WO2023000211A1 - 正极极片、包含该正极极片的电化学装置和电子装置 - Google Patents

正极极片、包含该正极极片的电化学装置和电子装置 Download PDF

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WO2023000211A1
WO2023000211A1 PCT/CN2021/107662 CN2021107662W WO2023000211A1 WO 2023000211 A1 WO2023000211 A1 WO 2023000211A1 CN 2021107662 W CN2021107662 W CN 2021107662W WO 2023000211 A1 WO2023000211 A1 WO 2023000211A1
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positive electrode
metal
sulfur
electrode sheet
amorphous metal
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French (fr)
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张雪
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Priority to CN202180006809.3A priority patent/CN114788040B/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • 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
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • 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
    • 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
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H01M4/5815—Sulfides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 energy storage technology, in particular to a positive pole piece, an electrochemical device and an electronic device including the positive pole piece.
  • Lithium-sulfur batteries have attracted much attention due to their high specific capacity (1672mAh ⁇ g -1 ), low price, abundant reserves and environmental friendliness of sulfur as the cathode material, and are expected to become the next generation of energy storage batteries to replace traditional lithium-ion batteries.
  • high specific capacity (1672mAh ⁇ g -1 )
  • low price abundant reserves
  • environmental friendliness of sulfur as the cathode material and are expected to become the next generation of energy storage batteries to replace traditional lithium-ion batteries.
  • the purpose of the present application is to provide a positive electrode sheet, an electrochemical device and an electronic device including the positive electrode sheet, so as to improve the energy density and cycle stability of the electrochemical device.
  • the first aspect of the present application provides a positive electrode sheet.
  • the positive electrode sheet includes a positive electrode material layer, and the positive electrode material layer includes a sulfur-based material, an amorphous metal sulfide, and metal particles.
  • the metal sites in the amorphous metal sulfides can serve as linking points for polysulfide ions during charge-discharge cycles, Li y MS x (x ⁇ 2, y ⁇ 2), effectively improve the shuttle effect in the electrochemical device; at the same time, the metal particles have good conductivity. On the one hand, they can play a role in building a good electronic pathway and improve the utilization of sulfur-based materials.
  • amorphous metal sulfides also have the characteristics of positive active materials, which are different from the porous carbon materials and metal oxide materials (such as Co 3 O 4 , CoOOH, etc.) Provides capacity while improving the shuttle effect. Therefore, under the synergistic effect of amorphous metal sulfides and metal particles, it is beneficial to improve the specific capacity and capacity retention at the same time.
  • metal particles refer to metal particles containing metal elements.
  • the element M in Li y MS x is a metal element in amorphous metal sulfide; polysulfide may include but not limited to at least one of Li 2 S 4 , Li 2 S 6 , Li 2 S 8 kind.
  • the surface of the metal particle has an amorphous metal sulfide.
  • the amorphous metal sulfide may exist on a part of the surface of the metal particle, or the amorphous metal sulfide may exist on the entire surface of the metal particle.
  • optimizing the synergistic effect of metal particles and amorphous metal sulfide Further improving the utilization rate of sulfur-based materials and the shuttling effect in electrochemical devices can further improve the energy density and cycle stability of electrochemical devices.
  • the metal elements in the amorphous metal sulfide and the metal particles each independently include at least one of iron, niobium, molybdenum, titanium or tungsten, preferably at least one of iron or molybdenum . That is, the metal elements in the amorphous metal sulfide may include at least one of iron, niobium, molybdenum, titanium or tungsten, and the metal elements in the metal particles may also include at least one of iron, niobium, molybdenum, titanium or tungsten.
  • the metal element in the amorphous metal sulfide may be the same or different from the metal element in the metal particles.
  • the ratio of metal atoms in the metal particles and the amorphous metal sulfide is 0.1 to 1.
  • the ratio of metal atoms in the metal particles and the amorphous metal sulfide may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any range therebetween.
  • the ratio of the number of metal atoms in the metal particles to the amorphous metal sulfide is too small (for example, less than 0.1), the number of metal atoms in the metal particles is less, and it is impossible to effectively construct the positive electrode material layer between particles and particles.
  • the utilization rate of sulfur-based materials decreases, thereby affecting the energy density of electrochemical devices;
  • the number of metal atoms in amorphous metal sulfides is more than that of amorphous metal sulfides, which can easily lead to side reactions between metal particles and electrolyte, thus affecting the cycle performance of electrochemical devices. Therefore, adjusting the ratio of the number of metal atoms in the metal particles and the amorphous metal sulfide within the above range is beneficial to improve the energy density and cycle performance of the electrochemical device.
  • the positive pole piece satisfies at least one of the following characteristics: (i) the mass of the amorphous metal sulfide is 100% (ii) the mass percentage of metal particles is 0.4% to 5%, preferably 0.4% to 2%; (iii) amorphous metal sulfide The total mass percent content of metal elements and metal elements in the metal particles is 2% to 10%, preferably 2% to 4%.
  • the mass percentage of amorphous metal sulfide can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11% or any range therebetween.
  • the mass percentage of metal particles can be 0.4%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range therebetween .
  • the total mass percentage of metal elements in amorphous metal sulfide and metal particles can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or between them any range.
  • the electrochemical device when the mass percentage of amorphous metal sulfide is too low (for example, less than 2%), the electrochemical device will form more polysulfides that cannot undergo reversible reactions during cycling, eventually causing The loss of sulfur-based materials in the positive electrode sheet leads to a gradual decrease in the capacity retention of the electrochemical device during cycling.
  • the mass percentage of amorphous metal sulfide gradually increases, the number of effective metal sites in the positive electrode material layer gradually increases, and the number of connection sites with polysulfide ions also increases, resulting in the formation of polysulfides that can undergo reversible reactions.
  • the capacity retention rate of the electrochemical device is effectively improved.
  • the capacity provided by the amorphous metal sulfide is only 1/4 to 1/2 of that of the sulfur-based material, so its content should not be too high (for example, higher than 11%). When the content thereof is too high, the energy density will be reduced, and the cost will also be increased. Therefore, controlling the mass percentage of the amorphous metal sulfide within the above range is beneficial to improving the capacity retention and energy density of the electrochemical device.
  • the mass percentage of metal particles increases, the utilization of sulfur-based materials increases, which is beneficial to the improvement of the energy density of electrochemical devices; but when the mass percentage of metal particles is too high (for example, higher than 5%), As the mass percentage of metal particles increases, the mass percentage of sulfur-based materials and amorphous metal sulfides in the positive electrode material layer decreases, resulting in a decrease in specific capacity, thereby affecting the energy density of the electrochemical device. In addition, excessive metal particles are prone to side reactions with the electrolyte, thereby affecting the cycle performance of electrochemical devices. Therefore, adjusting the mass percentage of the metal particles within the above range is beneficial to improving the energy density and cycle performance of the electrochemical device.
  • the total mass percentage content of the metal element in the amorphous metal sulfide and metal particles is too low (for example, less than 2%), the effect of improving the capacity retention rate of the electrochemical device is not obvious; when there is no
  • the total mass percentage of metal elements in the shaped metal sulfide and metal particles is too high (for example, higher than 10%)
  • the positive electrode sulfur-based material mass percentage in the positive electrode material layer will decrease, which will affect the energy of the electrochemical device. density. Therefore, controlling the total mass percentage content of the amorphous metal sulfide and metal elements in the metal particles within the above range is beneficial to improving the capacity retention and energy density of the electrochemical device.
  • the mass fraction of metal elements can be obtained by inductively coupled plasma spectrometry (ICP) on the powder on the positive pole piece, and the mass fraction of sulfur element can be obtained by testing the powder on the positive pole piece with a carbon-sulfur analyzer.
  • ICP inductively coupled plasma spectrometry
  • the positive electrode material layer only contains S element and metal element, so according to the obtained value, the mass percentage of amorphous metal sulfide and metal particles and the amount of amorphous metal sulfide and metal particles can be converted.
  • the mass fraction of S element in the sulfur-based material can be calculated according to the ratio of metal atoms in the metal particles and the amorphous metal sulfide, and the mass fraction of Li 2 S can be further calculated, so that Further conversion is performed to obtain the mass percentage of the amorphous metal sulfide and the metal particles and the total mass percentage of the amorphous metal sulfide and the metal elements in the metal particles.
  • the sulfur-based material is organic sulfide or high molecular carbon-sulfur material
  • the positive electrode material layer contains organic sulfide or high molecular carbon-sulfur material, metal particles, and metal sulfide.
  • the content of organic sulfide or polymer carbon-sulfur material in the pole piece can be obtained by analyzing the combined method of infrared-mass spectrometry-thermogravimetric analyzer; then, the mass fraction of metal elements can be obtained by ICP test, and then Through the ToF-SIMS test, the specific chain length of polysulfide ions in metal sulfide can be obtained. According to the ratio of metal particles and metal elements in metal sulfide, the mass percentage of amorphous metal sulfide and metal particles can be calculated and The total mass percentage of metal elements in amorphous metal sulfides and metal particles.
  • the average particle size of the amorphous metal sulfide is D1
  • the average particle size of the metal particles is D2, satisfying: D1/D2 is 0.5 to 3.5, preferably 1 to 2.5.
  • the value of D1/D2 can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5 or any range therebetween.
  • D1/D2 is too small (for example, less than 0.5), that is, the specific surface of the metal particles is relatively small, which is not conducive to the good dispersion of the metal particles in the positive electrode material layer, that is, it is not conducive to the electron transport path. Construct.
  • the average particle diameter D1 of the amorphous metal sulfide is 20 nm to 500 nm.
  • the average particle size of the amorphous metal sulfide can be 20nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm or any range therebetween.
  • the average particle size of the amorphous metal sulfide when the average particle size of the amorphous metal sulfide is too small (for example, less than 20nm), the particles are easy to agglomerate, resulting in uneven distribution of the amorphous metal sulfide, which affects the capacity retention of the electrochemical device;
  • the average particle size of the amorphous metal sulfide is too large (for example, greater than 500nm)
  • its specific surface decreases
  • the connection points for connecting polysulfide ions decrease
  • the rate of forming Li y MS x decreases
  • the effect of reducing polysulfide shuttling decreases. , thereby affecting the capacity retention of the electrochemical device. Therefore, by adjusting the average particle size of the amorphous metal sulfide within the above range, it is beneficial to improve the cycle performance of the electrochemical device.
  • the present application has no particular limitation on the average particle size of the metal particles, as long as D1/D2 meets the scope of the present application and achieves the purpose of the present application.
  • D2 may be 15nm to 500nm.
  • the porosity of the positive electrode material layer is 20% to 45%, preferably 30% to 45%.
  • the porosity of the positive electrode material layer is 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 45%, or any range therebetween.
  • the porosity of the positive electrode material layer when the porosity of the positive electrode material layer is too small (such as less than 20%), it will affect the transmission of lithium ions, thereby affecting the kinetic performance of the electrochemical device; when the porosity of the positive electrode material layer is too large (such as greater than 45%), it is easy to cause side reactions between the metal particles and the electrolyte, and will reduce the content of sulfur-based materials in the positive electrode material layer, thereby reducing the cycle performance and energy density of the electrochemical device. Therefore, by adjusting the porosity of the positive electrode material layer within the above range, it is beneficial to improve the kinetic performance and cycle performance of the electrochemical device.
  • the positive pole piece satisfies at least one of the following characteristics: (iv)
  • the sulfur-based material includes at least one of elemental sulfur, lithium sulfide, sulfur-containing organic compounds, or polymeric carbon-sulfur materials
  • the positive electrode material layer also includes a sulfur-loading material, and the sulfur-loading material includes Ketjen Black, carbon nanotubes, carbon nanowires, mesoporous carbon, microporous carbon, graphene, metal oxides or metal nitrides At least one; (vi)
  • the positive electrode material layer also contains a conductive agent, and the conductive agent includes at least one of carbon nanotubes, carbon nanosheets, graphene, graphite, carbon black or conductive polymers.
  • the above-mentioned carbon nanotubes may include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.
  • the conductive polymer there is no particular limitation on the conductive polymer, as long as the purpose of the present application can be achieved, for example, it may include but not limited to at least one of polyaniline, polythiophene, polyacetylene or polypyrrole.
  • the present application has no particular limitation on the sulfur-containing organic compound, as long as the purpose of the present application can be achieved.
  • the sulfur-containing organic compound may include but not limited to at least one of sulfide, anthraquinone sulfide, and benzoquinone sulfide.
  • Polymer carbon-sulfur material refers to a substance formed by mixing and heat - treating a polymer material and elemental sulfur, in which sulfur can exist as small molecules from S2 to S6 , and there are CS bonds in the formed substance.
  • the present application has no special limitation on the polymer material, as long as the purpose of the present application can be achieved, for example, it may include but not limited to at least one of polyacrylonitrile and polyvinylpyrrolidone.
  • the present application has no special limitation on the heat treatment temperature, as long as the purpose of the present application can be achieved, for example, the heat treatment temperature is 150°C to 300°C.
  • the polymeric carbon-sulfur material may include, but is not limited to, at least one of sulfur/polyacrylonitrile and sulfur/polyvinylpyrrolidone.
  • the second aspect of the present application provides an electrochemical device comprising the positive electrode sheet according to any embodiment of the present application, and the obtained electrochemical device has high energy density and capacity retention.
  • the electrochemical device further includes an electrolyte, and the electrolyte includes lithium nitrate.
  • the addition of lithium nitrate to the electrolyte helps to improve the dissolution of polysulfides and increase the utilization rate of the sulfur cathode; it helps to adjust the deposition morphology of the sulfur cathode and alleviate the passivation of the cathode; On the other hand, it helps to form a protective film on the surface of the negative electrode, prevents the consumption of the electrolyte, and inhibits the formation of lithium dendrites, thereby improving the safety and cycle stability of the electrochemical device.
  • the mass percentage of lithium nitrate is 1% to 3%, preferably 2% to 3%.
  • the mass percentage of lithium nitrate can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or any range therebetween.
  • the mass percentage of lithium nitrate is too low (for example, less than 1%), lithium nitrate does not significantly improve the performance of the electrochemical device.
  • lithium nitrate When the content of lithium nitrate is too high (such as higher than 3%), the decomposition of lithium nitrate at low potential will be intensified, resulting in the deterioration of the performance of the electrochemical device, and the excessive addition of lithium nitrate will also bring greater damage to the lithium-sulfur battery. security risks. Therefore, by adjusting the mass percentage of lithium nitrate within the above range, it is beneficial to improve the safety and cycle stability of the electrochemical device.
  • the electrolyte solution further includes fluoroethers.
  • fluoroethers help to form a stable SEI layer on the negative electrode side, which can avoid the irreversible consumption caused by polysulfide shuttle to the negative electrode.
  • fluoroethers have a higher flash point or even no flash point. It is beneficial to suppress the combustion of the electrolyte, and can improve the high temperature resistance performance of the electrochemical device.
  • This application has no special restrictions on fluoroethers, as long as the purpose of this application can be achieved, for example, it can include but not limited to tetrafluoroethyl tetrafluoropropyl ether, tetrafluoroethyl trifluoropropyl ether, decafluoromethoxy At least one of trifluoromethylpentane and bis(trifluoroethyl)ether.
  • the present application has no special restrictions on the content of fluoroether solvents, as long as the purpose of the application can be achieved, for example, based on the total volume of the electrolyte solvent, the volume percentage of fluoroether is 10% to 50%, preferably 20% to 40%.
  • the positive electrode sheet of the present application also includes a positive current collector, wherein the positive current collector is not particularly limited as long as the purpose of the present application can be achieved, for example, it may include but not limited to aluminum foil, aluminum alloy foil or a composite current collector.
  • the thickness of the positive electrode current collector is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness of the positive electrode current collector is 8 ⁇ m to 12 ⁇ m.
  • the positive electrode sheet may further include a conductive layer located between the positive electrode current collector and the positive electrode material layer.
  • the present application has no particular limitation on the composition of the conductive layer, which may be a commonly used conductive layer in the field, for example, may include but not limited to a binder and the above-mentioned conductive agent.
  • the present application has no special restrictions on the binder, as long as the purpose of the present application can be achieved, for example, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl At least one of cellulose, sodium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber or polyvinylidene fluoride.
  • the electrochemical device of the present application also includes a negative electrode sheet.
  • the negative electrode sheet in the present application is not particularly limited as long as the purpose of the application can be achieved.
  • the negative electrode sheet usually includes a negative electrode collector and a negative electrode material layer.
  • the negative electrode current collector is not particularly limited, as long as the purpose of this application can be achieved, for example, it can include but not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite collector. fluid etc.
  • the thickness of the current collector of the negative electrode is not particularly limited, as long as the purpose of the application can be achieved, for example, the thickness of the current collector of the negative electrode is 4 ⁇ m to 12 ⁇ m.
  • Negative electrode material layer usually includes negative electrode active material
  • negative electrode active material is not particularly limited, as long as the purpose of this application can be achieved, for example, can include but not limited to lithium metal, lithium-containing compounds (such as lithium titanate), lithium alloy (for example, at least one of lithium copper alloy), mesocarbon microspheres, soft carbon, hard carbon, silicon or silicon carbon.
  • the negative electrode material layer may also include a conductive agent.
  • the present application has no special limitation on the conductive agent, as long as the purpose of the present application can be achieved.
  • it may include but not limited to at least one of the above-mentioned conductive agents.
  • the negative electrode material layer may also include a binder.
  • the present application has no special limitation on the binder, as long as the purpose of the application can be achieved.
  • it may include but not limited to at least one of the above-mentioned binders. kind.
  • the negative electrode sheet may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer.
  • the present application has no particular limitation on the composition of the conductive layer, which may be a commonly used conductive layer in the field, and the conductive layer may include but not limited to the above-mentioned conductive agent and the above-mentioned binder.
  • the electrochemical device of the present application also includes a separator, which is not particularly limited in the present application, as long as the purpose of the application can be achieved, for example, may include but not limited to polyethylene (PE), polypropylene (PP), polytetrafluoroethylene Vinyl fluoride-based polyolefin (PO) separator, polyester film (such as polyethylene terephthalate (PET) film), cellulose film, polyimide film (PI), polyamide film (PA ), at least one of spandex or aramid film, woven film, non-woven film (non-woven fabric), microporous film, composite film, separator paper, rolled film or spun film, etc.
  • a separator which is not particularly limited in the present application, as long as the purpose of the application can be achieved, for example, may include but not limited to polyethylene (PE), polypropylene (PP), polytetrafluoroethylene Vinyl fluoride-based polyolefin (PO) separator, polyester film (such as polyethylene terephthal
  • the separator of the present application may have a porous structure, and the pore size is not particularly limited as long as the purpose of the present application can be achieved, for example, the pore size may be 0.01 ⁇ m to 1 ⁇ m.
  • the thickness of the isolation film is not particularly limited, as long as the purpose of the application can be achieved, for example, the thickness of the isolation film may be 5 ⁇ m to 500 ⁇ m.
  • a separator may include a substrate layer and a surface treatment layer.
  • the substrate layer can be a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer can include but not limited to polyethylene, polypropylene, polyethylene terephthalate or polyimide, etc. at least one of .
  • a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.
  • at least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.
  • the inorganic material layer can include inorganic particles and binders, and the application has no special limitation on inorganic particles, for example, it can include but not limited to aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide , nickel oxide, zinc oxide, calcium oxide, zirconia, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate.
  • the present application has no special limitation on the binder, for example, it may include but not limited to polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate , polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the polymer material may include but not limited to polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride At least one of ethylene, poly(vinylidene fluoride-hexafluoropropylene), and the like.
  • the electrolyte in the electrochemical device of the present application may also include a lithium salt and a non-aqueous solvent.
  • This application has no special restrictions on lithium salts, as long as the purpose of this application can be achieved, for example, it may include but not limited to LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3. At least one of LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB or lithium difluoroborate.
  • the non-aqueous solvent used in this application contains ether compounds, which specifically include but are not limited to dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1 , at least one of 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran.
  • ether compounds which specifically include but are not limited to dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1 , at least one of 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran.
  • the above-mentioned other organic solvents may include but not limited to dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2- At least one of pyrrolidone, formamide, dimethylformamide, and acetonitrile.
  • the preparation process of electrochemical devices is well known to those skilled in the art, and the present application is not particularly limited.
  • it may include but not limited to the following steps: stack the positive electrode sheet, separator and negative electrode sheet in sequence, and as required Put it into the casing after winding, folding, etc., inject the electrolyte into the casing and seal it.
  • anti-overcurrent elements, guide plates, etc. can also be placed in the casing as needed, so as to prevent pressure rise and overcharge and discharge inside the electrochemical device.
  • a third aspect of the present application provides an electronic device comprising the electrochemical device described in the above embodiments of the present application.
  • the electronic device of the present application is not particularly limited, and it may be used in any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, notebook computers, pen-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, Lighting appliances, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.
  • the present application provides a positive electrode sheet, an electrochemical device and an electronic device including the positive electrode sheet.
  • the positive electrode sheet includes a positive electrode material layer, and the positive electrode material layer includes a sulfur-based material, an amorphous metal sulfide and metal particles. Since the metal sites in amorphous metal sulfides can be used as connection points to connect polysulfide ions during the charge-discharge cycle, forming Li y MS x that can undergo reversible reactions, effectively improving the shuttle effect of electrochemical devices; at the same time, Metal particles have good electrical conductivity. On the one hand, they can play a role in building a good electronic pathway and improve the utilization rate of sulfur-based materials.
  • the amorphous metal sulfide also has the characteristics of the positive electrode active material, which improves the specific capacity of the positive electrode material layer. Therefore, under the synergistic effect of amorphous metal sulfides and metal particles, it is beneficial to improve the energy density and capacity retention of electrochemical devices.
  • Fig. 1 is a graph showing the variation of the discharge specific capacity of the positive electrode sheet with the number of cycles of the electrochemical devices of Example 9, Example 19, Comparative Example 1, Comparative Example 3 and Comparative Example 4 of the present application.
  • a lithium-sulfur battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to the lithium-sulfur battery.
  • X-ray photoelectron spectroscopy (XPS) test was carried out on the positive electrode material layer to obtain the Fe-2p spectrum, and the Fe-2p spectrum was divided into peaks Obtain the diffraction peaks of Fe and Fe-S, and calculate the ratio of the peak area of the diffraction peaks of Fe and Fe-S. Randomly select two different positions of the positive electrode material layer for testing, each place is sputtered for 0s, 100s, and 200s for testing, and the peak value is calculated for the ratio, and the final average value is the metal atom in the metal particle and amorphous metal sulfide Number ratio X.
  • XPS X-ray photoelectron spectroscopy
  • the mass fraction m1 of metal elements can be obtained by inductively coupled plasma spectrometry (ICP) on the powder on the positive pole piece, and the mass fraction m2 of sulfur element can be obtained by testing the powder on the positive pole piece with a carbon-sulfur analyzer.
  • ICP inductively coupled plasma spectrometry
  • the total mass percentage of metal elements m1/(m1+m2)
  • Mass percentage of metal particles (X/(1+X)) ⁇ (m1/(m1+m2));
  • Mass percentage of metal sulfide (1/(1+X)) ⁇ (m1/(m1+m2)) ⁇ M1/M2;
  • M1 is the molar mass of the metal sulfide
  • M2 is the molar mass of the metal element
  • X is the ratio X of metal atoms in the metal particle and the amorphous metal sulfide.
  • the average particle size D1 of amorphous metal sulfide and the average particle size D2 of metal particles are tested:
  • the average particle diameter D2 of the metal particles is measured with the above average particle diameter D1 of the amorphous metal sulfide.
  • the gas pressure value used in the test is 19.5PSI.
  • the prepared battery was tested with LAND equipment.
  • the test program was set to activate with a small rate cycle of 0.05C for the first 4 cycles, and cycle with a rate of 0.3C for 5 to 30 cycles.
  • the sulfur-based material adopts elemental sublimated sulfur, and introduces Ketjen black as the sulfur-loading material.
  • Sublimed sulfur (S) and Ketjen black were heat-treated at 155°C for 12 hours at a mass ratio of 8:2 to obtain a S/Ketjen black mixture, and then the S/Ketjen black mixture, metal particles with an average particle size of 500nm, and iron Powder, amorphous metal sulfide ferrous disulfide (FeS 2 ) with an average particle size of 500nm were mixed and ground according to a mass ratio of 12.1:0.1:0.215 to obtain a mixture, and the mixture, conductive carbon black (Super P), polyvinylidene fluoride Ethylene (PVDF) was mixed according to a mass ratio of 8:1:1, and then N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 20%, and stirred evenly.
  • Super P
  • the slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 ⁇ m, the coating thickness is 60 ⁇ m, dried at 60°C, and then cold pressed under a pressure of 1 ton to obtain the porosity of the positive electrode material layer 41% of the positive pole piece. After coating, the positive pole piece was cut into discs with a diameter of 1.4 cm in a dry environment by a punching machine for use.
  • Metal lithium sheets with a thickness of 10 ⁇ m were used, and cut into discs with a diameter of 1.4 cm in a dry environment by a punching machine for use.
  • LiTFSI LiN(CF 3 SO 2 ) 2
  • LiNO3 LiN(CF 3 SO 2 ) 2
  • PE polyethylene
  • the above prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, placed in a packaging case, injected with electrolyte, and then packaged on a packaging machine to obtain a button lithium-sulfur battery.
  • Embodiment 2 to Embodiment 4 except that D1 and D2 are adjusted according to Table 1, the rest are the same as Embodiment 1.
  • Example 5 except that the mass ratio of sulfur-based material/Ketjen Black, metal particles, and amorphous metal sulfide is 11.7:0.2:0.43, the rest is the same as Example 3.
  • Example 6 except that the mass ratio of sulfur-based material/Ketjen Black, metal particles, and amorphous metal sulfide is 10.5:0.5:1.07, the rest is the same as Example 3.
  • Example 7 is the same as Example 3 except that the mass ratio of sulfur-based material/ketjen black, metal particles, and amorphous metal sulfide is 11.3:0.11:0.6.
  • Embodiment 8 to Embodiment 11 except that the value of D2 is adjusted according to Table 1, the rest are the same as Embodiment 7.
  • Example 12 except that the mass ratio of sulfur-based material/Ketjen Black, metal particles, and amorphous metal sulfide is 11.5:0.04:0.78, the rest is the same as that of Example 3.
  • Example 13 except that in the step ⁇ preparation of the positive pole piece>, sublimated sulfur, Ketjen black and iron powder with a particle size of 50 nm were heat-treated at 155°C for 12 hours at a mass ratio of 9.6:2.4:0.4 to obtain sublimed sulfur , Ketjen Black, metal particle iron powder and amorphous iron sulfide (FeS 2 ), the above mixture, Super P, PVDF are mixed according to the mass ratio of 8:1:1 to prepare slurry, and the rest are the same as in Example 3 same.
  • Example 14 except that molybdenum powder is used instead of iron powder, and amorphous molybdenum trisulfide (MoS 3 ) is used instead of amorphous ferrous disulfide, the rest is the same as that of Example 2.
  • MoS 3 amorphous molybdenum trisulfide
  • Example 15 except that niobium powder is used instead of iron powder, and amorphous niobium trisulfide (NbS 3 ) is used instead of amorphous ferrous disulfide, the rest is the same as that of Example 2.
  • Example 16 and Example 17 except that the mass concentration of LiNO 3 in the electrolyte was adjusted as shown in Table 2, the others were the same as in Example 13.
  • Example 19 except that in the step ⁇ preparation of the positive electrode sheet>, the obtained positive electrode sheet was cold-pressed under a pressure of 3 tons, and the porosity of the positive electrode material layer was adjusted to 31%, the rest was the same as in Example 18 .
  • Example 23 except that the cold pressing pressure is 9 tons and the porosity of the positive electrode material layer is adjusted to 22%, the rest is the same as that of Example 19.
  • Comparative Example 1 except that it does not contain metal particle iron powder and amorphous metal sulfide FeS 2 , the others are the same as Example 1.
  • Comparative Example 2 except that the amorphous metal sulfide FeS 2 is not included, and the mass ratio of the S/Ketjen black mixture to 50 nm iron powder is 12:0.4, the rest is the same as that of Example 5.
  • Comparative Example 3 except that no metal particle iron powder is contained, amorphous FeS2 is replaced by crystalline FeS2 , and the mass ratio of S/Ketjen black mixture to crystalline FeS2 is 11.4:0.86, the rest are the same as in Example 5 same.
  • Comparative Example 4 except that the amorphous FeS2 was replaced by crystalline FeS2 , the average particle size of crystalline FeS2 and iron powder was 50nm, the mass of S/Ketjen black mixture, metal particle iron powder, and crystalline FeS2 The ratio is the same as in Example 5 except that the ratio is 11.7:0.2:0.43.
  • Example 1 to Example 15 Comparative Example 1 to Comparative Example 4, it can be seen that the capacity retention and specific capacity of the electrochemical device (button lithium-sulfur battery) obtained in Example 1 to Example 15 are higher than those of the Comparative Example 1 to Comparative Example 4, it shows that when the positive electrode material layer of the positive electrode sheet includes sulfur-based materials, amorphous metal sulfides and metal particles, the obtained electrochemical device has higher energy density and more excellent cycle performance.
  • Example 7 to Example 11 From Example 7 to Example 11, it can be seen that as the value of D1/D2 gradually increases, the capacity retention rate of the electrochemical device first increases and then decreases.
  • D1/D2 is in the range of 1 to 2.5, it has more excellent cycle stability. This is because when the value of D1/D2 is small (for example, less than 1), the specific surface of the metal particles is relatively small, and the catalytic polysulfide The rate of conversion decreases, thereby reducing the effect of reducing polysulfide shuttling; when the value of D1/D2 is large (for example, greater than 2.5), the specific surface of amorphous metal sulfide is relatively small at this time, and the polysulfide ion is connected. With fewer junctions, the rate of Li y MS x formation decreases, and the effect of reducing polysulfide shuttling decreases, thereby reducing the cycle performance of the electrochemical device.
  • Example 13 Example 16 and Example 17 that as the mass percentage of LiNO3 increases, the specific capacity of the 30th cycle and the capacity retention rate of the electrochemical device first increase and then decrease. The trend is small, but the specific capacity and capacity retention of the electrochemical device can be maintained in a high range when adding 2% to 3% LiNO 3 .
  • Example 18 From the comparison of Example 13 and Example 18, it can be seen that when the electrolyte solution includes a fluoroether solvent, the capacity retention rate of the electrochemical device can be further improved. From Example 18, Example 19, and Example 23, it can be seen that as the porosity of the positive electrode material layer decreases, the specific capacity of the first cycle and the specific capacity of the fifth cycle of the positive electrode material layer decrease slightly, and the specific capacity of the 30th cycle decreases. The capacity and capacity retention rate of the electrochemical device showed a trend of first increasing and then decreasing.

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Abstract

本申请提供了一种正极极片、包含该正极极片的电化学装置和电子装置，正极极片包含正极材料层，正极材料层包含硫基材料、无定形金属硫化物和金属粒子。具有本申请的正极极片的电化学装置具有高的能量密度和容量保持率。

Description

正极极片、包含该正极极片的电化学装置和电子装置 技术领域
本申请涉及储能技术领域，特别是涉及一种正极极片、包含该正极极片的电化学装置和电子装置。
背景技术
锂硫电池以其高比容量(1672mAh·g -1)以及正极材料硫价格低廉、储量丰富和环境友好等优点而备受关注，有望成为替代传统锂离子电池的下一代储能电池。随着近年来电动汽车和可移动电子设备的高速发展，人们对电池的比容量、安全性、循环性能等相关需求越来越高，期待着综合性能全面提升的新型电池的出现。
发明内容
本申请的目的在于提供一种正极极片、包含该正极极片的电化学装置和电子装置，以提高电化学装置的能量密度及循环稳定性。
本申请的第一方面提供了一种正极极片，正极极片包含正极材料层，正极材料层包含硫基材料、无定形金属硫化物和金属粒子。不限于任何理论，由于无定形金属硫化物中的金属位点在充放电循环过程中，可以作为连接多硫离子的连接点，形成可进行可逆反应的Li yMS x(x≥2，y≥2)，有效改善电化学装置中的穿梭效应；同时，金属粒子的导电性好，一方面，能够起到构建良好电子通路的作用，提高硫基材料的利用率，另一方面，能够催化多硫化物的转化，从而降低多硫化物的穿梭。此外，无定形金属硫化物也具有正极活性材料的特性，其不同于当下报道的用于抑制多硫离子穿梭的多孔碳材料、金属氧化物材料(如Co 3O 4、CoOOH等)，可以在改善穿梭效应的同时，提供容量。因此，在无定形金属硫化物和金属粒子的协同作用下，有利于同时提高比容量和容量保持率。在本申请中，金属粒子是指含有金属元素的金属颗粒。在本申请中，Li yMS x中的元素M为无定形金属硫化物中的金属元素；多硫化物可以包括但不限于Li 2S 4、Li 2S 6、Li 2S 8中的至少一种。
在本申请的一些实施方案中，金属粒子的表面具有无定形金属硫化物。例如，可以是无定形金属硫化物存在于金属粒子的部分表面，也可以是无定形金属硫化物存在于金属粒子的全部表面。不限于任何理论，当金属粒子的表面具有无定形金属硫化物时，更有利于正极材料层中颗粒与颗粒之间构建良好的电子通路，优化金属粒子与无定形金属硫化物产生的协同作用，进一步改善硫基材料的利用率和电化学装置中的穿梭效应，从而进一步提 高电化学装置的能量密度和循环稳定性。
在本申请的一些实施方案中，无定形金属硫化物和金属粒子中的金属元素各自独立地包括铁、铌、钼、钛或钨中的至少一种，优选为铁或钼中的至少一种。也即，无定形金属硫化物中的金属元素可以包括铁、铌、钼、钛或钨中的至少一种，金属粒子中的金属元素也可以包括铁、铌、钼、钛或钨中的至少一种，其中，无定形金属硫化物中的金属元素可以与金属粒子中的金属元素相同或者不相同。
在本申请的一些实施方案中，金属粒子和无定形金属硫化物中的金属原子数比为0.1至1。例如，金属粒子和无定形金属硫化物中的金属原子数比可以为0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9、1或为其间的任意范围。不限于任何理论，当金属粒子和无定形金属硫化物中的金属原子数比过小时(例如小于0.1)，金属粒子的金属原子数较少，不能有效构建正极材料层中颗粒与颗粒之间的电子通路，硫基材料的利用率下降，从而影响电化学装置的能量密度；当金属粒子和无定形金属硫化物中的金属原子数比过大时(例如大于1)，金属粒子中的金属原子数比无定形金属硫化物中的金属原子数多，容易导致金属粒子与电解液发生副反应，从而影响电化学装置的循环性能。因此，将金属粒子和无定形金属硫化物中的金属原子数比值调控在上述范围内，有利于提高电化学装置的能量密度和循环性能。
在本申请的一些实施方案中，基于硫基材料、无定形金属硫化物和金属粒子的质量之和，正极极片满足以下特征中的至少一者：(ⅰ)无定形金属硫化物的质量百分含量为2％至11％，优选为4％至8％；(ⅱ)金属粒子的质量百分含量为0.4％至5％，优选为0.4％至2％；(ⅲ)无定形金属硫化物和金属粒子中的金属元素总的质量百分含量为2％至10％，优选为2％至4％。例如，无定形金属硫化物的质量百分含量可以为2％、3％、4％、5％、6％、7％、8％、9％、10％、11％或为其间的任意范围。金属粒子的质量百分含量可以为0.4％、0.5％、0.8％、1％、1.5％、2％、2.5％、3％、3.5％、4％、4.5％、5％或为其间的任意范围。无定形金属硫化物和金属粒子中的金属元素总的质量百分含量可以为2％、3％、4％、5％、6％、7％、8％、9％、10％或为其间的任意范围。
不限于任何理论，当无定形金属硫化物的质量百分含量过低时(例如低于2％)，电化学装置在循环过程中会形成更多的不可进行可逆反应的多硫化物，最终造成正极极片中的硫基材料的损失，从而导致电化学装置在循环过程中的容量保持率逐渐降低。随着无定形金属硫化物的质量百分含量逐渐增加，正极材料层中有效的金属位点逐渐增多，与多硫离 子的连接位点也增多，从而生成的可进行可逆反应的多硫化物含量增加，电化学装置容量保持率则被有效提高。然而无定形金属硫化物提供的容量仅为硫基材料的四分之一到二分之一，因此其含量不宜过高(例如高于11％)。当其含量过高时，会导致能量密度的降低，同时也会带来成本的增加。因此，将无定形金属硫化物的质量百分含量调控在上述范围内，有利于提高电化学装置的容量保持率及能量密度。
不限于任何理论，当金属粒子的质量百分含量过低时(例如低于0.4％)，不能有效构建正极材料层中颗粒与颗粒之间的电子通路，硫基材料的利用率下降，从而影响电化学装置的能量密度；同时，催化多硫化物转化的速率降低，从而降低循环性能。随着金属粒子的质量百分含量增加，硫基材料的利用率提高，从而有利于电化学装置能量密度的提升；但是当金属粒子的质量百分含量过高时(例如高于5％)，随着金属粒子的质量百分含量增加，正极材料层中的硫基材料和无定形金属硫化物的质量百分含量下降，导致比容量下降，进而影响电化学装置的能量密度。此外，过多的金属粒子易于与电解液发生副反应，从而影响电化学装置的循环性能。因此，将金属粒子的质量百分含量调控在上述范围内，有利于提高电化学装置的能量密度和循环性能。
不限于任何理论，当无定形金属硫化物和金属粒子中的金属元素总的质量百分含量过低时(例如低于2％)，对电化学装置的容量保持率改善效果不明显；当无定形金属硫化物和金属粒子中的金属元素总的质量百分含量过高时(例如高于10％)，导致正极材料层中的正极硫基材料质量百分含量下降，影响电化学装置的能量密度。因此，将无定形金属硫化物和金属粒子中的金属元素总的质量百分含量调控在上述范围内，有利于提高电化学装置的容量保持率和能量密度。
关于上述无定形金属硫化物和金属粒子的质量百分含量以及无定形金属硫化物和金属粒子中的金属元素总的质量百分含量的测量方法，当硫基材料为单质硫及硫化锂时：对正极极片上的粉末进行电感耦合等离子光谱测试(ICP)，即可得到其中金属元素的质量分数，对正极极片上的粉末采用碳硫分析仪测试可以得到硫元素的质量分数。在采用单质硫的体系中，正极材料层仅含有S元素及金属元素，因此根据得到的值，可以换算得到无定形金属硫化物和金属粒子的质量百分含量以及无定形金属硫化物和金属粒子中的金属元素总的质量百分含量。在采用硫化锂的体系中，根据金属粒子和无定形金属硫化物中的金属原子数比可计算出硫基材料中S元素的质量分数，即可进一步计算得到Li 2S的质量分数，从而可进一步换算得到无定形金属硫化物和金属粒子的质量百分含量以及无定形金属 硫化物和金属粒子中的金属元素总的质量百分含量。当硫基材料为有机硫化物或高分子碳-硫材料时，正极材料层包含有机硫化物或高分子碳-硫材料、金属粒子、金属硫化物。对于该体系，首先可以采用红外-质谱-热重分析仪联用的方法分析得到有机硫化物或者高分子碳-硫材料在极片中的含量；然后，通过ICP测试得到金属元素质量分数，接着通过ToF-SIMS测试可以得到金属硫化物中多硫离子具体的链长，根据金属粒子和金属硫化物中金属元素的比值，从而可以计算得到无定形金属硫化物和金属粒子的质量百分含量以及无定形金属硫化物和金属粒子中的金属元素总的质量百分含量。
在本申请的一些实施方案中，无定形金属硫化物的平均粒径为D1，金属粒子的平均粒径为D2，满足：D1/D2为0.5至3.5，优选1至2.5。例如，D1/D2的值可以为0.5、1、1.5、2、2.5、3、3.5或为其间的任意范围。不限于任何理论，当D1/D2的值过小时(例如小于0.5)，即金属粒子的比表面相对较小，不利于金属粒子在正极材料层中很好的分散，即不利于电子传输通路的构建。此外，金属粒子比表面足够大时与无定形金属硫化物协同有助于催化多硫化物转化，因此当金属粒子比表面相对较小时，该种效应会减弱，导致提升电化学装置循环性能的效果降低；当D1/D2的值过大时(例如大于3.5)，此时无定形金属硫化物的比表面相对较小，连接多硫离子的连接点减少，形成Li yMS x的速率降低，减少多硫化物穿梭的效果降低，从而降低电化学装置的循环性能。因此，将D1/D2的值调控在上述范围内，有利于提高电化学装置的循环性能。
在本申请的一些实施方案中，无定形金属硫化物的平均粒径D1为20nm至500nm。例如，无定形金属硫化物的平均粒径可以为20nm、50nm、100nm、150nm、200nm、250nm、300nm、350nm、400nm、450nm、500nm或为其间的任意范围。不限于任何理论，当无定形金属硫化物的平均粒径过小时(例如小于20nm)，颗粒与颗粒之间容易团聚，导致无定形金属硫化物分布不均匀，影响电化学装置的容量保持率；当无定形金属硫化物的平均粒径过大时(例如大于500nm)，其比表面降低，连接多硫离子的连接点减少，形成Li yMS x的速率降低，减少多硫化物穿梭的效果降低，从而影响电化学装置的容量保持率。因此，通过调控无定形金属硫化物的平均粒径在上述范围内，有利于提高电化学装置的循环性能。
本申请对金属粒子的平均粒径没有特别限定，只要使得D1/D2满足本申请范围、实现本申请目的即可，例如D2可以为15nm至500nm。
在本申请的一些实施方案中，正极材料层的孔隙率为20％至45％，优选为30％至45％。例如，正极材料层的孔隙率为20％、23％、25％、28％、30％、33％、35％、38％、45％或 为其间的任意范围。不限于任何理论，当正极材料层的孔隙率过小时(例如小于20％)，影响锂离子的传输，从而影响电化学装置的动力学性能；当正极材料层的孔隙率过大时(例如大于45％)，容易导致金属粒子与电解液发生副反应，并且会降低正极材料层中硫基材料的含量，从而降低电化学装置的循环性能和能量密度。因此，通过调控正极材料层的孔隙率在上述范围内，有利于提高电化学装置的动力学性能和循环性能。
在本申请的一些实施方案中，正极极片满足以下特征中的至少一者：(ⅳ)硫基材料包括单质硫、硫化锂、含硫的有机化合物或高分子碳-硫材料中的至少一种；(ⅴ)正极材料层还包含载硫材料，载硫材料包括科琴黑、碳纳米管、碳纳米线、介孔碳、微孔碳、石墨烯、金属氧化物或金属氮化物中的至少一种；(ⅵ)正极材料层还包含导电剂，导电剂包括碳纳米管、碳纳米片、石墨烯、石墨、炭黑或导电聚合物中的至少一种。
上述碳纳米管可以包括单壁碳纳米管和多壁碳纳米管中的至少一种。在本申请中，对导电聚合物没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于聚苯胺、聚噻吩、聚乙炔或聚吡咯中的至少一种。
本申请对含硫有机化合物没有特别限制，只要能够实现本申请目的即可，例如含硫有机化合物可以包括但不限于硫醚、蒽醌硫化物、苯醌硫化物中的至少一种。高分子碳-硫材料是指由高分子材料与单质硫混合热处理后形成的物质，其中，硫可以S 2到S 6小分子存在，并且形成的物质中存在C-S键。其中，本申请对高分子材料没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于聚丙烯腈、聚乙烯吡咯烷酮中的至少一种。本申请对热处理温度没有特别限制，只要能实现本申请的目的即可，例如热处理温度为150℃至300℃。具体地，高分子碳-硫材料可以包括但不限于硫/聚丙烯腈、硫/聚乙烯吡咯烷酮中的至少一种。
本申请的第二方面提供了一种电化学装置，包含本申请任一实施方案中的正极极片，得到的电化学装置具有高的能量密度和容量保持率。
在本申请的一些实施方案中，电化学装置还包括电解液，电解液包括硝酸锂。不限于任何理论，电解液中加入硝酸锂，一方面，有助于提高对多硫化物的溶解，增加硫正极的利用率；有助于调节硫正极的沉积形貌，缓解正极的钝化；另一方面，有助于在负极表面形成保护膜，防止电解液的消耗，并抑制锂枝晶的形成，从而提高电化学装置的安全性和循环稳定性。
在本申请的一些实施方案中，基于电解液的质量，硝酸锂的质量百分含量为1％至3％， 优选为2％至3％。例如，硝酸锂的质量百分含量可以为1％、1.2％、1.4％、1.6％、1.8％、2％、2.2％、2.4％、2.6％、2.8％、3％或为其间的任意范围。不限于任何理论，当硝酸锂的质量百分含量过低时(例如低于1％)，硝酸锂对电化学装置性能改善不显著。当硝酸锂含量过高时(例如高于3％)，硝酸锂在低电位下的分解会加剧，导致电化学装置的性能恶化，同时硝酸锂的过量加入也会对锂硫电池带来更大的安全隐患。因此，通过调控硝酸锂的质量百分含量在上述范围内，有利于提高电化学装置的安全性和循环稳定性。
在本申请的一些实施方案中，电解液还包括氟代醚。不限于任何理论，氟代醚有助于在负极侧形成稳定的SEI层，可以避免多硫化物穿梭到负极造成的不可逆的消耗，同时氟代醚具有较高的闪点甚至无闪点，有利于抑制电解液的燃烧，能够提高电化学装置的耐高温性能。本申请对氟代醚没有特别限制，只要能实现本申请的目的即可，例如可以包括但不限于四氟乙基四氟丙基醚、四氟乙基三氟丙基醚、十氟甲氧基三氟甲基戊烷、双(三氟乙基)醚中的至少一种。本申请对氟代醚类溶剂的含量没有特别限制，只要能实现本申请的目的即可，例如，基于电解液溶剂总体积，氟代醚的体积百分含量为10％至50％，优选为20％至40％。
本申请的正极极片还包括正极集流体，其中，正极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包含但不限于铝箔、铝合金箔或复合集流体等。在本申请中，对正极集流体的厚度没有特别限制，只要能够实现本申请目的即可，例如，正极集流体的厚度为8μm至12μm。
任选地，正极极片还可以包括导电层，导电层位于正极集流体和正极材料层之间。本申请对导电层的组成没有特别限制，可以是本领域常用的导电层，例如，可以包括但不限于粘结剂和上述导电剂。本申请对粘结剂没有特别限制，只要能够实现本申请目的即可，例如，可以包含聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、羧甲基纤维素、羧甲基纤维素钠、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶或聚偏氟乙烯中的至少一种。
本申请的电化学装置还包括负极极片，本申请中的负极极片没有特别限制，只要能实现本申请的目的即可，例如，负极极片通常包括负极集流体和负极材料层。其中，负极集流体没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体等。在本申请中，对负极的集流体的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极的集流体的厚度 为4μm至12μm。负极材料层中通常包括负极活性材料，负极活性材料没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于锂金属、含锂化合物(例如钛酸锂)、锂合金(例如锂铜合金)、中间相碳微球、软碳、硬碳、硅或硅碳等中的至少一种。
在本申请中，负极材料层中还可以包括导电剂，本申请对导电剂没有特别限制，只要能够实现本申请目的即可，例如，可以包括但不限于上述导电剂中的至少一种。
在本申请中，负极材料层中还可以包括粘结剂，本申请对粘结剂没有特别限制，只要能够实现本申请目的即可，例如，可以包括但不限于上述粘结剂中的至少一种。
任选地，负极极片还可以包括导电层，导电层位于负极集流体和负极材料层之间。本申请对导电层的组成没有特别限制，可以是本领域常用的导电层，导电层可以包括但不限于上述导电剂和上述粘结剂。
本申请的电化学装置还包括隔离膜，本申请对隔离膜没有特别限制，只要能够实现本申请目的即可，例如，可以包括但不限于聚乙烯(PE)、聚丙烯(PP)、聚四氟乙烯为主的聚烯烃(PO)类隔膜、聚酯膜(例如聚对苯二甲酸二乙酯(PET)膜)、纤维素膜、聚酰亚胺膜(PI)、聚酰胺膜(PA)，氨纶或芳纶膜、织造膜、非织造膜(无纺布)、微孔膜、复合膜、隔膜纸、碾压膜或纺丝膜等中的至少一种。本申请的隔离膜可以具有多孔结构，孔径的尺寸没有特别限制，只要能实现本申请的目的即可，例如，孔径的尺寸可以为0.01μm至1μm。在本申请中，隔离膜的厚度没有特别限制，只要能实现本申请的目的即可，例如，隔离膜的厚度可以为5μm至500μm。
例如，隔离膜可以包括基材层和表面处理层。基材层可以为具有多孔结构的无纺布、膜或复合膜，基材层的材料可以包括但不限于聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯或聚酰亚胺等中的至少一种。任选地，可以使用聚丙烯多孔膜、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。任选地，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。
无机物层可以包括无机颗粒和粘结剂，本申请对无机颗粒没有特别限制，例如，可以包括但不限于氧化铝、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、氢氧化钙或硫酸钡等中的至少一种。本申请对粘结剂没有特别限制，例如，可以包括但不限于聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯 酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。聚合物层中包含聚合物，聚合物的材料可以包括但不限于聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)等中的至少一种。
本申请的电化学装置中的电解液还可以包括锂盐和非水溶剂。本申请对锂盐没有特别限制，只要能实现本申请的目的即可，例如，可以包括但不限于LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiB(C 6H 5) 4、LiCH 3SO 3、LiCF 3SO 3、LiN(SO 2CF 3) 2、LiC(SO 2CF 3) 3、LiSiF 6、LiBOB或二氟硼酸锂中的至少一种。
本申请中使用到的非水溶剂包含醚类化合物，具体可以包括但不限于二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃或四氢呋喃中的至少一种。上述其它有机溶剂可以包括但不限于二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈中的至少一种。
电化学装置的制备过程为本领域技术人员所熟知的，本申请没有特别的限制，例如，可以包括但不限于以下步骤：将正极极片、隔离膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作后放入壳体内，将电解液注入壳体并封口。此外，也可以根据需要将防过电流元件、导板等置于壳体中，从而防止电化学装置内部的压力上升、过充放电。
本申请的第三方面提供了一种电子装置，包含本申请上述实施方案中所述的电化学装置。
本申请的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
本申请提供了一种正极极片、包含该正极极片的电化学装置和电子装置，正极极片包含正极材料层，正极材料层包含硫基材料、无定形金属硫化物和金属粒子。由于无定形金属硫化物中的金属位点在充放电循环过程中，可以作为连接多硫离子的连接点，形成可进 行可逆反应的Li yMS x，有效改善电化学装置的穿梭效应；同时，金属粒子的导电性好，一方面，能够起到构建良好电子通路的作用，提高硫基材料的利用率，另一方面，能够催化多硫化物的转化，从而降低多硫化物的穿梭。此外，无定形金属硫化物也具有正极活性材料的特性，提高正极材料层的比容量。因此，在无定形金属硫化物和金属粒子的协同作用下，有利于提高电化学装置的能量密度和容量保持率。
附图说明
为了更清楚地说明本申请和现有技术的技术方案，下面对实施例和现有技术中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例。
图1为本申请实施例9、实施例19、对比例1、对比例3和对比例4的电化学装置的正极极片放电比容量随循环圈数的变化曲线图。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图和实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员所获得的所有其他技术方案，都属于本申请保护的范围。
需要说明的是，本申请的具体实施方式中，以锂硫电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂硫电池。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。另外，只要无特别说明，“份”、“％”为质量基准。
测试方法：
金属粒子和无定形金属硫化物中的金属原子数比值测试：
以金属粒子铁粉和无定形二硫化亚铁(FeS 2)为例，对正极材料层进行X射线光电子能谱(XPS)测试，得到Fe-2p谱图，对Fe-2p谱图进行分峰得到Fe和Fe-S的衍射峰，并计算Fe和Fe-S的衍射峰峰面积的比值。随机选择正极材料层的两处不同的位置进行测试，每处分别溅射0s、100s、200s进行测试并分峰计算比值，取最终的平均值为金属粒子和无定形金属硫化物中的金属原子数比值X。
金属元素总的质量百分含量、金属粒子和金属硫化物的质量百分含量测试：
对正极极片上的粉末进行电感耦合等离子光谱测试(ICP)，即可得到其中金属元素的质量分数m1，对正极极片上的粉末采用碳硫分析仪测试可以得到硫元素的质量分数m2。
金属元素总的质量百分含量＝m1/(m1+m2)；
金属粒子的质量百分含量＝(X/(1+X))×(m1/(m1+m2))；
金属硫化物的质量百分含量＝(1/(1+X))×(m1/(m1+m2))×M1/M2；
其中M1为金属硫化物的摩尔质量，M2为金属元素的摩尔质量，X为金属粒子和无定形金属硫化物中的金属原子数比值X。
无定形金属硫化物的平均粒径D1以及金属粒子的平均粒径D2测试：
以无定形金属硫化物的平均粒径D1为例，利用透射电子显微镜拍摄样品照片，然后，使用图像解析软件，随机选取50个无定形金属硫化物，求出这些无定形金属硫化物各自的面积，接着，假设无定形金属硫化物是球形，通过以下公式求出各自的粒径R(直径)：R＝2×(S1/π) 1/2；其中，S1为无定形金属硫化物的面积；并将所得50个无定形金属硫化物的粒径进行算数平均，从而求得所述无定形金属硫化物的平均粒径D1。
金属粒子的平均粒径D2同上述无定形金属硫化物的平均粒径D1测试。
正极材料层孔隙率测试：
本申请中，孔隙率表示正极材料层中孔隙的体积占正极材料层总体积的百分比，可以使用气体置换法进行测试。孔隙率P＝(V-V0)/V×100％，V0表示真体积，V表示表观体积。测试时采用的气体压力值为19.5PSI。
循环性能测试：
对制备得到的电池采用蓝电(LAND)设备进行测试，测试程序设置为，前4圈采用0.05C小倍率循环活化，5至30圈采用0.3C倍率循环。记录首圈(0.05C)的放电比容量、第5圈(0.3C)的放电比容量、第30圈(0.3C)的放电比容量，并计算以0.3C循环时，第30圈相对于第5圈的容量保持率。其中，首圈比容量、第5圈比容量、第30圈比容量按照下式计算：比容量＝放电容量/(极片总质量-集流体质量)。
实施例1
<正极极片的制备>
该实施例中硫基材料采用单质态的升华硫，并引入科琴黑作为载硫材料。将升华硫(S)和科琴黑按照质量比为8∶2在155℃下热处理12h，得到S/科琴黑混合物，再将S/科琴黑混合物、平均粒径为500nm的金属粒子铁粉、平均粒径为500nm的无定形金属硫化物二硫化亚铁(FeS 2)按照质量比为12.1∶0.1∶0.215混合并研磨得到混合物，将混合物、导电炭黑(Super P)、聚偏氟乙烯(PVDF)按照质量比为8∶1∶1混合，然后加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成为固含量为20％的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为10μm的正极集流体铝箔的一个表面上，涂层厚度为60μm，60℃条件下烘干，然后在1吨压力下进行冷压处理，得到正极材料层孔隙率为41％的正极极片。涂布完成后，将正极极片利用冲压机在干燥环境中切成直径为1.4cm的圆片待用。
<负极极片的制备>
采用厚度为10μm金属锂片，利用冲压机在干燥环境中切成直径为1.4cm的圆片待用。
<电解液的制备>
在干燥氩气气氛中，将1,3二氧戊环(DOL)和二甲醚(DME)按照体积比为1∶1进行混合，然后加入双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2(LiTFSI)和LiNO 3溶解并混合均匀，得到电解液。其中，LiTFSI在电解液中的浓度为1mol/L，LiNO 3在电解液中的质量浓度为2％。
<隔离膜的制备>
采用厚度为7μm的聚乙烯(PE)薄膜(Celgard公司提供)，利用冲压机在干燥环境中切成直径为1.9cm的圆片待用。
<锂硫电池的制备>
将上述制备得到的正极极片、隔离膜、负极极片按顺序叠好，置于封装壳内，注入电解液，然后在封装机上进行封装得到扣式锂硫电池。
实施例2至实施例4中，除了按照表1调整D1和D2以外，其余与实施例1相同。
实施例5中，除了硫基材料/科琴黑、金属粒子、无定形金属硫化物的质量比为11.7：0.2：0.43以外，其余与实施例3相同。
实施例6中，除了硫基材料/科琴黑、金属粒子、无定形金属硫化物的质量比为10.5：0.5：1.07以外，其余与实施例3相同。
实施例7除了硫基材料/科琴黑、金属粒子、无定形金属硫化物的质量比为11.3：0.11： 0.6以外，其余与实施例3相同。
实施例8至实施例11中，除了按照表1调整D2的值，其余与实施例7相同。
实施例12中，除了硫基材料/科琴黑、金属粒子、无定形金属硫化物的质量比为11.5：0.04：0.78以外，其余与实施例3相同。
实施例13中，除了在<正极极片的制备>步骤中将升华硫、科琴黑和粒径为50nm的铁粉按照质量比为9.6：2.4：0.4在155℃下热处理12h，得到升华硫、科琴黑、金属粒子铁粉及无定形铁的硫化物(FeS 2)的混合物，将上述混合物、Super P、PVDF按照质量比为8∶1∶1混合制备浆料，其余与实施例3相同。
实施例14中，除了采用钼粉替换铁粉、无定形三硫化钼(MoS 3)替换无定形二硫化亚铁，其余与实施例2相同。
实施例15中，除了采用铌粉替换铁粉、无定形三硫化铌(NbS 3)替换无定形二硫化亚铁，其余与实施例2相同。
实施例16和实施例17中，除了按照表2所示调整LiNO 3在电解液中的质量浓度以外，其余与实施例13相同。
实施例18中，除了在<电解液的制备>步骤中采用1,1,2,2-四氟乙基-2,2,3,3-四氟丙醚替换80％体积的DOL以外(即体积比1,1,2,2-四氟乙基-2,2,3,3-四氟丙醚：DOL:DME＝4：1：5)，其余与实施例13相同。
实施例19中，除了在<正极极片的制备>步骤中，将得到的正极极片在3吨的压力下进行冷压，调整正极材料层的孔隙率为31％，其余与实施例18相同。
实施例20中，除了在<电解液的制备>步骤中溶剂体积比为1,1,2,2-四氟乙基-2,2,3,3-四氟丙醚：DOL：DME＝10：40：50之外，其余均与实施例19相同。
实施例21中，除了在<电解液的制备>步骤中溶剂体积比为1,1,2,2-四氟乙基-2,2,3,3-四氟丙醚：DOL：DME＝20：30：50之外，其余均与实施例19相同。
实施例22中，除了在<电解液的制备>步骤中溶剂体积比为1,1,2,2-四氟乙基-2,2,3,3-四氟丙醚：DME＝50：50之外，其余均与实施例19相同。
实施例23中，除了冷压压力为9吨，调整正极材料层的孔隙率为22％，其余与实施例19相同。
对比例1中，除了不含金属粒子铁粉和无定形金属硫化物FeS 2以外，其余与实施例1相同。
对比例2中，除了不含无定形金属硫化物FeS 2、S/科琴黑混合物与50nm铁粉的质量比为12∶0.4以外，其余与实施例5相同。
对比例3中，除了不含金属粒子铁粉、将无定形FeS 2替换为晶态FeS 2、S/科琴黑混合物与晶态FeS 2的质量比为11.4∶0.86以外，其余与实施例5相同。
对比例4中，除了将无定形FeS 2替换为晶态FeS 2、晶态FeS 2和铁粉的平均粒径为50nm、S/科琴黑混合物、金属粒子铁粉、晶态FeS 2的质量比为11.7∶0.2∶0.43以外，其余与实施例5相同。
表1
Figure PCTCN2021107662-appb-000001
Figure PCTCN2021107662-appb-000002
注：表1中的“-”表示不存在该对应的物质或参数。
表2
Figure PCTCN2021107662-appb-000003
Figure PCTCN2021107662-appb-000004
注：表2中的“-”表示不存在该对应的物质或参数。
从实施例1至实施例15、对比例1至对比例4可以看出，实施例1至实施例15得到的电化学装置(扣式锂硫电池)的容量保持率和比容量均比对比例1至对比例4的高，表明当正极极片的正极材料层中同时包括硫基材料、无定形金属硫化物和金属粒子时，得到的电化学装置具有更高的能量密度以及更优异的循环性能。
从实施例7至实施例11可以看出，随着D1/D2的值逐渐增大，电化学装置的容量保持率呈现先增大后减小的趋势。当D1/D2在1至2.5的范围内时，具有更加优异的循环稳定性这是由于当D1/D2的值较小时(例如小于1)，金属粒子的比表面相对较小，催化多硫化物转化的速率降低，从而导致减少多硫化物穿梭的效果降低；当D1/D2的值较大时(例如大于2.5)，此时无定形金属硫化物的比表面相对较小，连接多硫离子的连接点减少，形成Li yMS x的速率降低，减少多硫化物穿梭的效果降低，从而降低电化学装置的循环性能。
参考表2，从实施例13、实施例16和实施例17可以看出，随着LiNO 3的质量百分含量增加，第30圈比容量和电化学装置的容量保持率呈现先增大后减小的趋势，但在添加2％至3％的LiNO 3时，电化学装置的比容量和容量保持率能够保持在一个较高的范围内。
从实施例13和实施例18的对比可以看出，当电解液中包括氟代醚类溶剂时，可以进一步提高电化学装置的容量保持率。从实施例18、实施例19、实施例23可以看出，随着正极材料层孔隙率减小，正极材料层的首圈比容量和第5圈比容量有小幅度的降低、第30圈比容量、电化学装置的容量保持率呈现先增大后减小的趋势。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (14)

  1. 一种正极极片，所述正极极片包含正极材料层，所述正极材料层包含硫基材料、无定形金属硫化物和金属粒子。
  2. 根据权利要求1所述的正极极片，其中，所述金属粒子的表面具有所述无定形金属硫化物。
  3. 根据权利要求1所述的正极极片，其中，所述无定形金属硫化物和所述金属粒子中的金属元素各自独立地包括铁、铌、钼、钛或钨中的至少一种。
  4. 根据权利要求1所述的正极极片，其中，所述金属粒子和所述无定形金属硫化物中的金属原子数比为0.1至1。
  5. 根据权利要求1所述的正极极片，其中，基于所述硫基材料、所述无定形金属硫化物和所述金属粒子的质量之和，所述正极极片满足以下特征中的至少一者：
    (ⅰ)所述无定形金属硫化物的质量百分含量为2％至11％；
    (ⅱ)所述金属粒子的质量百分含量为0.4％至5％；
    (ⅲ)所述无定形金属硫化物和所述金属粒子中的金属元素总的质量百分含量为2％至10％。
  6. 根据权利要求1所述的正极极片，其中，所述无定形金属硫化物的平均粒径为D1，所述金属粒子的平均粒径为D2，满足：D1/D2为0.5至3.5。
  7. 根据权利要求1所述的正极极片，其中，所述无定形金属硫化物的平均粒径D1为20nm至500nm。
  8. 根据权利要求1所述的正极极片，其中，所述正极材料层的孔隙率为20％至45％。
  9. 根据权利要求1所述的正极极片，其中，所述正极极片满足以下特征中的至少一者：
    (ⅳ)所述硫基材料包括单质硫、硫化锂、含硫的有机化合物或高分子碳-硫材料中的至少一种；
    (ⅴ)所述正极材料层还包含载硫材料，所述载硫材料包括科琴黑、碳纳米管、碳纳米线、介孔碳、微孔碳、石墨烯、金属氧化物或金属氮化物中的至少一种；
    (ⅵ)所述正极材料层还包含导电剂，所述导电剂包括碳纳米管、碳纳米片、石墨烯、石墨、炭黑或导电聚合物中的至少一种。
  10. 一种电化学装置，其包括权利要求1至9中任一项所述的正极极片。
  11. 根据权利要求10所述的电化学装置，所述电化学装置还包括电解液，所述电解液包括硝酸锂。
  12. 根据权利要求11所述的电化学装置，基于所述电解液的质量，所述硝酸锂的质量百分含量为1％至3％。
  13. 根据权利要求11所述的电化学装置，所述电解液还包括氟代醚。
  14. 一种电子装置，其包括权利要求10至13中任一项所述的电化学装置。
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