WO2022133894A1 - 正极及电化学装置 - Google Patents

正极及电化学装置 Download PDF

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WO2022133894A1
WO2022133894A1 PCT/CN2020/138985 CN2020138985W WO2022133894A1 WO 2022133894 A1 WO2022133894 A1 WO 2022133894A1 CN 2020138985 W CN2020138985 W CN 2020138985W WO 2022133894 A1 WO2022133894 A1 WO 2022133894A1
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positive electrode
transition metal
metal composite
composite oxide
lithium transition
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French (fr)
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王凯
吴霞
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Dongguan Amperex Technology Ltd
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Dongguan Amperex Technology Ltd
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Priority to CN202210819420.7A priority Critical patent/CN115275099B/zh
Priority to KR1020237017811A priority patent/KR20230084591A/ko
Priority to CN202080034071.7A priority patent/CN113875042B/zh
Priority to PCT/CN2020/138985 priority patent/WO2022133894A1/zh
Priority to JP2023513778A priority patent/JP7561973B2/ja
Priority to EP20966466.3A priority patent/EP4207354A4/en
Publication of WO2022133894A1 publication Critical patent/WO2022133894A1/zh
Priority to US18/193,938 priority patent/US20240021810A1/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
    • H01M4/13—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
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/446—Initial charging measures
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/448—End of discharge regulating measures
    • 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
    • H01M4/364—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
    • 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

  • the present application relates to the field of battery technology, and in particular, to positive electrodes and electrochemical devices.
  • an object of the present application is to propose a positive electrode, which can improve the side contact with the electrolyte by controlling the morphology of the lithium transition metal composite oxide and the orientation of the lithium transition metal composite oxide on the surface of the current collector.
  • the lithium transition metal composite oxide has the ability to deintercalate lithium ions, improve the stability of the positive electrode, and alleviate problems including powdering caused by particle phase transition.
  • the present application provides a positive electrode.
  • the positive electrode comprises: a positive electrode active material layer located on the current collector, the positive electrode active material layer comprises a lithium transition metal composite oxide, the average particle size of the lithium transition metal composite oxide in a direction parallel to the plane of the current collector is Dp, the lithium transition metal composite oxide The average particle size of the metal composite oxide in the direction perpendicular to the plane of the current collector is Dv, which satisfies 1.1 ⁇ Dp/Dv ⁇ 2.3.
  • the inventors found that by controlling the shape of the lithium transition metal composite oxide particles and regulating the orientation of their distribution on the surface of the current collector, the phase transition of the lithium transition metal composite oxide during the use process (charging and discharging) of the cathode can be alleviated. Problems such as pulverization caused by cracking, the cathode has good high-pressure cycle performance.
  • the lithium transition metal composite oxide satisfies: 5 ⁇ m ⁇ Dp ⁇ 25 ⁇ m. Therefore, the lithium transition metal composite oxide has a better orientation on the current collector, which can make the dominant crystal plane and the non-dominant crystal plane in the particles more reasonably arranged, so that the positive electrode can have a better high-pressure cycle. performance.
  • the lithium transition metal composite oxide satisfies: 0.8 ⁇ (Dp+Dv)/2D N50 ⁇ 1.25, where D N50 is the median particle size of the lithium transition metal composite oxide.
  • the lithium transition metal composite oxide has an R-3m space group structure.
  • the lithium transition metal composite oxide includes Li x1 Ni y1 Co z1 Mn k Z q O ba Ta , wherein Z includes B, Mg, Al, Si, P, S, Ti, Cr, Fe , at least one of Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb and Ce, T is halogen, and x1, y1, z1, k, q, a and b Respectively satisfy: 0.2 ⁇ x1 ⁇ 1.2, 0 ⁇ y1 ⁇ 1, 0 ⁇ z1 ⁇ 1, 0 ⁇ k ⁇ 1, 0 ⁇ q ⁇ 1, 1 ⁇ b ⁇ 2, and 0 ⁇ a ⁇ 1.
  • the lithium transition metal composite oxide has a P63mc space group structure.
  • the lithium transition metal composite oxide includes Li x2 Na z2 Co 1-y2 M y2 O 2 ⁇ n X n , where 0.6 ⁇ x2 ⁇ 0.95, 0 ⁇ y2 ⁇ 0.15, 0 ⁇ z2 ⁇ 0.03, 0 ⁇ n ⁇ 0.2, wherein M includes at least one of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr and Zr, and X is halogen.
  • the positive electrode when the electrochemical device including the positive electrode is charged to a voltage of 4.6V, the positive electrode satisfies: the X-ray diffraction spectrum has at least characteristic peak P 1 and characteristic peak P in the range of 17° to 20° 2 , and the peak intensity I 1 of P 1 is greater than the peak intensity I 2 of P 2 .
  • the positive electrode when the electrochemical device including the positive electrode is discharged to a voltage of 3.0 V, the positive electrode satisfies that the X-ray diffraction spectrum has a characteristic peak P 3 in the range of 17° to 20°.
  • the peak intensity I 3 of P 3 satisfies: (I 1 -I 2 ) ⁇ I 3 ⁇ (I 1 +I 2 ).
  • the positive electrode can have better cycle stability.
  • the ratio I 1 /I 3 of the peak intensity I 1 of P 1 and the peak intensity I 3 of P 3 is not less than 0.8.
  • the lithium transition metal composite oxide in the positive electrode can maintain good crystallinity during cycling.
  • the lithium transition metal composite oxide has a long-axis average particle diameter D 1 and a short-axis average particle diameter D 2 , which satisfy: 1.4 ⁇ (D 1 /D 2 ) ⁇ 5.5. According to some examples of the present application, the lithium transition metal composite oxide has a long-axis average particle size D 1 and a short-axis average particle size D 2 , which satisfy: 1.4 ⁇ (D 1 /D 2 ) ⁇ 3.8. Therefore, the lithium transition metal composite oxide has good particle morphology, and the ratio between active crystal planes and inactive crystal planes is moderate.
  • the positive electrode satisfies: when the electrochemical device including the positive electrode is in the range of 3.0V to 4.6V, when 8 charge-discharge cycles are performed and discharged to a voltage of 3.0V, compared with the positive electrode before cycling, the cycle In the X-ray diffraction spectrum of the cathode, the offset of the front position of the highest peak is not more than 0.1°; the change rate of the half-peak width of the highest peak is less than 5%. Therefore, the positive electrode particles have better cycle performance.
  • the present application proposes an electrochemical device.
  • the electrochemical device includes: the aforementioned positive electrode, a negative electrode, and a separator. Therefore, the secondary battery has all the features and advantages of the aforementioned positive electrode, which will not be repeated here.
  • the surface of the negative electrode has stripes.
  • the present application provides a method for preparing the aforementioned positive electrode.
  • the method includes providing a lithium transition metal composite oxide, and configuring the lithium transition metal composite oxide, a conductive agent and a binder to form a positive electrode slurry; coating the positive electrode slurry on the surface of the current collector;
  • the fluid is subjected to cold pressing, the cold pressing is carried out under the pressure of 30-40 tons, the cold pressing rate is 3-4 m/min, and the compaction is controlled to be 4.05-4.25 g/cm 3 .
  • the aforementioned positive electrode can be easily obtained, and the positive electrode can be made to have better cycle performance.
  • the weight ratio of the lithium transition metal composite oxide to the conductive agent and the binder in the positive electrode slurry is (94-99):(0.5-3):(0.5-3). In this way, a positive electrode slurry having an appropriate ratio of the conductive agent, the lithium transition metal composite oxide, and the binder can be obtained.
  • the method further includes drying the positive electrode slurry on the surface of the current collector; after the cold pressing treatment, the method further includes: drying the current collector. The fluid is cut.
  • the present application proposes a method for modifying a negative electrode.
  • the method includes spreading an additive on the surface of the negative electrode active material layer and performing a rolling process, where the additive includes at least one of lithium powder, lithium ribbon and a lithium-containing compound.
  • FIG. 1 is a schematic structural diagram of a positive electrode in an example of the present application.
  • FIG. 2 is a schematic structural diagram of an electrochemical device in an example of the present application.
  • FIG. 3 is a schematic flowchart of a method for preparing a positive electrode in an example of the present application
  • Example 4 is a scanning electron microscope photograph of a positive electrode in Example 1 of the present application.
  • Fig. 5 is the X-ray diffraction spectrum of the positive electrode in Example 1 of the present application.
  • FIG. 7 is an optical photograph of the negative electrode in Example 1 of the present application.
  • FIG. 9 is a graph showing the cycle performance test results of Example 1 and Comparative Example 1 of the present application.
  • 100 positive electrode; 110: current collector; 120A-120C: lithium transition metal composite oxide; 120: active material layer; 200: separator; 300: negative electrode; 1000: electrochemical device.
  • the current cathodes such as those of lithium-ion secondary batteries, can control the performance of the cathodes by controlling the particle size and morphology of the active Li-containing substances in the lithium transition metal composite oxides, the current cathodes still have a cycle performance that needs to be raise the issue.
  • the inventors found that, in addition to the morphology characteristics of the lithium transition metal composite oxide itself, the orientation of the lithium transition metal composite oxide on the current collector will also affect the performance of the positive electrode.
  • lithium transition metal composite oxides are usually not perfectly symmetrical spherical particles, and the shape of the cathode material is limited by the growth control of its crystal planes. The dominant crystal planes in the particles will grow faster, while other crystal planes are slower.
  • the lithium transition metal composite oxides are mostly ellipsoids rather than perfect spheres.
  • the proportion of crystal planes of the obtained lithium transition metal composite oxide also changes. For example, when there are too many dominant crystal planes in the lithium transition metal composite oxide, the long side of the ellipsoid of the obtained lithium transition metal composite oxide is much larger than the short side; while controlling the proportion of the dominant crystal plane and increasing the other crystal planes, the ellipsoid of the obtained lithium transition metal composite oxide can be obtained. spherical particles.
  • the dominant plane cannot deintercalate lithium, but it is very stable, while the crystal plane with the largest proportion in the non-dominant plane, such as the 104 crystal plane, can deintercalate lithium but is unstable and easy to phase change. . Therefore, when there are too many dominant faces, the delithiation of the material is affected, and the shape is too flat to be processed easily; on the contrary, when there are too many non-dominant faces, the particle surface is unstable and easy to phase change and fail.
  • the lithium transition metal composite oxide, conductive particles, binders and other components are generally configured into a slurry, and then the slurry is coated on the surface of the positive electrode current collector, and then dried, cold pressed, etc. After a series of treatments, the lithium transition metal composite oxide will be distributed on the surface of the current collector with a certain orientation.
  • lithium transition metal composite oxides are not symmetrical particles, if the orientation of lithium transition metal composite oxides distributed on the current collector is not controlled, the performance of lithium transition metal composite oxides cannot be fully utilized.
  • the surface is too much exposed on the side of the current collector facing the electrolyte, although the stability of the positive electrode is better, but the distance between the non-dominant surface and the electrolyte increases, the performance of the lithium extraction and intercalation of the positive electrode will be affected.
  • the non-dominant surface is too much exposed on the side of the current collector facing the electrolyte, the stability of the positive electrode is poor, and the positive electrode material is prone to pulverization.
  • the lithium transition metal composite oxide is damaged during processing, or is unevenly distributed on the surface of the positive electrode current collector, and the orientation is disordered, it is not conducive to the development of the electrochemical performance of the lithium transition metal composite oxide.
  • the present application provides such a positive electrode.
  • the positive electrode 100 includes a current collector 110 and an active material layer 120 , the active material layer 120 is located on the current collector 110 , and the active material layer 120 includes lithium transition metal composite oxides 120A, 120B, and 120C.
  • the ratio Dp/Dv between the average particle diameters Dv in the direction of BB' as shown in the figure satisfies 1.1 ⁇ Dp/Dv ⁇ 2.3.
  • the positive electrode has good high-voltage cycle performance.
  • the positive electrode can be alleviated during the use process (charging and discharging).
  • Lithium transition metal composite oxides have problems such as powdering caused by phase transformation and cracking.
  • the lithium transition metal composite oxides are distributed in a certain orientation during the current collector, controlling the ratio of Dp and Dv of the lithium transition metal composite oxides can better measure the lithium transition metal composite oxides Therefore, it can ensure that the electrochemical performance of the lithium transition metal composite oxide can be well reflected at the level of the positive electrode.
  • the long axis diameter of the lithium transition metal composite oxide is mostly distributed parallel to the plane where the current collector 110 is located (120B as shown in FIG. 1 )
  • the inactive surface is directly opposite to the negative electrode of the battery.
  • the migration path of lithium increases. In this state, the stability of the particles is better, and pulverization is not easy to occur.
  • the lithium transition metal composite oxide is mostly distributed in a state where the long axis diameter is perpendicular to the current collector 110, such as 120A as shown in the figure, at this time, the active surface is facing the negative electrode of the battery, and it is easy to be damaged during the processing. affect the performance of the positive electrode.
  • the processing parameters such as but not limited to the pressure of cold pressing and the direction of pressure, the ratio of Dp and Dv can be guaranteed to be within a certain range.
  • the lithium transition metal composite oxide at this time has enough non-dominant surfaces to face the negative electrode of the battery, which can make the positive electrode have better electrochemical performance, and at the same time, it will not be excessively exposed to the electrolyte due to the dominant surface. One side results in poor cycle performance.
  • Dp/Dv when Dp/Dv is in the range of 1.1-2.3, it can ensure that the positive electrode material particles are distributed evenly on the current collector 110, and at this time, the lithium transition metal composite oxidation is in the direction facing the negative electrode of the battery.
  • the active and inactive sides of the material are within a reasonable range and can be maintained after processing.
  • Dp/Dv is less than 1.1, there are too few inactive crystal planes in the positive electrode facing the negative electrode of the battery, and the lithium transition metal composite oxide is easily damaged and pulverized; if Dp/Dv is greater than 2.3, the lithium transition metal composite oxide on the surface of the positive electrode is too large. Flattened or subjected to overvoltage, affecting the electrochemical performance of the positive electrode.
  • the average particle size is the average diameter of the particles
  • the test method for the average diameter is to randomly select one position of the positive electrode and process it with a slicer to obtain a cross section. Particles in the cross section, their diameters are measured in the parallel and perpendicular directions, respectively, and the size is recorded. Diameter refers to the maximum length of a particle in a defined direction.
  • the statistical method is to select particles in order from left to right and from top to bottom, and the statistical number of the average particle size is 100 particles.
  • the Dp of the inclined lithium transition metal composite oxide 120C as shown in FIG. 1 is the length of the particle along the AA' direction on the cross section of the positive electrode (viewing angle as shown in FIG. 1 )
  • the maximum value, the Dv of the lithium transition metal composite oxide 120C is the maximum value of the length of the particle along the BB' direction.
  • the above-mentioned lithium transition metal composite oxide has a long-axis average particle size D 1 and a short-axis average particle size D 2 , which satisfy: 1.4 ⁇ (D 1 /D 2 ) ⁇ 5.5. According to some examples of this application, 1.4 ⁇ (D 1 /D 2 ) ⁇ 3.8. Therefore, the lithium transition metal composite oxide has good particle morphology, and the ratio between active crystal planes and inactive crystal planes is moderate.
  • the long-axis average particle diameter D 1 satisfies: 7 ⁇ D 1 ⁇ 28 ⁇ m. Therefore, the lithium transition metal composite oxide has good particle morphology, and the ratio between active crystal planes and inactive crystal planes is moderate.
  • the above-mentioned lithium transition metal composite oxide may also satisfy: 5 ⁇ Dp ⁇ 25 ⁇ m. Therefore, the lithium transition metal composite oxide can have a better orientation on the current collector, which can make the dominant crystal plane and the non-dominant crystal plane in the particles more reasonably arranged, so that the positive electrode can have a better high voltage cycle performance.
  • the lithium transition metal composite oxide may further satisfy: 0.8 ⁇ (Dp+Dv)/2D N50 ⁇ 1.25 .
  • D N50 is the median particle size of the lithium transition metal composite oxide.
  • the particle size of general cobalt-based cathode materials is not completely uniform, and the lithium transition metal composite oxide in the cathode may contain large particles, small particles or a mixture of large and small particles. But its particle size can be within a certain range.
  • the D N50 mentioned above in the present application is the average particle diameter of the particles of its median size. The above relationship between Dp, Dv and D N50 can determine whether the shape characteristics of the particle design of the lithium transition metal composite oxide are preserved during the processing process.
  • Dp+Dv when the value of Dp+Dv is much larger or smaller than 2D N50 , it indicates that the particles are damaged during processing, or the distribution of lithium transition metal composite oxides on the surface of the current collector is uneven, or the orientation is disordered. These are not conducive to the development of its electrochemical performance.
  • (Dp+Dv)/2D N50 is between 0.8-1.25, it can be ensured that the lithium transition metal composite oxide is not damaged during processing, or the damage is not enough to seriously affect the performance of the obtained positive electrode , and the lithium transition metal composite oxide can be relatively uniformly distributed on the surface of the current collector with a certain orientation.
  • the specific chemical composition and structure of the lithium transition metal composite oxide are not particularly limited, and those skilled in the art can select according to actual battery performance requirements.
  • the lithium transition metal composite oxide has an R-3m space group structure.
  • the chemical composition of the lithium transition metal composite oxide may be Li x1 Ni y1 Co z1 Mn k Z q O ba Ta , wherein Z includes B, Mg, Al, Si, P, S, At least one of Ti, Cr, Fe, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb and Ce, T is halogen, and x1, y1, z1, k, q, a, and b satisfy: 0.2 ⁇ x1 ⁇ 1.2, 0 ⁇ y1 ⁇ 1, 0 ⁇ z1 ⁇ 1, 0 ⁇ k ⁇ 1, 0 ⁇ q ⁇ 1, 1 ⁇ b ⁇ 2, and 0 ⁇ a ⁇ 1, respectively.
  • the lithium transition metal composite oxide has a P63mc space group structure.
  • the chemical composition of the lithium transition metal composite oxide may be Li x2 Na z2 Co 1-y2 M y2 O 2 ⁇ n X n , where 0.6 ⁇ x2 ⁇ 0.95, 0 ⁇ y2 ⁇ 0.15, 0 ⁇ z2 ⁇ 0.03, 0 ⁇ n ⁇ 0.2, wherein M includes at least one of Al, Mg, Ti, Mn, Fe, Ni, Zn, Cu, Nb, Cr and Zr, such as the element species of M can be one, 2, or 3 or more.
  • y is the sum of the atomic ratios of the plurality of M elements. More specifically, x in Li x2 Na z2 Co 1-y2 My2 O 2 ⁇ n X n may satisfy 0.6 ⁇ x ⁇ 0.85.
  • the electrochemical device including the positive electrode when the electrochemical device including the positive electrode is discharged to a voltage of 3.0 V, the X-ray diffraction spectrum of the lithium transition metal composite oxide has a characteristic peak P 3 in the range of 17° to 20°. And the electrochemical device including the positive electrode will show two phases when charged to 4.6V, the lithium content of the two is different, and the part with lower lithium content accounts for a larger proportion, that is, the battery cell with the positive electrode is charged to 4.6V.
  • the X-ray diffraction spectrum When the voltage is 4.6V, the X-ray diffraction spectrum has at least characteristic peak P 1 and characteristic peak P 2 in the range of 17° to 20°, and the peak intensity I 1 of P 1 is greater than the peak intensity I 2 of the P 2 .
  • the crystallinity determines the properties of the material. The better the crystallinity, the less likely the material will be pulverized, and the better the cycle stability. Specifically, the ratio I 1 /I 3 of the peak intensity I 1 of P 1 and the peak intensity I 3 of P 3 is not less than 0.8. That is to say, its crystallinity is reflected in that the peak intensity I 1 is in a close range compared to the initial peak intensity I 3. If its intensity is lower than 0.8 of I 3 , it indicates that the crystallinity of the material decreases significantly. When discharged to 3.0V, the lithium transition metal composite oxide returns to the initial state. If the material is strained and cracked at this time, I 3 will be lower than I 1 -I 2 .
  • pulverization refers to a process in which the crystallinity of the lithium transition metal composite oxide is reduced by cracking, degradation, and phase transformation. Therefore, the peak intensity I 3 of P 3 satisfies: (I 1 -I 2 ) ⁇ I 3 ⁇ (I 1 +I 2 ), which can make the positive electrode have better crystallinity and better cycle performance.
  • the surface of the negative electrode has stripes parallel to the direction of the crease.
  • the streaks originate from traces left after the additives in the negative electrode have been consumed.
  • the lithium transition metal composite oxide in the positive electrode cooperates with the structure of the negative electrode (such as additives) to have the characteristics of more stable cycle performance, so that the charge-discharge state structure of the positive electrode active material of the positive electrode can be kept stable during its application process. , that is, the crystal structure of the material changes less, that is, I 1 , I 2 and I 3 are more stable.
  • the shift and broadening of its I peak are very small.
  • the shift of the XRD characteristic front means the loss of active lithium
  • the broadening means the material pulverization.
  • the positive electrode exemplified in the present application when the electrochemical device including the positive electrode is in the range of 3.0V to 4.6V, 10 charge-discharge cycles are performed and discharged to a voltage of 3.0V, the highest peak in the X-ray diffraction spectrum can be satisfied.
  • the offset of the front position is not more than 0.1°, and the change rate of the peak width at half maximum of the highest peak is less than 5%. It can be seen that the positive electrode proposed in this application has good stability, and the loss of active lithium during the use of the material and the pulverization of the positive electrode active material (lithium transition metal composite oxide) are less.
  • the present application proposes an electrochemical device.
  • the electrochemical device 1000 includes a positive electrode 100 , a separator 200 and a negative electrode 300 .
  • the positive electrode 100 is as described above, and the separator 200 separates the positive electrode 100 and the negative electrode 300 . Therefore, the electrochemical device has all the features and advantages of the positive electrode described above, which will not be repeated here. In general, the electrochemical device has good cycle performance and capacity.
  • the electrochemical device may further have an electrolyte to realize the function of the electrochemical device.
  • the specific shape of the electrochemical device is not particularly limited, and those skilled in the art can select and design it according to actual needs.
  • the present application provides a method for preparing the aforementioned positive electrode.
  • the method may include:
  • the step may include an operation of providing a lithium transition metal composite oxide and forming a positive electrode slurry.
  • the aforementioned lithium transition metal composite oxide, a conductive agent, and a binder can be configured to form a positive electrode slurry.
  • the weight ratio of the lithium transition metal composite oxide to the conductive agent and the binder in the positive electrode slurry may be (94-99):(0.5-3):(0.5-3).
  • a positive electrode slurry having an appropriate ratio of the conductive agent, the lithium transition metal composite oxide, and the binder can be obtained.
  • the weight ratio of the lithium transition metal composite oxide to the conductive agent and the binder in the positive electrode slurry may be 97:1.4:1.6.
  • the composition and morphology of the lithium transition metal composite oxide have been described in detail above, and will not be repeated here. Those skilled in the art can select an appropriate lithium transition metal composite oxide according to the specific performance requirements of the positive electrode.
  • the specific type of the conductive agent is also not particularly limited, for example, it may be conductive carbon black, graphene, and the like.
  • the binder may be, but not limited to, polyvinylidene fluoride and the like.
  • the previously formed positive electrode slurry may be coated on the surface of the current collector.
  • the specific parameters and manner of coating the positive electrode slurry are not particularly limited, as long as the positive electrode slurry can be uniformly coated on the surface of the current collector side.
  • the current collector with the positive electrode slurry is subjected to cold pressing, specifically, the cold pressing may be performed at a pressure of 30-40 tons, and the cold pressing rate is 3-4 m/min, and control the compaction at 4.05-4.25 g/cm 3 .
  • a positive electrode having an average particle diameter Dp of the lithium transition metal composite oxide in the direction parallel to the plane of the current collector and the average particle diameter Dv of the lithium transition metal composite oxide in the direction perpendicular to the plane of the current collector satisfying the aforementioned conditions can be obtained.
  • the positive electrode has all the features and advantages of the aforementioned positive electrode, which will not be repeated here.
  • the cathode obtained by this method can have better cycle performance.
  • the inventors found that by adjusting the pressure value, the cold pressing rate and the cold pressing compaction in the cold pressing process, the lithium transition metal composite oxide with an appropriate particle shape can be controlled to be uniformly distributed on the surface of the current collector with a certain orientation. In this way, the morphology of the lithium transition metal composite oxide can be kept from being damaged by processes such as cold pressing, and the arrangement of the dominant and non-dominant crystal faces in the lithium transition metal composite oxide on the surface of the current collector can also be adjusted. Therefore, a positive electrode with better cycle performance and electrical performance can be obtained.
  • an operation of drying the positive electrode slurry on the surface of the current collector may be further included.
  • the specific parameters of the drying treatment are not particularly limited, and those skilled in the art can select the parameters and methods of the drying treatment according to the actual situation, so as to obtain a slurry layer with a uniform thickness.
  • the current collector After the cold pressing process, the current collector can be further cut. Thereby, a positive electrode with an appropriate size can be obtained.
  • the anode of the electrochemical device may further have additives.
  • an operation of covering the surface of the negative electrode active material layer with an additive is further included.
  • the additive may be formed on the negative electrode active material layer by performing rolling treatment, for example, the negative electrode with the additive may be rolled at a speed of 0.5-2 m/s under a pressure of 5-30 tons.
  • the additive may include at least one of lithium powder, lithium ribbon, and a lithium-containing compound. Thereby, the quality of the electrochemical device obtained by this method can be further improved.
  • Preparation of positive electrode sheet The positive electrode material obtained in the following example, the conductive carbon black as the conductive agent, and the polyvinylidene fluoride as the binder are mixed in an N-methylpyrrolidone (NMP) solvent system in a ratio of 97:1.5:1.5 by weight. After fully stirring and mixing in the medium, the positive electrode slurry is formed. Using aluminum foil as the current collector, the positive electrode slurry was coated on the current collector with a coating weight of 17.2 mg/cm 2 , and the positive electrode sheet was obtained after drying, cold pressing and cutting.
  • NMP N-methylpyrrolidone
  • negative pole piece copper foil is used for the current collector, artificial graphite is used for the negative electrode active material, and styrene-butadiene rubber and sodium carboxymethylcellulose are used as the binder; artificial graphite, styrene-butadiene rubber and sodium carboxymethylcellulose are used by weight After mixing in a ratio of 96:2:2, it is dispersed in deionized water to form a slurry, stirred evenly, coated on copper foil, dried to form a negative electrode active material layer, and subjected to cold pressing to obtain a negative electrode pole piece.
  • elemental lithium strips are further added on the surface of the negative electrode active material layer in an amount of 2.5 mg/cm 2 , and cold pressed to obtain a negative electrode pole piece containing the additive.
  • Preparation of lithium ion battery stack the positive pole piece, the separator and the negative pole piece in order, so that the separator is in the middle of the positive pole and the negative pole to play the role of isolation, and then the electrode assembly is obtained by winding.
  • the electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80 °C, the above electrolyte is injected and packaged, and the lithium ion battery is obtained through the process of forming, degassing, and shaping.
  • Cycle performance test method the temperature is 25°C, the charging process is 0.7C constant current charge to 4.6V, constant voltage to cut-off current 0.025C, and then 0.5C discharge to 3.0V. Taking the first cycle discharge capacity as 100%, the capacity retention rate of the lithium ion battery after 200 cycles was recorded.
  • X-ray powder diffraction test method adjust the lithium-ion battery to the corresponding voltage at a current density of 10mA/s, and after standing for 5 minutes, disassemble it in a glove box or a drying room. The central part of the positive electrode was selected and cut out to obtain a 3 ⁇ 3 cm piece. Characterization was performed on a Bruker X-ray powder diffractometer, collecting diffraction peaks in the 10-80° range at an acquisition rate of 1° per minute.
  • Test method for Dp and Dv Take the positive electrode piece and process it with a microtome to obtain a cross section perpendicular to the surface of the current collector. For the particles in the cross section, measure their diameters and record the size in the directions parallel to the plane of the current collector and perpendicular to the plane of the current collector. Diameter refers to the maximum length of a particle in a defined direction. And the statistical method is to select particles in order from left to right and from top to bottom, and the statistical number of the average particle size is 100 particles.
  • Add 0.5% of the additive ammonium oxalate of the precipitation quality to the precipitation mix uniformly, and sinter at 800° C. for 24 hours to obtain a precursor. After the precursor and sodium carbonate were uniformly mixed at a ratio of Co:Na chemical dose ratio of 0.99:0.75, the reaction was carried out at 800° C. for 36 hours to obtain a powder material.
  • the positive electrode material Li 0.73 Na 0.01 Co 0.99 Al 0.01 O 2 was obtained.
  • Li 0.73 Na 0.01 Co 0.99 Al 0.01 O 2 positive electrode material powder, conductive carbon, binder in a weight ratio of 97:1.5:1.5, and NMP are mixed together to prepare a slurry, which is coated on the surface of the Al current collector, and Bake in an oven at 120° C. for 2 hours to dryness, and then perform cold pressing under a pressure of 35 tons.
  • the cold pressing rate is 3.5 m/min, and the compaction is controlled at 4.15 g/cm 3 .
  • the positive pole piece is obtained after cutting.
  • An additive elemental lithium strip was arranged on the surface of the negative electrode active material layer, and the additive amount was 2.5 mg/cm 2 , and the negative electrode pole piece with the additive was obtained by rolling.
  • Example 3 It is the same as the preparation method of Example 1, except that the pH of the system is adjusted to 8.7, and the system is fully stirred for 24 hours; the precursor is obtained by sintering at 900 ° C for 36 hours, and finally the positive electrode material Li 0.73 Na 0.01 Co 0.99 Al 0.01 is obtained O 2 .
  • Example 4 It is the same as the preparation method of Example 2, except that sodium carbonate and ammonia water are added to adjust the pH of the system to 8.5, and the precursor is obtained by fully stirring for 24 hours and sintering at 950° C. for 48 hours.
  • Example 6 The preparation method was the same as that of Example 1, except that the negative electrode pole piece was not modified with additives.
  • Example 7 The preparation method was the same as that of Example 1, except that the precursor was obtained by reacting at 950° C. for 48 hours.
  • Example 8 Li 0.7 CoO 2 with R-3m space group structure was used as the positive electrode material.
  • the parameters of slurry and cold pressing are the same as those of Example 1.
  • the negative pole piece is not modified with additives.
  • Example 9 Li 0.75 Co 0.86 Mg 0.14 O 2 with R-3m space group structure was used as the positive electrode material.
  • the parameters of slurry and cold pressing are the same as those of Example 1.
  • the negative pole piece is not modified with additives.
  • Example 10 Li 0.99 Co 0.99 Al 0.01 O 2 with R-3m space group structure was used as the positive electrode material.
  • the parameters of slurry and cold pressing are the same as those of Example 1, and the negative pole piece is not modified with additives.
  • Add 0.5% of the additive ammonium oxalate by the precipitation quality to the precipitation mix uniformly, and sinter at 600° C. for 24 hours to obtain a precursor. After the precursor and sodium carbonate were uniformly mixed in a ratio of Co:Na chemical dose ratio of 0.99:0.77, the reaction was performed at 1000° C. for 36 hours to obtain powder materials.
  • the parameters of slurry and cold pressing are the same as those of Example 1.
  • the negative pole piece is not modified with additives.
  • Comparative Example 2 The preparation method was the same as that of Comparative Example 1, except that sodium hydroxide was added to adjust the pH of the system to 11.8.
  • Comparative Example 3 The preparation method is the same as that of Comparative Example 1, except that the precursor is obtained by sintering at 1000° C. for 24 hours, and the powder material is obtained by reacting at 1050° C. for 24 hours.
  • the negative pole piece is not modified with additives.
  • Comparative Example 4 The preparation method is the same as that of Example 8, except that Li 0.88 CoO 2 with R-3m space group structure is used as the positive electrode material.
  • Comparative Example 5 It is the same as the preparation method of Example 1, except that the cold pressing is carried out under a pressure of 65 tons, the cold pressing rate is 6 m/min, and the compaction is 4.29 g/cm 3 .
  • the negative pole piece is not modified with additives.
  • Comparative Example 6 The preparation method is the same as that of Example 10, but the difference is: Li 0.99 Co 0.99 Al 0.01 O 2 with R-3m space group structure with D1 of 6.4 ⁇ m and D2 of 4.6 ⁇ m is used as the positive electrode material.
  • the cold pressing was 3.94 g/cm 3 .
  • Example 1 X-ray powder diffraction test was carried out on Example 1 and Comparative Example 1.
  • FIGS. 7 and 8 it can be seen that the twisted streaks that appeared in Example 1 did not appear on the surface of Comparative Example 1.
  • FIG. 9 it can be seen that the cycle capacity retention rate of Comparative Example 1 was significantly decreased.
  • Table 1 The test results of the above embodiments and comparative examples are shown in Table 1 below, where Y indicates the presence of negative electrode streaks, and N denotes the absence of negative electrode streaks.

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Abstract

本申请提供了正极、电化学装置及电子装置。其中，正极包括：位于集流体上的正极活性物质层，正极活性物质层包含锂过渡金属复合氧化物，锂过渡金属复合氧化物在平行于集流体所在平面方向上的平均粒径为Dp，锂过渡金属复合氧化物在垂直于所述集流体所在平面方向上的平均粒径为Dv，满足1.1≤Dp/Dv≤2.3。

Description

正极及电化学装置 技术领域
本申请涉及电池技术领域，具体的，涉及正极及电化学装置。
背景技术
随着新能源技术的发展以及储能材料研究的进展，诸如锂离子电池等二次电池得到了更加广泛的应用，市场对于二次电池性能的要求也越发严苛。正极是影响二次电池性能的重要因素，锂过渡金属复合氧化物的形状对正极的容量和稳定性均具有重要影响。
因而，目前的正极及二次电池仍有待改进。
发明内容
本申请旨在至少在一定程度上解决相关技术中的技术问题。为此，本申请的一个目的在于提出一种正极，该正极通过控制锂过渡金属复合氧化物形貌，以及锂过渡金属复合氧化物在集流体表面的取向情况，可提高与电解液接触一侧的锂过渡金属复合氧化物脱嵌锂离子的能力，并可提高正极稳定性，缓解包括颗粒相变而导致的粉化等问题。
在本申请的一个方面，本申请提供了一种正极。该正极包括：位于集流体上的正极活性物质层，正极活性物质层包含锂过渡金属复合氧化物，锂过渡金属复合氧化物在平行于集流体所在平面方向上的平均粒径为Dp，锂过渡金属复合氧化物在垂直于集流体所在平面方向上的平均粒径为Dv，满足1.1≤Dp/Dv≤2.3。发明人发现，通过对锂过渡金属复合氧化物颗粒形状的控制并调控其在集流体表面分布的取向，可缓解正极在使用过程(充电和放电)中由于锂过渡金属复合氧化物发生相变、开裂而导致的粉化等问题，该正极具备较好的高压循环性能。
根据本申请的一些示例，锂过渡金属复合氧化物满足：5μm≤Dp≤25μm。由此，该锂过渡金属复合氧化物在集流体上具有较好的取向，可令颗粒中优势晶面和非优势晶面更加合理地进行排布，从而可令该正极具备较好的高压循环性能。
根据本申请的一些示例，锂过渡金属复合氧化物满足：0.8≤(Dp+Dv)/2D N50≤1.25，其中D N50为锂过渡金属复合氧化物的中值粒径。
根据本申请的一些示例，锂过渡金属复合氧化物具有R-3m空间群结构。
根据本申请的一些示例，锂过渡金属复合氧化物包括Li x1Ni y1Co z1Mn kZ qO b-aT a，其中，Z包括B、Mg、Al、Si、P、S、Ti、Cr、Fe、Cu、Zn、Ga、Y、Zr、Mo、Ag、W、In、Sn、Pb、Sb和Ce中的至少一种，T为卤素，并且x1、y1、z1、k、q、a和b分别满足：0.2<x1≤1.2、 0≤y1≤1、0≤z1≤1、0≤k≤1、0≤q≤1、1≤b≤2以及0≤a≤1。
根据本申请的一些示例，锂过渡金属复合氧化物具有P63mc空间群结构。
根据本申请的一些示例，锂过渡金属复合氧化物包括Li x2Na z2Co 1-y2M y2O 2±nX n，其中0.6<x2<0.95，0≤y2<0.15，0≤z2<0.03，0≤n≤0.2，其中M包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr中的至少一种，X为卤素。
一些示例根据本申请的一些示例，包括正极的电化学装置在充电至电压为4.6V时，正极满足：X射线衍射光谱在17°至20°的范围内至少存在特征峰P 1和特征峰P 2，且P 1的峰强度I 1大于P 2的峰强度I 2。
根据本申请的一些示例，包括正极的电化学装置在放电至电压为3.0V时，正极满足：X射线衍射光谱在17°至20°的范围内存在特征峰P 3。P 3的峰强度I 3满足：(I 1-I 2)≤I 3≤(I 1+I 2)。由此，该正极可具有更好的循环稳定性。
根据本申请的一些示例，P 1的峰强度I 1和P 3的峰强度I 3的比值I 1/I 3不小于0.8。由此，该正极中的锂过渡金属复合氧化物可在循环过程中保持较好的结晶性。
根据本申请的一些示例，锂过渡金属复合氧化物具有长轴平均粒径D 1以及短轴平均粒径D 2，满足：1.4≤(D 1/D 2)≤5.5。根据本申请的一些示例，锂过渡金属复合氧化物具有长轴平均粒径D 1以及短轴平均粒径D 2，满足：1.4≤(D 1/D 2)≤3.8。由此，该锂过渡金属复合氧化物具有较好的颗粒形态，活性晶面和非活性晶面之间的占比适中。
根据本申请的一些示例，7μm≤D 1≤28μm。
根据本申请的一些示例，正极满足：包括正极的电化学装置在3.0V至4.6V的范围内，进行8次充放电循环并且放电至电压为3.0V时，与循环前的正极相比，循环后的正极的X射线衍射光谱中最高峰的锋位置偏移量不大于0.1°；最高峰的半峰宽变化率低于5％。由此，该正极颗粒具有较好的循环性能。
在本申请的另一方面，本申请提出了一种电化学装置。该电化学装置包括：前述的正极、负极、以及隔膜。由此，该二次电池具有前述正极所具有的全部特征以及优点，在此不再赘述。
根据本申请的示例，电化学装置在放电至电压为3.0V时，负极表面具有条纹。
在本申请的又一方面，本申请提出了一种制备前面描述的正极的方法。该方法包括提供锂过渡金属复合氧化物，并将锂过渡金属复合氧化物和导电剂、粘结剂配置形成正极浆料；将正极浆料涂覆在集流体表面；对具有正极浆料的集流体进行冷压处理，冷压处理是在30-40吨的压力下进行的，冷压速率为3-4米/分钟，并控制压密为4.05-4.25g/cm 3。由此，可简便地获得前述的正极，并可令该正极具有较好的循环性能。
根据本申请的一些示例，正极浆料中锂过渡金属复合氧化物和导电剂、粘结剂的重量比为(94-99)：(0.5-3)：(0.5-3)。由此，可获得导电剂、锂过渡金属复合氧化物和粘结剂配比适当的正极浆料。
根据本申请的一些示例，将正极浆料涂覆在集流体表面之后，进行冷压处理之前，方法进一步包括对集流体表面的正极浆料进行干燥处理；冷压处理之后，进一步包括：对集流体进行裁切处理。
在本申请的又一方面，本申请提出了一种负极修饰方法。该方法包括在负极活性物质层表面铺展添加剂，并进行辊压处理，添加剂包括锂粉、锂带以及含锂化合物的至少一种。
附图说明
图1是本申请一个示例中的正极的结构示意图；
图2是本申请一个示例中的电化学装置的结构示意图；
图3是本申请一个示例中的制备正极的方法的流程示意图；
图4是本申请示例1中正极的扫描电子显微镜照片；
图5是本申请示例1中正极的X射线衍射谱图；
图6是本申请比较例1中正极的X射线衍射谱图；
图7是本申请示例1中负极的光学照片；
图8是本申请比较例1中负极的光学照片；
图9是本申请示例1和比较例1的循环性能测试结果图。
附图标记说明：
100：正极；110：集流体；120A-120C：锂过渡金属复合氧化物；120：活性物质层；200：隔膜；300：负极；1000：电化学装置。
具体实施方式
下面详细描述本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
本申请是基于发明人的以下认识和发现而完成的：
虽然目前的正极，如锂离子二次电池的正极可以通过控制锂过渡金属复合氧化物中活性含Li物质的颗粒大小、形貌来实现对正极性能的调控，但目前的正极仍旧存在循 环性能有待提高的问题。发明人发现，除了锂过渡金属复合氧化物自身的形貌特性，锂过渡金属复合氧化物在集流体上的取向也将影响正极的性能。特别地，通常情况下锂过渡金属复合氧化物并非完美对称的球状颗粒，正极材料的形状受限于其晶面的生长控制，颗粒中优势晶面会更快的生长，而其他晶面则较慢，因此，锂过渡金属复合氧化物多数情况下是椭球形而非完美的球形。当对合成条件进行调控时，得到的锂过渡金属复合氧化物的晶面的比例也会发生变化。例如当锂过渡金属复合氧化物中优势晶面过多时，得到的锂过渡金属复合氧化物的椭球长边远大于短边；而控制降低优势晶面的比例，增加其他晶面，则可以获得接近球形的颗粒。对于钴基材料，具体如钴酸锂而言，优势面不能脱嵌锂但十分稳定，而非优势面中的最大比例的晶面如104晶面，则能脱嵌锂但不稳定易相变。因此，当优势面过多的时候，则材料的脱锂受到影响，并且形状过于扁平而不易加工；反之，非优势面过多时则颗粒表面不稳定易相变而失效。而在形成正极时，一般会将锂过渡金属复合氧化物和导电颗粒、粘结剂等组分共同配置为浆料，随后将浆料涂布在正极集流体表面，经过干燥、冷压等一系列处理之后，锂过渡金属复合氧化物会以一定的取向分布于集流体的表面。
鉴于锂过渡金属复合氧化物并非是对称的颗粒，因此如不对锂过渡金属复合氧化物在集流体上分布的取向进行控制，则也不能够充分发挥锂过渡金属复合氧化物的性能，例如当优势面过多地暴露在集流体朝向电解液的一侧时，虽然正极的稳定性较好，但非优势面与电解液之间的距离增大，则正极脱嵌锂的性能将受到影响。而当非优势面过多地暴露在集流体朝向电解液的一侧时，则该正极的稳定性较差，正极材料容易发生粉化。并且，锂过渡金属复合氧化物如在加工过程中遭到损坏，或是在正极集流体表面分布不均，取向混乱均不利于锂过渡金属复合氧化物电化学性能的发挥。
有鉴于此，在本申请的一个方面，本申请提供了一种该正极。参考图1，该正极100包括集流体110和活性物质层120，活性物质层120位于集流体110上，活性物质层120中包含锂过渡金属复合氧化物120A、120B、120C。锂过渡金属复合氧化物120A、120B、120C在平行于集流体110所在平面方向上(如图中所示出的A-A’方向)的平均粒径Dp，以及垂直于集流体110所在平面方向(如图中所示出的B-B’方向)上的平均粒径Dv之间的比值Dp/Dv满足1.1≤Dp/Dv≤2.3。发明人发现，该正极具备较好的高压循环性能，通过对锂过渡金属复合氧化物颗粒形状的控制并调控其在集流体表面分布的取向，可缓解正极在使用过程(充电和放电)中由于锂过渡金属复合氧化物发生相变、开裂而导致的粉化等问题。
如前所述，由于锂过渡金属复合氧化物分布在集流体的过程中会以一定取向进行分布，因此控制锂过渡金属复合氧化物的Dp以及Dv的比例可以更好地衡量锂过渡金属复合氧化 物在集流体表面分布的情况，因此可保证锂过渡金属复合氧化物的电化学性能能够在正极的层面得到良好的体现。具体地，一般对于椭球型或扁平的颗粒，如果锂过渡金属复合氧化物多以颗粒的长轴直径平行于集流体110所在平面分布(如图1中所示出的120B)，则此时非活性面与电池负极正对，此时锂的迁移路径增加，该状态下颗粒的稳定性较好，不易发生粉化。而如锂过渡金属复合氧化物多以长轴直径垂直于集流体110的状态分布，如图中所示出的120A，则此时活性面与电池负极正对，容易在加工过程遭到损坏，影响正极的性能。通过对锂过渡金属复合氧化物自身的颗粒形貌进行控制，并对加工过程，如包括但不限于冷压的压力及施压方向等参数进行调控则可以保证Dp和Dv的比例处于一定的范围，也即是说此时的锂过渡金属复合氧化物中具有足够的非优势面正对电池负极，可令该正极具有较好的电化学性能，同时也不至于由于优势面过度暴露在电解液一侧导致循环性能较差。
根据本申请的一些示例，当Dp/Dv在1.1-2.3的范围内时，可以保证正极材料颗粒在集流体110上分布较为均匀，且此时在正对电池负极的方向上锂过渡金属复合氧化物的活性面和非活性面处于一个合理的范围内，并且可以在加工后得以保持。当Dp/Dv小于1.1时，正极中正对电池负极部分的非活性晶面过于少，锂过渡金属复合氧化物易损坏粉化；Dp/Dv大于2.3，则正极表面的锂过渡金属复合氧化物过于扁平或者遭到过压，影响该正极的电化学性能。
此处需要特别说明的是，在本申请中如无特殊说明，平均粒径即为颗粒的平均直径，平均直径的测试方法采用随机选取正极1个位置，用切片机进行加工，获得截面。在截面内的颗粒，分别在平行和垂直方向测量其直径并记录大小。直径指的是定义方向内颗粒的最大长度。并且统计方法为从左到右，从上到下的顺序选取颗粒，平均粒径的统计数量是100个颗粒。如图1中所示出的呈倾斜状的锂过渡金属复合氧化物120C的Dp为该颗粒在正极的截面(如图1中所示出的视角)上沿着A-A’方向上长度的最大值，锂过渡金属复合氧化物120C的Dv为该颗粒沿着B-B’方向上长度的最大值。
根据本申请的一些示例，上述锂过渡金属复合氧化物具有长轴平均粒径D 1以及短轴平均粒径D 2，满足：1.4≤(D 1/D 2)≤5.5。根据本申请的一些示例，1.4≤(D 1/D 2)≤3.8。由此，该锂过渡金属复合氧化物具有较好的颗粒形态，活性晶面和非活性晶面之间的占比适中。
根据本申请一些具体的示例，长轴平均粒径D 1满足：7≤D 1≤28μm。由此，该锂过渡金属复合氧化物具有较好的颗粒形态，活性晶面和非活性晶面之间的占比适中。
根据本申请的一些示例，上述锂过渡金属复合氧化物还可以满足：5≤Dp≤25μm。由此，该锂过渡金属复合氧化物可在集流体上具有较好的取向，可令颗粒中优势晶面和非优势晶 面更加合理地进行排布，从而可该令正极具备较好的高压循环性能。
根据本申请的一些示例，锂过渡金属复合氧化物可进一步满足：0.8≤(Dp+Dv)/2D N50≤1.25。其中D N50为所述锂过渡金属复合氧化物的中值粒径。本领域技术人员能够理解的是，一般的钴基正极材料的颗粒大小并不是完全一致的，正极中的锂过渡金属复合氧化物中可含有大颗粒，小颗粒或者大小颗粒的混合。但其粒径可处于一定范围之内。本申请前述的D N50即是其中位大小的颗粒的平均粒径。上述Dp，Dv和D N50的关系，可以确定该锂过渡金属复合氧化物在加工过程，颗粒设计的形状特征是否得到了保留。具体地，当Dp+Dv的数值远大于或者小于2D N50的时候，表明该颗粒在加工过程遭到了损坏，或者锂过渡金属复合氧化物在集流体表面的分布不均匀，或者取向混乱。这些都不利于其电化学性能的发挥。当(Dp+Dv)/2D N50在0.8-1.25之间时，可保证该锂过渡金属复合氧化物并未在加工过程中被损坏，或是被损坏的程度不足以严重影响获得的正极的性能，且该锂过渡金属复合氧化物可以以一定的取向较为均匀的分布于集流体的表面。
根据本申请的一些示例，锂过渡金属复合氧化物的具体化学组成和结构不受特别限制，本领域技术人员可以根据实际的电池性能需求进行选择。例如，根据本申请的一些示例，所述锂过渡金属复合氧化物具有R-3m空间群结构。根据本申请的一些示例，该锂过渡金属复合氧化物的化学组成可以为Li x1Ni y1Co z1Mn kZ qO b-aT a，其中，Z包括B、Mg、Al、Si、P、S、Ti、Cr、Fe、Cu、Zn、Ga、Y、Zr、Mo、Ag、W、In、Sn、Pb、Sb和Ce中的至少一种，T为卤素，并且x1、y1、z1、k、q、a和b分别满足：0.2<x1≤1.2、0≤y1≤1、0≤z1≤1、0≤k≤1、0≤q≤1、1≤b≤2以及0≤a≤1。根据本申请的一些示例，所述锂过渡金属复合氧化物具有P63mc空间群结构。根据本申请的一些示例，该锂过渡金属复合氧化物的化学组成可以为Li x2Na z2Co 1-y2M y2O 2±nX n，其中0.6<x2<0.95，0≤y2<0.15，0≤z2<0.03，0≤n≤0.2，其中M包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr中的至少一种，如M的元素种类可以为一个，2个，或3个及3个以上。当含有多个M元素时，y为多个M元素的原子比之和。更具体地，Li x2Na z2Co 1-y2M y2O 2±nX n中的x可以满足0.6<x<0.85。
根据本申请的一些示例，包括所述正极的电化学装置在放电至电压为3.0V时，锂过渡金属复合氧化物的X射线衍射光谱在17°至20°的范围内存在特征峰P 3。并且包括所述正极的电化学装置在充电至4.6V的时候，会呈现两相，两者的锂含量存在差别，且锂含量较低的部分占比较大，即具有该正极的电芯充电至电压为4.6V时，X射线衍射光谱在17°至20°的范围内至少存在特征峰P 1和特征峰P 2，且P 1的峰强度I 1大于所述P 2的峰强度I 2。如前所述的结晶性决定了材料性能，其结晶性越好，材料越不容易粉化，循环稳定性越好。具体地，P 1的峰强度I 1和P 3的峰强度I 3的比值I 1/I 3不小于0.8。也即是说，其结晶性体现在 峰强度I 1相比于初始的峰强度I 3处于接近的范围，如其强度低于I 3的0.8，则表明材料的结晶性下降比较明显。而放电至3.0V时，锂过渡金属复合氧化物恢复至初始状态，如果此时材料受应变开裂，则I 3会低于I 1-I 2。但如过初始态峰强度超过了I 1+I 2，则表明其在高电压的时候存在粉化的风险。具体地，粉化指的是锂过渡金属复合氧化物开裂、降解、相变等结晶性下降的过程。由此，P 3的峰强度I 3满足：(I 1-I 2)≤I 3≤(I 1+I 2)，可令该正极具有较好的结晶性，和较好的循环性能。
根据本申请的一些示例，该电化学装置在充满后放电至3.0V后，负极表面具有平行于折痕方向的条纹。该条纹源于负极中添加剂消耗后留下的痕迹。由此，该正极中的锂过渡金属复合氧化物配合负极的结构(例如添加剂)具有循环性能更加稳定的特点，进而可以令该正极在其应用过程中的正极活性材料的充放电状态结构保持稳定性，即材料晶体结构变化小，即I 1，I 2和I 3更稳定。此外，其满放至初始态后，其I 3峰的偏移和展宽都很小，通常情况下，XRD特征锋的偏移意味着活性锂损失，而展宽意味着材料粉化。
根据本申请示例的正极，可满足包括所述正极的电化学装置在3.0V至4.6V的范围内，进行10次充放电循环并且放电至电压为3.0V时，X射线衍射光谱中最高峰的锋位置偏移量不大于0.1°，最高峰的半峰宽变化率低于5％。由此可见，本申请提出的正极具有较好的稳定性，材料在使用过程中的活性锂损失以及正极活性材料(锂过渡金属复合氧化物)粉化情况均较少。
在本申请的另一方面，本申请提出了一种电化学装置。参考图2，该电化学装置1000包括正极100、隔膜200和负极300。其中正极100为前面所述的，隔膜200将正极100以及负极300分隔开。由此，该电化学装置具有前面所述的正极所具有的全部特征以及优点，在此不再赘述。总的来说，该电化学装置具有较好的循环性能以及容量。
本领域技术人员能够理解的是，该电化学装置还可具有电解质，以实现电化学装置的功能。该电化学装置的具体形状不受特别限制，本领域技术人员可根据实际需要进行选择和设计。
在本申请的又一方面，本申请提出了一种制备前面描述的正极的方法。参考图3，该方法可包括：
S100：提供正极材料，并形成正极浆料
根据本申请的一些示例，该步骤可以包括提供锂过渡金属复合氧化物，并形成正极浆料的操作。具体地，可以将前述的锂过渡金属复合氧化物和导电剂、粘结剂配置形成正极浆料。
根据本申请的一些示例，正极浆料中锂过渡金属复合氧化物和导电剂、粘结剂的重量比 可以为(94-99)：(0.5-3)：(0.5-3)。由此，可获得导电剂、锂过渡金属复合氧化物和粘结剂配比适当的正极浆料。例如具体地，正极浆料中锂过渡金属复合氧化物和导电剂、粘结剂的重量比可以为97:1.4:1.6。
关于锂过渡金属复合氧化物的组成以及形貌前面已经进行了详细的描述，在此不再赘述。本领域技术人员可以根据正极的具体性能需要，选择适当的锂过渡金属复合氧化物。导电剂的具体类型也不受特别限制，例如可以为导电炭黑、石墨烯等。粘结剂可以为但不限于聚偏二氟乙烯等。
S200：将所述正极浆料涂覆在集流体表面
根据本申请的一些示例，在该步骤中，可将前面形成的正极浆料涂覆在集流体表面。涂覆正极浆料的具体参数以及方式不受特别限制，只要能够将正极浆料均匀地涂覆于集流体一侧的表面即可。
S300：对具有所述正极浆料的所述集流体进行冷压处理
根据本申请的一些示例，在该步骤中对具有正极浆料的集流体进行冷压处理，具体地，冷压处理可以是在30-40吨的压力下进行的，冷压速率为3-4米/分钟，并控制压密为4.05-4.25g/cm 3。
由此，可得到平行于集流体所在平面的方向上锂过渡金属复合氧化物平均粒径Dp以及垂直于集流体所在平面的方向上锂过渡金属复合氧化物平均粒径Dv满足前述条件的正极。该正极具有前述的正极所具有的全部特征以及优点，在此不再赘述。总的来说，该方法获得的正极可具有较好的循环性能。
发明人发现，通过调节冷压处理中压力的数值、冷压速率和冷压压密，可控制具有适当颗粒形状的锂过渡金属复合氧化物均匀、以一定取向地分布于集流体的表面。由此，即可以保持锂过渡金属复合氧化物的形貌不受冷压等制程工艺的损伤，还可以调节锂过渡金属复合氧化物中优势晶面和非优势晶面在集流体表面的排布情况，从而获得循环性能和电学性能均较好的正极。
根据本申请的一些示例，将正极浆料涂覆在集流体表面之后，进行所述冷压处理之前，还可以进一步包括对集流体表面的所述正极浆料进行干燥处理的操作。干燥处理的具体参数不受特别限制，本领域技术人员可根据实际情况，选择干燥处理的参数以及方式，以获得厚度均一的浆料层。
进行冷压处理之后，还可以进一步对集流体进行裁切处理。由此，可获得尺寸适当的正极。
根据本申请的一些示例，电化学装置的负极还可进一步具有添加剂。由此，进一步包括 在负极活性物质层表面覆盖添加剂的操作。具体地，可以通过进行辊压处理将添加剂形成在负极活性物质层上，例如，可将具有添加剂的负极在5-30吨的压力下，以0.5-2米/秒的速度通过辊压。根据本申请的一些示例，添加剂可以包括锂粉、锂带以及含锂化合物的至少之一。由此，可进一步提高利用该方法获得的电化学装置的质量。
实施例
正极极片的制备：将以下示例中获得的正极材料、导电剂导电炭黑、粘结剂聚偏二氟乙烯按重量比97：1.5：1.5的比例在N-甲基吡咯烷酮(NMP)溶剂体系中充分搅拌混合均匀后，形成正极浆料。采用铝箔作为集流体，将正极浆料涂覆于集流体上，涂布重量为17.2mg/cm 2，经过干燥、冷压、裁切后得到正极极片。
负极极片的制备：集流体采用铜箔，负极活性材料采用人造石墨，粘结剂采用丁苯橡胶和羧甲基纤维素钠；将人造石墨、丁苯橡胶和羧甲基纤维素钠按重量比96：2：2混合后分散于去离子水中形成浆料，搅拌均匀后涂布于铜箔上，干燥，形成负极活性材料层，经过冷压，得到负极极片。部分实施例进一步在负极活性材料层表面添加单质锂带，添加量2.5mg/cm 2，冷压，得到含有添加剂的负极极片。
隔离膜的制备：采用8μm厚的聚乙烯多孔聚合物膜。
电解液的制备：在含水量小于10ppm的环境下，将六氟磷酸锂(1.15mol/L)与非水有机溶剂(碳酸乙烯酯(EC)：碳酸亚丙酯(PC)：碳酸二乙酯(DEC)＝1：1：1，重量比)混合得到电解液。
锂离子电池的制备：将正极极片、隔离膜、负极极片按顺序依次叠好，使隔离膜处于正极和负极中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装铝塑膜中，在80℃下脱去水分后，注入上述电解液并封装，经过化成，脱气，整形等工艺流程得到锂离子电池。
负极纹路的观测方法：锂离子电池充满后放电至3.0V，在干燥房或者手套箱内拆解，将负极铺展放平后用相机拍摄获得清晰的倍数合适的图片，观察负极表面是否具有条纹。
循环性能测试方法：温度为25℃，充电流程为0.7C恒流充电到4.6V，恒压到截止电流0.025C，然后再0.5C放电到3.0V。以首次循环放电容量为100％，记录循环200次之后的锂离子电池的容量保持率。
X射线粉末衍射测试方法：将锂离子电池在10mA/s的电流密度下调节至相应的电压，并静置5min后，在手套箱或者干燥房拆解。选取正极的中心部位，裁剪得到3×3cm大小的片。在布鲁克X射线粉末衍射仪上进行表征，采集10-80°范围的衍射峰，采集速度是1°每 分钟。
Dp和Dv的测试方法：取正极极片，用切片机进行加工，获得垂直于集流体表面的截面。在截面内的颗粒，分别在平行于集流体所在平面和垂直于集流体所在平面的方向测量其直径并记录大小。直径指的是定义方向内颗粒的最大长度。并且统计方法为从左到右，从上到下的顺序选取颗粒，平均粒径的统计数量是100个颗粒。
实施例1
将硝酸钴和硝酸铝按照摩尔比Co:Al＝99：1混合溶入5倍质量的去离子水中，加入碳酸钠和氨水调节体系pH至8.2，并充分搅拌24小时，得到沉淀。将沉淀中加入0.5％沉淀质量的添加剂草酸铵，混合均匀，在800℃烧结24小时得到前驱体。将前驱体与碳酸钠以Co:Na化学剂量比0.99：0.75的比例混合均匀后，在800℃反应36小时，得到粉体材料。将其充分研磨3小时后，将其与硝酸锂以摩尔比Na：Li＝1：5混合均匀，并且在250℃反应8小时，反应产物利用去离子水洗涤5遍以上，此后将粉体干燥得到正极材料Li 0.73Na 0.01Co 0.99Al 0.01O 2。将Li 0.73Na 0.01Co 0.99Al 0.01O 2正极材料粉体与导电碳、粘结剂以重量比97：1.5：1.5，并和NMP一起混合制备形成浆料，涂覆于Al集流体表面，并在120℃烘箱内烘2小时至干燥，此后在35吨压力下进行冷压，冷压速率是3.5米/分钟，压密控制在4.15g/cm 3。裁切后得到正极极片。
在负极活性材料层表面设置添加剂单质锂带，添加量2.5mg/cm 2，经辊压得到具有添加剂的负极极片。
实施例2
将硝酸钴和硝酸钛按照Co:Ti＝95：5混合溶入5倍质量的去离子水中，加入碳酸钠和氨水调节体系pH至6.5，并充分搅拌12小时，得到沉淀。将沉淀中加入0.5％沉淀质量的添加剂碳酸氢钠，混合均匀，在750℃烧结24小时得到前驱体。将前驱体与碳酸钠以Co:Na化学剂量比0.95：0.76的比例混合均匀后，在800℃反应36小时，得到粉体材料。将其充分研磨3小时后，将其与硝酸锂以Na：Li＝1：5混合均匀，并且在250℃反应8小时，反应产物利用去离子水洗涤5遍以上，此后将粉体干燥得到正极材料Li 0.74Na 0.01Co 0.95Ti 0.05O 2。
浆料、冷压参数以及添加剂均同实施例1。
实施例3：与实施例1的制备方法一致，不同的是调节体系pH至8.7，并充分搅拌24小时；在900℃烧结36小时得到前驱体，最终得到正极材料Li 0.73Na 0.01Co 0.99Al 0.01O 2。
实施例4：与实施例2的制备方法一致，不同的是加入碳酸钠和氨水调节体系pH 至8.5，并充分搅拌24小时，以及在950℃烧结48小时得到前驱体。
实施例5：与实施例1的制备方法一致，不同的是将前驱体与碳酸钠混合均匀后，在850℃反应24小时，得到粉体材料。将其充分研磨3小时后，与硝酸锂以摩尔比Na：Li＝1：5混合均匀，并且在450℃反应12小时。冷压处理在36吨压力下进行，冷压速率是3米/分钟，压密控制在4.16g/cm 3。
实施例6：与实施例1的制备方法一致，不同的是负极极片未进行添加剂的修饰。
实施例7：与实施例1的制备方法一致，不同的是在950℃反应48小时得到前驱体。
实施例8：采用R-3m空间群结构的Li 0.7CoO 2作为正极材料。浆料、冷压参数同实施例1。负极极片未进行添加剂的修饰。
实施例9：采用R-3m空间群结构的Li 0.75Co 0.86Mg 0.14O 2作为正极材料。浆料、冷压参数同实施例1。负极极片未进行添加剂的修饰。
实施例10：采用R-3m空间群结构的Li 0.99Co 0.99Al 0.01O 2作为正极材料。浆料、冷压参数同实施例1，负极极片未进行添加剂的修饰。
比较例1
硝酸钴和硝酸铝按照Co:Al＝99：1混合溶入5倍质量的去离子水中，加入碳酸钠和氨水调节体系pH至9.8，并充分搅拌36小时，得到沉淀。将沉淀中加入0.5％沉淀质量的添加剂草酸铵，混合均匀，在600℃烧结24小时得到前驱体。将前驱体与碳酸钠以Co:Na化学剂量比0.99：0.77的比例混合均匀后，在1000℃反应36小时，得到粉体材料。将其充分研磨3小时后，将其与硝酸锂以Na：Li＝1：5混合均匀，并且在600℃反应8小时，反应产物利用去离子水洗涤5遍以上，此后将粉体干燥得到正极材料Li 0.76Na 0.01Co 0.99Al 0.01O 2。
浆料、冷压参数同实施例1。负极极片未进行添加剂的修饰。
比较例2：与比较例1的制备方法一致，不同的是加入氢氧化钠调节体系pH至11.8。
比较例3：与比较例1的制备方法一致，不同的是在1000℃烧结24小时得到前驱体，并在1050℃反应24小时得到粉体材料。负极极片未进行添加剂的修饰。
比较例4：与实施例8的制备方法一致，不同的是：采用R-3m空间群结构的Li 0.88CoO 2作为正极材料。
比较例5：与实施例1的制备方法一致，不同的是在65吨压力下进行冷压，冷压速率是6米/分钟，压密为4.29g/cm 3。负极极片未进行添加剂的修饰。
比较例6：与实施例10的制备方法一致，但不同的是：采用D1为6.4μm、D2为 4.6μm的R-3m空间群结构的Li 0.99Co 0.99Al 0.01O 2作为正极材料。冷压压密为3.94g/cm 3。
对实施例1和比较例1进行X射线粉末衍射测试，参考图5以及图6可知，在相应的电压下(4.6V和3.0V)，实施例1的特征峰的展宽以及峰位移均小于比较例1。参考图7和图8可知，比较例1的表面未出现实施例1中出现的扭曲条纹。参考图9可知，比较例1的循环容量保持率降低较多。上述各个实施例以及比较例的测试结果如下表1所示，其中Y表示存在负极纹路，N表示不存在负极纹路。
表1
Figure PCTCN2020138985-appb-000001
由表1可知，不论是P63mc还是R-3m结构的正极材料，Dp/Dv在本申请所限定范围内的实施例均具有较好的循环性能，均优于比较例。且由实施例1至10可知，(Dp+Dv)/2D N50在0.8至1.25范围内，能够具有更加优异的循环稳定性。通过实施例1和实施例6的比较可知，对P63mc结构的正极材料利用添加剂进行补锂，能够进一步提升其循环稳定性。
另外，由比较例1和5可见，当正极材料的长轴平均粒径D 1与短轴平均粒径D 2的比值D1/D2过小和/或冷压条件不合适时，则均难以实现本申请所限定的Dp/Dv，其循环稳定性也相应较差。
对部分实施例以及比较例的样品进行X射线粉末衍射测试。测试结果参考下表2：
表2
  I1 I2 I3 I1/I3 4.6V循环200次保持率
实施例1 1.01 0.4 1.0 1.01 78.9％
实施例7 1.42 0.64 1.73 0.82 70.4％
比较例1 0.41 0.09 1.46 0.28 47.3％
由上表2可知，比较例1的I1/I3小于0.8，表明在高电压下存在粉化的风险。因而比较例1的循环保持率也显著低于实施例。
经过8次循环之后，测试X射线粉末衍射的I2/I3变化率、峰偏移量以及半峰宽变化率，测试结果见下表3：
表3
Figure PCTCN2020138985-appb-000002
由上表3可知，实施例1,8以及9均具有较小的峰偏移量，I2/I3变化率、半峰宽变化率也显著小于比较例4，说明具有较好的稳定性。4.6V循环200圈保持率也证实了上述观点。
以上所述，仅是本申请的示例，并非对本申请做任何形式的限制，虽然本申请以较佳实施例揭示如上，然而并非用以限制本申请，任何熟悉本专业的技术人员，在不脱离本申请技术方案的范围内，利用上述揭示的技术内容做出些许的变动或修饰均等同于等效实施案例，均在本申请技术方案的范围内。

Claims (12)

  1. 一种正极，包括：
    位于集流体上的正极活性物质层；
    所述正极活性物质层包含锂过渡金属复合氧化物；
    所述锂过渡金属复合氧化物在平行于所述集流体所在平面方向上的平均粒径为Dp，所述锂过渡金属复合氧化物在垂直于所述集流体所在平面方向上的平均粒径为Dv，满足：1.1≤Dp/Dv≤2.3。
  2. 根据权利要求1所述的正极，所述锂过渡金属复合氧化物满足：5μm≤Dp≤25μm。
  3. 根据权利要求1所述的正极，所述锂过渡金属复合氧化物满足：
    0.8≤(Dp+Dv)/2D N50≤1.25，其中D N50为所述锂过渡金属复合氧化物的中值粒径。
  4. 根据权利要求1所述的正极，满足以下条件的至少一者：
    a)所述锂过渡金属复合氧化物具有R-3m空间群结构；所述锂过渡金属复合氧化物包括Li x1Ni y1Co z1Mn kZ qO b-aT a，其中，Z包括B、Mg、Al、Si、P、S、Ti、Cr、Fe、Cu、Zn、Ga、Y、Zr、Mo、Ag、W、In、Sn、Pb、Sb和Ce中的至少一种，T为卤素，并且x1、y1、z1、k、q、a和b分别满足：0.2<x1≤1.2、0≤y1≤1、0≤z1≤1、0≤k≤1、0≤q≤1、1≤b≤2以及0≤a≤1；
    b)所述锂过渡金属复合氧化物具有P63mc空间群结构；所述锂过渡金属复合氧化物包括Li x2Na z2Co 1-y2M y2O 2±nX n，其中0.6<x2<0.95，0≤y2<0.15，0≤z2<0.03，0≤n≤0.2，其中M包括Al、Mg、Ti、Mn、Fe、Ni、Zn、Cu、Nb、Cr和Zr中的至少一种，X为卤素。
  5. 根据权利要求1所述的正极，其中，所述锂过渡金属复合氧化物具有长轴平均粒径D 1以及短轴平均粒径D 2，满足：1.4≤(D 1/D 2)≤5.5。
  6. 根据权利要求5所述的正极，所述锂过渡金属复合氧化物满足：7μm≤D 1≤28μm。
  7. 根据权利要求1所述的正极，包括所述正极的电化学装置在充电至电压为4.6V时，所述正极满足：X射线衍射光谱在17°至20°的范围内至少存在特征峰P 1和特征峰P 2，且所述P 1的峰强度I 1大于所述P 2的峰强度I 2；
    并且，所述电化学装置在放电至电压为3.0V时，所述正极满足：X射线衍射光谱在17°至20°的范围内存在特征峰P 3，所述P 3的峰强度I 3满足：(I 1-I 2)≤I 3≤(I 1+I 2)。
  8. 根据权利要求7所述的正极，所述P 1的峰强度I 1和所述P 3的峰强度I 3的比值I 1/I 3不小于0.8。
  9. 根据权利要求1所述的正极，其中，所述正极满足：包括所述正极的电化学装置在3.0V至4.6V的范围内，进行8次充放电循环并且放电至电压为3.0V时，与循环前的所述正极相比，循环后的所述正极的X射线衍射光谱中最高峰的锋位置偏移量不大于0.1°；所 述最高峰的半峰宽变化率低于5％。
  10. 一种电化学装置，包括正极、负极、隔膜，所述正极为根据权利要求1至9中任一项所述的正极。
  11. 根据权利要求10所述的电化学装置，在放电至电压为3.0V时，所述负极表面具有条纹。
  12. 一种电子装置，包括根据权利要求10至11中任一项所述的电化学装置。
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