WO2025199679A1 - 二次电池以及电子装置 - Google Patents

二次电池以及电子装置

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Publication number
WO2025199679A1
WO2025199679A1 PCT/CN2024/083567 CN2024083567W WO2025199679A1 WO 2025199679 A1 WO2025199679 A1 WO 2025199679A1 CN 2024083567 W CN2024083567 W CN 2024083567W WO 2025199679 A1 WO2025199679 A1 WO 2025199679A1
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WIPO (PCT)
Prior art keywords
silicon
secondary battery
containing active
electrolyte
active particles
Prior art date
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Pending
Application number
PCT/CN2024/083567
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English (en)
French (fr)
Inventor
任文臣
张丽娟
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Application filed by Ningde Amperex Technology Ltd filed Critical Ningde Amperex Technology Ltd
Priority to PCT/CN2024/083567 priority Critical patent/WO2025199679A1/zh
Publication of WO2025199679A1 publication Critical patent/WO2025199679A1/zh
Anticipated expiration legal-status Critical
Pending legal-status Critical Current

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Classifications

    • 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
    • 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 belongs to the technical field of secondary batteries, and specifically relates to a secondary battery and an electronic device.
  • Silicon a resource-rich material with a high theoretical specific capacity, holds enormous potential for use in secondary battery anodes.
  • silicon-containing anodes experience volume expansion and contraction during the insertion and precipitation of active materials, which can lead to stress concentration in the electrode material and fracture of silicon nanoparticles. These fractured silicon nanoparticles react with the electrolyte to form a solid electrolyte membrane, resulting in capacity loss and a rapid decrease in cycle performance.
  • Prior art proposes adding additives to the electrolyte to improve the performance of the solid electrolyte membrane and reduce side reactions between the electrolyte and silicon nanoparticles.
  • additives can lead to reduced active ion concentration in the electrolyte, increased electrolyte viscosity, and increased secondary battery impedance, which can still affect the initial efficiency and cycle performance of the secondary battery to a certain extent.
  • the present application provides a secondary battery that aims to address the problem of fragile silicon particles and the side reactions that occur in the prior art, thereby improving the coulombic efficiency, capacity retention, and over-discharge tolerance of the secondary battery. Furthermore, the present application provides an electronic device including the aforementioned secondary battery.
  • the present application provides a secondary battery comprising a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises silicon-containing active particles; the sphericity of the silicon-containing active particles is A; the electrolyte contains fluoroethylene carbonate (FEC); based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is B%; wherein A and B satisfy: 1.6 ⁇ (B/A) ⁇ 29.4.
  • the present application combines the sphericity of the silicon-containing active particles with the electrolyte by adding fluoroethylene carbonate to the electrolyte.
  • the mass percentage of fluoroethylene carbonate in the electrolyte is closely coordinated, so that the solid electrolyte (SEI) film formed by the decomposition of fluoroethylene carbonate can effectively cover the fresh silicon-containing interface exposed after the silicon-containing active particles are broken, reducing the side reaction between the exposed active silicon and the electrolyte.
  • SEI solid electrolyte
  • the secondary battery has a lower internal resistance, thereby improving the coulombic efficiency and cycle capacity retention rate of the secondary battery, and making the secondary battery have better over-discharge resistance.
  • the surface has fewer sharp corners. Combined with the aforementioned relationship between the sphericity and the fluoroethylene carbonate content, this can further reduce side reactions between the active silicon and the electrolyte, further improving the coulombic efficiency of the secondary battery and enhancing its over-discharge tolerance.
  • 1.1 ⁇ B ⁇ 20 1.1 ⁇ B ⁇ 20.
  • the SEI film that increases the internal resistance of the secondary battery can be reduced or avoided, further improving the initial coulombic efficiency of the secondary battery and enhancing its over-discharge resistance.
  • 2 ⁇ B ⁇ 7 This can maximize the quality of the SEI film and further enhance the over-discharge resistance of the secondary battery.
  • the minimum angle of the cross-sectional profile of the silicon-containing active particles with a diameter greater than 10 ⁇ m is C°, and 96 ⁇ C ⁇ 180.
  • the minimum angle of the cross-sectional profile of the silicon-containing active particles with a diameter greater than 10 ⁇ m meets the above range, it indicates that the silicon-containing active particles have gentle edges and corners, which can reduce the breakage of the silicon-containing active particles, further improve the coulombic efficiency of the secondary battery, and enhance its cycle performance and over-discharge tolerance.
  • the sphericity A of the silicon-containing active particles, the minimum cross-sectional profile angle C° of the silicon-containing active particles with a diameter greater than 10 ⁇ m, and the mass percentage of the fluoroethylene carbonate additive B% satisfy the following: 45.28 ⁇ (A ⁇ C - B) ⁇ 176.0.
  • A, B, and C satisfy: 60 ⁇ (A ⁇ C-B) ⁇ 120, further improving and optimizing the cycle performance and over-discharge resistance of the secondary battery.
  • the mass fraction of Si element is 42% to 55% based on the mass of the silicon-containing active particles.
  • the mass fraction of Si element is 2.1% to 22% based on the mass of the negative electrode active material layer. In some embodiments, the mass fraction of silicon-containing active particles is 5% to 40% based on the mass of the negative electrode active material layer.
  • the specific surface area of the silicon-containing active particles is 0.5 m 2 /g to 5 m 2 /g.
  • the specific surface area of the silicon-containing active particles is within the above range, the first coulombic efficiency of the secondary battery can be further improved.
  • the hydrofluoric acid content in the electrolyte is ⁇ 83 ⁇ g/g, which can further improve the kinetic performance of the secondary battery.
  • the present application further provides an electronic device comprising any one of the above-mentioned secondary batteries.
  • the secondary battery based on the present application has the following beneficial effects: the present application produces a synergistic effect by controlling the sphericity of the silicon-containing active particles and the content of fluoroethylene carbonate in the electrolyte.
  • the fluoroethylene carbonate can form a low-impedance SEI film, which can effectively cover the active surface generated by the crushing of the silicon-containing active particles, thereby reducing or avoiding side reactions between the silicon-containing active particles and the electrolyte, reducing the consumption of electrolyte and silicon-containing active particles caused by side reactions, improving the initial efficiency and cycle performance of the secondary battery, and at the same time reducing the gas generated by the side reactions, thereby improving the over-discharge resistance of the secondary battery.
  • the present application defines the synergistic cooperation between the sphericity of the silicon-containing active particles, the minimum angle of the particle cross-section profile, and the fluoroethylene carbonate in the electrolyte, which can further optimize the initial efficiency and cycle performance of the secondary battery, and the secondary battery produces less gas during over-discharge and has a strong over-discharge resistance.
  • the term "silicon-containing active particles” refers to a negative electrode material containing silicon elements in a solid particle state, for example, it can be a silicon-carbon composite material in a solid particle state.
  • the silicon-containing active particles include porous carbon particles having pores, and silicon formed inside the porous carbon particles and/or on the surface of the porous carbon particles.
  • the silicon-containing active particles can better cooperate with the fluoroethylene carbonate in the electrolyte through shape characteristics such as sphericity, thereby helping the secondary battery to achieve higher initial efficiency, cycle performance and improved over-discharge resistance.
  • the present application found that when adding FEC to the electrolyte to protect the fresh silicon interface generated by the crushing, the excessive amount of FEC added Additives can lead to problems such as reduced active ion concentration in the electrolyte, increased electrolyte viscosity and increased electrode impedance, which in turn affect the coulombic efficiency and capacity retention of secondary batteries.
  • the present application provides a secondary battery comprising a negative electrode plate and an electrolyte, wherein the negative electrode plate comprises a negative electrode active material layer, and the negative electrode active material layer comprises silicon-containing active particles; the sphericity of the silicon-containing active particles is A, and the electrolyte comprises fluoroethylene carbonate; based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is B%; wherein A and B satisfy: 1.6 ⁇ (B/A) ⁇ 29.4.
  • the present application limits the sphericity of the negative electrode silicon material particles and the fluoroethylene carbonate content in the electrolyte to meet the above-mentioned relationship, thereby giving full play to the synergistic effect between the sphericity of the material particles and the fluoroethylene carbonate content, reducing or avoiding the problem of the secondary battery being crushed due to the sharp corners of the silicon material particles during the negative electrode rolling process or the charging and discharging process, and enabling the fluoroethylene carbonate to form an SEI film to effectively cover the fresh silicon-containing interface exposed after the silicon-containing active particles are crushed, reducing the side reaction between the exposed active silicon and the electrolyte, and at the same time ensuring that the SEI film on the surface of the silicon-containing active particles has a low impedance, the secondary battery has a low internal resistance, and the capacity utilization and coulombic efficiency of the secondary battery are improved, as well as the over-discharge resistance of the secondary battery.
  • the combination of fluoroethylene carbonate and the spherical degree of silicon-containing active particles can enable the secondary battery to exhibit higher first coulombic efficiency and capacity retention rate, as well as better over-discharge resistance.
  • the conductivity of the electrolyte is 6.5 mS/cm to 11 mS/cm.
  • the hydrofluoric acid content in the electrolyte is ⁇ 83 ⁇ g/g, which can further improve the kinetic performance of the secondary battery.
  • the sphericity A of the silicon-containing active particles can be 0.65, 0.68, 0.71, 0.79, 0.82, 0.91, 1, or a value within a range consisting of any two of these values.
  • the silicon-containing active particles with a sphericity within this range have fewer sharp corners on the surface, which can reduce or avoid the silicon-containing active particles from being crushed during the cold pressing process of the electrode, reduce the exposure of active silicon, and, combined with the above-mentioned relationship between the sphericity and the content of fluoroethylene carbonate, can further reduce the side reaction between active silicon and the electrolyte, further improve the coulombic efficiency of the secondary battery and enhance its over-discharge resistance.
  • 0.71 ⁇ A ⁇ 1 can further improve the coulombic efficiency of the secondary battery and enhance its over-discharge resistance.
  • 1.1 ⁇ B ⁇ 20 In some embodiments, 1.1 ⁇ B ⁇ 20.
  • B can be 1.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a value within a range consisting of any two of these values.
  • further regulating the mass percentage of fluoroethylene carbonate can reduce or avoid the SEI film produced from increasing the internal resistance of the secondary battery, further improving the initial coulombic efficiency of the secondary battery.
  • the quality of the SEI film can be maximized, while protecting the silicon-containing active particles, improving the dynamic performance of the secondary battery and enhancing its over-discharge resistance.
  • the minimum angle of the cross-sectional profile of the silicon-containing active particles with a diameter greater than 10 ⁇ m is C°, 96 ⁇ C ⁇ 180.
  • C can be a value within the range of 96, 100, 110, 120, 129, 135, 140, 150, 160, 170, 180, or any two of these values.
  • the minimum angle of the cross-sectional profile of the silicon-containing active particles with a diameter greater than 10 ⁇ m meets the above range, it indicates that the edges and corners of the silicon-containing active particles are gentle, which is beneficial for uniform force on the silicon-containing active particles in the negative electrode active material layer, reduces the breakage of the silicon-containing active particles, improves the active ion transport, further improves the coulombic efficiency of the secondary battery, and enhances its cycle performance and over-discharge resistance.
  • the diameter of the silicon-containing active particle is the longest distance between any two points on the cross-sectional profile of the silicon-containing active particle.
  • the sphericity A of the silicon-containing active particles, the minimum angle C° of the cross-section of the silicon-containing active particles with a diameter greater than 10 ⁇ m, and the mass percentage B% of the fluoroethylene carbonate additive are sufficient.
  • a ⁇ CB may be 45.28, 45.3, 67.72, 63.4, 69.8, 70.59, 71.72, 76.72, 79.85, 80.72, 83.72, 85.72, 86.62, 86.72, 89.8, 90.8, 97.8, 97.91, 98.8, 101.78, 113.39, 151.5, or 176.0, or a range consisting of any two of these values.
  • the SEI film formed by fluoroethylene carbonate can be further ensured to cover the broken surfaces of the silicon-containing active particles, thereby reducing the internal impedance of the secondary battery, optimizing the secondary battery's cycling performance and over-discharge tolerance, and improving its initial coulombic efficiency and cycle capacity retention.
  • A, B, and C satisfy the following: 60 ⁇ (A ⁇ CB) ⁇ 120, further improving the cycling performance and over-discharge tolerance of the secondary battery.
  • the specific surface area of the silicon-containing active particles is 0.5 m 2 /g to 5 m 2 /g. In some embodiments, the specific surface area of the silicon-containing active particles is 0.5 m 2 /g to 2.8 m 2 /g. When the specific surface area of the silicon-containing active particles is within the above range, the active ion transport and diffusion rate can be guaranteed while reducing side reactions with the electrolyte, further improving the initial coulombic efficiency of the secondary battery.
  • the gram capacity of the silicon-containing active particles is 1621 mAh/g to 1796 mAh/g, and the first coulombic efficiency of the silicon-containing active particles is 75.3% to 83.5%.
  • the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polyvinyl chloride, polyvinyl chloride, polyvinyl chloride, polyvinyl chloride, polyvinyl chloride, polyvinyl chloride, polyethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polyvinyl chloride ...
  • Tetrafluoroethylene Polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated or acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.
  • the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof.
  • the carbon-based material is selected from carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver.
  • the conductive polymer is a polyphenylene derivative.
  • the secondary battery of the present application further includes a positive electrode, which includes a positive electrode current collector and a positive electrode active material layer, which includes a positive electrode active material, a binder, and a conductive agent.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.
  • the binder includes a binder polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber or polyurethane.
  • the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid.
  • the conductive agent includes a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black or carbon fiber; a metal-based material such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.
  • a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black or carbon fiber
  • a metal-based material such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.
  • a conductive polymer such as a polyphenylene derivative
  • the secondary battery of the present application also includes an isolating membrane.
  • the material and shape of the isolating membrane used in the secondary battery of the present application are not particularly limited, and it can be any technology disclosed in the prior art.
  • the isolating membrane includes a polymer or inorganic material formed from a material that is stable to the electrolyte of the present application.
  • the isolating membrane may include a substrate layer and a surface treatment layer.
  • the substrate layer is a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer is selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide.
  • a polypropylene porous membrane a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be used.
  • a surface treatment layer is provided on at least one surface of the substrate layer.
  • the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material.
  • the inorganic layer includes inorganic particles and a binder.
  • the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.
  • the binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.
  • the polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).
  • the secondary battery of the present application also includes an electrolyte.
  • the electrolyte in the present application includes an organic solvent, a lithium salt and optional additives.
  • the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.
  • the organic solvent includes an ether solvent, for example, including at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME).
  • the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt.
  • the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bis(trifluoromethanesulfonyl)imide LiN(CF 3 SO 2 ) 2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO 2 F) 2 )(LiFSI), lithium bis(oxalatoborate) LiB(C 2 O 4 ) 2 (LiBOB), or lithium difluorooxalatoborate LiBF 2 (C 2 O 4 ) (LiDFOB).
  • the additives may be electrolyte additives known in the art.
  • the secondary battery of the present application includes, but is not limited to: a lithium-ion battery or a sodium-ion battery. In some embodiments, the secondary battery includes a lithium-ion battery.
  • the present application further provides an electronic device, which includes the secondary battery according to the first aspect of the present application.
  • the electronic device or apparatus of the present application is not particularly limited.
  • the electronic device or apparatus of the present application Equipment includes, but is not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, 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 fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • the lithium-ion battery of this embodiment includes a negative electrode plate and an electrolyte.
  • the negative electrode plate includes a negative electrode active material layer, and the negative electrode active material layer includes silicon-containing active particles.
  • the sphericity A of the silicon-containing active particles is 0.68.
  • thermoplastic linear phenolic resin and 120g of hexamethylenetetramine curing agent were dissolved in 2.5L of methanol at 50°C for 1 hour.
  • the methanol solvent was then removed by vacuum distillation to obtain a uniform mixture of the phenolic resin and hexamethylenetetramine.
  • a 0.15 mol/L aqueous sodium dodecyl sulfate solution was prepared in an autoclave, and a uniform mixture of the phenolic resin and hexamethylenetetramine was dissolved therein.
  • the autoclave temperature was raised to 130°C and maintained for 30 minutes. After the autoclave was cooled, phenolic resin microspheres were obtained.
  • the phenolic resin microspheres had a sphericity of 0.72 and a minimum cross-sectional profile angle of 136°.
  • Phenolic resin microspheres and potassium hydroxide were mixed in an alkali-carbon ratio of 3:1, first treated in a rotary kiln at 400°C for 30 minutes, then the rotary kiln temperature was raised to 750°C and kept at this temperature for 45 minutes.
  • the porous carbon material can be obtained after the product is pickled, washed with water and dried.
  • porous carbon 1000g was added to a fluidized bed reactor and heated to 480°C under a 10L/min nitrogen atmosphere for 2 hours. Monosilane gas was then introduced at 2.5L/min for 300 minutes. After stopping the silane introduction, the fluidized bed was heated to 500°C and maintained for 1 hour. Acetylene gas was then introduced at 5L/min for 300 minutes. Upon completion of the reaction, silicon-containing active particles were obtained.
  • the specific surface area of the silicon-containing active particles is 2.80 m 2 /g, and the mass fraction of Si element is 46.2% based on the mass of the silicon-containing active particles.
  • the negative electrode active material (silicon-containing active particles and graphite mixed in a mass ratio of 1:9), carbon nanotubes, lithium carboxymethyl cellulose, and lithium polyacrylate were mixed in a mass ratio of 97.4:0.2:0.4:2.
  • Deionized water was added as a solvent and the mixture was stirred in a vacuum mixer to produce a negative electrode slurry with a solids content of 45 wt% and a viscosity of 6000 mPa ⁇ s.
  • the negative electrode slurry was evenly coated on one surface of a 6 ⁇ m-thick negative electrode current collector copper foil.
  • the foil was then dried at 80°C to produce a negative electrode sheet coated on one side with a negative electrode material layer and a coating weight of 100.1 mg/1540.25 mm2 .
  • the above steps were repeated on the other surface of the copper foil to produce a negative electrode sheet coated on both sides with a negative electrode material layer. After cold pressing, cutting, and slitting, the resulting negative electrode sheet measured 661 mm x 78 mm.
  • FIG1 is a backscattered SEM image of a cross section of a negative electrode sheet in a lithium-ion battery according to Example 1 of the present application along the thickness direction, wherein the mass fraction of Si element is 4.5% based on the mass of the negative electrode active material layer.
  • EC, PC, EP, and PP were mixed in a mass ratio of 17:25:40:18 to obtain an organic solvent.
  • LiPF6 and FEC were then added to the organic solvent to produce an electrolyte.
  • the mass percentage of LiPF6 and FEC was 12.5% and 1.1% based on the mass of the electrolyte.
  • the electrolyte had a conductivity of 7.83 mS/cm and a hydrofluoric acid content of 28.2 ⁇ g/g.
  • a porous polyethylene film with a thickness of 10 ⁇ m (supplied by Celgard) was used.
  • the sphericity of the silicon-containing active particles was tested using the equivalent diameter method.
  • the test method was to use a ZEISS-SEM (sigma-02-33) scanning electron microscope to observe the silicon-containing active particle powder or the silicon-containing active particles in the negative electrode sheet, remove incomplete particles, and calculate the equivalent diameter of the circumference of the complete particles and the equivalent diameter of the particle area.
  • Sphericity circumference equivalent diameter / area equivalent diameter.
  • the outline of the silicon-containing active particle is outlined, and then tangent lines are drawn along the edges on both sides of the sharp angle, and the angle between the two tangent lines is measured; the values of the measured angles are compared, and the minimum value is taken as the minimum angle value of the cross-sectional profile of the particle (as shown in the schematic diagram of Figure 2, Angle 1 is 115°, Angle 2 is 105°, Angle 3 is 142°, and Angle 4 is 140°, then Angle 2 is recorded as the minimum angle of the cross-sectional profile of the silicon-containing active particle, that is, the minimum angle of the cross-sectional profile of the silicon-containing active particle is 105°).
  • the degree of the minimum angle in the cross-sectional profile of at least 20 silicon-containing active particles is counted and the average value is calculated as the cross-sectional profile of the silicon-containing active particles with a diameter greater than 10 ⁇ m in this batch. Minimum contour angle.
  • EMC ethyl methyl carbonate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • Silicon-containing active particles gram capacity test After standing for 6 hours at 25°C, the button cell was discharged at 0.05C to 5 mV. Then, it was discharged at 50 ⁇ A to 5 mV. After standing for 5 minutes, it was discharged again at 10 ⁇ A to 5 mV. After standing for 5 minutes, it was charged at 0.05C to 0.8 V. The discharge capacity is recorded as G 0 , and the charge capacity is recorded as G 1 .
  • C 1 the battery was discharged at a constant current rate of 0.2C to 3.0V, and the discharge capacity at this step was recorded as C 2 .
  • C 2 is the first discharge capacity of the lithium-ion battery.
  • the initial coulombic efficiency of a lithium-ion battery C 2 /C 1 ⁇ 100%.
  • the voltage value when (T 2 -T 1 )/T 1 ⁇ 100% equals 10% is recorded as the over-discharge gas production test voltage of the lithium-ion battery.
  • the lithium-ion batteries of Examples 1-13 control the sphericity A of the silicon-containing active particles and the mass percentage B% of FEC in the electrolyte to satisfy 1.6 ⁇ (B/A) ⁇ 29.4. Their initial coulombic efficiency reaches 86.4% to 90.7%, and the capacity retention rate after 400 cycles reaches 92.0% to 97.2%, showing high initial efficiency and cycling performance.
  • the over-discharge gas production test voltage of the lithium-ion batteries of Examples 1-13 can reach 1.85V to 2.31V. It can be seen that the lithium-ion batteries of the present application can achieve a lower discharge voltage when producing the same volume of gas, indicating that the lithium-ion batteries of the present application produce less gas during discharge and have strong over-discharge resistance.
  • the sphericity degree A of the silicon-containing active particles is controlled to be 0.65 to 1, the initial efficiency, cycle performance and over-discharge resistance of the lithium-ion battery can be further improved.
  • Examples 8 to 11 Compared with Examples 8 to 11, the FEC content is the same, but the sphericity of the silicon-containing active particles changes. Among them, Examples 8 to 10, on the basis of meeting the B/A range, further optimize the shape characteristics of the sphericity, so that the sphericity of the silicon-containing active particles is above 0.79, and have higher first efficiency, cycle performance and over-discharge resistance than Example 11.
  • Examples 1 to 13 by controlling the sphericity A of the silicon-containing active particles, the minimum cross-sectional profile angle C of the silicon-containing active particles with a diameter greater than 10 ⁇ m, and the mass percentage B% of FEC in the electrolyte to meet the requirements of 45.28 ⁇ (A ⁇ CB) ⁇ 176.0, the lithium-ion batteries exhibit significantly improved initial efficiency and cycle capacity retention, as well as significantly enhanced cycling performance and over-discharge tolerance. Specifically, when A, B, and C meet the requirements of 60 ⁇ (A ⁇ CB) ⁇ 120, the performance of the secondary battery can be further enhanced, exhibiting even better cycling performance and over-discharge tolerance.

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Abstract

一种二次电池以及电子装置，属于电池技术领域。二次电池，包括负极极片和电解液，该负极极片包括负极活性物质层，负极活性物质层包括含硅活性颗粒；含硅活性颗粒的球形化度为A；电解液中含有氟代碳酸乙烯酯；基于电解液的质量，氟代碳酸乙烯酯的质量百分含量为B％；其中，A和B满足：1.6≤(B/A)≤29.4。这样可以充分发挥硅材料颗粒球形化度与氟代碳酸乙烯酯含量之间的协同效应，减少硅颗粒破碎以及与电解液的副反应，从而提高二次电池的初始库伦效率、循环性能和提升耐过放产气性能。

Description

二次电池以及电子装置 技术领域
本申请属于二次电池技术领域，具体涉及一种二次电池以及电子装置。
背景技术
硅作为一种资源丰富且具有较高理论比容量的材料，在二次电池负极中具有巨大的应用潜力。然而，含硅负极在活性物质嵌入和析出过程中会发生体积膨胀和收缩，容易导致电极材料的应力集中和硅纳米颗粒的破裂。破裂的硅纳米颗粒会不断和电解液发生副反应生成固态电解质膜，导致二次电池容量损失和循环性能迅速降低。
现有技术提出向电解液中加入添加剂，改善固态电解质膜的性能，以减少电解液与硅纳米颗粒的副反应。但是添加剂的使用会带来电解液中活性离子浓度降低、电解液粘度增加以及二次电池阻抗增加的问题，在一定程度上仍会影响二次电池的首次效率和循环性能。
发明内容
有鉴于此，本申请提供了一种二次电池，旨在解决现有技术中硅颗粒易碎发生副反应的问题，进而提高二次电池的库伦效率、容量保持率和耐过放能力。另一方面，本申请还提供了一种包括上述二次电池的电子装置。
第一方面，本申请提供了一种二次电池，包括负极极片和电解液，该负极极片包括负极活性物质层，负极活性物质层包括含硅活性颗粒；含硅活性颗粒的球形化度为A；电解液中含有氟代碳酸乙烯酯(FEC)；基于电解液的质量，氟代碳酸乙烯酯的质量百分含量为B％；其中，A和B满足：1.6≤(B/A)≤29.4。本申请通过向电解液中加入氟代碳酸乙烯酯，将含硅活性颗粒的球形化度与电 解液中氟代碳酸乙烯酯的质量百分含量进行紧密配合，能够使氟代碳酸乙烯酯分解形成的固态电解质(SEI)膜对含硅活性颗粒破碎后暴露的含硅新鲜界面进行有效覆盖，减少裸露的活性硅与电解液之间的副反应，二次电池具有较低内阻，从而提高二次电池的库伦效率和循环容量保持率，使二次电池具有较优的耐过放能力。
在一些实施例中，0.65≤A≤1。含硅活性颗粒的球形化度在该范围内时，表面尖角少，配合上述球形化度与氟代碳酸乙烯酯的含量关系，能够进一步减少活性硅与电解液的副反应，进一步提高二次电池的库伦效率和提升其耐过放能力。在一些实施例中，0.71≤A≤1。
在一些实施例中，1.1≤B≤20。当氟代碳酸乙烯酯的质量百分含量在此范围内，能够减少或避免产生的SEI膜升高二次电池内阻，进一步提高二次电池的首次库伦效率和提升其耐过放能力。
在一些实施例中，2≤B≤7。可最大限度地提高SEI膜的质量，进一步提升二次电池的耐过放能力。
在一些实施例中，直径大于10μm的含硅活性颗粒切面轮廓最小角为C°，96≤C≤180。当直径大于10μm的含硅活性颗粒切面轮廓最小角满足上述范围时，表明含硅活性颗粒的棱角平缓，可减少含硅活性颗粒破碎，进一步提高二次电池的库伦效率和提升其循环性能和耐过放能力。
在一些实施例中，含硅活性颗粒的球形化度A，直径大于10μm含硅活性颗粒切面轮廓最小角C°及氟代碳酸乙烯酯添加剂的质量百分含量B％满足：45.28≤(A×C-B)≤176.0。通过控制含硅活性颗粒的球形化度、切面轮廓最小角的形状特征与氟代碳酸乙烯酯的质量百分含量满足上述关系，可进一步保证氟代碳酸乙烯酯形成的SEI膜对含硅活性颗粒的破碎表面进行覆盖，优化二次电池的循环性能和耐过放能力，提高其首次库伦效率和循环容量保持率。
在一些实施例中，A、B和C满足：60≤(A×C-B)≤120，进一步改善优化二次电池的循环性能和耐过放能力。
在一些实施例中，含硅活性颗粒包括多孔碳基体和纳米硅；纳米硅分布在 多孔碳基体的内部和表面。
在一些实施例中，基于含硅活性颗粒的质量，Si元素的质量分数为42％～55％。
在一些实施例中，基于负极活性物质层的质量，Si元素的质量分数为2.1％～22％。在一些实施例中，基于负极活性物质层的质量，含硅活性颗粒的质量百分含量为5～40％。
在一些实施例中，含硅活性颗粒的比表面积为0.5m2/g～5m2/g。当含硅活性颗粒的比表面积在上述范围内时，可进一步提高二次电池的首次库伦效率。
在一些实施例中，电解液的电导率为6.5mS/cm～11mS/cm。通过控制电导率在上述范围内，可促进活性离子的传输，使二次电池具有改善的循环性能和耐过放能力。
在一些实施例中，电解液中的氢氟酸含量为≤83μg/g，可进一步提高二次电池的动力学性能。
第二方面，本申请还提供了一种电子装置，包括上述任意一种二次电池。
基于本申请的二次电池，有益效果包括：本申请通过控制含硅活性颗粒的球形化度与电解液中氟代碳酸乙烯酯的含量配合产生协同作用，氟代碳酸乙烯酯可形成低阻抗SEI膜，可有效覆盖含硅活性颗粒破碎产生的活性表面，从而减少或避免含硅活性颗粒与电解液之间的副反应，减少副反应带来的电解液和含硅活性颗粒的消耗，提高二次电池的首次效率和循环性能，同时减少副反应产生的气体，提高二次电池的耐过放能力。进一步地，本申请限定含硅活性颗粒球形化度、颗粒切面轮廓最小角度与电解液中氟代碳酸乙烯酯之间的协同配合，能够进一步优化二次电池的首次效率和循环性能，并且二次电池在过放时产气较少，具有较强的耐过放能力。
附图说明
图1为本申请实施例1的二次电池中负极极片沿厚度方向的横截面背散射SEM图像；
图2本申请具体实施方式提供的确定直径大于10μm含硅活性颗粒的切面轮廓最小角的示意图。
具体实施方式
为了使本申请的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本申请进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本申请，并不用于限定本申请。
为了简明，本申请仅具体地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本申请的描述中，除非另有说明，“以上”、“以下”包含本数。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测量方法进行测量(例如，可以按照在本申请的实施例中给出的方法进行测试)。
本申请中，术语“含硅活性颗粒”是指固体颗粒状态的含有硅元素的负极物质，例如可以是固体颗粒状态的硅碳复合材料。在一些示例性的实施方案中，含硅活性颗粒包括具有孔的多孔碳颗粒，以及形成在多孔碳颗粒的内部和/或多孔碳颗粒的表面上的硅。本申请的实施方案中含硅活性颗粒能够更好地通过球形化度等形状特征与电解液中的氟代碳酸乙烯酯配合，进而有利于二次电池达到更高的首次效率、循环性能和提升耐过放能力。
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明本申请而不用于限制本申请的范围。
为了解决硅纳米颗粒和电解液发生副反应的问题，本申请发现，采用往电解液中添加FEC的方式保护因破碎而产生的新鲜硅界面时，但过量的FEC添 加剂会导致电解液中活性离子浓度降低，电解液粘度增加及电极阻抗增加等问题，从而会影响二次电池的库伦效率及容量保持率等性能。
有鉴于此，本申请提供了一种二次电池，包括负极极片和电解液，该负极极片包括负极活性物质层，负极活性物质层包括含硅活性颗粒；含硅活性颗粒的球形化度为A，电解液包括氟代碳酸乙烯酯；基于电解液的质量，氟代碳酸乙烯酯的质量百分含量为B％；其中，A和B满足：1.6≤(B/A)≤29.4。本申请通过限定负极硅材料颗粒球形化度和电解液中氟代碳酸乙烯酯含量满足上述关系，可充分发挥材料颗粒球形化度与氟代碳酸乙烯酯含量之间的协同效应，减少或避免二次电池因硅材料颗粒尖角在负极辊压工序或充放电过程中被压碎的问题，能够使氟代碳酸乙烯酯形成SEI膜对含硅活性颗粒破碎后暴露的含硅新鲜界面进行有效覆盖，减少裸露的活性硅与电解液之间的副反应，同时保证含硅活性颗粒表面的SEI膜具有较低阻抗，二次电池具有较低内阻，提高二次电池容量发挥、库伦效率及提升二次电池的耐过放能力。
在一些实施方式中，氟代碳酸乙烯酯添加剂的质量百分含量B％与含硅活性颗粒的球形化度A的比值B/A可为1.6、2.9、4、4.4、4.9、5.1、5.9、6.2、7.3、8.8、9.8、10.1、10.3、16.2、18.3、22.0、23.5、24.4、29.4或这些值中任意两者组成的范围内的值。当B/A<1.6时，会导致氟代碳酸乙烯酯形成的SEI膜无法有效覆盖因颗粒破碎所产生含硅新鲜界面，最终会使裸露活性硅持续消耗电解液，造成二次电池库伦效率下降。当B/A>29.4时，过高的氟代碳酸乙烯酯添加剂含量会导致所形成的SEI膜阻抗增大，从而导致二次电池内阻升高，降低二次电池的首次库伦效率性能。
在一些实施方式中，B/A值满足6.2≤(B/A)≤16.2时，通过氟代碳酸乙烯酯和含硅活性颗粒球形化度的配合，能够使二次电池表现出更高的首次库伦效率和容量保持率，以及更优异的耐过放能力。
在一些实施例中，电解液的电导率为6.5mS/cm～11mS/cm。通过控制电导率在上述范围内，可促进活性离子的传输，使二次电池具有改善的循环性能和耐过放能力。
在一些实施例中，电解液中的氢氟酸含量为≤83μg/g，可进一步提高二次电池的动力学性能。
在一些实施方式中，0.65≤A≤1。例如，含硅活性颗粒的球形化度A可以为0.65、0.68、0.71、0.79、0.82、0.91、1或这些值中任意两者组成的范围的内的值。球形化度在该范围内的含硅活性颗粒表面尖角较少，能够减少或避免含硅活性颗粒在极片冷压过程中被压碎，减少活性硅的裸露，配合上述球形化度与氟代碳酸乙烯酯的含量关系，能够进一步减少活性硅与电解液的副反应，进一步提高二次电池的库伦效率和提升其耐过放能力。在一些实施方式中，0.71≤A≤1，能够进一步提高二次电池的库伦效率和提升其耐过放能力。
在一些实施方式中，1.1≤B≤20。例如B可以为1.1、2、3、4、5、6、7、8、9、10、11、12、13、14、15、16、17、18、19、20或这些值中任意两者组成的范围内的值。在含硅活性颗粒的球形化度与氟代碳酸乙烯酯的含量配合关系的基础上，进一步调控氟代碳酸乙烯酯的质量百分含量，能够减少或避免产生的SEI膜升高二次电池内阻，进一步提高二次电池的首次库伦效率。在一些实施方式中，2≤B≤7，通过进一步控制氟代碳酸乙烯酯的质量百分含量，能够最大限度地提高SEI膜的质量，在保护含硅活性颗粒的同时改善二次电池的动力学性能，提升其耐过放能力。
在一些实施方式中，直径大于10μm的含硅活性颗粒切面轮廓最小角为C°，96≤C≤180。例如，C可以为96、100、110、120、129、135、140、150、160、170、180或这些值中任意两者组成的范围内的值。当直径大于10μm的含硅活性颗粒切面轮廓最小角满足上述范围时，表明含硅活性颗粒的棱角平缓，有利于含硅活性颗粒在负极活性材料层中受力均匀，减少含硅活性颗粒破碎，改善活性离子传输，进一步提高二次电池的库伦效率和提升其循环性能和耐过放能力。在本申请中，含硅活性颗粒的直径为含硅活性颗粒的切面轮廓上任意两点之间的最长距离。
在一些实施方式中，含硅活性颗粒的球形化度A，直径大于10μm含硅活性颗粒切面轮廓最小角C°及氟代碳酸乙烯酯添加剂的质量百分含量B％满 足：45.3≤(A×C-B)≤176.0。例如，A×C-B可为45.28、45.3、67.72、63.4、69.8、70.59、71.72、76.72、79.85、80.72、83.72、85.72、86.62、86.72、89.8、90.8、97.8、97.91、98.8、101.78、113.39、151.5、176.0或这些值中任意两者组成的范围内的值。通过控制含硅活性颗粒的球形化度、切面轮廓最小角的形状特征与氟代碳酸乙烯酯的质量百分含量满足上述关系，可进一步保证氟代碳酸乙烯酯形成的SEI膜对含硅活性颗粒的破碎表面进行覆盖，降低二次电池内部阻抗，优化二次电池的循环性能和耐过放能力，提高其首次库伦效率和循环容量保持率。在一些实施方式中，A、B和C满足：60≤(A×C-B)≤120，进一步改善优化二次电池的循环性能和耐过放能力。
在一些实施方式中，含硅活性颗粒的比表面积为0.5m2/g～5m2/g。在一些实施方式中，含硅活性颗粒的比表面积为0.5m2/g～2.8m2/g。当含硅活性颗粒的比表面积在上述范围内时，可保证活性离子传输扩散速率，同时减少与电解液之间的副反应，进一步提高二次电池的首次库伦效率。
在一些实施方式中，含硅活性颗粒的克容量为1621mAh/g～1796mAh/g，含硅活性颗粒的首次库伦效率为75.3％～83.5％。
在一些实施方式中，本申请提供的含硅活性颗粒采用包括以下步骤的方法制备得到：步骤S100、将碳源与碱的混合物进行梯度升温保温处理，得到多孔碳材料；步骤S200、在惰性气体氛围下向多孔碳材料中通入硅烷气体进行反应，即得含硅活性颗粒。该方法有利于得到包括多孔碳颗粒和形成在多孔碳颗粒内部和/或多孔碳颗粒的表面上的硅的含硅活性颗粒，从而更好地通过形状特征与电解液中的氟代碳酸乙烯酯配合。
在一些实施方式中，梯度升温保温处理包括：将碳源与碱的混合物升温至350℃～550℃保温处理15min～45min，然后升温至600℃～900℃保温处理0.5h～2h。
在一些实施方式中，碳源选自酚醛树脂、煤炭、生物质材料、石油焦中的至少一种。
在一些实施方式中，碳源的球形化度为0.68～1，例如可为0.68、0.70、0.74、 0.78、0.82、0.92、0.93、0.96、1或这些值中任意两者的范围内的值。本申请中含硅活性颗粒的球形化度可以通过控制碳源的球形化度进行调控，采用上述球形化度的碳源配合梯度升温保温处理，能够得到具有较高球形化度的含硅活性颗粒，与FEC配合后有利于进一步提高二次电池的动力学性能和提升耐过放能力。
在一些实施方式中，碳源的切面轮廓最小角为105°～180°，例如可为105°、113°、121°、130°、136°、146°、152°、167°、172°、175°、180°或这些值中任意两者的范围内的值。本申请中含硅活性颗粒的切面轮廓最小角可以通过控制碳源的切面轮廓最小角进行调控，采用上述切面轮廓最小角的碳源配合梯度升温保温处理，能够得到具有较高切面轮廓最小角的含硅活性颗粒，与其球形化度以及电解液中FEC配合后有利于进一步优化二次电池的循环性能和耐过放能力，提高其首次库伦效率和循环容量保持率。
在一些实施方式中，步骤S200通入硅烷气体反应结束后，还包括向多孔碳材料中通入炔烃气体，保证多孔碳中沉积的硅颗粒的纯度。
在一些具体实施例中，含硅活性颗粒的制备方法包括以下步骤：
步骤S100、将酚醛树脂微球和氢氧化钾按照碱碳比(1～4):(1～2)的比例进行混合，首先在回转炉中300℃至400℃处理20min至40min，然后将回转炉温度升至600℃至800℃并保温20min至50min。将得到的产品经酸洗、水洗、烘干后即可得到多孔碳材料。
步骤S200、取上述多孔碳材料加入流化床反应器中，在7L/min至14L/min氮气氛围下加热至400℃至550℃并保温1h至3h，然后通入1.5L/min至3.5L/min的硅烷气体200min至400min。停止硅烷通入后，将流化床反应器升温至400℃至550℃并保温0.5h至2.5h，然后通入3.5L/min至6L/min的乙炔气体250min至350min，反应结束后即可得到含硅活性颗粒。在一些实施方式中，负极活性材料层还包括粘结剂和导电剂。在一些实施方式中，粘结剂包括，但不限于：聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚 四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸化或丙烯酸酯化的丁苯橡胶、环氧树脂或尼龙等。
在一些实施方式中，导电剂包括，但不限于：基于碳的材料、基于金属的材料、导电聚合物和它们的混合物。在一些实施例中，基于碳的材料选自碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，基于金属的材料选自金属粉、金属纤维、铜、镍、铝或银。在一些实施例中，导电聚合物为聚亚苯基衍生物。
本申请的二次电池还包括正极，正极包括正极集流体和正极活性材料层，正极活性材料层包括正极活性材料、粘结剂和导电剂。
根据本申请的一些实施方式，正极集流体可以采用金属箔片或复合集流体。例如，可以使用铝箔。复合集流体可以通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子基材上而形成。
根据本申请的一些实施方式，正极活性材料包括钴酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、磷酸锰铁锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、尖晶石型锰酸锂、尖晶石型镍锰酸锂和钛酸锂中的至少一种。在一些实施例中，粘结剂包括粘合剂聚合物，例如聚偏氟乙烯、聚四氟乙烯、聚烯烃类、羧甲基纤维素钠、羧甲基纤维素锂、改性聚偏氟乙烯、改性SBR橡胶或聚氨酯中的至少一种。在一些实施例中，聚烯烃类粘结剂包括聚乙烯、聚丙烯、聚烯酯、聚烯醇或聚丙烯酸中的至少一种。在一些实施例中，导电剂包括碳基材料，例如天然石墨、人造石墨、炭黑、乙炔黑、科琴黑或碳纤维；金属基材料，例如铜、镍、铝、银等的金属粉或金属纤维；导电聚合物，例如聚亚苯基衍生物；或它们的混合物。
本申请的二次电池还包括隔离膜，本申请的二次电池中使用的隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。例如隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中 的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的至少一种。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的至少一种。聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
本申请的二次电池还包括电解液。本申请的中的电解液包括有机溶剂、锂盐和可选的添加剂。在一些实施例中，有机溶剂包括，但不限于：碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚丙酯或丙酸乙酯。在一些实施例中，有机溶剂包括醚类溶剂，例如包括1，3-二氧五环(DOL)和乙二醇二甲醚(DME)中的至少一种。在一些实施例中，锂盐包括有机锂盐或无机锂盐中的至少一种。在一些实施例中，锂盐包括，但不限于：六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、二氟磷酸锂(LiPO2F2)、双三氟甲烷磺酰亚胺锂LiN(CF3SO2)2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO2F)2)(LiFSI)、双草酸硼酸锂LiB(C2O4)2(LiBOB)或二氟草酸硼酸锂LiBF2(C2O4)(LiDFOB)。添加剂可以为现有技术中已知的电解液添加剂。
根据本申请的一些实施方式，本申请的二次电池包括，但不限于：锂离子电池或钠离子电池。在一些实施例中，二次电池包括锂离子电池。
本申请进一步提供了一种电子装置，其包括本申请第一方面的二次电池。
本申请的电子设备或装置没有特别限定。在一些实施例中，本申请的电子 设备包括但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
下面以锂离子电池为例并结合以下具体实施例、对比例对本申请的方案进行说明。在下述实施例及对比例中，所使用到的试剂、材料以及仪器如没有特殊的说明，均可商购获得。
实施例1
本实施例的锂离子电池，包括负极极片和电解液，该负极极片包括负极活性物质层，负极活性物质层包括含硅活性颗粒；含硅活性颗粒的球形化度A为0.68；电解液中含有FEC，基于电解液的质量，FEC的质量百分含量B％为1.1％；其中，A和B满足：B/A＝1.6。
直径大于10μm的含硅活性颗粒的切面轮廓最小角C°为129°；(A×C-B)＝86.62。
本实施例的锂离子电池，采用包括以下步骤的方法制备而成：
<多孔碳的制备>
将1000g热塑性线性酚醛树脂、120g六次甲基四胺固化剂溶解在2.5L甲醇中，溶解温度为50℃，溶解时间为1h。然后利用减压蒸馏手段除去甲醇溶剂，得到酚醛树脂和六次甲基四胺的均匀混合物。
在高压釜中配置浓度为0.15mol/L的十二烷基硫酸钠水溶液，并将上述酚醛树脂和六次甲基四胺的均匀混合物溶解在其中，将高压釜温度升至130℃并保温30min，待高压釜冷却后即可得到酚醛树脂微球。其中，酚醛树脂微球的球形化度为0.72，切面轮廓最小角为136°。
将酚醛树脂微球和氢氧化钾按照碱碳比3:1的比例进行混合，首先在回转炉中400℃处理30min，然后将回转炉温度升至750℃并保温45min。将得到 的产品经酸洗、水洗、烘干后即可得到多孔碳材料。
<含硅活性颗粒的制备>
取上述1000g多孔碳加入流化床反应器中，在10L/min氮气氛围下加热至480℃并保温2h，然后通入2.5L/min的甲硅烷气体300min。停止硅烷通入后，将流化床升温至500℃并保温1h，然后通入5L/min的乙炔气体300min，反应结束后即可得到含硅活性颗粒。
含硅活性颗粒的比表面积为2.80m2/g，基于含硅活性颗粒的质量，Si元素的质量分数为46.2％。
<负极极片的制备>
将负极活性材料(含硅活性颗粒与石墨按照质量比1:9混合)、碳纳米管、羧甲基纤维素锂、聚丙烯酸锂按照质量比97.4:0.2:0.4:2进行混合，加入溶剂去离子水，在真空搅拌机作用下获得负极浆料，其中，负极浆料的固含量为45wt％，粘度为6000mPa.s。将负极浆料均匀涂覆在厚度为6μm的负极集流体铜箔的一个表面上，将铜箔在80℃下烘干，得到涂层重量为100.1mg/1540.25mm2的单面涂覆有负极材料层的负极极片。然后在铜箔的另一个表面上重复以上步骤，即得到双面涂覆负极材料层的负极极片。然后经过冷压、裁片、分切后，得到规格为661mm×78mm的负极极片。
图1为本申请实施例1的锂离子电池中负极极片沿厚度方向的横截面背散射SEM图像，其中，基于负极活性物质层的质量，Si元素的质量分数为4.5％。
<正极极片的制备>
将正极活性材料LiCoO2、导电剂导电炭黑、粘结剂聚偏二氟乙烯按照质量比为96.7:1.7:1.6进行混合，加入N-甲基吡咯烷酮(NMP)，在真空搅拌机作用下获得正极浆料，其中，正极浆料的固含量为76wt％。将正极浆料均匀涂覆于厚度为9μm的正极集流体铝箔的一个表面上，将铝箔在120℃下烘干，得到涂层重量为260mg/1540.25mm2的单面涂覆有正极材料层的正极极片。然后在铝箔的另一个表面上重复以上步骤，即得到双面涂覆正极材料层的正极极片。然后经过冷压、裁片、分切后，得到规格为661mm×76.5mm的正极极片。
<电解液的制备>
在含水量小于10ppm的氩气气氛手套箱中，将EC、PC、EP和PP按照质量比为17：25：40：18混合得到有机溶剂，然后向有机溶剂中加入锂盐LiPF6和FEC得到电解液。其中，基于电解液的质量，锂盐LiPF6的质量百分含量为12.5％，FEC的质量百分含量为1.1％，电解液的电导率7.83mS/cm，氢氟酸含量为28.2μg/g。
<隔离膜>
采用厚度为10μm的多孔聚乙烯薄膜(Celgard公司提供)。
<锂离子电池的制备>
将上述制备得到的正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正极极片和负极极片中间起到隔离的作用，卷绕得到电极组件。将电极组件置于铝塑膜包装袋中，干燥后注入电解液，经过真空封装、静置、化成、脱气、切边等工序得到锂离子电池。
实施例2
本实施例的锂离子电池，与实施例1的区别仅在于，基于电解液的质量，FEC的质量百分含量为2％；其中，B/A＝2.9。
实施例3
本实施例的锂离子电池，与实施例1的区别仅在于，基于电解液的质量，FEC的质量百分含量为4％；其中，B/A＝5.9。
实施例4
本实施例的锂离子电池，与实施例1的区别仅在于，基于电解液的质量，FEC的质量百分含量为7％；其中，B/A＝10.3。
实施例5
本实施例的锂离子电池，与实施例1的区别仅在于，基于电解液的质量，FEC的质量百分含量为11％；其中，B/A＝16.2。
实施例6
本实施例的锂离子电池，与实施例1的区别仅在于，基于电解液的质量， FEC的质量百分含量为16％；其中，B/A＝23.5。
实施例7
本实施例的锂离子电池，与实施例1的区别仅在于，基于电解液的质量，FEC的质量百分含量为20％；其中，B/A＝29.4。
实施例8
本实施例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为0.79，基于电解液的质量，FEC的质量百分含量为4％；其中，B/A＝5.1。
实施例9
本实施例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为0.82，基于电解液的质量，FEC的质量百分含量为4％；其中，B/A＝4.9。
实施例10
本实施例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为0.91，基于电解液的质量，FEC的质量百分含量为4％；其中，B/A＝4.4。
实施例11
本实施例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为0.65，基于电解液的质量，FEC的质量百分含量为4％；其中，B/A＝6.2。
实施例12
本实施例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为0.68，基于电解液的质量，FEC的质量百分含量B％为20％；其中，B/A＝29.4，直径大于10μm的含硅活性颗粒的切面轮廓最小角C°为96°,(A×C-B)＝45.28。
实施例13
本实施例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为1，基于电解液的质量，FEC的质量百分含量B％为4％；其中，B/A＝4，直径大于10μm的含硅活性颗粒的切面轮廓最小角C°为180°,(A×C-B)＝176.0。
对比例1
本对比例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为0.68，基于电解液的质量，FEC的质量百分含量为1％；其中，B/A＝1.5。
对比例2
本对比例的锂离子电池，与实施例1的区别仅在于，含硅活性颗粒的球形化度A为0.71，基于电解液的质量，FEC的质量百分含量为21％；其中，B/A＝29.6。
试验例
采用以下测试方法对本申请中实施例和对比例提供的锂离子电池的各种参数或性能进行测试：
1、球形化度测试
利用等效直径法测试含硅活性颗粒的球形化度，测试方法为采用ZEISS-SEM(sigma-02-33)扫描电子显微镜观察含硅活性颗粒粉末或负极极片中的含硅活性颗粒，剔除不完整颗粒，对完整颗粒的周长等效直径与颗粒面积等效直径进行计算。
球形化度＝周长等效直径/面积等效直径。
2、直径大于10μm颗粒切面轮廓最小角
将0.47g含硅活性颗粒和0.396g聚丙烯酸分散到水中，在匀浆机中混匀后用刮刀涂布到铜箔表面，烘干后用日本电子离子抛光仪(型号：IB-09010CP)进行切片处理。采用ZEIS-SEM(sigma-02-33)拍摄含硅活性颗粒的切面显微图像。选取直径大于10μm含硅活性颗粒的切面轮廓进行分析，图2给出了一种确定直径大于10μm含硅活性颗粒的切面轮廓最小角的示意图。如图2所示，对含硅活性颗粒的轮廓进行描边，然后沿尖角两侧边缘做切线，并测量两个切线夹角的角度；对比所测量角度的值大小，并取最小值作为该颗粒的切面轮廓最小角值(如图2的示意图中，角1为115°、角2为105°、角3为142°、角4为140°，则记角2为该含硅活性颗粒的切面轮廓最小角，即该含硅活性颗粒的切面轮廓最小角为105°)。统计至少20个含硅活性颗粒的切面轮廓中最小角的度数并求平均值，作为该批次内直径大于10μm含硅活性颗粒的切面 轮廓最小角。
3、比表面积测试
称取2.0g含硅活性颗粒置于样品管中，将样品管安装到脱气站口，加热温度设定为200℃脱气120min，向样品管内通入氮气，通过控制样品管中的平衡压力直接测得吸附分压，由气体状态方程得到该分压点的吸附量。测量过程中逐渐增加吸附质气体使吸附平衡压力逐渐变大，最终得到吸附等温线。通过逐渐吸附质气体被抽走来降低吸附平衡压力，得到脱附等温线。最后，采用BJH(Barrett-Joyner-Halenda)理论计算含硅活性颗粒的比表面积。
4、电解液中氢氟酸含量测试
取100g冰水混合物于塑料烧杯中，分别加入10滴浓度为1g/L的溴百里酚蓝指示剂并搅拌均匀。用浓度为0.01mol/L的NaOH标准溶液进行滴定，直至冰水混合物显示蓝色。记录滴定终点时所消耗的NaOH标准溶液标准体积V0(ml)。
用上述同样的方法配置冰水混合物及溴百里酚蓝指示剂混合溶液，并加入20g待测电解液，记录待测电解液的加入质量m(g)。用浓度为0.01mol/L的NaOH标准溶液进行滴定，直至冰水混合物显示蓝色。记滴定终点时所消耗的NaOH标准溶液标准体积V1(ml)。
最后，利用如下公式计算待测电解液中氢氟酸的含量：
HF(μg/g)＝(V1-V0)×200/m。
5、电解液电导率测试
参考HG/T 4067-2015六氟磷酸锂电解液中电导率的测定方法进行测试，所选用电极为DJS-1C型铂黑电极。
6、含硅活性颗粒克容量测试
将含硅活性颗粒、导电剂(SP)、粘结剂(PAA-Li)、碳纳米管(CNTs)、分散剂(CMC)按照质量比84:10:5:0.4:0.6进行混合，加入去离子水得到固含量为48％的负极浆料。将负极浆料混合均匀后涂敷到铜箔上，经过烘干、冷压、冲片后得到负极极片。
在水氧含量均小于10ppm的手套箱中，将碳酸甲乙酯(EMC)、碳酸乙烯酯(EC)与碳酸二乙酯(DEC)按照1:1:1的体积比进行混合得到混合溶剂，然后加入占上述混合溶剂体积分数为10％的FEC，最后加入锂盐LiPF6，得到电解液。其中，锂盐LiPF6浓度为1mol/L。
在水氧含量均小于10ppm的手套箱中，将上述负极极片、对电极金属锂片、聚丙烯(PP)隔膜及上述电解液组装成纽扣电池。
含硅活性颗粒克容量的测试：在25℃环境中将上述纽扣电池静置6h后，以0.05C的电流放电至5mV，接着以50μA的电流放电至5mV，静置5min后再以10μA的电流放电至5mV，静置5min，然后以0.05C的倍率充电至0.8V。上述放电容量记为G0，充电容量记为G1。
含硅活性颗粒克容量＝G1；含硅活性颗粒首次库伦效率＝G1/G0×100％。
7、锂离子电池首次放电容量及首次库伦效率测试
在25℃常压环境下，将新制备的锂离子电池以0.5C倍率恒流充电至4.53V，并恒压充电至0.05C，静置5min，记录该步充电容量为C1；以0.2C倍率恒流放电至3.0V，记录该步放电容量为C2，则C2为锂离子电池的首次放电容量。
锂离子电池首次库伦效率＝C2/C1×100％。
8、锂离子电池循环性能测试
将锂离子电池置于25℃恒温测试箱中，静置30min，使锂离子电池达到25℃恒温状态。以1C恒流充电至4.53V，恒压充电至电流为0.025C，静置5min，以0.5C恒流放电至3.0V，记录初始放电容量为C0。以此步骤循环400圈，记录循环400圈后的放电容量为C1。
循环400圈后容量保持率＝C1/C0×100％。
9、耐过放能力测试
测试温度为25℃，以0.2C恒流充放电到3.0V，静置5分钟后以10mA恒流放电到0.1V，静置30分钟后以1mA恒流放电到0.1V。采用在线测厚设备对锂离子电池厚度进行测试，测厚重量300g，采点时间间隔10s，锂离子电 池初始厚度记为T1，放电后厚度记为T2，并记录锂离子电池电压。
将(T2-T1)/T1×100％等于10％时的电压值记为锂离子电池的过放产气测试电压，过放产气测试电压的值越低证明锂离子电池的耐过放能力越强。
对本申请提供的实施例1～13和对比例1～2的锂离子电池通过上述测试所得的各项参数和性能表征结果如下表1所示。
表1

由表1可知，实施例1～13的锂离子电池控制含硅活性颗粒的球形化度A以及电解液中FEC的质量百分含量B％满足1.6≤(B/A)≤29.4，其首次库伦效率达到86.4％～90.7％，循环400圈后的容量保持率达到92.0％～97.2％，具有较高的首次效率和循环性能。另外，实施例1～13的锂离子电池的过放产气测试电压能够达到1.85V～2.31V，可见本申请实施例的锂离子电池在产生相同体积的气体时，能够达到更低的放电电压，表明本申请实施例的锂离子电池在放电过程中的产气量较少，具有较强的耐过放能力。
相比之下，对比例1～2的锂离子电池在B/A值在限定范围外时，其首次库伦效率为83.2％～85.4％，循环400圈后的容量保持率为88.6％～89.7％，过放产气测试电压能够为2.47V～2.58V，原因可能在于，含硅活性颗粒在受力时产生的新鲜界面无法被致密的SEI膜覆盖，导致活性硅和电解液持续发生副反应，锂离子电池的各项性能因此恶化严重。
当控制含硅活性颗粒的球形化度A为0.65～1时，能够进一步提高锂离子电池的首次效率、循环性能和耐过放能力。
从实施例1～7可以看出，FEC可以在含硅活性颗粒表面形成致密和低阻抗的SEI膜，能阻止活性硅的副反应及电解液的进一步分解，从而可以使更多的活性硅参与合金化/去合金化反应，提高了锂离子电池的首次库伦效率、循环400圈后的容量保持率，降低其过放产气测试电压，改善了锂离子电池的循环性能。进一步控制FEC的质量百分含量B％为2≤B≤7，锂离子电池的首次库伦效率和循环容量保持率更高，且在进行过放产气测试时发生膨胀时的放电电压更低，表明锂离子电池过放时产气量少，具有更强的耐过放能力。
实施例8～11之间相比，FEC含量相同，含硅活性颗粒的球形化度发生改变，其中实施例8～10在满足B/A范围的基础上，进一步优选球形化度的形状特征，使含硅活性颗粒的球形化度在0.79以上，相比实施例11具有更高的首次效率、循环性能和耐过放能力。
实施例1～13中，通过控制含硅活性颗粒的球形化度A、直径大于10μm的含硅活性颗粒的切面轮廓最小角C以及电解液中FEC的质量百分含量B％满足45.28≤(A×C-B)≤176.0，锂离子电池具有显著提高的首次效率和循环容量保持率和明显提升的循环性能和耐过放能力。其中，当A、B、C的满足60≤(A×C-B)≤120，二次电池的性能能够得到进一步提升，表现出更优的循环性能和耐过放能力。

Claims (10)

  1. 一种二次电池，包括负极极片和电解液，其特征在于，所述负极极片包括负极活性物质层，所述负极活性物质层包括含硅活性颗粒；所述含硅活性颗粒的球形化度为A；
    所述电解液包括氟代碳酸乙烯酯；基于所述电解液的质量，所述氟代碳酸乙烯酯的质量百分含量为B％；
    其中，A和B满足：1.6≤(B/A)≤29.4。
  2. 根据权利要求1所述的二次电池，其特征在于，0.65≤A≤1。
  3. 根据权利要求1或2所述的二次电池，其特征在于，1.1≤B≤20。
  4. 根据权利要求1至3中任一项所述的二次电池，其特征在于，2≤B≤7。
  5. 根据权利要求1至4中任一项所述的二次电池，其特征在于，直径大于10μm的所述含硅活性颗粒切面轮廓最小角为C°，96≤C≤180。
  6. 根据权利要求5所述的二次电池，其特征在于，A、B和C满足：45.28≤(A×C-B)≤176.0。
  7. 根据权利要求5或6所述的二次电池，其特征在于，A、B和C满足：60≤(A×C-B)≤120。
  8. 根据权利要求1至7中任一项所述的二次电池，其特征在于，所述含硅活性颗粒包括多孔碳基体和纳米硅；所述纳米硅分布在所述多孔碳基体的内部和表面。
  9. 根据权利要求1至8中任一项所述的二次电池，其特征在于，所述二次电池满足以下条件中的至少一者：
    (1)基于所述含硅活性颗粒的质量，Si元素的质量分数为42％～55％；
    (2)所述含硅活性颗粒的比表面积为0.5m2/g～5m2/g；或
    (3)所述电解液的电导率为6.5mS/cm～11mS/cm。
  10. 一种电子装置，其特征在于，包括权利要求1至9中任一项所述的二次电池。
PCT/CN2024/083567 2024-03-25 2024-03-25 二次电池以及电子装置 Pending WO2025199679A1 (zh)

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