WO2021184247A1 - 正极活性材料及包含其的电化学装置 - Google Patents

正极活性材料及包含其的电化学装置 Download PDF

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WO2021184247A1
WO2021184247A1 PCT/CN2020/079955 CN2020079955W WO2021184247A1 WO 2021184247 A1 WO2021184247 A1 WO 2021184247A1 CN 2020079955 W CN2020079955 W CN 2020079955W WO 2021184247 A1 WO2021184247 A1 WO 2021184247A1
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positive electrode
active material
electrode active
peak
electrochemical device
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PCT/CN2020/079955
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English (en)
French (fr)
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王凯
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宁德新能源科技有限公司
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Priority to CN202080096145.XA priority Critical patent/CN115066768B/zh
Priority to CN202311010002.4A priority patent/CN116864670A/zh
Priority to EP20925244.4A priority patent/EP4123752A4/en
Priority to US17/911,721 priority patent/US20230110649A1/en
Priority to PCT/CN2020/079955 priority patent/WO2021184247A1/zh
Publication of WO2021184247A1 publication Critical patent/WO2021184247A1/zh

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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
    • H01M4/13—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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M4/50—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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • 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 technology, and more specifically, to a positive electrode active material and an electrochemical device using the positive electrode active material.
  • lithium-ion batteries are widely used in the field of consumer electronics due to their advantages of large specific energy, high working voltage, low self-discharge rate, small size, and light weight.
  • the present application provides a positive electrode active material, a method for preparing the positive electrode active material, and an electrochemical device using the positive electrode active material, in an attempt to at least some extent solve at least one problem in the related field.
  • the application provides a positive electrode active material.
  • the 59Co NMR spectrum of the positive electrode active material has a first peak and a second peak, and the center of the first peak is located at A ppm , The center position of the second peak is at B ppm, where 13900 ⁇ A ⁇ B ⁇ 14300.
  • the half width of the first peak is HA and the half width of the second peak is HB, and 0.017 ⁇ HB/HA ⁇ 90.2.
  • the peak area of the first peak is SA and the peak area of the second peak is SB, and wherein 0 ⁇ SA/SB ⁇ 0.3.
  • the positive electrode active material includes the following compound of formula I:
  • M is selected from Al, Mg, Ca, Zn
  • E is selected from one or more of F, S, B, N or P element.
  • the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer includes The cathode active material of the application.
  • the positive electrode active material includes particles having a diameter of not less than 5 ⁇ m, and when the discharge capacity of the electrochemical device decays to 80% to 90% of the initial discharge capacity, the diameter is not less than 5 ⁇ m
  • the cracking rate of the particles is not more than 25%.
  • the growth rate of the DC impedance of the electrochemical device is less than 1.5% .
  • the surface of the positive electrode active material particles includes a by-product layer
  • the by-product layer when the discharge capacity of the electrochemical device decays to 80% to 90% of the initial discharge capacity, the by-product layer The thickness is ⁇ m, ⁇ 0.5.
  • the by-product layer contains carbon element, oxygen element, fluorine element, and nitrogen element, based on the total weight of the carbon element, oxygen element, fluorine element, and nitrogen element, wherein the fluorine element
  • the average percentage of ⁇ F is ⁇ F
  • the average percentage of nitrogen is ⁇ N, where ⁇ F- ⁇ N ⁇ 5%.
  • the electrolyte includes a nitrile-containing additive, wherein the nitrile-containing additive includes at least one of the following: adiponitrile, succinonitrile, 1,3,5-pentane Tricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile or triacetonitrile ammonia.
  • the content of the nitrile-containing additive is 0.1% to 10%.
  • the present application provides an electronic device including the electrochemical device according to the present application.
  • This application proposes a positive electrode active material with 59Co NMR double peaks for use in electrochemical devices. Since the positive electrode active material can maintain structural stability during high voltage charging and discharging, the electrochemical device using the positive electrode active material has excellent cycle performance and rate performance under high voltage.
  • FIG. 1A shows the full nuclear magnetic resonance spectrum of the cobalt element of the positive electrode active material in Example 1;
  • FIG. 1B shows the enlarged view and the split peak view of the highest peak in FIG. 1A;
  • Example 2 shows a broken line graph of the discharge capacity retention rate of the lithium ion batteries of Example 1 and Comparative Example 1 after 250 cycles;
  • Figure 3 shows a broken line chart of the discharge capacity retention rate of the lithium ion batteries of Example 1 and Comparative Example 1 at different currents;
  • FIG. 4 shows a scatter diagram of the average growth rate of the DC resistance DCR of the lithium ion batteries of Example 1 and Comparative Example 1 before and after each cycle.
  • the terms “approximately”, “substantially”, “substantially” and “about” are 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%.
  • the difference between two values is less than or equal to ⁇ 10% of the average value of the value (for example, 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%), then the two values can be considered "substantially" the same.
  • a list of items connected by the terms “one or more of”, “one or more of”, “one or more of” or other similar terms Can mean any combination of the listed items. 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.
  • lithium cobalt oxide (LiCoO 2 ) has become a leader in the field of electronic products due to its higher discharge voltage platform and higher volume energy density. Mainstream battery materials.
  • the discharge gram capacity of lithium cobalt oxide will increase with the increase of the working voltage. Generally speaking, every time the working voltage increases by 0.1V, the discharge gram capacity of lithium cobalt oxide can be increased by about 10%.
  • the charging cut-off voltage of lithium cobalt oxide has been continuously increased, from 4.2V and 4.3V to today's 4.4V.
  • the structure of the lithium cobalt oxide will undergo irreversible phase transition and structural collapse, causing its own layered structure to be destroyed.
  • lithium cobalt oxide is a layered oxide material with two-dimensional lithium ion deintercalation channels.
  • lithium vacancies will continue to form, causing the interlayer of lithium cobalt oxide to shrink.
  • the layered structure of lithium cobalt oxide may even collapse.
  • the inventor of the present application is committed to obtaining a positive electrode active material that can maintain a stable structure under a high voltage (above 4.4V) environment, thereby improving electrochemical devices Cycle performance and rate performance under high voltage.
  • the cathode active material of the present application includes a composite oxide containing at least metallic cobalt and lithium (hereinafter referred to as lithium cobalt oxide).
  • lithium cobalt oxide a composite oxide containing at least metallic cobalt and lithium
  • this application introduces a reasonable distribution of vacancies in the lithium cobalt oxide so that there are at least two different cobalt chemical environments—one of which has vacancies around the cobalt ion, and no vacancies around the other cobalt ion. Vacancy.
  • the peaks formed by the cobalt with vacancies in the nuclear magnetic resonance spectrum (abbreviated as 59Co NMR spectrum) of the cobalt element are shifted. Therefore, there are at least two in the 59Co NMR spectrum of the positive electrode active material. Peaks, each peak represents a cobalt in a different chemical environment.
  • first peak and a second peak in the 59Co NMR spectrum of the positive active material wherein the center of the first peak is at A ppm, and the center of the second peak is at B ppm Where 13900 ⁇ A ⁇ B ⁇ 14300.
  • the present application found that compared to cobalt with no vacancies around, cobalt with vacancies around has better structural stability, and is not easy to dissolve out or cause side reactions with electrolyte under high-voltage charging and discharging conditions.
  • the presence of vacancies can effectively reduce the strain caused by the volume expansion and contraction of the positive electrode active material during the charge and discharge process. Therefore, the electrochemical device using the positive electrode active material can exhibit excellent cycle stability and rate performance under high-voltage charging and discharging conditions.
  • FIG. 1A shows the full spectrum of cobalt of the positive electrode active material of Example 1
  • FIG. 1B is an enlarged view and a partial peak view of the highest peak in FIG. 1A.
  • the left and right sides of the highest cobalt peak of the positive electrode active material described in Example 1 have obvious asymmetry.
  • the right arc is relatively gentle .
  • Dmfit software to perform peak separation processing on the positive electrode active material described in Example 1, two fitting peaks can be obtained, namely fitting peak 1 (i.e., the first peak) and fitting peak 2 (i.e., the second peak).
  • the center position of fitting peak 1 is at about 14070 ppm
  • the center position of fitting peak 2 is at about 14090 ppm.
  • Figures 2 and 3 respectively reflect the cycle performance and rate performance of the lithium ion battery in Example 1 and Comparative Example 1 under high voltage. 2 and 3, it is not difficult to see that the cycle performance and rate performance of the lithium-ion battery of Example 1 are better than those of the lithium-ion battery of Comparative Example 1, which is mainly due to the internal positive electrode active material of Example 1. The distribution of vacancies enhances the structural stability of the material under high voltage.
  • the peak shape of the first peak usually appears as a short and broad peak
  • the peak shape of the second peak usually appears as a tall and thin peak.
  • the half width of the first peak of the positive active material is HA and the half width of the second peak is HB, and the half widths of the first peak and the second peak satisfy 0.017 ⁇ HB/ HA ⁇ 90.2 or 0.02 ⁇ HB/HA ⁇ 50.
  • the size of the peak area has a positive correlation with the content of the element in the positive electrode active material. Since the vacancy is related to the cobalt element of the first peak, the peak area of the first peak is proportional to the number of vacancies. By further controlling the proportion of vacancies inside the positive electrode active material within an appropriate range, the performance of the material can be further optimized.
  • the positive active material described in this application includes the following compound of formula I:
  • M includes or is selected from one of the following elements One or more: Al, Mg, Ca, Zn, Ti, Zr, Nb, Mo, La, Y, Ce, Ni, Mn, W or Ho; E includes or is selected from one or more of the following elements: F, S, B, N, or P.
  • the first peak is the peak of Co I and the second peak is the peak of Co II .
  • Another embodiment of the present application also provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.
  • the material layer includes the positive electrode active material according to the present application; wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer contains the negative electrode active material.
  • the positive electrode current collector may be a positive electrode current collector commonly used in the art, which includes, but is not limited to, aluminum foil or nickel foil.
  • the positive electrode active material layer described in the present application further includes a binder and a conductive agent.
  • the binder can not only improve the bond between the particles of the positive electrode active material, but also enhance the bond between the positive electrode active material and the positive electrode current collector.
  • the binder may include or be selected from one or more of the following materials: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, Polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylic acid (ester) Styrene butadiene rubber, epoxy resin, nylon, etc.
  • the conductive agent can be used to enhance the conductivity of the electrode.
  • This application can use any conductive material as the conductive agent, as long as the conductive material does not cause unwanted chemical changes.
  • the conductive material may include or be selected from one or more of the following materials: carbon-based materials (for example, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), Metallic materials (for example, metal powder, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (for example, polyphenylene derivatives), and mixtures thereof, and the like.
  • the negative active material can reversibly insert and extract lithium ions.
  • the negative active material may include or be selected from one or more of the following materials: carbonaceous materials, siliceous materials, alloy-based materials, lithium-containing metal composite oxide materials, and the like.
  • carbonaceous materials include crystalline carbon, amorphous carbon, and mixtures thereof.
  • the crystalline carbon may be amorphous or flake-shaped, flake-shaped, spherical or fibrous natural graphite or artificial graphite.
  • the amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and the like.
  • examples of the negative active material may include, but are not limited to, natural graphite, artificial graphite, mesophase carbon microspheres (referred to as MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite At least one of Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , spinel structure lithiated TiO 2 -Li 4 Ti 5 O 12 , and Li-Al alloy.
  • the negative electrode current collector may be a negative electrode current collector commonly used in the art, which includes, but is not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, and conductive metal coated The polymer substrate and its combination.
  • the negative electrode active material layer described in the present application further includes a binder and a conductive agent.
  • the binder and conductive agent in the negative electrode can be made of the same materials as described above, which will not be repeated here.
  • the positive electrode active material described in the present application can maintain good structural stability during high-voltage charge-discharge cycles.
  • the positive active material includes particles having a diameter of not less than 5 ⁇ m.
  • the cracking rate of the particles with a diameter of not less than 5 ⁇ m is not more than 30%, not more than 25%, not more than 20%, not more than 15% or not more than 10%.
  • the electrochemical device When the electrochemical device is subjected to a charge-discharge cycle at a high voltage, side reactions occur between the electrode active material and the electrolyte, resulting in by-products that accumulate on the surface of the electrode active material particles, resulting in an increase in impedance. Since the positive electrode active material described in this application has good interface stability, it will greatly reduce the occurrence of side reactions during the high-voltage charge and discharge cycle, and reduce the growth rate of the direct current resistance (DCR) of the electrochemical device. In some embodiments, when the discharge capacity of the electrochemical device decays to 80% of the initial discharge capacity, after each cycle, the DC impedance growth rate of the electrochemical device is less than 2%, less than 1.5%, less than 1%, or Less than 0.5%.
  • DCR direct current resistance
  • FIG. 4 shows a scatter diagram of the average growth rate of the DCR of the lithium ion batteries in Example 1 and Comparative Example 1 after each cycle.
  • this application takes 10 charge-discharge cycles of a lithium-ion battery as a unit, measures the DCR of the lithium-ion battery before and after these 10 charge-discharge cycles, calculates the difference, and divides the above difference Take 10 to get the average growth rate of the lithium-ion battery's DCR after each cycle.
  • the x-axis is the initial number of laps to start the DCR measurement.
  • the application starts counting 10 charge-discharge cycles at the first circle, the 15th circle, and the 27th circle, and uses these 10 charge-discharge cycles before and after the test.
  • the obtained DCR calculates the average growth rate of DCR. Referring to the scattered points in FIG. 4, it can be seen that the average growth rate of DCR of the lithium ion battery in Example 1 is significantly lower than that of the lithium ion battery in Comparative Example 1.
  • the thickness of the by-product layer will gradually increase. Since the positive electrode active material described in this application has good interface stability and can inhibit the occurrence of side reactions, in some embodiments, when the discharge capacity of the electrochemical device decays to 80% to 90% of the initial discharge capacity When, the thickness of the by-product layer is ⁇ m, where ⁇ 0.5, ⁇ 0.4, ⁇ 0.3 or ⁇ 0.2.
  • the by-product layer includes carbon element, oxygen element, fluorine element, and nitrogen element.
  • the fluorine element is beneficial to the stability of the interface of the positive electrode active material, while the nitrogen element is the opposite.
  • the average percentage of fluorine in the by-product layer is ⁇ F
  • the average percentage of nitrogen is ⁇ N, where the content of fluorine element and nitrogen element in the by-product layer satisfies ⁇ F- ⁇ N ⁇ 5%.
  • the fluorine element in the by-product layer when the discharge capacity of the electrochemical device decays to 80% to 90% of the initial discharge capacity, based on the total weight of carbon element, oxygen element, fluorine element, and nitrogen element, the fluorine element in the by-product layer The average percentage content and the average percentage content of nitrogen meet ⁇ F- ⁇ N ⁇ 5%.
  • the cobalt element in the positive electrode active material is dissolved in the electrolyte in the form of ions, moves to the negative electrode side through the separator, and is electroplated into the negative electrode active material layer during the charging process. Since the positive electrode active material described in this application contains a reasonable distribution of vacancies and the cobalt ions located near the vacancies are not easy to dissolve, the amount of dissolved cobalt ions is very small when the electrochemical device undergoes high-voltage charge and discharge cycles. Therefore, the content of cobalt element electroplated into the negative electrode active material layer is even smaller.
  • the increase of the Co concentration on the negative electrode is Q, where Q ⁇ 10ppm, Q ⁇ 7ppm, Q ⁇ 5ppm, Q ⁇ 3ppm, or Q ⁇ 2ppm.
  • the increase Q of the Co concentration on the negative electrode satisfies Q ⁇ 10ppm, Q ⁇ 7ppm, Q ⁇ 5ppm, Q ⁇ 3ppm, or Q ⁇ 2ppm.
  • the side reaction between the positive electrode active material and the electrolyte can be better suppressed, so as to better exert the electrochemical device under high voltage. Electrochemical performance.
  • the electrolyte may include organic solvents, lithium salts, 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 of the electrolytic solution.
  • the organic solvent of the electrolyte of the present application includes or is selected from: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), carbonic acid At least one of dimethyl ester (DMC), methyl propionate, ethyl propionate, or propyl propionate.
  • the lithium salt of the electrolyte of the present application includes or is selected from: lithium hexafluorophosphate (LiPF 6 ), lithium bistrifluoromethanesulfonimide LiN (CF 3 SO 2 ) 2 (abbreviated as LiTFSI), bis( Li(N(SO 2 F) 2 ) (abbreviated as LiFSI), lithium bisoxalate borate LiB(C 2 O 4 ) 2 (abbreviated as LiBOB), lithium tetrafluorophosphate oxalate (LiPF 4 C) 2 O 2 ), at least one of lithium difluorooxalate borate LiBF 2 (C 2 O 4 ) (abbreviated as LiDFOB), lithium hexafluorocesium oxide (LiCsF 6 ), or lithium difluorophosphate (LiPO 2 F 2 ).
  • LiPF 6 lithium hexafluorophosphate
  • LiFSI lithium bistrifluoromethanesulfonimi
  • the electrolyte of the present application further includes a nitrile-containing additive.
  • the nitrile-containing additive chemically reacts or physically adsorbs on the surface of the positive electrode active material during the charging and discharging process of the electrochemical device, and forms a specific and excellent nitrile protective film structure on the surface, which stabilizes the interface structure of the positive electrode and has a positive effect on the positive electrode.
  • the active material is protected to promote the structural stability of the positive electrode active material under high-voltage charging and discharging.
  • the nitrile-containing additive includes or is selected from adiponitrile, succinonitrile, glutaronitrile, malononitrile, 2-methylglutaronitrile, pimelic nitrile, sebaconitrile, azelaonitrile, 1,4-dicyano-2-butene, ethylene glycol bis(propionitrile) ether, 3,3'-oxydipropionitrile, thiomalononitrile, hex-2-ene dinitrile, butene dinitrile Nitrile, 2-pentanedionitrile, ethyl succinonitrile, hex-3-enedionitrile, 2-methylene glutaronitrile, 4-cyanopimelonitrile, 1,3,5-hexanetricarbonitrile , 1,2,3-propane tricarbonitrile, 1,2,3-tris(2-cyanooxy)propane, 1,3,5-pentane tricarbonitrile, 1,3,6-hexane
  • the nitrile-containing additive includes or selected from adiponitrile, succinonitrile, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6- At least one of hexane tricarbonitrile or triacetonitrile ammonia.
  • 1,3,6-hexanetricarbonitrile is an additive with moderate molecular length and rich in active groups.
  • the lithium cobalt oxide positive electrode active material with 59Co NMR bimodal according to the present invention it can Play a very good effect. This may be due to the fact that the cobalt in the positive electrode active material of the present application is in a slightly asymmetric chemical environment.
  • 1,3,6-hexanetricarbonitrile is also a slightly asymmetric substance. In the electrochemical system, it can It can better interact with the positive electrode active material.
  • a solid and stable solid electrolyte interface (SEI) film is formed on the surface of the positive electrode active material to strengthen the protection of the positive electrode active material, thereby optimizing the performance of the electrochemical device. Cycle stability and rate performance.
  • SEI solid electrolyte interface
  • the protective effect of nitrile-containing additives has a certain correlation with its dosage.
  • the content of the nitrile-containing additive is 0.01 wt% to 20 wt%, 0.01 wt% to 10 wt%, 0.1 wt% to 20 wt%, 0.1 wt% to 10 wt% , 1wt% to 20wt% or 1wt% to 10wt%.
  • the electrochemical device of the present application further includes a separator film disposed between the positive electrode and the negative electrode to prevent short circuits.
  • the present application does not particularly limit the material and shape of the isolation membrane used in the electrochemical device, and it can be any material and shape 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.
  • the material of the substrate layer may include or be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.
  • a polyethylene porous film, a polypropylene porous film, a polyethylene non-woven fabric, a polypropylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected.
  • the surface treatment layer may be, but is not limited to, a polymer layer, an inorganic substance layer, or a mixed layer formed of a polymer and an inorganic substance.
  • the inorganic layer may include inorganic particles and a binder.
  • Inorganic particles may include or be selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehm
  • the binder may include or be selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, poly One or a combination of vinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer may include a polymer.
  • the material of the polymer may include or be selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, poly(vinylidene fluoride- At least one of hexafluoropropylene).
  • the electrochemical device of the present application may be a lithium ion battery or any other suitable electrochemical device.
  • the electrochemical device of the present application includes any device that undergoes an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, solar cells, or capacitors.
  • the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.
  • this application also provides a method for preparing the above-mentioned positive electrode active material.
  • the positive electrode active material Li a Co I b1 Co II b2 M c O d E e Take the positive electrode active material Li a Co I b1 Co II b2 M c O d E e as an example, where M includes or is selected from one or more of the following elements: Al, Mg, Ca, Zn, Ti, Zr, Nb , Mo, La, Y, Ce, Ni, Mn, W, and Ho; E includes or is selected from one or more of the following elements: F, S, B, N, and P.
  • One of the methods is to add different additives to adjust the reaction conditions during the doping of M and E elements to achieve the doping of M and E elements. Additives can promote the diffusion and distribution of doped elements M and H, make them occupy the lattice position reasonably, create a reasonable distribution of vacancies, and thus have an impact on the chemical environment of cobalt.
  • the method may include the following steps:
  • the lithium source, the cobalt source, the M source and the additive Aa are mixed in a certain proportion to obtain a mixture
  • the molar ratio of lithium to cobalt between the lithium source and the cobalt source is 0.97 to 1.08; the molar ratio of M to Co between the M source and the cobalt source is 0.0001 to 0.2; the molar ratio of the additive Aa and the M source The ratio is not higher than 0.05.
  • Additive Aa includes but is not limited to one or more of sodium carbonate, sodium oxalate, ammonium fluoride, sodium fluoride and the like.
  • the standard for uniform powder mixing is that there is no obvious agglomeration and separation.
  • the mixture can be put into a stirring tank and stirred for 3 to 6 hours until the mixture is uniformly mixed.
  • the temperature range of the high temperature treatment is 800° C. to 1100° C.
  • the time of the high temperature treatment is 6 h to 24 h.
  • the molar ratio of H to Co in the H source and the cobalt source is 0.0001 to 0.1; the molar ratio of the additive Ab to the E source is not higher than 0.02.
  • the additive Ab includes, but is not limited to, one or more of ammonium sulfate, polyethylene glycol, and lithium oxalate.
  • the temperature range of the high temperature treatment is 300° C. to 1000° C.
  • the time of the high temperature treatment is 4 h to 24 h.
  • the atmosphere for high temperature treatment is air or inert gas.
  • the inert gas can be, but is not limited to, at least one of helium, argon, and nitrogen; the standard for sieving is 100 mesh to 500 mesh.
  • the positive electrode active material Li a Co I b1 Co II b2 M c O d E e As an example, another method is to control the synthesis process of the reaction precursor to obtain two different lithium cobalt oxide precursors, one of which is first Pre-burning, and then mixed with another precursor to react. Due to the difference in the degree of reaction of different components, the sintered product contains a certain concentration of vacancies, thereby creating two different chemical environments for Co in the positive electrode active material. Specifically, the method may include the following steps:
  • the lithium source and the cobalt source are mixed in a ratio of lithium-cobalt molar ratio of 0.97 to 1.08 to obtain a mixture A; another lithium source and another cobalt source are mixed in a ratio of lithium-cobalt molar ratio of 0.95 to 1.05 Mix to obtain B mixture;
  • the standard for uniform powder mixing is that there is no obvious agglomeration and separation.
  • the mixture can be put into a stirring tank and stirred for 3 to 6 hours until the mixture is uniformly mixed.
  • the temperature range of the high temperature treatment is 200°C to 500°C, and the time of the high temperature treatment is 1h to 6h; in the step (6), the temperature range of the high temperature treatment is 500°C to 1100 °C, the high temperature treatment time is 6h to 24h.
  • the atmosphere for high temperature treatment is air or inert gas.
  • the inert gas can be, but is not limited to, at least one of helium, argon, and nitrogen; the standard for sieving is 100 mesh to 500 mesh.
  • the lithium source can be, but is not limited to, one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate, lithium oxide, lithium chloride, lithium sulfate, and lithium nitrate. .
  • the cobalt source can be, but is not limited to, one or more of cobalt hydroxide, cobalt carbonate, cobalt acetate, cobalt oxalate, cobalt oxide, cobalt chloride, cobalt sulfate, and cobalt nitrate .
  • the source of M can be, but is not limited to, one or more of nitrate, hydroxide, oxide, peroxide, sulfate, and carbonate of element M.
  • the E source can be, but is not limited to, one or more of element E hydrides, oxides, acids, and salts.
  • the use of the electrochemical device of the present application is not particularly limited, and it can be used for any purpose known in the prior art. According to some embodiments of the present application, the electrochemical device of the present application can be used in electronic devices, where electronic devices include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, and portable faxes.
  • Printers Portable copiers, portable printers, stereo headsets, video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, spares Power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, lithium-ion capacitors, etc.
  • a lithium ion battery is taken as an example and combined with comparative examples and embodiments to further illustrate the technical solution of the present invention, but it is not limited thereto.
  • Those skilled in the art will understand that the preparation methods described in this application are only exemplary embodiments. Any modification or replacement of the technical solution of the present invention without departing from the scope of the technical solution of the present invention should be covered by the protection of the present invention. In the range.
  • the following preparation methods were used to prepare the positive electrode active materials in the examples and comparative examples into lithium ion full batteries.
  • PVDF polyvinylidene fluoride
  • the preparation of the negative electrode the negative active material artificial graphite, the binder styrene butadiene rubber (SBR), and the thickener sodium carbon methyl cellulose (CMC) are fully stirred in deionized water at a weight ratio of 97.5: 1.5:1 Mix uniformly to make a negative electrode slurry, and then evenly coat the negative electrode slurry on the front and back sides of the copper foil of the negative electrode collector, and then dry at 85°C to form the negative electrode active material layer, and then perform cold pressing to obtain the negative electrode active The material layer is stripped, cut into pieces, and the negative electrode tab is welded to obtain the negative electrode.
  • SBR styrene butadiene rubber
  • CMC thickener sodium carbon methyl cellulose
  • the isolation membrane adopts a ceramic-coated polyethylene (PE) material isolation membrane.
  • Lithium-ion battery assembly stack the positive electrode, separator, and negative electrode in order, so that the separator is in the middle of the positive and negative electrodes for separation. Then it is wound, placed in a packaging case, injected with electrolyte and encapsulated, and formed into the final lithium-ion battery.
  • the half-cell is prepared using almost the same method as the above-mentioned full-cell 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 full battery, wash with dimethyl carbonate (DMC), and remove one side to obtain a single-sided positive electrode sheet;
  • DMC dimethyl carbonate
  • the double-sided area is randomly selected from the positive electrode of the full battery, washed with DMC, and one side is removed to obtain a single-sided positive electrode sheet.
  • a single-sided positive electrode plate was prepared into a button cell with a pair of lithium plates. The button cell is discharged at a constant current at a current density of 10mA/g until the cut-off voltage is 3.0V. Let it stand for 5 minutes, and then discharge the button battery at a constant current at a current density of 10mA/g until the cut-off voltage is 3.0V so that the button battery is fully discharged. Scrape the positive electrode active material from the positive electrode sheet to be used in the nuclear magnetic resonance test.
  • a wide-cavity solid-state nuclear magnetic resonance spectrometer with a model of BRUKER AVANCE III and a frequency of 400 MHz was used to perform nuclear magnetic resonance tests on the positive electrode active material, and a 59Co nuclear magnetic resonance spectrum was obtained.
  • a rotor with a diameter of 1.3mm is selected, using magic angle rotation, the speed is 35kHz, and the spectrum collection time is 6min to 5h. Finally, all spectrogram results are normalized. Use origin software to read the half-width and peak area values from the obtained NMR spectrum.
  • a current of 0.5C that is, the current value of completely discharging the theoretical capacity within 2h
  • the upper limit voltage is 4.53V
  • C 1 of the first cycle also called the initial discharge capacity
  • the following formula is used to calculate the discharge capacity retention rate of the lithium ion battery at 2C: (C 2 /C 0.2 ) ⁇ 100%.
  • the whole battery was discharged to 3.0V at a current density of 10mA/g, and then discharged again to 3.0V at a current density of 10mA/g after standing for 10 minutes.
  • Disassemble the battery in a drying room or glove box obtain the positive and negative electrodes, and dry them.
  • an ion polisher Jopan Electronics-IB-09010CP
  • Select particles with a diameter not less than 5 ⁇ m inside the pole piece select the position with the largest thickness of the by-product layer on the same particle, and draw parallel lines at the lowest and highest points of the by-products. The distance between the parallel lines is the by-product of this particle Layer thickness.
  • Select 10 different particles that meet the above test conditions measure the thickness of the by-product layer of each particle, calculate the average value, and record it as the thickness of the by-product layer.
  • an ion polisher Jopan Electronics-IB-09010CP
  • the particles with cracks in the cross-section of the particles in the SEM image are regarded as cracked particles.
  • the continuous length is not less than 0.5 ⁇ m and the width is not less than 0.1
  • the negative electrode in the full battery is prepared into a button cell, and the charge and discharge cycle is performed under a voltage window of 3.0V to 4.53V.
  • the charge and discharge current is 10mA/g
  • the temperature of the cycle is 25°C
  • the number of cycles is 10 cycles.
  • the negative plates before and after the cycle were obtained and the cobalt content was measured by inductively coupled plasma (ICP).
  • ICP inductively coupled plasma
  • the difference of the cobalt content is divided by the number of cycles, and the average value is calculated as the increase Q of the Co concentration before and after each cycle.
  • the molar ratio of lithium to cobalt is 1:1.05
  • the molar ratio of aluminum and lanthanum to cobalt are 0.3% and 0.1%, respectively, sodium fluoride and nitric acid
  • the molar ratio of aluminum is 1:100. After mixing uniformly, sinter in air at 1000°C for 12h, after cooling, grinding and sieving. The sieved powder is mixed with alumina at a mass ratio of 2000:1. After fully mixing, it is filled and sintered in air at 600°C for 6h, cooled, ground and sieved to further coat the surface of the positive electrode active material with aluminum. .
  • the molar ratio of lithium to cobalt is 1:1.05
  • the molar ratio of magnesium and zirconium to cobalt are 0.2% and 0.1%, respectively, sodium fluoride and nitric acid
  • the molar ratio of magnesium is 1:200.
  • the molar ratio of lithium to cobalt is 1:1.05
  • the molar ratio of aluminum and lanthanum to cobalt is 0.3% and 0.1%, respectively.
  • the molar ratio is 1:100.
  • Lithium carbonate, cobalt tetroxide, aluminum nitrate and sodium oxalate are mixed in the following proportions: the molar ratio of lithium to cobalt is 1:1.05, the molar ratio of aluminum to cobalt is 0.3%, and the molar ratio of sodium oxalate to aluminum nitrate is 1:100.
  • the sieved powder and ammonium fluoride are mixed according to the molar ratio of cobalt fluoride to 0.1%, and lithium oxalate is added.
  • the molar ratio of lithium oxalate to ammonium fluoride is 1:100. After the above mixture is fully mixed and uniform, in the air Sintered at 600°C for 6h, cooled, ground and sieved.
  • Lithium carbonate and Co 3 O 4 containing 1.2% Al are mixed uniformly in the ratio of lithium to cobalt ratio of 1:1.05 to obtain mixture A; Lithium chloride and Co 3 O 4 containing 0.06% of La are mixed with lithium to cobalt ratio of 1. :1.045 mixed uniformly to obtain mixture B; react mixture A at 350°C for 2h, after cooling, mix thoroughly with mixture B at a mass ratio of 1:5, and react at 1000°C for 12h. Cool, grind and sieve.
  • Lithium carbonate and Co 3 O 4 containing 0.14% Ti element are mixed uniformly with a lithium-cobalt ratio of 1:1.05 to obtain mixture A; lithium chloride and Co 3 O 4 containing 0.011% Y element are mixed with a lithium-cobalt ratio of 1:1.045 Mix uniformly to obtain mixture B; react mixture A at 350°C for 2 hours, mix it thoroughly with mixture B at a mass ratio of 1:6 after cooling, and react at 1000°C for 12 hours. Cool, grind and sieve. Mix it with magnesium oxide at a mass ratio of 2000:1, and react at 600°C for 6 hours. Cooling, grinding and sieving to further coat the surface of the positive electrode active material with magnesium element.
  • Lithium carbonate, cobalt tetroxide, titanium oxide and ammonium fluoride are mixed in the following proportions: the molar ratio of lithium to cobalt is 1:1.05, the molar ratio of titanium to cobalt is 0.05%, and the molar ratio of ammonium fluoride to titanium oxide is 1:100.
  • the sieved powder and ammonium fluoride are mixed according to the molar ratio of cobalt fluoride to 0.195%, and lithium oxalate is added.
  • the molar ratio of lithium oxalate to ammonium fluoride is 1:100. After the above mixture is thoroughly mixed, the air Sintered at 600°C for 6h, cooled, ground and sieved.
  • the molar ratio of lithium to cobalt is 1:1.05
  • the molar ratio of magnesium to cobalt is 0.2%
  • the ratio of niobium to cobalt is 0.04%
  • ammonium fluoride and oxide The molar ratio of magnesium is 1:100.
  • sinter in air at 1000°C for 12h, after cooling, grinding and sieving.
  • the sieved powder and ammonium fluoride are mixed according to the molar ratio of cobalt fluoride to 0.095%, and lithium oxalate is added.
  • the molar ratio of lithium oxalate to ammonium fluoride is 1:100. After the above mixture is thoroughly mixed, the air Sintered at 600°C for 6h, cooled, ground and sieved.
  • Lithium carbonate, cobalt tetroxide and aluminum nitrate are mixed in the following proportions: the ratio of lithium to cobalt is 1:1.05, and the molar ratio of aluminum element to cobalt element is 0.3%.
  • sinter in air at 1000°C for 12h, after cooling, grinding and sieving.
  • the sieved powder was mixed with alumina at a mass ratio of 2000:1, and after fully mixed uniformly, it was sintered at 600 in air for 6 hours, cooled, ground and sieved to further coat the surface of the positive electrode active material with aluminum.
  • lithium carbonate and cobalt tetroxide according to the following ratio: lithium to cobalt ratio 1:1.05, sintered in air at 1000°C for 12 hours, after cooling, grinding and sieving.
  • Lithium carbonate, cobalt tetroxide and aluminum nitrate are mixed in the following proportions: the ratio of lithium to cobalt is 1:1.05, and the molar ratio of aluminum element to cobalt element is 0.3%. After mixing uniformly, sinter in the air at 900°C for 12 hours, after cooling, grinding and sieving.
  • Lithium carbonate, cobalt tetroxide and lanthanum oxide are mixed in the following proportions: the ratio of lithium to cobalt is 1:1.05, and the molar ratio of lanthanum element to cobalt element is 0.3%. After mixing uniformly, sinter in air at 1000°C for 12h, after cooling, grinding and sieving.
  • Lithium Ion Battery Lithium Ion Battery.
  • the discharge capacity retention rates of the lithium ion batteries of Examples 1 to 9 at a large current of 2C are all higher than those of Comparative Examples 1 to 4, which indicates that the lithium ion batteries of Examples 1 to 9 are better than those of Comparative Examples 1 to 4. It has excellent rate performance.
  • the cracking rate of the positive electrode active material particles having a diameter of not less than 5 ⁇ m in Examples 1 to 9 is also much smaller than that of the positive electrode active material particles in Comparative Examples 1 to 4.
  • the average growth rate of the DC resistance DCR of the lithium ion batteries in Examples 1 to 9 is almost less than 1.3%, which is significantly lower than that of the lithium ion batteries in Comparative Examples 1 to 4.
  • Examples 10 to 15 correspond to Example 1, but are different from Example 1 in that the composition and content in the electrolyte are further modified.
  • the specific components and contents as well as the obtained electrochemical data can be found in Table 2 below.
  • Example 10-15 two nitrile-containing additives were added to the electrolyte at the same time. Compared with Example 1, the cycle performance and rate performance of the electrochemical devices of Examples 10 to 15 have been further improved. In addition, under the premise that the total content of the added nitrile-containing additives remains unchanged, the addition of 1,3,6-hexanetricarbonitrile can further effectively improve the cycle performance and rate performance of the electrochemical device under the high voltage window.
  • the above embodiments fully illustrate that by introducing a reasonable vacancy distribution in the positive electrode active material, the positive electrode active material described in the present application can continuously maintain structural stability under a high voltage window. Therefore, the electrochemical device using the positive electrode active material described in the present application can exhibit excellent cycle performance and rate performance under high voltage.
  • the electrochemical performance of the electrochemical device under high voltage can be further optimized.
  • 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, 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 “exemplary”, 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

提供了一种正极活性材料及包含其的电化学装置。所述正极活性材料的59Co NMR谱中存在第一峰和第二峰，其中所述第一峰的中心位置位于A ppm处，所述第二峰的中心位置位于B ppm处，其中13900≤A<B≤14300。采用上述正极活性材料的电化学装置在高电压下能够呈现出优异的循环稳定性和倍率性能。

Description

正极活性材料及包含其的电化学装置 技术领域
本申请涉及储能技术领域，更具体地，涉及正极活性材料和应用该正极活性材料的电化学装置。
背景技术
随着智能产品的普及和应用，人们对手机、笔记本电脑、相机等电子产品的需求逐年增加，而电化学装置作为电子产品的电源在我们日常生活中扮演着越来越重要的角色。其中，锂离子电池凭借其具有比能量大、工作电压高、自放电率低、体积小、重量轻等优势而在消费电子领域中广泛应用。
然而，随着电化学装置在电动汽车、可移动电子设备和无人机中的广泛应用，人们对电化学装置提出了更高的要求。以电动汽车为例，人们要求电动汽车具有长的续航里程并且实现大功率下的充放电，这就要求电动汽车的能源设备具有高的能量密度和功率密度。而要想满足高能量密度的要求，需要电化学装置在高的电压窗口下能够稳定地工作；要想满足高功率密度的要求，需要电化学装置在大电流下能够快速的充放电(即，具有优异的倍率性能)；这些又对电化学装置的正负极活性材料和电解液提出了更高的要求。
发明内容
本申请提供一种正极活性材料、制备该正极活性材料的方法以及应用该正极活性材料的电化学装置，以试图在至少某种程度上解决至少一个存在于相关领域中的问题。
在本申请的一个层面中，本申请提供了一种正极活性材料，所述正极活性材料的59Co NMR谱中存在第一峰和第二峰，其中所述第一峰的中心位置位于A ppm处，所述第二峰的中心位置位于B ppm处，其中13900≤A<B≤14300。
在本申请的一些实施例中，所述第一峰的半峰宽为HA和所述第二峰的 半峰宽为HB，且其中0.017≤HB/HA≤90.2。
在本申请的一些实施例中，所述第一峰的峰面积为SA和所述第二峰的峰面积为SB，且其中0<SA/SB≤0.3。
在本申请的一些实施例中，所述正极活性材料包括下述式Ⅰ化合物：
Li aCo Ⅰ b1Co Ⅱ b2M cO dE e   (式Ⅰ)；
其中0.95≤a≤1.05，0<b1<b2<1，b1+b2≤1，0≤c≤0.2，0<d≤2，0≤e≤0.1；其中M选自Al、Mg、Ca、Zn、Ti、Zr、Nb、Mo、La、Y、Ce、Ni、Mn、W或Ho中的一种或多种元素；E选自F、S、B、N或P中的一种或多种元素。
在本申请的另一个层面中，本申请提供了一种电化学装置，其包括正极、负极和电解液，其中所述正极包括正极集流体和正极活性材料层，所述正极活性材料层包括根据本申请的正极活性材料。
在本申请的一些实施例中，所述正极活性材料包括直径不小于5μm的颗粒，当所述电化学装置的放电容量衰减为初始放电容量的80％至90％时，所述直径不小于5μm的颗粒的开裂率不大于25％。
在本申请的一些实施例中，其中当所述电化学装置的放电容量衰减至不低于初始放电容量的80％时，每圈循环后，所述电化学装置的直流阻抗增长率小于1.5％。
在本申请的一些实施例中，其中所述正极活性材料颗粒表面包含副产物层，当所述电化学装置的放电容量衰减为初始放电容量的80％至90％时，所述副产物层的厚度为ημm，η≤0.5。
在本申请的一些实施例中，其中所述副产物层包含碳元素、氧元素、氟元素和氮元素，以所述碳元素、氧元素、氟元素和氮元素的总重量计，其中氟元素的平均百分含量为ωF，氮元素的平均百分含量为ωN，其中ωF-ωN≥5％。
在本申请的一些实施例中，所述电解液包括含腈添加剂，其中所述含腈 添加剂包括以下各者中的至少一种：己二腈、丁二腈、1,3,5-戊烷三甲腈、1,3,6-己烷三甲腈、1,2,6-己烷三甲腈或三乙腈氨。
在本申请的一些实施例中，基于所述电解液的总重量，所述含腈添加剂的含量为0.1％至10％。
在本申请的另一个层面中，本申请提供了一种电子装置，其包含根据本申请的电化学装置。
本申请提出了一种具有59Co NMR双峰的正极活性材料以用于电化学装置。由于该正极活性材料在高电压充放电的过程中能够保持结构稳定性，因此应用该正极活性材料的电化学装置在高电压下具有优异的循环性能和倍率性能。
本申请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释。
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1A示出了实施例1中的正极活性材料的钴元素的核磁共振全谱图；图1B示出了图1A中的最高峰的放大图和分峰图；
图2示出了实施例1和对比例1的锂离子电池循环250圈的放电容量保持率的折线图；
图3示出了实施例1和对比例1的锂离子电池在不同电流下的放电容量保持率的折线图；
图4示出了实施例1和对比例1的锂离子电池在每次循环前后直流阻抗DCR的平均增长率的散点图。
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。在本申请说明书全文中，将相同或相似的组件以及具有相同或相似的功能的组件通过类似附图标记来表示。在此所描述的有关附图的实施例为说明性质的、图解性质的且用于提供对本申请的基本理解。本申请的实施例不应该被解释为对本申请的限制。
如本文中所使用，术语“大致”、“大体上”、“实质”及“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％。举例来说，如果两个数值之间的差值小于或等于所述值的平均值的±10％(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％)，那么可认为所述两个数值“大体上”相同。
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“中的一者或多者”、“中的一个或多个”、“中的一种或多种”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
当前提出的用于锂离子电池的正极活性材料数不胜数，而在众多的正极活性材料中，钴酸锂(LiCoO 2)凭借较高的放电电压平台和较高的体积能量密度成为了电子产品领域的主流电池材料。钴酸锂的放电克容量会随着工作电压的提高而提高，一般来讲，其工作电压每提高0.1V，钴酸锂的放电克容量可以提高约10％。出于对高能量密度的追求，钴酸锂工作的充电截止电压不断提高，从4.2V、4.3V发展到今天的4.4V。然而，当锂离子电池充电至4.4V以上时，钴酸锂的结构会出现不可逆相变和结构坍塌，导致自身层状结构遭到破坏。
具体来讲，钴酸锂是一种层状氧化物材料，具有二维锂离子脱嵌通道。一方面，在锂离子脱出的过程中，会不断地形成锂空位，导致钴酸锂的层间发生收缩。而且随着脱锂量的不断增加，钴酸锂的层状结构甚至会发生坍塌。另一方面，当锂离子电池充电至4.4V以上时，会导致更多的锂脱出，这会增强钴酸锂的氧化性，加剧钴酸锂与电解液之间的副反应，造成钴酸锂中的钴溶出，破坏钴酸锂颗粒的表面并发生产气现象，进而恶化电化学装置的电化学性能，尤其是循环性能和倍率性能。
至少基于本申请的发明人对现有技术的上述洞察，本申请的发明人致力于获得一种能够在高电压(4.4V以上)的环境下保持结构稳定的正极活性材料，从而改善电化学装置在高电压下的循环性能和倍率性能。
在一些实施例中，本申请的正极活性材料包括至少包含金属钴和锂的复合氧化物(下称，锂钴氧化物)。具体地，本申请通过在锂钴氧化物中引入合理的空位分布以使其内部存在至少两种不同的钴的化学环境—其中一种钴离子的周围有空位，另一种钴离子的周围没有空位。相较于周围没有空位的钴，周围存在空位的钴在钴元素的核磁共振谱(缩写为59Co NMR谱)中形成的峰会发生位移，因此所述正极活性材料的59Co NMR谱中至少存在两个峰，每个峰代表一种处于不同化学环境下的钴。
在一些实施例中，所述正极活性材料的59Co NMR谱中存在第一峰和第二峰，其中所述第一峰的中心位置位于A ppm处，所述第二峰的中心位置位于B ppm处，其中13900≤A<B≤14300。本申请发现相较于周围没有空位的钴，周围 存在空位的钴具有更好的结构稳定性，在高电压充放电条件下不易溶出或与电解液发生副反应。同时，空位的存在能够有效地降低正极活性材料在充放电过程中由于体积的膨胀和收缩带来的应变。因此，应用该正极活性材料的电化学装置能够在高电压充放电的条件下呈现出优异的循环稳定性和倍率性能。
图1A示出了实施例1的正极活性材料的钴的全谱图而图1B为图1A中的最高峰的放大图和分峰图。如图1B所示，实施例1所述的正极活性材料的钴的最高峰的左右两侧具有明显的不对称性，例如，相较于靠近图1B底部的左侧弧度，右侧弧度较为缓和。通过Dmfit软件对实施例1所述的正极活性材料进行分峰处理可以得到两个拟合峰，分别为拟合峰1(即，第一峰)和拟合峰2(即第二峰)，其中拟合峰1的中心位置位于约14070ppm处，拟合峰2的中心位置位于约14090ppm处。
图2和图3分别反映了实施例1和对比例1中的锂离子电池在高电压下的循环性能和倍率性能。参见图2和图3，不难看出，实施例1的锂离子电池的循环性能和倍率性能均优于对比例1的锂离子电池，这主要归功于实施例1的正极活性材料的内部具有合理的空位分布，增强了材料在高电压下的结构稳定性。
在一些实施例中，第一峰的峰型通常表现为矮而宽的峰，第二峰的峰型通常表现为高而细的峰。在一些实施例中，所述正极活性材料的第一峰的半峰宽为HA而第二峰的半峰宽为HB，且其中第一峰和第二峰的半峰宽满足0.017≤HB/HA≤90.2或者满足0.02≤HB/HA≤50。
峰面积的大小与元素在正极活性材料中的含量成正相关的关系。由于空位与第一峰的钴元素相关，因此第一峰的峰面积与空位的数量成正比。通过进一步将正极活性材料内部的空位比例控制在合适的区间内，能够进一步优化材料的性能。在一些实施例中，第一峰的峰面积为SA而第二峰的峰面积为SB，且其中第一峰和第二峰的峰面积满足0<SA/SB≤0.3。如果SA＝0，则正极活性材料的内部不存在空位，因此也就无法提升材料结构的稳定性。如果SA/SB>0.3，则正极活性材料会由于存在过多的空位而导致材料的结构稳定性下降。
在一些实施例中，本申请所述的正极活性材料包括下述式Ⅰ的化合物：
Li aCo Ⅰ b1Co Ⅱ b2M cO dE e  (式Ⅰ)；
其中0.95≤a≤1.05，0<b1<b2<1，b1+b2≤1，0≤c≤0.2，0<d≤2，0≤e≤0.1；其中M包括或选自以下元素中的一种或多种：Al、Mg、Ca、Zn、Ti、Zr、Nb、Mo、La、Y、Ce、Ni、Mn、W或Ho；E包括或选自以下元素中的一种或多种：F、S、B、N或P。在一些实施例中，在上述式Ⅰ的化合物的59Co NMR谱中，第一峰为Co Ⅰ的峰而第二峰为Co Ⅱ的峰。
二、电化学装置
本申请的另一实施例还提供了一种电化学装置，其包括正极、负极和电解液，其中所述正极包括正极集流体和设置在正极集流体上的正极活性材料层，所述正极活性材料层包括根据本申请的正极活性材料；其中所述负极包括负极集流体和设置在负极集流体上的负极活性材料层，所述负极活性材料层包含负极活性材料。
在一些实施例中，所述正极集流体可以是本领域常用的正极集流体，其包括，但不限于，铝箔或镍箔。
在一些实施例中，除了本申请的正极活性材料外，本申请所述的正极活性材料层还包含粘结剂和导电剂。
粘合剂不仅可以提高正极活性材料颗粒间的结合，还可以提高正极活性材料与正极集流体的结合。在一些实施例中，粘合剂可以包括或选自以下材料的一种或多种：聚乙烯醇、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、尼龙等。
导电剂可以用于增强电极的导电性。本申请可以采用任何导电材料作为导电剂，只要该导电材料不引起不想要的化学变化。在一些实施例中，导电材料可以包括或选自以下材料的一种或多种：基于碳的材料(例如，天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维等)、基于金属的材料(例如，金属粉、金属纤维等，包括例如铜、镍、铝、银等)、导电聚合物(例如，聚亚苯基衍生物)及其混合 物等。
负极活性材料能够可逆地嵌入和脱出锂离子。在一些实施例中，负极活性材料可以包括或选自以下材料的一种或多种：碳质材料、硅质材料、合金系材料、含锂金属的复合氧化物材料等。在一些实施例中，碳质材料的非限制性示例包括结晶碳、非晶碳及其混合物。在一些实施例中，结晶碳可以是无定形的或片形的、小片形的、球形的或纤维状的天然石墨或人造石墨。在一些实施例中，非晶碳可以是软碳、硬碳、中间相沥青碳化物、煅烧焦等。
负极活性材料的具体种类均不受到具体的限制，可根据需求进行选择。在一些实施例中，所述负极活性材料的实例可以包括，但不限于，天然石墨、人造石墨、中间相微碳球(简称为MCMB)、硬碳、软碳、硅、硅-碳复合物、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的锂化TiO 2-Li 4Ti 5O 12、Li-Al合金中的至少一种。
在一些实施例中，所述负极集流体可以是本领域常用的负极集流体，其包括，但不限于，铜箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜、覆有导电金属的聚合物基底及其组合。
在一些实施例中，除了负极活性材料以外，本申请所述的负极活性材料层还包含粘结剂和导电剂。负极中的粘结剂和导电剂可以采用以上所述相同的材料，在此不做过多赘述。
随着电化学装置在高电压下充放电的进行，电化学装置的放电容量会逐渐衰减，且其中正极活性材料所包含的颗粒可能会由于体积的剧烈膨胀和收缩而开裂。然而，本申请所述的正极活性材料在经历高电压充放电循环的过程中能够保持良好的结构稳定性。在一些实施例中，所述正极活性材料包括直径不小于5μm的颗粒。在采用包含上述颗粒粒径的正极活性材料作为电化学装置的正极的实施例中，以本申请的正极活性材料的质量作为基准，当电化学装置的放电容量衰减为初始容量的80％至90％时，所述直径不小于5μm的颗粒的开裂率不大于30％，不大于25％，不大于20％，不大于15％或者不大于10％。
当电化学装置在高电压下进行充放电循环时，电极活性物质会和电解液之间发生副反应从而产生副产物积累在电极活性材料颗粒的表面导致阻抗的增加。而 由于本申请所述的正极活性材料具有良好的界面稳定性，因此会大大地降低在高电压充放电循环的过程中副反应的发生，降低电化学装置的直流阻抗(DCR)的增长速率。在一些实施例中，当电化学装置的放电容量衰减至初始放电容量的80％时，每圈循环后，所述电化学装置的直流阻抗增长率小于2％，小于1.5％，小于1％或者小于0.5％。
图4示出了每圈循环后，实施例1和对比例1中的锂离子电池的DCR的平均增长率的散点图。关于DCR平均增长率的测定，本申请以对锂离子电池进行10次充放电循环作为一个单元，测定锂离子电池在这10次充放电循环前后的DCR，计算差值，并将上述差值除以10以得到每圈循环后锂离子电池的DCR的平均增长率。
具体参见图4，x轴为开始进行DCR测定的起始圈数。例如，针对实施例1和对比例1中的锂离子电池，本申请分别在第1圈、第15圈和第27圈开始计数10次的充放电循环，并利用这10次充放电循环前后测得的DCR计算DCR平均增长率。参见图4中的散点可知，实施例1中的锂离子电池的DCR平均增长率明显低于对比例1中的锂离子电池。
如上所述，在电化学装置充放电的过程中，正极活性物质和电解液之间会发生副反应而产生副产物积累在正极活性材料颗粒的表面。随着充放电的进行，副产物层的厚度会逐渐增加。而由于本申请所述的正极活性材料具有良好的界面稳定性从而能够抑制副反应的发生，因此，在一些实施例中，当电化学装置的放电容量衰减至初始放电容量的80％至90％时，所述副产物层的厚度为ημm，其中η≤0.5，η≤0.4，η≤0.3或者η≤0.2。
在一些实施例中，所述副产物层包含碳元素、氧元素、氟元素和氮元素，其中在某种程度上氟元素有利于正极活性材料界面的稳定而氮元素则与之相反。在一些实施例中，以碳元素、氧元素、氟元素和氮元素的总重量计，副产物层中的氟元素所占的平均百分含量为ωF，氮元素所占的平均百分含量为ωN，其中氟元素和氮元素在副产物层中的含量满足ωF-ωN≥5％。在一些实施例中，当电化学装置的放电容量衰减至初始放电容量的80％至90％时，以碳元素、氧元素、氟元素和氮元素的总重量计，副产物层中的氟元素所占的平均百分含量和氮元素所占的平均百分含量满足ωF-ωN≥5％。
在电化学装置充放电的过程中，正极活性材料中的钴元素会以离子的形式溶解至电解液中，经由隔离膜移动至负极侧，并在充电的过程中电镀至负极活性材料层中。由于本申请所述正极活性材料中含有合理的空位分布且位于空位附近的钴离子不易于溶出，因此在电化学装置经历高电压充放电循环的过程中，溶解出的钴离子的量是很少的，从而电镀至负极活性材料层中的钴元素的含量更是少量的。在一些实施例中，基于所述负极活性材料层的总重量，每圈循环后，所述负极上的Co浓度的增量为Q，其中Q≤10ppm，Q≤7ppm，Q≤5ppm，Q≤3ppm，或者Q≤2ppm。在一些实施例中，当电化学装置的放电容量衰减至初始容量的80％-90％时，每圈循环后，所述负极上的Co浓度的增量Q满足Q≤10ppm，Q≤7ppm，Q≤5ppm，Q≤3ppm，或者Q≤2ppm。
在对正极活性材料改性的基础上，若进一步对电解液体系进行改进，能够更好地抑制正极活性材料与电解液之间的副反应，从而更好地发挥电化学装置在高电压下的电化学表现。
电解液可包括有机溶剂、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。在一些实施例中，本申请的电解液的有机溶剂包括或选自：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)、丙酸甲酯、丙酸乙酯或丙酸丙酯中的至少一种。
在一些实施例中，本申请的电解液的锂盐包括或选自：六氟磷酸锂(LiPF 6)、双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2(简写为LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO 2F) 2)(简写为LiFSI)、双草酸硼酸锂LiB(C 2O 4) 2(简写为LiBOB)、四氟磷酸草酸锂(LiPF 4C 2O 2)、二氟草酸硼酸锂LiBF 2(C 2O 4)(简写为LiDFOB)、六氟铯酸锂(LiCsF 6)或二氟磷酸锂(LiPO 2F 2)中的至少一种。
作为对电解液体系的一种改进，在一些实施例中，本申请电解液还包括含腈添加剂。其中，含腈添加剂在电化学装置充放电的过程中，会在正极活性材料的表面发生化学反应或者物理吸附，在其表面形成特定的性能优良的腈保护膜结构，稳定正极界面结构，对正极活性材料实施保护，促使正极活性材料在高电压充放电下的结构稳定性。
在一些实施例中，所述含腈添加剂包括或者选自己二腈、丁二腈、戊二腈、丙二腈、2-甲基戊二腈、庚二腈、癸二腈、壬二腈、1,4-二氰基-2-丁烯、乙二醇双(丙腈)醚、3,3'-氧二丙腈、硫代丙二腈、己-2-烯二腈、丁烯二腈、2-戊烯二腈、乙基丁二腈、己-3-烯二腈、2-亚甲基戊二腈、4-氰基庚二腈、1,3,5-己烷三甲腈、1,2,3-丙烷三甲腈、1,2,3-三(2-氰氧基)丙烷、1,3,5-戊烷三甲腈、1,3,6-己烷三甲腈或三乙腈氨中的至少一种。在一些实施例中，所述含腈添加剂包括或者选自己二腈、丁二腈、1,3,5-戊烷三甲腈、1,3,6-己烷三甲腈、1,2,6-己烷三甲腈或三乙腈氨中的至少一种。
其中，1,3,6-己烷三甲腈是一种分子长度适中，富含活性基团的添加剂，与本发明所述具有59Co NMR双峰的锂钴氧化物正极活性材料配合应用时，能够发挥出非常好的效果。这可能是由于，本申请的正极活性材料中的钴处于轻微不对称的化学环境中，1,3,6-己烷三甲腈同样是一种轻微不对称的物质，在电化学体系中，能够更好地与正极活性材料相互作用，在首次充放电的过程中，在正极活性材料的表面形成坚固稳定的固体电解质界面(SEI)膜，加强对正极活性材料的保护，从而优化电化学装置的循环稳定性和倍率性能。
含腈添加剂的保护效果与其用量有一定的相关性。在一些实施例中，基于所述电解液的总重量，所述含腈添加剂的含量为0.01wt％至20wt％、0.01wt％至10wt％、0.1wt％至20wt％、0.1wt％至10wt％、1wt％至20wt％或者1wt％至10wt％。
在一些实施例中，本申请的电化学装置还包括设置在正极与负极之间的隔离膜以防止短路。本申请对电化学装置中使用的隔离膜的材料和形状没有特别限制，其可为现有技术中公开的任何材料和形状。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。
在一些实施例中，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。基材层的材料可以包括或者选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体地，可选用聚乙烯多孔膜、聚丙烯多孔膜、聚乙烯无纺布、聚丙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜等。
表面处理层可以是，但不限制于，聚合物层、无机物层或者由聚合物与无机 物形成的混合层。
其中，无机物层可以包括无机颗粒和粘结剂。无机颗粒可以包括或者选自氧化铝、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。粘结剂可以包括或者选自聚偏氟乙烯、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。
其中，聚合物层可以包括聚合物。聚合物的材料可以包括或者选自聚酰胺、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、聚(偏氟乙烯-六氟丙烯)中的至少一种。
本领域的技术人员将理解，本申请的电化学装置可以为锂离子电池，也可以为其他任何合适的电化学装置。在不背离本申请公开的内容的基础上，本申请的电化学装置包括发生电化学反应的任何装置，它的具体实例包括所有种类的一次电池、二次电池、太阳能电池或电容器。特别地，所述电化学装置是锂二次电池，包括锂金属二次电池、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、正极活性材料的制备方法
为了获得本申请所述的具有59Co NMR双峰的正极活性材料，本申请还提供了用于制备上述正极活性材料的方法。
以正极活性材料Li aCo Ⅰ b1Co Ⅱ b2M cO dE e为例，其中M包括或选自以下元素中的一种或多种：Al、Mg、Ca、Zn、Ti、Zr、Nb、Mo、La、Y、Ce、Ni、Mn、W和Ho；E包括或选自以下元素中的一种或多种：F、S、B、N和P。其中一种方法为在M元素和E元素掺杂的过程中，加入不同的添加剂调节反应条件以实现M和E元素的掺杂。添加剂能够促进掺杂元素M和H的扩散与分布，使其合理地占据晶格位置，创造合理的空位分布，从而对钴的化学环境产生影响。
具体地，该方法可以包括以下步骤：
(1)首先将锂源、钴源、M源和添加剂Aa按照一定比例混合，得到混合物；
(2)将(1)中的混合物搅拌至混合均匀；
(3)将(2)中混合均匀的粉末进行高温处理，并研磨，过筛；
(4)将(3)中经高温处理的粉末冷却后与E源和添加剂Ab按照一定比例混合；
(5)将(4)中的混合物搅拌至混合均匀；
(6)将(5)中混合均匀的粉末进行高温处理，并研磨，过筛后得到具有59Co NMR双峰的锂钴氧化物正极活性材料。
其中在上述步骤(1)的混合物中，锂源和钴源的锂钴摩尔比为0.97至1.08；M源与钴源的M与Co的摩尔比为0.0001至0.2；添加剂Aa与M源的摩尔比不高于0.05。添加剂Aa包括但不限于碳酸钠、草酸钠、氟化铵、氟化钠等的一种或多种。
其中在所述步骤(2)和(5)中，粉末混合均匀的标准是没有明显团聚和分离。例如，在所述步骤(2)和(5)中，可以将混合物放入搅拌罐中搅拌3h至6h至混合物均匀混合。
其中在所述步骤(3)中，高温处理的温度范围为800℃至1100℃，高温处理的时间为6h至24h。
其中在所述步骤(4)中，H源和钴源中的H与Co的摩尔比为0.0001-0.1；添加剂Ab与E源的摩尔比不高于0.02。添加剂Ab包括但不限于硫酸铵、聚乙二醇、草酸锂中的一种或多种。
其中在所述步骤(6)中，高温处理的温度范围为300℃至1000℃的，高温处理的时间为4h至24h。
其中在所述步骤(3)和(6)中，高温处理的气氛为空气或惰性气体。惰性气体可以为，但不限于，氦气、氩气、氮气中的至少一种；过筛的标准为100目至500目。
以正极活性材料Li aCo Ⅰ b1Co Ⅱ b2M cO dE e为例，另一种方法为控制反应前驱体的合成工艺得到两种不同的锂钴氧化物的前驱体，其中一种先预烧，然后再与另一种前驱体混合后反应。由于不同的组分反应程度存在差异，烧结后的产物就含有了一定浓度的空位，从而在正极活性材料中为Co创造两种不同的化学环境。具体地，该方法可以包括以下步骤：
(1)首先将锂源和钴源按照锂钴摩尔比为0.97至1.08的比例混合，得到A混合物；将另一种锂源和另一种钴源按照锂钴摩尔比为0.95至1.05的比例混合，得到B混合物；
(2)分别在不同的搅拌装置中搅拌A混合物和B混合物至混合均匀；
(3)将(2)中混合均匀的A混合物进行高温处理，并研磨，过筛；
(4)将(3)中经高温处理的粉末冷却后与(2)中的B混合物按照重量比2：1至10：1的比例进行混合；
(5)将(4)中的混合物搅拌至混合均匀；
(6)将(5)中混合均匀的粉末进行高温处理，并研磨，过筛后得到具有59Co NMR双峰的锂钴氧化物正极活性材料。
其中在上述步骤中，粉末混合均匀的标准是没有明显团聚和分离。例如，可以将混合物放入搅拌罐中搅拌3h至6h至混合物均匀混合。
其中在所述步骤(3)中，高温处理的温度范围为200℃至500℃，高温处理的时间为1h至6h；在所述步骤(6)中，高温处理的温度范围为500℃至1100℃，高温处理时间为6h至24h。
其中在所述步骤(3)和(6)中，高温处理的气氛为空气或惰性气体。惰性气体可以为，但不限于，氦气、氩气、氮气中的至少一种；过筛的标准为100目至500目。
本申请对锂源、钴源、M源和E源的种类没有特别限制，只要能够有效提供锂元素、钴元素、M元素和E元素的物质，本领域技术人员可以根据实际需要灵活选择。在本申请的一些实施例中，锂源可以，但不限制，为氢氧 化锂、碳酸锂、乙酸锂、草酸锂、氧化锂、氯化锂、硫酸锂、硝酸锂中的一种或几种。在本申请的一些实施例中，钴源可以，但不限制，为氢氧化钴、碳酸钴、乙酸钴、草酸钴、氧化钴、氯化钴、硫酸钴、硝酸钴中的一种或几种。在本申请的一些实施例中，M源可以，但不限制，为元素M的硝酸盐、氢氧化物、氧化物，过氧化物，硫酸盐、碳酸盐中的一种或多种。E源可以，但不限制，为元素E的氢化物、氧化物、酸、盐中的一种或多种。
四、应用
本申请电化学装置的用途没有特别限定，其可用于现有技术中已知的任何用途。根据本申请的一些实施例，本申请的电化学装置可以用于电子装置，其中电子装置包括，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、家庭用大型蓄电池和锂离子电容器等。
下面以锂离子电池为例并且结合对比例及实施例对本发明的技术方案作进一步的说明，但并不局限于此。本领域的技术人员将理解，本申请中描述的制备方法仅是示范实施例，凡是对本发明技术方案进行修改或者同替换，而不脱离本发明技术方案的范围，均应涵盖在本发明的保护范围中。
五、实施例
锂离子全电池的制备
采用以下制备方法将实施例和对比例中的正极活性材料制备成锂离子全电池。
(1)正极的制备：将以下实施例和对比例所制备的正极活性材料、导电碳黑、粘结剂聚偏二氟乙烯(PVDF)按重量比96：2：2在N-甲基吡咯烷酮中充分搅拌混合均匀制成正极浆料，然后将所得正极浆料均匀涂布在正极集电 体铝箔的正反两面上，之后在85℃下烘干，得到正极活性材料层，之后经过冷压得到正极活性材料层，分条、裁片、焊接正极极耳，得到正极。
(2)负极的制备：将负极活性物质人造石墨、粘结剂丁苯橡胶(SBR)、增稠剂碳甲基纤维素钠(CMC)按照重量比97.5：1.5：1在去离子水中充分搅拌混合均匀制成负极浆料，之后将负极浆料均匀涂覆在负极集电体铜箔的正反两面上，然后在85℃下烘干，形成负极活性材料层，然后进行冷压得到负极活性材料层，分条、裁片、焊接负极极耳，得到负极。
(3)电解液的制备：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LiPF 6溶解于上述溶剂，LiPF 6的含量为1mol/L，加入1.5％的1,3丙烷磺内酯和3％的氟代碳酸乙烯酯。其中各物质含量是以电解液的总重量计。
(4)隔离膜的制备：隔离膜采用陶瓷涂覆的聚乙烯(PE)材料隔离膜。
(5)锂离子电池的组装：将正极、隔离膜、负极按顺序叠好，使隔离膜处于正负极中间起到隔离的作用。然后卷绕、置于包装壳中，注入电解液并封装，进行化成之后制成最终的锂离子电池。
锂离子半电池(扣式电池)的制备
使用与上述全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：从全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。
(3)电解液的制备：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LiPF 6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、 0.5％的1,3,6-己烷三甲腈和2％的己二腈。其中各物质含量是以电解液的总重量计。
核磁共振测试的样品制备
从全电池的正极随机选取双面区，利用DMC清洗，除去其中一面，获得单面正极片。将单面正极片制备成对锂片的扣式电池。将扣式电池在10mA/g电流密度下恒流放电，至截止电压3.0V为止。静置5min，再次将扣式电池在10mA/g电流密度下恒流放电，至截止电压3.0V为止以使得扣式电池完全处于满放状态。将正极活性材料从正极片中刮下，待用于核磁共振测试。
正极活性材料的核磁共振测试
使用型号为BRUKER AVANCE III、频率为400MHz的宽腔固体核磁共振谱仪对正极活性材料进行核磁共振测试，获得59Co的核磁共振谱。选用直径为1.3mm的转子，采用魔角旋转，转速为35kHz，采谱时间为6min到5h。最后将所有的谱图结果进行归一化处理。使用origin软件从所得的核磁共振谱图中读取半峰宽和峰面积的数值。
循环充放电测试
将采用所有对比例和实施例的正极活性材料制备的锂离子全电池各组取5支，通过以下步骤对锂离子电池进行充放电，并计算锂离子电池的循环容量保持率。
首先，在25℃的环境中，进行第一次充放电循环。以0.5C的电流(即2h内完全放掉理论容量的电流值)对锂离子电池进行恒流充电和恒压充电，直到上限电压4.53V；然后以0.5C的电流对锂离子电池进行恒流放电，直到截止电压3.0V，记录首次循环的放电容量C 1(也称为初始放电容量)。随后，进行250次的充放电循环，记录第250次循环的放电容量C 250。
利用如下公式计算锂离子电池的循环容量保持率：(C 250/C 1)×C如下公。
倍率性能测试
采用所有对比例和实施例的正极活性材料制备的锂离子全电池，通过以下步骤对锂离子电池进行充放电，并以0.2C下的锂离子电池的放电容量为基准，计算锂离子电池在2C下的放电容量保持率。
首先，在25℃的环境中，静置5min后，用0.2C放电至3V，并且静置5min；之后以0.2C充电至4.5V，静置5min，再用0.2C放电至3.0V，记录容量C 0.2。此后重复该步骤，保持每次充电步骤一致，但放电倍率变为2C，并记录容量C 2。
利用如下公式计算锂离子电池在2C下的放电容量保持率：(C 2/C 0.2)×100％。
直流阻抗DCR测试
将全电池在10mA/g的电流密度下满充至4.53V，静置10min后，以10mA/g的电流密度放电至3.0V，记录其放电容量C。静置5min后，以0.7C的电流恒流充电至4.53V，然后恒压充电至电流小于0.05C。静置10min后，以0.1C的电流放电3h，随后以1C的电流放电1秒，采集数据分析获得DCR数据，获得初始数据，记为D0。
之后将全电池在0.7C的充电倍率和1.0C的放电倍率下，在3.0V至4.53V的电压区间进行10次充放电循环后，按照上述测试流程再次测得DCR，记为D10，平均增长率＝(D10-D0)/10。
副产物层厚度测试、副产物EDS测试、开裂测试和钴堆积测试的样品制备
将全电池在10mA/g的电流密度下放电至3.0V，静置10min后再次以10mA/g的电流密度放电至3.0V。在干燥房或者手套箱内将电池拆解，获取正极、负极，并晾干。拆剪2cm×2cm面积的极片，并立即真空封装。
副产物层厚度测试
随机选取一处极片位置，利用离子抛光机(日本电子-IB-09010CP)加工，得到垂直于集流体方向的断面。利用扫描电子显微镜对其断面进行拍摄，拍摄倍数不低于5.0K，获得图像。
选取处于极片内部的直径不小于5μm的颗粒，在同一颗粒上选取副产物层厚度最大的位置，在副产物的最低点和最高点画平行线，平行线间的距离即为此颗粒的副产物层厚度。选取10个满足上述测试条件的不同颗粒，测量各个颗粒的副产物层厚度，计算平均值，记为副产物层厚度。
副产物EDS测试
随机选取一处极片位置，利用离子抛光机(日本电子-IB-09010CP)加工，得到断面。利用扫描电子显微镜对其断面进行拍摄，拍摄倍数不低于5.0K，获得图像。
选取颗粒表面副产物的位置进行X射线能谱分析，以碳、氧、氮、氟四种元素的总重量为基准，分别测得氟元素和氮元素的平均百分含量，并分别记为ωF和ωN。ωF指的是氟元素在上述4种元素中的百分比，ωN指的是氮元素在上述4种元素中的百分比。选取3处以上副产物位置进行分析测定，将平均后的结果作为副产物中的元素含量。
开裂测试
随机选取一处极片位置，利用离子抛光机(日本电子-IB-09010CP)加工，得到断面。利用扫描电子显微镜对其断面进行拍摄，拍摄倍数不低于1.0K，获得图像。统计100个直径不小于5μm的颗粒，其中SEM图像中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的纹路，视为裂纹。记录开裂的颗粒总数N，开裂率＝N/100。
钴堆积测试
将全电池中的负极制备成扣式电池，并在3.0V至4.53V的电压窗口下进行充放电循环。充放电的电流大小为10mA/g，循环的温度为25℃，循环的圈数为10圈。分别获得循环前后的负极片并利用电感耦合等离子体(ICP)测定钴含量。将钴含量的差值除以循环圈数，计算得到平均值为每圈循环前后Co浓度的增量Q。
以下将详细描述本申请所提供的正极活性材料的具体实施方式。
实施例1-9和对比例1-4
实施例1
将碳酸锂、四氧化三钴、硝酸铝、氧化镧和氟化钠按照如下比例混合：锂钴摩尔比为1：1.05，铝和镧与钴的摩尔比分别为0.3％和0.1％，氟化钠与硝酸铝的摩尔比为1：100。混合均匀后，在空气中，1000℃下烧结12h，冷却后，研磨并过筛。将过筛后的粉末与氧化铝以质量比2000：1混合，充分混合均匀后，在空气中以600℃充烧结6h，冷却，研磨并过筛，以在正极活性材料表面进一步包覆铝元素。
实施例2
将碳酸锂、四氧化三钴、硝酸镁、氧化锆和氟化钠按照如下比例混合：锂钴摩尔比为1：1.05，镁和锆与钴的摩尔比分别为0.2％和0.1％，氟化钠与硝酸镁的摩尔比为1：200。混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛。将过筛后的粉末与氧化铝以质量比2000：1混合，充分混合均匀后，在空气中以600充烧结6h，冷却，研磨并过筛，以在正极活性材料表面进一步包覆铝元素。
实施例3
将碳酸锂、四氧化三钴、硝酸铝、氧化镧和草酸钠按照如下比例混合：锂钴摩尔比为1：1.05，铝和镧与钴的摩尔比分别为0.3％和0.1％，草酸钠与硝酸铝的摩尔比为1：100。混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛。将过筛后的粉末与氧化镁以质量比2000：1混合，充分混合均匀后，在空气中以600℃充烧结6h，冷却，研磨并过筛，以在正极活性材料表面进一步包覆镁元素。
实施例4
将碳酸锂、四氧化三钴、硝酸铝和草酸钠按照如下比例混合：锂钴摩尔比为1：1.05，铝钴的摩尔比为0.3％，草酸钠与硝酸铝的摩尔比为1：100。混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛。将过筛后的粉末与氟化铵按照氟钴的摩尔比为0.1％混合，并添加草酸锂，草酸锂与氟化铵的摩尔比为1： 100，将上述混合物充分混合均匀后，在空气中以600℃烧结6h，冷却，研磨并过筛。
实施例5
将碳酸锂和含1.2％Al元素的Co 3O 4以锂钴比1：1.05的比例混合均匀，得到混合物A；将氯化锂和含0.06％La元素的Co 3O 4以锂钴比1：1.045混合均匀，得到混合物B；将混合物A在350℃反应2h，冷却后与混合物B以质量比1：5充分混合，并在1000℃，下反应12h。冷却，研磨并过筛。
实施例6
将碳酸锂和含0.14％Ti元素的Co 3O 4以锂钴比1：1.05混合均匀，得到混合物A；将氯化锂和含0.011％Y元素的Co 3O 4以锂钴比1：1.045混合均匀，得到混合物B；将混合物A在350℃反应2h，冷却后与混合物B以质量比1：6充分混合，并在1000℃，反应12h。冷却，研磨并过筛。将其与氧化镁以质量比2000：1混合均匀，在600℃反应6h。冷却，研磨并过筛，以在正极活性材料表面进一步包覆镁元素。
实施例7
将碳酸锂、四氧化三钴、氧化钛和氟化铵按照如下比例混合：锂钴摩尔比为1：1.05，钛钴的摩尔比为0.05％，氟化铵与氧化钛的摩尔比为1：100。混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛。将过筛后的粉末与氟化铵按照氟钴的摩尔比为0.195％混合，并添加草酸锂，草酸锂与氟化铵的摩尔比为1：100，将上述混合物充分混合均匀后，在空气中以600℃烧结6h，冷却，研磨并过筛。
实施例8
将碳酸锂和含0.1％Mg元素的Co 3O 4以锂钴比1：1.05混合均匀，得到混合物A；将氯化锂和含0.05％Nb元素的Co 3O 4以锂钴比1：1.045混合均匀，得到混合物B；将混合物A在350℃反应2h，冷却后与混合物B以质量比1：4充分混合，并在1000℃，反应12h。冷却，研磨并过筛。将其与氧化钛以质量比2000：1混合均匀，在600℃反应6h，冷却，研磨并过筛，以在正极活性材料表面进一 步包覆钛元素。
实施例9
将碳酸锂、四氧化三钴、氧化镁、氧化铌和氟化铵按照如下比例混合：锂钴摩尔比为1：1.05，镁钴的摩尔比为0.2％，铌钴比为0.04％，氟化铵与氧化镁的摩尔比为1：100。混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛。将过筛后的粉末与氟化铵按照氟钴的摩尔比为0.095％混合，并添加草酸锂，草酸锂与氟化铵的摩尔比为1：100，将上述混合物充分混合均匀后，在空气中以600℃烧结6h，冷却，研磨并过筛。
对比例1
将碳酸锂、四氧化三钴和硝酸铝按照如下比例混合：锂钴比1：1.05，铝元素和钴元素的摩尔比为0.3％。混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛。将过筛后的粉末与氧化铝以质量比2000：1混合，充分混合均匀后，在空气中以600充烧结6h，冷却，研磨并过筛，以在正极活性材料表面进一步包覆铝元素。
对比例2
将碳酸锂、四氧化三钴按照如下比例混合：锂钴比1：1.05，在空气中，1000℃烧结12h，冷却后，研磨并过筛。
对比例3
将碳酸锂、四氧化三钴和硝酸铝按照如下比例混合：锂钴比1：1.05，铝元素和钴元素的摩尔比为0.3％。混合均匀后，在空气中，900℃烧结12h，冷却后，研磨并过筛。
对比例4
将碳酸锂、四氧化三钴和氧化镧按照如下比例混合：锂钴比1：1.05，镧元素和钴元素的摩尔比为0.3％。混合均匀后，在空气中，1000℃烧结12h，冷却后，研磨并过筛。
上述实施例1-9和对比例1至4中的锂离子电池中的电解液中均添加了含量 为2.5wt％的己二腈。参见下述表1-1，相较于对比例1至4，实施例1至9中的正极活性材料中的钴元素在59Co NMR谱图中的13900ppm至14300ppm的范围内存在两个峰，且这两个峰的半峰宽和峰面积的数值见表1-1。参见表1-1的电化学数据可知，实施例1至9的锂离子电池在3.0V-4.53V的电压窗口下的循环容量保持率均在85％以上，显著高于对比例1至4的锂离子电池。另外，实施例1至9的锂离子电池在2C大电流下的放电容量保持率均高于对比例1至4，这表明实施例1至9的锂离子电池相较于对比例1至4而言具备优异的倍率性能。
当实施例1至9中的锂离子电池的放电容量衰减至初始放电容量的80％时，测得如下述表1-2中的数据。实施例1至9中的锂离子电池中的负极活性材料层中的Co元素的浓度增量Q均显著小于对比例1至4中的锂离子电池。另外，实施例1至9中的锂离子电池中的正极活性材料颗粒表面的副产物层的厚度也均小于对比例1至4中的锂离子电池，且副产物中氟元素的平均百分含量与氮元素的平均百分含量的差值均大于6％。再者，实施例1至9中的直径不小于5μm的正极活性材料颗粒的开裂率也远远小于对比例1至4中的正极活性材料颗粒。最后，每圈循环前后，实施例1至9中的锂离子电池的直流阻抗DCR的平均增长率几乎小于1.3％，而这显著低于对比例1至4中的锂离子电池。
表1-1
Figure PCTCN2020079955-appb-000001
Figure PCTCN2020079955-appb-000002
注释：相较于过筛后的粉末，由于氧化铝、氧化镁或氧化钛的加入量较少，因此后期经包覆的铝元素、镁元素或钛元素没有写入表1所示的正极活性材料的分子式中。
表1-2
Figure PCTCN2020079955-appb-000003
Figure PCTCN2020079955-appb-000004
实施例10-15
实施例10至15对应于实施例1，但是其与实施例1的不同之处在于：进一步修改电解液中的组分和含量。具体的成分和含量以及所获得的电化学数据可参见下述表2。
表2
Figure PCTCN2020079955-appb-000005
实施例10至15均在电解液中同时添加了两种含腈添加剂。与实施例1 相比较，实施例10至15的电化学装置的循环性能和倍率性能均有了进一步的改进。此外，在所添加的含腈添加剂的总含量不变的前提下，1,3,6-己烷三甲腈的加入能够进一步有效地改善电化学装置在高电压窗口下的循环性能和倍率性能。
以上实施例充分说明了通过在正极活性材料中引入合理的空位分布，本申请所述的正极活性材料在高电压窗口下能够持续保持结构稳定性。因此，采用本申请所述的正极活性材料的电化学装置能够在高电压下呈现出出色的循环性能和倍率性能。此外，通过配合本申请所述的正极活性材料对电解液体系进行改进，能够进一步优化电化学装置在高电压下的电化学表现。
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 (11)

  1. 一种正极活性材料，所述正极活性材料的59Co NMR谱中存在第一峰和第二峰，其中所述第一峰的中心位置位于A ppm处，所述第二峰的中心位置位于B ppm处，其中13900≤A<B≤14300。
  2. 根据权利要求1所述的正极活性材料，其中所述第一峰的半峰宽为HA和所述第二峰的半峰宽为HB，且其中0.017≤HB/HA≤90.2。
  3. 根据权利要求1所述的正极活性材料，其中所述第一峰的峰面积为SA和所述第二峰的峰面积为SB，且其中0<SA/SB≤0.3。
  4. 根据权利要求1所述的正极活性材料，其包括下述式Ⅰ化合物：
    Li aCo Ⅰ b1Co Ⅱ b2M cO dE e  (式Ⅰ)；
    其中0.95≤a≤1.05，0<b1<b2<1，b1+b2≤1，0≤c≤0.2，0<d≤2，0≤e≤0.1；其中M选自Al、Mg、Ca、Zn、Ti、Zr、Nb、Mo、La、Y、Ce、Ni、Mn、W或Ho中的一种或多种元素；E选自F、S、B、N或P中的一种或多种元素。
  5. 一种电化学装置，其包括正极、负极和电解液，
    其中所述正极包括正极集流体和正极活性材料层，所述正极活性材料层包括权利要求1-4中任一项所述的正极活性材料。
  6. 根据权利要求5所述的电化学装置，其中所述正极活性材料包括直径不小于5μm的颗粒，当所述电化学装置的放电容量衰减为初始容量的80％至90％时，所述直径不小于5μm的颗粒的开裂率不大于25％。
  7. 根据权利要求5所述的电化学装置，其中当所述电化学装置的放电容量衰减至不低于初始放电容量的80％时，每圈循环后，所述电化学装置的直流阻抗增长率小于1.5％。
  8. 根据权利要求5所述的电化学装置，其中所述正极活性材料颗粒表面包含副产物层，当所述电化学装置的放电容量衰减为初始放电容量的80％至90％时，所述副产物层的厚度为ημm，η≤0.5。
  9. 根据权利要求8所述的电化学装置，其中所述副产物层包含碳元素、氧元素、氟元素和氮元素，以碳元素、氧元素、氟元素和氮元素的总重量计，其中氟元素的平均百分含量为ωF，氮元素的平均百分含量为ωN，其中ωF-ωN≥5％。
  10. 根据权利要求5所述的电化学装置，
    其中所述电解液包括含腈添加剂，其中所述含腈添加剂包括以下各者中的至少一种：己二腈、丁二腈、1,3,5-戊烷三甲腈、1,3,6-己烷三甲腈、1,2,6-己烷三甲腈或三乙腈氨；
    其中基于所述电解液的总重量，所述含腈添加剂的含量为0.1％至10％。
  11. 一种电子装置，其包含权利要求5-10中任一项所述的电化学装置。
PCT/CN2020/079955 2020-03-18 2020-03-18 正极活性材料及包含其的电化学装置 WO2021184247A1 (zh)

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