WO2020258764A1 - 一种正极活性材料及其制备方法和锂电池 - Google Patents

一种正极活性材料及其制备方法和锂电池 Download PDF

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WO2020258764A1
WO2020258764A1 PCT/CN2019/125847 CN2019125847W WO2020258764A1 WO 2020258764 A1 WO2020258764 A1 WO 2020258764A1 CN 2019125847 W CN2019125847 W CN 2019125847W WO 2020258764 A1 WO2020258764 A1 WO 2020258764A1
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positive electrode
active material
phosphate
lithium
pyrophosphate
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PCT/CN2019/125847
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French (fr)
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武怿达
黄学杰
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中国科学院物理研究所
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    • 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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • 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
    • 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
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a positive electrode active material for a lithium ion battery, a preparation method thereof, and a positive electrode and a lithium ion battery containing the positive electrode active material.
  • lithium ion secondary batteries Compared with other rechargeable battery systems, lithium ion secondary batteries have the advantages of high working voltage, light weight, small size, no memory effect, low self-discharge rate, long cycle life, and high energy density. They have been widely used at present Mobile terminal products such as mobile phones, laptops, and tablets. In recent years, due to environmental protection considerations, electric vehicles have been rapidly developed under the impetus of governments and automobile manufacturers, and lithium-ion secondary batteries have become an ideal source of power for a new generation of electric vehicles due to their excellent performance. .
  • the cathode materials of lithium-ion secondary batteries that people pay attention to can be roughly divided into three categories: layered materials represented by lithium cobalt oxide (LiCoO 2 ), and olivine type materials represented by lithium iron phosphate (LiFePO 4 ) Material and spinel structure material represented by lithium manganate (LiMn 2 O 4 ).
  • lithium batteries have been successfully commercialized as early as 1991, the energy density of existing materials needs to be further improved.
  • the high-voltage material with spinel structure as an advanced cathode material, is considered to be the most likely cathode material for the next generation of high-performance lithium batteries.
  • For high-pressure spinel cathode materials during the cycle, due to the interaction of the traditional carbonate-based electrolyte with the cathode material, oxygen is lost on the surface of the cathode material, and the surface of the material is dissolved, which ultimately leads to a reduction in active materials.
  • various doping schemes including various metal doping (such as Mg, Cr, Ti, Fe, Co, Ni or Cu, etc.). Doping with these metals can form new chemical bonds inside and on the surface of the material, thereby stabilizing the solid phase and the lattice oxygen on the surface.
  • metal doping has a limited effect on improving the stability of lithium nickel manganese oxide materials.
  • the object of the present invention is to provide a spinel positive electrode material with a simple preparation process and a stable doping structure, a preparation method thereof, and a positive electrode and a lithium ion battery containing the positive electrode active material.
  • the present invention provides a positive active material with a spinel structure, which comprises lithium-containing compound particles with the chemical formula Li 1+x Ni 0.5-y Mn 1.5-z O u , wherein -0.2 ⁇ x ⁇ 0.2, -0.2 ⁇ y ⁇ 0.2, -0.2 ⁇ z ⁇ 0.2, 3.8 ⁇ u ⁇ 4.2, characterized in that the surface of the lithium-containing compound particles has a rock salt phase surface layer, and the rock salt phase surface layer has a gradient phosphorus distribution and contains The metal element at the 16c or 8a position of the spinel octahedron, the metal element is Mg, Zn, Ni, Mn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, One or more of Ca, Ta and Sr.
  • the thickness of the rock salt phase surface layer may be 0.5-50 nm.
  • the content of phosphorus in the surface layer of the rock salt phase gradually decreases from the outside to the inside.
  • the positive electrode active material provided by the present invention is a lithium nickel manganate material with a spinel structure doped with surface gradient phosphorus, which is different from the phosphate-coated positive electrode active material in the prior art.
  • Phosphate-coated positive electrode active material refers to a material formed by covering the surface of the spinel positive electrode material with phosphate crystal structure or amorphous phosphate. A coating layer can be seen on the surface of the material through a transmission electron microscope.
  • the positive electrode active material with a surface gradient phosphorus-doped spinel structure provided by the present invention is that phosphorus elements are gradually doped from the surface of the particle to the inside of the spinel structure, and the main part of the surface structure is still spinel nickel manganese
  • the lattice structure of lithium oxide, and no coating layer on the surface is observed from the transmission electron microscope image.
  • the particle size of the lithium-containing compound particles may be 0.1-30 ⁇ m, preferably 0.2-20 ⁇ m.
  • the rock salt phase surface layer and the phosphor element gradient distribution layer on the surface can be characterized by commonly used characterization methods in the art, for example, scanning transmission electron microscope (STEM) and X-ray photoelectron spectroscopy microscope can be used.
  • STEM scanning transmission electron microscope
  • XPS X-ray photoelectron spectroscopy microscope
  • STEM line scan can also prove the gradient of phosphorus in the rock salt facies surface layer. distributed.
  • the etching analysis using X-ray photoelectron spectroscopy can also prove the gradient distribution of phosphorus in the gradient phosphorus distribution layer.
  • the present invention also provides a preparation method of the above-mentioned positive electrode active material, and the preparation method includes the following steps:
  • step (2) Sintering the mixture obtained in step (1) at 300 to 950° C. for 0.5 to 10 hours to obtain the positive active material with a spinel structure.
  • the phosphorus source may include nickel phosphate, cobalt phosphate, manganese phosphate, magnesium phosphate, calcium phosphate, iron phosphate, copper phosphate, zinc phosphate, titanium phosphate, zirconium phosphate, lithium phosphate, coke Cobalt phosphate, nickel pyrophosphate, manganese pyrophosphate, magnesium pyrophosphate, calcium pyrophosphate, iron pyrophosphate, copper pyrophosphate, zinc pyrophosphate, titanium pyrophosphate, zirconium pyrophosphate, ammonium phosphate, ammonium dihydrogen phosphate, dihydrogen phosphate One or more of ammonium, lithium dihydrogen phosphate, dilithium hydrogen phosphate, lithium pyrophosphate, pyrophosphate, phosphoric acid, and phosphorus pentoxide.
  • the rock salt phase inducer can be Mg, Zn, Ni, Mn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, One or more of oxides and salts of Ca, Ta and Sr, or the rock salt phase inducer is an acidic compound, such as one of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, formic acid, oxalic acid and citric acid Or multiple.
  • the mass ratio of the phosphorus source to the lithium-containing compound particles in step (1) may be 1:20 ⁇ 400, preferably 1:30 ⁇ 100.
  • the mass ratio of the rock salt phase inducer and the lithium-containing compound particles in step (1) can be 1:20-400, preferably 1:30-100.
  • the calcination in step (2) can be performed in oxygen, air, an atmosphere containing a reducing gas (such as hydrogen) or an inert atmosphere (such as nitrogen or argon) or under vacuum.
  • a reducing gas such as hydrogen
  • an inert atmosphere such as nitrogen or argon
  • the specific operation of the sintering process in step (2) is: heating up to 300-950°C at a heating rate of 0.5-10°C/min, then sintering for 0.5-10 hours, and then sintering at 0.5-10°C/min The cooling rate drops to room temperature.
  • the present invention also provides a positive electrode active material for a lithium ion battery prepared by adopting the above-mentioned preparation method.
  • the present invention provides the use of the positive electrode active material in a lithium ion secondary battery.
  • the present invention also provides a lithium ion secondary battery positive electrode, which includes a current collector and a positive electrode active material supported on the current collector, wherein the positive electrode active material is the positive electrode active material provided by the invention or The positive electrode active material prepared by the method of the present invention.
  • the positive electrode may further include a conductive additive and a binder.
  • the conductive additive may be a conventional electrical additive in the art, and the present invention is not particularly limited thereto.
  • the conductive additive is carbon black.
  • the binder may be a conventional binder in the field, and the present invention is not particularly limited thereto, and may be composed of polyvinylidene fluoride (PVDF), It can also be composed of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR). In some embodiments, the binder is polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • the present invention also provides a lithium ion secondary battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode is the positive electrode provided by the present invention.
  • the battery further includes a casing, and wherein the positive electrode, the negative electrode, the separator (collectively referred to as the electrode group) and the electrolyte are sealed in the casing.
  • the negative electrode, separator, and electrolyte may use conventional negative electrode, separator, and electrolyte materials in the art, and the present invention does not specifically limit them.
  • the negative electrode is lithium metal; in some embodiments, the separator is a three-layer film of PP/PE/PP coated with aluminum oxide on both sides; and in some embodiments, the electrolyte is LiPF 6 Ethylene carbonate (EC)/dimethyl carbonate (DMC) non-aqueous electrolyte with a concentration of 1 mol/L, wherein the volume ratio of EC to DMC is 1:1.
  • the preparation method of the positive electrode active material provided by the present invention uniformly mixes lithium-containing compound particles, rock salt phase inducer and phosphorus source, and finally undergoes high-temperature sintering to obtain a positive electrode active material with a spinel structure in which phosphorus elements are gradually doped from outside to inside.
  • the rock salt phase inducer can produce a rock salt phase on the surface of the lithium-containing compound by the metal element occupying the 16c or 8a position of the spinel octahedron, and the metal element occupying the 16c or 8a position of the spinel octahedron can be removed from Ni,
  • the composition of elements other than Mn such as one or more of Mg, Zn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, etc.
  • the rock salt phase inducer is one of oxides and salts of Mg, Zn, Fe, Co, Ti, Cr, Y, Sc, Ru, Cu, Mo, Ge, W, Zr, Ca, Ta, and Sr Or multiple. It can also be composed of Ni and Mn.
  • the rock salt phase inducer can be composed of metal-free acidic compounds, such as one or more of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, formic acid, oxalic acid and citric acid. Species, or one or more of Ni and Mn oxides and salts. This rock salt phase surface layer is conducive to the gradient doping of phosphorus on the surface of the spinel positive electrode.
  • the electrochemical performance of the spinel positive electrode active material can be significantly improved, including first effect, average efficiency and cycle stability .
  • the surface gradient phosphorus-doped spinel positive electrode active material for lithium ion batteries provided by the present invention has the following advantages: (1) The preparation method is simple and feasible, and the cost is low; (2) It can greatly improve the tip The comprehensive performance of spar cathode active materials has excellent development prospects.
  • the positive electrode active material provided by the present invention significantly reduces the reaction activity between the positive electrode material of the spinel structure and the electrolyte through doping, stabilizes the surface structure of the positive electrode active material of the spinel structure, and inhibits the high temperature and high pressure
  • the manganese on the surface of the spinel structure of the positive electrode active material dissolves during the cycle under conditions, thereby improving its capacity retention rate and charge-discharge coulombic efficiency.
  • the positive electrode active material provided by the present invention can be used as a positive electrode active material of a lithium ion secondary battery, and a battery made of the material has excellent cycle performance.
  • the positive electrode active material provided by the present invention obviously improves the cycle stability performance and coulombic efficiency of the existing positive electrode active material. Without wishing to be limited by theory, it is believed that through the method provided by the present invention, a spinel positive electrode active material with a gradient doped surface phosphorus element is formed. This doping improves the stability of the cathode material.
  • the lithium ion secondary battery containing the positive electrode active material of the present invention can be used as an energy source for applications such as electric tools, electric bicycles, hybrid electric vehicles, and pure electric vehicles.
  • FIG. 1 is a STEM image of LiNi 0.5 Mn 1.5 O 4 after phosphorus doping prepared in Example 1;
  • Example 2 is a STEM line scan of LiNi 0.5 Mn 1.5 O 4 after phosphorus doping prepared in Example 1;
  • Example 3 is a STEM image of the surface of LiNi 0.4 Mn 1.6 O 4 after phosphorus doping prepared in Example 2;
  • FIG. 4 shows the relative content change of phosphorus element on the surface obtained by XPS characterization of the LiNi 0.4 Mn 1.6 O 4 after phosphorus doping prepared in Example 2 at different etching depths;
  • Example 5 is a STEM image of the surface of LiNi 0.5 Mn 1.5 O 4 after phosphorus doping prepared in Example 3;
  • Example 6 is a charge-discharge cycle diagram of the original LiNi 0.5 Mn 1.5 O 4 and the phosphorus element doped LiNi 0.5 Mn 1.5 O 4 prepared in Example 1 at room temperature;
  • FIG. 7 is a graph of the coulombic efficiency of the original LiNi 0.5 Mn 1.5 O 4 and the phosphorus element doped LiNi 0.5 Mn 1.5 O 4 prepared in Example 1 at room temperature;
  • FIG. 8 is a charge-discharge cycle diagram of the original LiNi 0.5 Mn 1.5 O 4 and the phosphorus element doped LiNi 0.5 Mn 1.5 O 4 prepared in Example 1 at high temperature;
  • FIG. 9 is a graph of the coulombic efficiency of the original LiNi 0.5 Mn 1.5 O 4 and the phosphorus element doped LiNi 0.5 Mn 1.5 O 4 prepared in Example 1 at high temperature;
  • Fig. 10 is a charge-discharge cycle curve of the original LiNi 0.4 Mn 1.6 O 4 and the phosphorus element doped LiNi 0.4 Mn 1.6 O 4 prepared in Example 2 at high temperature;
  • Fig. 11 shows the coulombic efficiency curves of the original LiNi 0.4 Mn 1.6 O 4 and the phosphorus element doped LiNi 0.4 Mn 1.6 O 4 prepared in Example 2 at high temperature.
  • STEM is performed using a spherical aberration correction scanning transmission microscope model JEM ARM200F (JEOL, Tokyo, Japan);
  • X-ray photoelectron spectroscopy (XPS) is performed using ESCALAB 250 model X-ray photoelectron spectroscopy produced by Thermo Fisher
  • the instrument is used to study the types of elements on the surface of the powder sample and the chemical environment.
  • the X-ray radiation source is Mg K ⁇ .
  • Figure 1 shows the STEM image of the LiNi 0.5 Mn 1.5 O 4 doped with phosphorus element prepared in Example 1. From the STEM image of LiNi 0.5 Mn 1.5 O 4 after phosphorus doping in Fig. 1, it can be seen that the surface of the material has a rock-like salt phase generated by the spinel octahedral 16c atoms, and the thickness of the rock-like salt phase on the surface is about 12 nm.
  • Figure 2 (a) and (b) are STEM line scans of the surface of LiNi 0.5 Mn 1.5 O 4 after phosphorus doping prepared in Example 1. It can be seen from Figure 2 that the surface of lithium nickel manganese oxide is still A typical spinel structure of lithium nickel manganese oxide, combined with Figure 1, it can be seen that phosphorus is distributed in the rock-like salt phase on the surface of lithium nickel manganese oxide, and the content of phosphorus gradually decreases from the surface to the inside.
  • Fig. 3 shows the STEM image of LiNi 0.4 Mn 1.6 O 4 after phosphorus doping prepared in Example 2, where (a) and (b) are images at different magnifications. From the STEM image of LiNi 0.4 Mn 1.6 O 4 after phosphorus doping in Fig. 3, it can be seen that the surface of the material has a rock salt phase with 8a atoms occupied by spinel octahedrons, and the thickness of the rock salt phase on the surface is about 10 nm.
  • Figure 4 shows the relative content of phosphorus on the surface of the LiNi 0.4 Mn 1.6 O 4 after phosphorus doping prepared in Example 2 and characterized by XPS at different etching depths. We can see the phosphorus from the surface to the inside As the etching depth increases, the content decreases continuously.
  • FIG. 5 shows the STEM image of the LiNi 0.5 Mn 1.5 O 4 doped with phosphorus element prepared in Example 3. From the STEM image of LiNi 0.5 Mn 1.5 O 4 after phosphorus doping in Figure 5, it can be seen that there are 2 ⁇ 3nm spinel octahedrons 8a and 16c on the surface of the material. The thickness of the surface is about It is 2nm.
  • the positive electrode active material prepared in the examples was assembled into a button cell according to the following steps.
  • the positive electrode active material prepared in the examples, carbon black as a conductive additive and polyvinylidene fluoride (PVDF) as a binder were dispersed in N-methylpyrrolidone (NMP) at a weight ratio of 80:10:10, and mixed Uniform, prepared into a uniform positive electrode slurry. Coat the uniform positive electrode slurry uniformly on the aluminum foil current collector with a thickness of 15 ⁇ m, and dry it at 55°C to form a pole piece with a thickness of 100 ⁇ m. Place the pole piece on a roller press (pressure is about 1MPa). ⁇ 1.5cm 2 ), cut into diameter The discs were then placed in a vacuum oven at 120°C for 6 hours, and after natural cooling, they were taken out and placed in a glove box for use as a positive pole piece.
  • NMP N-methylpyrrolidone
  • lithium metal is used as the negative electrode of the battery, and a three-layer film of PP/PE/PP coated with aluminum oxide on both sides as a separator is placed between the positive and negative electrodes.
  • 1M LiPF 6 is added dropwise to dissolve in EC/DMC (volume ratio of 1:1) non-aqueous electrolyte, using the positive pole piece prepared in step (1) as the positive electrode, assembled into a button cell of model CR2032.
  • the prepared button battery was allowed to stand for 10 hours at room temperature (25°C), then the button battery was charged and discharged to activate, and then the blue battery charge and discharge tester was used to charge and discharge the button battery prepared above Cycle test. Firstly, at room temperature (25°C), cycle at a rate of 0.1C for 1 week, and then cycle at a rate of 0.2C for 4 weeks. The charge and discharge voltage range of the control battery is 3.5V ⁇ 4.9V. Then, the button battery was transferred to a high temperature environment of 55°C, and the cycle was continued for 50 weeks at a rate of 0.2C, while controlling the battery's charge and discharge voltage range to still be 3.5V to 4.9V.
  • the prepared button battery was allowed to stand for 10 hours at room temperature (25°C), then the button battery was charged and discharged to activate, and then the blue battery charge and discharge tester was used to charge and discharge the button battery prepared above Cycle test. Firstly, at room temperature (25°C), cycle for 1 week at a rate of 0.1C, and then continue to cycle at a rate of 0.2C for 200 weeks, where the charge and discharge voltage range of the control battery is 3.5V ⁇ 4.9V.
  • FIG. 6 and FIG. 7 show the charge-discharge cycle and efficiency graphs of the original LiNi 0.5 Mn 1.5 O 4 and the phosphorus element doped LiNi 0.5 Mn 1.5 O 4 prepared in Example 1 at room temperature.
  • the results show that the battery assembled from the original LiNi 0.5 Mn 1.5 O 4 material has a capacity of 93.6mAh/g, a coulombic efficiency of 99.25%, and a retention rate of about 69.7% after 200 weeks under a normal temperature test environment of 25°C. The capacity decays faster.
  • the P-doped material has a capacity of 120.4mAh after 200 weeks under a normal temperature test environment of 25°C. /g, the Coulomb efficiency is 99.71%, and the retention rate is about 94.36%.
  • the cycle stability of the battery is improved.
  • the electrolyte decomposes and the transition metal dissolves in a high temperature test environment, resulting in a faster capacity decay of the material; the material doped with phosphorus is tested at a high temperature of 55°C after 200 weeks The capacity is 113.9mAh/g, the coulombic efficiency is 98.24%, and the retention rate is about 86.61%. This is because after phosphorus doping, harmful side reactions between the cathode material and the electrolyte are alleviated, and the decomposition of the electrolyte is inhibited. The dissolution of transition metals improves the cycle stability of the battery.
  • FIG. 10 and FIG. 11 show the charge-discharge cycle and efficiency graphs of the original LiNi 0.4 Mn 1.6 O 4 and the phosphorus element doped LiNi 0.4 Mn 1.6 O 4 prepared in Example 2 at high temperature.
  • the results show that the battery assembled from the original LiNi 0.4 Mn 1.6 O 4 material has a capacity of 105.9 mAh/g, a coulombic efficiency of 98.54%, and a retention rate of about 81.9% under a high temperature test environment of 55°C after 100 weeks. The capacity decays faster.
  • the electrolyte decomposes and the transition metal dissolves in a high temperature test environment, which leads to a faster capacity decay of the material; the material doped with phosphorus is tested at a high temperature of 55°C after 100 weeks The capacity is 124.5mAh/g, the coulombic efficiency is 99%, and the retention rate is about 99.04%. This is because after phosphorus doping, harmful side reactions between the cathode material and the electrolyte are alleviated, and the decomposition of the electrolyte is inhibited. The dissolution of transition metals improves the cycle stability of the battery.

Abstract

提供一种具有尖晶石结构的正极活性材料，其包含化学式为Li 1+xNi 0.5-yMn 1.5-zO u的含锂化合物颗粒，其中-0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，3.8≤u≤4.2，其特征在于，所述含锂化合物颗粒的表面具有岩盐相表面层，所述岩盐相表面层具有梯度磷分布，并且包含占据尖晶石八面体16c或8a位置的金属元素。与现有技术相比，所提供的锂离子电池用表面梯度磷掺杂尖晶石正极活性材料具有如下优点：(1)制备方法工艺简单，成本低廉；(2)能大幅度提升尖晶石正极活性材料的综合性能，具有优异的发展前景。

Description

一种正极活性材料及其制备方法和锂电池 技术领域
本发明涉及一种用于锂离子电池的正极活性材料及其制备方法和包含该正极活性材料的正极和锂离子电池。
背景技术
锂离子二次电池与其它的可充电的电池体系相比，具有工作电压高、重量轻、体积小、无记忆效应、自放电率低、循环寿命长、能量密度高等优点，目前已广泛应用于手机、笔记本电脑、平板电脑等移动终端产品。近年来，出于对环境保护方面的考虑，电动汽车在各国政府和汽车制造商的推动下得到了迅速的发展，而锂离子二次电池凭借其优良的性能成为新一代电动汽车的理想动力源。
目前，人们关注的锂离子二次电池的正极材料大致可分为三类：以钴酸锂(LiCoO 2)为代表的层状型材料，以磷酸铁锂(LiFePO 4)为代表的橄榄石型材料和以锰酸锂(LiMn 2O 4)为代表的尖晶石结构材料。
尽管锂电池早在1991年就已经成功的商业化，但是对于目前现有的材料，其能量密度还需要进一步提高。尖晶石结构的高压材料，作为一种先进的正极材料，被认为是最有可能成为下一代高性能锂电池的正极材料。对于高压尖晶石正极材料来说，在循环过程中，由于传统的碳酸酯类电解液与正极材料相互作用，使正极材料表面丢氧，材料表面发生溶解，最终导致活性物质减少。
为了解决上述问题，人们提出了各种掺杂方案，其中包括各种金属掺杂(如Mg、Cr、Ti、Fe、Co、Ni或Cu等)。利用这些金属掺杂能够在材料内部以及表面形成新的化学键，从而稳固体相和表面的晶格氧。但是上述金属掺杂对镍锰酸锂材料的稳定性提高作用有限。
因此，提供一种制备过程简单，掺杂结构稳定的尖晶石正极材料及其制备方法是本领域技术人员需要迫切解决的问题。
发明内容
因此，本发明的目的是提供一种制备过程简单、掺杂结构稳定的尖晶石正极材料及其制备方法，以及包含该正极活性材料的正极和锂离子电池。
本发明提供了一种具有尖晶石结构的正极活性材料，其包含化学式为Li 1+xNi 0.5-yMn 1.5-zO u的含锂化合物颗粒，其中-0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，3.8≤u≤4.2，其特征在于，所述含锂化合物颗粒的表面具有岩盐相表面层，所述岩盐相表面层具有梯度磷分布，并且包含占据尖晶石八面体16c或8a位置的金属元素，所述金属元素为Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta和Sr中的一种或多种。
根据本发明提供的正极活性材料，其中，所述岩盐相表面层的厚度可以为0.5～50nm。所述岩盐相表面层中磷元素的含量由外向内逐渐降低。
本发明提供的正极活性材料是表面梯度磷掺杂的尖晶石结构的镍锰酸锂材料，其不同于现有技术中的磷酸盐包覆的正极活性材料。磷酸盐包覆的正极活性材料是指具有磷酸盐晶体结构的或者非晶态的磷酸盐覆盖在尖晶石正极材料表面所形成的材料，通过透射电镜能够看到材料表面有一层包覆层。本发明提供的表面梯度磷掺杂尖晶石结构的正极活性材料是磷元素从颗粒表面向内部呈梯度地掺杂到尖晶石结构内部，其表面结构的主体部分仍为尖晶石镍锰酸锂的晶格结构，并且从透射电镜图像中并未观察到表面具有包覆层。根据本发明提供的正极活性材料，其中，所述含锂化合物颗粒的粒径可以为0.1～30μm，优选为0.2～20μm。
根据本发明提供的正极材料，其中，表面的岩盐相表面层和磷元素梯度分布层可以用本领域常用的表征方法进行表征，例如可以采用扫描透射电子显微镜(STEM)和X射线光电子能谱显微镜(XPS)进行表征，其中利用STEM能够精确的看到表面由于部分金属元素占据尖晶石八面体16c或8a位置产生的岩盐相分布，STEM线扫也能够证明岩盐相表面层中磷元素的梯度分布。同时利用X射线光电子能谱的刻蚀分析也可以证明梯度磷元素分布层中磷元素的梯度分布。具体表征方法可以参见参见M.Lin,L.Ben,Y.Sun,H.Wang,Z.Yang,L.Gu,X.Yu,X.-Q.Yang,H.Zhao,R.Yu,M.Armand,X.Huang,Insight into the Atomic Structure of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material in the First Cycle.Chemistry of Materials 27,292-303(2015)，Y.Wu,L.Ben,H.Yu,W.Qi,Y.Zhan,W.Zhao,X.Huang,Understanding the Effect of Atomic-Scale Surface Migration of Bridging Ions in Binding Li3PO4 to the Surface of Spinel Cathode Materials.Acs Applied Materials&Interfaces 11,6937-6947(2019)，以及图1-5。
本发明还提供了上述正极活性材料的制备方法，所述制备方法包括以下步骤：
(1)将磷源、岩盐相诱导剂以及尖晶石结构的含锂化合物颗粒混合；
(2)将步骤(1)所得混合物于300～950℃下烧结0.5～10小时，得到所述具有尖晶石结构的正极活性材料。
根据本发明提供的制备方法，其中，所述磷源可以包括磷酸镍、磷酸钴、磷酸锰、磷酸镁、磷酸钙、磷酸铁、磷酸铜、磷酸锌、磷酸钛、磷酸锆、磷酸锂、焦磷酸钴、焦磷酸镍、焦磷酸锰、焦磷酸镁、焦磷酸钙、焦磷酸铁、焦磷酸铜、焦磷酸锌、焦磷酸钛、焦磷酸锆、磷酸铵、磷酸二氢铵、磷酸氢二铵、磷酸二氢锂、磷酸氢二锂、焦磷酸锂、焦磷酸、磷酸和五氧化二磷中一种或多种。
根据本发明提供的制备方法，其中，所述岩盐相诱导剂可以为Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta和Sr的氧化物和盐中的一种或多种，或者所述岩盐相诱导剂为酸性化合物，如盐酸、硝酸、硫酸、磷酸、乙酸、甲酸、草酸和柠檬酸中的一种或多种。
根据本发明提供的制备方法，其中，步骤(1)中磷源与含锂化合物颗粒的质量比可以为1:20～400，优选为1:30～100。步骤(1)中岩盐相诱导剂和含锂化合物颗粒的质量比可以为1:20～400，优选为1:30～100。
根据本发明提供的制备方法，其中，步骤(2)中所述煅烧可以在氧气、空气、含有还原性气体(如氢气)的气氛或惰性气氛(如氮气或氩气)或者在真空下进行。优选地，步骤(2)中的烧结过程的具体操作为：以0.5～10℃/min的升温速率升温至300～950℃，然后经过0.5～10h的烧结，随后以0.5～10℃/min的降温速率降至室温。
本发明还提供了采用如上所述的制备方法制备得到的锂离子电池用正极活性材料。
又一方面，本发明提供了所述正极活性材料在锂离子二次电池中的用途。
进一步地，本发明还提供了一种锂离子二次电池正极，该正极包括集流体以及负载在集流体上的正极活性材料，其中，所述正极活性材料为本发明提供的正极活性材料或者按照本发明方法制得的正极活性材料。
根据本发明提供的锂离子二次电池正极，其中，所述正极还可以包括 导电添加剂和粘结剂。
根据本发明提供的锂离子二次电池正极，其中，所述导电添加剂可以是本领域中常规的电添加剂，本发明对其没有特别限制。在一些实施方案中，所述导电添加剂为炭黑。
根据本发明提供的锂离子二次电池正极，其中，所述粘合剂可以是本领域中常规的粘合剂，本发明对其没有特别限制，可以由聚偏二氟乙烯(PVDF)构成，也可以由羧甲基纤维素(CMC)和丁苯橡胶(SBR)构成。在一些实施方案中，所述粘合剂为聚偏二氟乙烯(PVDF)。
进一步地，本发明还提供了一种锂离子二次电池，该电池包括正极、负极、隔膜和电解液，其中，所述正极是本发明提供的正极。
根据本发明提供的锂离子二次电池，其中，所述电池还包括壳体，以及其中，正极、负极、隔膜(统称为电极组)和电解液密封在壳体内。
根据本发明提供的金属锂二次电池，其中，所述负极、隔膜和电解液可以采用本领域中常规的负极、隔膜和电解液材料，本发明对它们没有特别限制。在一些实施方案中，负极为金属锂；在一些实施方案中，隔膜为双面涂覆有氧化铝的PP/PE/PP的三层膜；以及在一些实施方案中，电解液是LiPF 6的浓度为1mol/L的碳酸乙烯酯(EC)/碳酸二甲酯(DMC)非水系电解液，其中，EC与DMC的体积比为1:1。
本发明提供的正极活性材料的制备方法将含锂化合物颗粒、岩盐相诱导剂和磷源均匀混合，最后经过高温烧结即可得到磷元素由外向内梯度掺杂的尖晶石结构正极活性材料。其中，岩盐相诱导剂能够在含锂化合物表面产生由金属元素占据尖晶石八面体16c或8a位置产生的岩盐相，其中占据尖晶石八面体16c或8a位置的金属元素可以由除Ni、Mn以外的其他元素组成，如Mg、Zn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta等中的一种或多种，在这种情况下岩盐相诱导剂为Mg、Zn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta和Sr的氧化物和盐中的一种或多种。也可以由Ni、Mn组成，在这种情况下岩盐相诱导剂可以由不含金属的酸性化合物组成，如盐酸、硝酸、硫酸、磷酸、乙酸、甲酸、草酸和柠檬酸中的一种或多种，或者由Ni和Mn的氧化物和盐中的一种或多种。这层岩盐相表面层有利于磷元素在尖晶石正极表面的梯度掺杂，经过本方法处理后能显著提高尖晶石正极活性材料的电化学性能，包括首效、平均效率和循环稳定性。与现有技术相比，本发明提供的 锂离子电池用表面梯度磷掺杂尖晶石正极活性材料具有如下优点：(1)制备方法工艺简单可行，成本低廉；(2)能大幅度提升尖晶石正极活性材料的综合性能，具有优异的发展前景。
本发明提供的正极活性材料，经过掺杂明显地降低了尖晶石结构的正极材料与电解液之间的反应活性，稳定了尖晶石结构的正极活性材料的表面结构，抑制了在高温高压条件下循环过程中尖晶石结构的正极活性材料表面的锰溶解，从而提高了其容量保持率和充放电库伦效率。
本发明提供的正极活性材料可用作锂离子二次电池的正极活性材料，由该材料做成的电池具有优异的循环性能。
本发明提供的正极活性材料，明显提高了现有的正极活性材料的循环稳定性能和库伦效率。不希望受理论限制认为，通过本发明提供的方法，形成了表面磷元素梯度掺杂的尖晶石正极活性材料。这种掺杂提高了正极材料的稳定性。包含本发明的正极活性材料的锂离子二次电池可用作电动工具、电动自行车、混合动力电动交通工具和纯电动交通工具等应用的能量源。
附图的简要说明
图1为实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4的STEM图；
图2为实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4的STEM线扫图；
图3为实施例2制得的磷元素掺杂后LiNi 0.4Mn 1.6O 4表面的STEM图；
图4为实施例2制得的磷元素掺杂后LiNi 0.4Mn 1.6O 4在不同刻蚀深度下用XPS表征得到的表面磷元素的相对含量变化；
图5为实施例3制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4表面的STEM图；
图6为原始的LiNi 0.5Mn 1.5O 4和实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4在常温下的充放电循环图；
图7为原始的LiNi 0.5Mn 1.5O 4和实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4在常温下的库伦效率图；
图8为原始的LiNi 0.5Mn 1.5O 4和实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4在高温下的充放电循环图；
图9为原始的LiNi 0.5Mn 1.5O 4和实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4在高温下的库伦效率图；
图10为原始的LiNi 0.4Mn 1.6O 4和实施例2制得的磷元素掺杂后LiNi 0.4Mn 1.6O 4在高温下的充放电循环曲线；
图11为原始的LiNi 0.4Mn 1.6O 4和实施例2制得的磷元素掺杂后LiNi 0.4Mn 1.6O 4在高温下的库伦效率曲线。
实施发明的最佳方式
下面结合具体实施方式对本发明进行进一步的详细描述，给出的实施例仅为了阐明本发明，而不是为了限制本发明的范围。
以下实施例中，STEM采用型号为JEM ARM200F(JEOL，Tokyo，Japan)的球差矫正扫描透射显微镜进行；X射线光电子能谱(XPS)采用Thermo Fisher公司生产的ESCALAB 250型号的X射线光电子能谱仪来研究粉末样品表面元素的种类和化学环境，其中，X射线辐射源是Mg Kα。
实施例1
将18g的LiNi 0.5Mn 1.5O 4材料(山东齐兴能源材料有限公司)、0.54g CuO和0.267g(NH 4) 2HPO 4均匀混合，将所得混合物在氧气中600℃煅烧5h，升温速率为3℃/分钟，降温速率为5℃/分钟。
图1显示了实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4的STEM图。从图1磷元素掺杂后LiNi 0.5Mn 1.5O 4的STEM图可以看到，材料表面有尖晶石八面体16c原子占位产生的类岩盐相，表面类岩盐相的厚度约为12nm。
图2(a)和(b)为实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4表面的STEM线扫图，从图2可以看出掺杂后镍锰酸锂表面仍为典型的镍锰酸锂尖晶石结构，结合图1可以看出磷元素分布在镍锰酸锂表面的类岩盐相中，并且磷元素的含量从表面到内部逐渐递减。
实施例2
将18g的LiNi 0.4Mn 1.6O 4材料(山东齐兴能源材料有限公司)、0.54g H 3PO 4和1g草酸均匀混合，将所得混合物在氧气中600℃煅烧5h，升温速率为3℃/分钟，降温速率为5℃/分钟。
图3显示了实施例2制得的磷元素掺杂后LiNi 0.4Mn 1.6O 4的STEM图，其中(a)和(b)分别为不同倍率下的图像。从图3磷元素掺杂后LiNi 0.4Mn 1.6O 4的STEM图可以看到，材料表面有尖晶石八面体8a原子占位的类岩盐相，表面类岩盐相的厚度约为10nm。
图4显示了实施例2制得的磷元素掺杂后LiNi 0.4Mn 1.6O 4在不同刻蚀深度下用XPS表征得到的表面磷元素的相对含量变化，我们可以看出磷元素从表面到内部随着刻蚀深度的增加含量不断减少。
实施例3
将18g的LiNi 0.5Mn 1.5O 4材料(山东齐兴能源材料有限公司)、0.54g Cr 2O 3和0.267g(NH 4) 2HPO 4和20ml的去离子水加入烧杯中均匀混合，将烧杯置于120℃的油浴锅搅拌加热5h获得干燥混合物。将所得混合物在空气中725℃煅烧5h，升温速率为3℃/分钟，降温速率为5℃/分钟。
图5显示了实施例3制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4的STEM图。从图5磷元素掺杂后LiNi 0.5Mn 1.5O 4的STEM图可以看到，材料表面有2～3nm尖晶石八面体8a和16c原子占位的类岩盐相，表面类岩盐相的厚度约为2nm。
性能测试
将实施例中制备的正极活性材料按照如下的步骤装配成扣式电池。
(1)制备正极极片
将实施例中制备的正极活性材料、炭黑作为导电添加剂和聚偏二氟乙烯(PVDF)作为粘结剂，按照重量比80:10:10分散于N-甲基吡咯烷酮(NMP)中，混合均匀，制备成均匀的正极浆料。将均匀的正极浆料均匀涂覆在厚度为15μm的铝箔集流体上，在55℃下烘干，形成厚度为100μm的极片，将极片置于辊压机下辊压(压力约为1MPa×1.5cm 2)，裁剪成直径为
Figure PCTCN2019125847-appb-000001
的圆片，然后置于真空烘箱中于120℃下烘6小时，自然冷却后，取出置于手套箱中用作正极极片。
(2)装配锂离子二次电池
在充满惰性气氛的手套箱中，以金属锂作为电池的负极，双面涂覆氧化铝的PP/PE/PP的三层膜作为隔膜放在正极和负极之间，滴加1M LiPF 6溶解在EC/DMC(体积比为1：1)的非水系电解液，以步骤(1)制备的正极极片为正极，装配成型号为CR2032的扣式电池。
循环测试
(1)高温循环：
将制备的扣式电池在室温(25℃)条件下静置10个小时后，然后对扣式电池进行充放电活化，随后采用蓝电电池充放电测试仪对上述制备的扣式电池进行充放电循环测试。首先在室温条件下(25℃)，以0.1C的倍率循环1周，然后以0.2C的倍率继续循环4周，其中，控制电池的充放电电压范围为3.5V～4.9V。然后，将扣式电池转移至55℃的高温环境中，以0.2C的倍率继续循环50周，同时控制电池的充放电电压范围仍为3.5V～4.9V。
(2)室温循环：
将制备的扣式电池在室温(25℃)条件下静置10个小时后，然后对扣式电池进行充放电活化，随后采用蓝电电池充放电测试仪对上述制备的扣式电池进行充放电循环测试。首先在室温条件下(25℃)，以0.1C的倍率循环1周，然后以0.2C的倍率继续循环200周，其中，控制电池的充放电电压范围为3.5V～4.9V。
与采用本发明实施例包覆前的材料自身作为对照，测得的部分实施例数据列于表1中。
表1
Figure PCTCN2019125847-appb-000002
特别地，图6和图7显示了原始的LiNi 0.5Mn 1.5O 4和实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4在常温下的充放电循环和效率图。结果显示，原始的LiNi 0.5Mn 1.5O 4材料装配成的电池在25℃的常温测试环境下，经过200周之后的容量为93.6mAh/g，库伦效率为99.25％，保持率为约69.7％，容量衰减较快，这是由于电解液分解和正极材料过渡金属的溶解，导致材料的容量衰减较快；掺P后的材料在25℃的常温测试环境下，经过200周之 后的容量为120.4mAh/g，库伦效率为99.71％，保持率为约94.36％，这是由于经过磷掺杂后，缓解了正极材料与电解液之间的有害副反应，抑制了电解液分解以及过渡金属的溶解，从而使电池的循环稳定性提高。
图8和图9显示了原始的LiNi 0.5Mn 1.5O 4和实施例1制得的磷元素掺杂后LiNi 0.5Mn 1.5O 4在高温下的充放电循环和效率图。结果显示，原始的LiNi 0.5Mn 1.5O 4材料装配成的电池在55℃的高温测试环境下，经过200周之后的容量为8.7mAh/g，库伦效率为97.98％，保持率为约6.5％，容量衰减较快，这是由于在高温测试环境下，电解液分解，并且过渡金属溶解加剧，导致材料的容量衰减较快；掺磷后的材料在55℃的高温测试环境下，经过200周后的容量为113.9mAh/g，库伦效率为98.24％，保持率为约86.61％，这是由于经过磷掺杂后，缓解了正极材料与电解液之间的有害副反应，抑制了电解液分解以及过渡金属的溶解，从而使电池的循环稳定性提高。
特别地，图10和图11显示了原始的LiNi 0.4Mn 1.6O 4和实施例2制得的磷元素掺杂后LiNi 0.4Mn 1.6O 4在高温下的充放电循环和效率图。结果显示，原始的LiNi 0.4Mn 1.6O 4材料装配成的电池在55℃的高温测试环境下，经过100周之后的容量为105.9mAh/g，库伦效率为98.54％，保持率为约81.9％，容量衰减较快，这是由于在高温测试环境下，电解液分解，并且过渡金属溶解加剧，导致材料的容量衰减较快；掺磷后的材料在55℃的高温测试环境下，经过100周之后的容量为124.5mAh/g，库伦效率为99％，保持率为约99.04％，这是由于经过磷掺杂后，缓解了正极材料与电解液之间的有害副反应，抑制了电解液分解以及过渡金属的溶解，从而使电池的循环稳定性提高。
最后应说明的是，以上各实施例仅用于说明本发明的技术方案，而非对其限制；尽管参照前述各实施例对本发明进行了详细的说明，本领域技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的范围。

Claims (10)

  1. 一种具有尖晶石结构的正极活性材料，其包含化学式为Li 1+xNi 0.5-yMn 1.5-zO u的含锂化合物颗粒，其中-0.2≤x≤0.2，-0.2≤y≤0.2，-0.2≤z≤0.2，3.8≤u≤4.2，其特征在于，所述含锂化合物颗粒的表面具有岩盐相表面层，所述岩盐相表面层具有梯度磷分布，并且包含占据尖晶石八面体16c或8a位置的金属元素，所述金属元素为Mg、Zn、Ni、Mn、Fe、Co、Ti、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta和Sr中的一种或多种。
  2. 根据权利要求1所述的正极活性材料，其中，所述岩盐相表面层的厚度为0.5～50nm。
  3. 根据权利要求1所述的正极活性材料，其中，所述含锂化合物颗粒的粒径为0.1～30μm，优选为0.2～20μm。
  4. 根据权利要求1至3中任一项所述的正极活性材料，其中，所述岩盐相表面层中磷元素的含量由外向内逐渐降低。
  5. 权利要求1至4中任一项所述的具有尖晶石结构的正极活性材料的制备方法，所述制备方法包括以下步骤：
    (1)将磷源、岩盐相诱导剂以及尖晶石结构的含锂化合物颗粒混合；
    (2)将步骤(1)所得混合物于300～950℃下烧结0.5～10小时，得到所述具有尖晶石结构的正极活性材料。
  6. 根据权利要求5所述的制备方法，其中，所述磷源包括磷酸镍、磷酸钴、磷酸锰、磷酸镁、磷酸钙、磷酸铁、磷酸铜、磷酸锌、磷酸钛、磷酸锆、磷酸锂、焦磷酸钴、焦磷酸镍、焦磷酸锰、焦磷酸镁、焦磷酸钙、焦磷酸铁、焦磷酸铜、焦磷酸锌、焦磷酸钛、焦磷酸锆、磷酸铵、磷酸二氢铵、磷酸氢二铵、磷酸二氢锂、磷酸氢二锂、焦磷酸锂、焦磷酸、磷酸和五氧化二磷中一种或多种。
  7. 根据权利要求5所述的制备方法，其中，所述岩盐相诱导剂为Mg、Zn、Ni、Mn、Fe、Co、Ti、Cr、Y、Sc、Ru、Cu、Mo、Ge、W、Zr、Ca、Ta和Sr的氧化物和盐中的一种或多种，或者所述岩盐相诱导剂为盐酸、硝酸、硫酸、磷酸、乙酸、甲酸、草酸和柠檬酸中的一种或多种。
  8. 根据权利要求5所述的制备方法，其中，步骤(1)中磷源与含锂化合物颗粒的质量比为1:20～400，优选为1:30～100。步骤(1)中岩盐相诱导剂和含锂化合物颗粒的质量比为1:20～400，优选为1:30～100；
    优选地，步骤(2)中所述烧结的具体操作为：以0.5～10℃/min的升温速率升温至300～950℃，然后经过0.5～10h的烧结，随后以0.5～10℃/min的降温速率降至室温。
  9. 一种锂离子二次电池正极，该正极包括集流体以及负载在集流体上的正极活性材料，其中，所述正极活性材料为权利要求1至4中任一项所述的正极活性材料或者按照权利要求5至8中任一项所述方法制得的正极活性材料。
  10. 一种锂离子二次电池，该电池包括正极、负极、隔膜和电解液，其中，所述正极为权利要求9所述的锂离子二次电池正极。
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