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WO2021249400A1 - 一种正极活性材料及包含其的电化学装置 - Google Patents

一种正极活性材料及包含其的电化学装置 Download PDF

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Publication number
WO2021249400A1
WO2021249400A1 PCT/CN2021/098940 CN2021098940W WO2021249400A1 WO 2021249400 A1 WO2021249400 A1 WO 2021249400A1 CN 2021098940 W CN2021098940 W CN 2021098940W WO 2021249400 A1 WO2021249400 A1 WO 2021249400A1
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positive electrode
electrode active
active material
layer
electrochemical device
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PCT/CN2021/098940
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English (en)
French (fr)
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吴霞
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宁德新能源科技有限公司
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Publication of WO2021249400A1 publication Critical patent/WO2021249400A1/zh
Priority to US18/076,489 priority Critical patent/US20230118096A1/en

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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
    • H01M4/364—Composites as mixtures
    • 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
    • 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
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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

  • This application relates to the field of energy storage, and more specifically to a positive electrode active material and an electrochemical device containing the positive electrode active material, especially a lithium ion battery.
  • lithium-ion batteries are widely used in portable electronic products because of their high energy storage density, high power density, good safety, environmental friendliness, long life, low self-discharge rate, and wide temperature adaptation range. , Electric transportation, national defense aviation, energy reserve and other fields.
  • cathode materials have a significant impact on their performance, so the continuous optimization and improvement of cathode materials is particularly important.
  • the pursuit of high energy density and high power density has become the development trend of lithium-ion battery cathode materials.
  • lithium cobalt oxide As the earliest commercialized lithium-ion cathode material, lithium cobalt oxide has been extensively and in-depth studied, and has the best overall performance in terms of reversibility, discharge capacity, charging efficiency, and voltage stability. It is currently the most widely used lithium-ion battery The cathode material. After decades of development, the structural characteristics and electrochemical performance of lithium cobalt oxide have also been fully studied, and the synthesis process and industrial production have also been quite mature. With its higher discharge voltage platform and higher energy density, it has always occupied a dominant position in the cathode materials of consumer lithium-ion batteries.
  • LiCoO 2 cathode material in the 3C field has an O3 phase structure with a theoretical capacity of 273.8mAh/g. It has good cycling and safety performance, high compaction density and simple preparation process. Since Sony's commercialization in 1991, LiCoO 2 cathode material has always occupied a major position in the lithium-ion battery material market. In order to obtain a higher specific capacity, LiCoO 2 is moving in the direction of high voltage (>4.6Vvs.Li/Li + ). When LiCoO 2 is charged to 4.5V, the capacity can only reach 190 mAh/g.
  • This application provides a positive electrode active material, which has a considerable discharge capacity at a high voltage of 4.8V, good structural reversibility and cycle stability.
  • the present application provides a positive electrode active material comprising a compound having the structure of P6 3 mc, wherein, in the XRD pattern of the positive electrode active material, P6 3 mc compound having the structure ( 002)
  • the crystal plane is between 17.5°-19°, and its half-width is between 0.05-0.1.
  • the DSC spectrum of the positive electrode active material, the compound having the structure of P6 3 mc an exothermic peak exists between 250 °C -400 °C, the exothermic peak half width Between 15°C-40°C.
  • the compound having the P6 3 mc structure satisfies at least one of the conditions (a) to (e): (a) the average particle diameter of the compound having the P6 3 mc structure is 8 ⁇ m-30 ⁇ m (B) The tap density of the compound with P6 3 mc structure is 2.2 g/cm 3 -3 g/cm 3 ; (c) There are holes on the surface of the particles of the compound with P6 3 mc structure; (d) There are gaps in the particles of the compound with the P6 3 mc structure; (e) the compound with the P6 3 mc structure contains Li x Na z Co 1-y M y O 2 , where 0.6 ⁇ x ⁇ 0.85, 0 ⁇ y ⁇ 0.15, 0 ⁇ z ⁇ 0.03, and M is selected from at least one of the group consisting of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, and Zr.
  • the value of x will vary depending on the charging and discharging of the battery and whether the active material contains lithium-rich materials.
  • the above-mentioned cathode material provided in this application improves the crystal structure collapse and interface failure of the traditional LiCoO 2 material during the charging process (>4.6Vvs.Li/Li + ).
  • the material has good structural reversibility and cycle stability under high voltage, and its advantages include but are not limited to: (1) During the lithium insertion process, the Li x Na z Co 1-y M y O 2 cathode material is due to There are lithium vacancies in its own crystal structure, which can well accommodate volume changes and insert more Li; (2) In the process of lithium removal/lithium insertion, the Li x Na z Co 1-y M y O 2 cathode material is due to its own There are holes and cracks, which can effectively release the huge stress formed by the process of high-voltage lithium removal/intercalation, inhibit irreversible slip between layers, and achieve good cycle performance; (2) When the voltage is greater than 4.7V, Li x Na z Co 1- y M y O 2 cathode material has achieved 95% delithi
  • the present application provides an electrochemical device, the electrochemical device comprising a positive electrode piece, the positive electrode piece comprising a positive electrode current collector and a positive electrode active on at least one surface of the positive electrode current collector
  • the positive electrode active layer includes any one of the aforementioned positive electrode active materials (hereinafter referred to as "first positive electrode active material").
  • the cathode active layer further comprises a second cathode active material
  • the second cathode active material is selected from Li 1 ⁇ b Co 1-a R a O R-3m structure consisting of two, three nickel cobalt manganese The group consisting of metamaterials, lithium-rich manganese bases or lithium manganese oxides, where (0 ⁇ b ⁇ 0.1, 0 ⁇ a ⁇ 0.1), and where R is selected from Al, Mg, Ti, Mn, Fe, Ni, Zn, At least one of the group consisting of Cu, Nb, Cr, and Zr.
  • the above electrochemical device has excellent structural reversibility and cycle stability under a high voltage of 4.8V.
  • the first positive electrode active material makes up for the extremely unstable interface of the second positive electrode active material when used alone at a high voltage of 4.8V, and the interface failure causes serious capacity degradation and cannot achieve high-capacity stable cycles.
  • the higher theoretical capacity of the second positive electrode active material further increases the capacity of the electrochemical device.
  • the electrochemical device can take advantage of the respective advantages of the two materials to achieve higher energy density than the current mass-produced materials.
  • the positive active layer includes a first layer and a second layer, and the second layer is located between the current collector and the first layer, wherein the first layer includes the first layer. Positive active material.
  • the second layer includes the second positive electrode active material, and the compaction density of the second layer is 4.1 g/cm 3 -4.35 g/cm 3 .
  • the ratio of the thickness of the first layer to the second layer is 0.1-2.
  • the positive electrode active layer has a single-layer structure formed by mixing the first positive electrode active material and the second positive electrode active material.
  • the application provides a positive electrode active material, which is formed by mixing the first positive electrode active material and the second positive electrode active material.
  • the research in this application has found that the cycle stability and structural reversibility of the aforementioned lithium-ion battery prepared from the positive electrode sheet with a double-layer structure under high voltage are further improved.
  • the research of this application found that by coating the positive electrode active material containing the compound of the P6 3 mc structure on, for example, the surface of the positive electrode active material of LiCo 1-a R a O 2 with the R-3m structure (that is, the first layer includes The first positive electrode active material, the second layer includes the second positive electrode active material, and the second layer is located between the current collector and the first layer), which can effectively inhibit the electrolyte and the surface of the active material in the second layer The side reaction protects the interface of the active material in the second layer.
  • R-3m structure LiCo 1-a R a O 2 as an example is a composite positive electrode active layer, a second layer, the composite positive electrode active
  • the advantages of the layer are as follows: (1) In the process of lithium removal/intercalation, the positive electrode active material of the first layer can well isolate the corrosion of the active surface of the positive electrode active material of the second layer by the electrolyte due to its own interface stability.
  • the positive electrode active material of the first layer has holes and cracks, which can effectively release the huge stress formed by the high-voltage lithium removal/intercalation process, and inhibit irreversible slippage between layers , To achieve good cycle performance;
  • the positive electrode active material of the first layer has good flexibility and can be compacted arbitrarily without affecting the thickness of the composite positive electrode active layer, and the compaction density of the composite positive electrode active layer is high;
  • the doping elements introduced in the positive electrode active material of the first layer and the positive electrode active material of the second layer can effectively enhance the structure stabilizing effect of the crystal.
  • FIG. 1 A schematic diagram of the positive electrode sheet containing the aforementioned double-layer structure of the positive electrode active layer of the present application is shown in Figure 1 (wherein, the positive electrode current collector is not limited to Al foil, but may also be a positive electrode collector commonly used by those skilled in the art such as nickel foil. Fluid, and the cathode active material of the second layer is not limited to LiCo 1- a R a O 2 with R-3m structure, it can also be required to improve the material interface, cycle stability or structural reversibility under high voltage Other positive electrode materials include, but are not limited to: nickel-cobalt-manganese ternary materials, lithium-rich manganese-based or lithium manganese oxide).
  • the compacted density of the positive active layer is 4.0 g/cm 3 -4.5 g/cm 3 .
  • the electrochemical device satisfies at least one of the conditions (f) to (h): (f) When the discharge gram capacity is not less than 180mAh/g, it is cycled at a voltage of 4.8V and a rate of 0.5C 20 cycles, the growth rate of particle cracking of the positive electrode active material before and after the cycle is not higher than 5%; (g) When the discharge gram capacity is not less than 180mAh/g, cycle 20 cycles under 4.8V voltage and 0.5C rate, before and after the cycle The positive electrode active material has an average DC internal resistance DCR growth rate of less than 2% per cycle; (h) the electrochemical device further includes a negative electrode, and the negative electrode includes a negative electrode current collector and at least A negative electrode active layer on a surface, when the discharge gram capacity is not less than 180mAh/g, cycle 20 cycles at a voltage of 4.8V and a rate of 0.5C, and the accumulation concentration of Co on the surface of the negative electrode active layer increases per cycle on average.
  • the thickness of the positive electrode by-product is ⁇ , where ⁇ 0.5 ⁇ m.
  • the present application provides an electronic device, which includes any of the aforementioned electrochemical devices.
  • FIG. 1 is a schematic structural diagram of a positive pole piece including a positive active layer of a double-layer structure according to some embodiments of the present application.
  • Example 2 is a scanning electron microscope (SEM) image of secondary particles in a cross-section of the positive pole piece of Example 1 of the present application.
  • FIG. 3A is an X-ray diffraction (XRD) pattern of the positive electrode active material of Example 1 of the present application
  • FIG. 3B is an X-ray diffraction (XRD) pattern of the positive electrode active material of Comparative Example 1 of the present application.
  • XRD X-ray diffraction
  • DSC differential scanning calorimetry
  • 5A and 5B are respectively SEM images of the cross-section of the positive pole piece of the battery 1 in the embodiment of the present application before the first cycle and after the 20th cycle.
  • 5C and 5D are respectively SEM images of the cross-section of the positive pole piece of the battery 8 in the comparative example of the present application before the first cycle and after the 20th cycle.
  • FIG. 6 is a comparison diagram of the average growth rate of the DC internal resistance of the battery 1 in the embodiment of the present application and the battery 8 in the comparative example with the number of cycles.
  • FIG. 7 is a comparison diagram of the capacity retention ratio of the battery 1 in the embodiment of the present application and the battery 8 in the comparative example 1.
  • the term "about” is used to describe and illustrate small changes.
  • the term may refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very closely.
  • the term can refer to a range of variation less than or equal to ⁇ 10% of the stated value, such as less than or equal to ⁇ 5%, less than or equal to ⁇ 4%, less than or equal to ⁇ 3%, Less than or equal to ⁇ 2%, less than or equal to ⁇ 1%, less than or equal to ⁇ 0.5%, less than or equal to ⁇ 0.1%, or less than or equal to ⁇ 0.05%.
  • a list of items connected by the terms “one of”, “one of”, “one of” or other similar terms can mean any of the listed items.
  • Project A can contain a single element or multiple elements.
  • Project B can contain a single element or multiple elements.
  • Project C can contain a single element or multiple elements.
  • a list of items connected by the terms “at least one of”, “at least one of”, “at least one of” or other similar terms may mean the listed items Any combination of. For example, if items A and B are listed, then the phrase “at least one of A and B” means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C” means only A; or only B; only C; A and B (excluding C); A and C (exclude B); B and C (exclude A); or all of A, B, and C.
  • Project A can contain a single element or multiple elements.
  • Project B can contain a single element or multiple elements.
  • Project C can contain a single element or multiple elements.
  • a positive electrode active material comprising a compound having the structure of P6 3 mc, wherein, in the XRD pattern of the positive electrode active material, P6 3 mc compound having the structure ( 002) The crystal plane is between 17.5°-19°, and its half-width is between 0.05-0.1.
  • the compound with the P6 3 mc structure has an exothermic peak between 330°C and 360°C.
  • the DSC spectrum is obtained by the following test method: the active material is placed in a DSC test device (TOPEM TMDSC), and the powder is heated to 800° C. at a heating rate of 10° C./min to obtain a temperature-exothermic curve.
  • the compound having the P6 3 mc structure satisfies at least one of conditions (a) to (e):
  • the average particle size of the compound with the P6 3 mc structure is 8 ⁇ m-30 ⁇ m, specifically 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 11 ⁇ m, 12 ⁇ m, 13 ⁇ m, 14 ⁇ m, 16 ⁇ m, 18 ⁇ m, 20 ⁇ m, 22 ⁇ m, 24 ⁇ m, 26 ⁇ m, 28 ⁇ m or the range of any two of these values; among them, the measurement of the average particle size D50 of the positive electrode active particles can be measured by a Malvern particle size tester: the positive electrode material is dispersed in a dispersant (ethanol or acetone, or In other surfactants), after 30 minutes of sonication, add the sample to the Malvern particle size tester and start the test.
  • a dispersant ethanol or acetone, or In other surfactants
  • the tap density of the compound with the P6 3 mc structure is 2.2 g/cm 3 -3 g/cm 3 , specifically 2.2 g/cm 3 , 2.3 g/cm 3 , 2.4 g/cm 3 , 2.5 g/cm 3 , 2.6g/cm 3 , 2.7g/cm 3 , 2.8g/cm 3 , 2.9g/cm 3, or a range composed of any two of these values; wherein the tap density is obtained by the following method: using experiments Instrument FZS4-4B automatic tap density instrument, sample the object to be tested in a 25mL standard tapping cylinder, vibrate 3000 times, and record the tap density.
  • the compound with the P6 3 mc structure contains Li x Na z Co 1-y M y O 2 , where 0.6 ⁇ x ⁇ 0.85, 0 ⁇ y ⁇ 0.15, 0 ⁇ z ⁇ 0.03, and M is selected from Al, At least one of the group consisting of Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr, and Zr.
  • x is 0.61, 0.63, 0.65, 0.67, 0.69, 0.71, 0.72, 0.73, 0.74, 0.75, 0.8, or a range composed of any two of these values. In some embodiments, 0.7 ⁇ x ⁇ 0.75.
  • y is 0.0002, 0.0004, 0.0006, 0.0008, 0.001, 0.002, 0.004, 0.005, 0.006, 0.008, 0.009, 0.014, 0.015, 0.016, 0.017, 0.019, 0.02, 0.025, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, or a range composed of any two of these values.
  • z is a range of 0, 0.002, 0.003, 0.004, 0.006, 0.005, 0.008, 0.01, 0.015, 0.02, or any two of these values.
  • M is selected from at least one of the group consisting of Al, Mg, and Ti. In some embodiments, M is Al. In some embodiments, M is Al and Mg, Al and Ti, or Al, Mg and Ti.
  • the first positive electrode active material includes particles with pores, and the number of pores is m, where m ⁇ 2. In some embodiments, the number of gaps in the first positive electrode active material particles is n, where 0 ⁇ n ⁇ 30. In some embodiments, the number of pores on the surface of each particle of the first positive electrode active material is 1, 2, 5, 10, 15, or a range composed of any two of these values, and the number of gaps in each particle is It is a range composed of 4, 8, 12, 16, 20, 25, or any two of these values.
  • the holes on the surface of the particles are obtained by imaging the particles with SEM, and then counting the number of holes on the surface of a certain number of particles, and taking the average value; the number of gaps inside the particles is obtained by using CP (cross-section polishing, cross-section polishing) ) Technology cuts the particles, then imaged by SEM, takes a certain number of particles and counts the number of their gaps, and takes the average value.
  • CP cross-section polishing, cross-section polishing
  • an electrochemical device comprising a positive electrode piece, the positive electrode piece comprising a positive electrode current collector and a positive electrode provided on at least one surface of the positive electrode current collector
  • An active layer the positive electrode active layer comprising any one of the aforementioned positive electrode active materials containing a P6 3 mc structure compound (hereinafter referred to as "first positive electrode active material").
  • the cathode active layer further comprises a second cathode active material, the second cathode active material is selected from Li 1 ⁇ b Co 1-a R a O R-3m structure consisting of two, three nickel cobalt manganese The group consisting of metamaterials, lithium-rich manganese bases or lithium manganese oxides, where (0 ⁇ b ⁇ 0.1, 0 ⁇ a ⁇ 0.1), and where R is selected from Al, Mg, Ti, Mn, Fe, Ni, Zn, At least one of the group consisting of Cu, Nb, Cr, and Zr. In some embodiments, 0.001 ⁇ a ⁇ 0.005. In some embodiments, a is 0.002, 0.003, 0.004, or a range composed of any two of these values. In some embodiments, R is selected from at least one of the group consisting of Al, Mg, and Ti. In some embodiments, R is Al.
  • the positive active layer includes a first layer and a second layer, and the second layer is located between the current collector and the first layer, wherein the first layer includes the first layer. Positive active material.
  • the second layer includes the second positive electrode active material, and the compaction density of the second layer is 4.1 g/cm 3 -4.35 g/cm 3 .
  • the ratio of the thickness of the first layer to the second layer is 0.1-2, specifically 0.2, 0.3, 0.5, 0.7, 1.0, 1.3, 1.5, 1.7, or any two of these values.
  • the compacted density of the positive active layer is 4.0 g/cm 3 -4.5 g/cm 3 . In some embodiments, the resistance of the positive electrode is less than 3 ⁇ .
  • the electrochemical device satisfies at least one of the conditions (f) to (h): ((f) When the discharge gram capacity is not less than 180 mAh/g, at a voltage of 4.8V and a rate of 0.5C Cycle for 20 cycles, the growth rate of particle cracking of the positive electrode active material before and after the cycle is not higher than 5%; (g) When the discharge gram capacity is not less than 180mAh/g, cycle for 20 cycles at a voltage of 4.8V and a rate of 0.5C.
  • the electrochemical device further comprises a negative electrode piece, the negative electrode piece comprising a negative electrode current collector and being arranged on the The negative electrode active material layer on at least one surface of the negative electrode current collector, when the discharge gram capacity is not less than 180mAh/g, is cycled for 20 cycles at a voltage of 4.8V and a rate of 0.5C, and each cycle is cycled on the surface of the negative electrode active layer.
  • the increment of Co accumulation concentration is R, where R ⁇ 5ppm.
  • the cycle is performed for 20 cycles at a voltage of 4.8V and a rate of 0.5C, and the growth rate of particle cracking of the positive electrode active material before and after the cycle is not higher than that in the following group At least one: 4%, 3%, and 2%.
  • the positive electrode active material when the discharge gram capacity is not less than 180 mAh/g, the positive electrode active material is cycled for 20 cycles at a voltage of 4.8V and a rate of 0.5C, and the positive electrode active material has an average DC internal resistance DCR growth rate per cycle before and after the cycle is lower than At least one of the following groups: 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, 1.4%, and 1.3%.
  • the cycle is cycled for 20 cycles at a voltage of 4.8V and a rate of 0.5C, and the average Co accumulation concentration increase on the surface of the negative electrode active layer per cycle is R , wherein R is not greater than at least one of the following groups: 4.58 ppm, 4.0 ppm, 3.5 ppm, 3 ppm, 2.5 ppm, and 2.0 ppm.
  • the thickness of the positive electrode by-product is ⁇ , where ⁇ 0.5 ⁇ m. In some embodiments, ⁇ 0.4 ⁇ m. In some embodiments, ⁇ 0.3 ⁇ m.
  • the aforementioned electrochemical device includes any device that undergoes an electrochemical reaction.
  • the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors.
  • the electrochemical device is a lithium secondary battery.
  • the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.
  • the present application provides an electronic device, which can be any device using the electrochemical device according to the embodiment of the present application.
  • the electronic device includes, but is not limited to: notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, and stereo headsets , Video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles , Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries or lithium-ion capacitors, etc.
  • Li x Na z Co 1-y M y O 2 with P6 3 mc structure where 0.6 ⁇ x ⁇ 0.85, 0 ⁇ y ⁇ 0.15, 0 ⁇ z ⁇ 0.03, M is selected from Al, Mg, Ti, Mn At least one of the group consisting of, Fe, Ni, Zn, Cu, Nb, Cr, and Zr:
  • R is selected from the group consisting of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr and Zr At least one of the group:
  • R element-doped Co 3-a N a O 4 precursor soluble cobalt salt (e.g., cobalt chloride, cobalt acetate, cobalt sulfate, cobalt nitrate) and R Salt (e.g., sulfate, etc.) is added in proportion to the solvent (e.g., deionized water), precipitating agent (e.g. sodium carbonate, sodium hydroxide) and complexing agent (e.g. ammonia) are added to adjust the pH value (e.g., pH Adjust the value of 5-9) to make it precipitate; then the precipitate is sintered and ground to obtain Co 3-a R a O 4 powder.
  • solvent e.g., deionized water
  • precipitating agent e.g. sodium carbonate, sodium hydroxide
  • complexing agent e.g. ammonia
  • the LiCo R-3m structure 1-a R a O 2 positive active material positive electrode active material or other, including but not limited to: nickel cobalt manganese ternary materials, manganese-based or lithium-rich lithium manganate), conductive agent (e.g. , Acetylene black), binder (for example, polyvinylidene fluoride (PVDF)) at a certain weight ratio (for example, 97:2:1) in a solvent (for example, N-methylpyrrolidone) system, fully stir and mix well Afterwards, it is coated on a positive electrode current collector (for example, Al foil) and dried to obtain a primer film.
  • positive electrode active material positive electrode active material or other, including but not limited to: nickel cobalt manganese ternary materials, manganese-based or lithium-rich lithium manganate
  • conductive agent e.g. , Acetylene black
  • binder for example, polyvinylidene fluoride (PVDF)
  • PVDF polyvinyliden
  • the ratio for example, 97:2:1 is fully stirred and mixed evenly in a solvent (for example, N-methylpyrrolidone) system, and then coated on the aforementioned primer film, dried and cold pressed to obtain a double-layer structure of the positive electrode Pole piece.
  • the Li x Na z Co 1-y M y O 2 positive electrode active material (or other positive electrode active materials, including but not limited to: R-3m structure LiCo 1-a R a O 2 positive electrode active material, nickel Cobalt-manganese ternary material, lithium-rich manganese base or lithium manganate), conductive agent (for example, acetylene black), binder (for example, polyvinylidene fluoride (PVDF)) in a solvent (for example, N -Methylpyrrolidone) system is fully stirred and mixed uniformly, and then coated on a positive electrode current collector (for example, Al foil), dried, and cold pressed to obtain a single-layer structure positive electrode sheet.
  • the negative electrode piece, composition, and manufacturing method that can be used in the electrochemical device include any technology disclosed in the prior art.
  • the negative pole piece includes a negative current collector and a negative active material layer on at least one surface of the negative current collector.
  • the negative active material layer includes a binder.
  • the binder includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyfluoro Ethylene, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylic (ester) styrene butadiene Rubber, epoxy or nylon.
  • the negative active material layer includes a conductive material.
  • the conductive material includes, but is not limited to: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, copper, nickel, aluminum, silver, or polyphenylene derivative.
  • the current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or a polymer substrate coated with conductive metal.
  • the negative pole piece may be obtained by the following method: mixing the active material, conductive material, and binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector .
  • the solvent may include, but is not limited to: N-methylpyrrolidone.
  • the electrolyte that can be used in the embodiments of the present application may be an electrolyte known in the prior art.
  • the electrolyte includes an organic solvent, a lithium salt, and additives.
  • the organic solvent of the electrolytic solution according to the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolytic solution.
  • the electrolyte used in the electrolyte according to the present application is not limited, and it may be any electrolyte known in the prior art.
  • the additive of the electrolyte according to the present application may be any additive known in the prior art that can be used as an additive of the electrolyte.
  • the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.
  • the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.
  • the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), bistrifluoromethanesulfonimide Lithium LiN(CF 3 SO 2 ) 2 (LiTFSI), Lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), Lithium bisoxalate borate LiB(C 2 O 4 ) 2 (LiBOB ) Or LiBF 2 (C 2 O 4 ) (LiDFOB).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium difluorophosphate
  • LiPO 2 F 2 lithium difluorophosphate
  • LiTFSI bistrifluoromethanesulfonimide Lithium LiN(CF 3 SO 2 ) 2
  • LiFSI Lithium bis(flu
  • the concentration of the lithium salt in the electrolyte is about 0.5-3 mol/L, about 0.5-2 mol/L, or about 0.8-1.5 mol/L.
  • a separator is provided between the positive pole piece and the negative pole piece to prevent short circuits.
  • the material and shape of the isolation film that can be used in the embodiments of the present application are not particularly limited, and may be any technology disclosed in the prior art.
  • the isolation membrane includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.
  • the isolation film may include a substrate layer and a surface treatment layer.
  • the substrate layer is a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected.
  • a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic substance layer, or a layer formed by a mixed polymer and an inorganic substance.
  • the inorganic layer includes inorganic particles and a binder.
  • the inorganic particles are selected from alumina, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, One or a combination of yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.
  • the binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, One or a combination of polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer is selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or polyvinylidene fluoride. At least one of (vinylidene fluoride-hexafluoropropylene).
  • Step (1) Mix cobalt tetroxide and sodium carbonate powder in a ratio of Na to Co molar ratio of 0.75:1; sinter the uniformly mixed powder in an oxygen atmosphere at 800°C for 46 hours to obtain a P6 3 mc structure ⁇ Na 0.75 CoO 2 .
  • Step (2) Mix Na 0.75 CoO 2 and lithium nitrate uniformly according to the molar ratio of Na to Li at a ratio of 0.75:5, and react at 300°C in an air atmosphere for 6 hours. The reactants are washed with deionized water several times. The molten salt is cleaned, and the powder is dried to obtain Li 0.73 Na 0.02 CoO 2 with a P6 3 mc structure.
  • Step (1) Preparation of Al element-doped (Co 0.985 M 0.015 ) 3 O 4 precursor by liquid phase precipitation method and sintering method: Cobalt chloride and aluminum sulfate are in a ratio of 0.985:0.015 according to the molar ratio of Co to Al Add deionized water, add precipitant sodium carbonate and complexing agent ammonia to adjust the PH value to 7 to make it precipitate; then, the precipitate is sintered at 600°C for 7 hours and ground to obtain (Co 0.985 M 0.015 ) 3 O 4 powder.
  • Step (2) Mix (Co 0.985 Al 0.015 ) 3 O 4 powder and sodium carbonate powder according to the molar ratio of Na to Co of 0.63:0.985; put the uniformly mixed powder in an oxygen atmosphere at 800°C Sintered under the conditions for 46h, Na 0.63 Co 0.985 Al 0.015 O 4 was obtained .
  • Step (1) adding cobalt chloride and aluminum sulfate into deionized water in a ratio of Co to Al molar ratio of 0.985:0.015, adding precipitating agent sodium carbonate and complexing agent ammonia to adjust the pH to 7 to make it precipitate; Then the precipitate was sintered at 600° C. for 7 hours and ground to obtain (Co 0.985 Al 0.015 ) 3 O 4 powder.
  • Step (2) Mix (Co 0.985 Al 0.015 ) 3 O 4 powder and sodium carbonate powder according to the molar ratio of Na to Co of 0.64:0.985; put the uniformly mixed powder in an oxygen atmosphere at 800°C After sintering for 46 hours under the conditions, Na 0.64 Co 0.985 Al 0.015 O 2 was obtained .
  • Examples 4-16 The preparation method of Examples 4-16 is basically the same as that of Example 3, but the difference lies in the type and/or content of the doped element M.
  • Example 1 Li 0.73 Na 0.02 CoO 2
  • Example 2 Li 0.63 Co 0.985 Al 0.015 O 2
  • Example 3 Li 0.63 Na 0.01 Co 0.985 Al 0.015 O 2
  • Example 4 Li 0.69 Na 0.01 Co 0.985 Al 0.015 O 2
  • Example 5 Li 0.72 Na 0.01 Co 0.985 Al 0.015 O 2
  • Example 6 Li 0.73 Na 0.01 Co 0.985 Al 0.015 O 2
  • Example 7 Li 0.74 Na 0.008 Co 0.98 Al 0.02 O 2
  • Example 8 Li 0.74 Na 0.006 Co 0.975 Al 0.025 O 2
  • Example 9 Li 0.74 Na 0.006 Co 0.991 Mg 0.009 O 2
  • Example 10 Li 0.74 Na 0.01 Co 0.986 Mg 0.014 O 2
  • Example 11 Li 0.74 Na 0.006 Co 0.983 Al 0.015 Mg 0.002 O 2
  • Example 12 Li 0.74 Na 0.005 Co 0.981 Al 0.018 Mg 0.001 O 2
  • Example 13 Li 0.74 Na 0.004
  • Example 17 controls the sintering temperature and the raw material mixing method in step 1 to obtain different average particle diameters (D50) and different tap densities.
  • Example 18 controls the sintering temperature and the raw material mixing method in step 1 to obtain different average particle diameters (D50) and different tap densities.
  • P6 3 mc structure Li 0.73 Na 0.01 Co 0.985 Al 0.015 O 2 with no holes on the particle surface.
  • Example 19 controls the sintering temperature and the raw material mixing method in step 1 to obtain different average particle diameters (D50) and different tap densities. And the P6 3 mc structure of Li 0.73 Na 0.01 Co 0.985 Al 0.015 O 2 with no gaps in the particles.
  • Example 20 controls the sintering temperature and the raw material mixing method in step 1 to obtain different average particle diameters (D50) and different tap densities.
  • Table 2 below shows the specific values of D50 and tap density of the positive electrode active materials in Example 6 and Examples 17-20, as well as whether there are pores on the surface of the particles and internal gaps in the particles.
  • Step (1) Add cobalt chloride and aluminum sulfate into deionized water at a molar ratio of cobalt to aluminum of 0.985:0.015, add precipitating agent sodium carbonate and complexing agent ammonia, adjust the PH value to 7, and make it precipitate ; Then the precipitate is sintered and ground to obtain (Co 0.985 Al 0.015 ) 3 O 4 powder.
  • Step (1) Add cobalt chloride, aluminum sulfate and magnesium sulfate into deionized water in a molar ratio of 0.983:0.015:0.002 of cobalt, aluminum and magnesium, add precipitant sodium carbonate and complexing agent ammonia to adjust PH The value is 7, to make it precipitate; then the precipitate is sintered and ground to obtain (Co 0.983 Al 0.015 Mg 0.002 ) 3 O 4 powder.
  • Step (1) Add cobalt chloride, aluminum sulfate and titanium nitrate into deionized water at a molar ratio of cobalt, aluminum and titanium of 0.984:0.015:0.001, add precipitant sodium carbonate and complexing agent ammonia to adjust the pH The value is 7, to make it precipitate; then the precipitate is sintered and ground to obtain (Co 0.984 Al 0.015 Ti 0.001 ) 3 O 4 powder.
  • Step (1) Add cobalt chloride, aluminum sulfate, magnesium sulfate and titanium nitrate into deionized water at a molar ratio of 0.994:0.003:0.002:0.001 for cobalt, aluminum, magnesium and titanium, and add precipitating agents sodium carbonate and Complexing agent ammonia water, adjust the PH value to 7 to make it precipitate; then the precipitate is sintered and ground to obtain (Co 0.994 Al 0.003 Mg 0.002 Ti 0.001 ) 3 O 4 powder.
  • Step (2) After (Co 0.994 Al 0.003 Mg 0.002 Ti 0.001 ) 3 O 4 powder and lithium carbonate are uniformly mixed according to the molar ratio of lithium to cobalt of 0.57:0.994, they are sintered in air at 1000°C for 12 hours. After cooling, grinding and sieving to obtain Li 0.57 Na 0.003 Co 0.994 Al 0.003 Mg 0.002 Ti 0.001 O 2 with R-3m structure.
  • a lithium ion battery was prepared according to the following steps, and the corresponding electrochemical performance of each lithium ion battery was tested.
  • Positive pole piece Take the positive electrode active material in the previous embodiment and the comparative example, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) at a weight ratio of 97:2:1 in N-methylpyrrolidone solvent. After the system is fully stirred and mixed uniformly, it is coated on the positive electrode current collector Al foil, dried, and cold pressed to obtain a positive electrode sheet with a single-layer structure of the positive electrode active layer (hereinafter referred to as "single-layer structure positive electrode sheet”) .
  • PVDF polyvinylidene fluoride
  • Negative pole piece the active material artificial graphite, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carbon methyl cellulose (CMC) according to the mass ratio of about 95:2:2:1 After fully stirring and mixing in the deionized water solvent system, it is coated on the Cu foil, dried, and cold pressed to obtain the negative electrode.
  • SBR styrene butadiene rubber
  • CMC thickener sodium carbon methyl cellulose
  • Electrolyte In an argon atmosphere glove box with a water content of ⁇ 10ppm, ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC), propylene carbonate (abbreviated as PC), according to 2:6: Mix well with the weight ratio of 2, and then dissolve the fully dried lithium salt LiPF6 in the above solvent, the content of LiPF6 is 1mol/L, add 1.5% of 1,3-propane sultone, 3% of fluoroethylene carbonate, 2% adiponitrile. The content of each substance is based on the total weight of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • PC propylene carbonate
  • Isolation membrane PE porous polymer film is used as the isolation membrane.
  • the half-cell is prepared using almost the same method as the above-mentioned battery preparation method, but there are the following differences:
  • Preparation of the positive electrode randomly select the areas coated with the active material layer on the front and back sides of the current collector from the positive electrode of the above battery, wash with dimethyl carbonate (DMC), and remove one of the sides to obtain a single-sided positive electrode sheet;
  • DMC dimethyl carbonate
  • the positive electrode and the lithium metal negative electrode are used to prepare a button battery.
  • the PE porous polymer film is provided as a separator between the positive electrode sheet and the lithium metal negative electrode sheet, the electrolyte prepared above is injected into it, thereby obtaining a button battery.
  • Scanning electron microscopy uses the interaction of the electron beam with the sample and uses the secondary electron signal to image the topography of the sample.
  • the scanning electron microscope used in this experiment is the JSM-6360LV model of JEOL and its supporting X-ray energy spectrometer to analyze the morphology, structure and element distribution of the sample.
  • Cracking growth rate (total number of cracks after the 20th cycle-total number of cracks after the first cycle)/total number of cracks after the first cycle ⁇ 100%.
  • Discharge the battery to 0SOC% SOC: state of charge, state of charge
  • disassemble the battery clean, dry, and use an electronic balance to apply an electronic balance to the positive electrode of a certain area A (both sides of the positive electrode current collector are coated with a positive electrode active material layer)
  • Weigh the weight record the weight as W 1 , and measure the thickness T 1 of the positive electrode with a ten-meter ruler.
  • the weight W 0 and thickness T 0 of the positive electrode active material layer disposed on the positive electrode current collector side and the compaction density of the positive electrode active material layer are calculated by the following formula:
  • T 0 (T 1 -T 2 )/2
  • the capacity decay rate after the Nth cycle (discharge capacity at the first cycle-discharge capacity at the Nth cycle)/discharge capacity at the first cycle ⁇ 100%.
  • Capacity retention rate after the Nth cycle discharge capacity at the 20th cycle/discharge capacity at the first cycle ⁇ 100%.
  • the average growth rate of DCR after 20 cycles (DC resistance of the 20th cycle-DC resistance before the cycle) / DC resistance before the cycle ⁇ 100%
  • the average DCR growth rate per cycle for 20 cycles the average DCR growth rate for 20 cycles/20.
  • Use SEM Zeiss Sigma02-33) to take pictures of its cross-sections at a magnification of not less than 5.0K to obtain images.
  • ICP inductively coupled plasma mass spectrometry
  • the charge-discharge test was performed between 3.0V-4.8V with a current density of 10mA/g.
  • SOC is the capacity value at any point on the charge/discharge curve divided by the maximum capacity value of the charge/discharge.
  • Table 3 shows the peak positions of (002) and/or (003) crystal planes and the half-value widths of the materials in Examples 1-16 and Comparative Examples 1-4 and the lithium ion batteries composed of them. Circle discharge capacity and capacity retention rate after the 100th cycle (the test method and test conditions are consistent with the aforementioned "Capacity Decay Rate/Retention Rate Test Method” section).
  • 3A is an XRD pattern of Li 0.73 Na 0.02 CoO 2 with a P6 3 mc structure in Example 1 of the present application. It can be seen that the (002) crystal plane of this material is between 17.5°-19°, and its half-value width is between 0.05-0.1.
  • 3B is the XRD pattern of Li 0.8 Na 0.006 Co 0.983 Al 0.015 Mg 0.002 O 2 of the non-P6 3 mc structure of Comparative Example 2 of the present application. It can be seen that the material does not have (002) crystal planes between 17.5°-19°.
  • Figure 4 is the difference between Li 0.73 Na 0.01 Co 0.985 Al 0.015 O 2 of the positive electrode active material P6 3 mc structure of Example 6 of the present application and Li 0.58 Na 0.01 Co 0.985 Al 0.015 O 2 of the non-P6 3 mc structure of Comparative Example 1 Scanning calorimetry (DSC: Differential Scanning Calorimetry) spectrum. It can be seen that the positive electrode active material in Example 6 has an exothermic peak at 360°C, and the half-width of the exothermic peak is 18°C, while the positive electrode active material in Comparative Example 1 does not fall within the above range. There is an exothermic peak.
  • DSC Differential Scanning Calorimetry
  • the positive electrode active materials in the examples of the application all have an exothermic peak between 250°C and 400°C, and the half-value width of the exothermic peak is between 15°C and 40°C.
  • Table 4 shows the D50, tap density, and the holes and cracks in the particles of the materials of Example 6 and Examples 17-20. It can be seen that the performance of these materials with different D50, tap density, holes and cracks is better than the corresponding performance of the materials in the comparative example. And D50 is 10 ⁇ m-30 ⁇ m, the tap density is 2.5 g/cm 3 -3 g/cm 3 , and the performance of the material in Example 6 with holes and cracks is better.
  • Table 5 shows various performances related to the lithium ion battery including the single-layer structure positive electrode sheet prepared from the positive electrode active material layers of Examples 6, 7, 11, 13, 14 and Comparative Examples 1 and 2.
  • the material has good structural reversibility and cycle stability under high voltage, and its advantages include but are not limited to: (1) During the lithium insertion process, the Li x Na z Co 1-y M y O 2 cathode material is due to There are lithium vacancies in its own crystal structure, which can well accommodate volume changes and insert more Li; (2) In the process of lithium removal/lithium insertion, the Li x Na z Co 1-y M y O 2 cathode material is due to its own There are holes and cracks, which can effectively release the huge stress formed by the process of high-voltage lithium removal/intercalation, inhibit irreversible slip between layers, and achieve good cycle performance; (2) When the voltage is greater than 4.7V, Li x Na z Co 1- y M y O 2 cathode material has achieved 95% delithiation, so the requirement for oxidation resistance (high voltage) electrolyte is lower than that of O3 phase; (3) Li x Na z Co 1- y M y O 2 cathode material itself is being synthesized
  • this application also follows the following steps, taking the positive electrode active material of Example 6 to prepare a positive electrode piece containing a double-layer structure of the positive electrode active layer (hereinafter referred to as a double-layer structure positive electrode piece) ), and further prepared a lithium-ion battery.
  • the active material layer close to the Al foil is hereinafter referred to as the "second layer” .
  • the active material layer far away from the Al foil is hereinafter referred to as the "first layer”, and the ratio of the thickness of the first layer to the second layer is controlled to a certain value (see Table 6 for details).
  • the following Table 6 shows a lithium ion battery containing a double-layer structure positive electrode plate prepared from the positive electrode active material of Example 6 and another positive electrode active material and a single-layer structure positive electrode prepared from Example 6 and Comparative Example 1.
  • the specific parameters of the lithium-ion battery of the pole piece (marked with batteries 1-8 respectively in order).
  • batteries 1-7 (the positive electrode of battery 7 adopts a single-layer active layer structure, and its positive electrode active materials all contain P6 3 mc structure LiCo 0.975 Al 0.02 Mg 0.005 O 2 ; batteries 1-6
  • the positive pole piece adopts a double-layer active layer structure, the first layer contains P6 3 mc structure Li x Na z Co 1-y M y O 2 and the second layer contains R-3m structure LiCo 1-a R a O 2.
  • the capacity retention rate of nickel-cobalt-manganese ternary materials, lithium-rich manganese-based or lithium manganate) is higher than that of battery 1 (its positive electrode active material only contains LiCo 0.975 Al 0.02 Mg 0.005 O 2 with R-3m structure).
  • the test conditions are consistent with those in the aforementioned cracking growth rate test method. It can be seen that: Battery 1, which includes a double-layer positive electrode sheet prepared from the positive electrode active material of Example 6, before the first cycle and the first cycle After 20 cycles, the surface morphology of the particles remained significantly better than that of Battery 8, which contained a single-layer positive pole piece prepared from LiCo 0.975 Al 0.02 Mg 0.005 O 2 with a non-P6 3 mc structure.
  • the test conditions are consistent with those of the aforementioned DCR test. It can be seen that the DCR growth rate of the positive pole piece of battery 1 after each cycle is significantly lower than that of battery 8.
  • the aforementioned excellent performance of battery 1 is mainly due to: (1) During the lithium extraction/intercalation process, the first positive electrode active material contained in the first layer can well isolate the electrolyte from the second due to its own interface stability. Corrosion of the active surface of the second positive electrode active material contained in the layer, thereby maintaining the stability of the interface; (2) During the lithium extraction/intercalation process, the first positive electrode active material contained in the first layer can be effectively released due to its own holes and cracks. The huge stress formed by the process of high-voltage lithium removal/intercalation inhibits irreversible slippage between layers and achieves good cycle performance; (3) The first positive electrode active material contained in the first layer has good flexibility and can be compacted at will.
  • the composite positive electrode active layer has a high compaction density
  • the material including the electrochemical device of the present application has excellent structural reversibility and cycle stability at a high voltage of 4.8V.
  • references to “some embodiments”, “partial embodiments”, “one embodiment”, “another example”, “examples”, “specific examples” or “partial examples” throughout the specification mean At least one embodiment or example in this application includes the specific feature, structure, material, or characteristic described in the embodiment or example. Therefore, the descriptions appearing in various places throughout the specification, such as: “in some embodiments”, “in embodiments”, “in one embodiment”, “in another example”, “in an example “In”, “in a specific example” or “exemplified”, which are not necessarily quoting the same embodiment or example in this application.
  • the specific features, structures, materials, or characteristics herein can be combined in one or more embodiments or examples in any suitable manner.

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Abstract

本申请涉及一种正极活性材料及包含其的电化学装置。该正极活性材料包含具有P63mc结构的化合物，其中，在所述正极活性材料的XRD图谱中，所述具有P63mc结构的化合物的(002)晶面位于17.5°-19°之间，其半高宽在0.05-0.1之间。所述正极活性材料在4.8V高电压下具有可观的放电容量，较好的结构可逆性和循环稳定性。

Description

一种正极活性材料及包含其的电化学装置
优先权信息
本申请要求申请号为202010511491.1的中国专利申请的优先权。
技术领域
本申请涉及储能领域，且更具体来说涉及一种正极活性材料及包含该正极活性材料的电化学装置，特别是锂离子电池。
背景技术
随着电子类的产品如笔记本电脑，手机，掌上游戏机，平板电脑等的普及，大家对其电池的要求也越来越严格。在众多电池中，锂离子电池因其具有储能密度高、功率密度大、安全性好、环境友好、寿命长、自放电率低及温度适应范围宽等优点而被广泛的应用于便携式电子产品、电动交通、国防航空、能源储备等领域。正极材料作为锂离子电池的重要组成部分对其性能有着显著的影响，因而对正极材料的不断优化和改进也就显得尤为重要。随着电子产品的更新换代，追求高能量密度和高功率密度成为锂离子电池正极材料的发展趋势。作为最早商业化的锂离子正极材料，钴酸锂已经得到了广泛而深入研究，在可逆性、放电容量、充电效率和电压稳定性等方面综合性能最好，是目前锂离子电池中应用量最大的正极材料。经过几十年的发展，钴酸锂结构特性和电化学性能也都得到充分的研究，合成工艺及工业化生产也已相当成熟。其凭借较高的放电电压平台和较高的能量密度，一直在消费类锂离子电池正极材料中占据主导地位。
目前在3C领域商业化用最多的LiCoO 2正极材料为O3相结构，理论容量为273.8mAh/g，其具有良好的循环及安全性能，高的压实密度且制备工艺简单。自1991年Sony公司实现商业化以来，LiCoO 2正极材料在锂离子电池材料市场一直占据着主要地位。为了获取更高比容量，LiCoO 2正朝着高电压(>4.6Vvs.Li/Li +)方向发展。LiCoO 2充电到4.5V，容量也仅能达到190 mAh/g。人们试图通过从晶体结构中脱出更多的Li +来实现更高的比容量，但随着电压进一步升高，Li +大量脱出，晶体结构将发生一系列不可逆的相变(O3到H1-3，H1-3到O1)，使得材料循环性能和安全性能大大降低。加之，高电压下界面副反应加剧，Co金属溶出严重，而高电压电解液技术难以配套，常规电解液在高电压下分解加速、失效加快，因而容量衰减十分严重。
因此，急需寻求一种具有高比容量、高电压平台、结构可逆性好且在高电压下界面稳定的锂离子电池正极材料。
发明内容
本申请提供一种正极活性材料，其在4.8V高电压下具有可观的放电容量，较好的结构可逆性和循环稳定性。
在一个实施例中，本申请提供了一种正极活性材料，其包含具有P6 3mc结构的化合物，其中，在所述正极活性材料的XRD图谱中，所述具有P6 3mc结构的化合物的(002)晶面位于17.5°-19°之间，其半峰宽在0.05-0.1之间。
在一些实施例中，在所述正极活性材料的DSC图谱中，所述具有P6 3mc结构的化合物在250℃-400℃之间存在一个放热峰，所述放热峰的半峰宽在15℃-40℃之间。
在一些实施例中，所述具有P6 3mc结构的化合物满足条件(a)至(e)中的至少一者：(a)所述具有P6 3mc结构的化合物的平均粒径为8μm-30μm；(b)所述具有P6 3mc结构的化合物的振实密度为2.2g/cm 3-3g/cm 3；(c)所述具有P6 3mc结构的化合物的颗粒表面存在孔洞；(d)所述具有P6 3mc结构的化合物的颗粒内部存在缝隙；(e)所述具有P6 3mc结构的化合物包含Li xNa zCo 1-yM yO 2，其中0.6<x<0.85，0≤y<0.15，0≤z<0.03，M选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者。
在上述条件(e)中x值会根据电池的充放电、活性材料中是否包含富锂材料而变化。
本申请提供的上述正极材料改善了传统LiCoO 2材料在充电过程 (>4.6Vvs.Li/Li +)中发生晶体结构坍塌和界面失效。所述材料在高电压下具有较好的结构可逆性和循环稳定性，且优点包含但不限于：(1)在嵌锂过程中，Li xNa zCo 1-yM yO 2正极材料由于自身晶体结构中存在锂空位，可以很好地容纳体积变化，嵌入更多的Li；(2)在脱锂/嵌锂过程中，Li xNa zCo 1-yM yO 2正极材料由于自身存在孔洞和裂缝，能够有效释放高电压脱/嵌锂过程形成的巨大应力，抑制层间不可逆滑移，实现好的循环性能；(2)在电压大于4.7V时，Li xNa zCo 1- yM yO 2正极材料已实现95％脱锂，因而对耐氧化(高电压)电解液要求低于O3相；(3)Li xNa zCo 1-yM yO 2正极材料自身在合成过程会引入极少量Na，Na占据了部分Li位，作为支柱支撑晶体结构，可提高材料的结构稳定性；(4)Li xCo 1-yM yO 2正极材料相比于O3相LiCoO 2具有更低的锂离子迁移能；(5)Li xCo 1- yM yO 2正极材料中引入的优选元素M，能一定程度上加强结构稳定效果。在另一个方面，本申请提供了一种电化学装置，所述电化学装置包含正极极片，所述正极极片包含正极集流体和设置于所述正极集流体的至少一个表面上的正极活性层，所述正极活性层包含前述任一种正极活性材料(在后称作“第一正极活性材料”)。
在一些实施例中，所述正极活性层进一步包括第二正极活性材料，所述第二正极活性材料选自由R-3m结构的Li 1±bCo 1-aR aO 2、镍钴锰三元材料、富锂锰基或锰酸锂组成的群组，其中(0≤b<0.1，0≤a<0.1)，且其中R选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者。
上述电化学装置在4.8V高电压下具有优异的结构可逆性和循环稳定性。一方面，第一正极活性材料弥补了第二正极活性材料在4.8V高电压下单独使用时界面极其不稳定，界面失效导致容量衰减严重，无法实现高容量稳定循环的缺陷。另一方面，第二正极活性材料较高的理论容量进一步提高该电化学装置的容量。所述电化学装置可将两个材料各自的优势得到发挥，实现高于目前量产材料的能量密度。
在一些实施例中，所述正极活性层包含第一层和第二层，所述第二层位于所述集流体和所述第一层之间，其中所述第一层包括所述第一正极活性材料。
在一些实施例中，所述第二层包括所述第二正极活性材料，且所述第二层 的压实密度为4.1g/cm 3-4.35g/cm 3。
在一些实施例中，所述第一层与所述第二层的厚度的比值为0.1-2。
在一些实施例中，所述正极活性层是由所述第一正极活性材料与所述第二正极活性材料混合而成的单层结构。本申请提供了一种正极活性材料，其由所述第一正极活性材料与所述第二正极活性材料混合而成。
本申请研究发现，前述由具有双层结构的正极极片制备的锂离子电池在高电压下的循环稳定性和结构可逆性进一步得到改善。本申请研究发现，通过将包含P6 3mc结构的化合物的正极活性材料涂覆在，例如，具有R-3m结构的LiCo 1-aR aO 2的正极活性材料表面(即，第一层包括所述第一正极活性材料，第二层包括所述第二正极活性材料，且第二层位于集流体与第一层之间)，可以有效抑制电解液与第二层中的活性材料的表面的副反应，保护第二层中的活性材料的界面。以P6 3mc结构Li xNa zCo 1-yM yO 2为第一层，R-3m结构LiCo 1-aR aO 2为第二层的复合正极活性层为例，该复合正极活性层的优点如下：(1)在脱/嵌锂过程中，第一层的正极活性材料由于自身界面稳定性，可以很好地隔绝电解液对第二层的正极活性材料的活性面的腐蚀，保持界面稳定；(2)在脱/嵌锂过程中，第一层的正极活性材料由于自身存在孔洞和裂缝，能够有效释放高电压脱/嵌锂过程形成的巨大应力，抑制层间不可逆滑移，实现好的循环性能；(3)第一层的正极活性材料具有好的柔性，可以进行任意压实，不会影响复合正极活性层的厚度，复合正极活性层的压实密度高；(4)第一层的正极活性材料和第二层的正极活性材料中引入的掺杂元素能有效加强晶体的结构稳定效果。
包含前述本申请的双层结构的正极活性层的正极极片的示意图如图1所示(其中，正极集流体并不局限于Al箔，还可以是镍箔等本领域技术人员常用的正极集流体，且第二层的正极活性材料并不局限于具有R-3m结构的LiCo 1- aR aO 2，其也可以是需要改善在高电压下的材料界面、循环稳定性或结构可逆性的其它正极材料，包含但不限于：镍钴锰三元材料、富锂锰基或锰酸锂)。
在一些实施例中，所述正极活性层的压实密度为4.0g/cm 3-4.5g/cm 3。
在一些实施例中，所述电化学装置满足条件(f)至(h)中的至少一者： (f)放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，循环前后所述正极活性材料的颗粒开裂增长率不高于5％；(g)放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，循环前后所述正极活性材料平均每圈循环的直流内阻DCR增长率低于2％；(h)所述电化学装置进一步包含负极，所述负极包含负极集流体和设置于所述负极集流体的至少一个表面上的负极活性层，在放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，平均每圈循环在所述负极活性层表面的Co堆积浓度增量为R，其中R≤5ppm。
在一些实施例中，在其放电克容量在180mAh/g-200mAh/g时，其正极副产物厚度为η，其中η≤0.5μm。
在另一个方面，本申请提供了一种电子装置，其包含前述任一种电化学装置。
本申请实施例的额外层面及优点将部分地在后续说明中描述、显示或是经由本申请实施例的实施而阐述。
附图说明
在下文中将简要地说明为了描述本申请实施例或现有技术所必要的附图以便于描述本申请的实施例。显而易见地，下文描述中的附图仅只是本申请中的部分实施例。对本领域技术人员而言，在不需要创造性劳动的前提下，依然可以根据这些附图中所例示的结构来获得其他实施例的附图。
图1是本申请一些实施例的包含双层结构的正极活性层的正极极片的结构示意图。
图2是本申请实施例1的正极极片的横截面的二次颗粒的扫描式电子显微镜(SEM)图像。
图3A是本申请实施例1的正极活性材料的X射线衍射(XRD)图谱，图3B是本申请对比例1的正极活性材料的X射线衍射(XRD)图谱。
图4是本申请实施例6和对比例1的正极活性材料的差示扫描量热 (DSC)曲线。
图5A和5B分别是本申请实施例中的电池1的正极极片在首次循环前和第20次循环后的横截面的SEM图。图5C和5D分别是本申请对比例中的电池8的正极极片在首次循环前和第20次循环后的横截面的SEM图。
图6是根据本申请实施例中的电池1与对比例中的电池8的直流内阻随循环次数的进行的平均增长率的对比图。
图7是根据本申请实施例中的电池1与对比例1中的电池8的容量保持率对比图。
具体实施方式
本申请的实施例将会被详细的描示在下文中。本申请的实施例不应该被解释为对本申请的限制。
如本申请中所使用，术语“约”用以描述及说明小的变化。当与事件或情形结合使用时，所述术语可指代其中事件或情形精确发生的例子以及其中事件或情形极近似地发生的例子。举例来说，当结合数值使用时，术语可指代小于或等于所述数值的±10％的变化范围，例如小于或等于±5％、小于或等于±4％、小于或等于±3％、小于或等于±2％、小于或等于±1％、小于或等于±0.5％、小于或等于±0.1％、或小于或等于±0.05％。
另外，有时在本文中以范围格式呈现量、比率和其它数值。应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于所述范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围一般。
在具体实施方式及权利要求书中，由术语“中的一者”、“中的一个”、“中的一种”或其他相似术语所连接的项目的列表可意味着所列项目中的任一者。例如，如果列出项目A及B，那么短语“A及B中的一者”意味着仅A或仅B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的一者”意味着仅A；仅B；或仅C。项目A可包含单个元件或多个元件。项目B可包含单个 元件或多个元件。项目C可包含单个元件或多个元件。
在具体实施方式及权利要求书中，由术语“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元件。项目C可包含单个元件或多个元件。
一、正极活性材料
根据本申请的第一方面，提供了一种正极活性材料，其包含具有P6 3mc结构的化合物，其中，在所述正极活性材料的XRD图谱中，所述具有P6 3mc结构的化合物的(002)晶面位于17.5°-19°之间，其半峰宽在0.05-0.1之间。
在一些实施例中，在所述正极活性材料的DSC图谱中，所述具有P6 3mc结构的化合物在250℃-400℃之间存在一个放热峰，所述放热峰的半峰宽在15℃-40℃之间。在一些实施例中，所述具有P6 3mc结构的化合物在330℃-360℃之间存在一个放热峰。其中，DSC图谱通过如下的测试方法获得：将活性材料放置于DSC测试装置(TOPEM TMDSC)中，将粉体以10℃/min的升温速度加热至800℃，获得温度-放热曲线。
在一些实施例中，具有P6 3mc结构的化合物满足条件(a)至(e)中的至少一者：
(a)所述具有P6 3mc结构的化合物的平均粒径为8μm-30μm，具体可以为8μm、9μm、10μm、11μm、12μm、13μm、14μm、16μm、18μm、20μm、22μm、24μm、26μm、28μm或这些数值中任两者组成的范围；其中，对于正极活性颗粒的平均粒径D50的测量，可以通过马尔文粒度测试仪进行测量：将正极材料分散在分散剂中(乙醇或丙酮，或其他的表面活性剂中)，超声30min后，将样品加入到马尔文粒度测试仪内，开始测试。
(b)所述具有P6 3mc结构的化合物的振实密度为2.2g/cm 3-3g/cm 3，具体可以为2.2g/cm 3、2.3g/cm 3、2.4g/cm 3、2.5g/cm 3、2.6g/cm 3、2.7g/cm 3、2.8g/cm 3、2.9g/cm 3或这些数值中任两者组成的范围；其中振实密度通过如下方式获得：采用实验仪器FZS4-4B自动振实密度仪器，将待测物品取样置于25mL标准振实量筒，振动3000次，记录振实密度。
(c)所述具有P6 3mc结构的化合物的颗粒表面存在孔洞；
(d)所述具有P6 3mc结构的化合物的颗粒内部存在缝隙；
(e)所述具有P6 3mc结构的化合物包含Li xNa zCo 1-yM yO 2，其中0.6<x<0.85，0≤y<0.15，0≤z<0.03，M选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者。
在一些实施例中，x为0.61、0.63、0.65、0.67、0.69、0.71、0.72、0.73、0.74、0.75、0.8或这些数值中任意两者组成的范围。在一些实施例中，0.7≤x<0.75。
在一些实施例中，y为0.0002、0.0004、0.0006、0.0008、0.001、0.002、0.004、0.005、0.006、0.008、0.009、0.014、0.015、0.016、0.017、0.019、0.02、0.025、0.3、0.4、0.5、0.6、0.7、0.8、0.9、1、1.2或这些数值中任意两者组成的范围。
在一些实施例中，z为0、0.002、0.003、0.004、0.006、0.005、0.008、0.01、0.015、0.02或这些数值中任意两者组成的范围。
在一些实施例中，M选自由Al、Mg和Ti组成的群组中的至少一者。在一些实施例中，M为Al。在一些实施例中，M为Al与Mg、Al与Ti或Al、Mg与Ti。
在一些实施例中，所述第一正极活性材料中包含具有孔洞的颗粒，孔洞数量为m，其中m≥2。在一些实施例中，所述第一正极活性材料颗粒中有缝隙数量为n，其中0<n<30。在一些实施例中，所述第一正极活性材料的每个颗粒表面的孔洞数量为1、2、5、10、15或这些数值中任两者组成的范围，且每个颗粒内部的缝隙数量为4、8、12、16、20、25或这些数值中任两者组成的范围。 其中，颗粒表面的孔洞是采用SEM对颗粒进行成像，然后统计一定数目的颗粒表面的孔洞数量，取平均值而获得的；颗粒内部的缝隙数量是采用CP(横截面剖光，cross-section polishing)技术切开颗粒，然后经SEM成像，取一定数目的颗粒统计其缝隙数，取平均值而获得的。
二、电化学装置
根据本申请的第二方面，提供了一种电化学装置，所述电化学装置包含正极极片，所述正极极片包含正极集流体和设置于所述正极集流体的至少一个表面上的正极活性层，所述正极活性层包含前述任一种含有P6 3mc结构化合物的正极活性材料(在后称作“第一正极活性材料”)。
在一些实施例中，所述正极活性层进一步包括第二正极活性材料，所述第二正极活性材料选自由R-3m结构的Li 1±bCo 1-aR aO 2、镍钴锰三元材料、富锂锰基或锰酸锂组成的群组，其中(0≤b<0.1，0≤a<0.1)，且其中R选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者。在一些实施例中，0.001≤a≤0.005。在一些实施例中，a为0.002、0.003、0.004或这些数值中任意两者组成的范围。在一些实施例中，R选自由Al、Mg和Ti组成的群组中的至少一者。在一些实施例中，R为Al。
在一些实施例中，所述正极活性层包含第一层和第二层，所述第二层位于所述集流体和所述第一层之间，其中所述第一层包括所述第一正极活性材料。
在一些实施例中，所述第二层包括所述第二正极活性材料，且所述第二层的压实密度为4.1g/cm 3-4.35g/cm 3。
在一些实施例中，所述第一层与所述第二层的厚度的比值为0.1-2，具体可以为0.2、0.3、0.5、0.7、1.0、1.3、1.5、1.7或这些数值中任意两者组成的范围。
在一些实施例中，所述正极活性层的压实密度为4.0g/cm 3-4.5g/cm 3。在一些实施例中，所述正极的电阻小于3Ω。
在一些实施例中，所述电化学装置满足条件(f)至(h)中的至少一者：((f)放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20 圈，循环前后所述正极活性材料的颗粒开裂增长率不高于5％；(g)放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，循环前后所述正极活性材料平均每圈循环的直流内阻DCR增长率低于2％；(h)所述电化学装置进一步包含负极极片，所述负极极片包含负极集流体和设置于所述负极集流体的至少一个表面上的负极活性材料层，在放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，平均每圈循环在所述负极活性层表面的Co堆积浓度增量为R，其中R≤5ppm。
在一些实施例中，放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，循环前后所述正极活性材料的颗粒开裂增长率不高于以下群组中的至少一者：4％、3％和2％。
在一些实施例中，放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，循环前后所述正极活性材料平均每圈循环的直流内阻DCR增长率低于以下群组中的至少一者：1.9％、1.8％、1.7％、1.6％、1.5％、1.4％和1.3％。
在一些实施例中，在放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，平均每圈循环在所述负极活性层表面的Co堆积浓度增量为R，其中R不大于以下群组中的至少一者：4.58ppm、4.0ppm、3.5ppm、3ppm、2.5ppm和2.0ppm。
在一些实施例中，在其放电克容量在180mAh/g-200mAh/g时，其正极副产物厚度为η，其中η≤0.5μm。在一些实施例中，η≤0.4μm。在一些实施例中，η≤0.3μm。
前述电化学装置包括发生电化学反应的任何装置。在一些实施例中，本申请的电化学装置包括，但不限于：所有种类的一次电池、二次电池、燃料电池、太阳能电池或电容。
在一些实施例中，所述电化学装置是锂二次电池。
在一些实施例中，锂二次电池包括，但不限于：锂金属二次电池、锂离子二次电池、锂聚合物二次电池或锂离子聚合物二次电池。
三、电子装置
根据本申请的第三方面，本申请提供了一种电子装置，其可为任何使用根据本申请的实施例的电化学装置的装置。
在一些实施例中，所述电子装置包括，但不限于：笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池或锂离子电容器等。
四、电化学装置的制备方法
根据本申请的第四方面，提供了一种用于制备前述任一种电化学装置的方法，其包含如下部分。
1.制备P6 3mc结构的Li xNa zCo 1-yM yO 2，其中0.6<x<0.85，0≤y<0.15，0≤z<0.03，M选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者：
(1)液相沉淀法加烧结法制备M元素掺杂的Co 3-yM yO 4前躯体：将可溶性钴盐(例如，氯化钴、醋酸钴、硫酸钴、硝酸钴等)和M盐(例如，硫酸盐等)按照Co与M的摩尔比为(3-y)：y的比例加入溶剂(例如，去离子水)中，按0.1-3mol/L浓度加入沉淀剂(例如碳酸钠、氢氧化钠)和络合剂(例如氨水)，络合剂与沉淀剂的摩尔比为0.1-1，调节PH值(例如，将PH值调节5-9)，使之沉淀；然后将沉淀物在空气下400℃-800℃进行烧结5h-20h，并对烧结产物进行研磨以获得Co 3-yM yO 4粉体，其中0≤y<0.15。
(2)固相烧结法合成Na mCo 1-yM yO 2：将Co 3-yM yO 4粉体与Na 2CO 3粉体按照Na与Co的摩尔比为0.7：1至0.74：1的比例进行混合；将混合均匀的粉体在氧气气氛中、700℃-1000℃条件下烧结36h-56h得到P6 3mc结构的Na mCo 1- yM yO 2，其中0.6<m<1
(3)离子交换法合成P6 3mc结构的Li xNa zCo 1-yM yO 2正极活性材料：将Na mCo 1-yM yO 2与含锂熔盐(例如，硝酸锂、氯化锂、氢氧化锂等)按照Na与Li的摩尔比为0.01-0.2比例混合均匀，在200℃-400℃、空气气氛中反应2h-8h，反应物经去离子水多次洗涤，待熔盐清洗干净，烘干粉体得到P6 3mc结构的Li xNa zCo 1-yM yO 2正极材料。
2.制备R-3m结构的LiCo 1-aR aO 2，其中0≤a<0.1，R选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者：
(1)液相沉淀法加烧结法制备R元素掺杂的Co 3-aN aO 4前躯体：将可溶性钴盐(例如，氯化钴、醋酸钴、硫酸钴、硝酸钴等)和R盐(例如，硫酸盐等)按比例加入溶剂(例如，去离子水)中，加入沉淀剂(例如碳酸钠、氢氧化钠)和络合剂(例如氨水)，调节PH值(例如，将PH值调节5-9)，使之沉淀；然后将沉淀物进行烧结，研磨获得Co 3-aR aO 4粉体。
(2)固相烧结法制备Li 1±bCo 1-aR aO 2：将Co 3-aR aO 4粉体与Li 2CO 3按照如下条件混合：锂钴摩尔比为1：1-a。混合均匀后，将混合物在在空气气氛中、700℃-1200℃温度下烧结6h-48h，冷却后，研磨并过筛得到R-3m结构的LiCo 1- aR aO 2，其中(0≤b<0.1，0≤a<0.1)。
3.制备正极极片
(1)双层结构的正极极片
将R-3m结构的LiCo 1-aR aO 2正极活性材料(或其它正极活性材料，包含但不限于：镍钴锰三元材料、富锂锰基或锰酸锂)、导电剂(例如，乙炔黑)、粘结剂(例如，聚偏二氟乙烯(PVDF))按一定重量比(例如，97：2：1)在溶剂(例如，N-甲基吡咯烷酮)体系中充分搅拌混合均匀后，涂覆于正极集流体(例如，Al箔)上烘干，得到底涂膜片。
将具有P6 3mc结构的Li xNa zCo 1-yM yO 2正极活性材料、导电剂(例如，乙炔黑)、粘结剂(例如，聚偏二氟乙烯(PVDF))按一定重量比(例如，97：2：1)在溶剂(例如，N-甲基吡咯烷酮)体系中充分搅拌混合均匀后，涂覆于前述底涂膜片上，烘干、冷压，得到双层结构的正极极片。
(2)单层结构的正极极片
将具有P63mc结构的Li xNa zCo 1-yM yO 2正极活性材料(或其它正极活性材料，包含但不限于：R-3m结构的LiCo 1-aR aO 2正极活性材料、镍钴锰三元材料、富锂锰基或锰酸锂)、导电剂(例如，乙炔黑)、粘结剂(例如，聚偏二氟乙烯(PVDF))按一定重量比在溶剂(例如，N-甲基吡咯烷酮)体系中充分搅拌混合均匀后，涂覆于正极集流体(例如，Al箔)上，烘干、冷压，得到单层结构的正极极片。
4.负极极片
可用于所述电化学装置的负极极片、构成和其制造方法包括任何现有技术中公开的技术。
在一些实施例中，所述负极极片包括负极集流体和位于所述负极集流体的至少一个表面上的负极活性材料层。
在一些实施例中，负极活性材料层包括粘合剂。在一些实施例中，粘合剂包括，但不限于：聚乙烯醇、羧甲基纤维素、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙。
在一些实施例中，负极活性材料层包括导电材料。在一些实施例中，导电材料包括，但不限于：天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维、金属粉、金属纤维、铜、镍、铝、银或聚亚苯基衍生物。
在一些实施例中，集流体包括，但不限于：铜箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或覆有导电金属的聚合物基底。
在一些实施例中，负极极片可以通过如下方法获得：在溶剂中将活性材料、导电材料和粘合剂混合，以制备活性材料组合物，并将该活性材料组合物涂覆在集流体上。
在一些实施例中，溶剂可以包括，但不限于：N-甲基吡咯烷酮。
5.电解液
可用于本申请实施例的电解液可以为现有技术中已知的电解液。
在一些实施例中，所述电解液包括有机溶剂、锂盐和添加剂。根据本申请的电解液的有机溶剂可为现有技术中已知的任何可作为电解液的溶剂的有机溶剂。根据本申请的电解液中使用的电解质没有限制，其可为现有技术中已知的任何电解质。根据本申请的电解液的添加剂可为现有技术中已知的任何可作为电解液添加剂的添加剂。
在一些实施例中，所述有机溶剂包括，但不限于：碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚丙酯或丙酸乙酯。
在一些实施例中，所述锂盐包括有机锂盐或无机锂盐中的至少一种。
在一些实施例中，所述锂盐包括，但不限于：六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、二氟磷酸锂(LiPO 2F 2)、双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO 2F) 2)(LiFSI)、双草酸硼酸锂LiB(C 2O 4) 2(LiBOB)或二氟草酸硼酸锂LiBF 2(C 2O 4)(LiDFOB)。
在一些实施例中，所述电解液中锂盐的浓度为：约0.5-3mol/L、约0.5-2mol/L或约0.8-1.5mol/L。
6.隔离膜
在一些实施例中，正极极片与负极极片之间设有隔离膜以防止短路。可用于本申请的实施例中使用的隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。
例如，隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的一种或几种的组合。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的一种或几种的组合。
聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)中的至少一种。
下面以锂离子电池为例并且结合具体的实施例说明锂离子电池的制备，本领域的技术人员将理解，本申请中描述的制备方法仅是实例，其它任何合适的制备方法均在本申请的范围内。
实施例
以下说明根据本申请制备锂离子电池的实施例和对比例并对其进行性能评估。
实施例1
制备P6 3mc结构的Li 0.73Na 0.02CoO 2
步骤(1)：将四氧化三钴与碳酸钠粉体按照Na与Co的摩尔比为0.75：1的比例混合；将混合均匀的粉体在氧气气氛中、800℃条件下烧结46h，得到P6 3mc结构的Na 0.75CoO 2。
步骤(2)：将Na 0.75CoO 2与硝酸锂按照Na与Li的摩尔比为0.75:5的比例混合均匀，在300℃、空气气氛中反应6h，反应物经去离子水多次洗涤，待熔盐清洗干净，烘干粉体得到具有P6 3mc结构的Li 0.73Na 0.02CoO 2。
实施例2
制备P6 3mc结构的Li 0.63Co 0.985Al 0.015O 2
步骤(1)：液相沉淀法加烧结法制备Al元素掺杂的(Co 0.985M 0.015) 3O 4前躯体：将氯化钴和硫酸铝按照Co与Al的摩尔比为0.985：0.015的比例加入去离子水中，加入沉淀剂碳酸钠和络合剂氨水调节PH值为7，使之沉淀；然后将沉淀物在600℃进行烧结7h，研磨获得(Co 0.985M 0.015) 3O 4粉体。
步骤(2)：将(Co 0.985Al 0.015) 3O 4粉体与碳酸钠粉体按照Na与Co的摩尔比为0.63:0.985的比例混合；将混合均匀的粉体在氧气气氛中、800℃条件下烧结46h，得到Na 0.63Co 0.985Al 0.015O 4。
步骤(3)：将Na 0.63Co 0.985Al 0.015O 4粉体与硝酸锂按照Na与Li的摩尔比为0.63：5的比例混合均匀，在300℃、空气气氛中反应6h，反应物经去离子水多次洗涤，待熔盐清洗干净，烘干粉体得到具有P6 3mc结构的Li 0.63Co 0.985Al 0.015O 2。
实施例3
制备P6 3mc结构的Li 0.63Na 0.01Co 0.985Al 0.015O 2
步骤(1)：将氯化钴和硫酸铝按照Co与Al的摩尔比为0.985：0.015的比例加入去离子水中，加入沉淀剂碳酸钠和络合剂氨水调节PH值为7，使之沉淀；然后将沉淀物在600℃进行烧结7h，研磨获得(Co 0.985Al 0.015) 3O 4粉体。
步骤(2)：将(Co 0.985Al 0.015) 3O 4粉体与碳酸钠粉体按照Na与Co的摩尔比为0.64：0.985的比例混合；将混合均匀的粉体在氧气气氛中、800℃条件下烧结46h，得到Na 0.64Co 0.985Al 0.015O 2。
步骤(3)：将Na 0.64Co 0.985Al 0.015O 2与硝酸锂按Na与Li的摩尔比为0.64：5的比例混合均匀，在300℃、空气气氛中反应6h，反应物经去离子水多次洗涤，待熔盐清洗干净，烘干粉体得到具有P63mc结构的Li 0.63Na 0.01Co 0.985Al 0.015O 2。
实施例4-16
实施例4-16与实施例3的制备方法基本相同，不同之处在于参杂元素M的 种类和/或含量的不同。
如下表1详细给出了实施例1-16的化学式。
表1
编号 化学式
实施例1 Li 0.73Na 0.02CoO 2
实施例2 Li 0.63Co 0.985Al 0.015O 2
实施例3 Li 0.63Na 0.01Co 0.985Al 0.015O 2
实施例4 Li 0.69Na 0.01Co 0.985Al 0.015O 2
实施例5 Li 0.72Na 0.01Co 0.985Al 0.015O 2
实施例6 Li 0.73Na 0.01Co 0.985Al 0.015O 2
实施例7 Li 0.74Na 0.008Co 0.98Al 0.02O 2
实施例8 Li 0.74Na 0.006Co 0.975Al 0.025O 2
实施例9 Li 0.74Na 0.006Co 0.991Mg 0.009O 2
实施例10 Li 0.74Na 0.01Co 0.986Mg 0.014O 2
实施例11 Li 0.74Na 0.006Co 0.983Al 0.015Mg 0.002O 2
实施例12 Li 0.74Na 0.005Co 0.981Al 0.018Mg 0.001O 2
实施例13 Li 0.74Na 0.004Co 0.984Al 0.015Ti 0.001O 2
实施例14 Li 0.74Na 0.004Co 0.992Al 0.007Ti 0.001O 2
实施例15 Li 0.74Na 0.003Co 0.995Al 0.003Mg 0.001Ti 0.001O 2
实施例16 Li 0.74Na 0.003Co 0.994Al 0.003Mg 0.002Ti 0.001O 2
实施例17
制备P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2
实施例17与实施例6的步骤基本相同，其区别仅在于实施例17通过控制步骤1中的烧结温度和原料的混合方法，以得到具有不同的平均粒径(D50)和不同的振实密度的P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2。
实施例18
制备P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2
实施例18与实施例6的步骤基本相同，其区别仅在于实施例18通过控制步骤1中的烧结温度和原料的混合方法，以得到具有不同的平均粒径(D50)和不同的振实密度且颗粒表面没有孔洞的P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2。
实施例19
制备P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2
实施例19与实施例6的步骤基本相同，其区别仅在于实施例19通过控制步骤1中的烧结温度和原料的混合方法，以得到具有不同的平均粒径(D50)和不同的振实密度且颗粒内部没有缝隙的P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2。
实施例20
制备P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2
实施例20与实施例6的步骤基本相同，其区别仅在于实施例20通过控制步骤1中的烧结温度和原料的混合方法，以得到具有不同的平均粒径(D50)和不同的振实密度的P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2。
下表2示出了实施例6与实施例17-20中的正极活性材料的D50和振实密度的具体数值、以及是否存在颗粒表面孔洞以及颗粒内部缝隙。
表2
Figure PCTCN2021098940-appb-000001
对比例1
制备非P6 3mc结构的Li 0.58Na 0.01Co 0.985Al 0.015O 2
步骤(1)：将氯化钴和硫酸铝按照钴与铝的摩尔比为0.985:0.015的比例加入去离子水中，加入沉淀剂碳酸钠和络合剂氨水，调节PH值为7，使之沉淀；然后将沉淀物进行烧结，研磨获得(Co 0.985Al 0.015) 3O 4粉体。
步骤(2)：将(Co 0.985Al 0.015) 3O 4粉体与碳酸锂按照锂与钴的摩尔比为0.58：0.985的比例混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛得到具有R-3m结构的Li 0.58Na 0.01Co 0.985Al 0.015O 2。
对比例2
制备非P6 3mc结构的Li 0.8Na 0.006Co 0.983Al 0.015Mg 0.002O 2
步骤(1)：将氯化钴、硫酸铝和硫酸镁按照钴、铝和镁的摩尔比为0.983:0.015:0.002的比例加入去离子水中，加入沉淀剂碳酸钠和络合剂氨水，调节PH值为7，使之沉淀；然后将沉淀物进行烧结，研磨获得(Co 0.983Al 0.015Mg 0.002) 3O 4粉体。
步骤(2)：将(Co 0.983Al 0.015Mg 0.002) 3O 4粉体与碳酸锂按照锂与钴的摩尔比为0.8：0.983的比例混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛得到具有R-3m结构的Li 0.8Na 0.006Co 0.983Al 0.015Mg 0.002O 2。
对比例3
制备非P6 3mc结构的Li 0.55Na 0.004Co 0.984Al 0.015Ti 0.001O 2
步骤(1)：将氯化钴、硫酸铝和硝酸钛按照钴、铝和钛的摩尔比为0.984:0.015:0.001的比例加入去离子水中，加入沉淀剂碳酸钠和络合剂氨水，调节PH值为7，使之沉淀；然后将沉淀物进行烧结，研磨获得(Co 0.984Al 0.015Ti 0.001) 3O 4粉体。
步骤(2)：将(Co 0.984Al 0.015Ti 0.001) 3O 4粉体与碳酸锂按照锂与钴的摩尔比为0.55：0.984的比例混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛得到具有R-3m结构的Li 0.55Na 0.004Co 0.984Al 0.015Ti 0.001O 2。
对比例4
制备非P6 3mc结构的Li 0.57Na 0.003Co 0.994Al 0.003Mg 0.002Ti 0.001O 2
步骤(1)：将氯化钴、硫酸铝、硫酸镁和硝酸钛按照钴、铝、镁和钛的摩尔比为0.994:0.003:0.002:0.001的比例加入去离子水中，加入沉淀剂碳酸钠和络合剂氨水，调节PH值为7，使之沉淀；然后将沉淀物进行烧结，研磨获得(Co 0.994Al 0.003Mg 0.002Ti 0.001) 3O 4粉体。
步骤(2)：将(Co 0.994Al 0.003Mg 0.002Ti 0.001) 3O 4粉体与碳酸锂按照锂与钴的摩尔比为0.57：0.994的比例混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛得到具有R-3m结构的Li 0.57Na 0.003Co 0.994Al 0.003Mg 0.002Ti 0.001O 2。
性能测试方法
为了对前述正极极片进行电化学性能的测试，按照如下步骤制备锂离子电池，并对各锂离子电池进行相应的电化学性能的测试。
正极极片：分别取前述实施例与对比例中的正极活性材料、与导电剂乙炔黑以及粘结剂聚偏二氟乙烯(PVDF)按重量比97：2：1在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，涂覆于正极集流体Al箔上，烘干，冷压得到具有单层结构的正极活性层的正极极片(在后称作“单层结构正极极片”)。
负极极片：将活性物质人造石墨、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂碳甲基纤维素钠(CMC)按照质量比约为95：2：2：1在去离子水溶剂体系中充分搅拌混合均匀后，涂覆于Cu箔上烘干、冷压，得到负极。
电解液：在含水量<10ppm的氩气气氛手套箱中，将碳酸乙烯酯(简写为EC)、碳酸二乙酯(简写为DEC)、碳酸丙烯酯(简写为PC)、按照2:6:2的重量比混合均匀，再将充分干燥的锂盐LiPF6溶解于上述溶剂，LiPF6的含量为1mol/L，加入1.5％的1,3-丙烷磺内酯、3％的氟代碳酸乙烯酯、2％的己二腈。其中各物质含量是以电解液的总重量计。
隔离膜：以PE多孔聚合薄膜作为隔离膜。
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正负极中间起到隔离的作用，并卷绕、置于外包装中，注入配好的电解液并封装，经过化成，脱气，切边等工艺得到电池。
锂离子半电池(扣式电池)的制备
使用与上述电池的制备方法几乎相同的方法制备半电池，但是存在以下差异：
(1)正极的制备：从上述电池的正极中随机选取在集流体正反两面的涂覆活性材料层的区域，用碳酸二甲酯(DMC)清洗，去除其中一面，获得单面正极片；
(2)负极的制备：选用单面附着在集流体铜箔上的金属锂薄膜作为负极，在干燥房中对金属锂薄膜进行裁片、焊接负极极耳，得到负极片。
使用所述正极和锂金属负极制备扣式电池。在将PE多孔聚合薄膜作为隔离膜设置在所述正极片和所述锂金属负极片之间时，将上述制备的电解液注入到其中，由此获得扣式电池。
SEM测试
扫描电镜(SEM)是通过电子束与样品的相互作用，并利用二次电子信号成像得到样品的形貌结构。本实验中使用的扫描电镜为JEOL公司的JSM-6360LV型及其配套的X射线能谱仪对样品的形貌结构和元素分布进行分析。
开裂增长率测试方法
在25℃的环境中，进行第一次充电和放电，在0.5C(即2h内完全放掉理论容量的电流值)的充电电流下进行恒流充电，直到上限电压为4.8V；然后，在0.5C的放电电流下进行恒流放电，直到最终电压为3V，记录首次循环的放电容量；继续进行到第20次充电和放电循环。
利用离子抛光机(日本电子-IB-09010CP)对首次循环和第20次循环之后的正极极片进行加工，得到其断面。利用SEM对其断面进行拍摄，拍摄倍数不低于5.0K，获得图像。统计拍摄范围内满足条件的颗粒，剖面内具有裂纹的颗粒视为开裂的颗粒，在所述图像内颗粒的剖面内，连续的长度不小于0.5μm，宽度不小于0.1μm且从颗粒表面向颗粒内部延伸的纹路，视为裂纹，记录开裂的颗粒总数，统计数量范围为50-100，统计首次循环和第20次循环之后颗粒中的裂缝总数，按照如下公式计算得到开裂增长率：
开裂增长率＝(第20次循环后的总裂缝数-首次循环后的总裂缝数)/首次循环后的总裂缝数×100％。
压实密度测试方法
将电池放电至0SOC％(SOC：state of charge，充电状态)，拆解电池，清洗，烘干，使用电子天平对一定面积A的正极(正极集流体的双面涂覆有正极活性材料层)进行称重，重量记为W 1，并使用万分尺测得正极的厚度T 1。使用溶剂洗掉正极活性材料层，烘干，测量正极集流体的重量，记为W 2，并使用万分尺测得正极集流体的厚度T 2。通过下式计算设置在正极集流体一侧的正极活性材料层的重量W 0和厚度T 0以及正极活性材料层的压实密度：
W 0＝(W 1-W 2)/2
T 0＝(T 1-T 2)/2
压实密度＝W 0/(T0×A)。
容量衰减率/保持率测试方法
在25℃的环境中，进行第一次充电和放电，在0.5C(即2h内完全放掉理论容量的电流值)的充电电流下进行恒流充电，直到上限电压为4.8V；然后，在0.5C的放电电流下进行恒流放电，直到最终电压为3V，记录首次循环的放电容量；继续进行到第N次充电和放电循环(其中N可以根据实际需要来确定)，记录第N次循环的放电容量。按照如下公式计算得到锂离子电池的第N次循环后的容量衰减率和容量保持率：
第N次循环后的容量衰减率＝(首次循环的放电容量-第N次循环的放电容量)/首次循环的放电容量×100％。
第N次循环后的容量保持率＝第20次循环的放电容量/首次循环的放电容量×100％。
第一层和第二层的厚度测试方法
随机选取一处正极位置，利用离子抛光机(日本电子-IB-09010CP)对该正极进行加工，得到其断面。利用SEM(蔡司Sigma02-33)对其断面进行拍摄，拍摄倍数不低于5.0K，获得图像。分别从集流体的最高点、具有孔洞和裂缝的颗粒的最低点及正极的最高点出发画三条平行线，其中集流体的最高点与具有孔洞和裂缝的颗粒最低点之间的距离为第二层的厚度，且具有孔洞和裂缝的颗粒最低点与正极的最高点之间的距离为第一层的厚度。请参考附图2。
直流内阻(DCR)测试
1)将锂离子电池在10mA/g电流密度下满充至4.8V，静置10min后以10mA/g的电流密度放电至3.0V，记录得到的容量C；2)静置5min，0.7C的充电电流恒流充电至4.8V，然后4.8V恒压充电至电流小于0.05C；3)静置10min后，以0.1C的放电电流放电3h；4)以1C的放电电流放电1秒，采集循环前和第20圈循环或者直到放电克容量低于180mAh/g时的直流电阻数据，循环前后各取平均值，按照如下公式求取平均增长率：
循环20圈DCR平均增长率＝(第20次循环的直流电阻-循环前的直流电阻)/循环前的直流电阻×100％
循环20圈平均每圈循环的DCR增长率＝循环20圈DCR平均增长率/20。
副产物厚度测试
随机选取一处正极极片位置，利用离子抛光机(日本电子-IB-09010CP)加工，得到断面。利用SEM(蔡司Sigma02-33)对其断面进行拍摄，拍摄倍数不低于5.0K，获得图像。选取1个直径不小于5μm，处于正极极片内部而非上表面的颗粒。在同一颗粒上，选取副产物最厚位置的副产物最低点和最高点画平行线，平行线间的距离即为此颗粒副产物厚度。测试所有满足测试条件的不同颗粒，测量并记录，取20个点，计算平均值，记为副产物厚度。
Co堆积浓度测试
选取同一批次电池2个，将2个电池同时在25℃环境下，以10mA/g的电流密度做放电至3V，达到满放态，容量不低于200mAh/g，算作合格电池。取其中一个电池拆解，将负极冲20个100mm 2大小的圆片进行电感耦合等离子体质谱(ICP)测试得到其Co堆积浓度，取平均值，记为初始Co堆积浓度。
将另外一个电池在25℃环境下，在3.0V-4.8V之间继续进行20次充电-放电循环。拆解电池，将负极冲20个100mm 2大小的圆片进行电感耦合等离子体质谱(ICP)测试得到其Co堆积浓度，取平均值，记为循环后Co堆积浓度。
将循环后Co离子浓度减去初始Co堆积浓度，再除以循环圈数，即可得到循环每圈Co堆积浓度增量。
在25℃环境下，以10mA/g的电流密度在3.0V-4.8V之间进行20次充电-放电循环。分别对每圈循环前后的正极极片进行电感耦合等离子体质谱(ICP)测试得到其Co堆积浓度测试，取平均值。
充电状态(SOC state of charge)测试
在25℃，以10mA/g的电流密度在3.0V-4.8V之间进行充电放电测试。SOC即为充电/放电曲线上任意点容量值除以充电/放电最大容量值。
如下表3给出了实施例1-16与对比例1-4中的材料的(002)和/或(003)晶面的峰位置、半峰宽)和由其组成的锂离子电池的首圈放电容量以及第100次循环之后的容量保持率(其测试方法和测试条件与前述“容量衰减率/保持率 测试方法”部分一致)。
表3
Figure PCTCN2021098940-appb-000002
Figure PCTCN2021098940-appb-000003
分析表3中的XRD数据可知，本申请实施例1-16中的具有P6 3mc结构的Li xNa zCo 1-yM yO 2的(002)晶面位于17.5°-19°之间，其半峰宽在0.05-0.1之间。而对比例1-4中的非P6 3mc结构的Li xNa zCo 1-yM yO 2在17.5°-19°之间不存在(002)晶面，其中对比例2在19.2°存在(003)晶面，而对比例1、3和4分别在16.8°、16.5°和16.2°位置处存在(002)晶面。
进一步参考附图3A-3B中的XRD图谱。图3A是本申请实施例1的P6 3mc结构的Li 0.73Na 0.02CoO 2的XRD图谱。从中可以看出，该材料的(002)晶面位于17.5°-19°之间，其半峰宽在0.05-0.1之间。而图3B是本申请对比例2的非P6 3mc结构的Li 0.8Na 0.006Co 0.983Al 0.015Mg 0.002O 2的XRD图谱。从中可以看出，该材料在17.5°-19°之间并不存在(002)晶面。
分析表3中的电化学数据可知，本申请实施例1-16中的具有P6 3mc结构的Li xNa zCo 1-yM yO 2组成的锂离子电池的首圈放电容量和第100次循环时的容量保持率显著优于对比例1-4中的非P6 3mc结构的Li xNa zCo 1-yM yO 2组成的锂离子电池的相应电化学性能。
图4是本申请实施例6的正极活性材料P6 3mc结构的Li 0.73Na 0.01Co 0.985Al 0.015O 2与对比例1的非P6 3mc结构的Li 0.58Na 0.01Co 0.985Al 0.015O 2的差示扫描量热法(DSC：Differential Scanning Calorimetry)图谱。从中可以看出，实施例6中的正极活性材料在360℃存在一个放热峰，所述放热峰的半峰宽在18℃，而对比例1中的正极活性材料则在上述范围内不存在放热峰。
经本申请人研究发现，本申请实施例中的正极活性材料都在250℃-400℃之 间存在一个放热峰，所述放热峰的半峰宽都在15℃-40℃之间。
如下表4是实施例6与实施例17-20的材料的D50、振实密度、以及颗粒中孔洞和裂缝情况。从中可以看出，不同D50、振实密度、孔洞和裂缝的这些材料的性能均优于对比例中材料的相应性能。且D50在10μm-30μm，振实密度为2.5g/cm 3-3g/cm 3，且存在孔洞和裂缝的实施例6中的材料的性能更佳。
表4
Figure PCTCN2021098940-appb-000004
如下表5示出了包含由实施例6、7、11、13、14和对比例1、2的正极活性物质层制备的单层结构正极极片的锂离子电池相关的各项性能。
表5
Figure PCTCN2021098940-appb-000005
Figure PCTCN2021098940-appb-000006
分析表5可知，相较于包含由对比例1的非P6 3mc结构的化合物制备的正极极片的锂离子电池，包含由实施例6、7、11、13和14中的P6 3mc结构的化合物制备的正极的锂离子电池的DCR增长率显著改善，由对比例中的5％左右降到了1％左右；且正极副产物的厚度也大幅下降。这主要归因于本申请提供的上述正极活性材料改善了传统LiCoO 2材料在充电过程(>4.6Vvs.Li/Li +)中发生晶体结构坍塌和界面失效。所述材料在高电压下具有较好的结构可逆性和循环稳定性，且优点包含但不限于：(1)在嵌锂过程中，Li xNa zCo 1-yM yO 2正极材料由于自身晶体结构中存在锂空位，可以很好地容纳体积变化，嵌入更多的Li；(2)在脱锂/嵌锂过程中，Li xNa zCo 1-yM yO 2正极材料由于自身存在孔洞和裂缝，能够有效释放高电压脱/嵌锂过程形成的巨大应力，抑制层间不可逆滑移，实现好的循环性能；(2)在电压大于4.7V时，Li xNa zCo 1-yM yO 2正极材料已实现95％脱锂，因而对耐氧化(高电压)电解液要求低于O3相；(3)Li xNa zCo 1- yM yO 2正极材料自身在合成过程会引入极少量Na，Na占据了部分Li位，作为支柱支撑晶体结构，可提高材料的结构稳定性；(4)Li xCo 1-yM yO 2正极材料相比于O3相LiCoO 2具有更低的锂离子迁移能；(5)Li xCo 1-yM yO 2正极材料中引入的优选元素M，能一定程度上加强结构稳定效果。
为了进一步对上述正极活性材料进行研究，本申请又按照如下步骤，取实施例6的正极活性材料制备了包含双层结构的正极活性层的正极极片(在后称作双层结构正极极片)，并进一步制备了锂离子电池。
制备双层正极极片
步骤(a)：将下层正极活性材料(也称为“第二正极活性材料”)、与导电剂乙炔黑以及粘结剂聚偏二氟乙烯(PVDF)按重量比97：2：1在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，涂覆于正极集流体Al箔上，烘干，得到底涂膜片，其中靠近Al箔的该活性物质层在后称作“第二层”。
步骤(b)：分别将实施例6与对比例1中的正极活性材料(也称为“上层正极活性材料”或“第一正极活性材料”)与导电剂乙炔黑以及粘结剂聚偏二氟乙烯(PVDF)按重量比97：2：1在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，涂覆于前述底涂膜片上，烘干、冷压，得到双层结构正极极片，其中远离Al箔的该活性物质层在后称作“第一层”，且其中所述第一层与所述第二层的厚度的比值经控制为某一数值(具体参见表6)。
如下表6示出了包含由实施例6的正极活性材料和另一种正极活性材料制备的双层结构正极极片的锂离子电池和包含由实施例6和对比例1制备的单层结构正极极片的锂离子电池的具体参数(按照顺序分别以电池1-8来标注)。
表6
Figure PCTCN2021098940-appb-000007
Figure PCTCN2021098940-appb-000008
分析表6可知，电池1-7(其中，电池7的正极极片采用单层活性层结构，且其正极活性材料均包含P6 3mc结构的LiCo 0.975Al 0.02Mg 0.005O 2；电池1-6的正极极片采用双层活性层结构，其第一层包含P6 3mc结构的Li xNa zCo 1-yM yO 2且第二层包含R-3m结构的LiCo 1-aR aO 2、镍钴锰三元材料、富锂锰基或锰酸锂)的容量保持率较电池1(其正极活性材料只包含R-3m结构的LiCo 0.975Al 0.02Mg 0.005O 2)的容量保持率有了大幅改善。具体可参见图5-图7可知，相较于电池8，电池1的开裂增长率、容量衰减率、正极副产物厚度、DCR平均增长率、负极极片表面的Co堆积密度、正极极片的压实密度、正极极片的电阻以及4.8V循环10次和100次时的容量衰减率均显著改善。
参见图5A-5D，其测试条件与前述开裂增长率测试方法中的条件一致，可知：电池1，其包含由实施例6的正极活性材料制备的双层正极极片，在首次循环前和第20次循环后，其颗粒表面形貌保持明显好于电池8，其包含由非P6 3mc结构的LiCo 0.975Al 0.02Mg 0.005O 2制备的单层正极极片。
参见图6，其测试条件与前述DCR测试的条件一致，可知：电池1的正极极片在每次循环后的DCR增长率明显低于电池8。
参见图7，其测试条件与前述容量衰减测试方法中的条件一致，可知：从首次 循环开始直到多达200次循环，电池1的容量保持率一直高于电池8，且从图7的曲线趋势来看，电池1的容量保持率会继续高于电池8。
电池1的前述优异的性能，主要得益于：(1)在脱/嵌锂过程中，第一层包含的第一正极活性材料由于自身界面稳定性，可以很好地隔绝电解液对第二层包含的第二正极活性材料的活性面的腐蚀，从而保持界面稳定；(2)在脱/嵌锂过程中，第一层包含的第一正极活性材料由于自身存在孔洞和裂缝，能够有效释放高电压脱/嵌锂过程形成的巨大应力，抑制层间不可逆滑移，实现好的循环性能；(3)第一层包含的第一正极活性材料具有好的柔性，可以进行任意压实，不会影响复合正极活性层的厚度，复合正极活性层压实密度高；(4)第一层包含的第一正极活性材料和第二层包含的第二正极活性材料中引入掺杂元素能有效加强晶体的结构稳定效果。
综上所述，包含本申请的电化学装置所述材料在4.8V高电压下具有优异的结构可逆性和循环稳定性。
整个说明书中对“一些实施例”、“部分实施例”、“一个实施例”、“另一举例”、“举例”、“具体举例”或“部分举例”的引用，其所代表的意思是在本申请中的至少一个实施例或举例包含了该实施例或举例中所描述的特定特征、结构、材料或特性。因此，在整个说明书中的各处所出现的描述，例如：“在一些实施例中”、“在实施例中”、“在一个实施例中”、“在另一个举例中”，“在一个举例中”、“在特定举例中”或“举例“，其不必然是引用本申请中的相同的实施例或示例。此外，本文中的特定特征、结构、材料或特性可以以任何合适的方式在一个或多个实施例或举例中结合。
尽管已经演示和描述了说明性实施例，本领域技术人员应该理解上述实施例不能被解释为对本申请的限制，并且可以在不脱离本申请的精神、原理及范围的情况下对实施例进行改变，替代和修改。

Claims (12)

  1. 一种正极活性材料，其包含具有P6 3mc结构的化合物，其中，在所述正极活性材料的XRD图谱中，所述具有P6 3mc结构的化合物的(002)晶面位于17.5°-19°之间，其半峰宽在0.05-0.1之间。
  2. 根据权利要求1所述的正极活性材料，其中在所述正极活性材料的DSC图谱中，所述具有P6 3mc结构的化合物在250℃-400℃之间存在一个放热峰，所述放热峰的半峰宽在15℃-40℃之间。
  3. 根据权利要求1所述的正极活性材料，其中所述具有P6 3mc结构的化合物满足条件(a)至(e)中的至少一者：
    (a)所述具有P6 3mc结构的化合物的平均粒径为8μm-30μm；
    (b)所述具有P6 3mc结构的化合物的振实密度为2.2g/cm 3-3g/cm 3；
    (c)所述具有P6 3mc结构的化合物的颗粒存在孔洞；
    (d)所述具有P6 3mc结构的化合物的颗粒内部存在缝隙；
    (e)所述具有P6 3mc结构的化合物包含Li xNa zCo 1-yM yO 2，其中0.6<x<0.85，0≤y<0.15，0≤z<0.03，M选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者。
  4. 一种电化学装置，所述电化学装置包含正极极片，所述正极极片包含正极集流体和设置于所述正极集流体的至少一个表面上的正极活性层，所述正极活性层包含根据权利要求1-3中任一项所述的正极活性材料。
  5. 根据权利要求4所述的电化学装置，其中所述正极活性层进一步包括第二正极活性材料，所述第二正极活性材料选自由R-3m结构的Li 1±bCo 1- aR aO 2、镍钴锰三元材料、富锂锰基或锰酸锂组成的群组，其中(0≤b<0.1，0≤a<0.1)，且其中R选自由Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr组成的群组中的至少一者。
  6. 根据权利要求5所述的电化学装置，其中所述正极活性层包含第一层和第二层，其中所述第二层位于所述集流体和所述第一层之间，且其中所述第一层包括所述正极活性材料。
  7. 根据权利要求6所述的电化学装置，其中所述第二层包括所述第二正极活性材料，且所述第二层的压实密度为4.1g/cm 3-4.35g/cm 3。
  8. 根据权利要求6所述的电化学装置，其中所述第一层与所述第二层的厚度的比值为0.1-2。
  9. 根据权利要求4所述的电化学装置，其中所述正极活性层的压实密度为4.0g/cm 3-4.5g/cm 3。
  10. 根据权利要求4所述的电化学装置，所述电化学装置满足条件(f)至(h)中的至少一者：
    (f)放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，循环前后所述正极活性材料的颗粒开裂增长率不高于5％；
    (g)放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，循环前后所述正极活性材料平均每圈循环的直流内阻DCR增长率低于2％；
    (h)所述电化学装置进一步包含负极极片，所述负极极片包含负极集流体和设置于所述负极集流体的至少一个表面上的负极活性层，在放电克容量不低于180mAh/g时，在4.8V电压和0.5C倍率下循环20圈，平均每圈循环在所述负极活性层表面的Co堆积浓度增量为R，其中R≤5ppm。
  11. 根据权利要求4所述的电化学装置，在其放电克容量在180mAh/g-200mAh/g时，其正极极片副产物厚度为η，其中η≤0.5μm。
  12. 一种电子装置，其包含权利要求4-11中任一项所述的电化学装置。
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