WO2023173410A1 - Appareil électrochimique, appareil électronique et procédé de préparation de plaque d'électrode négative - Google Patents

Appareil électrochimique, appareil électronique et procédé de préparation de plaque d'électrode négative Download PDF

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WO2023173410A1
WO2023173410A1 PCT/CN2022/081714 CN2022081714W WO2023173410A1 WO 2023173410 A1 WO2023173410 A1 WO 2023173410A1 CN 2022081714 W CN2022081714 W CN 2022081714W WO 2023173410 A1 WO2023173410 A1 WO 2023173410A1
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layer
negative electrode
lithium
carbon nanotubes
electrochemical device
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PCT/CN2022/081714
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English (en)
Chinese (zh)
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刘晓静
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宁德新能源科技有限公司
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Priority to PCT/CN2022/081714 priority Critical patent/WO2023173410A1/fr
Priority to CN202280004959.5A priority patent/CN116097472A/zh
Publication of WO2023173410A1 publication Critical patent/WO2023173410A1/fr

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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of electrochemical energy storage, and in particular, to electrochemical devices, electronic devices and methods of preparing negative electrode plates.
  • the electrolyte decomposes on the surface of the negative electrode plate to form a solid electrolyte interface film (SEI film), which irreversibly consumes the active lithium from the positive electrode plate, causing the electrochemical device to malfunction.
  • SEI film solid electrolyte interface film
  • lithium is usually pre-supplied on the surface of the negative electrode sheet to reduce the consumption of active lithium from the positive electrode sheet and improve the first Coulombic efficiency, energy density and cycle performance of the electrochemical device.
  • problems of uneven lithium supplementation and residual lithium metal are prone to occur. We look forward to further improvements in this area.
  • Embodiments of the present application provide an electrochemical device.
  • the electrochemical device includes a negative electrode piece.
  • the negative electrode piece includes a negative electrode current collector, a first layer and a second layer, wherein the first layer is disposed between the negative electrode current collector and the second layer. Between two layers; wherein, the first layer includes negative active material, and the second layer includes carbon nanotubes and polymer binder.
  • the second layer has a thickness of 0.1 ⁇ m to 4 ⁇ m. In some embodiments, the thickness of the second layer is greater than or equal to 0.5 ⁇ m and less than 3 ⁇ m. In some embodiments, the mass percentage of carbon nanotubes in the second layer ranges from 80% to 99%. In some embodiments, the polymeric binder content in the second layer ranges from 1% to 20% by mass. In some embodiments, the carbon nanotubes include at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. In some embodiments, the diameter of the carbon nanotubes ranges from 0.4 nm to 100 nm.
  • the polymeric binder includes polyvinyl alcohol, polyvinyl acetal, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylate salt, polyvinylidene fluoride, or sodium alginate at least one of them.
  • the negative active material includes at least one of graphite, silicon, silicon alloy, silicon-oxygen material, silicon-carbon material, hard carbon, or tin-based material.
  • An embodiment of the present application also provides an electronic device, including the above electrochemical device.
  • Embodiments of the present application also provide a method for preparing a negative electrode sheet.
  • the method includes: coating a first slurry on the negative electrode current collector, drying, and cold pressing to form a first layer, wherein the first slurry
  • the material includes anode active material; carbon nanotubes and polymer binder are dispersed in deionized water to form a second slurry; the second slurry is coated on the first layer, dried and cold pressed to form a second slurry. layer; forming a lithium metal layer on the second layer to form a negative electrode piece.
  • a conductive electron path can be constructed on the surface of the negative electrode sheet, reducing the first layer and the need for lithium replenishment.
  • the gaps between the lithium metal layers improve the uniformity of lithium replenishment during the lithium metal contact lithium replenishment process and reduce the problem of lithium precipitation on the surface of the negative electrode piece; at the same time, it can help reduce the lithium metal residue on the negative electrode piece after lithium replenishment. Reduce the risk of short circuit between the positive electrode piece and the negative electrode piece and the battery self-discharge problem, and improve the safety performance of the electrochemical device.
  • Figure 1 shows a cross-sectional view of a negative electrode plate according to some embodiments of the present application.
  • an electrochemical device for example, a lithium-ion battery
  • the electrolyte decomposes on the surface of the negative electrode to form a solid electrolyte phase interface film (SEI film), which irreversibly consumes a large amount of active lithium from the positive electrode, causing the battery to fail.
  • SEI film solid electrolyte phase interface film
  • lithium is usually pre-supplied by adding lithium-rich materials to the negative electrode side. Active lithium is replenished at the negative electrode piece in advance to reduce the active lithium from the positive electrode piece. consumption, improving the first Coulombic efficiency and energy density of electrochemical devices.
  • increasing active lithium can also improve the cycle performance of electrochemical devices.
  • the existing pre-lithium replenishment method is to roll metal lithium foil, lithium powder, lithium strips, etc. onto the surface of the negative electrode sheet after coating and cold pressing through physical methods, which is also called contact lithium replenishment.
  • the potential of the negative electrode piece will quickly drop to 0.6V within 10 minutes, which is lower than the potential formed by the SEI film, and the negative electrode piece will spontaneously begin to embed lithium.
  • an electronic pathway and an ion pathway need to be formed.
  • the electronic pathway means that the lithium metal needs to be in electrical contact with the negative active material to conduct electrons.
  • the lithium foil is not completely in contact with the negative electrode sheet, there is some gap in the middle, or the conductive network of the silicon-containing negative electrode sheet is not perfectly constructed, it will cause the electronic path in the lithium replenishment area to be disconnected and the completion of the lithium replenishment cannot be completed.
  • Lithium insertion process Since spontaneous lithium insertion after contact-type lithium replenishment will occur preferentially in areas with better electron pathways, the lithium replenishment uniformity of this lithium replenishment method is poor. SEI films will be formed preferentially in areas with better electron conductivity, and some lithium will be embedded in the negative electrode activity.
  • the local CB Cell Balance, which refers to the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area
  • CB ⁇ 1 may occur.
  • this part of the negative electrode active material does not have enough vacancies to receive the active lithium deintercalated from the positive electrode, resulting in The problem of local lithium precipitation; in areas with poor conductivity, a small amount of negative active material forms an SEI film, the local CB increases, and the lithium metal in this area will remain on the negative electrode sheet, resulting in a mismatch between the initial lithium replenishment efficiency and the design, and the battery The capacity of the chemical unit is low.
  • lithium metal residues will puncture the isolation film, causing internal short circuit problems in the electrochemical device, and affecting the safety and reliability of hot box testing.
  • Embodiments of the present application provide an electrochemical device, which includes a negative electrode piece.
  • FIG. 1 shows a cross-sectional view of the cross-section along the width direction and thickness direction of the negative electrode plate according to some embodiments.
  • the negative electrode sheet includes a negative electrode current collector 101 , a first layer 102 and a second layer 103 , wherein the first layer 102 is disposed between the negative electrode current collector 101 and the second layer 103 .
  • first layer 102 includes negative active material.
  • second layer 103 includes carbon nanotubes and a polymer binder.
  • second layer 103 is formed from carbon nanotubes and a polymer binder.
  • the second layer 103 builds a conductive electron path on the surface of the negative electrode piece, which can improve the uniformity of lithium replenishment during the lithium metal contact lithium replenishment process and reduce lithium precipitation caused by local CB ⁇ 1 of the negative electrode piece. question.
  • the second layer 103 can help reduce the lithium metal residue on the negative electrode piece after lithium replenishment, reduce the risk of short circuit between the positive electrode piece and the negative electrode piece and the battery self-discharge problem, and improve the safety performance of the electrochemical device.
  • a lithium metal layer 104 may also be present on the second layer 103 of the negative electrode sheet to pre-supply lithium. After the chemical formation, the lithium metal layer 104 disappears due to the replenishment of lithium to the negative electrode plate. Therefore, in FIG. 1 , the lithium metal layer 104 is shown as a dotted line.
  • the first layer 102 and the second layer 103 are shown on one side of the negative electrode current collector 101 in FIG. 1 , this is only exemplary and the first layer 102 and the second layer 103 may be are located on both sides of the negative electrode current collector 101 .
  • the preparation method includes: coating a first slurry on a negative electrode current collector, drying, and cold pressing to form a first layer, wherein the first slurry includes a negative electrode active material.
  • the first slurry may further include a binder (eg, styrene-butadiene rubber), a conductive agent (eg, conductive carbon black), and a solvent (eg, deionized water).
  • the preparation method may also include: dispersing the carbon nanotubes and the polymer binder in deionized water to form a second slurry; then, coating the second slurry on the first layer, drying, and cold pressing, Form the second layer.
  • a lithium metal layer is formed on the second layer to form a negative electrode piece.
  • the lithium metal layer is formed on the second layer by rolling. It should be understood that during the preparation process of the finished lithium-ion battery, after the formation, the lithium metal layer may disappear due to the replenishment of lithium to the negative electrode piece, so that the negative electrode piece no longer includes the lithium metal layer.
  • the lithium metal layer includes at least one of lithium foil, lithium ribbon, or lithium block.
  • the thickness of second layer 103 is 0.1 ⁇ m to 4 ⁇ m. If the thickness of the second layer 103 is too small, the effect of the second layer 103 on improving the uniformity of lithium replenishment and reducing lithium metal residues is relatively weak; if the thickness of the second layer 103 is too large, it will adversely affect the battery life. Energy density of chemical devices. In some embodiments, the thickness of the second layer 103 is greater than or equal to 0.5 ⁇ m and less than 3 ⁇ m. The thickness of the second layer 103 is greater than or equal to 0.5 ⁇ m, which is beneficial to reducing the electronic resistivity of the negative electrode piece, thereby increasing the lithium absorption rate.
  • the thickness of the second layer 103 is greater than or equal to 3 ⁇ m, the temperature rise during lithium replenishment is large, side reactions between the lithium metal layer and the electrolyte increase, and the first lithium replenishment efficiency and energy density of the electrochemical device decrease.
  • the mass percentage of carbon nanotubes in the second layer 103 is 80% to 99%. In some embodiments, the polymer binder content in the second layer 103 ranges from 1% to 20% by mass. If the mass percentage of carbon nanotubes in the second layer 103 is too small, the conductive electron capability of the second layer 103 is reduced; if the mass percentage of the carbon nanotubes in the second layer 103 is too large, the lithium absorption rate is lower than Large, the temperature rise during lithium replenishment is large, the side reactions between the lithium metal layer and the electrolyte increase, and the first lithium replenishment efficiency and energy density of the electrochemical device decrease.
  • the carbon nanotubes include at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.
  • the diameter of the carbon nanotubes ranges from 0.4 nm to 100 nm. When adding a certain amount of carbon nanotubes, the diameter of the carbon nanotubes affects their conductivity. The smaller the diameter, the thinner the tube wall, and the stronger the conductivity. For example, the conductivity of single-walled carbon tubes (diameter 0.4-2nm) The performance is better than that of multi-walled carbon tubes (diameter 2-100nm).
  • the polymeric binder includes polyvinyl alcohol, polyvinyl acetal, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylate salt, polyvinylidene fluoride, or sodium alginate at least one of them.
  • the polymer binder serves to bind the carbon nanotubes, making the structure of the second layer more stable. Any binder can be used as long as it can achieve a bonding effect, but since the bonding effect between polymer binders and carbon nanotubes is better, polymer binders are preferred.
  • the negative active material includes at least one of graphite, silicon, silicon alloy, silicon-oxygen material, silicon-carbon material, hard carbon, or tin-based material.
  • the negative electrode current collector may use at least one of copper foil, nickel foil, or carbon-based current collector. Of course, other negative electrode current collectors commonly used in the art may also be used. In some embodiments, the thickness of the negative electrode current collector may be 1 ⁇ m to 200 ⁇ m.
  • first layer 102 may also include conductive agents and adhesives.
  • the conductive agent in the first layer 102 may include at least one of conductive carbon black, Ketjen black, flake graphite, graphene, carbon nanotubes or carbon fibers.
  • the binder in the first layer 102 may include carboxymethylcellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysilicone At least one of oxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin or polyfluorene.
  • CMC carboxymethylcellulose
  • the materials disclosed above are only exemplary, and any other suitable materials may be used for the first layer 102 as the negative active material layer.
  • the mass ratio of the negative active material, conductive agent and binder in the first layer 102 may be 91 ⁇ 99:0 ⁇ 3:1 ⁇ 6. It should be understood that the above are only examples and any other suitable mass ratios may be used.
  • the electrochemical device may include an electrode assembly, and the electrode assembly may include a separator, a positive electrode piece, and the above-mentioned negative electrode piece, wherein the isolation film is disposed between the positive electrode piece and the negative electrode piece.
  • the positive electrode sheet may include a positive current collector and a positive active material layer located on one or both sides of the positive current collector.
  • the positive electrode current collector may be an aluminum (Al) foil. Of course, other positive electrode current collectors commonly used in the art may also be used.
  • the thickness of the cathode current collector may be 1 ⁇ m to 200 ⁇ m.
  • the cathode active material layer may include a cathode active material, and the cathode active material may include lithium cobalt oxide, lithium manganate, lithium iron phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium nickel manganate. of at least one.
  • the positive active material layer further includes a binder and a conductive agent.
  • the binder in the positive active material layer may include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, Polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene At least one of vinyl fluoride or polyhexafluoropropylene.
  • the conductive agent in the cathode active material layer may include at least one of conductive carbon black, Ketjen black, flake graphite, graphene, carbon nanotubes or carbon fibers.
  • the mass ratio of the cathode active material, the conductive agent and the binder in the cathode active material layer may be 91 ⁇ 99:0.5 ⁇ 3:0.5 ⁇ 6. It should be understood that the above is only an example, and the positive active material layer may adopt any other suitable materials, thicknesses and mass ratios.
  • the release film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid.
  • polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.
  • the thickness of the isolation film ranges from about 5 ⁇ m to 20 ⁇ m.
  • the surface of the isolation membrane may also include a porous layer.
  • the porous layer is disposed on at least one surface of the isolation membrane.
  • the porous layer includes inorganic particles and a binder.
  • the inorganic particles are selected from aluminum oxide (Al 2 O 3 ), Silicon oxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), ceria (CeO 2 ), nickel oxide (NiO), oxide Zinc (ZnO), calcium oxide (CaO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or sulfuric acid At least one of barium.
  • the pores of the isolation film have a diameter in the range of about 0.01 ⁇ m to 1 ⁇ m.
  • the binder of the porous layer is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, poly At least one of vinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene or polyhexafluoropropylene.
  • the porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece.
  • the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.
  • the electrochemical device includes a lithium-ion battery, although the application is not limited thereto.
  • the electrochemical device may also include an electrolyte.
  • the electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution, and the electrolyte solution 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 , LiC(SO 2 CF 3 ) 3 , one or more of LiSiF 6 , LiBOB or lithium difluoroborate.
  • LiPF 6 was chosen for the lithium salt because it gives high ionic conductivity and improves cycle characteristics.
  • the non-aqueous solvent may be selected from carbonate compounds, carboxylate compounds, ether compounds, other organic solvents, or combinations thereof.
  • the carbonate compound may be selected from chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, or combinations thereof.
  • the chain carbonate compound may be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl carbonate Ethyl ester (MEC) and its combinations.
  • the cyclic carbonate compound may be selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC) or combinations thereof.
  • the fluorocarbonate compound may be selected from the group consisting of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, and 1,1,2-trifluoroethylene carbonate.
  • the carboxylate compound may be selected from the group consisting of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decanolactone, Valerolactone, mevalonolactone, caprolactone, methyl formate or combinations thereof.
  • the ether compound may be selected from dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxy ethane, 2-methyltetrahydrofuran, tetrahydrofuran or combinations thereof.
  • organic solvents may be selected from dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, methane Amides, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.
  • the positive electrode sheet, the separator film, and the negative electrode sheet are wound or stacked in order to form an electrode piece, and are then packaged in, for example, an aluminum plastic film, and electrolyte is injected liquid, formed, and packaged to make a lithium-ion battery. Then, the prepared lithium-ion battery was tested for performance.
  • electrochemical devices eg, lithium-ion batteries
  • electrochemical devices eg, lithium-ion batteries
  • Other methods commonly used in the art can be used without departing from the content disclosed in this application.
  • Embodiments of the present application also provide an electronic device including the above electrochemical device.
  • the electronic device in the embodiment of the present application is not particularly limited and may be used in any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, laptop computers, pen computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headsets, Video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, Lighting appliances, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • Preparation of the positive electrode sheet Dissolve the positive active material lithium cobalt oxide, the conductive agent acetylene black, and the binder polyvinylidene fluoride in an N-methylpyrrolidone (NMP) solution in a weight ratio of 94:3:3.
  • NMP N-methylpyrrolidone
  • Aluminum foil is used as the positive electrode current collector, and the positive electrode slurry is coated on the positive electrode current collector with a coating thickness of 80 ⁇ m. After drying, cold pressing, and cutting, the positive electrode pieces are obtained.
  • Preparation of the negative electrode sheet Dissolve the negative active material (10wt% Si and 90wt% graphite), the binder styrene-butadiene rubber and the conductive agent carbon nanotubes in deionized water in a weight ratio of 97:2.5:0.5 to form the third A slurry. Copper foil is used as the negative electrode current collector, and the first slurry is coated on the negative electrode current collector with a coating thickness of 120 ⁇ m. After drying, cold pressing, and cutting, the negative electrode piece is obtained, and the negative electrode piece is placed in a vacuum oven at 85°C. Bake for 24 hours until the moisture content of the negative electrode sheet is less than 300 ppm, and then compound a layer of lithium metal foil with a thickness of 1 ⁇ m on the negative electrode sheet by rolling.
  • the negative active material (10wt% Si and 90wt% graphite
  • the binder styrene-butadiene rubber and the conductive agent carbon nanotubes in deionized water in a weight ratio of
  • isolation film The base material of the isolation film is 8 ⁇ m thick polyethylene (PE). A 2 ⁇ m alumina ceramic layer is coated on both sides of the isolation film base material. Finally, 2.5 ⁇ m alumina ceramic layer is coated on both sides of the ceramic layer. mg of the binder polyvinylidene fluoride (PVDF), dried.
  • PE polyethylene
  • PVDF binder polyvinylidene fluoride
  • Preparation of lithium-ion battery Stack the positive electrode sheet, isolation film, and negative electrode sheet in order, so that the isolation film is between the positive electrode sheet and the negative electrode sheet for isolation, and wind it to obtain the electrode assembly.
  • the electrode assembly is placed in the outer packaging aluminum plastic film. After removing the moisture at 80°C, the above-mentioned electrolyte is injected and packaged. After formation, degassing, trimming and other processes, the thickness is 4mm, the width is 35mm, and the length is 80mm lithium-ion battery.
  • the embodiment is based on the steps of Comparative Example 1 with parameter changes. Only the preparation of the negative electrode piece is different from Comparative Example 1. Wherein, the preparation of the negative electrode piece of Example 1 is as follows:
  • the negative active material (10wt% Si and 90wt% graphite), the binder styrene-butadiene rubber and the conductive agent carbon nanotubes were dissolved in deionized water in a weight ratio of 97:2.5:0.5 to form a first slurry.
  • Copper foil is used as the negative electrode current collector, and the first slurry is coated on the negative electrode current collector with a coating thickness of 120 ⁇ m to obtain the first layer.
  • Carbon nanotubes (diameter: 50 nm) and lithium carboxymethyl cellulose were dispersed in deionized water at a mass ratio of 95:5 to obtain a second slurry, and the second slurry was applied on the first layer to obtain a second slurry.
  • the second layer is dried, cold-pressed, and cut to obtain the negative electrode piece.
  • the negative electrode piece is baked in a vacuum oven at 85°C for 24 hours until the moisture content of the negative electrode piece is less than 300ppm. Then, it is rolled on the negative electrode.
  • a layer of lithium metal foil with a thickness of 1 ⁇ m is compounded on the pole piece.
  • Examples 2 and 3 are different from Example 1 in terms of the mass percentage of carbon nanotubes in the second layer.
  • Example 4 is different from Example 2 in the type and diameter of the carbon nanotubes in the second layer.
  • Examples 5 to 7 differ from Example 2 in the thickness of the second layer. Specific parameter differences are shown in Table 1 below.
  • the charging rate is set to 0.2C, constant current charging at a rate of 0.2C to 4.45V, and then constant voltage charging to 0.025C.
  • the lithium-ion battery is fully charged, remove the lithium-ion battery.
  • the disassembling the lithium-ion battery determine whether there is any local lithium precipitation problem on the surface of the negative electrode piece.
  • the lithium-ion battery is charged at a constant current rate of 0.7C to the full charge voltage of 4.45V, charged at a constant voltage to 0.025C, and then fully discharged to 3.0V at a rate of 0.5C.
  • a charge-discharge cycle the performance of the lithium-ion battery after 800 cycles is recorded. Capacity retention rate.
  • Table 1 shows various parameters and evaluation results of Examples and Comparative Examples.
  • Example 1 By comparing Example 1 and Comparative Example 1, it can be seen that coating the surface of the negative electrode plate with a second layer including carbon nanotubes and a polymer binder and then replenishing lithium can significantly reduce the electronic resistivity of the negative electrode plate after replenishing lithium. , correspondingly, increasing the electronic contact between the lithium-supplementing metal and the first layer of the negative electrode plate.
  • the lithium-ion battery after being fully charged at 0.2C was disassembled and found that the surface of the negative electrode piece that was not coated with the second layer in Comparative Example 1 had a local lithium precipitation problem, and there was a certain amount of lithium metal remaining, while in Example 1, the negative electrode piece was not coated with the second layer.
  • the self-discharge of lithium-ion batteries can be expressed by the K value, which is the reduction value of the battery's open circuit voltage per unit time. The larger the K value, the faster the open circuit voltage decreases, and the more serious the self-discharge problem of lithium-ion batteries. Generally, the K value is required to be less than 0.08.
  • Example 1 Compared with Comparative Example 1, the K value of Example 1 was reduced from 0.10 to 0.04, which met the requirement that the K value be less than 0.08, indicating that when the lithium metal residue on the surface of the negative electrode plate is reduced, the risk of lithium metal puncturing the separator can be reduced.
  • the short circuit points between the positive electrode piece and the negative electrode piece are reduced, inhibiting the self-discharge behavior of the lithium-ion battery.
  • the first efficiency of lithium-ion batteries increased from 90.1% to 92.5% after lithium supplementation, and the energy density of lithium-ion batteries increased from 750Wh/L to 762Wh/L.
  • the active lithium shuttled between the positive electrode piece and the negative electrode piece increased, and the capacity retention rate after 800 cycles also increased from 79.6% to 82.2%.
  • Example 1 By comparing Example 1 to Example 3, it can be found that the proportions of carbon nanotubes in the second layer are 95%, 90% and 80% respectively. As the proportion of carbon nanotubes decreases, the electronic resistivity of the negative electrode plate increases. , the initial efficiency and energy density of lithium supplement first increase and then decrease. This is because when the proportion of carbon nanotubes is higher, the electron transmission resistance is smaller, the lithium absorption rate is faster, the temperature rise of lithium supplement is higher, and the relationship between lithium metal and electrolyte There are many side reactions, which affects the initial efficiency and energy density of lithium supplementation.
  • Example 2 By comparing Example 2 and Example 4, it can be found that when the thickness of the carbon nanotube layer and the mass ratio of the carbon tubes are the same, the electronic conductivity of the multi-walled carbon tube with a diameter of 15nm is worse than that of the single-walled carbon tube with a diameter of 1nm. Moreover, a single carbon tube with a diameter of 15 nm has a larger mass. When the added mass ratio is certain, its molar ratio is lower, that is, the number of carbon tubes is small, which is not conducive to conducting electrons.
  • the electronic resistivity of pole pieces prepared using 15nm carbon tubes increases, the lithium metal absorption effect decreases, resulting in a decrease in the first effect of lithium supplementation and a decrease in energy density, and an increase in the K value.
  • Example 2 By comparing Example 2 with Examples 5 to 7, when the mass percentage of carbon nanotubes in the second layer is 90% and the thickness of the second layer increases from 0.5 to 1 ⁇ m, 3 ⁇ m and 4 ⁇ m, the negative electrode The electronic resistivity of the sheet decreases as the thickness of the second layer increases, the lithium absorption rate accelerates, the lithium replenishment temperature rises, the side reactions between lithium metal and the electrolyte increase, and the first lithium replenishment efficiency and energy density decrease.
  • Comparative Example 1 when the thickness of the second layer is 4 ⁇ m, 0.2C is fully charged, there is no lithium metal residue at the interface, and there is no lithium precipitation problem caused by CB ⁇ 1.
  • the lithium absorption is relatively complete, but the lithium supplement generates heat.
  • the thickness of the second layer affects the total thickness of the lithium-ion battery, causing the energy density to be reduced to 740Wh/L.
  • the thickness of the second layer is 3 ⁇ m
  • the first lithium replenishment efficiency of the lithium-ion battery is 0.7% higher than that of Comparative Example 1, and the capacity retention rate after 800 cycles is increased by 0.8%.
  • the energy density is reduced. 5Wh/L.
  • the thickness of the second layer is ⁇ 3 ⁇ m, the first lithium replenishment efficiency, energy density and capacity retention rate of the lithium-ion battery are improved, so the thickness of the carbon tube buffer layer is preferably ⁇ 3 ⁇ m.
  • the surface of the negative electrode sheet coated with the second layer has stronger electronic conductivity, combined with the softer characteristics of the carbon nanotubes themselves, through rolling
  • the method can combine the lithium metal layer more closely on the surface of the negative electrode piece.
  • the existence of the second layer can eliminate the gap between the lithium metal layer and the first layer as much as possible.
  • Electronic pathways are evenly distributed on the entire negative electrode piece, and each area The electronic conductivity is close to ensure that the lithium-replenishing active lithium ions can be evenly embedded in different areas of the entire negative electrode sheet, improving the uniformity of lithium replenishment, reducing the lithium precipitation problem caused by local CB ⁇ 1, and also helping to control lithium replenishment.
  • the buffer layer can be adjusted Electronic resistance is beneficial to control the lithium replenishment speed of contact lithium replenishment and avoid thermal runaway problems caused by too fast lithium replenishment speed; the reduction of lithium metal residue in the negative electrode piece can reduce the risk of short circuit between the positive electrode piece and the negative electrode piece , the self-discharge problem of lithium-ion batteries is reduced, and the safety performance of lithium-ion batteries can be improved; in addition, the thickness of the second layer is thinner, and the thickness of the lithium-ion battery caused by the presence of the second layer increases to microns or sub-microns. level, has minimal impact on volumetric energy density.

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Abstract

Sont prévus dans la présente demande un appareil électrochimique, un appareil électronique et un procédé de préparation d'une plaque d'électrode négative. L'appareil électrochimique comprend une plaque d'électrode négative, la plaque d'électrode négative comprenant un collecteur de courant d'électrode négative, une première couche et une seconde couche, la première couche étant placée entre le collecteur de courant d'électrode négative et la seconde couche ; la première couche comprenant un matériau actif d'électrode négative ; et la seconde couche comprenant des nanotubes de carbone et un liant polymère. Une seconde couche comprenant des nanotubes de carbone et un liant polymère est formée sur une première couche comprenant un matériau actif d'électrode négative, de telle sorte qu'un sous-trajet conducteur peut être construit sur une surface d'une plaque d'électrode négative, ce qui permet de réduire un espace entre la première couche et une couche de lithium métal utilisée pour la supplémentation en lithium, d'améliorer l'uniformité de supplémentation en lithium dans un processus de supplémentation en lithium de type à contact au lithium métal et de réduire le problème de précipitation du lithium sur la surface de la plaque d'électrode négative ; et le lithium métal résiduel sur la plaque d'électrode négative après la supplémentation en lithium peut être réduit, ce qui permet de réduire le risque de court-circuit entre une plaque d'électrode positive et la plaque d'électrode négative et le problème d'auto-décharge de batterie et d'améliorer ainsi les performances de sécurité d'un appareil électrochimique.
PCT/CN2022/081714 2022-03-18 2022-03-18 Appareil électrochimique, appareil électronique et procédé de préparation de plaque d'électrode négative WO2023173410A1 (fr)

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CN202280004959.5A CN116097472A (zh) 2022-03-18 2022-03-18 电化学装置、电子装置和制备负极极片的方法

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JP2005038720A (ja) * 2003-07-15 2005-02-10 Sony Corp 負極の製造方法および電池の製造方法
CN103022413A (zh) * 2012-12-28 2013-04-03 东莞新能源科技有限公司 锂电池用负极片及其制备方法及包含该负极片的锂电池
CN106960945A (zh) * 2016-01-11 2017-07-18 宁德时代新能源科技股份有限公司 富锂负极片及二次电池
CN107799721A (zh) * 2016-09-07 2018-03-13 北京卫蓝新能源科技有限公司 预锂化负极、包括其的二次电池、以及它们的制造方法
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JP2005038720A (ja) * 2003-07-15 2005-02-10 Sony Corp 負極の製造方法および電池の製造方法
CN103022413A (zh) * 2012-12-28 2013-04-03 东莞新能源科技有限公司 锂电池用负极片及其制备方法及包含该负极片的锂电池
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