WO2020011179A1 - 正极材料及其制备方法、锂离子电池和车辆 - Google Patents

正极材料及其制备方法、锂离子电池和车辆 Download PDF

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WO2020011179A1
WO2020011179A1 PCT/CN2019/095353 CN2019095353W WO2020011179A1 WO 2020011179 A1 WO2020011179 A1 WO 2020011179A1 CN 2019095353 W CN2019095353 W CN 2019095353W WO 2020011179 A1 WO2020011179 A1 WO 2020011179A1
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positive electrode
electrode material
lithium oxide
precursor
sulfur
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PCT/CN2019/095353
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English (en)
French (fr)
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胡栋杰
魏昊
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比亚迪股份有限公司
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Priority to EP19833625.7A priority Critical patent/EP3823062A4/en
Priority to US17/259,100 priority patent/US20210292185A1/en
Publication of WO2020011179A1 publication Critical patent/WO2020011179A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G53/00—Compounds of nickel
    • C01G53/40—Nickelates
    • C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
    • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/56—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO3]2-, e.g. Li2[NixMn1-xO3], Li2[MyNixMn1-x-yO3
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of materials and new energy, and in particular, to a positive electrode material and a preparation method thereof, a lithium ion battery, and a vehicle.
  • lithium-ion batteries have attracted widespread attention due to their advantages such as higher specific energy, higher voltage, less self-discharge, better safety performance, and longer cycle life. industrialization.
  • the main components of a lithium-ion battery include an electrolyte, a separator, and positive and negative materials.
  • the positive material of lithium-ion batteries accounts for a large proportion in the battery, and the performance of the positive material directly affects the battery performance. Therefore, the positive material is the key to the development and improvement of the performance of the lithium-ion battery.
  • Adding sulfur to the positive electrode material can increase the lithium binding capacity of the positive electrode material, so that the battery has a higher theoretical specific capacity and a higher overall energy density.
  • the present application proposes a positive electrode material.
  • the positive electrode material includes positive electrode material particles, the positive electrode material particles including a central region and a surface layer region, the central region containing lithium oxide, the surface layer region containing lithium oxide and sulfur element; the lithium oxide includes ⁇ LiNi m Co n X (1-mn) O 2 ⁇ (1- ⁇ ) Li 2 MO 3 , where 0 ⁇ ⁇ ⁇ 1, X includes at least one selected from Mn, Al, Nb, and Fe, and M includes selected from Mn, At least one of Al, Nb, Fe, Co, and Ni is 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1, and 0 ⁇ m + n ⁇ 1.
  • the positive electrode material particle precursor has pores suitable for sulfur element filling.
  • the pores can prevent the polysulfide intermediate from dissolving in the electrolyte, and the particle structure of the positive electrode material does not reduce the overall compaction density of the positive electrode material. It is beneficial to increase the volume energy density of the positive electrode material.
  • the present application proposes a method for preparing a positive electrode material.
  • the positive electrode material includes positive electrode material particles, and the method includes: mixing a solution containing a metal ion, a complexing agent, and a precipitant under agitation conditions, and co-precipitating to obtain a core precursor, and the core is The precursor and the lithium source are mixed and calcined to obtain a positive electrode material particle precursor formed by the accumulation of lithium oxide nanoparticles.
  • the positive electrode material particle precursor includes a central region and a surface layer located outside the central region.
  • the metal includes at least one of Mn, Al, Nb, Fe, Co, and Ni
  • the lithium oxide nanoparticles include ⁇ LiNi m Co n X (1-mn) O 2 ⁇ (1- ⁇ ) Li 2 MO 3 , where 0 ⁇ ⁇ ⁇ 1, X includes at least one selected from Mn, Al, Nb, and Fe, and M includes at least one selected from Mn, Al, Nb, Fe, Co, and Ni , 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1, 0 ⁇ m + n ⁇ 1; mixing the positive electrode material particle precursor with a sulfur source, and performing a melt-solidification treatment so as to fill the surface element with sulfur Zone, and the positive electrode material particles are obtained.
  • the surface layer region of the precursor of the positive electrode material particles obtained by this method has a micro morphology suitable for sulfur element filling. Filling the sulfur elemental substance in the surface layer region can prevent sulfur from dissolving in the electrolyte; The overall compaction density of the positive electrode material is reduced, which is beneficial to increase the volume energy density of the positive electrode material.
  • the present application proposes a lithium-ion battery.
  • the lithium-ion battery includes the foregoing positive electrode material or the positive electrode material prepared by the foregoing method. Therefore, the lithium ion battery has a higher energy density and a better cycle life.
  • the present application proposes a vehicle.
  • the vehicle includes the aforementioned lithium-ion battery. Therefore, the vehicle has all the features and advantages of the lithium-ion battery described above, which will not be repeated here.
  • FIG. 1 shows a schematic flowchart of a preparation method according to an embodiment of the present application
  • FIG. 2 is a schematic flowchart of a part of a preparation method according to an embodiment of the present application
  • FIG. 3 is a schematic flowchart of a preparation method according to an embodiment of the present application.
  • FIG. 4 shows a scanning electron microscope image of a core precursor not subjected to lithiation, prepared according to an example of the present application
  • FIG. 5 shows a scanning electron microscope image of a precursor of a cathode material particle obtained after lithiation according to an example of the present application
  • FIG. 6 shows a scanning electron microscope image of a cathode material prepared according to an example of the present application.
  • the present application proposes a sulfur-containing cathode material.
  • the positive electrode material includes positive electrode material particles, and the positive electrode material particles include a central region and a surface layer region.
  • the central region contains lithium oxide
  • the surface layer region contains lithium oxide and sulfur.
  • the microscopic morphology of the surface layer region of the precursor of the positive electrode material particles is suitable for the filling of sulfur element.
  • the sulfur element is filled in the pores of the surface layer region, and the above positive electrode material can effectively prevent sulfur from dissolving in the electrolyte.
  • the particle structure of the positive electrode material does not reduce the overall compaction density of the material, which is conducive to increasing the volume energy density of the positive electrode material.
  • the specific chemical composition of the lithium oxide is not particularly limited, and those skilled in the art can select it according to actual conditions.
  • the above lithium oxide may be composed of a ternary material.
  • the chemical formula of the lithium oxide may be ⁇ LiNi m Co n X (1-mn) O 2 ⁇ (1- ⁇ ) Li 2 MO 3 , where 0 ⁇ ⁇ ⁇ 1, and X includes selected from Mn, Al, Nb, At least one of Fe and M includes at least one selected from Mn, Al, Nb, Fe, Co, and Ni, 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1, 0 ⁇ m + n ⁇ 1.
  • the M average valence state in Li 2 MO 3 may be +4 valence.
  • the average valence state of X in LiNi m Co n X (1-mn) O 2 can be between + 3- + 4.
  • the lithium oxide satisfying the above-mentioned chemical composition can be controlled by the synthesis process relatively easily to obtain a precursor structure of the cathode material particles having pores in the surface layer region, and the pores in the surface layer region are suitable for the filling of sulfur simple substance.
  • the above-mentioned ternary material may include a nickel-cobalt-manganese (NCM) ternary material, may also include a nickel-cobalt-aluminum (NCA) ternary material, and may also include a lithium-rich material.
  • NCM nickel-cobalt-manganese
  • NCA nickel-cobalt-aluminum
  • LiNi 1-xy Co x Mn y O 2 may be included, where Mn may be replaced by any one of Al, Nb, Fe, or it may contain two, three, or both of Mn, Al, Nb, and Fe, or 4, when containing multiple of Mn, Al, Nb, Fe, the total atomic content of multiple elements in Mn, Al, Nb, Fe should be satisfied.
  • the above-mentioned positive electrode material particle precursor may be formed by depositing lithium oxide nanoparticles.
  • the chemical composition of the lithium oxide nanoparticles may be the aforementioned lithium oxide.
  • the thickness of the surface layer region of the positive electrode material is 0.5-20 ⁇ m, for example, 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, etc.
  • the average particle diameter of the positive electrode material particles is 5-50 ⁇ m, for example, 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m. , 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, etc.
  • the “surface layer region” refers to a region along the radial direction of the positive electrode material particles with the surface of the positive electrode material particles as the thickness 0 point and the thickness range of 0.5-20 ⁇ m.
  • the region outside the surface layer region of the positive electrode material particles is the central region.
  • the above definitions of the surface layer region and the central region also apply to the precursor of the cathode material particles.
  • the above-mentioned positive electrode material particle precursor may be formed by stacking the lithium oxide nanoparticles described above, and the surface layer region has a pore structure.
  • the pores in the surface layer region of the precursor of the positive electrode material particles are filled with sulfur elemental substance at a later stage, and the positive electrode material particles can be obtained.
  • Sulfur elementary substance is formed in the surface layer region, and the main structure in the central region is still composed of lithium oxide, so the overall mechanical strength of the particles can be ensured.
  • no large-scale particle collapse and fragmentation will occur.
  • the depth of sulfur penetration can be achieved by controlling the thickness of the surface zone.
  • the lithium oxide nanoparticles are selected from one or more of rod-shaped lithium oxide and bulk lithium oxide.
  • the lithium oxide nanoparticles are stacked to form a precursor of a positive electrode material particle having pores in a surface layer region.
  • the lithium oxide nanoparticles have a length of 0.5-2 ⁇ m, a width of 200-500 nm, and an aspect ratio of 2-40. Because the lithium oxide nanoparticles have a large aspect ratio, the diameter of the pores formed by stacking is small and has a certain depth.
  • the size of the pores can be 50-1000 nm, such as 500 nm.
  • the sulfur element is filled in the pores, which can effectively prevent the electrolyte from entering the pores and dissolve the filled sulfur.
  • the positive electrode material particles formed by the precursor of the positive electrode material particles after being filled with the sulfur element substance may fill the pores in the surface region region, or may partially fill the pores in the surface region region, that is, the surface region of the positive electrode material particles In addition to the part filled with sulfur element, it can also have a partial pore structure.
  • the size of the pores in the surface layer region of the positive electrode material particles may be similar to the pore size in the precursor of the positive electrode material particles (before the sulfur element is filled).
  • the particle size and the like of the body can better fill the pores in the surface layer with sulfur atoms, thereby obtaining a considerable filling ratio and filling stability, and further increasing the specific capacity of the positive electrode material.
  • adjusting the size of the pores in the surface layer region can effectively alleviate the dissolution of sulfur atoms in the positive electrode material by the electrolyte, thereby obtaining good cycle stability, and further enabling the battery using the positive electrode material to have a long-term excellent calendar life.
  • the calendar life can be the time required for the battery to reach the end of its life in an open circuit state at a reference temperature, that is, the life of the battery in the standby state.
  • the particles with the above morphology can also increase the overall energy density of the positive electrode material without reducing the overall compaction density of the material, which is conducive to increasing the volume energy density of the positive electrode material.
  • the positive electrode material is used in lithium ion batteries At medium time, considerable battery performance can also be obtained. It should be particularly noted that, in the present application, the term "lithium oxide nanoparticles", or “primary particles”, specifically means that the dimension in any one dimension such as length, diameter, and width may be nanoscale.
  • rod-shaped or block-shaped lithium oxide nanoparticles having the above-mentioned size can make the surface layer region suitable In order to contain the pores of the sulfur element, and the pores can be more regular.
  • the shape of the precursor of the positive electrode material particles obtained by stacking the lithium oxide nanoparticles is not particularly limited.
  • the precursor of the positive electrode material particles may be one of a spherical shape, a rhombic shape, and an ellipsoidal shape.
  • the content of sulfur element may be 5% to 50% by weight, and the content of lithium oxide may be 50% to 95% by weight.
  • the sulfur content can be determined according to the pores in the surface layer region described above. The inventor found that the amount of sulfur element is too high, and excessive sulfur cannot be filled in the pores, which will nucleate alone, resulting in an increase in material resistance, easier dissolution in the electrolyte, and severe electrochemical degradation. According to a specific embodiment of the present application, when the sulfur elemental content is within the above range, the sulfur elemental substance can be prevented from nucleating alone.
  • the content of sulfur element may be 10 wt% to 30 wt%.
  • Sulfur simple substance can penetrate into the pores through melt infiltration. Unlike ordinary physical mixing, sulfur simple substance enters the pores through melt infiltration. The presence of sulfur can also be detected inside the lithium oxide particles.
  • a coating layer may be further formed on the outer surface of the positive electrode material particles.
  • the material of the coating layer may include a carbon material, tin dioxide, manganese dioxide, titanium dioxide, tricobalt tetroxide, vanadium pentoxide, iron disulfide, copper disulfide, cobalt disulfide, and bismuth trisulfide. Any one or several of them.
  • the content of the coating layer is 0.1 wt% to 10 wt%.
  • a carbon coating layer is used, and the carbon coating layer is formed on the outer surface of the lithium oxide particles filled with sulfur.
  • the performance of this positive electrode material can be improved.
  • the specific thickness, material, morphology, and synthesis method of the carbon coating layer are not particularly limited. Those skilled in the art can select familiar materials and methods to form the carbon coating layer according to actual conditions. Thereby, the electrolyte can be blocked from entering the pores of the lithium oxide particles, and the dissolution of the sulfur element by the electrolyte can be eased.
  • the coating layer is a titanium dioxide coating layer.
  • the mass ratio of lithium oxide, sulfur, and titanium dioxide in the positive electrode material may be (90 to 45): (5 to 50): (2 to 8).
  • the proportion of the coating amount of titanium dioxide in the positive electrode material particles may be 5% by weight.
  • the present application proposes a method for preparing a positive electrode material.
  • the positive electrode material may have all the features and advantages of the previously described positive electrode material. Specifically, referring to FIG. 1, the method includes:
  • a precursor of a cathode material particle is formed.
  • the precursor of the positive electrode material particles may be formed by stacking lithium oxide nanoparticles.
  • the lithium oxide nanoparticles are rod-shaped or block-shaped, and the surface layer region of the precursor of the positive electrode material particles formed has pores suitable for sulfur elemental filling.
  • the microscopic morphology of the positive electrode material particle precursor is suitable for sulfur element filling, and the surface layer region has small pores, which can prevent sulfur from dissolving in the electrolyte, and the particle structure of the finally obtained positive electrode material will not reduce the overall compaction density of the material. , Thereby increasing the volume energy density of the positive electrode material.
  • the above-mentioned positive electrode material particle precursor can be obtained by the following steps:
  • the solution containing the metal ion, the complexing agent, and the precipitant are mixed under stirring conditions to obtain a precursor solution.
  • the core precursor was obtained by co-precipitation.
  • a precipitating agent, a complexing agent, and a solution containing a metal are gradually added to the reaction container.
  • the core precursors made of lithium oxide nano-scale particles can have pores that are more suitable for sulfur element filling . Therefore, in this step, the morphology of the core precursor can be controlled by adjusting the stirring speed, the reaction temperature, the reaction pH, and the concentration of the complexing agent. Specifically, a solution such as a precipitant that is gradually added can provide a shear force during the formation of the core precursor, and lithium oxide nanoparticles gradually grow and accumulate as the core precursor.
  • the size and pores of the nano-core precursor formed can be adjusted, thereby controlling the size of the pores in the surface layer of the precursor of the positive electrode particle particles.
  • the above conditions can be controlled so that the lithium oxide nanoparticles obtained by lithiation have a length of 0.5-2 ⁇ m, a width of 200-500 nm, and an aspect ratio of the nano-lithium oxide particles of 2-40.
  • Lithium oxide nanoparticles having a size within the above range can be stacked to form a cathode material particle precursor having a surface layer region having pores suitable for sulfur element filling.
  • the size of the pores in the surface layer region of the precursor of the cathode material particles can be 50-1000 nm, for example, 500 nm. Therefore, not only nano-lithium oxide particles (for example, rod-shaped) with a specific morphology can be obtained, but also the positive electrode material particle precursor formed by stacking can also have a relatively uniform pore distribution and an ideal morphology.
  • the solution containing the metal ion may be provided by an inorganic salt solution containing the metal element.
  • the metal element includes at least one of Mn, Al, Nb, Fe, Co, and Ni, and the metal salt solution is added to the reaction container with stirring.
  • the above process can be performed under heating conditions. For example, it can be performed at 30-60 degrees Celsius. For example, it can be performed at 40 degrees, 45 degrees, 50 degrees, and 55 degrees. Specifically, the container can be placed at 40-60 degrees Celsius. In the water bath.
  • the metal salt solution may include a solution for forming NCM or NCA material (excluding Li), and may be at least one of a salt solution containing nickel, a salt solution containing cobalt, and a salt solution containing manganese.
  • Nitrate solution of metal ions Nitrate solution of metal ions.
  • the complexing agent used in the preparation process can form a stable complex with metal ions to further control the rate of precipitation.
  • a commonly used complexing agent is an alkaline solution, such as ammonia.
  • the mass concentration of the ammonia water may be 5 to 15 wt%.
  • the specific chemical composition of the metal salt solution can be determined according to the content of metal elements in the lithium oxide to be formed.
  • the chemical composition of the precursor of the positive electrode material particles has been described in detail above, and is not repeated here.
  • the above-mentioned metal salt solution and the complexing agent are added to the container in a fixed ratio in a stirred state.
  • the fixed ratio and the metal-containing solution are determined based on the chemical composition of the lithium oxide.
  • the total amount of the metal-containing solution in the mixed solution and the chemical composition of the metal can be determined according to the specific chemical composition of the lithium oxide to be synthesized.
  • the inventors found that the stirring speed has an important effect on the size of the nano-lithium oxide precursor particles formed and the morphology of the core precursor, and can affect the morphology of the final positive electrode material particles.
  • the stirring speed is 300-1000 rpm / min, nanoparticles as described above can be obtained.
  • the stirring speed may be 600-800 rpm / min.
  • the precipitating agent may be an agent capable of precipitating metal ions, such as an aqueous solution of hydroxide, such as potassium hydroxide, sodium hydroxide, and the like.
  • the precipitant can be pumped into the container containing the mixed solution via a variable speed transmitter.
  • the pumping speed of the precipitant can be based on the pH value of the reaction system (ie, the precursor solution).
  • the pH value is controlled at a fixed value during the reaction, or it can be a fixed value during the early, middle, and late stages of the reaction. With the formation of hydroxide co-precipitation during the reaction, the hydroxide in the system will be consumed, and the pH of the system will decrease.
  • the pH value rises to the set value, the addition of the precipitant is stopped.
  • the pH value does not change during the entire reaction process, that is, the pumping speed of the precipitant does not change, and the ratio of the added precipitant and the metal salt solution is about 2: 1.
  • the process of adding the precipitant described above can also be performed at 30-60 degrees Celsius. For example, it can be performed at 40 degrees Celsius.
  • the amount of the precipitating agent can determine the amount of the precipitating agent according to the specific chemical composition of the lithium oxide, the total amount of the mixed solution, and the ratio of the complexing agent and the metal salt solution in the mixed solution.
  • the amount of the precipitant added can control the pH of the obtained precursor solution to be 10-12, such as controlling the pH to 11.
  • the precursor solution obtained through the above operation can be left at 45-60 degrees Celsius for 15-30 hours to cause a co-precipitation reaction. Thereby, a core precursor can be easily obtained.
  • the core precursor and the lithium source obtained previously are mixed and subjected to a baking treatment, so as to lithify the core precursor, thereby obtaining a precursor of a positive electrode material particle and a precursor of a positive electrode material particle.
  • the body includes a central area, and a surface area located outside the central area.
  • an appropriate lithium-containing reagent in this step, those skilled in the art can select an appropriate lithium-containing reagent according to actual needs.
  • an inorganic salt of lithium such as a nitrate
  • the mixing ratio of the core precursor and the lithium source can be determined according to the chemical composition of the lithium oxide.
  • the baking treatment may be performed at a baking temperature of 600 to 800 degrees Celsius.
  • the lithiation of the core precursor may be mixing the core precursor obtained previously with a lithium salt (that is, a lithium source) in water.
  • a lithium salt that is, a lithium source
  • the precipitate is separated and dried by separation methods such as filtration, drying, and steam drying.
  • the dried precipitate is subjected to a baking treatment at the above baking temperature, and the baking treatment time may be 10-18 hours, such as 12 hours.
  • the above calcination treatment may further include Annealing step.
  • the above-mentioned roasting process may be performed by rapidly increasing the temperature to the roasting process temperature, and then maintaining the temperature for a short time before annealing. It can include:
  • the sample can be directly placed in a room temperature (the temperature can be 0 to 40 degrees Celsius).
  • the rapid cooling time can be 20 minutes to 1 hour
  • the annealing temperature can be 450 to 700 degrees Celsius, such as 500 degrees Celsius
  • the annealing time can be 3 to 8 hours, such as 5 hours.
  • this step the sulfur elemental substance is filled in the pores in the surface layer region of the precursor of the positive electrode material particle to obtain the positive electrode material particle containing the sulfur elementary substance.
  • this step may be achieved by mixing the precursor particles of the positive electrode active material prepared in advance with a sulfur source, and then performing a melt-solidification treatment. Sulfur element can penetrate into the pores through melt infiltration, which is different from general physical mixing. Sulfur element can enter into the pores through melt infiltration. The existence of sulfur can be detected inside the lithium oxide particles. Pure physical mixing cannot achieve this. of.
  • the shuttle effect refers to It is during the charge and discharge process that the polysulfide (Li2Sx) intermediate produced by the positive electrode is dissolved in the electrolyte, passes through the separator, diffuses to the negative electrode, and directly reacts with the lithium metal of the negative electrode, eventually causing the effective substances in the battery. Irreversible loss, decay of battery life, low Coulomb efficiency. .
  • the precursor of the positive electrode material particles and the sulfur source may be mixed at a mass ratio of (8-12): (0.5-2).
  • the sulfur source may be a simple element of sulfur.
  • the processing temperature of the melt-solidification treatment can be 120-180 degrees Celsius, such as 130, 140, 150, 160, 170 degrees Celsius, etc., and the processing time can be 10-15 hours, such as 11, 12, 13, 14 hours and so on. Specifically, it can be processed at 150 degrees Celsius for 12 hours. This makes it possible to easily fill sulfur into the pores of the previously formed lithium oxide particles.
  • the above-mentioned melt-solidification treatment may also be performed under an inert atmosphere.
  • it may be performed in an inert atmosphere, including nitrogen, argon, etc., in a sealed and pressurized container, and the pressure of the container may be 5-12 MPa. If it can be 8 MPa, for example, according to a specific embodiment of the present application, the lithium oxide particles and the sulfur source can be mixed and placed in a sealed container, and an inert gas is flushed into the container to pressurize it.
  • the pressure after pressing may be 10 MPa, 8 MPa, or the like.
  • the positive electrode material prepared by the above method after the melt-solidification process, referring to FIG. 3, it may further include:
  • a coating layer is formed outside the positive electrode material particles.
  • the specific method of forming the coating layer and the chemical composition of the coating layer can be selected by those skilled in the art according to the actual situation, such as carbon materials, tin dioxide, manganese dioxide, titanium dioxide, tricobalt tetroxide, vanadium pentoxide, Any one or more of iron sulfide, copper disulfide, cobalt disulfide, or bismuth trisulfide.
  • the carbon material may be graphite, Ketjen black, graphene, carbon nanotubes, activated carbon, and the like, and is formed by methods including, but not limited to, spray drying, hydrothermal method, and the like. Thereby, the elemental sulfur can be further separated from the electrolytic solution, and the cycle performance and stability of a battery using the positive electrode material can be improved.
  • the present application proposes a positive electrode material.
  • the cathode material is prepared by the method described above. Therefore, the positive electrode material has all the characteristics and advantages of the positive electrode material obtained by the method described above, and details are not described herein again.
  • the present application proposes a lithium-ion battery.
  • the lithium ion battery includes the aforementioned positive electrode material. Therefore, the lithium-ion battery has all the features and advantages of the aforementioned positive electrode material, which will not be repeated here. In general, the lithium-ion battery has a higher energy density and a better cycle life.
  • the present application proposes a vehicle.
  • the vehicle includes the aforementioned lithium-ion battery.
  • a plurality of battery packs composed of the aforementioned lithium-ion batteries may be included. Therefore, the vehicle has all the features and advantages of the lithium-ion battery described above, which will not be repeated here.
  • nickel nitrate was purchased from Shenzhen Brian
  • cobalt nitrate was purchased from Shenzhen Brian
  • lithium nitrate was purchased from Shenzhen Brian
  • ammonia water was purchased from Shenzhen Brian
  • lithium nitrate was purchased from Shenzhen Brian
  • the elemental sulfur was purchased from Aladdin.
  • step 2 The core precursor obtained in step 1) and lithium nitrate are mixed in water at a mass-to-molar ratio of 1 to 1.2 to obtain a precipitate.
  • the precipitate is filtered and separated, taken out and dried, and then calcined at 700 degrees Celsius for 10 hours. .
  • a ternary cathode material particle precursor was obtained.
  • ternary cathode material particle precursor and sulfur element are mixed according to a mass ratio of 10: 1, and then heat-treated in a muffle furnace, and reacted at 150 degrees Celsius for 12 hours. -Sulfur composite cathode material particles.
  • step 2 The core precursor and lithium nitrate obtained in step 1) are mixed in water at a molar ratio of 1 to 1.2 to obtain a precipitate. The precipitate is filtered and separated, taken out and dried, and then calcined at 700 degrees Celsius for 10 hours. . A ternary positive electrode material particle precursor was obtained.
  • the ternary cathode material particle precursor and the sulfur element are mixed according to a mass ratio of 10: 0.5. After the mixing, the reaction is performed in a hydrothermal reaction kettle at a temperature of 150 degrees Celsius. The reaction time was 12 hours.
  • the core precursor and lithium nitrate are mixed in water at a molar ratio of 1 to 1.2 to obtain a precipitate, which is then taken out and dried.
  • the precipitate was heated to 700 degrees Celsius in 40 minutes, then calcined at 700 degrees Celsius for 1 hour, then taken out, cooled to room temperature within 30 minutes, and then annealed at 500 degrees Celsius for 5 hours.
  • a ternary cathode material particle precursor was obtained.
  • the ternary cathode material particle precursor and sulfur element are mixed according to a mass ratio of 8: 1, and after the mixing, the reaction is performed in a hydrothermal reaction kettle at a temperature of 150 degrees Celsius. The reaction time was 12 hours.
  • the salt solution is pumped into a hydrothermal reactor under a stirring state (stirring speed 500 rpm), and then 5 g of ammonia water (concentration of 10) is slowly added. % By weight) and sodium hydroxide was added to adjust the pH to 11.
  • the co-precipitation reaction was performed at 30 degrees Celsius for 24 hours, and the core precursor was filtered.
  • the core precursor and lithium nitrate are mixed in water at a molar ratio of 1 to 1.2, and then taken out and dried, then baked at 700 degrees Celsius for 1 hour, then taken out at 700 degrees, and rapidly cooled to room temperature (room temperature is The conventional indoor temperature may be 10-35 ° C, for example, 25 ° C), and then annealed at 500 ° C for 5 hours.
  • room temperature is The conventional indoor temperature may be 10-35 ° C, for example, 25 ° C), and then annealed at 500 ° C for 5 hours.
  • a ternary cathode material particle precursor was obtained.
  • step (1) The core precursor and lithium nitrate obtained in step (1) are mixed in water at a molar ratio of 1 to 1.2 to obtain a precipitate.
  • the precipitate is filtered and separated, taken out and dried, and then calcined at 700 ° C for 10 minutes. hour.
  • a ternary cathode material particle precursor was obtained.
  • the ternary cathode material particle precursor and the sulfur element are mixed according to a mass ratio of 10: 2, and after the mixing, the reaction is performed in a hydrothermal reaction kettle at a temperature of 150 degrees Celsius. The reaction time was 12 hours, and ternary positive electrode material particles were obtained.
  • step (3) Disperse the ternary cathode material obtained in step (3) in n-butanol under the condition of heating and stirring at 40 degrees Celsius, add quantitative isopropyl titanate (determined according to the titanium dioxide coating amount of 5 wt%), and continue The final product is obtained by stirring, and ternary-sulfur composite cathode material particles coated with titanium dioxide are obtained after washing and drying.
  • step 2 The core precursor and lithium nitrate obtained in step 1) are mixed in water at a molar ratio of 1 to 1.2 to obtain a precipitate. The precipitate is filtered and separated, taken out and dried, and then calcined at 700 degrees Celsius for 10 hours. . A ternary cathode material particle precursor was obtained.
  • step (3) the precursor of the ternary cathode material particles and the sulfur element are mixed at a mass ratio of 12: 1, and after the mixing, the reaction is performed in a hydrothermal reaction kettle at a temperature of 150 degrees Celsius.
  • the reaction time was 12 hours, and ternary positive electrode material particles were obtained.
  • step (3) The graphite powder and the ternary positive electrode material particles obtained in step (3) are mixed in a molar ratio of 1 to 1.2, and spray drying is performed to form carbon on the surface of the ternary-sulfur composite positive electrode material particles filled with sulfur simple substance. Coating.
  • a ternary cathode material particle precursor was prepared according to the method of Example 1, and then the obtained ternary cathode material particle precursor and sulfur simple substance were directly mixed according to a mass ratio of 10: 1 to obtain a ternary-sulfur composite cathode material particle.
  • a core precursor body is prepared
  • the core precursor and lithium nitrate are mixed in water at a molar ratio of 1 to 1.2 to obtain a precipitate.
  • the precipitate is filtered and dried, and then baked at 700 ° C for 1 hour, and then taken out at 700 ° C. ,
  • the temperature is rapidly reduced to room temperature (room temperature is the conventional indoor temperature, which can be 10-35 ° C, for example, 25 ° C), and then annealed at 500 ° C for 5 hours.
  • room temperature is the conventional indoor temperature, which can be 10-35 ° C, for example, 25 ° C
  • annealed at 500 ° C for 5 hours A ternary cathode material particle precursor was obtained.
  • the scanning electron microscope (JEOL) was used to observe the morphology of the sample obtained in Example 1 above and the intermediate during the preparation process.
  • the core precursor (not lithiated) obtained in Example 1 is spherical particles with a diameter of about 5 to 8 ⁇ m, and is formed by stacking rod-shaped particles with a diameter of about 100 nm.
  • the length of the rod-shaped particles ranges from 0.5 to 5 ⁇ m, and the pore channels in the spherical particles formed by stacking are about 500 nm to 1 ⁇ m.
  • Example 5 The morphology of the ternary active material obtained in Example 1 is shown in FIG. 5. After lithiation, the pore size of the spherical particles has been further optimized. Comparing with FIG. 4, it can be seen that the pore size distribution of the spherical particles after lithiation is more uniform, which is conducive to the filling of sulfur simple substance.
  • Example 1 The morphology of Example 1 filled with a sulfur element (that is, the obtained positive electrode material) is shown in FIG. 6. By comparison, it can be seen that the sulfur element can be filled into the pores of the lithium oxide particles uniformly, and the filling amount is considerable.
  • the test results are shown in Table 1.
  • the sulfur content test was performed on the samples obtained in the above examples and comparative examples. Specific test methods and steps: The carbon and sulfur analyzer method is used to test the overall sulfur content of the material. The test results are shown in Table 1.
  • the specific test method is as follows: 5g of the positive electrode materials obtained in the above examples and comparative examples are respectively mixed with the positive electrode conductive agent carbon black and the positive electrode binder PVDF in a mass ratio of 94: 3: 3 and put into a mold with a diameter of 2cm. The powder was pressed at a pressure of 10 MPa.
  • the volume energy density value of the positive electrode active material is calculated by the following formula:
  • the energy density calculation formula is as follows:
  • Charging average voltage charging current * charging time / total charging capacity
  • Comparative Example 1 and Comparative Example 2 have higher sulfur content in the sulfur content test, their energy densities are significantly lower than the samples of the examples.
  • the sample is a positive electrode material during the sulfur content test
  • part of the sulfur element in the comparative sample formed by direct mixing is adsorbed on the surface of the ternary material through physical adsorption.
  • the process of preparing the battery such as coating, drying, and soot blowing
  • a part of the physically adsorbed sulfur element will be lost, and the heat-treated Examples 1 to 6 will not cause any problems. Proportion of the above.
  • Comparative Example 1 did not stir the core precursor during synthesis, and could not control the morphology of the core precursor well, and only a simple one-step heat treatment was performed when the core precursor was lithiated. The morphology cannot be maintained well, so that the finally obtained positive electrode material particles do not have a surface layer region.
  • the ternary cathode material particle precursor maintained a certain morphology (with a certain pore structure in the outer thickness range of 1-5 microns), but the sulfur elemental substance only adhered On the surface, the surface layer of the final positive electrode material only contains sulfur, which cannot prevent the dissolution of sulfur simple substance; and the sulfur source is not directly prepared by heating, so sulfur and ternary adhesion are poor, and it is easy to Subsequent loss of electrical contact results in electrochemical failure and unsatisfactory energy density.
  • the morphology of the micron particles in Examples 1 to 6 can also maintain the overall compacted density of the material after the compaction treatment, which is more conducive to obtaining a considerable energy density.

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Abstract

提出了正极材料及其制备方法、锂离子电池和车辆。该正极材料包括正极材料颗粒，所述正极材料颗粒包括中心区和表层区，所述中心区含有锂氧化物，所述表层区含有锂氧化物和硫单质；所述锂氧化物包括δLiNimConX(1-m-n)O2·(1-δ)Li2MO3，其中0≤δ≤1，X包括选自Mn、Al、Nb、Fe中的至少之一，M包括选自Mn、Al、Nb、Fe、Co、Ni中的至少之一，0≤m＜1，0≤n＜1。

Description

正极材料及其制备方法、锂离子电池和车辆
优先权信息
本申请请求2018年07月10日向中国国家知识产权局提交的、专利申请号为201810753629.1的专利申请的优先权和权益，并且通过参照将其全文并入此处。
技术领域
本申请涉及材料以及新能源领域，具体地，涉及正极材料及其制备方法、锂离子电池和车辆。
背景技术
在各类新能源电池中，锂离子电池由于具有较高的比能量、较高的电压、自放电小、安全性能较好、循环寿命较长等优势，吸引了广泛的关注，且成功实现了工业化。锂离子电池的主要构成包括电解液、隔离材料以及正极、负极材料。锂离子电池的的正极材料在电池中占有的比例较大，且正极材料的性能直接影响电池性能，因此正极材料是锂离子电池发展和提高性能的关键。
在正极材料中加入硫元素，可以提高正极材料的锂结合量，从而令电池具有较高的理论比容量，且整体的能量密度较高。
发明内容
在本申请的一个方面，本申请提出了一种正极材料。该正极材料包括正极材料颗粒，所述正极材料颗粒包括中心区和表层区，所述中心区含有锂氧化物，所述表层区含有锂氧化物和硫单质；所述锂氧化物包括δLiNi mCo nX (1-m-n)O 2·(1-δ)Li 2MO 3，其中0≤δ≤1，X包括选自Mn、Al、Nb、Fe中的至少之一，M包括选自Mn、Al、Nb、Fe、Co、Ni中的至少之一，0≤m＜1，0≤n＜1，0≤m+n＜1。该正极材料颗粒前驱体中具有适于硫元素填充的孔隙，该孔隙可防止多硫化物中间体溶解于电解液中，且正极材料的颗粒结构不会降低该正极材料的整体压实密度，有利于提高该正极材料的体积能量密度。
在本申请的另一方面，本申请提出了一种制备正极材料的方法。所述正极材料包括正极材料颗粒，所述方法包括：将含有金属离子的溶液、络合剂以及沉淀剂在搅拌的条件下进行混合，并通过共沉淀处理，获得核心前驱体，将所述核心前驱体以及锂源进行混合并进行焙烧处理，以便获得由锂氧化物纳米颗粒堆积而形成的正极材料颗粒前驱体，所述正极材料颗粒前驱体包括中心区，和位于所述中心区外部的表层区，其中，所述金属包括Mn、Al、Nb、Fe、Co、Ni中的至少之一，所述锂氧化物纳米颗粒包括δLiNi mCo nX (1-m-n)O 2·(1-δ) Li 2MO 3，其中0≤δ≤1，X包括选自Mn、Al、Nb、Fe中的至少之一，M包括选自Mn、Al、Nb、Fe、Co、Ni中的至少之一，0≤m＜1，0≤n＜1，0≤m+n＜1；将所述正极材料颗粒前驱体与硫源进行混合，并进行熔融固化处理，以便将硫单质填充在所述表层区中，并获得所述正极材料颗粒。该方法获得的正极材料颗粒前驱体的表层区中具有适于硫元素填充的微观形貌，将硫单质填充在所述表层区中可防止硫溶解于电解液中；且正极材料的颗粒结构不会降低该正极材料的整体压实密度，有利于提高该正极材料的体积能量密度。
在本申请的又一方面，本申请提出了一种锂离子电池。该锂离子电池包括前面所述的正极材料或前面所述的方法所制备的正极材料。由此，该锂离子电池具有较高的能量密度，且循环寿命较好。
在本申请的又一方面，本申请提出了一种车辆。该车辆包括前面所述的锂离子电池。由此，该车辆具有前面描述的锂离子电池所具有的全部特征以及优点，在此不再赘述。
附图说明
图1显示了根据本申请一个实施例的制备方法的流程示意图；
图2显示了根据本申请一个实施例的制备方法的部分流程示意图；
图3显示了根据本申请一个实施例的制备方法的流程示意图；
图4显示了根据本申请实施例中所制备的未进行锂化的核心前驱体的扫描电子显微镜图；
图5显示了根据本申请实施例中所制备的锂化后得到正极材料颗粒前驱体的扫描电子显微镜图；
图6显示了根据本申请实施例中所制备的正极材料的扫描电子显微镜图。
具体实施方式
下面详细描述本申请的实施例，所述实施例的示例在附图中示出，其中自始至终相同或类似的标号表示相同或类似的元件或具有相同或类似功能的元件。下面通过参考附图描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。
在本文中所披露的范围的端点和任何值都不限于该精确的范围或值，这些范围或值应当理解为包含接近这些范围或值的值。对于数值范围来说，各个范围的端点值之间、各个范围的端点值和单独的点值之间，以及单独的点值之间可以彼此组合而得到一个或多个新的数值范围，这些数值范围应被视为在本文中具体公开。
本申请是基于发明人对以下事实的发现和认识而作出的：
由于硫的电子惰性，和硫的嵌锂中间体易溶于有机溶剂，含有硫离子的正极材料在实 际应用中还有较大的阻碍。虽然上述问题可以通过在正极材料中进一步使用碳作为载体进行复合而得到一定程度的缓解，但单纯依靠碳单质隔绝电解液，来避免硫溶于电解液，一方面会提高正极材料的生产成本，延长生产制程，降低生产效率，另一方面也难以从根本上解决硫系正极材料的上述问题。发明人经过深入研究发现，硫系正极材料中，硫易溶于电解液的问题，很大程度上是由于正极活性材料的结构不适于硫原子填充而造成的。
在本申请的一个方面，本申请提出了一种含硫的正极材料。该正极材料包括正极材料颗粒，正极材料颗粒包括中心区和表层区，中心区含有锂氧化物，表层区含有锂氧化物和硫单质。上述正极材料颗粒前驱体表层区的微观形貌适于硫元素的填充，将硫单质填充在表层区的孔隙中，得到上述正极材料可有效阻碍硫溶解于电解液中。且正极材料的颗粒结构不会降低材料的整体压实密度，从而有利于提高正极材料的体积能量密度。
下面根据本申请的具体实施例，对该正极材料进行详细解释说明：
根据本申请的实施例，上述锂氧化物的具体化学组成不受特别限制，本领域技术人员可以根据实际情况进行选择。例如，根据本申请的一些实施例，上述锂氧化物可以由三元材料构成。具体的，锂氧化物的化学式可以为δLiNi mCo nX (1-m-n)O 2·(1-δ)Li 2MO 3，其中0≤δ≤1，X包括选自Mn、Al、Nb、Fe中的至少之一，M包括选自Mn、Al、Nb、Fe、Co、Ni中的至少之一，0≤m＜1，0≤n＜1，0≤m+n＜1。更具体地，Li 2MO 3中的M平均价态可以为+4价。LiNi mCo nX (1-m-n)O 2中的X平均价态可以为+3-+4价之间。满足上述化学构成的锂氧化物，可以较为简便地通过对合成过程进行控制，获得表层区具有孔隙的正极材料颗粒前驱体结构，且表层区中的孔隙适于硫单质的填充。
根据本申请的具体实施例，上述三元材料可以包括镍钴锰(NCM)三元材料，也可以包括镍钴铝(NCA)三元材料，还可以包括富锂材料。如可以包括LiNi 1-x-yCo xMn yO 2，其中的Mn可被Al、Nb、Fe中的任意一个替换，或同时含有Mn、Al、Nb、Fe中的2个、3个，或是4个，当含有Mn、Al、Nb、Fe中多个时，应满足Mn、Al、Nb、Fe中多个元素的总原子含量在三元材料中满足LiNi mCo nX (1-m-n)O 2中的(1-m-n)。
根据本申请的实施例，上述正极材料颗粒前驱体可以是由锂氧化物纳米颗粒堆积形成的。锂氧化物纳米颗粒的化学组成可以为前述的锂氧化物。正极材料的表层区的厚度为0.5-20μm，例如可以为5μm、10μm、15μm等，正极材料颗粒的平均粒径为5-50μm，例如可以为5μm、10μm、15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm等。需要说明的是，在本申请中，“表层区”是指沿着正极材料颗粒径向方向上，以正极材料颗粒的表面为厚度的0点，厚度范围在0.5-20μm的区域。正极材料颗粒中表层区以外的区域，即为中心区。上述关于表层区以及中心区的定义，同样适用于正极材料颗粒前驱体。
根据本申请的实施例，上述正极材料颗粒前驱体可以是由前面描述的锂氧化物纳米颗 粒堆积而成，表层区具有孔隙结构。后期在正极材料颗粒前驱体表层区的孔隙中填充硫单质，即可获得正极材料颗粒。硫单质形成在表层区，中心区中主体结构仍旧为锂氧化物构成，因此可以保证颗粒的整体机械强度，在后续制备电池的压实过程中，不会发生大范围的颗粒崩塌破碎。硫渗透的深度，可以通过控制表层区的厚度来实现。
具体的，上述锂氧化物纳米颗粒选自棒状锂氧化物、块状锂氧化物中的一种或几种，锂氧化物纳米颗粒通过堆积形成表层区具有孔隙的正极材料颗粒前驱体。锂氧化物纳米颗粒的长度为0.5-2μm，宽度为200-500nm，长径比为2～40。由于锂氧化物纳米颗粒具有较大的长径比，因此堆积形成的孔隙的直径较小，且具有一定深度，孔隙的尺寸可以为50-1000nm，如可以为500nm。硫单质填充在孔隙中，可以有效防止电解液进入孔隙内部，溶解填充的硫。正极材料颗粒前驱体在填充硫单质之后形成的正极材料颗粒，表层区中填充的硫单质可以填满表层区中的孔隙，也可以部分填满表层区中的孔隙，即正极材料颗粒的表层区，除去被硫单质填充的部分，还可以具有部分孔隙结构。正极材料颗粒中表层区中的孔隙的尺寸，可以与正极材料颗粒前驱体(填充硫单质之前)中的孔隙尺寸相似。
发明人发现，通过调节锂氧化物纳米颗粒以及由其堆积而成的正极材料颗粒前驱体的形貌，例如锂氧化物纳米颗粒的尺寸、锂氧化物纳米颗粒之间的间隙、正极材料颗粒前驱体的粒径等，可以令硫原子更好地填充在表层区的孔隙中，从而获得可观的填充比例和填充稳定性，进而可以提高该正极材料的比容量。并且，调节表层区孔隙的尺寸，可以有效缓解电解液溶解正极材料中的硫原子，从而可以获得很好的循环稳定性，进而可令使用该正极材料的电池具有长期的优异的日历寿命。日历寿命可以为将该电池在某参考温度下、开路状态达到寿命终止所需的时间，即电池在备用状态下的寿命。具有上述形貌的颗粒，还可以令该正极材料的整体能量密度提升的同时，不降低材料整体的压实密度，从而有利于提高正极材料的体积能量密度，该正极材料在应用于锂离子电池中时，也可以获得较为可观的电池性能。需要特别说明的是，在本申请中，术语“锂氧化物纳米颗粒”，或称为“一次粒子”，特指在长度、直径以及宽度等任意一个维度上的尺寸为纳米级别即可。
发明人发现，与片状或是颗粒状的锂氧化物纳米颗粒相比，具有上述尺寸的棒状或块状的锂氧化物纳米颗粒在堆积形成正极材料颗粒前驱体之后，可以令表层区具有适于容纳硫单质的孔隙，且孔隙可以较为规则。由锂氧化物纳米颗粒堆积而成的正极材料颗粒前驱体的形状不受特别限制，例如，正极材料颗粒前驱体可以为球形、菱形、椭球形中的一种。
根据本申请的一些实施例，以正极材料的总质量为基准，硫单质的含量可以为5wt％-50wt％，锂氧化物的含量为50wt％-95wt％。根据本申请的具体实施例，硫的含量可以根据前面所述的表层区的孔隙来确定。发明人发现，硫单质的负载量过高，过量硫无法在孔隙中填充就会单独成核，造成材料阻抗增大，更易于溶于电解液中，发生严重的电化学劣化。 根据本申请的具体实施例，硫单质含量在上述范围内时，可以防止硫单质单独成核。例如，硫单质的含量可以为10wt％-30wt％。硫单质可以通过熔融渗透进入孔隙中，不同于一般的物理混合，通过熔融渗透进入孔隙中硫单质，在锂氧化物颗粒的内部也可以检测到硫的存在。
根据本申请的一些实施例为了提高该正极材料的性能，正极材料颗粒的外表面还可以形成有包覆层。根据本申请的具体实施例，包覆层的材料可以包括碳材料、二氧化锡、二氧化锰、二氧化钛、四氧化三钴、五氧化二钒、二硫化铁、二硫化铜、二硫化钴以及三硫化铋中的任意一种或几种。
根据本申请的具体实施例，以正极材料的总质量为基准，包覆层的含量为0.1wt％-10wt％。
根据本申请的具体实施例，采用碳包覆层，碳包覆层形成在上述填充有硫的锂氧化物颗粒的外表面。由此，可以提高该正极材料的性能。关于碳包覆层的具体厚度、材料、形貌以及合成方法均不受特别限制，本领域技术人员可以根据实际情况，选择熟悉的材料和方法，形成碳包覆层。由此，可阻挡电解质进入锂氧化物颗粒的孔隙内部，缓解电解质对硫单质的溶解。
根据本申请的具体实施例，包覆层为二氧化钛包覆层。正极材料中锂氧化物、硫、二氧化钛的质量比可以为(90～45)：(5～50)：(2～8)。例如，具体的，正极材料颗粒中，二氧化钛的包覆量所占比例可以为5wt％。
在本申请的另一方面，本申请提出了一种制备正极材料的方法。该正极材料可以具有前面描述的正极材料的全部特征以及优点。具体的，参考图1，该方法包括：
S100：形成正极材料颗粒前驱体，所述正极材料颗粒前驱体具有中心区和表层区
根据本申请的实施例，在该步骤中，形成正极材料颗粒前驱体。如前所述，该正极材料颗粒前驱体可以由锂氧化物纳米颗粒堆叠而成。锂氧化物纳米颗粒呈棒状或块状，构成的正极材料颗粒前驱体表层区具有适于硫单质填充的孔隙。该正极材料颗粒前驱体的微观形貌适于硫元素的填充，表层区孔隙较小，可防止硫溶解于电解液中，且最终获得的正极材料的颗粒结构不会降低材料的整体压实密度，从而提高该正极材料的体积能量密度。
根据本申请的具体实施例，参考图2，上述正极材料颗粒前驱体可通过以下步骤获得：
S110：形成核心前驱体
根据本申请的实施例，在该步骤中，含有金属离子的溶液、络合剂以及沉淀剂在搅拌的条件下进行混合，以获得前驱体溶液。并通过共沉淀，获得核心前驱体。其中，沉淀剂、络合剂和含有金属的溶液是逐步加反应容器中的。
如前所述，由锂氧化物纳米级颗粒堆积而成的核心前驱体(后续和锂源进行锂化的过 程不会显著影响颗粒的微观形貌)，可以具有较为适于硫元素填充的孔隙。因此，在该步骤中，可通过调整搅拌的速度、反应温度、反应pH值，以及络合剂的浓度，控制核心前驱体的形貌。具体而言，逐渐加入的沉淀剂等溶液可以在核心前驱体形成的过程中提供剪切力，锂氧化物纳米颗粒逐渐生长堆积为核心前驱体。通过综合控制搅拌的速度、反应温度、反应pH值，以及络合剂的浓度，可以调控形成的纳米核心前驱体的尺寸和孔隙，从而控制最终获得的正极材料颗粒前驱体表层区孔隙的尺寸。具体而言，可以通过控制上述条件，使得锂化得到锂氧化物纳米颗粒的长度为0.5-2μm，宽度为200-500nm，纳米锂氧化物颗粒的长径比为2～40。尺寸在上述范围内的锂氧化物纳米颗粒，可以通过堆积形成表层区具有适于硫单质填充的孔隙的正极材料颗粒前驱体。根据本申请的一些实施例，可以通过控制上述条件，令正极材料颗粒前驱体表层区中孔隙的尺寸为50-1000nm，如可以为500nm。由此，不仅可以获得具有特定形貌的纳米锂氧化物颗粒(例如可以为棒状)，且堆积形成的正极材料颗粒前驱体也可以具有较为均一的孔隙分布，和较为理想的形貌。
根据本申请的实施例，上述含有金属离子的溶液可以由包含该金属元素的无机盐溶液提供。金属元素包括Mn、Al、Nb、Fe、Co、Ni中的至少之一，将金属盐溶液在搅拌状态下加入反应容器中。上述过程可以在加热的条件下进行，例如，可在30-60摄氏度下进行，如可以在40度、45度、50度、55度下进行，具体可将容器置于在40-60摄氏度的水浴中。上述金属盐溶液可以包括用于形成NCM或NCA材料的溶液(不含Li)，可以为含有镍的盐溶液、含有钴的盐溶液以及含有锰的盐溶液的至少之一，如可以为含有上述金属离子的硝酸盐溶液。制备过程中使用络合剂可以与金属离子形成稳定的络合物，进一步控制沉淀产生的速度，常用的络合剂为碱性溶液，例如可以为氨水。氨水的质量浓度可为5～15wt％。金属盐溶液的具体化学组分可以根据需要形成的锂氧化物中金属元素的含量来确定。关于正极材料颗粒前驱体的化学组分，前面已经进行了详细的描述，在此不再赘述。
根据本申请的实施例，在搅拌状态下，将上述金属盐溶液以及络合剂按照固定配比加入容器中。上述固定配比以及含有金属的溶液，是根据锂氧化物的化学组成而确定的。混合溶液中含有金属的溶液的总量、金属的化学组成均可根据具体需要合成的锂氧化物的化学组成确定。发明人发现，搅拌的速度对于形成的纳米锂氧化物前驱体颗粒的尺寸，以及核心前驱体的形貌具有重要影响，可影响最终的正极材料颗粒的形貌。搅拌的搅拌速度为300-1000rpm/min时，可以获得如前所述的纳米颗粒。具体的，搅拌速度可以为600-800rpm/min。
根据本申请的实施例，沉淀剂可以是可令金属离子发生沉淀的试剂，如可以为氢氧化物的水溶液，如氢氧化钾、氢氧化钠等。沉淀剂可以通过可调速变送器泵入含有混合溶液的容器中。沉淀剂的泵入速度可以是按照反应体系(即前驱体溶液)的pH值来的，反应过 程中pH值控制在一个固定值，或者反应的初期中期晚期为固定值。反应过程中随着氢氧化物共沉淀的形成，会消耗体系中的氢氧根，体系pH值降低，因此需要随之加入沉淀剂，保证前驱体溶液的pH值。当pH值上升到设定值的时候，则停止沉淀剂的加入。通常，整个反应过程中pH值不变化，也就是沉淀剂泵入速度不变化，加入的沉淀剂和金属盐溶液的比例大约为2：1。或者，根据本申请的另一些实施例，也可以有反应的早期控制pH较低，后续提高pH值。
类似的，上述沉淀剂加入的过程也可以在30-60摄氏度下进行。如，可以在40摄氏度下进行。本领域技术人员可以根据锂氧化物的具体化学组成、混合溶液的总量以及混合溶液中络合剂和金属盐溶液的比例确定沉淀剂的加入量。根据本申请的具体实施例，加入的沉淀剂的量可以控制获得的前驱体溶溶液pH为10-12，如控制pH值为11。
经上述操作获得的前驱体溶液可在45-60摄氏度下静置15-30小时，以发生共沉淀反应。由此，可以简便的获得核心前驱体。
S120：核心前驱体锂化
根据本申请的实施例，在该步骤中，将前面获得的核心前驱体以及锂源进行混合，并进行焙烧处理，以便将核心前驱体锂化，从而获得正极材料颗粒前驱体，正极材料颗粒前驱体包括中心区，和位于所述中心区外部的表层区。
根据本申请的实施例，在该步骤中，本领域技术人员可以根据实际需要，选择适当的含锂试剂。例如，根据本申请的具体实施例，可以选择锂的无机盐，如硝酸盐。核心前驱体以及锂源的混合比例可以根据锂氧化物的化学组成确定。焙烧处理可以是在600-800摄氏度的焙烧温度下进行的。
根据本申请的一些实施例，核心前驱体的锂化可以是将前面获得的核心前驱体，与锂盐(即锂源)在水中进行混合。放置一段时间后，通过诸如过滤、烘干、蒸干等分离方法，分离出沉淀并烘干。将烘干过的沉淀在上述焙烧温度下进行焙烧处理，焙烧处理的时间可以为10-18小时，如可以为12小时。
为了提高获得的正极材料颗粒前驱体的质量，在形成较好的锂氧化物晶型(如三元晶型)的同时，保持前面形成的核心前驱体中的孔隙，上述焙烧处理之后还可以包括退火的步骤。并且，可以令上述焙烧处理过程为急速升温至焙烧处理温度，然后恒温较短时间后，退火。可以具体包括：
在较短时间内，如15分钟～1小时内，快速升温至焙烧温度，恒温保持0.5-2小时，随后迅速降温至室温。迅速降温时可以为直接将样品置于室温(温度可为0～40摄氏度)环境中。迅速降温的降温时间可以为20分钟～1小时，退火处理的温度可以为450～700摄氏度，如可以为500摄氏度，退火时间可以为3-8小时，如可以为5小时。
S200：将硫单质填充在表层区中
根据本申请的实施例，在该步骤中，将硫单质填充在正极材料颗粒前驱体表层区的孔隙中，得到含有硫单质的正极材料颗粒。根据本申请的具体实施例，该步骤可以是通过将预先制备得到的正极活性材料的前驱体颗粒，与硫源进行混合，随后进行熔融固化处理而实现的。硫单质可以通过熔融渗透进入孔隙中，不同于一般的物理混合，通过熔融渗透进入孔隙中硫单质，在锂氧化物颗粒的内部可以检测到硫的存在，单纯的物理混合，是无法实现这一点的。且单纯的物理混合后，硫和正极材料颗粒的附着力较差，容易在后续失去电接触，导致电化学失效；也更加容易溶于电解液中，造成严重的穿梭效应，穿梭效应，指的是在充放电过程中，正极产生的多硫化物(Li2Sx)中间体溶解到电解液中，并穿过隔膜，向负极扩散，与负极的金属锂直接发生反应，最终造成了电池中有效物质的不可逆损失、电池寿命的衰减、低的库伦效率。。
根据本申请的实施例，上述正极材料颗粒前驱体与硫源可按质量比为(8-12)：(0.5-2)进行混合。例如，可以按照5:1、6:1、7:1、8:1、9:1、10:1、11:1、12:1、13:1、14:1、15:1、16:1、17:1、18:1、19:1、20:1、21:1、22:1、23：1:等的质量比进行混合。上述硫源可以为硫单质。熔融固化处理的处理温度可为120-180摄氏度，如可以没130、140、150、160、170摄氏度等，处理时间可为10-15小时，如11、12、13、14小时等。具体地，可以为在150摄氏度下，处理12小时。由此，可以简便的将硫填充至前面形成的锂氧化物颗粒的孔隙中。
根据本申请的实施例，上述熔融固化处理还可以是在惰性气氛下进行的。或者，可以在惰性气氛下，惰性气氛包括氮气、氩气等，在密封加压的容器中进行的，容器的压力可以为5-12MPa。如可以为8MPa例如，根据本申请的具体实施例，可以将锂氧化物颗粒和硫源混合后，置于密封容器中，并向容器中冲入惰性气体进行加压。加压后的压力可以为10MPa、8MPa等。
根据本申请的实施例，为了提高利用上述方法制备的正极材料的性能，在熔融固化处理之后，参考图3，还可以包括：
S300：形成包覆层
根据本申请的实施例，在该步骤中，在正极材料颗粒外形成包覆层。形成包覆层的具体方法、包覆层的化学组成，本领域技术人员可以根据实际情况进行选择，如可选择碳材料、二氧化锡、二氧化锰、二氧化钛、四氧化三钴、五氧化二钒、二硫化铁、二硫化铜、二硫化钴或三硫化铋中的任意一种或几种。碳材料可以为石墨、科琴黑、石墨烯、碳纳米管、活性炭等，通过包括但不限于喷雾干燥、水热法等方式形成。由此，可以进一步将硫单质与电解液隔离开，从而可提高利用该正极材料的电池的循环性能以及稳定性。
在本申请的又一方面，本申请提出了一种正极材料。根据本申请的实施例，该正极材料是利用前面所述的方法制备的。由此，该正极材料具备前面所述的方法获得的正极材料所具备的全部特征以及优点，在此不再赘述。
在本申请的又一方面，本申请提出了一种锂离子电池。该锂离子电池包括前面所述的正极材料。由此，该锂离子电池具备前面所述的正极材料所具备的全部特征以及优点，在此不再赘述。总的来说，该锂离子电池具有较高的能量密度，且循环寿命较好。
在本申请的又一方面，本申请提出了一种车辆。根据本申请的实施例，该车辆包括前面所述的锂离子电池。例如，可包括多个由前面所述的锂离子电池构成的电池组。由此，该车辆具备前面所述的锂离子电池所具备的全部特征以及优点，在此不再赘述。
下面通过具体实施例对本申请进行说明，需要说明的是，下面的具体实施例仅仅是用于说明的目的，而不以任何方式限制本申请的范围，另外，如无特殊说明，未具体记载条件或者步骤的方法均为常规方法，所采用的试剂和材料均可从商业途径获得。
以下原料中，硝酸镍购自深圳博莱恩，硝酸钴购自深圳博莱恩，硝酸锂购自深圳博莱恩，氨水购自深圳博莱恩，硝酸锂购自深圳博莱恩，硫单质购自阿拉丁。
实施例1制备正极材料
(1)将50mmol硝酸镍和50mmol硝酸钴溶于100g水中，形成盐液，将该盐液在搅拌(搅拌速度500rpm)状态下泵入水热反应釜，随后在10分钟内，匀速加入5g的氨水(浓度为10重量％)，氨水按照和盐液匀速泵入。并加入氢氧化钠至调节pH为11。以在30摄氏度下进行共沉淀反应24小时，过滤得到核心前躯体。
(2)将步骤1)中得到的核心前驱体和硝酸锂按照质摩尔比1～1.2在水中进行混合得到沉淀物，过滤分离出沉淀物后取出并烘干，再在700摄氏度下焙烧10小时。得到三元正极材料颗粒前驱体。
(3)将三元正极材料颗粒前驱体和硫单质按照质量比例为10:1进行混合，然后在马弗炉中热处理，在150摄氏度之间进行反应12小时，取出后烘干粉碎得到三元-硫复合正极材料颗粒。
实施例2制备正极材料
(1)将50mmol硝酸镍和50mmol硝酸钴溶于100g水中，形成盐液，将该盐液在搅拌(搅拌速度500rpm)状态下泵入水热反应釜，随后在10分钟内，匀速加入5g的氨水(浓度为10重量％)，氨水按照和盐液匀速泵入。并加入氢氧化钠至调节pH为11。以在30摄氏度下进行共沉淀反应24小时，过滤得到核心前躯体。
(2)将步骤1)中得到的核心前驱体和硝酸锂按照摩尔比为1～1.2在水中进行混合得到沉淀物，过滤分离出沉淀物后取出并烘干，再在700摄氏度下焙烧10小时。得到三元正 极材料颗粒前驱体。
(3)将三元正极材料颗粒前驱体和硫单质按照质量比例为10:0.5进行混合，混合后，在水热反应釜中进行反应，温度为150摄氏度。反应时间为12小时。
实施例3制备正极材料
(1)将50mmol硝酸镍和50mmol硝酸钴溶于100g水中，形成盐液，将该盐液在搅拌(搅拌速度500rpm)状态下泵入水热反应釜，随后在10分钟内，匀速加入5g的氨水(浓度为10重量％)，氨水按照和盐液匀速泵入。并加入氢氧化钠至调节pH为11。以在30摄氏度下进行共沉淀反应24小时，过滤得到核心前躯体。
(2)将核心前驱体和硝酸锂在水中按照摩尔比1～1.2进行混合得到沉淀物，而后取出并烘干。在40分钟内将沉淀物升温至700摄氏度，再在700摄氏度下焙烧1小时，然后取出，在30分钟内降温到室温，继而在500摄氏度下退火5小时。得到三元正极材料颗粒前驱体。
(3)，将三元正极材料颗粒前驱体和硫单质按照质量比例为8:1进行混合，混合后，在水热反应釜中进行反应，温度为150摄氏度。反应时间为12小时。
实施例4制备正极材料
(1)将50mmol硝酸镍和50mmol硝酸钴溶于100g水中，形成盐液，将该盐液在搅拌状态(搅拌速度500rpm)下泵入水热反应釜，而后缓慢加入5g的氨水(浓度为10重量％)，并加入氢氧化钠至调节pH为11。以在30摄氏度下进行共沉淀反应24小时，过滤得到核心前躯体。
(2)将核心前驱体和硝酸锂在水中按照摩尔比1～1.2进行混合，而后取出并烘干，再在700摄氏度下焙烧1小时，然后在700度时取出，急速降温到室温(室温即常规的室内温度，可以为10-35℃，例如可以为25℃)，继而在500摄氏度下退火5小时。得到三元正极材料颗粒前驱体。
(3)将前面所述的三元正极材料颗粒前驱体、硫单质进行混合，按照质量比例为14:1，然后放入水热反应釜中，冲入惰性氩气加压密封，压力范围为10MPa，在150摄氏度之间进行反应12小时，取出后烘干粉碎得到三元-硫复合正极材料颗粒。
实施例5
(1)将50mmol硝酸镍和50mmol硝酸钴溶于100g水中，形成盐液，将该盐液在搅拌(搅拌速度500rpm)状态下泵入水热反应釜，随后在10分钟内，匀速加入5g的氨水(浓度为10重量％)，氨水按照和盐液匀速泵入。并加入氢氧化钠至调节pH为11。以在30摄氏度下进行共沉淀反应24小时，过滤得到核心前躯体。
(2)将步骤(1)中得到的核心前驱体和硝酸锂按照摩尔比为1～1.2在水中进行混合得 到沉淀物，过滤分离出沉淀物后取出并烘干，再在700摄氏度下焙烧10小时。得到三元正极材料颗粒前驱体。
(3)将三元正极材料颗粒前驱体和硫单质按照质量比例为10:2进行混合，混合后，在水热反应釜中进行反应，温度为150摄氏度。反应时间为12小时，得到三元正极材料颗粒。
(4)在40摄氏度加热搅拌条件下，将步骤(3)中得到的三元正极材料分散在正丁醇中，加入定量钛酸异丙酯(按照二氧化钛包覆量为5wt％确定)，继续搅拌得到最终产物，洗涤烘干后得到具有二氧化钛包覆的三元-硫复合正极材料颗粒。
实施例6
(1)将50mmol硝酸镍和50mmol硝酸钴溶于100g水中，形成盐液，将该盐液在搅拌(搅拌速度500rpm)状态下泵入水热反应釜，随后在10分钟内，匀速加入5g的氨水(浓度为10重量％)，氨水按照和盐液匀速泵入。并加入氢氧化钠至调节pH为11。以在30摄氏度下进行共沉淀反应24小时，过滤得到核心前躯体。
(2)将步骤1)中得到的核心前驱体和硝酸锂按照摩尔比为1～1.2在水中进行混合得到沉淀物，过滤分离出沉淀物后取出并烘干，再在700摄氏度下焙烧10小时。得到三元正极材料颗粒前驱体。
步骤(3)中，将三元正极材料颗粒前驱体和硫单质按照质量比例为12:1进行混合，，混合后，在水热反应釜中进行反应，温度为150摄氏度。反应时间为12小时，得到三元正极材料颗粒。
(4)将石墨粉和步骤(3)获得的三元正极材料颗粒按照摩尔比为1～1.2进行混合，并通过喷雾干燥，在填充有硫单质的三元-硫复合正极材料颗粒表面形成碳包覆层。
对比例1
按照实施例1的方式制备得到三元正极材料颗粒前驱体，然后将得到的三元正极材料颗粒前驱体、硫单质按照质量比10:1直接进行混合得到三元-硫复合正极材料颗粒。
对比例2
(1)按照实施例中的步骤(1)制备得到核心前躯体；
(2)将核心前驱体和硝酸锂按照摩尔比为1～1.2在水中进行混合得到沉淀物，过滤分离出沉淀物后并烘干，再在700摄氏度下焙烧1小时，然后在700度时取出，急速降温到室温(室温即常规的室内温度，可以为10-35℃，例如可以为25℃)，继而在500摄氏度下退火5小时。得到三元正极材料颗粒前驱体。
(3)将所述的三元正极材料颗粒前驱体、硫单质按照摩尔比为1～1.2直接进行混合。
性能测试
1、形貌表征
利用扫描电子显微镜(JEOL)对上述实施例1获得的样品，以及制备过程中的中间体的形貌进行观察。
参考图4，实施例1获得的核心前驱体(未进行锂化)为有5～8μm左右的球形颗粒，由直径为100nm左右的棒状颗粒堆积而成。棒状颗粒的长度在0.5～5μm不等，堆积形成的球形颗粒中的孔道在500nm～1μm左右。
实施例1中获得的三元活性材料的形貌如图5所示。经过锂化后，球形颗粒的孔径得到了进一步的优化，与图4对比可知，锂化后的球形颗粒的孔径分布更为均匀，进而有利于硫单质的填充。
实施例1中填充有硫单质(即获得的正极材料)的形貌如图6所示。对比可知，硫单质可以较为均匀的填充至锂氧化物颗粒的孔隙中，填充量较为可观。测试结果见表1。
2、硫含量测试
对上述实施例以及对比例获得的样品进行含硫量测试。具体测试方法及步骤：使用碳硫分析仪方法测试材料整体的硫含量。测试结果见表1。
表1.样品的测试结果
Figure PCTCN2019095353-appb-000001
由测试结果可知，上述实施例以及对比例均具有较为可观的含硫量。并且，由于两个对比例中的硫单质以及三元正极材料是直接进行混合的，未经过加热处理，因此直接进行硫含量测试时，反而显示了较高的硫含量结果。
3、体积能量密度测试
具体测试方法为：分别取5g上述实施例以及对比例中的获得的正极材料，与正极导电剂炭黑和正极粘结剂PVDF按照质量比94：3：3混合放入直径为2cm的模具之中，以10Mpa的压力压制粉体。并通过以下公式计算得到正极活性材料的体积能量密度值：
在上述压力下粉体能够压缩的最高高度为h，粉体的压实密度为ρ＝5/πr 2h。
能量密度计算公式如下：
能量密度＝比容量*充电平均电压*粉体的压实密度。
比容量＝容量/活性物质质量
充电平均电压＝充电电流*充电时间/充电总容量
测量结果如表2所示：
表2.样品能量密度量测试结果
Figure PCTCN2019095353-appb-000002
由测试结果可知，虽然对比例1以及对比例2在硫含量测试中具有较高的硫含量，但其能量密度要显著低于实施例的样品。这一方面是由于硫含量测试时样品为正极材料，因此直接混合形成的对比例样品中，有部分硫元素是通过物理吸附吸附在三元材料表面的。而正极材料经过上述制备电池的过程中(如涂覆、干燥、吹灰等操作)，物理吸附的硫单质会有一部分损失，而经过加热处理的实施例1～实施例6则不会出现对比例的上述情况。并且，正极样品和电解质接触之后，由于对比例1以及对比例2制备的正极材料不能够具有实施例1～实施例6的颗粒的形貌，因此无法缓解其中所负载的硫单质在和电解质接触之后，发生溶解的问题：对比例1在合成核心前驱体时未进行搅拌，不能较好控制核心前驱体形貌，且核心前驱体锂化时仅进行了简单的一步加热处理，核心前驱体的形貌也不能够较好的保持，从而最终获得的正极材料颗粒不具有表层区。对比例2中虽然在锂化过程中通过急速降温和退火处理，三元正极材料颗粒前驱体保持了一定的形貌(外部1-5微米厚度范围内具有一定孔隙结构)，但硫单质仅附着在表面，因此最终正极材料的表层仅含有硫，不能较好的防止硫单质的溶解；且硫源没有通过加热处理，而是直接混合制备的，因此硫和三元附着力较差，容易在后续失去电接触，导致电化学失效，导致能量密度不理想。并且，实施例1～实施例6的微米颗粒的形貌也可以在压实处理之后，保持材料整体的压实密度，进而更加有利于获得较为可观的能量密度。
在本说明书的描述中，参考术语“一个实施例”、“另一个实施例”等的描述意指结合该实施例描述的具体特征、结构、材料或者特点包含于本申请的至少一个实施例中。在本说明书中，对上述术语的示意性表述不必须针对的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任一个或多个实施例或示例中以合适的方式结合。此外，在不互相矛盾的情况下，本领域技术人员可以将本说明书中描述的不同实施例或示例以及不同实施例或示例的特征进行结合和组合。
尽管上面已经示出和描述了本申请的实施例，上述实施例是示例性的，不能理解为对本申请的限制，本领域的普通技术人员在本申请的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (19)

  1. 一种正极材料，包括正极材料颗粒，所述正极材料颗粒包括中心区和表层区，所述中心区含有锂氧化物，所述表层区含有所述锂氧化物和硫单质；
    所述锂氧化物包括δLiNi mCo nX (1-m-n)O 2·(1-δ)Li 2MO 3，
    其中0≤δ≤1，X包括选自Mn、Al、Nb、Fe中的至少之一，M包括选自Mn、Al、Nb、Fe、Co、Ni中的至少之一，0≤m＜1，0≤n＜1，0≤m+n＜1。
  2. 根据权利要求1所述的正极材料，所述正极材料颗粒的平均粒径为5-50μm，所述表层区的厚度为0.5-20μm。
  3. 根据权利要求1或2所述的正极材料，所述正极材料颗粒为球形、菱形、椭球形中的一种。
  4. 根据权利要求1-3中任一项所述的正极材料，以所述正极材料颗粒的总质量为基准，所述硫单质的含量为5wt％-50wt％，所述锂氧化物的含量为50wt％-95wt％。
  5. 根据权利要求1-4中任一项所述的正极材料，所述中心区的锂氧化物是由锂氧化物纳米颗粒堆积形成的，所述锂氧化物纳米颗粒包括选自棒状锂氧化物、块状锂氧化物中的一种或几种。
  6. 根据权利要求5所述的正极材料，所述锂氧化物纳米颗粒的长度为0.5-2μm，宽度为200-500nm，长径比为2～40。
  7. 根据权利要求1所述的正极材料，所述正极材料颗粒的外表面形成有包覆层。
  8. 根据权利要求7所述的正极材料，形成所述包覆层的材料包括碳材料、二氧化锡、二氧化锰、二氧化钛、四氧化三钴、五氧化二钒、二硫化铁、二硫化铜、二硫化钴以及三硫化铋中的任意一种或几种。
  9. 根据权利要求7所述的正极材料，以所述正极材料的总质量为基准，所述包覆层的含量为0.1wt％-10wt％。
  10. 根据权利要求7所述的正极材料，所述包覆层是二氧化钛形成的，所述正极材料中，所述锂氧化物、所述硫单质、所述二氧化钛的质量比为(90～45)：(5～50)：(2～8)。
  11. 根据权利要求1-10任一项所述的正极材料，所述表层区具有孔隙，所述硫单质填充在所述孔隙中。
  12. 根据权利要求1-11任一项所述的正极材料，所述锂氧化物包括镍钴锰三元材料、镍钴铝三元材料以及富锂材料的至少之一。
  13. 一种制备正极材料的方法，所述正极材料包括正极材料颗粒，所述方法包括：
    将含有金属离子的溶液、络合剂以及沉淀剂在搅拌的条件下进行混合，并通过共沉淀 处理，获得核心前驱体，将所述核心前驱体以及锂源进行混合并进行焙烧处理，以便获得由锂氧化物纳米颗粒堆积而形成的正极材料颗粒前驱体，所述正极材料颗粒前驱体包括中心区，和位于所述中心区外部的表层区，
    其中，所述金属包括Mn、Al、Nb、Fe、Co、Ni中的至少之一，所述锂氧化物纳米颗粒包括δLiNi mCo nX (1-m-n)O 2·(1-δ)Li 2MO 3，其中0≤δ≤1，X包括选自Mn、Al、Nb、Fe中的至少之一，M包括选自Mn、Al、Nb、Fe、Co、Ni中的至少之一，0≤m＜1，0≤n＜1，0≤m+n＜1；
    将所述正极材料颗粒前驱体与硫源进行混合，并进行熔融固化处理，以便将硫单质填充在所述表层区中，并获得所述正极材料颗粒。
  14. 根据权利要求13所述的方法，形成所述正极材料颗粒前驱体包括：控制所述锂氧化物纳米颗粒的长度为0.5-2μm，宽度为200-500nm，所述锂氧化物纳米颗粒的长径比为2～40。
  15. 根据权利要求13或14所述的方法，所述表层区具有孔隙，所述硫单质填充在所述表层区的所述孔隙中；形成所述正极材料颗粒前驱体包括：控制所述孔隙的尺寸为50-1000nm。
  16. 根据权利要求13-15任一项所述的方法，形成所述核心前驱体包括：
    在30-60摄氏度条件下，所述共沉淀处理过程中溶液的pH为10-12，所述搅拌的搅拌速度为300-1000rpm/min，所述络合剂的质量百分数为5～15wt％。
  17. 根据权利要求13-16任一项所述的方法，所述正极材料颗粒前驱体以及所述硫源按质量比为(8-12)：(0.5-2)进行混合，所述熔融固化处理的处理温度为120-180摄氏度，处理时间为10-15小时。
  18. 一种锂离子电池，包括权利要求1-12任一项所述的正极材料，或者权利要求13-17任一项所述的方法所制备的正极材料。
  19. 一种车辆，包括权利要求18所述的锂离子电池。
PCT/CN2019/095353 2018-07-10 2019-07-10 正极材料及其制备方法、锂离子电池和车辆 WO2020011179A1 (zh)

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