WO2022100661A1 - 一种负极片及其应用 - Google Patents

一种负极片及其应用 Download PDF

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Publication number
WO2022100661A1
WO2022100661A1 PCT/CN2021/130042 CN2021130042W WO2022100661A1 WO 2022100661 A1 WO2022100661 A1 WO 2022100661A1 CN 2021130042 W CN2021130042 W CN 2021130042W WO 2022100661 A1 WO2022100661 A1 WO 2022100661A1
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Prior art keywords
negative electrode
electrode sheet
safety function
lithium
layer
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PCT/CN2021/130042
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English (en)
French (fr)
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张双虎
彭宁
谢斌
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珠海冠宇电池股份有限公司
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Priority to KR1020237004964A priority Critical patent/KR20230043126A/ko
Priority to EP21891181.6A priority patent/EP4160731A1/en
Priority to JP2022580887A priority patent/JP2023531545A/ja
Publication of WO2022100661A1 publication Critical patent/WO2022100661A1/zh
Priority to US18/146,577 priority patent/US20230135612A1/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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • 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
    • H01M10/42—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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • 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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • 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 invention belongs to the field of lithium ion batteries, and relates to a negative electrode sheet and its application.
  • Lithium-ion battery is an ideal electrochemical energy storage device, which has the advantages of high energy density, long cycle life and long standby time, and is widely used in the fields of consumer electronics and electric vehicles. With the popularity of electric vehicles, the safety of lithium-ion batteries under low-temperature and high-rate charging is facing severe challenges.
  • lithium-ion batteries are greatly affected by kinetic properties. Specifically, when lithium ions are embedded in graphite materials, they need to be desolvated, so this process consumes a certain amount of energy and hinders the diffusion of lithium ions into graphite; Conversely, when lithium ions are deintercalated from graphite materials, they can be rapidly deintercalated from graphite materials because they do not need to be desolvated, resulting in significantly poorer charge acceptability than discharge acceptability of graphite materials.
  • the electrochemical polarization of the negative electrode is significantly intensified during the charging process. As a result, a large number of lithium ions accumulate on the surface of the negative electrode, and the negative electrode reaches the precipitation potential of lithium to generate lithium precipitation.
  • lithium stripping will occur during the subsequent discharge process.
  • Part of the lithium can continue to electrochemically contact the graphite material, and part of the lithium can form dead lithium.
  • Part of the lithium reacts with the electrolyte electrochemically, resulting in active lithium.
  • Lithium loss The more serious situation is that lithium precipitation will accelerate the increase of polarization of lithium-ion batteries, increase internal resistance, fast capacity decay, shorten cycle life, and if a large amount of lithium is deposited on the surface of the negative electrode to form lithium dendrites, it is easy to pierce the separator and lead to positive The negative electrode is short-circuited, resulting in thermal runaway and explosion.
  • the invention provides a negative electrode sheet.
  • the negative electrode sheet can effectively improve the negative electrode potential and the nucleation energy of metal lithium during the low temperature and high rate charging process of the lithium ion battery by arranging a safety functional layer containing metal and ceramics on the negative electrode active layer. It can prevent the occurrence of lithium deposition in the negative electrode, and at the same time, due to the good thermal insulation performance of ceramics, it can effectively prevent the occurrence of thermal runaway in acupuncture experiments and improve the safety performance of the battery.
  • the present invention also provides a lithium ion battery, including the negative electrode sheet. Since the battery avoids the occurrence of lithium deposition in the negative electrode and thermal runaway in acupuncture experiments, the lithium ion battery has the advantages of good cycle performance and high safety performance.
  • a first aspect of the present invention provides a negative electrode sheet, the negative electrode sheet includes a current collector, a negative electrode active layer disposed on at least one functional surface of the current collector, and a safety functional layer disposed on a surface of the negative electrode active layer away from the current collector; wherein,
  • the security functional layer includes metals and ceramics.
  • the negative electrode sheet as described above includes a current collector, a negative electrode active layer, and a safety function layer.
  • the current collector includes two functional surfaces (the two functional surfaces of the current collector refer to the two surfaces with the largest current collector area, which are used for the coating of the functional layer), and the negative active layer can only be arranged on one of the functional surfaces. , it can also be arranged on both functional surfaces, or the negative active layer can be arranged on the entire area of any functional surface of the current collector, or only a part of the area on any functional surface of the current collector.
  • the negative electrode active layer also includes two functional surfaces (the two functional surfaces of the negative electrode active layer refer to the two surfaces with the largest area of the negative electrode active layer, which are used for the coating of the functional layer), one of the functional surfaces and the current collector functional surface. Adjacent, another functional surface is away from the current collector, and the safety functional layer is arranged on the functional surface of the negative electrode active layer away from the current collector.
  • the safety functional layer can be arranged on the entire area of the negative active layer away from the functional surface of the current collector, It can also be provided only in a partial region of the functional surface of the negative electrode active layer away from the current collector.
  • Metals and ceramics are included in the above-mentioned security functional layer.
  • the negative electrode sheet of this embodiment includes a current collector 101 , a negative electrode active layer 102 disposed on a functional surface of the current collector 101 , and a negative electrode active layer 102 disposed on the current collector 101 .
  • the negative electrode active layer 102 is far away from the safety functional layer 103 on the functional surface of the current collector 101, wherein the negative electrode active layer is provided in the entire area on one functional surface of the current collector 101, and the safety functional layer 103 is also provided on the negative electrode active layer 102 away from the current collector. All areas on the functional surface of 101.
  • FIG. 2 is a schematic diagram of a negative electrode sheet according to another embodiment of the present invention.
  • the negative electrode sheet of this embodiment includes a current collector 101 , a negative electrode active layer 102 disposed on a functional surface of the current collector 101 , and The safety function layer 103 on the functional surface of the negative electrode active layer 102 away from the current collector 101, wherein the negative electrode active layer 102 is arranged on a partial area of a functional surface of the current collector 101, and the safety function layer 103 is only arranged on the negative electrode active layer 102 away from the partial area on the functional surface of the current collector 101 .
  • FIG. 3 is a schematic diagram of a negative electrode sheet according to another embodiment of the present invention.
  • the negative electrode sheet of this embodiment includes a current collector 101 , and a negative electrode active layer 102 disposed on the upper and lower functional surfaces of the current collector 101 , And the safety function layer 103 arranged on the upper and lower two negative electrode active layers 102 away from the functional surface of the current collector 101, wherein the negative electrode active layer 102 is arranged in the partial area of the upper and lower two functional surfaces of the current collector 101, and the safety function layer 103 is only
  • the upper and lower two negative electrode active layers 102 are disposed on the partial regions on the functional surfaces of the upper and lower layers away from the current collector 101 .
  • the safety function layer 103 contains metal and ceramics.
  • the presence of metal can increase the electrode potential of the negative electrode surface during the charging process and increase the nucleation energy barrier of metal lithium on the negative electrode surface, so as to avoid the occurrence of lithium deposition in the negative electrode.
  • the existence of ceramics on the one hand, can effectively avoid the thermal runaway of the battery during the acupuncture process, and enhance the safety performance of the battery; on the other hand, the capillary pores on the surface of the ceramic can further promote the infiltration rate of the electrolyte and improve the negative electrode.
  • the kinetic performance can promote the transport of lithium ions to the negative electrode, and improve the power of lithium ions intercalated into the negative electrode, which has a certain synergistic effect on the inhibition of lithium precipitation.
  • the negative electrode active layer 102 is arranged on a part of the functional surface of the current collector 101 , and the negative electrode active layer 102 includes six surfaces. In addition to the two functional surfaces with the largest area, there are also four side surfaces. , one of the sides is the surface close to the tab, the surface is provided with an insulating layer 104, and one end of the insulating layer 104 extends to the safety function layer 103 and covers part of the safety function layer 103, and the other end of the insulating layer 104 extends to the current collector 101 functional surface.
  • the surface of the negative electrode active layer 102 close to the tab may be a curved surface without the safety function layer 103, and the insulating layer 104 may be insulating tape.
  • the negative electrode sheet of this embodiment can enhance the safety of the battery during the winding process on the one hand, and on the other hand, since the negative electrode active layer 102 usually has a thick edge effect during the coating process, the thickness of the edge region of the negative electrode active layer 102 is It is 3-8 ⁇ m, which leads to the risk of over-thickness in the area where the thickness of the edge area is the largest when the cell is wound.
  • the compensation of the safety function layer 103 in the edge area can make the edge area flat, and the adhesive tape can be attached more closely.
  • the metal in the safety function layer 103 generally exists in the form of metal particles, so the surface and the inside of the safety function layer 103 will have a pore structure.
  • the porosity of the safety function layer 103 may be 20-45% by controlling the particle size of the metal particles, the composition of the safety function slurry, or the setting of the compaction density when preparing the safety function layer 103 .
  • the porosity of the safety functional layer 103 has a significant impact on the cycle performance of the lithium ion battery containing the negative electrode sheet.
  • the rate is too low, the wettability of the electrolyte to the negative electrode sheet is poor, which is not conducive to the transfer of lithium ions to the negative electrode sheet, aggravates the accumulation of lithium ions on the surface of the negative electrode, and then deteriorates the cycle of the battery in the form of lithium dendrites. performance; when the porosity is too high, the interface contact area between the safety functional layer 103 and the negative electrode active layer 102 will decrease, and the adhesion will decrease. The structure is damaged, causing metal particles in the safety functional layer 103 to migrate to the positive electrode through the separator, causing deterioration of electrical properties.
  • the average pore size in the safety function layer 103 is 10-500 nm, more preferably 20-200 nm, and even more preferably 20-100 nm; and the difference between the maximum value and the minimum value of the pore size is not greater than 80 nm, more preferably not greater than 70 nm, and further It is preferably not more than 50 nm.
  • the thickness of the safety function layer 103 is 0.3-10 ⁇ m, more preferably 0.5-5 ⁇ m.
  • the thickness of the safety function layer 103 can be achieved by controlling the coating weight during the coating process.
  • the coating weight can be controlled to be 0.2-0.9 mg/cm 2 , thereby ensuring the safety function.
  • the thickness of layer 103 is within a suitable range.
  • the metal in the security functional layer 103 is selected from copper or nickel. Copper or nickel does not participate in the electrochemical reaction of the negative electrode, nor does it have an alloying reaction with metal lithium, and can exist stably in the negative electrode, effectively improving the electrode potential of the negative electrode surface and the nucleation energy barrier of metal lithium on the negative electrode surface.
  • the ceramic in the safety function layer 103 is selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, At least one of boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, aluminum nitride, boron nitride, barium carbonate, and barium titanate.
  • the above-mentioned ceramics all have good thermal insulation properties and sufficient capillary pores, which are beneficial to prevent thermal runaway during acupuncture tests on the one hand, and promote the infiltration of electrolyte in the negative electrode sheet on the other hand.
  • the particle size D50 of the above metal is 50-500 nm; the particle size D50 of the ceramic is 0.5-5 ⁇ m, and the particle size D50 of the ceramic is more preferably 1-3 ⁇ m. It can be understood that the appropriate metal particle size and ceramic particle size are conducive to the formation of the safety functional layer 103 with uniform pores and suitable pore size, which is conducive to electrolyte infiltration and ion conduction, and improves the kinetic performance of the negative electrode.
  • the security functional layer 103 in the present invention also includes a binder and a dispersant in addition to metal and ceramics.
  • each component constituting the safety function layer 103 includes, by mass percentage: 48-60% of metal, 28-40% of ceramic, 3-8% of binder and 1-4% of dispersant.
  • the sources of the above-mentioned binders and dispersants are not particularly limited, and conventional materials in the art can be used.
  • the binder can be a water-based binder or an oil-based binder, and can be selected from polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic acid One or a combination of ester, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the dispersant may be selected from one or a combination of sodium carboxymethyl cellulose (CMC), lithium carboxymethyl cellulose, polyvinylpyrrolidone (PVP), and polyvinyl alcohol.
  • the preparation of the above-mentioned safety function layer 103 can be prepared by including the following process of preparing the safety function slurry: 1) after mixing the metal, the binder and the dispersant, add a part of the solvent and stir to obtain the first slurry; 2) Add the remaining solvent to the first slurry and stir to obtain the second slurry; 3) After adding the ceramic to the second slurry, stir to obtain the safety function slurry.
  • the first slurry has a relatively high viscosity.
  • the viscosity range of the first slurry can be controlled to be 30000-100000 mPa ⁇ s by controlling the amount of the solvent added.
  • the stirring process can effectively shear and mix the particles for the purpose of uniform dispersion.
  • step 2) the remaining solvent is added to the first slurry and stirred to obtain a second slurry.
  • FIG. 4 is a scanning electron microscope image of the second slurry. It can be seen from the picture that the metal is uniformly dispersed in the form of particles.
  • step 3 adding ceramics to the second slurry and stirring can make the metal particles evenly distributed on the surface and the gaps of the ceramics, which is beneficial to obtain the security functional layer 103 which is dense and smooth with uniform pores.
  • Figure 5 is a scanning electron microscope image of the safety functional paste, from which it can be seen that the metal particles are evenly distributed on the surface and gaps of the ceramic.
  • the solvent used in the preparation process of the above-mentioned safety functional paste is selected from one of deionized water, ethanol or N-methylpyrrolidone (NMP).
  • the solid content of the safety function paste can be controlled to be 10-50%, more preferably 14-35%, by adjusting the content of each component, the amount of solvent used, the type of solvent, etc. in the above preparation process; the viscosity of the safety function paste It is 50-1500 mPa ⁇ s, more preferably 50-500 mPa ⁇ s; the pH value of the safety function slurry is 3-10, more preferably 5-9.
  • the preparation of the safety function layer 103 further includes: coating the safety function slurry on the negative electrode active layer 102 and drying it to obtain the safety function layer 103 .
  • the drying temperature is 80-125 °C.
  • the current collector 101 can be a common negative electrode current collector copper foil.
  • the negative electrode active layer 102 includes a negative electrode active material, a binder and a conductive agent, wherein the negative electrode active material can be selected from at least one of artificial graphite, natural graphite, mixed graphite and intermediate carbon microspheres, and the binder can be selected from styrene-butadiene Rubber (SBR), vinylidene fluoride-hexafluoropropylene polymer, polyacrylonitrile, sodium carboxymethyl cellulose, butadiene-acrylonitrile polymer, polymethyl acrylate, polyethyl acrylate, polyacrylic acid-styrene At least one of polymer, polyvinylidene fluoride, polyvinyl alcohol, polyurethane, polyacrylate, butyl rubber, epoxy resin, vinyl acetate resin, chlorinated rubber, the conductive agent
  • a second aspect of the present invention provides a lithium ion battery
  • the negative electrode sheet of the lithium ion battery is the negative electrode sheet provided in the first aspect of the present invention.
  • the lithium ion battery also includes a positive electrode sheet, a separator, and an electrolyte.
  • the sources of the positive electrode sheet, the separator, and the electrolyte are not specifically limited, and conventional materials in the field can be used, which will not be repeated here.
  • the negative electrode sheet provided by the present invention can effectively improve the electrode potential of the negative electrode surface during the low temperature and high rate charging process of the battery through the regulation of the metal content in the safety functional layer, so as to prevent the negative electrode from reaching the precipitation potential of lithium, and on the other hand, it is safe
  • the addition of metal in the functional layer can improve the nucleation energy barrier of lithium, and the combination of two factors can inhibit the occurrence of lithium deposition in the negative electrode.
  • the existence of ceramics in the safety function layer of the negative electrode sheet provided by the present invention can provide enough capillary channels for the negative electrode sheet on the one hand, which is conducive to promoting the rapid and sufficient infiltration of the electrolyte, improving the kinetic performance of the negative electrode, and inhibiting precipitation. Lithium has a certain synergistic effect. On the other hand, the good thermal insulation performance of ceramics can effectively avoid the occurrence of thermal runaway in the acupuncture test and enhance the safety performance of the battery.
  • the lithium ion battery provided by the present invention has the advantages of good cycle performance and high safety because the occurrence of lithium deposition in the negative electrode of the battery is effectively suppressed.
  • FIG. 1 is a schematic diagram of a negative electrode sheet according to an embodiment of the present invention.
  • FIG. 2 is a schematic diagram of a negative electrode sheet according to another embodiment of the present invention.
  • FIG. 3 is a schematic diagram of a negative electrode sheet according to yet another embodiment of the present invention.
  • Fig. 4 is the scanning electron microscope picture of the second slurry
  • Figure 5 is a scanning electron microscope image of the safety functional paste.
  • Graphite, conductive carbon black, styrene-butadiene latex (SBR), and sodium carboxymethyl cellulose (CMC) were added to deionized water in a mass ratio of 96:1.5:1.5:1 and stirred evenly to prepare a negative electrode active slurry; the preparation
  • the obtained negative electrode active slurry is evenly coated on the upper and lower functional surfaces of the copper foil of the negative electrode current collector 101, the width of the pole piece is 50mm, and the total length of the pole piece is 942mm, and the negative electrode active slurry is coated on the upper and lower functional surfaces of the copper foil.
  • the coating length of the functional surface is 888mm, the coating length of the lower functional surface is 776mm, the negative active slurry coated on the upper and lower functional surfaces of the copper foil is aligned at one end, and the coating weight is 9.85mg/cm 2 , after drying and compacting
  • the negative electrode active layer 102 is prepared, and the compaction density is 1.7 g/cm 3 ;
  • NMP N-methylpyrrolidone
  • Second slurry add boehmite with a mass percentage of 42% to the second slurry, stir evenly, vacuumize, remove air bubbles to obtain a safety function with a solid content of 20%, a viscosity of 230 mPa ⁇ s and a pH of 7.2 slurry, wherein the particle size D50 of the boehmite is 1 ⁇ m; the safety function slurry is coated on the prepared current collector 101 and the upper and lower layers of the negative electrode active layer 102 on the functional surface of the partial area, wherein the upper negative electrode active layer 102 The functional surface
  • the coating length on the upper surface is 887 mm
  • the coating length on the functional surface of the lower negative electrode active layer 102 is 775 mm
  • the coating weight is 0.745 mg/cm 2
  • the drying is performed at a temperature of 80° C.
  • the rolling density is 1.72 g.
  • a safety function layer 103 with a thickness of 3.6 ⁇ m for both upper and lower layers is obtained, wherein the safety function layer 103 has a porosity of 30%, an average pore size of 63 nm, and a difference between the maximum and minimum pore sizes of 50 nm. .
  • a part of the right end of the upper functional surface of the copper foil is reserved for welding the nickel tabs. The surface portion of the negative active layer 102 located on the upper functional surface of the copper foil close to the nickel tabs is not coated with the safety functional layer 103, and this part is pasted.
  • insulating tape which extends from the left end to the end of the safety function layer 103 and covers part of the safety function layer 103, and extends from the right end to the upper functional surface of the copper foil.
  • the width of the tape is 16mm and the thickness is 22 ⁇ m.
  • Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a mass ratio of 95:3:2 and mixed uniformly to prepare a positive electrode active layer slurry; the prepared The positive electrode active layer slurry is uniformly coated on the positive electrode current collector aluminum foil, dried and compacted to obtain a positive electrode sheet.
  • NMP N-methylpyrrolidone
  • LiPF 6 lithium hexafluorophosphate
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • EMC ethyl methyl carbonate
  • FEC fluoroethylene carbonate
  • the prepared negative electrode sheet, the positive electrode sheet and the separator polypropylene microporous membrane are stacked once, and then the lithium ion battery cell is obtained by the winding process.
  • the lithium-ion battery is assembled after the formation, capacity and other processes.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 is that the mass percentage of each component of the safety function layer 103 in the negative electrode sheet is 55% nickel, 35% boehmite, 6% polyvinylidene fluoride ( PVDF), 4% polyvinylpyrrolidone (PVP). The remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Example 1 The difference between this example and Example 1 is that the mass percentage of each component of the safety function layer 103 in the negative electrode sheet is 60% nickel, 30% boehmite, 6% polyvinylidene fluoride ( PVDF), 4% polyvinylpyrrolidone (PVP). The remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Example 1 The difference between this example and Example 1 is that the mass percentage of each component of the safety function layer 103 in the negative electrode sheet is 48% copper, 42% boehmite, 6% polyvinylidene fluoride ( PVDF), 4% polyvinylpyrrolidone (PVP). The remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Example 1 The difference between this example and Example 1 is that the mass percentage of each component of the safety functional layer 103 in the negative electrode sheet is 55% copper, 35% boehmite, 6% polyvinylidene fluoride ( PVDF), 4% polyvinylpyrrolidone (PVP). The remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Example 1 The difference between this example and Example 1 is that the mass percentage of each component of the safety function layer 103 in the negative electrode sheet is 60% copper, 30% boehmite, 6% polyvinylidene fluoride ( PVDF), 4% polyvinylpyrrolidone (PVP). The remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 is that after the safety function layer 103 is coated, the safety function layer 103 is subjected to dry roll pressing, the compaction density is set to 1.78 g/cm 3 , and the porosity of the safety function layer 103 is set to 1.78 g/cm 3 . was 18%. The remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Embodiment 1 The difference between this embodiment and Embodiment 1 is that after the coating of the safety function layer 103 is completed, the safety function layer 103 is subjected to dry rolling, the compaction density is set to 1.85g/cm 3 , and the average pore size of the safety function layer 103 is is 20 nm, and the difference between the maximum value and the minimum value of the pore size is 35 nm.
  • the remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Example 1 The difference between this comparative example and Example 1 is that there is no safety function layer 103 in the negative electrode sheet.
  • the remaining steps are the same as those in Embodiment 1, and are not repeated here.
  • Detection method At 25°C, charge the lithium-ion battery to 4.35V with a constant current of 1C, then charge it to 0.05C with a constant voltage, let it stand for 5 minutes, and then discharge it to 3.0V with a constant current of 1C. This is the first cycle, repeat the above Process, cycle performance test of lithium-ion battery.
  • the capacity retention rate (%) of the lithium ion battery after 800 cycles discharge capacity after 800 cycles/discharge capacity after the first cycle ⁇ 100%.
  • Detection method At 0°C, charge the lithium-ion battery with a constant current of 0.2C to 4.35V, and then charge it with a constant voltage until the current drops to 0.05C; the discharge process is to discharge with a constant current of 1C to 3.0 V, which is a charge-discharge cycle. After 10 charge-discharge cycles of the lithium-ion battery, the lithium deposition of the battery was observed.
  • Detection method At 10°C, charge the lithium-ion battery with a constant current of 0.5C to 4.35V, then charge it with a constant voltage to 0.05C, let it stand for 5 minutes, and then discharge it with a constant current of 1C to 3.0V. This is the first cycle, repeat The above process is used to test the cycle performance of the lithium-ion battery.
  • the capacity retention rate (%) of the lithium ion battery after 100 cycles discharge capacity after 100 cycles/discharge capacity after the first cycle ⁇ 100%.
  • Detection method at 25 ⁇ 5°C, discharge 0.5C to 3.0V, and let it stand for 5min; put the cell in a 25°C incubator, 0.5C constant current to 4.35V, constant voltage to cut-off current C, before recording the test Voltage and internal resistance, check the appearance and take pictures; at the temperature of 25 ° C, the needle height is 610mm, the steel needle descending speed is 150mm/s, the steel needle diameter is 2.5mm, and the length of the nail head is 6mm. Carry out acupuncture test.
  • the open circuit voltage (OCV) and cell surface temperature are monitored in real time; the test is stopped after 5 minutes or the cell surface temperature drops to 50°C; after the test, Record the OCV after the test, AC impedance, check the appearance and take a picture. Judgment standard: no fire, no explosion. Expressed as a pass rate, for example, if 10 cells are tested and 5 pass, the acupuncture pass rate is 5/10.
  • the cycle performance of the lithium-ion battery is better than that of the lithium-ion battery that does not contain a safety functional layer in the negative electrode sheet when it is charged at a high rate; in addition, it can be seen from the data of the capacity retention rate (10°C, 0.5C/1C, 100 cycles) It can be seen that the lithium ion battery with the safety functional layer in the negative electrode sheet has better cycle performance at low temperature, while the lithium ion battery without the safety functional layer in the negative electrode sheet has serious lithium deposition, resulting in the loss of active lithium and poor battery cycle performance.
  • the acupuncture pass rate of the lithium ion battery with the safety functional layer in the negative electrode sheet is significantly better than that of the lithium ion battery without the safety functional layer in the negative electrode sheet, so the safety performance of the battery is better. high.
  • the nickel-containing safety functional layer has the inhibitory effect on lithium precipitation of the battery, the capacity retention rate of the battery under low temperature and high rate charging, and the acupuncture pass rate. It can be seen from the data comparison of Examples 1, 2 and 3 that increasing the content of nickel in the safety functional layer can improve the lithium deposition and cycle performance of the battery under low temperature and high rate charging.
  • Example 7 From the comparison between Example 7 and Example 1, it can be seen that when the porosity of the safety functional layer is lower than 20%, the lithium-ion battery at low temperature has aggravated lithium deposition, but it is still better than the lithium-ion battery of Comparative Example 1. Low temperature lithium precipitation has obvious advantages. From the comparison between Example 8 and Example 1, it can be seen that when the average pore size is 20 nm, the low-temperature lithium precipitation is improved, indicating that as the pore size decreases, the migration path of lithium ions in the pores is shortened, the electrical contact is enhanced, and the kinetic performance of the negative electrode is improved. .

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Abstract

本发明提供一种负极片及其应用。本发明提供的负极片通过在负极活性层上涂布含有金属和陶瓷的安全功能层，有效提高了锂离子电池在低温高倍率充电过程中的负极电极电位以及金属锂的成核能垒，避免了负极析锂现象的发生，同时由于陶瓷具有良好的绝热性能，能够有效阻止针刺实验热失控现象的发生，提高了电池的安全性能。将此负极片应用于锂离子电池中，所得到的锂离子电池具有循环性能好、安全性高的优点。

Description

一种负极片及其应用
本申请要求于2020年11月16日提交中国专利局、申请号为202011280978.X、申请名称为“一种负极片及其应用”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明属于锂离子电池领域，涉及一种负极片及其应用。
背景技术
锂离子电池是一种理想的电化学储能装置，具有能量密度高、循环寿命长和待机时间久等优点，被广泛应用于消费电子和电动汽车领域。随着电动汽车的普及，锂离子电池低温高倍率充电下的安全问题面临着严峻的挑战。
锂离子电池的电性能受动力学性能影响比较大，具体的，当锂离子在嵌入到石墨材料时需要进行去溶剂化，因此该过程会消耗一定的能量而阻碍锂离子向石墨内部的扩散；相反的，当锂离子从石墨材料中脱嵌时，由于无需去溶剂化，因此能够快速从石墨材料中脱嵌，进而导致了石墨材料的充电接受能力明显差于放电接受能力。
低温高倍率充电时，石墨材料的动力学性能进一步变差，如电解液粘度升高，锂离子传输速率降低，嵌入石墨材料的动力学不足，因此充电过程中负极的电化学极化明显加剧，导致锂离子大量聚集于负极表面，负极达到锂的析出电位而产生析锂。
负极表面一旦有金属锂析出，在随后的放电过程中都会产生锂的剥离，部分锂可以继续与石墨材料电化学接触，部分形成死锂，还有部分锂与电解液发生电化学反应，导致活性锂损失。更加严重的情况是析锂会加速锂离子电池极化增加，内阻升高，容量衰减快，循环寿命缩短，并且若是有大量锂沉积在负极表面上形成锂枝晶就容易刺穿隔膜导致正负极短路，从而热失控发生爆炸。
因此，如何抑制锂离子电池在低温高倍率充电下的负极析锂现象是本领域亟待解决的问题。
发明内容
本发明提供一种负极片，该负极片通过在负极活性层上设置含有金属和陶瓷的安全功能层，有效提高了锂离子电池在低温高倍率充电过程中的负极电极电位以及金属锂的成核能垒，避免了负极析锂现象的发生，同时由于陶瓷具有良好的绝热性能，能够有效阻止针刺实验热失控现象的发生，提高了电池的安全性能。
本发明还提供一种锂离子电池，包括上述负极片，由于电池避免了负极析锂以及针刺实验热失控现象的出现，因此该锂离子电池具有循环性能好、安全性能高的优点。
本发明第一方面提供一种负极片，该负极片包括集流体、设置于集流体至少一功能表面的负极活性层、以及设置于负极活性层的远离集流体的表面的安全功能层；其中，所述安全功能层包括金属和陶瓷。
如上所述的负极片包括集流体、负极活性层和安全功能层。
集流体包括两个功能表面(集流体的两个功能表面是指集流体面积最大的两个面，其用于进行功能层的涂覆)，负极活性层可以只设置在其中的一个功能表面上，也可以在两个功能表面上都设置，或者负极活性层可以设置在集流体任一功能表面上的全部区域，也可以只设置在集流体任一功能表面上的部分区域。
负极活性层也包括两个功能表面(负极活性层的两个功能表面是指负极活性层面积最大的两个面，其用于进行功能层的涂覆)，其中一个功能表面与集流体功能表面相接，另外一个功能表面远离集流体，安全功能层设置于负极活性层远离集流体的功能表面上，相应地，安全功能层可以设置在负极活性层远离集流体的功能表面上的全部区域，也可以只设置在负极活性层远离集流体的功能表面上的部分区域。
上述安全功能层中包括有金属和陶瓷。
图1为本发明一种实施方式的负极片示意图，如图1所示，此种实施方式的负极片包括集流体101，设置于集流体101一个功能表面上的负极活性层 102，以及设置于负极活性层102远离集流体101的功能表面上的安全功能层103，其中负极活性层设置在集流体101的一个功能表面上的全部区域，安全功能层103也设置在负极活性层102远离集流体101的功能表面上的全部区域。
图2为本发明另外一种实施方式的负极片示意图，如图2所示，此种实施方式的负极片包括集流体101，设置于集流体101一个功能表面上的负极活性层102，以及设置于负极活性层102远离集流体101的功能表面上的安全功能层103，其中负极活性层102设置在集流体101的一个功能表面上的部分区域，安全功能层103也仅设置在负极活性层102远离集流体101的功能表面上的部分区域。
图3为本发明再一种实施方式的负极片示意图，如图3所示，此种实施方式的负极片包括集流体101，设置于集流体101上下两个功能表面上的负极活性层102，以及设置于上下两层负极活性层102远离集流体101的功能表面的安全功能层103，其中负极活性层102设置在集流体101的上下两个功能表面上的部分区域，安全功能层103也仅设置在上下两层负极活性层102远离集流体101的功能表面上的部分区域。
本发明提供的负极片，其安全功能层103含有金属和陶瓷。其中金属的存在可以提高充电过程中负极表面的电极电位以及增大金属锂在负极表面的成核能垒，从而可以避免负极析锂现象的发生。陶瓷的存在一方面其良好的绝热性能可以有效避免针刺过程中电池热失控情况的出现，增强电池的安全性能；另一方面陶瓷表面的毛细孔隙可以进一步促进电解液的浸润速率，提升负极的动力学性能，促进锂离子向负极的传输，提升锂离子嵌入负极的动力，对抑制析锂有一定的协同作用。
图2和图3所示的负极片，负极活性层102设置于集流体101功能表面的部分区域，负极活性层102包括六个表面，除两个面积最大的功能表面外，还有四个侧面，其中一个侧面为靠近极耳的表面，该表面设置有绝缘层104，且绝缘层104的一端延伸至安全功能层103且覆盖部分安全功能层103，绝缘层104的另一端延伸至集流体101功能表面。具体的，负极活性层102靠近极耳的表面可以为曲面且未设置安全功能层103，绝缘层104可以为绝缘胶纸。这种实施方式的负极片，一方面可以增强电池在卷绕过程中的安全性，另一方面由于负极活性层102在涂布过程中通常会有厚边效应，负极活性层102 边缘区域的厚度有3-8μm，导致电芯卷绕时边缘区域厚度最大的地方有超厚风险，通过安全功能层103在边缘区域的补偿，能够使边缘区域平整，胶纸贴合更加紧密。
本发明的负极片中，安全功能层103中的金属一般多是以金属颗粒的形式存在，因此会使安全功能层103的表面以及内部具有孔隙结构。在一种实施方式中，例如可以通过控制金属颗粒粒径、安全功能浆料的组成或者制备安全功能层103时压实密度的设置等使安全功能层103的孔隙率为20-45％。
发明人在研究过程中发现，安全功能层103的孔隙率对包含该负极片的锂离子电池的循环性能有着显著影响，原因可能在于孔隙率会直接影响电解液对负极片的浸润性能，当孔隙率过低时，电解液对负极片的浸润性能较差从而会不利于锂离子向负极片的传输，加剧了锂离子在负极表面的聚集现象，进而以锂枝晶的形式劣化了电池的循环性能；当孔隙率过高时，安全功能层103会与负极活性层102的界面接触面积减小，附着力下降，在电池循环过程中，由于负极循环膨胀的应力作用，导致安全功能层103的结构破坏，引起安全功能层103中的金属颗粒通过隔膜迁移至正极，引起电性能的恶化。
虽然影响锂离子电池循环性能的因素较多，例如活性材料不同、粘结剂不同、导电剂不同、电解液不同等因素，但是当将安全功能层103的孔隙率控制在20-45％时，能够基本使锂离子电池循环性能具有较好的表现。
安全功能层103中孔径均值为10-500nm，进一步优选为20-200nm，更进一步优选为20-100nm；并且孔径的最大值与最小值之差不大于80nm，进一步优选为不大于70nm，更进一步优选为不大于50nm。通过对安全功能层103孔径的控制，可以促进电解液在负极片中的浸润，有利于锂离子向负极中传输。
安全功能层103的厚度为0.3-10μm，进一步优选为0.5-5μm。安全功能层103的厚度越大，安全阻隔效果好，但极片内阻就越大，导致迁移至负极表面安全功能层103的锂离子进一步嵌入负极活性层102中活性材料的阻力增加，动力学性能下降；厚度太小，则其安全阻隔的作用太小，不能有效避免针刺过程中热失控现象的发生。
安全功能层103的厚度可以通过涂布过程中的对涂布重量的控制而实现，例如在一种具体的实施方式中，可以控制涂布重量为0.2-0.9mg/cm 2，进而保证安全功能层103的厚度在一个合适的范围内。
安全功能层103中的金属选自铜或镍。铜或镍不参与负极的电化学反应，也不会与金属锂发生合金化反应，能够在负极稳定存在，有效发挥提高负极表面电极电位和金属锂在负极表面成核能垒的作用。
安全功能层103中的陶瓷选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙、硫酸钡、氮化铝、氮化硼、碳酸钡、钛酸钡中的至少一种。上述陶瓷均具有良好的绝热性能以及足够的毛细孔隙，一方面有利于防止针刺测试时热失控的发生，另一方面有利于促进电解液在负极片中的浸润。
进一步地，上述金属的粒径D50为50-500nm；陶瓷的粒径D50为0.5-5μm，陶瓷的粒径进一步优选D50为1-3μm。可以理解的是，合适的金属粒径以及陶瓷粒径有利于形成孔隙均匀、孔径大小适宜的安全功能层103，从而有利于电解液浸润和离子导通，提升负极的动力学性能。
本发明中的安全功能层103除金属和陶瓷外，还包括粘结剂和分散剂。其中，组成安全功能层103的各个组分按照质量百分含量包括：金属48-60％、陶瓷28-40％、粘结剂3-8％以及分散剂1-4％。通过对安全功能层103各个组分质量百分含量的调节可以调控负极表面充电过程的电极电位，避免负极达到金属锂的析出电位。
对上述粘结剂和分散剂的来源不作具体限制，均可以使用本领域常规材料。粘结剂可以是水系粘结剂也可以是油系粘结剂，具体可选自聚偏氟乙烯(PVDF)、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的一种或其组合。分散剂可选自羧甲基纤维素钠(CMC)、羧甲基纤维素锂、聚乙烯吡咯烷酮(PVP)、聚乙烯醇中的一种或其组合。
上述安全功能层103的制备可以通过包括以下制备安全功能浆料的过程的制备得到：1)将金属、粘结剂和分散剂混合后，加入部分溶剂并搅拌，得到第一浆料；2)向第一浆料中加入剩余溶剂并搅拌得到第二浆料；3)向第二浆料中加入陶瓷后，搅拌，得到安全功能浆料。
上述步骤1)中由于制备第一浆料时只加入了总溶剂中的部分溶剂，因此可以保证第一浆料具有较高的粘度。具体的，可以通过控制加入溶剂的量控 制第一浆料的粘度范围为30000-100000mPa·s。在高粘状态下，搅拌过程能够有效地对颗粒进行剪切混合，起到均匀分散的目的。
步骤2)中向第一浆料中加入剩余溶剂并搅拌得到第二浆料，图4为第二浆料的扫描电镜图，从图中可以看到金属以颗粒形态均匀分散。
步骤3)中向第二浆料中加入陶瓷搅拌，能够使得金属颗粒均匀地分布在陶瓷的表面和间隙，有利于获得致密平整、孔隙均匀的安全功能层103。图5为安全功能浆料的扫描电镜图，从图中可以看到金属颗粒均匀地分布在陶瓷的表面和间隙。
上述安全功能浆料的制备过程中所使用的溶剂选自去离子水、乙醇或N-甲基吡咯烷酮(NMP)中的一种。
可以通过调节上述制备过程中各组分的含量、所使用的溶剂量、溶剂种类等控制安全功能浆料的固含量为10-50％，进一步优选为14-35％；安全功能浆料的粘度为50-1500mPa·s，进一步优选为50-500mPa·s；安全功能浆料的pH值为3-10，进一步优选为5-9。
在获得安全功能浆料后，安全功能层103的制备还包括：将安全功能浆料涂布于负极活性层102上，进行干燥，即得到安全功能层103。其中，干燥温度为80-125℃。
对本发明负极片中的集流体101和负极活性层102不作具体要求。集流体101可以为常用的负极集流体铜箔。负极活性层102包括负极活性材料、粘结剂和导电剂，其中负极活性物质可选自人造石墨、天然石墨、混合石墨和中间炭微球中的至少一种，粘结剂可选自丁苯橡胶(SBR)、偏氟乙烯-六氟丙烯聚合物、聚丙烯腈、羧甲基纤维素钠、丁二烯-丙烯腈聚合物、聚丙烯酸甲酯、聚丙烯酸乙酯、聚丙烯酸-苯乙烯聚合物、聚偏氟乙烯、聚乙烯醇、聚氨酯、聚丙烯酸酯、丁基橡胶、环氧树脂、醋酸乙烯树脂、氯化橡胶中的至少一种，导电剂可选自导电炭黑、超导炭黑、导电石墨、乙炔黑、石墨烯、碳纳米管中的至少一种。
本发明第二方面提供一种锂离子电池，该锂离子电池的负极片为本发明第一方面所提供的负极片，除负极片外，该锂离子电池还包括正极片、隔膜、电解液。其中，对正极片、隔膜、电解液的来源不作具体限制，均可以采用本领域的常规材料，此处不再赘述。
本发明的实施，至少具有以下优势：
1、本发明所提供的负极片一方面通过对安全功能层中金属含量的调控，能有效提高电池低温高倍率充电过程中负极表面的电极电位，避免负极达到锂的析出电位，另一方面安全功能层中金属的加入可以提高锂的成核能垒，两方面因素综合可以抑制负极析锂现象的发生。
2、本发明所提供的负极片其安全功能层中陶瓷的存在一方面可以为负极片提供足够多的毛细孔道，有利于促进电解液的快速充分浸润，提高负极的动力学性能，对抑制析锂有一定的协同作用，另一方面陶瓷良好的绝热性能可以有效避免针刺测试中热失控情况的出现，增强电池的安全性能。
3、本发明所提供的锂离子电池，由于有效抑制了电池负极析锂现象的发生，因而其具有循环性能好、安全性高等优点。
附图说明
图1为本发明一种实施方式的负极片示意图；
图2为本发明另外一种实施方式的负极片示意图；
图3为本发明再一种实施方式的负极片示意图；
图4为第二浆料的扫描电镜图；
图5为安全功能浆料的扫描电镜图。
附图标记说明：
101：集流体；
102：负极活性层；
103：安全功能层；
104：绝缘层。
具体实施方式
为使本发明的目的、技术方案和优点更加清楚，下面将结合本发明的实施例，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
实施例1
本实施例的负极片示意图如图3所示，负极片及锂离子电池的制备方式如下：
1)负极片的制备
将石墨、导电炭黑、丁苯胶乳(SBR)、羧甲基纤维素钠(CMC)按质量比＝96：1.5：1.5：1加入到去离子水中搅拌均匀制成负极活性浆料；将制备得到的负极活性浆料均匀涂布在负极集流体101铜箔的上下功能表面上，极片宽度50mm，极片总长942mm,负极活性浆料涂布在铜箔上下功能表面的部分区域，其中上功能表面的涂布长度为888mm,下功能表面的涂布长度为776mm，铜箔上下功能表面涂布的负极活性浆料靠一端对齐，涂布重量为9.85mg/cm 2，烘干压实后制备得到负极活性层102，压实密度为1.7g/cm 3；
将质量百分含量为48％的镍、6％的聚偏氟乙烯(PVDF)以及4％的聚乙烯吡咯烷酮(PVP)加入到占总溶剂质量含量30％的N-甲基吡咯烷酮(NMP)中，搅拌均匀制成粘度为25000mPa·s的第一浆料，其中镍的粒径D50为200nm；将剩余的30％N-甲基吡咯烷酮(NMP)溶剂加入第一浆料中搅拌均匀，得到第二浆料；向第二浆料中加入质量百分含量为42％的勃姆石搅拌均匀，抽真空，除气泡得到固含量为20％，粘度为230mPa·s，pH值为7.2的安全功能浆料，其中勃姆石的粒径D50为1μm；将安全功能浆料涂布于制备好的集流体101上下两层负极活性层102功能表面上的部分区域，其中上负极活性层102功能表面上的涂布长度为887mm，下负极活性层102功能表面上涂布长度为775mm，涂布重量为0.745mg/cm 2，在温度为80℃下进行干燥，辊压，压实密度为1.72g/cm 3，得到上下两层的厚度均为3.6μm的安全功能层103，其中，安全功能层103的孔隙率为30％，孔径均值为63nm，并且孔径的最大值与最小值之差为50nm。铜箔的上功能表面右侧尾端留有部分区域用于焊接镍极耳，位于铜箔上功能表面的负极活性层102靠近镍极耳的曲面部分未涂布安全功能层103，此部分贴有绝缘胶纸，并从左端延伸至安全功能层103的尾端且覆盖部分安全功能层103，从右端延伸至铜箔的上功能表面，胶纸宽度为16mm，厚度为22μm。
2)正极片的制备
将钴酸锂、导电炭黑、聚偏氟乙烯(PVDF)按质量比＝95：3：2加入到N-甲基吡咯烷酮(NMP)中混合均匀制成正极活性层浆料；将制得的正极活 性层浆料均匀涂布在正极集流体铝箔上，烘干压实后得正极片。
3)电解液的制备
以浓度为1M的六氟磷酸锂(LiPF 6)为锂盐，以碳酸乙烯酯(EC)、碳酸二甲酯(DMC)和碳酸甲乙酯(EMC)的混合物为非水有机溶剂(其中质量比为EC：DMC：EMC＝3：4：3)，再加入含有3wt％氟代碳酸乙烯酯(FEC)和1wt％碳酸亚乙烯酯的添加剂混合均匀即得到电解液。
4)锂离子电池的组装
将制备好的负极片、正极片和隔膜聚丙烯微孔膜一次叠加后通过卷绕工艺制得锂离子电池电芯，将电芯装入壳体中，注入制备好的电解液，封口，经化成、容量等工序后完成锂离子电池的组装。
实施例2
本实施例与实施例1的不同之处在于：其负极片中安全功能层103各组分的质量百分含量为55％的镍、35％的勃姆石、6％的聚偏氟乙烯(PVDF)、4％的聚乙烯吡咯烷酮(PVP)。其余步骤均与实施例1相同，此处不再赘述。
实施例3
本实施例与实施例1的不同之处在于：其负极片中安全功能层103各组分的质量百分含量为60％的镍、30％的勃姆石、6％的聚偏氟乙烯(PVDF)、4％的聚乙烯吡咯烷酮(PVP)。其余步骤均与实施例1相同，此处不再赘述。
实施例4
本实施例与实施例1的不同之处在于：其负极片中安全功能层103各组分的质量百分含量为48％的铜、42％的勃姆石、6％的聚偏氟乙烯(PVDF)、4％的聚乙烯吡咯烷酮(PVP)。其余步骤均与实施例1相同，此处不再赘述。
实施例5
本实施例与实施例1的不同之处在于：其负极片中安全功能层103各组分的质量百分含量为55％的铜、35％的勃姆石、6％的聚偏氟乙烯(PVDF)、4％的聚乙烯吡咯烷酮(PVP)。其余步骤均与实施例1相同，此处不再赘述。
实施例6
本实施例与实施例1的不同之处在于：其负极片中安全功能层103各组分的质量百分含量为60％的铜、30％的勃姆石、6％的聚偏氟乙烯(PVDF)、4％的聚乙烯吡咯烷酮(PVP)。其余步骤均与实施例1相同，此处不再赘述。
实施例7
本实施例与实施例1的不同之处在于：涂布完成安全功能层103后，对安全功能层103进行干燥辊压，压实密度设置为1.78g/cm 3，安全功能层103的孔隙率为18％。其余步骤均与实施例1相同，此处不再赘述。
实施例8
本实施例与实施例1的不同之处在于：安全功能层103涂布完成后，对安全功能层103进行干燥辊压，压实密度设置为1.85g/cm 3,安全功能层103的孔径均值为20nm，孔径的最大值与最小值之差为35nm。其余步骤均与实施例1相同，此处不再赘述。
对比例1
本对比例与实施例1的不同之处在于：其负极片中无安全功能层103的存在。其余步骤均与实施例1相同，此处不再赘述。
试验例
对本发明实施例1-8以及对比例1制备得到的负极片以及锂离子电池进行以下参数的检测，结果见表1所示：
1)容量保持率(25℃，1C/1C，循环800次)
检测方法：在25℃下，将锂离子电池以1C恒流充电至4.35V，再恒压充电至0.05C，静置5min，之后以1C恒流放电至3.0V，此为首次循环，重复上述过程，对锂离子电池进行循环性能测试。锂离子电池800次循环后的容量保持率(％)＝800次循环后的放电容量/首次循环后的放电容量×100％。
2)析锂情况(0℃，0.2C/1C，循环10次)
检测方法：在0℃下，将锂离子电池以0.2C的充电倍率恒流充电到4.35V，然后再恒压充电直至电流降至0.05C；放电过程为以1C的放电倍率恒流放电 到3.0V，此为一个充放电循环。对锂离子电池进行10个充放电循环后，观察电池的析锂情况。
3)容量保持率(10℃，0.5C/1C，循环100次)
检测方法：在10℃下，将锂离子电池以0.5C恒流充电至4.35V，再恒压充电至0.05C，静置5min，之后以1C恒流放电至3.0V，此为首次循环，重复上述过程，对锂离子电池进行循环性能测试。锂离子电池100次循环后的容量保持率(％)＝100次循环后的放电容量/首次循环后的放电容量×100％。
4)针刺通过率
检测方法：在25±5℃下，0.5C放电至3.0V,静置5min；将电芯放在25℃恒温箱中，0.5C恒流到4.35V，恒压至截止电流C，记录测试前电压、内阻并检查外观并拍照；在温度为25℃，针刺高度为610mm，钢针下降速度为150mm/s，钢针直径为2.5mm，钉头部位长度为6mm下对锂离子电池进行针刺测试，测试过程中对开路电压(Open Circuit Voltage，简写：OCV)及电芯表面温度进行实时监控；测试进行到5min或电芯表面温度降到50℃以后停止测试；结束测试后，记录测试后的OCV，交流阻抗，检查外观并拍照。判断标准：不起火，不爆炸。以通过率表示，比如测试10个电芯，通过5个，则针刺通过率为5/10。
表1
Figure PCTCN2021130042-appb-000001
Figure PCTCN2021130042-appb-000002
在表1中，通过实施例1-8与对比例1的析锂情况(0℃，0.2C/1C，循环10次)对比可以看出，负极片中包括安全功能层的锂离子电池，其析锂情况明显优于负极片中无安全功能层的锂离子电池；其次从容量保持率(25℃，1C/1C，循环800次)的数据中可以看出，负极片中包含安全功能层的锂离子电池在高倍率充电时其循环性能优于负极片中不包含安全功能层的锂离子电池；再者从从容量保持率(10℃，0.5C/1C，循环100次)的数据可以看出，负极片中包含安全功能层的锂离子电池低温下循环性能较好，而负极片中无安全功能层的锂离子电池由于其析锂严重，导致电池活性锂损失，电池的循环性能较差；最后从针刺通过率的对比可以看出，负极片中有安全功能层的锂离子电池其针刺通过率明显优于负极片中无安全功能层的锂离子电池，因而电池的安全性能更高。
从实施例1-3与实施例4-6的数据对比可以看出，含镍的安全功能层其对电池析锂的抑制效果、电池在低温高倍率充电下的容量保持率以及针刺通过率都优于含铜的安全功能层；从实施例1、2、3的数据对比可以看出，增加安全功能层中镍的含量能够改善低温高倍率充电下电池的析锂情况以及循环性能。
从实施例7与实施例1的对比可以看出，当安全功能层孔隙率低于20％时，锂离子电池在低温下的析锂情况有所加重，但仍比对比例1的锂离子电池低温析锂情况有明显优势。从实施例8与实施例1的对比可以看出，孔径均值为20nm时，低温析锂有所改善，说明随着孔径降低，孔隙中锂离子迁移路径缩短，电接触增强，负极动力学性能提升。
最后应说明的是：以上各实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述各实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的范围。

Claims (10)

  1. 一种负极片，其特征在于，所述负极片包括集流体、设置于所述集流体至少一功能表面的负极活性层、以及设置于所述负极活性层的远离所述集流体的表面的安全功能层；
    其中，所述安全功能层包括金属和陶瓷。
  2. 根据权利要求1所述的负极片，其特征在于，所述安全功能层的孔隙率为20-45％。
  3. 根据权利要求1或2所述的负极片，其特征在于，所述安全功能层的孔径均值为10-500nm，且所述孔径的最大值与最小值之差不大于80nm。
  4. 根据权利要求3所述的负极片，其特征在于，所述安全功能层的孔径均值为20-200nm。
  5. 根据权利要求1-4任一项所述的负极片，其特征在于，所述安全功能层的厚度为0.3-10μm。
  6. 根据权利要求1-5任一项所述的负极片，其特征在于，所述金属选自镍或铜，和/或，
    所述陶瓷选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙、硫酸钡、氮化铝、氮化硼、碳酸钡、钛酸钡中的至少一种。
  7. 根据权利要求6所述的负极片，其特征在于，所述金属的粒径D50为50-500nm，和/或，
    所述陶瓷的粒径D50为0.5-5μm。
  8. 根据权利要求1-7任一项所述的负极片，其特征在于，所述安全功能层按照质量百分含量包括：金属48-60％、陶瓷28-40％、粘结剂3-8％以及分散剂1-4％。
  9. 根据权利要求1所述的负极片，其特征在于，所述负极活性层靠近极耳的表面设置有绝缘层，所述绝缘层的一端延伸至所述安全功能层且覆盖部分所述安全功能层，所述绝缘层的另一端延伸至所述功能表面。
  10. 一种锂离子电池，其特征在于，所述锂离子电池的负极片为权利要求1-9任一项所述的负极片。
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