WO2024065250A1 - 一种负极极片及由其制备的电池 - Google Patents

一种负极极片及由其制备的电池 Download PDF

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Publication number
WO2024065250A1
WO2024065250A1 PCT/CN2022/122013 CN2022122013W WO2024065250A1 WO 2024065250 A1 WO2024065250 A1 WO 2024065250A1 CN 2022122013 W CN2022122013 W CN 2022122013W WO 2024065250 A1 WO2024065250 A1 WO 2024065250A1
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Prior art keywords
negative electrode
density
low
pressure
electrode sheet
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PCT/CN2022/122013
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English (en)
French (fr)
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田亚西
唐代春
王曦童
姬廷振
夏雨润
覃雄
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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 PCT/CN2022/122013 priority Critical patent/WO2024065250A1/zh
Priority to PCT/CN2023/120503 priority patent/WO2024067363A1/zh
Publication of WO2024065250A1 publication Critical patent/WO2024065250A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to a negative electrode sheet, wherein the negative electrode material layer includes a structure of high-pressure density regions and low-pressure density regions that are continuously staggered and arranged alternately, and the low-pressure density regions have an upper surface width and a lower surface width with a width difference.
  • the present application also relates to a method for preparing the negative electrode sheet, a secondary battery including the negative electrode sheet, a battery pack including the secondary battery, and an electric device.
  • Secondary batteries have become the most popular energy storage system due to their low cost, long life and good safety. They are now widely used in pure electric vehicles, hybrid electric vehicles and smart grids. Secondary batteries are mainly composed of positive electrode plates, negative electrode plates, separators and electrolytes, wherein the negative electrode plates include a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material. The negative electrode material layer needs to be infiltrated with an electrolyte so that lithium can be inserted into the surface and the interior of the negative electrode material layer.
  • the prior art usually promotes internal lithium insertion by making the negative electrode material layer contain a large number of pores, so that the electrolyte has a higher liquid transfer rate inside the negative electrode material layer.
  • this not only increases the material cost, but also these pore formers need to be removed through cumbersome and expensive operations in subsequent steps.
  • the present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate to solve the technical problems of insufficient liquid transfer rate of the negative electrode plate and poor charging performance of the battery prepared therefrom.
  • the present application provides a negative electrode sheet in a first aspect, comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active material, wherein the negative electrode material layer has a structure of high-density regions and low-density regions continuously and alternately arranged, the density of the high-density regions is 1.6-1.9 g/cm 3 , the density of the low-density regions is 1.3-1.8 g/cm 3 , and the difference between the density of the high-density regions and the low-density regions is 0.1-0.6 g/cm 3 , optionally 0.2-0.4 g/cm 3 ,
  • the low-pressure-tightness region has an upper surface width x1 and a lower surface width x2 , and the difference between the upper surface width and the lower surface width is 0 ⁇
  • the negative electrode plate of the present application includes a negative electrode material layer with a specific structure, so that different areas inside the material layer have different porosities without using any pore-forming agent, thereby increasing the liquid transmission rate of the electrolyte in the negative electrode plate, thereby achieving improved charging performance.
  • the difference between the upper surface width and the lower surface width of the low-pressure density region is 0 ⁇
  • the width x of the low-pressure density region is 100 ⁇ m-100 mm, optionally 200 ⁇ m-30 mm. In any embodiment, the width mi of the high-pressure density region is 10-100 mm, optionally 20-60 mm. The widths of the low-pressure density region and the high-pressure density region can be adjusted according to the length of the negative electrode sheet to be prepared.
  • the negative electrode plate satisfies the following formula: 0.1 ⁇ n*m i /L ⁇ 1, where n is the number of low-pressure density regions, m i is the width of the high-pressure density region, and L is the length of the plate.
  • the direction of the low-pressure density region is defined as ⁇ , which satisfies ⁇ 2 ⁇ ⁇ 1 , where 0 ⁇ 1 / ⁇ 2 ⁇ 1, and ⁇ 1 and ⁇ 2 are the angles between the tangent directions on both sides of the low-pressure density region and the horizontal direction, respectively.
  • the cross-sectional structural shape of the low-pressure density region is a rectangular, trapezoidal or arc-shaped structure, or an irregular structure.
  • the length direction of the low-pressure density region and the high-pressure density region is parallel to the direction of the negative electrode tab.
  • the negative electrode current collector is a metal foil or a composite current collector, and the composite current collector includes a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • the negative electrode active material is selected from one or more of graphite, soft carbon, hard carbon, mesophase carbon microbeads, carbon fibers, carbon nanotubes, elemental silicon, silicon oxides, silicon-carbon composites, and lithium titanate.
  • the density of the low pressure density regions may be the same or different; in the case of different densities, the difference in density between the low pressure density regions is ⁇ 0.5 g/cm 3 .
  • the present application also relates to a method for preparing the negative electrode sheet of the first aspect of the present application, which comprises the following steps:
  • the negative electrode material layers are cold pressed to have the same thickness.
  • a second aspect of the present application provides a secondary battery, which includes a negative electrode sheet selected from the first aspect of the present application.
  • a third aspect of the present application provides a battery pack, which includes a secondary battery selected from the second aspect of the present application.
  • a fourth aspect of the present application provides an electrical device, which includes a secondary battery selected from the second aspect of the present application or a battery pack according to the third aspect of the present application.
  • FIG. 1 is a schematic diagram of a lithium-ion secondary battery in one embodiment of the present application.
  • FIG. 2 is an exploded view of the lithium ion secondary battery in one embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery pack in one embodiment of the present application.
  • FIG. 4 is an exploded view of the battery pack shown in FIG. 3 according to one embodiment of the present application.
  • FIG. 5 is a schematic diagram of a device in which a battery pack is used as a power source in one embodiment of the present application.
  • FIG6 is a schematic diagram showing an alternating arrangement of high-pressure density regions and low-pressure density regions in a negative electrode plate in one embodiment of the present application.
  • FIG. 7 is a schematic diagram of the directions of different density regions and the directions of the tabs in a negative electrode sheet in one embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, and any upper limit can be combined with any other upper limit to form an undefined range.
  • each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an undefined range.
  • a conventional method in the prior art is to add a pore former to the mixture for preparing the negative electrode active material layer, so that the porosity inside the formed negative electrode active material layer is significantly improved.
  • the porosity in the negative electrode active material layer is relatively consistent, it is still difficult for the electrolyte to penetrate into the interior of the negative electrode active material layer because its liquid transmission kinetics are insufficient at a relatively consistent porosity.
  • the prior art generally uses one or more pore formers selected from calcium oxide, magnesium oxide, germanium oxide and tin oxide, and these pore formers need to be removed in subsequent steps. This not only increases the material cost, but also makes the method of preparing the negative electrode plate more complicated and cumbersome.
  • the first aspect of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active material, wherein the negative electrode material layer has a structure of high-density regions and low-density regions continuously and alternately arranged, the density of the high-density regions is 1.6-1.9 g/cm 3 , the density of the low-density regions is 1.3-1.8 g/cm 3 , and the difference between the density of the high-density regions and the low-density regions is 0.1-0.6 g/cm 3 , optionally 0.2-0.4 g/cm 3 ,
  • the low-pressure-density region has an upper surface width x1 and a lower surface width x2 , and the difference between the upper surface width and the lower surface width is 0 ⁇
  • the negative electrode sheet of the present application can have a significantly improved transmission rate for the electrolyte by including a negative electrode material layer with a specific structure, thereby obtaining improved charging performance.
  • the inventors believe that by coating different weights of negative electrode active materials when preparing the active material layer of the negative electrode sheet, and pressing the negative electrode material layer to the same thickness in the subsequent cold pressing stage, different regions of the material layer can have different densities. Different densities mean that the porosity of each region is different; the porosity of the low-density region is high, and the porosity of the high-density region is low.
  • the different porosity of the adjacent regions improves the transmission kinetics of the electrolyte and increases the transmission rate, thereby improving its wetting ability for the negative electrode sheet.
  • Factors affecting the transmission rate include both the difference in density between adjacent regions and the shape characteristics of the low-density region, that is, the difference in width between the upper and lower surfaces. The inventors have found that by controlling the density difference between the high-density area and the low-density area and the difference between the upper surface width and the lower surface width of the low-density area within a specific range, a negative electrode plate with significantly improved liquid transfer rate and charging performance can be obtained.
  • the density of the high-density region and the low-density region of the negative electrode material layer of the negative electrode plate should be within a reasonable range, so the density range of the high-density region and the low-density region is limited.
  • the density of each region refers to the density of the negative electrode active material contained therein.
  • one of the widths of the upper and lower surfaces of the low-density region may be zero, that is, the region intersects with the surface at only one point.
  • the negative electrode plate does not contain any pore former.
  • the difference between the upper surface width and the lower surface width of the low-density region is 0 ⁇
  • the width x of the low-pressure-density region is 100 ⁇ m-100 mm, optionally 200 ⁇ m-30 mm. In some embodiments, the width mi of the high-pressure-density region is 10-100 mm, optionally 20-60 mm.
  • the width x of the low-pressure-density region and the width mi of the high-pressure-density region are the average widths of the regions, respectively. The widths of the low-pressure-density region and the high-pressure-density region can be adjusted according to the length of the negative electrode sheet to be prepared.
  • the negative electrode plate satisfies the following formula: 0.1 ⁇ n*m i /L ⁇ 1, where n is the number of low-pressure density regions, m i is the width of the high-pressure density region, and L is the length of the plate.
  • n is the number of low-pressure density regions
  • m i is the width of the high-pressure density region
  • L is the length of the plate.
  • the direction of the low-pressure density region is defined as ⁇ , which satisfies ⁇ 2 ⁇ ⁇ 1 , wherein 0 ⁇ 1 / ⁇ 2 ⁇ 1, and ⁇ 1 and ⁇ 2 are the angles between the tangent directions on both sides of the low-pressure density region and the horizontal direction, respectively.
  • the above formula further defines the shape of the low-pressure density region on the transverse cross section of the negative electrode plate, so that the transmission rate of the electrolyte therein can be adjusted by changing the shape of the region.
  • the structural shape of the cross section of the low-pressure density region is a rectangular, trapezoidal or arc-shaped structure, or an irregular structure.
  • the structural shape of the cross section of the low-pressure density region is a rectangle or a trapezoid, wherein in the case of a trapezoid, the difference between the upper and lower widths of the cross section of the low-pressure density region is ⁇ 100 ⁇ m.
  • the length direction of the low-pressure-density region and the high-pressure-density region is parallel to the direction of the negative electrode tab.
  • the length direction of the low-pressure-density region and the high-pressure-density region is parallel to the length direction of the negative electrode tab.
  • the negative electrode tab may include a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector.
  • the negative electrode current collector is a metal foil or a composite current collector, which includes a polymer material base layer and a metal layer formed on at least one surface of a polymer material substrate.
  • the negative electrode material layer includes a negative electrode active material, and the negative electrode active material is selected from one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, elemental silicon, silicon oxides, silicon carbon composites, and lithium titanate.
  • the density of the low-pressure density regions may be the same or different; in the case of different densities, the difference in density between the low-pressure density regions is ⁇ 0.5 g/cm 3.
  • the difference in density between the low-pressure density regions is greater than 0.5 g/cm 3 , the concentration polarization in the active material layer is too large, so that the improvement in the electrolyte infiltration rate is not significant.
  • the present application also relates to a method for preparing a negative electrode sheet according to the first aspect of the present application, which comprises the following steps:
  • the negative electrode material layers are cold pressed to have the same thickness.
  • the negative electrode sheet of the present invention has no special requirements for the current collector and the negative electrode active material, so various materials conventionally used in the battery field can be used. Specific materials can be found in the detailed description of the negative electrode sheet below. Conventional preparation methods can also be used for the preparation of the negative electrode sheet, for example, by configuring a negative electrode slurry containing a negative electrode active material, a conductive agent, a binder and a thickener, and applying the obtained slurry to different regions of the current collector with different weights, a negative electrode material layer with regions with different coating weights can be formed on the current collector. Subsequently, the negative electrode sheet can be obtained by drying, cold pressing, and slitting.
  • the thickness of the negative electrode material layer is pressed to a uniform thickness so that the negative electrode material layer has a substantially horizontal surface.
  • the density in each region is also different.
  • its porosity is also different.
  • a negative electrode sheet having multiple alternating regions of different porosities is obtained.
  • the method for preparing a negative electrode sheet described in the present application does not include the use of any pore forming agent.
  • a second aspect of the present application provides a secondary battery, which includes a negative electrode sheet selected from the first aspect of the present application.
  • a third aspect of the present application provides a battery pack, which includes a secondary battery selected from the second aspect of the present application.
  • a fourth aspect of the present application provides an electrical device, which includes a secondary battery selected from the second aspect of the present application or a battery pack according to the third aspect of the present application.
  • the materials of the components of the secondary battery mentioned in the present application can be selected from a wide range.
  • the secondary battery is particularly a lithium-ion secondary battery.
  • the battery cells of the lithium-ion secondary battery are described in detail below.
  • lithium-ion secondary batteries include a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.
  • active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the separator is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation.
  • the electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.
  • the electrolyte includes electrolyte salt and solvent.
  • the electrolyte salt may be a common electrolyte salt in a lithium ion secondary battery, such as a lithium salt, including the lithium salt as a high thermal stability salt, a lithium salt as a low impedance additive, or a lithium salt that inhibits corrosion of aluminum foil.
  • a lithium salt including the lithium salt as a high thermal stability salt, a lithium salt as a low impedance additive, or a lithium salt that inhibits corrosion of aluminum foil.
  • the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobisoxalate phosphate (LiDFOP), lithium fluorosulfonate (LiSO 3 F), difluorobisoxalate (NDFOP), Li 2 F(SO 2 N) 2 SO 2 F, KFSI, CsFSI, Ba(FSI) 2 , and LiFSO 2 NSO 2 CH 2 CH 2 CH 2 CH 2
  • the solvent is a non-aqueous solvent.
  • the solvent may include one or more of linear carbonate, cyclic carbonate, and carboxylate.
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4
  • the electrolyte may also optionally include other additives.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature performance.
  • the additive is selected from at least one of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonic acid compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound, a borate compound, and a carboxylate compound.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material and a conductive agent.
  • the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode active material layer disposed on the surface of the positive electrode current collector includes a positive electrode active material.
  • the positive electrode active material used in the present application may have any conventional positive electrode active material used in a secondary battery.
  • the positive electrode active material may include one or more selected from lithium transition metal oxides, lithium phosphates containing olivine structures, and their respective modified compounds.
  • lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds.
  • lithium phosphates containing olivine structures may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and a modified compound thereof. These materials can all be obtained commercially. Carbon may be coated on the surface of the positive electrode active material.
  • the positive electrode active material layer may optionally include a conductive agent.
  • a conductive agent there is no specific limitation on the type of the conductive agent, and those skilled in the art may select it according to actual needs.
  • the conductive agent used for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the positive electrode active material layer also includes a binder.
  • the binder is the binder composition described above.
  • the binder may also include other binders.
  • other binders may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive electrode sheet can be prepared according to methods known in the art.
  • the carbon-coated positive electrode active material, the conductive agent and the aqueous binder can be dispersed in a solvent (such as water) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet is obtained.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer includes a negative electrode active material.
  • the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the metal foil copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode material layer generally comprises a negative electrode active material and an optional binder, an optional conductive agent and other optional auxiliary agents, and is generally formed by coating and drying a negative electrode slurry.
  • the negative electrode slurry coating is generally formed by dispersing the negative electrode active material and the optional conductive agent and binder in a solvent and stirring them uniformly.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water.
  • the specific type of the negative electrode active material is not limited, and the active material known in the art that can be used for the negative electrode of a lithium ion secondary battery can be used, and those skilled in the art can select it according to actual needs.
  • the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fibers, carbon nanotubes, elemental silicon, silicon oxides, silicon-carbon composites, and lithium titanate.
  • the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the negative electrode active material layer also includes a binder.
  • the binder is the binder composition described above.
  • the binder may also include other binders.
  • other binders may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • auxiliary agents include, for example, thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).
  • thickeners such as sodium carboxymethyl cellulose (CMC-Na)
  • the lithium-ion secondary battery using an electrolyte also includes a separator.
  • the separator is arranged between the positive electrode plate and the negative electrode plate to play an isolating role.
  • the present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without particular restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular restrictions.
  • the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG1 is a lithium-ion secondary battery 5 of a square structure as an example.
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • lithium-ion secondary batteries can be assembled into a battery module 4, and the number of lithium-ion secondary batteries contained in the battery module 4 can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module 4.
  • a plurality of lithium-ion secondary batteries 5 can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other manner. Further, the plurality of lithium-ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may also include a housing having a housing space, and a plurality of lithium-ion secondary batteries 5 are accommodated in the housing space.
  • the lithium-ion secondary batteries 5 or battery modules 4 may be assembled into a battery pack 1 , and the number of lithium-ion secondary batteries 5 or battery modules 4 contained in the battery pack 1 may be selected by those skilled in the art based on the application and capacity of the battery pack 1 .
  • FIG3 and FIG4 are battery packs 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery cells disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery cells.
  • the present application also provides a device, which includes a battery pack provided in the present application.
  • the battery pack can be used as a power source for the device, and can also be used as an energy storage unit for the device.
  • the device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.
  • a battery pack can be selected according to its usage requirements.
  • FIG5 is a device as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module may be used.
  • Figure 6 is a schematic diagram of the alternating arrangement of high-pressure and low-pressure regions in the negative electrode sheet in one embodiment of the present application, wherein the length direction of the high-pressure and low-pressure regions is consistent with the length direction of the electrode sheet.
  • the lower part of Figure 6 shows a cross-sectional schematic diagram of the electrode sheet, wherein x1 is the upper surface width of the low-pressure region, x2 is the lower surface width of the low-pressure region, mi is the width of the high-pressure region, and ⁇ 1 and ⁇ 2 are the angles between the tangent direction on both sides of the low-pressure region and the horizontal direction.
  • FIG. 7 is a schematic diagram of the directions of different density regions in a negative electrode pole piece and the direction of the pole lug in one embodiment of the present application, wherein the directions of different density regions are respectively parallel, perpendicular and inclined to the direction of the pole lug.
  • Embodiment 1 is a diagrammatic representation of Embodiment 1:
  • NCM nickel-cobalt-manganese
  • conductive agent carbon black conductive agent carbon black
  • PVDF binder polyvinylidene fluoride
  • the active material artificial graphite, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium hydroxymethyl cellulose (CMC) were dissolved in the solvent deionized water in a weight ratio of 96.8:0.7:1.3:1.2, and the prepared negative electrode slurry was coated on the current collector after being evenly mixed.
  • the water content in the slurry a negative electrode slurry with two viscosities was obtained, and the slurries with different viscosities were coated on the current collector to obtain a pole piece with high and low coating weights.
  • the density of the high-pressure density area is 1.7g/ cm3
  • the density of the low-pressure density area is 1.3g/ cm3
  • the number of high-pressure density areas and low-pressure density areas is the same
  • the average width is also basically the same.
  • the upper and lower surface widths of the areas with different densities are measured by an offline laser thickness gauge, and the density of each area is adjusted by calculating the width of the coating area and the weight. Subsequently, the negative electrode pole piece is obtained after drying, cold pressing, and slitting.
  • the positive electrode sheet, separator, and negative electrode sheet prepared as described above are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare cell, and the bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery.
  • the uncharged battery is then subjected to the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the lithium-ion secondary battery product of Example 1.
  • Embodiment 2-10 are identical to Embodiment 2-10:
  • Example 1 was repeated, except that the structure and density of the negative electrode active material layer of the negative electrode plate were as shown in Table 1 below (controlled by adjusting the coating amount of the negative electrode slurry in different regions).
  • the corresponding negative electrode plate and the corresponding lithium ion secondary battery product were prepared as described above.
  • Example 1 was repeated, except that the negative electrode active material layer of the negative electrode plate did not contain an alternating arrangement structure of high-density and low-density regions, but had the same density.
  • the densities were 1.6, 1.7, 1.8 and 1.9 g/cm 3 , respectively.
  • the corresponding negative electrode plate and the corresponding lithium-ion secondary battery product were prepared as described above.
  • Measurement of the width of a specific area in the negative electrode active material layer of the negative electrode sheet During the coating process, an offline laser thickness gauge is used to monitor the thickness of the coating area in real time. The thickness is positively correlated with the coating weight, thereby determining the width of the specific area.
  • Measurement of charging performance of lithium-ion secondary battery The 20-80% SOC charging time of the battery was measured by a three-electrode test method.
  • the secondary battery including the negative electrode sheet with alternating high-density region and low-density region in the embodiment of the present invention shows a significantly shorter 20-80% SOC charging time, indicating that its charging performance has been substantially improved.
  • the 20-80% SOC charging time of the battery can be further improved by selecting the difference in density between the high-density region and the low-density region, and the difference between the upper surface width and the lower width of the low-density region.

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Abstract

本申请涉及一种负极极片，其包含的负极材料层具有连续交错相间排列的高压密区域和低压密区域的结构，并且所述低压密区域具有存在特定宽度差的上表面宽度和下表面宽度。本申请还涉及所述负极极片的制备方法、包含所述负极极片的电池极片组合物的二次电池以及包含该二次电池的电池包以及用电装置。

Description

一种负极极片及由其制备的电池 技术领域
本申请涉及一种负极极片，其包含的负极材料层具有连续交错相间排列的高压密区域和低压密区域的结构，并且所述低压密区域具有存在宽度差的上表面宽度和下表面宽度。本申请还涉及所述负极极片的制备方法、包含所述负极极片的二次电池以及包含该二次电池的电池包以及用电装置。
背景技术
二次电池因其成本低、寿命长、安全性好等特点成为最受欢迎的能量存储系统，现已被广泛应用于纯电动汽车、混合电动汽车以及智能电网等领域。二次电池主要由正极极片、负极极片、隔离膜及电解质组成，其中负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质。所述负极材料层需要让电解液浸润，使得负极材料层的表面以及内部均可实现嵌锂。为此目的，现有技术中通常通过使负极材料层包含大量的孔隙来促进内部的嵌锂作用，使得电解液在负极材料层内部具有较高的液体传输速率。为形成内部孔隙，通常需要向制备负极材料层的混合物中加入造孔剂。然而，这不仅增加了物料成本，而且这些造孔剂需要在后续步骤中通过繁琐的、昂贵的操作而去除。
因此，目前仍然需要提供一种新的负极极片，其可具有提高的液体传输速率以及改善的充电性能，并且可以不使用任何造孔剂而达到造孔作用，降低生产成本。
发明内容
本申请是鉴于上述课题而进行的，其目的在于提供一种负极极片，以解决负极极片的液体传输速率不足以及由其制备的电池的充电性能不佳的技术问题。
为了达到上述目的，本申请第一方面提供一种负极极片，其包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质，其中所述负极材料层具有连续交错相间排列的高压密区域和低压密区域的结构，所述高压密区域的密度为1.6-1.9g/cm 3，所述低压密区域的密度为1.3-1.8g/cm 3，并且所述高压密区域和所述低压密区域的密度之差为0.1-0.6g/cm 3，可选地为0.2-0.4g/cm 3，
其中所述低压密区域具有上表面宽度x 1和下表面宽度x 2，并且所述上表面宽度和下表面宽度之差为0≤|x 1-x 2|≤100mm。
本申请的负极极片通过包含具有特定结构的负极材料层，可以在不使用任何造孔剂的情况下，使得材料层内部不同区域具有不同的孔隙率，从而增加电解液在负极极片中的液体传输速率，进而 实现充电性能的改善。
在任意实施方式中，所述低压密区域的上表面宽度和下表面宽度之差为0≤|x 1-x 2|≤120μm，可选地为60μm≤|x 1-x 2|≤120μm，进一步可选地为80μm≤|x 1-x 2|≤120μm。通过进一步调节所述低压密区域的上表面宽度和下表面宽度之差，可以改变低压密区域的形状，从而控制电解液在负极材料层中的传输速率。
在任意实施方式中，所述低压密区域的宽度x为100μm-100mm，可选地为200μm-30mm。在任意实施方式中，所述高压密区域的宽度m i为10-100mm，可选地为20-60mm。所述低压密区域和高压密区域的宽度可根据所需制备的负极极片的长度而调节。
在任意实施方式中，所述负极极片满足下式：0.1≤n*m i/L＜1，其中n为低压密区域的数量，m i为高压密区域的宽度，L为极片长度。在另外的实施方案中，将所述低压密区域的方向定义为θ，其满足θ 2≤θ≤θ 1，其中0＜θ 1/θ 2≤1，θ 1和θ 2分别为所述低压密区域的两侧切线方向与水平方向的夹角。
在任意实施方式中，所述低压密区域的横截面的结构形状为长方形、梯形或弧形结构，或者为不规则的结构。在任意实施方式中，所述低压密区域和高压密区域的长度方向与负极极耳的方向平行。在任意实施方式中，所述负极集流体为金属箔片或复合集流体，所述复合集流体包括高分子材料基层和形成于高分子材料基层的至少一个表面上的金属层。在另外的实施方案中，所述负极活性物质选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或多种。
在任意实施方式中，所述低压密区域的密度可为相同或不同；在密度不同的情况下，各低压密区域的密度之差≤0.5g/cm 3。
本申请还涉及一种制备本申请的第一方面的负极极片的方法，其包括以下步骤：
通过调节在集流体的不同区域中涂覆在集流体上的负极活性物质的粘度和/或重量，从而形成具有不同负极活性物质含量的区域；以及
对负极材料层进行冷压，使其具有相同的厚度。
本申请的第二方面提供一种二次电池，其包括选自本申请的第一方面的负极极片。
本申请的第三方面提供一种电池包，其包括选自本申请的第二方面的二次电池。
本申请的第四方面提供一种用电装置，其包括选自本申请的第二方面的二次电池或者本申请的第三方面的电池包。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请实施例中所需要使用的附图作简单的介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请一个实施方式中的锂离子二次电池的示意图。
图2是图1所示的本申请一个实施方式中的锂离子二次电池的分解图。
图3是本申请一个实施方式中的电池包的示意图。
图4是图3所示的本申请一个实施方式中的电池包的分解图。
图5是本申请一个实施方式中的电池包用作电源的装置的示意图。
图6是本申请一个实施方式中的负极极片中高压密区域和低压密区域交替排列的示意图。
图7是本申请一个实施方式中的负极极片中不同密度区域的方向与极耳方向的示意图。
附图标记说明
1电池包
2上箱体
3下箱体
4电池模块
5锂离子二次电池
51壳体
52电极组件
53盖板
具体实施方式
为了简明，本申请具体地公开了一些数值范围。然而，任意下限可以与任意上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
随着电动汽车等电动交通工具的快速普及，市场对充电性能强的锂离子电池的需求也越来越迫切。要改善锂电池的充电性能，一种有效的途径是提高电解液对于负极极片的浸润速率，使得即使是负极极片内部的负极活性物质的嵌锂能力也能得到有效保持。但是，由于负极极片的表面在嵌锂之后容易钝化，并且嵌入的锂离子容易堵塞极片表面的孔隙，使得后续的锂离子难以深入负极活性材料层的内部进行嵌锂。现有技术中的一种常规方法是通过将造孔剂加入到制备负极活性材料层的混合物中，使得形成的负极活性材料层内部的孔隙率明显提高。然而，由于负极活性材料层中的孔隙率较为一致，电解液仍然较难深入到负极活性材料层的内部，因为在较为一致的孔隙率下，其液体传输动力学不足。另外，现有技术中通常使用选自氧化钙、氧化镁、氧化锗和氧化锡中的一种或几种的造孔剂，而这些造孔剂需要在后续步骤中去除。这不但增加了物料成本，而且使得制备负极极片的方法更复杂繁琐。
因此，本领域需要提供一种新的负极极片，其具有改善的电解液传输速率以及充电性能，并且 可在不使用造孔剂的情况下制备。
具体的，本申请第一方面提供一种负极极片，其包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质，其中所述负极材料层具有连续交错相间排列的高压密区域和低压密区域的结构，所述高压密区域的密度为1.6-1.9g/cm 3，所述低压密区域的密度为1.3-1.8g/cm 3，并且所述高压密区域和所述低压密区域的密度之差为0.1-0.6g/cm 3，可选地为0.2-0.4g/cm 3，
其中低压密区域具有上表面宽度x 1和下表面宽度x 2，并且所述上表面宽度和下表面宽度之差为0≤|x 1-x 2|≤100mm。
本发明人发现，本申请的负极极片通过包含具有特定结构的负极材料层，可具有明显提高的对于电解液的传输速率，从而获得改善的充电性能。不囿于任何理论，本发明人认为，通过在制备负极极片的活性材料层时涂覆不同重量的负极活性物质，并在随后的冷压阶段将所述负极材料层压制到相同的厚度，可使得所述材料层的不同区域具有不同的密度。不同的密度就意味着各区域的孔隙率不同；密度低的区域孔隙率高，而密度高的区域空隙率低。在电解液由一个区域向相邻的区域传输时，这种相邻区域的不同的孔隙率使得电解液的传输动力学改善，传输速率增加，从而提高其对于负极极片的浸润能力。影响该传输速率的因素既包含相邻区域的密度之差，也包含低压密区域的形状特征，即上下表面的宽度之差。本发明人发现，通过将高压密区域和低压密区域的密度之差以及低压密区域的上表面宽度和下表面宽度之差控制在特定的范围内，可得到具有明显改善的液体传输速率和充电性能的负极极片。
从实际的角度出发，所述负极极片的负极材料层的高压密区域和低压密区域各自的密度应位于合理的范围内，因此限定了高压密区域和低压密区域各自的密度范围。各区域的密度指的是其中包含的负极活性物质的密度。另外，所述低压密区域的上下表面的宽度之一可为零，即包含该区域与该表面只在一个点上相交的情况。特别地，所述负极极片不含有任何造孔剂。
在一些实施方式中，所述低压密区域的上表面宽度和下宽度之差为0≤|x 1-x 2|≤120μm，可选地为60μm≤|x 1-x 2|≤120μm，进一步可选地为80μm≤|x 1-x 2|≤120μm。通过进一步调节所述低压密区域的上表面宽度和下表面宽度之差，可以改变低压密区域的形状，从而控制电解液在负极材料层中的传输速率。
在一些实施方式中，所述低压密区域的宽度x为100μm-100mm，可选地为200μm-30mm。在一些实施方式中，所述高压密区域的宽度m i为10-100mm，可选地为20-60mm。所述低压密区域的宽度x和所述高压密区域的宽度m i分别为所述各区域的平均宽度。所述低压密区域和高压密区域的宽度可根据所需制备的负极极片的长度而调节。如果各区域的长度过长，则会使得电解液在单一区域中的传输速率变慢，由不同区域孔隙率的差异带来的提升效果不明显；如果各区域的长度过短，则不但加工较为困难，液体传输速率也不稳定。
在一些实施方式中，所述负极极片其满足下式：0.1≤n*m i/L＜1，其中n为低压密区域的数量，m i为高压密区域的宽度，L为极片长度。本发明人发现，当负极极片满足上述式的要求时，其充电 性能具有进一步的改善。所述高压密区域在极片长度方向上的总宽度不应过低，否则孔隙率的差异带来的提升效果不明显。
在另一些实施方案中，将所述低压密区域的方向定义为θ，其满足θ 2≤θ≤θ 1，其中0＜θ 1/θ 2≤1，θ 1和θ 2分别为所述低压密区域的两侧切线方向与水平方向的夹角。上述式进一步限定了所述低压密区域在负极极片的横向截面上的形状，使得可通过改变该区域的形状来调节电解液在其中的传输速率。在一些实施方式中，所述低压密区域的横截面的结构形状为长方形、梯形或弧形结构，或者为不规则的结构。特别地，所述低压密区域的横截面的结构形状为长方形或梯形，其中在梯形的情况下，低压密区域的横截面的上下宽度之差≤100μm。
在一些实施方式中，所述低压密区域和高压密区域的长度方向与负极极耳的方向平行。所述低压密区域和高压密区域的长度方向平行于负极极片的长度方向。本发明人发现，相比于其他方向排布，当所述低压密区域和高压密区域的长度方向与负极极耳的方向平行时，电解液在负极极片的活性材料层中的浸润速率最大。对于所述负极极片的活性材料层的组成没有特别限制，可使用本领域常规应用的材料与结构，例如该负极极片可包含负极集流体以及设置在负极集流体至少一个表面上的负极材料层。在一些实施方式中，所述负极集流体为金属箔片或复合集流体，所述包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。在另一些实施方案中，所述负极材料层包含负极活性物质，并且所述负极活性物质选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或多种。
在一些实施方式中，所述低压密区域的密度可为相同或不同；在密度不同的情况下，各低压密区域的密度之差≤0.5g/cm 3。当各低压密区域的密度之差大于0.5g/cm 3时，活性材料层中的浓差极化过大，使得电解液浸润速率的改善不显著。
本申请还涉及一种制备根据本申请的第一方面的负极极片的方法，其包括以下步骤：
通过调节在集流体的不同区域中涂覆在集流体上的负极活性物质的粘度和/或重量，从而形成具有不同负极活性物质含量的区域；以及
对负极材料层进行冷压，使其具有相同的厚度。
本发明的负极极片对于集流体与负极活性材料没有特别的要求，因此可使用电池领域中常规使用的各种材料。具体的材料可见于下文对于负极极片的详细描述。对于所述负极极片的制备也可采用常规的制备方法，例如通过配置包含负极活性物质、导电剂、粘结剂和增稠剂的负极浆料，并将得到的浆料以不同的重量涂覆到集流体的不同区域上，即可在集流体上形成具有不同涂覆重量的区域的负极材料层。随后可通过烘干、冷压、分切得到负极极片。冷压时，将负极材料层的厚度压制到均匀的厚度，使得负极材料层具有呈基本水平的表面。此时，由于负极材料层的各区域中涂覆的负极浆料的重量不同，使得各区域中的密度也就不同。在不同的密度下，其孔隙率也不同。最终，得到了具有多个交替排列的不同孔隙率的区域的负极极片。特别地，本申请所述制备负极极片的方法不包含使用任何造孔剂。
本申请的第二方面提供一种二次电池，其包括选自本申请的第一方面的负极极片。
本申请的第三方面提供一种电池包，其包括选自本申请的第二方面的二次电池。
本申请的第四方面提供一种用电装置，其包括选自本申请的第二方面的二次电池或者本申请的第三方面的电池包。
本申请中所提到的二次电池的各组件的材料可在宽范围内进行选择。在一些实施方案中，所述二次电池特别地为锂离子二次电池。下文对所述锂离子二次电池的电池单体进行详细阐述。
通常情况下，锂离子二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
[电解液]
电解液在正极极片和负极极片之间起到传导离子的作用。电解液包括电解质盐和溶剂。
在本申请中，电解质盐可为锂离子二次电池中的常用电解质盐，例如锂盐，包括可为上述作为高热稳定性盐的锂盐、作为低阻抗添加剂的锂盐或抑制铝箔腐蚀的锂盐。作为实例，电解质盐可选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)、氟磺酸锂(LiSO 3F)、二氟二草酸盐(NDFOP)、Li 2F(SO 2N) 2SO 2F、KFSI、CsFSI、Ba(FSI) 2及LiFSO 2NSO 2CH 2CH 2CF 3中的一种以上。
溶剂的种类没有特别的限制，可根据实际需求进行选择。在一些实施方式中，溶剂为非水性溶剂。可选地，溶剂可包括链状碳酸酯、环状碳酸酯、羧酸酯中的一种或几种。在一些实施方式中，溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、四氢呋喃、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种以上。
在一些实施方式中，电解液中还可选地包括其他添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、以及改善电池低温性能的添加剂等。作为示例，添加剂选自含有不饱和键的环状碳酸酯化合物、卤素取代的环状碳酸酯化合物、硫酸酯化合物、亚硫酸酯化合物、磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、磷腈化合物、环状酸酐化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物、羧酸酯化合物中的至少一种。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极活性物质层，正极活性物质层包括正极活性材料和导电剂。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极活性物质层设置在正极集流体相对的两个表面的其中任意一者或两者上。
本申请的锂离子二次电池中，正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(例如铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
设置于正极集流体的表面上的正极活性物质层包括正极活性材料。本申请中所用的正极活性材料可具有二次电池中使用的任意常规正极活性材料。在一些实施方式中，正极活性材料可包含选自锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。正极活性材料表面上可包覆有碳。
正极活性物质层可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材料的导电剂可以选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。
正极活性物质层还包括粘结剂。粘接剂为上文所述的粘接剂组合物。除上文所述的粘接剂组合物外，粘接剂还可包含其它粘接剂。作为示例，其它粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
本申请中可按照本领域已知的方法制备正极极片。作为示例，可以将包覆碳的正极活性材料、导电剂和水性粘结剂分散于溶剂(例如水)中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极材料层设置在负极集流体相对的两个表面中的任意一者或两者上。
本申请的锂离子二次电池中，负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(例如铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等) 形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
本申请的锂离子二次电池中，负极材料层通常包含负极活性物质以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极浆料涂布干燥而成的。负极浆料涂通常是将负极活性物质以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水。
负极活性物质的具体种类不作限制，可以采用本领域已知的能够用于锂离子二次电池负极的活性物质，本领域技术人员可以根据实际需求进行选择。作为示例，负极活性物质可选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或几种。
作为示例，导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。
负极活性物质层还包括粘结剂。粘接剂为上文所述的粘接剂组合物。除上文所述的粘接剂组合物外，粘接剂还可包含其它粘接剂。作为示例，其它粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种以上。
其他可选助剂例如是增稠剂(如羧甲基纤维素钠(CMC-Na))等。
[隔离膜]
采用电解液的锂离子二次电池中还包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种以上。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，所述二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，所述二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。所述二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)等。
本申请对所述二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的锂离子二次电池5。
在一些实施方式中，参照图2，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形 成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。锂离子二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，锂离子二次电池可以组装成电池模块4，电池模块4所含锂离子二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块4的应用和容量进行选择。在电池模块4中，多个锂离子二次电池5可以是沿电池模块的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个锂离子二次电池5进行固定。可选地，电池模块4还可以包括具有容纳空间的外壳，多个锂离子二次电池5容纳于该容纳空间。
在一些实施方式中，上述锂离子二次电池5或者电池模块4可以组装成电池包1，电池包1所含锂离子二次电池5或者电池模块4的数量可由本领域技术人员根据电池包1的应用和容量进行选择。
图3和图4是作为一个示例的电池包1。参照图3和图4，在电池包1中可以包括电池箱和设置于电池箱中的多个电池单体。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池单体的封闭空间。
另外，本申请还提供一种装置，所述装置包括本申请提供的电池包。所述电池包可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。作为所述装置，可以根据其使用需求来选择电池包。
图5是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对锂离子二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
图6是本申请一个实施方式中的负极极片中高压密区域和低压密区域交替排列的示意图，其中高压密区域和低压密区域的长度方向与极片长度方向一致。图6的下部显示了极片的横截面示意图，其中x 1为低压密区域的上表面宽度，x 2为低压密区域的下表面宽度，m i为高压密区域的宽度，而θ 1和θ 2分别为低压密区域的两侧切线方向与水平方向的夹角。
图7为本申请一个实施方式中的负极极片中不同密度区域的方向与极耳方向的示意图，其中不同密度区域的方向分别与极耳方向呈平行、垂直以及倾斜状态。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。如果无特殊标明，所有含量比例均为重量比，并且所有实验均在常温(25℃)和常压下进行。
实施例1：
锂离子电池的制备：
正极极片的制备
将镍钴锰(NCM)三元材料、导电剂碳黑、粘结剂聚偏二氟乙烯(PVDF)按重量比为96.7：1.7：1.6搅拌混合均匀，得到正极浆料；之后将正极浆料均匀涂覆于正极集流体上，之后经过烘干、冷压、分切，得到正极极片。
负极极片的制备
随后将活性物质人造石墨、导电剂碳黑、粘结剂丁苯橡胶(SBR)、增稠剂羟甲基纤维素钠(CMC)按照重量比为96.8：0.7：1.3：1.2溶于溶剂去离子水中，混合均匀后制备成的负极浆料涂覆在集流体上。通过调控浆料中水含量，获得具有两种粘度的负极浆料，将不同粘度的浆料涂覆在集流体上，即可获得高低涂布重量相间的极片。其中，高压密区域的密度为1.7g/cm 3，低压密区域的密度为1.3g/cm 3，且高压密区域和低压密区域的数量相同，平均宽度也基本相同。其中，通过离线激光测厚仪测量具有不同密度的区域的上下表面宽度，并通过涂布区域宽度以及重量计算来调整各区域的密度。随后，经过烘干、冷压、分切得到负极极片。
电解液的制备
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，将有机溶剂EC/EMC按照体积比3/7混合均匀，加入12.5％LiPF 6锂盐溶解于有机溶剂中，搅拌均匀，得到相应的电解液。
以8μm PE多孔薄膜为基底，双面涂布2μm后的陶瓷涂层后作为隔离膜。
将如上所述制备的正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，然后卷绕得到裸电芯，给裸电芯焊接极耳，并将裸电芯装入铝壳中，并在80℃下烘烤除水，随即注入电解液并封口，得到不带电的电池。不带电的电池再依次经过静置、热冷压、化成、整形、容量测试等工序，获得实施例1的锂离子二次电池产品。
实施例2-10：
重复实施例1，不同在于负极极片的负极活性材料层的结构和密度如下表1所示(通过调节不同区域的负极浆料的涂覆量进行控制)。各实施例中均如上文所述，制得相应的负极极片以及相应的锂离子二次电池产品。
对比例1-4
重复实施例1，不同在于负极极片的负极活性材料层不含高压密和低压密区域的交替排列结构，而是具有相同的密度。对于对比例1-4，其密度分别为1.6、1.7、1.8和1.9g/cm 3。各对比例中均如上文所述，制得相应的负极极片以及相应的锂离子二次电池产品。
对实施例1-10以及对比例1-4的负极极片以及锂离子二次电池进行测试，结果如下表1所示。表1：
Figure PCTCN2022122013-appb-000001
负极极片的活性材料层中特定区域的压实密度的测量：在涂布过程中，利用离线激光测厚仪实时监测涂布区域的厚度，厚度与涂布重量正相关。取特定区域的极片称重，利用以下公式：极片厚度＝涂布重量/压密密度+基材厚度，即可算出特定区域的压实密度。
负极极片的负极活性材料层中特定区域的宽度的测量：在涂布过程中，利用离线激光测厚仪实时监测涂布区域的厚度，厚度与涂布重量正相关，从而确定特定区域的宽度。
锂离子二次电池的充电性能的测量：通过三电极测试方法测量该电池的20-80％SOC充电时间。
由上表的测量结果可以看出，与对比例中具有均一密度的负极极片相比，包含本发明实施例中 具有高压密区域和低压密区域交替排列结构的负极极片的二次电池显示出明显更短的20-80％SOC充电时间，表明其充电性能得到了实质的改善。另外，由本发明实施例之间的对比可以看出，通过对高压密区域和低压密区域的密度之差，以及低压密区域的上表面宽度和下宽度之差进行选择，可以进一步改善电池的20-80％SOC充电时间。
虽然已经参考实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (16)

  1. 一种负极极片，包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质，其中所述负极材料层具有连续交错相间排列的高压密区域和低压密区域的结构，所述高压密区域的密度为1.6-1.9g/cm 3，所述低压密区域的密度为1.3-1.8g/cm 3，并且所述高压密区域和所述低压密区域的密度之差为0.1-0.6g/cm 3，可选地为0.2-0.4g/cm 3，
    其中低压密区域具有上表面宽度x 1和下表面宽度x 2，并且所述上表面宽度和下表面宽度之差为0≤|x 1-x 2|≤100mm。
  2. 根据权利要求1所述的负极极片，其中所述低压密区域的上表面宽度和下宽度之差为0≤|x 1-x 2|≤120μm，可选地为60μm≤|x 1-x 2|≤120μm，进一步可选地为80μm≤|x 1-x 2|≤120μm。
  3. 根据权利要求1至2中任一项所述的负极极片，其中所述低压密区域的宽度x为100μm-100mm，可选地为200μm-30mm。
  4. 根据权利要求1至3中任一项所述的负极极片，其中所述高压密区域的宽度m i为10-100mm，可选地为20-60mm。
  5. 根据权利要求4所述的负极极片，其满足下式：0.1≤n*m i/L＜1，其中n为低压密区域的数量，m i为高压密区域的宽度，L为极片长度。
  6. 根据权利要求1至5中任一项所述的负极极片，其中将所述低压密区域的方向定义为θ，其满足θ 2≤θ≤θ 1，其中0＜θ 1/θ 2≤1，θ 1和θ 2分别为所述低压密区域的两侧切线方向与水平方向的夹角。
  7. 根据权利要求1至6中任一项所述的负极极片，其中所述低压密区域的横截面的结构形状为长方形、梯形或弧形结构，或者为不规则的结构。
  8. 根据权利要求1至7中任一项所述的负极极片，其中所述低压密区域和高压密区域的长度方向与负极极耳的方向平行。
  9. 根据权利要求1至8中任一项所述的负极极片，其中所述负极集流体为金属箔片或复合集流体，所述包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。
  10. 根据权利要求1至9中任一项所述的负极极片，其中所述负极活性物质选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或多种。
  11. 根据权利要求1至10中任一项所述的负极极片，其中所述低压密区域的密度可为相同或不同；在密度不同的情况下，各低压密区域的密度之差小于0.5g/cm 3。
  12. 一种制备根据权利要求1至11中任一项所述的负极极片的方法，其包括以下步骤：
    通过调节在集流体的不同区域中涂覆在集流体上的负极活性物质的粘度和/或重量，从而形成具有不同负极活性物质含量的区域；以及
    对负极材料层进行冷压，使其具有相同的厚度。
  13. 根据权利要求12所述的方法，其中不使用造孔剂。
  14. 一种二次电池，其包含根据权利要求1至11中任一项所述的负极极片。
  15. 一种电池包，其包含根据权利要求14所述的二次电池。
  16. 一种用电装置，其包含根据权利要求14所述的二次电池或者根据权利要求15所述的电池包。
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