Positive electrode material, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a positive electrode material, a preparation method thereof and a battery. The positive electrode material comprises an inner core and a carbon coating layer coating at least part of the surface of the inner core, wherein the inner core comprises LiMn < 1-x > V < x > PO4 and Li < 3 > V < 2-y > Mn < y > (PO4) 3; wherein 0 < = x < = 0.1, and 0 < = y < = 0.15. The positive electrode material has good rate capability, cycling stability and relatively high theoretical capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode material, a preparation method thereof, and a battery. Background Art

[0002] In recent years, with the continuous development of science and technology and economy, people's demand for high-efficiency energy storage batteries has also increased. Lithium-ion batteries are currently the most widely used secondary batteries. The positive electrode material of lithium-ion batteries is one of its core components, which directly determines the energy density, cycle life, safety and cost of the battery. 3- Strong PO covalent bonds make the internal structure of this series of materials stable and have high safety performance. Commercial LiFePO4 is a typical example. The redox potential of LiFePO4 is 3.45V (VS.Li + / Li); Theoretical specific capacity is 170mAh g -1 Currently, the research and development process of LiFePO4 is becoming increasingly mature, and it is already used as the cathode material for lithium-ion batteries in commercial electric and hybrid vehicles. However, compared with other cathode materials, such as ternary cathode materials (NCM), LiFePO4 has a relatively low electrochemical energy.

[0003] Therefore, there is an urgent need to provide a phosphate-based positive electrode material with higher specific capacity and / or higher voltage. Summary of the Invention

[0004] In view of this, the present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present invention provides a positive electrode material and a preparation method thereof and a battery, wherein the positive electrode material has a higher specific capacity and a higher voltage.

[0005] In order to solve the above technical problems, this application is implemented as follows:

[0006] According to one aspect of the present application, an embodiment of the present application provides a positive electrode material, the positive electrode material comprising: a core and a carbon coating layer coated on at least a portion of the surface of the core;

[0007] Wherein, the core comprises LiMn 1-x V x PO4 and Li3V 2-y Mn y (PO4)3;

[0008] Among them, 0≤x≤0.1, 0≤y≤0.15.

[0009] In some embodiments, the LiMn 1-x V x PO4、Li3V 2-yMn y The molar ratio of (PO4)3 and carbon is 1:1:(0.01~0.1).

[0010] According to another aspect of the present application, an embodiment of the present application provides a method for preparing a positive electrode material, comprising the following steps: mixing a manganese source solution and a vanadium source solution and performing a hydrothermal reaction to obtain an intermediate Mn(VO3)2;

[0011] The intermediate Mn(VO3)2, lithium source, phosphoric acid source, carbon source and acid source are mixed in a solvent to obtain a mixed solution, which is then ball-milled, sintered and ground to obtain a positive electrode material.

[0012] In some embodiments, the solvent in the manganese source solution includes water and / or an organic solvent.

[0013] In some embodiments, the molar concentration of the manganese source solution is 0.03 mol / L to 0.5 mol / L.

[0014] In some embodiments, the manganese source includes at least one of MnCl2, MnSO4, Mn(NO3)2, or Mn3(PO4)2.

[0015] In some embodiments, the solvent in the vanadium source solution includes water and / or an organic solvent.

[0016] In some embodiments, the molar concentration of the vanadium source solution is 0.06 mol / L to 1 mol / L.

[0017] In some embodiments, the vanadium source includes V2O3, VO2, V2O4, V2O5, NH4VO3, H4V2O 10 , V(OH)3, Na3VO4 or Na4V2O7.

[0018] In some embodiments, the hydrothermal reaction temperature is 170° C. to 190° C., and the time is 1 h to 30 h.

[0019] In some embodiments, the molar ratio of the intermediate Mn(VO3)2, the lithium source, the phosphate source, the carbon source, and the acid source is (1-5):(1-10):(1-10):(0.02-20):(2-20).

[0020] In some embodiments, the molar concentration of the intermediate Mn(VO3)2 in the mixed solution is 0.01 mol / L to 1 mol / L.

[0021] In some embodiments, the solvent includes water and / or an organic solvent.

[0022] In some embodiments, the carbon source includes at least one of polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan laurate, glucose, asphalt, polydopamine, resorcinol, formaldehyde, starch, sucrose, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl pyrrolidone, tannic acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene or aniline.

[0023] In some embodiments, the ball milling speed is 300 rpm to 400 rpm, and the time is 0.5 h to 9 h.

[0024] In some embodiments, the sintering is performed under an inert atmosphere, and the sintering includes pre-firing and baking.

[0025] In some embodiments, the pre-calcination temperature is 250° C. to 450° C., and the pre-calcination time is 1 hour to 6 hours.

[0026] In some embodiments, the calcination temperature is 650° C. to 750° C., and the calcination time is 1 hour to 12 hours.

[0027] In some embodiments, the particle size of the ground product is 100 nm ≤ Dv50 ≤ 50 μm.

[0028] According to another aspect of the present application, an embodiment of the present application provides a battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode material, and the positive electrode material is the aforementioned positive electrode material or the positive electrode material prepared according to the aforementioned preparation method.

[0029] The implementation of the technical solution of the present invention has at least the following beneficial effects:

[0030] In the embodiment of the present application, the positive electrode material core provided includes LiMn 1-x V x PO4 and Li3V 2-y Mn y (PO4)3, Li3V2(PO4)3 has a three-dimensional lithium ion diffusion channel, and its lithium ion diffusion coefficient (10 -9 ~10 -10 cm 2 ·s -1 ) than LiMnPO4(10 -15 cm 2 ·s -1) is at least five orders of magnitude higher, exhibiting excellent rate capability and high electrochemical activity. By combining LiMnPO4 with it, the electrochemical activity of Li3V2(PO4)3 can be enhanced, and some Mn and V can be cross-doped, thereby improving the electrochemical performance of the entire LiMnPO4 and Li3V2(PO4)3 composite material.

[0031] Furthermore, because some Mn and V can be doped with each other, the contact between the core materials is closer, which can reduce the surface energy of the core material, making the contact between the carbon coating and the core material more stable, and not easy to fall off during long cycles, effectively avoiding electrolyte failure caused by direct contact between the core material and the electrolyte, avoiding polarization of the positive electrode material, and improving the cycle stability of the positive electrode material. Compared with the conventional LiMnPO4 and Li3V2(PO4)3 composite, the contact is closer, making it difficult for manganese elements in lithium manganate to dissolve, and the smaller-scale close contact significantly improves the electronic conductivity and ionic conductivity. In addition, the carbon coating layer of the positive electrode material can improve the electronic conductivity of the positive electrode material, form a conductive network, and reduce the charge transfer impedance, thereby improving the overall rate performance of the positive electrode material.

[0032] Additional aspects and advantages of the present application will be given in part in the following description and in part will become obvious from the following description or will be learned through practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Shown is a scanning electron microscope (SEM) image of the positive electrode material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The present application will be further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0035] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0039] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0040] Compared with ternary cathode materials, the electrochemical energy of commercialized LiFePO4 is low. However, LiMnPO4 has a stable crystal structure and a theoretical specific capacity of 170 mAh g -1 , but its redox potential is 4.1V (vs.Li + / Li), its theoretical energy density is about 20% higher than that of LiFePO4 (LiMnPO4697Wh kg -1 , LiFePO4 586Wh kg -1 ). However, the electronic conductivity of LiMnPO4 (<10 -10 S cm -1 ), the ion diffusion coefficient is about 5.1×10 -14 cm 2 ·s -1 This results in the low activity of conventionally prepared LiMnPO4 materials, and the charge-discharge capacity is far lower than the theoretical value. In addition, Mn in the LiMnPO4 system 2+ The low-spin configuration of the material easily leads to Jahn-Teller distortion, and the distortion of the material structure weakens the electrochemical cycling performance.

[0041] [Cathode material]

[0042] In view of this, an embodiment of the present application provides a positive electrode material, the positive electrode material comprising: a core and a carbon coating layer coated on at least a portion of the surface of the core;

[0043] Among them, the core includes LiMn 1-x V x PO4 and Li3V 2-y Mn y (PO4)3;

[0044] Among them, 0≤x≤0.1, 0≤y≤0.15.

[0045] The phrase "carbon coating layer coated on at least a portion of the surface of the core" means that the carbon coating layer can be disposed on a portion of the surface of the core or on the entire surface of the core. As in this embodiment, the carbon coating layer can be coated on the entire surface of the core. This application does not impose any particular limitation on this, as long as the objectives of this application can be achieved.

[0046] In this application, the cathode material core includes LiMn 1-x V x PO4 and Li3V 2-y Mn y (PO4)3, Li3V2(PO4)3 has a three-dimensional lithium ion diffusion channel, and its lithium ion diffusion coefficient (10 -9 ~10 -10 cm 2 ·s -1 ) than LiMnPO4(10 -15 cm 2 ·s -1 ) is at least five orders of magnitude higher, exhibiting excellent rate capability and high electrochemical activity. By combining LiMnPO4 with it, the electrochemical activity of Li3V2(PO4)3 can be enhanced, and some Mn and V can be cross-doped, thereby improving the electrochemical performance of the entire LiMnPO4 and Li3V2(PO4)3 composite material.

[0047] Furthermore, because some Mn and V can be doped with each other, the contact between the core materials is closer, which can reduce the surface energy of the core material, making the contact between the carbon coating and the core material more stable, and not easy to fall off during long cycles, effectively avoiding electrolyte failure caused by direct contact between the core material and the electrolyte, avoiding polarization of the positive electrode material, and improving the cycle stability of the positive electrode material. Compared with the conventional LiMnPO4 and Li3V2(PO4)3 composite, the contact is closer, making it difficult for manganese elements in lithium manganate to dissolve, and the smaller-scale close contact significantly improves the electronic conductivity and ionic conductivity. In addition, the carbon coating layer of the positive electrode material can improve the electronic conductivity of the positive electrode material, form a conductive network, and reduce the charge transfer impedance, thereby improving the overall rate performance of the positive electrode material.

[0048] In the present application, mutual doping of Mn and V means that during the crystal growth process, vanadium ions enter the lithium manganese phosphate unit cell to replace manganese atoms, and manganese ions enter the lithium vanadium phosphate unit cell structure to replace vanadium atoms, performing in-situ doping.

[0049] In some embodiments, LiMn 1-x V xPO4、Li3V 2-y Mn y The molar ratio of (PO4)3 to carbon is 1:1:(0.01-0.1). As an example, LiMn 1-x V x PO4、Li3V 2-y Mn y The molar ratio of (PO4)3 to carbon can be any one of 1:1:0.01, 1:1:0.05, 1:1:0.1 or any range between them. The above-mentioned "carbon" refers to the carbon in the carbon coating layer, and all the carbon exists in the carbon coating layer. If LiMn 1-x V x PO4 or Li3V 2-y Mn y If the proportion of one component (PO4)3 is too large, the structural stability between the two materials will decrease, which will lead to a decrease in cycle stability; if LiMn 1-x V x PO4 or Li3V 2-y Mn y If the proportion of any one component (PO4)3 is too small, the material will fall off during the cycle, resulting in a decrease in cycling performance. If the proportion of carbon is too large, the system energy and capacity density will be reduced, and the material's rate performance and specific capacity will also be reduced; if the proportion of carbon is too small, the material's conductivity will decrease.

[0050] Thus, based on the above solution, a positive electrode material is provided, comprising a core and a carbon coating layer coated on at least a portion of the surface of the core. 1-x V x PO4 and Li3V 2-y Mn y (PO4)3, Li3V2(PO4)3 in the two materials has a three-dimensional lithium ion diffusion channel, and its lithium ion diffusion coefficient (10 -9 ~10 -10 cm 2 ·s -1 ) than LiMnPO4(10 - 15 cm 2 ·s -1 ) is at least five orders of magnitude higher, exhibiting excellent rate capability and high electrochemical activity. By combining LiMnPO4 with it, the electrochemical activity of Li3V2(PO4)3 can be enhanced, and some Mn and V can be cross-doped, thereby improving the electrochemical performance of the entire LiMnPO4 and Li3V2(PO4)3 composite material.

[0051] Furthermore, because some Mn and V can be doped with each other, the contact between the core materials is closer, which can reduce the surface energy of the core material, making the contact between the carbon coating and the core material more stable, and not easy to fall off during long cycles, effectively avoiding electrolyte failure caused by direct contact between the core material and the electrolyte, avoiding polarization of the positive electrode material, and improving the cycle stability of the positive electrode material. Compared with the conventional LiMnPO4 and Li3V2(PO4)3 composite, the contact is closer, making it difficult for manganese elements in lithium manganate to dissolve, and the smaller-scale close contact significantly improves the electronic conductivity and ionic conductivity. In addition, the carbon coating layer of the positive electrode material can improve the electronic conductivity of the positive electrode material, form a conductive network, and reduce the charge transfer impedance, thereby improving the overall rate performance of the positive electrode material.

[0052] [Method for preparing positive electrode material]

[0053] Based on the same inventive concept, an embodiment of the present application provides a method for preparing a positive electrode material, comprising the following steps: mixing a manganese source solution and a vanadium source solution and performing a hydrothermal reaction to obtain an intermediate Mn(VO3)2;

[0054] The intermediate Mn(VO3)2, lithium source, phosphoric acid source, carbon source and acid source are mixed in a solvent to obtain a mixed solution, which is then ball-milled, sintered and ground to obtain a positive electrode material.

[0055] It should be understood that all the features and advantages described above for the “positive electrode material” are also applicable to the “method for preparing the positive electrode material” and will not be described in detail here.

[0056] In some embodiments, the solvent in the manganese source solution includes water and / or an organic solvent. Specifically, the organic solvent includes, but is not limited to, an alcohol organic solvent or a ketone organic solvent. As an example, the organic solvent may be ethanol or acetone.

[0057] In some embodiments, when the solvent is a mixture of water and an organic solvent, the volume of water is ≥40%. As an example, when the solvent is a mixture of water and an organic solvent, the volume of water can be 40%, 50%, or 60%.

[0058] In some specific embodiments, the molar concentration of the manganese source solution is 0.03 mol / L to 0.5 mol / L. As an example, the molar concentration of the manganese source solution can be 0.03 mol / L, 0.1 mol / L, 0.5 mol / L, etc., or any point within the above range, which is not specifically limited here.

[0059] In some embodiments, the manganese source includes, but is not limited to, at least one of MnCl2, MnSO4, Mn(NO3)2, or Mn3(PO4)2. As an example, the manganese source may be MnCl2 or MnSO4.

[0060] In some embodiments, the solvent in the vanadium source solution includes water and / or an organic solvent. Specifically, the organic solvent includes an alcohol organic solvent or a ketone organic solvent. As an example, the organic solvent can be ethanol or acetone.

[0061] In some embodiments, when the solvent is a mixture of water and an organic solvent, the volume of water is ≥40%. As an example, when the solvent is a mixture of water and an organic solvent, the volume of water can be 40%, 50%, or 60%.

[0062] In some specific embodiments, the molar concentration of the vanadium source solution is 0.06 mol / L to 1 mol / L. As examples, the molar concentration of the vanadium source solution is 0.06 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, etc. Of course, it can also be a point value within the above range, which is not specifically limited here.

[0063] In some embodiments, the vanadium source includes, but is not limited to, V2O3, VO2, V2O4, V2O5, NH4VO3, H4V2O 10 , V(OH)3, Na3VO4 or Na4V2O7. As an example, the vanadium source may be V2O3 or VO2.

[0064] In some specific embodiments, the hydrothermal reaction temperature is 170°C to 190°C, and the time is 1 hour to 30 hours. As an example, the hydrothermal reaction temperature can be 170°C, 180°C, 190°C, etc., and of course it can also be a point value within the above range, and is not specifically limited here. The hydrothermal reaction time can be 1 hour, 5 hours, 10 hours, 15 hours, 20 hours, 30 hours, etc., and of course it can also be a point value within the above range, and is not specifically limited here.

[0065] In some specific embodiments, the molar ratio of the intermediate Mn(VO3)2, lithium source, phosphate source, carbon source, and acid source is (1-5):(1-10):(1-10):(0.02-20):(2-20). As an example, the molar ratio of the intermediate Mn(VO3)2, lithium source, phosphate source, carbon source, and acid source can be 1:1:1:0.02:2, 2:3:5:10:12, 5:10:10:20:20, etc. Of course, it can also be any ratio within the above range, and is not specifically limited here.

[0066] In some specific embodiments, the molar concentration of the intermediate Mn(VO3)2 in the mixed solution is 0.01 mol / L to 1 mol / L. As an example, the molar concentration of the intermediate Mn(VO3)2 in the mixed solution can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, etc., and of course it can also be a value within the above range, which is not specifically limited here.

[0067] In some embodiments, the solvent includes water and / or an organic solvent. Specifically, the organic solvent includes an alcohol organic solvent or a ketone organic solvent. As an example, the organic solvent can be ethanol or acetone.

[0068] In some embodiments, when the solvent is a mixture of water and an organic solvent, the volume of water is ≥40%. As an example, when the solvent is a mixture of water and an organic solvent, the volume of water can be 40%, 50%, or 60%.

[0069] In some specific embodiments, the lithium source includes, but is not limited to, at least one of lithium carbonate, lithium hydroxide, and lithium oxide.

[0070] In some specific embodiments, the phosphoric acid source includes, but is not limited to, at least one of ammonium dihydrogen phosphate, sodium hypophosphite, and ammonium pyrophosphate.

[0071] In some specific embodiments, the acid source includes, but is not limited to, oxalic acid dihydrate, acetic acid, and benzoic acid.

[0072] In some embodiments, the carbon source includes, but is not limited to, at least one of polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan laurate, glucose, asphalt, polydopamine, resorcinol, formaldehyde, starch, sucrose, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl pyrrolidone, tannic acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene, or aniline. For example, the carbon source may be polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan laurate, or glucose. Preferably, the carbon source is at least one of polyoxyethylene sorbitan monooleate or polyoxyethylene sorbitan laurate, and more preferably, a mixture of polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan laurate in a 1:1 weight ratio.

[0073] In this application, two environmentally friendly polysorbate lipid nonionic surfactants were selected as carbon sources, polyoxyethylene sorbitan monooleate (Tween80) and polyoxyethylene sorbitan laurate (Tween20) were compounded, and the remaining materials (intermediate Mn(VO3)2, lithium source, phosphoric acid source, acid source) were carbon-coated by wet ball milling. On the one hand, with the emulsification effect of polyoxyethylene sorbitan monooleate, LiMn 1-x V x PO4 and Li3V 2- y Mn y The (PO4)3 (0≤x≤0.1, 0≤y≤0.15) primary particles are dispersed. After the surfactant is pyrolyzed, a uniform residual carbon layer is formed on the particle surface, which hinders further agglomeration of the particles and serves the purpose of refining the particles. This helps shorten the lithium ion transmission distance, improve ionic conductivity, and increase the material's rate performance. The residual carbon formed by the pyrolysis of polyoxyethylene sorbitan laurate has a high degree of graphitization, which helps improve the material's electronic conductivity. The above two surfactants are selected to replace traditional carbon sources, and their synergistic effect is utilized to improve ionic and electronic conductivity, thereby enhancing the electrochemical performance of the positive electrode material.

[0074] In some specific embodiments, the ball milling speed is 300rpm to 400rpm, and the time is 0.5h to 9h. As an example, the ball milling speed can be 300rpm, 350rpm, 400rpm, etc., and of course it can also be a certain value within the above range, which is not specifically limited here. The ball milling time can be 0.5h, 1h, 3h, 6h, 9h, etc., and of course it can also be a certain value within the above range, which is not specifically limited here. It should be noted that the core material LiMn in this application 1-x V x PO4 and Li3V 2- y Mn y (PO4)3 (0≤x≤0.1, 0≤y≤0.15) is formed during the ball milling mixing process.

[0075] In some specific embodiments, sintering is performed under an inert atmosphere and includes pre-calcining and roasting. Pre-calcining can fully adjust the atomic structure, make the reaction more complete, and volatilize ash.

[0076] In some specific embodiments, the pre-calcination temperature is 250°C to 450°C, and the pre-calcination time is 1 hour to 6 hours. As an example, the pre-calcination temperature can be 250°C, 350°C, 450°C, etc., and of course it can also be a value within the above range, and is not specifically limited here. The pre-calcination time can be 1 hour, 3 hours, 6 hours, etc., and of course it can also be a value within the above range, and is not specifically limited here.

[0077] In some specific embodiments, the calcination temperature is 650°C to 750°C, and the calcination time is 1 hour to 12 hours. As an example, the calcination temperature can be 650°C, 700°C, 750°C, etc., or any value within the above range, and is not specifically limited here. If the calcination temperature is too high, the increase in oxygen vacancies in the crystal structure can easily cause the crystal structure to collapse; if the calcination temperature is too low, the crystal structure may be unstable.

[0078] The calcination time can be 1 hour, 3 hours, 6 hours, 9 hours, 12 hours, etc., or any value within the above range, and is not specifically limited here. If the calcination time is too long, oxygen vacancies in the crystal structure increase, which may cause the crystal structure to collapse; if the calcination time is too short, the crystal structure may be unstable.

[0079] In some specific embodiments, the particle size of the ground product is 100 nm ≤ Dv50 ≤ 50 μm. As an example, the particle size Dv50 of the ground product can be 100 nm, 500 nm, 1 μm, 10 μm, 20 μm, 50 μm, etc., and can also be any value within the above range, which is not specifically limited here.

[0080] Therefore, based on the above, the present invention first prepares a Mn(VO3)2 precursor, and then in situ grows LiMn on the basis of the precursor. 1-x V x PO4 and Li3V 2-y Mn y (PO4)3(0≤x≤0.1, 0≤y≤0.15), this method: with the help of Mn(VO3)2, which has both manganese and vanadium sources, the crystal structures are in close contact with each other during the phosphate formation process, mixed at a smaller particle scale, and during the crystal growth process, vanadium ions enter the lithium manganese phosphate crystal cell to replace some manganese atoms, and manganese ions enter the lithium vanadium phosphate crystal cell structure to replace some vanadium atoms, performing in-situ doping. This type of atomic doping can reduce the surface energy of the material, making the contact between the two materials closer, while improving the electronic conductivity and ionic conductivity of lithium manganese phosphate. Compared with the conventional LiMnPO4 and Li3V2(PO4)3 composite, the contact is closer, making it difficult for manganese elements in lithium manganate to dissolve. The smaller-scale close contact significantly improves the electronic conductivity and ionic conductivity.

[0081] Based on the same inventive concept, an embodiment of the present application provides a battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode material, and the positive electrode material is the aforementioned positive electrode material or the positive electrode material prepared according to the aforementioned preparation method.

[0082] [Cathode sheet preparation]

[0083] The positive electrode material, conductive agent and binder are mixed in a solvent to obtain a slurry, the slurry is coated on a current collector, and the positive electrode sheet is obtained after drying.

[0084] In some specific embodiments, the mass ratio of the positive electrode material, the conductive agent, and the binder is 95% to 99%: 0.1% to %: 0.5% to 3%.

[0085] In some specific embodiments, the current collector comprises at least one of aluminum foil or nickel foil.

[0086] In some specific embodiments, the coating thickness of the slurry is 10 μm to 200 μm.

[0087] In some specific embodiments, after the positive electrode sheet is prepared, it can be cut into a desired size by a cutter.

[0088] Since the battery includes a positive electrode plate made of the positive electrode material provided in the embodiments of the present application, it has the advantages of higher energy density, longer cycle life and faster charging speed.

[0089] In some embodiments, the battery further comprises a negative electrode sheet, an electrolyte, and a separator. That is, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator.

[0090] In this embodiment, there is no limitation on the materials and structures of the negative electrode sheet, the negative electrode current collector, the conductive agent, the binder in the negative electrode active material layer, and the like. Any negative electrode sheet structure and composition known in the art that can be used in secondary batteries can be selected.

[0091] In this embodiment, there is no limitation on the type of the separator, and any separator known in the art that can be used in secondary batteries can be selected.

[0092] It should also be noted that the battery of the present application is not limited to the specific material or type of the electrolyte, and any components and types that are known in the art and can be used for secondary batteries can be selected as long as the purpose of the present application can be achieved.

[0093] Since the battery provided by the embodiment of the present invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0094] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents, materials, or instruments used that do not specify the manufacturer are all conventional products that can be purchased commercially.

[0095] Example 1

[0096] Dissolve 1 mmol of MnCl2·4H2O and 2 mmol of NH4VO3 in 10 mL and 20 mL of water, respectively. Heat the NH4VO3 at 50°C and stir to dissolve. Add the MnCl2 solution dropwise to the NH4VO3 solution, mix thoroughly with magnetic stirring, and hydrothermally react at 180°C for 18 hours. Cool, filter, wash, and dry to obtain a brown product, Mn(VO3)2.

[0097] 0.05 mol Mn(VO3)2, 0.06 mol lithium carbonate, 0.1 mol ammonium dihydrogen phosphate, 1.2612 g oxalic acid dihydrate, 0.2 g polyoxyethylene sorbitan monooleate, 0.2 g polyoxyethylene sorbitan laurate, 5 ml deionized water, and 2 ml anhydrous ethanol were mixed and set to 350 rpm, ball milled for 4 h, and dried to obtain a yellow-white powder; loaded into a corundum boat, sealed, and sintered at high temperature in an argon atmosphere, pre-calcined at 350 ° C for 2 h, calcined at 700 ° C for 12 h, then cooled to room temperature, ball milled, the diameter of the agate grinding beads of the ball mill was 1 mm, the mass ratio of the grinding beads to the sample was 20:1, and ground for 1 h to obtain a black powder product (Dv50 = 5 μ) which is the positive electrode material.

[0098] The SEM image of the positive electrode material is shown in the appendix of the manual. Figure 1 ,Depend on Figure 1 It can be seen that the particle size of the positive electrode material is uniform, and the thickness of the surface carbon material is thin and fine.

[0099] Example 2

[0100] The difference between Example 2 and Example 1 is that the temperature of the hydrothermal reaction is 170° C. and the time is 20 h.

[0101] Example 3

[0102] The difference between Example 3 and Example 1 is that the temperature of the hydrothermal reaction is 150° C. and the time is 12 h.

[0103] Example 4

[0104] The difference between Example 4 and Example 1 is that the temperature of the hydrothermal reaction is 210° C. and the time is 24 h.

[0105] Example 5

[0106] The difference between Example 5 and Example 1 is that polyoxyethylene sorbitan monooleate is not added.

[0107] Example 6

[0108] The difference between Example 6 and Example 1 is that polyoxyethylene sorbitan laurate is not added.

[0109] Example 7

[0110] The difference between Example 7 and Example 1 is that polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan laurate are replaced by glucose.

[0111] Example 8

[0112] The difference between Example 8 and Example 1 is that the calcination temperature is 800° C. and the calcination time is 6 h.

[0113] Comparative Example 1

[0114] The difference between Comparative Example 1 and Example 1 is that polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan laurate are not added in Comparative Example 1, that is, Comparative Example 1 does not include a carbon coating layer.

[0115] Comparative Example 2

[0116] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, surface-carbon-coated lithium manganese phosphate and lithium vanadium phosphate are simply mixed in a molar ratio of 1:1 as the positive electrode material.

[0117] Performance Testing

[0118] 1. Battery preparation

[0119] Positive electrode sheet: The positive electrode materials prepared in each embodiment and comparative example were mixed with a conductive agent and a binder in a solvent (the mass ratio of the positive electrode material, the conductive agent, and the binder was 98%:0.5%:1.5%), and then coated on an aluminum foil with a coating thickness of 180 μm. The size of the positive electrode sheet was 96 mm × 51 mm.

[0120] Negative electrode sheet: Graphite is used as the negative electrode active material. After mixing it with a conductive agent and a binder in a solvent (the mass ratio of graphite, conductive agent, and binder is 97.5%:1%:1.5%), it is coated on aluminum foil with a coating thickness of 140μm. After drying and pressing, the negative electrode sheet is made. The size of the negative electrode sheet is 100mm×55mm.

[0121] Diaphragm: Whatman glass fiber diaphragm GF / D is used as the diaphragm.

[0122] Electrolyte: In a glove box filled with inert gas, ethylene carbonate and diethyl carbonate were mixed in a mass ratio of 1:1 to obtain an organic solvent, and then lithium salt LiPF6 was dissolved in the organic solvent. The concentration of the lithium salt was 1 mol / L to obtain an electrolyte.

[0123] Battery assembly: stack the positive electrode sheet, modified separator, and negative electrode sheet in order to obtain a battery cell. Hot-press the stacked battery cell and place it in an aluminum-plastic film for top and side sealing. Inject the electrolyte into the battery and seal the battery after injection. The injection coefficient is 3g / Ah. The packaged battery is then subjected to formation treatment.

[0124] 2. Test the electrochemical performance of the battery

[0125] (1) First coulombic efficiency test: The batteries prepared in each embodiment and comparative example were respectively taken and the first coulombic efficiency test was performed under the test conditions of a charge and discharge current of 1 A / g, a charge cut-off voltage of 2.5 V, and a discharge cut-off voltage of 4 V.

[0126] (2) Capacity retention rate test after 500 cycles: Take the batteries made in each embodiment and comparative example respectively, and repeat 500 times under the test conditions of charge and discharge current of 1A / g, charge cut-off voltage of 2.5V, and discharge cut-off voltage of 4V. The ratio of the discharge capacity in the 500th cycle to the discharge capacity in the first cycle is recorded as the capacity retention rate (Note: the higher the capacity retention rate, the longer the service life of the electrode).

[0127] (3) DC internal resistance (DCR) test: Charge to 4V at 0.33C constant current and constant voltage, let it stand for 30 minutes, then discharge at 0.33C constant current for 90 minutes to adjust the state of charge to 50% SOC, let it stand for 30 minutes, and discharge at 2C current for 10 seconds. Record the voltage before and after discharge. Where, DCR = (V 放电前 -V 放电末期 ) / current.

[0128] The above test results are shown in Table 1.

[0129] Table 1

[0130]

[0131]

[0132] As shown in Table 1, different prepared materials, hydrothermal reaction time, and reaction temperature all affect the initial efficiency and cycle performance of the material. The results show that a hydrothermal reaction temperature of 180°C and a reaction time of 18 hours are optimal. Referring to Example 3, when the reaction temperature is too low, the 500-cycle capacity retention rate is poor and the DC internal resistance (DCR) is high. This may be due to poor crystal structure stability caused by the low reaction temperature. Referring to Example 4, when the reaction temperature is too high, the 500-cycle capacity retention rate is poor and the DC internal resistance (DCR) is high. This may be due to excessive oxygen vacancies at high temperature, which causes the material structure to collapse. Referring to Example 5, only polyoxyethylene sorbitan laurate was used as the carbon source to prepare the positive electrode material. The final 500-cycle capacity retention rate data was poor and the DC internal resistance DCR was high. This was because the surfactant strength of polyoxyethylene sorbitan laurate was large, and the surface of the material was wrapped too thickly. Referring to Example 6, only polyoxyethylene sorbitan monooleate was used as the carbon source. The final 500-cycle capacity retention rate data was poor and the DC internal resistance DCR was high. This was because the polyoxyethylene sorbitan monooleate coating had defects. Referring to Example 7, glucose was used as the carbon source. The final 500-cycle capacity retention rate data was poor and the DC internal resistance DCR was high. This was because the glucose coating had uneven thickness and poor contact stability with the material.

[0133] The positive electrode material of Comparative Example 1 does not contain a carbon coating layer. The final first coulombic efficiency and 500-cycle capacity retention rate data are extremely poor, and the DC internal resistance DCR is significantly increased, indicating that the carbon coating layer has a significant impact on the material performance.

[0134] Comparative Example 2 simply mixes the surface-carbonized lithium manganese phosphate and lithium vanadium phosphate in a molar ratio of 1:1. The final first coulombic efficiency, 500-cycle capacity retention rate, and DC internal resistance DCR test results are all unsatisfactory, indicating that after some Mn and V are doped with each other, the contact between the core materials is closer, which can reduce the surface energy of the core material, make the carbon coating layer more stable in contact with the core material, and not easily fall off during long cycles. It effectively avoids electrolyte failure caused by direct contact between the core material and the electrolyte, avoids polarization of the positive electrode material, and improves the cycle stability of the positive electrode material. Compared with the conventional LiMnPO4 and Li3V2(PO4)3 mixing, the contact is closer, making it difficult for manganese elements in lithium manganate to dissolve, and the smaller-scale close contact significantly improves the electronic conductivity and ionic conductivity, while simple mixing cannot play a synergistic role of co-doping.

[0135] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0136] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in the present invention are merely illustrative and non-limiting, and should not be construed as necessarily possessed by each embodiment of the present invention. Furthermore, the specific details disclosed above are provided for illustrative purposes and to facilitate understanding, and are not intended to be limiting. These details do not necessarily limit the present invention to being implemented using these specific details.

[0137] It should be noted that the terms "and / or" or " / " used herein are merely a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The singular forms "a," "the," and "the" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0138] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0139] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material comprises: a core and a carbon coating layer coated on at least a portion of the surface of the core; Wherein, the core comprises LiMn 1-x V x PO4 and Li3V 2-y Mn y (PO4)3; Among them, 0≤x≤0.1, 0≤y≤0.

15.

2. The positive electrode material according to claim 1, characterized in that The LiMn 1-x V x PO4、Li3V 2-y Mn y The molar ratio of (PO4)3 and carbon is 1:1:(0.01~0.1).

3. A method for preparing a positive electrode material, characterized in that: The following steps are involved: The manganese source solution and the vanadium source solution are mixed and subjected to a hydrothermal reaction to obtain the intermediate Mn(VO3)2; The intermediate Mn(VO3)2, lithium source, phosphoric acid source, carbon source and acid source are mixed in a solvent to obtain a mixed solution, which is then ball-milled, sintered and ground to obtain a positive electrode material.

4. The method for preparing the positive electrode material according to claim 3, wherein: The solvent in the manganese source solution includes water and / or an organic solvent; and / or, the molar concentration of the manganese source solution is 0.03 mol / L to 0.5 mol / L; And / or, the manganese source includes at least one of MnCl2, MnSO4, Mn(NO3)2 or Mn3(PO4)2.

5. The method for preparing the positive electrode material according to claim 3, wherein: The solvent in the vanadium source solution includes water and / or an organic solvent; and / or, the molar concentration of the vanadium source solution is 0.06 mol / L to 1 mol / L; And / or, the vanadium source includes V2O3, VO2, V2O4, V2O5, NH4VO3, H4V2O 10 , V(OH)3, Na3VO4 or Na4V2O7.

6. The method for preparing the positive electrode material according to claim 3, wherein: The temperature of the hydrothermal reaction is 170° C. to 190° C., and the time is 1 hour to 30 hours.

7. The method for preparing the positive electrode material according to claim 3, wherein: The molar ratio of the intermediate Mn(VO3)2, the lithium source, the phosphoric acid source, the carbon source, and the acid source is (1-5):(1-10):(1-10):(0.02-20):(2-20); and / or, the molar concentration of the intermediate Mn(VO3)2 in the mixed solution is 0.01 mol / L to 1 mol / L; And / or, the solvent includes water and / or an organic solvent.

8. The method for preparing the positive electrode material according to claim 3, wherein: The carbon source includes at least one of polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan laurate, glucose, asphalt, polydopamine, resorcinol, formaldehyde, starch, sucrose, sodium carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl pyrrolidone, tannic acid, polyvinyl alcohol, polypyrrole, vitamin C, polyethylene glycol, anthracene or aniline.

9. The method for preparing the positive electrode material according to claim 3, wherein: The ball milling speed is 300 rpm to 400 rpm, and the time is 0.5 h to 9 h; and / or, the sintering is performed under an inert atmosphere, and the sintering includes pre-firing and roasting; The pre-calcination temperature is 250°C to 450°C, and the time is 1h to 6h; The calcination temperature is 650°C to 750°C, and the calcination time is 1h to 12h; And / or, the particle size of the product after grinding is 100 nm ≤ Dv50 ≤ 50 μm.

10. A battery comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode material, characterized in that: The positive electrode material is the positive electrode material according to any one of claims 1 to 2 or the positive electrode material prepared by the preparation method according to any one of claims 3 to 9.

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