WO2022267535A1 - 锂金属负极极片、电化学装置及电子设备 - Google Patents

锂金属负极极片、电化学装置及电子设备 Download PDF

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WO2022267535A1
WO2022267535A1 PCT/CN2022/079252 CN2022079252W WO2022267535A1 WO 2022267535 A1 WO2022267535 A1 WO 2022267535A1 CN 2022079252 W CN2022079252 W CN 2022079252W WO 2022267535 A1 WO2022267535 A1 WO 2022267535A1
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lithium
lithium metal
negative electrode
electrolyte
protective layer
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PCT/CN2022/079252
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English (en)
French (fr)
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曾毓群
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宁德时代新能源科技股份有限公司
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Priority to EP22827040.1A priority Critical patent/EP4220759A1/en
Publication of WO2022267535A1 publication Critical patent/WO2022267535A1/zh
Priority to US18/197,727 priority patent/US20230307618A1/en

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    • 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 application belongs to the technical field of energy storage, and in particular relates to a lithium metal negative pole piece, an electrochemical device and an electronic device.
  • the negative electrode active material of the commercialized secondary battery is mainly graphite. Due to the low theoretical lithium intercalation capacity of graphite itself, which is only 372mAh/g, and it is difficult to improve the energy density only by improving the battery design structure and manufacturing process. Its application in fields requiring high energy output is limited, so anode active materials with higher specific energy are required.
  • the lithium metal anode Due to its high theoretical capacity (3860mAh/g), low electrochemical potential (-3.040V vs. SHE), and high electrochemical reversible capacity, the lithium metal anode is considered to be the ultimate solution for the anode of lithium-ion batteries.
  • the huge volume expansion of the lithium metal anode during charging and discharging and the growth of lithium dendrites lead to serious shortcomings in cycle life and safety, making it impossible to realize commercial applications.
  • the industry In order to alleviate the above problems, the industry generally uses solid electrolytes to replace the existing liquid electrolytes to greatly reduce lithium metal side reactions and improve life and safety performance.
  • the inherent problems of solid electrolytes such as low conductivity and poor interfacial bonding cannot be effectively solved.
  • the present application provides a lithium metal negative pole piece, an electrochemical device and an electronic device, which can effectively reduce lithium metal side reactions and improve the first coulombic efficiency and cycle performance of the battery.
  • the first aspect of the present application provides a lithium metal negative electrode sheet
  • the lithium metal negative electrode sheet includes: copper foil; an active material layer formed on at least part of the surface of the copper foil, the active material layer includes lithium metal alloy; and a composite protective layer formed on at least part of the surface of the active material layer, the thickness of the composite protective layer is less than or equal to 10 ⁇ m, and the composite protective layer includes a lithium fluoride inorganic layer and a polymer organic layer.
  • the lithium metal negative electrode sheet satisfies at least one of the following conditions:
  • the thickness of the composite protective layer is 0.3 ⁇ m to 10 ⁇ m;
  • the thickness of the composite protective layer is 1 ⁇ m to 7 ⁇ m.
  • the lithium metal negative electrode sheet satisfies at least one of the following conditions:
  • the mass ratio of the lithium fluoride inorganic layer to the polymer organic layer is 1:5 to 5:1.
  • the polymer organic layer includes at least one of polydimethylsiloxane, polyacrylonitrile, polypyrrole, polyimide, polyacrylic acid, and polymethylmethacrylate.
  • the lithium fluoride inorganic layer is formed by in-situ reaction of polyvinylidene fluoride and the lithium metal alloy.
  • the lithium metal negative electrode sheet satisfies at least one of the following conditions:
  • the chemical formula of the lithium metal alloy is LiR, and the R metal is selected from at least one of Ag, Mo, In, Ge, Bi and Zn;
  • the chemical formula of the lithium metal alloy is LiR, and the mass content of the R element in the lithium metal alloy is 1% to 10%;
  • the lithium metal alloy is a solid solution alloy.
  • the second aspect of the present application provides an electrochemical device, including a positive pole piece, a negative pole piece, a separator, and an electrolyte, and the negative pole piece is the negative pole piece described in the first aspect.
  • the electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte
  • the electrolyte includes a solvent and a lithium salt
  • the electrolyte satisfies at least one of the following conditions:
  • the lithium salt includes lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bistrifluoromethanesulfonylimide, lithium bis(fluorosulfonyl)imide, lithium bisoxalate borate or lithium difluorooxalate borate at least one of;
  • the solvent includes ethylene glycol dimethyl ether and 1,3-dioxolane;
  • the solvent includes ethylene glycol dimethyl ether and 1,3-dioxolane, and the volume ratio of the ethylene glycol dimethyl ether to the 1,3-dioxolane is (0.5 ⁇ 10): 1;
  • the concentration of the electrolyte is 0.5mol/L to 7mol/L.
  • the electrolyte meets at least one of the following conditions:
  • the electrolyte also includes an additive, and the additive includes at least one of paraformaldehyde, lithium nitrate, dioxane, lithium fluorosulfonate, and fluoroethylene carbonate;
  • the electrolyte solution further includes an additive, and the mass content of the additive in the electrolyte solution is 0.1% to 10%.
  • a third aspect of the present application provides an electronic device, the electronic device comprising the electrochemical device according to the second aspect above.
  • the lithium metal negative electrode sheet, electrochemical device and electronic equipment provided by the present application, wherein the lithium metal negative electrode sheet forms an active material layer containing a lithium metal alloy on the surface of the copper foil, wherein the lithium metal alloy can pass through its own alloy phase A phase change occurs during the intercalation and extraction process, so that lithium ions grow along the alloy phase and close to the copper foil during the intercalation process, instead of growing close to the isolation film to form lithium dendrites, which can effectively inhibit the growth of lithium dendrites; lithium metal
  • the composite protective layer on the surface of the alloy in which the lithium fluoride inorganic layer and the polymer organic layer have a structure similar to a solid electrolyte film, can effectively prevent the direct contact between the electrolyte and lithium metal, increase the polarization degree of the lithium metal surface, and reduce lithium The occurrence of metal side reactions improves the first Coulombic efficiency and cycle performance of the battery.
  • FIG. 1 is a schematic structural view of a lithium metal negative electrode sheet provided in an embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with any other lower limit to form an unexpressed range, just as any upper limit can be combined with any other upper limit to form an unexpressed range.
  • every point or individual value between the endpoints of a range is included within that range, although not expressly stated herein. Thus, each point or individual value may serve as its own lower or upper limit in combination with any other point or individual value or with other lower or upper limits to form a range not expressly recited.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B.” More specifically, the condition “A or B” is satisfied by either of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; or both A and B are true (or exist).
  • FIG. 1 shows a schematic structural view of a lithium metal negative electrode sheet 1 provided in an embodiment of the present application.
  • the lithium metal negative electrode sheet 1 includes: a copper foil 11; an active material layer 12 formed on at least part of the surface of the copper foil 11, the active material layer 12 comprising a lithium metal alloy; and
  • the lithium metal negative electrode sheet forms an active material layer containing a lithium metal alloy on the surface of the copper foil.
  • lithium dendrites grow along the alloy phase and close to the copper foil instead of growing close to the isolation film, which can effectively inhibit the growth of lithium dendrites;
  • the polymer organic layer has a structure similar to a solid electrolyte membrane, which can effectively prevent the direct contact between the electrolyte and lithium metal, increase the polarization degree of the lithium metal surface, reduce the occurrence of lithium metal side reactions, and improve the first coulombic efficiency and cycle performance of the battery .
  • the lithium metal alloy is a solid solution alloy. It is understandable that the solid solution alloy phase of the lithium metal alloy provides a higher diffusion coefficient of lithium atoms than lithium metal, and the lithium atoms generated at the lithium metal alloy/electrolyte interface during the lithium intercalation process will diffuse into the pole piece. Lithium alloys, and in the delithiation process, the lithium atoms produced by de-alloying can be released quickly within the discharge time, thereby improving the first charge and discharge Coulombic efficiency of the battery.
  • the lithium metal alloy Since the lithium metal alloy has a solid solution alloy phase, it can undergo a phase change during the lithium intercalation and desorption process through its own solid solution alloy phase, so that the extracted lithium atoms can penetrate into the lithium metal alloy to form an alloy phase instead of being deposited on the negative electrode sheet.
  • Metal lithium is generated on the surface, that is, lithium atoms grow along the alloy phase to the inside of the lithium metal alloy during the intercalation process, which inhibits the growth of lithium dendrites.
  • the chemical formula of the lithium metal alloy is LiR, and the R metal is selected from at least one of Ag, Mo, In, Ge, Bi and Zn.
  • the mass content of the R element in the lithium metal alloy is 1% to 10%, specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 10%. %, etc., of course, can also be other values within the above range, which are not limited here.
  • the mass content of the R element in the lithium metal alloy is too high, that is, the lithium content in the lithium metal alloy decreases, it will affect the kinetic performance of the battery, resulting in a decrease in the energy density and rate performance of the battery.
  • the mass content of the R element in the lithium metal alloy is too low, the content of the solid solution alloy in the lithium metal alloy decreases, and the solid solution alloy phase transformation cannot be used to inhibit the growth of lithium dendrites.
  • the mass content of the R element in the lithium metal alloy is 3% to 7%.
  • the thickness of the composite protective layer 13 is 0.3 ⁇ m to 10 ⁇ m; specifically, it can be 0.3 ⁇ m, 0.5 ⁇ m, 1.0 ⁇ m, 1.4 ⁇ m, 1.8 ⁇ m, 2.2 ⁇ m, 3.5 ⁇ m, 4.0 ⁇ m, 4.5 ⁇ m, 4.9 ⁇ m, 5.5 ⁇ m, 6.0 ⁇ m, 7.0 ⁇ m, 8.0 ⁇ m, 9.2 ⁇ m, or 10 ⁇ m, etc., of course, can also be other values within the above range, which are not limited here.
  • the composite protective layer 13 When the composite protective layer 13 is too thick, the energy density of the battery decreases; when the composite protective layer 13 is too thin, the mechanical strength of the composite protective layer decreases, and the protection of the composite protective layer on the lithium metal alloy decreases, causing lithium dendrites to easily move towards the separator. growth, deteriorating battery cycle performance.
  • the composite protective layer 13 has a thickness of 1 ⁇ m to 7 ⁇ m; more preferably, the composite protective layer 13 has a thickness of 3 ⁇ m to 5 ⁇ m.
  • the composite protective layer 13 includes a lithium fluoride inorganic layer 131 and a polymer organic layer 132 .
  • the lithium fluoride inorganic layer is formed by in-situ reaction of polyvinylidene fluoride and the lithium metal alloy.
  • Lithium fluoride can be one of the components of solid electrolyte membrane, which has good ionic conductivity, mechanical properties and electrochemical stability.
  • the combination of lithium fluoride and polymer can form an effect similar to a solid electrolyte membrane, thereby inhibiting the side reaction between lithium metal and electrolyte, and improving the stability of lithium metal alloy and electrolyte.
  • lithium fluoride and lithium metal are covalently bonded, so that the stability of the combination of lithium fluoride and lithium metal alloy is enhanced, and the coating on the surface of the copper foil is not easy to fall off during the cycle.
  • the lithium fluoride inorganic layer can be formed in situ by reacting the copper foil formed with the lithium metal alloy and polyvinylidene fluoride.
  • the lithium fluoride inorganic layer can improve the conductivity of lithium ion diffusion and inhibit the formation and growth of lithium dendrites.
  • the thickness of the lithium fluoride inorganic layer may be 0.1 ⁇ m to 2 ⁇ m, specifically 0.1 ⁇ m, 0.2 ⁇ m, 0.5 ⁇ m, 0.8 ⁇ m, 1.0 ⁇ m, 1.2 ⁇ m, 1.5 ⁇ m, 1.8 ⁇ m or 2.0 ⁇ m, etc., of course, It can be other values within the above range, which is not limited here.
  • the thickness of the lithium fluoride inorganic layer can be controlled according to the reaction time. If the thickness of the lithium fluoride inorganic layer is too thick, the pole pieces are prone to breakage during cycling, which affects the electrochemical performance. If the thickness of the lithium fluoride inorganic layer is too thin, the electrochemical stability and ion conductivity of the composite protective layer 13 will decrease, and the cycle performance of the battery will decrease.
  • the polymeric organic layer can guide the uniform nucleation of lithium with strong viscosity and mechanical strength.
  • the combined use of the polymer organic layer and the lithium fluoride inorganic layer can make the composite protective layer have both strong mechanical strength and high ionic conductivity, can coat the lithium metal alloy, and can improve the contact between the lithium metal alloy and the copper foil.
  • the integrity of the interface can inhibit the direct contact between lithium metal and electrolyte to cause side reactions and lithium dendrite growth.
  • the polymer organic layer can be formed on the surface of the lithium fluoride inorganic layer by spraying, coating, deposition and other processes.
  • the thickness of the polymer organic layer may be 0.2 ⁇ m to 2 ⁇ m, specifically 0.2 ⁇ m, 0.5 ⁇ m, 0.8 ⁇ m, 1.0 ⁇ m, 1.2 ⁇ m, 1.5 ⁇ m, 1.8 ⁇ m or 2.0 ⁇ m, etc., Of course, other values within the above range may also be used, which are not limited here. If the thickness of the polymer organic layer is too thick, the energy density of the battery will decrease; if the thickness of the polymer organic layer is too thin, the integrity, mechanical strength, and elasticity of the composite protective layer will decrease, and it will easily break during cycling, which will affect the electrochemical performance.
  • the polymer organic layer includes polydimethylsiloxane (PDMS), polyacrylonitrile (PAN), polypyrrole (Ppy), polyimide (PI), polyacrylic acid (PAA), polymethyl methacrylate (PMMA) at least one.
  • PDMS polydimethylsiloxane
  • PAN polyacrylonitrile
  • Ppy polypyrrole
  • PI polyimide
  • PAA polyacrylic acid
  • PMMA polymethyl methacrylate
  • the mass ratio of the lithium fluoride inorganic layer to the polymer organic layer is 1:10 to 10:1; specifically, it can be 1:10, 2:10, 3:10, 4:10, 5:10, 8:10, 10:10, 10:8, 10:5, 10:3, 10:1, etc. Of course, other values within the above range may also be used, which are not limited here.
  • the content of the lithium fluoride inorganic layer in the composite protective layer is too high, that is, the content of the polymer organic layer in the composite protective layer decreases, the integrity, mechanical strength and elasticity of the composite protective layer decrease, making it easy for the pole piece to occur during cycling. Broken, affecting electrochemical performance.
  • the mass ratio of the lithium fluoride inorganic layer to the polymer organic layer is 1:5 to 5:1.
  • the preparation method of the lithium metal negative electrode sheet includes the following steps:
  • lithium metal Under the Ar atmosphere, put lithium metal into a stainless steel crucible and heat it to 280°C to 350°C to melt it completely, then add the alloy component powder into the liquid lithium metal and stir for 2h to 6h to ensure that the metal powder and lithium The metal liquid is evenly mixed, and after cooling, the lithium metal alloy active material can be obtained.
  • the lithium metal alloy active material is compounded on the surface of the copper foil by cold pressing to obtain a pole piece.
  • the pole piece is placed in a solution containing polyvinylidene fluoride, so that lithium metal reacts with polyvinylidene fluoride to form a lithium fluoride inorganic layer in situ.
  • the organic slurry containing the polymer is sprayed on the surface of the lithium fluoride inorganic layer, and then placed in a vacuum at 60°C to 100°C Drying at a lower temperature to obtain a lithium metal negative electrode sheet.
  • the present application provides an electrochemical device, comprising a positive pole piece, a negative pole piece and an electrolyte solution, wherein the negative pole piece is the lithium metal negative pole piece according to the first aspect above.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on at least part of the surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.
  • the positive electrode active material can be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide
  • the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials of lithium ion batteries can also be used.
  • the positive electrode active material includes lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate and lithium titanate at least one of the
  • the positive electrode active material layer may further include a positive electrode conductive material, thereby imparting conductivity to the electrode.
  • the positive electrode conductive material may include any conductive material as long as it does not cause chemical changes.
  • Non-limiting examples of positive electrode conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powder, metal fibers, etc., Including, eg, copper, nickel, aluminum, silver, etc.), conductive polymers (eg, polyphenylene derivatives), and mixtures thereof.
  • the positive electrode active material layer may further include a binder to firmly bind the positive electrode active material and optional conductive agent to the positive electrode current collector.
  • a binder to firmly bind the positive electrode active material and optional conductive agent to the positive electrode current collector. This application does not specifically limit the type of binder, which can be selected according to actual needs.
  • the binder can be polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene-butadiene At least one of rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMA) and carboxymethyl chitosan (CMCS).
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PAA polyacrylic acid
  • PVA polyvinyl alcohol
  • EVA ethylene-vinyl acetate copolymer
  • SBR styrene-butadiene
  • SBR carboxymethyl cellulose
  • SA sodium alginate
  • PMA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • the positive current collector can be a conductive carbon sheet, metal foil, carbon-coated metal foil or porous metal plate, wherein the conductive carbon material of the conductive carbon sheet can be superconducting carbon, acetylene black, carbon black One or more of ketjen black, carbon dots, carbon nanotubes, graphite, graphene and carbon nanofibers, the metal material of metal foil, carbon-coated metal foil and porous metal plate can be independently selected from copper , aluminum, nickel and stainless steel at least one.
  • the positive current collector 11 is, for example, one or more of copper foil, aluminum foil, nickel foil, stainless steel foil, stainless steel mesh, and carbon-coated aluminum foil, preferably aluminum foil.
  • the above-mentioned positive electrode sheet can be prepared according to conventional methods in the art.
  • the positive electrode active material and optional conductive agent and binder are dispersed in a solvent (such as N-methylpyrrolidone, referred to as NMP) to form a uniform positive electrode slurry, and the positive electrode slurry is coated on the positive electrode current collector. , after drying and cold pressing, the positive electrode sheet is obtained.
  • a solvent such as N-methylpyrrolidone, referred to as NMP
  • the isolation film in the electrochemical device of the present application can be various materials suitable for the isolation film of electrochemical energy storage devices in the field, for example, it can be including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, At least one of polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fiber.
  • the electrolytic solution in the electrochemical device of the present application includes a solvent, lithium salt and additives.
  • the lithium salt in the electrolyte is selected from at least one of organic lithium salts or inorganic lithium salts.
  • the lithium salt can be selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate, lithium difluorophosphate, lithium bistrifluoromethanesulfonylimide LiN(CF3SO2)2 (abbreviated as LiTFSI), bis(fluorosulfonyl)
  • LiFSI lithium bisoxalate borate LiB(C2O4)2
  • LiDFOB lithium difluorooxalate borate LiBF2(C2O4)
  • the solvent in the electrolyte includes ethylene glycol dimethyl ether (abbreviated as DME) and 1,3-dioxolane (abbreviated as DOL).
  • DME ethylene glycol dimethyl ether
  • DOL 1,3-dioxolane
  • the volume ratio of the ethylene glycol dimethyl ether to the 1,3-dioxolane is (0.5-10):1, specifically 0.5:1, 0.8:1, 1:1, 1.5:1 , 1.8:1, 2.5:1, 3:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc.
  • DME ethylene glycol dimethyl ether
  • DOL 1,3-dioxolane
  • the volume ratio of the ethylene glycol dimethyl ether to the 1,3-dioxolane is (1-7):1. It should be noted that the mixed use of the above two solvents is beneficial for the electrolyte to form a more stable solid-state electrolyte film on the surface of the pole piece, reducing the occurrence of side reactions and inhibiting the growth of lithium dendrites.
  • the concentration of the electrolyte is 0.5 mol/L to 7 mol/L, specifically 0.5 mol/L, 0.8 mol/L, 1 mol/L, 1.5 mol/L, 2.0 mol/L L, 3 mol/L, 4 mol/L, 5 mol/L, 6 mol/L or 7 mol/L, etc., of course, can also be other values within the above range, which are not limited here. Excessive concentration of the electrolyte will lead to excessive viscosity of the electrolyte, which will affect the processing and dynamic performance of the battery.
  • the electrolyte has a concentration of 2mol/L to 5mol/L. It can be understood that using the electrolyte within the above concentration range can increase the lithium ion concentration at the interface between lithium metal and electrolyte, eliminate concentration polarization as much as possible, and alleviate the resulting growth of polarized lithium dendrites.
  • the electrolyte solution further includes additives, and the additives include at least one of paraformaldehyde, lithium nitrate, dioxane, lithium fluorosulfonate, and fluoroethylene carbonate.
  • the mass content of the additive in the electrolyte is 0.1% to 10%, specifically 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% %, 3.5%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., of course, can also be other values within the above range, which are not limited here.
  • the mass content of the additive in the electrolyte is 0.5% to 5%.
  • the isolation film is selected from one or more composites of polyethylene film, polypropylene film, and polyvinylidene fluoride film. Of course, it can also be used on the isolation film substrate according to actual needs
  • the surface is coated with an inorganic or organic coating to enhance the hardness of the battery or to improve the adhesion between the separator and the cathode-negative interface.
  • the preparation method of the above-mentioned electrochemical device includes the following steps:
  • the separator is between the positive pole piece and the negative pole piece to play the role of isolation, and the battery cell can be obtained, or the battery core can be obtained after winding ;
  • Place the electric core in the packaging shell can be a soft bag, a square aluminum shell, a square steel shell, a cylindrical aluminum shell and a cylindrical steel shell), inject electrolyte and seal it to obtain an electrochemical device.
  • the electrochemical device is a lithium secondary battery, wherein the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion battery. Polymer secondary battery.
  • the present application also provides an electronic device, which includes the electrochemical device described in the second aspect above. Electrochemical devices can be used to provide power to electronic devices.
  • the electronic devices include, but are not limited to: notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted Stereo headphones, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, power assist Bicycles, bicycles, lighting equipment, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries or lithium-ion capacitors, etc.
  • the lithium metal Under the Ar atmosphere, put the lithium metal into a stainless steel crucible and heat it to 300°C to melt it completely, then add the alloy component powder into the liquid lithium metal and stir for 2 hours to ensure that the metal powder and the lithium metal liquid are evenly mixed, After cooling, the lithium metal alloy active material can be obtained.
  • the lithium metal alloy active material is compounded on the surface of copper foil by cold pressing to obtain a pole piece; the pole piece is placed in a solution containing polyvinylidene fluoride, so that lithium metal and polyvinylidene fluoride react in situ to form a lithium fluoride inorganic layer ; After drying the pole piece containing the lithium fluoride inorganic layer under vacuum at 80°C, spraying the polymer-containing organic slurry onto the surface of the lithium fluoride inorganic layer, and then drying under vacuum at 80°C to obtain Lithium metal negative electrode sheet.
  • PE Polyethylene
  • a mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) is used as an organic solvent, and then fully dried lithium hexafluorophosphate is dissolved in the mixed organic solvent to prepare an electrolyte solution.
  • the above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play the role of isolation, and the above-mentioned electrolyte is added to assemble a button battery.
  • Examples 1 to 36 of negative electrode sheets and comparative examples 1 to 17 were prepared according to the above preparation method, and the specific parameters of the electrolyte formulations are shown in Table 1.
  • SEM was used to image the cross-section of the pole piece quenched and cut in liquid nitrogen, and the thickness of the composite protective layer was measured by secondary electron images.
  • Example 1 sample first coulombic efficiency Number of cycles Example 1 91 601 Example 2 94 632 Example 3 95 681 Example 4 95 666 Example 5 95 643 Example 6 94 611 Example 7 94 594 Example 8 95 621 Example 9 94 646 Example 10 93 622 Example 11 93 607 Example 12 94 631 Example 13 93 617 Example 14 92 602 Example 15 93 625 Example 16 90 588
  • Example 17 89 541 Example 18 93 662 Example 19 94 672 Example 20 93 653 Example 21 93 631 Example 22 82 501 Example 23 89 588 Example 24 92 621 Example 25 87 571 Example 26 89 555 Example 27 91 598 Example 28 93 644 Example 29 90 577 Example 30 83 505 Example 31 92 594 Example 32 94 652 Example 33 93 630 Example 34 91 580 Example 35 90 623 Example 36 91 635 Comparative example 1 93 598 Comparative example 2 89 571 Comparative example 3 92 588 Comparative example 4 93 569 Comparative example 5 89 524 Comparative example 6 90 544 Comparative example 7 87 513 Comparative example 8 91 600 Comparative example 9 85 523 Comparative example 10 80 471 Comparative example 11 87 535 Comparative example 12 85 505 Comparative example 13 80 481 Comparative example 14 72 105 Comparative example 15 89 579 Comparative example 16 82 481 Comparative example 17 80 480
  • the composite protective layer has a thickness of 1 ⁇ m to 7 ⁇ m.
  • the mass ratio of the lithium fluoride inorganic layer to the polymer organic layer is 1:5 to 5:1.
  • Example 3 According to the test results of Example 3 and Examples 12 to 16, it can be seen that when the alloying elements in the lithium metal alloy change, some metals will hardly form a solid solution with lithium metal, which will cause lithium dendrites to grow outward and penetrate the separator, and the battery The cycle performance is degraded.
  • Example 3 According to the test results of Example 3, Examples 17 to 21, and Comparative Examples 7 and 8, it can be seen that when the mass content of the R element in the lithium metal alloy is in the range of 1% to 10%, the lithium intercalation overpotential can be effectively reduced, and the lithium intercalation overpotential can be effectively reduced. Inhibits the growth of lithium dendrites.
  • the mass content of the R element in the lithium metal alloy of Comparative Example 7 is too low, the solid solution alloy content in the lithium metal alloy decreases, and the phase transformation of the solid solution alloy cannot be used to inhibit the growth of lithium dendrites.
  • the mass content of the R element in the lithium metal alloy of Comparative Example 8 is too high, that is, the lithium content in the lithium metal alloy decreases, the kinetic performance of the battery will be affected, resulting in a decrease in the energy density and rate performance of the battery.
  • the mass content of the R element in the lithium metal alloy is 3% to 7%.
  • Example 3 According to the test results of Example 3 and Comparative Example 9, it can be known that the surface of the copper foil of Comparative Example 9 is replaced by pure lithium metal alloy, lithium metal does not have an alloy phase, and the solid solution alloy phase transformation cannot be used to suppress the formation of lithium dendrites. growth, the cycle performance of the battery decreases.
  • Example 3 Examples 22 to 25, and Comparative Examples 10 and 11 it can be seen that when the concentration of the electrolyte is in the range of 0.5mol/L to 7mol/L, the kinetic performance of the battery is better, which can ensure the battery life. cycle performance.
  • Comparative Example 10 it can be seen that if the concentration of the electrolyte is too small, the concentration of lithium salt will be too low, the concentration difference polarization will be intensified during the cycle, the growth of lithium dendrites will be promoted, and the cycle performance of the battery will decrease.
  • the electrolyte has a concentration of 2mol/L to 5mol/L.
  • Example 3 According to the test results of Example 3, Examples 26 to 30, and Comparative Examples 12 and 13, it can be seen that when the volume ratio of DME to DOL is in the range of (0.5-10):1, it is beneficial for the electrolyte to form a more stable electrolyte on the surface of the lithium metal alloy.
  • the stable solid electrolyte membrane reduces the occurrence of side reactions and inhibits the growth of lithium dendrites, which is conducive to improving the cycle performance of the battery.
  • the synergy between oxycyclopentane and ethylene glycol dimethyl ether forms a stable solid electrolyte film, and the cycle performance of the battery decreases; preferably, the ethylene glycol dimethyl ether and the 1,3-diox
  • the volume ratio of cyclopentane is (1-7):1.
  • the mass content of the additive in the electrolyte is 0.5% to 5%.
  • lithium nitrate will decompose to form lithium nitride at a low potential, and the inorganic protective layer formed in situ will uniformly cover the surface of lithium metal so that Stabilize the overall structure of SEI (Solid Electrolyte Interface Film) and improve battery cycle performance.
  • SEI Solid Electrolyte Interface Film
  • fluoroethylene carbonate and lithium fluorosulfonate additives have a slight impact on the stability of the electrolyte, but they can also effectively improve the cycle performance of the battery.
  • Comparative Example 17 the above-mentioned additives were not added, which resulted in intensified side reactions on the surface of the pole piece and decreased battery cycle performance.

Abstract

本申请提供了一种锂金属负极极片、电化学装置及电子设备。锂金属负极极片包括铜箔及形成于所述铜箔的至少部分表面上的活性物质层，所述活性物质层包括锂金属合金；以及形成于所述活性物质层的至少部分表面上的复合保护层，所述复合保护层的厚度小于等于10μm，所述复合保护层包括氟化锂无机层以及聚合物有机层。本申请提供的锂金属负极极片、电化学装置及电子设备，能够有效降低锂金属副反应，提升电池的首次库伦效率及循环性能。

Description

锂金属负极极片、电化学装置及电子设备
相关申请的交叉引用
本申请要求享有于2021年06月26日提交的名称为“锂金属负极极片、电化学装置及电子设备”的中国专利申请202110741456.3的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于储能技术领域，具体涉及一种锂金属负极极片、电化学装置及电子设备。
背景技术
随着能源与环境问题的日益凸显，新能源产业得到了越来越多的重视。二次电池因其能量密度高、循环性能好等特点，近年来作为一种重要的新型储能装置被广泛应用。目前商品化的二次电池的负极活性材料多以石墨为主，由于石墨本身的理论嵌锂容量较低，仅为372mAh/g，且仅通过改进电池设计结构和制造工艺也难以提高能量密度，使其在需要高能量输出的领域的应用受到限制，因此需要更高比能量的负极活性材料。
锂金属负极由于具有很高的理论容量(3860mAh/g)，电化学电势低(-3.040V vs.SHE)，电化学可逆容量高等优势，被认为是锂离子电池负极的最终解决方案。但是，锂金属负极在充放电过程中产生的巨大体积膨胀以及锂枝晶生长的问题，导致其在循环寿命与安全性方面存在严重短板，无法真正实现商业化应用。为缓解以上问题，业界普遍采用固态电解质来替代现有的液态电解质从而大幅降低锂金属副反应，提升寿命与安全性能。但是固态电解质自身电导率低，界面结合度差等本征问题仍无法得到有效解决。
因此，如何降低锂金属副反应，提升电池的首次库伦效率及循环性能是目前亟待解决的问题。
发明内容
本申请提供一种锂金属负极极片、电化学装置及电子设备，能够有效降低锂金属副反应，提升电池的首次库伦效率及循环性能。
本申请第一方面提供一种锂金属负极极片，所述锂金属负极极片包括：铜箔；形成于所述铜箔的至少部分表面上的活性物质层，所述活性物质层包括锂金属合金；以及形成于所述活性物质层的至少部分表面上的复合保 护层，所述复合保护层的厚度小于等于10μm，所述复合保护层包括氟化锂无机层以及聚合物有机层。
在本申请任意实施方式中，所述锂金属负极极片满足以下条件的至少一者：
(1)所述复合保护层的厚度为0.3μm至10μm；
(2)所述复合保护层的厚度为1μm至7μm。
在本申请任意实施方式中，所述锂金属负极极片满足以下条件的至少一者：
(3)所述氟化锂无机层与所述聚合物有机层的质量比为1：10至10：1；
(4)所述氟化锂无机层与所述聚合物有机层的质量比为1：5至5：1。
在本申请任意实施方式中，所述聚合物有机层包括聚二甲基硅氧烷、聚丙烯腈、聚吡咯、聚酰亚胺、聚丙烯酸、聚甲基丙烯酸甲酯中的至少一种。
在本申请任意实施方式中，所述氟化锂无机层由聚偏氟乙烯与所述锂金属合金原位反应形成。
在本申请任意实施方式中，所述锂金属负极极片满足以下条件的至少一者：
(5)所述锂金属合金的化学式为LiR，R金属选自Ag、Mo、In、Ge、Bi和Zn中的至少一种；
(6)所述锂金属合金的化学式为LiR，所述锂金属合金中的R元素的质量含量为1％至10％；
(7)所述锂金属合金为固溶合金。
本申请第二方面提供一种电化学装置，包括正极极片、负极极片、隔离膜及电解液，所述负极极片为第一方面所述的负极极片。
在本申请任意实施方式中，所述电化学装置包括正极极片、负极极片、隔离膜及电解液，所述电解液包括溶剂及锂盐，所述电解液满足以下条件的至少一者：
(9)所述锂盐包括六氟磷酸锂、四氟硼酸锂、二氟磷酸锂、双三氟甲烷磺酰亚胺锂、双(氟磺酰)亚胺锂、双草酸硼酸锂或二氟草酸硼酸锂中的至少一种；
(10)所述溶剂包括乙二醇二甲醚及1,3-二氧环戊烷；
(11)所述溶剂包括乙二醇二甲醚及1,3-二氧环戊烷，所述乙二醇二甲醚与所述1,3-二氧环戊烷的体积比为(0.5～10)：1；
(12)所述电解液的浓度为0.5mol/L至7mol/L。
在本申请任意实施方式中，所述电解液满足以下条件的至少一者：
(13)所述电解液还包括添加剂，所述添加剂包括三聚甲醛、硝酸锂、二恶烷、氟磺酸锂、氟代碳酸乙烯酯中的至少一种；
(14)所述电解液还包括添加剂，所述添加剂在所述电解液中的质量含量为0.1％至10％。
本申请第三方面提供一种电子设备，所述电子设备包括根据上述第二方面所述的电化学装置。
本申请提供的锂金属负极极片、电化学装置及电子设备，其中，锂金属负极极片通过在铜箔的表面形成含锂金属合金的活性物质层，其中，锂金属合金可以通过自身合金相在嵌脱锂过程中发生相变，使得锂离子在嵌入过程中沿合金相向靠近铜箔方向生长，而不是向靠近隔离膜方向生长形成锂枝晶，可以有效抑制锂枝晶的生长；锂金属合金表面的复合保护层，其中的氟化锂无机层与聚合物有机层有着类似固态电解质膜的结构，能够有效阻碍电解液与锂金属直接接触，增大锂金属表面极化程度，可以减少锂金属副反应的发生，提升电池的首次库伦效率及循环性能。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，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为本申请实施例提供的锂金属负极极片的结构示意图。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或几种”中“几种”的含义是两种或两种以上。
在本文的描述中，除非另有说明，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
应理解，术语“第一”、“第二”、等之类的关系术语仅仅用来将一 个实体或者操作与另一个实体或操作区分开来，而不一定要求或暗示这些实体或操作之间存在任何实际的关系或顺序。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
第一方面
本申请提供一种锂金属负极极片。图1示出了本申请实施例提供的锂金属负极极片1的结构示意图。如图1所示，所述锂金属负极极片1包括：铜箔11；形成于所述铜箔11的至少部分表面上的活性物质层12，所述活性物质层12包括锂金属合金；以及
形成于所述活性物质层12的至少部分表面上的复合保护层13，所述复合保护层13的厚度小于等于10μm，所述复合保护层13包括氟化锂无机层131以及聚合物有机层132。
在上述方案中，锂金属负极极片通过在铜箔的表面形成含锂金属合金的活性物质层，其中，锂金属合金可以通过自身合金相在嵌脱锂过程中发生相变，使得锂离子在嵌入过程中沿合金相向靠近铜箔方向生长，而不是向靠近隔离膜方向生长形成锂枝晶，可以有效抑制锂枝晶的生长；锂金属合金表面的复合保护层中的氟化锂无机层与聚合物有机层有着类似固态电解质膜的结构，能够有效阻碍电解液与锂金属直接接触，增大锂金属表面极化程度，可以减少锂金属副反应的发生，提升电池的首次库伦效率及循环性能。
作为本申请可选的技术方案，所述锂金属合金为固溶合金。可以理解地，锂金属合金的固溶合金相提供了比锂金属更高的锂原子扩散系数，在嵌锂过程中在锂金属合金/电解质界面处产生的锂原子会在扩散到极片内部生成锂合金，而在脱锂过程中，去合金化产生的锂原子能够在放电时间内快速脱出来，从而提高电池的首次充放电库仑效率。
由于锂金属合金具有固溶合金相，可以通过自身固溶合金相在嵌脱锂过程中发生相变，使得脱出的锂原子能够穿入锂金属合金内部形成合金相，而不是沉积在负极极片表面生成金属锂，即锂原子在嵌入过程中沿合金相向锂金属合金内部生长，抑制锂枝晶生长。
作为本申请可选的技术方案，所述锂金属合金的化学式为LiR，R金属选自Ag、Mo、In、Ge、Bi和Zn中的至少一种。具体地，所述锂金属合金中的R元素的质量含量为1％至10％，具体可以是1％、2％、3％、4％、5％、6％、7％、8％或10％等，当然也可以是上述范围内的其他值，在此不做限定。当锂金属合金中的R元素的质量含量过高时，即锂金属合金中的锂含量下降，会影响电池的动力学性能，导致电池的能量密度与倍率性能下降。当锂金属合金中的R元素的质量含量过低时，锂金属合金中的固溶合金含量减少，无法利用固溶合金相变来抑制锂枝晶的生长。优选地，所述锂金属合金中的R元素的质量含量为3％至7％。
作为本申请可选的技术方案，所述复合保护层13的厚度为0.3μm至10μm；具体可以是0.3μm、0.5μm、1.0μm、1.4μm、1.8μm、2.2μm、3.5μm、4.0μm、4.5μm、4.9μm、5.5μm、6.0μm、7.0μm、8.0μm、9.2μm或10μm等，当然也可以是上述范围内的其他值，在此不做限定。当复合保护层13过厚，电池能量密度下降；当复合保护层13过薄，会造成复合保护层机械强度下降，复合保护层对锂金属合金覆盖保护力度下降，造成锂枝晶容易朝向隔离膜生长，恶化电池循环性能。优选地，所述复合保护层13的厚度为1μm至7μm；更优选地，复合保护层13的厚度为3μm至5μm。
作为本申请可选的技术方案，所述复合保护层13包括氟化锂无机层131以及聚合物有机层132。
其中，氟化锂无机层由聚偏氟乙烯与所述锂金属合金原位反应形成。氟化锂可以是固态电解质膜的组成成分之一，具有良好的离子电导率、机械性能以及电化学稳定性。氟化锂与聚合物搭配使用，可以形成类似固态电解质膜的效果，从而抑制锂金属与电解液发生副反应，提升锂金属合金与电解液的稳定性。在本实施例中，氟化锂与锂金属以共价键结合，使得氟化锂与锂金属合金结合稳定性增强，在循环过程中，铜箔表面的涂层不易脱落。在制备过程中，可以将形成有锂金属合金的铜箔与聚偏氟乙烯反应原位生成氟化锂无机层。氟化锂无机层可以提高锂离子扩散的电导率，抑制锂枝晶的形成和生长。
具体地，氟化锂无机层的厚度可以为0.1μm至2μm，具体可以是0.1μm、0.2μm、0.5μm、0.8μm、1.0μm、1.2μm、1.5μm、1.8μm或2.0μm等，当然也可以是上述范围内的其他值，在此不做限定。氟化锂无机层的厚度可以根据反应时间来控制。氟化锂无机层的厚度过厚，极片在循环过程中容易发生破碎，影响电化学性能。氟化锂无机层的厚度过薄，复合保护层13的电化学稳定性和离子电导率下降，电池循环性能下降。
聚合物有机层可以引导锂的均匀成核，具有较强的粘度和机械强度。聚合物有机层与氟化锂无机层的配合使用，可以使得复合保护层兼具较强的机械强度及较高的离子电导率，可以包覆锂金属合金，可以提高锂金属合金与铜箔接触界面的完整性，抑制锂金属与电解液直接接触发生副反应及锂枝晶生长。具体地，聚合物有机层可以通过喷涂、涂覆、沉积等工艺形成于氟化锂无机层的表面。
作为本申请可选的技术方案，聚合物有机层的厚度可以为0.2μm至2μm，具体可以是0.2μm、0.5μm、0.8μm、1.0μm、1.2μm、1.5μm、1.8μm或2.0μm等，当然也可以是上述范围内的其他值，在此不做限定。聚合物有机层的厚度过厚，电池能量密度下降；聚合物有机层的厚度过薄，复合保护层的完整性、机械强度、弹性下降，在循环过程中容易发生破碎，影响电化学性能。
作为本申请可选的技术方案，所述聚合物有机层包括聚二甲基硅氧烷(PDMS)、聚丙烯腈(PAN)、聚吡咯(Ppy)、聚酰亚胺(PI)、聚丙烯 酸(PAA)、聚甲基丙烯酸甲酯(PMMA)中的至少一种。
作为本申请可选的技术方案，所述氟化锂无机层与所述聚合物有机层的质量比为1：10至10：1；具体可以是1:10、2:10、3:10、4:10、5:10、8:10、10:10、10:8、10:5、10:3、10:1等，当然也可以是上述范围内的其他值，在此不做限定。当复合保护层中的氟化锂无机层含量过高，即复合保护层中的聚合物有机层含量下降，复合保护层的完整性、机械强度及弹性下降，使得极片在循环过程中容易发生破碎，影响电化学性能。当复合保护层中的氟化锂无机层含量过低，复合保护层的电化学稳定性与离子电导率下降，恶化电池循环性能。优选地，所述氟化锂无机层与所述聚合物有机层的质量比为1：5至5：1。
作为本申请可选的技术方案，上述锂金属负极极片的制备方法包括以下步骤：
在Ar气氛下，将锂金属放入到不锈钢坩埚中加热至280℃至350℃使其完全融化，然后将合金组分粉末加入到液态锂金属中并充分搅拌2h至6h，确保金属粉末与锂金属液体均匀混合，冷却后即可得到锂金属合金活性物质。
将锂金属合金活性物质通过冷压复合在铜箔表面，得到极片。
将极片置于含聚偏氟乙烯的溶液中，使得锂金属与聚偏氟乙烯反应原位生成氟化锂无机层。
将含氟化锂无机层的极片置于60℃至100℃真空下烘干后，将含聚合物的有机浆料喷涂至氟化锂无机层的表面，再置于60℃至100℃真空下烘干，得到锂金属负极极片。
第二方面
本申请提供一种电化学装置，包括正极极片、负极极片及电解液，所述负极极片为上述第一方面的锂金属负极极片。
正极极片包括正极集流体及形成于所述正极集流体的至少部分表面上的正极活性物质层，正极活性物质层包括正极活性材料。
作为本申请可选的技术方案，所述正极活性材料可选自锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、橄榄石结构的含锂磷酸盐等，但本申请并不限定于这些材料，还可以使用其他可被用作锂离子电池正极活性材料的传统公知的材料。具体地，所述正极活性材料包括钴酸锂、镍钴锰酸锂、镍钴铝酸锂、锰酸锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、磷酸铁锂和钛酸锂中的至少一种。
作为本申请可选的技术方案，正极活性物质层还可以包括正极导电材料，从而赋予电极导电性。所述正极导电材料可以包括任何导电材料，只要它不引起化学变化。正极导电材料的非限制性示例包括基于碳的材料(例如，天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维等)、基于金属的材料(例如，金属粉、金属纤维等，包括例如铜、镍、铝、银等)、导电聚合物(例如，聚亚苯基衍生物)和它们的混合物。
作为本申请可选的技术方案，正极活性物质层还可以包括粘结剂，以将正极活性物质和可选的导电剂牢固地粘结在正极集流体上。本申请对粘结剂的种类不做具体限制，可以根据实际需求进行选择。作为示例，粘结剂可以为聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚丙烯酸(PAA)、聚乙烯醇(PVA)、乙烯-醋酸乙烯酯共聚物(EVA)、丁苯橡胶(SBR)、羧甲基纤维素(CMC)、海藻酸钠(SA)、聚甲基丙烯酸(PMA)及羧甲基壳聚糖(CMCS)中的至少一种。
作为本申请可选的技术方案，正极集流体可以采用导电碳片、金属箔材、涂炭金属箔材或多孔金属板，其中导电碳片的导电碳材质可以为超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨、石墨烯及碳纳米纤维中的一种或几种，金属箔材、涂炭金属箔材和多孔金属板的金属材质各自独立地可以选自铜、铝、镍及不锈钢中的至少一种。
正极集流体11例如为铜箔、铝箔、镍箔、不锈钢箔、不锈钢网及涂炭铝箔中的一种或几种，优选采用铝箔。
可以按照本领域常规方法制备上述正极极片。通常将正极活性物质及可选的导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮，简称为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、冷压后，得到正极极片。
本申请的电化学装置中的隔离膜可以是本领域各种适用于电化学储能装置隔离膜的材料，例如，可以是包括但不限于聚乙烯、聚丙烯、聚偏氟乙烯、芳纶、聚对苯二甲酸乙二醇酯、聚四氟乙烯、聚丙烯腈、聚酰亚胺，聚酰胺、聚酯和天然纤维中的至少一种。
本申请的电化学装置中的电解液包括溶剂、锂盐和添加剂。
其中，电解液中的锂盐选自有机锂盐或无机锂盐中的至少一种。具体地，锂盐可以选自六氟磷酸锂(LiPF6)、四氟硼酸锂、二氟磷酸锂、双三氟甲烷磺酰亚胺锂LiN(CF3SO2)2(简写为LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO2F)2)(简写为LiFSI)、双草酸硼酸锂LiB(C2O4)2(简写为LiBOB)、二氟草酸硼酸锂LiBF2(C2O4)(简写为LiDFOB)中的至少一种。
作为本申请可选的技术方案，电解液中的溶剂包括乙二醇二甲醚(简写为DME)及1,3-二氧环戊烷(简写为DOL)。所述乙二醇二甲醚与所述1,3-二氧环戊烷的体积比为(0.5～10)：1，具体可以是0.5:1、0.8:1、1:1、1.5:1、1.8:1、2.5:1、3:1、5:1、6:1、7:1、8:1、9:1或10:1等，当然也可以是上述范围内的其他值，在此不做限定。当乙二醇二甲醚与1,3-二氧环戊烷的比值过大，即乙二醇二甲醚含量过高，1,3-二氧环戊烷含量过低，则难以利用1,3-二氧环戊烷与乙二醇二甲醚之间的协同作用，形成稳定的固态电解质膜；当乙二醇二甲醚与1,3-二氧环戊烷的比值过小，1,3-二氧环戊烷含量过高，1,3-二氧环戊烷容易发生自聚合反应，难以形成有效的固态电解质膜，造成电池析锂。优选地，所述乙二醇二甲醚与所述1,3-二氧环戊烷的体积比为(1～7)：1。需要说明的是，上述两种溶剂的混合使用，有利于电解液在 极片表面形成更加稳定的固态电解质膜，减少副反应的发生，抑制锂枝晶生长。
作为本申请可选的技术方案，所述电解液的浓度为0.5mol/L至7mol/L，具体可以是0.5mol/L、0.8mol/L、1mol/L、1.5mol/L、2.0mol/L、3mol/L、4mol/L、5mol/L、6mol/L或7mol/L等，当然也可以是上述范围内的其他值，在此不做限定。电解液浓度过大，会导致电解液粘度过大，影响电池的加工与动力学性能，电解液浓度过小，会造成锂盐浓度过低，循环过程中浓度差极化加剧，促进锂枝晶生长，电池循环性能下降。优选地，所述电解液的浓度为2mol/L至5mol/L。可以理解地，采用上述浓度范围内的电解液，可以提升锂金属与电解液界面的锂离子浓度，尽可能消除浓差极化，缓解由此引起的极化锂枝晶生长。
作为本申请可选的技术方案，所述电解液还包括添加剂，所述添加剂包括三聚甲醛、硝酸锂、二恶烷、氟磺酸锂、氟代碳酸乙烯酯中的至少一种。
作为本申请可选的技术方案，所述添加剂在所述电解液中的质量含量为0.1％至10％，具体可以是0.1％、0.5％、1％、1.5％、2％、2.5％、3％、3.5％、4％、5％、6％、7％、8％、9％或10％等，当然也可以是上述范围内的其他值，在此不做限定。电解液中的添加剂的质量含量过高，在电池循环过程中，会消耗大量活性锂离子，影响固态电解质膜的质量，降低电池寿命；电解液中的添加剂的质量含量过低，难以利用添加剂的化学活性来抑制1,3-二氧环戊烷聚合，会造成电池析锂严重。优选地，所述添加剂在所述电解液中的质量含量为0.5％至5％。
作为本申请可选的技术方案，所述隔离膜选自聚乙烯膜、聚丙烯膜、聚偏氟乙烯膜中的一种或多种的复合，当然，也可以根据实际需求在隔离膜基材表面涂覆无机或有机涂层以增强电芯的硬度或提升隔离膜与阴负极界面的粘附性。
作为本申请可选的技术方案，上述电化学装置的制备方法包括以下步骤：
将上述正极极片、隔离膜、负极极片按顺序堆叠好，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电芯，也可以是经卷绕后得到电芯；将电芯置于包装外壳(可以是软包、方形铝壳、方形钢壳、圆柱铝壳和圆柱钢壳)中，注入电解液并封口，得到电化学装置。
在具体实施例中，所述电化学装置是锂二次电池，其中，锂二次电池包括，但不限于：锂金属二次电池、锂离子二次电池、锂聚合物二次电池或锂离子聚合物二次电池。
第三方面
本申请还提供一种电子设备，电子设备包括上述第二方面所述的电化学装置。电化学装置可用于为电子设备提供电源。
作为本申请可选的技术方案，所述电子设备包括，但不限于：笔记本 电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池或锂离子电容器等。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于重量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
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％磷酸铁锂正极活性材料制成分散均匀的正极浆料。将正极浆料均匀涂敷在铝箔表面，然后转移到真空干燥箱中充分干燥。将得到的极片进行辊压，然后进行冲裁，得到目标圆片。
负极极片的制备
在Ar气氛下，将锂金属放入到不锈钢坩埚中加热至300℃使其完全融化，然后将合金组分粉末加入到液态锂金属中并充分搅拌2h，确保金属粉末与锂金属液体均匀混合，冷却后即可得到锂金属合金活性物质。
将锂金属合金活性物质通过冷压复合在铜箔表面，得到极片；将极片置于含聚偏氟乙烯的溶液中，使得锂金属与聚偏氟乙烯反应原位生成氟化锂无机层；将含氟化锂无机层的极片置于80℃真空下烘干后，将含聚合物的有机浆料喷涂至氟化锂无机层的表面，再置于80℃真空下烘干，得到锂金属负极极片。
隔离膜
采用聚乙烯(PE)多孔聚合物薄膜。
电解液的制备
将乙二醇二甲醚(DME)与1,3-二氧环戊烷(DOL)的混合液作为有机溶剂，接着将充分干燥的六氟磷酸锂溶解于混合后的有机溶剂中，配制成电解液。
扣式电池的制备
将上述正极极片、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扣式电池。
根据上述制备方法制得负极极片实施例1至36，以及对比例1至17，其电解液配方的具体参数如表1所示。
表1
Figure PCTCN2022079252-appb-000001
Figure PCTCN2022079252-appb-000002
其中，“/”表示物质的含量为0。
测试部分
负极极片的性能参数测试
1)复合保护层的厚度：
采用SEM对液氮淬冷切割的极片进行截面成像，通过二次电子图像测量复合保护层的厚度。
2)电池的性能测试
在25℃下，将实施例和对比例制备得到的电池以0.1C倍率充电到4V、以0.1C倍率放电到1V，进行满充满放循环测试，直至锂离子电池的容量小于初始容量的80％，记录首次库伦效率、循环圈数，其具体数据见表2所示。
表2
样本 首次库伦效率 循环圈数
实施例1 91 601
实施例2 94 632
实施例3 95 681
实施例4 95 666
实施例5 95 643
实施例6 94 611
实施例7 94 594
实施例8 95 621
实施例9 94 646
实施例10 93 622
实施例11 93 607
实施例12 94 631
实施例13 93 617
实施例14 92 602
实施例15 93 625
实施例16 90 588
实施例17 89 541
实施例18 93 662
实施例19 94 672
实施例20 93 653
实施例21 93 631
实施例22 82 501
实施例23 89 588
实施例24 92 621
实施例25 87 571
实施例26 89 555
实施例27 91 598
实施例28 93 644
实施例29 90 577
实施例30 83 505
实施例31 92 594
实施例32 94 652
实施例33 93 630
实施例34 91 580
实施例35 90 623
实施例36 91 635
对比例1 93 598
对比例2 89 571
对比例3 92 588
对比例4 93 569
对比例5 89 524
对比例6 90 544
对比例7 87 513
对比例8 91 600
对比例9 85 523
对比例10 80 471
对比例11 87 535
对比例12 85 505
对比例13 80 481
对比例14 72 105
对比例15 89 579
对比例16 82 481
对比例17 80 480
根据实施例1至6以及对比例1及2的测试结果可知，当极片表面的复合保护层的厚度在0.3μm至10μm范围内时，电池具有较高的能量密度，复合物保护层能够抑制锂枝晶形成，提高电池的循环性能。根据对比例1的测试结果可知，复合保护层厚度过厚，电池能量密度下降。根据对比例2的测试结果可知，复合保护层厚度过薄，会造成复合保护层机械强度下降，复合保护层对锂金属合金覆盖保护力度下降，造成锂枝晶容易朝向隔离膜生长，恶化电池循环性能。优选地，复合保护层的厚度为1μm至7μm。
根据实施例7至11以及对比例3至6的测试结果可知，当复合保护层中的氟化锂无机层与聚合物有机层的质量比控制在1：10至10：1范围内时，极片在循环过程中，极片表面的副反应减少，电池循环性能提升。根据对比例3及对比例5的测试结果可知，当复合保护层中的氟化锂无机层含量过高，即复合保护层中的聚合物有机层含量下降，或复合保护层仅含有氟化锂无机层时，复合保护层的完整性、机械强度及弹性下降，使得极片在循环过程中容易发生破碎，影响电化学性能。根据对比例4以及对比例6的测试结果可知，当复合保护层中的氟化锂无机层含量过低，或复合保护层仅含有聚合物有机层时，复合保护层的电化学稳定性与离子电导率下降，恶化电池循环性能。优选地，所述氟化锂无机层与所述聚合物有机层的质量比为1：5至5：1。
根据实施例3以及实施例12至16的测试结果可知，当锂金属合金中的合金元素变化时，部分金属会难以与锂金属形成固溶体，从而导致锂枝晶向外生长刺穿隔膜，电池的循环性能下降。
根据实施例3以及实施例17至21以及对比例7及8的测试结果可知，锂金属合金中的R元素的质量含量在1％至10％范围内时，可以有效降低嵌锂过电势，可以抑制锂枝晶的生长。对比例7的锂金属合金中的R元素的质量含量过低时，锂金属合金中的固溶合金含量减少，无法利用固溶合金相变来抑制锂枝晶的生长。对比例8的锂金属合金中的R元素的质量含量过高时，即锂金属合金中的锂含量下降，会影响电池的动力学性能，导致电池的能量密度与倍率性能下降。优选地，所述锂金属合金中的R元素的质量含量为3％至7％。
根据实施例3以及对比例9的测试结果可知，对比例9的铜箔表面用纯锂金属来替代锂金属合金，锂金属不存在合金相，无法利用固溶合金相变来抑制锂枝晶的生长，电池循环性能下降。
根据实施例3以及实施例22至25以及对比例10及11的测试结果可知，当电解液的浓度在0.5mol/L至7mol/L范围内时，电池动力学性能较好，可以保障电池的循环性能。根据对比例10的测试结果可知，电解液浓度过小，会造成锂盐浓度过低，循环过程中浓度差极化加剧，促进锂枝晶生长，电池循环性能下降。根据对比例11的测试结果可知，电解液浓度过大，会导致电解液粘度过大，影响电池的动力学性能下降。优选地，所述电解液的浓度为2mol/L至5mol/L。
根据实施例3以及实施例26至30以及对比例12及13的测试结果可知，DME与DOL的体积比在(0.5～10)：1范围内时，有利于电解液在锂金属合金表面形成更加稳定的固态电解质膜，减少副反应的发生，抑制锂枝晶生长，有利于提升电池的循环性能。根据对比例12的测试结果可知，当DME与DOL的体积比过小，1,3-二氧环戊烷含量过高，1,3-二氧环戊烷容易发生自聚合反应，难以形成有效的固态电解质膜，造成电池析锂，循环性能下降。根据对比例13的测试结果可知，DME与DOL的体积比过大，即乙 二醇二甲醚含量过高，1,3-二氧环戊烷含量过低，则难以利用1,3-二氧环戊烷与乙二醇二甲醚之间的协同作用，形成稳定的固态电解质膜，电池的循环性能下降；优选地，所述乙二醇二甲醚与所述1,3-二氧环戊烷的体积比为(1～7)：1。
根据实施例3以及对比例14的测试结果可知，对比例14采用碳酸酯作为电解液的溶剂，碳酸酯无法抑制锂枝晶生长，电池内易发生短路，电池循环性能大幅下降。
根据实施例3以及实施例31至34以及对比例15及16的测试结果可知，添加剂在所述电解液中的质量含量为0.1％至10％时，可以抑制锂析出，有利于提高电池的循环性能。根据对比例15的测试结果可知，电解液中的添加剂的质量含量过低，难以利用添加剂的化学活性来抑制1,3-二氧环戊烷(DOL)聚合，会造成电池析锂严重，电池循环性能下降。根据对比例16的测试结果可知，电解液中的添加剂的质量含量过高，在电池循环过程中，会消耗大量活性锂离子，影响固态电解质膜的质量，电池容量衰减严重。优选地，所述添加剂在所述电解液中的质量含量为0.5％至5％。
根据实施例3、实施例35至36以及对比例17的测试结果可知，硝酸锂在低电位下会分解形成氮化锂，这种原位形成的无机保护层会均匀的覆盖在锂金属表面从而稳固SEI(固体电解质界面膜)整体结构，提升电池循环性能。氟代碳酸乙烯酯、氟磺酸锂添加剂相较于硝酸锂对电解液的稳定性略有影响，但也能够有效提高电池的循环性能。而对比例17未添加上述添加剂，导致极片表面副反应加剧，电池循环性能下降。
本申请虽然以较佳实施例公开如上，但并不是用来限定权利要求，任何本领域技术人员在不脱离本申请构思的前提下，都可以做出若干可能的变动和修改，因此本申请的保护范围应当以本申请权利要求所界定的范围为准。

Claims (10)

  1. 一种锂金属负极极片，包括：
    铜箔；
    形成于所述铜箔的至少部分表面上的活性物质层，所述活性物质层包括锂金属合金；以及
    形成于所述活性物质层的至少部分表面上的复合保护层，所述复合保护层的厚度小于等于10μm，所述复合保护层包括氟化锂无机层以及聚合物有机层。
  2. 根据权利要求1所述的负极极片，满足以下条件的至少一者：
    (1)所述复合保护层的厚度为0.3μm至10μm；
    (2)所述复合保护层的厚度为1μm至7μm。
  3. 根据权利要求1所述的负极极片，满足以下条件的至少一者：
    (3)所述氟化锂无机层与所述聚合物有机层的质量比为1：10至10：1；
    (4)所述氟化锂无机层与所述聚合物有机层的质量比为1：5至5：1。
  4. 根据权利要求1或3所述的负极极片，其中，所述聚合物有机层包括聚二甲基硅氧烷、聚丙烯腈、聚吡咯、聚酰亚胺、聚丙烯酸、聚甲基丙烯酸甲酯中的至少一种。
  5. 根据权利要求1或3所述的负极极片，其中，所述氟化锂无机层由聚偏氟乙烯与所述锂金属合金原位反应形成。
  6. 根据权利要求5所述的负极极片，满足以下条件的至少一者：
    (5)所述锂金属合金的化学式为LiR，R金属选自Ag、Mo、In、Ge、Bi和Zn中的至少一种；
    (6)所述锂金属合金的化学式为LiR，所述锂金属合金中的R元素的质量含量为1％至10％；
    (7)所述锂金属合金为固溶合金。
  7. 一种电化学装置，包括正极极片、负极极片、隔离膜及电解液，其中，所述负极极片为权利要求1至6任一项所述的负极极片。
  8. 根据权利要求7所述的电化学装置，其中，所述电解液包括溶剂及锂盐，并满足以下条件的至少一者：
    (9)所述锂盐包括六氟磷酸锂、四氟硼酸锂、二氟磷酸锂、双三氟甲烷磺酰亚胺锂、双(氟磺酰)亚胺锂、双草酸硼酸锂或二氟草酸硼酸锂中的至少一种；
    (10)所述溶剂包括乙二醇二甲醚及1,3-二氧环戊烷；
    (11)所述溶剂包括乙二醇二甲醚及1,3-二氧环戊烷，所述二甲醚与所述1,3-二氧环戊烷的体积比为(0.5～10)：1；
    (12)所述电解液的浓度为0.5mol/L至7mol/L。
  9. 根据权利要求8所述的电化学装置，其中，所述电解液满足以下条件的至少一者：
    (13)所述电解液还包括添加剂，所述添加剂包括三聚甲醛、硝酸锂、二恶烷、氟磺酸锂、氟代碳酸乙烯酯中的至少一种；
    (14)所述电解液还包括添加剂，所述添加剂在所述电解液中的质量含量为0.1％至10％。
  10. 一种电子设备，包括根据权利要求7至9任一项所述的电化学装置。
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