Positive electrode material, method for preparing the same, and battery

Abstract

The application provides a positive electrode material, a preparation method thereof and a battery. The preparation method comprises the following steps: uniformly mixing a coating raw material and a positive electrode base material to obtain a mixture, wherein the coating raw material comprises a lithium salt coating agent; heating the mixture to a coating temperature, so that the coating raw material is melted and coated onto the surface of the positive electrode base material to form a coating layer; and cooling to obtain the positive electrode material. The lithium salt coating agent is melted and coated, the coating temperature is controlled, a uniform and stable coating layer is formed in the positive electrode base material, and the electrochemical stability of the positive electrode material is improved.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, and in particular to a cathode material, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries have been widely used in portable devices such as mobile phones and computers due to their advantages such as high energy density, high discharge platform, long cycle life and environmental friendliness. They are also increasingly used in electric vehicles, aerospace and large-scale energy storage technologies.

[0003] However, cathode materials suffer from problems such as poor stability and poor conductivity during use. Therefore, improving the electrochemical performance of cathode materials has become an urgent technical problem to be solved. Summary of the Invention

[0004] This invention provides a cathode material, its preparation method, and a battery. The present application involves coating the surface of the cathode material with a lithium salt coating agent by heating and melting to form a uniform and stable coating layer, thereby reducing the dissolution of cathode metal elements or improving electrochemical performance.

[0005] In a first aspect, this application provides a method for preparing a cathode material, the method comprising:

[0006] The coating material is mixed evenly with the positive electrode matrix material to obtain a mixture, wherein the coating material includes a lithium salt coating agent;

[0007] The mixture is heated to the coating temperature, causing the coating material to melt and coat the surface of the positive electrode substrate to form a coating layer. The positive electrode material is then prepared by cooling.

[0008] In some embodiments, the lithium salt coating agent includes at least one of Li3PO4, LiPO3, and LiF.

[0009] In some embodiments, the cathode substrate material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium nickel manganese oxide.

[0010] In some embodiments, the coating material also includes a flux.

[0011] Optionally, the flux includes B2O3.

[0012] Further optionally, the molar ratio of B2O3 to the lithium salt coating agent is 1:(5-20), for example, 1:5, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18 or 1:20.

[0013] In some embodiments, the mass ratio of the coating material to the positive electrode substrate material is 1:(80-500), for example, 1:80, 1:100, 1:150, 1:200, 1:250, 1:300, 1:350, 1:400, 1:450 or 1:500.

[0014] In some embodiments, the thickness of the coating layer is 1 to 10 nm, for example, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm.

[0015] In some embodiments, the coating material undergoes a first ball milling process.

[0016] Optionally, the speed of the first ball mill is 400 to 600 rpm, for example, 400 rpm, 420 rpm, 440 rpm, 460 rpm, 480 rpm, 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm or 600 rpm.

[0017] Optionally, the first ball milling time is 2 to 24 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours.

[0018] In some embodiments, the coating material and the positive electrode substrate material are mixed using a second ball milling process.

[0019] Optionally, the speed of the second ball mill is 50 to 400 rpm, for example, 50 rpm, 80 rpm, 110 rpm, 140 rpm, 170 rpm, 200 rpm, 230 rpm, 270 rpm, 300 rpm, 330 rpm, 360 rpm or 400 rpm.

[0020] Optionally, the second ball milling time is 2 to 12 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0021] In some embodiments, the coating temperature is higher than the melting point of the lithium salt coating agent and lower than the upper limit sintering temperature of the cathode substrate material.

[0022] In some embodiments, the constant temperature time during the coating process is 1 to 12 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0023] In some embodiments, the heating process is carried out at a rate of 3 to 10 °C / min, for example, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min.

[0024] In some embodiments, the atmosphere during the coating process is an oxygen-containing atmosphere.

[0025] Optionally, the oxygen volume concentration of the oxygen-containing atmosphere is 21% to 100%, for example, 21%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%.

[0026] In some embodiments, during the cooling process, the temperature of the mixture is first lowered to 100-250°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C, and then cooled to room temperature.

[0027] Optionally, the cooling rate during the cooling process is 2 to 5℃ / min, for example, 2.0℃ / min, 2.2℃ / min, 2.4℃ / min, 2.6℃ / min, 2.8℃ / min, 3.0℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min, 4.0℃ / min, 4.4℃ / min, 4.8℃ / min or 5.0℃ / min.

[0028] Secondly, this application provides a cathode material, which is prepared by the cathode material preparation method described in the first aspect.

[0029] Thirdly, this application provides a battery, the positive electrode of which comprises the positive electrode material as described in the second aspect.

[0030] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0031] This application has the following beneficial effects:

[0032] This application employs a melt coating method to coat lithium salt coating agents onto the surface of the cathode substrate material. During the preparation process, the coating raw materials are melted into a liquid state, which increases the contact area with the cathode substrate material, forms a uniform and stable coating layer, reduces the dissolution of metal elements from the cathode material, simplifies the coating process, and improves the coating effect. The lithium salt coating agent provides lithium ion channels for lithium ion transport, thereby increasing the lithium ion diffusion rate and effectively improving the electrochemical stability and ionic conductivity of the prepared cathode material. Detailed Implementation

[0033] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0034] 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. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0035] Traditional technologies employ liquid-phase or conventional solid-phase methods to coat cathode materials. Liquid-phase methods not only increase the number of process steps but also generate wastewater, increasing environmental costs. Conventional solid-phase methods, on the other hand, have simple processes but poor coating uniformity, making it difficult to form a continuous coating layer. Therefore, an improved method for cathode materials is needed to ensure uniform and stable coating of cathode materials.

[0036] The first aspect of this application provides a method for preparing a cathode material, the method comprising:

[0037] The coating material is mixed evenly with the positive electrode substrate material to obtain a mixture, wherein the coating material includes a lithium salt coating agent;

[0038] The mixture is heated to the coating temperature, causing the coating material to melt and coat the surface to form a coating layer. The cathode material is then prepared by cooling.

[0039] This application employs a melt coating method to coat lithium salt coating agents onto the surface of the cathode substrate material. During the preparation process, the coating raw materials are melted into a liquid state, which can increase the contact area with the cathode substrate material, form a uniform and stable coating layer, reduce the dissolution of metal elements from the cathode material, simplify the coating process, and improve the coating effect. The lithium salt coating agent provides lithium ion channels for lithium ion transport, thereby increasing the lithium ion diffusion rate and effectively improving the electrochemical stability and ionic conductivity of the prepared cathode material.

[0040] In some embodiments, the lithium salt coating agent includes at least one of Li3PO4, LiPO3, and LiF.

[0041] In some embodiments, the cathode substrate material includes at least one selected from lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium nickel manganese oxide, preferably lithium nickel cobalt manganese oxide. For example, the cathode material includes LiNi. 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 or LiFePO4.

[0042] In this application, Li3PO4, LiPO3 and LiF are selected as coating agents to further coat the surfaces of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate and lithium nickel manganese oxide. The selection of the positive electrode substrate material has good thermal stability, avoiding the impact on the performance of the positive electrode substrate material during the melt coating process.

[0043] In some embodiments, the coating material further includes a flux. Optionally, the flux includes B2O3. In this application, by adding B2O3 flux, a eutectic is formed with the lithium salt coating agent, which lowers the melting temperature and enhances the uniformity of the coating. Furthermore, during the cooling crystallization process, defect microstructures can be formed at the grain boundaries between B2O3 and the lithium salt coating agent. These defect microstructures can provide fast channels for lithium-ion transport and effectively reduce the interfacial impedance of the coating layer.

[0044] Optionally, the molar ratio of B2O3 to the lithium salt coating agent is 1:(5-20). This application controls the amount of B2O3 added to ensure that the lithium salt coating agent and B2O3 in the coating layer form ion transport channels while avoiding the relatively large proportion of flux affecting the performance of the coating layer.

[0045] In some embodiments, the mass ratio of the coating material to the positive electrode substrate material is 1:(80-500). In this application, by controlling the mass ratio of the coating material to the positive electrode substrate material, it is ensured that the coating material forms a continuous and stable coating layer, and the excessive thickness of the coating layer is avoided from hindering the diffusion of lithium ions during the insertion and extraction process, thereby affecting the electrical performance of the battery.

[0046] In some embodiments, the thickness of the coating layer is 1 to 10 nm.

[0047] In some embodiments, the coating material is a lithium salt coating agent.

[0048] Optionally, the coating material is subjected to a first ball milling process, for example, the coating material is prepared by first ball milling a lithium salt coating agent, or the coating material is prepared by first ball milling a mixture of lithium salt coating agent and flux.

[0049] In this application, ball milling is used to adjust the particle size of the coating material to the nanoscale, so that the coating material and the positive electrode matrix material are mixed more evenly. In turn, during the heating and melting coating process, the coating material can be uniformly melted and coated, thereby improving the coating effect.

[0050] Alternatively, the speed of the first ball mill is 400-600 rpm, and the time of the first ball mill is 2-24 hours.

[0051] In some embodiments, the coating material and the positive electrode matrix material are mixed by a second ball milling process.

[0052] Optionally, the speed of the second ball mill is 50 to 400 rpm.

[0053] Optionally, the second ball milling time is 2 to 12 hours.

[0054] In some embodiments, the coating temperature is higher than the melting point of the lithium salt coating agent and lower than the upper sintering temperature limit of the cathode substrate material. The upper sintering temperature limit represents the temperature at which the cathode substrate material does not deform, soften, or overheat and expand; that is, the temperature during the coating process should not affect the inherent performance of the cathode substrate material. Optionally, the coating temperature is slightly higher than the melting point of the lithium salt coating agent, allowing the coating agent to melt, thus avoiding excessively high coating temperatures that could damage the cathode material's performance.

[0055] In some embodiments, the isothermal time during the coating process is 1–12 hours. Optionally, the heating rate during the heating process is 3–10 °C / min. Optionally, the atmosphere during the coating process is an oxygen-containing atmosphere, and further optionally, the oxygen volume concentration of the oxygen-containing atmosphere is 21–100%.

[0056] In some embodiments, during the cooling process, the temperature of the mixture is first lowered to 100–250°C, and then cooled to room temperature at a cooling rate of 2–5°C / min. In this application, the temperature is lowered to 100–250°C at a rate of 2–5°C / min during the cooling crystallization process. This low-speed cooling crystallization operation ensures stable crystallization of the lithium salt coating agent and flux, reducing the degree of lithium-nickel mixing in the cathode substrate material.

[0057] It should be noted that the cooling rate during the cooling process to room temperature can be 2-5°C or is not limited.

[0058] According to one specific embodiment, the method for preparing the positive electrode material includes the following steps:

[0059] The coating material is weighed and subjected to a first ball milling process. The ball milling speed is 400-600 rpm and the ball milling time is 2-24 h. The coating material includes at least one lithium salt coating agent selected from Li3PO4, LiPO3 and LiF. Optionally, the coating material also includes B2O3 flux, and the molar ratio of B2O3 flux to lithium salt coating agent is 1:(5-20).

[0060] The coating raw material and the positive electrode matrix material are weighed at a mass ratio of 1:(80-500) and subjected to a second ball milling process to obtain a mixture. The positive electrode matrix material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate and lithium nickel manganese oxide. During the mixing process, the mixture is ball-milled at a speed of 50-400 rpm for 2-12 hours.

[0061] The mixture is heated to the coating temperature at a heating rate of 3-10℃ / min in an oxygen-containing atmosphere, held at the temperature for 1-12 hours, and then cooled to 100-250℃ at a rate of 2-5℃ / min. After natural cooling to room temperature, the mixture is crushed and sieved to obtain the positive electrode material. Optionally, the sieve mesh size is 325 mesh.

[0062] In some embodiments, the coating material includes Li3PO4 and optionally B2O3, and the coating temperature is 790–810°C.

[0063] The second aspect of this application provides a cathode material, which is prepared by the method for preparing the cathode material described in the first aspect.

[0064] A third aspect of the embodiments of this application provides a battery, wherein the positive electrode of the battery comprises the positive electrode material described in the second aspect.

[0065] Optionally, the battery includes a lithium-ion battery.

[0066] Optionally, the lithium-ion battery includes a casing, a cell, and an electrolyte. The casing is filled with electrolyte, and the cell is immersed in the electrolyte. The cell is formed by stacking a positive electrode, a separator, and a negative electrode. The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The positive active layer is formed by coating a slurry prepared from a positive electrode material, a binder, a conductive agent, and a dispersant.

[0067] The following are specific embodiments of this application.

[0068] The Li3PO4 was purchased from McLean, with the grade L812271.

[0069] LiNi 0.6 Co 0.2 Mn 0.2 O2 was purchased from Tianjin Bamo Technology Co., Ltd., with the brand name BSC60.

[0070] B2O3 was purchased from McLean Company, with the brand name B804097.

[0071] The LiPO3 was purchased from McLean, and its grade is L830890.

[0072] Example 1

[0073] 1000g of Li3PO4 was ball-milled at 500rpm for 5 hours in a high-energy ball mill to obtain the coated raw material. 100g of the coated raw material was then mixed with 10000g of LiNi. 0.6 Co 0.2 Mn 0.2 O2 was added to a high-energy ball mill and ball-milled at 300 rpm for 3 hours to obtain a mixture.

[0074] The mixture was heated to 840°C at a heating rate of 5°C / min in an oxygen-containing atmosphere with a volume concentration of 99.9%, held at the temperature for 3 hours, and then cooled to 180°C at a rate of 3°C / min. After natural cooling to room temperature, the mixture was crushed and passed through a 325-mesh sieve to obtain the positive electrode material with a coating thickness of approximately 3 nm, denoted as F1.

[0075] Example 2

[0076] 1157.9g of Li3PO4 and 69.6g of B2O3 were ball-milled in a high-energy ball mill at 500rpm for 5 hours to obtain the coated raw material. 100g of the coated raw material was then mixed with 10000g of LiNi. 0.6 Co 0.2 Mn 0.2 O2 was added to a high-energy ball mill and ball-milled at 300 rpm for 3 hours to obtain a mixture.

[0077] The mixture was heated to 800°C at a heating rate of 5°C / min in an oxygen-containing atmosphere with a volume concentration of 99.9%, held at the temperature for 3 hours, and then cooled to 180°C at a rate of 3°C / min. After natural cooling to room temperature, the mixture was crushed and passed through a 325-mesh sieve to obtain the positive electrode material with a coating thickness of about 3 nm, denoted as F2.

[0078] Example 3

[0079] 859.1g of LiPO3 and 69.6g of B2O3 were ball-milled in a high-energy ball mill at 500rpm for 5 hours to obtain the coated raw material. 100g of the coated raw material was then mixed with 10000g of LiNi 0.6 Co 0.2 Mn 0.2 O2 was added to a high-energy ball mill and ball-milled at 300 rpm for 3 hours to obtain a mixture.

[0080] The mixture was heated to 660°C at a heating rate of 5°C / min in an oxygen-containing atmosphere with a volume concentration of 30%, held at the temperature for 3 hours, and then cooled to 180°C at a rate of 3°C / min. After natural cooling to room temperature, the mixture was crushed and passed through a 325-mesh sieve to obtain the positive electrode material with a coating thickness of 3 nm, denoted as F3.

[0081] Example 4

[0082] 859.1g of LiPO3 and 139.2g of B2O3 were ball-milled in a high-energy ball mill at 600rpm for 2 hours to obtain the coated raw material. 100g of the coated raw material was then mixed with 50000g of LiNi 0.6 Co 0.2 Mn 0.2 O2 was added to a high-energy ball mill and ball-milled at 400 rpm for 2 hours to obtain a mixture.

[0083] The mixture was heated to 640°C at a heating rate of 10°C / min in an oxygen-containing atmosphere with a volume concentration of 50%, held at the temperature for 1 hour, and then cooled to 200°C at a rate of 2°C / min. After natural cooling to room temperature, the mixture was crushed and passed through a 325-mesh sieve to obtain the positive electrode material with a coating thickness of 1 nm, denoted as F4.

[0084] Example 5

[0085] 859.1g of LiPO3 and 34.8g of B2O3 were ball-milled in a high-energy ball mill at 400rpm for 24h to obtain the coated raw material. 100g of the coated raw material was then mixed with 30000g of LiNi 0.6 Co 0.2 Mn 0.2O2 was added to a high-energy ball mill and ball-milled at 50 rpm for 12 hours to obtain a mixture.

[0086] The mixture was heated to 650°C at a heating rate of 3°C / min in an oxygen-containing atmosphere with a volume concentration of 70%, held at the temperature for 12 hours, and then cooled to 220°C at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed and passed through a 325-mesh sieve to obtain the positive electrode material with a coating thickness of 2 nm, denoted as F5.

[0087] Example 6

[0088] The cathode material was prepared according to the method in Example 2, the difference being that LiNi was used. 0.6 Co 0.2 Mn 0.2 The mass of O2 was adjusted to 60,000g, meaning the mass ratio of the coating material to the cathode substrate was 1:600. The prepared cathode material was designated F6, and no complete coating layer was formed.

[0089] Example 7

[0090] The cathode material was prepared according to the method in Example 2, except that LiNi was used. 0.6 Co 0.2 Mn 0.2 The mass of O2 is adjusted to 8000g, that is, the mass ratio of coating material to positive electrode substrate material is 1:80. The prepared positive electrode material is denoted as F7, and the coating layer thickness is 10nm.

[0091] Example 8

[0092] The cathode material was prepared according to the method of Example 2, except that the mass of B2O3 was adjusted to 174g, that is, the molar ratio of B2O3 to Li3PO4 was 1:4. The prepared cathode material was designated as F8, and the coating thickness was 4nm.

[0093] Example 9

[0094] The cathode material was prepared according to the method of Example 8, except that the coating temperature was adjusted to 780°C. The prepared cathode material was designated as F9, and the coating thickness was 4 nm.

[0095] Example 10

[0096] The cathode material was prepared according to the method of Example 2, except that the mass of Li3PO4 was adjusted to 2894.75g, that is, the molar ratio of B2O3 to Li3PO4 was 1:25. The prepared cathode material was denoted as F10, and the coating thickness was 3nm.

[0097] Example 11

[0098] The cathode material was prepared according to the method of Example 10, except that the coating temperature was adjusted to 840°C. The prepared cathode material was denoted as F11, and the coating thickness was 3 nm.

[0099] Example 12

[0100] The cathode material was prepared according to the method of Example 2, except that the cooling rate was adjusted to 10℃ / min. The prepared cathode material was denoted as F12, and the coating thickness was 3nm.

[0101] Comparative Example 1

[0102] The cathode material was prepared according to the method of Example 1, except that the heating temperature of the mixture was 500°C and held at that temperature for 6 hours. Instead of melt coating, a conventional solid-state method was used. The prepared cathode material was designated as D-F1, and the thickness of the coating layer was 3-5 nm.

[0103] Comparative Example 2

[0104] The cathode material was prepared by referring to the method of Comparative Example 1, except that the lithium salt coating agent was replaced with LiPO3. The prepared cathode material was denoted as D-F2, and the thickness of the coating layer was 3-5 nm.

[0105] Comparative Example 3

[0106] This comparative example provides a cathode material, which is LiNi. 0.6 Co 0.2 Mn 0.2 O2, the positive electrode material is designated as D-F3.

[0107] Test case

[0108] The cathode materials F1-F12 and D-F1-D-F3 prepared in the above embodiments and comparative examples are used to assemble batteries. The battery assembly method includes:

[0109] The positive electrode material, PVDF and conductive graphite were weighed in a mass ratio of 90:5:5 and dispersed in NMP to form a positive electrode slurry with a solid content of 42%. The positive electrode slurry was coated onto the surface of aluminum foil and vacuum dried at 120°C for 12 hours to prepare a positive electrode with a positive electrode active layer thickness of 30 μm.

[0110] A 2032 coin cell was assembled using a lithium sheet as the counter electrode, a 1M LiPF6 electrolyte, and a ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) solvent in a volume ratio of 1:1:1.

[0111] The above-mentioned batteries were subjected to performance tests, including elemental leakage detection, charge-discharge testing, and ion conductivity.

[0112] Elemental leaching detection: After charging the battery to 4.5V, the positive electrode was removed and washed with dimethyl carbonate solvent to remove residual electrolyte from the surface of the electrode. The electrode was then transferred to 3mL of electrolyte (1M LiPF6, EC:EMC=3 / 7(v / v)), sealed, and stored at 45℃ for 14 days. After filtering the electrolyte used for storage, elemental analysis was performed. The test results are shown in Table 1.

[0113] Charge / discharge test: Tested using a constant current charge / discharge tester under the following conditions: 25℃, 2.8-4.5V vs Li + / Li, the first cycle was tested at a rate of 0.1C charge / 0.1C discharge, and the subsequent 50 cycles were tested at a rate of 1C charge / 1C discharge. The test results are shown in Table 2.

[0114] Ion conductivity test: Test conditions were 25℃, 2.8-4.5V vs Li + / Li, charge at 0.1C for 15 minutes, let stand for 2 hours until 4.5V, discharge at 0.1C for 15 minutes, let stand for 2 hours until 2.8V. The test results are shown in Table 3.

[0115] Table 1

[0116]

[0117]

[0118] Table 2

[0119]

[0120] Table 3

[0121]

[0122]

[0123] The table above shows that:

[0124] (1) Compared with Example 2, it can be seen that by adding B2O3 flux in this application, a eutectic is formed with lithium salt coating agent, which reduces the melting temperature and enhances the uniformity of coating. In addition, during the cooling crystallization process, defect microstructures can be formed at the grain boundaries of B2O3 and lithium salt coating agent. These defect microstructures can provide a fast channel for lithium ion transport and effectively reduce the interfacial impedance of the coating layer.

[0125] (2) Compared with Examples 6 and 7, in Example 2, this application controls the mass ratio of coating material to positive electrode substrate material to ensure that the coating material forms a continuous and stable coating layer, and avoids the coating layer being too thick, which would hinder the diffusion of lithium ions during the insertion and extraction process and thus affect the electrical performance of the battery.

[0126] (3) Compared with Examples 8-11, Example 2 controls the amount of B2O3 added. While ensuring that the lithium salt coating agent and B2O3 in the coating layer form a channel that helps ion transport, the application avoids the relatively large proportion of flux affecting the performance of the coating layer.

[0127] (4) Compared with Example 12, Example 2 controls the cooling rate during the cooling crystallization process and adopts a low-speed cooling crystallization operation to ensure that the lithium salt coating agent and flux can crystallize stably, which helps to form a stable lithium ion channel at the grain boundary between B2O3 and the lithium salt coating agent.

[0128] (5) Compared with Comparative Examples 1-3, Example 1 shows that the lithium salt coating agent is coated onto the surface of the cathode substrate material by melt coating in this application. During the preparation process, the coating raw material is melted into a liquid state to increase the contact area with the cathode substrate material, form a uniform and stable coating layer, reduce the dissolution of metal elements in the cathode material, simplify the coating process and improve the coating effect. The lithium salt coating agent provides lithium ion channels for lithium ion transport, thereby increasing the diffusion rate of lithium ions and effectively improving the electrochemical stability and ionic conductivity of the cathode material.

[0129] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a positive electrode material, characterized in that, The preparation method includes: The coating material is mixed evenly with the positive electrode substrate material to obtain a mixture. The coating material includes a lithium salt coating agent and a flux. The flux includes B2O3. The molar ratio of B2O3 to the lithium salt coating agent is 1:(5~20). The lithium salt coating agent includes at least one of Li3PO4, LiPO3 and LiF. The mixture is heated to the coating temperature, causing the coating material to melt and coat the surface of the positive electrode substrate to form a coating layer. The mixture is then cooled to 100-250°C at a cooling rate of 2-5°C / min, and then cooled to room temperature to prepare the positive electrode material.

2. The method for preparing the cathode material as described in claim 1, characterized in that, The cathode substrate material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium nickel manganese oxide.

3. The method for preparing the cathode material as described in claim 1 or 2, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The mass ratio of the coating material to the positive electrode substrate material is 1:(80~500); (2) The thickness of the coating layer is 1~10nm.

4. The method for preparing the cathode material as described in claim 1 or 2, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The coating material is subjected to a first ball milling process, the speed of the first ball milling is 400~600 rpm, and the time of the first ball milling is 2~24 h; (2) The coating material and the positive electrode matrix material are mixed by a second ball mill, the speed of the second ball mill is 50~400 rpm, and the time of the second ball mill is 2~12 h.

5. The method for preparing the cathode material as described in claim 1 or 2, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The coating temperature is higher than the melting point of the lithium salt coating agent and lower than the upper limit of the sintering temperature of the positive electrode substrate material; (2) During the coating process, the coating temperature is kept constant for 1 to 12 hours; (3) During the heating process, the heating rate is 3~10℃ / min; (4) During the coating process, the atmosphere is an oxygen-containing atmosphere, and the oxygen volume concentration of the oxygen-containing atmosphere is 21~100%.

6. A positive electrode material, characterized in that, The cathode material is prepared by the method for preparing the cathode material according to any one of claims 1-5.

7. A battery, characterized in that, The positive electrode of the battery comprises the positive electrode material as described in claim 6.

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