Method for preparing coated positive electrode material and battery positive electrode prepared therefrom

Abstract

The present invention relates to a method for preparing a coated positive electrode material and a positive electrode prepared by the method. The method comprises: (1) mixing the positive electrode material into a solution containing an alkali metal hydroxide; (2) adding polyphosphoric acid to the solution obtained in step (1), and stirring at a temperature of 0-40°C for 1-12 hours, wherein the mass ratio of the polyphosphoric acid is 0.1-20% based on the mass of the positive electrode material; and (3) filtering to obtain a positive electrode material coated with an alkali metal salt of polyphosphoric acid. By adopting the above method of the present invention, the rate performance and cycle performance of batteries such as lithium-ion batteries can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of electrochemistry, and more particularly to a method for preparing a coated positive electrode material and a positive electrode prepared by the method. Background Art

[0002] With the rapid development of carbon neutrality, there is an urgent need for the widespread application of high-energy-density lithium-ion batteries (LIBs) to meet the growing demand for commercial applications. In these batteries, the lower energy density of cathode materials compared to anode materials has been a major limitation on the development of LIBs. This is mainly manifested in the low high-rate discharge capacity and poor cycling performance of high-energy-density electrode materials. In recent years, many modification strategies have been developed to address these issues, including surface coating and element doping.

[0003] Surface coating, as a modification strategy, is more direct for solving these problems without damaging the overall structure. For example, the use of various functional coatings, such as metal oxides (Al2O3, TiO2, CeO2) (see Advanced Energy Materials 2013, 3, 1299; ACS Applied Materials & Interfaces 2015, 7, 19189-19200; Nano Energy 2020, 75, 104995.) and metal fluorides (AlF3, MgF2, CaF2) (see Journal of Materials Chemistry A 2020, 8, 7991; Chemistry of Materials 2014, 26, 6320; NanoEnergy 2022, 92, 106760), can suppress the irreversible oxygen release of the cathode material during high-voltage charge and discharge, and physically separate the cathode from the electrolyte to suppress interfacial side reactions. In addition, electron conductors (carbon-based materials, etc.) (see NanoEnergy 2019, 59, 184) and lithium ion conductors (LiTaO3, LiNbO3, Li3PO4) (see Adv Sci (Weinh) 2020, 7, 1902538; ACS Appl Mater Interfaces 2021, 13, 61248-61257; Chemical Engineering Journal 2022, 427) can also be used to separate the positive electrode and the electrolyte, while improving the electron and lithium ion conductivity.

[0004] However, only a few studies have attempted this type of modification with universality, but these often involve toxic chemicals, long annealing times, or high-cost reagents, making them unsuitable for large-scale commercialization (see Nano Energy 2021, 79; Advanced Energy Materials 2020, 10; ACS Sustainable Chemistry & Engineering 2019). Therefore, there is an urgent need to develop a universal and efficient method for preparing high-performance lithium-ion battery cathode materials. Summary of the Invention

[0005] One aspect of the present invention provides a method for preparing a coated positive electrode material, the method comprising: (1) mixing a positive electrode material into a solution containing an alkali metal hydroxide; (2) adding polyphosphoric acid to the solution obtained in step (1), and stirring at a temperature of 0-40° C. for 1-12 hours, wherein the mass ratio of the polyphosphoric acid is 0.1-20% based on the mass of the positive electrode material; and (3) filtering to obtain a positive electrode material coated with an alkali metal salt of polyphosphate.

[0006] In one embodiment, the polyphosphoric acid is dipolyphosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, pentapolyphosphoric acid or any combination thereof. In another embodiment, the polyphosphoric acid is dissolved in an alcohol, such as methanol. In another embodiment, the mass ratio of the polyphosphoric acid is 1-15% based on the mass of the positive electrode material. In one embodiment, the alkali metal hydroxide is lithium hydroxide, sodium hydroxide, potassium hydroxide or any combination thereof. In another embodiment, the solution containing the alkali metal hydroxide is an anhydrous alcohol solution containing the alkali metal hydroxide, such as an anhydrous methanol solution. In another embodiment, the concentration of the solution containing the alkali metal hydroxide is 0.01-10 mol / L.

[0007] In one embodiment, the polyphosphoric acid reacts with the alkali metal hydroxide to form an alkali polyphosphate, and then a phase transition of the positive electrode material from a layered phase to a spinel phase occurs in situ on the contact surface of the alkali polyphosphate and the positive electrode material. In another embodiment, the alkali polyphosphate coated positive electrode material is a 1-10% by mass alkali polyphosphate coated positive electrode material. In a further embodiment, an integrated layer of alkali polyphosphate-spinel phase-layered is formed on the surface of the alkali polyphosphate coated positive electrode material.

[0008] In one embodiment, the positive electrode material is selected from a material based on lithium cobalt oxide, a material based on lithium manganese oxide, a material based on lithium nickel oxide, a material based on lithium iron phosphate, or a combination thereof. In another embodiment, the positive electrode material is selected from a cobalt-free lithium-rich manganese-based material, a lithium-rich manganese-based material, a high nickel material, a lithium cobalt oxide material, or a combination thereof. In one embodiment, the composition of the high nickel material is LiNi 1-x-y Co x M y O2, wherein M is selected from Mn, Al and combinations thereof, and wherein 0≤x≤0.2, 0≤y≤0.2. In another embodiment, the composition of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2, wherein M is selected from Ni, Co, Mn and combinations thereof, and wherein 0.1≤x≤0.9.

[0009] In one embodiment, the positive electrode material coated with an alkali metal polyphosphate is a positive electrode material coated with 4-10% by mass of lithium polyphosphate. In another embodiment, the crystalline phase structure of the positive electrode material is a hexagonal layered structure with an R-3m space group. In yet another embodiment, an integrated layer of lithium polyphosphate-spinel phase-layered is formed on the surface of the lithium polyphosphate-coated positive electrode material.

[0010] Another aspect of the present invention provides a battery positive electrode comprising a polyphosphate-coated positive electrode material prepared by the following method, and a battery comprising such a positive electrode: (1) mixing the positive electrode material into a solution comprising an alkali metal hydroxide; (2) adding polyphosphoric acid to the solution obtained in step (1), and stirring at a temperature of 0-40° C. for 1-12 hours, wherein the mass ratio of the polyphosphoric acid is 0.1-20% based on the mass of the positive electrode material; and (3) filtering to obtain the polyphosphate-coated positive electrode material.

[0011] In one embodiment, the polyphosphoric acid is dipolyphosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, pentapolyphosphoric acid or any combination thereof. In another embodiment, the polyphosphoric acid is dissolved in an alcohol, such as methanol. In another embodiment, the mass ratio of the polyphosphoric acid is 1-15% based on the mass of the positive electrode material. In one embodiment, the alkali metal hydroxide is lithium hydroxide, sodium hydroxide, potassium hydroxide or any combination thereof. In another embodiment, the solution containing the alkali metal hydroxide is an anhydrous alcohol solution containing the alkali metal hydroxide, such as an anhydrous methanol solution. In another embodiment, the concentration of the solution containing the alkali metal hydroxide is 0.01-10 mol / L.

[0012] In one embodiment, the polyphosphoric acid reacts with the alkali metal hydroxide to form an alkali polyphosphate, and then a phase transition of the positive electrode material from a layered phase to a spinel phase occurs in situ on the contact surface of the alkali polyphosphate and the positive electrode material. In another embodiment, the alkali polyphosphate coated positive electrode material is a 1-10% by mass alkali polyphosphate coated positive electrode material. In a further embodiment, an integrated layer of alkali polyphosphate-spinel phase-layered is formed on the surface of the alkali polyphosphate coated positive electrode material.

[0013] In one embodiment, the positive electrode material is selected from a material based on lithium cobalt oxide, a material based on lithium manganese oxide, a material based on lithium nickel oxide, a material based on lithium iron phosphate, or a combination thereof. In another embodiment, the positive electrode material is selected from a cobalt-free lithium-rich manganese-based material, a lithium-rich manganese-based material, a high nickel material, a lithium cobalt oxide material, or a combination thereof. In one embodiment, the composition of the high nickel material is LiNi 1-x-y Co x M y O2, wherein M is selected from Mn, Al and combinations thereof, and wherein 0≤x≤0.2, 0≤y≤0.2. In another embodiment, the composition of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2, wherein M is selected from Ni, Co, Mn and combinations thereof, and wherein 0.1≤x≤0.9.

[0014] In one embodiment, the positive electrode material coated with an alkali metal polyphosphate is a positive electrode material coated with 4-10% by mass of lithium polyphosphate. In another embodiment, the crystalline phase structure of the positive electrode material is a hexagonal layered structure with an R-3m space group. In yet another embodiment, an integrated layer of lithium polyphosphate-spinel phase-layered is formed on the surface of the lithium polyphosphate-coated positive electrode material.

[0015] Another aspect of the present invention provides the use of a positive electrode material prepared according to the following method as a positive electrode of a battery: (1) mixing the positive electrode material into a solution containing an alkali metal hydroxide; (2) adding polyphosphoric acid to the solution obtained in step (1) and stirring at a temperature of 0-40°C for 1-12 hours, wherein the mass ratio of the polyphosphoric acid is 0.1-20% based on the mass of the positive electrode material; and (3) filtering to obtain a positive electrode material coated with an alkali metal salt of polyphosphate.

[0016] In one embodiment, the polyphosphoric acid is dipolyphosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, pentapolyphosphoric acid or any combination thereof. In another embodiment, the polyphosphoric acid is dissolved in an alcohol, such as methanol. In another embodiment, the mass ratio of the polyphosphoric acid is 1-15% based on the mass of the positive electrode material. In one embodiment, the alkali metal hydroxide is lithium hydroxide, sodium hydroxide, potassium hydroxide or any combination thereof. In another embodiment, the solution containing the alkali metal hydroxide is an anhydrous alcohol solution containing the alkali metal hydroxide, such as an anhydrous methanol solution. In another embodiment, the concentration of the solution containing the alkali metal hydroxide is 0.01-10 mol / L.

[0017] In one embodiment, the polyphosphoric acid reacts with the alkali metal hydroxide to form an alkali polyphosphate, and then a phase transition of the positive electrode material from a layered phase to a spinel phase occurs in situ on the contact surface of the alkali polyphosphate and the positive electrode material. In another embodiment, the alkali polyphosphate coated positive electrode material is a 1-10% by mass alkali polyphosphate coated positive electrode material. In a further embodiment, an integrated layer of alkali polyphosphate-spinel phase-layered is formed on the surface of the alkali polyphosphate coated positive electrode material.

[0018] In one embodiment, the positive electrode material is selected from a material based on lithium cobalt oxide, a material based on lithium manganese oxide, a material based on lithium nickel oxide, a material based on lithium iron phosphate, or a combination thereof. In another embodiment, the positive electrode material is selected from a cobalt-free lithium-rich manganese-based material, a lithium-rich manganese-based material, a high nickel material, a lithium cobalt oxide material, or a combination thereof. In one embodiment, the composition of the high nickel material is LiNi 1-x-y Co x M y O2, wherein M is selected from Mn, Al and combinations thereof, and wherein 0≤x≤0.2, 0≤y≤0.2. In another embodiment, the composition of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2, wherein M is selected from Ni, Co, Mn and combinations thereof, and wherein 0.1≤x≤0.9.

[0019] In one embodiment, the positive electrode material coated with an alkali metal polyphosphate is a positive electrode material coated with 4-10% by mass of lithium polyphosphate. In another embodiment, the crystalline phase structure of the positive electrode material is a hexagonal layered structure with an R-3m space group. In yet another embodiment, an integrated layer of lithium polyphosphate-spinel phase-layered is formed on the surface of the lithium polyphosphate-coated positive electrode material.

[0020] For some cathode materials, such as lithium-rich manganese-based materials, constructing spinel / layered heterostructures on the surface of particle materials can alleviate the irreversible O2 release by reducing the surface oxygen partial pressure, improve the diffusion of alkali metal ions such as lithium ions by providing three-dimensional lithium ion diffusion channels, and suppress the Mn by regulating the two-phase interface orbital sequence. 3+ Jahn-Teller distortion. Therefore, surface coating, which combines the above factors, is an ideal solution. For lithium-ion batteries, lithium-ion conductors are ideal candidates for surface coating materials because the cathode preparation process contains electronic conductive additives and lithium-ion battery cathode materials with low lithium ion conductivity.

[0021] The inventors of this case have found that the rate performance and cycle performance of batteries such as lithium-ion batteries can be effectively improved by the above-mentioned coating strategy. In addition, compared with the coating method (which has the disadvantages of insufficient and indefinite reaction) of introducing acid and residual alkali and / or salt on the surface of the positive electrode material in the art, the method of the present invention can effectively control the reaction ratio of alkali and acid, and can also more fully form spinel / layered heterostructures on the surface of the positive electrode material in situ, such as lithium polyphosphate-spinel phase-layered integrated layers, specifically, the integrated layers are nanoscale, and are layered-spinel phase-polyphosphate alkali metal salts from the bulk phase of the positive electrode material to the surface. Such a process can not only effectively control the coating weight or coating thickness, but also greatly improve the coating quality.

[0022] Compared with other modification methods already known in the art, the method of the present invention can inhibit the interfacial side reactions between the electrode and the electrolyte during the charge and discharge process; at the same time, since the polyphosphate alkali metal salt and the spinel phase have a higher lithium ion conductivity rate, the rate performance of the electrode material can be improved; the spinel-layered structure is naturally formed on the surface, which can not only physically isolate, but also adjust the structure of the material itself, inhibit the release of oxygen during high-voltage charging, and thus improve the electrochemical performance of the material in a multi-effect combination. More importantly, the modification process of the method of the present invention is generated in situ under normal temperature and pressure conditions. Compared with other existing technologies, it is simpler to operate, has lower raw material costs, and is more universal, so it has greater potential for large-scale commercialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are included to provide a further understanding and explanation of the present inventive concept, illustrate embodiments of the present inventive concept, and together with the description serve to explain the principle of the present inventive concept. In the drawings:

[0024] Figure 1 The results show that the different amounts of lithium polyphosphate coated cobalt-free lithium-rich manganese-based materials (Li 1.2 Ni 0.2 Mn0.6 O2) rate performance.

[0025] Figure 2 The results show that the different amounts of lithium polyphosphate coated cobalt-free lithium-rich manganese-based materials (Li 1.2 Ni 0.2 Mn 0.6 O2) cycle performance.

[0026] Figure 3 The cobalt-free lithium-rich manganese-based material (Li 1.2 Ni 0.2 Mn 0.6 O2)'s XRD pattern.

[0027] Figure 4 The cobalt-free lithium-rich manganese-based material (Li 1.2 Ni 0.2 Mn 0.6 O2) TEM image.

[0028] Figure 5 The cobalt-free lithium-rich manganese-based material (Li 1.2 Ni 0.2 Mn 0.6 TEM Mapping of O2).

[0029] Figure 6 The cobalt-free lithium-rich manganese-based material (Li 1.2 Ni 0.2 Mn 0.6 O2) first cycle charge and discharge curve.

[0030] Figure 7 The cobalt-free lithium-rich manganese-based material (Li 1.2 Ni 0.2 Mn 0.6 O2) rate performance.

[0031] Figure 8 The cobalt-free lithium-rich manganese-based material (Li 1.2 Ni 0.2 Mn 0.6 O2) cycle performance.

[0032] Figure 9 The cobalt-free lithium-rich manganese-based material (Li 1.2 Ni 0.2 Mn 0.6 O2) cycle performance comparison.

[0033] Figure 10 The lithium-rich manganese-based material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2) rate performance.

[0034] Figure 11 The lithium-rich manganese-based material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2) cycle performance.

[0035] Figure 12 The high nickel 811 material (LiNi) coated with lithium polyphosphate according to Example 3 is shown. 0.8 Co 0.1 Mn 0.1 O2) rate performance.

[0036] Figure 13 The high nickel 811 material (LiNi) coated with lithium polyphosphate according to Example 3 is shown. 0.8 Co 0.1 Mn 0.1 O2) cycle performance.

[0037] Figure 14 The rate performance of the lithium cobalt oxide material (LiCoO2) coated with lithium polyphosphate according to Example 4 is shown.

[0038] Figure 15 The cycling performance of the lithium cobalt oxide material (LiCoO2) coated with lithium polyphosphate according to Example 4 is shown. DETAILED DESCRIPTION

[0039] In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the various embodiments. As used herein, the terms "embodiment" and "implementation" are used interchangeably and are non-limiting examples of one or more of the inventive concepts disclosed herein. However, it will be apparent that the various embodiments can be practiced without these specific details, or can be practiced with one or more equivalent arrangements.

[0040] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. These terms should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless explicitly defined as such herein.

[0041] The present invention provides a method for treating a positive electrode material, which first forms an alkali metal polyphosphate by reacting polyphosphoric acid with an alkali metal hydroxide, and then in situ causes a phase transition of the positive electrode material from a layered phase to a spinel phase on the contact surface of the alkali metal polyphosphate and the positive electrode material, that is, a gradual structure of layered-spinel phase-alkali metal polyphosphate is formed. In this regard, the positive electrode material has a layered structure, for example, its crystal phase structure can be a hexagonal layered structure with an R-3m space group. Preferably, the alkali metal ions of the added alkali metal hydroxide are present in proportion to the polyphosphoric acid, for example, in a molar ratio of 1-10, preferably, in a chemical equivalent, for example, when the polyphosphoric acid is tripolyphosphoric acid, the molar ratio of the alkali metal ion to the tripolyphosphoric acid is 5:1, and so on.

[0042] The positive electrode material of the present invention may include a material based on lithium cobalt oxide, a material based on lithium manganese oxide, a material based on lithium nickel oxide, a material based on lithium iron phosphate, etc. having a layered structure. Specifically, it may be a cobalt-free lithium-rich manganese-based material, a lithium-rich manganese-based material, a high-nickel material, a lithium cobalt oxide material, etc. Preferably, the positive electrode material may be: a high-nickel material, whose composition is LiNi 1-x- y Co x M y O2, wherein M is selected from Mn, Al and combinations thereof, and wherein 0≤x≤0.2, 0≤y≤0.2; or, a lithium-rich manganese-based material having a composition of xLi2MnO3·(1-x)LiMO2, wherein M is selected from Ni, Co, Mn and combinations thereof, and wherein 0.1≤x≤0.9. In the above, x, y and z can be any value within the defined range, for example, for high nickel materials, x and y can each be 0.1 or 0.2, while for lithium-rich manganese-based materials, x can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8.

[0043] The treatment method of the present invention can fully control the reaction ratio of the base and acid, thereby effectively adjusting the phase change structure formed on the positive electrode surface. Under ideal conditions, a layer of polyphosphate is uniformly coated on the surface of the positive electrode material. Taking lithium-ion batteries as an example, a layer of lithium polyphosphate can be coated on the surface of the positive electrode material of a lithium-ion battery. Between the positive electrode material and the lithium polyphosphate layer, a phase transition from layered to spinel phase is formed, thereby forming an integrated layer of layered-spinel phase-alkali metal polyphosphate.

[0044] The content of the coated alkali metal polyphosphate can be 1-10% by mass, preferably 4-10% by mass, based on the mass of the positive electrode material. Taking lithium polyphosphate as an example, the content can be 4-10% by mass, preferably 6% by mass. Of course, the content of the alkali metal polyphosphate can also be any value within the range of 1-10% by mass, such as 2, 3, 4, 5, 6, 7, 8, or 9% by mass.

[0045] In this context, polyphosphoric acid has the following structure:

[0046]

[0047] wherein n is an integer from 1 to 10, such as 2, 3, 4, 5, 6, etc. Correspondingly, the polyphosphoric acid is dipolyphosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, pentapolyphosphoric acid, etc. However, in actual applications, due to limitations in the synthesis method, the n value of the polyphosphoric acid varies slightly, but preferably n is 3 on average. In addition, the alkali metal hydroxide is lithium hydroxide, sodium hydroxide, potassium hydroxide, or any combination thereof, preferably lithium hydroxide.

[0048] The method for preparing a coated positive electrode material of the present invention comprises: (1) mixing a positive electrode material into a solution containing an alkali metal hydroxide; (2) adding polyphosphoric acid to the solution obtained in step (1), and stirring at a temperature of 0-40° C. for 1-12 hours, wherein the mass ratio of the polyphosphoric acid is 0.1-20% based on the positive electrode material; and (3) filtering to obtain a positive electrode material coated with an alkali metal salt of polyphosphate.

[0049] The solution containing an alkali metal hydroxide is an anhydrous alcohol solution containing an alkali metal hydroxide, such as an anhydrous methanol solution, and its concentration can be 0.01-10 mol / L, for example, 0.1, 0.2, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, or 9 mol / L. The specific concentration can be determined according to the type of alkali metal hydroxide and alcohol selected, but is preferably 0.2-0.5 mol / L.

[0050] Similarly, polyphosphoric acid can be dissolved directly in an anhydrous alcohol solution containing an alkali metal hydroxide, or it can be first dissolved in an alcohol, such as methanol. Regardless of the method used, the mass ratio of polyphosphoric acid is 1-15%, such as 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14%, based on the mass of the positive electrode material. Of course, the amount of polyphosphoric acid added is not particularly limited, as long as it can achieve the coating amount of the polyphosphoric acid alkali metal salt specified above.

[0051] The method of the present invention can be carried out at room temperature, or can be appropriately adjusted according to circumstances. For example, after adding polyphosphoric acid, the reaction can be carried out at a temperature of 5, 10, 15, 20, 25, 30, 35 or 40° C., preferably with stirring, vibration or the like, so that the reaction is more complete. The reaction time can be 1-12 hours, for example 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11 hours, or can be appropriately shortened according to the increase in temperature. In addition, after filtering the reaction product, the reaction product can be washed with an alcohol solvent to remove impurities, preferably with a methanol solution, and then dried to remove the washing solvent.

[0052] The positive electrode material coated with an alkali metal polyphosphate obtained by the present invention can be used as the positive electrode of a battery. Preferably, a positive electrode material coated with lithium polyphosphate is used as the positive electrode of a lithium ion battery. When constructing the positive electrode, a conductive additive (such as graphene, Super P, etc.) and a binder (such as PVDF) can be added. Specifically, the positive electrode material, conductive additive and binder of the present application are ground and evenly dispersed in a solvent (such as N-methylpyrrolidone) to form a slurry, the slurry is applied to the surface of an aluminum foil current collector, and then vacuum-heated and dried to form a positive electrode film, which is cut into corresponding positive electrode sheets; the positive electrode sheet and the counter electrode are separated by a diaphragm, an appropriate amount of electrolyte is added, and a button-type lithium ion battery is assembled.

[0053] In this regard, the mass ratio of the positive electrode material, conductive additive and binder of the present application can be (70-95):(20-1):(20-1). The electrolyte used is a solution obtained by dissolving different lithium salts in different organic solvents, and the concentration of the electrolyte salt can be 0.5-4.0 mol / L, preferably about 1.0 mol / L. The lithium salt can be selected from one or more of lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide or lithium hexafluorophosphate salts, mixed in any proportion. The organic solvent used can be one or more of ethylene glycol dimethyl ether (DME), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), fluoroethyl methyl carbonate (FEMC), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (HFE) mixed in any proportion. The selected counter electrode materials are graphite, lithium titanate, silicon carbon material, lithium sheet, etc.

[0054] Example

[0055] The present invention is further described in detail below with reference to specific examples, but the scope of the present invention is not limited thereto. The reagents used in the examples are all commercially available, the instruments used to perform the operations are all commonly used laboratory equipment, and unless otherwise specified, the operations are performed at room temperature, normal pressure, and ventilation conditions.

[0056] General test method:

[0057] The material obtained in the embodiment or comparative example is used as the active positive electrode material to prepare a lithium-ion battery: the active positive electrode material, Super P as a conductive additive, and PVDF as a binder are added to an N-methylpyrrolidone solvent in a mass ratio of 8:8:1, ground to form a uniform slurry, and the slurry is applied to the surface of the aluminum foil current collector with a scraper. After vacuum drying at 80°C overnight, a positive electrode film is obtained. The positive electrode film is cut to obtain a positive electrode sheet. The positive electrode sheet is used as the positive electrode, the metal lithium foil is used as the negative electrode, a solution of LiPF6 salt in an EC:DMC mixed solvent (volume ratio of 7:3) (concentration 1M) is used as the electrolyte, and a Gelgard2325 separator is used as the separator. The battery is assembled into a button cell in an argon-filled glove box.

[0058] The positive electrode electrochemical performance of the lithium-ion battery was tested at 0-60 ° C, where 1C = 200mAh g -1 .

[0059] Example 1: Preparation of cobalt-free lithium-rich manganese material coated with lithium polyphosphate

[0060] Example 1-1

[0061] Take cobalt-free lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2, 30g, 0.35mol) powder was added to an anhydrous methanol (100ml) solution containing LiOH (0.672g, 28mmol) under stirring (700rpm), and stirred at 700rpm for 30 minutes. Then, a methanol solution of polyphosphoric acid (1.668g, purchased from McLean, CAS 8017-16-1, purity: content (P2O5)% ≥85%, unless otherwise specified, this polyphosphoric acid is used) was added dropwise and stirred at 700rpm for 2 hours. After filtration, methanol washing and drying, a cobalt-free lithium-rich manganese-based positive electrode material (positive electrode material 1) coated with 6% by mass of lithium polyphosphate was obtained.

[0062] Example 1-2

[0063] Except for changing the proportion of polyphosphoric acid, the same steps as Example 1-1 were followed to obtain 4 mass%, 8 mass% and 10 mass% lithium polyphosphate-coated cobalt-free lithium-rich manganese-based positive electrode materials (positive electrode material 2, positive electrode material 3 and positive electrode material 4, respectively).

[0064] The uncoated cobalt-free lithium-rich manganese-based cathode material was used as a blank group to test the rate performance and cycle performance of the above cathode materials. Figure 1 and Figure 2 Shown in. Figure 3 The polyphosphate-coated Li 1.2 Ni 0.2 Mn 0.6 XRD pattern of O2, Figure 4 The polylithium phosphate coated Li 1.2 Ni 0.2 Mn 0.6 TEM image of O2, Figure 5 The polyphosphate-coated Li 1.2 Ni 0.2 Mn 0.6 TEM Mapping of O2. The first cycle charge and discharge curves, rate performance and cycle performance of the uncoated positive electrode material (blank group) and the positive electrode material of Example 1-1 are respectively Figure 6 、 Figure 7 and Figure 8 Shown in. Figure 9 The cycle performances of the uncoated positive electrode material (blank group), the lithium phosphate-coated positive electrode material of the comparative example, and the positive electrode material of Example 1-1 are shown.

[0065] Example 2: Preparation of lithium-rich manganese material coated with lithium polyphosphate

[0066] Take lithium-rich manganese-based positive electrode materials (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2, 30g, 0.35mol) powder was added to anhydrous methanol (100ml) solution containing LiOH (0.672g, 28mmol) under stirring (700rpm) and stirred at 700rpm for 30 minutes. Then a methanol solution of polyphosphoric acid (1.668g) was added dropwise and stirred at 700rpm for 2 hours. After filtration, methanol washing and drying, a 6% by mass lithium polyphosphate-coated lithium manganese-based positive electrode material was obtained. The uncoated lithium manganese-based positive electrode material was used as a blank group, and its rate performance and cycle performance were tested respectively with the coated lithium manganese-based positive electrode material obtained above. The results were as follows: Figure 10 and Figure 11 Shown in.

[0067] Example 3: Preparation of high nickel 811 material coated with lithium polyphosphate

[0068] Take high nickel 811 positive electrode material (LiNi 0.8 Co 0.1 Mn 0.1O2, 30g, 0.31mol) powder was added to anhydrous methanol (100ml) solution containing LiOH (0.672g, 28mmol) under stirring (700rpm) and stirred at 700rpm for 30 minutes. Then a methanol solution of polyphosphoric acid (1.668g) was added dropwise and stirred at 700rpm for 2 hours. After filtration, methanol washing and drying, a 6% by mass lithium polyphosphate coated high nickel 811 positive electrode material was obtained. The uncoated high nickel 811 material was used as a blank group, and its rate performance and cycle performance with the coated high nickel 811 positive electrode material obtained above were tested respectively. The results were Figure 12 and Figure 13 Shown in.

[0069] Example 4: Preparation of lithium cobalt oxide material coated with lithium polyphosphate

[0070] Take the powder of lithium cobalt oxide positive electrode material (LiCoO2, 30g, 0.31mol), add it to anhydrous methanol (100ml) solution containing LiOH (0.448g, 18.7mmol) under stirring (700rpm), and stir at 700rpm for 30 minutes. Then add a methanol solution of polyphosphoric acid (1.112g) dropwise and stir at 700rpm for 2 hours. After filtration, methanol washing and drying, a 4% by mass lithium polyphosphate-coated lithium cobalt oxide positive electrode material is obtained. The uncoated lithium cobalt oxide material is used as a blank group, and its rate performance and cycle performance with the coated lithium cobalt oxide positive electrode material obtained above are tested respectively. The results are as follows: Figure 14 and Figure 15 Shown in.

[0071] Comparative Example 1: Preparation of Cobalt-Free Lithium-Rich Manganese Material Coated with Lithium Phosphate

[0072] Take cobalt-free lithium-rich manganese-based positive electrode material (Li 1.2 Ni 0.2 Mn 0.6 O2, 30g, 0.35mol) powder was added to an anhydrous methanol (100ml) solution containing LiOH (0.672g, 28mmol) under vigorous stirring (700rpm) and stirred at 700rpm for 30 minutes. Then, a methanol solution of phosphoric acid (2.744g) was added dropwise and stirred at 700rpm for 2 hours. After filtration, methanol washing and drying, a cobalt-free lithium-rich manganese-based positive electrode material coated with lithium phosphate was obtained, which was used as a control.

[0073] Although certain embodiments and implementations have been described herein, other embodiments and modifications will be apparent from this specification. Therefore, the inventive concept is not limited to such embodiments, but rather to the broader scope of the appended claims and various obvious modifications and equivalent arrangements that will be apparent to those skilled in the art.

Claims

1. A method for preparing a coated positive electrode material, the method comprising: (1) mixing the positive electrode material into a solution containing an alkali metal hydroxide; (2) adding polyphosphoric acid to the solution obtained in step (1), and stirring at a temperature of 0-40° C. for 1-12 hours, wherein the mass ratio of the polyphosphoric acid is 5.56-20% based on the mass of the positive electrode material; (3) filtering to obtain a positive electrode material coated with an alkali metal polyphosphate; Wherein, the positive electrode material coated with an alkali metal polyphosphate is a positive electrode material coated with an alkali metal polyphosphate in an amount of 6-8% by mass; An integrated layer of alkali metal polyphosphate-spinel phase-layers is formed on the surface of the alkali metal polyphosphate-coated positive electrode material.

2. The method according to claim 1, wherein the polyphosphoric acid is dipolyphosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, pentapolyphosphoric acid or any combination thereof.

3. The method according to claim 2, wherein the polyphosphoric acid in step (2) refers to a solution containing polyphosphoric acid formed by dissolving polyphosphoric acid in alcohol.

4. The method according to claim 3, wherein the polyphosphoric acid in step (2) refers to a solution containing polyphosphoric acid formed by dissolving polyphosphoric acid in methanol. 5 . The method according to claim 2 , wherein the mass ratio of the polyphosphoric acid is 5.56-15% based on the mass of the positive electrode material.

6. The method of claim 1, wherein the alkali metal hydroxide is lithium hydroxide, sodium hydroxide, potassium hydroxide, or any combination thereof.

7. The method according to claim 6, wherein the solution comprising an alkali metal hydroxide is an anhydrous alcohol solution comprising an alkali metal hydroxide.

8. The method according to claim 7, wherein the solution containing an alkali metal hydroxide is an anhydrous methanol solution containing an alkali metal hydroxide.

9. The method according to claim 7, wherein the concentration of the solution containing the alkali metal hydroxide is 0.01-10 mol / L.

10. The method according to any one of claims 1 to 9, wherein the polyphosphoric acid reacts with the alkali metal hydroxide to form an alkali metal polyphosphate salt, and then a phase transition of the positive electrode material from a layered phase to a spinel phase occurs in situ on the contact surface of the alkali metal polyphosphate salt and the positive electrode material.

11. The method according to any one of claims 1 to 9, wherein the cathode material is selected from a lithium cobaltate-based material, a lithium manganate-based material, a lithium nickelate-based material, a lithium iron phosphate-based material, or a combination thereof.

12. The method according to any one of claims 1 to 9, wherein the positive electrode material is selected from lithium-rich manganese-based materials, high nickel materials, lithium cobalt oxide materials, and combinations thereof.

13. The method according to any one of claims 1 to 9, wherein the positive electrode material is a cobalt-free lithium-rich manganese-based material.

14. The method according to claim 12, wherein the composition of the high nickel material is LiNi 1-x-y Co x M y O2, wherein M is selected from Mn, Al, and combinations thereof, and wherein 0≤x≤0.2, 0≤y≤0.

2.

15. The method according to claim 12, wherein the composition of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMO2, wherein M is selected from Ni, Co, Mn and combinations thereof, and wherein 0.1≤x≤0.

9.

16. The method according to claim 11, wherein the crystalline phase structure of the positive electrode material is a hexagonal layered structure, an R-3m space group, the positive electrode material coated with an alkali metal polyphosphate is a positive electrode material coated with lithium polyphosphate, and a lithium polyphosphate-spinel phase-layered integrated layer is formed on the surface of the lithium polyphosphate-coated positive electrode material.

17. A battery positive electrode comprising a positive electrode material coated with an alkali metal polyphosphate prepared by the method of any one of claims 1 to 16, wherein: The positive electrode material coated with alkali metal polyphosphate is a positive electrode material coated with lithium polyphosphate in an amount of 6-8% by mass.

18. The battery positive electrode according to claim 17, wherein the crystalline phase structure of the positive electrode material is a hexagonal layered structure, an R-3m space group, and a polylithium phosphate-spinel phase-layered integrated layer is formed on the surface of the polylithium phosphate-coated positive electrode material.

19. Use of the coated positive electrode material prepared by the method according to any one of claims 1 to 16 as a positive electrode of a battery.

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