WO2021134800A1 - Ensemble électrode, dispositif électrochimique et dispositif électronique - Google Patents

Ensemble électrode, dispositif électrochimique et dispositif électronique Download PDF

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WO2021134800A1
WO2021134800A1 PCT/CN2020/070348 CN2020070348W WO2021134800A1 WO 2021134800 A1 WO2021134800 A1 WO 2021134800A1 CN 2020070348 W CN2020070348 W CN 2020070348W WO 2021134800 A1 WO2021134800 A1 WO 2021134800A1
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electrode assembly
silicon
pole piece
active material
lithium
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PCT/CN2020/070348
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English (en)
Chinese (zh)
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章婷
姜道义
陈志焕
崔航
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宁德新能源科技有限公司
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Priority to PCT/CN2020/070348 priority Critical patent/WO2021134800A1/fr
Publication of WO2021134800A1 publication Critical patent/WO2021134800A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • 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
    • H01M4/62—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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated 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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/426—Fluorocarbon polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines

Definitions

  • the present disclosure relates to the field of electronic technology, and in particular to an electrode assembly, an electrochemical device, and an electronic device.
  • electrode assemblies are widely used in electrochemical devices such as lithium ion batteries. Due to the volume expansion of the positive and negative pole pieces during the charge-discharge cycle, the electrode assembly has the problems of deformation and wrinkles after the formation and capacity test. Especially, for example, the electrode assembly using silicon-based anode material, because the silicon-based anode material has a volume expansion of about 300% during the lithium insertion process, the electrode assembly using the silicon-based anode material is more prone to deformation after formation and capacity testing. The deformation of the electrode assembly will cause the cycle stability of the electrode assembly to decrease.
  • the purpose of the present disclosure is to provide an electrode assembly, an electrochemical device, and an electronic device.
  • the electrode assembly of the present disclosure has a capacity per unit area of the negative pole piece and a separation membrane within a specific range. Half-charge shrinkage rate to relieve the deformation of the electrode assembly.
  • the negative pole piece has a negative active material layer
  • the negative active material layer includes a silicon-based material
  • the positive pole piece has a positive active material layer
  • the positive active material layer includes one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickelate, and lithium nickel cobaltate Or multiple.
  • the silicon-based material includes one or more of nano-silicon-based particles, silicon oxide, silicon-carbon composite particles, and silicon alloys; the silicon-based material contains lithium and magnesium
  • the average particle size of the silicon-based material is 500 nm-30 ⁇ m; the surface of the silicon-based material has one or two of carbon materials and polymer materials.
  • the average particle diameter of the nano-silicon-based particles is less than 100 nm.
  • the carbon material includes one or more of amorphous carbon, carbon nanotubes, carbon nanoparticles, carbon fibers, and graphene; and/or the polymer material includes polyvinylidene fluoride , Polyvinylidene fluoride derivatives, carboxymethyl cellulose, carboxymethyl cellulose derivatives, sodium carboxymethyl cellulose, sodium carboxymethyl cellulose derivatives, polyvinylpyrrolidone, polyvinylpyrrolidone derivatives, One or more of polyacrylic acid, polyacrylic acid derivatives and polystyrene butadiene rubber.
  • the separation film includes one or more of polyethylene, polypropylene, and polyvinylidene fluoride.
  • the electrode assembly is a wound electrode assembly.
  • the present disclosure also provides an electrochemical device, including the above-mentioned electrode assembly.
  • the present disclosure also provides an electronic device including the above-mentioned electrode assembly or the above-mentioned electrochemical device.
  • the present disclosure controls the capacity a per unit area of the negative pole piece of the electrode assembly and the half-charge shrinkage rate s t of the separator so that a and st meet 19.4 ⁇ a/s t ⁇ 1768, which can reduce the deformation of the electrode assembly and improve the The cycle stability of the electrochemical device of the electrode assembly.
  • FIG. 1 is a schematic diagram of the electrode assembly of the present disclosure.
  • FIG. 2 is a schematic diagram of the electrode assembly after 100 cycles of the lithium ion battery in Comparative Example 1 of the present disclosure.
  • Example 3 is a schematic diagram of the electrode assembly after 100 cycles of the lithium ion battery in Example 2 of the present disclosure.
  • Example 4 is a schematic diagram of the electrode assembly after 100 cycles of the lithium ion battery in Comparative Example 4 of the present disclosure.
  • FIG. 5 is a diagram of the wrinkle state of the separator after the lithium ion battery is cycled for 100 cycles in Comparative Example 3 of the present disclosure.
  • the positive pole piece 10 may include a positive current collector and a positive active material layer coated on the positive current collector.
  • the positive pole piece 10 has a positive active material layer, and the positive active material layer may only be coated on a partial area of the positive current collector.
  • the positive active material layer may include a positive active material, a conductive agent, and a binder. Al foil can be used as the positive electrode current collector, and similarly, other positive electrode current collectors commonly used in this field can also be used.
  • the conductive agent may include one or a combination of conductive carbon black, flake graphite, graphene, and carbon nanotubes.
  • the binder may include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, poly Acrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene or one of Several combinations.
  • the positive electrode active material includes, but is not limited to, one or more of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, lithium nickel cobaltate, lithium iron phosphate, lithium nickel cobalt aluminate, and lithium nickel cobalt manganate.
  • the above positive active material may include a positive active material that has been doped or coated.
  • the isolation film 11 includes one or a combination of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, and aramid.
  • polyethylene includes one or a combination of several 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 surface of the isolation membrane may further 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, and the inorganic particles are selected from alumina (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 and sulfuric acid One or a combination of barium.
  • alumina Al 2 O 3
  • Silicon oxide SiO 2
  • magnesium oxide MgO
  • titanium oxide TiO 2
  • hafnium dioxide HfO 2
  • the binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyethylene pyrrole One or a combination of alkanone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte infiltration performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece.
  • the negative pole piece 12 may include a negative current collector, and the negative current collector may be one or a combination of copper foil, aluminum foil, nickel foil, and carbon-based current collector.
  • the negative pole piece 12 has a negative active material layer.
  • the negative active material layer may be disposed on the negative current collector.
  • the negative pole piece has a first side and a second side.
  • a negative active material layer may be provided on either or both of the first side and the second side. Including negative active material.
  • the capacity per unit area of the negative pole piece is a mAh/cm 2 , and 0.97 ⁇ a ⁇ 8.84.
  • the capacity per unit area of the negative electrode piece refers to the capacity per unit area of the area on the negative electrode piece with the negative electrode active material layer when one surface of the current collector of the negative electrode piece is provided with the negative electrode active material layer.
  • the negative electrode active material is arranged on the coating area on either side of the copper foil to form a negative electrode piece with a negative electrode active material layer on one side.
  • the unit of the negative electrode piece on the coating area is The area capacity is the unit area capacity of the negative pole piece.
  • the capacity per unit area of the negative pole piece depends on the selected negative active material and the amount of negative active material coated on the unit area. When there are negative active material layers on both sides of the negative pole piece, the capacity per unit area of the negative pole piece can be measured by removing the negative active material layer on one side.
  • the initial length refers to the length of the wound electrode assembly before being wound
  • L1 is the electrode assembly being charged to 3.7-4.0V (for example, 3.85V)
  • the charging process can be constant current charging or constant voltage charging.
  • the half-charge shrinkage rate is mainly caused by the different winding tensions applied during the winding process.
  • the half-charge shrinkage rate can be used to characterize the winding tension.
  • the shrinkage rate is also greater.
  • the half-fill shrinkage rate can be adjusted by controlling the winding tension.
  • the present disclosure takes the wound electrode assembly as an example, the disclosure is not limited to this, and may also include stacked electrode assemblies.
  • the half-charge shrinkage rate of the separator is affected by the expansion of the positive and negative pole pieces. Impact.
  • 0.5% ⁇ s t ⁇ 5%, and a and st satisfy: 19.4 ⁇ a/st ⁇ 1768.
  • the experimental verification by the deformation condition when said electrode assembly and a s t meet can significantly improve the deformation of the electrode assembly and to improve the cycle stability, in particular, can be improved so that the wound electrode assembly Improve cycle stability, thereby increasing the yield of products.
  • the positive pole piece of the electrode assembly has a positive active material layer, and the positive active material layer includes one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickelate, and lithium nickel cobaltate Or multiple.
  • aluminum foil may be used for the positive pole piece.
  • the positive electrode active material of the positive electrode active material layer in the embodiment of the present disclosure includes, for example, LiNi 0.55 Co 0.05 M 0.4 O 2 , LiNi 0.55 Co 0.1 M 0.35 O 2 , LiNi 0.55 Co 0.12 M 0.33 O 2, etc. It may be the above-mentioned positive electrode active material doped with a transition metal.
  • the negative active material layer includes a silicon-based material.
  • the average particle size of the silicon-based material is 500 nm-30 ⁇ m.
  • the average particle size of the silicon-based material may be one of 600nm-20 ⁇ m, 800nm-10 ⁇ m, and 900nm-5 ⁇ m. This ensures that the content of fine particles in the negative electrode active material is low, and can reduce the side reaction of the electrolyte on the surface of the positive electrode active material, thereby inhibiting gas production and reducing heat generation, thereby improving the deformation of the electrode assembly and improving cycle stability.
  • the average particle size of the silicon-based material is too large, the strength of the negative pole piece will decrease, and if the average particle size of the silicon-based material is too small, it will hinder the movement of lithium ions.
  • the silicon-based material includes one or more of nano-silicon-based particles, silicon oxide, silicon-carbon composite particles, and silicon alloys.
  • the average particle size of the nano-silicon-based particles is less than 100 nm. The existence of nano-silicon-based particles can fill the tiny gaps in the negative electrode active material layer, which is beneficial to increase the compaction density and thus the specific energy, and can improve the transport performance of lithium ions and electrons. If the average particle size of the nano-silicon-based particles is too large, the nano-silicon-based particles will lose this advantage.
  • the silicon-based material contains one or both of lithium and magnesium.
  • the negative active material layer can be pre-strained, thereby reducing the amount of deformation of the negative active material layer during charging and discharging, and preventing the negative active material layer from being excessively deformed. Cracks or peeling from the negative current collector.
  • the surface of the silicon-based material may not have any other materials, or other materials may be present.
  • the structure of the silicon-based material can be stabilized, the oxidation activity of the electrolyte on the surface of the silicon-based material can be reduced, the side reaction of the electrolyte on the surface of the silicon-based material can be reduced, the gas production can be suppressed, and the heat production can be reduced.
  • one or both of carbon materials and polymer materials are present on the surface of the silicon-based material.
  • the specific capacity of silicon-based materials is much higher than that of graphite, but silicon-based materials have serious volume expansion during charging and discharging.
  • Carbon anode materials have small volume changes during charging and discharging, and have good cycle stability.
  • the crystal structure and chemical properties of carbon and silicon are similar, and the two can be closely combined. Therefore, when carbon materials are used, silicon-based materials provide higher specific capacity, and carbon materials can buffer the volume changes of silicon-based materials during charge and discharge. Improve the conductivity of silicon-based materials to avoid agglomeration of silicon-based materials during the charge-discharge cycle.
  • the carbon material includes one or more of amorphous carbon, carbon nanotubes, carbon nanoparticles, carbon fibers, and graphene.
  • the polymer material includes polyvinylidene fluoride, polyvinylidene fluoride derivatives, carboxymethyl cellulose, carboxymethyl cellulose derivatives, sodium carboxymethyl cellulose, carboxymethyl cellulose One or more of sodium derivatives, polyvinylpyrrolidone, polyvinylpyrrolidone derivatives, polyacrylic acid, polyacrylic acid derivatives, and polystyrene butadiene rubber.
  • the electrode assembly is a wound electrode assembly.
  • the embodiments of the present disclosure also provide an electrochemical device including the above-mentioned electrode assembly.
  • the electrochemical device includes a lithium ion battery, but the present disclosure is not limited thereto.
  • the electrochemical device may include the above-mentioned electrode assembly and electrolyte.
  • the electrolyte includes dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), propylene propionate At least two of esters (PP).
  • the electrolyte may additionally include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and dinitrile compounds as electrolyte additives.
  • the positive pole piece, the separator film, and the negative pole piece are sequentially wound or stacked to form an electrode piece, and then packed in, for example, an aluminum plastic film for packaging, and injection electrolysis Lithium-ion battery is made by liquid, formed and packaged. Then, perform performance test and cycle test on the prepared lithium-ion battery.
  • the embodiments of the present disclosure also provide an electronic device including the above-mentioned electrode assembly or an electronic device including the above-mentioned electrochemical device.
  • the electronic device may include any electronic device that uses a rechargeable battery, such as a mobile phone, a tablet computer, and a charging device.
  • a lithium ion battery with a wound electrode assembly is used as an example, and the raw materials, the ratio of raw materials, and the preparation method used to prepare the lithium ion battery are only used as Examples, the present disclosure is not limited to the raw materials, raw material ratios, and production methods used in the following examples.
  • Preparation of positive pole piece After taking positive active material LiCoO 2 , conductive carbon black, and binder polyvinylidene fluoride (PVDF) at a weight ratio of 96.7:1.7:1.6 in an N-methylpyrrolidone solvent system, stir and mix well. Coating on the aluminum foil, and then drying and cold pressing to obtain a positive pole piece. In Examples 1-12 and Comparative Examples 1-8, the prepared positive pole pieces are the same.
  • PVDF polyvinylidene fluoride
  • Negative pole piece preparation mix graphite and silicon-based materials in a certain ratio to design a mixed powder with a capacity of 500mAh/g as the negative active material, and mix the mixed powder, conductive agent acetylene black, and polyacrylic acid in a weight ratio of 95:1.2:3.8 After fully stirring and mixing uniformly in a deionized water solvent system, coating on the copper foil to form a negative active material layer, and drying and cold pressing the coated copper foil to obtain a negative pole piece. In Examples 1-12 and Comparative Examples 1-8, by controlling the amount of the negative electrode active material coated on the copper foil, negative electrode pieces with different unit area capacities were obtained.
  • Battery preparation Polyethylene porous polymer film is used as the separator, and the positive pole piece, separator film, and negative pole piece are stacked in sequence, so that the separator is in the middle of the positive and negative pole pieces for isolation, and rolled Wind the electrode assembly.
  • the electrode assembly is placed in the outer packaging aluminum plastic film, and the electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) is injected and packaged. After forming, degassing, trimming and other processes, a lithium ion battery is obtained. In Examples 1-12 and Comparative Examples 1-8, by controlling the tension during the winding process, a lithium ion battery with a corresponding isolation film st was obtained.
  • the negative active material, conductive carbon black, and binder polyacrylic acid used in the examples were mixed with deionized water in a mass ratio of 95:1.2:3.8 to form a slurry, and then coated with a 100um thick coating. After being dried in a vacuum drying oven for an hour, use a punch in a dry environment to cut into a disc with a diameter of 1.4cm (area 1.5386cm 2 ), use a metal lithium sheet as the counter electrode in the glove box, and select a plug for the isolation membrane. Germany (ceglard) composite membrane, adding electrolyte to assemble a button cell.
  • PPG thickness of the plate surface of the electrode assembly.
  • MMC point thickness of the electrode assembly.
  • the test temperature is 45°C, and it is charged to 4.4V at a constant current of 0.7C, then charged to 0.025C at a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes.
  • the capacity obtained in this step is the initial capacity, and the 0.7C charge/0.5C discharge is carried out for a cycle test.
  • the capacity at each step is used as the ratio of the initial capacity to obtain the capacity attenuation curve, and the number of cycles at which the capacity attenuates to 80% of the initial capacity is counted. .
  • Example 1 Comparing the results of Example 1, Example 2 and Comparative Example 1 in conjunction with Figure 2 and Figure 3, it can be seen that when the capacity per unit area of the negative pole piece is the same, by controlling the different half-charge shrinkage rates of the separator, the cycle The degree of deformation of the rear electrode assembly is different. It can be seen from Comparative Example 1 that when the half-charge shrinkage rate of the separator reaches 5.6% (greater than 5%), the electrode assembly deforms greatly after the cycle, and the Ripple reaches 3.5%. The cycle stability of Comparative Example 1 deteriorated significantly, and the number of cycles at which the capacity decayed to 80% was significantly less than that of Example 1 and Example 2.
  • Example 4 and Comparative Example 2 Comparing the results of Example 3, Example 4 and Comparative Example 2 in combination with Figures 4 and 5, or comparing the results of Example 5, Example 6 and Comparative Example 3, the same conclusion can be obtained.
  • the capacity per unit area of the sheet is the same, after the half-charge shrinkage rate of the separator exceeds 5%, the electrode assembly will undergo greater deformation, and the number of cycles at which the capacity decays to 80% will be significantly reduced, and the cycle stability will be poor. This can also be seen from the comparison results between Example 7 and Comparative Example 4 and the comparison results between Example 8 and Comparative Example 5.
  • the half-charge shrinkage rate of the separators in Comparative Example 4 and Comparative Example 5 is greater than 5%.
  • the electrode assembly is severely deformed, so the st of the electrode assembly is defined to be less than 5% in the embodiment of the present disclosure.
  • Example 10 and Comparative Example 6 From the results of Example 10 and Comparative Example 6, it can be seen that when the half-charge shrinkage rate of the separator is less than 0.5%, the electrode assembly is also severely deformed. When the half-charge shrinkage rate of the separator is less than 0.5%, the electrode assembly deforms seriously. The reason may be that the tension of the isolation film during the winding process is too small, causing the isolation film itself to appear wrinkles, causing deformation after winding, which affects the subsequent cycle test. It can be seen that, in the embodiments of the present disclosure, limiting the electrode assembly to satisfy 0.5% ⁇ st ⁇ 5% can reduce deformation and improve cycle test performance.
  • the increase in the unit area capacity a of the negative pole piece means an increase in the negative electrode active material per unit area, that is, the increase in silicon content.
  • Different silicon content will cause the pole piece
  • the capacity a per unit area of the negative pole piece of the electrode assembly is less than 8.84 mAh/cm 2 .
  • the application of different winding tensions of the separator film will cause the difference in the degree of deformation of the electrode assembly.
  • reducing the corresponding shrinkage of the separator film can further suppress the deformation of the electrode assembly.
  • the capacity per unit area of the negative pole piece is in the interval of 0.97 ⁇ a ⁇ 8.84mAh/cm 2
  • the half-charge shrinkage rate of the separator is adjusted to be in the interval of 0.5% ⁇ st ⁇ 5%, so that the capacity per unit area of the negative pole piece is in the interval a and
  • the quotient of the winding tension of the separator is in the range of 19.4 ⁇ a/s t ⁇ 1768, and the deformation degree of the electrode assembly is significantly reduced.
  • the application of reducing the winding tension of the isolation film can further reduce the internal stress of the isolation film (internal stress of the isolation film: when the isolation film is subjected to an external force, the internal parts interact to resist this deformation force is called stress.
  • internal stress of the isolation film the tension of the isolation film substrate itself + the coating tension + the slitting tension + the winding tension-the tension released during the preparation process ), so as to suppress the deformation of the electrode assembly after cycling, improve the cycle stability, and increase the yield of the product.
  • the large winding tension (the main factor for the shrinkage of the separator)
  • the application coupled with the force generated by the volume expansion of the silicon-based negative electrode material during the cycle, increases the internal stress of the isolation membrane, which together lead to severe deformation of the electrode assembly.
  • the internal stress of the separator is a major factor, which is mainly composed of the tension of the separator substrate itself, coating tension, slitting tension, winding tension, and tension released during the preparation process.
  • the winding tension of the separator is the last production process that produces the internal stress of the separator.
  • the control of the winding tension during the preparation process affects the internal stress of the separator in the electrode assembly.
  • the stress has a great influence, thereby affecting the degree of deformation of the electrode assembly.
  • the severe deformation of the electrode assembly resulted in the formation of voids between the pole piece and the isolation membrane, and the formation of micro-cracks on the pole piece.
  • the solid electrolyte interphase (SEI) membrane ruptured and reorganized, which consumed the electrolyte and changed the cycle performance of the electrode assembly. difference.

Abstract

Ensemble électrode, dispositif électrochimique et dispositif électronique. L'ensemble électrode comprend : une pièce d'électrode positive (10); une pièce d'électrode négative (12); une membrane d'isolation (11) disposée entre la pièce d'électrode positive (10) et la pièce d'électrode négative (12); la capacité par unité de surface de l'élément d'électrode négative (12) est a mAh/cm2, 0,97 < a < 8,84, le taux de retrait de demi-charge de la membrane d'isolation (11) est s t, s t = (L0-L1)/L0, L0 est la longueur initiale de la membrane d'isolation (11) de l'ensemble électrode, L1 est la longueur de la membrane d'isolation (11) lorsque l'ensemble électrode est chargé à 3,7 V-4,0 V, 0,5 % < s t < 5 %, et a et s t satisfont le rapport : 19,4 < a/s t < 1 768. La capacité par unité de surface a de l'élément d'électrode négative (12) de l'ensemble électrode et le taux de retrait de demi-charge s t de la membrane d'isolation (11) sont contrôlés de sorte que a et s t satisfont le rapport 19,4 < a/s t < 1 768, ce qui permet de réduire la déformation de l'ensemble électrode, et d'améliorer la stabilité de cycle du dispositif électrochimique comprenant l'ensemble électrode.
PCT/CN2020/070348 2020-01-03 2020-01-03 Ensemble électrode, dispositif électrochimique et dispositif électronique WO2021134800A1 (fr)

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CN115188921A (zh) * 2022-06-24 2022-10-14 江苏正力新能电池技术有限公司 一种硅基负极极片、二次电池和用电装置

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