WO2020011177A1 - 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

Info

Publication number
WO2020011177A1
WO2020011177A1 PCT/CN2019/095351 CN2019095351W WO2020011177A1 WO 2020011177 A1 WO2020011177 A1 WO 2020011177A1 CN 2019095351 W CN2019095351 W CN 2019095351W WO 2020011177 A1 WO2020011177 A1 WO 2020011177A1
Authority
WO
WIPO (PCT)
Prior art keywords
positive electrode
electrode material
sulfur
hollow structure
material according
Prior art date
Application number
PCT/CN2019/095351
Other languages
English (en)
French (fr)
Inventor
胡栋杰
魏昊
Original Assignee
比亚迪股份有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 比亚迪股份有限公司 filed Critical 比亚迪股份有限公司
Priority to EP19834823.7A priority Critical patent/EP3823064A4/en
Priority to US17/259,106 priority patent/US20210292186A1/en
Publication of WO2020011177A1 publication Critical patent/WO2020011177A1/zh

Links

Images

Classifications

    • 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
    • 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
    • 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
    • H01M4/38—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
    • C01P2004/30—Particle morphology extending in three dimensions
    • C01P2004/32—Spheres
    • C01P2004/34—Spheres hollow
    • 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
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer
    • 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 a sulfur simple substance and secondary particles formed by primary particle accumulation, the secondary particles have a hollow structure, and the sulfur simple substance fills a gap between the primary particles and the hollow structure;
  • Primary particles contain lithium oxide, which includes ⁇ LiNi m Co n X (1-mn) O 2 ⁇ (1- ⁇ ) Li 2 MO 3 , where 0 ⁇ ⁇ ⁇ 1, and X includes a member selected from Mn, Al
  • At least one of Nb, Fe, and M include at least one selected from Mn, Al, Nb, Fe, Co, and Ni, 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1, 0 ⁇ m + n ⁇ 1 .
  • the hollow structure of the secondary particles is suitable for the filling of sulfur element.
  • the shell structure of the secondary particles formed by the primary particle stacking is more compact, the porosity is lower, and the sulfur can be prevented from dissolving in the electrolyte.
  • the structure does not reduce the overall compaction density of the material, thereby increasing the volume energy density of the cathode material.
  • the present application proposes a method for preparing a positive electrode material.
  • the method comprises: adding a solution containing a metal ion, a complexing agent, and a precipitant into a reaction container under stirring conditions, and co-precipitating at a pH value of 11-12 to form a primary particle precursor.
  • the primary particle precursors are stacked to form a core precursor, and then the primary particle precursors continue to be stacked at a pH value of 9-10.5 to obtain secondary particle precursors; and the secondary particle precursors are mixed with a lithium source, And roasting treatment is performed to obtain secondary particles having a hollow structure; the secondary particles are mixed with a sulfur source, and melt-solidification treatment is performed so as to fill the hollow element with sulfur; wherein the secondary The particles contain a shell layer for defining a hollow structure, the shell layer being formed by the accumulation of primary particles; the primary particles contain lithium oxide, which 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, Al, Nb, Fe, Co, and Ni At least one of 0, m ⁇ 1, 0 ⁇ n ⁇ 1, 0 ⁇ m + n ⁇ 1.
  • the secondary particles obtained by this method have a micro-morphology suitable for sulfur element filling.
  • the outer shell of the hollow structure of the secondary particles is densely packed. Under high temperature conditions, liquid sulfur can enter the internal pores, and the tightly structured outer shell can The polysulfide intermediate is prevented from being dissolved in the electrolytic solution, and the particle structure of the secondary particles does not reduce the overall compacted density of the material, so that the volume energy density of the positive electrode material can be increased.
  • 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 secondary particle having a hollow structure prepared in an example of the present application
  • FIG. 5 shows a scanning electron microscope image of a cathode material prepared in an example of the present application.
  • the present application proposes a sulfur-containing cathode material.
  • the positive electrode material includes sulfur simple substance and secondary particles formed by the accumulation of primary particles.
  • the secondary particles have a hollow structure, and the sulfur simple substance fills the gap between the primary particles and the hollow structure.
  • the primary particles contain lithium oxide.
  • the above secondary particle hollow structure is suitable for filling with sulfur element.
  • the primary particles in the shell layer are densely packed to prevent sulfur from dissolving in the electrolyte, and the structure of the secondary particles does not reduce the overall compaction density of the material, so that The volume energy density of the positive electrode material is increased.
  • the specific chemical composition of the lithium oxide is not particularly limited, and a person 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. More specifically, 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 that satisfies the above-mentioned chemical composition can relatively easily obtain the above-mentioned secondary particles by controlling the synthesis process.
  • 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
  • Nickel-cobalt-aluminum (NCA) ternary materials can be LiNi 0.8 Co 0.15 Al 0.05 O 2 and so on.
  • the lithium oxide may include LiNi 1-xy Co x Mn y O 2 , where Mn may be replaced by any one of Al, Nb, and Fe, or may contain Mn, Al, and Nb at the same time. , Fe, 2, 3, or 4, when containing more than Mn, Al, Nb, Fe, the total atomic content of multiple elements in Mn, Al, Nb, and Fe should be satisfied in the ternary material Satisfies LiNi 1-xy Co x Mn y O 2 .
  • the above secondary particles may be formed from nanoparticles containing lithium oxide, that is, primary particles are stacked.
  • the secondary particle hollow structure refers to a cavity region defined by a shell layer obtained by closely packing primary particles. Therefore, the secondary particles have a core-shell structure, and the shell layer obtained by the close packing of the primary particles is the "shell", and the hollow structure is the "core”.
  • the outer surface of the secondary particles with the core-shell structure is 0 thickness.
  • the average thickness of the shell layer can be 1-10 ⁇ m, such as 0.5-5 ⁇ m, or 2-3 ⁇ m.
  • the average particle diameter of the secondary particles is 5 -50 ⁇ m.
  • the shell layer is formed by the above-mentioned nano particles in a relatively close-packed manner, and the shell layer has certain pores, so that the sulfur elemental substance can enter the hollow structure to be filled through the pores.
  • the area within the shell of the secondary particles is the hollow structure cavity.
  • the particles are first stacked in a relatively loose manner, and then are stacked in a more compact manner. As a result, precursors with loose internal accumulation and relatively dense external accumulation are formed. By heating, a loose structure can be accumulated inside to form a hollow structure.
  • the average pore diameter of the hollow structure is larger than the gap between the primary particles in the secondary particles finally obtained.
  • the gap between the primary particles may be 0.02-1 ⁇ m, for example, 0.5 ⁇ m.
  • the hollow structure may be filled with sulfur simple substance, or may be partially filled with sulfur simple substance.
  • the content of sulfur element in the hollow structure is higher than the content of sulfur element in the space between the primary particles. That is to say, the sulfur element is mainly filled in the hollow structure. Based on the total mass of the positive electrode material, the sulfur element content in the hollow structure is 5-40 wt%; the sulfur element content in the gap between the primary particles is 0-15 wt%.
  • the shell layer can protect the sulfur elementary substance in the hollow structure, and prevent the small amount of sulfur elementary substance in the gap between the shell layers from being dissolved by the electrolyte during the cycle during actual use, resulting in the degradation of the performance of the positive electrode material.
  • the sulfur element in the shell gap can be effectively reduced.
  • the primary particles are selected from one or more of rod-shaped lithium oxide and bulk lithium oxide, and the primary particles are formed into a secondary particle precursor by stacking.
  • the specific morphology and size of the primary particles may not be particularly limited. Specifically, the length of the primary particles may be 0.5-2 ⁇ m, the width may be 200-500 nm, and the aspect ratio may be 2-40.
  • the above-mentioned primary particles are stacked in a relatively loose manner, and when the outer shell layer is formed, the primary particles are stacked in a relatively dense manner. Therefore, through subsequent simple heating treatment, secondary particles that are relatively loose in the middle, including the cavity, and that are densely packed on the periphery can be obtained.
  • the porosity of the secondary particles may be 20-30%.
  • a mercury intrusion test is performed on the secondary particle precursor before heating and the secondary particles formed with a hollow structure after heating.
  • the comparison test results show that the The pore size distribution is mainly in a small range, and no hollow part has been formed at this time, so the pores are mainly determined by the pores between the loosely packed primary particles and the pores between the densely packed primary particles at the periphery.
  • pores with a size of 2-10 ⁇ m accounted for the majority, indicating that a hollow structure was formed after the heat treatment.
  • nanoparticles or “primary particles”, specifically means that the dimension in any one dimension such as length, diameter, and width may be nanoscale.
  • shape of the secondary particles formed by stacking the nanoparticles is not particularly limited, and may be, for example, one of a spherical shape, a rhombic shape, and an ellipsoidal shape.
  • the content of sulfur in the positive electrode material is not particularly limited, and those skilled in the art can select according to actual conditions.
  • the content of sulfur element may be 2wt% -50wt%, and the content of lithium oxide may be 50wt% -98wt%.
  • the content of sulfur can be determined according to the volume of the hollow structure described above. The inventors found that the amount of sulfur element loaded is too high, and excessive sulfur easily causes damage to the main structure of the secondary particles.
  • the content of sulfur element may be 10 wt% to 30 wt%.
  • the sulfur element can be melt-infiltrated into the hollow structure of the core-shell structure.
  • the above-mentioned hollow structure has a shell with a dense structure and a complete covering of the hollow structure.
  • the sulfur element in the hollow structure can be better isolated from the electrolyte.
  • the shell layer that functions as an electrolyte barrier contains lithium oxide, which is different from a single positive electrode material that uses a coating layer such as a carbon material to separate sulfur simple substance.
  • the positive electrode material according to the embodiment of the present application can be formed by using lithium oxide.
  • the isolation structure prevents the elemental sulfur from being dissolved by the electrolyte while not reducing the overall compaction density and electrochemical performance of the cathode material.
  • the secondary particles having a hollow structure are first formed, and then the sulfur simple substance is filled in the hollow structure of the secondary particles. Therefore, on the one hand, the sulfur element can be completely filled with hollow structures or partially filled with hollow structures according to actual needs. No matter what the sulfur element is filled with, the outside of the sulfur element has a closed shell protection. Unlike a coated positive electrode material which is simply mixed with sulfur and a coating material (such as a powder of a positive electrode active material) and formed through post-processing (such as evaporation of a solvent, heating, etc.), the positive electrode material according to the embodiment of the application can be better Prevent the dissolution of sulfur element in the electrolyte.
  • a coating material such as a powder of a positive electrode active material
  • post-processing such as evaporation of a solvent, heating, etc.
  • the prior art also provides a structure of a sulfur-containing positive electrode material that uses a sulfur element as a core and forms a coating on the periphery of the core.
  • the positive electrode material of this structure does not contain a hollow structure. Once it occurs in actual use, Expansion or contraction, there is no buffer space inside the positive electrode.
  • a coating layer may be further formed on the outer surface of the secondary particles.
  • the material of the cladding layer is not particularly limited, and those skilled in the art may select familiar materials to form the cladding layer.
  • the material of the cladding layer may include a carbon material, tin dioxide, manganese dioxide, titanium dioxide, tricobalt tetroxide, vanadium pentoxide, iron disulfide, copper disulfide, cobalt disulfide, or three Any one or more of bismuth sulfide.
  • the content of the coating layer is 0.1 wt% to 10 wt% based on the total mass of the positive electrode material.
  • a carbon coating layer is used, and the carbon coating layer is formed on the outer surface of the secondary particles filled with sulfur. This can improve the electrochemical performance of the positive electrode material.
  • 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 inside of the secondary 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 may be 5 wt%.
  • 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:
  • the secondary particles are formed.
  • the secondary particles may be formed by stacking primary particles (nanoparticles).
  • the shells of the secondary particles are densely packed. Due to the hollow structure at the center, the porosity of the shells is lower than that of the central region.
  • the hollow structure of the secondary particles is suitable for the sulfur element filling, and the shell layer is densely packed, which can prevent sulfur from being dissolved in the electrolyte, and the particle structure does not reduce the overall compaction density of the material, thereby improving the positive electrode material. Volume energy density.
  • the detailed structure of the secondary particles has been described in detail above, and will not be repeated here.
  • the secondary particles may have a core-shell structure, and a shell layer obtained by closely packing the primary particles is a “shell”, and a hollow structure is a “core”.
  • the above-mentioned structure with a tightly packed surface and a cavity in the center can be obtained by controlling the reaction rate when the secondary particles are formed.
  • the above-mentioned secondary particles having a core-shell structure, that is, a porous microsphere structure in the center and a shell structure that is tightly coated on the outer layer the secondary particles can be obtained by the following steps:
  • S110 Co-precipitate a solution containing a metal ion, a complexing agent, and a precipitating agent at a pH value of 11-12 to form a primary particle precursor, and the primary particle precursors are stacked to form a core precursor.
  • a solution containing a metal ion, a precipitating agent, and a complexing agent are added to a reaction container (such as a hydrothermal reaction kettle or other container) under stirring conditions, and are co- Precipitation and co-precipitation formed primary particle precursors to accumulate core precursors.
  • the pH value of the reaction solution can be controlled to 11-12, so as to achieve rapid precipitation and form loosely accumulated nuclei.
  • the growth rate of the core precursors formed by co-precipitation can be controlled by adjusting the rate of addition of the metal ion solution and the complexing agent and the rate of adding the precipitant (which can be used to control the pH of the mixed solution). Speed and stacking speed.
  • the pumping speed or dropping speed of the metal ion solution, the complexing agent, and the precipitating agent can be controlled, and then the adding speed thereof can be controlled.
  • the reaction can be faster, forming a core precursor with a relatively loose accumulation.
  • the stirring speed 300-2000rpm
  • the reaction temperature 30-50 ° C
  • the reaction pH 11-12
  • the concentration of the complexing agent 0.01-0.03mol / L.
  • the gradually added precipitating agent can provide a shearing force during the formation of the core precursor, so that the primary particle precursor in the reaction container gradually grows and accumulates.
  • the above metal may be provided by a solution containing metal ions, and more specifically, may be provided by an inorganic salt solution containing a 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 metal salt solution and the complexing agent are added to the solvent with stirring to obtain a mixed solution.
  • 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 45 degrees, 50 degrees, and 55 degrees.
  • the container can be placed in a water bath at 40-60 degrees Celsius.
  • the metal salt solution may include a solution (non-Li) for forming NCM or NCA material, and may be at least one of a salt solution containing nickel, a salt solution containing cobalt, and a salt solution containing manganese. Ionic nitrate solution.
  • the complexing agent used in the preparation process can form a stable complex with metal ions to further control the rate of precipitation.
  • the 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 lithium oxide particles has been described in detail above, and will not be repeated here.
  • the above-mentioned metal salt solution, complexing agent, and precipitating agent are added to the container according to a fixed ratio in a stirred state.
  • the fixed ratio is determined according to the chemical composition of the lithium oxide.
  • the rate of addition of the above substances into the reaction vessel can be adjusted by those skilled in the art according to the volume of the reaction vessel and the total dose of the above substances. For example, the slower addition process described above can last 2-6 hours, such as 4 hours or 5 hours.
  • the precipitating agent may be a reagent capable of causing a precipitation reaction of the metal ion solution, mainly various alkaline solutions, including aqueous solutions of hydroxides, 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), and the pH value is controlled at a fixed value during 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 of the mixed solution can be controlled to be higher and higher than the subsequent stacking process, for example, it can be 12.0 or 11.0.
  • the core precursor is allowed to continue to accumulate under the condition of a pH value of 9-10.5, so as to obtain a secondary particle precursor.
  • a metal salt solution, a complexing agent, and a precipitant are supplied to the reaction vessel at a pH value of 9-10.5, so that the primary particle precursor is slowly precipitated to form a relatively Dense shell to obtain a secondary particle precursor.
  • the primary particle precursor can continue to be densely packed on the basis of the core precursor formed in step S110, so that During processing, a denser shell is formed.
  • the supply speed in this step may be 1/3 to 1/2 of the supply speed in step S110.
  • the stacking time at the second pH may be 10-25 hours, such as 20 hours.
  • the pH of the reaction solution can be controlled to be slightly lower than the aforementioned step of obtaining the core precursor by adjusting the amount of the precipitant added, for example, the pH can be controlled to 10 or 10.5. As a result, a surface structure with a relatively compact structure can be formed.
  • the above reactants can be all added to the reaction container within 18-24 hours (including the aforementioned time for obtaining the core precursor).
  • the secondary particle precursor and the lithium source obtained in step S120 are mixed and subjected to a baking treatment, so as to lithify the secondary particle precursor and form a hollow structure at the same time, thereby obtaining Secondary particles.
  • the specific type of the lithium source is not particularly limited, and those skilled in the art may select an appropriate lithium-containing reagent according to actual needs.
  • an inorganic salt of lithium such as a nitrate, may be selected.
  • the mixing ratio of the secondary particle precursor and the lithium source is also not particularly limited, and 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 secondary particle precursor may be mixing the secondary particle precursor obtained in step S120 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 inventors have discovered that the central region of the secondary particle precursor formed in step S120 is loose due to the accumulation of primary particles. Therefore, during the roasting process, a hollow structure with a cavity can be formed, and the densely packed shell layer also has a certain gap. Therefore, in the subsequent steps, the sulfur element can pass through the shell layer and enter the cavity for filling.
  • a core-shell structure with a compact surface layer stack and a cavity in the center can be obtained.
  • an annealing step may be further included after the baking process.
  • 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. Therefore, while maintaining the morphology of the secondary particles (core-shell structure particles) formed in step S130, a better ternary material crystal form can be obtained. 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.
  • the secondary particles are mixed with a sulfur source, and a melt-solidification process is performed so as to fill sulfur in the hollow structure.
  • the elemental sulfur can penetrate into the hollow structure through melt infiltration.
  • the secondary particles and the sulfur source may be mixed in 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. Thereby, the cavity formed in step S130 can be easily filled with sulfur.
  • the above-mentioned melt-solidification treatment may also be performed under an inert atmosphere.
  • the inert atmosphere may be nitrogen, argon, or the like, which is performed in a sealed and pressurized container, and the pressure of the container may be 5-12 MPa. If it can be 8MPa.
  • the secondary particles and the sulfur source may be mixed and then placed in a sealed container, and the container may be filled with an inert gas for pressurization. The pressure after pressing may be 10 MPa.
  • 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 on the outside of the secondary particles filled with a sulfur element.
  • the specific method of forming the coating layer and the chemical composition of the coating layer are not particularly limited. Those skilled in the art can choose according to the actual situation.
  • the material of the coating layer can be selected from carbon materials, tin dioxide, manganese dioxide, Any one or more of titanium dioxide, tricobalt tetroxide, vanadium pentoxide, iron disulfide, copper disulfide, cobalt disulfide, or bismuth trisulfide.
  • the carbon material may be graphite, Ketjen black, graphene, carbon nanotubes, activated carbon, and the like; methods for forming the coating layer include, but are not limited to, spray drying, hydrothermal methods, and the like.
  • a coating layer on the outer surface of the secondary particles filled with sulfur simple substance, the isolation effect between the sulfur simple substance and the electrolyte can be enhanced.
  • the positive electrode material is applied to a battery, the cycle performance and stability of the battery can be improved.
  • the content of the coating layer may be 0.1 wt% to 10 wt%. For example, it may be 5 wt%.
  • 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.
  • step (3) The secondary particle precursor obtained in step (2) and 100 mmol of lithium nitrate are mixed in water, then taken out and dried, and the precipitate obtained after drying is heated to 700 degrees Celsius within 40 minutes, and then It is baked at 700 degrees Celsius for 1 hour, then taken out, and cooled down to room temperature within 30 minutes (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 secondary particle having a hollow structure, that is, a ternary cathode material is obtained.
  • step (3) The ternary cathode material obtained in step (3) is mixed with the sulfur simple substance according to a mass ratio of 10: 1, and then heat-treated, and the reaction is performed at 150 degrees Celsius for 12 hours. Sulfur composite cathode material.
  • step (3) The secondary particle precursor obtained in step (2) and 100 mmol of lithium nitrate are mixed in water, then taken out and dried, and the precipitate obtained after drying is heated to 700 degrees Celsius within 40 minutes, and then It was fired at 700 degrees Celsius for 1 hour, then taken out, cooled to room temperature (25 ° C) within 30 minutes, and then annealed at 500 degrees Celsius for 5 hours.
  • a secondary particle having a hollow structure, that is, a ternary cathode material is obtained.
  • step (3) Mix the ternary cathode material obtained in step (3) with sulfur simple substance, according to the mass ratio of 10: 0.5, and then heat-treat, and perform a reaction at 150 degrees Celsius for 12 hours, take out and pulverize to obtain the ternary- Sulfur composite cathode material.
  • step (3) The secondary particle precursor obtained in step (2) and 100 mmol of lithium nitrate are mixed in water, then taken out and dried, and the precipitate obtained after drying is heated to 700 degrees Celsius within 40 minutes, and then It was fired at 700 degrees Celsius for 1 hour, then taken out, cooled to room temperature (25 ° C) within 30 minutes, and then annealed at 500 degrees Celsius for 5 hours.
  • a secondary particle having a hollow structure, that is, a ternary cathode material is obtained.
  • step (3) The ternary cathode material obtained in step (3) is mixed with the sulfur simple substance, according to a mass ratio of 8: 1, inert argon is introduced, pressurized to 10 MPa, and then heat-treated, and the reaction is performed at 150 degrees Celsius. 12 After 3 hours, the ternary-sulfur composite cathode material was obtained by drying and crushing.
  • step (3) The secondary particle precursor obtained in step (2) and 100 mmol of lithium nitrate are mixed in water, then taken out and dried, and the precipitate obtained after drying is heated to 700 degrees Celsius within 40 minutes, and then It was fired at 700 degrees Celsius for 1 hour, then taken out, cooled to room temperature (25 ° C) within 30 minutes, and then annealed at 500 degrees Celsius for 5 hours.
  • a secondary particle having a hollow structure, that is, a ternary cathode material is obtained.
  • step (3) Mix the ternary cathode material obtained in step (3) with sulfur simple substance, according to the mass ratio of 10: 0.5, and then heat-treat, and perform a reaction at 150 degrees Celsius for 12 hours, take out and pulverize to obtain the ternary- Sulfur composite cathode material.
  • Elemental sulfur was dissolved in a 10% by mass sodium polyacrylate aqueous solution and stirred.
  • Lithium manganate was added to an aqueous solution containing 5% of a surfactant, and the mass ratio of the mass of lithium manganate to the sulfur element added to the aqueous solution of sodium polyacrylate was 1: 9.
  • the dispersion liquid containing sulfur simple substance and the dispersion liquid containing lithium manganate are mixed uniformly, the pH value is adjusted to 8, and the lithium manganate coated with sulfur simple substance is obtained by static filtration, and vacuum dried at 80 degrees Celsius for 12 hours to obtain a positive electrode material.
  • Elemental sulfur was dissolved in a 10% by mass sodium polyacrylate aqueous solution and stirred.
  • Glucose was added to an aqueous solution containing 5% of a surfactant, and the mass ratio of the mass of glucose to the amount of sulfur added to the sodium polyacrylate aqueous solution was 1: 9.
  • the dispersion liquid containing sulfur elementary substance and the dispersion liquid containing glucose are mixed uniformly, and the lithium manganate coated with sulfur elementary substance is obtained by static filtration, and vacuum dried at 70 ° C. for 12 hours to obtain a positive electrode material.
  • Elemental sulfur was dissolved in a 10% by mass sodium polyacrylate aqueous solution and stirred. Lithium nickel cobalt oxide particles were added and mixed, and the mass ratio was 1: 9. Vacuum drying was performed at 70 degrees Celsius for 12 hours to obtain a positive electrode material.
  • Elemental sulfur was dissolved in a 10% by mass sodium polyacrylate aqueous solution and stirred.
  • a primary particle precursor is added to an aqueous solution containing 5% of a surfactant, and the mass ratio of the precursor to the mass of sulfur added to the sodium polyacrylate aqueous solution is 1: 9.
  • the primary particle precursor was calcined at 700 degrees Celsius for 1 hour, then taken out at 700 degrees, rapidly cooled to room temperature, and then annealed at 500 degrees Celsius for 5 hours.
  • Primary particles of a ternary positive electrode active material were obtained. Elemental sulfur was dissolved in a 10% by mass sodium polyacrylate aqueous solution and stirred. Primary particles were added to an aqueous solution containing 5% surfactant, and the mass ratio was 1: 9.
  • the primary element-coated sulfur element was subjected to static filtration to obtain a primary-particle-coated sulfur composite particulate material, which was vacuum-dried at 80 degrees Celsius for 12 hours to obtain a positive electrode material.
  • 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 ternary-sulfur composite cathode material obtained in Example 1 is spherical particles having a hollow structure and an average thickness of a shell of about 1-2 ⁇ m, and the average particle diameter of the particles is about 10 ⁇ m.
  • EDS Energy dispersive X-ray spectroscopy
  • the specific test method is as follows: 5g of the obtained positive electrode materials in the above examples and comparative examples are respectively mixed with the positive electrode conductive agent carbon black and the positive electrode binder PVDF at a mass ratio of 94: 3: 3 and placed in 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 Examples 1-3 have a higher sulfur content in the sulfur content test, their energy density is 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. After the positive electrode material undergoes the above-mentioned preparation process, a part of the physically adsorbed sulfur element is lost, but in Examples 1 to 3 after the heat treatment, the above-mentioned situation of the comparative example does not occur.
  • Comparative Example 2 has the appearance of tightly packed outside and loosely packed inside, it does not form a complete core-shell structure, that is, it does not have a hollow structure, so the sulfur element cannot be located in a hollow structure completely protected by the shell, which is not good.
  • the energy density is also low.
  • the morphology of the particles of Examples 1 to 3 can also maintain the overall compaction density of the material after the compaction treatment, and the energy density of the positive electrode material can also be improved.
  • the positive electrode material prepared in Comparative Example 3 does not have the core-shell structure of the secondary particles according to the embodiment of the present invention, although the sulfur content test results also show a certain sulfur content, the energy density is low, and the cycle performance of the positive electrode material is low. It is also inferior to the positive electrode materials prepared in Examples 1 to 3.
  • the single positive electrode material using carbon material coating to isolate sulfur elementary material prepared in Comparative Example 4 and the pure sulfur and coating material prepared in Comparative Example 5 were mixed and processed by post-processing (such as steaming). Dry solvent, heating, etc.), the coated positive electrode material formed by mixing the sulfur prepared in Comparative Example 6 with the coating material, and the sulfur element prepared in Comparative Example 7 using the sulfur element as a core, forming a package around the core.
  • the coated sulfur-containing positive electrode material also has a certain sulfur content in the sulfur content test results, but the energy density is low, and the cycle performance of the positive electrode material is also inferior to that of the positive electrode materials prepared in Examples 1 to 3. . It is proved that the positive electrode material according to the embodiment of the present application can better prevent the dissolution of sulfur elemental substance in the electrolyte, can better improve the energy density and cycle performance of the positive electrode material, and improve the use performance of the positive electrode material.
  • first and second are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Inorganic Chemistry (AREA)
  • Composite Materials (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Organic Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

提出了正极材料及其制备方法、锂离子电池和车辆。该正极材料包括硫单质和由一次颗粒堆积形成的二次颗粒，所述二次颗粒具有中空结构，所述硫单质填充在一次颗粒之间的间隙中和所述中空结构中；所述一次颗粒含有锂氧化物，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。

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201810753608.X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。该正极材料包括硫单质和由一次颗粒堆积形成的二次颗粒，所述二次颗粒具有中空结构，所述硫单质填充在所述一次颗粒之间的间隙中和所述中空结构中；所述一次颗粒含有锂氧化物，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。该二次颗粒的中空结构适于硫元素的填充，由一次颗粒堆积形成的二次颗粒的壳层结构堆积较为紧密，孔隙率较低，可防止硫溶解于电解液中，且二次颗粒的结构不会降低材料的整体压实密度，从而可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。该方法包括：将含有金属离子的溶液、络合剂以及沉淀剂，在搅拌的条件下加入至反应容器中，并在pH值为11-12下进行共沉淀，形成一次颗粒前驱体，所述一次颗粒前驱体堆积形成核心前驱体，随后在pH值为9-10.5，令所述一次颗粒前驱体继续堆积，得到二次颗粒前驱体；将所述二次颗粒前驱体与锂源进行混合，并进行焙烧处理，得到具有中空结构的二次颗粒；将所述二次颗 粒与硫源进行混合，并进行熔融固化处理，以便将硫单质填充在所述中空结构中；其中，所述二次颗粒含有用于限定中空结构的壳层，所述壳层由一次颗粒堆积而成；所述一次颗粒含有锂氧化物，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。该方法获得的二次颗粒具有适于硫元素填充的微观形貌，二次颗粒中空结构外部的壳层堆积较为紧密，高温条件下，液体硫能够进入内部孔道，而结构紧密的外部壳层可防止多硫化物中间体溶解于电解液中，且二次颗粒的颗粒结构不会降低材料的整体压实密度，从而可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者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显示了本申请实施例中所制备的具有中空结构的二次颗粒的扫描电子显微镜图；
图5显示了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。该正极材料包括硫单质和由一次颗粒堆积形成的二次颗粒，二次颗粒具有中空结构，硫单质填充在一次颗粒之间的间隙，和中空结构中。一次颗粒含有锂氧化物。上述二次颗粒中空结构，适于硫元素的填充，壳层中一次颗粒堆积较为紧密，可防止硫溶解于电解液中，且二次颗粒的结构不会降低材料的整体压实密度，从而可提高该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，本领域金属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，获得上述二次颗粒。
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。镍钴锰三元材料(NCM)可以为111型(N：C：M＝1:1:1，后续型号数字代表镍钴锰在三元材料中的原子比，后面不再赘述)、433型、532型、666型、811型等；镍钴铝(NCA)三元材料可以为LiNi 0.8Co 0.15Al 0.05O 2等。根据本申请的另一些实施例，上述锂氧化物可以包括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 1-x-yCo xMn yO 2。
根据本申请的实施例，上述二次颗粒可以是由含有锂氧化物的纳米颗粒，即一次颗粒堆积形成的。需要说明的是，二次颗粒中空结构是指，由一次颗粒紧密堆积得到的壳层限定出来的空腔区域。因此，该二次颗粒具有核壳结构，由一次颗粒紧密堆积得到的壳层即为“壳”，中空结构即为“核”。以核壳结构的二次颗粒的外表面为厚度的0点，壳层的平均厚度可以为1-10μm，如可以为0.5-5μm，或为2-3μm，二次颗粒的平均粒径为5-50μm。该壳层由上述纳米颗粒经过较为紧密的堆积方式形成，壳层具有一定孔隙，以便硫单质可以通过孔隙进入中空结构内部进行填充。二次颗粒中，壳层以内的区域，即为中空结构空 腔。在形成该二次颗粒的过程中，颗粒首先通过较为松散的方式进行堆积，随后再通过较为紧密的方式进行堆积。由此形成内部堆积松散、外部堆积较为致密的前驱体。通过加热，内部堆积松散的结构即可形成中空结构。
根据本申请的实施例，上述中空结构的平均孔径大于最终获得的二次颗粒中，一次颗粒之间的间隙。一次颗粒之间的间隙可以为0.02-1μm，如可以为0.5μm。需要特别说明的是，中空结构可以被硫单质充满，也可以被硫单质部分填充。并且，中空结构中的硫单质含量，高于一次颗粒之间的间隙中硫单质的含量。也即是说，硫单质主要填充在中空结构中。以正极材料的总质量为基准，中空结构中的硫单质含量为5-40wt％；一次颗粒之间的间隙中硫单质的含量为0-15wt％。由此，壳层可以起到保护中空结构中的硫单质的作用，防止在实际使用过程中，壳层间隙中的少量硫单质可能在循环过程中被电解液溶解，造成正极材料性能的下降，通过控制前驱体颗粒和硫单质的比例，可以有效降低壳层间隙的硫单质。
根据本申请的实施例，上述一次颗粒选自棒状锂氧化物、块状锂氧化物中的一种或几种，一次颗粒通过堆积形成二次颗粒前驱体。一次颗粒的具体形貌和尺寸可以不受特别限制，具体地，一次颗粒的长度可以为0.5-2μm，宽度可以为200-500nm，长径比为2～40。在形成二次颗粒前驱体的初期时，上述一次颗粒以较为疏松的方式进行堆积，而在形成外围的壳层时，一次颗粒以较为紧密的方式进行堆积。因此，通过后续进行简单的加热处理，即可以获得中间较为疏松、包括空腔，同时外围堆积较为紧密的二次颗粒。二次颗粒的孔隙率可以为20-30％。根据本申请的实施例，对加热处理之前的二次颗粒前驱体，以及经过加热，形成有中空结构的二次颗粒分别进行压汞测试，对比测试结果可知，加热前的二次颗粒前驱体的孔径分布主要在较小范围内，此时尚未形成中空部分，因此孔隙主要由松散堆积的一次颗粒之间的孔隙，以及外围紧密堆积的一次颗粒之间的孔隙决定。加热处理后，压汞测试显示的孔径分布中，尺寸在2-10μm的孔径占多数，说明加热处理后形成了中空结构。
需要特别说明的是，在本申请中，术语“纳米颗粒”，或称为“一次颗粒”，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。由纳米颗粒堆积而成的二次颗粒的形状不受特别限制，例如，可以为球形、菱形、椭球形中的一种。
根据本申请的实施例，正极材料中硫的含量不受特别限制，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，以正极材料的总质量为基准，硫单质的含量可以为2wt％-50wt％，锂氧化物的含量为50wt％-98wt％。根据本申请的具体实施例，硫的含量可以根据前面所述的中空结构的体积来确定。发明人发现，硫单质的负载量过高，过量的硫容易造成二次颗粒主体结构的损伤。根据本申请的具体实施例，硫单质 的含量可以为10wt％-30wt％。硫单质可以通过熔融渗透进入上述核壳结构的中空结构中。
根据本申请的实施例，上述中空结构外围，具有结构较为致密的、完整包覆中空结构的壳层。由此，中空结构中的硫单质，可以被较好的和电解液隔离开。并且，起到隔绝电解质作用的壳层中含有锂氧化物，与单一的利用碳材料等包覆层隔绝硫单质的正极材料不同，根据本申请实施例的正极材料可以利用锂氧化物形成较好的隔离结构，在防止硫单质被电解液溶解的同时，还不会降低正极材料的整体压实密度和电化学性能。根据本申请实施例的正极材料，首先形成具有中空结构的二次颗粒，再将硫单质填充在二次颗粒的中空结构中。由此，一方面硫单质可以根据实际需求，完全充满中空结构，或是部分填充中空结构。不论硫单质的填充情况如何，硫单质的外部均具有封闭的壳层保护。与单纯的将硫和包覆材料(如正极活性材料的粉末)混合，通过后期处理(如蒸干溶剂、加热等)形成的包覆正极材料不同，根据本申请实施例的正极材料能够更好的防止硫单质在电解液中的溶解问题。而将硫和包覆材料混合而制备的包覆正极材料，难以保证包覆材料可以在硫单质的外层形成密闭的壳层。现有技术中还给出以硫单质为核，在核的外围形成包覆层的含硫正极材料的结构，这种结构的正极材料中，不含有中空结构，在实际使用过程中，一旦发生膨胀或收缩，正极内部不具有缓冲空间。
在本申请的一些实施例中，为了提高该正极材料的电化学性能，二次颗粒的外表面还可以形成有包覆层。包覆层的材料不受特别限制，本领域技术人员可以选择熟悉的材料形成包覆层。例如，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、二硫化钴或三硫化铋中的任意一种或几种。在本申请的另一些实施例中，以正极材料的总质量为基准，包覆层的含量为0.1wt％-10wt％。在本申请的再一个实施例中，采用碳包覆层，碳包覆层形成在上述填充有硫的二次颗粒的外表面。由此，可以提高该正极材料的电化学性能。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，可阻挡电解质进入二次颗粒的内部，缓解电解质对硫单质的溶解。在本申请一些具体的实施例中，包覆层为二氧化钛包覆层。在本申请的另一些具体实施例中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，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：形成由一次颗粒堆积而成的二次颗粒，二次颗粒具有中空结构
根据本申请的实施例，在该步骤中，形成二次颗粒。如前所述，该二次颗粒可以由一次颗粒(纳米颗粒)堆叠而成。二次颗粒的壳层堆积较为紧密，由于中心处具有中空结构， 因此壳层的孔隙率低于中心区域的孔隙率。该二次颗粒的中空结构适于硫元素的填充，壳层堆积较为紧密，可防止硫溶解于电解液中，且上述颗粒结构不会降低材料的整体压实密度，从而可提高该正极材料的体积能量密度。关于二次颗粒的具体结构，前面已经进行了详细的描述，在此不再赘述。具体的，该二次颗粒可以为核壳结构，由一次颗粒紧密堆积得到的壳层即为“壳”，中空结构即为“核”。上述表面堆积紧密、中心具有空腔的结构，可以是通过控制形成该二次颗粒时的反应速率而获得的。
根据本申请的具体实施例，参考图2，上述具有核壳结构的二次颗粒，即中心的多孔微球结构和外层紧密包覆的壳层结构，二次颗粒可以通过以下步骤获得：
S110：将含有金属离子的溶液、络合剂以及沉淀剂，在pH值为11-12条件下进行共沉淀，形成一次颗粒前驱体，一次颗粒前驱体堆积形成核心前驱体。
根据本申请的实施例，在该步骤中，将含有金属离子的溶液、沉淀剂以及络合剂在搅拌的条件下加入反应容器(如可以为水热反应釜或是其他容器)，并通过共沉淀，共沉淀形成的一次颗粒前驱体堆积获得核心前驱体。在该步骤中，可以控制反应溶液的pH值为11-12，从而实现快速沉淀，形成松散堆积的核。具体的，可以通过调节金属离子溶液以及络合剂的加入速度，加入沉淀剂的速度(可以用于控制混合溶液的pH值)，控制共沉淀形成的一次颗粒前驱体堆积形成核心前驱体的生长速度以及堆积速度。具体的，可以控制金属离子溶液、络合剂以及沉淀剂的泵入速度或滴加速度等，进而控制其加入速度。在这一阶段，反应可以较快，从而形成堆积较为松散的核心前驱体。
在该步骤中，可通过调整搅拌的速度(300-2000rpm)、反应温度(30-50℃)、反应pH值(11-12)，以及络合剂的浓度(0.01-0.03mol/L)，控制核心前驱体的形貌。具体而言，逐渐加入的沉淀剂可以在核心前驱体形成的过程中提供剪切力，从而令反应容器中的一次颗粒前驱体，逐渐生长堆积。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，可以调控形成的一次颗粒前驱体的尺寸。由此，可以获得具有特定形貌的一次颗粒前驱体(例如可以为棒状)。
根据本申请的实施例，上述金属可以通过含有金属离子的溶液提供，更具体的，可以由包含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。将金属盐溶液与络合剂在搅拌状态下加入溶剂中，以便获得混合溶液。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。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。关于锂氧化物颗粒的化学组分，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、络合剂以及沉淀剂按照固定配比加入容器中。上述固定配比是根据锂氧化物的化学组成而确定的。上述物质加入反应容器中的加入速度，本领域技术人员可以根据反应容器的体积、上述物质加入的总剂量进行调节。例如，上述较慢的加入过程，可以持续2-6小时，如可以为4小时或是5小时。
根据本申请的实施例，沉淀剂可以是可使金属离子溶液发生沉淀反应的试剂，主要是各种碱性溶液，包括氢氧化物的水溶液，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。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，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。根据本申请的实施例，在该步骤中，可控制混合溶液的pH值较高，高于后续的堆积过程，例如可以为12.0或11.0。
S120：在pH值为9-10.5条件下令所述核心前驱体继续堆积，以便获得二次颗粒前驱体。
根据本申请的实施例，在该步骤中，在pH值为9-10.5条件下下向反应容器中供给金属盐溶液、络合剂以及沉淀剂的，以便一次颗粒前驱体进行缓慢沉淀，形成较为致密的外壳，获得二次颗粒前驱体。可通过降低向反应容器中供给金属盐溶液、络合剂以及沉淀剂的速度，从而令一次颗粒前驱体在步骤S110中形成的核心前驱体的基础上，继续进行较为紧密的堆积，以便在后续处理中，形成较为致密的壳层。
根据本申请的实施例，该步骤中的供给速度，即向反应容器中加入上述反应物的速度，可以是步骤S110供给速度的1/3～1/2。在上述第二pH值下进行堆积的时间可以为10-25小时，如可以为20小时。在该步骤中，可通过调节加入的沉淀剂的量，控制反应溶液的pH值略低于前述获得核心前驱体的步骤，如可以控制pH值为10或是10.5。由此，可形成结构较为紧密的表层结构。
根据本申请的具体实施例，上述反应物可以在18-24小时(包括前述的获得核心前驱体的时间)以内，全部加入至反应容器中。
S130：将所述二次颗粒前驱体以及锂源进行混合，并进行焙烧处理，以便获得所述二次颗粒。
根据本申请的实施例，在该步骤中，将步骤S120获得的二次颗粒前驱体以及锂源进行 混合，并进行焙烧处理，以便将二次颗粒前驱体锂化，同时形成中空结构，从而获得二次颗粒。
根据本申请的实施例，在该步骤中，锂源的具体类型不受特别限制，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。二次颗粒前驱体以及锂源的混合比例也不受特别限制，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，二次颗粒前驱体的锂化可以是将步骤S120获得的二次颗粒前驱体，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。发明人发现，步骤S120形成的二次颗粒前驱体中心区域由于一次颗粒的堆积较为松散，因此在焙烧处理过程中，可以形成具有空腔的中空结构，堆积较为致密的壳层也具有一定间隙，从而在后续步骤中，硫单质可以通过壳层，进入至空腔中进行填充。由此，可以获得表层堆积较为紧密，中心具有空腔的核壳结构。
为了提高二次颗粒的质量，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。由此，可以在保持步骤S130形成的二次颗粒(核壳结构颗粒)的形貌的同时，获得较好的三元材料晶型。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：将硫单质填充在中空结构中
根据本申请的实施例，在该步骤中，将所述二次颗粒与硫源进行混合，并进行熔融固化处理，以便将硫单质填充在所述中空结构中。硫单质可以通过熔融渗透进入中空结构中。
根据本申请的实施例，上述二次颗粒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，如可以为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步骤S130形成的空腔中。
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，惰性气氛可以为氮气、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。根据本申请的具体实施例，可以将二次颗粒和硫源混合后，置于密封容器中，并向容器中充入惰性气体进行加压。加压后的压力可以为10MPa。
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，在填充有硫单质的二次颗粒外形成包覆层。形成包覆层的具体方法、包覆层的化学组成均不受特别限制，本领域技术人员可以根据实际情况进行选择，如包覆层的材料可选择碳材料、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；形成包覆层的方法包括但不限于喷雾干燥、水热法等方式。通过在填充有硫单质的二次颗粒外表面形成包覆层可以增强硫单质与电解液的隔绝效果，将该正极材料应用于电池是，可提高电池的循环性能以及稳定性。以正极材料的总质量为基准，包覆层的含量可以为0.1wt％-10wt％。例如，可以为5wt％。
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。
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，而后加入5g的络合剂氨水(浓度为10重量％)，并加入沉淀剂氢氧化钠调节pH为11，以在50摄氏度下进行共沉淀反应4小时，过滤得到核心前躯体。
(2)调节加入的氢氧化钠的量，令pH值调至10.5，降低反应速度为之前的二分之一， 进行缓慢紧密的堆积。20小时之后获得二次颗粒前驱体。
(3)将步骤(2)得到的二次颗粒前驱体和100mmol的硝酸锂在水中进行混合，而后取出并烘干，在40分钟内将烘干后得到的沉淀物升温至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(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。得到具有中空结构的二次颗粒，即三元正极材料。
(4)将步骤(3)得到的三元正极材料和硫单质进行混合，按照质量比例为10:1，然后热处理，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。
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，而后加入5g的络合剂氨水(浓度为10重量％)，并加入沉淀剂氢氧化钠调节pH为11，以在50摄氏度下进行共沉淀反应4小时，过滤得到核心前躯体。
(2)调节加入的氢氧化钠的量，令pH值调至10.5，降低反应速度为之前的二分之一，进行缓慢紧密的堆积。20小时之后获得二次颗粒前驱体。
(3)将步骤(2)得到的二次颗粒前驱体和100mmol的硝酸锂在水中进行混合，而后取出并烘干，在40分钟内将烘干后得到的沉淀物升温至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(25℃)，继而在500摄氏度下退火5小时。得到具有中空结构的二次颗粒，即三元正极材料。
(4)将步骤(3)得到的三元正极材料和硫单质进行混合，按照质量比例为10:0.5，然后热处理，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。
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，而后加入5g的络合剂氨水(浓度为10重量％)，并加入沉淀剂氢氧化钠调节pH为11，以在50摄氏度下进行共沉淀反应4小时，过滤得到核心前躯体。
(2)调节加入的氢氧化钠的量，令pH值调至10.5，降低反应速度为之前的二分之一，进行缓慢紧密的堆积。20小时之后获得二次颗粒前驱体。
(3)将步骤(2)得到的二次颗粒前驱体和100mmol的硝酸锂在水中进行混合，而后取出并烘干，在40分钟内将烘干后得到的沉淀物升温至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(25℃)，继而在500摄氏度下退火5小时。得到具有中空结构的二次颗粒，即三元正极材料。
(4)将步骤(3)得到的三元正极材料和硫单质进行混合，按照质量比例为8:1，通入惰性氩气，加压到10MPa，然后热处理，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。
实施例4 制备具有包覆层的正极材料
(1)将50mmol硝酸镍和50mmol硝酸钴溶于100g水中，而后加入5g的络合剂氨水(浓度为10重量％)，并加入沉淀剂氢氧化钠调节pH为11，以在50摄氏度下进行共沉淀反应4小时，过滤得到核心前躯体。
(2)调节加入的氢氧化钠的量，令pH值调至10.5，降低反应速度为之前的二分之一，进行缓慢紧密的堆积。20小时之后获得二次颗粒前驱体。
(3)将步骤(2)得到的二次颗粒前驱体和100mmol的硝酸锂在水中进行混合，而后取出并烘干，在40分钟内将烘干后得到的沉淀物升温至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(25℃)，继而在500摄氏度下退火5小时。得到具有中空结构的二次颗粒，即三元正极材料。
(4)将步骤(3)得到的三元正极材料和硫单质进行混合，按照质量比例为10:0.5，然后热处理，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。
(5)在步骤(4)中形成的三元-硫复合正极材料的包覆包覆层材料，以便形成具有包覆层的三元-硫复合正极材料。
对比例1
(1)50mmol硝酸镍和50mmol硝酸钴溶于100g水中，而后加入5g的氨水(浓度为10重量％)并加入氢氧化钠调节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进行混合，而后取出并烘干，再在700摄氏度下焙烧5小时，得到三元正极活性材料。
(3)将所述的三元正极材料、硫单质直接进行混合。
对比例2
(1)50mmol硝酸镍和50mmol硝酸钴溶于100g水中，而后加入5g的氨水(浓度为10重量％)并加入氢氧化钠调节pH为11，以在30摄氏度下进行共沉淀反应4小时，过滤得到核心前躯体；之后改变pH值，调至10.5，降低反应速度为之前的二分之一，进行缓慢紧密的堆积。反应20小时之后获得二次颗粒前驱体。
(2)将二次颗粒前驱体和硝酸锂在水中进行混合，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，继而在500摄氏度下退火5小时。得到三元正极活性材料。
(3)将所述的三元正极材料、硫单质按照质量比10:1直接进行混合。
对比例3
将单质硫溶于质量百分比为10％的聚丙烯酸钠水溶液中进行搅拌。在含有5％的表面活性剂的水溶液中加入锰酸锂，锰酸锂的质量与加入聚丙烯酸钠水溶液中的硫单质的质量比为1:9。将含有硫单质的分散液与含有锰酸锂的分散液混合均匀，调节pH值至8，静置过滤获得硫单质包覆的锰酸锂，在80摄氏度下真空干燥12小时，获得正极材料。
对比例4
将单质硫溶于质量百分比为10％的聚丙烯酸钠水溶液中进行搅拌。在含有5％的表面活性剂的水溶液中加入葡萄糖，葡萄糖的质量与加入聚丙烯酸钠水溶液中的硫单质的质量比为1:9。将含有硫单质的分散液与含有葡萄糖的分散液混合均匀，静置过滤获得硫单质包覆的锰酸锂，在70摄氏度下真空干燥12小时，获得正极材料。
对比例5
将单质硫溶于质量百分比为10％的聚丙烯酸钠水溶液中进行搅拌。加入锂镍钴氧化物颗粒混合，质量比为1:9。在70摄氏度下真空干燥12小时，获得正极材料。
对比例6
将单质硫溶于质量百分比为10％的聚丙烯酸钠水溶液中进行搅拌。在含有5％的表面活性剂的水溶液中加入一次颗粒前驱体，前驱体的质量与加入聚丙烯酸钠水溶液中的硫单质的质量比为1:9。将含有硫单质的分散液与含有锰酸锂的分散液混合均匀，调节pH值至8，静置过滤获得硫单质包覆的一次颗粒前驱体，在80摄氏度下真空干燥12小时，获得正极材料。
对比例7
将一次颗粒前驱体在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，继而在500摄氏度下退火5小时。得到三元正极活性材料一次颗粒。单质硫溶于质量百分比为10％的聚丙烯酸钠水溶液中进行搅拌。在含有5％的表面活性剂的水溶液中加入一次颗粒，质量比为1:9。将包覆了一次颗粒前驱体的硫单质静置过滤获得一次颗粒包覆的硫复合颗粒材料，在80摄氏度下真空干燥12小时，获得正极材料。
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中获得的三元-硫复合正极材料为具有中空结构的、壳体平均厚度约为1-2μm的球形颗粒，颗粒的平均粒径在10μm左右。
由图5可知，实施例1中获得的三元-硫复合正极材料中，硫单质可以较为均匀的填充至二次颗粒的空腔中，填充量较为可观。测试结果见表1。
2、硫含量测试
在日本JEOL公司JSM-7600F型场发射扫描电镜上进行能量色散X射线谱(EDS)进行球型剖面中心元素分析。测试结果见表1。
表1.样品的测试结果
Figure PCTCN2019095351-appb-000001
由测试结果可知，上述实施例具有较为可观的含硫量。对比例由于不具有外围堆积紧密，中心堆积疏松的结构，因此硫主要依靠吸附在颗粒外围。
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以质量比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 PCTCN2019095351-appb-000002
由测试结果可知，虽然对比例1-3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 过上述制备过程之后，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3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3制备的正极材料不能够具有实施例1～实施例3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2虽然具有外部紧密堆积，内部松散堆积的形貌，但未形成完整的核壳结构，即不具备中空结构，因此硫单质不能够位于完全被壳层保护的中空结构中，不能较好地防止硫单质的溶解，能量密度也较低。并且，实施例1～实施例3的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，正极材料的能量密度也得到了提高。
对比例3制备的正极材料，由于不具有根据本发明实施例的二次颗粒的核壳结构，因此虽然硫含量测试结果也显示具有一定的硫含量，但能量密度较低，且正极材料循环性能较实施例1～实施例3中制备的正极材料相比也较差。
并且，通过实验测得，对比例4中制备的单一的利用碳材料包覆层隔绝硫单质的正极材料、对比例5中制备的单纯的将硫和包覆材料混合，通过后期处理(如蒸干溶剂、加热等)形成的包覆正极材料、对比例6中制备的硫和包覆材料混合形成的包覆正极材料以及对比例7中制备的以硫单质为核，在核的外围形成包覆层的含硫正极材料，在硫含量测试结果显示也具有一定的硫含量，但能量密度较低，且正极材料循环性能和实施例1～实施例3中制备的正极材料相比也比较差。证明了根据本申请实施例的正极材料能够更好的防止硫单质在电解液中的溶解，能够较好地提高正极材料的能量密度和循环性能，提高正极材料的使用性能。
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。
此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。
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 (20)

  1. 一种正极材料，包括硫单质和由一次颗粒堆积形成的二次颗粒，所述二次颗粒具有中空结构，所述硫单质填充在所述一次颗粒之间的间隙中和所述中空结构中；所述一次颗粒含有锂氧化物，
    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，所述二次颗粒的平均粒径为5-50μm，所述中空结构的平均孔径为2-10μm。
  3. 根据权利要求1或2所述的正极材料，所述二次颗粒含有用于限定中空结构的壳层，所述壳层由所述一次颗粒堆积而成，所述壳层的平均厚度为1-10μm。
  4. 根据权利要求1-3任一项所述的正极材料，其特征在于，所述中空结构中的所述硫单质含量高于所述一次颗粒之间的间隙中的所述硫单质的含量。
  5. 根据权利要求1-4任一项所述的正极材料，以正极材料的总质量为基准，所述中空结构中的所述硫单质的含量为5-40wt％；所述一次颗粒之间的间隙中的所述硫单质的含量为0-15wt％。
  6. 根据权利要求1-5任一项所述的正极材料，所述一次颗粒之间的所述间隙的长度为0.02-1μm。
  7. 根据权利要求1-6任一项所述的正极材料，所述一次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。
  8. 根据权利要求7所述的正极材料，所述一次颗粒的长度为0.5-2μm，宽度为200-500nm，长径比为2～40。
  9. 根据权利要求1-8任一项所述的正极材料，以正极材料的总质量为基准，所述硫单质的含量为2wt％-50wt％，所述锂氧化物的含量为50wt％-98wt％。
  10. 根据权利要求1-9任一项所述的正极材料，其特征在于，所述二次颗粒的形状为球形、菱形、椭球形中的一种或几种。
  11. 根据权利要求1-10任一项所述的正极材料，所述二次颗粒的孔隙率为20-30％。
  12. 根据权利要求1-11任一项所述的正极材料，所述正极材料的外表面还含有包覆层。
  13. 根据权利要求12所述的正极材料，以正极材料的总质量为基准，所述包覆层的含量为0.1wt％-10wt％。
  14. 根据权利要求12或13所述的正极材料，形成所述包覆层的材料包括碳、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。
  15. 一种制备正极材料的方法，包括：
    将含有金属离子的溶液、络合剂以及沉淀剂，在搅拌的条件下加入至反应容器中，并在pH值为11-12下进行共沉淀，形成一次颗粒前驱体，所述一次颗粒前驱体堆积形成核心前驱体，随后在pH值为9-10.5下，令所述一次颗粒前驱体继续堆积，得到二次颗粒前驱体；
    将所述二次颗粒前驱体与锂源进行混合，并进行焙烧处理，得到具有中空结构的二次颗粒；将所述二次颗粒与硫源进行混合，并进行熔融固化处理，以便将硫单质填充在所述中空结构中；其中，
    所述二次颗粒含有用于限定中空结构的壳层，所述壳层由一次颗粒堆积而成；
    所述一次颗粒含有锂氧化物，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。
  16. 根据权利要求15所述的方法，所述pH值为11-12条件下，进行所述共沉淀的反应时间为2-6小时，在所述pH值为9-10.5条件下，所述继续堆积的时间为10-25小时。
  17. 根据权利要求15或16所述的方法，其特征在于，所述二次颗粒与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. 根据权利要求15-17任一项所述的方法，所述含有金属离子的溶液包括含Mn离子的溶液、含Al离子的溶液、含Nb离子的溶液、含Fe离子的溶液、含Co离子的溶液、含Ni离子的溶液中的一种或几种；
    所述络合剂包括氨水；
    所述沉淀剂包括氢氧化钾以及氢氧化钠中的一种或两种。
  19. 一种锂离子电池，包括权利要求1-14任一项所述的正极材料，或者权利要求15-18任一项所述的方法所制备的正极材料。
  20. 一种车辆，包括权利要求19所述的锂离子电池。
PCT/CN2019/095351 2018-07-10 2019-07-10 正极材料及其制备方法、锂离子电池和车辆 WO2020011177A1 (zh)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP19834823.7A EP3823064A4 (en) 2018-07-10 2019-07-10 CATHODE MATERIAL AND METHOD OF MANUFACTURING THEREOF, LITHIUM-ION BATTERY AND VEHICLE
US17/259,106 US20210292186A1 (en) 2018-07-10 2019-07-10 Cathode material and manufacturing method thereof, lithium ion battery, and vehicle

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CN201810753608.X 2018-07-10
CN201810753608.XA CN110707296B (zh) 2018-07-10 2018-07-10 正极材料及其制备方法、锂离子电池和车辆

Publications (1)

Publication Number Publication Date
WO2020011177A1 true WO2020011177A1 (zh) 2020-01-16

Family

ID=69142271

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2019/095351 WO2020011177A1 (zh) 2018-07-10 2019-07-10 正极材料及其制备方法、锂离子电池和车辆

Country Status (4)

Country Link
US (1) US20210292186A1 (zh)
EP (1) EP3823064A4 (zh)
CN (1) CN110707296B (zh)
WO (1) WO2020011177A1 (zh)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114291855A (zh) * 2022-01-14 2022-04-08 万华化学(四川)有限公司 一种全浓度梯度正极材料前驱体的制备方法、一种全浓度梯度正极材料及其制备方法

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114512729B (zh) * 2020-11-16 2023-07-14 比亚迪股份有限公司 纳米材料、负极保护浆料、锂负极及锂电池
WO2022140962A1 (zh) * 2020-12-28 2022-07-07 宁德新能源科技有限公司 负极材料、电化学装置和电子设备
CN115084500A (zh) * 2022-04-29 2022-09-20 远景动力技术(江苏)有限公司 多晶型三元材料及其应用
CN116239162A (zh) * 2023-03-31 2023-06-09 蜂巢能源科技(无锡)有限公司 一种正极材料前驱体及其制备方法和应用

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103187563A (zh) * 2011-12-27 2013-07-03 比亚迪股份有限公司 一种锂离子电池正极材料及其制备方法和一种锂离子电池
CN103700860A (zh) * 2012-09-27 2014-04-02 比亚迪股份有限公司 一种锂离子电池
CN105336915A (zh) * 2014-08-13 2016-02-17 微宏动力系统（湖州）有限公司 锂离子二次电池用正极材料、其制备方法及锂离子二次电池

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3649953B2 (ja) * 1999-06-23 2005-05-18 三洋電機株式会社 活物質、電極、非水電解液二次電池及び活物質の製造方法
KR101453486B1 (ko) * 2012-05-03 2014-10-23 한양대학교 산학협력단 카본 황 복합체의 제조 방법, 이에 의하여 제조된 카본 황 복합체 및 이를 포함하는 전기 화학 소자
CN103199258B (zh) * 2013-03-07 2016-06-22 中航锂电（江苏）有限公司 锂离子电池正极材料、正极制备方法及锂离子电池
US9917303B2 (en) * 2013-04-22 2018-03-13 Nanotek Instruments, Inc. Rechargeable lithium-sulfur battery having a high capacity and long cycle life
CN106549157A (zh) * 2015-09-18 2017-03-29 中国科学院宁波材料技术与工程研究所 空心球形类石墨相c3n4和单质硫复合材料及其制法和应用
CN105406059A (zh) * 2015-12-30 2016-03-16 王晓伟 一种高纯度硫/炭包覆的钴酸锂正极材料及其制备方法
WO2018220972A1 (ja) * 2017-05-29 2018-12-06 太平洋セメント株式会社 リチウムイオン二次電池用正極活物質複合体及びこれを用いた二次電池、並びにリチウムイオン二次電池用正極活物質複合体の製造方法

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103187563A (zh) * 2011-12-27 2013-07-03 比亚迪股份有限公司 一种锂离子电池正极材料及其制备方法和一种锂离子电池
CN103700860A (zh) * 2012-09-27 2014-04-02 比亚迪股份有限公司 一种锂离子电池
CN105336915A (zh) * 2014-08-13 2016-02-17 微宏动力系统（湖州）有限公司 锂离子二次电池用正极材料、其制备方法及锂离子二次电池

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of EP3823064A4 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114291855A (zh) * 2022-01-14 2022-04-08 万华化学(四川)有限公司 一种全浓度梯度正极材料前驱体的制备方法、一种全浓度梯度正极材料及其制备方法
CN114291855B (zh) * 2022-01-14 2024-02-02 万华化学(四川)有限公司 一种全浓度梯度正极材料前驱体的制备方法、一种全浓度梯度正极材料及其制备方法

Also Published As

Publication number Publication date
CN110707296A (zh) 2020-01-17
EP3823064A1 (en) 2021-05-19
CN110707296B (zh) 2021-05-14
EP3823064A4 (en) 2022-03-30
US20210292186A1 (en) 2021-09-23

Similar Documents

Publication Publication Date Title
WO2020011177A1 (zh) 正极材料及其制备方法、锂离子电池和车辆
JP5798681B2 (ja) サイズ依存性の組成を有する正極材料
WO2012131779A1 (ja) ニッケル複合水酸化物粒子および非水系電解質二次電池
KR101630209B1 (ko) 양극 활물질, 그를 갖는 리튬이차전지 및 그의 제조 방법
JP2020177860A (ja) ニッケルマンガンコバルト含有複合水酸化物およびその製造方法、リチウムニッケルマンガンコバルト含有複合酸化物およびその製造方法、リチウムイオン二次電池用正極活物質およびその製造方法、並びに、リチウムイオン二次電池
JP7121283B2 (ja) ニッケルコバルト複合水酸化物の製造方法及び非水系電解質二次電池用正極活物質の製造方法
JP7238880B2 (ja) 金属複合水酸化物とその製造方法、非水電解質二次電池用正極活物質とその製造方法、および非水電解質二次電池
JP7245422B2 (ja) 金属複合水酸化物とその製造方法、非水電解質二次電池用正極活物質とその製造方法、および非水電解質二次電池
WO2021251416A1 (ja) リチウムイオン二次電池用正極活物質、その製造方法、およびリチウムイオン二次電池
JP7392464B2 (ja) 全固体型リチウムイオン二次電池用正極活物質とその製造方法、および全固体型リチウムイオン二次電池
JP7452570B2 (ja) 非水系電解質二次電池用正極活物質
JP7452569B2 (ja) 非水系電解質二次電池用正極活物質
CN110649230A (zh) 一种纳米铆钉核壳结构正极材料及制备方法
CN108432003B (zh) 用于非水性电解质二次电池的正极活性物质及其前体、以及它们的制造方法
JP2023539302A (ja) 正極及び電気化学装置
JP2021005475A (ja) リチウムイオン二次電池用正極活物質およびその製造方法、並びに、リチウムイオン二次電池
JP7531163B2 (ja) 非水電解質二次電池用正極活物質及び非水電解質二次電池用正極
JP7389376B2 (ja) 非水系電解質二次電池用正極活物質
WO2020011179A1 (zh) 正极材料及其制备方法、锂离子电池和车辆
CN115881944B (zh) 具有过渡金属层超晶格结构的层状氧化物正极材料及制备
KR20200101853A (ko) 비수전해질 2차 전지용 정극 활물질 및 그 제조방법
KR102015425B1 (ko) 표면 코팅층이 형성된 리튬 이차전지용 양극 활물질, 이를 포함하는 리튬 이차전지 및 그 제조방법
WO2020011178A1 (zh) 正极材料及其制备方法、锂离子电池
JP7274125B2 (ja) 全固体リチウムイオン二次電池用正極活物質および全固体リチウムイオン二次電池
JP7177395B2 (ja) 全固体リチウムイオン二次電池用正極活物質および全固体リチウムイオン二次電池

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 19834823

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE