WO2023240595A1 - 负极极片及其制造方法、电极组件、及二次电池 - Google Patents

负极极片及其制造方法、电极组件、及二次电池 Download PDF

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Publication number
WO2023240595A1
WO2023240595A1 PCT/CN2022/099437 CN2022099437W WO2023240595A1 WO 2023240595 A1 WO2023240595 A1 WO 2023240595A1 CN 2022099437 W CN2022099437 W CN 2022099437W WO 2023240595 A1 WO2023240595 A1 WO 2023240595A1
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Prior art keywords
active material
negative electrode
lithium
material layer
capacity
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PCT/CN2022/099437
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English (en)
French (fr)
Inventor
曹艳明
吴桂森
谭宏娟
李伟
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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/CN2022/099437 priority Critical patent/WO2023240595A1/zh
Priority to CN202280032295.3A priority patent/CN117256058A/zh
Publication of WO2023240595A1 publication Critical patent/WO2023240595A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • 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
    • H01M4/04—Processes of manufacture in general
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • 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
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • 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 the field of batteries, and in particular to a negative electrode plate and its manufacturing method, an electrode assembly equipped with the same, a secondary battery, a battery module, a battery pack and an electrical device.
  • Secondary batteries have the advantages of reliable working performance, no pollution, and no memory effect, so they are widely used. For example, as environmental protection issues become more and more important and new energy vehicles become more popular, the demand for power secondary batteries will grow explosively. However, as the application range of secondary batteries becomes more and more extensive, severe challenges are also posed to the performance of secondary batteries.
  • This application was made in view of the above-mentioned problems, and its purpose is to provide a negative electrode plate and a manufacturing method thereof, a secondary battery equipped with the same, a battery module, a battery pack, and an electric device.
  • the negative electrode plate is partially double-sided. Coating different active materials layer by layer can reduce the risk of lithium precipitation in secondary batteries, improve the safety performance of secondary batteries, and extend the service life of the battery without reducing the energy density of the battery.
  • the first aspect of the present application is to provide a negative electrode sheet, including: a current collector; a first active material layer disposed on at least one surface of the current collector; and a second active material layer disposed on the current collector.
  • the first active material layer is on a surface away from the current collector; the first active material layer includes a first active material, the second active material layer includes a second active material, and the lithium-embedded battery of the second active material and delithiation potential are both higher than the first active material.
  • the second active material layer can be selectively selected to be coated with the second active material layer at locations prone to lithium deposition, and the safety risk of lithium deposition caused by insufficient lithium embedding capacity in the locations prone to lithium deposition in the secondary battery can be improved, thereby improving the safety performance and cycle performance of the secondary battery. properties and energy density.
  • the lithium insertion potential of the second active material is higher than the lithium insertion potential of the first active material.
  • the delithiation potential of the second active material is higher than the delithiation potential of the first active material.
  • the second active material can enrich and lock the lithium ions that may have been reduced to generate lithium dendrites on the surface of the negative electrode sheet, thereby improving the local embedding of the negative electrode in secondary batteries. Lithium precipitation caused by insufficient lithium capacity improves the safety performance of secondary batteries.
  • the second active material has a higher gram capacity than the first active material.
  • the lithium insertion capacity of the negative electrode can be further increased, the lithium deposition improvement effect can be improved, and the safety performance of the secondary battery can be improved.
  • the ratio of the mass of the second active material to the mass of the first active material is 0.1 ⁇ 2, optionally 0.1 ⁇ 1. Therefore, the second active material layer coated with the second active material layer is less, and the change in the quality of the secondary battery after adding the second active material layer is negligible, and the energy density of the secondary battery can be improved without reducing the energy density of the secondary battery. Safety performance of secondary batteries.
  • the second aspect of the present application is to provide an electrode assembly, including the negative electrode piece, the positive electrode piece and the isolation film in any of the above embodiments; the positive electrode piece includes a positive active material layer; wherein the second active material layer
  • the capacity a, the capacity b of the first active material layer, and the capacity c of the positive active material layer satisfy formula (1)
  • the units of a, b and c in the formula (1) are mAh/cm 2 .
  • the lithium insertion capacity of the negative electrode can be further increased, the negative electrode lithium deposition of the secondary battery can be improved, and the Safety performance and cycle characteristics of secondary batteries.
  • the negative electrode sheet, the isolation film and the positive electrode sheet are rolled into a rolled structure along the winding direction; the rolled structure includes a planar part and a corner part connecting the planar part ;
  • the second active material layer is at least partially located at the corner. This can improve the lithium deposition at the corners of the secondary battery and improve the safety of the secondary battery.
  • the corner portion includes a first corner portion and a second corner portion close to the winding starting end of the electrode assembly; the second active material layer is located at the first corner portion and the second corner portion. . This can further improve the lithium deposition at the corners of the inner ring of the secondary battery and improve the safety of the secondary battery.
  • the current collector of the negative electrode plate further includes a tab portion; the second active layer is also located on a side of the planar portion connected to the tab portion. This can improve the lithium deposition near the tab of the negative electrode piece and improve the safety of the secondary battery.
  • the negative electrode piece, the isolation film and the positive electrode piece are stacked in sequence to form a lamination structure; the lamination structure includes a central part and edge parts arranged around the central part; The second active material layer is at least partially located on the edge. This can improve the lithium deposition at the edge of the negative electrode piece and improve the safety of the secondary battery.
  • the current collector of the negative electrode plate further includes a tab portion; the second active material layer is also located on a side of the edge portion connected to the tab portion. This can improve the lithium deposition near the tab of the negative electrode piece and improve the safety of the secondary battery.
  • a third aspect of the present application is to provide a method for manufacturing a negative electrode piece, which is used to manufacture the negative electrode piece in any of the above embodiments.
  • a double-layer coating method is used, and the process is highly controllable, flexible and simple.
  • the use of double-layer coating to form composite negative electrodes can avoid process difficulties caused by differences in material systems.
  • a fourth aspect of the present application is to provide a secondary battery, which includes the electrode assembly according to the second aspect of the present application.
  • a fifth aspect of the present application is to provide a battery module, which includes the secondary battery according to the fourth aspect of the present application.
  • a sixth aspect of the present application is to provide a battery pack, which battery module includes the battery module according to the fifth aspect of the present application.
  • the seventh aspect of the present application is to provide an electrical device.
  • the electrical device includes the secondary battery according to the fourth aspect of the present application, the battery module according to the fifth aspect of the present application and the battery module according to the sixth aspect of the present application. at least one of the battery packs described above.
  • Figure 1 is a schematic cross-sectional view of a negative electrode piece according to an embodiment of the present application.
  • FIG. 2 is a schematic top view of a negative electrode piece according to an embodiment of the present application.
  • FIG. 3 is a schematic top view of an electrode assembly according to an embodiment of the present application.
  • FIG. 4 is a detailed schematic diagram of the corner portion of the electrode assembly according to an embodiment of the present application shown in FIG. 3 .
  • FIG. 5 is a schematic top view of the negative electrode piece of the electrode assembly according to an embodiment of the present application.
  • FIG. 6 is a schematic top view of an electrode assembly according to an embodiment of the present application.
  • FIG. 7 is a schematic top view of the negative electrode piece of the electrode assembly according to an embodiment of the present application shown in FIG. 6 .
  • FIG. 8 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 9 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 8 .
  • FIG. 10 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 11 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 12 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 11 .
  • FIG. 13 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • FIG. 14 is a lithium deintercalation curve of the first active material and the second active material according to an embodiment of the present application.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 ⁇ 4 and 2 ⁇ 5.
  • the numerical range “a ⁇ b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0 ⁇ 5" means that all real numbers between "0 ⁇ 5" have been listed in this article, and "0 ⁇ 5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles and electric cars, as well as in many fields such as military equipment and aerospace. . As the application fields of power batteries continue to expand, their market demand is also constantly expanding.
  • the inventor designed a negative electrode plate after in-depth research, which includes: a current collector, and at least one surface of the current collector. a first active material layer on the first active material layer and a second active material layer disposed on the surface of the first active material layer away from the current collector.
  • the first active material layer includes a first active material
  • the second active material layer includes a second active material
  • the lithium insertion potential and delithiation potential of the second active material are both higher than the first active material.
  • the above-mentioned negative electrode sheet is coated with a second active material layer with high lithium insertion potential and high lithium removal potential at a position prone to lithium precipitation, which can improve the lithium precipitation in the negative electrode of the secondary battery, improve the safety performance of the secondary battery, and extend the service life of the battery. And does not reduce the energy density of the battery.
  • the secondary batteries disclosed in the embodiments of the present application can be, but are not limited to, used in electrical devices such as vehicles, ships, or aircrafts.
  • Embodiments of the present application provide an electrical device that uses a secondary battery as a power source.
  • the electrical device can be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric vehicle, a ship, a spacecraft, etc.
  • electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, electric airplane toys, etc.
  • spacecraft can include airplanes, rockets, space shuttles, spaceships, etc.
  • a negative electrode plate 7 including: a current collector 100; a first active material layer 101 disposed on at least one surface of the current collector 100; and a third Two active material layers 102 are disposed on the surface of the first active material layer 101 away from the current collector 100; the first active material layer 101 includes a first active material, the second active material layer 102 includes a second active material, and the second active material
  • the lithium insertion potential and delithiation potential are both higher than that of the first active material.
  • the first active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and the like.
  • the inventor of the present application found that by partially coating the second active material layer 102 with high lithium insertion potential and high delithiation potential on the first active material layer 101, lithium can be first embedded in the second active material coated on the upper layer, Furthermore, it is possible to avoid the lithium embedded in the second active material from escaping and being embedded in the first active material again, resulting in lithium evolution, thereby improving the lithium evolution in the negative electrode and improving the safety and cycle stability of the secondary battery.
  • the increase in the overall lithium insertion capacity of the negative electrode also improves the gram capacity of the battery positive electrode and increases the energy density of the battery.
  • the second active material layer can be selectively selected to coat the position where lithium is easily deposited, thereby improving the lithium deposit in the negative electrode of the secondary battery and improving the cycle characteristics and energy density of the secondary battery.
  • Spaced apart means that there is a gap between at least two second active material layers among the plurality of second active material layers. According to actual production needs, the distance between any two adjacent second active material layers may be equal or unequal, and this application does not limit this.
  • the lithium insertion potential of the second active material is higher than the lithium insertion potential of the first active material.
  • the delithiation potential of the second active material is higher than the delithiation potential of the first active material.
  • the second active material can enrich and lock the lithium ions that may have been reduced to generate lithium dendrites on the surface of the negative electrode sheet, thereby improving the local embedding of the negative electrode in secondary batteries. Lithium precipitation caused by insufficient lithium capacity improves the safety performance of secondary batteries.
  • the second active material has a higher gram capacity than the first active material. Specifically, the gram capacity of the second active material in the potential range >0.5V (vs Li/Li + ) is higher than that of the first active material. This can further increase the lithium intercalation capacity of the negative electrode, improve the lithium precipitation of the secondary battery due to insufficient local lithium intercalation capacity of the negative electrode, and improve the safety performance of the secondary battery.
  • the second active material includes, but is not limited to, one or more of transition metal oxides, lithium titanate, and the like.
  • the ratio of the mass of the second active material to the mass of the first active material is 0.1 ⁇ 2, optionally 0.1 ⁇ 1. Therefore, the second active material layer coated with the second active material layer is less, and the change in the quality of the secondary battery after adding the second active material layer is negligible, and the energy density of the secondary battery can be improved without reducing the energy density of the secondary battery. Safety performance of secondary batteries.
  • the negative active material of this application adopts a double-layer coating method, which has high process controllability, flexibility and simplicity.
  • the use of double-layer coating to form composite negative electrodes can avoid process difficulties caused by differences in material systems.
  • an electrode assembly 52 including a negative electrode piece 7, a positive electrode piece 6 and a separator 9; the positive electrode piece 7 includes a positive active material layer; wherein, The capacity a of the second active material layer, the capacity b of the first active material layer, and the capacity c of the positive active material layer satisfy equation (1)
  • the units of a, b and c in the formula (1) are mAh/cm2.
  • capacity gram capacity of active material (mAh/g) * mass of active material in active material layer (g/cm2)
  • n is less than 1.07, the lithium insertion capacity provided by the second active material is insufficient and the risk of lithium evolution cannot be effectively reduced; when n is greater than 5, although the risk of lithium evolution in the secondary battery can be reduced, the second active material enriches excess lithium. , it is easy to cause lithium loss, and at the same time the battery mass increases, causing the battery energy density to decrease.
  • the lithium insertion capacity of the negative electrode can be further increased, the lithium precipitation of the negative electrode of the secondary battery can be improved, and the safety performance, cycle characteristics and energy density of the secondary battery can be improved.
  • the electrode assembly 52 may be of a rolled structure. Specifically, the positive electrode piece 6 and the negative electrode piece 7 are both one, and the positive electrode piece 6 and the negative electrode piece 7 have a strip structure. The positive electrode piece 6 , the separator 9 and the negative electrode piece 7 are sequentially stacked and wound more than two times to form the electrode assembly 52 .
  • the electrode assembly 52 may be flat.
  • the negative electrode piece 7 , the isolation film 9 and the positive electrode piece 6 are rolled into a rolled structure along the winding direction; the rolled structure includes a planar portion 111 and a corner connecting the planar portion 111 portion 112; the second active material layer 102 is at least partially located at the corner portion 112. This can improve the lithium deposition at the corners of the secondary battery and improve the safety of the secondary battery.
  • the corner portion 112 includes a first corner portion 112 a and a second corner portion 112 b close to the starting end of the electrode assembly winding; the second active material layer 102 is located at the first corner portion 112 a and the second corner portion 112b. This can further improve the lithium deposition at the inner ring corners of the secondary battery.
  • the current collector 100 of the negative electrode piece 7 further includes a tab portion 100 a; the second active material layer 102 is also located on the side of the planar portion 111 connected to the tab portion 100 a. This can improve lithium deposition near the negative electrode tab of the secondary battery and improve the safety of the secondary battery.
  • the electrode assembly 52 may also have a laminated structure. Specifically, a plurality of positive electrode pieces 6 are provided, and a plurality of negative electrode pieces 7 are provided. The plurality of positive electrode pieces 6 and negative electrode pieces 7 are alternately stacked, and the isolation film 9 separates the positive electrode pieces 6 and the negative electrode pieces 7 separated.
  • the negative electrode piece 7, the isolation film 9 and the positive electrode piece 9 are stacked in sequence to form a laminate structure; the laminate structure includes a central part and edge parts arranged around the central part; The second active material layer is at least partially located on the edge. This can improve lithium deposition at the edge of the negative electrode piece that has no active material layer at the position of the opposite positive electrode piece of the secondary battery.
  • the current collector of the negative electrode plate 7 also includes a tab portion 100a; the second active material layer 102 is also located on the edge portion and connected to the tab portion. side. This can improve lithium deposition near the negative electrode tab of the secondary battery and improve the safety of the secondary battery.
  • FIG. 8 shows a square-structured secondary battery 5 .
  • secondary batteries include lithium ion batteries, lithium sulfur batteries, sodium lithium ion batteries, sodium ion batteries or magnesium ion batteries, etc.
  • the concept of this application will be mainly described using lithium ion batteries as an example. It should be understood that any other suitable type of rechargeable battery is suitable.
  • a secondary battery 5 includes an outer shell (including a case 51 and a cover plate 53 ) and an electrode assembly 52 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • This application has no particular limitation on the shape of the housing 51, which can be cylindrical, square or any other shape.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • Electrode terminals 55 There are two electrode terminals 55 and they are provided on the cover plate 53 .
  • There are two connecting members 54 one connecting member 54 connects one electrode terminal 55 and the positive electrode tab 6 of the electrode assembly 52 , and the other connecting member 54 connects the other electrode terminal 55 and the negative electrode tab 7 of the electrode assembly 52 .
  • a secondary battery is provided.
  • a secondary battery typically includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator.
  • active ions are inserted and detached back and forth between the positive and negative electrodes.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows 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.
  • the positive electrode film layer includes the positive electrode active material of the first aspect of the present application.
  • the positive electrode current collector has two surfaces facing each other in its own 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.
  • the metal foil aluminum foil can 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 base layer.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the cathode active material may be a cathode active material known in the art for batteries.
  • the cathode 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 of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxides (such as LiNiO 2 ), lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (can also be abbreviated to NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (can also be abbreviated to NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (can also be abbreviated to NCM 622 ), LiNi At least one of 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as Li Li
  • the olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • composites of lithium iron phosphate and carbon such as LiMnPO 4
  • LiMnPO 4 lithium manganese phosphate and carbon.
  • At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • the positive electrode film layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the positive electrode film layer optionally further includes a conductive agent.
  • the conductive agent may include 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 by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a 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 piece 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, where the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own 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 composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the first active material of the negative electrode may be a negative electrode active material known in the art for batteries.
  • the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, and the like.
  • 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 present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative second active material may include at least one of the following materials: transition metal oxides (eg. Fe2O3, Fe3O4, Mn2O3, Co3O4, NiO, ZnO), lithium-containing transition metal oxides (eg. Li 4 Ti 5 O12), etc., it can be understood that any one of the above substances alone or mixed with any multiple substances as the second negative electrode active material layer material can achieve a lithium insertion capacity of 0 ⁇ in the negative electrode. In the range of 300 mAh/g, the lithium insertion potential is higher than the lithium insertion potential of the first active material. In the range of the negative electrode lithium removal capacity of 10 to 300 mAh/g, the lithium removal potential is higher than the lithium removal potential of the first active material. high.
  • transition metal oxides eg. Fe2O3, Fe3O4, Mn2O3, Co3O4, NiO, ZnO
  • lithium-containing transition metal oxides eg. Li 4 Ti 5 O12
  • the gram capacity of the second negative electrode active material layer material may be greater than that of the first negative electrode active material layer material.
  • the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative electrode film layer optionally further includes a binder.
  • the binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly Methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride -At least one of hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS
  • the negative electrode film layer optionally further includes a conductive agent.
  • the conductive agent 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 optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • the negative electrode sheet including the first active material can be prepared by using the above components for preparing the negative electrode slurry including the first active material, such as the first negative active material, the conductive agent, the binder
  • the agent and any other components are dispersed in a solvent (such as deionized water) to form the first active material negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, it can be A negative electrode piece including the first active coating layer is obtained.
  • the negative electrode sheet containing the first and second active materials can be prepared by: using the above-mentioned components for preparing the second active material negative electrode slurry, such as the second active material, the conductive agent, the binder, and the second active material.
  • the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a second active material negative electrode slurry; the second active material negative electrode slurry is coated on the negative electrode including the first active coating layer On the chip, after drying and other processes, the positive electrode piece can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally further includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • 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 film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and 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 bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 10 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • Figure 13 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the solid content in the negative electrode slurry is 53wt%, and the mass ratio of graphite, Super P, CMC and adhesive styrene-butadiene rubber (SBR) in the solid components is 96:2:1:1.
  • NiO as the second negative electrode active material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) evenly to make a second negative electrode slurry.
  • NMP N-methylpyrrolidone
  • the solid content in the negative electrode slurry is 43wt%, and the mass ratio of NiO, Super P, CMC and adhesive styrene-butadiene rubber (SBR) in the solid components is 92:6:2.
  • the first negative electrode slurry is coated on the current collector copper foil and dried at 85° C. to form a first negative electrode active material layer. Then, the second negative electrode slurry is coated on the first negative electrode active material layer at a prescribed position, and dried at 85°C. Then, cold pressing, trimming, cutting, and striping are performed, and then dried under vacuum conditions at 120°C for 12 hours to make negative electrode sheets.
  • the cathode material lithium iron phosphate, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are made into cathode slurry in N-methylpyrrolidone (NMP).
  • NMP N-methylpyrrolidone
  • the solid content in the positive electrode slurry is 64wt%, and the mass ratio of lithium iron phosphate, Super P, and PVDF in the solid content is 97:1:2.
  • the positive electrode slurry is coated on the current collector aluminum foil and dried at 85°C, then cold pressed, then trimmed, cut into pieces, and slit, and dried under vacuum conditions at 85°C for 4 hours to make the positive electrode. piece.
  • Polyethylene film is used as the isolation film.
  • the secondary batteries of Examples 2 to 11 and the secondary batteries of Comparative Examples 1 to 3 are similar to the secondary batteries of Example 1, but the composition of the second active material and the second active material and the first active material are adjusted.
  • the mass ratio, different product parameters are detailed in Table 1.
  • the negative electrode material powder is made into electrode pieces according to a certain formula, it is assembled into a semi-button battery with electrode pieces and lithium pieces, and the total charge and discharge capacity of the negative electrode material at different potentials is obtained through small-rate charge and discharge, and then the second cycle is The total charge and discharge capacity is divided by the mass of the active material of the pole piece to obtain the potential-charge and discharge capacity curve of the material.
  • the value of the lithium insertion potential is the potential value corresponding to the corresponding capacity of the potential-capacity curve during the second cycle of discharge.
  • the negative electrode material powder is made into electrode pieces according to a certain formula, it is assembled into a semi-button battery with electrode pieces and lithium pieces, and the total charge and discharge capacity of the negative electrode material at different potentials is obtained through small-rate charge and discharge, and then the second cycle is The total charge and discharge capacity is divided by the mass of the active material of the pole piece to obtain the potential-charge and discharge capacity curve of the material.
  • the value of the delithiation potential is the potential value corresponding to the corresponding capacity of the potential-capacity curve during the second cycle of charging.
  • the corner area is full of golden yellow on the surface of the negative electrode. Wipe it with dust-free paper. There is no gray metal lithium powder on the paper.
  • Slight lithium precipitation The corner area is full of dark yellow on the surface of the negative electrode. Wipe it with dust-free paper. There is gray metallic lithium powder on the paper.
  • Gray spots The corner area is full of local gray on the negative electrode surface, with no golden color passing through.
  • Severe lithium precipitation The surface of the fully charged negative electrode in the corner area is gray with no golden color passing through.
  • the preferred order of lithium precipitation on the convex surface of the negative electrode is no lithium precipitation>grey spots>slight lithium precipitation>severe lithium precipitation.
  • the lithium insertion or delithiation potential refers to the potential corresponding to a lithium insertion or delithiation capacity of 100 mAh/g.
  • the lithium insertion potential of the first active material refers to the potential corresponding to the specific capacity of 100 mAh/g on the lithium insertion curve of the first active material.
  • the delithiation potential of the first active material refers to the potential corresponding to the specific capacity of 100 mAh/g on the delithiation curve of the first active material.
  • the lithium insertion or delithiation potential of the second active material can be obtained.
  • the above potentials are all relative to Li/Li + , and the unit is V.
  • the lithium insertion potential of the second active material is higher than that of the first active material, and in the range of lithium removal capacity of 10 to 300 mAh /g range, the delithiation potential of the second active material is higher than the delithiation potential of the first active material.
  • the unit of gram capacity is mAh/g, and the unit of capacity is mAh/cm 2 .
  • the mass ratio of the second active material in the negative electrode material is preferably 2 or less, and more preferably 1 or less.

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Abstract

本申请提供一种负极极片，包括：集流体；第一活性物质层，设置于集流体的至少一个表面；以及第二活性物质层，设置于第一活性物质层远离集流体的表面上；第一活性物质层包括第一活性材料，第二活性物质层包括第二活性材料，第二活性材料的嵌锂电位和脱锂电位均高于第一活性材料。根据本申请的负极极片，能够提高二次电池的安全性和循环特性。

Description

负极极片及其制造方法、电极组件、及二次电池 技术领域
本申请涉及电池领域，尤其涉及一种负极极片及其制造方法、具备其的电极组件、二次电池、以及电池模块、电池包和用电装置。
背景技术
二次电池具有工作性能可靠，以及无污染、无记忆效应等优点，因而被广泛应用。例如，随着环境保护问题日益受到重视，新能源汽车日益普及，动力型二次电池的需求将呈现爆发式增长。然而，随着二次电池的应用范围越来越广泛，对二次电池的性能也提出了严峻挑战。
但是，对于二次电池而言，随着所设计电池的能量密度的提高，负极极片的部分位置由于嵌锂能力不足容易发生析锂现象。随着锂枝晶的不断生成，隔离膜被刺破，引发电池短路，降低电池安全性能。因此，亟待设计和开发出一种不降低电池能量密度又能有效降低析锂风险的二次电池。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种负极极片及其制造方法、具备其的二次电池、以及电池模块、电池包和用电装置，该负极极片通过局部双层涂布不同的活性物质，能够降低二次电池的析锂风险、提高二次电池的安全性能，延长电池使用寿命，并且不降低电池的能量密度。
为了实现上述目的，本申请第一方面在于提供一种负极极片，包括：集流体；第一活性物质层，设置于所述集流体的至少一个表面；以及第二活性物质层，设置于所述第一活性物质层远离所述集流体的表面上；所述第一活性物质层包括第一活性材料，所述第二活性物质层包括第二活性材料，所述第二活性材料的嵌锂电位和脱锂电位均高 于所述第一活性材料。
通过在第一活性物质层上局部地涂覆嵌锂电位和脱锂电位高的第二活性材料层，能够改善二次电池的负极析锂、提高二次电池的安全性能，延长电池使用寿命，并且不降低电池的能量密度。
在一些实施方式中，所述第二活性物质层为多个，且多个所述第二活性物质层间隔设置。由此，能够选择性地选取容易析锂的位置涂覆第二活性物质层，能够针对二次电池易析锂部位嵌锂能力不足导致的析锂安全风险，提高二次电池的安全性能、循环特性和能量密度。
在一些实施方式中，在所述负极极片嵌锂容量为0～300mAh/g范围内，所述第二活性材料的嵌锂电位比所述第一活性材料的嵌锂电位高。通过在特定的嵌锂容量区间内，使第二活性材料和第一活性材料的嵌锂电位满足上述关系，保证来自正极材料的锂可以首先嵌入第二活性材料中，从而可以降低第二活性材料锂过嵌的风险，降低二次电池的负极析锂风险，提高二次电池的安全性能。
在一些实施方式中，在所述负极极片脱锂容量为10～300mAh/g范围内，所述第二活性材料的脱锂电位比所述第一活性材料的脱锂电位高。通过在特定的嵌锂容量区间内，使第二活性材料和第一活性材料的脱锂电位满足上述关系，能够使嵌入第二活性材料的锂离子在电池后续充放电过程中仅部分脱出或不脱出，未脱出的锂离子将无法还原并生成锂枝晶，即第二活性材料能够富集锁附原本可能在负极极片表面还原生成锂枝晶的锂离子，改善二次电池由于负极局部嵌锂能力不足导致的析锂，提高二次电池的安全性能。
在一些实施方式中，所述第二活性材料的克容量高于所述第一活性材料。由此，能够进一步增加负极的嵌锂容量，提升析锂改善效果，提高二次电池的安全性能。
在一些实施方式中，所述第二活性材料的质量与所述第一活性材料的质量之比为0.1～2，可选为0.1～1。由此，第二活性物质层的涂覆的第二活性材料较少，二次电池质量在增加二活性物质层后的变化可忽略不计，能够在不降低二次电池的能量密度的同时提高二次电池的安全性能。
本申请第二方面在于提供一种电极组件，包括上述任意实施方式 中的负极极片、正极极片以及隔离膜；所述正极极片包括正极活性物质层；其中，所述第二活性物质层的容量a、所述第一活性物质层的容量b及所述正极活性物质层的容量c之间满足式(1)
a+b＝nc，n＝1.07～5     式(1)
所述式(1)中a、b以及c的单位为mAh/cm 2。
通过第二活性物质层的容量a、所述第一活性物质层的容量b及所述正极活性物质层的容量c，能够进一步增加负极的嵌锂容量，改善二次电池的负极析锂，提高二次电池的安全性能、循环特性。
在一些实施方式中，所述负极极片、所述隔离膜以及所述正极极片沿卷绕方向卷绕成卷绕结构；所述卷绕结构包括平面部和连接所述平面部的拐角部；所述第二活性物质层至少部分位于所述拐角部。由此，能够改善二次电池的拐角部析锂，提高二次电池的安全性。
在一些实施方式中，所述拐角部包括靠近所述电极组件卷绕起始端的第一拐角部和第二拐角部；所述第二活性物质层位于所述第一拐角部和第二拐角部。由此，能够进一步改善二次电池的内圈拐角处析锂，提高二次电池的安全性。
在一些实施方式中，所述负极极片的所述集流体还包括极耳部；所述第二活性层还位于所述平面部的与所述极耳部连接的一侧。由此，能够改善负极极片极耳部附近的析锂，提高二次电池的安全性。
在一些实施方式中，所述负极极片、所述隔离膜以及所述正极极片依次堆叠形成叠片结构；所述叠片结构包括中心部和设置于所述中心部四周的边缘部；所述第二活性物质层至少部分位于所述边缘部。由此，能够改善负极极片的边缘处的析锂，提高二次电池的安全性。
在一些实施方式中，所述负极极片的所述集流体还包括极耳部；所述第二活性物质层还位于所述边缘部的与所述极耳部连接的一侧。由此，能够改善负极极片极耳部附近的析锂，提高二次电池的安全性。
本申请第三方面在于提供一种负极极片的制造方法，用于制造上述任意实施方式中的负极极片。根据本申请的负极极片的制造方法，采用双层涂覆的方式，工艺可控性高，灵活简便。针对不同体系的负极材料，采用双层涂覆方式形成复合负极可避免材料体系差异带来的工艺困难。
本申请第四方面在于提供一种二次电池，该二次电池包括根据本申请第二方面所述的电极组件。
本申请第五方面在于提供一种电池模块，该电池模块包括根据本申请第四方面所述的二次电池。
本申请第六方面在于提供一种电池包，该电池模块包括根据本申请第五方面所述的电池模块。
本申请第七方面在于提供一种用电装置，该用电装置包括根据本申请第四方面所述的二次电池、根据本申请第五方面所述的电池模块和根据本申请第六方面所述的电池包中的至少一种。
附图说明
图1是本申请一实施方式的负极极片的截面示意图。
图2是本申请一实施方式的负极极片的俯视示意图。
图3是本申请一实施方式的电极组件的俯视示意图。
图4是图3所示的本申请一实施方式的电极组件的拐角部的详细示意图。
图5是本申请一实施方式的电极组件的负极极片的俯视示意图。
图6是本申请一实施方式的电极组件的俯视示意图。
图7是图6所示的本申请一实施方式的电极组件的负极极片的俯视示意图。
图8是本申请一实施方式的二次电池的示意图。
图9是图8所示的本申请一实施方式的二次电池的分解图。
图10是本申请一实施方式的电池模块的示意图。
图11是本申请一实施方式的电池包的示意图。
图12是图11所示的本申请一实施方式的电池包的分解图。
图13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。
图14是本申请一实施方式的第一活性材料和第二活性材料的脱嵌锂曲线图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳 体；52电极组件；53顶盖组件；54连接构件；55电极端子；6正极极片；7负极极片；9隔离膜；100集流体；101第一活性物质层；102第二活性物质层；111平面部；112拐角部；112a第一拐角部；112b第二拐角部；100a极耳部；
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的正极活性材料及其制造方法、正极极片、二次电池、电池模块、电池包和电学装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60～120和80～110的范围，理解为60～110和80～120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1～3、1～4、1～5、2～3、2～4和2～5。在本申请中，除非有其他说明，数值范围“a～b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0～5”表示本文中已经全部列出了“0～5”之间的全部实数，“0～5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示 开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
目前，从市场形势的发展来看，动力电池的应用越加广泛。动力电池不仅被应用于水力、火力、风力和太阳能电站等储能电源系统，而且还被广泛应用于电动自行车、电动摩托车、电动汽车等电动交通工具，以及军事装备和航空航天等多个领域。随着动力电池应用领域的不断扩大，其市场的需求量也在不断地扩增。
本发明人注意到，动力电池在实际的使用过程中存在：负极极片的部分位置由于嵌锂能力不足容易发生析锂现象。随着锂枝晶的不断生成，隔离膜被刺破，引发电池短路，降低电池安全性能。
为了缓解负极极片的析锂情况，以及兼顾提高电池的能量密度的问题，发明人经过深入研究，设计了一种负极极片，其包括：集流体、设置于所述集流体的至少一个表面上的第一活性物质层、设置于第一活性物质层远离集流体的表面上的第二活性物质层。第一活性物质层包括第一活性材料，第二活性物质层包括第二活性材料，第二活性材料的嵌锂电位和脱锂电位均高于所述第一活性材料。
上述负极极片在易于析锂的位置涂覆嵌锂电位和脱锂电位高的第二活性材料层，能够改善二次电池的负极析锂、提高二次电池的安全性能，延长电池使用寿命，并且不降低电池的能量密度。
本申请实施例公开的二次电池可以但不限用于车辆、船舶或飞行器等用电装置中。本申请实施例提供一种使用二次电池作为电源的用电装置，用电装置可以为但不限于手机、平板、笔记本电脑、电动玩具、电动工具、电瓶车、电动汽车、轮船、航天器等等。其中，电动玩具可以包括固定式或移动式的电动玩具，例如，游戏机、电动汽车玩具、电动轮船玩具和电动飞机玩具等等，航天器可以包括飞机、火箭、航天飞机和宇宙飞船等等。
[极片结构]
如图1、2所示，本申请的一个实施方式中，提出了一种负极极片7，包括：集流体100；第一活性物质层101，设置于集流体100的至少一个表面；以及第二活性物质层102，设置于第一活性物质层101远离集流体100的表面上；第一活性物质层101包括第一活性材料，第二活性物质层102包括第二活性材料，第二活性材料的嵌锂电位和脱锂电位均高于第一活性材料。
第一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、硬炭和硅基材料等。
本申请发明人发现：通过在第一活性物质层101上局部地涂覆嵌锂电位和脱锂电位高的第二活性物质层102，可以使锂先嵌入涂覆于上层的第二活性材料，并且，能够避免嵌入第二活性材料的锂脱出而再次嵌入第一活性材料导致析锂，从而改善负极析锂，提高二次电池的安全性和循环稳定性。此外，负极整体的嵌锂容量提升也提高了电池正极的克容量发挥，提高电池的能量密度。
在一些实施方式中，可选地，第二活性物质层102为多个，且多个第二活性物质层102间隔设置。由此，能够选择性地选取容易析锂的位置涂覆第二活性物质层，能够改善二次电池的负极析锂，提高二次电池的循环特性和能量密度。
“间隔设置”是指多个第二活性物质层中的至少两个第二活性物质层之间存在间隙。根据实际生产的需要，任意两个相邻的第二活性物质层之间的间距可以是相等的，也可以是不等的，本申请对此不做限制。
在一些实施方式中，在负极极片7嵌锂容量为0～300mAh/g的范围内，第二活性材料的嵌锂电位比第一活性材料的嵌锂电位高。通过在特定的嵌锂容量区间内，使第二活性材料和第一活性材料的嵌锂电位满足上述关系，保证来自正极材料的锂可以首先嵌入第二活性材料中，从而可以提升负极的嵌锂能力，降低二次电池的负极析锂风险，提高二次电池的安全性能。
在一些实施方式中，在负极极片7脱锂容量为10～300mAh/g的范围内，第二活性材料的脱锂电位比第一活性材料的脱锂电位高。通过 在特定的嵌锂容量区间内，使第二活性材料和第一活性材料的脱锂电位满足上述关系，能够使嵌入第二活性材料的锂离子在电池后续充放电过程中仅部分脱出或不脱出，未脱出的锂离子将无法还原并生成锂枝晶，即第二活性材料能够富集锁附原本可能在负极极片表面还原生成锂枝晶的锂离子，改善二次电池由于负极局部嵌锂能力不足导致的析锂，提高二次电池的安全性能。
在一些实施方式中，第二活性材料的克容量高于第一活性材料。具体而言，第二活性材料在电位>0.5V(vs Li/Li +)电位区间的克容量高于第一活性材料。由此，能够进一步增加负极的嵌锂容量，改善二次电池由于负极局部嵌锂能力不足导致的析锂，提高二次电池的安全性能。第二活性材料包括但不限于过渡金属氧化物、钛酸锂等中的一种或多种。
在一些实施方式中，所所述第二活性材料的质量与所述第一活性材料的质量之比为0.1～2，可选为0.1～1。由此，第二活性物质层的涂覆的第二活性材料较少，二次电池质量在增加二活性物质层后的变化可忽略不计，能够在不降低二次电池的能量密度的同时提高二次电池的安全性能。
此外，本申请的负极活性物质采用双层涂覆的方式，工艺可控性高，灵活简便。针对不同体系的负极材料，采用双层涂覆方式形成复合负极可避免材料体系差异带来的工艺困难。
[电极组件]
如图3～6所示，本申请的一个实施方式中，提供一种电极组件52，包括负极极片7、正极极片6以及隔离膜9；正极极片7包括正极活性物质层；其中，第二活性物质层的容量a、第一活性物质层的容量b及正极活性物质层的容量c之间满足式(1)
a+b＝nc，n＝1.07～5     式(1)
所述式(1)中a、b以及c的单位为mAh/cm2。
在此，容量的计算方法为：容量＝活性物质克容量(mAh/g)*活性物质层中活性物质的质量(g/cm2)
当n小于1.07时，第二活性物质提供的嵌锂容量不足，不能有效 降低析锂风险；当n大于5时，虽然二次电池的析锂风险能够降低，但第二活性物质富集过量锂，易造成锂损失，同时电池质量增加，造成电池能量密度降低。
通过正负极容量比在上述范围内，能够进一步增加负极的嵌锂容量，改善二次电池的负极析锂，提高二次电池的安全性能、循环特性和能量密度。
如图3所示，电极组件52可为卷绕式结构。具体地，正极极片6和负极极片7均为一个，且正极极片6和负极极片7为带状结构。将正极极片6、隔离膜9和负极极片7依次层叠并卷绕两圈以上以形成电极组件52。电极组件52可为扁平状。
在一些实施方式中，如图3所示，负极极片7、隔离膜9以及正极极片6沿卷绕方向卷绕成卷绕结构；卷绕结构包括平面部111和连接平面部111的拐角部112；第二活性物质层102至少部分位于拐角部112。由此，能够改善二次电池的拐角部析锂，提高二次电池的安全性。
在一些实施方式中，如图4所示，拐角部112包括靠近所述电极组件卷绕起始端的第一拐角部112a和第二拐角部112b；第二活性物质层102位于第一拐角部112a和第二拐角部112b。由此，能够进一步改善二次电池的内圈拐角处析锂。
在一些实施方式中，如图5所示，负极极片7的集流体100还包括极耳部100a；第二活性物质层102还位于平面部111的与极耳部100a连接的一侧。由此，能够改善二次电池的负极极耳部附近的析锂，提高二次电池的安全性。
可替代地，如图6所示，电极组件52也可为叠片式结构。具体地，正极极片6设置为多个，负极极片7设置为多个，所述多个正极极片6和负极极片7交替层叠，隔离膜9将正极极片6和负极极片7隔开。
在一些实施方式中，如图7所示，负极极片7、隔离膜9以及正极极片9依次堆叠形成叠片结构；叠片结构包括中心部和设置于所述中心部四周的边缘部；所述第二活性物质层至少部分位于所述边缘部。由此，能够改善二次电池的相对的正极极片位置没有活性材料层的负极极片的边缘处的析锂。
在一些实施方式中，如图7所示，负极极片7的所述集流体还包 括极耳部100a；所述第二活性物质层102还位于所述边缘部的与所述极耳部连接的一侧。由此，能够改善二次电池的负极极耳部附近的析锂，提高二次电池的安全性。
[二次电池]
图8示出方形结构的二次电池5。本申请中，二次电池包括锂离子电池、锂硫电池、钠锂离子电池、钠离子电池或镁离子电池等，下文中将主要以锂离子电池为例来描述本申请的构思。应当理解的是，其他任意适当类型的可充电电池都是适用的。
参照图9，本申请一实施例的二次电池5包括外壳(包括壳体51和盖板53)、电极组件52。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。本申请对壳体51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。壳体51具有与容纳腔连通的开口，盖板53能够盖设于开口，以封闭容纳腔。电极组件52封装于容纳腔内。电解液浸润于电极组件52中。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。
电极端子55为两个且设置于盖板53。连接构件54为两个，一个连接构件54连接一个电极端子55和电极组件52的正极极片6，另一个连接构件54连接另一个电极端子55和电极组件52的负极极片7。
另外，以下适当参照附图对本申请的二次电池、电池模块、电池包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，所述正极膜层包括本申请第一方面的正极活性材料。
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，负极第一活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，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。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，负极第二活性材料可包括以下材料中的至少一种：过渡金属氧化物(eg.Fe2O3、Fe3O4、Mn2O3、Co3O4、NiO、ZnO)、含锂过渡金属氧化物(eg.Li 4Ti 5O12)等中的一种或多种，可以理解，将以上任意一种物质单独或任意多种物质混合作为第二负极活 性物质层材料，可达到在负极嵌锂容量为0～300mAh/g范围内，嵌锂电位比所述第一活性材料的嵌锂电位高，在负极脱锂容量为10～300mAh/g范围内，脱锂电位比所述第一活性材料的脱锂电位高。优选的，第二负极活性物质层材料的克容量可大于第一负极活性物质层材料。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)、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，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包含第一活性材料的负极极片：将上述用于制备包含第一活性材料负极浆料的组分，例如第一负极活性材料、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，形成第一活性材料负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到包含第一活性涂层的负极极片。
在一些实施方式中，可以通过以下方式制备包含第一、第二活性材料的负极极片：将上述用于制备第二活性材料负极浆料的组分，例如第二活性材料、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，形成第二活性材料负极浆料；将第二活性材料负极浆料涂覆在包含第一活性涂层的负极极片上，经烘干等工序后，即可得到正极极片。
[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。
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。
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。
图10是作为一个示例的电池模块4。参照图10，在电池模块4中，多个二次电池5可以是沿电池模块4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，多个二次电池5容纳于该容纳空间。
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。
图11和图12是作为一个示例的电池包1。参照图11和图12，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模块4。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模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
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(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，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13是作为一个示例的用电装置。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。为了满足该用电装置对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。
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。该装置通常要求轻薄化，可以采用二次电池作为电源。
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。
一、二次电池的制备
<实施例1>
(1) 负极材料的制备
将作为的第一负极活性材料的石墨与导电剂Super P、增稠剂CMC、粘接剂丁苯橡胶(SBR)在去离子水中混合均匀，制成第一负极浆料。负极浆料中固体含量为53wt％，固体成分中石墨、Super P、CMC及粘接剂丁苯橡胶(SBR)的质量比为96:2:1:1。
将作为的第二负极活性材料的NiO与导电剂Super P、粘结剂聚偏二氟乙烯(PVDF)在N-甲基吡咯烷酮(NMP)中混合均匀，制成第二负极浆料。负极浆料中固体含量为43wt％，固体成分中NiO、Super P、CMC及粘接剂丁苯橡胶(SBR)的质量比为92:6:2。
(2) 负极极片的制备
将第一负极浆料涂布在集流体铜箔上并在85℃下烘干从而形成第一负极活性物质层。然后将第二负极浆料按规定位置涂覆于第一负极活性物质层上，并在85℃下烘干。然后进行冷压、切边、裁片、分条后，在120℃真空条件下烘干12h，制成负极极片。
(3) 正极极片的制备
将正极材料磷酸铁锂、导电剂Super P、粘结剂聚偏二氟乙烯(PVDF)在N-甲基吡咯烷酮(NMP)中制成正极浆料。正极浆料中固体含量为64wt％，固体成分中磷酸铁锂、Super P、PVDF的质量比为97:1:2。将正极浆料涂布在集流体铝箔上并在85℃下烘干后进行冷压，然后进行切边、裁片、分条后，在85℃的真空条件下烘干4h，制成正极极片。
(4) 锂离子电池的制备：
以聚乙烯薄膜(PE)作为隔离膜。将制得的正极片、隔离膜、负极片按顺序叠好，使隔离膜处于正负极片中间起到隔离正负极的作用，卷绕得到裸电芯，焊接极耳，将裸电芯置于外包装中，将上述制备的电解液注入到干燥后的电芯中，封装、静置、化成、整形、容量测试等，完成锂离子电池的制备。
<实施例2>～<实施例11>、<对比例1～3>
实施例2～11的二次电池和对比例1～3的二次电池与实施例1的二次电池制备方法相似，但是调整了第二活性材料的组成和第二活性材料与第一活性材料的质量比，不同的产品参数详见表1。
接下来说明电极组件相关参数的测试过程。
[1]第一及第二活性材料的嵌锂电位的测定方法
将负极材料粉末按一定配方制作成极片后，组装成极片-锂片的半扣式电池并通过小倍率的充放电得到负极材料的不同电位下的充放电总容量，再将第二圈充放电总容量除以极片活性物质质量得到材料的电位-充放电容量曲线。在此，嵌锂电位的取值为第二圈放电过程中电位-容量曲线相应容量对应的电位值。
[2]第一及第二活性材料的脱锂电位的测定方法
将负极材料粉末按一定配方制作成极片后，组装成极片-锂片的半扣式电池并通过小倍率的充放电得到负极材料的不同电位下的充放电总容量，再将第二圈充放电总容量除以极片活性物质质量得到材料的电位-充放电容量曲线。在此，脱锂电位的取值为第二圈充电过程中电 位-容量曲线相应容量对应的电位值。
[3]第一及第二负极活性物质层的容量测定方法
将材料粉末按一定配方制作成极片后，组装成极片-锂片的半扣式电池并通过小倍率的充放电得到扣电容量，再将容量除以极片活性物质质量得到克容量参数，在此，容量的计算方法为：容量(mAh/cm2)＝活性物质克容量(mAh/g)*活性物质层中活性物质的质量(g/cm2)。
[4]正极活性物质层的容量的测定方法
将材料粉末按一定配方制作成极片后，组装成极片-锂片的半扣式电池并通过小倍率的充放电得到扣电容量，再将容量除以极片活性物质质量得到克容量参数，在此，容量的计算方法为：容量(mAh/cm2)＝活性物质克容量(mAh/g)*活性物质层中活性物质的质量(g/cm2)。
二、电池性能测试
对于上述一、[1]～[4]中制得的二次电池，通过下述方法进行性能测试。结果示于表2中。
[1]负极析锂情况
将化成后的电池在25℃下，以2C恒流充电至3.65V，然后以3.65V恒压充电至电流小于0.05C，然后再以1C放电到2.5V，循环10圈后，再以0.33C恒流充电至3.65V，然后以3.65V恒压充电至电流小于0.05C得到满充电池。
将循环了10圈以后的电池拆解，观察负极凸面析锂情况，并记录在下面表格中的“负极凸面析锂情况”一栏中。
观察后的评价基准如下。
不析锂：拐角区域满充负极表面金黄色，用无尘纸擦拭，纸上无灰色金属锂粉。
轻微析锂：拐角区域满充负极表面暗黄色，用无尘纸擦拭，纸上有灰色金属锂粉。
灰斑：拐角区域满充负极表面局部灰色，无金黄色透过。
严重析锂：拐角区域满充负极表面全部是灰色，无金黄色透过。
本申请中，负极凸面析锂的优选次序为不析锂>灰斑>轻微析锂>严重析锂。
[表1]
Figure PCTCN2022099437-appb-000001
表1中，嵌锂或脱锂电位是指嵌锂或脱锂容量为100mAh/g对应的电位。具体地，如图14所示，第一活性材料的嵌锂电位是指在第一活性材料的嵌锂曲线上，对应于比容量为100mAh/g处对应的电位。第一活性材料的脱锂电位是指在第一活性材料的脱锂曲线上，对应于比容量为100mAh/g处对应的电位。类似地，可以得到第二活性材料的嵌锂或脱锂电位。上述电位均是相对于Li/Li +的电位，单位为V。另外，从图14可以看出，在嵌锂容量为0～300mAh/g的范围内，第二活性材料的嵌锂电位比第一活性材料的嵌锂电位高，在脱锂容量为10～300mAh/g范围内，第二活性材料的脱锂电位比第一活性材料的脱锂电位高。
[表2]
Figure PCTCN2022099437-appb-000002
表2中，克容量的单位为mAh/g，容量的单位为mAh/cm 2。
三、各实施例、对比例测试结果分析
从上述表1可以看出：
根据实施例1～11和对比例1的对比可知，通过使负极材料具备第一活性物质层和第二活性物质层且第二活性材料的嵌锂电位和脱锂电位均高于所述第一活性材料，能够大幅改善负极析锂。而对比例1中未设置第二活性物质层，其负极出现轻微析锂。
根据实施例1～6和对比例2的对比可知，通过使负极材料中的第二活性材料的质量比达到一定含量以上，均能够大幅改善负极析锂。但是对比例2中的第二活性材料过多会导致电池质量增加，从保证电池能量密度的角度出发，第二活性材料相对于第一活性材料的质量比优选为2以下，更优选为1以下。
根据实施例1～6和对比例3的对比可知，通过使负极材料中的第二活性材料的质量比达到一定含量以上，能够进一步改善负极析锂。而对比例3中，第二活性材料的质量比较低，其负极出现灰斑。
从上述表2可以看出：
根据实施例1～11和对比例1～3的对比可知，通过第二活性物质层的容量a、所述第一活性物质层的容量b及所述正极活性物质层的容量c之间满足a+b＝nc，n＝1.07～5，能够大幅改善负极析锂。
根据实施例1～11的结果可知，通过使第二负极活性物质的克容量大于第一负极活性物质的克容量，能够提升析锂改善效果。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (17)

  1. 一种负极极片，其中，
    所述负极极片包括：
    集流体；
    第一活性物质层，设置于所述集流体的至少一个表面；以及
    第二活性物质层，设置于所述第一活性物质层远离所述集流体的表面上；
    所述第一活性物质层包括第一活性材料，所述第二活性物质层包括第二活性材料，所述第二活性材料的嵌锂电位和脱锂电位均高于所述第一活性材料。
  2. 根据权利要求1所述的负极极片，其中，
    所述第二活性物质层为多个，且多个所述第二活性物质层间隔设置。
  3. 根据权利要求1或2所述的负极极片，其中，
    在所述负极极片嵌锂容量为0～300mAh/g的范围内，所述第二活性材料的嵌锂电位比所述第一活性材料的嵌锂电位高。
  4. 根据权利要求1或2所述的负极极片，其中，
    在所述负极极片脱锂容量为10～300mAh/g的范围内，所述第二活性材料的脱锂电位比所述第一活性材料的脱锂电位高。
  5. 根据权利要求1～4中任一项所述的负极极片，其中，
    所述第二活性材料的克容量高于所述第一活性材料。
  6. 根据权利要求1～5中任一项所述的负极极片，其中，
    所述第二活性材料的质量与所述第一活性材料的质量之比为0.1～2，可选为0.1～1。
  7. 一种电极组件，其中，
    所述电极组件包括权利要求1～6中任一项所述的负极极片、正极极片以及隔离膜；所述正极极片包括正极活性物质层；
    其中，所述第二活性物质层的容量a、所述第一活性物质层的容量b及所述正极活性物质层的容量c之间满足式(1)
    a+b＝nc，n＝1.07～5  式(1)
    所述式(1)中a、b以及c的单位为mAh/cm 2。
  8. 根据权利要求7所述的电极组件，其中，
    所述负极极片、所述隔离膜以及所述正极极片沿卷绕方向卷绕成卷绕结构；所述卷绕结构包括平面部和连接所述平面部的拐角部；所述第二活性物质层至少部分位于所述拐角部。
  9. 根据权利要求8所述的电极组件，其中，
    所述拐角部包括靠近所述电极组件卷绕起始端的第一拐角部和第二拐角部；所述第二活性物质层位于所述第一拐角部和第二拐角部。
  10. 根据权利要求8或9所述的电极组件，其中，所述负极极片的所述集流体还包括极耳部；所述第二活性物质层还位于所述平面部的与所述极耳部连接的一侧。
  11. 根据权利要求7所述的电极组件，其中，
    所述负极极片、所述隔离膜以及所述正极极片依次堆叠形成叠片结构；所述叠片结构包括中心部和设置于所述中心部四周的边缘部；所述第二活性物质层至少部分位于所述边缘部。
  12. 根据权利要求11所述的电极组件，其中，所述负极极片的所述集流体还包括极耳部；所述第二活性物质层还位于所述边缘部的与所述极耳部连接的一侧。
  13. 一种负极极片的制造方法，用于制造权利要求1～6中任一项所述的负极极片。
  14. 一种二次电池，其中，
    所述二次电池包括权利要求7～12中任一项所述的电极组件。
  15. 一种电池模块，其中，
    所述电池模块包括权利要求14所述的二次电池。
  16. 一种电池包，其中，
    所述电池包包括权利要求15所述的电池模块。
  17. 一种用电装置，其中，
    所述用电装置包括选自权利要求14所述的二次电池、权利要求15所述的电池模块和权利要求16所述的电池包中的至少一种。
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