WO2021189285A1 - 电极组件、电化学装置和电子装置 - Google Patents

电极组件、电化学装置和电子装置 Download PDF

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WO2021189285A1
WO2021189285A1 PCT/CN2020/081048 CN2020081048W WO2021189285A1 WO 2021189285 A1 WO2021189285 A1 WO 2021189285A1 CN 2020081048 W CN2020081048 W CN 2020081048W WO 2021189285 A1 WO2021189285 A1 WO 2021189285A1
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electrolyte
protective layer
electrode assembly
lithium
carbonate
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PCT/CN2020/081048
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English (en)
French (fr)
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李大光
陈茂华
谢远森
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宁德新能源科技有限公司
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Priority to PCT/CN2020/081048 priority Critical patent/WO2021189285A1/zh
Priority to EP20926545.3A priority patent/EP4131476A1/en
Priority to CN202080096396.8A priority patent/CN115104201A/zh
Publication of WO2021189285A1 publication Critical patent/WO2021189285A1/zh
Priority to US17/951,480 priority patent/US20230027113A1/en

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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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • 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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • 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
    • H01M4/134—Electrodes based on metals, Si 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0048—Molten electrolytes used at high temperature
    • H01M2300/0051—Carbonates
    • 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 disclosure relates to the field of electrochemical technology, and in particular to an electrode assembly, an electrochemical device, and an electronic device.
  • Lithium metal is the metal with the smallest relative atomic mass (6.94) and the lowest standard electrode potential (-3.045V) among all metal elements, and its theoretical gram capacity can reach 3860mAh/g. Therefore, using lithium metal as the negative electrode of the battery, combined with some high-energy density positive electrode materials, can greatly increase the energy density of the battery and the operating voltage of the battery.
  • the existing lithium metal batteries have the following problems: 1) The lithium metal itself is extremely active, especially the newly generated lithium metal, it is very easy to have a series of side reactions with the existing organic small molecule electrolyte, resulting in lithium metal and The electrolyte is consumed at the same time. In the traditional liquid electrolyte system, the circulating coulombic efficiency is generally less than 90%, which is much lower than the general graphite anode system (99% to 99.9%); 2) During the charging process of lithium metal batteries, lithium will Deposited on the surface of the negative current collector.
  • the true density of lithium metal is about 0.534g/cc, while the deposition density of lithium metal can only reach about 0.2g/cc, which reduces the energy density of lithium metal batteries by more than 100Wh/L.
  • the purpose of the present disclosure is to at least improve the cycle performance of the lithium metal battery.
  • an electrode assembly including:
  • An electrolyte the electrolyte includes a solvent and an additive, the additive includes fluoroethylene carbonate; the ratio of the mass of the fluoroethylene carbonate to the total mass of the solvent and the additive is 10% to 30%;
  • a negative electrode the negative electrode has an active material and a protective layer covering the active material, the protective layer is located between the electrolyte and the active material, the protective layer is in contact with the electrolyte, and the active
  • the substance contains lithium metal, and the protective layer contains silicon.
  • the thickness of the protective layer is 0.001 ⁇ m to 100 ⁇ m.
  • the active material includes at least one of elemental lithium metal or a composite material containing lithium metal.
  • the volume ratio of lithium element to silicon element is greater than 10:1.
  • the protective layer includes at least one of a silicon-containing alloy SiM y or a silicon-oxygen compound, wherein y ⁇ 0.05, and M is B, Al, P, Fe, Co, Ni, Zn, Ge, At least one of Ga, As, Zr, In, or Sn.
  • the solvent includes at least one of a cyclic ester or a chain ester
  • the cyclic ester includes at least one of ethylene carbonate, propylene carbonate, ⁇ -butyrolactone, ethylene carbonate substituted with fluorine-containing groups, propylene carbonate substituted with fluorine-containing groups, or butylene carbonate;
  • the chain esters include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl acetate, ethyl propionate, propyl propionate, methyl propionate, butyric acid Methyl ester, ethyl butyrate, ethyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, At least one of ethyl fluoroacetate, methyl fluoroacetate, or propyl fluoroacetate.
  • the electrolytic solution further includes vinylene carbonate.
  • the electrode assembly further includes a positive electrode and a separator film, and the separator film is disposed between the positive electrode and the negative electrode.
  • the present disclosure also provides an electrochemical device, including: the electrode assembly of any one of the above.
  • the present disclosure also provides an electronic device, including: the electrochemical device described above.
  • the electrode assembly improves the unevenness of the lithium metal surface by forming a silicon-containing protective layer on the surface of the active material, and blocks the direct contact between the lithium metal and the electrolyte, thereby improving the deposition morphology and inhibiting lithium. Side reactions and lithium dendrite growth occur between the metal and the electrolyte, which improves safety.
  • a stable SEI (solid electrolyte interface) film is formed on the surface of the silicon-containing protective layer by using a specific concentration of fluorine-containing electrolyte, which solves the problem of unstable film formation of the silicon-containing protective layer in the electrolyte. Improve the cycle performance of the electrode assembly.
  • FIG. 1 is a schematic diagram of the structure of a negative electrode in an electrode assembly of an embodiment of the present disclosure.
  • Fig. 2 is a side view of a negative electrode according to an embodiment of the present disclosure.
  • Fig. 3 is a top view of a negative electrode according to an embodiment of the present disclosure.
  • Lithium metal batteries use lithium metal as the negative electrode.
  • the existing lithium metal batteries have the following problems:
  • Lithium metal itself is extremely active, and its potential relative to the hydrogen standard electrode is -3.05V.
  • the newly formed lithium metal has no passivation layer on the surface, and it is very easy to have a series of side reactions with the electrolyte system, such as reacting with a small amount of hydrogen fluoride in the electrolyte to form lithium fluoride, or reacting with the electrolyte solvent propylene carbonate to form propylene carbonate
  • Lithium ester C 3 H 6 OCO 2 Li causes lithium metal and electrolyte to be consumed at the same time, and the circulating coulombic efficiency is much lower than that of graphite anode (99% to 99.9%);
  • lithium will be deposited on the surface of the negative electrode current collector. Due to the inhomogeneity of the current density and the concentration of lithium ions in the electrolyte, the deposition rate of some sites will be too fast during the deposition process, and then a sharp dendritic structure will be formed. The lithium dendrites may pierce the diaphragm and form a short circuit. Cause safety issues. The presence of lithium dendrites will lead to a great decrease in the deposition density, resulting in a decrease in the energy density. In some lithium metal batteries, the actual deposition density of lithium metal is about 0.2 g/cc, which is much smaller than the true density of lithium metal of 0.534 g/cc. Due to the loose deposition of lithium metal, the energy density will be reduced by more than 100Wh/L.
  • a protective layer of silicon material can be prepared on the surface of the lithium metal negative electrode.
  • the negative electrode protection of silicon material can block the side reaction between the electrolyte and the lithium metal pole piece, and Can significantly inhibit dendrite growth.
  • silicon or silicon alloys are poorly compatible with conventional electrolytes, and it is difficult for silicon-containing materials to form stable SEI (solid electrolyte interface) membranes in conventional electrolytes. SEI membranes will be repeatedly broken as the lithium metal battery cycles. , To accelerate the consumption of electrolyte and lithium metal, resulting in poor cycle performance of lithium metal batteries.
  • Electrode assembly may be a lithium metal battery.
  • the electrode assembly includes an electrolyte and a negative electrode, and may also include a positive electrode.
  • the electrolyte includes a solvent and additives, and the additives include fluoroethylene carbonate (FEC); the ratio of the mass of the fluoroethylene carbonate to the total mass of the solvent and additives is 10%-30%; in some embodiments of the present disclosure, The additives may include only fluoroethylene carbonate.
  • FEC fluoroethylene carbonate
  • the negative electrode has an active material 11 and a protective layer 12 covering the active material 11.
  • the active material 11 is located on one or both sides of the current collector 10, and the current collector 10 may be copper. Foil.
  • the protective layer 12 is located between the electrolyte and the active material 11, the protective layer 12 is in contact with the electrolyte liquid, the active material contains lithium metal, and the protective layer contains silicon.
  • a protective layer containing silicon is provided on the active material 11.
  • the silicon material may be deposited on the surface by chemical vapor deposition, physical vapor deposition, or atomic layer deposition.
  • a protective layer is formed on the surface of lithium metal, and silicon and lithium metal will spontaneously react to form a lithium-silicon alloy.
  • the reaction equation is: Si+xLi ⁇ Li x Si where 1 ⁇ x ⁇ 5. 2 and 3 show a side view and a top view of a negative electrode in some embodiments of the disclosure, respectively.
  • the electrolyte can be prevented from contacting the lithium metal in the negative electrode, thereby inhibiting the side reaction between the lithium metal and the electrolyte, and the protective layer can improve the pole piece during cycling.
  • the uniformity of surface current distribution provides a uniform and good path for lithium ion transmission during the deposition and stripping process, thereby preventing uneven lithium ion deposition, inhibiting lithium dendritic growth, and improving battery rate, safety and cycle performance.
  • the electrolyte contains FEC.
  • FEC can form vinylene carbonate (VC) molecules by losing one hydrogen fluoride HF molecule.
  • the reaction equation is: FEC ⁇ VC+ROH+LiF.
  • VC and FEC are superior to the solvent of electrolyte due to their low lowest unoccupied molecular orbitals. They will be reduced and decomposed when they first come into contact with the negative electrode, forming a layer of SEI film with a large amount of inorganic components on the surface of the negative electrode to inhibit electrolysis. Decomposition of the solvent in the liquid.
  • the composition of the SEI film will change after VC is added to produce polyalkyl lithium carbonate polymers, which makes the SEI film more flexible and adhesive.
  • the LiF produced by the decomposition of FEC can play the role of bonding the silicon-containing protective layer and the SEI film, reducing the generation of micro-cracks, thereby improving the stability of the protective layer and the SEI film, and improving the cycle performance of the battery.
  • the main components of the SEI film formed in the conventional electrolyte are inorganic lithium salt and a small amount of alkyl lithium, which has poor flexibility.
  • the electrolyte added with FEC in this embodiment is more conducive to the formation of a stable SEI on the surface of the protective layer, and prevents the SEI film from being repeatedly broken and regenerated during the cycle.
  • FEC is not stable on the positive electrode and will react with the positive electrode to cause gas production. Therefore, the concentration of FEC in the electrolyte needs to be controlled.
  • the ratio of the mass of FEC to the total mass of the solvent and additives exceeds 30%, FEC reacts with the positive electrode.
  • the increase in gas production causes a decrease in the cycle performance of the electrode assembly.
  • the ratio of the quality of the FEC to the total mass of the solvent and additives is less than 10%, due to the low concentration, the chemical reaction between the electrolyte and the protective layer is weak, and the SEI The film formation effect of the film is poor, and the cycle performance of the electrode assembly cannot be significantly improved.
  • the ratio of the FEC mass to the total mass of the solvent and additives is controlled to be 10% to 30%.
  • the ratio between the FEC and the positive electrode is suppressed. The gas is generated during the period, which can significantly improve the cycle performance of the electrode assembly.
  • the side reaction between lithium metal and the electrolyte is prevented by providing a silicon-containing protective layer on the surface of the active material to inhibit the growth of lithium dendrites.
  • the thickness of the protective layer is 0.001 ⁇ m to 100 ⁇ m.
  • the thinner SEI formed on the protective layer will cause the SEI film to be unstable, which is likely to be broken repeatedly during the cycle, which consumes electrode liquid and lithium metal, and when the thickness of the protective layer is too thick, lithium It is difficult for the metal to pass through the protective layer, which will increase the resistance and degrade the performance of the electrode assembly. Therefore, in some embodiments of the present disclosure, the thickness of the protective layer is controlled to be 0.001 ⁇ m-100 ⁇ m.
  • the active material includes at least one of elemental lithium metal or a composite material containing lithium metal.
  • the negative electrode of the electrode assembly uses lithium metal, which has high chemical activity. The use of composite materials containing lithium metal can reduce the chemical reaction between the lithium metal and the external environment.
  • the elemental lithium metal and/or the composite material containing lithium metal may be powder or thin film.
  • the volume ratio of lithium element to silicon element is greater than 10:1.
  • the volume ratio of lithium to silicon reflects the content ratio of lithium to silicon. When the volume ratio of lithium to silicon is less than 10:1, too much silicon will increase the resistance and decrease the capacity.
  • the protective layer includes at least one of a silicon-containing alloy SiM y or a silicon-oxygen compound, where y ⁇ 0.05, and M is B, Al, P, Fe, Co, Ni, Zn, Ge, At least one of Ga, As, Zr, In, or Sn.
  • the protective layer needs to be able to transport lithium ions but not electronically conductive. Excessive M content can easily lead to an increase in the metallicity of the protective layer, and an increase in metallicity will lead to an increase in electronic conductivity of the protective layer. Therefore, it is necessary to limit the M content in the silicon alloy.
  • the silicon-oxygen compound may be SiO x , and x may be 0-2. Silicon oxide compounds are lower in cost and do not have electronic conductivity.
  • the solvent includes at least one of cyclic esters or chain esters; cyclic esters include ethylene carbonate, propylene carbonate, ⁇ -butyrolactone, ethylene carbonate substituted with fluorine-containing groups At least one of esters, propylene carbonate substituted with fluorine-containing groups, or butylene carbonate; chain esters include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, and acetic acid Ethyl, ethyl propionate, propyl propionate, methyl propionate, methyl butyrate, ethyl butyrate, fluoromethyl ethyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, fluorine At least one of ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluor
  • the electrolyte further includes vinylene carbonate (VC).
  • VC vinylene carbonate
  • the lowest unoccupied molecular orbital of vinylene carbonate is low, so it can precede the solvent in the electrolyte. It is reduced and decomposed when the negative electrode first comes into contact with it.
  • a layer of SEI film with more inorganic components is formed on the surface of the negative electrode to suppress the electrolyte. Solvent decomposition, and VC as a film-forming additive, the composition of the SEI film will change after being added to produce polyalkyl lithium carbonate polymers, making the SEI film more flexible and adhesive.
  • the electrolyte further includes a salt
  • the salt may be one of organic salt or inorganic salt
  • the salt may include at least one of lithium salt, sodium salt, or potassium salt
  • the salt may contain At least one of fluorine element, boron element, or phosphorus element.
  • the lithium salt includes lithium hexafluorophosphate LiPF 6 , lithium bistrifluoromethanesulfonimide LiN(CF 3 SO 2 ) 2 , lithium bis(fluorosulfonyl)imide Li(N(SO 2 F ) 2 ), lithium bisoxalate borate LiB (C 2 O 4 ) 2 , lithium difluorooxalate LiBF 2 (C 2 O 4 ), lithium hexafluoroarsenate LiAsF 6 , lithium perchlorate LiClO 4 or trifluoromethanesulfonate At least one of lithium acid LiCF 3 SO 3.
  • LiPF 6 lithium bistrifluoromethanesulfonimide LiN(CF 3 SO 2 ) 2
  • lithium bisoxalate borate LiB (C 2 O 4 ) 2 lithium difluorooxalate LiBF 2 (C 2 O 4
  • the electrode assembly further includes a positive electrode and a separator film, and the separator film is disposed between the positive electrode and the negative electrode.
  • the positive pole piece may include a positive current collector and a positive active material layer coated on the positive current collector.
  • the positive electrode has a positive electrode active material layer, and the positive electrode active material layer may be coated only on a partial area of the positive electrode current collector.
  • the positive active material layer may include a positive active material, a conductive agent, and a binder. Al foil can be used as the positive electrode current collector, and similarly, other positive electrode current collectors commonly used in this field can also be used.
  • the conductive agent of the positive pole piece may include at least one of conductive carbon black, sheet graphite, graphene, or carbon nanotubes.
  • the binder in the positive pole piece may include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, Polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene At least one of them.
  • the positive active material includes, but is not limited to, at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, lithium nickel cobaltate, lithium iron phosphate, lithium nickel cobalt aluminate or lithium nickel cobalt manganate,
  • the above positive active material may include a positive active material that has been doped or coated.
  • the isolation film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid.
  • polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.
  • polyethylene and polypropylene they have a good effect on preventing short circuits, and can improve the stability of the battery through the shutdown effect.
  • the surface of the isolation membrane may further include a porous layer, the porous layer is disposed on at least one surface of the isolation membrane, the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from alumina (Al 2 O 3 ), silicon oxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), cerium oxide (CeO 2 ), nickel oxide (NiO) ), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, hydroxide At least one of calcium or barium sulfate.
  • alumina Al 2 O 3
  • silicon oxide SiO 2
  • magnesium oxide MgO
  • titanium oxide TiO 2
  • hafnium dioxide HfO
  • the binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyethylene pyrrole At least one of alkanone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.
  • the porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte infiltration performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece.
  • the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.
  • the present disclosure also provides an electrochemical device, including: the electrode assembly of any one of the above.
  • the electrochemical device includes a lithium metal battery, but the present disclosure is not limited thereto.
  • the present disclosure also provides an electronic device, including: the above-mentioned electrochemical device.
  • the electronic device may include any electronic device that uses a rechargeable battery, such as a mobile phone, a tablet computer, and a charging device.
  • lithium metal batteries are used as examples, and the raw materials, raw material ratios, preparation methods, etc. used in the preparation of lithium ion batteries are only examples, and the present disclosure does not Limited to the raw materials, raw material ratios and preparation methods used in the following examples.
  • the preparation of the negative pole piece The silicon is plated on the lithium metal pole piece by magnetron sputtering to form a protective layer containing silicon.
  • the thickness of the protective layer is about 1 ⁇ m.
  • the lithium metal pole piece is cut into (40mm ⁇ 60mm) specifications. use.
  • Preparation of positive pole piece mix positive active material lithium cobalt oxide (LiCoO 2 ), conductive carbon black (Super P), polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.0:1.5, and add N-methyl Pyrrolidone (NMP) is used as a solvent to prepare a slurry with a solid content of 0.75, and stir it evenly.
  • the slurry is uniformly coated on the positive electrode current collector aluminum foil and dried at 90° C. to obtain a positive electrode pole piece. After coating, cut the pole piece into (38mm ⁇ 58mm) specifications for later use.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • Lithium-ion battery preparation Polyethylene (PE) with a thickness of 15 ⁇ m is selected as the isolation film and placed in the middle, the upper and lower layers are respectively the pole piece, and the isolation film is between the pole piece and the pole piece. After stacking, the four corners of the entire laminate structure are fixed with tape, and then placed in the aluminum plastic film, and after top-side sealing, liquid injection, and packaging, the lithium metal laminate battery is finally obtained.
  • PE Polyethylene
  • Example 2 In a dry argon atmosphere, the organic solvents are ethylene carbonate (EC), diethyl carbonate (DEC) and carbonic acid.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • VC vinylene ester
  • LiPF6 lithium salt lithium hexafluorophosphate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluorine Ethylene carbonate
  • LiPF6 lithium salt lithium hexafluorophosphate
  • Example 4 The difference between Example 4 and Example 1 lies in the preparation of the negative pole piece and the preparation of the electrolyte.
  • the preparation of the negative pole piece silicon is used as the target material and oxygen is used as the process gas.
  • SiOx is plated on the lithium metal pole piece by magnetron sputtering to form a SiOx protective layer with a thickness of about 1 ⁇ m. Cut the lithium metal pole piece into (40mm ⁇ 60mm) specifications for later use.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • VC vinylene ester
  • LiPF 6 lithium salt lithium hexafluorophosphate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluorine Ethylene carbonate
  • LiPF 6 lithium salt lithium hexafluorophosphate
  • Comparative Example 1 The difference between Comparative Example 1 and Example 1 lies in the preparation of the negative pole piece.
  • Comparative Example 1 In Comparative Example 1:
  • Preparation of the negative pole piece Cut the lithium metal pole piece into (40mm ⁇ 60mm) specifications for later use.
  • Comparative Example 2 The difference between Comparative Example 2 and Comparative Example 1 lies in the preparation of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluorinated Ethylene carbonate
  • LiPF 6 lithium salt lithium hexafluorophosphate
  • Comparative Example 3 The difference between Comparative Example 3 and Comparative Example 1 lies in the preparation of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluorinated Ethylene carbonate
  • LiPF6 lithium salt lithium hexafluorophosphate
  • Comparative Example 4 The difference between Comparative Example 4 and Comparative Example 1 lies in the preparation of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluorinated Ethylene carbonate
  • LiPF 6 lithium salt lithium hexafluorophosphate
  • Comparative Example 5 The difference between Comparative Example 5 and Comparative Example 1 lies in the preparation of the electrolyte solution.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluorinated Ethylene carbonate
  • LiPF 6 lithium salt lithium hexafluorophosphate
  • Comparative Example 6 The difference between Comparative Example 6 and Comparative Example 1 lies in the preparation of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • FEC fluorinated Ethylene carbonate
  • Comparative Example 7 The difference between Comparative Example 7 and Comparative Example 1 lies in the preparation of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • VC ethylene carbonate Vinyl ester
  • Comparative Example 8 The difference between Comparative Example 8 and Comparative Example 1 lies in the preparation of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • VC ethylene carbonate Vinyl ester
  • Comparative Example 9 The difference between Comparative Example 9 and Comparative Example 1 lies in the preparation of the electrolyte.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • VC ethylene carbonate Vinyl ester
  • the cycle performance of Examples 1 to 6 and Comparative Examples 1 to 9 is proposed to use the number of cycles when the full battery capacity retention rate is lower than or equal to 80% to characterize the effectiveness of the scheme.
  • the specific steps are as follows: The rate is first charged to 4.53V, then the constant voltage is charged until the current is less than 0.05C, and then the rate is discharged to 3V at a rate of 0.1C, and the above process is repeated twice for activation. After activation, charge at a rate of 0.3C to 4.53V, then charge at a constant voltage until the current is less than 0.05C, and then discharge at a rate of 0.5C to 3V. After 48 laps, the cycle starts from the first activation until the battery capacity is less than 80%, and the number of cycles is read through the electrochemical test curve output by LAND or NEWARE.
  • Example 3 Si/1um 20% NA 150
  • Example 4 SiOx/1um NA NA 60
  • Example 5 SiOx/1um NA 20% 140
  • Example 6 SiOx/1um 20% NA 180
  • Comparative examples 1 to 6 show that adding FEC to the electrolyte can improve the cycle performance, but the concentration of FEC in the electrolyte should not exceed 30%. This is because when the concentration of FEC is too high, gas will be generated in the positive electrode and the cycle performance will be deteriorated.
  • Comparative Examples 1 and 7-9 show that adding VC to the electrolyte can also improve the cycle performance, and the concentration of VC in the electrolyte should not exceed 30%, and the best value is 20%.
  • the electrolyte with VC added has better cycle performance than the electrolyte without additives (the main component of SEI is LiF). This is because the VC additive can improve the toughness of the SEI membrane, and the SEI membrane is more stable during the cycle and is not easily broken.
  • Example 1 As shown in Example 1 and Comparative Example 1, although a silicon-containing protective layer is used, the electrolyte does not contain FEC additives, and the cycle performance of the battery is not significantly improved compared with Comparative Example 1 without a silicon-containing protective layer. This is because it is difficult for silicon or silicon alloys to form a stable solid electrolyte interface (SEI) film in the electrolyte without FEC. With the repeated breakage of SEI during the cycle, new ones are continuously formed on the exposed silicon or silicon alloy surface. The SEI film aggravates the corrosion of silicon or silicon alloy and the consumption of electrolyte. Therefore, silicon or silicon alloys cannot play a negative role in the electrolyte system without FEC, and the cycle performance of the battery has not been improved.
  • SEI solid electrolyte interface
  • Example 2 Please refer to Example 1 and Example 2.
  • a silicon-containing protective layer is provided, and VC is added to the electrolyte.
  • 20 is added to the electrolyte.
  • % VC the battery capacity is less than 80%, the number of cycles reaches 120 cycles. This is because compared with the electrolyte without VC, the SEI generated by the electrolyte with VC is more tough and not easily broken during the cycle.
  • Example 2 and Comparative Example 8 In both Example 2 and Comparative Example 8, 20% VC is added to the electrolyte, but the negative electrode of Comparative Example 8 does not have a silicon-containing protective layer. Compared with Comparative Example 8, implementation The number of cycles in Example 2 has increased by 20%, indicating that in the electrolyte system containing VC, silicon or silicon alloy can play a negative role in protecting the negative electrode, that is, blocking the side reaction between the electrolyte and lithium metal, inhibiting the growth of dendrites, and further Increased the number of loops.
  • Example 3 and Comparative Example 3 both contain 20% FEC in the electrolyte.
  • the negative electrode of Example 3 has a silicon-containing protective layer, while Comparative Example 3 does not contain Compared with Comparative Example 3, the number of cycles of the protective layer in Example 3 with the silicon-containing protective layer is increased by 25%. This is because the silicon-containing protective layer inhibits the side reaction of lithium metal in the negative electrode with the electrolyte.
  • Example 2 and Example 3 Please refer to Example 2 and Example 3.
  • the difference between Example 2 and Example 3 is that the electrolyte of Example 3 contains 20% FEC, the electrolyte of Example 2 contains 20% VC, and the circulation of Example 3 Compared with Example 2, the number of turns is also increased by 25%.
  • FEC has high reactivity, which can lead to faster passivation of the silicon anode protection and inhibit lithium consumption.
  • the LiF produced by decomposition can play a role in binding the silicon anode protection and the SEI film, reducing the generation of micro-cracks, thereby Improve the stability of SEI film.
  • Example 2 and Example 3, Comparative Example 8 and Comparative Example 4 all show that the electrolyte with FEC added has better cycle performance than the electrolyte with VC added. This is because the SEI film formed in the electrolyte with the VC additive has a large charge exchange resistance, which leads to a significant increase in the polarization of the negative electrode during the rapid charging process, which affects the cycle performance of the battery.
  • Examples 4 to 6 Please refer to Examples 4 to 6.
  • the comparison results of Examples 4 to 6 show that the improved film formation of FEC and VC additives is also applicable to systems where the protective layer is a silicon oxide compound.
  • Examples 1 to 6 Please refer to Examples 1 to 6.
  • the cycle performance of Examples 4 to 6 is better than that of Examples 1 to 3 because of the diffusion coefficient of lithium in Li x SiO y (10 -4 ⁇ 10 -8 cm 2 /s) is higher than the diffusion coefficient of lithium ions in Li x Si (10 -12 ⁇ 10 -13 cm 2 /s), so it has better cycle performance at a large rate.
  • Example 6 that is, the material of the protective layer is a silicon-oxygen compound, and the FEC content in the electrolyte is 20%.
  • the SEI film on the surface of the protective layer is improved, thereby significantly improving the battery’s performance. Cycle performance.

Abstract

一种电极组件、电化学装置和电子装置。其中，电极组件，包括：电解液，电解液包括溶剂和添加剂，添加剂包括氟代碳酸乙烯酯；氟代碳酸乙烯酯的质量与溶剂和添加剂的总质量的比值为10％～30％；负极，负极具有活性物质（11）和覆盖活性物质（11）的保护层（12），保护层（12）位于电解液与活性物质（11）之间，保护层（12）与电解液相接触，活性物质（11）含有锂金属，保护层（12）含有硅元素。该电极组件能够大幅度提高锂金属电池的循环性能。

Description

电极组件、电化学装置和电子装置 技术领域
本公开涉电化学技术领域，尤其涉及一种电极组件、电化学装置和电子装置。
背景技术
锂金属是所有金属元素中相对原子质量最小(6.94)、标准电极电位(-3.045V)最低的金属，其理论克容量可达到3860mAh/g。因此，使用锂金属作为电池的负极，配合一些高能量密度的正极材料，可以大大提高电池的能量密度以及电池的工作电压。
然而，现有锂金属电池存在如下问题：1)锂金属本身活泼性极高，尤其是新生成的锂金属，非常容易与现有的有机小分子电解液发生一系列副反应，导致锂金属与电解液同时被消耗，在传统的液态电解液体系中循环库伦效率一般小于90％，大大低于一般的石墨负极体系(99％～99.9％)；2)锂金属电池在充电过程中，锂会在负极集流体表面沉积。由于电流密度以及电解液中锂离子浓度的不均匀性，沉积过程中会出现某些位点沉积速度过快的现象，进而形成尖锐的枝晶结构。锂枝晶的存在可能会刺穿隔膜导致正负极短路，引发安全问题，而且锂枝晶的存在会导致沉积密度的大大降低。锂金属的真密度约为0.534g/cc，而锂金属的沉积密度仅能达到0.2g/cc左右，这使得锂金属电池的能量密度降低超过100Wh/L。
发明内容
鉴于以上现有技术的缺点，本公开的目的在于至少改善锂金属电池的循环性能。
本公开提供一种电极组件，包括：
电解液，所述电解液包括溶剂和添加剂，所述添加剂包括氟代碳酸乙烯酯；所述氟代碳酸乙烯酯的质量与所述溶剂和添加剂的总质量的比值为10％～30％；
负极，所述负极具有活性物质和覆盖所述活性物质的保护层，所述保护层位于所述电解液与所述活性物质之间，所述保护层与所述电解液相接触，所述活性物质含有锂金属，所述保护层含有硅元素。
在上述电极组件中，所述保护层的厚度为0.001μm～100μm。
在上述电极组件中，所述活性物质包括单质锂金属或含有锂金属的复合材料中的至少一种。
在上述电极组件中，在所述活性物质和所述保护层中，锂元素与硅元素的体积比大于10:1。
在上述电极组件中，所述保护层包括含硅合金SiM y或硅氧化合物中的至少一种，其中，y<0.05，M为B、Al、P、Fe、Co、Ni、Zn、Ge、Ga、As、Zr、In或Sn中的至少一种。
在上述电极组件中，所述溶剂包括环状酯或链状酯中的至少一种；
所述环状酯包括碳酸乙烯酯、碳酸丙烯酯、γ-丁内酯、含氟基团取代的碳酸乙烯酯、含氟基团取代的碳酸丙烯酯或碳酸丁烯酯中的至少一种；
所述链状酯包括碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、甲酸甲酯、甲酸乙酯、乙酸乙酯、丙酸乙酯、丙酸丙酯、丙酸甲酯、丁酸甲酯、丁酸乙酯、氟代碳酸甲乙酯、氟代碳酸二甲酯、氟代碳酸二乙酯、氟代丙酸乙酯、氟代丙酸丙酯、氟代丙酸甲酯、氟代乙酸乙酯、氟代乙酸甲酯或氟代乙酸丙酯中的至少一种。
在上述电极组件中，所述电解液中还包括碳酸亚乙烯酯。
在上述电极组件中，所述电极组件还包括正极和隔离膜，所述隔离膜设置在所述正极和所述负极之间。
本公开还提供一种电化学装置，包括：上述任一项的电极组件。
本公开还提供一种电子装置，包括：上述电化学装置。
本公开实施例提供的电极组件，通过在活性物质表面形成含硅的保护层，改善了锂金属表面不均匀性，阻隔了锂金属与电解液的直接接触，进而改善了沉积形貌，抑制锂金属与电解液之间发生副反应和锂枝晶生长，提高了安全性。同时，利用特定浓度的含氟电解液在含硅的保护层表面形成稳定的SEI(solid electrolyte interface，固体电解质界面)膜，解决了含硅保护层在电解液中成膜不稳定等问题，从而提高了电极组件的循环性能。
附图说明
结合附图并参考以下具体实施方式，本公开各实施例的上述和其他特征、优点及方面将变得更加明显。贯穿附图中，相同或相似的附图标记表示相同或相似的元素。应当理解附图是示意性的，元件和元素不一定按照比例绘制。
图1是本公开实施例的电极组件中负极的结构示意图。
图2是本公开实施例的一种负极的侧视图。
图3是本公开实施例的一种负极的俯视图。
具体实施方式
下面将参照附图更详细地描述本公开的实施例。虽然附图中显示了本公开的某些实施例，然而应当理解的是，本公开可以通过各种形式来实现，而且不应该被解释为限于这里阐述的实施例，相反提供这些实施例是为了更加透彻和完整地理解本公开。应当理解的是，本公开的附图及实施例仅用于示例性作用，并非用于限制本公开的保护范围。
下面的实施例可以使本领域技术人员更全面地理解本申请，但不以任何方式限制本申请。
以下将结合附图，对本申请实施例提供的方案进行详细描述。
锂金属电池采用锂金属作为负极，现有的锂金属电池存在如下问题：
1)锂金属本身活泼性极高，相对氢标准电极的电位是-3.05V。新生成的锂金属表面没有钝化层，非常容易与电解液体系发生一系列副反应，例如与电解液中的微量氟化氢反应生成氟化锂，或是与电解液溶剂碳酸丙烯酯反应生成碳酸丙烯酯锂C 3H 6OCO 2Li，导致锂金属与电解液同时被消耗，循环库伦效率大大低于石墨负极(99％～99.9％)；
2)锂金属电池在充电过程中，锂会在负极集流体表面沉积。由于电流密度以及电解液中锂离子浓度的不均匀性，沉积过程中会出现某些位点沉积速度过快的现象，进而形成尖锐的枝晶结构，锂枝晶可能会刺穿隔膜形成短路，引发安全问题。锂枝晶的存在会导致沉积密度的大大降低，使得能量密度降低。在一些锂金属电池中，锂金属的实际沉积密度为0.2g/cc左右，远小于锂 金属的真密度0.534g/cc。由于锂金属的疏松沉积，能量密度会降低超过100Wh/L。
3)为了减少锂金属与电解液反应、抑制锂枝晶的生长，可以在锂金属负极表面制备硅材料保护层，硅材料的负极保护能够阻隔电解液与锂金属极片间的副反应，并可以显著抑制枝晶生长。然而，硅或硅合金与常规电解液匹配性差，含硅材料在常规电解液中难以形成稳定的SEI(solid electrolyte interface，固体电解质界面)膜，SEI膜随锂金属电池循环的进行会反复破碎生成，加速电解液和锂金属的消耗，造成锂金属电池循环性能差。
由上述内容可知，采用硅保护层防止电解液与锂金属接触的方案中，由于电解液与硅保护层之间不匹配，导致电解液和锂金属快速消耗，因此，锂金属电池的循环性能会显著降低。
本公开的一些实施例中提出一种电极组件，电极组件可以是锂金属电池。
本公开的一些实施例中，电极组件包括电解液和负极，也可以还包括正极。
电解液包括溶剂和添加剂，添加剂包括氟代碳酸乙烯酯(FEC)；氟代碳酸乙烯酯的质量与溶剂和添加剂的总质量的比值为10％～30％；在本公开的一些实施例中，添加剂可以只包括氟代碳酸乙烯酯。
请参考图1，负极具有活性物质11和覆盖活性物质11的保护层12，在本公开的一些实施例中，活性物质11位于集流体10的一侧或两侧上，集流体10可以是铜箔。
保护层12位于电解液与活性物质11之间，保护层12与电解液相接触，活性物质含有锂金属，保护层含有硅元素。
在本公开的一些实施例中，在活性物质11上设置含硅的保护层，在本公开的一些实施例中，可以通过化学气相沉积、物理气相沉积或原子层沉积的方法将硅材料沉积在锂金属表面形成保护层，硅与锂金属会自发反应形成锂硅合金。反应方程式为：Si+xLi→Li xSi其中，1≤x≤5。图2和图3所示分别为本公开的一些实施例中一种负极的侧视图与俯视图。
未处理的锂金属表面存在大量非均匀分布的杂质，包含氧化锂Li 2O、氢氧化锂LiOH和碳酸锂Li 2CO 3等，这可能导致循环过程中极片表面电流分布的不均匀，进而导致锂金属形核不均匀，促进锂枝晶生长，恶化沉积形貌， 引起电池倍率性能、安全性能和循环性能下降。本公开的一些实施例中通过设置含硅的保护层，能够防止电解液与负极中的锂金属接触，从而抑制锂金属与电解液之间的副反应，并且保护层能够改善循环过程中极片表面电流分布的均匀性，为沉积和剥离过程中的锂离子传输提供一个均匀的、良好的通路，进而防止锂离子不均匀沉积，抑制锂枝晶生长，提高电池的倍率、安全和循环性能。
常规电解液与含硅保护层匹配性差，不易形成稳定的SEI膜，常规的电解液中，最开始时在负极表面成分主要是碳酸乙烯酯(EC)分解产生的碳酸亚乙酯锂(LEDC)和LiF成分，LEDC是一种不稳定的成分，在电极组件循环过程中会逐渐转变为无机成分，并释放出气体，从而使SEI膜成分发生持续的变化并疏松多孔，因此电解液会持续与负极发生反应。随着此过程的进行，SEI膜不断增厚，直至锂离子不能通过，且严重消耗了电解液中的锂离子，导致电池循环性能严重下降。要使保护层保护充分发挥其作用，改善电池循环性能，就必须在其表面形成致密且稳定的SEI模。因此，在本公开的一些实施例中，电解液中含有FEC，FEC可以通过失去一个氟化氢HF分子形成碳酸亚乙烯酯(VC)分子，反应方程式为：FEC→VC+ROH+LiF。VC和FEC由于最低未占分子轨道低，VC和FEC能够优于电解液的溶剂，在与负极刚开始接触时就还原分解，在负极表面生成一层无机成分含量较多的SEI膜，抑制电解液中溶剂的分解。而且VC作为一种成膜添加剂，加入后SEI膜的成分会发生变化，生成聚烷基碳酸锂类的聚合物，使得SEI膜的柔韧性和粘附力更强。此外，FEC分解产生的LiF更是能够起到粘合含硅的保护层和SEI膜的作用，减少微裂纹的产生，从而提高保护层和SEI膜的稳定性，改善电池循环性能。而常规电解液中形成的SEI膜主要成分是无机锂盐和少量烷基锂，柔韧性差。本实施例中加入FEC的电解液更利于在保护层表面形成稳定的SEI，防止SEI膜在循环过程中反复破碎和再生。
但是，FEC在正极并不稳定，会与正极反应导致产气，因此需要控制FEC在电解液中的浓度，当FEC的质量与溶剂和添加剂的总质量的比值超过30％时，FEC与正极反应产气增加造成电极组件的循环性能下降，而当FEC的质量与溶剂和添加剂的总质量的比值不到10％时，由于浓度过低，电解液与保护层之间的化学反应较弱，SEI膜的成膜效果差，不能明显提升电极组件的 循环性能。因而，在本公开的一些实施例中的电极组件中，控制FEC质量与溶剂和添加剂的总质量的比值为10％～30％，在保证SEI膜成膜效果的基础上，抑制FEC与正极之间的产气，从而能够明显提升电极组件的循环性能。
综上所述，在本公开的一些实施例中，通过在活性物质表面设置含硅保护层防止锂金属与电解液之间的副反应，抑制锂枝晶生长，通过在电解液中加入FEC，增加SEI膜的稳定性，防止循环过程中SEI膜反复破裂生长，通过控制FEC的浓度，在保证SEI膜成膜质量的同时抑制产气，进而改善了电极组件的循环性能。
在本公开的一些实施例中，保护层的厚度为0.001μm～100μm。当保护层太薄时，保护层上形成的SEI厚度较薄将导致SEI膜不稳定，容易在循环过程中反复破裂生成，消耗电极液和锂金属，而当保护层的厚度太厚时，锂金属难以通过保护层将会导致电阻增加，劣化电极组件的性能，因此在本公开的一些实施例中控制保护层的厚度为0.001μm～100μm。
在本公开的一些实施例中，活性物质包括单质锂金属或含有锂金属的复合材料中的至少一种。本公开的一些实施例中的电极组件的负极采用的是锂金属，锂金属本身具有较高的化学活性，采用含有锂金属的复合材料可以减少锂金属与外界环境之间的化学反应。在本公开的一些实施例中，单质锂金属和/或含有锂金属的复合材料可以是粉末，也可以是薄膜。
在本公开的一些实施例中，在活性物质和保护层中，锂元素与硅元素的体积比大于10:1。锂元素和硅元素的体积比反映了锂元素和硅元素的含量比，当锂元素与硅元素的体积比小于10:1时，硅元素过多导致电阻增加，容量下降。
在本公开一些实施例中，保护层包括含硅合金SiM y或硅氧化合物中的至少一种，其中，y<0.05，M为B、Al、P、Fe、Co、Ni、Zn、Ge、Ga、As、Zr、In或Sn中的至少一种。保护层需要能够传输锂离子但不具有电子导电性，M含量过大容易导致保护层中的金属性增加，金属性增加会导致保护层电子导电性增加，因此需要限制硅合金中的M含量。在本公开的一些实施例中，硅氧化合物可以为SiO x，x可以为0～2。硅氧化合物成本更低，且不具有电子导电性。
在本公开的一些实施例中，溶剂包括环状酯或链状酯中的至少一种；环状酯包括碳酸乙烯酯、碳酸丙烯酯、γ-丁内酯、含氟基团取代的碳酸乙烯酯、含氟基团取代的碳酸丙烯酯或碳酸丁烯酯中的至少一种；链状酯包括碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、甲酸甲酯、甲酸乙酯、乙酸乙酯、丙酸乙酯、丙酸丙酯、丙酸甲酯、丁酸甲酯、丁酸乙酯、氟代碳酸甲乙酯、氟代碳酸二甲酯、氟代碳酸二乙酯、氟代丙酸乙酯、氟代丙酸丙酯、氟代丙酸甲酯、氟代乙酸乙酯、氟代乙酸甲酯或氟代乙酸丙酯中的至少一种。
在本公开的一些实施例中，电解液中还包括碳酸亚乙烯酯(VC)。碳酸亚乙烯酯的最低未占分子轨道低，因此能够先于电解液中的溶剂，在于负极刚开始接触时就还原分解，在负极表面生成一层无机成分较多的SEI膜，抑制电解液中溶剂的分解，而且VC作为一种成膜添加剂，加入后SEI膜的成分会发生变化，生成聚烷基碳酸锂类的聚合物，使得SEI膜的柔韧性和粘附力更强。
在本公开的一些实施例中，电解液中还包括有盐，盐可以是有机盐或无机盐中的一种，盐可以包括锂盐、钠盐或钾盐中的至少一种，盐可以含有氟元素、硼元素或磷元素中的至少一种。在本公开的一些实施例中，锂盐包括六氟磷酸锂LiPF 6、双三氟甲烷磺酰亚胺锂LiN(CF 3SO 2) 2、双(氟磺酰)亚胺锂Li(N(SO 2F) 2)、双草酸硼酸锂LiB(C 2O 4) 2、二氟草酸硼酸锂LiBF 2(C 2O 4)、六氟砷酸锂LiAsF 6、高氯酸锂LiClO 4或三氟甲磺酸锂LiCF 3SO 3中的至少一种。
在本公开的一些实施例中，电极组件还包括正极和隔离膜，隔离膜设置在正极和负极之间。在本公开的一些实施例中，正极极片可以包括正极集流体和涂覆在正极集流体上的正极活性物质层。正极具有正极活性物质层，正极活性物质层可以仅涂覆在正极集流体的部分区域上。正极活性物质层可以包括正极活性物质、导电剂和粘结剂。正极集流体可以采用Al箔，同样，也可以采用本领域常用的其他正极集流体。正极极片的导电剂可以包括导电炭黑、片层石墨、石墨烯或碳纳米管中的至少一种。正极极片中的粘结剂可以包括聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、苯乙烯-丙烯酸酯共聚物、苯乙烯-丁二烯共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素纳、聚醋酸乙烯酯、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。正极活性物质包括但不限于钴酸锂、镍酸锂、锰酸锂、镍锰酸锂、镍钴酸锂、磷酸铁锂、镍钴铝酸锂或镍钴锰酸锂中的至少一种，以上正极活性物质可以包括经过掺杂或包覆处理的正极活性物质。
在本公开的一些实施例中，隔离膜包括聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的稳定性。
在本公开的一些实施例中，隔离膜表面还可包括多孔层，多孔层设置在隔离膜的至少一个表面上，多孔层包括无机颗粒和粘结剂，无机颗粒选自氧化铝(Al 2O 3)、氧化硅(SiO 2)、氧化镁(MgO)、氧化钛(TiO 2)、二氧化铪(HfO 2)、氧化锡(SnO 2)、二氧化铈(CeO 2)、氧化镍(NiO)、氧化锌(ZnO)、氧化钙(CaO)、氧化锆(ZrO 2)、氧化钇(Y 2O 3)、碳化硅(SiC)、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡中的至少一种。粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素纳、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。隔离膜表面的多孔层可以提升隔离膜的耐热性能、抗氧化性能和电解质浸润性能，增强隔离膜与极片之间的粘接性。
在本公开的一些实施例中，电化学装置的电极组件为卷绕式电极组件或堆叠式电极组件。
本公开还提出一种电化学装置，包括：上述任一项的电极组件。在本公开的一些实施例中，电化学装置包括锂金属电池，但是本公开不限于此。
本公开还提出一种电子装置，包括：上述的电化学装置。在本公开的一些实施例中，电子装置可以包括手机、平板电脑、充电等使用充电电池的任何电子装置。
下面列举了一些具体实施例和对比例以更好地对本公开进行说明。
在本公开的以下实施例1～6及对比例1～9中，采用锂金属电池作为示例，其中制备锂离子电池所用的原材料、原材料配比、制备方法等均只作为示例，本公开并不限以下示例中所用的原材料、原材料配比和制备方法。
实施例1
负极极片的制备：通过磁控溅射方式将硅镀于锂金属极片上，形成含硅的保护层，保护层厚度约1μm，将锂金属极片裁切成(40mm×60mm)的规格待用。
正极极片的制备：将正极活性材料钴酸锂(LiCoO 2)、导电炭黑(Super P)、聚偏二氟乙烯(PVDF)按照重量比97.5:1.0:1.5进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成为固含量为0.75的浆料，并搅拌均匀。将浆料均匀涂覆在正极集流体铝箔上，90℃条件下烘干，得到正极极片。涂布完成后，将极片裁切成(38mm×58mm)的规格待用。
电解液的制备：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)和碳酸二乙酯(DEC)以质量比EC:DEC＝1:1混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
锂离子电池的制备：选用厚度15μm的聚乙烯(PE)作为隔离膜置于中间，上下两层分别为极片，极片与极片之间为隔离膜。叠好后，用胶带将整个叠片结构的四个角固定好后，置入铝塑膜中，经顶侧封、注液、封装后，最终得到锂金属叠片电池。
实施例2
实施例2与实施例1的区别仅在于电解液的制备不同，在实施例2中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸亚乙烯酯(VC)以质量比EC:DEC:VC＝40:40:20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
实施例3
实施例3与实施例1的区别仅在于电解液的制备不同，在实施例3中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和氟代碳酸乙烯酯(FEC)以质量比EC:DEC:FEC＝40:40:20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
实施例4
实施例4与实施例1的区别在于负极极片的制备和电解液的制备不同，在实施例4中：
负极极片的制备：硅作为靶材，氧气作为工艺气体，通过磁控溅射方式将SiOx镀于锂金属极片上，形成SiOx保护层，保护层厚度约1μm。将锂金属极片裁切成(40mm×60mm)的规格待用。
电解液的制备：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)和碳酸二乙酯(DEC)以质量比EC:DEC＝1:1混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
实施例5
实施例5与实施例4的区别仅在于电解液的制备不同，在实施例5中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸亚乙烯酯(VC)以质量比EC:DEC:VC＝40:40:20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
实施例6
实施例6与实施例4的区别仅在于电解液的制备不同，在实施例6中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和氟代碳酸乙烯酯(FEC)以质量比EC:DEC:FEC＝40:40:20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例1
对比例1与实施例1的区别在于负极极片的制备不同，在对比例1中：
负极极片的制备：将锂金属极片裁切成(40mm×60mm)的规格待用。
对比例2
对比例2与对比例1的区别在于电解液的制备不同，在对比例2中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和氟代碳酸乙烯酯(FEC)以质量比EC:DEC:FEC＝47.5:47.5:5混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例3
对比例3与对比例1的区别在于电解液的制备不同，在对比例3中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和氟代碳酸乙烯酯(FEC)以质量比EC:DEC:FEC＝45:45:10混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例4
对比例4与对比例1的区别在于电解液的制备不同，在对比例4中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和氟代碳酸乙烯酯(FEC)以质量比EC:DEC:FEC＝40:40:20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例5
对比例5与对比例1的区别在于电解液的制备不同，在对比例5中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和氟代碳酸乙烯酯(FEC)以质量比EC:DEC:FEC＝35:35:30混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例6
对比例6与对比例1的区别在于电解液的制备不同，在对比例6中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和氟代碳酸乙烯酯(FEC)以质量比EC:DEC:FEC＝30:30:40混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例7
对比例7与对比例1的区别在于电解液的制备不同，在对比例7中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸亚乙烯酯(VC)以质量比EC:DEC:VC＝45:45:10混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例8
对比例8与对比例1的区别在于电解液的制备不同，在对比例8中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸亚乙烯酯(VC)以质量比EC:DEC:VC＝40:40:20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
对比例9
对比例9与对比例1的区别在于电解液的制备不同，在对比例9中：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸亚乙烯酯(VC)以质量比EC:DEC:VC＝35:35:30混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.0M的电解液。
电池性能测试
实施例1～6和对比例1～9的循环性能拟用全电池容量保持率低于或等于80％时的循环圈数来表征该方案的有效性，具体步骤如下：全电池以0.1C的倍率先充电至4.53V，之后恒压充电至电流小于0.05C，再0.1C倍率放电至3V截至，以上流程重复2次进行活化。活化后，0.3C倍率充电至4.53V，之后恒压充电至电流小于0.05C，再0.5C倍率放电至3V截至。循环48圈后，从第1步活化开始往复循环直至电池容量低于80％，通过LAND或NEWARE输出的电化学测试曲线读取循环圈数。
对比例1～9和实施例1～6的循环性能测试结果如表1所示(NA表示无)：
表1
  保护层材料/厚度 电解液中FEC含量 电解液中VC含量 循环圈数
对比例1 NA NA NA 50
对比例2 NA 5％ NA 60
对比例3 NA 10％ NA 70
对比例4 NA 20％ NA 120
对比例5 NA 30％ NA 100
对比例6 NA 40％ NA 60
对比例7 NA NA 10％ 60
对比例8 NA NA 20％ 100
对比例9 NA NA 30％ 80
实施例1 Si/1um NA NA 50
实施例2 Si/1um NA 20％ 120
实施例3 Si/1um 20％ NA 150
实施例4 SiOx/1um NA NA 60
实施例5 SiOx/1um NA 20％ 140
实施例6 SiOx/1um 20％ NA 180
对比例1～6表明，在电解液中添加FEC可以改善循环性能，但电解液中FEC的浓度应当不超过30％，这是因为当FEC的浓度过高会在正极产气，恶化循环性能。
对比例1、7～9表明，在电解液中添加VC也可以改善循环性能，且电解液中VC的浓度应当不超过30％，最优为20％。添加VC的电解液比无添加剂的电解液(SEI主要成分为LiF)的循环性能好，这是因为，VC添加剂可以改善SEI膜的韧性，SEI膜在循环过程中更加稳定，不易破碎。
从对比例1～9的比对结果可知，在电解液中添加适当浓度的FEC和VC可以改善循环性能。
如实施例1和对比例1所示。在实施例1中，虽然采用了含硅的保护层，但电解液中不含有FEC添加剂，电池的循环性能与没有含硅保护层的对比例1相比并没有得到明显改善。这是因为硅或硅合金在不含FEC的电解液中难以形成稳定的固体电解质界面(SEI)膜，伴随着循环过程中SEI的反复破碎，在暴露出的硅或硅合金表面不断形成新的SEI膜，加剧了硅或硅合金的腐蚀和电解液的消耗。因此，硅或硅合金在不含FEC的电解液体系中无法发挥出负极保护作用，电池循环性能没有得到改善。
请参看实施例1和实施例2，实施例2中设置有含硅的保护层，同时在电解液中添加了VC，相比于实施例1，实施例2中，在电解液中添加了20％的VC，电池容量低于80％的循环圈数达到了120圈，这是因为与没有VC的电解液相比，添加了VC的电解液生成的SEI韧性更高，循环过程中不易破碎。
请参看实施例2和对比例8，实施例2与对比例8都在电解液中添加了20％VC，但对比例8的负极中没有含硅的保护层，相比于对比例8，实施例2的循环圈数提升了20％，表明在含有VC的电解液体系中，硅或硅合金能发挥出负极保护作用，即阻隔电解液与锂金属发生副反应，抑制枝晶生长，从而进一步提高了循环圈数。
请参看实施例3和对比例3，实施例3和对比例3的电解液中都含有电解液中含20％FEC，实施例3的负极中具有含硅的保护层，而对比例3不含 保护层，相比于对比例3，具有含硅保护层的实施例3的循环圈数提升了25％，这是因为含硅的保护层抑制了负极中锂金属与电解液的副反应。
从实施例2与对比例8的比对结果，以及实施例3和对比例3的比对结果可知，同时设置含硅的保护层，以及使用含VC或FEC的电解液可以进一步改善循环性能。
请参看实施例2和实施例3，实施例2与实施例3的区别在于：实施例3的电解液中含有20％FEC，实施例2的电解液中含有20％VC，实施例3的循环圈数相比于实施例2也提升25％。这是因为FEC反应活性高，能导致硅负极保护更快的完成钝化并抑制锂的消耗，分解产生的LiF能够起到粘合硅负极保护和SEI膜的作用，减少微裂纹的产生，从而提高SEI膜的稳定性。
实施例2与实施例3，对比例8与对比例4均表明，添加FEC的电解液比添加VC电解液的循环性能好。这是因为，在添加VC添加剂的电解液中形成的SEI膜，电荷交换阻抗较大，导致在快速充电的过程中负极产生的极化显著增加，影响电池的循环性能。
请参看实施例4～6，实施例4～6的比对结果可知，FEC和VC添加剂改善成膜同样也适用于保护层为硅氧化合物的体系。
请参看实施例1～6，实施例4～6的循环性能优于实施例1～3的循环性能，这是因为锂在Li xSiO y中的扩散系数(10 -4～10 -8cm 2/s)高于锂离子在Li xSi中的扩散系数(10 -12～10 -13cm 2/s)，因此在大倍率下具有更优异的循环性能。
综上可知，以上对比例与实施例中，最优方案为实施例6，即保护层的材料采用硅氧化合物，电解液中FEC含量为20％。
本公开中通过同时引入含硅保护层和含FEC的电解液，并控制FEC的浓度在特定范围，从而在对负极形成保护的同时，改善了保护层表面的SEI膜，从而显著提高了电池的循环性能。
以上描述仅为本公开的较佳实施例以及对所运用技术原理的说明。本领域技术人员应当理解，本公开中所涉及的公开范围，并不限于上述技术特征的特定组合而成的技术方案，同时也应涵盖在不脱离上述公开构思的情况下，由上述技术特征或其等同特征进行任意组合而形成的其它技术方案。例如上述特征与本公开中公开的(但不限于)具有类似功能的技术特征进行互相替换而形成的技术方案。

Claims (10)

  1. 一种电极组件，其特征在于，包括：
    电解液，所述电解液包括溶剂和添加剂，所述添加剂包括氟代碳酸乙烯酯；所述氟代碳酸乙烯酯的质量与所述溶剂和添加剂的总质量的比值为10％～30％；
    负极，所述负极具有活性物质和覆盖所述活性物质的保护层，所述保护层位于所述电解液与所述活性物质之间，所述保护层与所述电解液相接触，所述活性物质含有锂金属，所述保护层含有硅元素。
  2. 根据权利要求1所述的电极组件，其特征在于，
    所述保护层的厚度为0.001μm～100μm。
  3. 根据权利要求1所述的电极组件，其特征在于，
    所述活性物质包括单质锂金属或含有锂金属的复合材料中的至少一种。
  4. 根据权利要求1所述的电极组件，其特征在于，
    在所述活性物质和所述保护层中，锂元素与硅元素的体积比大于10:1。
  5. 根据权利要求1所述的电极组件，其特征在于，
    所述保护层包括含硅合金SiM y或硅氧化合物中的至少一种，其中，y<0.05，M为B、Al、P、Fe、Co、Ni、Zn、Ge、Ga、As、Zr、In或Sn中的至少一种。
  6. 根据权利要求1所述的电极组件，其特征在于，
    所述溶剂包括环状酯或链状酯中的至少一种；
    所述环状酯包括碳酸乙烯酯、碳酸丙烯酯、γ-丁内酯、含氟基团取代的碳酸乙烯酯、含氟基团取代的碳酸丙烯酯或碳酸丁烯酯中的至少一种；
    所述链状酯包括碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、甲酸甲酯、甲酸乙酯、乙酸乙酯、丙酸乙酯、丙酸丙酯、丙酸甲酯、丁酸甲酯、丁酸乙酯、氟代碳酸甲乙酯、氟代碳酸二甲酯、氟代碳酸二乙酯、氟代丙酸乙酯、氟代丙酸丙酯、氟代丙酸甲酯、氟代乙酸乙酯、氟代乙酸甲酯或氟代乙酸丙酯中的至少一种。
  7. 根据权利要求1所述的电极组件，其特征在于，所述电解液中还包括碳酸亚乙烯酯。
  8. 根据权利要求1所述的电极组件，其特征在于，所述电极组件还包括正极和隔离膜，所述隔离膜设置在所述正极和所述负极之间。
  9. 一种电化学装置，其特征在于，包括：
    如权利要求1～8中任一项所述的电极组件。
  10. 一种电子装置，其特征在于，包括：如权利要求9所述的电化学装置。
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