization, and reducing oxygen vacancy formation. The gas flow rate of the oxygen atmosphere within the above range is beneficial for providing sufficient oxygen to further oxidize transition metal elements and suppress cation mixing and lithium volatilization.

[0033] In some embodiments, the second lithium source is selected from at least one of lithium carbonate and lithium hydroxide.

[0034] Step S3: Mix the matrix material and the coating material and perform a third sintering to form a coating layer on the surface of the matrix material, thereby obtaining a ternary cathode material.

[0035] In some embodiments, the coating material includes at least one of alumina, aluminum phosphate, and zirconium oxide.

[0036] After the base material and coating material are uniformly mixed, a third sintering process is performed. This third sintering process can include a first stage sintering and a second stage sintering performed sequentially. The first stage sintering temperature is 300℃~600℃, and the sintering time is 6h~10h. The second stage sintering temperature is 150℃~250℃, and the sintering time is 2h~4h. That is, the first stage of high-temperature coating is performed, followed by the second stage of low-temperature annealing. During high-temperature coating, the surface of the base material reacts strongly with the coating material, allowing the coating material to form a strong and uniform coating layer on the surface of the base material, thereby improving the stability of the coating layer. Low-temperature annealing can reduce thermal stress in the coating layer and improve its structure, making the coating layer more uniform and dense, further improving the stability and structural integrity of the coating layer.

[0037] The first sintering stage can be conducted in an oxygen atmosphere, which helps maintain a high oxidation state of the transition metal elements in the ternary cathode material and reduces cation mixing. The second sintering stage can be conducted in an air atmosphere, which helps improve the stability of the coating layer.

[0038] In some embodiments, after the third sintering, a crushing process (e.g., air jet milling dispersion) can be performed to obtain single-crystal ternary cathode material particles with a median particle size D50 of 3.5 μm to 3.6 μm and 1.05 ≤ span ≤ 1.2. Furthermore, the material can be crushed under low-intensity air jet milling conditions, thereby controlling the particle size of the ternary cathode material without damaging the particles.

[0039] In this embodiment, a ternary carbonate precursor is used as the raw material. Ternary carbonate precursors have the advantages of low cost and easy availability, effectively reducing the preparation cost of ternary cathode materials. However, the morphology control of ternary carbonate precursors is difficult, resulting in a wider particle size distribution. Compared to hydroxide ternary precursors prepared by sodium hydroxide co-precipitation, ternary carbonate precursors have a larger specific surface area and lower bulk density. These factors lead to difficulties in completely and uniformly dispersing lithium when the ternary carbonate precursor is mixed with the lithium source, resulting in localized shifts in the molar ratio of lithium to nickel, cobalt, and manganese. This leads to uneven reaction during sintering and reduces the electrochemical performance of the ternary cathode material.

[0040] To address the aforementioned deficiencies, this application employs a stepwise quantitative lithium replenishment and multi-step sintering method. First, the ternary carbonate precursor and the first lithium source are mixed and sintered for the first time. Simultaneously, the ratio of the total molar amount M1 of transition metal elements in the ternary carbonate precursor to the molar amount L1 of lithium elements in the first lithium source is controlled. The addition of the first lithium source can reduce the temperature and time of the first sintering through fluxing, thereby reducing soft agglomeration of particles and allowing the first lithium source to penetrate uniformly and fully into the interior of the ternary carbonate precursor. This improves the uniformity of the reaction between the ternary carbonate precursor and the first lithium source, thus enhancing the uniformity of lithium distribution in the ternary cathode material. Lowering the temperature and time of the first sintering reduces the crystallinity of the first-sintered product surface, facilitating the continued penetration of the second lithium source into the ternary carbonate precursor during the subsequent second sintering. Lowering the temperature and time of the first sintering also inhibits excessively rapid and excessive growth of the first-sintered product, improving its morphology and resulting in a first-sintered product with uniform particle size and high roundness.

[0041] Based on the first sintering, a second sintering is carried out by quantitatively adding lithium, which is beneficial to forming a matrix material with higher crystallinity and more uniform lithium distribution. The overall performance of the resulting matrix material (such as rate performance and cycle performance) is better than that of directly performing a single high-temperature sintering, thereby improving the stability, rate performance and cycle performance of the ternary cathode material.

[0042] Furthermore, based on the use of carbonate ternary precursors combined with stepwise lithium replenishment and sintering to reduce the cost of ternary cathode materials and improve the uniformity of the matrix material, this application modifies the matrix material through coating to enhance the stability of the ternary cathode material. The coating material can form a coating layer on the surface of the matrix material, effectively isolating the matrix material from external air or moisture, reducing pyrolysis reactions, and reducing direct contact between the matrix material and the electrolyte. It can also improve the mechanical strength of the ternary cathode material, thereby enhancing its chemical and structural stability.

[0043] In addition, ternary cathode materials are single-crystal ternary cathode materials with a high degree of single crystallization, which is beneficial to improving the energy density, cycle life, electronic conductivity, ionic conductivity and stability of ternary cathode materials.

[0044] Compared with existing technologies, the preparation method of the ternary cathode material in this application has the following advantages: 1. Using carbonate ternary precursors as raw materials, carbonate ternary precursors have the advantages of low cost and easy availability, which helps to reduce the preparation cost of ternary cathode materials (the cost is about 10%~15% lower than that of phosphate ternary precursors). Low-cost preparation of single-crystal ternary cathode materials is conducive to the large-scale production of ternary cathode materials.

[0045] 2. Stepwise quantitative lithium replenishment and multi-step sintering help reduce uneven lithium distribution and particle agglomeration in ternary cathode materials. Specifically, by using a first lithium source to lower the temperature and time of the first sintering, the first lithium source penetrates fully and uniformly into the carbonate ternary precursor, reducing particle agglomeration and improving the uniformity of the lithiation reaction. Lowering the temperature of the first sintering also reduces the surface crystallinity of the first-sintering product, promoting a full reaction between the second lithium source and the first-sintering product for a second sintering. This results in a matrix material with higher crystallinity and a more uniform lithium distribution. The overall performance of the resulting matrix material (e.g., rate performance and cycle performance) is superior to that of a single high-temperature sintering, thus improving the stability, rate performance, and cycle performance of the ternary cathode material.

[0046] 3. By coating and modifying the matrix material, a coating layer is formed on the surface of the matrix material, which is beneficial to improving the stability of the ternary cathode material.

[0047] Based on the same inventive concept, this application also provides a ternary cathode material, which is prepared by the aforementioned preparation method. The ternary cathode material includes a matrix material containing a ternary cathode active substance and a coating layer located on the surface of the matrix material.

[0048] Compared with existing technologies, the ternary cathode material of this application has both low cost and high physicochemical properties. While effectively reducing the preparation cost of ternary cathode materials, it also effectively improves the structural stability, rate performance and cycle performance of ternary cathode materials, which is conducive to the large-scale application of ternary cathode materials.

[0049] This application also provides an electrochemical device (e.g., a secondary battery) that includes a positive electrode plate, the positive electrode plate including a positive electrode material, wherein the positive electrode material is the aforementioned ternary positive electrode material.

[0050] Compared with the prior art, the electrochemical device provided in this application has a lower price, higher rate performance and longer cycle life.

[0051] 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 scope of the application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically described are all conventional commercially available products or publicly disclosed.

[0052] Example 1 Step S1: Add the carbonate ternary precursor Ni 0.6 Co 0.1 Mn 0.3CO3 and the first lithium source, lithium hydroxide monohydrate, were stirred and mixed in a plow mixer for 60 min and then subjected to a first sintering for 6 h in an oxygen atmosphere with a gas flow rate of 100 mL / min to 200 mL / min. The first sintering temperature was 650 °C, and a first sintering product was obtained. The ratio of the total molar amount of transition metal elements M1 in the carbonate ternary precursor to the molar amount of lithium elements L1 in the first lithium source was 1:0.9.

[0053] Step S2: The first sintering product and the second lithium source lithium carbonate are stirred and mixed in a plow mixer for 30 min and then sintered for 6 h in an oxygen atmosphere with a gas flow rate of 100 mL / min to 200 mL / min. The second sintering temperature is 900 °C to obtain the matrix material. The ratio of the total molar amount of transition metal elements M1 in the carbonate ternary precursor to the molar amount of lithium L2 in the second lithium source is 1:0.18, so that the ratio of the total molar amount of transition metal elements M1 in the carbonate ternary precursor to the total molar amount of lithium (L1+L2) in the first and second lithium sources is 1:1.08.

[0054] Step S3: Mix the matrix material and the coating material Al2O3 and perform a third sintering to form a coating layer on the surface of the matrix material. Disperse the mixture using an air jet mill to obtain a ternary cathode material with a median particle size D50 = 3.58 μm and a span = 1.15. The third sintering includes a first stage sintering and a second stage sintering performed sequentially. The first stage sintering is performed at 400°C for 8 hours in an oxygen atmosphere, and the second stage sintering is performed at 200°C for 2 hours in an air atmosphere. The amount of Al2O3 added is 0.1 wt% of the matrix material.

[0055] Example 2: The difference from Example 1 is that the second sintering temperature in step S2 is 950°C, and the second sintering time is 5 hours. The preparation methods of the remaining ternary cathode materials are basically the same as those in Example 1.

[0056] Example 3: The difference from Example 1 is that in step S1, the ratio of M1 to L1 is 1:1; in step S2, the ratio of M1 to L2 is 1:0.08, and M1 / (L1+L2) is 1:1.08. The preparation methods of the remaining ternary cathode materials are basically the same as those in Example 1.

[0057] Example 4: The difference from Example 1 is that in step S1, the ratio of M1 to L1 is 1:0.8; in step S2, the ratio of M1 to L2 is 1:0.5, and M1 / (L1+L2) is 1:1.3. The preparation methods of the remaining ternary cathode materials are basically the same as those in Example 1.

[0058] Comparative Example 1: The difference from Example 1 is that in step S1, the ternary precursor is a hydroxide ternary precursor Ni. 0.6 Co 0.1 Mn 0.3 (OH)2. The preparation methods for the remaining ternary cathode materials are basically the same as in Example 1.

[0059] Comparative Example 2: Step S1: Add the carbonate ternary precursor Ni 0.6 Co 0.1 Mn 0.3 CO3 and lithium carbonate were stirred and mixed in a plow mixer for 60 min and then sintered for 12 h in an oxygen atmosphere with a gas flow rate of 100 mL / min to 200 mL / min. The temperature of the first sintering was 900 °C to obtain the matrix material. The ratio of the total molar amount of transition metal elements in the carbonate ternary precursor to the molar amount of lithium elements in the lithium carbonate was 1:1.08.

[0060] Step S2: The matrix material and the coating material Al2O3 are mixed and sintered a second time to form a coating layer on the surface of the matrix material. The mixture is then dispersed using an air jet mill to obtain a ternary cathode material with a median particle size D50 of 3.56 μm and a span of 1.13. The second sintering includes a first stage sintering and a second stage sintering performed sequentially. The first stage sintering is performed at 400°C for 8 hours in an oxygen atmosphere, and the second stage sintering is performed at 200°C for 2 hours in an air atmosphere. The amount of Al2O3 added is 0.1 wt% of the matrix material.

[0061] Comparative Example 3 The difference from Example 1 is that in step S1, the ratio of M1 to L1 is 1:1.15; in step S2, the ratio of M1 to L2 is 1:0.25, and M1 / (L1+L2) is 1:1.4. The preparation methods of the remaining ternary cathode materials are basically the same as those in Example 1.

[0062] The ternary cathode materials obtained in Examples 1-4 and Comparative Examples 1-3 were subjected to the following tests.

[0063] 1. Scanning electron microscopy (SEM) test: A scanning electron microscope (model: Sigma360) with high-resolution imaging capability was used to observe the microscopic morphology and structural features of the material magnified 3000 times.

[0064] 2. Particle size test: A Malvern 3000 particle size analyzer was used. After ultrasonic dispersion for 5 minutes, the particle size distribution was tested. Span is the width of the particle size distribution. Span = (Dv90-Dv10) / Dv50, which reflects the uniformity of particle size. The smaller the Span value (closer to 0), the more concentrated the particle size distribution and the better the particle uniformity.

[0065] 3. Electrochemical performance testing: Battery preparation: Ternary cathode material, conductive agent SP and binder PVDF are mixed evenly in a mass ratio of 90:5:5 to prepare a half cell.

[0066] First charge / discharge specific capacity test: The LAND battery testing system was used for constant current charge / discharge testing. During the test, the working voltage range for the first discharge capacity test was 2.8V~4.35V, the temperature was 25℃, the charge / discharge rate was +0.1C / -0.1C, the CV cutoff current was 0.01C, and the first coulombic efficiency (referred to as first efficiency, first efficiency = first discharge specific capacity / first charge specific capacity) and the first discharge specific capacity of the battery were measured.

[0067] High-temperature cycle performance test: At 45℃, the half-cell was subjected to 1C / 1C charge-discharge cycles, with an operating voltage range of 2.8V-4.35V and a CV cutoff current of 0.01C, to test the cycle retention rate of the battery.

[0068] The test results of Examples 1-4 and Comparative Examples 1-3 are shown in Table 1 and 2. Figure 2 As shown.

[0069] The above results indicate that: Combination Figure 2 Table 1 compares the particle morphology and electrochemical performance of the ternary cathode materials in Example 1 and Comparative Examples 1-3.

[0070] In Example 1, the ternary cathode material prepared using a carbonate ternary precursor exhibits a uniform overall particle distribution. Compared to the ternary cathode material prepared using a hydroxide precursor in Comparative Example 1, the overall morphology of the ternary cathode materials in Example 1 is similar to that of Comparative Example 1, with the single crystal particle size and distribution being essentially the same. Regarding electrochemical performance, the 0.1C initial discharge capacity of the ternary cathode material in Example 1 reaches 192.2 mAh / g, achieving the same level as the 191.9 mAh / g of the ternary cathode material in Comparative Example 1. From both morphology and performance perspectives, Example 1 achieves the same level as Comparative Example 1, and even slightly surpasses it in initial discharge specific capacity and cycle retention. However, Comparative Example 1 uses a co-precipitated hydroxide ternary precursor, resulting in higher preparation costs. Example 1, using a low-cost carbonate ternary precursor, can save 10%–15% of production costs. Example 1 achieves the same electrochemical performance level as Comparative Example 1 under conditions of lower preparation costs.

[0071] Comparing Example 1 and Comparative Example 2, it can be seen that Comparative Example 2 uses a one-step direct sintering process to obtain single-crystal ternary cathode material particles. In Comparative Example 2, the particle size distribution is wide, with many small particles and some large single crystals. Furthermore, the crystals in Comparative Example 2 have sharp edges, indicating that the single crystal particles in Comparative Example 2 grow too quickly. In contrast, Example 1 uses a step-by-step lithium supplementation and multi-step sintering process, which significantly improves the rate capability and cycle performance of the ternary cathode material.

[0072] Comparing Example 1 and Comparative Example 3, it can be seen that Comparative Example 3 adjusted M1 / L1 and M1 / L2 compared to Example 1. Comparative Example 3 simultaneously increased the lithium source addition ratio twice, and M1 / L1 exceeded 1:(0.8~1.1). Due to the excessive addition of the first lithium source, lithium dispersion was uneven, and the cycle performance of Comparative Example 3 was lower than that of Example 1. Other performance comparisons showed no significant changes, but because Comparative Example 3 used more first and second lithium sources, the raw material cost increased without a significant performance gain. Therefore, Examples 1-4 can balance the low cost and good performance of ternary cathode materials.

[0073] Based on the analysis of Table 1, the batteries prepared by the ternary cathode materials in Examples 1-4 all have a first discharge specific capacity of over 191 mAh / g, a first efficiency of over 89.5%, and a 100-cycle retention rate at high temperature of over 89%. This indicates that by using a carbonate ternary precursor combined with stepwise lithium replenishment and multi-step sintering, high-performance ternary cathode materials with high single crystallization, uniform particle size, and complete structure can be prepared at low cost.

[0074] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a ternary cathode material, characterized in that, The method comprises: mixing a carbonate ternary precursor and a first lithium source and performing first sintering to obtain a first sintered product, wherein the carbonate ternary precursor contains transition metal elements, and a ratio of a total mole amount M1 of the transition metal elements in the carbonate ternary precursor to a mole amount L1 of lithium elements in the first lithium source is 1:(0.8-1.1); mixing the first sintered product and a second lithium source and performing second sintering to obtain a base material, wherein a ratio of the total mole amount M1 of the transition metal elements in the carbonate ternary precursor to a mole amount L2 of lithium elements in the second lithium source is 1:(0.06-0.5); and mixing the base material and a coating material and performing third sintering to form a coating layer on a surface of the base material from the coating material, to obtain the ternary positive electrode material.

2. The production method according to claim 1, wherein M1, L1 and L2 satisfy: M1 / (L1+L2)=1:(1.02-1.35).

3. The production method according to claim 1, wherein The carbonate ternary precursor has a chemical formula of Ni x Co y Mn 1-x-y CO3, wherein 0.5≤x<0.9, 0.05y≤0.25, 0.05<1-x-y≤0.

3.

4. The production method according to claim 1, wherein The first sintering is performed at a temperature of 600-800°C for 5-10 hours.

5. The production method according to claim 1, wherein The second sintering is performed at a temperature of 800-950°C for 5-10 hours.

6. The production method according to claim 1, wherein The third sintering comprises first-stage sintering and second-stage sintering performed in sequence, the first-stage sintering is performed at a temperature of 300-600°C for 6-10 hours, and the second-stage sintering is performed at a temperature of 150-250°C for 2-4 hours.

7. The production method according to claim 1, wherein The first sintering and the second sintering are both performed in an oxygen atmosphere, and a gas flow rate of the oxygen atmosphere is 100-200 mL / min.

8. The production method according to claim 1, wherein The first lithium source and the second lithium source are each selected from at least one of lithium carbonate and lithium hydroxide; and / or The coating material comprises at least one of aluminum oxide, aluminum phosphate and zirconium oxide.

9. A ternary cathode material, characterized in that, The ternary positive electrode material is obtained by the preparation method of any one of claims 1-8, and comprises a base material containing a ternary positive electrode active material and a coating layer on a surface of the base material.

10. An electrochemical device, characterized by, The electrochemical device comprises a positive electrode sheet, and the positive electrode sheet comprises a positive electrode material, which is the ternary positive electrode material as described in claim 9.

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