WO2024255339A1 - 一种正极活性材料、正极片及锂离子电池 - Google Patents

一种正极活性材料、正极片及锂离子电池 Download PDF

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Publication number
WO2024255339A1
WO2024255339A1 PCT/CN2024/080523 CN2024080523W WO2024255339A1 WO 2024255339 A1 WO2024255339 A1 WO 2024255339A1 CN 2024080523 W CN2024080523 W CN 2024080523W WO 2024255339 A1 WO2024255339 A1 WO 2024255339A1
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Prior art keywords
positive electrode
electrode active
active material
lithium
coating layer
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French (fr)
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曾家江
李素丽
夏定国
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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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
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—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
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 a pole piece material, and in particular to a positive electrode active material, a positive electrode piece and a lithium ion battery, belonging to the technical field of secondary batteries.
  • the capacity of the positive electrode active material plays a vital role in the capacity of lithium-ion batteries.
  • the present application provides a positive electrode active material.
  • the lithium ion battery can have both excellent specific capacity and cycle stability, and is particularly suitable for a high-voltage environment.
  • the present application provides a positive electrode sheet, which includes the above-mentioned positive electrode active material, thereby helping to improve the gram capacity and cycle performance of the battery.
  • the present application also provides a lithium-ion battery, which includes the above-mentioned positive electrode active material or positive electrode sheet, so the lithium-ion battery has excellent performance in terms of gram capacity and cycle performance.
  • the present application provides a positive electrode active material, the positive electrode active material comprising a substrate and a coating layer covering at least a portion of the surface of the substrate;
  • the substrate comprises a lithium metal oxide represented by Formula 1 and/or Formula 2, and the coating layer comprises selenium; Li n1-y1 Na y1 Co e1 M1 b1 M2 a1 O 2 Formula 1 Li n2-y2-b2 Na y2 Co e2 M1 b2 M2 a2 O 2 Formula 2
  • M1 is selected from at least one of Te, W, Al, B, P, Se, Ti, La, Zr and K; M2 is a doping element different from M1;
  • the lithium metal oxide is a cubic crystal of Cmca space group, and has a 002 peak with 2 ⁇ of 17.9° to 18.1° and a 131 peak with 2 ⁇ of 67.0° to 67.5°.
  • the coating layer includes a first coating layer and a second coating layer in a direction away from the substrate;
  • the first coating layer includes at least one of a metal compound and the selenium element, and the second coating layer includes at least one of a metal compound and the selenium element;
  • the first coating layer and the second coating layer have different compositions.
  • the first coating layer includes selenium, and the second coating layer includes a metal compound.
  • the coating layer containing the selenium element is a selenium single substance layer or a selenium-metal alloy layer.
  • the lithium-containing oxide includes at least one of LATP, LLTO, LLZO, Li 3 BO 3 , and Li 3 PO 4 .
  • the present application provides a positive electrode sheet, which includes any of the positive electrode active materials described above.
  • the positive electrode sheet as described above has a gram capacity of ⁇ 225 mAh/g under the condition that the button battery has a voltage of ⁇ 4.55 V.
  • the present application also provides a lithium-ion battery, which includes any of the above-mentioned positive electrode active materials or positive electrode sheets.
  • the positive electrode active material of the present application has a special crystal phase structure, chemical composition and Se coating structure. After being applied to lithium-ion batteries, the cycle performance and gram capacity of the battery are significantly improved. Even under high-voltage conditions of 4.5V and above, the positive electrode active material will not have structural collapse due to poor pressure resistance. The good structural stability can ensure the deintercalation of more lithium ions, thereby showing excellent gram capacity and cycle performance of lithium-ion batteries.
  • FIG1 is a partial structural schematic diagram of an embodiment of a negative electrode sheet in a lithium-ion battery of the present application
  • FIG2 is a TEM image of the intermediate positive electrode active material 1B in Example 1 of the present application.
  • FIG3 is a TEM image of the positive electrode active material 1C of Example 1 of the present application.
  • FIG4 is a charge and discharge curve of a button cell assembled from the positive electrode active material of Example 1 of the present application;
  • FIG5 is an XRD diagram of the positive electrode active material of Example 1 of the present application.
  • FIG. 6 is an XRD diagram of the positive electrode active material of Example 6 of the present application.
  • the present application provides a positive electrode active material, the positive electrode active material comprising a substrate and a coating layer covering at least a portion of the surface of the substrate;
  • the substrate comprises a lithium metal oxide represented by Formula 1 and/or Formula 2, and the coating layer comprises selenium; Li n1-y1 Na y1 Co e1 M1 b1 M2 a1 O 2 Formula 1 Li n2-y2-b2 Na y2 Co e2 M1 b2 M2 a2 O 2 Formula 2
  • M1 is selected from at least one of Te, W, Al, B, P, Se, Ti, La, Zr and K;
  • M2 is a doping element different from M1;
  • the lithium metal oxide is a cubic crystal of Cmca space group, and has a 002 peak with 2 ⁇ of 17.9° to 18.1° and a 131 peak with 2 ⁇ of 67.0° to 67.5°.
  • the positive electrode active material of the present application has a core-shell coating structure, wherein the substrate exists as the core and the coating layer is coated on at least part of the surface of the substrate.
  • the matrix includes the lithium metal oxide shown in Formula 1 and/or Formula 2, that is, the lithium metal oxide may include only the compound shown in Formula 1, or may include only the compound shown in Formula 2, or may include both the compounds shown in Formula 1 and Formula 2.
  • the present application does not limit the specific selection of M2, which may be a common doping element in the art, for example, at least one of Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B and P elements; the coating layer includes selenium.
  • n1 in Formula 1 and n2 in Formula 2 are parameters related to the molar amount of elemental lithium in lithium metal oxide.
  • n1 and n2 in Formula 2 are parameters related to the molar amount of elemental lithium in lithium metal oxide.
  • n1 and n2 will change under different charge and discharge mechanisms and charge and discharge nodes.
  • n1 and n2 of the lithium metal oxide are between 0.7 and 1.0. Need It is noted that the change in the values of n1 and n2 refers to the number of charge and discharge cycles within 10.
  • the lithium metal oxides represented by Formula 1 and Formula 2 having the aforementioned crystal structure have some vacancies, so when they are charged and discharged, their vacancies can accept lithium atoms from the lithium negative electrode, thereby increasing the molar amount of lithium ions compared to before the charge and discharge application. This feature helps to further improve the cycle performance and specific capacity of the battery.
  • the positive electrode active material can be detected by an inductively coupled plasma spectrometer (ICP).
  • ICP inductively coupled plasma spectrometer
  • the discharged battery is disassembled and the positive electrode sheet is taken out.
  • the positive electrode sheet is soaked in dimethyl carbonate (DMC) for 1-3 hours or rinsed with DMC, and then naturally dried in a drying room. It is then placed in a muffle furnace and calcined at 300-600°C for 2-5 hours. After that, the active layer falls off the current collector and is sieved with 200 mesh to obtain a powder to be detected. Subsequently, the metal elements in the powder to be detected are detected by ICP, and n1 and n2 are calculated.
  • DMC dimethyl carbonate
  • n1 and n2 are calculated.
  • the positive electrode active material including the lithium metal oxide is applied to the lithium ion battery, the specific capacity and cycle performance of the lithium ion battery are significantly improved, and the electrical performance of the lithium ion battery will not deteriorate even under high voltage working conditions.
  • the present application provides a coating layer containing Se elements so that the positive electrode active material is a core-shell structure including a lithium metal oxide inner core and a coating layer covering the inner core.
  • the coating layer helps to reduce or inhibit the side reactions between the lithium metal oxide and the electrolyte. Even when the battery is working under high voltage, a stable interface can still be formed between the positive electrode active material and the electrolyte.
  • the cycle performance of the battery is improved by avoiding the transitional dissolution of metal ions in the positive electrode active ions and avoiding liquid shortage.
  • the inhibition or reduction of side reactions can also reduce the gas production inside the battery, thereby ensuring the safety performance of the battery.
  • the selenium element in the coating layer has good electron transport properties, which makes the positive electrode active material have excellent conductivity, thereby improving the discharge capacity and cycle performance of the lithium-ion battery.
  • the lithium metal oxide with the above-mentioned crystal characteristics has a more complete layered crystal phase structure, which can reduce or inhibit the occurrence of internal mixing of the crystal phase, thereby enabling the smooth deintercalation of lithium ions, especially in the high-voltage charging and discharging process, showing multiple small charging and discharging platforms with excellent discharge capacity, ensuring the discharge and cycle stability under high voltage.
  • the first-stage discharge capacity of the positive electrode active material accounts for C1/C0 ⁇ 9%, and the second-stage discharge capacity accounts for C2/C0 ⁇ 25%; wherein C0 is the discharge capacity of a half-cell including the positive electrode active material when subjected to a discharge treatment at a voltage of 3.0 to 4.55V; in the discharge treatment, the capacity of the half-cell when discharged from the initial discharge voltage to 4.4V is defined as C1, and the capacity released when the half-cell is discharged from 3.8 to 3.7V is defined as C2.
  • the above discharge capacity is carried out under a special discharge mechanism. Specifically, after the half-battery consisting of the positive electrode sheet of the positive electrode active material and the lithium metal negative electrode is charged to a SOC of 100% (the charging mechanism is not specifically limited), it is discharged at 0.1C at 3.0-4.55V. Among them, when it is discharged from 4.55V to 4.4V at 0.1C, the amount of electricity released is C1, and when it continues to discharge from 3.8V to 3.7V, the amount of electricity released in the voltage reduction stage is C2, and when it continues to discharge to 3.0V (at this time, the SOC is 0), the total amount of electricity released at the beginning of its self-discharge is C0.
  • the positive electrode active material including the lithium metal oxide of the present application has strong pressure resistance, so that the specific capacity of the battery can be increased by performing a voltage boost treatment on it.
  • the coating layer of the present application includes a first coating layer and a second coating layer in a direction away from the substrate, and the first coating layer includes at least one of a metal compound and selenium, and the second coating layer includes a metal compound and the At least one of the elements selenium.
  • the above-mentioned double-layer coating arrangement can not only further reduce or inhibit the side reaction between lithium metal oxide and electrolyte, but also promote the improvement of discharge capacity and discharge stability of positive electrode active materials to a certain extent.
  • the material of the first coating layer and the material of the second coating layer independently include at least one of a metal compound and a selenium element, that is, the two can be the same or different. Especially when the two are different, the degree of improvement in the electrical performance of the lithium-ion battery is more prominent.
  • the first coating layer includes a metal compound
  • the second coating layer includes selenium. That is, the first coating layer and the second coating layer have different compositions, and the material of the first coating layer includes a metal compound, and the material of the second coating layer includes selenium.
  • the first coating layer includes selenium
  • the second coating layer includes a metal compound. That is, the first coating layer and the second coating layer have different compositions, and the material of the first coating layer includes selenium, and the material of the second coating layer includes a metal compound.
  • the inventors have found that when the first coating layer includes a metal compound and the second coating layer includes selenium, not only is the operability of preparing the positive electrode active material higher, but the electrical properties of the lithium-ion battery, including cycle performance and specific capacity, are also better.
  • the coating layer including selenium is a single-substance selenium layer or a selenium-metal alloy layer.
  • the present application does not limit the selection of the metal alloy, such as lithium-selenium alloy, ferro-selenium alloy, selenium-zinc alloy, etc.
  • the preparation process of using a single-substance selenium layer as the coating layer including selenium is simpler, saves costs, and has good capacity and cycle performance.
  • the mass percentage of selenium in the positive electrode active material is less than 5000 ppm, it is beneficial to improve the lithium ion insertion and extraction performance of the positive electrode active material, so that the specific capacity and cycle performance of the lithium ion battery are more significantly improved.
  • the present application does not limit the specific selection of the metal compound, which may include at least one of lithium-containing oxides, aluminum-containing oxides, magnesium-containing oxides, zirconium-containing oxides, and titanium-containing oxides.
  • the specific capacity of the positive electrode active material can be further improved by limiting the lithium ion conductivity of the lithium-containing oxide.
  • the lithium-ion conductivity of the lithium-containing oxide is at least greater than 1 ⁇ 10 ⁇ 3 S/cm.
  • the lithium-containing oxide includes at least one of LATP (lithium aluminum titanium phosphate), LLTO (lithium lanthanum titanium oxide), LLZO (lithium lanthanum zirconium oxide), Li 3 BO 3 , and Li 3 PO 4 .
  • LATP lithium aluminum titanium phosphate
  • LLTO lithium lanthanum titanium oxide
  • LLZO lithium lanthanum zirconium oxide
  • Li 3 BO 3 Li 3 PO 4 .
  • one of the first coating layer and the second coating layer in the positive electrode active material of the present application also includes selenium.
  • the Dv50 particle size when the cumulative volume reaches 50% of the total volume of all positive electrode active materials
  • the positive electrode active material of this particle size has excellent performance in fluidity and is more likely to form a densely packed state.
  • the present application does not impose too many restrictions on the thickness of the first coating layer and the second coating layer.
  • the thickness of the first coating layer is not greater than 20 nm, and/or the thickness of the second coating layer is not greater than 100 nm, it is beneficial to the deintercalation of lithium ions, further increasing the gram capacity of the positive electrode active material.
  • the thickness of the first coating layer may be, for example, 2 nm, 5 nm, 7 nm, 10 nm, 13 nm, 15 nm, 18 nm, or 20 nm; the thickness of the second coating layer may be, for example, 10 nm, 15 nm, 27 nm, 40 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.
  • the positive electrode active material of the present application may be in a single crystal or polycrystalline morphology, and the specific morphology is related to the selection and proportion of the doping elements. Specifically, when it is a polycrystalline morphology, it is a spherical or quasi-spherical particle; when it is a single crystal morphology, it may be It can be in the shape of whiskers, flakes, or any other irregular shapes.
  • the present application does not limit the preparation method of the positive electrode active material. Taking the example that the first coating layer includes a metal compound and the second coating layer includes selenium, for example, the first coating layer is coated on the surface of the lithium metal oxide shown in Formula 1 and/or Formula 2 using atomic layer vapor deposition (ALD) to obtain an intermediate positive electrode active material; then the intermediate positive electrode active material is mixed with the second coating source and sintered to form a second coating layer on the surface of the first coating layer to obtain the positive electrode active material of the present application.
  • ALD atomic layer vapor deposition
  • the lithium metal oxide represented by Formula 1 and/or Formula 2 is placed in a reaction chamber of an ALD reaction device, the reaction temperature is controlled, and a first coating source is introduced into the reaction chamber using an inert gas as a carrier gas, and an atomic layer is vapor-deposited on the surface of the lithium metal oxide in an interval pulse manner to form a first coating layer (i.e., an intermediate positive electrode active material) including a metal compound on the lithium metal oxide; subsequently, the intermediate positive electrode active material and the second coating source are evenly mixed using a mixing device, and the mixture is introduced into a corresponding sintering device for sintering treatment to obtain the positive electrode active material of the present application.
  • a first coating source is introduced into the reaction chamber using an inert gas as a carrier gas, and an atomic layer is vapor-deposited on the surface of the lithium metal oxide in an interval pulse manner to form a first coating layer (i.e., an intermediate positive electrode active material) including a metal compound on the lithium metal oxide; subsequently, the intermediate positive electrode active
  • the above-mentioned first coating source refers to the raw material used to form the first coating layer.
  • the first coating source is a lithium source (for example, lithium tert-butoxide, lithium di(trimethylsilyl)amide and other organic lithium-containing compounds), an aluminum source (for example, trimethylaluminum and other aluminum-containing organic compounds), a phosphorus source (for example, trimethylphosphorus and other phosphorus-containing organic compounds) and a titanium source (for example, titanium tetrachloride and other titanium-containing organic compounds);
  • the first coating layer is aluminum oxide
  • the first coating source is, for example, trimethylaluminum and other aluminum-containing organic compounds;
  • the first coating source is, for example, bismuthocene magnesium-containing organic compounds.
  • the reaction temperature is 120°C to 350°C, for example, 150°C, 170°C, 180°C, 220°C, 250°C, 270°C, 300°C, 330°C, or 350°C.
  • the number of interval pulses is 20 to 220 times, for example, 30 times, 50 times, 70 times, 90 times, 100 times, 120 times, 140 times, 150 times, 150 times, or 200 times.
  • the inert gas includes argon or nitrogen. Further, the flow rate of the inert gas as a carrier gas into the reaction chamber is 20-100 mL/min, for example, 20 mL/min, 40 mL/min, 50 mL/min, 80 mL/min, 100 mL/min.
  • the second coating source is a raw material used to form the second coating layer.
  • the second coating source is selenium single substance;
  • the second coating source can be a lithium-selenium alloy, a selenium-iron alloy, a selenium-zinc alloy, etc.
  • the selenium content in the positive electrode active material is controlled by controlling the mass of selenium in the second coating source.
  • the sintering temperature is 200 to 350° C., further 250 to 350° C.; the sintering time is 5 to 60 min, further 25 to 50 min.
  • the present application does not limit the preparation method of the lithium metal oxides shown in Formula 1 and Formula 2.
  • the lithium metal oxide of the present application can be prepared by mixing the sodium metal oxide shown in Formula 1a and 2a with a lithium compound and performing ion treatment.
  • the above-mentioned ion exchange treatment is a heat treatment process, specifically refers to mixing sodium metal oxide and lithium compound and then heat treating them at 80°C to 300°C for no more than 10 hours. After the ion exchange treatment, the system after ion exchange is washed and dried to finally obtain lithium metal oxide.
  • the drying temperature is 80 to 180°C and the time is at least 10 hours. There is no limitation on the equipment for ion exchange treatment and drying equipment.
  • the equipment for ion exchange treatment can be a device with a dense
  • the closed container equipment can be with sealing function and stirring ability, such as wet coating reaction equipment, co-precipitation reaction equipment, etc.
  • the drying equipment can be a blast oven, vacuum drying oven, rotary kiln, tray dryer, oven, etc.
  • the lithium compound can be a lithium source compound commonly used in the art, such as at least one of lithium carbonate, lithium chloride, lithium bromide, lithium iodide, lithium nitrate, lithium hydroxide, and lithium fluoride.
  • the mass ratio of the lithium compound to the sodium metal oxide is not less than 1:1, preferably (1-3):1.
  • sodium metal compounds shown in Formula 1a and Formula 2a for example, they can be prepared by a method including the following process:
  • the cobalt source, the sodium source, the M1 source and the M2 source are mixed in a target ratio and then calcined to obtain the sodium metal compounds represented by Formula 1a and Formula 2a.
  • the calcination temperature is 700-900°C
  • the time is 8-50 hours
  • the calcination can be carried out in an oxygen or air atmosphere.
  • the calcination equipment can be, for example, a muffle furnace, a tunnel furnace, a roller kiln, a tubular furnace, or other high-temperature sintering equipment.
  • the mixing of the above sources can be performed by high-speed mixing equipment, sand milling equipment, ball milling equipment, plowshare mixing equipment, oblique mixing equipment, etc. It should be noted that if sand milling equipment or ball milling equipment is used and solvent (water, ethanol or other solvent medium) is added during the ball milling or sand milling process, the mixed system needs to be dried after the mixing process is completed. Generally, the mixing time is not more than 4 hours.
  • cobalt source is selected from one or more of cobalt hydroxide, cobalt trioxide, doped cobalt trioxide, cobaltous oxide, cobalt oxyhydroxide, cobalt nitrate, cobalt sulfate, etc.
  • the sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, sodium sulfate, etc.
  • the M1 source can be any compound containing M1, such as an oxide of M1.
  • the M1 source is, for example, tungstic acid and/or sodium tungstate, etc.; when M1 is Te, the M1 source is, for example, telluric acid and/or sodium tellurate, etc.; when M1 is Al, the M1 source is, for example, aluminum sulfate , aluminum nitrate, aluminum hydroxide, etc.; when M1 is B, the M1 source is, for example, boric acid and/or sodium borate, etc.; when M1 is P, the M1 source is, for example, phosphoric acid and/or sodium phosphate, etc.; when M1 is K, the M1 source is, for example, one or more of potassium carbonate, potassium nitrate, potassium hydroxide, potassium bicarbonate, potassium sulfate, etc.; the M2 source can be any compound containing M2, such as an oxide of M2, such as one or more of basic magnesium carbonate, magnesium hydroxide, zirconium oxide, yttrium oxide, lanthan
  • a second aspect of the present application provides a positive electrode sheet, which includes the positive electrode active material described in the first aspect.
  • the positive electrode sheet of the present application helps to improve the cycle performance and specific capacity of the battery.
  • the positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active layer includes the aforementioned positive electrode active material.
  • the positive electrode active layer also includes a conductive agent and a binder.
  • the positive electrode active layer includes 70-99wt% of the positive electrode active material, 0.5-15wt% of the conductive agent, and 0.5-15wt% of the binder according to the mass percentage, and further includes 80-98wt% of the positive electrode active material, 1-10wt% of the conductive agent, and 1-10wt% of the binder.
  • the selection of the conductive agent and the binder is not special and can be selected conventionally in the art.
  • the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon fiber
  • the binder is selected from polyvinylidene fluoride (PVDF), PVDF-HFP, polyvinyl fluoride (PVDF-HFP), ... At least one of tetrafluoroethylene (PTFE), polyacrylate lithium (PAALi), and polypropylene (PAA).
  • a safety layer can be provided between the positive electrode active layer and the current collector.
  • the material of the safety layer can be a non-conductive safety material, such as iron-containing compounds (such as lithium iron phosphate, lithium phosphate, etc.), aluminum-containing compounds (such as aluminum oxide), silicon oxide, high-impedance carbon black, PTC materials, etc.
  • the safety layer also includes a binder, and the ratio of the binder to the safety material can be further determined according to specific needs.
  • the safety layer may also be a conductive material, such as conductive titanium dioxide.
  • the third aspect of the present application provides a lithium-ion battery, which includes the positive electrode active material of the first aspect or the positive electrode sheet of the second aspect, and thus has outstanding performance in terms of cycle performance and specific capacity.
  • the present application does not limit the specific structure of the lithium-ion battery, for example, it may be a square shell or a cylindrical battery, etc.
  • the lithium-ion battery of the present application also includes a negative electrode sheet, a separator and an electrolyte.
  • the electrolyte is a conventional electrolyte known in the art including a lithium salt and a solvent, and the solvent contains ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC), propylene carbonate (abbreviated as PC), and fluoroethylene carbonate (abbreviated as FEC).
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • PC propylene carbonate
  • FEC fluoroethylene carbonate
  • the additive also includes an additive represented by formula T, whose mass percentage in the electrolyte is 0.1-10%.
  • the additive is combined with the positive electrode material to meet the battery working under high voltage ( ⁇ 4.5V) conditions.
  • the negative electrode sheet may be a negative electrode sheet containing a lithium layer, for example, a lithium foil or a negative electrode sheet as shown in FIG1 .
  • the negative electrode sheet in FIG1 includes a negative electrode current collector 101, a negative electrode active layer 20 and a lithium material layer 30 which are stacked.
  • the negative electrode sheet in FIG1 is double-sided, and of course, it may also be a negative electrode sheet in which the negative electrode active layer 20 and the lithium material layer 30 are only arranged on one side of the negative electrode current collector 101.
  • the lithium material layer is, for example, a lithium foil, and further, the surface density of the metal lithium in the lithium material layer is 0.09 mg/cm 2 to 3.5 mg/cm 2 ;
  • the negative electrode active layer includes a negative electrode active material, a conductive agent and a binder.
  • the negative electrode active layer includes 70-99wt% of negative electrode active material, 0.5-15wt% of conductive agent, and 0.5-15wt% of binder according to mass percentage, and further includes 80-98wt% of negative electrode active material, 1-10wt% of conductive agent, and 1-10wt% of binder.
  • the negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbon, and silicon oxide.
  • the diaphragm is a material with polypropylene as the base material, or a rubber-coated diaphragm with ceramic coated on one side or both sides thereof.
  • the lithium-ion battery of the present application is suitable for high-voltage systems, including a lithium-ion button battery with the aforementioned positive electrode sheet.
  • the positive electrode sheet Under the condition of ⁇ 4.55V (relative to lithium), the positive electrode sheet has a gram capacity of ⁇ 225mAh/g, and has excellent cycle performance at ⁇ 4.50V (corresponding to the aforementioned negative electrode sheet).
  • the lithium-ion battery of the present application has good cycle stability and high gram capacity at higher voltages such as 4.50V, which can meet the demand for lightweight and thin use of high-end digital products.
  • FIG. 3 is the TEM image of the positive electrode active material 1C of Example 1 of the present application. As shown in Figure 3 (wherein area A is the core, area B is the first coating layer, and area C is the second coating layer), it can be seen that the thickness of the second coating layer is 17 to 20nm.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that: in step (5), 5 g of sample 1A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment, the reaction temperature is controlled to be 290°C, lithium tert-butoxide, trimethylaluminum, titanium tetrachloride, and trimethylphosphine are introduced into the reaction chamber by an inert gas as a carrier gas, and the atomic layer is vapor-deposited on the surface of 1A with 100 interval pulses, thereby forming an intermediate positive electrode active material 2B having a first coating layer.
  • the TEM test of the 2B sample shows that the thickness of the first coating layer is 8 to 9 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that: in step (5), 5 g of sample 1A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment, the reaction temperature is controlled to be 290° C., and lithium tert-butoxide, trimethylaluminum, titanium tetrachloride, and trimethylphosphine are introduced into the reaction chamber with an inert gas as a carrier gas. In the reaction chamber, the atomic layer was vapor deposited on the surface of 1A with 80 interval pulses, thereby forming the intermediate positive electrode active material 3B with the first coating layer. The TEM test of the 3B sample showed that the thickness of the first coating layer was 6-7 nm. The relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that step (6): 3.5 g of 1B sample and 7.0 mg of selenium powder are weighed, mixed with a small high-speed mixer for 10 min, and then placed in a corresponding VBF-1200X muffle furnace equipment, sintered at 300°C for 15 min to obtain the positive electrode active material 4C of this embodiment; TEM test of the 4C sample shows that the thickness of the coating layer is 14-16 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that step (6): 3.5 g of 1B sample and 10.5 mg of selenium powder are weighed, mixed with a small high-speed mixer for 10 min, and then placed in a corresponding VBF-1200X muffle furnace equipment, sintered at 300°C for 15 min to obtain the positive electrode active material 5C of this embodiment; TEM test of the 5C sample shows that the thickness of its second coating layer is 25-30 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that:
  • step (1) 38.153 g of sodium carbonate powder, 1.96 g of phosphoric acid powder, 276.498 g of cobalt nitrate hexahydrate powder and 1.529 g of nano alumina powder are taken and placed in a high-speed mixing device.
  • the mixing program is set to mix at 300 rpm for 3 minutes, then at 500 rpm for 5 minutes, and then at 1000 rpm for 10 minutes. After taking out the mixture, it is confirmed that there are no white sodium carbonate spots in the mixture, and the mixture is considered to be uniform;
  • the sodium metal oxide obtained in step (2) is Na 0.72 Co 0.95 Al 0.03 P 0.02 O 2 ;
  • sample 6A After treatment in step (4), sample 6A was obtained, whose chemical formula was Li 0.717 Na 0.003 Co 0.95 Al 0.03 P 0.02 O 2 ;
  • sample 6C was obtained.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment, the reaction temperature is controlled to be 290°C, lithium tert-butoxide, triethyl borate and deionized water are introduced into the reaction chamber by an inert gas as a carrier gas, and the atomic layer is vapor-deposited on the surface of the lithium metal oxide with 150 interval pulses, thereby forming an intermediate positive electrode active material 7B having a first coating layer.
  • the TEM test of the 7B sample shows that the thickness of the first coating layer is 11 to 13 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 6, except that: step (5) 5 g of the sample 6A powder obtained in step (4) was weighed and placed in the reaction chamber of the ALD reaction equipment, the reaction temperature was controlled to be 220° C. trimethylaluminum and deionized water were introduced into the reaction chamber by inert gas as carrier gas, and the atomic layer was vapor-deposited on the surface of the lithium metal oxide with 150 interval pulses, thereby forming an intermediate positive electrode active material 8B having a first coating layer.
  • the TEM test of the 8B sample showed that the thickness of the first coating layer was 11 to 13 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment, the reaction temperature is controlled to be 220°C, bismuthocene magnesium and deionized water are introduced into the reaction chamber by inert gas as carrier gas, and atomic layer vapor deposition is performed on the surface of lithium metal oxide with 150 interval pulses, thereby forming an intermediate positive electrode active material 9B having a first coating layer.
  • the 9B sample is tested by TEM, and it is known that the thickness of the first coating layer is 11 to 13 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that step (6): 3.5 g of 1B sample and 35 mg of selenium powder are weighed, mixed with a small high-speed mixer for 10 min, and then placed in a corresponding VBF-1200X muffle furnace equipment, sintered at 300°C for 15 min to obtain the positive electrode active material 10C of this embodiment; TEM test of the 10C sample shows that the thickness of the second coating layer is 120-125 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment, the reaction temperature is controlled to be 290°C, lithium tert-butoxide, tri(N,N-diisopropylformamidine) lanthanum (LaFAMD), titanium tetrachloride, and deionized water are introduced into the reaction chamber by an inert gas as a carrier gas, and the atomic layer is vapor-deposited on the surface of the lithium metal oxide with 150 interval pulses, thereby forming an intermediate positive electrode active material 11B having a first coating layer.
  • the 11B sample is tested by TEM, and it is known that the thickness of the first coating layer is 11 to 13 nm.
  • Table 1 The relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment, the reaction temperature is controlled to be 290°C, lithium tert-butoxide, tri(N,N-diisopropylformamidine) lanthanum (LaFAMD), tetrakis(dimethylamino)zirconium (TDMAZ), and deionized water are introduced into the reaction chamber by an inert gas as a carrier gas, and the atomic layer is vapor-deposited on the surface of the lithium metal oxide with 150 interval pulses, thereby forming an intermediate positive electrode active material 12B having a first coating layer.
  • the 12B sample is subjected to TEM test, and it is known that the thickness of the first coating layer is 11 to 13 nm.
  • Table 1 The relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that step (6): 3.5 g of 1B sample and 8.75 mg of lithium-selenium alloy powder are weighed, mixed with a small high-speed mixer for 10 min, and then placed in a corresponding VBF-1200X muffle furnace equipment, sintered at 300°C for 15 min to obtain the positive electrode active material 13C of this embodiment; TEM test of the 13C sample shows that the thickness of the second coating layer is 17-20 nm.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that: step 5) and step 6) in embodiment 1 are replaced in sequence to obtain the positive electrode active material 14C of embodiment 14.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that the ALD coating temperature and pulse number in step (5) are used.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that the treatment of step (5) is not performed, and the treatment of step (6) is directly performed after step (4) to obtain the positive electrode active material of embodiment 16.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the positive electrode active material of this comparative example includes a conventional high voltage doped lithium cobalt oxide positive electrode material, and the chemical composition of sample 10A is Li 1.0027 Co 0.97 Al 0.03 O 2 .
  • the above-mentioned lithium cobalt oxide positive electrode material 10A was weighed according to step (5) of Example 1 and placed in the reaction chamber of the ALD reaction equipment. The reaction temperature was controlled to 290°C. Lithium tert-butoxide, trimethylaluminum, titanium tetrachloride and trimethylphosphine were introduced into the reaction chamber using inert gas as carrier gas. Atomic layer vapor deposition was performed on the surface of lithium metal oxide with 150 interval pulses to form a material 10B having a first coating layer. TEM test was performed on the 10B sample, and it was found that the thickness of the first coating layer was 10 to 12 nm.
  • the preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that: the treatments in steps (5) and (6) are not performed, and the 1A sample obtained in step (4) is directly used as the positive electrode active material of comparative example 2.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that the treatment in step (6) is not performed, and the 1B sample obtained in step (5) is directly used as the positive electrode active material of comparative example 3.
  • the relevant preparation parameters in the preparation process are shown in Table 1.
  • the positive electrode active materials obtained in all the examples and comparative examples were subjected to TEM test and ICP test to detect the coating thickness, chemical composition and Se content of the positive electrode active materials.
  • the intermediate positive electrode active material subjected to the first coating treatment was also subjected to TEM test to observe the thickness of the first coating layer. The results are shown in Table 1.
  • the positive electrode active materials obtained in all the embodiments and comparative examples are made into positive electrode sheets, they are assembled with negative electrode sheets, electrolytes and separators according to the following method to obtain lithium-ion batteries.
  • the method includes:
  • the positive electrode active materials in the embodiment and the comparative example were mixed with conductive carbon black and PVDF in a weight ratio of 96%:2%:2% respectively, and a positive electrode slurry was obtained by dispersion. The slurry was coated on an aluminum foil current collector and rolled to obtain a positive electrode sheet;
  • the lithium material layer is a lithium foil, and the surface density of the metal lithium is 1.0 mg/cm 2 , and finally a negative electrode sheet containing lithium metal is obtained.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • PC propylene carbonate
  • FEC fluoroethylene carbonate
  • LiPF 6 lithium hexafluorophosphate
  • T an additive shown in formula T are added, and the content of the additive accounts for 2% of the total content of the
  • the capacity retention rate of each lithium-ion battery obtained was tested.
  • the specific test method is: at 25°C, charge at a constant current of 1C to 4.50V, then charge at a constant voltage of 0.05C to 4.50V, and then discharge at a discharge rate of 1C to 3.0V. Repeat this charge and discharge cycle 500 times, measure the discharge capacity at the first cycle and the discharge capacity at the 500th cycle, and calculate the capacity retention rate after 500 cycles according to the following formula. The results are shown in Table 2.
  • Capacity retention rate Q (discharge capacity at the 500th cycle) / (discharge capacity at the first cycle) * 100%
  • the positive electrode active materials obtained in all the embodiments and comparative examples are made into positive electrode sheets, they are assembled with negative electrode sheets, electrolytes and separators according to the following method to obtain button batteries.
  • the method includes:
  • the positive electrode active materials in the examples and comparative examples were mixed with conductive carbon black (SP) and PVDF in a weight ratio of 80%:10%:10% respectively, and a positive electrode slurry was obtained by dispersion.
  • the slurry was coated on an aluminum foil current collector and rolled to obtain a positive electrode.
  • the positive electrode is then punched into a small disc with a diameter of 12 mm using a film mold. After drying and weighing, it is assembled into a button battery in a glove box under an Ar protective atmosphere using a 2025 button battery shell, a Li metal disc as the negative electrode, and a conventional high-voltage lithium cobalt oxide electrolyte.
  • the positive electrode active material of the present application is beneficial to improving the discharge capacity and cycle performance of lithium-ion batteries.

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Abstract

一种正极活性材料、正极片及锂离子电池，该正极活性材料包括基体和在基体至少部分表面的包覆层；基体包括锂金属氧化物，锂金属氧化物为立方晶系的Cmca空间群，且具有2θ为17.9°～18.1°的002峰，以及2θ为67.0°～67.5°的131峰；包覆层包括硒元素。该正极活性材料有助于提升电池的比容量以及循环性能。

Description

一种正极活性材料、正极片及锂离子电池
本申请要求于2023年06月14日提交中国专利局、申请号为202310709284.0、申请名称为“一种正极活性材料、正极片及锂离子电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及一种极片材料，尤其涉及一种正极活性材料、正极片及锂离子电池，属于二次电池技术领域。
背景技术
随着锂离子电池技术的发展和进步，对其容量提出了越来越高的要求。在锂离子电池的组成中，正极活性材料容量的高低，对锂离子电池的容量起着至关重要的作用。
为了提高锂离子电池的容量，目前最常用的方法就是提高其充放电电压。但是随着电压的提高，正极活性材料会出现晶体结构坍塌的现象，进而导致电池出现容量快速衰减和循环性能大幅降低等一系列问题。
因此，开发出一种具有高比容量、循环性能优异的锂离子电池正极活性材料是本领域亟待解决的技术问题。
发明内容
本申请提供一种正极活性材料，通过对该正极活性材料表面包覆含有Se元素，将该正极活性材料应用于锂离子电池后，能够使锂离子电池同时兼具优异的比容量和循环稳定性，尤其适用于高压环境。
本申请提供一种正极片，该正极片包括上述正极活性材料，因此有助于提升电池的克容量和循环性能。
本申请还提供一种锂离子电池，该锂离子电池包括上述正极活性材料或正极片，因此该锂离子电池在克容量和循环性能方面具有优异表现。
本申请提供一种正极活性材料，所述正极活性材料包括基体和覆盖在所述基体至少部分表面的包覆层；
其中，所述基体包括式1和/或式2所示的锂金属氧化物，所述包覆层包括硒元素；
Lin1-y1Nay1Coe1M1b1M2a1O2   式1
Lin2-y2-b2Nay2Coe2M1b2M2a2O2   式2
式1中，0.6≤n1≤1.0，0＜y1≤0.05，0.8≤e1≤1.03，0≤a1≤0.1，0＜b1≤0.1，0<b1/1-a1-b1<0.1；式2中，0.6≤n2≤1.0，0＜y2≤0.05，0.8≤e2≤1.03，0≤a2≤0.1，0＜b2≤0.02； 式1和式2中，M1选自Te、W、Al、B、P、Se、Ti、La、Zr以及K中的至少一种；M2为不同于M1的掺杂元素；
所述锂金属氧化物为立方晶系的Cmca空间群，且具有2θ为17.9°～18.1°的002峰，以及2θ为67.0°～67.5°的131峰。
如上所述的正极活性材料，其中，所述包覆层按照远离所述基体的方向包括第一包覆层和第二包覆层；所述第一包覆层包括金属化合物和所述硒元素中的至少一种，所述第二包覆层包括金属化合物和所述硒元素中的至少一种；
优选地，所述第一包覆层和第二包覆层的组成不同。
如上所述的正极活性材料，其中，所述第一包覆层包括金属化合物，所述第二包覆层包括硒元素；或，
所述第一包覆层包括硒元素，所述第二包覆层包括金属化合物。
如上所述的正极活性材料，其中，含所述硒元素的包覆层为硒单质层或硒-金属合金层。
如上所述的正极活性材料，其中，硒元素在所述正极活性材料中的质量百分含量小于5000ppm。
如上所述的正极活性材料，其中，所述金属化合物包括含锂氧化物、含铝氧化物、含镁氧化物、含锆氧化物、含钛氧化物中的至少一种。
如上所述的正极活性材料，其中，所述含锂氧化物的锂离子电导率大于或等于1×10-3S/cm；和/或，
所述含锂氧化物包括LATP、LLTO、LLZO、Li3BO3、Li3PO4中的至少一种。
如上所述的正极活性材料，其中，所述第一包覆层的厚度不大于20nm；和/或，所述第二包覆层的厚度不大于100nm。
如上所述的正极活性材料，其中，所述基体的Dv50为12～18μm；和/或，M2包括Mg、Ti、Mn、Al、Te、W、Ni、Nb、Zr、La、F、Ce、Sr、Y、K、B和P元素中的至少一种。
本申请提供一种正极片，所述正极片包括上述任一项所述的正极活性材料。
如上所述的正极片，所述正极片在扣式电池≥4.55V的条件下，正极片克容量≥225mAh/g。
本申请还提供一种锂离子电池，所述锂离子电池包括上述任一项所述的正极活性材料或者正极片。
如上所述的锂离子电池，所述锂离子电池的工作电压大于或等于4.5V。
如上所述的锂离子电池，其中，所述锂离子电池还包括负极片，所述负极片包括含锂层。
本申请的正极活性材料具有特殊的晶相结构、化学组成以及Se包覆结构，其在应用于锂离子电池中后，电池的循环性能和克容量得到显著提升，即使在4.5V及以上的高压条件下，正极活性材料不会发生由于耐压性差而出现结构坍塌的问题，该良好的结构稳定性能够保证更多锂离子的脱嵌，进而表现出优异的锂离子电池的克容量和循环性能。
附图说明
图1为本申请锂离子电池中的负极片一实施例的部分结构示意图；
图2为本申请实施例1中的中间正极活性材料1B的TEM图；
图3为本申请实施例1的正极活性材料1C的TEM图；
图4为本申请实施例1的正极活性材料组装得到的扣式电池的充放电曲线；
图5为本申请实施例1的正极活性材料的XRD图；
图6为本申请实施例6的正极活性材料的XRD图。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合本申请的实施例，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本申请第一方面提供一种正极活性材料，所述正极活性材料包括基体和覆盖在所述基体至少部分表面的包覆层；
其中，所述基体包括式1和/或式2所示的锂金属氧化物，所述包覆层包括硒元素；
Lin1-y1Nay1Coe1M1b1M2a1O2   式1
Lin2-y2-b2Nay2Coe2M1b2M2a2O2   式2
式1中，0.6≤n1≤1.0，0＜y1≤0.05，0.8≤e1≤1.03，0≤a1≤0.1，0＜b1≤0.1，0<b1/1-a1-b1<0.1；式2中，0.6≤n2≤1.0，0＜y2≤0.05，0.8≤e2≤1.03，0≤a2≤0.1，0＜b2≤0.02；式1和式2中，M1选自Te、W、Al、B、P、Se、Ti、La、Zr以及K中的至少一种；M2为不同于M1的掺杂元素；
所述锂金属氧化物为立方晶系的Cmca空间群，且具有2θ为17.9°～18.1°的002峰，以及2θ为67.0°～67.5°的131峰。
本申请的正极活性材料具有核壳包覆结构，其中，基体作为内核存在且包覆层包覆在基体的至少部分表面。
其中，基体包括式1和/或式2所示的锂金属氧化物，即锂金属氧化物可以仅包括式1所示的化合物，也可以仅包括式2所示的化合物，或者可以同时包括式1和式2所示的化合物。当然，基于式1和式2的组成，式1和式2亦可以表示相同的化合物，此外，本申请不限定M2的具体选择，可以为本领域常见的掺杂元素，例如可以是Mg、Ti、Mn、Al、Te、W、Ni、Nb、Zr、La、F、Ce、Sr、Y、K、B和P元素中的至少一种；包覆层包括硒元素。
需要说明的是，式1中的n1和式2中的n2均是锂金属氧化物中和元素锂摩尔量相关的参数。详细而言，当上述正极活性材料未经过任何充放电处理时，0.6≤n1≤0.8，0.6≤n2≤0.8；当该正极活性材料应用于锂离子电池中进行充放电处理后，在不同的充放电机制以及充放电节点下，n1和n2会发生变化。示例性地，当将包括正极活性材料的正极片和锂金属负极片组装为电池后进行充放电后，当电池的剩余电量SOC为0(即处于完全放电状态)且放电截止电压为3.0～3.6V时，锂金属氧化物的n1和n2的值在0.7～1.0之间。需要 说明的是，n1和n2的值的变化是指充放电循环圈数在10之内。原因在于，具有前述晶型结构的式1和式2所示的锂金属氧化物中具有部分空位，因此当将其进行充放电应用时，其空位能够接受来自于锂负极的锂原子，进而使锂离子的摩尔量相较于充放电应用前得到提升。该特性有助于进一步提升电池的循环性能和比容量。
本申请不限定n1和n2的检测方式，例如，可以采用电感耦合等离子光谱发生仪(ICP)对正极活性材料进行检测，或者，当对正极片中的正极活性材料进行检测时，对放电后的电池进行拆解并取出正极片，正极片利用碳酸二甲酯(DMC)浸泡1-3h或者DMC淋洗后，干燥房自然晾干后，置于马弗炉300～600℃焙烧2～5h后活性层从集流体上脱落，用200目过筛后得到待检测粉末，随后通过ICP对待检测粉末中的金属元素进行检测，计算n1和n2。
根据本申请提供的上述方案，相较于其他正极活性材料，将包括该锂金属氧化的正极活性材料应用于锂离子电池后，锂离子电池的比容量和循环性能得到显著提升，即使在高电压的工作条件下，锂离子电池的电性能也不会出现劣化。
发明人基于此现象进行分析，认为可能是：一方面，本申请通过设置含有Se元素包覆层，使正极活性材料为包括锂金属氧化物的内核、包覆层覆盖内核的核壳结构，该包覆层有助于减少或抑制锂金属氧化物和电解液的副反应，即使当电池在高压环境下工作时，正极活性材料和电解液之间依旧能够形成稳定的界面，通过避免正极活性离子中金属离子的过渡溶出以及避免缺液现象而使电池的循环性能得到改善，同时，副反应的抑制或减少也能够降低电池内部的产气量，从而也保证了电池的安全性能；另一方面，包覆层中的硒元素具有良好的电子传输性能，使正极活性材料具有优异的导电性能，进而提高锂离子电池的放电克容量和循环性能。
除此之外，具有上述晶体特征的该锂金属氧化物具有更为完善的层状晶相结构，得以减少或抑制晶相内部混排现象的发生，进而能够使锂离子发生顺利的脱嵌，尤其在高压的充放电过程中展现出多个具有优异放电量的充放电小平台，保证了高压下的放电和循环稳定性。
具体地，正极活性材料的第一阶段放电容量占比C1/C0≥9％，第二阶段放电容量占比C2/C0≥25％；其中，C0为包括所述正极活性材料的半电池在3.0～4.55V电压下进行放电处理时的放电容量；所述放电处理中，所述半电池由初始放电电压放电至4.4V时的容量定义为C1，所述半电池在3.8放电至3.7V时放出的容量定义为C2。
需要解释的是，上述放电容量是在特殊的放电机制下进行的。具体地，包括正极活性材料的正极片和锂金属负极组成的半电池充电至SOC为100％后(对充电机制不做特殊限定)，在3.0～4.55V下以0.1C进行放电处理。其中自4.55V以0.1C放电至4.4V时其释放的电量为C1，继续放电当从3.8V放电至3.7V时该降压阶段释放的电量为C2，继续放电至3.0V(此时SOC为0)时其自放电初始释放的全部电量为C0。
很明显，在高压环境下的放电处理中，第一阶段放电电量占比和第二阶段放电容量占比皆表现优异。因此，包括本申请锂金属氧化物的正极活性材料耐压性强，从而能够通过对其进行升压处理而提升电池的比容量。
进一步地，本申请上述包覆层按照远离基体的方向依次包括第一包覆层和第二包覆层，且第一包覆层包括金属化合物和硒元素中的至少一种，第二包覆层包括金属化合物和所述 硒元素中的至少一种。
上述双层包覆的设置不仅能够进一步减少或抑制锂金属氧化物和电解液的副反应，对正极活性材料的放电克容量和放电稳定性的提升亦有一定程度的促进。
详细而言，第一包覆层的材料和第二包覆层的材料相互独立的包括金属化合物和硒元素中的至少一种，即二者可以相同或者不同，尤其当二者不同时，对于锂离子电池电性能的改善程度更为突出。
在一种具体实施方式中，所述第一包覆层包括金属化合物，所述第二包覆层包括硒元素。即，第一包覆层和第二包覆层的组成不同，且第一包覆层的材料包括金属化合物，第二包覆层的材料包括硒元素。
在另一种具体实施方式中，所述第一包覆层包括硒元素，所述第二包覆层包括金属化合物。即，第一包覆层和第二包覆层的组成不同，且第一包覆层的材料包括硒元素，第二包覆层的材料包括金属化合物。
发明人发现，第一包覆层包括金属化合物，第二包覆层包括硒元素时，不仅制备正极活性材料的可操作性更高，锂离子电池包括循环性能和比容量在内的电性能也更为优异。
具体而言，上述包括硒元素的包覆层为硒单质层或硒-金属合金层，其中，当为硒-金属合金层时，本申请不限定金属合金的选择，例如为锂硒合金、硒铁合金、硒锌合金等。在实施过程中，由于硒单质的熔点更低，因此采用硒单质层作为包括硒元素的包覆层的制备工艺更为简单，节约成本，同时具备良好的容量和循环性能。
进一步地，当硒元素在正极活性材料中的质量百分含量小于5000ppm时，有利于提升正极活性材料的锂离子脱嵌性能，使锂离子电池的比容量和循环性能得到更显著的改善。
本申请不限定金属化合物的具体选择，可以包括含锂氧化物、含铝氧化物、含镁氧化物、含锆氧化物、含钛氧化物中的至少一种。
在具体应用过程中，还可以通过限定含锂氧化物的锂离子电导率而进一步提升正极活性材料的比容量。
在一种具体的实施方式中，含锂氧化物的锂离子电导率至少大于1×10-3S/cm。
示例性地，含锂氧化物包括LATP(磷酸钛铝锂)、LLTO(锂镧钛氧)、LLZO(锂镧锆氧)、Li3BO3、Li3PO4中的至少一种。
如前述，本申请正极活性材料中第一包覆层和第二包覆层中的一个还包括硒元素，此外，当本申请的正极活性材料的Dv50(累积体积达到全部正极活性材料的总体积的50％时的粒径)为12～18μm时，又助于实现材料的加工。发明人推测，可能是由于该粒度的正极活性材料在流动性方面具有优异表现，更容易形成紧密堆积状态。
进一步地，本申请对第一包覆层和第二包覆层的厚度不做过多限定。当第一包覆层的厚度不大于20nm，和/或，第二包覆层的厚度不大于100nm时，有利于锂离子的脱嵌，进一步提升正极活性材料的克容量。
示例性地，第一包覆层的厚度例如可以为2nm、5nm、7nm、10nm、13nm、15nm、18nm、20nm；第二包覆层的厚度例如可以为10nm、15nm、27nm、40nm、60nm、70nm、80nm、90nm、100nm。
本申请的正极活性材料可以是单晶形貌或多晶形貌，具体形貌与其掺杂元素的选择以及比例相关。具体地，当为多晶形貌时，其为球状或类球状颗粒；当为单晶形貌时，其可 以为须状、片状、或其他任意不规则的形状。
本申请不限定该正极活性材料的制备方法，以第一包覆层包括金属化合物且第二包覆层包括硒元素为例，示例性，利用原子层气相沉积法(ALD)在式1和/或式2所示的锂金属氧化物表面包覆第一包覆层，得到中间正极活性材料；再将中间正极活性材料与第二包覆源混合烧结，在第一包覆层表面形成第二包覆层，得到本申请的正极活性材料。
在一种具体实施方式中，将式1和/或式2所示的锂金属氧化物放置于ALD反应设备的反应腔体中，控制反应温度，将第一包覆源由惰性气体作为载气通入反应腔体中，以间隔脉冲的方式将原子层气相沉积在锂金属氧化物表面，在锂金属氧化物形成包括金属化合物的第一包覆层(即中间正极活性材料)；随后，利用混合设备将中间正极活性材料和第二包覆源混合均匀后，将混合物通入相应的烧结设备中进行烧结处理后，得到本申请的正极活性材料。
上述第一包覆源是指用于形成第一包覆层的原料，例如，当第一包覆层为LATP时，第一包覆源为锂源(例如叔丁醇锂、二(三甲基硅基)胺锂等有机含锂化合物)、铝源(例如三甲基铝等含铝有机化合物)、磷源(例如三甲基磷等含磷有机化合物)和钛源(例如四氯化钛等含钛有机化合物)；当第一包覆层为氧化铝时，第一包覆源例如为三甲基铝等含铝有机化合物；当第一包覆层为氧化镁时，第一包覆源例如为二茂镁等含镁有机化合物。
上述形成第一包覆层的过程中，反应温度为120℃～350℃，例如可以为150℃、170℃、180℃、220℃、250℃、270℃、300℃、330℃、350℃。
上述形成第一包覆层的过程中，间隔脉冲的次数为20～220次，例如可以为30次、50次、70次、90次、100次、120次、140次、150次、150次、200次。
上述形成第一包覆层的过程中，惰性气体包括氩气或氮气。进一步的，将惰性气体作为载气通入反应腔体中的流量为20-100mL/min，例如可以为20mL/min、40mL/min、50mL/min、80mL/min、100mL/min。
上述第二包覆源是指用于形成第二包覆层的原料，例如，当第二包覆层为硒单质层时，第二包覆源为硒单质；当第二包覆层为硒-金属合金层时，第二包覆源可为锂硒合金、硒铁合金、硒锌合金等。在形成第二包覆层的过程中，通过控制第二包覆源中硒的质量实现正极活性材料中硒含量的控制。
上述形成第二包覆层的过程中，烧结处理的温度为200～350℃，进一步为250～350℃；烧结处理的时间为5～60min，进一步为25～50min。
本申请不限定上述式1和式2所示的锂金属氧化物的制备方法，在一种具体实施方式中，本申请的锂金属氧化物可以通过将式1a和2a所示的钠金属氧化物与锂化合物混合并进行离子处理的方法制备得到。
Nax1Coe1M1b1M2a1O2   式1a Nax2Coe2M1b2M2a1O2   式2a
式1a中，0.68＜x1＜0.74，0.8≤e1≤1.03，0<b1<0.1，0≤a＜0.10，0＜b1/1-a1＜0.05；式2a中，0.68＜x2＜0.74，0.8≤e2≤1.03，0＜b2＜0.02，0≤a2＜0.1。
上述离子交换处理是一种热处理过程，具体是指将钠金属氧化物和锂化合物混合后在80℃～300℃下进行不高于10h的热处理。在离子交换处理后，通过对离子交换后的体系进行洗涤、干燥，最终得到锂金属氧化物。其中，干燥的温度为80～180℃，时间至少为10h。对进行离子交换处理的设备和干燥设备不做限定，例如离子交换处理的设备可以是带有密 闭功能和搅拌能力的密闭容器设备，如湿法包覆反应设备，共沉淀反应设备等；干燥设备可以是鼓风烘箱、真空干燥烘箱、回转窑、盘式干燥机、烤箱等。
上述锂化合物可以是本领域常用的锂源化合物，例如碳酸锂、氯化锂、溴化锂、碘化锂、硝酸锂、氢氧化锂、氟化锂中的至少一种。离子交换处理中，锂化合物和钠金属氧化物的质量比为不低于1:1，优选为(1-3)：1。
进一步地，当需要制备在锂金属氧化物外覆盖包覆层的正极活性材料时，在离子交换处理中除了包括钠金属氧化物和锂化合物的原料之外，还需要添加包覆层原料。
对于式1a和式2a所示的钠金属化合物，示例性，可以通过包括以下过程的方法制备得到：
将钴源、钠源、M1源以及M2源按照目标比例混合后进行煅烧处理，得到式1a和式2a所示的钠金属化合物。
具体地，煅烧处理的温度为700～900℃，时间为8～50h，煅烧处理可以在氧气或空气气氛下进行。煅烧处理的设备例如可以是马弗炉、隧道炉、辊道窑炉、管式炉等高温烧结设备。
上述各个源的混合可以通过高速混料设备、砂磨设备、球磨设备、犁刀混料设备、斜式混料设备等执行，需要注意的是，若使用砂磨设备、球磨设备且在球磨或砂磨过程中加入溶剂(水、乙醇或者其它溶剂介质)时，在混合处理结束后需要对混合后的体系进行干燥。一般的，混合时间不高于4h。
本申请不限定钴源、钠源、M1源以及M2源的具体选择。示例性地，钴源选自氢氧化钴、四氧化三钴、掺杂型四氧化三钴、氧化亚钴、羟基氧化钴、硝酸钴、硫酸钴等中的一种或多种；钠源选自碳酸钠、硝酸钠、氢氧化钠、碳酸氢钠、硫酸钠等中的一种或多种；M1源可以是任何含有M1的化合物，例如M1的氧化物，当M1为W时，M1源例如为钨酸和/或钨酸钠等；当M1为Te时，M1源例如为碲酸和/或碲酸钠等；当M1为Al时，M1源例如为硫酸铝、硝酸铝、氢氧化铝等中的一种或多种；当M1为B时，M1源例如为硼酸和/或硼酸钠等；当M1为P时，M1源例如为磷酸和/或磷酸钠等；当M1为K时，M1源例如为碳酸钾、硝酸钾、氢氧化钾、碳酸氢钾、硫酸钾等中的一种或多种；M2源例可以是任何含有M2的化合物，例如M2的氧化物，例如为碱式碳酸镁、氢氧化镁、氧化锆、氧化钇、氧化镧、氟化镧、氧化镍、氧化铌等中的一种或多种。
本申请第二方面提供一种正极片，该正极片包括上述第一方面所述的正极活性材料。
基于第一方面的正极活性材料的特性，本申请的正极片有助于改善电池的循环性能和比容量。
本申请不限定正极片的具体结构，例如，本申请的正极片包括正极集流体和设置在正极集流体至少一表面的正极活性层，该正极活性层包括前述正极活性材料。能够理解，除了正极活性材料之外，正极活性层还包括导电剂和粘结剂。示例性地，正极活性层按照质量百分含量包括70-99wt％的正极活性材料、0.5-15wt％的导电剂、0.5-15wt％的粘结剂，进一步地，包括80-98wt％的正极活性材料、1-10wt％的导电剂、1-10wt％的粘结剂。
导电剂和粘结剂的选择并无特殊，可以为本领域常规选择。例如，导电剂选自导电炭黑、乙炔黑、科琴黑、导电石墨、导电碳纤维、碳纳米管、单壁碳纳米管、多壁碳纳米管、碳纤维中的至少一种，粘结剂选自聚偏氟乙烯(PVDF)、PVDF-HFP、聚 四氟乙烯(PTFE)、聚丙烯酸锂(PAALi)、聚丙烯(PAA)中的至少一种。
进一步地，为了提升安全性能，还可以在正极活性层和集流体之间设置安全层。安全层的材料可为非导电性的安全材料，例如含铁的化合物(如磷酸铁锂、磷酸锂等)、含铝的化合物(如氧化铝)、氧化硅、高阻抗炭黑、PTC材料等。当然，安全层中也包括粘结剂，粘结剂和安全材料的比例可以根据具体需求而进一步确定。
可选地，所述安全层也可以为导电材料、如导电钛白粉等。
本申请第三方面提供一种锂离子电池，该锂离子电池包括上述第一方面的正极活性材料或第二方面的正极片，因此在循环性能和比容量方面表现突出。
本申请不限定锂离子电池的具体结构，例如可以是方形壳或圆柱电池等。除了正极片之外，本申请的锂离子电池还包括负极片、隔膜和电解液。
示例性地，电解液为本领域已知的包括锂盐和溶剂的常规电解液，溶剂含有碳酸乙烯酯(简写为EC)、碳酸二乙酯(简写为DEC)、碳酸丙烯酯(简写为PC)、氟代碳酸乙烯酯(简写为FEC)。
进一步地，还包括一种式T所示的添加剂，其在电解液中的质量百分含量为0.1～10％。该添加剂与该正极材料结合，可以满足电池在高电压(≥4.5V)条件下工作。
示例性地，负极片可以为是含锂层的负极片，例如可以是锂箔或者如图1所示的负极片。具体地，图1中的负极片包括层叠设置的负极集流体101、负极活性层20和锂材料层30。图1中的负极片为双面设置，当然也可以为仅在负极集流体101单面设置负极活性层20和锂材料层30的负极片。锂材料层例如为锂箔，进一步地，锂材料层中金属锂的面密度为0.09mg/cm2～3.5mg/cm2；负极活性层包括负极活性材料、导电剂以及粘结剂。
在一种具体实施方式中，负极活性层按照质量百分含量包括70-99wt％的负极活性材料、0.5-15wt％的导电剂、0.5-15wt％的粘结剂，进一步地，包括80-98wt％的负极活性材料、1-10wt％的导电剂、1-10wt％的粘结剂。其中，负极活性材料选自人造石墨、天然石墨、硬炭、中间相碳微球、钛酸锂、硅碳、氧化亚硅中的一种或多种。
示例性地，隔膜为聚丙烯为基材的材料，或在此基础上单面或双面涂覆陶瓷的涂胶隔膜。
本申请的锂离子电池适用于高压体系，包括前述正极片的锂离子扣式电池≥4.55V(相对锂)的条件下，正极片克容量发挥≥225mAh/g，且在≥4.50V(对应前述负极片)同时具有优异的循环性能。
因此，本申请在4.50V等更高电压具有良好的循环稳定性和较高的克容量的锂离子电池，可满足高端数码产品轻薄化的使用需求。
以下，将结合具体的实施例对本申请的技术方案进行进一步的解释说明。
实施例1
本实施例的正极活性材料按照以下方法制备：
(1)取质量为38.153g的碳酸钠粉末、1.854g的硼酸粉末、276.498g的六水合硝酸钴粉末和1.020g的纳米氧化铝粉末，将其放入高速混料设备中，设定混料程序，用300rpm混料3分钟后，用500rpm混料5分钟，再用1000rpm混料10分钟后取出混合料，确认混合料中没有白色的碳酸钠小白点存在后，认为混料均匀；
(2)取30g左右混合均匀的混合料，均匀装入陶瓷坩埚中，使用设备型号为VBF-1200X的井式马弗炉进行高温烧结，烧结的升温曲线为5℃/min，升温至780℃时进行恒温烧结10h，烧结后自然降温至常温后将样品取出，经电感耦合等离子光谱发生仪(ICP)检测得到钠金属氧化物Na0.72Co0.95B0.03Al0.02O2；
(3)取一个反应容器里先称取重量为10.49g的一水合氢氧化锂和质量为17.24g的硝酸锂颗粒，将两种锂的化合物分别加入反应容器中，称取质量为10g的步骤(2)合成的Na0.72Co0.95B0.03Al0.02O2，倒入反应容器中初步混合后，于280℃离子交换0.5h，得到粗品；
(4)粗品经过3次去离子水抽滤洗涤后，在90℃，干燥8h后得到样品1A，经ICP检测，1A的化学式为Li0.715Na0.002Co0.95B0.03Al0.02O2；
(5)称取5g步骤(4)得到的样品1A粉末放置于ALD反应设备的反应腔体中，控制反应温度为290℃，将叔丁醇锂、三甲基铝、四氯化钛、三甲基膦由惰性气体作为载气通入反应腔体中，以间隔脉冲150次将原子层气相沉积在1A表面，从而形成具有第一包覆层的中间正极活性材料1B。对1B进行TEM测试，图2为本申请实施例1中的中间正极活性材料1B的TEM图，如图2所示，第一包覆层的厚度为10～12nm。
(6)称取3.5g 1B样品和8.75mg硒粉末，用小型的高速混料机混合10min后，将其放入相应的VBF-1200X马弗炉设备中，进行300℃烧结15min后得到本实施例的正极活性材料1C。对1C进行TEM测试，图3为本申请实施例1的正极活性材料1C的TEM图，如图3(其中，区域A为内核，区域B为第一包覆层，区域C为第二包覆层)所示，可知第二包覆层的厚度为17～20nm。
制备过程中的相关制备参数见表1。
实施例2
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：步骤(5)中，称取5g步骤(4)得到的样品1A粉末放置于ALD反应设备的反应腔体中，控制反应温度为290℃，将叔丁醇锂、三甲基铝、四氯化钛、三甲基膦由惰性气体作为载气通入反应腔体中，以间隔脉冲100次将原子层气相沉积在1A表面，从而形成具有第一包覆层的中间正极活性材料2B，对2B样品进行TEM测试，可知第一包覆层的厚度为8～9nm。制备过程中的相关制备参数见表1。
实施例3
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：步骤(5)中，称取5g步骤(4)得到的样品1A粉末放置于ALD反应设备的反应腔体中，控制反应温度为290℃，将叔丁醇锂、三甲基铝、四氯化钛、三甲基膦由惰性气体作为载气通入 反应腔体中，以间隔脉冲80次将原子层气相沉积在1A表面，从而形成具有第一包覆层的中间正极活性材料3B，对3B样品进行TEM测试，可知第一包覆层的厚度为6～7nm。制备过程中的相关制备参数见表1。
实施例4
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于步骤(6)：称取3.5g 1B样品和7.0mg硒粉末，用小型的高速混料机混合10min后，将其放入相应的VBF-1200X马弗炉设备中，进行300℃烧结15min后得到本实施例的正极活性材料4C；对4C样品进行TEM测试，可知包覆层的厚度为14～16nm。制备过程中的相关制备参数见表1。
实施例5
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于步骤(6)：称取3.5g 1B样品和10.5mg硒粉末，用小型的高速混料机混合10min后，将其放入相应的VBF-1200X马弗炉设备中，进行300℃烧结15min后得到本实施例的正极活性材料5C；对5C样品进行TEM测试，可知其第二包覆层的厚度为25～30nm。制备过程中的相关制备参数见表1。
实施例6
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：
步骤(1)中，取重量为38.153g的碳酸钠粉末、1.96g的磷酸粉末、276.498g的六水合硝酸钴粉末和1.529g的纳米氧化铝粉末，将其放入高速混料设备中，设定混料程序，用300rpm混料3分钟后，用500rpm混料5分钟，再用1000rpm混料10分钟后取出混合料，确认混合料中没有白色的碳酸钠小白点存在后，认为混料均匀；
步骤(2)得到的钠金属氧化物为Na0.72Co0.95Al0.03P0.02O2；
经步骤(4)处理后，得到样品6A，其化学式为Li0.717Na0.003Co0.95Al0.03P0.02O2；
经步骤(5)处理后，得到样品6B。
经步骤(6)处理后，得到样品6C。制备过程中的相关制备参数见表1。
实施例7
本实施例的正极活性材料的制备方法与实施例6基本相同，不同之处在于：步骤(5)中，称取5g步骤(4)得到的样品6A粉末放置于ALD反应设备的反应腔体中，控制反应温度为290℃，将叔丁醇锂、硼酸三乙酯和去离子水由惰性气体作为载气通入反应腔体中，以间隔脉冲150次将原子层气相沉积在锂金属氧化物表面，从而形成具有第一包覆层的中间正极活性材料7B，对7B样品进行TEM测试，可知第一包覆层的厚度为11～13nm。制备过程中的相关制备参数见表1。
实施例8
本实施例的正极活性材料的制备方法与实施例6基本相同，不同之处在于：步骤(5) 中，称取5g步骤(4)得到的样品6A粉末放置于ALD反应设备的反应腔体中，控制反应温度为220℃，将三甲基铝和去离子水由惰性气体作为载气通入反应腔体中，以间隔脉冲150次将原子层气相沉积在锂金属氧化物表面，从而形成具有第一包覆层的中间正极活性材料8B，对8B样品进行TEM测试，可知第一包覆层的厚度为11～13nm。制备过程中的相关制备参数见表1。
实施例9
本实施例的正极活性材料的制备方法与实施例6基本相同，不同之处在于：步骤(5)中，称取5g步骤(4)得到的样品6A粉末放置于ALD反应设备的反应腔体中，控制反应温度为220℃，将二茂镁和去离子水由惰性气体作为载气通入反应腔体中，以间隔脉冲150次将原子层气相沉积在锂金属氧化物表面，从而形成具有第一包覆层的中间正极活性材料9B，对9B样品进行TEM测试，可知第一包覆层的厚度为11～13nm。制备过程中的相关制备参数见表1。
实施例10
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于步骤(6)：称取3.5g 1B样品和35mg硒粉末，用小型的高速混料机混合10min后，将其放入相应的VBF-1200X马弗炉设备中，进行300℃烧结15min后得到本实施例的正极活性材料10C；对10C样品进行TEM测试，可知第二包覆层的厚度为120～125nm。制备过程中的相关制备参数见表1。
实施例11
本实施例的正极活性材料的制备方法与实施例6基本相同，不同之处在于：步骤(5)中，称取5g步骤(4)得到的样品6A粉末放置于ALD反应设备的反应腔体中，控制反应温度为290℃，将叔丁醇锂、三(N,N-二异丙基甲脒)镧(LaFAMD)、四氯化钛、和去离子水由惰性气体作为载气通入反应腔体中，以间隔脉冲150次将原子层气相沉积在锂金属氧化物表面，从而形成具有第一包覆层的中间正极活性材料11B，对11B样品进行TEM测试，可知第一包覆层的厚度为11～13nm。制备过程中的相关制备参数见表1。
实施例12
本实施例的正极活性材料的制备方法与实施例6基本相同，不同之处在于：步骤(5)中，称取5g步骤(4)得到的样品6A粉末放置于ALD反应设备的反应腔体中，控制反应温度为290℃，将叔丁醇锂、三(N,N-二异丙基甲脒)镧(LaFAMD)、四(二甲氨基)锆(TDMAZ)、和去离子水由惰性气体作为载气通入反应腔体中，以间隔脉冲150次将原子层气相沉积在锂金属氧化物表面，从而形成具有第一包覆层的中间正极活性材料12B，对12B样品进行TEM测试，可知第一包覆层的厚度为11～13nm。制备过程中的相关制备参数见表1。
实施例13
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于步骤(6)：称取3.5g 1B样品和8.75mg锂硒合金粉末，用小型的高速混料机混合10min后，将其放入相应的VBF-1200X马弗炉设备中，进行300℃烧结15min后得到本实施例的正极活性材料13C；对13C样品进行TEM测试，可知第二包覆层的厚度为17～20nm。制备过程中的相关制备参数见表1。
实施例14
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：实施例1中的步骤5)和步骤6)顺序更换，得到实施例14的正极活性材料14C。制备过程中的相关制备参数见表1。
实施例15
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：步骤(5)中的ALD的包覆温度和和脉冲次数。制备过程中的相关制备参数见表1。
实施例16
本实施例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：不进行步骤(5)的处理，步骤(4)后直接进行步骤(6)的处理，得到实施例16的正极活性材料。制备过程中的相关制备参数见表1。
对比例1
本对比例的正极活性材料包括常规高电压掺杂型钴酸锂正极材料，其化学组成10A样品为Li1.0027Co0.97Al0.03O2。
将上述钴酸锂正极材料10A按照实施例1的步骤(5)称取5g后放置于ALD反应设备的反应腔体中，控制反应温度为290℃，将叔丁醇锂、三甲基铝、四氯化钛、三甲基膦由惰性气体作为载气通入反应腔体中，以间隔脉冲150次将原子层气相沉积在锂金属氧化物表面，从而形成具有第一包覆层物质10B，对10B样品进行TEM测试，可知第一包覆层的厚度为10～12nm。
(6)称取3.5g 10B样品和8.75mg硒粉末，用小型的高速混料机混合10min后，将其放入相应的VBF-1200X马弗炉设备中，进行300℃烧结15min后得到对比例1的正极活性材料10C；对10C样品进行TEM测试，可知第二包覆层的厚度为17～20nm。制备过程中的相关制备参数见表1。
对比例2
本对比例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：不进行步骤(5)和(6)的处理，直接使用步骤(4)得到的1A样品作为对比例2的正极活性材料。制备过程中的相关制备参数见表1。
对比例3
本对比例的正极活性材料的制备方法与实施例1基本相同，不同之处在于：不进行步骤(6)的处理，直接使用步骤(5)得到的1B样品作为对比例3的正极活性材料。制备过程中的相关制备参数见表1。
试验例1
对所有实施例和对比例得到的正极活性材料进行TEM测试和ICP测试，检测正极活性材料的包覆层厚度、化学组成和Se含量。同时，对进行第一包覆处理的中间正极活性材料也进行TEM测试，观测第一包覆层的厚度。结果见表1。
试验例2
对所有实施例和对比例得到的正极活性材料进行XRD衍射，其XRD对应的002峰和131峰的2θ，结果如图5、图6以及表2所示。
试验例3
将所有实施例和对比例中得到的正极活性材料制作为正极片后，与负极片、电解液以及隔膜按照以下方法组装得到锂离子电池。方法包括：
1)将实施例和对比例中的正极活性材料分别与导电碳黑、PVDF按照96％:2％:2％的重量比混合，通过分散得到正极浆料。将该浆料涂布在铝箔集流体上，辊压制备得到正极片；
2)将人造石墨、苯乙烯二烯橡胶(SBR)、及羧甲基纤维素钠、导电碳黑以94％:3％:2％:1％的重量比混合，将混合物分散于水中通过双行星混合后得到负极浆液。将该浆液涂覆于铜集流体上，接着进行辊压及干燥；
随后通过轧制方式在负极活性层表面叠加锂材料层，锂材料层为锂箔，金属锂的面密度为1.0mg/cm2，最终得到含有锂金属的负极片。
3)然后将正极片、负极片和隔膜组装成锂离子电池，并注入非水电解液。
其中，电解液为本领域已知的常规电解液，按碳酸乙烯酯(简写为EC)：碳酸二乙酯(简写为DEC)：碳酸丙烯酯(简写为PC)＝2：5：3的质量比混合后，加入占电解液总质量的5％的氟代碳酸乙烯酯(简写为FEC)、加入占电解液总质量的13％的六氟磷酸锂(简写为LiPF6)，以及式T所示的添加剂，添加剂含量占电解液总含量的2％。
对得到的各个锂离子电池的容量保持率进行测试，具体测试方法为：在25℃下，以1C的充电倍率恒流充电至4.50V，再以0.05C的充电倍率恒压充电至4.50V，然后以1C的放电倍率放电至3.0V，反复500次这种充放电循环，测定第一次循环时的放电容量和第500次循环时的放电容量，按照下式求出500圈循环后的容量保持率，结果见表2。
容量保持率Q＝(第500次循环时的放电容量)/(第一次循环时的放电容量)*100％
试验例4
将所有实施例和对比例中得到的正极活性材料制作为正极片后，与负极片、电解液以及隔膜按照以下方法组装得到扣式电池。方法包括：
将实施例和对比例中的正极活性材料分别与导电碳黑(SP)、PVDF按照80％:10％:10％的重量比混合，通过分散得到正极浆料。将该浆料涂布在铝箔集流体上，辊压制备得到正 极片，然后将正极片用膜具冲型直径为12mm的小圆片，烘干称重处理后，在Ar保护气氛下的手套箱中，使用2025的扣式电池壳，用Li金属圆片做负极，常规高电压钴酸锂电解液一起组装成扣式电池。
对得到的各个扣式电池在常规环境下静置4h后，进行首次充放电容量测试，测试条件为：0.1C充电至4.55V，恒压充电至0.025C截止后，静置3min后，0.1C放电至3.0V。在放电过程中，分别记录4.4～4.55V的放电电量C1、3.7～3.8V的放电电量C2、首次放电全电量C0、首次充电克容量，并计算首次效率、第一阶段放电容量占比C1/C0以及第二阶段放电容量占比C2/C0。结果见表2。图4为本申请实施例1的正极活性材料组装得到的扣式电池的充放电曲线。
表1

表2

根据表2可知：本申请的正极活性材料有利于提升锂离子电池的放电容量和循环性能。
最后应说明的是：以上各实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述各实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：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申请各实施例技术方案的范围。

Claims (14)

  1. 一种正极活性材料，其中，所述正极活性材料包括基体和覆盖在所述基体至少部分表面的包覆层；
    其中，所述基体包括式1和/或式2所示的锂金属氧化物，所述包覆层包括硒元素；
    Lin1-y1Nay1Coe1M1b1M2a1O2   式1
    Lin2-y2-b2Nay2Coe2M1b2M2a2O2   式2
    式1中，0.6≤n1≤1.0，0＜y1≤0.05，0.8≤e1≤1.03，0≤a1≤0.1，0＜b1≤0.1，0<b1/1-a1-b1<0.1；式2中，0.6≤n2≤1.0，0＜y2≤0.05，0.8≤e2≤1.03，0≤a2≤0.1，0＜b2≤0.02；式1和式2中，M1选自Te、W、Al、B、P、Se、Ti、La、Zr以及K中的至少一种；M2为不同于M1的掺杂元素；
    所述锂金属氧化物为立方晶系的Cmca空间群，且具有2θ为17.9°～18.1°的002峰，以及2θ为67.0°～67.5°的131峰。
  2. 根据权利要求1所述的正极活性材料，其中，所述包覆层按照远离所述基体的方向包括第一包覆层和第二包覆层；所述第一包覆层包括金属化合物和所述硒元素中的至少一种，所述第二包覆层包括金属化合物和所述硒元素中的至少一种；
    优选地，所述第一包覆层和第二包覆层的成分不同。
  3. 根据权利要求2所述的正极活性材料，其中，所述第一包覆层包括金属化合物，所述第二包覆层包括硒元素；
    或，所述第一包覆层包括硒元素，所述第二包覆层包括金属化合物。
  4. 根据权利要求1-3任一项所述的正极活性材料，其中，含所述硒元素的包覆层为硒单质层或硒-金属合金层。
  5. 根据权利要求1-4任一项所述的正极活性材料，其中，硒元素在所述正极活性材料中的质量百分含量小于5000ppm。
  6. 根据权利要求2-5任一项所述的正极活性材料，其中，所述金属化合物包括含锂氧化物、含铝氧化物、含镁氧化物、含锆氧化物、含钛氧化物中的至少一种。
  7. 根据权利要求6所述的正极活性材料，其中，所述含锂氧化物的锂离子电导率大于或等于1×10-3S/cm；
    和/或，所述含锂氧化物包括LATP、LLTO、LLZO、Li3BO3、Li3PO4中的至少一种。
  8. 根据权利要求2或3所述的正极活性材料，其中，所述第一包覆层的厚度不大于20nm；和/或，所述第二包覆层的厚度不大于100nm。
  9. 根据权利要求1所述的正极活性材料，其中，所述基体的Dv50为12～18μm；和/或，M2包括Mg、Ti、Mn、Al、Te、W、Ni、Nb、Zr、La、F、Ce、Sr、Y、K、B和P元素中的至少一种。
  10. 一种正极片，其中，所述正极片包括权利要求1-9任一项所述的正极活性材料。
  11. 根据权利要求10所述的正极片，其中，所述正极片在扣式电池≥4.55V的条件下，正极片克容量≥225mAh/g。
  12. 一种锂离子电池，其中，所述锂离子电池包括权利要求1-9任一项所述的正极活性材料或者权利要求10所述的正极片。
  13. 根据权利要求12所述的锂离子电池，其中，所述锂离子电池的工作电压大于或等于4.5V。
  14. 根据权利要求12或13所述的锂离子电池，其中，所述锂离子电池还包括负极片，所述负极片包括含锂层。
PCT/CN2024/080523 2023-06-14 2024-03-07 一种正极活性材料、正极片及锂离子电池 Ceased WO2024255339A1 (zh)

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CN120613372A (zh) * 2024-03-08 2025-09-09 宁德时代新能源科技股份有限公司 正极活性层组合物、正极活性包覆颗粒、正极膜、固态电池、用电装置和应用
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