Coated positive electrode material and preparation method thereof, positive electrode plate and battery

Abstract

The invention relates to the technical field of batteries, and provides a coated positive electrode material, a preparation method thereof, a positive electrode plate and a battery. The coated positive electrode material comprises a core material and a coating layer arranged on at least part of the surface of the core material, the core material comprises a positive electrode active material, and the coating layer comprises a high-entropy metal organic framework material. The coated positive electrode material is stable in structure, the lithium ion transmission speed is effectively improved, the transfer resistance of lithium ions at the interface of an electrode and an electrolyte can be reduced, and the first charge-discharge efficiency, the rate capability and the cycle performance of the battery are improved through cooperation.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to coated cathode materials and their preparation methods, cathode sheets, and batteries. Background Technology

[0002] With the rapid development of lithium-ion and sodium-ion batteries, higher requirements have been placed on the performance of cathode materials. Coating is a common method to improve cathode material performance, with oxides and fluorides being the most frequently used coating materials. The main functions of the coating layer include: 1. acting as a physical barrier to isolate the cathode material from the electrolyte and reduce side reactions; 2. removing HF and reducing metal ion dissolution; 3. stabilizing the surface structure and reducing phase transition stress; 4. reacting with residual lithium on the material surface to reduce the amount of residual lithium, preventing decomposition and gas generation during charging, and forming a highly conductive coating layer to improve rate performance. However, cathode materials coated with oxides and fluorides experience increased impedance and decreased rate performance because the coating layer does not participate in the electrochemical reaction and has poor ionic conductivity. Summary of the Invention

[0003] Therefore, it is necessary to provide coated cathode materials that can improve lithium-ion transport speed and have stable structure, as well as their preparation methods, cathode sheets, and batteries.

[0004] In a first aspect, this application provides a coated cathode material, which includes a core material and a coating layer disposed on at least a portion of the surface of the core material; the core material contains a cathode active material, and the coating layer contains a high-entropy metal-organic framework material.

[0005] In some embodiments, the coated cathode material satisfies at least one of the following conditions:

[0006] (1) The mass of the cladding layer is 0.5% to 8% of the mass of the core material;

[0007] (2) The volume average particle size Dv50 of the coated cathode material is 0.5 μm to 10 μm;

[0008] (3) High-entropy metal-organic framework materials contain at least five of the following metal ions: iron, cobalt, nickel, copper, manganese, cadmium and zinc.

[0009] (4) The organic ligands contained in high-entropy metal-organic framework materials include at least one of terephthalic acid ligand, tricresyl ligand and 1,4-dihydroxyanthraquinone ligand;

[0010] (5) The chemical formula of the positive electrode active material is Li(Ni) a Co b Mn c ) d Me O2; wherein a+b+c=1, d+e=1, 0.5≤a<1.0, 0<b≤0.3, 0<c≤0.3, 0.98≤d≤1, 0≤e≤0.02; M includes at least one of Ga, W, Zr, B, Al, Sb, Mo, Ti, La, Na and Sn.

[0011] Secondly, this application provides a method for preparing a coated cathode material, the method comprising:

[0012] Prepare a mixed slurry containing positive electrode active material and high-entropy metal-organic framework material;

[0013] The mixed slurry is dried and then heat-treated to coat at least a portion of the surface of the positive electrode active material with a high-entropy metal-organic framework material to form a coating layer.

[0014] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0015] (1) The mass of the high-entropy metal-organic framework material in the mixed slurry is 0.5% to 8% of the mass of the positive electrode active material;

[0016] (2) The mesh size of the positive electrode active material is 200 mesh to 400 mesh;

[0017] (3) The mass percentage of solvent in the mixed slurry is 0.5%~1.5%;

[0018] (4) The heat treatment temperature is 350℃~700℃, the time is 2h~7h, and the atmosphere is an oxygen-containing atmosphere.

[0019] In some embodiments, the method for forming the mixed slurry includes:

[0020] A first dispersion containing a positive electrode active material is prepared; a second dispersion containing a high-entropy metal-organic framework material is prepared; the first dispersion and the second dispersion are mixed and then heated and evaporated to form the mixed slurry.

[0021] Optionally, the first dispersion contains 50% to 70% by mass of the positive electrode active material.

[0022] Optionally, the second dispersion contains 40% to 60% by mass of high-entropy metal-organic framework material.

[0023] Optionally, the heating and evaporation temperature is 40℃~80℃.

[0024] In some embodiments, the preparation method of high-entropy metal-organic framework materials includes:

[0025] A precursor solution is obtained by mixing at least five metal sources with an organic ligand source; wherein each metal source contains a different metal element.

[0026] High-entropy metal-organic framework materials were prepared by hydrothermal reaction of precursor solution and carbon paper.

[0027] In some embodiments, the preparation method of high-entropy metal-organic framework materials satisfies at least one of the following conditions:

[0028] (1) The ratio of the amount of metal elements in any two metal sources in the precursor solution is (0.9~1.1):1, and the ratio of the amount of organic ligands in the organic ligand source to the amount of metal elements in any metal source is (0.9~1.1):1.

[0029] (2) The total molar concentration of the metal source in the precursor solution is 1.0 mol / L to 2.0 mol / L;

[0030] (3) The precursor solution contains an organic ligand source at a concentration of 1.5 mol / L to 2.0 mol / L;

[0031] (4) The precursor solution contains solvents including N,N-dimethylformamide, water and ethanol; the volume ratio of N,N-dimethylformamide, water and ethanol is (13~18):(1~2):1;

[0032] (5) The temperature of the hydrothermal reaction is 80℃~180℃, and the time is 8h~24h;

[0033] (6) The metal source includes at least five of the following: iron source, cobalt source, nickel source, copper source, manganese source, cadmium ion and zinc ion;

[0034] (7) The organic ligand source includes at least one of the following: materials containing terephthalic acid groups, materials containing triphenyl benzoic acid groups, and materials containing 1,4-dihydroxyanthraquinone groups.

[0035] In some embodiments, the preparation method of the positive electrode active material includes:

[0036] The precursor of the positive electrode active material and the lithium source are mixed to obtain a mixture, and the mixture is sintered to prepare the positive electrode active material.

[0037] Optionally, the ratio of the amount of lithium in the lithium source to the total amount of metal elements in the precursor of the positive electrode active material is (1~1.1):1.

[0038] Optionally, the mixture may also contain an M source, M including at least one of Ga, W, Zr, B, Al, Sb, Mo, Ti, La, Na and Sn, wherein the ratio of the amount of metal element in the M source to the total amount of metal element in the precursor of the positive electrode active material is (0~0.02):1.

[0039] Optionally, the precursor of the positive electrode active material has the chemical formula Ni x Co y Mn z (OH)2, where 0.50≤x<1.0, 0<y≤0.30, 0<z≤0.30, and x+y+z=1.

[0040] Optionally, the sintering process includes: sequentially subjecting the mixture to a first sintering stage and a second sintering stage; the temperature of the first sintering stage is 400℃~700℃, the holding time is 1h~4h, the heating rate is 2℃ / min~4℃ / min, and the atmosphere is an oxygen-containing atmosphere; the temperature of the second sintering stage is 850℃~950℃, the holding time is 10h~16h, the heating rate is 2℃ / min~4℃ / min, and the atmosphere is an oxygen-containing atmosphere.

[0041] Thirdly, this application provides a positive electrode sheet, including a coated positive electrode material prepared by the preparation method of the coated positive electrode material of the first aspect or the coated positive electrode material of the second aspect.

[0042] Fourthly, this application provides a battery including the positive electrode sheet of the third aspect.

[0043] Compared with traditional technologies, this application has at least the following beneficial effects:

[0044] This application employs a high-entropy metal-organic framework (MOF) to coat the positive electrode active material. MOFs possess structural diversity, multiple active adsorption sites, and high specific surface area, allowing them to effectively adsorb onto the surface of the positive electrode active material, forming a uniform coating structure. This stabilizes the surface structure and reduces phase transition stress. Furthermore, it helps alleviate the problem of uncontrolled lattice oxygen redox activity and enhances interface protection, preventing direct contact between the material and the electrolyte and inhibiting the dissolution of transition metal ions at high potentials, thus further improving the material's cycle stability. Moreover, the porous structure of the MOF is less prone to distortion during charge and discharge, providing more lithium-ion diffusion channels during lithium-ion insertion and extraction. This facilitates lithium-ion migration within the MOF structure, improving the lithium-ion transport rate and structural stability of the electrode material at high voltages. This effectively reduces capacity decay during cycling, enhances cycle performance, and results in higher capacity.

[0045] In addition, the high-entropy metal-organic framework coating of this application can reduce the formation of solid electrolyte interfacial films and alleviate the corrosion of positive electrode active materials by hydrofluoric acid in the electrolyte, thereby improving the cycle stability and rate performance of the material.

[0046] Therefore, the coated cathode material of this application has a stable structure, effectively improves the lithium-ion transport speed, and can also reduce the transfer resistance of lithium ions at the electrode-electrolyte interface, thus synergistically improving the battery's first charge-discharge efficiency, rate performance, and cycle performance. Attached Figure Description

[0047] Figure 1 This is a SEM image of the coated cathode material prepared in Example 1 of this application;

[0048] Figure 2 The image shows the XRD pattern of the coated cathode material obtained in Example 1 of this application.

[0049] Figure 3 This is a particle size distribution diagram of the coated cathode material obtained in Example 1 of this application;

[0050] Figure 4 The graph shows a comparison of the cycle performance of Examples 1-4 and Comparative Example 1 of this application. Detailed Implementation

[0051] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are only for illustrating the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. In addition, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0052] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0053] In this application, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first aspect," "second aspect," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0054] "High entropy" refers to materials composed of five or more elements in near equimolar ratios, characterized by "high entropy stable structure and multi-component synergistic effect".

[0055] Metal-organic frameworks (MOFs), also known as porous coordination polymers, are a class of porous crystalline materials with a periodic network structure formed by the self-assembly of metal ions or metal clusters and organic ligands. Their structure contains a large number of pores and spacious cavities.

[0056] "High-entropy metal-organic framework materials" refer to metal-organic framework materials composed of five or more metal ions in near equimolar ratios.

[0057] In traditional technologies, fast ion conductors are used as a coating layer to coat the cathode material, which can improve the ionic conductivity of the material surface. However, due to the difference in mechanical properties between fast ion conductor materials and cathode materials, coating with fast ion conductor materials is difficult and unstable, and they are prone to detachment during the expansion and contraction of the cathode material.

[0058] The first aspect of this application provides a coated cathode material, which includes a core material and a coating layer disposed on at least a portion of the surface of the core material; the core material includes a cathode active material, and the coating layer includes a high-entropy metal-organic framework material.

[0059] This application employs high-entropy metal-organic frameworks (MOFs) to coat the positive electrode active material. High-entropy MOFs possess structural diversity, multiple active adsorption sites, and high specific surface area, enabling them to effectively adsorb onto the surface of the positive electrode active material, forming a uniform coating structure. This stabilizes the surface structure and reduces phase transition stress. Furthermore, it helps alleviate the problem of uncontrolled lattice oxygen redox activity and enhances interface protection, preventing direct contact between the material and the electrolyte and inhibiting the dissolution of transition metal ions at high potentials, thus contributing to further improving the material's cycle stability.

[0060] Moreover, high-entropy metal-organic framework materials have a porous structure, which is not easily distorted during charging and discharging. During the lithium-ion insertion and extraction process, they can provide more lithium-ion diffusion channels, which is conducive to the migration of lithium ions in the metal-organic framework structure. This improves the lithium-ion transport speed and structural stability of the electrode material under high voltage, effectively improves the capacity decay of the battery during cycling, enhances its cycle performance, and has a high capacity.

[0061] In addition, the high-entropy metal-organic framework coating of this application can reduce the formation of solid electrolyte interfacial films and alleviate the corrosion of positive electrode active materials by hydrofluoric acid in the electrolyte, thereby improving the cycle stability and rate performance of the material.

[0062] Understandably, the introduction of multiple metal elements into high-entropy metal-organic framework materials occupies the internal lattice of the solid solution, thereby forming multiple adsorption sites. This can induce lithium reduction during lithium transport, leading to more interaction combinations. Furthermore, high entropy helps mitigate the problem of uncontrolled lattice oxygen redox activity, further improving the material's cycling stability.

[0063] In some embodiments, the mass of the coating layer is 0.5% to 8% of the mass of the core material, for example, it can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, or 8.0%. The coating amount selected above in this application synergistically improves the stability of the coating layer and enhances the electrochemical performance of the cathode material. If the coating amount is relatively high, lithium-ion transport may be hindered, resulting in a decrease in rate performance. If the coating amount is relatively low, the coating layer may be too thin, making it difficult to effectively isolate electrolyte corrosion, leading to a decrease in cycle life.

[0064] In some embodiments, the volume average particle size Dv50 of the coated cathode material is 0.5 μm to 10 μm, for example, it can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0065] In some embodiments, the high-entropy metal-organic framework material contains at least five metal ions selected from iron, cobalt, nickel, copper, manganese, cadmium, and zinc. Optionally, the high-entropy metal-organic framework material contains iron, cobalt, nickel, copper, and manganese ions. This application selects the metal ions in the high-entropy metal-organic framework material as described above. The five metal ions have similar radii, enabling them to synergistically improve the electrochemical performance of the cathode material, while also being low in cost and toxicity.

[0066] It is understandable that the organic ligands in high-entropy metal-organic framework materials only need to meet the requirement of not reacting during encapsulation and use, thus preventing the metal-organic framework material from failing. In some embodiments, the organic ligands contained in the high-entropy metal-organic framework material include at least one of terephthalic acid ligands, 1,4-dihydroxyanthraquinone ligands, and tribenzoic acid ligands.

[0067] In some embodiments, the chemical formula of the positive electrode active material is Li(Ni) a Co b Mn c ) d M e O2; where a+b+c=1, d+e=1, 0.5≤a<1.0, 0<b≤0.3, 0<c≤0.3, 0.98≤d≤1, 0≤e≤0.02; M includes at least one of Ga, W, Zr, B, Al, Sb, Mo, Ti, La, Na, and Sn. Where a can be 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or 0.99; b can be 0.05, 0.10, 0.15, 0.20, 0.25, or 0.30; c can be 0.05, 0.10, 0.15, 0.20, 0.25, or 0.30; d can be... The is 0.980, 0.982, 0.984, 0.986, 0.988, 0.990, 0.992, 0.994, 0.996, 0.998, or 1.000; e can be 0, 0.002, 0.004, 0.006, 0.008, 0.010, 0.012, 0.014, 0.016, 0.018, or 0.020. This application can employ a positive electrode active material doped with element M, thereby synergistically improving the electrochemical performance of the positive electrode material in conjunction with the coating layer.

[0068] A second aspect of this application provides a method for preparing a coated cathode material, the method comprising:

[0069] Prepare a mixed slurry containing positive electrode active material and high-entropy metal-organic framework material;

[0070] The mixed slurry is dried and then heat-treated to coat at least a portion of the surface of the positive electrode active material with a high-entropy metal-organic framework material to form a coating layer.

[0071] This application employs physical mixing and heat treatment to uniformly coat the surface of the positive electrode active material with a high-entropy metal-organic framework material. The coating layer exhibits a stable structure, high capacity, and excellent charge-discharge reversibility, while also improving high-temperature cycling performance. The coating method described in this application is simple and suitable for large-scale production.

[0072] In some embodiments, the mass of the high-entropy metal-organic framework material in the mixed slurry is 0.5% to 8% of the mass of the positive electrode active material, for example, it can be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5% or 8.0%.

[0073] In some embodiments, the mesh size of the positive electrode active material is 200 mesh to 400 mesh, for example, it can be 200 mesh, 220 mesh, 240 mesh, 260 mesh, 280 mesh, 300 mesh, 320 mesh, 340 mesh, 360 mesh, 380 mesh or 400 mesh.

[0074] In some embodiments, the solvent content in the mixed slurry is 0.5% to 1.5% by mass, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%. The solvent content in the mixed slurry selected above in this application makes the mixed slurry a paste-like substance, ensuring coating stability and good coating uniformity.

[0075] In some embodiments, the drying temperature of the mixed slurry can be 100℃~200℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃; the drying time can be 2h~4h, for example, 2.0h, 2.5h, 3.0h, 3.5h or 4.0h.

[0076] In some embodiments, the heat treatment temperature is 350°C to 700°C, for example, 350°C, 380°C, 410°C, 440°C, 470°C, 500°C, 530°C, 560°C, 590°C, 620°C, 650°C, 680°C, or 700°C. The treatment time is 2 hours to 7 hours, for example, 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, 6.0 hours, 6.5 hours, or 7.0 hours. The atmosphere is an oxygen-containing atmosphere.

[0077] The heat treatment temperature selected in this application ensures that the high-entropy metal-organic framework material is stably coated on the surface of the positive electrode active material, while also preventing the decomposition of the high-entropy metal-organic framework material. If the heat treatment temperature is relatively low, uneven coating may occur. If the heat treatment temperature is relatively high, the structure of the positive electrode material may be damaged, resulting in a decrease in battery performance.

[0078] In some embodiments, the method for forming the mixed slurry includes:

[0079] A first dispersion containing a positive electrode active material is prepared; a second dispersion containing a high-entropy metal-organic framework material is prepared; the first and second dispersions are mixed and then heated and evaporated to form the mixed slurry.

[0080] The first and second dispersions can be formed by at least one of ball milling, stirring, and ultrasonic oscillation. Optionally, the formation of the first dispersion may include: first subjecting the first dispersion to ultrasonic oscillation treatment, and then subjecting it to ball milling treatment. The ultrasonic oscillation time can be 10 min to 30 min, and the ultrasonic oscillation frequency can be 50 kHz to 70 kHz. The ball milling time can be 2 h to 4 h, and the ball-to-material ratio is 6 to 9. Further optionally, the formation of the second dispersion can be the same as that of the first dispersion.

[0081] Optionally, the solvents used in the first dispersion and the second dispersion may each independently include ethanol.

[0082] The first dispersion contains 50% to 70% of the positive electrode active material by mass. The second dispersion contains 40% to 60% of the high-entropy metal-organic framework material by mass. The concentrations of the first and second dispersions selected as above in this application are beneficial to improving the dispersion uniformity of the materials, thereby ensuring that the positive electrode active material and the high-entropy metal-organic framework material are uniformly dispersed after mixing.

[0083] The heating and evaporation temperature is 40℃~80℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃.

[0084] Optionally, during the mixing of the first and second dispersions, the second dispersion is added to the first dispersion. The addition rate of the second dispersion is 0.5 mL / min to 1.5 mL / min.

[0085] In some embodiments, the preparation method of high-entropy metal-organic framework materials includes:

[0086] A precursor solution is obtained by mixing at least five metal sources with an organic ligand source; wherein each metal source contains a different metal element.

[0087] High-entropy metal-organic framework materials were prepared by hydrothermal reaction of precursor solution and carbon paper.

[0088] In the precursor solution, the ratio of the amount of metal elements contained in any two metal sources is (0.9~1.1):1, which can be selected as 1:1; the ratio of the amount of organic ligands contained in the organic ligand source to the amount of metal elements in any metal source is (0.9~1.1):1, which can be selected as 1:1.

[0089] Optionally, the total molar concentration of the metal source in the precursor solution is 1.0 mol / L to 2.0 mol / L, for example, it can be 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2.0 mol / L. The molar concentration of the organic ligand source in the precursor solution is 1.5 mol / L to 2.0 mol / L, for example, it can be 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, or 2.0 mol / L.

[0090] The precursor solution contains solvents including N,N-dimethylformamide, water, and ethanol. Optionally, the volume ratio of N,N-dimethylformamide, water, and ethanol is (13~18):(1~2):1, or optionally 15:1:1.

[0091] In some embodiments, the temperature of the hydrothermal reaction is 80℃~180℃, for example, it can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃ or 180℃, and can be selected from 80℃~150℃. The time is 8h~24h, for example, it can be 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, and can be selected from 8h~14h.

[0092] This application selects a hydrothermal reaction as described above to ensure the formation of a structurally stable high-entropy metal-organic framework material, thereby improving the coating stability.

[0093] In some embodiments, the metal source includes at least five of the following: iron source, cobalt source, nickel source, copper source, manganese source, cadmium ions, and zinc ions. It is understood that the metal source may be at least one of the following: sulfate, nitrate, and chloride, comprising the corresponding metal element.

[0094] Organic ligand sources include at least one of materials containing a terephthalic acid group, a 1,4-dihydroxyanthraquinone group, and a triphenyl benzoic acid group. It is understood that an organic ligand source refers to a material having the corresponding group. For example, a material containing a terephthalic acid group could be 2,5-dihydroxyterephthalic acid.

[0095] In some embodiments, the carbon paper is removed, washed, and then dried to obtain the high-entropy metal-organic framework material. Optionally, the carbon paper is cleaned by water and ethanol exchange. Optionally, the drying method is vacuum drying, with a temperature of 50°C to 70°C and a time of 10 to 12 hours.

[0096] In some embodiments, the method for preparing the positive electrode active material includes:

[0097] The precursor of the positive electrode active material and the lithium source are mixed to obtain a mixture, and the mixture is sintered to prepare the positive electrode active material.

[0098] The ratio of the amount of lithium in the lithium source to the total amount of metal elements in the precursor of the positive electrode active material is (1~1.1):1, for example, it can be 1.0:1, 1.02:1, 1.04:1, 1.06:1, 1.08:1 or 1.10:1.

[0099] In some embodiments, the positive electrode active material contains a dopant element. A source M is also added to the mixture, where M includes at least one selected from Ga, W, Zr, B, Al, Sb, Mo, Ti, La, Na, and Sn. Optionally, the molar ratio of the metal element in the source M to the total molar ratio of the metal elements in the precursor of the positive electrode active material is (0~0.02):1, for example, it can be 0.002:1, 0.004:1, 0.006:1, 0.008:1, 0.010:1, 0.012:1, 0.014:1, 0.016:1, 0.018:1, or 0.020:1. It is understood that the source M can be at least one selected from oxides, hydroxides, carbonates, and nitrates containing the corresponding metal element.

[0100] In some embodiments, the chemical formula of the precursor of the positive electrode active material is Ni. x Co y Mn z (OH)₂, wherein 0.50 ≤ x < 1.0, 0 < y ≤ 0.30, 0 < z ≤ 0.30, and x + y + z = 1. Where x can be 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or 0.99; y can be 0.05, 0.10, 0.15, 0.20, 0.25, or 0.30; and z can be 0.05, 0.10, 0.15, 0.20, 0.25, or 0.30. The lithium source can include at least one of lithium hydroxide and lithium carbonate.

[0101] In some embodiments, the sintering process includes sequentially performing a first sintering stage and a second sintering stage on the mixture.

[0102] Optionally, the temperature of the first sintering stage is 400℃~700℃, for example, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃ or 700℃; the holding time is 1h~4h, for example, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h or 4.0h; the heating rate is 2℃ / min~4℃ / min, for example, 2.0℃ / min, 2.5℃ / min, 3.0℃ / min, 3.5℃ / min or 4.0℃ / min; the atmosphere is an oxygen-containing atmosphere.

[0103] Optionally, the temperature of the second sintering stage is 850℃~950℃, for example, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃ or 950℃; the holding time is 10h~16h, for example, 10.0h, 12.0h, 12.5h, 13.0h, 13.5h, 14.0h, 14.5h, 15.0h, 15.5h or 16.0h; the heating rate is 2℃ / min~4℃ / min, for example, 2.0℃ / min, 2.5℃ / min, 3.0℃ / min, 3.5℃ / min or 4.0℃ / min; the atmosphere is an oxygen-containing atmosphere.

[0104] Exemplary, a method for preparing the above-mentioned coated cathode material is provided, comprising the following steps:

[0105] A mixture is prepared by mixing a lithium source, a precursor of the positive electrode active material, and an M source. The ratio of the amount of lithium in the lithium source to the total amount of metal elements in the precursor is (1~1.1):1, and the ratio of the amount of metal elements in the M source to the total amount of metal elements in the precursor is (0~0.02):1. The mixture is subjected to a first sintering stage and a second sintering stage sequentially. After cooling and crushing, the mixture is sieved to obtain a positive electrode active material with a mesh size of 200-400 mesh. The temperature of the first sintering stage is 400℃~700℃, the holding time is 1h~4h, the heating rate is 2℃ / min~4℃ / min, and the atmosphere is oxygen-containing. The temperature of the second sintering stage is 850℃~950℃, the holding time is 10h~16h, the heating rate is 2℃ / min~4℃ / min, and the atmosphere is oxygen-containing.

[0106] A precursor solution is prepared by mixing at least five metal sources with an organic ligand source. The total molar concentration of the metal sources in the precursor solution is 1.0 mol / L to 2.0 mol / L, and the molar concentration of the organic ligand source is 1.5 mol / L to 2.0 mol / L. The metal sources contain different metal elements, and the molar ratio of the metal elements in any two metal sources in the precursor solution is (0.9~1.1):1, and the molar ratio of the organic ligand in the organic ligand source to the metal element in any metal source is (0.9~1.1):1. The solvent used is N,N-dimethylformamide, water, and ethanol in a volume ratio of (13~18):(1~2):1. The precursor solution and carbon paper are subjected to a hydrothermal reaction at 80℃~180℃ for 8h~24h. After washing and drying, a high-entropy metal-organic framework material is prepared.

[0107] Prepare a first dispersion containing 50% to 70% by mass of positive electrode active material; prepare a second dispersion containing 40% to 60% by mass of high-entropy metal-organic framework material; add the first dispersion to the second dispersion for mixing, and heat and evaporate at 40°C to 80°C to form a mixed slurry. The mixed slurry contains 0.5% to 1.5% by mass of solvent, and the mass of high-entropy metal-organic framework material is 0.5% to 8% of the mass of positive electrode active material.

[0108] After drying the above mixed slurry at 100~200℃ for 2~4h, it is heat-treated at 350℃~700℃ for 2h~7h in air atmosphere, ground and sieved to prepare the coated cathode material.

[0109] The third aspect of this application provides a positive electrode sheet, including a coated positive electrode material prepared by the preparation method of the coated positive electrode material of the first aspect or the coated positive electrode material of the second aspect.

[0110] The aforementioned positive electrode sheet includes a positive current collector and a positive active material layer located on at least one side of the positive current collector. This positive active material layer includes the aforementioned coated positive electrode material, a conductive agent, and a binder. The conductive agent and binder can be commonly used in this technical field.

[0111] Fourthly, this application provides a battery including the positive electrode sheet of the third aspect.

[0112] The aforementioned battery may include, for example, the positive electrode, negative electrode, electrolyte, and separator described in this application. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes, while simultaneously allowing active ions to pass through. The electrolyte, located between the positive and negative electrodes, serves to conduct active ions. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. This application does not impose any particular limitation on the negative electrode, electrolyte, and separator; any negative electrode, electrolyte, and separator prepared using methods commonly used in this technical field, or any other commonly used negative electrode, electrolyte, and separator in this art, may be used. Optionally, the aforementioned battery includes a lithium-ion battery.

[0113] Furthermore, another embodiment of this application provides an electrical device including the battery described above.

[0114] The aforementioned electrical devices may include any battery-powered equipment or apparatus, such as mobile phones, laptops, electric vehicles, ships, satellites, energy storage devices, smart home appliances, etc., but are not limited thereto.

[0115] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0116] Example 1

[0117] (1) Positive electrode active material

[0118] Lithium carbonate, Ni 0.60 Co 0.10 Mn 0.30 (OH)₂, strontium carbonate, and aluminum oxide were mixed in a high-speed mixer at 1500 r / min for 30 min to obtain a mixture. The amount of lithium in the lithium carbonate and the amount of Ni... 0.60 Co 0.10 Mn 0.30 The total molar ratio of metallic elements in (OH)₂ is 1.05:1, and the molar ratio of strontium to Ni is... 0.60 Co 0.10 Mn 0.30 The total molar ratio of metallic elements in (OH)₂ is 0.001:1, and the molar ratio of aluminum to Ni is... 0.60 Co 0.10 Mn 0.30 The total molar ratio of metallic elements in (OH)2 is 0.005:1.

[0119] The above mixture was subjected to a first sintering stage and a second sintering stage in sequence. After cooling and crushing, it was sieved to obtain a 300-mesh positive electrode active material Li(Ni) 0.6 Co 0.1 Mn 0.3 ) 0.994 Sr 0.001 Al 0.005 O2. The first sintering stage has a temperature of 500℃, a holding time of 2h, a heating rate of 4℃ / min, and an oxygen-containing atmosphere with an oxygen volume concentration of 99.5%; the second sintering stage has a temperature of 930℃, a holding time of 11h, a heating rate of 2.5℃ / min, and an oxygen-containing atmosphere with an oxygen volume concentration of 99.5%.

[0120] (2) High-entropy metal-organic framework materials

[0121] 0.02 mmol of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cu(NO3)2·6H2O, and Mn(NO3)2·4H2O were weighed out and added to 40 mL of solvent for mixing. Then, 0.02 mmol of 2,5-dihydroxyterephthalic acid was added and the mixture was stirred for 4 h to obtain the precursor solution. The solvent included N,N-dimethylformamide, deionized water, and anhydrous ethanol in a volume ratio of 15:1:1.

[0122] The precursor solution and carbon paper were subjected to a hydrothermal reaction at 100°C for 9 hours. The carbon paper was then removed and washed four times with deionized water and anhydrous ethanol, and finally vacuum dried at 55°C for 11 hours to prepare a high-entropy metal-organic framework material.

[0123] (3) Coated cathode material

[0124] The above-mentioned positive electrode active material and the above-mentioned high-entropy metal-organic framework material were weighed at a mass ratio of 1:0.05. Both the positive electrode active material and the high-entropy metal-organic framework material were dissolved in anhydrous ethanol, and then subjected to ultrasonic vibration for 20 min followed by ball milling for 4 h to obtain a first dispersion containing 60% of the positive electrode active material and a second dispersion containing 50% of the high-entropy metal-organic framework material. The second dispersion was added dropwise to the first dispersion at a rate of 1.2 mL / min under a 60°C water bath heating condition. The mixture was stirred and evaporated to obtain a paste-like slurry. The solvent content in the slurry was 5% by mass.

[0125] The above-mentioned mixed slurry was dried at 150℃ for 2 hours, then heat-treated at 400℃ for 4 hours in air, ground for 10 minutes, and sieved to prepare the coated cathode material. Its SEM image is shown below. Figure 1As shown in the figure, the coating is uniformly distributed on the surface of the ternary cathode material; the XRD diffraction curve is shown in the figure. Figure 2 As shown in the figure, the characteristic peaks are nickel-cobalt-manganese and there are no impurity peaks, indicating good crystallinity; the particle size distribution diagram is as follows. Figure 3 As shown, the particle size distribution is uniform and exhibits a single-peak distribution, with a Dv50 of 3.6 μm.

[0126] Example 2

[0127] The coated cathode material was prepared according to the method in Example 1, except that the method for preparing the high-entropy metal-organic framework material includes:

[0128] 0.01 mmol of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Ni(NO3)2·6H2O, Cu(NO3)2·6H2O, and Mn(NO3)2·4H2O were weighed out and added to 40 mL of solvent for mixing. Then, 0.01 mmol of 2,5-dihydroxyterephthalic acid was added and the mixture was stirred for 4 h to obtain the precursor solution. The solvent included N,N-dimethylformamide, deionized water, and anhydrous ethanol in a volume ratio of 15:1:1.

[0129] The precursor solution and carbon paper were subjected to a hydrothermal reaction at 110°C for 8 hours. The carbon paper was then removed and washed four times with deionized water and anhydrous ethanol, and finally vacuum dried at 55°C for 11 hours to prepare a high-entropy metal-organic framework material.

[0130] Example 3

[0131] The coated cathode material was prepared according to the method of Example 1, except that the mass ratio of the cathode active material to the high-entropy metal-organic framework material was 1:0.02 during the preparation of the coated cathode material.

[0132] Example 4

[0133] The coated cathode material was prepared according to the method of Example 1, except that the mass ratio of the cathode active material to the high-entropy metal-organic framework material was 1:0.01 during the preparation of the coated cathode material.

[0134] Example 5

[0135] The coated cathode material was prepared according to the method in Example 1, except that the mass ratio of the cathode active material to the high-entropy metal-organic framework material was 1:0.005 during the preparation of the coated cathode material; the heat treatment temperature was 350°C and the time was 7 hours.

[0136] Example 6

[0137] The coated cathode material was prepared according to the method in Example 1, except that the mass ratio of the cathode active material to the high-entropy metal-organic framework material was 1:0.08 during the preparation of the coated cathode material; the heat treatment temperature was 700℃ and the time was 2h.

[0138] Example 7

[0139] The coated cathode material was prepared according to the method of Example 1, except that the mass ratio of the cathode active material to the high-entropy metal-organic framework material was 1:0.09 during the preparation of the coated cathode material.

[0140] Example 8

[0141] The coated cathode material was prepared according to the method of Example 1, except that the heat treatment temperature was 300°C.

[0142] Example 9

[0143] The coated cathode material was prepared according to the method of Example 1, except that the heat treatment temperature was 750°C.

[0144] Comparative Example 1

[0145] The positive electrode active material prepared in Example 1 was directly used as the positive electrode material.

[0146] Comparative Example 2

[0147] The coated cathode material was prepared according to the method of Example 1, except that the high-entropy metal-organic framework material was replaced with a high-entropy oxide (FeCoNiCuMn)3O4 containing an equal amount of metal elements.

[0148] Comparative Example 3

[0149] The coated cathode material was prepared according to the method of Example 1, except that the high-entropy metal-organic framework material was replaced with a Co-based metal-organic framework material. Specifically, the metal source in the high-entropy metal-organic framework material prepared in Example 1 was replaced with Co(NO3)2·6H2O.

[0150] Coin cells were prepared using the cathode materials obtained in the above embodiments and comparative examples. The preparation methods included:

[0151] The above-mentioned positive electrode material, acetylene black, and PVDF were mixed uniformly at a mass ratio of 90:4:6 and dispersed in NMP to obtain a uniform positive electrode slurry. This slurry was coated onto aluminum foil, vacuum baked at 80°C for 12 hours, and then rolled to obtain the positive electrode sheet. Using lithium metal sheets as the negative electrode, the positive electrode sheet and the slurry were assembled into a 2032 coin cell in a vacuum glove box. After a 10-hour settling period, the battery underwent its first charge-discharge capacity test at 0.1C within a voltage window of 3.0–4.4V on a blue-light test cabinet. The test results are shown in Table 1. The cycle performance curves of Examples 1-4 and Comparative Example 1 are shown in Table 1. Figure 4 As shown.

[0152] Table 1

[0153]

[0154] As can be seen from the table above:

[0155] (1) Compared with Examples 3-4 and 7, Example 1 shows that the present application controls the amount of high-entropy metal-organic framework material coating, which comprehensively improves the cycle performance, capacity performance and rate performance of the battery.

[0156] (2) Compared with Examples 8-9, Example 1 shows that the present application controls the heat treatment temperature to ensure the uniformity and stability of the coating, so that the cathode material has high ionic conductivity and electronic conductivity, thereby improving the rate performance and cycle performance.

[0157] (3) Compared with Comparative Examples 1-3, Comparative Example 1 was not coated, resulting in lower first-efficiency and cycle retention rates. Comparative Example 2 only used high-entropy oxide coating. Compared with high-entropy metal-organic framework materials, it does not have a pore structure, has a lower specific surface area, fewer active adsorption sites, and no diverse structure. Therefore, its coating structure has poor stability and slow lithium-ion transport, which cannot effectively utilize the advantages of high-entropy materials, affecting the material's capacity and rate performance. Comparative Example 3 only used Co-based metal-organic framework material coating. Compared with high-entropy metal-organic framework materials, although it can also use the pore structure to reduce the problem of material distortion during charge and discharge, and has a certain degree of structural reversibility, it cannot alleviate the problem of uncontrolled lattice oxygen redox activity in the cathode material. During cycling, lattice oxygen release may occur, affecting the material's structural stability and thus affecting the material's cycle performance. Moreover, Co-based metal-organic framework materials have fewer active adsorption sites, slower lithium-ion transport speed, and poorer capacity performance.

[0158] In summary, this application employs a high-entropy metal-organic framework (MOF) to coat the positive electrode active material. MOFs possess structural diversity, multiple active adsorption sites, and high specific surface area, allowing them to effectively adsorb onto the surface of the positive electrode active material, forming a uniform coating structure. This stabilizes the surface structure and reduces phase transition stress. Furthermore, it helps alleviate the problem of uncontrolled lattice oxygen redox activity and enhances interface protection, preventing direct contact between the material and the electrolyte and inhibiting the dissolution of transition metal ions at high potentials, thus further improving the material's cycle stability. Moreover, the porous structure of the MOF is less prone to distortion during charge and discharge, providing more lithium-ion diffusion channels during lithium-ion insertion and extraction. This facilitates lithium-ion migration within the MOF structure, improving the lithium-ion transport rate and structural stability of the electrode material at high voltages. This effectively reduces capacity decay during cycling, enhances cycle performance, and results in higher capacity.

[0159] In addition, the high-entropy metal-organic framework coating of this application can reduce the formation of solid electrolyte interfacial films and alleviate the corrosion of positive electrode active materials by hydrofluoric acid in the electrolyte, thereby improving the cycle stability and rate performance of the material.

[0160] Therefore, the coated cathode material of this application has a stable structure, effectively improves the lithium-ion transport speed, and can also reduce the transfer resistance of lithium ions at the electrode-electrolyte interface, thus synergistically improving the battery's first charge-discharge efficiency, rate performance, and cycle performance.

[0161] 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.

[0162] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the application. 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 modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A coated positive electrode material, characterized by, The coated positive electrode material comprises a core material and a coating layer arranged on at least part of the surface of the core material; the core material comprises a positive electrode active material, and the coating layer comprises a high-entropy metal organic framework material.

2. The coated positive electrode material of claim 1, wherein, The coated positive electrode material satisfies at least one of the following conditions: (1) the mass of the coating layer is 0.5% to 8% of the mass of the core material; (2) the volume average particle size Dv50 of the coated positive electrode material is 0.5 μm to 10 μm; (3) the metal ions contained in the high-entropy metal organic framework material include at least five of iron ions, cobalt ions, nickel ions, copper ions, manganese ions, cadmium ions and zinc ions; (4) the organic ligand contained in the high-entropy metal organic framework material includes at least one of terephthalic acid ligand, benzene tricarboxylic acid ligand and 1,4-dihydroxy anthraquinone ligand; (5) The chemical formula of the positive electrode active material is Li(Ni) a Co b Mn c ) d M e O2; wherein a+b+c=1, d+e=1, 0.5≤a<1.0, 0<b≤0.3, 0<c≤0.3, 0.98≤d≤1, 0≤e≤0.02; M includes at least one of Ga, W, Zr, B, Al, Sb, Mo, Ti, La, Na and Sn.

3. A method for producing a coated positive electrode material, characterized by, The preparation method comprises: preparing a mixed slurry comprising a positive electrode active material and a high-entropy metal organic framework material; drying the mixed slurry and then performing heat treatment to enable the high-entropy metal organic framework material to coat at least part of the surface of the positive electrode active material to form a coating layer.

4. The method for preparing the coated cathode material as described in claim 3, characterized in that, The preparation method satisfies at least one of the following conditions: (1) the mass of the high-entropy metal organic framework material in the mixed slurry is 0.5% to 8% of the mass of the positive electrode active material; (2) the mesh number of the positive electrode active material is 200 mesh to 400 mesh; (3) the mass ratio of the solvent contained in the mixed slurry is 0.5% to 1.5%; (4) the temperature of the heat treatment is 350°C to 700°C, the time is 2h to 7h, and the atmosphere is an oxygen-containing atmosphere.

5. The method of claim 3, wherein the coated positive electrode material is prepared by mixing the lithium transition metal oxide powder and the coating material in a weight ratio of 1 : 0.01 to 1 : 0.

5. The formation method of the mixed slurry comprises: preparing a first dispersion liquid containing the positive electrode active material; preparing a second dispersion liquid containing the high-entropy metal organic framework material; mixing the first dispersion liquid and the second dispersion liquid and then heating and evaporating to form the mixed slurry; Optionally, the mass ratio of the positive electrode active material contained in the first dispersion liquid is 50% to 70%; Optionally, the mass ratio of the high-entropy metal organic framework material contained in the second dispersion liquid is 40% to 60%; Optionally, the temperature of the heating and evaporation is 40°C to 80°C.

6. The method of claim 3, wherein the coated positive electrode material is prepared by the steps of: preparing a lithium transition metal oxide powder; and coating the lithium transition metal oxide powder with a lithium phosphate compound. The preparation method of the high-entropy metal organic framework material comprises: mixing at least five metal sources and an organic ligand source to obtain a precursor solution; wherein each of the metal sources contains different metal elements; performing hydrothermal reaction on the precursor solution and carbon paper to prepare the high-entropy metal organic framework material.

7. The method for preparing the coated cathode material as described in claim 6, characterized in that, The preparation method of the high-entropy metal organic framework material satisfies at least one of the following conditions: (1) the molar ratio of the metal elements contained in any two of the metal sources in the precursor solution is (0.9-1.1):1, and the molar ratio of the organic ligand contained in the organic ligand source to the metal elements in any one of the metal sources is (0.9-1.1):1; (2) the concentration of the total amount of substances of the metal sources contained in the precursor solution is 1.0 mol / L to 2.0 mol / L; (3) the precursor solution contains the organic ligand source in a concentration of 1.5 mol / L to 2.0 mol / L; (4) the solvent contained in the precursor solution includes N,N-dimethylformamide, water and ethanol; the volume ratio of the N,N-dimethylformamide, the water and the ethanol is (13-18):(1-2):1; (5) the hydrothermal reaction is performed at a temperature of 80°C to 180°C for 8h to 24h; (6) the metal source includes at least five of iron source, cobalt source, nickel source, copper source, manganese source, cadmium ion and zinc ion; (7) the organic ligand source includes at least one of a material containing terephthalic acid group, a material containing trimesic acid group and a material containing 1,4-dihydroxyanthraquinone group.

8. The method for producing a coated positive electrode material according to any one of claims 3 to 7, wherein The preparation method of the positive electrode active material includes: mixing a precursor of the positive electrode active material and a lithium source to obtain a mixture, and performing sintering treatment on the mixture to prepare the positive electrode active material; Optionally, the ratio of the amount of substance of lithium in the lithium source to the total amount of substance of metal elements in the precursor of the positive electrode active material is (1-1.1):1; Optionally, a M source is further added to the mixture, M including at least one of Ga, W, Zr, B, Al, Sb, Mo, Ti, La, Na and Sn, and the ratio of the amount of substance of metal elements in the M source to the total amount of substance of metal elements in the precursor of the positive electrode active material is (0-0.02):1; Optionally, the chemical formula of the precursor of the positive electrode active material is Ni x Co y Mn z (OH)2, wherein 0.50≤x<1.0, 0 (OH)2, wherein 0.50≤x<1.0, 0 (OH)2, wherein 0.50≤x<1.0, 0 Optionally, the sintering treatment includes: sequentially performing a first sintering stage and a second sintering stage on the mixture; the first sintering stage is performed at a temperature of 400°C to 700°C for 1h to 4h at a heating rate of 2°C / min to 4°C / min in an oxygen-containing atmosphere; the second sintering stage is performed at a temperature of 850°C to 950°C for 10h to 16h at a heating rate of 2°C / min to 4°C / min in an oxygen-containing atmosphere.

9. A positive electrode sheet characterized by comprising: The coated positive electrode material prepared by the preparation method of the coated positive electrode material of claim 1 or 2 or any one of claims 3-8.

10. A battery, characterized by The positive electrode sheet of claim 9.

Images