WO2024113992A1 - 一种用于钠离子电池的正极极片及钠离子电池 - Google Patents

一种用于钠离子电池的正极极片及钠离子电池 Download PDF

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WO2024113992A1
WO2024113992A1 PCT/CN2023/115855 CN2023115855W WO2024113992A1 WO 2024113992 A1 WO2024113992 A1 WO 2024113992A1 CN 2023115855 W CN2023115855 W CN 2023115855W WO 2024113992 A1 WO2024113992 A1 WO 2024113992A1
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sodium
positive electrode
electrode sheet
mof
transition metal
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PCT/CN2023/115855
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English (en)
French (fr)
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秦猛
官英杰
杨惠玲
许跃
温严
黄起森
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宁德时代新能源科技股份有限公司
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Publication of WO2024113992A1 publication Critical patent/WO2024113992A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • 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
    • 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 a positive electrode sheet of a sodium ion battery, which comprises one or more functional coatings selected from a molecular sieve coating or an MOF coating.
  • the present application also relates to a sodium ion secondary battery comprising the positive electrode sheet and an electrical device comprising the secondary battery.
  • Lithium-ion batteries are now widely used in pure electric vehicles, hybrid electric vehicles, and smart grids. However, as the price of lithium mineral resources continues to rise, the power battery industry is constantly looking for other ways to reduce costs, one of the most important of which is the development of sodium-ion batteries.
  • Sodium-ion batteries are a type of secondary battery that relies mainly on the embedding and deintercalation of sodium ions between the positive and negative electrodes. During the charge and discharge process, Na + is intercalated and deintercalated back and forth between the two electrodes: during charging, Na + is deintercalated from the positive electrode and embedded in the negative electrode through the electrolyte; during discharge, the opposite is true. Its working principle is similar to that of lithium-ion batteries.
  • sodium has a more active chemical property and is more reactive with water, so sodium ion batteries need to remove water more.
  • sodium ion batteries have poor oxidation resistance at high voltages and are prone to forming sodium dendrites.
  • the positive electrode sheet is immersed in an organic solvent, which easily produces a solvated structure, resulting in a decrease in coulombic efficiency. Therefore, the art needs to develop a positive electrode sheet for sodium ion batteries, which can improve oxidation resistance at high voltages, inhibit the formation of sodium dendrites, and improve the cycle performance of sodium ion batteries.
  • the present disclosure aims to solve at least one of the technical problems in the related art to a certain extent.
  • one purpose of the present disclosure is to provide a positive electrode sheet for a sodium ion battery, which can improve the oxidation resistance at the high voltage of the sodium ion battery and effectively inhibit the growth of sodium dendrites, thereby solving the technical problem in the prior art that the growth of sodium dendrites leads to a decrease in the cycle efficiency of the sodium ion battery and an increase in the safety risk.
  • the first aspect of the present application provides a positive electrode plate of a sodium ion battery, wherein the plate includes a functional coating, wherein the functional coating includes one or more coatings selected from the group consisting of a molecular sieve coating and a MOF coating.
  • the positive electrode plate of the present application can change the solvation structure composition of the sodium salt, reduce the desolvation energy, inhibit trace but continuous oxidative decomposition, greatly improve the oxidation resistance of the electrolyte in the sodium battery, and thus inhibit the formation of sodium dendrites.
  • the thickness of the functional coating is 0.3-20 ⁇ m, optionally 0.5-15 ⁇ m, and further optionally 1-8 ⁇ m.
  • the thickness of the functional coating has a substantial impact on the formation of sodium dendrites and the cycle performance of sodium ion batteries. If the functional coating is too thick, the battery energy density decreases; if the functional coating is too thin, the solvation structure cannot be effectively changed, resulting in limited effect of improving oxidation resistance.
  • the molecular sieve in the molecular sieve coating includes one or more of 3A (potassium A type), 4A (sodium A type), 5A (calcium A type), 10Z (calcium Z type), 13Z (sodium Z type), Y (sodium Y type), and sodium mordenite type molecular sieves.
  • the MOF in the MOF coating is selected from one or more of Fe-MOF, Ni-MOF, Co-MOF, Mn-MOF, and Cu-MOF. By selecting different coating materials, the coulombic efficiency and cycle performance of the sodium ion battery can be further adjusted.
  • the positive electrode sheet comprises a positive electrode active material layer, and the positive electrode active material comprises one or more of a layered transition metal oxide, a polyanion compound, and a Prussian blue analog.
  • the layered transition metal oxide comprises Na x MO 2 , wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, and 0 ⁇ x ⁇ 1.
  • the polyanionic compound comprises a class of compounds having sodium ions, transition metal ions and tetrahedral (YO 4 ) n- anion units, wherein the transition metal comprises at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y comprises at least one of P, S and Si, and n represents the valence state of (YO 4 ) n- ; or the polyanionic compound comprises a class of compounds having sodium ions, transition metal ions, tetrahedral (YO 4 ) n- anion units and halogen anions, wherein the transition metal comprises at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y comprises at least one of P, S and Si, n represents the valence state of (YO 4 ) n- , and the halogen comprises at least one of F, Cl and Br; or the polyanionic compound comprises a class of compounds
  • the Prussian blue analogue comprises a class of compounds having sodium ions, transition metal ions and cyanide ions ( CN- ), wherein the transition metal comprises at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce.
  • the positive electrode active material comprises NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 , NaFePO 4 , Na 3 V 2 (PO 4 ) 3 and NaMnFe(CN) 6 .
  • the functional coating layer covers the positive electrode active material layer.
  • the amount of the functional coating is 1-5% by weight, optionally 1.5-2.5% by weight, based on the total weight of the positive electrode active material layer and the functional coating in the positive electrode sheet.
  • a second aspect of the present application provides a sodium ion secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet comprises the positive electrode sheet according to the first aspect of the present application.
  • the electrolyte is an electrolyte formed by dissolving a sodium salt electrolyte in a solvent.
  • the solvent includes an ether solvent, optionally including ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and one or more of crown ethers.
  • the sodium salt electrolyte includes sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium bisoxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate, and sodium bis(trifluoromethylsulfonyl)imide.
  • the negative electrode includes a sodium metal negative electrode, a carbon material negative electrode, and other non-carbon material negative electrodes.
  • the molar concentration of the sodium salt electrolyte is 0.5 mol/L to 8 mol/L, optionally 1 mol/L to 4 mol/L.
  • a third aspect of the present application provides an electrical device, which includes the sodium ion secondary battery according to the second aspect of the present application.
  • FIG. 1 is a schematic diagram of a sodium ion secondary battery in one embodiment of the present application.
  • FIG. 2 is an exploded view of the sodium ion secondary battery in one embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery pack in one embodiment of the present application.
  • FIG. 4 is an exploded view of the battery pack shown in FIG. 3 according to one embodiment of the present application.
  • FIG. 5 is a schematic diagram of a device in which a battery pack is used as a power source in one embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, and any upper limit can be combined with any other upper limit to form an undefined range.
  • each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an undefined range.
  • Sodium-ion batteries have obvious cost advantages over lithium-ion batteries and are currently developing rapidly.
  • sodium is more chemically active than lithium and is prone to solvation with organic solvents in the electrolyte at high operating voltages, making it more susceptible to oxidation.
  • the porosity and size effect of the functional coating can change the solvation structure composition of the sodium salt, reduce the desolvation energy, inhibit trace but continuous oxidative decomposition, and greatly improve the oxidation resistance of the electrolyte in the sodium ion battery.
  • the high reversibility of the anode of the sodium ion battery is also well protected.
  • the first aspect of the present application provides a positive electrode plate of a sodium ion battery, the plate comprising a functional coating, wherein the functional coating comprises one or more coatings selected from a molecular sieve coating or a MOF coating.
  • the applied functional coating has a large number of voids of different sizes, thereby generating a certain size effect.
  • the solvation structure formed by sodium ions in the organic solvent in the electrolyte is changed, the desolvation energy is reduced, and the trace but continuous oxidative decomposition is inhibited.
  • the inhibition of oxidative decomposition greatly improves the oxidation resistance of the electrolyte in the sodium battery, thereby inhibiting the formation of sodium dendrites.
  • the thickness of the functional coating is 0.3-20 ⁇ m, optionally 0.5-15 ⁇ m, and further optionally 1-8 ⁇ m.
  • the functional coating can be coated on the positive electrode active material layer of the positive electrode plate by various suitable coating methods, such as by spraying, scraping, roller coating or dip coating.
  • the thickness of the functional coating has a substantial impact on the formation of sodium dendrites and the cycle performance of sodium ion batteries. If the functional coating is too thick, the battery energy density will decrease; if the functional coating is too thin, the solvation structure cannot be effectively changed, resulting in limited effect of improving antioxidant properties.
  • the molecular sieve in the molecular sieve coating is selected from one or more of 3A (potassium A type), 4A (sodium A type), 5A (calcium A type), 10Z (calcium Z type), 13Z (sodium Z type), Y (sodium Y type), and sodium mordenite type molecular sieves.
  • Conventional molecular sieves are artificially synthesized hydrated aluminosilicates (zeolites) or natural zeolites that have the function of screening molecules.
  • M′ 2 M O ⁇ Al 2 O 3 ⁇ xSiO 2 ⁇ yH 2 O
  • M′ and M are monovalent and divalent cations such as K + , Na + , Ca 2+ and Ba 2+ , respectively. It has many channels with uniform pore sizes and neatly arranged pores in its structure.
  • Molecular sieves of different pore sizes separate molecules of different sizes and shapes. Molecular sieves of different pore sizes can be obtained according to the different molecular ratios of SiO 2 and Al 2 O 3.
  • Molecular sieves with different crystal structures can generally be classified, such as 3A type, 4A type, and 5A type molecular sieves.
  • Type 4A is a type A molecular sieve with a pore size of The A-type molecular sieve containing Na + is recorded as Na-A; if the Na + is replaced by K + , the pore size is about That is 3A type molecular sieve; if more than 1/3 of Na + in Na-A is replaced by Ca2 + , the pore size is about That is type 5A molecular sieve.
  • molecular sieves with other elements have also been synthesized in the prior art.
  • molecular sieves can be divided into silicon-aluminum molecular sieves, phosphorus-aluminum molecular sieves and framework heteroatom molecular sieves according to the composition of the framework elements.
  • molecular sieves with pore sizes less than 2nm, 2-50nm and greater than 50nm are respectively called microporous, mesoporous and macroporous molecular sieves.
  • the MOF in the MOF coating is selected from one or more of Fe-MOF, Ni-MOF, Co-MOF, Mn-MOF, and Cu-MOF.
  • MOF is called Metal Organic Framework, which refers to a type of coordination polymer with a three-dimensional pore structure, generally with metal ions as connection points, and organic ligands supporting the spatial 3D extension. It includes nodes and bridges, and the framework structure is composed of organic ligands (bridges) with different connection numbers and metal ion nodes. This framework structure can be rigid or flexible and has a large inner surface. MOF can be prepared by self-assembly of metal salts and organic ligands, and has a diverse and controllable structure.
  • Metal ions can be selected from ions of metals such as Al, Fe, Co, Ni, Cu, Mn, Zn, Ti, etc., and organic coordination can be selected from terephthalic acid, terphenyl dicarboxylic acid, trimesic acid, 2,5-dihydroxyterephthalic acid, porphyrin, folic acid, cyclodextrin and its derivatives.
  • the functional coating may be selected from one or more of the molecular sieve coatings or MOF coatings described above, such as a coating formed by a single molecular sieve or MOF, a coating formed by two or more molecular sieves or two or more MOFs, and a coating formed by mixing one or more molecular sieves with one or more MOFs.
  • the functional coating may be formed by dispersing the molecular sieve and/or MOF powder in an organic solvent to form a uniform slurry, optionally adding a suitable binder, and then coating the slurry on the surface of the positive electrode to form a functional coating of a predetermined thickness.
  • the porosity of the functional coating may be 30-80%, optionally 50-75%, based on the total volume of the functional coating.
  • the organic solvent in the electrolyte enters the pores of the functional coating and forms a solvated structure with the sodium ions at the interface between the functional coating and the positive electrode active material layer. Due to the size effect of the functional coating, the composition of the solvated structure formed can be effectively changed, the desolvation energy can be reduced, and thus its trace but continuous oxidative decomposition can be inhibited.
  • the positive electrode active material is selected from one or more of layered transition metal oxides, polyanionic compounds, and Prussian blue analogs.
  • the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce.
  • the layered transition metal oxide is, for example, Na x MO 2 , wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 ⁇ x ⁇ 1.
  • the polyanion compound may be a compound having sodium ions, transition metal ions and tetrahedral (YO 4 ) n- anion units.
  • the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce;
  • Y may be at least one of P, S and Si; and
  • n represents the valence state of (YO 4 ) n- .
  • the polyanion compound may also be a compound having sodium ions, transition metal ions, tetrahedral (YO 4 ) n- anion units and halogen anions.
  • the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce;
  • Y may be at least one of P, S and Si, and n represents the valence state of (YO 4 ) n- ;
  • the halogen may be at least one of F, Cl and Br.
  • the polyanionic compound may also be a compound having sodium ions, tetrahedral (YO 4 ) n- anion units, polyhedral units (ZO y ) m+ and optional halogen anions.
  • Y may be at least one of P, S and Si, n represents the valence of (YO4) n- ;
  • Z represents a transition metal, which may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, m represents the valence of (ZOy) m+ ;
  • the halogen may be at least one of F, Cl and Br.
  • the polyanion compound is at least one of NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , NaM′PO 4 F (M′ is one or more of V, Fe, Mn and Ni), and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y (0 ⁇ y ⁇ 1).
  • the Prussian blue analogue may be a class of compounds having sodium ions, transition metal ions and cyanide ions (CN - ).
  • the transition metal may be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce.
  • the Prussian blue analogue is, for example, Na a Me b Me' c (CN) 6 , wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 ⁇ a ⁇ 2, 0 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1.
  • the specific positive electrode active material is, for example , NaNi1 / 3Fe1 / 3Mn1 /3O2, Na4Fe3(PO4)2P2O7 , NaFePO4 , Na3V2 ( PO4 ) 3 , NaMnFe (CN) 6 , but is not particularly limited, so the positive electrode active material conventionally used for sodium ion batteries can be selected.
  • the positive electrode active material, the binder, the conductive agent, etc. can be dispersed in an organic solvent (such as N-methylpyrrolidone (NMP)) to form a uniform slurry, which is coated on the positive electrode collector and then dried at high temperature.
  • NMP N-methylpyrrolidone
  • the pole piece obtained after drying can be rolled and cut into a predetermined shape.
  • the slurry in which the molecular sieve and/or MOF are dispersed in an organic solvent can be coated on the pole piece to form a functional coating of a predetermined thickness, and dried at high temperature so that the functional coating is covered on the surface of the pole piece in the form of a film.
  • the choice of the adhesive is not particularly limited.
  • it can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the conductive agent for the positive electrode material can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the weight ratio of the positive electrode active material, the conductive agent and the binder contained in the positive electrode sheet slurry is 70-90: 5-15: 5-15, optionally 75-85: 8-12: 8-12.
  • the amount of the functional coating is 1-5% by weight, optionally 1.5-2.5% by weight, based on the total weight of the positive electrode active material layer and the functional coating in the positive electrode sheet.
  • a second aspect of the present application provides a sodium ion secondary battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet is the positive electrode sheet according to the first aspect of the present application.
  • the electrolyte is an electrolyte formed by dissolving a sodium salt electrolyte in a solvent.
  • the solvent is an ether solvent, optionally selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether.
  • the solvent is selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, particularly diethylene glycol dimethyl ether or diethylene glycol diethyl ether.
  • the organic solvent is not a carbonate solvent.
  • the sodium salt electrolyte is selected from one or more of sodium hexafluorophosphate (NaPF 6 ), sodium difluorooxalatoborate (NaDFOB), sodium tetrafluoroborate (NaBF 4 ), sodium bisoxalatoborate (NaBOB), sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethylsulfonate, sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).
  • NaPF 6 sodium hexafluorophosphate
  • NaDFOB sodium difluorooxalatoborate
  • NaBF 4 sodium tetrafluoroborate
  • NaBOB sodium bisoxalatoborate
  • NaFSI sodium bis(fluorosulfonyl)imide
  • NaTFSI sodium trifluoromethylsulfonate
  • the sodium salt electrolyte is selected from sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide, and is particularly sodium hexafluorophosphate.
  • the molar concentration of the sodium salt electrolyte is 0.5 mol/L to 8 mol/L, optionally 1 mol/L to 4 mol/L.
  • the negative electrode is selected from a sodium metal negative electrode, a carbon material negative electrode and other non-carbon material negative electrodes.
  • the sodium metal negative electrode includes a scheme without a negative electrode. There is no particular limitation on the selection of the negative electrode, and the negative electrode material conventionally used for sodium ion batteries can be selected.
  • a third aspect of the present application provides an electrical device, which includes the sodium ion secondary battery according to the second aspect of the present application.
  • sodium-ion batteries include a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.
  • active sodium ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the separator is set between the positive electrode sheet and the negative electrode sheet to play a role of isolation.
  • the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the sodium ion secondary battery according to the present application includes an electrolyte.
  • the electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate.
  • the electrolyte includes an electrolyte salt and a solvent.
  • the electrolyte salt may be a common electrolyte salt in sodium ion batteries, such as a sodium salt.
  • the electrolyte salt may be selected from one or more of sodium hexafluorophosphate (NaPF 6 ), sodium difluorooxalatoborate (NaDFOB), sodium tetrafluoroborate (NaBF 4 ), sodium bisoxalatoborate (NaBOB), sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethylsulfonate, and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).
  • NaPF 6 sodium hexafluorophosphate
  • NaDFOB sodium difluorooxalatoborate
  • NaBF 4 sodium tetrafluoroborate
  • NaBOB sodium bisoxalatoborate
  • NaFSI sodium bis
  • the solvent is a non-aqueous solvent.
  • the solvent is an ether solvent, optionally selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ether.
  • the solvent is selected from ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, particularly diethylene glycol dimethyl ether or diethylene glycol diethyl ether.
  • the organic solvent is not a carbonate solvent.
  • the electrolyte may also optionally include other additives.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature performance.
  • the additive is selected from at least one of sulfate compounds containing unsaturated bonds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, and carboxylate compounds.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material and a conductive agent.
  • the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode active material layer disposed on the surface of the positive electrode current collector includes a positive electrode active material.
  • the positive electrode active material used in the present application may have any conventional positive electrode active material used in a secondary battery.
  • the positive electrode active material may be selected from one or more of a layered transition metal oxide, a polyanion compound, and a Prussian blue analog. Specific materials are, for example, NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 , NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , NaMnFe(CN) 6 . These materials can all be obtained commercially. Carbon may be coated on the surface of the positive electrode active material.
  • the positive electrode active material layer may optionally include a conductive agent.
  • a conductive agent there is no specific limitation on the type of the conductive agent, and those skilled in the art may select the conductive agent according to actual needs.
  • the conductive agent used for the positive electrode material may be selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, One or more of carbon nanotubes, graphene and carbon nanofibers.
  • the positive electrode active material layer may also optionally include a binder.
  • the binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive electrode sheet can be prepared according to methods known in the art.
  • the carbon-coated positive electrode active material, the conductive agent and the binder can be dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet is obtained.
  • NMP N-methylpyrrolidone
  • the molecular sieve and/or MOF slurry can be coated on the pole piece to form a functional coating of a predetermined thickness, and dried at a high temperature so that the functional coating is covered on the pole piece surface in the form of a film.
  • a uniform slurry can be formed by dispersing the molecular sieve and/or MOF powder in a solvent, optionally adding a suitable adhesive, and then coating the slurry on the surface of the positive electrode piece to form a functional coating with a thickness of 0.3-20 ⁇ m.
  • solvents and adhesives can be the same as described above for the preparation of the positive electrode piece.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer includes a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • a metal foil a copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode material layer generally comprises a negative electrode active material and an optional binder, an optional conductive agent and other optional additives, and is generally formed by coating and drying a negative electrode slurry.
  • the negative electrode slurry coating is generally formed by dispersing the negative electrode active material and the optional conductive agent and binder in a solvent and stirring them uniformly.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water.
  • the specific type of negative electrode active material is not limited, and active materials known in the art that can be used for the negative electrode of a sodium ion secondary battery can be used, and those skilled in the art can select according to actual needs.
  • the negative electrode active material can be selected from a sodium metal negative electrode, a carbon material negative electrode, and other non-carbon material negative electrodes.
  • the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder can be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • auxiliary agents include, for example, thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).
  • thickeners such as sodium carboxymethyl cellulose (CMC-Na)
  • the electrode assembly using the electrolyte also includes a separator.
  • the separator is arranged between the positive electrode plate and the negative electrode plate to play an isolating role.
  • the present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without particular restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular restrictions.
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG1 is a sodium ion secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the sodium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the secondary battery of the present application may include a battery cell form, a battery module form, or a battery pack form.
  • the battery The monomers can be assembled into battery modules.
  • the above-mentioned battery monomers can be assembled into battery packs.
  • the above-mentioned battery modules can also be assembled into battery packs.
  • the number of sodium-ion secondary batteries contained in the battery module 4 can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module 4.
  • a plurality of sodium-ion secondary batteries 5 can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other manner.
  • the plurality of sodium-ion secondary batteries 5 can further be fixed by fasteners.
  • the battery module 4 can also include a housing having a housing space, and a plurality of sodium-ion secondary batteries 5 are accommodated in the housing space.
  • the sodium ion secondary batteries 5 or battery modules 4 can be assembled into a battery pack 1 , and the number of sodium ion secondary batteries 5 or battery modules 4 contained in the battery pack 1 can be selected by those skilled in the art according to the application and capacity of the battery pack 1 .
  • FIG3 and FIG4 are battery packs 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery cells disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery cells.
  • the present application also provides an electrical device, the device includes a sodium ion secondary battery provided in the present application.
  • the sodium ion secondary battery can be used as a power source for the device, and can also be used as an energy storage unit for the device.
  • the device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.
  • a battery pack can be selected according to its usage requirements.
  • FIG5 is a device as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module can be used.
  • 3A (potassium A-type) molecular sieve, 4A (sodium A-type) molecular sieve and 5A (calcium A-type) molecular sieve were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;
  • Fe-MOF MIL-100(Fe), the ligand is trimesic acid, which is formed by self-assembly of iron ions and the ligand trimesic acid;
  • Co-MOF Co-MOF-74, ligand is 2,5-dihydroxyterephthalic acid,
  • Ni-MOF Ni-MOF-74, ligand is 2,5-dihydroxyterephthalic acid,
  • Mn-MOF Mn-MOF-74
  • the ligand is 2,5-dihydroxyterephthalic acid, and all three are formed by self-assembly of the corresponding metal ions and the ligand 2,5-dihydroxyterephthalic acid.
  • 10wt% polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and 10wt% carbon black conductive agent and 80wt% positive electrode active material Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 were added to prepare a uniformly dispersed slurry.
  • the slurry was evenly coated on the surface of aluminum foil, and then transferred to a vacuum drying oven for complete drying.
  • the obtained pole piece was roll-pressed.
  • the coating amount of the positive electrode active material on the obtained pole piece was 0.3g/1540.25mm 2 .
  • Polypropylene film is used as the isolation film.
  • Comparative Example 1-2 is the same as Example 1, except that the positive electrode of Comparative Example 1 does not include a functional coating, while the functional coating on the positive electrode of Comparative Example 2 is a sodium carboxymethyl cellulose (CMC-Na) coating.
  • CMC-Na sodium carboxymethyl cellulose
  • the positive electrode sheet, the separator, and the negative electrode sheet described in Example 1 are stacked in order, so that the separator is located between the positive and negative electrode sheets to play an isolating role, and the above-mentioned electrolyte is added to assemble a stacked battery, which is the sodium ion secondary battery of Example 1.
  • the sodium ion battery products of Examples 2-20 and Comparative Examples 1-2 were also prepared according to the above steps.
  • the electrolyte needs to be able to exist stably within the operating voltage range of the battery.
  • the voltage range in which the electrolyte is electrochemically stable is usually called the electrochemical window.
  • the electrochemical window test mainly tests the cyclic voltammetry curve.
  • the potential of the research electrode is controlled to scan from Ei (starting potential) to the negative potential direction at a rate V, and the scanning direction is changed after time t, and the potential is scanned back to the starting potential at the same rate, and then the potential is reversed again, and the scanning is repeated.
  • the area where no redox peak appears is the electrochemical window obtained by the test.
  • Example 1 the prepared sodium ion secondary battery is charged to 4.2V at a constant current of 1/3C at 25°C, and then charged at a constant voltage of 4.2V until the current drops to 0.05C to obtain the first charging capacity (Cc1); then discharged to 2.5V at a constant current of 1/3C to obtain the first discharge capacity (Cd1), and the coulombic efficiency of the sodium ion battery is calculated according to the following formula.
  • Example 1 the sodium ion battery is charged to 4.2V at a constant current of 1C at 45°C, then charged at a constant voltage of 4.2V until the current drops to 0.05C, and then discharged to 2.5V at a constant current of 1C to obtain the first cycle discharge capacity (Cd1); the charging and discharging are repeated to the nth cycle, and the discharge capacity of the sodium ion battery after n cycles is obtained, which is recorded as Cdn, and the sodium ion battery capacity retention rate is calculated according to the following formula:
  • Capacity retention rate discharge capacity after n cycles (Cdn) / first cycle discharge capacity (Cd1).
  • the sodium ion battery after 200 cycles was disassembled in an argon atmosphere glove box (H 2 O ⁇ 0.1ppm, O 2 ⁇ 0.1ppm), and the surface morphology of the negative electrode was visually observed to determine whether sodium dendrites were generated. If there were no white spots on the negative electrode, it was determined that there were no sodium dendrites, if there were sporadic white spots on the negative electrode, it was determined that the sodium dendrites were mild, and if there were dense white spots on the negative electrode, it was determined that the sodium dendrites were severe.
  • the test results in Table 1 show that the positive electrode sheet of the present invention can significantly improve the coulombic efficiency and cycle performance of the sodium ion secondary battery containing it by including a functional coating, and no obvious sodium dendrite formation is observed, or sodium dendrites are only slightly formed.
  • Comparative Example 1 in the absence of a functional coating, severe sodium dendrite precipitation was observed, and the coulombic efficiency and capacity retention rate of the battery were also significantly reduced.
  • the functional coating is another type of coating, such as the CMC-Na coating used in Comparative Example 2, a decrease in coulombic efficiency and capacity retention rate, as well as severe sodium dendrite precipitation, can also be observed.
  • the thickness of the functional coating on the positive electrode sheet also has a substantial impact on the performance of the electrode sheet. As shown in Example 19, when the thickness of the functional coating on the positive electrode sheet is as low as 0.2 ⁇ m, the effect of inhibiting sodium dendrites is slightly insufficient, and slight sodium dendrite precipitation can be observed on the surface of the negative electrode sheet, and the coulombic efficiency and capacity retention rate of the battery are also reduced.
  • the type of functional coating, the electrolyte in the electrolyte, and the selection of organic solvents also have a certain effect on the electrical properties of sodium ion secondary batteries.
  • ethyl methyl carbonate is selected as the organic solvent, which shows a reduced coulombic efficiency and capacity retention rate compared to ether solvents, and slight sodium dendrite precipitation is observed.
  • 3A potential A type

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Abstract

本申请涉及一种钠离子电池的正极极片，所述极片包括功能涂层，其中，所述功能涂层包括分子筛涂层或MOF涂层中的一种或多种涂层。本申请还涉及包含所述正极极片的钠离子二次电池以及包含所述钠离子二次电池的用电装置。

Description

一种用于钠离子电池的正极极片及钠离子电池
优先权信息
本申请请求2022年12月02日向中国国家知识产权局提交的专利申请的优先权和权益，并且通过参照将其全文并入此处。
技术领域
本申请涉及一种钠离子电池的正极极片，其包含选自分子筛涂层或MOF涂层中的一种或多种的功能涂层。本申请还涉及包含所述正极极片的钠离子二次电池以及包含所述二次电池的用电装置。
背景技术
锂离子电池现已被广泛应用于纯电动汽车、混合电动汽车以及智能电网等领域。然而，由于锂矿资源价格持续上涨，动力电池业界正在不断寻找其他途径来降低成本，其中最重要的途径之一就是开发钠离子电池。钠离子电池是一种二次电池，主要依靠钠离子在正极和负极之间嵌入和脱嵌来工作。在充放电过程中，Na+在两个电极之间往返嵌入和脱出：充电时，Na+从正极脱嵌，经过电解质嵌入负极；放电时则相反。其工作原理与锂离子电池工作原理相似。
相比于锂，钠的化学性质更加活泼，与水的反应性更强，因此钠离子电池更加需要除水。另外，钠离子电池在高电压下抗氧化性差，容易形成钠枝晶。正极极片浸泡在有机溶剂中，容易产生溶剂化结构，导致库伦效率降低。因此，本领域需要开发一种用于钠离子电池的正极极片，其可改善在高电压下的抗氧化性，抑制钠枝晶的形成，并提高钠离子电池的循环性能。
发明内容
本公开旨在至少在一定程度上解决相关技术中的技术问题之一。为此，本公开的一个目的在于提供一种用于钠离子电池的正极极片，其可以在钠离子电池工作的高电压下提高抗氧化性，有效地抑制钠枝晶的生长，从而解决现有技术中钠枝晶生长导致钠离子电池循环效率降低并且安全风险升高的技术问题。
为了达到上述目的，本申请第一方面提供一种钠离子电池的正极极片，所述极片包括功能涂层，其中，所述功能涂层包括分子筛涂层或MOF涂层中的一种或多种涂层。
通过设置选自特定涂层材料的功能涂层，本申请的正极极片可以改变钠盐的溶剂化结构组成，降低去溶剂化能，抑制微量但持续的氧化分解，大幅提升电解液在钠电池中的抗氧化性，从而抑制钠枝晶的形成。
在任意实施方案中，所述功能涂层的厚度为0.3-20μm，可选地为0.5-15μm，进一步可选地为1-8μm。功能涂层的厚度对于钠枝晶的形成以及钠离子电池的循环性能具有实质影响。如果功能涂层过厚，则电池能量密度下降；如果功能涂层过薄，则无法有效地改变溶剂化结构，导致提升抗氧化性的效果有限。
在任意实施方案中，所述分子筛涂层中的分子筛包括3A(钾A型)、4A(钠A型)、5A(钙A型)、10Z(钙Z型)、13Z(钠Z型)、Y(钠Y型)、钠丝光沸石型分子筛中的一种或多种。在另外的实施方案中，所述MOF涂层中的MOF选自Fe-MOF、Ni-MOF、Co-MOF、Mn-MOF、Cu-MOF中的一种或多种。通过选择不同的涂层材料，可以进一步调节钠离子电池的库仑效率和循环性能。
在任意实施方案中，所述正极极片包含正极活性材料层，所述正极活性材料包括层状过渡金属氧化物、聚阴离子化合物以及普鲁士蓝类似物中的一种或多种。在一些实施方案中，所述层状过渡金属氧化物包括NaxMO2，其中M为Ti、V、Mn、Co、Ni、Fe、Cr及Cu中的一种或多种，0＜x≤1。在一些实施方案中，所述聚阴离子化合物包括具有钠离子、过渡金属离子及四面体型(YO4)n-阴离子单元的一类化合物，其中过渡金属包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种，Y包括P、S及Si中的至少一种，n表示(YO4)n-的价态；或所述聚阴离子化合物包括具有钠离子、过渡金属离子、四面体型(YO4)n-阴离子单元及卤素阴离子的一类化合物，其中过渡金属包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种，Y包括P、S及Si中的至少一种，n表示(YO4)n-的价态，卤素包括F、Cl及Br中的至少一种；或所述聚阴离子化合物包括具有钠离子、四面体型(YO4)n-阴离子单元、多面体单元(ZOy)m+及可选的卤素阴离子的一类化合物，Y包括P、S及Si中的至少一种，n表示(YO4)n-的价 态，Z包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种的过渡金属，m表示(ZOy)m+的价态，卤素包括F、Cl及Br中的至少一种。在一些实施方案中，所述普鲁士蓝类似物包括具有钠离子、过渡金属离子及氰根离子(CN-)的一类化合物，其中过渡金属包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种。在一些实施方案中，所述正极活性材料包括NaNi1/3Fe1/3Mn1/3O2、Na4Fe3(PO4)2P2O7、NaFePO4、Na3V2(PO4)3和NaMnFe(CN)6。
在任意实施方案中，所述功能涂层覆盖在所述正极活性材料层上。
在任意实施方案中，所述功能涂层的量为1-5重量％，可选地为1.5-2.5重量％，基于正极极片中正极活性材料层与功能涂层的总重量计。
本申请第二方面提供一种钠离子二次电池，包括正极极片、负极极片、隔离膜及电解液，其中，所述正极极片包括根据本申请第一方面所述的正极极片。
在任意实施方案中，所述电解液为钠盐电解质溶于溶剂中形成的电解液。在一些实施方案中，所述溶剂包括醚类溶剂，可选地包括乙二醇二甲醚、乙二醇二乙醚、二乙二醇二甲醚、三乙二醇二甲醚、四乙二醇二甲醚、二乙二醇二乙醚、1,3-二氧戊环、四氢呋喃、甲基四氢呋喃、二苯醚、冠醚中的一种或多种。所述钠盐电解质包括六氟磷酸钠、二氟草酸硼酸钠、四氟硼酸钠、双草酸硼酸钠、高氯酸钠、六氟砷酸钠、双(氟磺酰)亚胺钠、三氟甲基磺酸钠、双(三氟甲基磺酰)亚胺钠中的一种或多种。在一些实施方案中，所述负极包括钠金属负极、碳材料负极及其他非碳材料负极。
在任意实施方案中，所述钠盐电解质的摩尔浓度为0.5mol/L至8mol/L，可选地为1mol/L至4mol/L。
本申请第三方面提供一种用电装置，其包括根据本申请的第二方面所述的钠离子二次电池。
本公开的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本公开的实践了解到。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请实施例中所需要使用的附图作简单的介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请一个实施方式中的钠离子二次电池的示意图。
图2是图1所示的本申请一个实施方式中的钠离子二次电池的分解图。
图3是本申请一个实施方式中的电池包的示意图。
图4是图3所示的本申请一个实施方式中的电池包的分解图。
图5是本申请一个实施方式中的电池包用作电源的装置的示意图。
附图标记说明
1 电池包
2 上箱体
3 下箱体
4 电池模块
5 钠离子二次电池
51 壳体
52 电极组件
53 盖板
发明详细描述
为了简明，本申请具体地公开了一些数值范围。然而，任意下限可以与任意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。
钠离子电池相比于锂离子电池具有明显的成本优势，目前正处于迅速发展的态势。然而，钠的化学性质比锂更加活泼，在高工作电压下容易与电解液中的有机溶剂产生溶剂化结构，使得其更容易氧化。由于正极活性材料的微量但持续的氧化分解，使得钠枝晶不断生长，导致电池循环性能下降，甚至产生安全风险。
通过在用于钠离子电池的正极极片上设置一种功能涂层，由于功能涂层的孔隙和尺寸效应可以改变钠盐溶剂化结构组成，降低去溶剂化能，抑制微量但持续的氧化分解，大幅提升电解液在钠离子电池中的抗氧化性。另外，钠离子电池的阳极的高可逆性也得到了很好的保护。
具体地，本申请第一方面提供一种钠离子电池的正极极片，所述极片包括功能涂层，其中所述功能涂层包含选自分子筛涂层或MOF涂层中的一种或多种涂层。
不囿于任何具体理论，通过设置选自特定涂层材料的功能涂层，使得所施加的功能涂层具有大量不同尺寸的空隙，由此产生一定的尺寸效应。在这种效应的影响下，钠离子在电解液中的有机溶剂中形成的溶剂化结构得以改变，降低去溶剂化能，抑制了微量但持续的氧化分解。氧化分解的抑制大幅提升电解液在钠电池中的抗氧化性，从而抑制钠枝晶的形成。
在一些实施方案中，所述功能涂层的厚度为0.3-20μm，可选地为0.5-15μm，进一步可选地为1-8μm。所述功能涂层可以通过各种合适的涂覆方式覆盖在所述正极极片的正极活性材料层上，例如通过喷涂、刮涂、辊涂或者浸渍涂覆的方式。功能涂层的厚度对于钠枝晶的形成以及钠离子电池的循环性能具有实质影响。功能涂层过厚，电池能量密度下降；功能涂层过薄，无法有效地改变溶剂化结构，导致提升抗氧化性的效果有限。
在一些实施方案中，所述分子筛涂层中的分子筛选自3A(钾A型)、4A(钠A型)、5A(钙A型)、10Z(钙Z型)、13Z(钠Z型)、Y(钠Y型)、钠丝光沸石型分子筛中的一种或多种。常规的分子筛是一种人工合成的具有筛选分子作用的水合硅铝酸盐(泡沸石)或天然沸石，其化学通式为(M′2M)O·Al2O3·xSiO2·yH2O，M′、M分别为一价、二价阳离子如K+、Na+、Ca2+和Ba2+等。它在结构上有许多孔径均匀的孔道和排列整齐的孔穴，不同孔径的分子筛把不同大小和形状的分子分开。根据SiO2和Al2O3的分子比不同，可得到不同孔径的分子筛。一般可将晶体结构不同的分子筛加以分类，如3A型、4A型、5A型分子筛。4A型即为A类分子筛，孔径含Na+的A型分子筛记作Na-A；若其中Na+被K+置换，孔径约为即为3A型分子筛；如Na-A中有1/3以上的Na+被Ca2+置换，孔径约为即为5A型分子筛。
现有技术中还合成了具有其他元素的分子筛。例如，分子筛按骨架元素组成可分为硅铝类分子筛、磷铝类分子筛和骨架杂原子分子筛。另外，按孔道大小划分，孔道尺寸小于2nm、2-50nm和大于50nm的分子筛分别称为微孔、介孔和大孔分子筛。由于含有电价较低而离子半径较大的金属离子和化合态的水，水分子在加热后连续地失去，但晶体骨架结构不变，形成了许多大小相同的空腔，空腔又有许多直径相同的微孔相连，这些微小的孔穴直径大小均匀，能把比孔道直径小的分子吸附到孔穴的内部中来，而把比孔道大的分子排斥在外,因而能把形状直径大小不同的分子、极性程度不同的分子、沸点不同的分子或者饱和程度不同的分子分离开来，即具有“筛分”分子的作用，故称为分子筛。以上所提及的分子筛均可通过商购获得。
在另外的实施方案中，所述MOF涂层中的MOF选自Fe-MOF、Ni-MOF、Co-MOF、Mn-MOF、Cu-MOF中的一种或多种。MOF称为金属-有机框架结构(Metal Organic Framework)，指的是一类配位聚合物，具有三维的孔结构，一般以金属离子为连接点，有机配位体支撑构成空间3D延伸。其包括节点和连接桥，由不同连接数的有机配体(连接桥)和金属离子节点组合而成框架结构。这种框架结构可以是刚性的，也可以是柔性的，并具有极大的内表面。MOF可通过金属盐与有机配体的自组装而制备，具有多样的和可控的结构。金属离子可选自金属如Al、Fe、Co、Ni、Cu、Mn、Zn、Ti等的离子，有机配位则可选自对苯二甲酸、三联苯二甲酸、均苯三甲酸、2,5-二羟基对苯二甲酸、卟啉、叶酸、环糊精及其衍生物等。
在一些实施方案中，所述功能涂层可选自如上所述的分子筛涂层或MOF涂层中的一种或多种，例如单一的分子筛或MOF形成的涂层，两种或更多种分子筛或两种或更多种MOF形成的涂层，以及一种或多种分子筛与一种或多种MOF混合形成的涂层。可通过将分子筛和/或MOF的粉料分散在有机溶剂中形成均匀的浆料，任选地加入合适的粘接剂，然后将该浆料涂覆在正极极片表面，形成预定厚度的功 能涂层。在一些实施方案中，所述功能涂层的孔隙率可以为30-80％，可选地为50-75％，基于功能涂层的总体积计。当将正极极片浸渍在电解液中时，电解液中的有机溶剂进入功能涂层的孔隙中，并在功能涂层与正极活性材料层的界面处与钠离子形成溶剂化的结构。由于功能涂层的尺寸效应，可有效改变形成的溶剂化结构的组成，降低去溶剂化能，从而抑制其微量但持续的氧化分解。
在一些实施方案中，所述正极活性材料选自层状过渡金属氧化物、聚阴离子化合物以及普鲁士蓝类似物中的一种或多种。
在层状过渡金属氧化物中，过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种。层状过渡金属氧化物例如为NaxMO2，其中M为Ti、V、Mn、Co、Ni、Fe、Cr及Cu中的一种或几种，0＜x≤1。
聚阴离子化合物可以是具有钠离子、过渡金属离子及四面体型(YO4)n-阴离子单元的一类化合物。过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种；Y可以是P、S及Si中的至少一种；n表示(YO4)n-的价态。
聚阴离子化合物还可以是具有钠离子、过渡金属离子、四面体型(YO4)n-阴离子单元及卤素阴离子的一类化合物。过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种；Y可以是P、S及Si中的至少一种，n表示(YO4)n-的价态；卤素可以是F、Cl及Br中的至少一种。
聚阴离子化合物还可以是具有钠离子、四面体型(YO4)n-阴离子单元、多面体单元(ZOy)m+及可选的卤素阴离子的一类化合物。Y可以是P、S及Si中的至少一种，n表示(YO4)n-的价态；Z表示过渡金属，可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种，m表示(ZOy)m+的价态；卤素可以是F、Cl及Br中的至少一种。
在一些实施方案中，聚阴离子化合物例如是NaFePO4、Na3V2(PO4)3、NaM’PO4F(M’为V、Fe、Mn及Ni中的一种或几种)及Na3(VOy)2(PO4)2F3-2y(0≤y≤1)中的至少一种。
在一些实施方案中，普鲁士蓝类似物可以是具有钠离子、过渡金属离子及氰根离子(CN-)的一类化合物。过渡金属可以是Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种。普鲁士蓝类似物例如为NaaMebMe’c(CN)6，其中Me及Me’各自独立地为Ni、Cu、Fe、Mn、Co及Zn中的至少一种，0＜a≤2，0＜b＜1，0＜c＜1。
在一些实施方案中，具体的正极活性材料为例如NaNi1/3Fe1/3Mn1/3O2、Na4Fe3(PO4)2P2O7、NaFePO4、Na3V2(PO4)3、NaMnFe(CN)6，但没有特别限制，因此可选择常规用于钠离子电池的正极活性材料。
在正极极片的制备中，可将所述正极活性材料与粘接剂、导电剂等分散于有机溶剂(例如N-甲基吡咯烷酮(NMP))中制成均匀的浆料，涂覆在正极集流体上，随后在高温下干燥。干燥后得到的极片可进行辊压并切成预定形状。如上所述，可将分子筛和/或MOF分散于有机溶剂中的浆料涂覆在极片上形成预定厚度的功能涂层，在高温下干燥，使得所述功能涂层以膜的形式覆在极片表面。粘接剂的选择没有特别限制，作为示例，其可以为丁苯橡胶(SBR)、水性丙烯酸树脂、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。对于导电剂的种类也不作具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材料的导电剂可以选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。在一些实施方式中，所述正极极片浆料中包含的正极活性材料、导电剂和粘接剂的重量比为70-90：5-15：5-15，可选地为75-85：8-12：8-12。在一些实施方式中，所述功能涂层的量为1-5重量％，可选地为1.5-2.5重量％，基于正极极片中正极活性材料层与功能涂层的总重量计。
本申请第二方面提供一种钠离子二次电池，包括正极极片、负极极片、隔离膜及电解液，其中所述正极极片为根据本申请第一方面所述的正极极片。
在一些实施方案中，所述电解液为钠盐电解质溶于溶剂中形成的电解液。在一些实施方案中，所述溶剂为醚类溶剂，可选地选自乙二醇二甲醚、乙二醇二乙醚、二乙二醇二甲醚、三乙二醇二甲醚、四乙二醇二甲醚、二乙二醇二乙醚、1,3-二氧戊环、四氢呋喃、甲基四氢呋喃、二苯醚、冠醚中的一种或多种。在进一步的实施方案中，所述溶剂选自乙二醇二甲醚、乙二醇二乙醚、二乙二醇二甲醚、三乙二醇二甲醚、四乙二醇二甲醚、二乙二醇二乙醚，特别地为二乙二醇二甲醚或二乙二醇二乙醚。在一些实施方案 中，所述有机溶剂不是碳酸酯类溶剂。
在一些实施方案中，所述钠盐电解质选自六氟磷酸钠(NaPF6)、二氟草酸硼酸钠(NaDFOB)、四氟硼酸钠(NaBF4)、双草酸硼酸钠(NaBOB)、高氯酸钠、六氟砷酸钠、双(氟磺酰)亚胺钠(NaFSI)、三氟甲基磺酸钠、双(三氟甲基磺酰)亚胺钠(NaTFSI)中的一种或多种。在进一步的实施方案中，所述钠盐电解质选自六氟磷酸钠、双(氟磺酰)亚胺钠以及双(三氟甲基磺酰)亚胺钠，并且特别地为六氟磷酸钠。
在一些实施方案中，所述钠盐电解质的摩尔浓度为0.5mol/L至8mol/L，可选地为1mol/L至4mol/L。
在一些实施方案中，所述负极选自钠金属负极、碳材料负极及其他非碳材料负极。钠金属负极包括无负极的方案。对于负极的选择没有特别的限制，可选择常规用于钠离子电池的负极材料。
本申请第三方面提供一种用电装置，其包括根据本申请的第二方面所述的钠离子二次电池。
下面对钠离子电池的组成和结构进行详细阐述。
通常情况下，钠离子电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性钠离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
[电解液]
根据本申请的钠离子二次电池包含电解液。电解液在正极极片和负极极片之间起到传导离子的作用。电解液包括电解质盐和溶剂。
在本申请中，电解质盐可为钠离子电池中的常用电解质盐，例如钠盐。作为实例，电解质盐可选自六氟磷酸钠(NaPF6)、二氟草酸硼酸钠(NaDFOB)、四氟硼酸钠(NaBF4)、双草酸硼酸钠(NaBOB)、高氯酸钠、六氟砷酸钠、双(氟磺酰)亚胺钠(NaFSI)、三氟甲基磺酸钠、双(三氟甲基磺酰)亚胺钠(NaTFSI)中的一种或多种。
溶剂的种类可根据实际需求进行选择。在一些实施方式中，溶剂为非水性溶剂。在一些实施方案中，所述溶剂为醚类溶剂，可选地选自乙二醇二甲醚、乙二醇二乙醚、二乙二醇二甲醚、三乙二醇二甲醚、四乙二醇二甲醚、二乙二醇二乙醚、1,3-二氧戊环、四氢呋喃、甲基四氢呋喃、二苯醚、冠醚中的一种或多种。在进一步的实施方案中，所述溶剂选自乙二醇二甲醚、乙二醇二乙醚、二乙二醇二甲醚、三乙二醇二甲醚、四乙二醇二甲醚、二乙二醇二乙醚，特别地为二乙二醇二甲醚或二乙二醇二乙醚。在一些实施方案中，所述有机溶剂不是碳酸酯类溶剂。
在一些实施方式中，电解液中还可选地包括其他添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、以及改善电池低温性能的添加剂等。作为示例，添加剂选自含有不饱和键的硫酸酯化合物、亚硫酸酯化合物、磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、磷腈化合物、环状酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物、羧酸酯化合物中的至少一种。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极活性材料层，正极活性材料层包括正极活性材料和导电剂。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极活性材料层设置在正极集流体相对的两个表面的其中任意一者或两者上。
正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(例如铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
设置于正极集流体的表面上的正极活性材料层包括正极活性材料。本申请中所用的正极活性材料可具有二次电池中使用的任意常规正极活性材料。在一些实施方式中，正极活性材料可选自层状过渡金属氧化物、聚阴离子化合物以及普鲁士蓝类似物中的一种或多种。具体的材料为例如NaNi1/3Fe1/3Mn1/3O2、Na4Fe3(PO4)2P2O7、NaFePO4、Na3V2(PO4)3、NaMnFe(CN)6。这些材料均可以通过商业途径获得。正极活性材料表面上可包覆有碳。
正极活性材料层可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材料的导电剂可以选自超导碳、乙炔黑、炭黑、科琴黑、碳点、 碳纳米管、石墨烯及碳纳米纤维中的一种以上。
正极活性材料层还可选地包括粘结剂。作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
本申请中可按照本领域已知的方法制备正极极片。作为示例，可以将包覆碳的正极活性材料、导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮(NMP))中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
在一些实施方案中，可将分子筛和/或MOF的浆料涂覆在极片上形成预定厚度的功能涂层，在高温下干燥，使得所述功能涂层以膜的形式覆在极片表面。在一些实施方案中，可通过将分子筛和/或MOF的粉料分散在溶剂中形成均匀的浆料，任选地加入合适的粘接剂，然后将该浆料涂覆在正极极片表面，形成厚度为0.3-20μm的功能涂层。溶剂与粘接剂的选择可与上文对于正极极片的制备所述相同。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，负极材料层包括负极活性物质。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极材料层设置在负极集流体相对的两个表面中的任意一者或两者上。
本申请的电极组件中，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(例如铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
本申请的电极组件中，负极材料层通常包含负极活性物质以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极浆料涂布干燥而成的。负极浆料涂通常是将负极活性物质以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水。
负极活性物质的具体种类不做限制，可以采用本领域已知的能够用于钠离子二次电池负极的活性物质，本领域技术人员可以根据实际需求进行选择。作为示例，负极活性物质可选自钠金属负极、碳材料负极及其他非碳材料负极。
作为示例，导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。
作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种以上。
其他可选助剂例如是增稠剂(如羧甲基纤维素钠(CMC-Na))等。
[隔离膜]
采用电解液的电极组件中还包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种以上。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，所述二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，所述二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。所述二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)等。
本申请对所述二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的钠离子二次电池5。
在一些实施方式中，参照图2，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。钠离子二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
本申请的二次电池可包括电池单体形式、电池模块形式或者电池包形式。在一些实施方案中，电池 单体可以组装成电池模块。在一些实施方式中，上述电池单体可以组装成电池包。在一些实施方式中，上述电池模块也可以组装成电池包。电池模块4所含钠离子二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块4的应用和容量进行选择。在电池模块4中，多个钠离子二次电池5可以是沿电池模块的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个钠离子二次电池5进行固定。可选地，电池模块4还可以包括具有容纳空间的外壳，多个钠离子二次电池5容纳于该容纳空间。
在一些实施方式中，上述钠离子二次电池5或者电池模块4可以组装成电池包1，电池包1所含钠离子二次电池5或者电池模块4的数量可由本领域技术人员根据电池包1的应用和容量进行选择。
图3和图4是作为一个示例的电池包1。参照图3和图4，在电池包1中可以包括电池箱和设置于电池箱中的多个电池单体。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池单体的封闭空间。
另外，本申请还提供一种用电装置，所述装置包括本申请提供的钠离子二次电池。所述钠离子二次电池可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。作为所述装置，可以根据其使用需求来选择电池包。
图5是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对钠离子二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。如未特别说明，所有实验步骤在常压下进行。
使用的原料：
3A(钾A型)分子筛分子式KnNa12-n[(AlO2)12(SiO2)12]·xH2O
4A(钠A型)分子筛分子式Na12[(AlO2)12(SiO2)12]·xH2O
5A(钙A型)分子筛分子式CanNa12-2n[(AlO2)12(SiO2)12]·xH2O
3A(钾A型)分子筛、4A(钠A型)分子筛以及5A(钙A型)分子筛均购自于上海阿拉丁生化科技股份有限公司；
Fe-MOF：为MIL-100(Fe)，配体为均苯三甲酸，其为铁离子与配体均苯三甲酸通过自组装而形成；
Co-MOF:为Co-MOF-74，配体为2,5-二羟基对苯二甲酸，
Ni-MOF:为Ni-MOF-74，配体为2,5-二羟基对苯二甲酸，
Mn-MOF:为Mn-MOF-74，配体为2,5-二羟基对苯二甲酸，三者均为相应金属离子与配体2,5-二羟基对苯二甲酸通过自组装而形成。
所有MOF材料均购自于与公司合作的高校实验室。
实施例1
【正极极片的制备】
将10wt％聚偏氟乙烯粘结剂充分溶解于N甲基吡咯烷酮中，加入10wt％炭黑导电剂与80wt％正极活性材料Na4Fe3(PO4)2P2O7制成分散均匀的浆料。将浆料均匀涂敷在铝箔表面，然后转移到真空干燥箱中完全干燥。将得到的极片进行辊压。所得极片上正极活性材料的涂覆量为0.3g/1540.25mm2。
将20wt％聚偏氟乙烯粘结剂充分溶解于N甲基吡咯烷酮中，加入80wt％3A分子筛粉料制成分散均匀的浆料。将浆料均匀涂敷在上述极片表面，然后转移到真空干燥箱中完全干燥。将得到的极片进行冲切，得到正极极片。所得极片上3A分子筛的涂覆量为0.006g/1540.25mm2。
【负极极片的制备】
将4wt％碳纳米管材料和1.6wt％聚合物粘结剂羧甲基纤维素钠加到水中搅拌成均匀的浆料，将浆料涂覆在铜箔表面上，然后转移到真空干燥箱中完全干燥，然后进行冲切，得到负极极片。
【电解液的制备】
在氩气气氛手套箱中(H2O<0.1ppm，O2<0.1ppm)，将钠盐六氟磷酸钠NaPF6溶解于有机溶剂二乙二醇二甲醚中，搅拌均匀，得到钠盐浓度1mol/L的电解液，即实施例1的电解液。
【隔离膜】
以聚丙烯膜作为隔离膜。
实施例2-7和15-19
除功能涂层不同以外，实施例2-7以及15-19的其他步骤与实施例1相同。
实施例8-14和20
除电解液不同以外，实施例8-14以及20的其他步骤与实施例1相同。
对比例1-2
对比例1-2与实施例1相同，区别在于对比例1的正极不包含功能涂层，而对比例2的正极上的功能涂层为羧甲基纤维素钠(CMC-Na)涂层。
【钠离子电池的制备】
将实施例1所述正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极极片之间，起到隔离的作用，加入上述电解液组装成叠片电池，即为实施例1的钠离子二次电池。
实施例2-20和对比例1-2的钠离子电池产品同样按照上述步骤制备。
【电池性能测试】
1、电化学窗口
电解液需要满足在电池的工作电压范围能够稳定存在，通常将电解液电化学稳定的电压范围称为电化学窗口。
电化学窗口测试主要测试循环伏安曲线。控制研究电极的电势以速率V从Ei(起始电位)开始向电势负方向扫描，到时间t后改变扫描方向，以相同速率回扫至起始电势，然后电势再次换向，反复扫描，没有出现氧化还原峰的区域即为检测所获得的电化学窗口。
2、库伦效率
以实施例1为例，将制得的钠离子二次电池在25℃下以1/3C的恒定电流充电至4.2V，之后以4.2V恒压充电至电流降到0.05C，得到首次充电容量(Cc1)；再以1/3C的恒定电流放电至2.5V，得到首次放电容量(Cd1)，并按照下式计算钠离子电池库伦效率。
钠离子电池库伦效率＝首次放电容量(Cd1)/首次充电容量(Cc1)
对比例以及其他实施例的测试过程同上。
3、容量保持率
以实施例1为例，将钠离子电池在45℃下以1C的恒定电流充电至4.2V，之后以4.2V恒压充电至电流降到0.05C，再以1C的恒定电流放电至2.5V，得到首圈放电容量(Cd1)；如此反复充放电至第n圈，得钠离子电池循环n圈后的放电容量，记为Cdn，并按照下式计算钠离子电池容量保持率：
容量保持率＝循环n圈后的放电容量(Cdn)/首圈放电容量(Cd1)。
对比例以及其他实施例的测试过程同上。
4、钠枝晶
将上述循环200圈后的钠离子电池在氩气气氛手套箱中(H2O<0.1ppm，O2<0.1ppm)进行拆解，目视观察负极极片表面形貌，确定是否有钠枝晶生成。负极极片无白点判定为钠枝晶情况无，负极极片有零星白点判定为钠枝晶情况轻微，而负极极片有密密麻麻白点判定为钠枝晶情况严重。
将实施例1-20以及对比例1-2中制备的钠离子电池进行如上所述的性能测试，并将测试结果汇总于 下表1中。
表1

表1的测试结果表明，本发明的正极极片通过包含功能涂层，可以显著改善包含其的钠离子二次电池的库伦效率和循环性能，同时未观察到明显的钠枝晶形成，或钠枝晶仅轻微形成。与之相比，在对比例1中，在没有涂覆功能涂层的情况下，观察到严重的钠枝晶析出，并且电池的库伦效率和容量保持率也显著降低。另外，当所述功能涂层为其他类型的涂层，例如对比例2中使用的CMC-Na涂层时，同样可以观察到库伦效率和容量保持率降低，以及严重的钠枝晶析出。
正极极片上功能涂层的厚度对于极片性能也具有实质影响。如实施例19所示，当正极极片上功能涂层的厚度低至0.2μm时，抑制钠枝晶的效果就稍显不足，可观察到负极极片表面有轻微的钠枝晶析出，同时电池的库伦效率和容量保持率也降低。
另外，功能涂层的种类、电解液中的电解质以及有机溶剂的选择对于钠离子二次电池的电学性能也有一定的影响。例如，在实施例20中选择碳酸甲乙酯作为有机溶剂，则相比于醚类溶剂，其显示出降低的库伦效率和容量保持率，并且观察到轻微的钠枝晶析出。从本发明实施例来看，选择3A(钾A型)分子筛作为功能涂层的材料、NaPF6作为电解质盐和/或二乙二醇二甲醚作为有机溶剂得到了进一步改善的效果。
虽然已经参考实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (18)

  1. 一种钠离子电池的正极极片，所述极片包括功能涂层，其中，所述功能涂层包括分子筛涂层或MOF涂层中的一种或多种涂层。
  2. 根据权利要求1所述的正极极片，其中，所述功能涂层的厚度为0.3-20μm，可选地为0.5-15μm，进一步可选地为1-8μm。
  3. 根据权利要求1或2所述的正极极片，其中，所述分子筛涂层中的分子筛包括3A(钾A型)、4A(钠A型)、5A(钙A型)、10Z(钙Z型)、13Z(钠Z型)、Y(钠Y型)、钠丝光沸石型分子筛中的一种或多种。
  4. 根据权利要求1至3中任一项所述的正极极片，其中，所述MOF涂层中的MOF包括Fe-MOF、Ni-MOF、Co-MOF、Mn-MOF、Cu-MOF中的一种或多种。
  5. 根据权利要求1至4中任一项所述的正极极片，其中，所述正极极片包含正极活性材料层，所述正极活性材料包括层状过渡金属氧化物、聚阴离子化合物以及普鲁士蓝类似物中的一种或多种。
  6. 根据权利要求5所述的正极极片，其中，所述层状过渡金属氧化物包括NaxMO2，其中M包括Ti、V、Mn、Co、Ni、Fe、Cr及Cu中的一种或多种，0＜x≤1。
  7. 根据权利要求5所述的正极极片，其中，所述聚阴离子化合物包括具有钠离子、过渡金属离子及四面体型(YO4)n-阴离子单元的一类化合物，其中过渡金属包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种，Y包括P、S及Si中的至少一种，n表示(YO4)n-的价态；或
    所述聚阴离子化合物包括具有钠离子、过渡金属离子、四面体型(YO4)n-阴离子单元及卤素阴离子的一类化合物，其中过渡金属包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种，Y包括P、S及Si中的至少一种，n表示(YO4)n-的价态，卤素包括F、Cl及Br中的至少一种；或
    所述聚阴离子化合物包括具有钠离子、四面体型(YO4)n-阴离子单元、多面体单元(ZOy)m+及可选的卤素阴离子的一类化合物，Y包括P、S及Si中的至少一种，n表示(YO4)n-的价态，Z包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种的过渡金属，m表示(ZOy)m+的价态，卤素包括F、Cl及Br中的至少一种。
  8. 根据权利要求5所述的正极极片，其中，所述普鲁士蓝类似物包括具有钠离子、过渡金属离子及氰根离子(CN-)的一类化合物，其中过渡金属包括Mn、Fe、Ni、Co、Cr、Cu、Ti、Zn、V、Zr及Ce中的至少一种。
  9. 根据权利要求5所述的正极极片，其中，所述正极活性材料包括NaNi1/3Fe1/3Mn1/3O2、Na4Fe3(PO4)2P2O7、NaFePO4、Na3V2(PO4)3和NaMnFe(CN)6。
  10. 根据权利要求5至9中任一项所述的正极极片，其中所述功能涂层覆盖在所述正极活性材料层上。
  11. 根据权利要求1至5中任一项所述的正极极片，其中所述功能涂层的量为1-5重量％，可选地为1.5-2.5重量％，基于正极极片中正极活性材料层与功能涂层的总重量计。
  12. 一种钠离子二次电池，包括正极极片、负极极片、隔离膜及电解液，其中，所述正极极片包括权利要求1至11中任一项所述的正极极片。
  13. 根据权利要求12所述的二次电池，其中，所述电解液为钠盐电解质溶于溶剂中形成的电解液。
  14. 根据权利要求13所述的二次电池，其中，所述溶剂包括醚类溶剂，可选地包括乙二醇二甲醚、乙二醇二乙醚、二乙二醇二甲醚、三乙二醇二甲醚、四乙二醇二甲醚、1,3-二氧戊环、四氢呋喃、甲基四氢呋喃、二苯醚、冠醚中的一种或多种。
  15. 根据权利要求13或14中任一项所述的二次电池，其中，所述钠盐电解质包括六氟磷酸钠、二氟草酸硼酸钠、四氟硼酸钠、双草酸硼酸钠、高氯酸钠、六氟砷酸钠、双(氟磺酰)亚胺钠、三氟甲基磺酸钠、双(三氟甲基磺酰)亚胺钠中的一种或多种。
  16. 根据权利要求13至15中任一项所述的二次电池，其中，所述钠盐电解质的摩尔浓度为0.5mol/L至8mol/L，可选地为1mol/L至4mol/L。
  17. 根据权利要求12至16中任一项所述的二次电池，其中，所述负极包括钠金属负极、碳材料负极及含硅材料负极中的一种或多种。
  18. 一种用电装置，其中，包括权利要求12至17中任一项所述的钠离子二次电池。
PCT/CN2023/115855 2022-12-02 2023-08-30 一种用于钠离子电池的正极极片及钠离子电池 WO2024113992A1 (zh)

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