WO2024098175A1 - 二次电池及其制备方法、用电装置 - Google Patents

二次电池及其制备方法、用电装置 Download PDF

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WO2024098175A1
WO2024098175A1 PCT/CN2022/130222 CN2022130222W WO2024098175A1 WO 2024098175 A1 WO2024098175 A1 WO 2024098175A1 CN 2022130222 W CN2022130222 W CN 2022130222W WO 2024098175 A1 WO2024098175 A1 WO 2024098175A1
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negative electrode
active material
secondary battery
silicon
electrode sheet
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PCT/CN2022/130222
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English (en)
French (fr)
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程志鹏
邓亚茜
吕瑞景
王羽臻
陈宁
金海族
李白清
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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/CN2022/130222 priority Critical patent/WO2024098175A1/zh
Publication of WO2024098175A1 publication Critical patent/WO2024098175A1/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
    • 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
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • H01M4/78—Shapes other than plane or cylindrical, e.g. helical

Definitions

  • the present application relates to the technical field of secondary batteries, and more specifically to secondary batteries and methods for preparing the same, and electrical devices.
  • lithium ions are extracted from the positive electrode and then embedded in the negative electrode.
  • some lithium ions may not be embedded in the negative electrode, but instead gain electrons on the surface of the negative electrode to form single lithium.
  • This is the "lithium plating" phenomenon often mentioned in the field of secondary batteries. Lithium plating not only significantly shortens the cycle life of the battery, but also limits the fast charging capacity of the battery, and may lead to serious consequences such as combustion and explosion. Therefore, how to avoid the occurrence of the "lithium plating" phenomenon is one of the important topics in the field of secondary battery research.
  • a secondary battery and a method for preparing the same, and an electrical device are provided.
  • a secondary battery comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet;
  • the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode plate comprises one or more planar areas, and one or more curved areas, at least one of the negative electrode active material layers in the planar areas comprises active material A, and at least one of the negative electrode active material layers in the curved areas comprises active material B, and the expansion rate of the active material B is greater than the expansion rate of the active material A.
  • the present application adds different active materials to the flat area and curved area of the negative electrode plate of the battery, so that at least one negative electrode active material layer in the flat area includes active material A, and at least one negative electrode active material layer in the curved area includes active material B, and the expansion rate of active material B is greater than the expansion rate of active material A.
  • the active material B includes a silicon-based material; optionally, the silicon-based material includes one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; optionally, the silicon-based material includes one or more of silicon-oxygen compounds and silicon-carbon composites. Silicon-based materials have the characteristic of large expansion during charging, which can effectively shorten the distance between the positive and negative pole pieces in the curved surface area of the battery after charging, so that electrons are better embedded in the negative active material, thereby avoiding lithium deposition on the negative surface.
  • the mass percentage of the silicon-based material in the negative electrode active material layer located in the curved surface area, is 3% to 40%; alternatively, in the negative electrode active material layer located in the curved surface area, the mass percentage of the silicon-based material is 5% to 20%.
  • the negative electrode active material layer of the curved surface area including the active material B further includes a carbon-based material; optionally, in the negative electrode active material layer located in the curved surface area, the mass percentage of the carbon-based material is 55% to 97%; further optionally, in the negative electrode active material layer located in the curved surface area, the mass percentage of the carbon-based material is 75% to 90%. Setting the mass percentage of the carbon-based material in the active material layer of the curved surface area within a suitable range and compounding with a certain amount of active material B can further control the expansion degree of the curved surface area within a suitable range, effectively balancing the capacity, first efficiency and cycle performance of the battery.
  • the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon; optionally, the silicon-based material includes one or more of silicon-oxygen compounds and silicon-carbon composites.
  • the shortest distance between the negative electrode sheet located in the curved surface area and the adjacent positive electrode sheet is 18 ⁇ m to 170 ⁇ m; optionally, in the fully discharged state, the shortest distance between the negative electrode sheet located in the curved surface area and the adjacent positive electrode sheet is 20 ⁇ m to 120 ⁇ m. Controlling the initial distance between the positive and negative electrode sheets in the curved surface area in the fully discharged state within a suitable range can make the distance after charging within an appropriate range, and on the premise of reducing the diffusion distance of lithium ions, avoid excessive extrusion and poor electrolyte infiltration caused by too short distance between the positive and negative electrode sheets.
  • the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m to 62 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 1C, the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m to 59 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 2C, the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m to 54 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 3C, the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m to 45 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 4C, the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m to 33 ⁇
  • the active material A includes a silicon-based material, and the mass percentage of the silicon-based material in the negative electrode active material layer located in the curved surface area is greater than the mass percentage of the silicon-based material in the negative electrode active material layer located in the planar area.
  • the surface density of the negative electrode active material layer on the surface of the negative electrode current collector is 80mg/1540.25mm 2 to 190mg/1540.25mm 2 ; optionally, the surface density of the negative electrode active material layer on the surface of the negative electrode current collector is 115mg/1540.25mm 2 to 160mg/1540.25mm 2 . Controlling the surface density of the active material layer within a suitable range can effectively balance the energy density and kinetic performance of the battery while being able to slow down lithium deposition.
  • the thickness of the negative electrode active material layer is 65 ⁇ m to 140 ⁇ m; optionally, the thickness of the negative electrode active material layer is 90 ⁇ m to 110 ⁇ m. Controlling the thickness of the negative electrode active material layer within a suitable range can better match the distance between the positive and negative electrode sheets set in the above embodiments, so that lithium ions can be embedded in the negative electrode active material in time, further slowing down the occurrence of lithium precipitation.
  • the thickness of the negative electrode sheet is 70 ⁇ m to 145 ⁇ m; optionally, the thickness of the negative electrode sheet is 95 ⁇ m to 115 ⁇ m. Controlling the thickness of the negative electrode sheet within a suitable range can make the battery have a more suitable mechanical strength and better match the conventional processing technology, so that it is easy to control the distance between the positive and negative electrode sheets within the range set in the above embodiment, further slowing down the occurrence of lithium precipitation.
  • a method for preparing a secondary battery according to one or more of the above embodiments comprising the following steps:
  • the positive electrode slurry is coated on the surface of the positive electrode current collector, and the positive electrode sheet is obtained by drying and pressing.
  • the negative electrode sheet, the positive electrode sheet and the separator are wound according to a preset winding process.
  • the solid content of the negative electrode slurry containing active material B is 42% to 60%; alternatively, the solid content of the negative electrode slurry containing active material B is 44% to 56%. Controlling the solid content of the negative electrode slurry within a suitable range is conducive to obtaining a more uniformly coated negative electrode active material layer, thereby making the silicon-based material in the curved surface area more evenly distributed, and better slowing down the occurrence of lithium desorption.
  • an electrical device comprising a secondary battery as described in one or more of the aforementioned embodiments.
  • FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • FIG. 4 is a schematic diagram of a cross section of a secondary battery according to an embodiment of the present application.
  • Lithium plating is an undesirable phenomenon that often occurs during the use of secondary batteries. Lithium plating is often caused by two situations: (1) the N/P ratio of the battery (the ratio of the negative electrode reversible surface capacity to the positive electrode reversible surface capacity in the same stage and under the same operating conditions) is insufficient; (2) the electrolyte is not well wetted. For the above-mentioned known situations, a lot of research has been done to improve them, such as adjusting the N/P ratio and improving the electrolyte wetting ability, but lithium plating still exists.
  • the inventors of the present application have found through extensive research, summary and analysis that: currently, most secondary batteries are prepared by a winding process, and the secondary batteries prepared based on the current winding process have a curved surface area at the corner. Since the distance between the positive and negative pole pieces cannot be effectively reduced by a pressing process like the flat area, the curved surface area is prone to a large distance between the positive and negative pole pieces, resulting in a long lithium ion diffusion distance and severe polarization. The lithium ions fail to be embedded in the negative electrode active material in time and accept electrons on the surface of the negative electrode active material to become single lithium ions and precipitate.
  • the first aspect of the present application provides a secondary battery, including a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet;
  • the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode plate includes one or more planar areas, and one or more curved areas, the negative electrode active material layer in at least one planar area includes active material A, and the negative electrode active material layer in at least one curved area includes active material B, and the expansion rate of active material B is greater than the expansion rate of active material A.
  • the present application adds different active materials to the flat area and curved area of the negative electrode plate of the battery, so that at least one negative electrode active material layer in the flat area includes active material A, and at least one negative electrode active material layer in the curved area includes active material B, and the expansion rate of active material B is greater than the expansion rate of active material A.
  • curved area refers to the part of the pole piece located at the corner of the battery with a non-zero curvature;
  • flat area refers to the area of the pole piece other than the “curved area”.
  • the active material B includes a silicon-based material; optionally, the silicon-based material includes one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon compounds, silicon-nitrogen compounds, and silicon alloys; optionally, the silicon-based material includes one or more of silicon-oxygen compounds and silicon-carbon compounds.
  • Suitable types of silicon-based materials have more appropriate expansion coefficients, which can help control the expansion degree of the curved surface area within a more appropriate range.
  • the mass percentage of the silicon-based material in the negative electrode active material layer located in the curved surface area, is 3% to 40%; alternatively, in the negative electrode active material layer located in the curved surface area, the mass percentage of the silicon-based material can be, for example, 5%, 10%, 15%, 20%, 25%, 30% or 35%, and can also be 5% to 20%.
  • the negative electrode active material layer of the curved surface area including active material B also includes a carbon-based material; optionally, in the negative electrode active material layer located in the curved surface area, the mass percentage of the carbon-based material is 55% to 97%; further optionally, in the negative electrode active material layer located in the curved surface area, the mass percentage of the carbon-based material is 75% to 90%; the mass percentage of the carbon-based material in the negative electrode active material layer located in the curved surface area can also be, for example, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95%.
  • the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.
  • the shortest distance between the negative electrode plate located in the curved surface area and the adjacent positive electrode plate is 18 ⁇ m to 170 ⁇ m; optionally, in the fully discharged state, the shortest distance between the negative electrode plate located in the curved surface area and the adjacent positive electrode plate can be, for example, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m, 75 ⁇ m, 80 ⁇ m, 85 ⁇ m, 90 ⁇ m, 95 ⁇ m, 100 ⁇ m, 105 ⁇ m, 110 ⁇ m, 115 ⁇ m, 120 ⁇ m, 135 ⁇ m, 140 ⁇ m, 145 ⁇ m, 150 ⁇ m, 155 ⁇ m, 160 ⁇ m or 165 ⁇ m, and can also be 20 ⁇ m to 120 ⁇ m.
  • Controlling the initial distance between the positive and negative pole pieces in the curved area in the fully discharged state within a suitable range can ensure that the distance after charging is within an appropriate range.
  • it can avoid excessive extrusion and poor electrolyte infiltration caused by too short a distance between the positive and negative pole pieces.
  • the shortest distance between the negative electrode sheet and the adjacent positive electrode sheet located in the curved area is 15 ⁇ m to 62 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 1C, the shortest distance between the negative electrode sheet and the adjacent positive electrode sheet located in the curved area is 15 ⁇ m to 59 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 2C, the shortest distance between the negative electrode sheet and the adjacent positive electrode sheet located in the curved area is 15 ⁇ m to 54 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 3C, the shortest distance between the negative electrode sheet and the adjacent positive electrode sheet located in the curved area is 15 ⁇ m to 45 ⁇ m; or, after the secondary battery is charged to 4.25V with a current of 4C, the shortest distance between the negative electrode sheet and the adjacent positive electrode sheet located in the curved area is 15 ⁇ m to 33 ⁇ m
  • controlling the distance between the positive and negative pole pieces within a suitable range can further slow down the occurrence of lithium plating.
  • the shortest distance between the negative pole piece located in the curved surface area and the adjacent positive pole piece is 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, etc.
  • the shortest distance between the negative pole piece located in the curved surface area and the adjacent positive pole piece is 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, etc.
  • the secondary battery is charged to 4.25V with a current of 2C
  • the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, etc.
  • the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, etc.
  • the shortest distance between the negative electrode sheet located in the curved area and the adjacent positive electrode sheet is 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, etc.
  • the negative electrode active material layer in the planar region does not contain silicon-based materials. Since the planar region needs to be pressed after winding, avoiding the introduction of silicon-based materials in the planar region can slow down the mutual squeezing of the positive and negative electrode sheets in the planar region after charging and prevent poor electrolyte infiltration.
  • the active material A includes a silicon-based material, and the mass percentage of the silicon-based material in the negative electrode active material layer located in the curved surface area is greater than the mass percentage of the silicon-based material in the negative electrode active material layer located in the flat surface area.
  • the surface density of the negative electrode active material layer is 80mg/ 1540.25mm2-190mg / 1540.25mm2 ; optionally, on the surface of the negative electrode current collector, the surface density of the negative electrode active material layer can also be, for example, 85mg/ 1540.25mm2 , 90mg/ 1540.25mm2 , 95mg/ 1540.25mm2 , 100mg / 1540.25mm2, 105mg/1540.25mm2 , 110mg/1540.25mm2, 115mg/1540.25mm2 , 120mg/1540.25mm2, 125mg/1540.25mm2, 130mg / 1540.25mm2 , 135mg/1540.25mm 2 , 140mg/1540.25mm 2 , 145mg/1540.25mm 2 , 150mg/1540.25mm 2 , 155mg/1540.25mm 2 , 160mg/1540.
  • the thickness of the negative electrode active material layer is 65 ⁇ m to 140 ⁇ m; optionally, the thickness of the negative electrode active material layer can also be, for example, 70 ⁇ m, 75 ⁇ m, 80 ⁇ m, 85 ⁇ m, 90 ⁇ m, 95 ⁇ m, 100 ⁇ m, 105 ⁇ m, 110 ⁇ m, 115 ⁇ m, 120 ⁇ m, 125 ⁇ m, 130 ⁇ m or 135 ⁇ m, and can also be 90 ⁇ m to 110 ⁇ m.
  • Controlling the thickness of the negative electrode active material layer within a suitable range can better match the distance between the positive and negative electrode sheets set in the aforementioned embodiments, so that lithium ions can be embedded in the negative electrode active material in a timely manner, further slowing down the occurrence of lithium precipitation.
  • the thickness of the negative electrode plate is 70 ⁇ m to 145 ⁇ m; alternatively, the thickness of the negative electrode plate can be, for example, 75 ⁇ m, 80 ⁇ m, 85 ⁇ m, 90 ⁇ m, 95 ⁇ m, 100 ⁇ m, 105 ⁇ m, 110 ⁇ m, 115 ⁇ m, 120 ⁇ m, 125 ⁇ m, 130 ⁇ m, 135 ⁇ m or 140 ⁇ m, and can also be 95 ⁇ m to 115 ⁇ m.
  • Controlling the thickness of the negative electrode plate within a suitable range can make the battery have a more suitable mechanical strength and better match the conventional processing technology, so that it is easy to control the distance between the positive and negative electrode plates within the range set in the aforementioned embodiment, further slowing down the occurrence of lithium precipitation.
  • a method for preparing a secondary battery according to one or more of the above embodiments comprising the following steps:
  • the positive electrode slurry is coated on the surface of the positive electrode current collector, and the positive electrode sheet is obtained by drying and pressing;
  • the negative electrode sheet, the positive electrode sheet and the isolation film are wound according to a preset winding process.
  • the solid content of the negative electrode slurry containing active material B is 42% to 60%; alternatively, the solid content of the negative electrode slurry containing active material B can be, for example, 44%, 46%, 48%, 50%, 52%, 54%, 56% or 58%, and can also be 44% to 56%. Controlling the solid content of the negative electrode slurry within a suitable range is conducive to obtaining a more uniformly coated negative electrode active material layer, so that the active material B in the curved surface area is more evenly distributed, which can better slow down the occurrence of lithium desorption.
  • an electrical device comprising a secondary battery according to one or more of the aforementioned embodiments.
  • a secondary battery is provided.
  • a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • the separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite 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 (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 may be a positive electrode active material for a battery known in the art.
  • the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • lithium transition metal oxides may include, but are not limited to , lithium cobalt oxide (such as LiCoO2 ), lithium nickel oxide (such as LiNiO2 ), lithium manganese oxide (such as LiMnO2 , LiMn2O4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1 / 3Co1 / 3Mn1 / 3O2 (also referred to as NCM333 ), LiNi0.5Co0.2Mn0.3O2 (also referred to as NCM523 ) , LiNi0.5Co0.25Mn0.25O2 (also referred to as NCM211 ) , LiNi0.6Co0.2Mn0.2O2 (also referred to as NCM622 ), LiNi0.8Co0.1Mn0.1O2 (also referred to as NCM811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate and carbon
  • the positive electrode film layer may also optionally include a binder.
  • the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • a conductive agent which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film 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 film 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 (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 active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further include a binder.
  • the binder may be selected from at least one 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).
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive electrode plate and the negative electrode plate.
  • the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.
  • the electrolyte can be liquid, gel or all-solid.
  • the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.
  • the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.
  • the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte may further include additives, such as 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 or low temperature performance, etc.
  • additives such as 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 or low temperature performance, etc.
  • the secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • 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 that can 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, polybutylene terephthalate, and polybutylene succinate.
  • FIG1 is a secondary battery 1 of a square structure as an example.
  • the outer package may include a shell 11 and a cover plate 13.
  • the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 11 has an opening connected to the receiving cavity, and the cover plate 13 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 12 through a winding process or a lamination process.
  • the electrode assembly 12 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 12.
  • the number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries may be assembled into a battery module.
  • the number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
  • the battery modules described above may also be assembled into a battery pack.
  • the battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device.
  • the electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • the mobile device may be, for example, a mobile phone, a laptop computer, etc.;
  • the electric vehicle may be, for example, 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., but are not limited to these.
  • a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.
  • Fig. 3 shows an electric device 2 as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • the device may be a mobile phone, a tablet computer, a laptop computer, etc.
  • the positive electrode active material ternary material NCM811, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone at a mass ratio of 97:2:1, and the positive electrode slurry is uniformly coated on a 15 ⁇ m thick aluminum foil; after drying, the positive electrode slurry is cold pressed, die-cut, and striped to form a positive electrode sheet for a lithium-ion battery;
  • Polyethylene is used as a base film, and aluminum oxide with a thickness of 3 ⁇ m is coated on the base film to obtain an isolation film;
  • the positive electrode sheet, the negative electrode sheet and the separator are wound to obtain an electrode assembly; wherein the distance between adjacent positive electrode sheets and negative electrode sheets in the curved surface area of the negative electrode sheet (denoted as gap1) is 120 ⁇ m;
  • the electrode assembly is packaged, injected, and formed to obtain a lithium-ion battery.
  • step (2)b the formula of the high expansion negative electrode slurry is: the mass ratio of the negative electrode active material artificial graphite, silicon oxide material (including at least SiO x , wherein 0 ⁇ x ⁇ 2), conductive carbon Super P, thickener (CMC), and binder (SBR) is 92:3:3:1:1.
  • step (2)b the formula of the high expansion negative electrode slurry is: the mass ratio of the negative electrode active material artificial graphite, silicon oxide material (including at least SiO x , wherein 0 ⁇ x ⁇ 2), conductive carbon Super P, thickener (CMC), and binder (SBR) is 55:40:3:1:1.
  • Example 2 It is basically the same as Example 1, except that the winding process is controlled so that the distance between the adjacent positive electrode sheet and the negative electrode sheet in the curved area of the negative electrode sheet (denoted as gap1) is 18 ⁇ m.
  • Example 2 It is basically the same as Example 1, except that the winding process is controlled so that the distance between the adjacent positive electrode sheet and the negative electrode sheet in the curved surface area of the negative electrode sheet (denoted as gap1) is 170 ⁇ m.
  • the method is basically the same as that in Example 1, except that when preparing the negative electrode sheet, no distinction is made between the flat area and the curved area, and the entire area is coated with the high expansion negative electrode slurry prepared in step (2) b of Example 1.
  • the method is basically the same as Example 1, except that when preparing the negative electrode sheet, no distinction is made between the flat area and the curved area, and the entire area is coated with the common negative electrode slurry prepared in step (2) a of Example 1.
  • the above-mentioned small discs are weighed to obtain the surface density of the pole piece.
  • Test process Let the battery stand for 30 minutes, then charge at a rate of 0.5C to a voltage of 4.25V, further charge at a constant voltage of 4.25V to a current of 0.05C, and let it stand for 5 minutes.
  • gap2 the distance between the adjacent positive electrode sheet and the negative electrode sheet in the curved area of the negative electrode sheet is measured (denoted as gap2).
  • Test process let the battery stand for 30 minutes, then charge at 0.5C rate to 4.25V, then charge at 4.25V constant voltage to 0.05C, let stand for 5 minutes, then discharge at 0.5C rate to 2.5V, this is a charge and discharge cycle. Record the discharge capacity at each cycle.
  • Capacity retention rate after n cycles (%) (discharge capacity at the nth cycle/discharge capacity at the first cycle) ⁇ 100%.
  • Severe lithium deposition bright white.
  • Example 2 Analyzing the data in Table 1, compared with Example 1, in Example 2, the proportion of silicon-based materials in the curved surface area is relatively small. After charging, the reduction of the gap in the curved surface area is limited, and the lithium ion migration path is still relatively long, which will lead to slight lithium precipitation; in Example 3, the silicon-based content is relatively high, and the electrode expands more seriously after charging, which will also lead to a certain degree of lithium precipitation; in Example 4, the original gap value before charging is relatively low, and it expands after charging, and the gap is further reduced, resulting in a certain degree of lithium precipitation, and the capacity retention rate decreases more; in Example 5, the original gap value before charging is relatively large, resulting in the gap after charging failing to be reduced to a more suitable range, so there is also a certain degree of lithium precipitation; in Example 6, a high-expansion slurry is also coated in the plane area, and the electrode expands more as a whole after charging, which will also lead to a certain degree of lithium precipitation; in Comparative Example

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Abstract

一种二次电池，包括正极极片、负极极片和隔离膜，隔离膜设置于正极极片和负极极片之间；其中，所述负极极片包括负极集流体和设置于所述负极集流体至少一个表面之上的负极活性材料层，所述负极极片包括一个或多个平面区，以及一个或多个曲面区，至少有一个所述平面区的负极活性材料层包括活性材料A，至少有一个所述曲面区的负极活性材料层包括活性材料B，所述活性材料B的膨胀率大于所述活性材料A的膨胀率。

Description

二次电池及其制备方法、用电装置 技术领域
本申请涉及二次电池技术领域，更具体地涉及二次电池及其制备方法、用电装置。
背景技术
这里的陈述仅提供与本申请有关的背景信息，而不必然构成现有技术。
正常情况下，锂离子电池在进行充电时，锂离子从正极脱嵌，然后嵌入负极。然而，当出现某些异常情况时，可能导致部分锂离子无法嵌入负极，而在负极表面得到电子，形成单质锂，这就是二次电池领域常被提及的“析锂”现象。析锂不仅会导致电池的循环寿命大幅缩短，还限制了电池的快充容量，而且可能导致燃烧、爆炸等严重后果，因此，如何避免“析锂”现象的发生是二次电池研究领域的重要课题之一。
发明内容
根据本申请的各种实施例，提供一种二次电池及其制备方法、用电装置。
本申请的第一方面，提供了一种二次电池，包括正极极片、负极极片和隔离膜，所述隔离膜设置于所述正极极片和所述负极极片之间；
其中，所述负极极片包括负极集流体和设置于所述负极集流体至少一个表面之上的负极活性材料层，所述负极极片包括一个或多个平面区，以及一个或多个曲面区，至少有一个所述平面区的负极活性材料层包括活性材料A，至少有一个所述曲面区的负极活性材料层包括活性材料B，所述活性材料B的膨胀率大于所述活性材料A的膨胀率。
本申请通过在电池的负极极片的平面区和曲面区添加不同的活性材料，使至少有一个平面区的负极活性材料层包括活性材料A，至少有一个曲面区的负极活性材料层包括活性材料B，并且活性材料B的膨胀率大于活性材料A的膨胀率，通过活性材料A和活性材料B的添加，可以使得充电后电池曲面区的正负极极片之间的距离缩短，能有效避免传统卷绕工艺制得的电池中由于曲面区锂离子的扩散距离太长而导致锂离子倾向于在负极的表面得到电子造成析锂、未能正常嵌入负极活性材料中的现象。
在一些实施方式中，所述活性材料B包括硅基材料；可选地，所述硅基材料包括单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的一种或多种；可选地， 所述硅基材料包括硅氧化合物和硅碳复合物中的一种或多种。硅基材料具有在充电时膨胀较大的特性，可以使得充电后电池曲面区的正负极极片之间的距离得到有效缩短，使电子更好地嵌入到负极活性材料中，进而避免负极表面出现析锂。
在一些实施方式中，在位于所述曲面区的负极活性材料层中，所述硅基材料的质量百分含量为3％～40％；可选地，在位于所述曲面区的负极活性材料层中，所述硅基材料的质量百分含量为5％～20％。控制硅基材料在曲面区的活性材料层中的质量占比在合适范围内，在有效降低锂离子扩散距离的前提下，能够避免正负极极片之间的距离过短而造成极片膨胀挤压过度，或是电解液浸润不良导致的析锂，进一步减缓电池的析锂现象。
在一些实施方式中，包括所述活性材料B的曲面区的负极活性材料层还包括碳基材料；可选地，在位于所述曲面区的负极活性材料层中，所述碳基材料的质量百分含量为55％～97％；进一步可选地，在位于所述曲面区的负极活性材料层中，所述碳基材料的质量百分含量为75％～90％。设置碳基材料在曲面区的活性材料层中的质量占比在合适范围内，与一定用量的活性材料B复配，能够进一步控制曲面区的膨胀程度在合适范围内，有效平衡电池的容量、首效和循环性能。
在一些实施方式中，所述碳基材料包括人造石墨、天然石墨、软炭以及硬炭中的一种或多种；可选地，所述硅基材料包括硅氧化合物和硅碳复合物中的一种或多种。
在一些实施方式中，在完全放电的状态下，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为18μm～170μm；可选地，在完全放电的状态下，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为20μm～120μm。控制完全放电状态下曲面区的正负极极片之间的初始距离在合适范围内，能使得充电后的距离处于适当范围内，在降低锂离子扩散距离的前提下，避免正负极极片之间距离太短而造成过度挤压和电解液浸润不良。
在一些实施方式中，以0.5C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～62μm；或者，以1C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～59μm；或者，以2C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～54μm；或者，以3C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～45 μm；或者，以4C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～33μm。在较常规的充电条件下充电后，控制正负极极片之间的距离在合适范围，能进一步减缓析锂现象的发生。
在一些实施方式中，所述活性材料A包括硅基材料，位于所述曲面区的负极活性材料层中的硅基材料的质量百分含量大于位于所述平面区的负极活性材料层中的硅基材料的质量百分含量。
在一些实施方式中，在所述负极集流体表面，所述负极活性材料层的面密度为80mg/1540.25mm 2～190mg/1540.25mm 2；可选地，在所述负极集流体表面，述负极活性材料层的面密度为115mg/1540.25mm 2～160mg/1540.25mm 2。控制活性材料层的面密度在合适范围内，在能够实现减缓析锂的前提下，能有效平衡电池的能量密度和动力学性能。
在一些实施方式中，所述负极活性材料层的厚度为65μm～140μm；可选地，所述负极活性材料层的厚度为90μm～110μm。控制负极活性材料层厚度在合适范围内，能与前述实施方式中设定的正负极极片距离更匹配，使得锂离子能够及时嵌入负极活性材料中，进一步减缓析锂现象的发生。
在一些实施方式中，所述负极极片的厚度为70μm～145μm；可选地，所述负极极片的厚度为95μm～115μm。控制负极极片的厚度在合适范围内，能使得电池具有更合适的机械强度，更匹配常规的加工工艺，从而易于将正负极极片之间的距离控制在前述实施方式中设定的范围内，进一步减缓析锂现象的发生。
本申请的第二方面，提供了前述一种或多种实施方式所述的二次电池的制备方法，包括以下步骤：
根据卷绕工艺确定负极极片的所述平面区和所述曲面区，在至少一个所述曲面区对应的负极集流体表面涂覆包含活性材料B的负极浆料，经干燥、压制得到负极极片；
在正极集流体表面涂覆正极浆料，经干燥、压制得到正极极片；
将所述负极极片、所述正极极片和隔离膜按照预设的卷绕工艺进行卷绕。
在一些实施方式中，所述包含活性材料B的负极浆料的固含量为42％～60％；可选地，所述包含活性材料B的负极浆料的固含量为44％～56％。控制负极浆料的固含量在合适范围内，有利于获得涂布更均匀的负极活性材料层，从而使得曲面区硅基材料分布更均匀，能更好地缓解析锂现象的发生。
本申请的第三方面，提供了一种用电装置，包括前述一种或多种实施方式所述的 二次电池。
本申请的一个或多个实施例的细节在下面的附图和描述中提出。本申请的其他特征、目的和优点将从说明书、附图以及权利要求书变得明显。
附图说明
为了更好地描述和说明这里公开的那些发明的实施例或示例，可以参考一幅或多幅附图。用于描述附图的附加细节或示例不应当被认为是对所公开的发明、目前描述的实施例或示例以及目前理解的这些发明的最佳模式中的任何一者的范围的限制。
图1是本申请一实施方式的二次电池的示意图。
图2是图1所示的本申请一实施方式的二次电池的分解图。
图3是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1：二次电池；11：壳体；12：电极组件；13：盖板；2：用电装置。
图4是本申请一实施方式的二次电池横截面的示意图。
具体实施方式
为了使本申请的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本申请进行进一步详细说明。应当理解，此处描述的具体实施例仅仅用以解释本申请，并不用于限定本申请。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同。本文中在本申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。本文所使用的术语“和/或”包括一个或多个相关的所列项目的任意的和所有的组合。
析锂问题是二次电池使用过程中常常出现的一种不良现象。析锂往往由两种情况导致：(1)电池的N/P比(同一阶段内，相同的操作条件下，负极可逆面容量与正极可逆面容量的比值)不足；(2)电解液浸润不良。对于上述已知的情况，已有大量研究进行改善，例如调整N/P比、改善电解液浸润能力等，然而，析锂现象依然存在。
为了解决这一问题，本申请的发明人通过大量研究、总结和分析发现：目前，大部分二次电池通过卷绕工艺制备，而基于当前的卷绕工艺制得的二次电池在拐角处的曲面区中，由于未能像平面区一样通过压制工艺有效降低正负极极片之间的距离，因此，曲面区域容易因为正负极极片之间的距离较大，造成锂离子扩散距离较长、极化 严重，未能及时嵌入负极活性材料中就在负极活性材料表面接受电子变成单质锂析出。
基于上述研究结果，本申请的第一方面，提供了一种二次电池，包括正极极片、负极极片和隔离膜，隔离膜设置于正极极片和负极极片之间；
其中，负极极片包括负极集流体和设置于负极集流体至少一个表面之上的负极活性材料层，负极极片包括一个或多个平面区，以及一个或多个曲面区，至少有一个平面区的负极活性材料层包括活性材料A，至少有一个曲面区的负极活性材料层包括活性材料B，活性材料B的膨胀率大于活性材料A的膨胀率。
本申请通过在电池的负极极片的平面区和曲面区添加不同的活性材料，使至少有一个平面区的负极活性材料层包括活性材料A，至少有一个曲面区的负极活性材料层包括活性材料B，并且活性材料B的膨胀率大于活性材料A的膨胀率，通过活性材料A和活性材料B的添加，可以使得充电后电池曲面区的正负极极片之间的距离缩短，能有效避免传统卷绕工艺制得的电池中由于曲面区锂离子的扩散距离太长而导致锂离子倾向于在负极的表面得到电子造成析锂、未能正常嵌入负极活性材料中的现象。
本申请中，“曲面区”是指极片中位于电池的拐角处、曲率不为零的部分；“平面区”是极片中除了“曲面区”以外的区域。可以理解，由于电池需要放置在壳体中，因此极片需要进行卷绕，卷绕导致极片部分区域发生弯曲变形，这些发生弯曲变形、具备一定曲率的区域即本申请所述的“曲面区”，可参考电池横截面的示意图(图4)中标注的“曲面区”进行判断。
在一些实施方式中，活性材料B包括硅基材料；可选地，硅基材料包括单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的一种或多种；可选地，硅基材料包括硅氧化合物和硅碳复合物中的一种或多种。合适类型的硅基材料具有更恰当的膨胀系数，能够帮助将曲面区的膨胀程度控制在更合适的范围内。
在一些实施方式中，在位于曲面区的负极活性材料层中，硅基材料的质量百分含量为3％～40％；可选地，在位于曲面区的负极活性材料层中，硅基材料的质量百分含量例如可以是5％、10％、15％、20％、25％、30％或35％，又如还可以是5％～20％。控制硅基材料在曲面区的活性材料层中的质量占比在合适范围内，在有效降低锂离子扩散距离的前提下，能够避免正负极极片之间的距离过短而造成极片膨胀挤压过度，或是电解液浸润不良导致的析锂，进一步减缓电池的析锂现象。
在一些实施方式中，包括活性材料B的曲面区的负极活性材料层还包括碳基材料；可选地，在位于曲面区的负极活性材料层中，碳基材料的质量百分含量为55％～97％； 进一步可选地，在位于曲面区的负极活性材料层中，碳基材料的质量百分含量为75％～90％；位于曲面区的负极活性材料层中的碳基材料的质量百分含量例如还可以是60％、65％、70％、75％、80％、85％、90％或95％。设置碳基材料在包括活性材料B的曲面区的负极活性材料层中的质量占比在合适范围内，与一定用量的硅基材料复配，能够进一步控制曲面区的膨胀程度在合适范围内，有效平衡电池的容量、首效和循环性能。
在一些实施方式中，碳基材料包括人造石墨、天然石墨、软炭以及硬炭中的一种或多种。
在一些实施方式中，在完全放电的状态下，位于曲面区的负极极片与相邻的正极极片之间的最短距离(记作gap，可参考图4)为18μm～170μm；可选地，在完全放电的状态下，位于曲面区的负极极片与相邻的正极极片之间的最短距离例如可以是20μm、25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、75μm、80μm、85μm、90μm、95μm、100μm、105μm、110μm、115μm、120μm、135μm、140μm、145μm、150μm、155μm、160μm或165μm，又如还可以是20μm～120μm。控制完全放电状态下曲面区的正负极极片之间的初始距离在合适范围内，能使得充电后的距离处于适当范围内，在降低锂离子扩散距离的前提下，避免正负极极片之间距离太短而造成过度挤压和电解液浸润不良。
在一些实施方式中，以0.5C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm～62μm；或者，以1C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm～59μm；或者，以2C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm～54μm；或者，以3C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm～45μm；或者，以4C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm～33μm。在较常规的充电条件下充电后，控制正负极极片之间的距离在合适范围，能进一步减缓析锂现象的发生。可选地，以0.5C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm等。以1C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm、 55μm等。以2C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm等。以3C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm、20μm、25μm、30μm、35μm、40μm、45μm等。以4C的电流将二次电池充电至4.25V后，位于曲面区的负极极片与相邻的正极极片之间的最短距离为15μm、20μm、25μm、30μm等。
在一些实施方式中，平面区的负极活性材料层均不包含硅基材料。由于平面区域在卷绕完成后需要进行压制，避免在平面区域引入硅基材料，能够减缓充电后平面区正负极极片的互相挤压，防止电解液浸润不良。
在一些实施方式中，活性材料A包括硅基材料，位于曲面区的负极活性材料层中的硅基材料的质量百分含量大于位于平面区的负极活性材料层中的硅基材料的质量百分含量。
在一些实施方式中，在负极集流体表面，负极活性材料层的面密度为80mg/1540.25mm 2～190mg/1540.25mm 2；可选地，在负极集流体表面，述负极活性材料层的面密度例如还可以是85mg/1540.25mm 2、90mg/1540.25mm 2、95mg/1540.25mm 2、100mg/1540.25mm 2、105mg/1540.25mm 2、110mg/1540.25mm 2、115mg/1540.25mm 2、120mg/1540.25mm 2、125mg/1540.25mm 2、130mg/1540.25mm 2、135mg/1540.25mm 2、140mg/1540.25mm 2、145mg/1540.25mm 2、150mg/1540.25mm 2、155mg/1540.25mm 2、160mg/1540.25mm 2、165mg/1540.25mm 2、170mg/1540.25mm 2、175mg/1540.25mm 2、180mg/1540.25mm 2或185mg/1540.25mm 2，又如还可以是115mg/1540.25mm 2～160mg/1540.25mm 2。控制活性材料层的面密度在合适范围内，在能够实现减缓析锂的前提下，能有效平衡电池的能量密度和动力学性能。
在一些实施方式中，负极活性材料层的厚度为65μm～140μm；可选地，负极活性材料层的厚度例如还可以是70μm、75μm、80μm、85μm、90μm、95μm、100μm、105μm、110μm、115μm、120μm、125μm、130μm或135μm，又如还可以是90μm～110μm。控制负极活性材料层厚度在合适范围内，能与前述实施方式中设定的正负极极片距离更匹配，使得锂离子能够及时嵌入负极活性材料中，进一步减缓析锂现象的发生。
在一些实施方式中，负极极片的厚度为70μm～145μm；可选地，负极极片的厚度例如可以是75μm、80μm、85μm、90μm、95μm、100μm、105μm、110μm、115 μm、120μm、125μm、130μm、135μm或140μm，又如还可以是95μm～115μm。控制负极极片的厚度在合适范围内，能使得电池具有更合适的机械强度，更匹配常规的加工工艺，从而易于将正负极极片之间的距离控制在前述实施方式中设定的范围内，进一步减缓析锂现象的发生。
本申请的第二方面，提供了前述一种或多种实施方式的二次电池的制备方法，包括以下步骤：
根据卷绕工艺确定负极极片的平面区和曲面区，在至少一个曲面区对应的负极集流体表面涂覆包含活性材料B的负极浆料，经干燥、压制得到负极极片；
在正极集流体表面涂覆正极浆料，经干燥、压制得到正极极片；
将负极极片、正极极片和隔离膜按照预设的卷绕工艺进行卷绕。
在一些实施方式中，包含活性材料B的负极浆料的固含量为42％～60％；可选地，包含活性材料B的负极浆料的固含量例如可以是44％、46％、48％、50％、52％、54％、56％或58％，又如还可以是44％～56％。控制负极浆料的固含量在合适范围内，有利于获得涂布更均匀的负极活性材料层，从而使得曲面区活性材料B分布更均匀，能更好地缓解析锂现象的发生。
本申请的第三方面，提供了一种用电装置，包括前述一种或多种实施方式的二次电池。
另外，以下适当参照附图对本申请的二次电池和用电装置进行说明。
本申请的一个实施方式中，提供一种二次电池。
通常情况下，二次电池包括正极极片、负极极片、电解质和隔离膜。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。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
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膜层，所述正极膜层包括正极活性材料。
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，正极膜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。
在一些实施方式中，所述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(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。
在一些实施方式中，正极活性材料可采用本领域公知的用于电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、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(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。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(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、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中的至少一种。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，所述粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述导电剂可以包括超导碳、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至少一种。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
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膜层，所述负极膜层包括负极活性材料。
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，负极膜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。
在一些实施方式中，所述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(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。
在一些实施方式中，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述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)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。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至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
电解质
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类 没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、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、改善电池高温或低温性能的添加剂等。
隔离膜
在一些实施方式中，二次电池中还包括隔离膜。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至少一种。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，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，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。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、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对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二次电池1。
在一些实施方式中，参照图2，外包装可包括壳体11和盖板13。其中，壳体11 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11具有与容纳腔连通的开口，盖板13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12。电极组件12封装于所述容纳腔内。电解液浸润于电极组件12中。二次电池1所含电极组件12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，二次电池可以组装成电池模块，电池模块所含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的应用和容量进行选择。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块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包的应用和容量进行选择。
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备、电动车辆、电气列车、船舶及卫星、储能系统等，但不限于此。其中，移动设备例如可以是手机、笔记本电脑等；电动车辆例如可以是纯电动车、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，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图3是作为一个示例的用电装置2。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。
实施例1
(1)正极极片的制备
将正极活性物质三元材料NCM811、导电剂乙炔黑、粘结剂聚偏氟乙烯(PVDF)按质量比97：2：1加入N-甲基吡咯烷酮中，均匀搅拌后制成正极浆料；将正极浆料均匀涂布在15μm厚的铝箔上；烘干后冷压，进行模切、分条，制成锂离子电池正极极片；
(2)负极极片的制备
a.将负极活性物质人造石墨、导电碳Super P、增稠剂(CMC)、粘结剂(SBR)按质量 比95：3：1：1加入水中，均匀搅拌后制得固含量为50％的普通负极浆料；
b.将负极活性物质人造石墨、硅氧材料(至少包括SiO x，其中，0＜x＜2)、导电碳Super P、增稠剂(CMC)、粘结剂(SBR)按质量比75：20：3：1：1加入水中，均匀搅拌后制得固含量为50％的高膨胀负极浆料；
c.取6μm厚的铜箔作为负极集流体，根据电池卷绕工艺划分平面区和曲面区，将步骤a中制得的普通负极浆料涂布于平面区，将步骤b中制得的高膨胀负极浆料涂布于曲面区，烘干后冷压，进行模切、分条，制成锂离子电池负极极片，所得负极极片中，负极活性材料层的面密度为140mg/1540.25mm 2，负极活性材料层的厚度为101μm，负极极片的厚度为106μm；
(3)隔离膜的制备
采用聚乙烯为基膜，在基膜上涂覆3μm厚的三氧化二铝，得到隔离膜；
(4)电解液的制备
将六氟磷酸锂溶于DMC:DEC:EC体积比为1:1:1的溶剂中，得到锂离子电池电解液；
(5)锂离子电池的制备
将上述正极极片、负极极片以及隔离膜进行卷绕得到电极组件；其中，负极极片中曲面区中相邻的正极极片和负极极片之间的距离(记作gap1)为120μm；
将上述电极组件经过封装、注液、化成，得到锂离子电池。
实施例2
与实施例1基本一致，区别在于，步骤(2)b中，高膨胀负极浆料的配方为：负极活性物质人造石墨、硅氧材料(至少包括SiO x，其中，0＜x＜2)、导电碳Super P、增稠剂(CMC)、粘结剂(SBR)的质量比为92：3：3：1：1。
实施例3
与实施例1基本一致，区别在于，步骤(2)b中，高膨胀负极浆料的配方为：负极活性物质人造石墨、硅氧材料(至少包括SiO x，其中，0＜x＜2)、导电碳Super P、增稠剂(CMC)、粘结剂(SBR)的质量比为55：40：3：1：1。
实施例4
与实施例1基本一致，区别在于，控制卷绕工艺，使得负极极片中曲面区中相邻的正极极片和负极极片之间的距离(记作gap1)为18μm。
实施例5
与实施例1基本一致，区别在于，控制卷绕工艺，使得负极极片中曲面区中相邻的正极极片和负极极片之间的距离(记作gap1)为170μm。
实施例6
与实施例1基本一致，区别在于，进行负极极片制备时，不区分平面区和曲面区，全部涂覆实施例1步骤(2)b中制备的高膨胀负极浆料。
对比例1
与实施例1基本一致，区别在于，进行负极极片制备时，不区分平面区和曲面区，全部涂覆实施例1步骤(2)a中制备的普通负极浆料。
表征测试：
(1)面密度测试步骤：
将样品放置在标准冲样器(面积1540.25mm 2)平台上，冲取下压极片，得到面积为1540.25mm 2的小圆片；
称重上述小圆片，得到极片的面密度。
(2)将上述各实施例和对比例中制得的锂离子电池按照如下条件进行充电：
测试流程：将电池静置30分钟，之后以0.5C倍率充电至电压为4.25V，进一步以4.25V恒压充电至电流为0.05C，静置5分钟。
充电结束后测量负极极片中曲面区中相邻的正极极片和负极极片之间的距离(记作gap2)。
(3)可逆容量测试：
测试流程：将电池静置30分钟，之后以0.5C倍率充电至电压为4.25V，进一步以4.25V恒压充电至电流为0.05C，静置5分钟，然后以0.5C倍率放电至电压为2.5V，此为一个充放电循环过程。每次循环时记录放电容量。
循环n次后的容量保持率(％)＝(第n循环的放电容量/首次循环的放电容量) ×100％。
(4)析锂程度判断：
将电池满充后，在空气湿度低于2％的环境下拆解观察，通过析锂颜色深度来判定析锂程度：
轻微析锂：淡灰色；
中度析锂：灰白色；
严重析锂：亮白色。
将各项测试结果列入表1中：
表1
Figure PCTCN2022130222-appb-000001
分析表1数据，相较于实施例1，实施例2中曲面区硅基材料占比较少，充电后，对曲面区gap的降低有限，锂离子迁移路径依然较长，因此会导致轻微的析锂；实施例3中，硅基含量较高，充电后极片膨胀较严重，也会导致一定程度的析锂；实施例4中，充电前原始的gap值较低，充电后膨胀，gap进一步减小，导致一定程度的析锂，容量保持率下降较多；实施例5中，充电前原始的gap值较大，导致充电后gap未能减小到更合适的范围内，因此也存在一定程度的析锂；实施例6中，平面区域中也涂覆了高膨胀浆料，充电后极片整体膨胀较多，也会导致一定程度的析锂；对比例1中，由于曲面区未引入硅基材料，充电后gap值依然较大，且由于碳基材料具有较低的容量，导致电池析锂严重，且容量保持率有了明显的下降。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实 施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本申请的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本申请构思的前提下，还可以做出若干变形和改进，这些都属于本申请的保护范围。因此，本申请的保护范围应以所附权利要求为准。

Claims (14)

  1. 一种二次电池，包括正极极片、负极极片和隔离膜，所述隔离膜设置于所述正极极片和所述负极极片之间；
    其中，所述负极极片包括负极集流体和设置于所述负极集流体至少一个表面之上的负极活性材料层，所述负极极片包括一个或多个平面区，以及一个或多个曲面区，至少有一个所述平面区的负极活性材料层包括活性材料A，至少有一个所述曲面区的负极活性材料层包括活性材料B，所述活性材料B的膨胀率大于所述活性材料A的膨胀率。
  2. 根据权利要求1所述的二次电池，其特征在于，所述活性材料B包括硅基材料；可选地，所述硅基材料包括单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的一种或多种；可选地，所述硅基材料包括硅氧化合物和硅碳复合物中的一种或多种。
  3. 根据权利要求2所述的二次电池，其特征在于，在位于所述曲面区的负极活性材料层中，所述硅基材料的质量百分含量为3％～40％；可选地，在位于所述曲面区的负极活性材料层中，所述硅基材料的质量百分含量为5％～20％。
  4. 根据权利要求1～3任一项所述的二次电池，其特征在于，包括所述活性材料B的曲面区的负极活性材料层还包括碳基材料；可选地，在位于所述曲面区的负极活性材料层中，所述碳基材料的质量百分含量为55％～97％；进一步可选地，在位于所述曲面区的负极活性材料层中，所述碳基材料的质量百分含量为75％～90％。
  5. 根据权利要求4所述的二次电池，其特征在于，所述碳基材料包括人造石墨、天然石墨、软炭以及硬炭中的一种或多种。
  6. 根据权利要求1～5任一项所述的二次电池，其特征在于，在完全放电的状态下，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为18μm～170μm；可选地，在完全放电的状态下，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为20μm～120μm。
  7. 根据权利要求1～6任一项所述的二次电池，其特征在于，
    以0.5C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～62μm；或者，
    以1C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～59μm；或者，
    以2C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～54μm；或者，
    以3C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～45μm；或者，
    以4C的电流将所述二次电池充电至4.25V后，位于所述曲面区的所述负极极片与相邻的所述正极极片之间的最短距离为15μm～33μm。
  8. 根据权利要求2～7任一项所述的二次电池，其特征在于，所述活性材料A包括硅基材料，位于所述曲面区的负极活性材料层中的硅基材料的质量百分含量大于位于所述平面区的负极活性材料层中的硅基材料的质量百分含量。
  9. 根据权利要求1～8任一项所述的二次电池，其特征在于，在所述负极集流体表面，所述负极活性材料层的面密度为80mg/1540.25mm 2～190mg/1540.25mm 2；可选地，在所述负极集流体表面，述负极活性材料层的面密度为115mg/1540.25mm 2～160mg/1540.25mm 2。
  10. 根据权利要求1～9任一项所述的二次电池，其特征在于，所述负极活性材料层的厚度为65μm～140μm；可选地，所述负极活性材料层的厚度为90μm～110μm。
  11. 根据权利要求1～10任一项所述的二次电池，其特征在于，所述负极极片的厚度为70μm～145μm；可选地，所述负极极片的厚度为95μm～115μm。
  12. 根据权利要求1～11任一项所述的二次电池的制备方法，包括以下步骤：
    根据卷绕工艺确定负极极片的所述平面区和所述曲面区，在至少一个所述曲面区对应的负极集流体表面涂覆包含活性材料B的负极浆料，经干燥、压制得到负极极片；
    在正极集流体表面涂覆正极浆料，经干燥、压制得到正极极片；
    将所述负极极片、所述正极极片和隔离膜按照预设的卷绕工艺进行卷绕。
  13. 根据权利要求12所述的制备方法，其特征在于，所述包含活性材料B的负极浆料的固含量为42％～60％；可选地，所述包含活性材料B的负极浆料的固含量为44％～56％。
  14. 一种用电装置，包括权利要求1～11任一项所述的二次电池。
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CN105493317A (zh) * 2013-09-27 2016-04-13 三洋电机株式会社 非水电解质二次电池用负极
CN108258193A (zh) * 2017-12-28 2018-07-06 湖南三迅新能源科技有限公司 一种负极片及其制备方法、锂离子电池
WO2021184262A1 (zh) * 2020-03-18 2021-09-23 宁德新能源科技有限公司 一种锂离子电池的电芯、其制备方法及包含其的锂离子电池

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105493317A (zh) * 2013-09-27 2016-04-13 三洋电机株式会社 非水电解质二次电池用负极
CN108258193A (zh) * 2017-12-28 2018-07-06 湖南三迅新能源科技有限公司 一种负极片及其制备方法、锂离子电池
WO2021184262A1 (zh) * 2020-03-18 2021-09-23 宁德新能源科技有限公司 一种锂离子电池的电芯、其制备方法及包含其的锂离子电池

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