Cathode material, preparation method thereof, cathode sheet, battery and electric device

Abstract

The present application relates to a kind of positive electrode material and its preparation method, positive electrode sheet, battery and electric device.The positive electrode material includes positive electrode matrix material, carbon coating layer and aluminum fluoride coating layer, the carbon coating layer is coated on the positive electrode matrix material, the aluminum fluoride coating layer is coated on the carbon coating layer;Wherein, the positive electrode matrix material is selected from lithium manganate;Wherein, the aluminum fluoride coating layer is intermittent coating layer.The positive electrode material has excellent high-temperature cycle performance, while having excellent rate performance and capacity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode material, a preparation method thereof, a positive electrode sheet, a battery and an electric device. BACKGROUND

[0002] The demand for lithium-ion batteries is rapidly growing, which puts a lot of pressure on the supply chain of metals such as Ni, Co and Li. In order to alleviate the pressure of Ni and Co supply, automobile manufacturers and battery manufacturers are applying manganese-based positive electrode materials as substitutes for nickel-rich positive electrode materials in appropriate applications. Manganese-based positive electrode materials have attracted widespread attention due to their low raw material prices and excellent low-temperature performance. At the same time, manganese-based positive electrode materials are generally safer than nickel-rich positive electrode materials, and manganese (Mn) is one of the more abundant transition metals used in battery cell manufacturing. However, due to the dissolution of manganese ions for various reasons, the structure of the positive electrode material is destroyed, and the dissolved manganese ions will deposit at the negative electrode, which will degrade the solid electrolyte interface (SEI) and cause active material loss, consume a large amount of active lithium, and thus cause severe battery capacity decay. Mn ion dissolution depends on temperature and voltage, which greatly reduces the high-temperature performance of manganese-based positive electrode materials. Therefore, inhibiting the dissolution of Mn ions in manganese-based positive electrode materials is crucial to improve the life of manganese-based positive electrode materials and promote the application of manganese-based positive electrode materials in the battery field.

[0003] Common manganese-based positive electrode materials mainly include lithium manganate, lithium nickel manganate, lithium-rich manganese-based positive electrode materials, lithium manganese iron phosphate, nickel-cobalt-manganese NCM ternary materials, etc. Among these manganese-based positive electrode materials, the influence of manganese ion dissolution on the material stability is a serious problem that must be addressed in practical applications. As an example, spinel-type lithium manganate with a spinel phase structure (wherein, x=0~0.2) has a full capacity of 110mAh / g, an average voltage of about 3.9V, and an energy density comparable to that of lithium iron phosphate material. Due to the three-dimensional Li diffusion channels in the structure of the spinel positive electrode material, the spinel-type lithium manganate positive electrode material has high power density, making it suitable for many high-power applications. Its excellent processing performance, higher material compaction density, lower cost, abundant manganese reserves and excellent rate performance have attracted attention in low-cost applications requiring medium energy density and life, such as short-distance low-cost electric vehicles, 3C consumer batteries, etc.

[0004] Currently, modification of lithium manganate material often adopts means such as doping, coating and crystal face induction to stabilize the crystal structure of the material, inhibit the Jahn-Teller effect and manganese ion dissolution. For example, Chinese patent application CN202510042662.3 realizes synchronous and uniform doping of elements M and M' at the precursor stage by co-precipitation method, effectively stabilizes the crystal structure of the lithium manganate positive electrode material by utilizing the synergistic effect of these elements in the subsequent sintering process, and realizes selective induction growth of the crystal face. The preferred orientation is conducive to inhibiting the dissolution of Mn and improving the stability of the lithium manganate material. Chinese patent application CN202510025511.7 constructs a composite manganese-based positive electrode material with a lithium manganate core and a lithium-rich nickel-cobalt-manganese positive electrode material shell by co-precipitation method at the precursor preparation stage, and prepares a manganese-based composite positive electrode material with high capacity, high safety, long cycle and high compaction. Chinese patent application CN202510302118.8 prepares lithium triborate coated lithium manganate positive electrode material by sol-gel method, which significantly improves the lattice structure stability of the lithium manganate positive electrode material after annealing treatment, and inhibits manganese dissolution. However, the prior art still cannot realize long high-temperature cycle performance of the lithium manganate material. Chinese patent application CN202010223608.6 uses Al, Zr and F as ternary ion doping to modify lithium manganate, which can improve the order degree of lithium manganate, stabilize the spinel structure, inhibit lattice distortion, and use aluminum fluoride to coat the ternary ion doped lithium manganate, which can effectively alleviate capacity attenuation and effectively prevent corrosion of electrolyte and reduce dissolution of manganese ions. However, the non-conductive aluminum fluoride coating used in the invention patent application will affect the rate performance and capacity of the material, and the coating layer formed by the traditional coating method is not uniform and the coating effect is poor. While improving the stability of the base material, the rate performance and capacity of the positive electrode material will be seriously affected.

[0005] Therefore, it is necessary to provide a manganese-based positive electrode material which can effectively inhibit the dissolution of manganese ions and has excellent high-temperature cycle performance, as well as excellent rate performance and capacity. SUMMARY

[0006] Therefore, it is necessary to provide a manganese-based positive electrode material which can effectively inhibit the dissolution of manganese ions and has excellent high-temperature cycle performance, as well as excellent rate performance and capacity.

[0007] In order to achieve the above object, the first aspect of the present application provides a positive electrode material, comprising a positive electrode base material, a carbon coating layer and an aluminum fluoride coating layer, the carbon coating layer is coated on the positive electrode base material, and the aluminum fluoride coating layer is coated on the carbon coating layer; wherein the positive electrode base material is selected from lithium manganate; and the aluminum fluoride coating layer is an intermittent coating layer.

[0008] In some embodiments, the thickness of the aluminum fluoride coating layer is 1 nm to 30 nm.

[0009] In some embodiments, the positive electrode base material is selected from spinel lithium manganate , wherein x = 0 to 0.2.

[0010] The second aspect of the present application provides a method for preparing the positive electrode material of the first aspect of the present application, comprising the following steps:

[0011] Step S1: mixing the positive electrode base material with a polymer solution to obtain a mixed solution, and drying the mixed solution to obtain a first intermediate product in which the polymer is uniformly attached to the surface of the positive electrode base material; the polymer comprises a molar ratio of 1 or less, a molar ratio of 0.01 to 0.5;

[0012] Step S2: sintering the first intermediate product at a temperature of 150°C to 400°C under an inert gas atmosphere to obtain a second intermediate product;

[0013] Step S3: placing the second intermediate product into an atomic layer deposition coating device, sequentially introducing an aluminum source precursor, a cleaning agent, a fluorine source precursor and a cleaning agent into the device, so that aluminum fluoride is deposited on the second intermediate product to obtain a third intermediate product;

[0014] Step S4: tempering the third intermediate product at a temperature of 300°C to 700°C under an inert gas atmosphere to obtain the positive electrode material.

[0015] In some embodiments, in step S1, the polymer is selected from one or more of chitosan, polyvinyl alcohol, an amino sugar, polyvinyl alcohol amine, and an amino phenolic aldehyde resin.

[0016] In some embodiments, in step S1, the drying is selected from one or more of spray drying, oven drying and freeze drying.

[0017] In some embodiments, in step S2, the sintering time is 0.5 hours to 4 hours.

[0018] In some embodiments, in step S3, the operations of sequentially introducing the aluminum source precursor, the cleaning agent, the fluorine source precursor and the cleaning agent into the device are repeated multiple times until an aluminum fluoride coating layer with a thickness of 1-30 nm is obtained.

[0019] In some embodiments, in step S3, the aluminum source precursor is selected from one or more of trimethylaluminum, triethylaluminum and aluminum triacetate.

[0020] In some embodiments, in step S3, the fluorine source precursor is selected from one or more of hydrogen fluoride, fluoromethane and fluoroethane.

[0021] In some embodiments, in step S3, the cleaning agent is selected from one or more of nitrogen, helium and argon.

[0022] In some embodiments, in step S3, the aluminum source precursor is introduced for 0.5-30 seconds.

[0023] In some embodiments, in step S3, the fluorine source precursor is introduced for 0.5-30 seconds.

[0024] In some embodiments, the cleaning agent is introduced for 5-150 seconds.

[0025] In some embodiments, in step S4, the tempering is performed for 1-6 hours.

[0026] The third aspect of the present application provides a positive electrode material, which is prepared by the method of the second aspect of the present application.

[0027] The fourth aspect of the present application provides a positive electrode sheet, which comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode material of the first aspect of the present application or the positive electrode material prepared by the method of the second aspect of the present application.

[0028] The fifth aspect of the present application provides a battery, which comprises the positive electrode sheet of the fourth aspect of the present application.

[0029] The sixth aspect of the present application provides a power utilization device, which comprises the battery of the fifth aspect of the present application.

[0030] The beneficial effects of the present application are as follows:

[0031] (1) By depositing carbon source on the positive electrode base material, due to the presence of a certain amount of hydroxyl on the carbon source, it will react with aluminum fluoride to decompose, so that the site where the hydroxyl exists cannot form aluminum fluoride deposition, thereby obtaining an intermittent aluminum fluoride coating layer. This intermittent discontinuous aluminum fluoride coating layer overcomes the problem of reduced material rate performance caused by poor conductivity of aluminum fluoride. On the other hand, the area without aluminum fluoride coating will form carbon coating, which is beneficial to improve the conductivity of the material and stabilize the surface of the material, and reduce the side reaction between the electrolyte and the positive electrode material.

[0032] (2) In the sintering step, the easily cracked and volatile groups such as amino groups of the polymer can be decomposed to provide sites and space for aluminum fluoride surface deposition, and then the aluminum fluoride coating area is accurately controlled by controlling the content of hydroxyl. According to the actual needs, the aluminum fluoride coating area and coating thickness can be adjusted by selecting the content of hydroxyl in the polymer, and the rate and cycle performance of the material are balanced.

[0033] (3) The aluminum fluoride coating layer formed by atomic layer deposition (ALD) is a uniform and dense ultra-thin coating layer, which can effectively inhibit the interface side reaction between the electrolyte and the positive electrode material. At the same time, the ultra-thin coating layer coated by ALD has less effect on the ion diffusion rate of the material compared with the traditional process, which is beneficial to the rate performance of the material, so that the positive electrode material has excellent rate performance.

[0034] (4) The manganese-based positive electrode material of the present application can effectively inhibit the cycle decay caused by the corrosion of the electrolyte and the deposition of manganese ions on the negative electrode side, and has excellent high-temperature cycle performance, as well as excellent rate performance and capacity. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a schematic diagram of the core-shell structure of the positive electrode material prepared in Examples 1 to 4 of the present application;

[0036] Figure 2 It is a scanning electron microscope (SEM) image of the positive electrode material prepared in Comparative Example 1 of the present application;

[0037] Figure 3 It is a scanning electron microscope (SEM) image of the positive electrode material prepared in Example 1 of the present application;

[0038] Figure 4 It is the first two cycles of charge-discharge curves of the button cell prepared using the positive electrode material prepared in Comparative Example 1 of the present application;

[0039] Figure 5 It is the first two cycles of charge-discharge curves of the button cell prepared using the positive electrode material prepared in Example 1 of the present application;

[0040] Figure 6A comparison chart of the capacity retention rate of 1.38 Ah soft pack batteries prepared using the positive electrode material prepared in Comparative Example 1 and Example 1 of the present application;

[0041] Figure 7 A comparison chart of the cycle retention rate at 45°C of 1.38 Ah soft pack batteries prepared using the positive electrode material prepared in Comparative Example 1, Comparative Example 3 and Example 1 of the present application.

[0042] BRIEF DESCRIPTION OF DRAWINGS

[0043] 1: positive electrode base material; 2: carbon coating layer; 3: aluminum fluoride coating layer. DETAILED DESCRIPTION

[0044] Other advantages and merits of the present application will be readily appreciated by those skilled in the art from the foregoing disclosure, in conjunction with the accompanying drawings and preferred embodiments. The present application can also be put into practice in various different embodiments and applications, and various modifications and changes can be made thereto without departing from its spirit. It is therefore intended that the preferred embodiments be considered in all respects as illustrative and not restrictive, particularly considering that the scope of the present application is indicated in the appended claims rather than in the foregoing description.

[0045] Manganese-based positive electrode materials have attracted extensive attention due to their low raw material prices and excellent low-temperature performance. At the same time, manganese-based positive electrode materials are generally safer than nickel-rich positive electrode materials, and manganese (Mn) is one of the more abundant transition metals used in battery cell manufacturing. However, due to the dissolution of manganese ions for various reasons, the structure of the positive electrode material is destroyed, and the dissolved manganese ions will be deposited at the negative electrode, which will degrade the solid electrolyte interface (SEI) and cause active material loss, consume a large amount of active lithium, and thus cause severe battery capacity decay. Mn ion dissolution depends on temperature and voltage, which greatly reduces the high-temperature performance of manganese-based positive electrode materials.

[0046] In the related art, aluminum fluoride is used to coat manganese-based positive electrode materials to achieve capacity decay mitigation, prevent corrosion of the electrolyte, and reduce the dissolution of manganese ions. However, the aluminum fluoride coating used is non-conductive, which affects the rate performance and capacity of the material. Moreover, the coating layer formed by the traditional coating method is not uniform, and the coating effect is poor, which seriously affects the rate performance and capacity of the positive electrode material while improving the stability of the positive electrode base material.

[0047] Therefore, it is necessary to provide a manganese-based positive electrode material that can effectively inhibit the dissolution of manganese ions, has excellent high-temperature cycle performance, and at the same time has excellent rate performance and capacity.

[0048] Therefore, the first aspect of the present application provides a positive electrode material. The positive electrode material comprises a positive electrode base material, a carbon coating layer and an aluminum fluoride coating layer, the carbon coating layer is coated on the positive electrode base material, and the aluminum fluoride coating layer is coated on the carbon coating layer. The positive electrode base material is selected from lithium manganate; and the aluminum fluoride coating layer is an intermittent coating layer.

[0049] In the positive electrode material of the present application, the positive electrode base material is a manganese-based positive electrode base material, the carbon coating layer is coated on the surface of the manganese-based positive electrode base material, and the aluminum fluoride coating layer is coated on the carbon coating layer. The aluminum fluoride coating layer is an intermittent coating layer. The aluminum fluoride coating layer can effectively inhibit the corrosion of the manganese-based positive electrode base material by the electrolyte and reduce the dissolution of manganese in the material. Since the dissolution of manganese has a destructive effect on the negative electrode and the electrolyte, the coating of aluminum fluoride greatly improves the stability of the positive electrode material, especially the high-temperature cycle performance of the material. On the other hand, the aluminum fluoride coating layer of the present application is an intermittent discontinuous coating layer, which overcomes the reduction of the rate performance of the material caused by the poor conductivity of aluminum fluoride. In the area without aluminum fluoride coating, a carbon coating is formed, which is beneficial to improve the conductivity of the material and stabilize the surface of the material, and reduces the side reaction between the electrolyte and the positive electrode material. Therefore, under the combined action of the carbon coating layer and the intermittent aluminum fluoride coating layer, the positive electrode material of the present application can effectively inhibit the dissolution of manganese ions and has excellent high-temperature cycle performance, excellent rate performance and capacity.

[0050] In some embodiments, the thickness of the aluminum fluoride coating layer is 1 nm to 30 nm. For example, the thickness of the aluminum fluoride coating layer can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm or a value between any two of them. Alternatively, the thickness of the aluminum fluoride coating layer can be 1 nm to 10 nm, and optionally 2 nm to 8 nm. The aluminum fluoride coating layer is beneficial to inhibit the corrosion of the manganese-based positive electrode base material by the electrolyte and reduce the dissolution of manganese in the material. Since the dissolution of manganese has a destructive effect on the negative electrode and the electrolyte, the coating of aluminum fluoride greatly improves the stability of the positive electrode material, especially the high-temperature cycle performance of the material. At the same time, the thickness of the aluminum fluoride coating layer in the present application is small. Such ultra-thin aluminum fluoride coating layer has little effect on the ion diffusion rate of the positive electrode material, so it has excellent rate performance while improving the stability of the positive electrode material, especially the high-temperature cycle performance of the material.

[0051] In some embodiments, the weight percentage content of the carbon coating layer is 0.1% to 1.5% relative to the total weight of the positive electrode matrix material. For example, the weight percentage content of the carbon coating layer can be 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a value between any two of the above values. The carbon coating layer has electrical conductivity. The carbon coating layer on the surface of the positive electrode matrix material forms a continuous conductive network, which is conducive to reducing the charge transfer impedance and thus improving the electronic conductivity of the positive electrode material. On the other hand, the carbon coating layer can physically block the direct contact between the positive electrode matrix material and the electrolyte, further inhibiting the manganese dissolution of the manganese-based positive electrode matrix material and the side reaction between the positive electrode matrix material and the electrolyte. Setting the weight percentage content of the carbon coating layer within the above range is conducive to the carbon coating layer playing the above roles. If the content of the carbon coating layer exceeds the upper limit, it will have an adverse effect on the lithium ion transmission of the positive electrode material. If the content of the carbon coating layer exceeds the lower limit, it will have limited effect on improving the electrical conductivity of the positive electrode material.

[0052] In some embodiments, the positive electrode matrix material is selected from spinel lithium manganate wherein x = 0 to 0.2.

[0053] In some embodiments, the positive electrode matrix material is selected from .

[0054] In some embodiments, the aluminum fluoride coating layer is formed by atomic layer deposition. Compared with traditional coating methods, the aluminum fluoride coating layer formed by atomic layer deposition is more uniform and dense, and has an ultrathin thickness. Such an ultrathin aluminum fluoride coating layer can effectively inhibit the interface side reaction between the electrolyte and the positive electrode material, and has less effect on the ion diffusion rate of the material, which is conducive to the performance of the rate capability of the material. Thus, the positive electrode material has excellent rate capability.

[0055] Another aspect of the present application provides a method for preparing the positive electrode material of the first aspect of the present application. The method comprises the following steps:

[0056] Step S1: mixing the positive electrode matrix material with a polymer solution to obtain a mixed solution, and drying the mixed solution to obtain a first intermediate product in which the polymer is uniformly attached to the surface of the positive electrode matrix material; the polymer comprises a molar ratio of 1 or less, a molar ratio of 0.01 to 0.5;

[0057] Step S2: sintering the first intermediate product at a temperature of 150°C to 400°C under an inert gas atmosphere to obtain a second intermediate product;

[0058] Step S3: placing the second intermediate product into an atomic layer deposition coating device, sequentially introducing an aluminum source precursor, a cleaning agent, a fluorine source precursor, and a cleaning agent into the device, so that aluminum fluoride is deposited on the second intermediate product to obtain a third intermediate product;

[0059] Step S4: tempering the third intermediate product at a temperature of 300-700°C under an inert gas atmosphere to obtain the positive electrode material.

[0060] In the method of the present application, in the polymer used in step S1, the molar ratio of the polymer is 1 or less, the molar ratio of the polymer is 0.01-0.5. Exemplarily, the molar ratio can be 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, or a value between any two of these values. Alternatively, the molar ratio can be 0.1-0.3, or 0.2-0.3. Exemplarily, the molar ratio can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a value between any two of these values. Alternatively, the molar ratio can be 0.01-0.3, or 0.05-0.2. In the polymer, a certain amount of hydroxyl groups are present, which will react with aluminum fluoride and decompose, so that the sites where hydroxyl groups are present cannot form aluminum fluoride deposition, while aluminum fluoride deposition can form at sites where there are no hydroxyl groups. In this way, an intermittent aluminum fluoride coating layer can be formed on the surface of the substrate. Compared with a continuous aluminum fluoride coating layer, this intermittent discontinuous aluminum fluoride coating layer overcomes the problem of reduced material rate performance caused by poor conductivity of aluminum fluoride. On the other hand, the region without aluminum fluoride coating will form a carbon coating, which is beneficial to improving the conductivity of the material and stabilizing the surface of the material, reducing the side reaction between the electrolyte and the positive electrode material.

[0061] ​​​In the method of this invention, in step S2, the first intermediate product is sintered in an inert gas atmosphere at a temperature of 150°C to 400°C to obtain a second intermediate product. For example, the sintering temperature can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 250°C, 300°C, 350°C, 400°C, or any two of these values. Optionally, the sintering temperature can be 150°C to 400°C, and optionally 180°C. By sintering the first intermediate product at the above temperatures, easily volatile groups such as amino groups in the polymer can be decomposed, providing sites and space for subsequent aluminum fluoride surface deposition. The coating area of ​​the aluminum fluoride can then be precisely controlled by controlling the hydroxyl content. The coating area and thickness of the aluminum fluoride can be adjusted by selecting the hydroxyl content in the polymer according to actual needs, balancing the rate capability and cycle performance of the material.

[0062] In the method of the present invention, in step S3, a uniform and dense ultrathin aluminum fluoride coating layer is formed by atomic layer deposition. The aluminum fluoride coating layer formed thereby can effectively suppress the interfacial side reactions between the electrolyte and the cathode material. At the same time, the ultrathin coating layer deposited by ALD has less impact on the ion diffusion rate of the material compared with the traditional process, which is beneficial to the rate performance of the material and is suitable for obtaining cathode materials with excellent rate performance.

[0063] In the method of the present invention, in step S4, the third intermediate product is tempered in an inert gas atmosphere at a temperature of 300°C to 700°C to obtain the cathode material. For example, the tempering temperature can be 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, or any two of these values. Optionally, the tempering temperature can be 400°C to 600°C. By tempering at the above temperatures, the carbon source, i.e., the polymer, applied in step S1 can be converted into carbon, thereby forming a carbon coating layer on the surface of the cathode substrate material. Tempering can also convert the aluminum fluoride deposited in step S3 into a more stable, more uniform, and denser coating layer, enhancing its resistance to electrolyte corrosion.

[0064] In this article, "Molar ratio" refers to the molar ratio of nitrogen (N) and carbon (C) elements in a polymer. The N content in a polymer is related to nitrogen-containing groups such as amino groups. During the low-temperature sintering step, easily volatile groups such as amino groups in the polymer decompose, providing sites and space for aluminum fluoride deposition on the surface.

[0065] In this article, The "molar ratio" refers to the molar ratio of -OH groups and C elements in the polymer, wherein the hydroxyl group is relatively more stable and is retained during the low-temperature sintering step. During ALD aluminum fluoride coating, -OH reacts with aluminum fluoride and decomposes, so that the aluminum fluoride coating layer cannot be formed there, thereby forming an intermittent discontinuous aluminum fluoride coating layer.

[0066] The "molar ratio" refers to the molar ratio of -OH groups and C elements in the polymer, wherein the hydroxyl group is relatively more stable and is retained during the low-temperature sintering step. During ALD aluminum fluoride coating, -OH reacts with aluminum fluoride and decomposes, so that the aluminum fluoride coating layer cannot be formed there, thereby forming an intermittent discontinuous aluminum fluoride coating layer. The "molar ratio" can be tested by conventional test methods in the art. Illustratively, elemental analysis, Dumas combustion method, chemical titration method, etc. can be used to measure.

[0067] In some embodiments, in step S1, the polymer is selected from one or more of chitosan, polyvinyl alcohol, amino sugar, polyvinyl alcohol amine, amino phenolic resin. Alternatively, the polymer is selected from chitosan.

[0068] As for the solvent of the polymer solution, there is no particular limitation as long as it can dissolve the polymer. Alternatively, the solvent has a low boiling point and is easy to volatilize, thereby facilitating the removal of the solvent in the subsequent drying process to obtain a first intermediate product in which the polymer is uniformly attached to the surface of the positive electrode base material. In some embodiments, in step S1, the solvent of the polymer solution can be selected from one or more of water, ethanol, acetone, etc.

[0069] As for the concentration of the polymer solution, there is no particular limitation as long as the polymer can be well dissolved at this concentration. Alternatively, the concentration of the polymer solution can be 0.2wt%~20.0wt%. Illustratively, the concentration of the polymer solution can be 0.2wt%, 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, 2.5wt%, 3.0wt%, 3.5wt%, 4.0wt%, 4.5wt%, 5.0wt%, 10.0wt%, 15.0wt%, 20.0wt% or a value between any two of them. Setting the concentration of the polymer solution within the above range is conducive to the uniform attachment of the polymer to the surface of the positive electrode base material and the subsequent drying operation.

[0070] As for the drying method, there is no particular limitation as long as it does not change the structure and properties of the positive electrode base material and the polymer. In some embodiments, in step S1, the drying can be selected from one or more of spray drying, oven drying, freeze drying.

[0071] In some embodiments, in step S1, the drying temperature can be 60-150°C. For example, the drying temperature can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or a value between any two of them. Alternatively, the drying temperature can be 80-120°C, and alternatively 120°C. Drying at the above temperature is conducive to keeping the structure and performance of the positive electrode base material and the polymer unchanged.

[0072] In some embodiments, in step S2, the sintering time can be 0.5-4 hours. For example, the sintering time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or a value between any two of them. Alternatively, the sintering time can be 1 hour. Through sintering, the easily cracked and volatile groups such as amino groups in the polymer can be removed, thereby providing sites and space for subsequent aluminum fluoride surface deposition. During sintering, these groups undergo decomposition reactions. However, due to the selection of reaction temperature and time during sintering, the hydroxyl groups and carbon skeleton are not affected. During sintering, the hydroxyl groups remain, thereby inhibiting the deposition of aluminum fluoride at sites with hydroxyl groups during subsequent ALD deposition. At sites without hydroxyl groups, aluminum fluoride can be deposited, and conversely, at sites with hydroxyl groups, aluminum fluoride cannot be deposited. Thereby, an intermittent discontinuous aluminum fluoride coating layer can be formed.

[0073] In some embodiments, in step S3, the operation of sequentially introducing an aluminum source precursor, a cleaning agent, a fluorine source precursor, and a cleaning agent into the device is repeated multiple times until an aluminum fluoride coating layer with a thickness of 1-30 nm is obtained. In the present application, "sequentially introducing an aluminum source precursor, a cleaning agent, a fluorine source precursor, and a cleaning agent into the ALD coating device" can be referred to as one cycle. Each cycle can form a very thin layer of aluminum fluoride on the surface of the substrate. By performing multiple cycles, the aluminum fluoride layer can be uniformly coated on the entire surface of the substrate, avoiding local over-thickness or under-thickness. Each cycle forms a deposition layer of a certain thickness, and by performing multiple cycles, the desired thickness can be gradually accumulated. Thereby, a uniform ultra-thin aluminum fluoride coating layer can be obtained.

[0074] In some embodiments, in step S3, the aluminum source precursor is selected from one or more of trimethylaluminum, triethylaluminum, and aluminum triacetate. Alternatively, the aluminum source precursor is trimethylaluminum. In the atomic layer deposition process, the aluminum source precursor is used to provide aluminum elements to react with the fluorine source precursor to form the target compound aluminum fluoride, thereby forming the desired aluminum fluoride coating layer on the material surface.

[0075] In some embodiments, in step S3, the fluorine source precursor is selected from one or more of hydrogen fluoride, fluoromethane (CH3F) ), and fluoroethane (C2H5F) ). Optionally, the fluorine source precursor is selected from fluoroethane. In the atomic layer deposition process, the fluorine source precursor is used to provide fluorine element to react with the aluminum source precursor to form the target compound aluminum fluoride, thereby forming the desired aluminum fluoride coating layer on the surface of the material.

[0076] In some embodiments, in step S3, the purge gas is selected from one or more of nitrogen, helium, and argon. The purge gas is used to purge the unreacted precursor materials and reaction byproducts generated in the reaction out of the reaction chamber, reducing the interference of these substances on the subsequent deposition process. The selected purge gas such as nitrogen and helium is chemically inert, which can effectively remove the reaction byproducts and unreacted precursors without negatively affecting the deposition process, thereby facilitating the formation of a high-quality aluminum fluoride coating layer with uniform deposition.

[0077] In some embodiments, in steps S2 and S4, the inert gas can be selected from one or more of nitrogen, helium, and argon, wherein the purity of the gas is above 98% and the oxygen content is below 0.01%.

[0078] In some embodiments, in step S3, the aluminum source precursor can be introduced for a time period of 0.5 seconds to 30 seconds. For example, the aluminum source precursor can be introduced for a time period of 0.5 seconds, 1 second, 2 seconds, 4 seconds, 6 seconds, 8 seconds, 10 seconds, 12 seconds, 15 seconds, 20 seconds, 25 seconds, 30 seconds, or a value within a range between any two of these values. Optionally, the aluminum source precursor can be introduced for a time period of 1 second. In the atomic layer deposition process, the aluminum element is introduced into the reaction system by introducing the aluminum source precursor. The aluminum source precursor chemisorbs on the surface of the substrate to form a uniform layer of aluminum atoms, which reacts with the introduced fluorine source precursor, thereby forming a uniform and ultra-thin aluminum fluoride deposition layer. By setting the introduction time of the aluminum source precursor within the above range, it is beneficial to deposit a uniform and ultra-thin aluminum fluoride deposition layer.

[0079] In some embodiments, in step S3, the fluorine source precursor can be introduced for 0.5-30 seconds. For example, the fluorine source precursor can be introduced for 0.5 seconds, 1 second, 2 seconds, 4 seconds, 6 seconds, 8 seconds, 10 seconds, 12 seconds, 15 seconds, 20 seconds, 25 seconds, 30 seconds, or a value between any two of the aforementioned values. Alternatively, the fluorine source precursor can be introduced for 1 second. During the atomic layer deposition process, the fluorine source precursor is introduced to introduce fluorine into the reaction system. The fluorine source precursor chemisorbs on the substrate surface to form a uniform fluorine atomic layer, which reacts with the aluminum source precursor introduced subsequently to form a uniform and ultra-thin aluminum fluoride deposition layer. By setting the introduction time of the fluorine source precursor within the aforementioned range, a uniform and ultra-thin aluminum fluoride deposition layer can be formed.

[0080] In some embodiments, in step S3, the cleaning agent can be introduced for 5-150 seconds. For example, the cleaning agent can be introduced for 5 seconds, 10 seconds, 20 seconds, 30 seconds, 40 seconds, 50 seconds, 60 seconds, 80 seconds, 100 seconds, 120 seconds, 150 seconds, or a value between any two of the aforementioned values. Alternatively, the cleaning agent can be introduced for 30 seconds. During the atomic layer deposition process, the cleaning agent is introduced to purge the unreacted precursor materials remaining in the atomic layer deposition ALD coating device and the reaction byproducts generated during the reaction out of the reaction chamber, thereby reducing the interference of these substances with the subsequent deposition process. Thus, a high-quality aluminum fluoride coating layer with uniform deposition can be formed. By setting the introduction time of the cleaning agent within the aforementioned range, the aforementioned purpose can be achieved.

[0081] In some embodiments, in step S4, the annealing time can be 1-6 hours. For example, the annealing time can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or a value between any two of the aforementioned values. Alternatively, the annealing time can be 3 hours. By annealing, the carbon source, i.e., the polymer, applied in step S1, can be converted into carbon, thereby forming a carbon coating layer on the surface of the positive electrode base material. By annealing, the aluminum fluoride deposited in step S3 can also be converted into a more stable, more uniform, and more dense coating layer, thereby enhancing its resistance to electrolyte corrosion. By setting the annealing time within the aforementioned range, the aforementioned annealing purpose can be achieved.

[0082] The third aspect of the present application provides a positive electrode material, which is prepared by the method of the second aspect of the present application.

[0083] The fourth aspect of the present application provides a positive electrode tab. The positive electrode tab comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode material of the first aspect of the present application or the positive electrode material prepared by the method of the second aspect of the present application.

[0084] The positive electrode current collector has two opposite surfaces in the thickness direction of the positive electrode current collector, and the positive electrode active material layer can be disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0085] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc. on a polymer material base material. For example, the polymer material can be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0086] The fifth aspect of the present application provides a battery. The battery comprises the positive electrode tab of the fourth aspect of the present application.

[0087] The sixth aspect of the present application provides an electric device. The electric device comprises the battery of the fifth aspect of the present application.

[0088] The embodiments of the present application are specifically described below in conjunction with the examples and the accompanying drawings. It can be understood that the following examples are only illustrative of the present application and should not be construed as limiting the present application.

[0089] Example 1

[0090] (1) 100 g of a lithium manganate positive electrode base material with the chemical formula LiMn2O4was mixed with 25 mL of a chitosan aqueous solution (the concentration of the chitosan aqueous solution was 2 wt%), to obtain a mixed solution, wherein the molar ratio of the chitosan was about 0.2,

[0091] (2) The obtained first intermediate product was sintered at 180°C for 1 hour using a box furnace, and the sintering atmosphere was nitrogen atmosphere, so that the amino group of the chitosan was decomposed, to obtain a second intermediate product.

[0092] ​​​(3) The second intermediate product obtained in step (2) is placed into an atomic layer deposition (ALD) coating device, trimethylaluminum is introduced and reacted for 1 s to complete aluminum deposition, nitrogen gas is introduced for 20 s for cleaning, fluoroethane is introduced and reacted for 1 s to perform fluorine deposition, nitrogen gas is introduced for 30 s for cleaning, and the above steps are repeated until the deposition thickness of the aluminum fluoride coating layer reaches 2 nm, to obtain a third intermediate product, and then the third intermediate product is taken out.

[0093] (4) The third intermediate product, i.e., the sample after ALD coating, is tempered at a temperature of 600 ℃ for 3 hours in a box furnace under a nitrogen atmosphere, to obtain a lithium manganate positive electrode base material with an intermittent aluminum fluoride coating.

[0094] Example 2

[0095] The positive electrode material is prepared in the same manner as in Example 1, except that the chitosan used in step (1) of Example 1 is replaced by chitosan with a molar ratio of about 0.2, chitosan with a molar ratio of about 0.2.

[0096] Example 3

[0097] The positive electrode material is prepared in the same manner as in Example 1, except that the chitosan used in step (1) of Example 1 is replaced by chitosan with a molar ratio of about 0.3, chitosan with a molar ratio of about 0.05.

[0098] Example 4

[0099] The positive electrode material is prepared in the same manner as in Example 1, except that the number of repetitions of the operation of introducing trimethylaluminum, then introducing nitrogen gas, then introducing fluoroethane, and then introducing nitrogen gas in step (3) of Example 1 is changed until the deposition thickness of the aluminum fluoride coating layer reaches 4 nm.

[0100] The schematic diagram of the core-shell structure of the positive electrode material prepared in Examples 1 to 4 is shown in Figure 1 From Figure 1 it can be seen that the positive electrode base material 1 is coated with a continuous carbon coating layer 2 on the surface, and the carbon coating layer 2 is coated with an intermittent and discontinuous aluminum fluoride coating layer 3. At the intermittent part of the aluminum fluoride coating layer, carbon coating is formed. Through the joint action of the carbon coating layer and the intermittent aluminum fluoride coating layer, the cycle decay caused by the corrosion of the electrolyte to the positive electrode base material 1 and the deposition of manganese on the negative electrode side is effectively inhibited, so that the positive electrode material has excellent high-temperature cycle performance, while the rate performance and capacity of the positive electrode material are also considered.

[0101] Comparative Example 1

[0102] The cathode material was prepared in the same way as in Example 1, except that the sintering temperature in step (2) of Example 1 was replaced with 600°C and the sintering time was replaced with 3 hours. Therefore, in the sintering step (2), the carbon source applied in step (1) has been sintered and converted into carbon.

[0103] Comparative Example 2

[0104] (1) Take 100g of chemical formula The lithium manganese oxide cathode substrate material is placed in an atomic layer deposition (ALD) coating device. Trimethylaluminum is first introduced and reacted for 1 second to complete aluminum deposition. Then, nitrogen gas is introduced for cleaning for 20 seconds. After that, fluoroethane is introduced and reacted for 1 second to perform fluorine deposition. Then, nitrogen gas is introduced for cleaning for 30 seconds. The above steps are repeated until the deposition thickness of the aluminum fluoride coating layer reaches 2 nm to obtain an intermediate product. The intermediate product is then removed.

[0105] (2) The lithium manganese oxide cathode substrate material coated with aluminum fluoride was tempered in a box furnace at 600°C for 3 hours under a nitrogen atmosphere to obtain the lithium manganese oxide cathode substrate material continuously coated with aluminum fluoride.

[0106] Comparative Example 3

[0107] Directly take the chemical formula as The lithium manganese oxide cathode matrix material is used as the cathode material.

[0108] The positive electrode matrix material and chitosan used in Examples 1 to 4 molar ratio The molar ratio, the thickness of the aluminum fluoride coating, the tempering temperature, and the tempering time are shown in Table 1 below.

[0109] Table 1

[0110]

[0111] The positive electrode matrix material and chitosan used in Examples 1 and Comparative Examples 1 to 3 molar ratio The molar ratios and some preparation conditions are shown in Table 2 below.

[0112] Table 2

[0113]

[0114] Figure 2 The image shows a scanning electron microscope (SEM) image of the cathode material prepared in Comparative Example 1. Figure 3 The image shows a scanning electron microscope (SEM) image of the cathode material prepared in Example 1 of this invention. Figure 2 It can be seen that the cathode material obtained by continuous ALD coating has a smooth and uniform surface and a regular shape. Through...Figure 3 It can be seen that the positive electrode material prepared in Example 1 has a rougher surface than Comparative Example 1, which is caused by the discontinuous aluminum fluoride coating.

[0115] Button cells were prepared using the positive electrode materials of Examples 1 to 4 and Comparative Examples 1 to 3, in which CR2025 type battery cases were used and lithium sheets were used as the negative electrode. The discharge capacity at 25°C at a rate of 0.1C and the capacity retention rate after 60 cycles at 50°C were tested. The constant current charge-discharge test was performed in a voltage window of 3.0~4.3V. The test results of the button cells are shown in Table 3 below and Figures 4 to 5 .

[0116] Table 3

[0117]

[0118] As can be seen from Table 3, the positive electrode material obtained using the method of the present application can balance the capacity and high-temperature cycle stability, while in Comparative Examples 1 to 3, the three materials cannot balance the higher capacity and excellent cycle stability. Specifically, the positive electrode material without any coating (Comparative Example 3) exhibits a higher capacity of 125.41 mAh g -1 , but its high-temperature cycle capacity retention rate after 60 cycles is only 96.32%. The positive electrode material with complete aluminum fluoride coating (Comparative Examples 1 and 2) has better high-temperature cycle performance, but its capacity is reduced to 110.52 mAh g -1 and 108.16 mAh g -1 , which is significantly reduced compared to Comparative Example 3. In contrast, the positive electrode material in Example 1 has a capacity that is only about 3 mAh g -1 different from that of the uncoated material (Comparative Example 3), and its high-temperature cycle performance is comparable to that of the completely coated positive electrode material (Comparative Examples 1 and 2). In Example 2, the hydroxyl content in chitosan is higher than that in Example 1, and the hydroxyl content is related to the aluminum fluoride coating area. When the hydroxyl content increases, the aluminum fluoride coating area decreases. In the case of a decrease in the aluminum fluoride coating area, the capacity of the positive electrode material is slightly improved compared to Example 1, and the cycle performance is slightly reduced. In Example 3, although the amino content in chitosan is higher than that in Example 1, the capacity and high-temperature cycle performance of the positive electrode material are also comparable to those of the positive electrode material of Example 1. In Example 4, the thickness of the aluminum fluoride coating layer is increased, the high-temperature cycle performance is improved, and the capacity is slightly reduced. In summary, the positive electrode materials with intermittent aluminum fluoride coating layers in Examples 1 to 4 have a capacity that is better than that of the positive electrode materials with complete aluminum fluoride coating in Comparative Examples 1 and 2, and at the same time, the high-temperature cycle performance is comparable to that of Comparative Examples 1 and 2.

[0119] Figure 4The first two cycles of charge-discharge curves of a button cell prepared using the positive electrode material prepared in Comparative Example 1 of the present application are shown. From Figure 4 it can be seen that the initial efficiency and capacity of the positive electrode material are both low.

[0120] Figure 5 The first two cycles of charge-discharge curves of a button cell prepared using the positive electrode material prepared in Example 1 of the present application are shown. From Figure 5 it can be seen that the initial efficiency of the material is significantly improved compared to Comparative Example 1, and the capacity is also higher.

[0121] 1.38 Ah soft package batteries were prepared using the positive electrode materials of Example 1, Comparative Example 1 and Comparative Example 3, wherein the negative electrode material was graphite and the separator was PE ceramic separator. The material capacity retention rate at 1C, 2C, 3C and 4C was tested at 25℃, and the high-temperature cycle capacity retention rate was tested at 45℃. The test voltage window was 3.0-4.2 V. The test results of the soft package batteries are shown in Figure 6 and Figure 7 .

[0122] From Figure 6 it can be seen that the capacity retention rate of the positive electrode material with the intermittent aluminum fluoride coating layer in Example 1 of the present application is better than that of the positive electrode material with the continuous aluminum fluoride coating layer in Comparative Example 1. From Figure 7 it can be seen that, compared to the positive electrode material without aluminum fluoride coating in Comparative Example 3, the high-temperature cycle stability of the positive electrode material with the intermittent aluminum fluoride coating layer in Example 1 of the present application is significantly improved, and is comparable to that of the positive electrode material with the continuous aluminum fluoride coating layer in Comparative Example 1. In combination with Figure 6 and Figure 7 , it can be seen that the positive electrode material with the intermittent aluminum fluoride coating layer of the present application has excellent high-temperature cycle stability while also having excellent rate performance.

[0123] The above examples are only preferred examples for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Any equivalent substitutions or transformations made by those skilled in the art based on the present application are within the protection scope of the present application.

Claims

1. A positive electrode material, characterized in that, The positive electrode material comprises a positive electrode base material, a carbon coating layer and an aluminum fluoride coating layer, the carbon coating layer is coated on the positive electrode base material, and the aluminum fluoride coating layer is coated on the carbon coating layer; wherein the positive electrode base material is selected from lithium manganate; wherein the aluminum fluoride coating layer is an intermittent coating layer.

2. The positive electrode material of claim 1, wherein, The thickness of the aluminum fluoride coating layer is 1 nm to 30 nm.

3. The positive electrode material according to claim 1 or 2, wherein The positive electrode base material is selected from spinel lithium manganate wherein x = 0 to 0.

2.

4. A method for preparing the positive electrode material of claim 1, characterized in that, The method comprises the following steps: Step S1: mixing the positive electrode base material with a polymer solution to obtain a mixed solution, and drying the mixed solution to obtain a first intermediate product in which the polymer is uniformly attached to the surface of the positive electrode base material; the polymer in the first intermediate product has a molecular weight of 1,000 to 1,000,000 a molar ratio of 1 or less, a molar ratio of 0.01 to 0.

5. Step S2: sintering the first intermediate product under an inert gas atmosphere at a temperature of 150 DEG C to 400 DEG C to obtain a second intermediate product; Step S3: placing the second intermediate product into an atomic layer deposition coating device, sequentially introducing an aluminum source precursor, a cleaning agent, a fluorine source precursor and a cleaning agent into the device, so that aluminum fluoride is deposited on the second intermediate product to obtain a third intermediate product; Step S4: tempering the third intermediate product under an inert gas atmosphere at a temperature of 300 DEG C to 700 DEG C to obtain the positive electrode material.

5. The method of claim 4, wherein, In step S1, the polymer is selected from one or more of chitosan, polyvinyl alcohol, amino sugar and amino phenolic aldehyde resin.

6. The method of claim 4 or 5, wherein, In step S1, the drying is selected from one or more of spray drying, oven drying and freeze drying.

7. The method of claim 4 or 5, wherein, In step S2, the sintering time is 0.5 hours to 4 hours.

8. The method of claim 4 or 5, wherein, In step S3, the operation of sequentially introducing an aluminum source precursor, a cleaning agent, a fluorine source precursor and a cleaning agent into the device is repeated multiple times until an aluminum fluoride coating layer with a thickness of 1 nm to 30 nm is obtained.

9. The method of claim 4 or 5, wherein, In step S3, the aluminum source precursor is selected from one or more of trimethylaluminum, triethylaluminum and aluminum triacetate.

10. The method of claim 4 or 5, wherein, In step S3, the fluorine source precursor is selected from one or more of hydrogen fluoride, fluoromethane and fluoroethane.

11. The method of claim 4 or 5, wherein, In step S3, the cleaning agent is selected from one or more of nitrogen, helium and argon.

12. The method of claim 4 or 5, wherein, In step S3, the introduction time of the aluminum source precursor is 0.5 seconds to 30 seconds; and / or, the introduction time of the fluorine source precursor is 0.5 seconds to 30 seconds; and / or, the introduction time of the cleaning agent is 5 seconds to 150 seconds.

13. The method of claim 4 or 5, wherein, In step S4, the tempering time is 1 hour to 6 hours.

14. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode material of any one of claims 1 to 3 or the positive electrode material prepared by the method of any one of claims 4 to 13.

15. A battery, characterized by The battery comprises the positive electrode sheet of claim 14.

16. An electrical device, comprising: The electric device comprises the battery of claim 15.

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