WO2021134755A1 - 负极和包含其的电化学装置及电子装置 - Google Patents

负极和包含其的电化学装置及电子装置 Download PDF

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WO2021134755A1
WO2021134755A1 PCT/CN2020/070130 CN2020070130W WO2021134755A1 WO 2021134755 A1 WO2021134755 A1 WO 2021134755A1 CN 2020070130 W CN2020070130 W CN 2020070130W WO 2021134755 A1 WO2021134755 A1 WO 2021134755A1
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negative electrode
silicon
active material
current collector
material layer
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PCT/CN2020/070130
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English (en)
French (fr)
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王超
廖群超
崔航
谢远森
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宁德新能源科技有限公司
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Priority to PCT/CN2020/070130 priority Critical patent/WO2021134755A1/zh
Priority to JP2022540790A priority patent/JP2023509150A/ja
Priority to KR1020227026717A priority patent/KR20220116063A/ko
Priority to EP20909824.3A priority patent/EP4084138A4/en
Publication of WO2021134755A1 publication Critical patent/WO2021134755A1/zh
Priority to US17/708,508 priority patent/US20220223835A1/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
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • 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
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • 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
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This application relates to the field of energy storage technology, and in particular to a negative electrode, an electrochemical device and an electronic device including the negative electrode.
  • electrochemical devices for example, lithium-ion batteries
  • electrochemical devices that provide energy for electronic devices need to exhibit higher energy density, higher rate, higher safety, and smaller capacity decay after repeated charging and discharging processes.
  • the present application provides a negative electrode, an electrochemical device and an electronic device including the negative electrode, in an attempt to at least some extent solve at least one problem existing in the related field.
  • the present application provides a negative electrode.
  • the negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes a silicon-based material.
  • the negative electrode of this application defines the relationship between the weight ratio of the silicon-based material and the absolute strength of the negative electrode current collector, which can effectively reduce the XY expansion and deformation of the negative electrode active material layer during the charge and discharge cycle, thereby reducing the cycle of the electrochemical device. Expansion rate and improve its cycle performance and safety performance.
  • the present application provides an electrochemical device, which includes: a positive electrode, a separator, and the aforementioned negative electrode.
  • the present application provides an electronic device including the above-mentioned electrochemical device.
  • FIG. 1 is a graph of the circulation capacity of Example 1 and Example 6 of this application.
  • FIG. 2 is a graph of the cyclic expansion rate of the lithium ion battery in Example 1 and Example 6 of the application.
  • Fig. 3 is an X-ray diffraction diagram of Example 16 of the application.
  • Fig. 4 is an X-ray diffraction diagram of Example 19 of the present application.
  • the terms “approximately”, “substantially”, “substantially” and “about” are used to describe and illustrate small changes.
  • the term can refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very closely.
  • the term can refer to a range of variation less than or equal to ⁇ 10% of the value, such as less than or equal to ⁇ 5%, less than or equal to ⁇ 4%, less than or equal to ⁇ 3%, less than Or equal to ⁇ 2%, less than or equal to ⁇ 1%, less than or equal to ⁇ 0.5%, less than or equal to ⁇ 0.1%, or less than or equal to ⁇ 0.05%.
  • the difference between two values is less than or equal to ⁇ 10% of the average value of the value (for example, less than or equal to ⁇ 5%, less than or equal to ⁇ 4%, less than or equal to ⁇ 3%, less than or Equal to ⁇ 2%, less than or equal to ⁇ 1%, less than or equal to ⁇ 0.5%, less than or equal to ⁇ 0.1%, or less than or equal to ⁇ 0.05%), then the two values can be considered "substantially" the same.
  • a list of items connected by the terms “at least one of”, “at least one of”, “at least one of” or other similar terms may mean the listed items Any combination of. For example, if items A and B are listed, then the phrase “at least one of A and B” means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C” means only A; or only B; only C; A and B (excluding C); A and C (exclude B); B and C (exclude A); or all of A, B, and C.
  • Project A can contain a single element or multiple elements.
  • Project B can contain a single element or multiple elements.
  • Project C can contain a single element or multiple elements.
  • CN107925074A exemplifies specific examples of silicon-based materials as negative electrode active materials in the Chinese patent application of CN107925074A, which is incorporated herein by reference in its entirety.
  • the silicon-based material will expand in the process of lithium insertion, and then exert a greater force on the negative electrode current collector, which will cause the negative electrode to undergo XY expansion and structural deformation.
  • Chinese patent CN103579578B discloses that by limiting the tensile strength and thickness of the copper foil current collector, the extension of the negative electrode during charging and discharging is suppressed.
  • the copper foil current collector with high tensile strength will cause the thickness of the copper foil to be too thick and the structure of the negative electrode to be too hard, resulting in a decrease in the energy density of the lithium ion battery and a decrease in processing performance.
  • XY expansion means the volume expansion of the negative electrode active material layer in a direction horizontal to the surface of the negative electrode current collector.
  • This application defines the relationship between the content of the silicon-based material in the negative electrode and the absolute strength of the negative electrode current collector, so that the strength of the negative electrode current collector is greater than the stress intensity generated by the expansion of the silicon-based material, and enhances the resistance of the negative electrode current collector to the volume expansion of the negative electrode. Sex.
  • the present application provides a negative electrode, which includes a negative electrode current collector and a negative electrode active material layer.
  • the correlation coefficient is approximately, for example, about 4500N/m, about 5000N/m, about 5500N/m, about 6000N/m, about 6500N/m, about 7000N/m, or any two of these values.
  • the negative electrode of the present application can effectively suppress the XY expansion of the negative electrode active material layer, reduce the deformation of the negative electrode structure, and increase the cycle life of its electrochemical device.
  • absolute strength is also referred to as “ultimate strength” or “breaking stress” means the highest stress that an object can withstand without deformation, extension or fracture when subjected to an external force.
  • the absolute strength of the negative electrode current collector is greater than or equal to about 500 N/m. In other embodiments, the absolute strength of the negative electrode current collector is approximately, for example, about 500N/m, about 600N/m, about 700N/m, about 1000N/m, about 1500N/m, about 2000N/m, about 2600N /m or a range composed of any two of these values. In some other embodiments, the absolute strength of the negative electrode current collector is about 1000 N/m to about 2600 N/m.
  • the thickness of the negative electrode current collector is about 1 ⁇ m to about 15 ⁇ m. In other embodiments, the thickness of the negative electrode current collector is approximately, for example, about 1 ⁇ m, about 2 ⁇ m, about 3 ⁇ m, about 5 ⁇ m, about 10 ⁇ m, about 12 ⁇ m, about 15 ⁇ m, or a range composed of any two of these values. In other embodiments, the thickness of the negative electrode current collector is about 3 ⁇ m to about 10 ⁇ m.
  • the negative electrode current collector includes at least one of copper foil, nickel foil, titanium foil, chromium foil, and stainless steel foil. It should be understood that, without violating the spirit of the present application, those skilled in the art can select any conventional conductive foil as the negative electrode current collector according to specific requirements without limitation.
  • the silicon-based material includes, but is not limited to, one or more of elemental silicon, silicon oxide material, silicon carbon, and silicon alloy.
  • the silicon-based material comprises a component group of the general formula M y SiO x represents one or more silicone material, wherein 0 ⁇ y ⁇ 4,0 ⁇ x ⁇ 4, and M is Li comprising At least one of, Mg, Ti and Al.
  • the intensity of the second peak in the XRD diffraction pattern obtained by the X-ray diffraction test (X-ray diffraction, XRD) of the silica material I 2 in the range of 28.0°-29.0° is attributable to 20.5°-21.5° a first peak intensity ratio of I in the range of 1 I 2 / I 1, to reflect the silicone material is subjected to disproportionation impact.
  • the second peak of intensity I 2 of the silicone material to the first peak intensity ratio of I 1 I 2 / I 1 is greater than 0 and less than or equal to 10. In other embodiments, the second peak of intensity I 2 of the silicone material to the first peak intensity ratio of I 1 I 2 / I 1 is less than or equal to 1.
  • the negative active material layer further includes, but is not limited to, carbon-based materials, metal compounds, sulfides, lithium nitrides (for example, LiN3), lithium metal, metals that form alloys with lithium, and polymers Materials and other negative active materials capable of absorbing and releasing lithium.
  • carbon-based materials may include low graphitization carbon, easy graphitization carbon, artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, pyrolysis carbon, coke, glassy carbon, organic polymer compounds Sintered body, carbon fiber and activated carbon.
  • the negative active material layer further includes a carbon-based material.
  • the weight ratio of the silicon-based material is about 1% to about 70% based on the total weight of the negative active material layer. In other embodiments, the weight ratio of the silicon-based material is approximately, for example, about 1%, about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, about 60%, Approximately 70% or a range composed of any two of these values. In other embodiments, the weight ratio of the silicon-based material is about 10% to about 40% based on the total weight of the negative active material layer.
  • the negative active material layer further includes a binder and a conductive agent
  • the binder includes polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl Base cellulose, sodium carboxymethyl cellulose, polyimide, polyamide imide, styrene butadiene rubber and polyvinylidene fluoride
  • the conductive agent includes conductive carbon black, carbon nanotubes, carbon fibers and At least one of Ketjen Black.
  • the silicon-based material in the negative active material layer further includes a coating layer.
  • the coating layer can restrain the expansion of the silicon-based material during lithium insertion, and act as a buffer layer for volume changes to enhance the structural stability of the negative electrode.
  • the coating layer can effectively avoid direct contact between the silicon-based material and the electrolyte during the lithium insertion process, thereby stabilizing the formation of a solid electrolyte interface (SEI) film on the surface of the negative electrode, reducing irreversible capacity loss and increasing lithium ions Cycle performance of the battery.
  • SEI solid electrolyte interface
  • the highly conductive coating layer can effectively improve the surface conductivity of the silicon-based material, improve the electronic conductivity and ionic conductivity of the negative electrode material, and improve the rate performance of the lithium ion battery.
  • the coating layer includes at least one of a carbon material and a polymer material, wherein the carbon material includes at least one of amorphous carbon, carbon nanotubes, carbon nanoparticles, vapor deposited carbon fibers, and graphene.
  • the polymer material includes polyvinylidene fluoride or its derivatives, carboxymethyl cellulose or its derivatives, sodium carboxymethyl cellulose or its derivatives, polyvinylpyrrolidone or its derivatives, polyacrylic acid or its derivatives And at least one of polystyrene butadiene rubber.
  • the thickness of the negative active material layer is about 50 ⁇ m to about 200 ⁇ m
  • the compacted density of the negative active material layer is about 1.4 g/cm 3 to about 1.9 g/cm 3 .
  • compact density is the weight of the active material per unit area of the current collector divided by the total thickness of the active material layer in the direction perpendicular to the surface of the current collector after cold pressing.
  • the porosity of the negative active material layer is about 15% to about 35%.
  • the method for preparing the negative electrode of the present application includes the following steps:
  • some embodiments of the present application also provide an electrochemical device including the anode of the present application.
  • the electrochemical device is a lithium ion battery.
  • the lithium ion battery includes the negative electrode, the separator and the positive electrode in the above embodiments, and the separator is arranged between the positive electrode and the negative electrode.
  • the positive electrode includes a positive current collector.
  • the positive electrode current collector can be aluminum foil or nickel foil, however, other positive electrode current collectors and negative electrode current collectors commonly used in the art can be used without limitation.
  • the positive electrode includes a positive electrode active material capable of absorbing and releasing lithium (Li) (hereinafter, sometimes referred to as "a positive electrode active material capable of absorbing/releasing lithium Li").
  • positive electrode active materials capable of absorbing/releasing lithium (Li) may include lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, One or more of lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials.
  • the chemical formula of lithium cobalt oxide can be Li y Co a M1 b O 2-c , where M1 represents selected from nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al) , Boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca) At least one of, strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr), and silicon (Si).
  • the values of y, a, b, and c are within the following ranges: 0.8 ⁇ y ⁇ 1.2, 0.8 ⁇ a ⁇ 1, 0 ⁇ b ⁇ 0.2, -0.1 ⁇ c ⁇ 0.2;
  • the chemical formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate can be Li z Ni d M2 e O 2-f , where M2 represents selected from cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin At least one of (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr) and silicon (Si), the values of z, d, e and f are in the following ranges: 0.8 ⁇ z ⁇ 1.2, 0.3 ⁇ d ⁇ 0.98, 0.02 ⁇ e ⁇ 0.7, -0.1 ⁇ f ⁇ 0.2;
  • the chemical formula of lithium manganate is Li u Mn 2-g M 3g O 4-h , where M3 represents selected from cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al) , Boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca) At least one of strontium (Sr) and tungsten (W), and the values of z, g, and h are within the following ranges: 0.8 ⁇ u ⁇ 1.2, 0 ⁇ g ⁇ 1.0, and -0.2 ⁇ h ⁇ 0.2.
  • the positive electrode can further include at least one of a binder and a conductive agent. It should be understood that those skilled in the art can select conventional adhesives and conductive agents in the art according to actual needs without limitation.
  • the isolation film includes, but is not limited to, at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid.
  • polyethylene includes at least one component selected from high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.
  • polyethylene and polypropylene they have a good effect on preventing short circuits, and can improve the stability of the battery through the shutdown effect.
  • the lithium ion battery of the present application also includes an electrolyte.
  • the electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte.
  • the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt is selected from LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , One or more of LiC(SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB and lithium difluoroborate.
  • LiPF 6 is selected for lithium salt because it can give high ionic conductivity and improve cycle characteristics.
  • the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.
  • the aforementioned carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
  • Examples of the above-mentioned other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, Formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.
  • the non-aqueous solvent is selected from ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluorocarbon Group of ethylene carbonate and its combination.
  • the preparation methods of the negative electrode, the positive electrode, the separator and the lithium ion battery in the embodiments of the present application can select any suitable conventional method in the field according to specific needs without limitation.
  • the method of manufacturing a lithium ion battery includes: winding, folding, or stacking the negative electrode, separator, and positive electrode in the above embodiment into an electrode assembly in sequence, and loading the electrode assembly into For example, the aluminum plastic film is injected with electrolyte, and then vacuum packaging, standing, forming, shaping and other processes are performed to obtain a lithium-ion battery.
  • the lithium ion battery is used as an example above, after reading this application, those skilled in the art can think that the negative electrode of this application can be used in other suitable electrochemical devices.
  • Such an electrochemical device includes any device that undergoes an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, 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.
  • Some embodiments of the present application further provide an electronic device, and the electronic device includes the electrochemical device in the embodiments of the present application.
  • electronic devices may include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, headsets, Video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.
  • a tensile testing machine with a range of 0N to 1000N and an indication error of ⁇ 1% and a vernier caliper with a range of 0mm to 300mm and a minimum graduation of 0.02mm or a corresponding precision measuring tool are used. Cut the sample to be tested with a length of 200 ⁇ 0.5mm and a width of 15 ⁇ 0.25mm. At the sampling position, take 2 samples to be tested in the vertical and horizontal directions in the width direction of the object to be tested. Subsequently, the sample to be tested is placed in a tensile testing machine, where the chuck distance is 125 ⁇ 0.1mm, the chuck stretching speed is 50mm/min, and the test temperature is 20 ⁇ 10°C.
  • the laser particle size test is based on the principle that particles of different sizes can cause the laser to produce different intensity scattering to test the particle distribution.
  • the main indicators that characterize the characteristics of particles are Dn10, Dv10, Dv50, Dv90, Dv99, etc., among which Dv50 is called the particle size, which means that the material is in the volume-based particle distribution, starting from the small particle size side, reaching 50% of the cumulative volume Particle size.
  • the Examples and Comparative Examples of this application use the Mastersizer 2000 laser particle size distribution tester to analyze the particle size of the sample: Disperse the sample of the positive electrode material in 100 mL of dispersant (deionized water) to achieve a shading degree of 8-12%. The samples were then sonicated for 5 minutes at an ultrasonic intensity of 40KHz and 180W. After ultrasonic treatment, the sample will be analyzed for laser particle size distribution to obtain particle size distribution data.
  • test voltage is 40kV
  • current is 30mA
  • scanning angle range It is 10° to 85°
  • scanning step size is 0.0167°
  • time set for each step size is 0.24 s to obtain the XRD diffraction pattern.
  • 2 ⁇ peak intensity attributed to record the highest intensity value I 2 and the home range of 28.0 ° -29.0 ° -21.5 ° in the range of 20.5 ° to I 1, to calculate the ratio I 2 / I 1 a.
  • a small disc active material sample with an area of 1540.25 mm 2 was taken from the negative electrode active material layer on the negative electrode to be tested along the surface of the negative electrode current collector. After removing the negative electrode current collector, the weight of the negative electrode active material was recorded. Take 12 active material samples at different positions in each group, and calculate the weight per unit area of the negative active material layer.
  • Cycle retention rate (%) of the lithium ion battery at 25°C discharge capacity at the 400th cycle (mAh)/discharge capacity after the first cycle (mAh) ⁇ 100%.
  • the 45°C cycle retention rate (%) of the lithium ion battery the discharge capacity at the 200th cycle (mAh)/the discharge capacity after the first cycle (mAh) ⁇ 100%.
  • a spiral micrometer was used to test the thickness of the lithium-ion battery in the first cycle in the fully charged state and the thickness in the fully charged state at the 400th cycle of the lithium ion battery of the following examples.
  • the cyclic thickness expansion rate of the 400th cycle of the lithium ion battery (%) (fully charged thickness of the 400th cycle/first fully charged thickness-1) ⁇ 100%.
  • the XY expansion rate (%) of the lithium ion battery at the 400th cycle (surface area of the negative electrode active material layer at the 400th cycle/surface area of the negative electrode active material layer at the first cycle-1) ⁇ 100%.
  • the lithium ion battery of the following examples was placed in a thermostat at 25°C ⁇ 2°C for 2 hours, and discharged to 3.0V at a constant current of 0.2C. Then charge to 4.4V at a constant current of 0.5C, then charge to 0.05C at a constant voltage of 4.4V and let stand for 5 minutes; then discharge at a constant current of 0.2C to 3.0V. Record the discharge capacity of the lithium-ion battery discharged at a constant current of 0.2C.
  • Discharge rate 2.0C constant current discharge discharge capacity (mAh)/0.2C constant current discharge discharge capacity (mAh).
  • Lithium cobaltate (LiCoO 2 ), conductive carbon black, and polyvinylidene fluoride (PVDF) are dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 96:2:2 to form a positive electrode slurry.
  • NMP N-methylpyrrolidone
  • Aluminum foil is used as the positive electrode current collector, the positive electrode slurry is coated on the positive electrode current collector, and the positive electrode is obtained after drying, cold pressing, and cutting procedures.
  • a polyethylene (PE) porous polymer film is used as the isolation membrane.
  • the above-mentioned positive electrode, separator, and the negative electrodes of the following examples and comparative examples are stacked in order, so that the separator is placed between the positive electrode and the negative electrode for isolation, and then wound into an electrode assembly. Subsequently, the electrode assembly was put into an aluminum-plastic film packaging bag, and the water was removed at 80° C. to obtain a dry electrode assembly. Subsequently, the above-mentioned electrolyte is injected into the dry electrode assembly, and the preparation of the lithium-ion batteries of the following examples and comparative examples is completed through the steps of vacuum packaging, standing, forming, and shaping.
  • Silicon oxide material SiO x (0.5 ⁇ x ⁇ 1.6) and artificial graphite are added to a stirrer and mixed to form a negative electrode active material, wherein the silicon oxide material has an I 2 /I 1 ratio of 0.38 after X-ray diffraction testing.
  • polyacrylic acid and conductive carbon black are added to the stirring negative electrode active material (the weight ratio of negative electrode active material, conductive carbon black, and polyacrylic acid is 95:2:3), at a revolution speed of 20 cycles/min and rotation Stir at a speed of 1200 cycles/min for 60 minutes, and then add deionized water and stir for 120 minutes to obtain a mixed slurry, wherein the weight ratio of the silicon-oxygen material SiO x is 1%.
  • Copper foil is used as the negative electrode current collector, wherein the thickness of the negative electrode current collector is 9 ⁇ m and the absolute strength is 1800 N/m.
  • the mixed slurry is coated on the negative electrode current collector and dried. After drying, a cold pressing process is performed to obtain a negative electrode active material layer, wherein the thickness of the negative electrode active material layer is 90 ⁇ m and the compaction density is 1.75 g/cm 3 , and then the negative electrode is obtained after a cutting process.
  • the preparation method is the same as that of Example 1, but the difference is that the weight ratio of the silicon-oxygen material SiO x in Examples 2-8 is 7%, 11%, 15%, 20%, 30%, 50%, 70% in order. .
  • the preparation method is the same as that of Example 3, but the difference is that the thickness of the negative electrode current collector in Examples 9-15 is 8 ⁇ m, 7 ⁇ m, 6 ⁇ m, 5 ⁇ m, 4 ⁇ m, 2.5 ⁇ m, 1 ⁇ m and the absolute strength of the negative electrode current collector is in order. It is 1600N/m, 1400N/m, 1200N/m, 1000N/m, 800N/m, 500N/m, 200N/m.
  • the preparation method is the same as in Example 3, except that in Examples 16-19, nickel foil, titanium foil, chromium foil, and stainless steel foil are sequentially used as the negative electrode current collector.
  • the preparation method is the same as that of Example 3, but the difference is that the I 2 /I 1 ratios of the silicon-oxygen materials in Examples 20-23 after the X-ray diffraction test are 0.41, 0.64, 1, 2.5 in order.
  • the preparation method is the same as that of Example 3, but the difference is that the silicon-oxygen material in Examples 24-27 is doped with the metal elements lithium, magnesium, titanium, and aluminum in sequence, and the metal elements in Example 24-27 are doped in sequence.
  • the amount of impurities in the weight ratio of the negative electrode material is 1.17%, 2%, 2%, 1.5%, respectively.
  • the negative electrodes of the above examples and comparative examples were tested for unit weight and compaction density. Subsequently, the lithium ion battery was subjected to cycle performance test, cycle expansion test and discharge rate test, and the test results were recorded.
  • the weight ratio R of the silicon-based material in the negative electrode is based on the total weight of the negative electrode active material layer and the negative electrode set.
  • the lithium ion battery of the present application that meets the above-mentioned silicon-based material weight ratio and the absolute strength of the negative electrode current collector can maintain a cycle retention rate of over 80% at 25°C and 400 cycles and a 25°C cycle retention rate.
  • the 400-cycle thickness expansion rate can be maintained at 25°C 400-cycle thickness expansion rate below 9.5% and XY expansion rate at 25°C 400-cycle cycle below 0.34%, and discharge rate above 83.5%.
  • Examples 1-5 and 6-86 it can be seen that when the content of the silicon-based material in the negative electrode active material layer is higher, the cycle expansion rate of the lithium ion battery will also increase greatly.
  • Examples 6-8 it can be seen that when the content of the silicon-based material in the negative electrode active material layer exceeds the strength range of the negative electrode current collector provided in the examples of this application, the strength of the negative electrode current collector is insufficient to restrain the expansion of the silicon-based material. In turn, the XY expansion rate of the negative electrode active material layer is greatly increased, and the expansion and deformation of the lithium ion battery are caused, thereby affecting the cycle performance and safety performance of the lithium ion battery.
  • FIG. 1 and FIG. 2 are respectively the cycle capacity curve diagram and the cycle expansion rate curve diagram of the lithium ion battery of Example 1 and Example 6 of the present application.
  • Example 1 due to its low silicon-based material content, the negative electrode active material layer generated less stress during the cycle, when the negative electrode current collector has a certain absolute When it is strong, it can make it difficult to produce XY expansion and deformation, thereby ensuring the combination of the negative electrode active material layer and the negative electrode current collector, and the cycleability of the lithium ion battery.
  • Example 6 due to the large content of silicon-based materials, the stress generated by the negative electrode active material layer during the cycle exceeds the absolute strength of the negative electrode current collector, which in turn leads to the deformation of the negative electrode and makes the lithium ion
  • the cycle retention rate of the battery deteriorates rapidly from the beginning of the cycle. Therefore, the capacity retention rate of the lithium ion battery of Example 4 drops rapidly.
  • Example 3 and 4 are X-ray diffraction diagrams of the silicon-based material in Example 20 and Example 23 of this application, respectively.
  • I 2 /I 1 reflects the degree to which the material in the material is affected by disproportionation. The larger the value, the larger the size of the silicon grains produced by the disproportionation of silicon oxide generated inside, which will lead to negative electrode activity during the lithium insertion process. The stress in the local area of the material layer increases sharply, which leads to the destruction of the crystal structure of the silicon-based material during the charge-discharge cycle.
  • this application can effectively reduce the irregular expansion and deformation of the negative electrode in a lithium ion battery by limiting the weight ratio of the silicon-based material in the negative electrode and the absolute strength of the negative electrode current collector. At the same time, it can also improve the peeling of the negative electrode active material layer from the negative electrode current collector to a certain extent, thereby improving the cycle performance and safety performance of the lithium ion battery.
  • 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

一种负极及包含该负极的电化学装置及电子装置。负极包括：负极集流体以及负极活性材料层，且负极活性材料层包含硅基材料。其中，硅基材料以负极活性材料层的总重量计的重量比R与负极集流体的绝对强度σ满足以下公式：K＝σ/(1.4×R+0.1)，其中K为关系系数，且关系系数大于或等于4000N/m。上述电化学装置通过采用上述负极能够有效改善负极活性材料层的XY膨胀与变形，从而提升电化学装置的循环性能和安全性能。

Description

负极和包含其的电化学装置及电子装置 技术领域
本申请涉及储能技术领域，尤其涉及负极以及包括该负极的电化学装置及电子装置。
背景技术
随着移动电子技术的高速发展，人们使用诸如手机、平板、笔记本电脑、无人机等的移动电子装置的频率和体验要求越来越高。因此，为电子装置提供能源的电化学装置(例如，锂离子电池)需要表现出更高的能量密度、更大的倍率、更高的安全性以及在反复充放电过程后更小的容量衰减。
在电化学装置领域中，采用具有高能量密度的材料作为负极活性材料是其中一个主要的研究方向。然而，具有高能量密度的材料(例如，硅基材料)往往存在与现有电芯结构不相匹配的问题，例如，电导性过低、膨胀率过高、加工性能不足等等。因此，针对采用高能量密度的材料作为负极活性材料的电化学装置，对其电芯结构(例如，负极、隔离膜及正极)的改进与优化是目前急需的研究课题。
发明内容
本申请提供一种负极和包含该负极的电化学装置及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。
根据本申请的一个方面，本申请提供了一种负极，负极包括：负极集流体以及负极活性材料层，且负极活性材料层包含硅基材料。以负极活性材料层的总重量计，硅基材料的重量比R与负极集流体的绝对强度σ符合满足以下公式：K＝σ/(1.4×R+0.1)，其中K为关系系数，且关系系数大于或等于约4000N/m。
本申请负极通过限定硅基材料的重量比与负极集流体的绝对强度之间的关系，能够有效的降低负极活性材料层在充放电循环过程中的XY膨胀与变形，进而降低电化学装置的循环膨胀率并提高其循环性能及安全性能。
根据本申请的另一个方面，本申请提供了一种电化学装置，其包括：正极、隔离膜 以及上述负极。
根据本申请的另一个方面，本申请提供了一种电子装置，电子装置包含上述的电化学装置。
本申请实施例的额外层面及优点将部分地在后续说明中描述、显示、或是经由本申请实施例的实施而阐释。
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1为本申请实施例1与实施例6的循环容量曲线图。
图2为本申请实施例1与实施例6的锂离子电池循环膨胀率曲线图。
图3为本申请实施例16的X射线衍射图。
图4为本申请实施例19的X射线衍射图。
具体实施方式
本申请的实施例将会被详细的描示在下文中。在本申请说明书全文中，将相同或相似的组件以及具有相同或相似的功能的组件通过类似附图标记来表示。在此所描述的有关附图的实施例为说明性质的、图解性质的且用于提供对本申请的基本理解。本申请的实施例不应该被解释为对本申请的限制。
如本文中所使用，术语“大致”、“大体上”、“实质”及“约”用以描述及说明小的变化。当与事件或情形结合使用时，该术语可指代其中事件或情形精确发生的例子以及其中事件或情形极近似地发生的例子。举例来说，当结合数值使用时，术语可指代小于或等于该数值的±10％的变化范围，例如小于或等于±5％、小于或等于±4％、小于或等于±3％、小于或等于±2％、小于或等于±1％、小于或等于±0.5％、小于或等于±0.1％、或小于或等于±0.05％。举例来说，如果两个数值之间的差值小于或等于该值的平均值的±10％(例如小于或等于±5％、小于或等于±4％、小于或等于±3％、小于或等 于±2％、小于或等于±1％、小于或等于±0.5％、小于或等于±0.1％、或小于或等于±0.05％)，那么可认为两个数值“大体上”相同。
在本说明书中，除非经特别指定或限定之外，相对性的用词例如：“中央的”、“纵向的”、“侧向的”、“前方的”、“后方的”、“右方的”、“左方的”、“内部的”、“外部的”、“较低的”、“较高的”、“水平的”、“垂直的”、“高于”、“低于”、“上方的”、“下方的”、“顶部的”、“底部的”以及其衍生性的用词(例如“水平地”、“向下地”、“向上地”等等)应该解释成引用在讨论中所描述或在附图中所描示的方向。这些相对性的用词仅用于描述上的方便，且并不要求将本申请以特定的方向建构或操作。
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，而且包含涵盖于该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“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元件。项目C可包含单个元件或多个元件。
在电化学装置领域中，为了追求更高能量密度的电化学装置，替换具有更高克容量的负极活性材料是其中一个研究方向。硅具有高的理论克容量(4200mAh/g)，在锂离子电池中的应用有着广阔的前景。其中，中国专利CN107925074A公开了具有一定歧化的硅基材料(SiO X，0≤x)晶体作为负极活性材料能够有效的提高锂离子电池的首次充放电效率和循环性能。中国专利公开号为：CN107925074A的中国专利申请案中例示了硅基材料作为负极活性材料的具体实施例，其全文以引用方式并入本文中。但在充放电循环过程中，硅基材料在嵌锂的过程中会产生较大的体积膨胀，进而对负极集流体产生较大的作用力，从而导致负极发生XY膨胀与结构的变形。
中国专利CN103579578B公开了通过限定铜箔集流体的抗张强度和厚度，来抑制负极在充放电过程中的延伸。然而，具有高抗张强度的铜箔集流体会造成铜箔 厚度过厚及负极结构过硬，造成锂离子电池的能量密度的下降以及加工性能的下降。
以上，中国专利公开号为：CN107925074A的中国专利申请案中例示了硅基材料作为负极活性材料的具体实施例，其全文以引用方式并入本文中。中国专利公开号为：CN103579578B的中国专利申请案中例示了不同抗张强度的铜箔集流体的具体实施例，其全文以引用方式并入本文中。
在本文中，术语“XY膨胀”表示负极活性材料层在与负极集流体表面水平的方向上的体积膨胀。
本申请通过限定负极中硅基材料的含量与负极集流体绝对强度之间的关系，使得负极集流体的强度大于硅基材料膨胀所产生的应力强度，增强负极集流体对负极体积膨胀的耐受性。
根据本申请的一个方面，本申请提供了一种负极，其包括负极集流体及负极活性材料层。负极活性材料层包含硅基材料，其中以负极活性材料层的总重量计硅基材料的重量比R与负极集流体的绝对强度σ符合满足以下公式：K＝σ/(1.4×R+0.1)，其中K为关系系数，且关系系数大于或等于约4000N/m。在另一些实施例中，关系系数为约4000N/m。在另一些实施例中，关系系数为大致为，例如，约4500N/m、约5000N/m、约5500N/m、约6000N/m、约6500N/m、约7000N/m或这些数值中任意两者组成的范围。本申请负极能够有效抑制负极活性材料层的XY膨胀，减小负极结构的变形，增加其电化学装置的循环寿命。
在本文中，术语“绝对强度”也称作“极限强度”或“破坏应力”是表示物体受到外力时在不产生形变、延伸或断裂的情况下所能承受的最高应力。
在一些实施例中，负极集流体的绝对强度大于或等于约500N/m。在另一些实施例中，负极集流体的绝对强度大致为，例如，约500N/m、约600N/m、约700N/m、约1000N/m、约1500N/m、约2000N/m、约2600N/m或这些数值中任意两者组成的范围。在另一些实施例中，负极集流体的绝对强度为约1000N/m至约2600N/m。
在一些实施例中，负极集流体的厚度为约1μm至约15μm。在另一些实施例中，所述负极集流体的厚度大致为，例如，约1μm、约2μm、约3μm、约5μm、约10μm、约12μm、约15μm或这些数值中任意两者组成的范围。在另一些实施例中，负极集流体的厚度为约3μm至约10μm。
在一些实施例中，负极集流体包含铜箔、镍箔、钛箔、铬箔及不锈钢箔中的至少一种。应理解，在不违背本申请的精神下，本领域技术人员可以根据具体需求选择任何常规的导电箔片作为负极集流体，而不受其限制。
在一些实施例中，硅基材料包含，但不限于，单质硅、硅氧材料、硅碳及硅合金中的一种或多种。在一些实施例中，硅基材料包含通式M ySiO x所代表的组份中的一种或多种硅氧材料，其中0≤y≤4，0≤x≤4，且M为包含Li、Mg、Ti及Al中的至少一种。
硅氧材料通过X射线衍射测试(X-ray diffraction，XRD)所得到的XRD衍射图案中位在归属于28.0°-29.0°范围内的第二峰的强度I 2与归属于20.5°-21.5°范围内的第一峰强度I 1间的比值I 2/I 1，能够反映硅氧材料受到歧化的影响程度。第二峰的强度I 2与第一峰强度I 1的比值I 2/I 1越大，代表硅氧材料的内部产生的SiO歧化产生的纳米硅晶粒的尺寸越大。在一些实施例中，硅氧材料第二峰的强度I 2与第一峰强度I 1的比值I 2/I 1大于0且小于或等于10。在另一些实施例中，硅氧材料第二峰的强度I 2与第一峰强度I 1的比值I 2/I 1小于或等于1。
在一些实施例中，负极活性材料层还包含，但不限于，碳基材料、金属化合物、硫化物、锂的氮化物(例如，LiN3)、锂金属、与锂一起形成合金的金属和聚合物材料等能够吸收和释放锂的负极活性材料。碳基材料的例子可以包括低石墨化的碳、易石墨化的碳、人造石墨、天然石墨、中间相碳微球、软碳、硬碳、热解碳、焦炭、玻璃碳、有机聚合物化合物烧结体、碳纤维和活性碳。在一些实施例中，负极活性材料层进一步包含碳基材料。
在一些实施例中，以负极活性材料层的总重量计，硅基材料的重量比为约1％至约70％。在另一些实施例中，硅基材料的重量比大致为，例如，约1％、约5％、约10％、约20％、约30％、约40％、约50％、约60％、约70％或这些数值中任意两者组成的范围。在另一些实施例中，以负极活性材料层的总重量计，硅基材料的重量比为约10％至约40％。
在一些实施例中，负极活性材料层还包含粘结剂及导电剂，其中粘结剂包括聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、羧甲基纤维素、羧甲基纤维素钠、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶及聚偏氟乙烯中的至少一种，且导电剂包括导电炭黑、碳纳米管、碳纤维及科琴黑中的至少一种。
应理解，本领域技术人员可以根据实际需要选择添加本领域任何常规的粘结剂或导 电剂，而不受期限制。
在一些实施例中，负极活性材料层中的硅基材料进一步包含包覆层。通过对硅基材料进行碳材料或高分子材料包覆，包覆层可以约束硅基材料嵌锂时的膨胀，并作为体积变化的缓冲层，增强负极的结构稳定性。同时，包覆层可以有效地避免嵌锂过程中硅基材料与电解液直接接触，从而稳定负极表面的固体电解质介面(Solid electrolyte interface，SEI)膜的形成，降低不可逆的容量损失并提高锂离子电池的循环性能。此外，导电性高的包覆层可以有效提高硅基材料的表面导电性，提升负极材料的电子电导率和离子电导率，提升锂离子电池的倍率性能。
在一些实施例中，包覆层包含碳材料及高分子材料中的至少一种，其中碳材料包含无定形碳、碳纳米管、碳纳米粒子、气相沉积碳纤维及石墨烯中的至少一种。，且高分子材料包含聚偏氟乙烯或其衍生物、羧甲基纤维素或其衍生物、羧甲基纤维素钠或其衍生物、聚乙烯基吡咯烷酮或其衍生物、聚丙烯酸或其衍生物及聚丁苯橡胶中的至少一种。
在一些实施例中，负极活性材料层的厚度为约50μm至约200μm
在一些实施例中，负极活性材料层的压实密度为约1.4g/cm 3至约1.9g/cm 3。
在本文中，术语“压实密度”为单位面积集流体上的活性材料的重量除以冷压后活性材料层在集流体表面垂直方向上的总厚度。
在一些实施例中，负极活性材料层的孔隙率为约15％至约35％。
在一些实施例中，本申请负极的制备方法包括以下步骤：
取一定量的硅基材料与石墨，将其与粘结剂、导电剂按固定重量比混合后，融入去离子水中搅拌均匀。搅拌后，通过筛选得到混合浆料。将混合浆料涂布于铜箔集流体上，并进行烘干。烘干后，进行冷压处理，以得到负极活性材料层，随后通过裁切程序后得到负极。
应理解，本申请实施例中的负极的制备方法中的各步骤，在不违背本申请的精神下，可以根据具体需要选择或替换本领域的其他的常规处理方法，而不受其限制。
根据本申请的另一个方面，本申请的一些实施例还提供了包括本申请负极的电化学装置。在一些实施例中，电化学装置为锂离子电池。锂离子电池包括：上述实施例中的负极、隔离膜以及正极，隔离膜设置于正极与负极之间。
在一些实施例中，正极包含正极集流体。正极集流体可以为铝箔或镍箔，然而，可以采用本领域常用的其他正极集流体及负极集流体，而不受其限制。
在一些实施例中，正极包括能够吸收和释放锂(Li)的正极活性材料(下文中，有时称为“能够吸收/释放锂Li的正极活性材料”)。能够吸收/释放锂(Li)的正极活性材料的实例可以包括钴酸锂、镍钴锰酸锂、镍钴铝酸锂、锰酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、磷酸铁锂、钛酸锂和富锂锰基材料中的一种或多种。
在上述正极活性材料中，钴酸锂的化学式可以为Li yCo aM1 bO 2-c，其中，M1表示选自镍(Ni)、锰(Mn)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)、钨(W)、钇(Y)、镧(La)、锆(Zr)和硅(Si)中的至少一种，y、a、b和c值分别在以下范围内：0.8≤y≤1.2、0.8≤a≤1、0≤b≤0.2、-0.1≤c≤0.2；
在上述正极活性材料中，镍钴锰酸锂或镍钴铝酸锂的化学式可以为Li zNi dM2 eO 2-f，其中，M2表示选自钴(Co)、锰(Mn)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)、钨(W)、锆(Zr)和硅(Si)中的至少一种，z、d、e和f值分别在以下范围内：0.8≤z≤1.2、0.3≤d≤0.98、0.02≤e≤0.7、-0.1≤f≤0.2；
在上述正极活性材料中，锰酸锂的化学式为Li uMn 2-gM 3gO 4-h，其中M3表示选自钴(Co)、镍(Ni)、镁(Mg)、铝(Al)、硼(B)、钛(Ti)、钒(V)、铬(Cr)、铁(Fe)、铜(Cu)、锌(Zn)、钼(Mo)、锡(Sn)、钙(Ca)、锶(Sr)和钨(W)中的至少一种，z、g和h值分别在以下范围内：0.8≤u≤1.2、0≤g≤1.0和-0.2≤h≤0.2。
在一些实施例中，正极能够进一步包含粘结剂及导电剂中的至少一种。应理解，本领域技术人员可以根据实际需要选择本领域常规的粘结剂及导电剂，而不受其限制。
在一些实施例中，隔离膜包括，但不限于，选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺和芳纶中的至少一种。举例来说，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯和超高分子量聚乙烯中的至少一种组分。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的稳定性。
本申请的锂离子电池还包括电解质，电解质可以是凝胶电解质、固态电解质和电解液中的一种或多种，电解液包括锂盐和非水溶剂。
在一些实施例中，锂盐选自LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiB(C 6H 5) 4、LiCH 3SO 3、 LiCF 3SO 3、LiN(SO 2CF 3) 2、LiC(SO 2CF 3) 3、LiSiF 6、LiBOB和二氟硼酸锂中的一种或多种。举例来说，锂盐选用LiPF 6，因为它可以给出高的离子导电率并改善循环特性。
非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、其它有机溶剂或它们的组合。
上述碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。
上述其它有机溶剂的实例为二甲亚砜、1，2-二氧戊环、环丁砜、甲基环丁砜、1，3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯、磷酸三辛酯、和磷酸酯及其组合。
在一些实施例中，非水溶剂选自由碳酸乙烯酯、碳酸丙烯酯、碳酸二乙酯、碳酸二甲酯、碳酸甲乙酯、碳酸亚丙酯、醋酸甲酯、丙酸乙酯、氟代碳酸乙烯酯及其组合所组成的群组。
应理解，本申请实施例中的负极、正极、隔离膜以及锂离子电池的制备方法，在不违背本申请的精神下，可以根据具体需要选择本领域任何合适的常规方法，而不受其限制。在制造电化学装置的方法的一个实施方案中，锂离子电池的制备方法包括：将上述实施例中的负极、隔离膜及正极按顺序卷绕、折叠或堆叠成电极组件，将电极组件装入例如铝塑膜中，并注入电解液，随后进行真空封装、静置、化成、整形等工序，以获得锂离子电池。
虽然上面以锂离子电池进行了举例说明，但是本领域技术人员在阅读本申请之后，能够想到由本申请的负极可以用于其他合适的电化学装置。这样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、燃料电池、太阳能电池或电容。特别地，该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。
本申请的一些实施例进一步提供了一种电子装置，电子装置包含本申请实施例中的电化学装置。
本申请实施例的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，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。
具体实施例
下面列举了一些具体实施例并对其负极进行单位重量及压实密度测试并对其电化学装置(锂离子电池)进行循环性能测试、循环膨胀率测试及放电倍率测试以更好地对本申请的技术方案进行说明。
一、测试方法
绝对强度测试方法：
采用量程为0N至1000N，示值误差为±1％的拉力试验机以及量程为0mm至300mm，最小分度值为0.02mm的游标卡尺或相应精度的量具。对待测物切取长度为200土0.5mm、宽度为15±0.25mm的待测样品。取样位置在待测物宽度方向处上沿纵、横方向各取2个待测样品。随后，将待测样品置于拉力试验机中，其中夹头距离为125士0.1mm、夹头拉伸速度为50mm/min且试验温度为20±10℃。对待测样品在长度方向上进行连续施荷直至拉断，由测力度盘或拉伸曲线上读出最大负荷F，并计算绝对强度：σ＝F/L，其中L为待测样品宽度。取4个试样试验结果的算术平均值以获得该待测物的绝对强度。
激光粒度分析：
激光粒度测试是根据不同大小的颗粒能使激光产生不同强度散射的原理来测试颗粒分布的。表征颗粒特性的主要指标有Dn10、Dv10、Dv50、Dv90、Dv99等等，其中，Dv50被称为颗粒度，表示材料在体积基准的颗粒分布中，从小粒径侧起、达到体积累积50％的粒径。本申请实施例及对比例采用Mastersizer 2000激光粒度分布测试仪分析样品的颗粒的粒度：将正极材料的样品分散在100mL的分散剂(去离子水)中，使遮光度达到8～12％。随后在超声强度为40KHz及180W下对样品进行超声处理5分钟。待超声处理后，将对样品进行激光粒度分布分析，得到粒度分布数据。
X射线衍射测试：
采用X射线衍射测试仪(布鲁克，D8)，并依据“X射线衍射分析法通则”标准：JJS K 0131-1996进行测试，具体测试设定如下：测试电压为40kV，电流为30mA，扫描角度范围为10°至85°，扫描步长为0.0167°，每个步长所设置的时间为0.24s，以 得到XRD衍射图案。纪录2θ归属于28.0°-29.0°范围内的最高强度数值I 2，与归属于20.5°-21.5°范围内的最高强度I 1，从而计算出I 2/I 1的比值。
单位重量及压实密度测试：
从待测负极上的负极活性材料层沿负极集流体表面取得面积为1540.25mm 2的小圆片的活性材料样品。在去除负极集流体后，记录其负极活性材料的重量。每组取12处不同位置的活性材料样品，并计算负极活性材料层的单位面积重量。
量测负极上的负极活性材料层在负极集流体表面垂直方向上的总厚度(去除集流体厚度)。每组取12处不同位置的活性材料层样品，并计算负极活性材料层的压实密度。压实密度＝负极活性材料的重量/在集流体表面垂直方向上的总厚度。
循环性能测试：
在25℃±2℃及45℃±2℃的恒温箱中，分别将以下实施例及对比例的锂离子电池静置2小时，以0.7C恒流充电至4.4V，然后以4.4V恒压充电至0.02C并静置5分钟；再以0.5C恒流放电至3.0V，此为一次充放电循环过程，记录锂离子电池在25℃±2℃及45℃±2℃下的首次循环的放电容量；而后按上述方法重复进行充放电循环过程，并记录每次充放电循环过程的放电容量，随后将其与首次循环的放电容量比较得到循环容量曲线。
每组取4块锂离子电池，计算锂离子电池的容量保持率的平均值。
锂离子电池的25℃循环保持率(％)＝第400次循环的放电容量(mAh)/首次循环后的放电容量(mAh)×100％。
锂离子电池的45℃循环保持率(％)＝第200次循环的放电容量(mAh)/首次循环后的放电容量(mAh)×100％。
循环膨胀率测试：
采用螺旋千分尺测试以下实施例的锂离子电池首次循环时在满充状态下的厚度与以及第400次循环时在满充状态下的厚度。锂离子电池第400次循环的循环厚度膨胀率(％)＝(第400次循环的满充厚度/首次满充厚度-1)×100％。
采用测量仪器纪录将以下实施例的锂离子电池首次循环时在满充状态下拆开后的负极活性物质层的与负极集流体表面平行的表面积以及第400次循环时在满充状态下拆开后的负极活性物质层的与负极集流体表面平行的表面积。锂离子电池第400次循环的 XY膨胀率(％)＝(第400次循环的负极活性物质层的表面积/首次循环的负极活性物质层的表面积-1)×100％。
放电倍率测试：
将以下实施例的锂离子电池置于25℃±2℃的恒温箱中静置2小时，以0.2C恒流放电至3.0V。随后以0.5C恒流充电至4.4V，然后以4.4V恒压充电至0.05C并静置5分钟；再以0.2C恒流放电至3.0V。记录锂离子电池以0.2C恒流放电的放电容量。
再将锂离子电池以0.5C恒流充电至4.35V，然后以4.35V恒压充电至0.05C满充，随后以2.0C恒流放电至3.0V。记录锂离子电池以以2.0C恒流放电的放电容量。
每组取4块锂离子电池测试，计算锂离子电池的放电倍率的平均值。放电倍率＝2.0C恒流放电的放电容量(mAh)/0.2C恒流放电的放电容量(mAh)。
二、制备方法
正极的制备
将钴酸锂(LiCoO 2)、导电炭黑、聚偏二氟乙烯(PVDF)按重量比96∶2∶2的比例溶于N-甲基吡咯烷酮(NMP)溶液中，形成正极浆料。采用铝箔作为正极集流体，将正极浆料涂覆于正极集流体上，经过干燥、冷压、裁切程序后得到正极。
电解液的制备
在含水量小于10ppm的环境下，将六氟磷酸锂、氟代碳酸乙烯酯(FEC)与非水有机溶剂(碳酸乙烯酯(EC)∶碳酸二甲酯(DMC)∶碳酸二乙酯(DEC)＝1∶1∶1，重量比)配制成氟代碳酸乙烯酯的重量浓度为10wt％且六氟磷酸锂浓度为1mol/L的电解液。
锂离子电池的制备
采用以聚乙烯(PE)多孔聚合薄膜作为隔离膜。将上述正极、隔离膜与以下实施例与对比例的负极的依顺序堆叠，使隔离膜处于正极与负极中间起到隔离的作用，然后卷绕成电极组件。随后将该电极组件装入铝塑膜包装袋中，并在80℃下脱去水分后，获得干电极组件。随后将上述电解液注入干电极组件中，经过真空封装、静置、化成、整形等工序，即完成以下各实施例和对比例的锂离子电池的制备。
实施例1
将硅氧材料SiO x(0.5≤x≤1.6)和人造石墨加入到搅拌器中混合以形成负极活性材料，其中硅氧材料经X射线衍射测试后的I 2/I 1的比值为0.38。随后，将聚丙烯酸、导电炭黑加入到搅拌中的负极活性材料内(负极活性材料、导电炭黑、聚丙烯酸的重量比为95∶2∶3)，在公转速度为20圈/分钟及自转转速为1200圈/分钟下搅拌60分钟，再加入去离子水搅拌120分钟，得到混合浆料，其中硅氧材料SiO x的重量比为1％。
采用铜箔作为负极集流体，其中负极集流体的厚度为9μm且绝对强度为1800N/m。将混合浆料涂布于负极集流体上，并进行烘干。烘干后，进行冷压处理，以得到负极活性材料层，其中负极活性材料层的厚度为90μm且压实密度为1.75g/cm 3，随后通过裁切程序后得到负极。
实施例2-8
与实施例1的制备方式相同，不同的地方是实施例2-8中硅氧材料SiO x的重量比依序为7％、11％、15％、20％、30％、50％、70％。
实施例9-15
与实施例3的制备方式相同，不同的地方是实施例9-15中负极集流体的厚度依序为8μm、7μm、6μm、5μm、4μm、2.5μm、1μm且负极集流体的绝对强度依序为1600N/m、1400N/m、1200N/m、1000N/m、800N/m、500N/m、200N/m。
实施例16-19
与实施例3的制备方式相同，不同的地方是实施例16-19中依序采用镍箔、钛箔、铬箔、不锈钢箔作为负极集流体。
实施例20-23
与实施例3的制备方式相同，不同的地方是实施例20-23中硅氧材料经X射线衍射测试后的I 2/I 1的比值依序为0.41、0.64、1、2.5。
实施例24-27
与实施例3的制备方式相同，不同的地方是实施例24-27中的硅氧材料中依序掺杂了金属元素锂、镁、钛、铝，且实施例24-27中的金属元素掺杂的量占负极材料的重量比分别为1.17％、2％、2％、1.5％。
对以上实施例及对比例的负极，并对其进行单位重量及压实密度测试。随后对锂离 子电池进行循环性能测试、循环膨胀率测试及放电倍率测试，并记录其测试结果。
实施例1-27的负极及锂离子电池的统计数值及通过循环性能测试、循环膨胀率测试及放电倍率测试的结果如下表1所示。
表1
Figure PCTCN2020070130-appb-000001
如表1所示，本申请实施例1-5、9-12、16-27中的锂离子电池，其负极中的硅基材料以负极活性材料层的总重量计的重量比R与负极集流体的绝对强度符合σ满足以下公式：K＝σ/(1.4×R+0.1)，其中K为4000N/m。相较于其他实施例，本申请符合上述 硅基材料的重量比与负极集流体绝对强度范围内的实施例的锂离子电池都能够保有在80％以上的25℃400圈循环保持率以及25℃400圈循环厚度膨胀率，同时能够保持在9.5％以下的25℃400圈循环厚度膨胀率和0.34％以下的25℃400圈循环XY膨胀率，以及83.5％以上的放电倍率。
具体，通过比较实施例1-5和实施例6-86可知，当负极活性物质层中的硅基材料含量越高时，其锂离子电池的循环膨胀率也会随之大量提升。参考实施例6-8可知，当负极活性物质层中的硅基材料含量超出本申请实施例所提供的其与负极集流体的强度范围时，由于负极集流体强度不足以牵制硅基材料的膨胀率，进而导致负极活性材料层的XY膨胀率大量提升，并造成锂离子电池的膨胀与变形，从而影响锂离子电池的循环性能与安全性能。
图1与图2分别为本申请实施例1与实施例6的锂离子电池的循环容量曲线图及循环膨胀率曲线图。
如图1所示，经过400圈循环后，实施例1由于其硅基材料的含量较低，其负极活性材料层在循环过程中所产生的应力较小，当在其负极集流体具有一定绝对强度时，能够使其不容易产生XY膨胀与形变，进而确保负极活性材料层与负极集流体的结合，以及锂离子电池的循环性。相较之下实施例6，由于其硅基材料的含量较大，其负极活性材料层在循环过程中所产生的应力超出了负极集流体的绝对强度，进而导致了负极的形变，使得锂离子电池的循环保持率从循环一开始变急遽恶化。因此，实施例4的锂离子电池的容量保持率会急速的下降。
通过比较实施例9-12和13-15可知，在负极活性材料一致时，负极集流体的不同绝对强度反映了其能够承受的来自负极活性材料层的应力强度，进而反映负极对XY膨胀和形变的抑制程度。负极集流体的绝对强度越小，负极的XY膨胀率和变形率越大，进而使得电池的循环性能变差，循环相同圈数下的容量保持率降低；同时，由于负极形变的影响也使得锂离子电池的倍率性能下降。
图3与图4分别为本申请实施例20与实施例23的硅基材料的X射线衍射图。
从实施例20-23的对比可以发现，随着I 2/I 1的值不断增加，其锂离子电池的循环保持率不断降低，循环膨胀率增加，且倍率性能变差。I 2/I 1的值反映了材料中材料受到歧化的影响程度，其值越大，其内部产生的氧化硅歧化产生的硅晶粒的尺寸也越大，在嵌锂过程中会导致负极活性材料层局部区域的应力急剧增大，从而在充放电循环过程中导 致硅基材料的晶体结构破坏。
通过上述实施例及对比例的比较，可以清楚的理解本申请通过限定负极中硅基材料的重量比与负极集流体绝对强度的关系，能够有效的降低锂离子电池中负极的不规律膨胀及变形，同时也能够一定程度上改善负极活性材料层从负极集流体剥离的现象，从而提升了锂离子电池的循环性能跟安全性能。
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. 一种负极，其包括：
    负极集流体；及
    负极活性材料层，所述负极活性材料层包含硅基材料，
    其中所述硅基材料以所述负极活性材料层的总重量计的重量比R与所述负极集流体的绝对强度σ符合满足以下公式：K＝σ/(1.4×R+0.1)，其中K为关系系数，且所述关系系数大于或等于4000N/m。
  2. 根据权利要求1所述的负极，其中所述负极集流体的所述绝对强度大于或等于500N/m。
  3. 根据权利要求1所述的负极，其中所述负极集流体的厚度为1μm至15μm。
  4. 根据权利要求1所述的负极，其中所述硅基材料包含通式M ySiO x所代表的组份中的一种或多种硅氧材料，其中0≤y≤4，0≤x≤4，且M为包含Li、Mg、Ti及Al中的至少一种。
  5. 根据权利要求4所述的负极，所述硅氧材料的一次颗粒通过X射线衍射测试的衍射图案中归属于20.5°-21.5°范围内的第一峰强度为I 1，归属于28.0°-29.0°范围内的第二峰强度为I 2，其中0＜I 2/I 1≤10。
  6. 根据权利要求1所述的负极，其中所述硅基材料以所述负极活性材料层的总重量计的所述重量比为1％至70％。
  7. 根据权利要求1所述的负极，其中所述负极活性材料层进一步包含粘结剂及导电剂，其中所述粘结剂包括聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、羧甲基纤维素、羧甲基纤维素钠、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶及聚偏氟乙烯中的至少一种，且所述导电剂包括导电炭黑、碳纳米管、碳纤维及科琴黑中的至少一种。
  8. 根据权利要求1所述的负极，其中所述负极集流体包含铜箔、镍箔、钛箔、铬箔及不锈钢箔中的至少一种。
  9. 根据权利要求1所述的负极，其中所述硅基材料进一步包含包覆层，所述包覆层包含碳材料及高分子材料中的至少一种，其中所述碳材料包含无定形碳、碳纳米管、碳纳米粒子、气相沉积碳纤维及石墨烯中的至少一种，且所述高分子材料包含聚偏氟乙烯或其衍生物、羧甲基纤维素或其衍生物、羧甲基纤维素钠或其衍生物、聚乙烯基吡咯烷酮或其衍生物、聚丙烯酸或其衍生物及聚丁苯橡胶中的至少一种。
  10. 一种电化学装置，其包括：
    正极；
    隔离膜；以及
    根据权利要求1至9中任一项所述的负极。
  11. 一种电子装置，其包含权利要求10所述的电化学装置。
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