WO2021189455A1 - 电化学装置及包含其的电子装置 - Google Patents

电化学装置及包含其的电子装置 Download PDF

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WO2021189455A1
WO2021189455A1 PCT/CN2020/081800 CN2020081800W WO2021189455A1 WO 2021189455 A1 WO2021189455 A1 WO 2021189455A1 CN 2020081800 W CN2020081800 W CN 2020081800W WO 2021189455 A1 WO2021189455 A1 WO 2021189455A1
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positive electrode
active material
particles
electrode active
material layer
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PCT/CN2020/081800
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English (en)
French (fr)
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岳影影
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宁德新能源科技有限公司
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Priority to CN202080047061.7A priority Critical patent/CN114041226A/zh
Priority to EP20927990.0A priority patent/EP4131540A4/en
Priority to PCT/CN2020/081800 priority patent/WO2021189455A1/zh
Publication of WO2021189455A1 publication Critical patent/WO2021189455A1/zh
Priority to US17/954,084 priority patent/US20230042151A1/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
    • 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
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • 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 electrochemical devices and electronic devices containing them.
  • 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 an electrochemical device and an electronic device using the electrochemical device, in an attempt to solve at least one problem in the related field at least to some extent.
  • the present application provides an electrochemical device comprising a positive electrode, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer comprising particles A and particles B, the particles a circularity of R a, S a is the cross-sectional area; circularity of B is R B, cross-sectional area S B, wherein R B ⁇ 0.4 ⁇ R a, S B ⁇ 20 ⁇ m 2 ⁇ S a Based on the total area of the cross section of the positive electrode perpendicular to the direction of the positive electrode current collector, the ratio of the total area ratio of the particles A to the total area ratio of the particles B is 1:9 to 8:2.
  • the particle A satisfies at least one of the relational expressions (a) to (c): (a) based on the total area of the cross section of the positive electrode perpendicular to the direction of the positive electrode current collector, The total area of the particle A accounts for 5% to 50%; (b) the resistivity of the particle A is 6 ⁇ cm to 10 ⁇ cm; (c) the particle A contains the formula Li 1+a Ni x Mn y Co z M m O 2 compound, where -0.05 ⁇ a ⁇ 0.3, 0.8 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 0.2, 0 ⁇ z ⁇ 0.2, 0 ⁇ m ⁇ 0.2, where the element M is selected from Al One or more of, Ti, W, Zr, Nb, In, Ru, Sb, Sr, Y.
  • the particles A include broken particles, and the broken particles satisfy at least one of the relations (d) to (e): (d) the positive electrode is perpendicular to the direction of the positive electrode current collector Based on the total area of the cross section, the total area of the crushed particles is not more than 15%; (e) based on the total area of the particle A, the total area of the crushed particles is not more than 30%.
  • the particle B satisfies at least one of the relations (f) to (h): (f) based on the total area of the cross section of the positive electrode perpendicular to the direction of the positive electrode current collector, the The proportion of the total area of the particles B is 5% to 60%; (g) the resistivity of the particles B is 20 ⁇ cm to 40 ⁇ cm; (h) the particles B contain the formula Li 1+a Ni x A compound of Mn y Co z M m O 2 where -0.05 ⁇ a ⁇ 0.3, 0.8 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 0.2, 0 ⁇ z ⁇ 0.2, 0 ⁇ m ⁇ 0.2, wherein the element M is selected from Al, One or more of Ti, W, Zr, Nb, In, Ru, Sb, Sr, and Y.
  • the positive electrode active material layer satisfies at least one of the relations (i) to (j): (i) the porosity of the positive electrode active material layer ⁇ 25%; (j) in TG -In the MS test, the positive electrode active material has an oxygen release peak at 230°C to 245°C.
  • the specific surface area of the positive electrode active material is 0.1 m 2 /g to 1.2 m 2 /g.
  • the positive electrode active material layer further includes a binder and a conductive agent, wherein the content of the binder is 1.25% to 5% based on the total mass of the positive electrode active material layer.
  • the positive electrode further includes a functional layer disposed on the positive active material layer and/or between the positive active material layer and the positive current collector.
  • the functional layer satisfies at least one of relations (1) to (4): (1) the functional layer is disposed on the positive electrode active material layer, and the positive electrode active material layer is disposed On the positive electrode current collector, the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer is 99:1 to 50:50; (2) the functional layer is disposed on the positive electrode active material layer and the Between the positive electrode current collectors, the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer is 99:1 to 50:50; (3) the functional layer is disposed on the positive electrode active material layer, and The functional layer is disposed between the positive electrode active material layer and the positive electrode current collector, and the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer is 99:1 to 50:50; (4) The functional layer includes material C, the material C includes at least one of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, or lithium manganese oxide, and the particle size Dv
  • the deformation rate of the positive electrode current collector is ⁇ 32%.
  • the present application provides an electronic device, which includes the electrochemical device of the present application.
  • the particles A and the particles B as the positive electrode active material of the electrochemical device, it can effectively solve the problem of particle breakage, surface side reactions, and oxygen release in the electrochemical device during high-temperature storage and charging and discharging.
  • the particles A and B have different circularity and cross-sectional area respectively.
  • Figures 1A and 1B are scanning electron microscope (SEM) images of LiNi 0.88 Co 0.09 Mn 0.03 O 2 particles A and LiNi 0.88 Co 0.09 Mn 0.03 O 2 particles B, respectively;
  • FIG. 2A shows the SEM image of LiN i0.88 Co 0.09 Mn 0.028 Zr 0.002 O 2 particles A, and FIG. 2B shows the bulk distribution diagram of the doping element Zr in the polycrystalline particles;
  • 3A and 3B show the interface diagrams of the positive electrode after cold pressing in Comparative Example 1 and Example 3, respectively.
  • the terms “one or more of”, “one or more of”, “one or more of”, “at least one of” or other A list of items connected by 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.
  • a roundness meter is used to measure the roundness of the positive electrode active material particles, and the specific test method can be found in the following specific embodiments.
  • crack particles means that under the scanning electron microscope, in the cross-section of the particles in the image, continuous lines with a length of not less than 0.1 ⁇ m and a width of not less than 0.01 ⁇ m are regarded as cracks, and the particles with cracks are regarded as broken particles.
  • median particle size Dv50 means a particle size that reaches 50% of the cumulative volume in the particle size distribution on a volume basis, measured from a small particle size.
  • the positive electrode active materials with great application prospects are nickel-containing materials, especially high-nickel materials, where high-nickel materials refer to other metal elements other than lithium metal contained in the positive electrode active materials.
  • the total content of nickel, the molar content of nickel at least accounted for more than 50% of the material.
  • the main function of nickel is to increase the energy density. In the same charge and discharge voltage range, the higher the nickel content, the higher the gram capacity.
  • high-nickel materials have a high amount of lithium removal under the same voltage, and the unit cell volume expands and shrinks greatly, causing particles to be easily broken and easy to interact with the electrolyte. side effects. After the particles are broken, a new interface will be exposed, causing the electrolyte to penetrate into the particles through the cracks and have side reactions with the positive electrode active material at the new interface, aggravating the occurrence of gas production and causing the capacity of the electrochemical device to vary.
  • this application proposes to simultaneously introduce particles A and particles B of the positive electrode active material into the positive electrode active material layer as the positive electrode of the electrochemical device to overcome the above-mentioned drawbacks of using high-nickel materials.
  • the particle A is a collection of numerous single crystal particles, and the single crystal is a crystal in which the particles in the single crystal are regularly and periodically arranged in a three-dimensional space.
  • the morphology particles A appear as spherical or ellipsoidal, which circularity R A larger and larger cross-sectional area S A also.
  • the particles A are polycrystalline particles.
  • particle B is a collection of single crystals with a larger grain size.
  • the topography is irregular particles B, R B which circularity is small, and the cross-sectional area S B is small.
  • particle B is a single crystal-like particle.
  • the positive electrode active material particles A and the particles B satisfies R B ⁇ 0.4 ⁇ R A and S B ⁇ 20 ⁇ m 2 ⁇ S A.
  • the electrochemical performance of the electrochemical device can be further optimized by controlling the addition ratio of particles A and B.
  • the ratio of the total area of the particles A to the total area of the particles B is 1:9 to 8:2. In the range.
  • the ratio of the total area ratio of the particle A to the total area ratio of the particle B is in the range of 2:8 to 8:2.
  • the charging and discharging process of the electrochemical device is the process of inserting or extracting lithium ions from the positive electrode active material. During this process, the unit cell volume of the positive electrode active material will shrink and expand violently. Since the particle size of the particle A is relatively large and the contact between multiple particles A is rigid contact, when the unit cell volume of each particle A undergoes violent expansion and contraction, rigid collisions will occur between the multiple particles A, which intensifies Fragmentation of particles. In contrast, the morphology of the particle B is irregular and the particle size is small. When the particle B is added to the particle A, the particle B can play a good buffering effect between the two particles A and reduce Rigid collision between particles A, thereby reducing the fragmentation of particles and inhibiting the occurrence of side reactions.
  • Particle A has a larger circularity and cross-sectional area, which has the advantage of low resistivity, but particle A is prone to particle breakage during cold pressing and/or circulation.
  • the electrochemical performance of the electrochemical device can be further optimized by optimizing at least one of the area ratio of the particles A in the positive electrode active material layer, the resistivity or specific components thereof.
  • the total area ratio of the particles A is in the range of 5% to 50%.
  • the total area of the particles A occupies a range of 5% to 45%.
  • the area ratio of the particles A is in the range of 8% to 30%.
  • the electrochemical device obtained with the total area ratio of the particles A within this range has excellent electrochemical performance, especially its gas production degree under high temperature storage conditions will be significantly reduced and its cycle stability will be significantly improved.
  • the particles A have a low powder resistivity to promote the rapid transmission of electrons between the particles A.
  • the powder resistivity of the particles A is below 10 ⁇ cm.
  • the powder resistivity of the particles A is below 9 ⁇ cm.
  • the powder resistivity of the particles A is below 8 ⁇ cm.
  • the powder resistivity of the particles A is in the range of 6 ⁇ cm to 10 ⁇ cm.
  • particle A is a nickel-containing ternary material.
  • ternary material is a well-known ternary material in the field, for example, it is recorded in "Lithium-ion battery ternary material-process technology and production application” (Wang Weidong, Qiu Weihua, Ding Qianqian, etc. eds, Chemical Industry Press, May 2015 ) In the ternary material.
  • the nickel-containing ternary material described in this application includes lithium nickel cobalt manganese oxide.
  • the particle A includes or is selected from at least one compound having the formula Li 1+a Ni x Mn y Co z M m O 2 , where -0.05 ⁇ a ⁇ 0.3, 0.8 ⁇ x ⁇ 1.0 ⁇ y ⁇ 0.2, 0 ⁇ z ⁇ 0.2, 0 ⁇ m ⁇ 0.2, where the element M includes or is selected from one or more of Al, Ti, W, Zr, Nb, In, Ru, Sb, Sr, Y .
  • the above-mentioned element M can be uniformly doped in the bulk and surface of the particle A.
  • the composition of the particle A of Example 4 of the present application is LiNi 0.88 Co 0.09 Mn 0.028 Zr 0.002 O 2 , and the doped Zr element is uniformly distributed on the surface and bulk of the particle A.
  • the positive electrode active material particles need to be tightly pressed together by a cold pressing process to increase the compaction density (referred to as compaction) of the positive electrode active material layer, thereby increasing the energy density of the electrochemical device And reduce the direct current resistance (DCR) of the electrochemical device.
  • compaction compaction density
  • DCR direct current resistance
  • the above-mentioned cold pressing process also tightly presses the positive electrode active material layer and the positive electrode current collector together to prevent the separation between the positive electrode active material layer and the positive electrode current collector during the charging and discharging process of the electrochemical device.
  • the cold pressing process will cause the crushing of the particles A, and the size of the compaction is positively related to the degree of crushing of the particles A, that is, the greater the compaction, the more severe the crushing of the particles A. Therefore, while keeping the pole pieces in a high-pressure and dense state, reducing the degree of crushing of the particles A is also one of the technical issues that this application focuses on.
  • the addition of particles B can play a good buffering effect
  • a compaction density for example, at a compaction density of 3.5g/cc
  • the total area of the broken particles in the particles A accounts for no more than 15%.
  • the particles A are broken The total area of the particles accounts for no more than 14%.
  • the fragmentation in the particle A is The area ratio of the particles is not more than 12%.
  • the particles in A The proportion of the total area of the broken particles is not more than 11%.
  • the total area of the broken particles accounts for no more than 30%. In some embodiments, at a compacted density (for example, at a compacted density of 3.5 g/cc), based on the total area of the particles A, the total area of the broken particles accounts for no more than 24%. In some embodiments, at a compacted density (for example, at a compacted density of 3.5 g/cc), based on the total area of the particles A, the total area of the broken particles accounts for no more than 20%.
  • Particle B has a small circularity and cross-sectional area, and its main function is to reduce the crushing degree of particle A during electrode preparation process (especially the cold pressing process) and the charging and discharging process of electrochemical device; improve the compaction of the pole piece Density; and provide more electrochemically active sites to increase the discharge specific capacity.
  • the electrochemical performance of the electrochemical device can be further optimized by optimizing at least one of the area ratio of the particles B in the positive electrode active material layer, the resistivity, or specific components thereof. In some embodiments, based on the total area of the cross section of the positive electrode perpendicular to the direction of the positive electrode current collector, the area ratio of the particles B is in the range of 5% to 60%.
  • the area ratio of the particles B is in the range of 8% to 55%. In some embodiments, based on the total area of the cross section of the positive electrode perpendicular to the direction of the positive electrode current collector, the area ratio of the particles B is in the range of 10% to 40%.
  • the powder resistivity of the particles B is in the range of 20 ⁇ cm to 40 ⁇ cm. In some embodiments, the powder resistivity of the particles B is in the range of 25 ⁇ cm to 35 ⁇ cm. Among them, this application uses a resistivity tester to test the resistivity.
  • the particle B includes or is selected from at least one compound having the formula Li 1+a Ni x Mn y Co z M m O 2 , where -0.05 ⁇ a ⁇ 0.3, 0.8 ⁇ x ⁇ 1.0 ⁇ y ⁇ 0.2, 0 ⁇ z ⁇ 0.2, 0 ⁇ m ⁇ 0.2, where the element M includes or is selected from one or more of Al, Ti, W, Zr, Nb, In, Ru, Sb, Sr, Y .
  • the porosity of the positive electrode active material layer also affects the gas production of the electrochemical device. Specifically, when the porosity of the positive electrode active material layer is larger, the amount of electrolyte that can be stored therein is larger, and more side reactions are induced, resulting in larger gas production. In some embodiments, the porosity of the positive active material layer is not greater than 25%. In some embodiments, the porosity of the positive active material layer is not greater than 19%. If the porosity is too large, the side reactions in the electrochemical device will increase, and the gas production will increase.
  • thermogravimetric-mass spectrometry test ie, TG-MS test
  • TG-MS test a thermogravimetric-mass spectrometry test
  • the particle size of the positive electrode active material also affects its electrochemical performance in an electrochemical device.
  • the particle size is too small, it will also bring certain side effects. For example, when the particle size is smaller, the larger the exposed surface is, the more serious the side reaction between the particle and the electrolyte will be, and the risk of particle crushing and gas production will increase accordingly. Therefore, controlling the particle size and specific surface area of the positive electrode active material within an appropriate range will further optimize the electrochemical performance of the positive electrode active material.
  • the specific surface area described herein is a cathode active material of 0.05m 2 / g to within the range of 2.0m 2 / g of. In some embodiments, the specific surface area of the positive electrode active material described in this application is in the range of 0.1 m 2 /g to 1.5 m 2 /g. In some embodiments, the specific surface area of the positive active material described in the present application is in the range of 0.1 m 2 /g to 1.2 m 2 /g. Among them, this application uses a BET physical adsorption instrument to determine the specific surface area of the positive electrode active material. For the specific test method, please refer to the following examples.
  • the positive electrode current collector used in the present application 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 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.
  • binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing The polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylic (ester) styrene butadiene rubber, epoxy resin, nylon Wait.
  • 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.
  • conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, Metal fibers and the like include, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (for example, polyphenylene derivatives) and mixtures thereof, and the like.
  • the content of the binder in the positive electrode is too small, the positive electrode active material layer of the electrochemical device will be separated from the positive electrode current collector during the cycle of charging and discharging and high temperature storage, which will aggravate the occurrence of gas production and side reactions, and greatly improve The impedance of the electrochemical device. Therefore, as an improvement of the present application, by optimizing the content of the binder in the positive electrode active material layer, the electrochemical performance of the electrochemical device can be further optimized.
  • the content of the binder is in the range of 1% to 5%. In some embodiments of the present application, the content of the binder is in the range of 1.25% to 5%.
  • the content of the binder is in the range of 1.5% to 5%. In some embodiments of the present application, the content of the binder is in the range of 1.5% to 4.5%. In some embodiments of the present application, the content of the binder is in the range of 1.5% to 4%. In some embodiments of the present application, the content of the binder is in the range of 1.8% to 4%.
  • the positive electrode further includes one or more functional layers disposed on the positive electrode active material layer, and/or disposed on the positive electrode active material layer and the positive electrode current collector. Time to achieve specific functions.
  • the functional layer includes a first functional layer disposed between the positive electrode active material layer and the positive electrode current collector, wherein the thickness of the positive electrode active material layer is equal to the thickness of the first functional layer.
  • the thickness ratio is in the range of 99:1 to 50:50. Compared with particles with a large particle size, particles with a small particle size are more flexible under the same pressure and are less prone to particle breakage. Therefore, in some embodiments, the first functional layer includes or is selected from particles having a median diameter Dv50 in the range of 1.5 ⁇ m to 6 ⁇ m.
  • the first functional layer is located between the positive electrode active material layer and the positive electrode current collector, and can reduce the deformation rate of the positive electrode current collector during the cold pressing process so as to maintain the corrosion resistance of the positive electrode current collector.
  • the first functional layer can play a buffering role during the cold pressing process, and protect the particles A in the positive electrode active material layer from being broken due to cold pressing stress during the cold pressing process.
  • the first functional layer includes or is selected from one or more of the single crystal-like particles B, LMFP, and LMO described in the present application.
  • the chemical formula of LMFP is LiFe 1-x Me x XO 4
  • the element Me is one or more of the elements in the VIIB group and the VIII group in the periodic table
  • the element X includes or is selected from P, Si One or more of, S, As and Sb, where 0 ⁇ x ⁇ 1.
  • the chemical formula of LMO is LiMn y Md 2-y O 4
  • the element Md is Al, Mg, Mn, Ni, Co, Fe, Gr, V, Ti, Cu, B, Ga, Zn, Zr, Nb, Mo, One or more of Sr, Sb, W and Bi, where 0 ⁇ y ⁇ 2.
  • the first functional layer includes or is selected from at least one of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, or lithium manganese oxide.
  • the functional layer includes a second functional layer disposed on the positive electrode active material layer and the positive electrode active material layer is disposed on the positive electrode current collector, wherein the positive electrode active material layer
  • the ratio of the thickness to the thickness of the second functional layer is in the range of 99:1 to 50:50.
  • the second functional layer similar to the first functional layer, includes or is selected from particles having a median diameter Dv50 in the range of 0.5 ⁇ m to 6 ⁇ m.
  • the second functional layer includes or is selected from one or more of the particles B, LMFP, and LMO described in this application.
  • the second functional layer includes or is selected from at least one of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, or lithium manganese oxide.
  • the second functional layer covers the surface of the positive electrode active material layer and can play a buffering role to protect the polycrystalline particles A in the positive electrode active material layer from being broken due to cold pressing stress during the cold pressing process.
  • the functional layer includes both the first functional layer and the second functional layer described above, wherein the thickness of the positive active material layer is the same as that of the first functional layer and the second functional layer.
  • the ratio of the sum of the thicknesses is in the range of 99:1 to 50:50. In some embodiments, the ratio of the thickness of the positive active material layer to the sum of the thicknesses of the first functional layer and the second functional layer is in the range of 99:1 to 50:50.
  • the deformation rate of the positive electrode current collector (for example, aluminum foil) will increase, resulting in the coating of the positive electrode current collector per unit area.
  • the weight of the positive electrode active material is reduced, thereby affecting the processing performance.
  • the surface of the positive electrode current collector usually contains a protective layer to prevent corrosion of the electrolyte.
  • the protective layer on the surface of the positive electrode current collector will be damaged, thereby reducing the resistance of the positive electrode current collector to the electrolyte. Corrosive.
  • the deformation rate of the positive electrode current collector is not more than 40%. In some embodiments, when the compaction density is above 3.4 g/cc, the deformation rate of the positive electrode current collector is not more than 30%. In some embodiments, when the compaction density is above 3.4 g/cc, the deformation rate of the positive electrode current collector is not more than 20%. In some embodiments, when the compaction density is above 3.4 g/cc, the deformation rate of the positive electrode current collector is not more than 10%. In some embodiments, when the compaction density is above 3.4 g/cc, the deformation rate of the positive electrode current collector is not more than 5%.
  • the deformation rate of the positive electrode current collector refers to the ratio of the undeformed portion in the thickness direction of the positive electrode current collector to the thickness of the positive electrode current collector itself.
  • the calculation formula of the deformation rate of the positive electrode current collector is: (thickness of the positive electrode current collector-d)/thickness of the positive electrode current collector ⁇ 100%.
  • the electrochemical device described in the present application further includes a negative electrode, wherein the negative electrode includes a negative active material layer and a negative current collector, and the negative active material layer includes the negative active material described in the present application.
  • the negative active material can reversibly insert and extract lithium ions.
  • the specific types of negative electrode active materials are not subject to specific restrictions, and can be selected according to requirements.
  • 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.
  • non-limiting examples of 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, and will not be repeated here.
  • Electrolytes can be divided into water-based electrolytes and non-aqueous electrolytes. Compared with water-based electrolytes, electrochemical devices using non-aqueous electrolytes can operate under a wider voltage window, thereby achieving higher energy density.
  • the non-aqueous electrolyte includes organic solvents, lithium salts, and additives.
  • the electrolyte of the present application includes lithium difluorophosphate (LiPO 2 F 2 ).
  • LiPO 2 F 2 lithium difluorophosphate
  • a chemical reaction occurs between the electrolyte and the positive electrode active material to form a stable solid electrolyte interface (SEI) film on the surface of the positive electrode, and the addition of lithium difluorophosphate can increase the SEI film LiF component, thereby enhancing the stability of the SEI film.
  • SEI solid electrolyte interface
  • the mass percentage of the lithium difluorophosphate ranges from 0.001% to 2%.
  • the mass percentage of the lithium difluorophosphate ranges from 0.001% to 1%. In some embodiments, based on the total mass of the electrolyte, the mass percentage of the lithium difluorophosphate ranges from 0.001% to 0.5%.
  • the electrolyte of the present application further includes a sulfur-containing additive, which can form a stable SEI film on the surface of the positive electrode, strengthen the protection of the positive electrode, and thereby improve the cycle stability of the electrochemical device.
  • the sulfur-containing additive includes 1,3-propane sultone (PS), wherein, based on the total mass of the electrolyte, the mass of the 1,3-propane sultone The range of the percentage is 0.01% to 3%.
  • the electrolyte of the present application further includes a polynitrile compound, the polynitrile compound comprising or selected from glutaronitrile, adiponitrile, 1,3,5-glutaronitrile, 1,2,3- Tricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris( 2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethyl) At least one of oxy)hexane or 1,2,5-tris(cyanoethoxy)pentane.
  • a polynitrile compound
  • the organic solvent of the electrolyte of the present application includes or is selected from at least one of the following: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, or dimethyl carbonate.
  • the organic solvent in the electrolyte includes ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC), and based on the total mass of the electrolyte, The mass percentage of EMC and DMC is not more than 20%.
  • the electrolyte can interact with the positive electrode active material described in this application, effectively reducing the gas production of the electrochemical device in a high-temperature environment, improving the safety performance of the electrochemical device and improving the electrochemical performance.
  • the cyclic stability of the device can interact with the positive electrode active material described in this application, effectively reducing the gas production of the electrochemical device in a high-temperature environment, improving the safety performance of the electrochemical device and improving the electrochemical performance.
  • the lithium salt of the electrolyte of the present application includes or is selected from at least one of the following: lithium hexafluorophosphate (LiPF 6 ), lithium bistrifluoromethanesulfonimide LiN(CF 3 SO 2 ) 2 (Abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 ) (abbreviated as LiFSI), lithium bisoxalate borate LiB(C 2 O 4 ) 2 (abbreviated as LiBOB), four Lithium fluorophosphate oxalate (LiPF 4 C 2 O 2 ), lithium difluorooxalate borate LiBF 2 (C 2 O 4 ) (abbreviated as LiDFOB), or lithium hexafluorocesium oxide (LiCsF 6 ).
  • LiPF 6 lithium hexafluorophosphate
  • LiFSI lithium bistrifluoromethanesulfonimide LiN(
  • 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, or 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.
  • the 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, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate one or a combination of several.
  • the binder may include or be selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyethylene One or a combination of pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer may include a polymer.
  • the polymer material may include or be selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, At least one of poly(vinylidene fluoride-hexafluoropropylene).
  • the electrochemical device of the present application may be a lithium ion battery or any other suitable electrochemical device.
  • the electrochemical devices in the embodiments of the present application include 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.
  • 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, electric 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.
  • the positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) prepared in the following examples and comparative examples were prepared at a weight ratio of 94:3:3 in N-methyl Stir and mix thoroughly in pyrrolidone to make a positive electrode slurry. Then, the obtained positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried at 85°C and cold pressed to obtain the positive electrode active material layer, which is divided into strips, cut pieces, Weld the positive electrode tabs to obtain the positive electrode.
  • PVDF polyvinylidene fluoride
  • the artificial graphite, styrene butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are mixed thoroughly in deionized water at a weight ratio of 97:2:1 to make a negative electrode slurry.
  • the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and then dried at 85° C. to form a negative electrode active material layer, and then cold pressing, slitting, cutting, and welding the negative electrode tabs are performed to obtain the negative electrode.
  • ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are prepared in accordance with the quality
  • the concentration of LiPF 6 is 1.10 mol/L.
  • the percentage of the electrolyte is based on the total weight of the electrolyte.
  • PE polyethylene
  • 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 isolation, and wind, place in the aluminum plastic film, and inject the matched
  • the electrolyte is encapsulated, and the final lithium-ion battery is made after chemical conversion.
  • the roundness of the positive electrode active material particles was tested with a roundness meter of model DTP-550A.
  • the laser particle size method was used to analyze the median diameter Dv50 of the positive electrode active material particles, and the judgment standard was GB/T19077-2016.
  • the median diameter was used to calculate the cross-sectional area of the positive electrode active material.
  • the FT-361FM series low-resistance four-probe powder resistivity tester was used to test the powder resistivity of the positive electrode active material, and the test pressure was 5000 kg.
  • the total area of the cross section of the positive electrode sheet is S
  • the total area of particle A is S 1 (including broken particles)
  • the total area of broken particles in particle A is S 2
  • the area of the positive electrode current collector is S 3
  • the porosity is P, which is ignored
  • the area ratio of the conductive agent and the adhesive is greater than or equal to 0.4
  • the cross-sectional area of a single particle A is greater than or equal to 20 ⁇ m 2 .
  • the ratio of the total area of the broken particles to the total area of the particle A S 2 /S 1 ⁇ 100%;
  • the proportion of the total area of the particle B (SS 1 -S 3 )/S ⁇ 100%-P.
  • thermogravimetric analyzer and a mass spectrometer are used to test the position of the oxygen release peak and the amount of oxygen released of the positive electrode active material.
  • the test basis is ASTM D3418-15, GB/T 13464-2008 and GB/T 6041-2002.
  • a specific surface area analyzer (Tristar II 3020M) was used to test the specific surface area of the positive electrode active materials in the examples and comparative examples by nitrogen adsorption/desorption method measurement. Among them, the specific test is carried out in accordance with the national standard GB/T 19587-2017.
  • a Malvern particle size tester was used to test the particle size distribution of the positive electrode active materials in the examples and comparative examples to obtain the median particle size Dv50 of the positive electrode active material. Among them, the specific test is carried out according to the national standard GB/T19077-2016.
  • the thickness of the positive electrode current collector itself is the thickness of the current collector in the area where the positive electrode active material layer is not coated in the positive electrode;
  • the thickness of the positive electrode current collector itself is the thickness of the current collector before cold pressing of the positive electrode.
  • a scanning electron microscope (SEM) was used to test the positive electrode active material powder, the morphology of the positive electrode active material was observed with a suitable magnification, and the element distribution of the sample was analyzed with the X-ray energy spectrometer.
  • the thickness L 1 of the lithium ion batteries was measured with a micrometer. Then, the same lithium-ion battery was placed in a thermostat at 85° C. for storage for 12 hours, and the thickness L 2 of the lithium-ion battery was measured with a micrometer. The ratio of (L 2 -L 1 )/L 1 is calculated as the thickness change rate of the lithium ion battery under high temperature storage.
  • the lithium ion battery in the comparative example and the examples of the present application was charged and discharged through the following steps, and the cycle capacity retention rate of the lithium ion battery was calculated.
  • the cycle capacity retention rate of the lithium ion battery is calculated using the following formula: (C 300 /C 1 ) ⁇ 100%.
  • polycrystalline and single-crystalline materials are mixed according to a certain weight ratio to obtain the positive electrode active material described in Example 1 of the present application.
  • Example 2 to Example 8 The difference between Example 2 to Example 8 and Example 1 is that the weight ratio of the particles A and the particles B added to the positive electrode active material is different.
  • the weight of particles A and B can be reflected by the proportion of the total area of the particles A and the proportion of the total area of the particles B in Table 1 below.
  • Example 9-11 The difference between Example 9-11 and Example 1 is that the positive electrode active material of Example 9-11 is LiNi 0.88 Co 0.09 Mn 0.03 O 2 .
  • particles A and particles B with different weight ratios are respectively added to the positive electrode active materials described in Examples 9-11.
  • the weight of particles A and B can be calculated from the proportion of the total area of the particles A and the total area of the particles B in Table 1 below. The area accounted for to reflect.
  • Example 12 The difference between Example 12 and Example 1 is that the doping element in Example 1 is replaced with Ti element.
  • the difference between the embodiment 13 and the embodiment 1 is that the doping element in the embodiment 1 is replaced with the W element.
  • the difference between the embodiment 14 and the embodiment 1 is that the doping element in the embodiment 1 is replaced with the Zr element.
  • Example 15 The difference between Example 15 and Example 1 is that the doping element in Example 1 is replaced with Y element.
  • Embodiment 16 The difference between Embodiment 16 and Embodiment 1 is that the doping element in Embodiment 1 is replaced with Al element.
  • Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that only the particles B in Example 1 are used as the positive electrode active material.
  • Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that only the particles A in Example 1 are used as the positive electrode active material.
  • Comparative Examples 3 and 4 and Example 1 The difference between Comparative Examples 3 and 4 and Example 1 is that the weight ratio of the particles A and the particles B added to the positive electrode active material is different.
  • the weight of particles A and B can be reflected by the ratio of the cross section occupied by the particle A and the ratio of the cross section occupied by the particle B in Table 1 below.
  • Tables 1 to 3 list the structural parameter information of the positive electrode active materials obtained in Examples 1 to 16 and Comparative Examples 1 to 4 and the electrochemical performance of the obtained electrochemical device.
  • the total area of particle A and the size of particle B The total area is adjusted by controlling the mass ratio of particle A and particle B.
  • Example 1 to Example 5 in Table 2 it can be seen that by adjusting the proportion of particles A and particles B, especially controlling the total area of particles A within 32%, the deformation rate and particle crushing of aluminum foil can be significantly improved. And further improve the thickness expansion and electrochemical cycling performance of the electrochemical device under high-temperature environmental storage conditions.
  • Examples 12 to 16 changed the doping elements therein.
  • the crushing rate of the polycrystalline particles and the aluminum foil deformation rate in the positive electrode active material layer in Examples 12 to 16 can be maintained at a low level as in Example 1, and the thickness expansion degree of the electrochemical device under high-temperature environment storage conditions And electrochemical cycle performance can also be maintained.
  • the powder resistivities of the polycrystalline particles A used in Examples 1 to 16 are all in the range of 6 ⁇ cm to 10 ⁇ cm, while the types used in Examples 1 to 16
  • the powder resistivity of the single crystal particles B are all in the range of 20 ⁇ cm to 40 ⁇ cm.
  • the positive electrode active materials in Examples 1 to 16 have an oxygen release peak in the temperature range of 230°C to 245°C.
  • Examples 17 to 19 correspond to Example 5, but the difference from Example 5 is that the mass ratios of the active material, the conductive agent and the PVDF are different, and the specific ratios can be seen in Table 4 below.
  • the data in Table 4 shows that by controlling the content of the binder PVDF in the positive electrode active material layer within a certain range, the corresponding electrochemical device can exhibit excellent electrochemical performance, especially under high-temperature storage conditions. Lower thickness expansion and higher cycle capacity retention rate.
  • Examples 20 to 24 correspond to Example 5.
  • the difference between Examples 21 to 24 and Example 5 is that a first functional layer and/or a second functional layer are further added to the positive electrode, wherein the first functional layer is disposed between the positive electrode active material layer and the positive electrode current collector and the second functional layer The layer is disposed on the surface of the positive electrode active material layer.
  • the composition of the first functional layer and the second functional layer in Examples 20 to 22 is: the particles B prepared in Example 5, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 96 : 2.5:1.5 ratio in the N-methylpyrrolidone solvent system, fully stir and mix uniformly for coating.
  • PVDF polyvinylidene fluoride
  • the composition of the first functional layer and the second functional layer in Example 23 is: LiFePO 4 , conductive agent acetylene black, binder polyvinylidene fluoride (PVDF) in a weight ratio of 96:2.5:1.5 in N-form In the base pyrrolidone solvent system, stir and mix well for coating.
  • LiFePO 4 conductive agent acetylene black
  • PVDF binder polyvinylidene fluoride
  • the composition of the first functional layer and the second functional layer in Example 24 is: LiFe 0.442 Mn 0.558 PO 4 , conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) in a weight ratio of 96:2.5:1.5 In the N-methylpyrrolidone solvent system, stir and mix well for coating.
  • VDF polyvinylidene fluoride
  • Example 5 the deformation rate of the aluminum foil of Examples 20 to 24 is further reduced, while the particle breakage rate and the thickness change rate stored at high temperature are further reduced, and the cycle capacity retention rate is further improved.
  • the substances in the first functional layer and/or the second functional layer can play a good buffering role, protect the positive electrode current collector, and ensure that the polycrystalline particles A in the positive electrode active material layer are in the electrode preparation process (especially It is a cold pressing process) and the process of charging and discharging the electrochemical device is not prone to particle breakage.
  • Example 25 the formulation of the electrolyte solution of Example 5 was adjusted, and the components and their contents added in the electrolyte solution were as shown in Table 6.
  • the mass percentage is not more than 1% Lithium difluorophosphate, a polynitrile compound with a mass percentage of not more than 4%, a fluoroethylene carbonate (FEC) with a mass percentage of not more than 5%, or a combination thereof, the resulting electrochemical devices can all show excellent electricity Chemical properties.
  • PS 1,3-propane sultone
  • FEC fluoroethylene carbonate
  • 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 “exemplified”, which are not necessarily quoting the same embodiment or example in this application.
  • the specific features, structures, materials or characteristics herein can be combined in one or more embodiments or examples in any suitable manner.

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Abstract

本申请涉及电化学装置及包含其的电子装置。所述电化学装置包含正极，所述正极包含正极集流体和正极活性材料层，所述正极活性材料层包含颗粒A和颗粒B，所述颗粒A的圆形度为R A，截面积为SA；所述颗粒B的圆形度为RB，截面积为SB，其中RB＜0.4≤RA，SB＜20μm2≤SA，其中以所述正极垂直于所述正极集流体方向的截面的总面积计，所述颗粒A的总面积占比与所述颗粒B的总面积占比的比值为1:9至8:2。本申请所述的电化学装置能够呈现出优异的电化学性能，尤其是能够降低产气并改善电化学装置的循环稳定性。

Description

电化学装置及包含其的电子装置 技术领域
本申请涉及储能技术领域，更具体地，涉及电化学装置及包含其的电子装置。
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，这就要求电动汽车中的能源设备具有高的能量密度；同时，人们还要求其能源设备具有长的使用寿命，这就要求所述能源设备的容量不能随着充放电循环的进行而发生快速衰减。为了满足人们的上述需求，合成具有高的比容量和循环稳定性的正负极材料成为了近年来的研究热点之一。
发明内容
本申请提供一种电化学装置和应用所述电化学装置的电子装置，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。
根据本申请的一个层面，本申请提供了一种电化学装置，其包含正极，所述正极包含正极集流体和正极活性材料层，所述正极活性材料层包含颗粒A和颗粒B，所述颗粒A的圆形度为R A，截面积为S A；所述颗粒B的圆形度为R B，截面积为S B，其中R B＜0.4≤R A，S B＜20μm 2≤S A，以所述正极垂直于所述正极集流体方向的截面的总面积计，所述颗粒A的总面积占比与所述颗粒B的总面积占比的比值为1:9至8:2。
根据本申请的实施例，所述颗粒A满足关系式(a)至(c)中的至少一者：(a)以所述正极垂直于所述正极集流体方向的截面的总面积计，所述颗粒A的总面积占比为5％至50％；(b)所述颗粒A的电阻率为6Ω·cm至10Ω·cm；(c)所述颗粒A包含具有式为Li 1+aNi xMn yCo zM mO 2的化合物，其中-0.05≤a＜0.3，0.8≤x＜1，0＜y≤0.2，0＜z≤0.2，0＜m＜0.2，其中元素M选自Al、Ti、W、Zr、Nb、In、Ru、Sb、Sr、Y中的一种或多种。
根据本申请的实施例，所述颗粒A中包含破碎颗粒，所述破碎颗粒满足关系(d)至(e)中的至少一者：(d)以所述正极垂直于所述正极集流体方向的截面的总面积计，所述破碎颗粒的总面积占比为不大于15％；(e)以所述颗粒A的总面积计，所述破碎颗粒的总面积占比为不大于30％。
根据本申请的实施例，所述颗粒B满足关系(f)至(h)中的至少一者：(f)以所述正极垂直于所述正极集流体方向的截面的总面积计，所述颗粒B的总面积占比为5％至60％；(g)所述颗粒B的电阻率为20Ω·cm至40Ω·cm；(h)所述颗粒B包含具有式为Li 1+aNi xMn yCo zM mO 2的化合物，其中-0.05≤a＜0.3，0.8≤x＜1，0＜y≤0.2，0＜z≤0.2，0＜m＜0.2，其中元素M选自Al、Ti、W、Zr、Nb、In、Ru、Sb、Sr、Y中的一种或多种。
根据本申请的实施例，其中所述正极活性材料层满足关系(i)至(j)中的至少一者：(i)所述正极活性材料层的孔隙率≤25％；(j)在TG-MS测试中，所述正极活性材料在230℃至245℃具有释氧峰。
根据本申请的实施例，所述正极活性材料的比表面积为0.1m 2/g至1.2m 2/g。
根据本申请的实施例，所述正极活性材料层进一步包含粘结剂和导电剂，其中以所述正极活性材料层的总质量计，所述粘结剂的含量为1.25％至5％。
根据本申请的实施例，所述正极进一步包含功能层，所述功能层设置于所述正极活性材料层上，和/或设置于所述正极活性材料层与所述正极集流体之间。
根据本申请的实施例，所述功能层满足关系(1)至(4)中的至少一者：(1)所述功能层设置于所述正极活性材料层上，所述正极活性材料层设置于所述正极集流体上，所述正极活性材料层的厚度与所述功能层的厚度比为99:1至 50:50；(2)所述功能层设置于所述正极活性材料层与所述正极集流体之间，所述正极活性材料层的厚度与所述功能层的厚度比为99:1至50:50；(3)所述功能层设置于所述正极活性材料层上，且所述功能层设置于所述述正极活性材料层与所述正极集流体之间，所述正极活性材料层的厚度与所述功能层的厚度比为99:1至50:50；(4)所述功能层包括物质C，所述物质C包含锂钴氧化物、磷酸铁锂、磷酸锰铁锂或锂锰氧化物中的至少一种，所述物质C的粒径Dv50在0.5μm至6μm范围内。
根据本申请的实施例，所述正极集流体的变形率≤32％。
根据本申请的一个层面，本申请提供了一种电子装置，其包括本申请的电化学装置。
在至少一个方面，通过将颗粒A和颗粒B同时用作电化学装置的正极活性材料，能够有效地解决电化学装置在高温存储和充放电的过程中存在的颗粒破碎、表面副反应、释氧等问题，从而降低电化学装置的产气程度并且改善电化学装置的循环稳定性，其中颗粒A和颗粒B分别具有不同的圆形度和截面积。
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和图1B分别为LiNi 0.88Co 0.09Mn 0.03O 2颗粒A和LiNi 0.88Co 0.09Mn 0.03O 2颗粒B的扫描电子显微镜(SEM)图；
图2A示出了LiN i0.88Co 0.09Mn 0.028Zr 0.002O 2颗粒A的SEM图，而图2B示出了掺杂元素Zr在所述多晶颗粒中的体相分布图；
图3A和图3B分别示出了对比例1和实施例3中的正极冷压后的界面 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。
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”、“中的至少一者”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。
术语“圆形度”是指颗粒的横截面接近理论圆的程度。圆形度R＝(4π×面积)/(周长×周长)，R为1时，颗粒即为圆形；R越小，颗粒的形貌越不规律，与圆形的差距越大。本申请采用圆度仪测量正极活性材料颗粒的圆形度，具体测试方法可参见下述具体实施例的部分。
术语“破碎颗粒”是指在扫描电镜下，在图像内颗粒的剖面内，连续的长度不小于0.1μm，宽度不小于0.01μm的纹路，视为裂纹，具有裂纹的颗粒视为破碎颗粒。
术语“中值粒径Dv50”表示在体积基准的粒度分布中，从小粒径测起，达到体积累积50％的粒径。
一、电化学装置
目前市场上的锂离子电池大多采用钴酸锂作为正极活性材料。然而，钴元素是一种高毒、高成本且资源有限的元素，因此开发低钴正极活性材料是电化学装置发展的必然趋势。在新一代的锂离子电池中，极具应用前景的正极活性材料是含镍材料，尤其是高镍材料，其中高镍材料指的是以正极活性材料中含有的除了金属锂以外的其它金属元素的含量总和计，镍的摩尔含量至少占比50％以上的材料。
在正极活性材料含镍三元材料中，镍元素的主要作用是提升能量密度。在相同的充放电电压范围，镍元素含量越高，克容量越高。然而，在将高镍材料用于电化学装置的实际应用中，高镍材料由于在相同的电压下脱锂量高，晶胞体积膨胀和收缩大，导致颗粒容易发生破碎且容易与电解液发生副反应。而在颗粒破碎后，会暴露出新的界面，导致电解液通过裂缝渗入至颗粒内部并与处于新的界面处的正极活性材料发生副反应，加剧产气的发生并且导致电化学装置的容量随着充放电循环的进行而快速衰减。此外，在电化学装置充电的过程中，随着锂离子从正极活性材料中不断地脱出，正极活性材料中的活性金属(例如，镍元素)与氧的结合作用力减弱，发生释氧，释出的氧将氧化电解液，加剧产气。上述这些问题严重限制了高镍材料在高能量密度电化学装置中的应用。
至少基于对高镍材料的上述洞察，本申请提出了将正极活性材料的颗粒A和颗粒B同时引入至正极活性材料层中作为电化学装置的正极来克服应用高镍材料的上述缺陷。
颗粒A为众多单晶颗粒的集合，其中单晶为在其内部的微粒在三维空间呈有规律地、周期性地排列的结晶体。如本申请图1A所示，颗粒A的形貌呈现为球形或椭球形，其圆形度R A较大，且截面积S A也较大。在本申请的一些实施例中，颗粒A为多晶颗粒。相较于颗粒A，颗粒B是晶粒尺寸较大的单晶的集合。如本申请图1B所示，颗粒B的形貌是不规则的，其圆形度R B较小，且截面积S B也较小。在本申请的一些实施例中，颗粒B为类单晶颗粒。
在一些实施例中，正极活性材料的颗粒A和颗粒B满足R B＜0.4≤R A且S B ＜20μm 2≤S A。通过控制颗粒A和颗粒B的加入比例能够进一步优化电化学装置的电化学性能。在一些实施例中，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒A的总面积占比与颗粒B的总面积占比的比值在1:9至8:2的范围内。在一些实施例中，颗粒A的总面积占比与颗粒B的总面积占比的比值在2:8至8:2的范围内。
本申请所述的电化学装置的电化学性能之所以能够得到改善的原因之一为：颗粒B的加入能够有效地降低颗粒A的破碎程度。电化学装置充放电的过程即为锂离子从正极活性材料中嵌入或脱出的过程，在这一过程中，正极活性材料的晶胞体积会发生剧烈的收缩和膨胀。由于颗粒A的粒径较大且多个颗粒A之间的接触为刚性接触，当各个颗粒A的晶胞体积发生剧烈的膨胀和收缩时，该多个颗粒A之间会发生刚性碰撞从而加剧颗粒的破碎。与之相比，颗粒B的形貌是不规则的且颗粒粒径较小，当在颗粒A中加入颗粒B时，颗粒B能够在两个颗粒A之间起到很好的缓冲作用，减少颗粒A之间的刚性碰撞，从而减少颗粒的破碎并抑制副反应的发生。
颗粒A具有较大的圆形度和截面积，其具有电阻率低的优势，但颗粒A在冷压和/或循环过程中易发生颗粒破碎问题。通过优化颗粒A在正极活性材料层中的面积占比、电阻率或其具体成分中的至少一者能够进一步优化电化学装置的电化学性能。在一些实施例中，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒A的总面积占比在5％至50％的范围内。在一些实施例中，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒A的总面积占比在5％至45％的范围内。在一些实施例中，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒A的面积占比在8％至30％的范围内。颗粒A的总面积占比在此范围内所得到的电化学装置具有优异的电化学性能，尤其是其在高温存储条件下的产气程度会显著降低且其循环稳定性会得到明显改善。
在本申请中，颗粒A具有较低的粉末电阻率以促进电子在颗粒A之间的快速传输。在一些实施例中，所述颗粒A的粉末电阻率在10Ω·cm以下。在一些实施例中，所述颗粒A的粉末电阻率在9Ω·cm以下。在一些实施例中，所述颗粒A的粉末电阻率在8Ω·cm以下。在一些实施例中，所述颗粒A的粉末电阻率处于6Ω·cm至10Ω·cm的范围内。
在一些实施例中，颗粒A为含镍三元材料。术语“三元材料”为本领域公知的三元材料，例如记载于《锂离子电池三元材料-工艺技术及生产应用》(王伟东，仇卫华，丁倩倩等编著，化学工业出版社，2015年5月)中的三元材料。在一些实施例中，本申请所述的含镍三元材料包括镍钴锰酸锂。
在一些实施例中，颗粒A包括或选自至少一种具有式为Li 1+aNi xMn yCo zM mO 2的化合物，其中-0.05≤a＜0.3，0.8≤x＜1，0＜y≤0.2，0＜z≤0.2，0＜m＜0.2，其中元素M包括或选自Al、Ti、W、Zr、Nb、In、Ru、Sb、Sr、Y中的一种或多种。在一些实施例中，上述元素M能够均匀地掺杂在颗粒A的体相和表面中。例如，如图2B所示，本申请实施例4的颗粒A的组成为LiNi 0.88Co 0.09Mn 0.028Zr 0.002O 2，而经掺杂的Zr元素均匀地分布在颗粒A的表面和体相。
在将颗粒A制备成正极的过程中，需要采用冷压工艺将正极活性材料颗粒紧密压制在一起来提高正极活性材料层的压实密度(简称，压密)，从而提高电化学装置的能量密度并降低电化学装置的直流阻抗(DCR)。此外，上述冷压工艺还会将正极活性材料层与正极集流体紧密压制在一起以防止在电化学装置充放电过程中正极活性材料层与正极集流体之间的分离。然而，冷压工艺会导致颗粒A的破碎，压密的大小与颗粒A的破碎程度成正相关的关系，即压密越大，颗粒A的破碎也越严重。因此，在保持极片处于高压密状态下，减轻颗粒A的破碎程度也是本申请所关注的技术问题之一。
在本申请中，由于颗粒B的加入能够起到很好的缓冲作用，因此，在一些实施例中，在高压实密度下(例如，在3.5g/cc的压实密度下)，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒A中的破碎颗粒的总面积占比不大于15％。在一些实施例中，在高压实密度下(例如，在3.5g/cc的压实密度下)，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒A中破碎颗粒的总面积占比不大于14％。在一些实施例中，在高压实密度下(例如，在3.5g/cc的压实密度下)，以所述正极垂直于所述正极集流体方向的的总面积计，颗粒A中的破碎颗粒的面积占比不大于12％。在一些实施例中，在高压实密度下(例如，在3.5g/cc的压实密度下)，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒A中的破碎颗粒的总面积占比不大于11％。
在一些实施例中，在高压实密度下(例如，在3.5g/cc的压实密度下)，以颗粒A的总面积计，破碎颗粒的总面积占比不大于30％。在一些实施例中，在高压实密度下(例如，在3.5g/cc的压实密度下)，以颗粒A的总面积计，破碎颗粒的总面积占比不大于24％。在一些实施例中，在高压实密度下(例如，在3.5g/cc的压实密度下)，以颗粒A的总面积计，破碎颗粒的总面积占比不大于20％。
颗粒B具有较小的圆形度和截面积，其主要作用为：降低颗粒A在电极制备过程(尤其是冷压过程)和电化学装置充放电过程中的破碎程度；提高极片的压实密度；以及提供较多的电化学活性位点来提高放电比容量。通过优化颗粒B在正极活性材料层中的面积占比、电阻率或其具体成分中的至少一者能够进一步优化电化学装置的电化学性能。在一些实施例中，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒B的面积占比在5％至60％的范围内。在一些实施例中，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒B的面积占比在8％至55％的范围内。在一些实施例中，以所述正极垂直于所述正极集流体方向的截面的总面积计，颗粒B的面积占比在10％至40％的范围内。
由于颗粒B的粒径较小，因此在相同的压力下，颗粒B之间的接触紧密度低于颗粒A，从而导致在相同压力下所测定的颗粒B的粉末电阻率高于颗粒A。在一些实施例中，所述颗粒B的粉末电阻率在20Ω·cm至40Ω·cm的范围内。在一些实施例中，所述颗粒B的粉末电阻率在25Ω·cm至35Ω·cm的范围内。其中本申请是采用电阻率测试仪测试电阻率的。
颗粒B的具体成分可以与颗粒A相同，也可以与颗粒A不同。在一些实施例中，颗粒B包括或选自至少一种具有式为Li 1+aNi xMn yCo zM mO 2的化合物，其中-0.05≤a＜0.3，0.8≤x＜1，0＜y≤0.2，0＜z≤0.2，0＜m＜0.2，其中元素M包括或选自Al、Ti、W、Zr、Nb、In、Ru、Sb、Sr、Y中的一种或多种。
正极活性材料层的孔隙率也会影响到电化学装置的产气。具体来讲，当正极活性材料层的孔隙率较大时，其中可存储的电解液的量较大，引发的副反应较多，从而导致产气量越大。在一些实施例中，所述正极活性材料层的孔隙率不大于25％。在一些实施例中，所述正极活性材料层的孔隙率不大于19％。孔隙率过大，会导致电化学装置中副反应增多，产气量增多。
在一些实施例中，采用热重-质谱联用测试(即，TG-MS测试)测定正极活性材料，所述正极活性材料在230℃至245℃的范围具有释氧峰。这说明掺杂可以抑制材料当中的氧释出，增强材料的结构稳定性。
正极活性材料的颗粒粒径(例如，中值粒径Dv50)也会影响到其在电化学装置中的电化学表现。正极活性材料的颗粒粒径越小，其比表面积会越大，其所提供的电化学活性点位也会越多，相应地正极活性材料的放电比容量也会增大。然而，当颗粒粒径过小时，也会带来一定的副作用。例如，当颗粒粒径较小时，其暴露的表面越大，其与电解液之间的副反应也会越严重，从而导致颗粒破碎并发生产气现象的风险也会相应地增加。因此，控制正极活性材料的颗粒粒径和比表面积在合适的区间内将会进一步优化正极活性材料的电化学性能。
在一些实施例中，本申请所述的正极活性材料的比表面积处于0.05m 2/g至2.0m 2/g的范围内。在一些实施例中，本申请所述的正极活性材料的比表面积处于0.1m 2/g至1.5m 2/g的范围内。在一些实施例中，本申请所述的正极活性材料的比表面积处于0.1m 2/g至1.2m 2/g的范围内。其中，本申请是利用BET物理吸附仪测定正极活性材料的比表面积，具体测试方法可参见下述实施例部分。
在一些实施例中，本申请所采用的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，除了本申请所述的正极活性材料外，所述正极活性材料层进一步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。在本申请中，粘合剂的非限制性示例包括聚乙烯醇、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。在本申请中，导电材料的非限制性示例包括基于碳的材料(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。
本申请发现如果正极中粘结剂的含量过少，则电化学装置在循环充放电和高温存储过程中正极活性材料层会脱离于正极集流体，加剧产气和副反应的发生，并且大幅提高电化学装置的阻抗。因此，作为本申请的一个改进，通过优化粘结剂在所述正极活性材料层中的含量，能够进一步优化电化学装置的电化学性能。在本申请的一些实施例中，以所述正极活性材料层的总质量计，所述粘结剂的含量在1％至5％的范围内。在本申请的一些实施例中，所述粘结剂的含量在1.25％至5％的范围内。在本申请的一些实施例中，所述粘结剂的含量在1.5％至5％的范围内。在本申请的一些实施例中，所述粘结剂的含量在1.5％至4.5％的范围内。在本申请的一些实施例中，所述粘结剂的含量在1.5％至4％的范围内。在本申请的一些实施例中，所述粘结剂的含量在1.8％至4％的范围内。
在一些实施例中，所述正极还包含一或多个功能层，所述功能层设置于所述正极活性材料层上，和/或设置于所述正极活性材料层与所述正极集流体之间以实现特定功能。
在一些实施例中，所述功能层包括第一功能层，其设置于所述正极活性材料层与所述正极集流体之间，其中所述正极活性材料层的厚度与所述第一功能层的厚度比在99:1至50:50的范围内。相较于大粒径的颗粒，小粒径的颗粒在相同的压力下柔性较好，而不容易发生颗粒破碎。因此，在一些实施例中，所述第一功能层包括或选自中值粒径Dv50在1.5μm至6μm范围内的颗粒。所述第一功能层位于所述正极活性材料层与所述正极集流体之间，能够降低在冷压过程中正极集流体的变形率从而维持正极集流体的耐腐蚀性。此外，所述第一功能层能够在冷压过程中起到缓冲的作用，保护正极活性材料层中的颗粒A在冷压过程中不会由于冷压应力而导致颗粒破碎。
在一些实施例中，所述第一功能层包括或选自本申请所述的类单晶颗粒B、LMFP和LMO中的一种或多种。其中，LMFP的化学式为LiFe 1-xMe xXO 4，元素Me为元素周期表中的第VIIB族和第VIII族中的元素中的一种或多种，元素X包括或选自P、Si、S、As和Sb中的一种或多种，其中0≤x＜1。其中，LMO的化学式为LiMn yMd 2-yO 4，元素Md为Al、Mg、Mn、Ni、Co、Fe、Gr、V、Ti、 Cu、B、Ga、Zn、Zr、Nb、Mo、Sr、Sb、W及Bi中的一种或多种，其中0＜y≤2。在一些实施例中，所述第一功能层包括或选自锂钴氧化物、磷酸铁锂、磷酸锰铁锂或锂锰氧化物中的至少一种。
在一些实施例中，所述功能层包括第二功能层，其设置于所述正极活性材料层上而所述正极活性材料层设置于所述正极集流体上，其中所述正极活性材料层的厚度与所述第二功能层的厚度比在99:1至50:50的范围内。在一些实施例中，与所述第一功能层类似，所述第二功能层包括或选自中值粒径Dv50在0.5μm至6μm范围内的颗粒。在一些实施例中，所述第二功能层包括或选自本申请所述的颗粒B、LMFP和LMO中的一种或多种。在一些实施例中，所述第二功能层包括或选自锂钴氧化物、磷酸铁锂、磷酸锰铁锂或锂锰氧化物中的至少一种。第二功能层覆盖在正极活性材料层的表面，能够起到缓冲的作用，保护正极活性材料层中的多晶颗粒A在冷压过程中不会由于冷压应力而导致颗粒破碎。
在一些实施例中，所述功能层同时包括上文所描述的第一功能层和第二功能层，其中所述正极活性材料层的厚度与所述第一功能层和所述第二功能层的厚度之和的比值在99:1至50:50的范围内。在一些实施例中，所述正极活性材料层的厚度与所述第一功能层和所述第二功能层的厚度之和的比值在99:1至50:50的范围内。
在较大的压实密度下(例如，当压实密度在3.4g/cc以上时)，正极集流体(例如，铝箔)的变形率会上升，导致在单位面积的正极集流体上涂覆的正极活性材料的重量下降，从而影响加工性能。同时，正极集流体的表面通常含有防止电解液腐蚀的保护层，当正极集流体的变形率较高时，正极集流体表面的保护层会遭到破坏，从而降低正极集流体对电解液的耐腐蚀性。
但是，在本申请的一些实施例中，当压实密度在3.4g/cc以上时，所述正极集流体的变形率不大于40％。在一些实施例中，当压实密度在3.4g/cc以上时，所述正极集流体的变形率不大于30％。在一些实施例中，当压实密度在3.4g/cc以上时，所述正极集流体的变形率不大于20％。在一些实施例中，当压实密度在3.4g/cc以上时，所述正极集流体的变形率不大于10％。在一些实施例中，当压实密度在3.4g/cc以上时，所述正极集流体的变形率不大于5％。在本申请中，正极 集流体的变形率是指正极集流体厚度方向上未变形部分与正极集流体本身厚度的比值。例如，参见图3A和3B所示的SEM图，正极集流体的变形率的计算公式为：(正极集流体本身厚度-d)/正极集流体本身厚度×100％。
在一些实施例中，本申请所述的电化学装置还包括负极，其中所述负极包括负极活性材料层和负极集流体，所述负极活性材料层包含本申请所述的负极活性材料。负极活性材料能够可逆地嵌入和脱出锂离子。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，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。
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与前述相同的材料，在此不做过多赘述。
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，能够更好地稳定正极活性材料的界面，抑制正极活性材料与电解液之间的副反应，从而降低产气并改善电化学装置的循环性能。电解液可以分为水系电解液和非水系电解液，其中相较于水系电解液，采用非水系电解液的电化学装置可以在较宽的电压窗口下工作，从而达到较高的能量密度。在一些实施例中，非水系电解液包括有机溶剂、锂盐和添加剂。
在一些实施例中，本申请的电解液包括二氟磷酸锂(LiPO 2F 2)。在电化学首次充放电的过程中，电解液和正极活性材料之间会发生化学反应而在正极表面形成稳定的固态电解质界面(SEI)膜，而二氟磷酸锂的加入能够增加SEI膜中的LiF成分，从而增强SEI膜的稳定性。在一些实施例中，以所述电解液的总质量计，所述二氟磷酸锂的质量百分比的范围为0.001％至2％。在一些实施例中，以所述电解液的总质量计，所述二氟磷酸锂的质量百分比的范围为0.001％至1％。在一些实施例中，以所述电解液的总质量计，所述二氟磷酸锂的质量百分比的范围为0.001％至0.5％。
在一些实施例中，本申请的电解液还包括含硫添加剂，所述含硫添加剂能够在正极表面形成稳定的SEI膜，加强对正极的保护，从而改善电化学装置的循环稳定性。在一些实施例中，所述含硫添加剂包括1,3-丙烷磺酸内酯(PS)，其中，以所述电解液的总质量计，所述1,3-丙烷磺酸内酯的质量百分比的范围为0.01％至3％。
在一些实施例中，本申请的电解液还包括多腈化合物，所述多腈化合物包含或选自戊二腈、己二腈、1,3,5-戊三甲腈、1,2,3-丙三甲腈、1,3,6-己三甲腈、1,2,6-己三甲腈、1,2,3-三(2-氰基乙氧基)丙烷、1,2,4-三(2-氰基乙氧基)丁烷、1,1,1-三(氰基乙氧基亚甲基)乙烷、1,1,1-三(氰基乙氧基亚甲基)丙烷、3-甲基-1,3,5-三(氰基乙氧基)戊烷、1,2,7-三(氰基乙氧基)庚烷、1,2,6-三(氰基乙氧基)己烷或1,2,5-三(氰基乙氧基)戊烷中的至少一种。在一些实施例中，以所述电解液的总质量计，所述多腈化合物的质量百分比的范围为0.01％至10％。
在一些实施例中，本申请的电解液的有机溶剂包括或选自以下各者中的至少一种：碳酸乙烯酯、碳酸丙烯酯、碳酸二乙酯、碳酸甲乙酯或碳酸二甲酯。作为对本申请的另一改进，在一些实施例中，所述电解液中的有机溶剂包括碳酸甲乙酯(EMC)和碳酸二甲酯(DMC)，且以所述电解液的总质量计，所述EMC和DMC的质量百分比不大于20％。在这些实施例中，所述电解液能够与本申请所述的正极活性材料之间相互作用，有效地降低电化学装置在高温环境下的产气，提高电化学装置的安全性能并改善电化学装置的循环稳定性。
在一些实施例中，本申请的电解液的锂盐包括或选自以下各者中的至少一种： 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)或六氟铯酸锂(LiCsF 6)。
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。在一些实施例中，基材层为具有多孔结构的无纺布、膜或复合膜。在一些实施例中，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或聚酰亚胺中的至少一种。在一些实施例中，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。
在一些实施例中，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。
无机物层可以包括无机颗粒和粘结剂。在一些实施例中，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。在一些实施例中，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。
聚合物层可以包括聚合物。在一些实施例中，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，本申请实施例中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。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。
二、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。
三、实施例
锂离子电池的制备
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、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比94：3：3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流体铝箔上，之后在85℃下烘干，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：将人造石墨、丁苯橡胶(SBR)、羧甲基纤维素钠(CMC) 按照重量比97：2：1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流体铜箔上，然后在85℃下烘干，形成负极活性材料层，然后进行冷压、分条、裁片、焊接负极极耳，得到负极。
(3)电解液的制备：在干燥的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照质量比为EC:PC:EMC:DEC＝15:15:30:40进行混合，接着加入3％的氟代碳酸乙烯酯(FEC)，1.5％的1,3-丙烷磺内酯(PS)，1％的1,3,6-己三甲腈，溶解并充分搅拌后加入锂盐LiPF 6，混合均匀后获得电解液。其中，LiPF 6的浓度为1.10mol/L。电解液中的百分含量是基于电解液的总重量。(4)隔离膜的制备：隔离膜采用聚乙烯(PE)多孔聚合薄膜。
(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，并卷绕、置于铝塑膜中，注入配好的电解液并封装，进行化成之后制成最终的锂离子电池。
颗粒圆形度和截面积的测试方法
利用型号为DTP-550A的圆度仪测试正极活性材料颗粒的圆形度。
利用激光粒度法分析正极活性材料颗粒的中值粒径Dv50，判断标准为GB/T19077-2016。利用中值粒径计算正极活性材料的截面积。
粉末电阻率测试
利用型号为FT-361FM系列低阻四探针粉末电阻率测试仪测试正极活性材料的粉末电阻率，其中测试采用的压力为5000公斤。
破碎多晶颗粒的面积占比测试
利用离子抛光机(型号为日本电子-IB-09010CP)，沿垂直于正极集流体方向切割正极，得到断面。利用扫描电子显微镜以合适的放大倍数观察上述断面，使用背散模式拍摄图片，利用Image J软件识别图形形貌的功能而识别出颗粒A、颗粒A中的破碎颗粒、集流体，并相应地计算出其各自对应的面积。正极片截面的总面积为S，颗粒A的总面积为S 1(包含破碎颗粒)，颗粒A中破碎颗粒的总面积为S 2，正极集流体的面积为S 3，孔隙率为P，忽 略导电剂和粘结的面积占比。在本申请中，颗粒A的圆形度大于或等于0.4，单个颗粒A的截面积大于或等于20μm 2。
颗粒A的总面积占比＝S 1/S×100％；
颗粒A中破碎颗粒总面积占比＝S 2/S×100％；
破碎颗粒的总面积占颗粒A的总面积占比＝S 2/S 1×100％；
颗粒B的总面积占比＝(S-S 1–S 3)/S×100％-P。
正极活性材料层的孔隙率测试
利用气体置换法测试正极活性材料层的孔隙率P，P＝(V-V0)/V×100％，其中V0为真体积，V为表观体积，测试依据为GB/T 24586-2009铁矿石表观密度、真密度和孔隙率的测定。
热重-质谱(TG-MS)联用测试
利用热重分析仪器和质谱仪联用对正极活性材料的释氧峰的位置和释氧量进行测试，测试依据为ASTM D3418-15、GB/T 13464-2008和GB/T 6041-2002。
BET比表面积测试
使用比表面积分析仪(TristarⅡ3020M)，通过氮吸附/脱附法测量对实施例和对比例中的正极活性材料进行比表面积测试。其中，具体的测试依据国家标准GB/T 19587-2017进行。
中值粒径Dv50测试
使用马尔文粒度测试仪对实施例和对比例中的正极活性材料进行粒径分布测试，得到正极活性材料的中值粒径Dv50。其中，具体的测试依据国家标准GB/T19077-2016进行。
正极的压实密度测试
利用单位质量的活性物质/单位体积得到。利用电子秤称量单位面积为A的集流体和正极片，重量分别记为M1和M2；利用万分尺测量集流体和正极 片的厚度，厚度分别记为C1和C2。正极的压实密度＝[(M2-M1)/(C2-C1)]/A
正极集流体的变形率测试
利用离子抛光机(型号为日本电子-IB-09010CP)，沿垂直于正极集流体方向切割正极，得到断面。利用扫描电子显微镜以合适的放大倍数观察上述断面，利用扫描电子显微镜自身的标尺测定正极集流体厚度方向上未变形部分d。
利用如下计算公式计算正极集流体的变形率：(正极集流体本身厚度-d)/正极集流体本身厚度×100％；
当正极中存在未涂覆正极活性材料层区域时，正极集流体本身厚度为正极中未涂覆正极活性材料层区域集流体的厚度；
当正极中不存在未涂覆正极活性材料层区域时，正极集流体本身厚度为正极冷压前集流体的厚度。
扫描电子显微镜(SEM)测试
利用扫描电子显微镜(SEM)对正极活性材料粉末进行测试，使用合适的放大倍数观测正极活性材料的形貌，并使用与之配套的X射线能谱仪对样品的元素分布进行分析。
锂离子电池在高温存储下的厚度变化率测试
在将实施例和对比例中的锂离子电池放置于温度为25℃的恒温环境下24h后，利用千分尺测试锂离子电池的厚度L 1。然后再将相同的锂离子电池放置于温度为85℃的恒温箱中存储12h，利用千分尺测试锂离子电池的厚度L 2。计算(L 2-L 1)/L 1的比值作为锂离子电池的高温存储下的厚度变化率。
锂离子电池在45℃下的循环充放电测试
通过以下步骤对本申请对比例和实施例中的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45℃的环境中，进行第一次充放电循环。以0.5C的电流对锂离子电池进行恒流和恒压充电，直到上限电压为4.25V；然后以0.5C的电流 对锂离子电池进行恒流放电，直到截止电压为2.8V，记录首次循环的放电容量C 1。随后，按照上述充放电流程进行300次的充放电循环，记录第300次循环的放电容量C 300。
利用如下公式计算锂离子电池的循环容量保持率：(C 300/C 1)×100％。
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至16和对比例1至4
实施例1至实施例8
按照LiNi 0.88Co 0.09Mn 0.028Al 0.001Zr 0.002O 2的化学剂量比准备Dv50为12μm的前驱体Ni 0.88Co 0.09Mn 0.028(OH) 2、氢氧化锂和纳米Al 2O 3，并将其研磨均匀，在740℃下进行煅烧12h，研磨过筛，得到Dv50为12μm多晶形貌的材料。
按照LiNi 0.88Co 0.09Mn 0.028Al 0.001Zr 0.002O 2的化学剂量比准备Dv50为4μm的前驱体、氢氧化锂和纳米Al 2O 3、ZrO 2，并将其研磨均匀，在780℃下进行煅烧14h，研磨过筛，得到Dv50为2.5μm类单晶形貌的材料。
将上述多晶和类单晶材料按照一定的重量比混合，得到本申请实施例1所述的正极活性材料。
实施例2至实施例8与实施例1的区别在于正极活性材料中加入的颗粒A和颗粒B的重量比不同。其中颗粒A和B的重量可以由下表1中的颗粒A总面积占比和颗粒B总面积占比来反映。
实施例9至实施例11
实施例9-11与实施例1的差异在于：实施例9-11的正极活性材料为LiNi 0.88Co 0.09Mn 0.03O 2。其中，在实施例9-11所述的正极活性材料中分别加入重量比不同的颗粒A和颗粒B，颗粒A和B的重量可以由下表1中的颗粒A总面积占比和颗粒B总面积占比来反映。
实施例12
实施例12和实施例1的差异在于：将实施例1中的掺杂元素替换为Ti元素。
实施例13
实施例13和实施例1的差异在于：将实施例1中的掺杂元素替换成W元素。
实施例14
实施例14和实施例1的差异在于：将实施例1中的掺杂元素替换成Zr元素。
实施例15
实施例15和实施例1的差异在于：将实施例1中的掺杂元素替换成Y元素。
实施例16
实施例16和实施例1的差异在于：且将实施例1中的掺杂元素替换成Al元素。
对比例1-4
对比例1和实施例1的区别在于：仅采用实施例1中的颗粒B作为正极活性材料。
对比例2和实施例1的区别在于：仅采用实施例1中的颗粒A作为正极活性材料。
对比例3和4和实施例1的区别在于：正极活性材料中加入的颗粒A和颗粒B的重量比不同。其中颗粒A和B的重量可以由下表1中的颗粒A所占截面的比值和颗粒B所占截面的比值来反映。
下述表1至表3列出了实施例1至16和对比例1至4所得正极活性材料的结构参数信息和所得电化学装置的电化学性能，表中颗粒A的总面积和颗粒B的总面积通过控制颗粒A和颗粒B的质量比来调整。
参见表1的数据可知，相较于对比例1-4，通过在正极活性材料中采用颗粒A(多晶颗粒)和颗粒B(单晶颗粒)的混合物并且控制颗粒A的总面积占比与颗 粒B的总面积占比的比值在1:9至8:2的范围内，实施例1至实施例11的电化学装置在高温环境存储条件下的厚度膨胀程度和电化学循环性能得到了改善。
参见表1的数据可知，从整体水平来看，相较于实施例1-8，实施例9-11的电化学数据稍差。这是因为，相较于实施例9-11，实施例1-8的正极活性材料经过了元素掺杂，掺杂元素起到稳定材料中氧的作用，减少了氧的释出，从而减少氧对电解液的氧化，达到降低产气的目的。
参见表2实施例1至实施例5的数据可知，通过调整颗粒A和颗粒B的占比，尤其是控制颗粒A的总面积占比在32％以内，能够显著改善铝箔的变形率和颗粒破碎率，并且进一步改善电化学装置在高温环境存储条件下的厚度膨胀程度和电化学循环性。
相较于实施例1，实施例12至16改变了其中的掺杂元素。实施例12至16中的正极活性材料层中的多晶颗粒的破碎率和铝箔变形率能够与实施例1一样保持在较低的水平，且电化学装置在高温环境存储条件下的厚度膨胀程度和电化学循环性能也能得到保持。
此外，参见下述表3的数据可知，实施例1至16所采用的多晶颗粒A的粉末电阻率均在6Ω·cm至10Ω·cm的范围内，而实施例1至16所采用的类单晶颗粒B的粉末电阻率均在20Ω·cm至40Ω·cm的范围内。另外，通过TG-MS测试，可以测得实施例1至16中的正极活性材料在230℃至245℃的温度范围内具有释氧峰。
表1
Figure PCTCN2020081800-appb-000001
Figure PCTCN2020081800-appb-000002
表2
Figure PCTCN2020081800-appb-000003
Figure PCTCN2020081800-appb-000004
表3
Figure PCTCN2020081800-appb-000005
实施例17至19
实施例17至19对应于实施例5，但是其与实施例5的差异在于活性物质、导电剂和PVDF的质量比例不同，具体比例可参见下表4。
表4
Figure PCTCN2020081800-appb-000006
参见表4中的数据可知，通过控制粘结剂PVDF在正极活性材料层中的含量在一定范围内，所对应的电化学装置能够表现出优异的电化学性能，尤其是在高温存储条件下的较低的厚度膨胀程度和较高的循环容量保持率。
实施例20至24
实施例20至24对应于实施例5。实施例21至24与实施例5的差异在于在正极中进一步增加第一功能层和/或第二功能层，其中第一功能层设置于正极活性材料层和正极集流体之间而第二功能层安置于正极活性材料层的表面上。
实施例20至22中的第一功能层和第二功能层的组成为：采用实施例5所制备的颗粒B、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比96：2.5：1.5的比例在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀进行涂覆。
实施例23中的第一功能层和第二功能层的组成为：将LiFePO 4、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比96：2.5：1.5在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀进行涂覆。
实施例24中的第一功能层和第二功能层的组成为：将LiFe 0.442Mn 0.558PO 4、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比96：2.5：1.5在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀进行涂覆。
表5-1
Figure PCTCN2020081800-appb-000007
Figure PCTCN2020081800-appb-000008
表5-2
Figure PCTCN2020081800-appb-000009
参见表5-2所示的数据可知，相较于对比例2，实施例5和实施例20至24的铝箔变形率、颗粒破碎率以及在高温下存储的厚度变化率均显著小于对比例2，且循环容量保持率均高于对比例2。
此外，相较于实施例5，实施例20至24的铝箔变形率有了进一步的降低，同时颗粒破碎率以及在高温下存储的厚度变化率进一步降低，且循环容量保持率进一步得以改善。这说明了第一功能层和/或第二功能层中的物质能够起到很好的缓冲的作用，保护正极集流体，同时确保正极活性材料层中的多晶颗粒A在电极制备过程(尤其是冷压过程)和电化学装置充放电过程中不易发生颗粒破碎。
实施例25-29
实施例25至29对实施例5的电解液的配方进行了调整，其在电解液中分别加入的组分及其含量如表6所示。
参见实施例25至29与实施例5的电化学数据可知，通过在原有的电解液中添加质量百分比不大于3％的1,3-丙烷磺酸内酯(PS)、质量百分比不大于1％的二氟磷酸锂、质量百分比不大于4％的多腈化合物、质量百分比不大于5％的氟代碳酸乙烯酯(FEC)、或其组合，对应所得的电化学装置均能够表现出优异的电 化学性能。
表6
Figure PCTCN2020081800-appb-000010
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. 一种电化学装置，其包含正极，所述正极包含正极集流体和正极活性材料层，所述正极活性材料层包含颗粒A和颗粒B，所述颗粒A的圆形度为R A，截面积为S A；所述颗粒B的圆形度为R B，截面积为S B，其中R B＜0.4≤R A，S B＜20μm 2≤S A，其中以所述正极垂直于所述正极集流体方向的截面的总面积计，所述颗粒A的总面积占比与所述颗粒B的总面积占比的比值为1:9至8:2。
  2. 根据权利要求1所述的电化学装置，其中所述颗粒A满足关系式(a)至(c)中的至少一者：
    (a)以所述正极垂直于所述正极集流体方向的截面的总面积计，所述颗粒A的总面积占比为5％至50％；
    (b)所述颗粒A的电阻率为6Ω·cm至10Ω·cm；
    (c)所述颗粒A包含具有式为Li 1+aNi xMn yCo zM mO 2的化合物，其中-0.05≤a＜0.3，0.8≤x＜1，0＜y≤0.2，0＜z≤0.2，0＜m＜0.2，其中元素M选自Al、Ti、W、Zr、Nb、In、Ru、Sb、Sr、Y中的一种或多种。
  3. 根据权利要求1所述的电化学装置，其中所述颗粒A中包含破碎颗粒，所述破碎颗粒满足关系(d)至(e)中的至少一者：
    (d)以所述正极垂直于所述正极集流体方向的截面的总面积计，所述破碎颗粒的总面积占比为不大于15％；
    (e)以所述颗粒A的总面积计，所述破碎颗粒的总面积占比为不大于30％。
  4. 根据权利要求1所述的电化学装置，其中所述颗粒B满足关系(f)至(h)中的至少一者：
    (f)以所述正极垂直于所述正极集流体方向的截面的总面积计，所述颗粒B的总面积占比为5％至60％；
    (g)所述颗粒B的电阻率为20Ω·cm至40Ω·cm；
    (h)所述颗粒B包含具有式为Li 1+aNi xMn yCo zM mO 2的化合物，其中-0.05≤a＜0.3，0.8≤x＜1，0＜y≤0.2，0＜z≤0.2，0＜m＜0.2，，其中元素M选自Al、Ti、W、Zr、Nb、In、Ru、Sb、Sr、Y中的一种或多种。
  5. 根据权利要求1所述的电化学装置，其中所述正极活性材料层满足关系(i)至(j)中的至少一者：
    (i)所述正极活性材料层的孔隙率≤25％；
    (j)在TG-MS测试中，所述正极活性材料在230℃至245℃具有释氧峰。
  6. 根据权利要求1所述的电化学装置，其中所述正极活性材料的比表面积为0.1m 2/g至1.2m 2/g。
  7. 根据权利要求1所述的电化学装置，其中所述正极活性材料层进一步包含粘结剂和导电剂，其中以所述正极活性材料层的总质量计，所述粘结剂的含量为1.25％至5％。
  8. 根据权利要求1所述的电化学装置，其中所述正极进一步包含功能层，所述功能层设置于所述正极活性材料层上，和/或设置于所述正极活性材料层与所述正极集流体之间。
  9. 根据权利要求9所述的电化学装置，其中所述功能层满足关系(1)至(4)中的至少一者：
    (1)所述功能层设置于所述正极活性材料层上，所述正极活性材料层设置于所述正极集流体上，所述正极活性材料层的厚度与所述功能层的厚度比为99:1至50:50；
    (2)所述功能层设置于所述正极活性材料层与所述正极集流体之间，所述正极活性材料层的厚度与所述功能层的厚度比为99:1至50:50；
    (3)所述功能层设置于所述正极活性材料层上，且所述功能层设置于所述述正极活性材料层与所述正极集流体之间，所述正极活性材料层的厚度与所述功能层的厚度比为99:1至50:50；
    (4)所述功能层包括物质C，所述物质C包含锂钴氧化物、磷酸铁锂、磷酸锰铁锂、锂锰氧化物中的至少一种，所述物质C的粒径Dv50在0.5μm至6μm范围内。
  10. 根据权利要求1所述的电化学装置，其中所述正极集流体的变形率≤32％。
  11. 一种电子装置，其包括权利要求1-10中任一项所述的电化学装置。
PCT/CN2020/081800 2020-03-27 2020-03-27 电化学装置及包含其的电子装置 WO2021189455A1 (zh)

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