WO2024103858A1 - 补锂极片及其制备方法、以及包含该补锂极片的电池和用电设备 - Google Patents

补锂极片及其制备方法、以及包含该补锂极片的电池和用电设备 Download PDF

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WO2024103858A1
WO2024103858A1 PCT/CN2023/112008 CN2023112008W WO2024103858A1 WO 2024103858 A1 WO2024103858 A1 WO 2024103858A1 CN 2023112008 W CN2023112008 W CN 2023112008W WO 2024103858 A1 WO2024103858 A1 WO 2024103858A1
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active layer
self
layer
lithium
active
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PCT/CN2023/112008
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English (en)
French (fr)
Inventor
王东浩
景二东
谢浩添
张楠楠
孙信
陈晓
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宁德时代新能源科技股份有限公司
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Publication of WO2024103858A1 publication Critical patent/WO2024103858A1/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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • 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
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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 technical field of secondary batteries, and in particular to a lithium-supplementing electrode sheet and a preparation method thereof, as well as a battery and an electrical device comprising the lithium-supplementing electrode sheet.
  • Positive electrode lithium replenishment is the addition of lithium-containing compounds with high irreversible capacity to the positive electrode of the lithium-ion battery.
  • it can be divided into binary lithium-containing compounds represented by Li 2 O, Li 2 O 2 , and Li 2 S, ternary lithium-containing compounds represented by Li 6 CoO 4 and Li 5 FeO 4 , and organic lithium-containing compounds represented by Li 2 DHBN and Li 2 C 2 O 4 .
  • Positive electrode lithium replenishment materials can be added directly during the homogenization process of the positive electrode slurry, without the need for additional process improvements and at a lower cost, making them more suitable for the current lithium-ion battery manufacturing process and hailed as the most promising lithium replenishment technology.
  • the positive electrode lithium replenishment material has difficulty in effectively exerting its capacity during the process of exerting its capacity.
  • the main purpose of this application is to provide a lithium-replenishing electrode, aiming to improve the capacity of the lithium-replenishing agent in the lithium-replenishing electrode and improve the battery life.
  • the present application proposes a lithium replenishing electrode, which includes a current collector and a coating area arranged on at least one side of the current collector, the coating area includes at least two active layers, and the at least two active layers include a pore former.
  • the two adjacent active layers including the pore former are defined as a first active layer and a second active layer, respectively.
  • the first active layer is arranged on the current collector, and the second active layer is arranged on the side of the first active layer away from the current collector, and the porosity in the second active layer is greater than the porosity in the first active layer.
  • the porosity formed by the pore former in the second active layer is greater than the porosity formed by the pore former in the first active layer.
  • the present application forms different porosities in different active layers through pore-forming agents, and the large porosity of the second active layer close to the electrolyte side is beneficial to improving the electrolyte wettability of the second active layer, improving the efficiency of the first active layer contacting the electrolyte, and further improving the capacity of the lithium supplement in the first active layer to improve the battery life.
  • the pore former comprises a self-sacrificial lithium salt.
  • self-sacrificial lithium salt is used as a pore-forming agent, which is beneficial to improving the energy density of the electrode and avoiding other pore-forming agents that do not exert their capacity occupying the electrode space, resulting in a decrease in the energy density of the electrode.
  • a volume change value of the self-sacrificial lithium salt in the second active layer before and after the reaction is greater than a volume change value of the self-sacrificial lithium salt in the first active layer before and after the reaction.
  • the self-sacrificial lithium salt exerts its capacity or reacts, voids are generated.
  • the volume change value of the self-sacrificial lithium salt in the second active layer before and after the reaction is greater than that of the self-sacrificial lithium salt in the first active layer before and after the reaction.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than that of the self-sacrificial lithium salt in the first active layer; it can also be understood that when the first active layer and the second active layer use different self-sacrificial lithium salts, the greater the volume change value of the self-sacrificial lithium salt before and after the reaction, the larger the pores left, and the more suitable it is for the second active layer.
  • oxalic acid Li 2 C 2 O 4 , Li 2 O, and Li 2 O 2 will react directly, and the volume change value is the largest, which is suitable for the second active layer.
  • Li 2 S can be applied to the first active layer to achieve a porosity difference between the two active layers.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than or equal to the concentration of the self-sacrificial lithium salt in the first active layer.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than or equal to the concentration of the self-sacrificial lithium salt in the first active layer.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than the concentration of the self-sacrificial lithium salt in the first active layer, and the two active layers can have a porosity difference.
  • the concentration of the self-sacrificial lithium salt in the second active layer can be equal to the concentration of the self-sacrificial lithium salt in the first active layer, and the two active layers can have a porosity difference.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than the concentration of the self-sacrificial lithium salt in the first active layer.
  • the volume change values produced by the reaction of the self-sacrificial lithium salts in the two active layers are the same.
  • the concentration of the self-sacrificial lithium salt in the second active layer needs to be greater than the concentration of the self-sacrificial lithium salt in the first active layer, so that the two active layers can have a porosity difference.
  • the total concentration of self-sacrificial lithium salts is defined as x%
  • the total concentration of self-sacrificial lithium salts (the mass of all self-sacrificial lithium salts in each active layer ⁇ the sum of the mass of all active substances and all self-sacrificial lithium salts in each active layer) * 100%
  • the range value of the total concentration x% of self-sacrificial lithium salts is 2%-10%.
  • the total concentration x% of the self-sacrificial lithium salt ranges from 2% to 10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., without specific limitation.
  • the layer concentration of the self-sacrificial lithium salt is defined as yi
  • the layer concentration of the self-sacrificial lithium salt (the mass of the self-sacrificial lithium salt in each active layer ⁇ the sum of the mass of the active material and the self-sacrificial lithium salt in each active layer) * 100%
  • the layer concentration of the self-sacrificial lithium salt in the second active layer is y(i+1), where i ⁇ 1
  • the layer concentration of the self-sacrificial lithium salt in the first active layer is y(i)
  • the difference between the concentration y(i+1) of the self-sacrificial lithium salt in the second active layer and the concentration y(i) of the self-sacrificial lithium salt in the first active layer is 1%-4%, where i ⁇ 1. This indicates that the concentrations of the self-sacrificial lithium salt in the two adjacent active layers are different to form different porosities.
  • the difference in the concentration of the self-sacrificial lithium salt in the two adjacent active layers is 1%-4%, for example, it can be 1%, 2%, 2.5%, 3%, 3.5%, 4%, etc., without specific limitation.
  • the at least two active layers are defined as an A layer active layer and a B layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the concentration y1 of the self-sacrificial lithium salt in the A layer active layer ranges from (x-2)% to (x-0.5)%.
  • At least two active layers are provided with an A layer active layer and a B layer active layer in sequence from a direction close to the current collector to a direction away from the current collector, which means that the A layer active layer and the B layer active layer are provided in sequence from a side close to the current collector to a side away from the current collector, that is, the A layer active layer is the active layer containing a self-sacrificial lithium salt which is closest to the current collector.
  • the layer concentration y1 of the self-sacrificial lithium salt in the active layer of layer A is lower than that of other active layers.
  • the layer concentration y1 of the self-sacrificial lithium salt in the active layer of layer A is in the range of (x-2)%-(x-0.5)%, for example, it can be (x-2)%, (x-1.5)%, (x-1)%, (x-0.5)%, etc., without specific limitation, wherein the range of x is 2-10 as mentioned above, for example, x can be 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., without specific limitation.
  • the concentration y1 of the self-sacrificial lithium salt in the active layer A is in the range of 2%-5%;
  • the concentration y2 of the self-sacrificial lithium salt in the B active layer is in the range of 5%-7%;
  • the at least two active layers are defined as an A layer active layer, a B layer active layer and a C layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the concentration y3 of the self-sacrificial lithium salt in the C layer active layer is in the range of 7%-10%.
  • At least two active layers are defined, and an A-layer active layer, a B-layer active layer, and a C-layer active layer are sequentially arranged from the direction close to the current collector to the direction away from the current collector.
  • the A-layer active layer is closest to the current collector, and the layer concentration y1 of the self-sacrificial lithium salt in the A-layer active layer is lower than that in other active layers.
  • the layer concentration y1 of the self-sacrificial lithium salt in the A-layer active layer is in the range of 2%-5%, for example, it can be 2%, 3%, 4%, 5%, etc., and is not specifically limited.
  • the layer concentration y2 of the self-sacrificial lithium salt in the B-layer active layer is in the range of 5%-7%, for example, it can be 5%, 6%, 7%, etc., and is not specifically limited.
  • the layer concentration y3 of the self-sacrificial lithium salt in the C-layer active layer is in the range of 7%, 8%, 9%, 10%, etc., and is not specifically limited.
  • a concentration difference is formed in each layer of the active layer.
  • the total porosity of the active layer refers to the volume of all pores in each active layer of the lithium-replenishing electrode divided by the sum of the volumes of each active layer in the lithium-replenishing electrode.
  • the total porosity p of the active layer ranges from 20% to 30%, for example, it can be 20%, 22%, 25%, 27%, 30%, etc., without specific limitation. It can be understood that the porosity is not only related to the concentration of the self-sacrificial lithium salt, but also to the compaction density.
  • the porosity of each active layer refers to the pore volume in each active layer of the lithium supplement electrode divided by the volume of each active layer.
  • the difference between the porosity of the second active layer and the porosity of the first active layer is 2%-8%, indicating that the porosity of the second active layer is higher than that of the first active layer, which helps the electrolyte to penetrate into the first active layer through the second active layer.
  • the difference between the porosity of the second active layer and the porosity of the first active layer is 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc., and there is no specific limitation.
  • the at least two active layers are defined as an A-layer active layer and a B-layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the porosity n1 of the A-layer active layer is in the range of 20%-25%.
  • the A-layer active layer is closest to the current collector, and the porosity of the A-layer active layer is lower than that of other active layers.
  • the porosity of the A-layer active layer is 20%-25%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, etc., without specific limitation.
  • the self-sacrificial lithium salt includes at least one of Li 2 C 2 O 4 , Li 2 M1O 2 , Li 2 M2O 3 , Li 5 Fe x M3 (1-x) O 4 and Li 6 Mn y M4 (1-y) O 4 ; wherein M1 includes at least one of Ni, Mn, Cu, Fe, Cr and Mo, M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr and Ru, M3 includes at least one of Al, Nb, Co, Mn, Ni, Mo, Ru and Cr, and M4 includes at least one of Ni, Fe, Cu and Ru.
  • the lithium replenishing material is not limited in the present application.
  • the positive electrode lithium replenishing materials currently reported in the literature can be applied to the present application, including at least one of Li 2 C 2 O 4 , Li 2 M1O 2 , Li 2 M2O 3 , Li 5 Fe x M3 (1-x) O 4 and Li 6 Mn y M4 (1-y) O 4 ; wherein M1 includes at least one of Ni, Mn, Cu, Fe, Cr and Mo, M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr and Ru, M3 includes at least one of Al, Nb, Co, Mn, Ni, Mo, Ru and Cr, and M4 includes at least one of Ni, Fe, Cu and Ru.
  • the positive electrode material in the at least two active layers has a general structural formula of LiMn x Fe y M (1-xy) PO 4 , wherein 0 ⁇ x ⁇ 0.8; 0.1 ⁇ y ⁇ 0.6; 0 ⁇ 1-xy ⁇ 0.2, and M represents a doping element, which may optionally include at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge;
  • the general structural formula of the positive electrode material is LiNi a Co b N (1-ab) O 2 , wherein N optionally includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb, and La, wherein 0.35 ⁇ a ⁇ 1.0, 0 ⁇ b ⁇ 0.35, and 0 ⁇ 1-ab ⁇ 0.35.
  • the general structural formula of the positive electrode material is LiMnxFeyM (1-xy) PO4 , wherein 0 ⁇ x ⁇ 0.8; 0.1 ⁇ y ⁇ 0.6; 0 ⁇ 1-xy ⁇ 0.2, and M represents a doping element, optionally including at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge;
  • the general structural formula of the positive electrode material is LiNiaCobN (1-ab) O2 , wherein N optionally includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb and La, wherein 0.35 ⁇ a ⁇ 1.0, 0 ⁇ b ⁇ 0.35 and 0 ⁇ 1-ab ⁇ 0.35.
  • the positive electrode active materials in the at least two active layers are the same.
  • the present application adopts the same positive electrode active material in at least two active layers, and the same positive electrode coating forms different porosities to avoid the problem of low energy efficiency.
  • the active layer of the lithium supplement electrode further includes a conductive agent and a binder, and the conductive agent includes at least one of graphite, carbon nanotubes, nanofibers, carbon black and graphene;
  • the binder includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene.
  • the conductive agent is used to improve the conductivity of the active layer.
  • the present application does not limit the conductive agent.
  • the conductive agent includes at least one of graphite, carbon nanotubes, nanofibers, carbon black and graphene.
  • it can be selected from SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor grown carbon fiber VGCF, carbon nanotubes CNTs and graphene and at least one of their composite conductive agents.
  • the present application does not limit the binder.
  • the binder is a commonly used binder in the art, and the binder includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene.
  • the present application provides a method for preparing a lithium supplement electrode, comprising the following steps:
  • At least two layers of slurry including pore formers are coated on the current collector, and the lithium replenishing electrode is obtained after drying and cold pressing, wherein the at least two layers of slurry including pore formers form at least two active layers, one of the active layers is arranged on the current collector, and the other active layer is arranged on the side of the one active layer away from the current collector, and the porosity in the other active layer is greater than the porosity in the one active layer.
  • the porosity of the other active layer is greater than that of the first active layer.
  • the large porosity of the other active layer close to the electrolyte is beneficial to improving the electrolyte wettability of the other active layer, improving the efficiency of the first active layer contacting the electrolyte, and further improving the capacity of the lithium supplement in the first active layer to improve the battery life.
  • the porosity formed by the pore former in the other active layer is greater than the porosity formed by the pore former in the first active layer.
  • the present application forms different porosities in different active layers through pore-forming agents, and the large porosity of the other active layer close to the electrolyte side is beneficial to improving the electrolyte wettability of the other active layer, improving the efficiency of one active layer contacting the electrolyte, and further improving the capacity of the lithium supplement agent in one active layer to improve the battery life.
  • the pore former comprises a self-sacrificial lithium salt.
  • self-sacrificial lithium salt is used as a pore-forming agent, which is beneficial to improving the energy density of the electrode and avoiding other pore-forming agents that do not exert their capacity occupying the electrode space, resulting in a decrease in the energy density of the electrode.
  • the present application provides a battery, comprising: a negative electrode plate, a positive electrode plate, a separator and an electrolyte, wherein the positive electrode plate is the lithium supplement plate as described above.
  • the service life of the battery using the above-mentioned lithium-supplementing electrode is improved.
  • the present application provides an electrical device, wherein the electrical device comprises the above-mentioned battery.
  • the performance of the electrical equipment using the battery is improved.
  • the lithium replenishing pole piece of the present application includes a current collector and a coating area arranged on at least one side of the current collector, the coating area includes at least two active layers, at least two active layers include pore formers, and the two adjacent active layers including the pore formers are defined as a first active layer and a second active layer, the first active layer is arranged on the current collector, the second active layer is arranged on the side of the first active layer away from the current collector, and the porosity in the second active layer is greater than the porosity in the first active layer.
  • the large porosity of the second active layer close to the electrolyte side is conducive to improving the electrolyte wettability of the second active layer, improving the efficiency of the first active layer contacting the electrolyte, and further improving the capacity of the lithium replenishing agent in the first active layer to improve the battery life.
  • FIG1 is a schematic diagram of a process for preparing a lithium-supplementing electrode of the present application
  • FIG2 is a schematic structural diagram of an embodiment of a lithium supplement electrode of the present application.
  • FIG3 is a schematic structural diagram of an embodiment of a lithium supplement electrode of the present application.
  • FIG4 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG5 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG4 ;
  • FIG6 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG7 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG8 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG7 ;
  • FIG. 9 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • range disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range.
  • the range defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and 80-110 is listed for a specific parameter, it is understood that the range of 60-110 and 80-120 is also expected.
  • the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is just the abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • Batteries mentioned in this field can be divided into disposable batteries and rechargeable batteries according to whether they are rechargeable.
  • the types of lithium-ion batteries are: lead-acid batteries, nickel-metal hydride batteries and lithium-ion batteries.
  • Lithium-ion batteries are currently widely used in pure electric vehicles and hybrid vehicles. The capacity of lithium-ion batteries used for this purpose is relatively low, but they have larger output and charging current, and also have a longer service life, but the cost is higher.
  • the battery described in the embodiments of the present application refers to a rechargeable battery.
  • the embodiments disclosed in the present application will be described below mainly by taking a lithium-ion battery as an example. It should be understood that the embodiments disclosed in the present application are applicable to any other appropriate type of rechargeable battery.
  • the battery mentioned in the embodiments disclosed in the present application can be directly or indirectly applied to an appropriate device to power the device.
  • the battery mentioned in the embodiments disclosed in this application refers to a single physical module including one or more battery cells to provide a predetermined voltage and capacity.
  • Battery cells are the basic units in a battery, and can generally be divided into cylindrical battery cells, rectangular battery cells, and soft-pack battery cells according to the packaging method. The following will mainly focus on rectangular battery cells. It should be understood that the embodiments described below are also applicable to cylindrical battery cells or soft-pack battery cells in some aspects.
  • a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.
  • Lithium-ion battery cells mainly rely on the movement of lithium ions between the positive electrode sheet and the negative electrode sheet to work.
  • cylindrical battery cells the film structure of three layers of material is wound into a cylindrical electrode assembly, while in rectangular battery cells, the film structure is wound or stacked into an electrode assembly with a roughly rectangular shape.
  • the battery cell includes a shell, an electrode assembly and an electrolyte.
  • the electrode assembly is contained in the shell of the battery cell, and the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator.
  • the shell includes a shell and an end cap.
  • the shell includes a housing formed by a plurality of walls and an opening. The end cap is arranged at the opening to close the housing chamber.
  • the housing chamber also contains an electrolyte.
  • the positive electrode sheet and the negative electrode sheet in the electrode assembly include tabs. In order to ensure that a large current passes without melting, the number of positive tabs is multiple and stacked together, and the number of negative tabs is multiple and stacked together.
  • the tabs are electrically connected to the electrode terminals located outside the battery cell through connecting members, and the electrode terminals generally include a positive electrode terminal and a negative electrode terminal.
  • the electrode terminal is generally arranged at the end cap portion.
  • a plurality of battery cells are connected in series and/or in parallel via the electrode terminals for application in various applications.
  • the application of batteries includes three levels: battery cells, battery modules and batteries.
  • the battery module is formed by electrically connecting a certain number of battery cells together and placing them in a frame in order to protect the battery cells from external impact, heat, vibration, etc.
  • the battery refers to the final state of the battery system installed in the electric vehicle.
  • the battery generally includes a box for encapsulating one or more battery cells.
  • the box generally consists of a cover and a box shell.
  • a plurality of mounting points for connecting with the vehicle body are arranged on the frame of the box or in the middle of the box shell. In order to improve the stability of the connection between the vehicle body and the battery, mounting parts are often arranged at the mounting points.
  • multiple battery cells are first integrated into a battery module, and then the battery module is packaged in a battery box to form a battery pack/battery box.
  • Commonly used battery modules generally include two end plates, between which multiple battery cells are arranged.
  • the end plate with the output pole of the battery module is also called the output pole end plate, and the end plate without the output pole of the battery module is also called the non-output pole end plate.
  • a battery pack may contain multiple battery modules in one row or multiple rows.
  • the arrangement of multiple rows of multiple battery modules may be double rows and multiple columns, multiple rows and double columns, multiple rows and multiple columns, etc.
  • the first end plate of each column is generally a head output extreme plate
  • the two adjacent end plates between two rows of battery modules are middle non-output extreme plates
  • the last end plate of each column is a tail non-output extreme plate
  • the head output extreme plate and one of the middle non-output extreme plates belong to the first row of battery modules
  • one of the middle non-output extreme plates and the tail output extreme plate belong to the second row of battery modules.
  • the battery module needs to be packaged into the battery box with the help of tooling, which is generally equipped with a clamping mechanism for clamping the battery module, such as a clamping claw, a suction cup, etc.
  • a clamping claw groove that matches the clamping claw is generally provided on the side of the end plate away from the battery cell, so that the clamping claw can be inserted to clamp and transport the battery module.
  • the lithium-supplementing material In the process of releasing Li + , the lithium-supplementing material needs a certain space and medium to transfer Li + from the active layer. In theory, the closer the lithium-supplementing material is to the electrolyte, the more conducive it is to releasing Li + and replenishing the loss of Li + . Similarly, the lithium-supplementing material close to the current collector is farther away from the electrolyte, the electrolyte infiltration is poor, the ion conductivity is poor, and it is not conducive to Li + release, which makes it difficult to fully utilize the capacity of the lithium-supplementing material.
  • the present application provides a lithium replenishing electrode, which includes a current collector and a coating area arranged on at least one side of the current collector, the coating area includes at least two active layers, and at least two active layers include a pore former.
  • the two adjacent active layers including the pore former are defined as a first active layer and a second active layer, respectively.
  • the first active layer is arranged on the current collector, and the second active layer is arranged on the side of the first active layer away from the current collector, and the porosity in the second active layer is greater than the porosity in the first active layer.
  • the current collector refers to the structure or part that collects current. In lithium-ion batteries, it mainly refers to metal foil, such as copper foil and aluminum foil.
  • the current collector is used as a substrate to attach the positive or negative active material, and plays the role of collecting the current generated by the active material and outputting a large current to the outside.
  • aluminum foil is used as the positive current collector
  • copper foil is used as the negative current collector.
  • the active layer refers to a layered structure including an active material, wherein the active material refers to the positive electrode active material involved in the positive electrode, and the positive electrode active material can use a compound that can reversibly embed and de-embed Li + .
  • Pore-forming agent is an additive that creates a pore structure in the material.
  • the two adjacent active layers including the pore former are respectively the first active layer and the second active layer, which refers to the two adjacent active layers containing the pore former, which are respectively the first active layer and the second active layer.
  • the first active layer and the second active layer can be two active layers in contact, and a third active layer not containing the pore former can also be arranged between the first active layer and the second active layer, that is, the active layer not containing the pore former separates the two active layers containing the pore former.
  • the first active layer is arranged on the current collector, and the second active layer is arranged on the side of the first active layer away from the current collector, which means that the first active layer is closer to the current collector than the second active layer. It can be understood that the first active layer is directly arranged on the current collector. It can also be understood that an active layer not containing a lithium supplement agent is arranged between the first active layer and the current collector.
  • the porosity of the second active layer close to the electrolyte side is made higher than the porosity of the first active layer close to the current collector side, so as to facilitate the infiltration of the electrolyte from the second active layer to the first active layer and improve the capacity of the lithium replenisher distributed in the first active layer, that is, to facilitate the release of Li + from the lithium replenisher material close to the current collector side.
  • the porosity formed by the pore former in the second active layer is greater than the porosity formed by the pore former in the first active layer.
  • the present application forms different porosities in different active layers through pore-forming agents, and the large porosity of the second active layer close to the electrolyte side is beneficial to improving the electrolyte wettability of the second active layer, improving the efficiency of the first active layer contacting the electrolyte, and further improving the capacity of the lithium supplement in the first active layer to improve the battery life.
  • FIG. 2 it is a structural schematic diagram of an embodiment of the lithium replenishing electrode of the present application.
  • Active layers on both sides are arranged on the current collector 10, namely, an A layer active layer and a B layer active layer.
  • the A layer active layer is closer to the current collector.
  • Pore formers are arranged in the A layer active layer and the B layer active layer, and the porosity formed by the pore former in the B layer active layer is greater than the porosity formed by the pore former in the A layer active layer.
  • the ability of the A layer active layer to infiltrate the electrolyte is improved, which is beneficial to the release of Li + of the lithium replenishing material in the A layer active layer, so that the lithium replenishing agent can effectively exert its capacity and improve the battery life.
  • the pore former includes a self-sacrificial lithium salt.
  • Self-sacrificial lithium salts also known as lithium supplement materials
  • lithium supplement materials refer to pore-forming agents that can provide lithium ions, that is, after the self-sacrificial lithium salts exert their capacity, gaps are left. It can be understood that after the lithium supplement materials exert their capacity, the material density is significantly reduced (for example, Li 2 S becomes S), or is directly completely reacted (lithium oxalate generates CO 2 ), unlike the positive electrode active material that repeatedly expands and contracts during the cycle process, which can leave permanent gaps in the electrode.
  • self-sacrificial lithium salt is used as a pore-forming agent, which is beneficial to improving the energy density of the electrode and avoiding other pore-forming agents that do not exert their capacity occupying the electrode space, resulting in a decrease in the energy density of the electrode.
  • volume change value of the self-sacrificial lithium salt in the second active layer before and after the reaction is greater than the volume change value of the self-sacrificial lithium salt in the first active layer before and after the reaction.
  • the self-sacrificial lithium salt exerts its capacity or reacts, voids are generated.
  • the volume change value of the self-sacrificial lithium salt in the second active layer before and after the reaction is greater than that of the self-sacrificial lithium salt in the first active layer before and after the reaction.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than that of the self-sacrificial lithium salt in the first active layer; it can also be understood that when the first active layer and the second active layer use different self-sacrificial lithium salts, the greater the volume change value of the self-sacrificial lithium salt before and after the reaction, the larger the pores left, and the more suitable it is for the second active layer.
  • oxalic acid Li 2 C 2 O 4 , Li 2 O, and Li 2 O 2 will react directly, and the volume change value is the largest, which is suitable for the second active layer.
  • Li 2 S can be applied to the first active layer to achieve a porosity difference between the two active layers.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than or equal to the concentration of the self-sacrificial lithium salt in the first active layer.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than or equal to the concentration of the self-sacrificial lithium salt in the first active layer.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than the concentration of the self-sacrificial lithium salt in the first active layer, and the two active layers can have a porosity difference.
  • the concentration of the self-sacrificial lithium salt in the second active layer can be equal to the concentration of the self-sacrificial lithium salt in the first active layer, and the two active layers can have a porosity difference.
  • the concentration of the self-sacrificial lithium salt in the second active layer is greater than the concentration of the self-sacrificial lithium salt in the first active layer.
  • the volume change values produced by the reaction of the self-sacrificial lithium salts in the two active layers are the same.
  • the concentration of the self-sacrificial lithium salt in the second active layer needs to be greater than the concentration of the self-sacrificial lithium salt in the first active layer, so that the two active layers can have a porosity difference.
  • the total concentration of self-sacrificial lithium salts is defined as x%
  • the total concentration of self-sacrificial lithium salts (the mass of all self-sacrificial lithium salts in each active layer ⁇ the sum of the mass of all active substances and all self-sacrificial lithium salts in each active layer) * 100%
  • the range value of the total concentration of self-sacrificial lithium salts x% is 2%-10%.
  • the mass of all self-sacrificial lithium salts in each active layer refers to the sum of the mass of the self-sacrificial lithium salts in each active layer of the lithium supplement electrode.
  • the sum of the mass of all active materials and all self-sacrificial lithium salts in each active layer refers to the sum of the mass of active materials and self-sacrificial lithium salts in each active layer of the lithium supplement electrode.
  • the total concentration of self-sacrificial lithium salt refers to the total concentration of self-sacrificial lithium salt in the lithium replenishing electrode.
  • the total concentration x% of the self-sacrificial lithium salt ranges from 2% to 10%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., without specific limitation.
  • the layer concentration of self-sacrificial lithium salt refers to the concentration of self-sacrificial lithium salt in each active layer of the lithium-replenishing electrode.
  • the lithium-replenishing electrode has two active layers, active layer A (98g of active material, 2g of self-sacrificial lithium salt) and active layer B (96g of active material, 4g of self-sacrificial lithium salt).
  • the difference between the concentration y(i+1) of the self-sacrificial lithium salt in the second active layer and the concentration y(i) of the self-sacrificial lithium salt in the first active layer is 1%-4%, where i ⁇ 1. This indicates that the concentrations of the self-sacrificial lithium salt in the two adjacent active layers are different to form different porosities.
  • the difference in the concentration of the self-sacrificial lithium salt in the two adjacent active layers is 2%-4%, for example, it can be 1%, 2%, 2.5%, 3%, 3.5%, 4%, etc., without specific limitation.
  • the concentration of the self-sacrificial lithium salt in the second active layer close to the electrolyte is greater than the concentration of the self-sacrificial lithium salt in the first active layer close to the current collector, which facilitates the self-sacrificial lithium salt in the second active layer to exert its capacity. Because the second active layer is close to the electrolyte, the electrolyte is well infiltrated, the ions are well conductive, and the high concentration of the self-sacrificial lithium salt can effectively exert its capacity.
  • the self-sacrificial lithium salt after the self-sacrificial lithium salt exerts its capacity, the self-sacrificial lithium salt leaves pores in the active layer, that is, the porosity of the second active layer close to the electrolyte is high, and the porosity of the first active layer close to the current collector is low.
  • the electrolyte can effectively infiltrate the first active layer with low porosity through the second active layer with high porosity, thereby improving the rate performance.
  • this structural setting not only enables the lithium-replenishing materials in the second active layer to exert their capacity, but also changes the distribution of the porosity of the active layer and improves the wetting effect of the first active layer, thereby helping to improve the capacity of the lithium-replenishing materials in the first active layer and improve the rate performance.
  • At least two active layers are defined as an A layer active layer and a B layer active layer arranged in sequence from close to the current collector to far away from the current collector, and the concentration y1 of the self-sacrificial lithium salt in the A layer active layer ranges from (x-2)% to (x-0.5)%.
  • At least two active layers are provided with an A layer active layer and a B layer active layer in sequence from a direction close to the current collector to a direction away from the current collector, which means that the A layer active layer and the B layer active layer are provided in sequence from a side close to the current collector to a side away from the current collector, that is, the A layer active layer is the active layer containing a self-sacrificial lithium salt which is closest to the current collector.
  • the layer concentration y1 of the self-sacrificial lithium salt in the active layer of layer A is lower than that of other active layers.
  • the layer concentration y1 of the self-sacrificial lithium salt in the active layer of layer A is in the range of (x-2)%-(x-0.5)%, for example, it can be (x-2)%, (x-1.5)%, (x-1)%, (x-0.5)%, etc., without specific limitation, wherein the range of x is 2-10 as mentioned above, for example, x can be 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., without specific limitation.
  • the layer concentration y1 of the self-sacrificial lithium salt in the A layer active layer is in the range of 2%-5%; and/or, the layer concentration y2 of the self-sacrificial lithium salt in the B layer active layer is in the range of 5%-7%; and/or, at least two active layers are defined as being arranged in sequence from close to the current collector to far away from the current collector, namely, the A layer active layer, the B layer active layer and the C layer active layer, and the layer concentration y3 of the self-sacrificial lithium salt in the C layer active layer is in the range of 7%-10%.
  • At least two active layers are defined, and an A-layer active layer, a B-layer active layer, and a C-layer active layer are sequentially arranged from the direction close to the current collector to the direction away from the current collector.
  • the A-layer active layer is closest to the current collector, and the layer concentration y1 of the self-sacrificial lithium salt in the A-layer active layer is lower than that of other active layers.
  • the layer concentration y1 of the self-sacrificial lithium salt in the A-layer active layer is in the range of 2%-5%, for example, it can be 2%, 3%, 4%, 5%, etc., and is not specifically limited.
  • the layer concentration y2 of the self-sacrificial lithium salt in the B-layer active layer is in the range of 5%-7%, for example, it can be 5%, 6%, 7%, etc., and is not specifically limited.
  • the layer concentration y3 of the self-sacrificial lithium salt in the C-layer active layer is in the range of 7%, 8%, 9%, 10%, etc., and is not specifically limited.
  • a concentration difference is formed in each layer of the active layer.
  • the total porosity p of the active layer is (pore volume ⁇ the sum of the volumes of each active layer)*100%, and the range of the total porosity p of the active layer is 20%-30%.
  • V0 is the volume of the material in its natural state
  • V is the volume of all voids in the material.
  • the total porosity of the active layer refers to the volume of all pores in each active layer of the lithium-replenishing electrode divided by the sum of the volumes of each active layer in the lithium-replenishing electrode.
  • the total porosity of the active layer ranges from 20% to 30%, for example, it can be 20%, 22%, 25%, 27%, 30%, etc., without specific limitation. It can be understood that the porosity is not only related to the concentration of the self-sacrificial lithium salt, but also to the compaction density.
  • the porosity of each active layer refers to the pore volume in each active layer of the lithium supplement electrode divided by the volume of each active layer.
  • the difference between the porosity of the second active layer and the porosity of the first active layer is 2%-8%, indicating that the porosity of the second active layer is higher than that of the first active layer, which helps the electrolyte to infiltrate the first active layer through the second active layer.
  • the difference between the porosity of the second active layer and the porosity of the first active layer is 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc., and there is no specific limitation.
  • At least two active layers are sequentially provided with an A layer active layer and a B layer active layer from close to the current collector to far away from the current collector, and the porosity n1 of the A layer active layer is in the range of 20%-25%.
  • the A-layer active layer is closest to the current collector, and the porosity of the A-layer active layer is lower than that of other active layers.
  • the porosity of the A-layer active layer is 20%-25%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, etc., without specific limitation.
  • the self-sacrificial lithium salt includes at least one of Li 2 C 2 O 4 , Li 2 M1O 2 , Li 2 M2O 3 , Li 5 Fe x M3 (1-x) O 4 and Li 6 Mn y M4 (1-y) O 4 ; wherein M1 includes at least one of Ni, Mn, Cu, Fe, Cr and Mo, M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr and Ru, M3 includes at least one of Al, Nb, Co, Mn, Ni, Mo, Ru and Cr, and M4 includes at least one of Ni, Fe, Cu and Ru.
  • the lithium replenishing material is not limited in the present application.
  • the positive electrode lithium replenishing materials currently reported in the literature can be applied to the present application, including at least one of Li 2 C 2 O 4 , Li 2 M1O 2 , Li 2 M2O 3 , Li 5 Fe x M3 (1-x) O 4 and Li 6 Mn y M4 (1-y) O 4 ; wherein M1 includes at least one of Ni, Mn, Cu, Fe, Cr and Mo, M2 includes at least one of Ni, Mn, Fe, Mo, Zr, Si, Cu, Cr and Ru, M3 includes at least one of Al, Nb, Co, Mn, Ni, Mo, Ru and Cr, and M4 includes at least one of Ni, Fe, Cu and Ru.
  • the positive electrode material in at least two active layers has a general structural formula of LiMnxFeyM (1-xy) PO4 , wherein 0 ⁇ x ⁇ 0.8; 0.1 ⁇ y ⁇ 0.6; 0 ⁇ 1-xy ⁇ 0.2, and M represents a doping element, optionally including at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge ; and/or, the positive electrode material has a general structural formula of LiNiaCobN (1-ab) O2 , wherein N optionally includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb and La, wherein 0.35 ⁇ a ⁇ 1.0, 0 ⁇ b ⁇ 0.35, and 0 ⁇ 1-ab ⁇ 0.35.
  • the general structural formula of the positive electrode material is LiMnxFeyM (1-xy) PO4 , wherein 0 ⁇ x ⁇ 0.8; 0.1 ⁇ y ⁇ 0.6; 0 ⁇ 1-xy ⁇ 0.2, and M represents a doping element, optionally including at least one of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb and Ge;
  • the general structural formula of the positive electrode material is LiNiaCobN (1-ab) O2 , wherein N optionally includes at least one of Mn, Zr, Al, B, Ta, Mo, W, Nb, Sb and La, wherein 0.35 ⁇ a ⁇ 1.0, 0 ⁇ b ⁇ 0.35 and 0 ⁇ 1-ab ⁇ 0.35.
  • the positive electrode active materials in at least two active layers are the same.
  • the present application adopts the same positive electrode active material in at least two active layers, and the same positive electrode coating forms different porosities to avoid the problem of low energy efficiency.
  • the active layer of the lithium replenishing electrode also includes a conductive agent and a binder
  • the conductive agent includes at least one of graphite, carbon nanotubes, nanofibers, carbon black and graphene
  • the binder includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene.
  • the conductive agent is used to improve the conductivity of the active layer.
  • the present application does not limit the conductive agent.
  • the conductive agent includes at least one of graphite, carbon nanotubes, nanofibers, carbon black and graphene.
  • it can be selected from SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor grown carbon fiber VGCF, carbon nanotubes CNTs and graphene and at least one of their composite conductive agents.
  • the present application does not limit the binder.
  • the binder is a commonly used binder in the art, and the binder includes at least one of polypropylene, polyethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene and polyhexafluoropropylene.
  • the present application provides a method for preparing a lithium supplement electrode, comprising the following steps:
  • At least two layers of slurry including pore formers are coated on the current collector, and the lithium replenishing electrode is obtained after drying and cold pressing, wherein the at least two layers of slurry including pore formers form at least two active layers, one active layer is arranged on the current collector, and the other active layer is arranged on the side of the one active layer away from the current collector, and the porosity in the other active layer is greater than the porosity in the one active layer.
  • the porosity of the other active layer is greater than that of the first active layer.
  • the large porosity of the other active layer close to the electrolyte is beneficial to improving the electrolyte wettability of the other active layer, improving the efficiency of the first active layer contacting the electrolyte, and further improving the capacity of the lithium supplement in the first active layer to improve the battery life.
  • the porosity formed by the pore former in the other active layer is greater than the porosity formed by the pore former in the one active layer.
  • the present application forms different porosities in different active layers through pore-forming agents, and the large porosity of the other active layer close to the electrolyte side is beneficial to improving the electrolyte wettability of the other active layer, improving the efficiency of one active layer contacting the electrolyte, and further improving the capacity of the lithium supplement agent in one active layer to improve the battery life.
  • the pore former includes a self-sacrificial lithium salt.
  • self-sacrificial lithium salt is used as a pore-forming agent, which is beneficial to improving the energy density of the electrode and avoiding other pore-forming agents that do not exert their capacity occupying the electrode space, resulting in a decrease in the energy density of the electrode.
  • the present application also provides a battery, including: a negative electrode plate, a positive electrode plate, a separator and an electrolyte, wherein the positive electrode plate is the lithium supplement plate as described above. Since the lithium supplement plate adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.
  • the service life of the battery using the above-mentioned lithium-supplementing electrode is improved.
  • the present application also provides an electrical device, which includes the above-mentioned battery. Since the battery adopts all the technical solutions of all the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be described one by one here.
  • the performance of the electrical equipment using the battery is improved.
  • 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 removed 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 arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time to allow ions to pass through.
  • the separator is the separator improved above in this application.
  • the positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.
  • 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 when the secondary battery is a lithium-ion battery, may be a positive electrode active material for lithium-ion batteries 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 battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states.
  • the molar content of Li is the initial state of the material, that is, the state before feeding.
  • the positive electrode material is used in the battery system, and the molar content of Li will change after charge and discharge cycles.
  • the molar content of O is only a theoretical value.
  • the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.
  • 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, for example, 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 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 may be prepared by the following method: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the 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 processes such as drying and cold pressing, 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.
  • a metal foil a 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 adopt the negative electrode active material for the battery known in the art.
  • 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 a role in conducting ions between the positive electrode and the negative electrode.
  • the present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.
  • 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 structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the diaphragm can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the diaphragm 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.
  • FIG4 is a battery cell 5 of a square structure as an example.
  • the outer package may include a housing 51 and a cover plate 53.
  • the housing 51 may include a bottom plate and a connection plate.
  • the side plates on the bottom plate, the bottom plate and the side plates enclose to form a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can choose according to specific actual needs.
  • battery cells may be assembled into a battery module.
  • the number of battery cells 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.
  • FIG6 is a battery module 4 as an example.
  • multiple battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the multiple battery cells 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.
  • 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.
  • FIG7 and FIG8 are battery packs 1 as an example.
  • 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 body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4.
  • the plurality of 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 in the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device.
  • the electrical 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, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • FIG9 is an example of an electric device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module may be used.
  • the device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • a device is usually required to be light and thin, and a secondary battery may be used as a power source.
  • the positive electrode active material, lithium supplement material, conductive agent (CNT), and binder (PVDF) are mixed evenly in different mass ratios, and then NMP is added as a solvent.
  • the mixture is stirred under the action of a vacuum mixer until the system becomes uniform to obtain a positive electrode active slurry.
  • Different positive electrode active slurries are uniformly coated on the substrate in turn, dried, and cold pressed to obtain a positive electrode sheet.
  • the positive electrode sheet, isolation film, and negative electrode sheet are stacked in order so that the isolation film is placed between the cathode and the negative electrode to play an isolating role, and then wound to obtain a bare battery cell.
  • the bare battery cell is placed in an outer package, and the electrolyte is injected and packaged to obtain a battery cell.
  • Active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carbon methyl cellulose (CMC) are fully stirred and mixed in a deionized water solvent system in a certain weight ratio (such as 96.5:0.7:1.8:1), and then coated on a current collector (such as copper foil), dried, and cold pressed to obtain a negative electrode sheet.
  • a deionized water solvent system such as 96.5:0.7:1.8:1
  • Lithium-replenishing electrode including two active layers
  • the active layer formula of layer A is 97% (98% LFP + 2% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the active layer formula of layer B is 97% (93% LFP + 7% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium replenishing electrode is m
  • the mass of Li 2 C 2 O 4 is n
  • the layer concentration of self-sacrificial lithium salt in the A layer active layer is 2%
  • the layer concentration of self-sacrificial lithium salt in the B layer active layer is 7%.
  • Lithium-replenishing electrode including three active layers
  • the active layer formula of layer A is 97% (98% LFP + 2% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the active layer formula of layer B is 97% (93% LFP + 5% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the C layer active layer formula is 97% (93% LFP + 7% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium-replenishing electrode is m
  • the mass of Li 2 C 2 O 4 is n
  • the layer concentration of self-sacrificial lithium salt in the A layer active layer is 2%
  • the layer concentration of self-sacrificial lithium salt in the B layer active layer is 5%
  • the layer concentration of self-sacrificial lithium salt in the C layer active layer is 7%.
  • Lithium-replenishing electrode including three active layers
  • the active layer formula of layer A is 97% (98% LFP + 2% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the active layer formula of layer B is 97% (93% LFP + 6% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the C layer active layer formula is 97% (93% LFP + 7% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium-replenishing electrode is m
  • the mass of Li 2 C 2 O 4 is n
  • the layer concentration of self-sacrificial lithium salt in the A layer active layer is 2%
  • the layer concentration of self-sacrificial lithium salt in the B layer active layer is 6%
  • the layer concentration of self-sacrificial lithium salt in the C layer active layer is 7%.
  • Lithium-replenishing electrode including two active layers
  • the active layer formula of layer A is 97% (98% LFP + 2% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the active layer formula of layer B is 97% (93% LFP + 5% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium supplement electrode is m
  • the mass of Li 2 C 2 O 4 is n
  • the layer concentration of self-sacrificial lithium salt in the A layer active layer is 2%
  • the layer concentration of self-sacrificial lithium salt in the B layer active layer is 5%.
  • Lithium-replenishing electrode including two active layers
  • the active layer formula of layer B is 97% (95% LFP + 5% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium replenishing electrode is m
  • the mass of Li 2 C 2 O is n1
  • the mass of Li 2 S is n2
  • the layer concentration of self-sacrificial lithium salt in the A layer active layer is 5%
  • the layer concentration of self-sacrificial lithium salt in the B layer active layer is 5%.
  • Lithium-replenishing electrode including two active layers
  • the active layer formula of layer A is 97% (99.5% LFP + 0.5% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the active layer formula of layer B is 97% (96.5% LFP + 3.5% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium supplement electrode is m
  • the mass of Li 2 C 2 O 4 is n
  • the concentration of self-sacrificial lithium salt in the A active layer is 0.5%
  • the concentration of self-sacrificial lithium salt in the B active layer is 3.5%.
  • Lithium-replenishing electrode including two active layers
  • the active layer formula of layer A is 97% (92% LFP + 8% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the active layer formula of layer B is 97% (88% LFP + 12% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium supplement electrode is m
  • the mass of Li 2 C 2 O 4 is n
  • the layer concentration of self-sacrificial lithium salt in the A layer active layer is 8%
  • the layer concentration of self-sacrificial lithium salt in the B layer active layer is 12%.
  • the active layer formula of layer A is 97% (95% LFP + 5% Li 2 C 2 O 4 ) + 0.8% CNT + 2.2% PVDF;
  • the mass of LFP in the lithium supplement electrode is m
  • the mass of Li 2 C 2 O 4 is n
  • the active layer formula of layer A is 97% LFP+0.8% CNT+2.2% PVDF.
  • the mass of LFP in the lithium supplement electrode is m
  • the mass of Li 2 C 2 O 4 is n1
  • the mass of Li 2 S is n2.
  • the battery (D0) is charged to a certain voltage to allow the lithium supplement material to exert its capacity and leave permanent gaps in the electrode.
  • the battery is then discharged to the initial state (D1).
  • the electrolyte in the electrode is evaporated, and a new isolation membrane is replaced.
  • the batteries are reassembled into batteries E0 and E1 respectively, and the electrolyte infiltration rates V0 and V1 of E0 and E1 are tested.
  • the battery state in this experiment is 3.0V.
  • the lithium-ion battery was charged at a constant current of 1/3C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, left to stand for 5 min, and then discharged at 1/3C to 2.5V to record the discharge capacity C0.
  • the lithium-ion battery was then charged at a constant current of 1.0C to 3.65V, left to stand for 5 minutes, and then discharged at 1/3C to 2.5V and the discharge capacity C1 was recorded.
  • Tables 1-3 are the parameters of various embodiments and comparative examples, and Table 4 is the performance parameter table of various embodiments and comparative examples. It can be seen from Table 4 that:
  • Embodiment 1, embodiment 4, embodiment 5, embodiment 6 and embodiment 7 are two-layer active layer structures. It can be seen that as the total concentration of self-sacrificial lithium salt decreases by X%, the capacity retention rate and the capacity performance of lithium supplement material decrease. Therefore, while maintaining the concentration gradient of self-sacrificial lithium salt in each layer, the total concentration of self-sacrificial lithium salt still needs to be maintained within a certain range. It can be understood that too little lithium supplement leads to a small improvement in the cycle. Therefore, the total concentration x% of self-sacrificial lithium salt is not less than 2%; at the same time, too much lithium supplement and lithium supplement generally have poor conductivity.
  • the total concentration x% of sacrificial lithium salt does not exceed 10%.
  • Comparative Example 3 is a lithium-replenishing electrode sheet including an active layer. Compared with Example 5, under the same total concentration of self-sacrificial lithium salt, the performance of the layered lithium-replenishing electrode sheet is better than that of the single-layer lithium-replenishing electrode sheet. For example, the capacity retention rate and the capacity utilization performance of the lithium-replenishing material of Example 5 are higher than those of Comparative Example 3.
  • Embodiments 2 and 3 are lithium-supplementing electrodes comprising three active layers. Compared with Embodiment 3 and Embodiment 5, the more layers there are, the faster the electrolyte infiltration rate is, and the higher the rate performance is.

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Abstract

一种补锂极片及其制备方法、以及包含该补锂极片的电池和用电设备。补锂极片包括集流体和设置在集流体至少一侧面的涂布区域，涂布区域包括至少两层活性层，至少两层活性层中包括造孔剂，包括造孔剂的相邻的两活性层分别为第一活性层和第二活性层，第一活性层设于集流体，第二活性层设于第一活性层背离集流体的一侧，第二活性层中的孔隙率大于第一活性层中的孔隙率。靠近电解液侧的第二活性层的大的孔隙率有利于提高第二活性层的电解液浸润性，提高第一活性层接触电解液的效率，进一步提高第一活性层中补锂剂的容量发挥，以改善电池寿命。

Description

补锂极片及其制备方法、以及包含该补锂极片的电池和用电设备
相关申请
本申请要求于2022年11月17日申请的、申请号为202211442548.2的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及二次电池技术领域，特别涉及一种补锂极片及其制备方法、以及包含该补锂极片的电池和用电设备。
背景技术
正极补锂是向锂离子电池的正极中添加具有高不可逆容量的含锂化合物，根据化合物的种类不同，可以分为以Li2O、Li2O2、Li2S为代表的二元含锂化合物，以Li6CoO4、Li5FeO4为代表的三元含锂化合物和以Li2DHBN、Li2C2O4为代表的有机含锂化合物。
正极补锂材料可以直接在正极浆料的匀浆过程中添加，无需额外的工艺改进且成本较低，因而更加适合现在的锂离子电池制造工艺，被誉为最有前景的补锂技术。尽管如此，补锂工艺还存在一些问题，例如，正极补锂材料在发挥容量的过程中，存在补锂剂难以有效发挥容量的问题。
发明内容
本申请的主要目的是提供一种补锂极片，旨在提高补锂极片中补锂剂的容量发挥，改善电池寿命。
为实现上述目的，本申请提出的一种补锂极片，所述补锂极片包括集流体和设置在所述集流体至少一侧面的涂布区域，所述涂布区域包括至少两层活性层，所述至少两层活性层中包括造孔剂，定义包括造孔剂的相邻的两所述活性层分别为第一活性层和第二活性层，所述第一活性层设于所述集流体，所述第二活性层设于所述第一活性层背离所述集流体的一侧，所述第二活性层中的孔隙率大于所述第一活性层中的孔隙率。
可选地，所述第二活性层中的造孔剂形成的孔隙率大于所述第一活性层中的造孔剂形成的孔隙率。
本申请通过造孔剂在不同活性层中形成不同的孔隙率，且靠近电解液侧的第二活性层的大的孔隙率有利于提高第二活性层的电解液浸润性，提高第一活性层接触电解液的效率，进一步提高第一活性层中补锂剂的容量发挥，以改善电池寿命。
可选地，所述造孔剂包括自牺牲锂盐。
本申请中采用自牺牲锂盐作为造孔剂，有利于提高极片的能量密度，避免其他不发挥容量的造孔剂占用极片空间，造成极片能量密度降低。
可选地，所述第二活性层中的自牺牲锂盐的反应前后的体积变化值大于所述第一活性层中的自牺牲锂盐的反应前后的体积变化值。
自牺牲锂盐在发挥容量后或发生反应后产生空隙，为了使第二活性层的孔隙率大于第一活性层的孔隙率，则第二活性层中的自牺牲锂盐的反应前后的体积变化值大于第一活性层中的自牺牲锂盐的反应前后的体积变化值。可以理解的是，在第一活性层和第二活性层采用同种自牺牲锂盐的情况下，第二活性层中的自牺牲锂盐的浓度大于第一活性层中的自牺牲锂盐的浓度；还可以理解的是，在第一活性层和第二活性层采用不同种自牺牲锂盐的情况下，自牺牲锂盐反应前后的体积变化值越大，留下的孔越大，越适合第二活性层，例如，草酸Li2C2O4、Li2O、Li2O2会直接反应完，体积变化值最大，适合第二活性层，相比之下，Li2S可以应用于第一活性层，以实现两活性层具有孔隙率差。
可选地，所述第二活性层中的至少一种自牺牲锂盐与所述第一活性层中的至少一种自牺牲锂盐种类不同时，所述第二活性层中的自牺牲锂盐的浓度大于等于所述第一活性层中的自牺牲锂盐的浓度。
考虑到活性层中的自牺牲锂盐的种类可能是多种，当第二活性层中的至少一种自牺牲锂盐与第一活性层中的至少一种自牺牲锂盐种类不同时，第二活性层中的自牺牲锂盐的浓度大于等于第一活性层中的自牺牲锂盐的浓度。例如，当两种不同的自牺牲锂盐反应后产生的体积变化值相同时，则第二活性层中的自牺牲锂盐的浓度在大于第一活性层中的自牺牲锂盐的浓度时，可以形成两活性层具有孔隙率差。当两种不同的自牺牲锂盐反应后产生的体积变化值不同时，且第二活性层中的自牺牲锂盐反应后产生的体积变化值大于第一活性层中的自牺牲锂盐反应后产生的体积变化值，则第二活性层中的自牺牲锂盐的浓度可以在等于第一活性层中的自牺牲锂盐的浓度时，可以形成两活性层具有孔隙率差。
可选地，所述第二活性层中的自牺牲锂盐与所述第一活性层中的自牺牲锂盐种类相同时，所述第二活性层中的自牺牲锂盐的浓度大于所述第一活性层中的自牺牲锂盐的浓度。
在第二活性层中的自牺牲锂盐与第一活性层中的自牺牲锂盐种类相同时，两层活性层中的自牺牲锂盐反应后产生的体积变化值相同，此时需要第二活性层中的自牺牲锂盐的浓度大于第一活性层中的自牺牲锂盐的浓度，如此可以形成两活性层具有孔隙率差。
可选地，所述至少两层活性层中，定义自牺牲锂盐的总浓度为x％，自牺牲锂盐的总浓度＝(各活性层中的所有自牺牲锂盐的质量÷各活性层中的所有活性物质与所有自牺牲锂盐的质量之和)*100％，所述自牺牲锂盐的总浓度x％的范围值为2％-10％。
自牺牲锂盐的总浓度x％的范围值为2％-10％，例如，可以是2％、3％、4％、5％、6％、7％、8％、9％、10％等，具体不作限定。
可选地，定义自牺牲锂盐的层中浓度为yi，自牺牲锂盐的层中浓度＝(每一活性层中的自牺牲锂盐的质量÷每一活性层中的活性物质与自牺牲锂盐的质量之和)*100％，所述第二活性层中的自牺牲锂盐的层中浓度为y(i+1)，其中，i≥1，所述第一活性层中的自牺牲锂盐的层中浓度y(i)，则y(i+1)-y(i)＝a，其中，1％≤a≤4％。
第二活性层中的自牺牲锂盐的层中浓度y(i+1)与第一活性层中的自牺牲锂盐的层中浓度y(i)的差值为1％-4％，其中，i≥1。说明相邻两层活性层中的自牺牲锂盐浓度不同，以形成不同的孔隙率。相邻两层活性层中的自牺牲锂盐浓度差值为1％-4％，例如，可以是1％、2％、2.5％、3％、3.5％、4％等，具体不作限定。
可选地，定义所述至少两活性层从靠近所述集流体到远离所述集流体的方向依次设置有A层活性层和B层活性层，所述A层活性层中的自牺牲锂盐的层中浓度y1的范围值为(x-2)％-(x-0.5)％。
至少两活性层从靠近集流体到远离集流体的方向依次设置有A层活性层和B层活性层，指的是从靠近集流体侧到远离集流体侧的方向依次设置A层活性层和B层活性层，也即，A层活性层是最靠近集流体的含有自牺牲锂盐的活性层。
基于最靠近集流体的活性层中的自牺牲锂盐不容易发挥容量，因此，A层活性层中的自牺牲锂盐的层中浓度y1相比其他活性层更低。A层活性层中的自牺牲锂盐的层中浓度y1范围为(x-2)％-(x-0.5)％，例如，可以是(x-2)％、(x-1.5)％、(x-1)％、(x-0.5)％等，具体不作限定，其中，x的范围为如前文的2-10，例如，x可取2、3、4、5、6、7、8、9、10等，具体不作限定。
可选地，所述A层活性层中的自牺牲锂盐的层中浓度y1的范围值为2％-5％；
和/或，所述B层活性层中的自牺牲锂盐的层中浓度y2的范围值为5％-7％；
和/或，定义所述至少两活性层从靠近所述集流体的到远离所述集流体的方向依次设置有A层活性层、B层活性层和C层活性层，所述C层活性层中的自牺牲锂盐的层中浓度y3的范围值为7％-10％。
定义至少两活性层从靠近集流体的到远离集流体的方向依次设置有A层活性层、B层活性层和C层活性层，A层活性层最靠近集流体，则A层活性层中的自牺牲锂盐的层中浓度y1相比其他活性层更低，A层活性层中的自牺牲锂盐的层中浓度y1范围为2％-5％，例如，可以是2％、3％、4％、5％等，具体不作限定。B层活性层中的自牺牲锂盐的层中浓度y2范围为5％-7％，例如，可以是5％、6％、7％等，具体不作限定。C层活性层中的自牺牲锂盐的层中浓度y3范围为7％、8％、9％、10％等，具体不作限定。并且，各层活性层中形成浓度差。
可选地，所述至少两层活性层中，定义活性层的总孔隙率为p，活性层的总孔隙率＝(各活性层中的所有孔隙体积÷各活性层的体积之和)*100％，所述活性层的总孔隙率p的范围值为20％-30％。
活性层的总孔隙率，指的是补锂极片各活性层中的所有孔隙体积除以补锂极片中各活性层的体积之和。活性层的总孔隙率p的范围值为20％-30％，例如，可以是20％、22％、25％、27％、30％等，具体不作限定。可以理解的是孔隙率不仅与自牺牲锂盐的浓度有关，还与压实密度有关。
可选地，定义每一活性层的孔隙率为n，每一活性层的孔隙率＝(每一活性层中的孔隙体积÷每一活性层的体积)*100％，所述第二活性层的孔隙率为n(i+1)，其中，i≥1，所述第一活性层的孔隙率为ni，则n(i+1)-n(i)＝b，其中，2％≤b≤8％。
每一活性层的孔隙率，指的是补锂极片每一活性层中的孔隙体积除以每一活性层的体积。第二活性层的孔隙率与第一活性层的孔隙率的差值为2％-8％，说明第二活性层的孔隙率高于第一活性层的孔隙率，有助于电解液通过第二活性层浸润至第一活性层，例如第二活性层的孔隙率与第一活性层的孔隙率的差值为2％、3％、4％、5％、6％、7％、8％等，具体不作限定。
可选地，定义所述至少两活性层从靠近所述集流体到远离所述集流体的方向依次设置有A层活性层和B层活性层，所述A层活性层的孔隙率n1的范围值为20％-25％。
A层活性层最靠近集流体，A层活性层的孔隙率相比其他活性层的孔隙率更低，A层活性层的孔隙率为20％-25％，例如，可以是20％、21％、22％、23％、24％、25％等，具体不作限定。
可选地，所述自牺牲锂盐包括Li2C2O4、Li2M1O2、Li2M2O3、Li5FexM3(1-x)O4和Li6MnyM4(1-y)O4中的至少一种；其中，M1包括Ni、Mn、Cu、Fe、Cr及Mo中的至少一种，M2包括Ni、Mn、Fe、Mo、Zr、Si、Cu、Cr和Ru中的至少一种，M3包括Al、Nb、Co、Mn、Ni、Mo、Ru和Cr中的至少一种，M4包括Ni、Fe、Cu和Ru中的至少一种。
本申请中并不对补锂材料进行限定，目前文献报道的正极补锂材料均可应用于本申请，Li2C2O4、Li2M1O2、Li2M2O3、Li5FexM3(1-x)O4和Li6MnyM4(1-y)O4中的至少一种；其中，M1包括Ni、Mn、Cu、Fe、Cr及Mo中的至少一种，M2包括Ni、Mn、Fe、Mo、Zr、Si、Cu、Cr和Ru中的至少一种，M3包括Al、Nb、Co、Mn、Ni、Mo、Ru和Cr中的至少一种，M4包括Ni、Fe、Cu和Ru中的至少一种。
可选地，所述至少两活性层中的正极材料的结构通式为LiMnxFeyM(1-x-y)PO4，式中，0≤x≤0.8；0.1≤y≤0.6；0≤1-x-y≤0.2，M表示掺杂元素，可选地包括Al、Cu、Mg、Zn、Ni、Ti、V、Zr、Co、Ga、Sn、Sb、Nb和Ge中的至少一种；
和/或，所述正极材料的结构通式为LiNiaCobN(1-a-b)O2，式中，N可选地包括Mn、Zr、Al、B、Ta、Mo、W、Nb、Sb、La中的至少一种，其中，0.35≤a<1.0，0≤b≤0.35，0≤1-a-b≤0.35。
申请中对正极材料并不做限定，例如正极材料的结构通式为LiMnxFeyM(1-x-y)PO4，式中，0≤x≤0.8；0.1≤y≤0.6；0≤1-x-y≤0.2，M表示掺杂元素，可选地包括Al、Cu、Mg、Zn、Ni、Ti、V、Zr、Co、Ga、Sn、Sb、Nb和Ge中的至少一种；正极材料的结构通式为LiNiaCobN(1-a-b)O2，式中，N可选地包括Mn、Zr、Al、B、Ta、Mo、W、Nb、Sb、La中的至少一种，其中，0.35≤a<1.0，0≤b≤0.35，0≤1-a-b≤0.35。
可选地，所述至少两活性层中的正极活性材料相同。
考虑到异种正极分层涂布存在能量效率低的问题，本申请采用至少两活性层中的正极活性材料相同，相同正极涂层形成不同的孔隙率，避免导致能量效率低的问题。
可选地，所述补锂极片的活性层中还包括导电剂和粘结剂，所述导电剂包括石墨、碳纳米管、纳米纤维、炭黑和石墨烯中的至少一种；
所述粘结剂包括聚丙烯、聚乙烯、聚偏氟乙烯、偏氟乙烯-六氟丙烯、聚四氟乙烯和聚六氟丙烯中的至少一种。
导电剂用以提高活性层的导电性，本申请并不对导电剂做限定，导电剂包括石墨、碳纳米管、纳米纤维、炭黑和石墨烯中的至少一种，例如，可选自SP、KS-6，乙炔黑、有支链结构的科琴黑ECP，SFG-6，气相生长碳纤维VGCF，碳纳米管CNTs和石墨烯及其复合导电剂中的至少一种。
本申请并不对粘结剂做限定，粘结剂采用本领域常用的粘结剂，粘结剂包括聚丙烯、聚乙烯、聚偏氟乙烯、偏氟乙烯-六氟丙烯、聚四氟乙烯和聚六氟丙烯中的至少一种。
本申请提供一种补锂极片的制备方法，包括以下步骤：
在集流体上涂布至少两层包括造孔剂的浆料，烘干、冷压后得到补锂极片，其中，至少两层包括造孔剂的浆料形成至少两层活性层，一所述活性层设置在所述集流体上，另一所述活性层设置在一所述活性层背离所述集流体的一侧，另一所述活性层中的孔隙率大于一所述活性层中的孔隙率。
另一活性层中的孔隙率大于一活性层中的孔隙率。靠近电解液侧的另一活性层的大的孔隙率有利于提高另一活性层的电解液浸润性，提高一活性层接触电解液的效率，进一步提高一活性层中补锂剂的容量发挥，以改善电池寿命。
可选地，另一所述活性层中的造孔剂形成的孔隙率大于一所述活性层中的造孔剂形成的孔隙率。
本申请通过造孔剂在不同活性层中形成不同的孔隙率，且靠近电解液侧的另一活性层的大的孔隙率有利于提高另一活性层的电解液浸润性，提高一活性层接触电解液的效率，进一步提高一活性层中补锂剂的容量发挥，以改善电池寿命。
可选地，所述造孔剂包括自牺牲锂盐。
本申请中采用自牺牲锂盐作为造孔剂，有利于提高极片的能量密度，避免其他不发挥容量的造孔剂占用极片空间，造成极片能量密度降低。
本申请提供一种电池，包括：负极极片、正极极片、隔离膜及电解液，其中所述正极极片为如上述的补锂极片。
采用上述的补锂极片的电池使用寿命得到改善。
本申请提供一种用电设备，所述用电设备包括上述的电池。
采用上述的电池的用电设备，使用性能得到改善。
本申请的补锂极片，补锂极片包括集流体和设置在集流体至少一侧面的涂布区域，涂布区域包括至少两层活性层，至少两层活性层中包括造孔剂，定义包括造孔剂的相邻的两活性层分别为第一活性层和第二活性层，第一活性层设于集流体，第二活性层设于第一活性层背离集流体的一侧，第二活性层中的孔隙率大于第一活性层中的孔隙率。靠近电解液侧的第二活性层的大的孔隙率有利于提高第二活性层的电解液浸润性，提高第一活性层接触电解液的效率，进一步提高第一活性层中补锂剂的容量发挥，以改善电池寿命。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图示出的结构获得其他的附图。
图1为本申请补锂极片的制备方法的流程示意图；
图2为本申请补锂极片一实施例的结构示意图；
图3为本申请补锂极片一实施例的结构示意图；
图4是本申请一实施方式的二次电池的示意图；
图5是图4所示的本申请一实施方式的二次电池的分解图；
图6是本申请一实施方式的电池模块的示意图；
图7是本申请一实施方式的电池包的示意图；
图8是图7所示的本申请一实施方式的电池包的分解图；
图9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。
附图标号说明：
本申请目的的实现、功能特点及优点将结合实施例，参照附图做进一步说明。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请的一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
以下，适当地参照附图详细说明具体公开了本申请的粘结剂及其制备方法、以及包含该粘结剂的隔膜、二次电池、电池模块、电池包和用电装置的实施方式。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，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
本领域中所提到的电池按是否可充电可以分为一次性电池和可充电电池。目前常见的可充电电池 的类型有：铅酸电池、镍氢电池和锂离子电池。锂离子电池目前广泛应用于纯电动车及混合动力车，用于这种用途的锂离子电池的容量相对略低，但有较大的输出、充电电流，也有较长的使用寿命，但成本较高。
本申请实施例中所描述的电池是指可充电电池。下文中将主要以锂离子电池为例来描述本申请公开的实施例。应当理解的是，本申请公开的实施例对于其他任意适当类型的可充电电池都是适用的。本申请中公开的实施例所提到的电池可以直接或者间接应用于适当的装置中来为该装置供电。
本申请公开的实施例中所提到的电池是指包括一个或多个电池单体以提供预定的电压和容量的单一的物理模块。电池单体是电池中的基本单元，一般按封装的方式可以分为：柱形电池单体、长方体电池单体和软包电池单体。下文中将主要围绕长方体电池单体来展开。应当理解的是，下文中所描述的实施例在某些方面对于柱形电池单体或软包电池单体而言也是适用的。
电池单体包括正极极片、负极极片、电解液和隔离膜。锂离子电池单体主要依靠锂离子在正极极片和负极极片之间的移动来工作。柱形电池单体中三层材料的薄膜结构被卷绕成柱形形状的电极组件，而在长方体电池单体中薄膜结构被卷绕或者叠置成具有大致长方体形状的电极组件。
在通常的电池单体结构中，电池单体包括外壳、电极组件和电解液。电极组件被容纳在电池单体的外壳中，电极组件包括正极极片、负极极片和隔离膜。外壳包括外壳和端盖。外壳包括由多个壁形成的容纳腔以及开口。端盖布置在开口处以封闭容纳腔。除了电极组件之外，容纳腔中还容纳有电解液。电极组件中的正极极片和负极极片包括极耳。为了保证通过大电流而不发生熔断，正极极耳的数量为多个且层叠在一起，负极极耳的数量为多个且层叠在一起。极耳通过连接构件与位于电池单体外部的电极端子电连接，电极端子一般包括正电极端子和负电极端子。对长方体电池单体而言，电极端子一般设置在端盖部分。多个电池单体经由电极端子而被串联和/或并联在一起以应用于各种应用场合。
在一些诸如电动车辆等的大功率应用场合，电池的应用包括三个层次：电池单体、电池模块和电池。电池模块是为了从外部冲击、热、振动等中保护电池单体，将一定数目的电池单体电连接在一起并放入一个框架中而形成的。电池则指的是装入电动车辆的电池系统的最终状态。电池一般包括用于封装一个或多个电池单体的箱体。箱体一般由盖体和箱壳组成。
箱体的边框上或箱壳中部设置有多个用于与车辆主体连接的挂载点，为提高车辆主体与电池连接的稳定性，多在挂载点设置挂载部。
在一些电池生产加工技术中，首先将多个电池单体先整合为电池模块，然后将电池模块封装于电池的箱体中，形成电池包/电池箱。
常用的电池模块一般包括两块端板，两块端板之间排布有多个电池单体。设置有电池模块输出极的端板又称输出极端板，未设置电池模块输出极的端板又称非输出极端板。
电池包内可封装一排多个电池模块，也可封装多排多个电池模块，多排多个电池模块的排列方式可以是双排多列、多排双列、多排多列等。以封装双排多列电池模块的电池包为例，每一列第一个端板一般为头部输出极端板，两排电池模块间相邻的两块端板为中部非输出极端板，每一列最后一个端板为尾部非输出极端板，头部输出极端板和其中一个中部非输出极端板属于第一排电池模块，其中一个中部非输出极端板和尾部输出极端板属于第二排电池模块。
电池模块封装入电池的箱体需要依托工装才可实现，工装上一般设置有夹持电池模块的夹持机构，如夹爪、吸盘等。当采用设置夹爪的工装封装电池模块时，一般会在端板背离电池单体一侧设置与夹爪适配的夹爪槽，以供夹爪插入实现对电池模块的夹持与转运。
电池技术的发展要同时考虑多方面的设计因素，例如，能量密度、循环寿命、放电容量、充放电倍率等性能参数，另外，还需要考虑电池的生产成本以及加工工艺，以提高电池的质量以及生产效率。
补锂材料在释放Li+的过程中，需要有一定的空间和介质将Li+从活性层中传递出去，理论上补锂材料越靠近电解液，越有利于释放出Li+，补充Li+的损耗，同理，靠近集流体的补锂材料距离电解液更远，电解液浸润不良，离子导通差，不利于Li+释放，由此导致补锂材料的容量难以发挥。
为此，本申请提供一种补锂极片，补锂极片包括集流体和设置在集流体至少一侧面的涂布区域，涂布区域包括至少两层活性层，至少两层活性层中包括造孔剂，定义包括造孔剂的相邻的两活性层分别为第一活性层和第二活性层，第一活性层设于集流体，第二活性层设于第一活性层背离集流体的一侧，第二活性层中的孔隙率大于第一活性层中的孔隙率。
集流体，是指汇集电流的结构或零件，在锂离子电池上主要指的是金属箔，如铜箔、铝箔。集流体作为基材用于附着正极或负极活性物质，起到将活性材料产生的电流汇集，对外进行大电流输出的作用。一般铝箔作为正极集流体，铜箔作为负极集流体。
活性层，是指包括有活性材料的层状结构，其中的活性材料是指正极涉及的正极活性物质，正极活性物质可以使用能可逆地嵌入与脱嵌Li+的化合物。
造孔剂，使材料中产生孔洞结构的添加剂。
包括造孔剂的相邻的两活性层分别为第一活性层和第二活性层，指的是含有造孔剂的相邻的两活性层，分别为第一活性层和第二活性层，可以理解的是第一活性层和第二活性层可以是相接触的两活性层，第一活性层和第二活性层之间还可以设置不含有造孔剂的第三活性层，也即，不含造孔剂的活性层将两含造孔剂的活性层分隔开。
第一活性层设于集流体，第二活性层设于第一活性层背离集流体的一侧，指的是第一活性层相比第二活性层更靠近集流体，可以理解的是，第一活性层直接设置在集流体上，还可以理解的是，第一活性层和集流体之间设置不含补锂剂的活性层。
为了方便电解液对靠近集流体侧的活性层的浸润，使靠近电解液侧的第二活性层的孔隙率高于靠近集流体侧的第一活性层的孔隙率，方便电解液从第二活性层浸润至第一活性层，提高分布在第一活性层中的补锂剂的容量发挥，也即，方便靠近集流体侧的补锂材料的Li+释放出去。
进一步地，第二活性层中的造孔剂形成的孔隙率大于第一活性层中的造孔剂形成的孔隙率。
本申请通过造孔剂在不同活性层中形成不同的孔隙率，且靠近电解液侧的第二活性层的大的孔隙率有利于提高第二活性层的电解液浸润性，提高第一活性层接触电解液的效率，进一步提高第一活性层中补锂剂的容量发挥，以改善电池寿命。
如图2所示，为本申请补锂极片一实施例的结构示意图，集流体10上设置有两侧活性层，A层活性层和B层活性层，A层活性层更靠近集流体，A层活性层和B层活性层中均设有造孔剂，且，B层活性层中的造孔剂形成的孔隙率大于A层活性层中的造孔剂形成的孔隙率，如此，提高A层活性层浸润电解液的能力，利于A层活性层中的补锂材料的Li+释放出去，使补锂剂有效发挥容量，提高电池寿命。
进一步地，造孔剂包括自牺牲锂盐。
自牺牲锂盐，也即补锂材料，指的是能提供锂离子的造孔剂，也即，在自牺牲锂盐发挥容量后，留下空隙。可以理解的是，补锂材料发挥容量后，材料密度发生显著降低(例如，Li2S变为S)，或直接被完全反应(草酸锂生成CO2)，不像正极活性物质循环过程中重复膨胀与收缩，可在极片中留下永久空隙。
本申请中采用自牺牲锂盐作为造孔剂，有利于提高极片的能量密度，避免其他不发挥容量的造孔剂占用极片空间，造成极片能量密度降低。
进一步地，第二活性层中的自牺牲锂盐的反应前后的体积变化值大于第一活性层中的自牺牲锂盐的反应前后的体积变化值。
自牺牲锂盐在发挥容量后或发生反应后产生空隙，为了使第二活性层的孔隙率大于第一活性层的孔隙率，则第二活性层中的自牺牲锂盐的反应前后的体积变化值大于第一活性层中的自牺牲锂盐的反应前后的体积变化值。可以理解的是，在第一活性层和第二活性层采用同种自牺牲锂盐的情况下，第二活性层中的自牺牲锂盐的浓度大于第一活性层中的自牺牲锂盐的浓度；还可以理解的是，在第一活性层和第二活性层采用不同种自牺牲锂盐的情况下，自牺牲锂盐反应前后的体积变化值越大，留下的孔越大，越适合第二活性层，例如，草酸Li2C2O4、Li2O、Li2O2会直接反应完，体积变化值最大，适合第二活性层，相比之下，Li2S可以应用于第一活性层，以实现两活性层具有孔隙率差。
进一步地，第二活性层中的至少一种自牺牲锂盐与第一活性层中的至少一种自牺牲锂盐种类不同时，第二活性层中的自牺牲锂盐的浓度大于等于第一活性层中的自牺牲锂盐的浓度。
考虑到活性层中的自牺牲锂盐的种类可能是多种，当第二活性层中的至少一种自牺牲锂盐与第一活性层中的至少一种自牺牲锂盐种类不同时，第二活性层中的自牺牲锂盐的浓度大于等于第一活性层中的自牺牲锂盐的浓度。例如，当两种不同的自牺牲锂盐反应后产生的体积变化值相同时，则第二活性层中的自牺牲锂盐的浓度在大于第一活性层中的自牺牲锂盐的浓度时，可以形成两活性层具有孔隙率差。当两种不同的自牺牲锂盐反应后产生的体积变化值不同时，且第二活性层中的自牺牲锂盐反应后产生的体积变化值大于第一活性层中的自牺牲锂盐反应后产生的体积变化值，则第二活性层中的自牺牲锂盐的浓度可以在等于第一活性层中的自牺牲锂盐的浓度时，可以形成两活性层具有孔隙率差。
进一步地，第二活性层中的自牺牲锂盐与第一活性层中的自牺牲锂盐种类相同时，第二活性层中的自牺牲锂盐的浓度大于第一活性层中的自牺牲锂盐的浓度。
在第二活性层中的自牺牲锂盐与第一活性层中的自牺牲锂盐种类相同时，两层活性层中的自牺牲锂盐反应后产生的体积变化值相同，此时需要第二活性层中的自牺牲锂盐的浓度大于第一活性层中的自牺牲锂盐的浓度，如此可以形成两活性层具有孔隙率差。
进一步地，至少两层活性层中，定义自牺牲锂盐的总浓度为x％，自牺牲锂盐的总浓度＝(各活性层中的所有自牺牲锂盐的质量÷各活性层中的所有活性物质与所有自牺牲锂盐的质量之和)*100％，自牺牲锂盐的总浓度x％的范围值为2％-10％。
各活性层中的所有自牺牲锂盐的质量，指的是补锂极片中各活性层的自牺牲锂盐的质量加和。例如，补锂极片具有两层活性层，A层活性层(活性物质98g，自牺牲锂盐2g)和B层活性层(活性物质96g，自牺牲锂盐4g)，则各活性层中的所有自牺牲锂盐的质量为2g+4g＝6g。
各活性层中的所有活性物质与所有自牺牲锂盐的质量之和，指的是补锂极片中各活性层的活性物质与自牺牲锂盐的质量加和。如上所说的A层活性层(活性物质98g，自牺牲锂盐2g)和B层活性层(活性物质96g，自牺牲锂盐4g)，则各活性层中的所有活性物质与所有自牺牲锂盐的质量之和为98+2g+96+4g＝200g。
自牺牲锂盐的总浓度，指的是补锂极片中自牺牲锂盐的总浓度，如上所说的A层活性层(活性物质98g，自牺牲锂盐2g)和B层活性层(活性物质96g，自牺牲锂盐4g)，则自牺牲锂盐的总浓度为(6g/200g)*100％＝3％。
自牺牲锂盐的总浓度x％的范围值为2％-10％，例如，可以是2％、3％、4％、5％、6％、7％、8％、9％、10％等，具体不作限定。
进一步地，定义自牺牲锂盐的层中浓度为yi，自牺牲锂盐的层中浓度＝(每一活性层中的自牺牲锂盐的质量÷每一活性层中的活性物质与自牺牲锂盐的质量之和)*100％，第二活性层中的自牺牲锂盐的层中浓度y(i+1)，其中，i≥1，第一活性层中的自牺牲锂盐的层中浓度y(i)，则y(i+1)-y(i)＝a，其中，1％≤a≤4％。
自牺牲锂盐的层中浓度，指的是补锂极片每一活性层中自牺牲锂盐的浓度，例如，补锂极片具有两层活性层，A层活性层(活性物质98g，自牺牲锂盐2g)和B层活性层(活性物质96g，自牺牲锂盐4g)，则A层活性层中的自牺牲锂盐的层中浓度y1为(2g/100g)*100％＝2％；则B层活性层中的自牺牲锂盐的层中浓度y2为(4g/100g)*100％＝4％。
第二活性层中的自牺牲锂盐的层中浓度y(i+1)与第一活性层中的自牺牲锂盐的层中浓度y(i)的差值为1％-4％，其中，i≥1。说明相邻两层活性层中的自牺牲锂盐浓度不同，以形成不同的孔隙率。相邻两层活性层中的自牺牲锂盐浓度差值为2％-4％，例如，可以是1％、2％、2.5％、3％、3.5％、4％等，具体不作限定。
同时，靠近电解液侧的第二活性层的自牺牲锂盐浓度大于靠近集流体侧的第一活性层的自牺牲锂盐浓度，方便第二活性层中的自牺牲锂盐发挥容量，因为，第二活性层靠近电解液，电解液浸润好，离子导通好，高浓度的自牺牲锂盐能有效发挥容量。且，在自牺牲锂盐发挥容量后，自牺牲锂盐在活性层中留下孔隙，也就是靠近电解液侧的第二活性层孔隙率高，靠近集流体侧的第一活性层的孔隙率低，电解液通过高孔隙率的第二活性层能有效浸润低孔隙率的第一活性层，提高倍率性能。
可以理解的是，归因于第二活性层补锂材料浓度高，第一活性层补锂材料浓度低，通过这种结构设置，使得不仅能使第二活性层中的补锂材料发挥容量，还能改变活性层孔隙率的分布，提高第一活性层的浸润效果，从而有助于提高第一活性层中补锂材料的容量发挥，以及提高倍率性能。
进一步地，定义至少两活性层从靠近集流体到远离集流体的方向依次设置有A层活性层和B层活性层，A层活性层中的自牺牲锂盐的层中浓度y1的范围值为(x-2)％-(x-0.5)％。
至少两活性层从靠近集流体到远离集流体的方向依次设置有A层活性层和B层活性层，指的是从靠近集流体侧到远离集流体侧的方向依次设置A层活性层和B层活性层，也即，A层活性层是最靠近集流体的含有自牺牲锂盐的活性层。
基于最靠近集流体的活性层中的自牺牲锂盐不容易发挥容量，因此，A层活性层中的自牺牲锂盐的层中浓度y1相比其他活性层更低。A层活性层中的自牺牲锂盐的层中浓度y1范围为(x-2)％-(x-0.5)％，例如，可以是(x-2)％、(x-1.5)％、(x-1)％、(x-0.5)％等，具体不作限定，其中，x的范围为如前文的2-10，例如，x可取2、3、4、5、6、7、8、9、10等，具体不作限定。
进一步地，A层活性层中的自牺牲锂盐的层中浓度y1范围为2％-5％；和/或，B层活性层中的自牺牲锂盐的层中浓度y2范围为5％-7％；和/或，定义至少两活性层从靠近集流体的到远离集流体的方向依次设置有A层活性层、B层活性层和C层活性层，C层活性层中的自牺牲锂盐的层中浓度y3范围为7％-10％。
如图3所示，定义至少两活性层从靠近集流体的到远离集流体的方向依次设置有A层活性层、B层活性层和C层活性层，A层活性层最靠近集流体，则A层活性层中的自牺牲锂盐的层中浓度y1相比其他活性层更低，A层活性层中的自牺牲锂盐的层中浓度y1范围为2％-5％，例如，可以是2％、3％、4％、5％等，具体不作限定。B层活性层中的自牺牲锂盐的层中浓度y2范围为5％-7％，例如，可以是5％、6％、7％等，具体不作限定。C层活性层中的自牺牲锂盐的层中浓度y3范围为7％、8％、9％、10％等，具体不作限定。并且，各层活性层中形成浓度差。
进一步地，至少两层活性层中，定义活性层的总孔隙率为p，活性层的总孔隙率＝(各活性层中的所 有孔隙体积÷各活性层的体积之和)*100％，活性层的总孔隙率p的范围值为20％-30％。
孔隙率计算公式是P＝[V/V0]*100％。V0是材料在自然状态下的体积，V是材料中所有空隙的体积。
活性层的总孔隙率，指的是补锂极片各活性层中的所有孔隙体积除以补锂极片中各活性层的体积之和。活性层的总孔隙率的范围值为20％-30％，例如，可以是20％、22％、25％、27％、30％等，具体不作限定。可以理解的是孔隙率不仅与自牺牲锂盐的浓度有关，还与压实密度有关。
进一步地，定义每一活性层的孔隙率为n，每一活性层的孔隙率＝(每一活性层中的孔隙体积÷每一活性层的体积)*100％，第二活性层的孔隙率为n(i+1)，其中，i≥1，第一活性层的孔隙率为n(i)，则n(i+1)-n(i)＝b，其中，2％≤b≤8％。
每一活性层的孔隙率，指的是补锂极片每一活性层中的孔隙体积除以每一活性层的体积。第二活性层的孔隙率与第一活性层的孔隙率的差值为2％-8％，说明第二活性层的孔隙率高于第一活性层的孔隙率，有助于电解液通过第二活性层浸润至第一活性层，例如第二活性层的孔隙率与第一活性层的孔隙率的差值为2％、3％、4％、5％、6％、7％、8％等，具体不作限定。
进一步地，定义至少两活性层从靠近集流体到远离集流体的方向依次设置有A层活性层和B层活性层，A层活性层的孔隙率n1的范围值为20％-25％。
A层活性层最靠近集流体，A层活性层的孔隙率相比其他活性层的孔隙率更低，A层活性层的孔隙率为20％-25％，例如，可以是20％、21％、22％、23％、24％、25％等，具体不作限定。
进一步地，自牺牲锂盐包括Li2C2O4、Li2M1O2、Li2M2O3、Li5FexM3(1-x)O4和Li6MnyM4(1-y)O4中的至少一种；其中，M1包括Ni、Mn、Cu、Fe、Cr及Mo中的至少一种，M2包括Ni、Mn、Fe、Mo、Zr、Si、Cu、Cr和Ru中的至少一种，M3包括Al、Nb、Co、Mn、Ni、Mo、Ru和Cr中的至少一种，M4包括Ni、Fe、Cu和Ru中的至少一种。
本申请中并不对补锂材料进行限定，目前文献报道的正极补锂材料均可应用于本申请，Li2C2O4、Li2M1O2、Li2M2O3、Li5FexM3(1-x)O4和Li6MnyM4(1-y)O4中的至少一种；其中，M1包括Ni、Mn、Cu、Fe、Cr及Mo中的至少一种，M2包括Ni、Mn、Fe、Mo、Zr、Si、Cu、Cr和Ru中的至少一种，M3包括Al、Nb、Co、Mn、Ni、Mo、Ru和Cr中的至少一种，M4包括Ni、Fe、Cu和Ru中的至少一种。
进一步地，至少两活性层中的正极材料的结构通式为LiMnxFeyM(1-x-y)PO4，式中，0≤x≤0.8；0.1≤y≤0.6；0≤1-x-y≤0.2，M表示掺杂元素，可选地包括Al、Cu、Mg、Zn、Ni、Ti、V、Zr、Co、Ga、Sn、Sb、Nb和Ge中的至少一种；和/或，正极材料的结构通式为LiNiaCobN(1-a-b)O2，式中，N可选地包括Mn、Zr、Al、B、Ta、Mo、W、Nb、Sb、La中的至少一种，其中，0.35≤a<1.0，0≤b≤0.35，0≤1-a-b≤0.35。
申请中对正极材料并不做限定，例如正极材料的结构通式为LiMnxFeyM(1-x-y)PO4，式中，0≤x≤0.8；0.1≤y≤0.6；0≤1-x-y≤0.2，M表示掺杂元素，可选地包括Al、Cu、Mg、Zn、Ni、Ti、V、Zr、Co、Ga、Sn、Sb、Nb和Ge中的至少一种；正极材料的结构通式为LiNiaCobN(1-a-b)O2，式中，N可选地包括Mn、Zr、Al、B、Ta、Mo、W、Nb、Sb、La中的至少一种，其中，0.35≤a<1.0，0≤b≤0.35，0≤1-a-b≤0.35。
进一步地，至少两活性层中的正极活性材料相同。
考虑到异种正极分层涂布存在能量效率低的问题，本申请采用至少两活性层中的正极活性材料相同，相同正极涂层形成不同的孔隙率，避免导致能量效率低的问题。
进一步地，补锂极片的活性层中还包括导电剂和粘结剂，导电剂包括石墨、碳纳米管、纳米纤维、炭黑和石墨烯中的至少一种；粘结剂包括聚丙烯、聚乙烯、聚偏氟乙烯、偏氟乙烯-六氟丙烯、聚四氟乙烯和聚六氟丙烯中的至少一种。
导电剂用以提高活性层的导电性，本申请并不对导电剂做限定，导电剂包括石墨、碳纳米管、纳米纤维、炭黑和石墨烯中的至少一种，例如，可选自SP、KS-6，乙炔黑、有支链结构的科琴黑ECP，SFG-6，气相生长碳纤维VGCF，碳纳米管CNTs和石墨烯及其复合导电剂中的至少一种。
本申请并不对粘结剂做限定，粘结剂采用本领域常用的粘结剂，粘结剂包括聚丙烯、聚乙烯、聚偏氟乙烯、偏氟乙烯-六氟丙烯、聚四氟乙烯和聚六氟丙烯中的至少一种。
如图1所示，本申请提高一种补锂极片的制备方法，包括以下步骤：
在集流体上涂布至少两层包括造孔剂的浆料，烘干、冷压后得到补锂极片，其中，至少两层包括造孔剂的浆料形成至少两层活性层，一活性层设置在集流体上，另一活性层设置在一活性层背离集流体的一侧，另一活性层中的孔隙率大于一活性层中的孔隙率。
另一活性层中的孔隙率大于一活性层中的孔隙率。靠近电解液侧的另一活性层的大的孔隙率有利于提高另一活性层的电解液浸润性，提高一活性层接触电解液的效率，进一步提高一活性层中补锂剂的容量发挥，以改善电池寿命。
进一步地，另一活性层中的造孔剂形成的孔隙率大于一活性层中的造孔剂形成的孔隙率。
本申请通过造孔剂在不同活性层中形成不同的孔隙率，且靠近电解液侧的另一活性层的大的孔隙率有利于提高另一活性层的电解液浸润性，提高一活性层接触电解液的效率，进一步提高一活性层中补锂剂的容量发挥，以改善电池寿命。
进一步地，造孔剂包括自牺牲锂盐。
本申请中采用自牺牲锂盐作为造孔剂，有利于提高极片的能量密度，避免其他不发挥容量的造孔剂占用极片空间，造成极片能量密度降低。
本申请还提供一种电池，包括：负极极片、正极极片、隔离膜及电解液，其中正极极片为如上述的补锂极片。由于补锂极片采用了上述所有实施例的全部技术方案，因此至少具有上述实施例的技术方案所带来的所有有益效果，在此不再一一赘述。
采用上述的补锂极片的电池使用寿命得到改善。
本申请还提供一种用电设备，用电设备包括上述的电池。由于电池采用了上述所有实施例的全部技术方案，因此至少具有上述实施例的技术方案所带来的所有有益效果，在此不再一一赘述。
采用上述的电池的用电设备，使用性能得到改善。
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。隔膜为本申请上述提高的隔膜。
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。
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，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，当二次电池为锂离子电池时，正极活性材料可采用本领域公知的用于锂离子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LiCoO2)、锂镍氧化物(如LiNiO2)、锂锰氧化物(如LiMnO2、LiMn2O4)、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LiNi1/3Co1/3Mn1/3O2(也可以简称为NCM333)、LiNi0.5Co0.2Mn0.3O2(也可以简称为NCM523)、LiNi0.5Co0.25Mn0.25O2(也可以简称为NCM211)、LiNi0.6Co0.2Mn0.2O2(也可以简称为NCM622)、LiNi0.8Co0.1Mn0.1O2(也可以简称为NCM811)、锂镍钴铝氧化物(如LiNi0.85Co0.15Al0.05O2)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LiFePO4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO4)、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。
电池在充放电过程中会伴随Li的脱嵌及消耗，电池在放电到不同状态时Li的摩尔含量不同。本申请中关于正极材料的列举中，Li的摩尔含量为材料初始状态，即投料前状态，正极材料应用于电池体系中，经过充放电循环，Li的摩尔含量会发生变化。
本申请中关于正极材料的列举中，O的摩尔含量仅为理论状态值，晶格释氧会导致氧的摩尔含量发生变化，实际O的摩尔含量会出现浮动。
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，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，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，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，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、锡基材料和钛酸锂等。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。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。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，电解质采用电解液。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，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。
在一些实施方式中，二次电池中还包括隔膜。本申请对隔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膜。
在一些实施方式中，隔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4是作为一个示例的方形结构的电池单体5。
在一些实施方式中，参照图5，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接 于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于开口，以封闭容纳腔。正极极片、负极极片和隔膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于容纳腔内。电解液浸润于电极组件52中。电池单体5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，电池单体可以组装成电池模块，电池模块所含电池单体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6是作为一个示例的电池模块4。参照图6，在电池模块4中，多电池单体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电池单体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，多个电池单体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7和图8是作为一个示例的电池包1。参照图7和图8，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，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。二次电池、电池模块、或电池包可以用作用电装置的电源，也可以用作用电装置的能量存储单元。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9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
补锂极片制备
将正极活性材料、补锂材料、导电剂(CNT)、粘结剂(PVDF)按照不同质量比混合均匀，然后加入NMP作为溶剂，在真空搅拌机作用下搅拌至体系呈均一状，得到正极活性浆料。将不同的正极活性浆料依次均匀涂覆在基材上，烘干、冷压得到正极极片，将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于阴负极中间起到隔离的作用，并卷绕得到裸电芯。将裸电芯置于外包装中，注入电解液并封装得到电芯
负极极片制备
将活性物质人造石墨、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂碳甲基纤维素钠(CMC)按照一定重量比(如96.5：0.7：1.8：1)在去离子水溶剂体系中充分搅拌混合均匀后，涂覆于集流体(如铜箔)上烘干、冷压，得到负极极片。
实施例1
包括两层活性层的补锂极片
A层活性层配方97％(98％LFP+2％Li2C2O4)+0.8％CNT+2.2％PVDF；
B层活性层配方97％(93％LFP+7％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n，自牺牲锂盐的总浓度x％＝n/(m+n)*100％＝4.5％，A层活性层中的自牺牲锂盐的层中浓度为2％，B层活性层中的自牺牲锂盐的层中浓度为7％。
实施例2
包括三层活性层的补锂极片
A层活性层配方97％(98％LFP+2％Li2C2O4)+0.8％CNT+2.2％PVDF；
B层活性层配方97％(93％LFP+5％Li2C2O4)+0.8％CNT+2.2％PVDF；
C层活性层配方97％(93％LFP+7％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n，自牺牲锂盐的总浓度x％＝n/(m+n)*100％＝4.7％，A层活性层中的自牺牲锂盐的层中浓度为2％，B层活性层中的自牺牲锂盐的层中浓度为5％，C层活性层中的自牺牲锂盐的层中浓度为7％。
实施例3
包括三层活性层的补锂极片
A层活性层配方97％(98％LFP+2％Li2C2O4)+0.8％CNT+2.2％PVDF；
B层活性层配方97％(93％LFP+6％Li2C2O4)+0.8％CNT+2.2％PVDF；
C层活性层配方97％(93％LFP+7％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n，自牺牲锂盐的总浓度x％＝n/(m+n)*100％＝5％，A层活性层中的自牺牲锂盐的层中浓度为2％，B层活性层中的自牺牲锂盐的层中浓度为6％，C层活性层中的自牺牲锂盐的层中浓度为7％。
实施例4
包括两层活性层的补锂极片
A层活性层配方97％(98％LFP+2％Li2C2O4)+0.8％CNT+2.2％PVDF；
B层活性层配方97％(93％LFP+5％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n，自牺牲锂盐的总浓度x％＝n/(m+n)*100％＝3.5％，A层活性层中的自牺牲锂盐的层中浓度为2％，B层活性层中的自牺牲锂盐的层中浓度为5％。
实施例5
包括两层活性层的补锂极片
A层活性层配方97％(95％LFP+5％Li2S)+0.8％CNT+2.2％PVDF；
B层活性层配方97％(95％LFP+5％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O质量为n1，Li2S质量为n2，自牺牲锂盐的总浓度x％＝(n1+n2)/(m+n1+n2)*100％＝5％，A层活性层中的自牺牲锂盐的层中浓度为5％，B层活性层中的自牺牲锂盐的层中浓度为5％。
实施例6
包括两层活性层的补锂极片
A层活性层配方97％(99.5％LFP+0.5％Li2C2O4)+0.8％CNT+2.2％PVDF；
B层活性层配方97％(96.5％LFP+3.5％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n，自牺牲锂盐的总浓度x％＝n/(m+n)*100％＝2％，A层活性层中的自牺牲锂盐的层中浓度为0.5％，B层活性层中的自牺牲锂盐的层中浓度为3.5％。
实施例7
包括两层活性层的补锂极片
A层活性层配方97％(92％LFP+8％Li2C2O4)+0.8％CNT+2.2％PVDF；
B层活性层配方97％(88％LFP+12％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n，自牺牲锂盐的总浓度x％＝n/(m+n)*100％＝10％，A层活性层中的自牺牲锂盐的层中浓度为8％，B层活性层中的自牺牲锂盐的层中浓度为12％。
对比例1
包括一层活性层的补锂极片
A层活性层配方97％(95％LFP+5％Li2C2O4)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n，自牺牲锂盐的总浓度x％＝n/(m+n)*100％＝5％。
对比例2
不含有补锂剂的极片
A层活性层配方97％LFP+0.8％CNT+2.2％PVDF。
对比例3
包括一层活性层的补锂极片
A层活性层配方
97％(95％LFP+3％Li2C2O4+2％Li2S)+0.8％CNT+2.2％PVDF；
补锂极片中LFP质量为m，Li2C2O4质量为n1，Li2S质量为n2自牺牲锂盐的总浓度x％＝(n1+n2)/(m+n1+n2)*100％＝5％。
表1各实施例参数列表

表2各实施例参数列表
表3各实施例参数列表

性能测试
1.倍率性能测试
在25℃下，以x C放电至放电截止电压容量为Cx，可以以C0.33为base，比较C2/C0.33大小，衡量倍率改善程度。
2.电解液浸润效果评估测试
将电池(D0)充电到一定电压，使得补锂材料发挥容量，同时在极片中留下永久空隙，再将电池放电到初始状态(D1)，将D0及D1两种状态电池拆解后，把极片中的电解液蒸干，换全新隔离膜，再次组装分别为电池E0、E1，测试E0、E1的电解液浸润速率V0、V1，本次实验取电池状态为3.0V。
电解液浸润速率测试方法；电芯顶部有注液孔，孔上连一个注液杯，杯内放有足量电解液(本实验为100g)，一定时间T后拿走注液杯(本次实验T＝1h)，称量注液杯内电解液减少量▲m，浸润速率v＝▲m/T。
3.循环改善性能测试
(1)在45℃下，将锂离子电池分别以1/3C恒流充电至3.65V，再3.65V恒压充电至电流为0.05C，静置5min，再以1/3C放电至2.5V记录放电容量C0。
(2)再将锂离子电池以1.0C恒流充电至3.65V，静置5min，再以1/3C放电至2.5V记录放电容量C1。
重复上述步骤(2)200次，记录循环第200次后锂离子电池的放电容量C200，容量保持率P200＝C200/C0×100％
4.补锂材料容量发挥改善测试
在25℃下，比较电芯首次充电到上限电压(如下为4.5V)时的容量C@4.5V(控制不同实施例电芯中正极活性物质、正极补锂材料质量一致，如不是，则需计算克容量)，同时补锂材料容量发挥多，循环改善也会好。
表4各实施例和对比例的性能参数表
表1-3是各实施例和对比例的参数，表4是各实施例和对比例的性能参数表，从表4中可以看出，
实施例1、实施例4、实施例5、实施例6和实施例7是两层活性层结构，可以看出，随着自牺牲锂盐的总浓度X％降低，容量保持率和补锂材料容量发挥性能降低，因此，在保持各层中自牺牲锂盐具有浓度梯度的情况下，仍需保持自牺牲锂盐的总浓度在一定范围内。可以理解的是，补锂剂太少导致循环改善幅度小，因此，自牺牲锂盐的总浓度x％不低于2％；同时，补锂剂太多，且补锂剂一般电导较差，虽然带来更多的孔，有利于电解液浸润，但极片的电子电导反而变差，极片的倍率性能变差，导致容量发挥也会受到限制，导致循环不改善甚至恶化，因此，牺牲锂盐的总浓度x％不超过10％。
对比例3为包括一层活性层的补锂极片，对比例3与实施例5相比，在相同的自牺牲锂盐的总浓度情况下，分层分布的补锂极片的性能要优于单层的补锂极片，例如，实施例5的容量保持率和补锂材料容量发挥性能高于对比例3。
实施例2和实施例3为包括三层活性层的补锂极片，实施例3和实施例5相比，层数越多，电解液浸润速率得到提高，倍率性能得到提升。
上仅为本申请的优选实施例，并非因此限制本申请的专利范围，凡是在本申请的申请构思下，利用本申请说明书及附图内容所作的等效结构变换，或直接/间接运用在其他相关的技术领域均包括在本申请的专利保护范围内。

Claims (22)

  1. 一种补锂极片，其中，所述补锂极片包括集流体和设置在所述集流体至少一侧面的涂布区域，所述涂布区域包括至少两层活性层，所述至少两层活性层中包括造孔剂；
    定义包括造孔剂的相邻的两所述活性层分别为第一活性层和第二活性层，所述第一活性层设于所述集流体，所述第二活性层设于所述第一活性层背离所述集流体的一侧，所述第二活性层的孔隙率大于所述第一活性层的孔隙率。
  2. 如权利要求1所述的补锂极片，其中，所述第二活性层中的造孔剂形成的孔隙率大于所述第一活性层中的造孔剂形成的孔隙率。
  3. 如权利要求1或2所述的补锂极片，其中，所述造孔剂包括自牺牲锂盐。
  4. 如权利要求3所述的补锂极片，其中，所述第二活性层中的自牺牲锂盐的反应前后的体积变化值大于所述第一活性层中的自牺牲锂盐的反应前后的体积变化值。
  5. 如权利要求4所述的补锂极片，其中，所述第二活性层中的至少一种自牺牲锂盐与所述第一活性层中的至少一种自牺牲锂盐种类不同时，所述第二活性层中的自牺牲锂盐的浓度大于等于所述第一活性层中的自牺牲锂盐的浓度。
  6. 如权利要求4所述的补锂极片，其中，所述第二活性层中的自牺牲锂盐与所述第一活性层中的自牺牲锂盐种类相同时，所述第二活性层中的自牺牲锂盐的浓度大于所述第一活性层中的自牺牲锂盐的浓度。
  7. 如权利要求3至6中任一项所述的补锂极片，其中，所述至少两层活性层中，定义自牺牲锂盐的总浓度为x％，自牺牲锂盐的总浓度＝(各活性层中的所有自牺牲锂盐的质量÷各活性层中的所有活性物质与所有自牺牲锂盐的质量之和)*100％，所述自牺牲锂盐的总浓度x％的范围值为2％-10％。
  8. 如权利要求7所述的补锂极片，其中，定义自牺牲锂盐的层中浓度为yi，自牺牲锂盐的层中浓度＝(每一活性层中的自牺牲锂盐的质量÷每一活性层中的活性物质与自牺牲锂盐的质量之和)*100％，所述第二活性层中的自牺牲锂盐的层中浓度为y(i+1)，其中，i≥1，所述第一活性层中的自牺牲锂盐的层中浓度y(i)，则y(i+1)-y(i)＝a，其中，1％≤a≤4％。
  9. 如权利要求7或8所述的补锂极片，其中，定义所述至少两活性层从靠近所述集流体到远离所述集流体的方向依次设置有A层活性层和B层活性层，所述A层活性层中的自牺牲锂盐的层中浓度y1的范围值为(x-2)％-(x-0.5)％。
  10. 如权利要求9所述的补锂极片，其中，所述A层活性层中的自牺牲锂盐的层中浓度y1的范围值为2％-5％；
    和/或，所述B层活性层中的自牺牲锂盐的层中浓度y2的范围值为5％-7％；
    和/或，定义所述至少两活性层从靠近所述集流体的到远离所述集流体的方向依次设置有A层活性层、B层活性层和C层活性层，所述C层活性层中的自牺牲锂盐的层中浓度y3的范围值为7％-10％。
  11. 如权利要求1至10中任一项所述的补锂极片，其中，所述至少两层活性层中，定义活性层的总孔隙率为p，活性层的总孔隙率＝(各活性层中的所有孔隙体积÷各活性层的体积之和)*100％，所述活性层的总孔隙率p的范围值为20％-30％。
  12. 如权利要求11所述的补锂极片，其中，定义每一活性层的孔隙率为n，每一活性层的孔隙率＝(每一活性层中的孔隙体积÷每一活性层的体积)*100％，所述第二活性层的孔隙率为n(i+1)，其中，i≥1，所述第一活性层的孔隙率为n(i)，则n(i+1)-n(i)＝b，其中，2％≤b≤8％。
  13. 如权利要求12所述的补锂极片，其中，定义所述至少两活性层从靠近所述集流体到远离所述集流体的方向依次设置有A层活性层和B层活性层，所述A层活性层的孔隙率n1的范围值为20％-25％。
  14. 如权利要求3至13中任一项所述的补锂极片，其中，所述自牺牲锂盐包括Li2C2O4，Li2M1O2、Li2M2O3、Li5FexM3(1-x)O4和Li6MnyM4(1-y)O4中的至少一种；其中，M1包括Ni、Mn、Cu、Fe、Cr及Mo中的至少一种，M2包括Ni、Mn、Fe、Mo、Zr、Si、Cu、Cr和Ru中的至少一种，M3包括Al、Nb、Co、Mn、Ni、Mo、Ru和Cr中的至少一种，M4包括Ni、Fe、Cu和Ru中的至少一种。
  15. 如权利要求1至14中任一项所述的补锂极片，其中，所述至少两活性层中的正极材料的结构通式为LiMnxFeyM1-x-yPO4，式中，0≤x≤0.8；0.1≤y≤0.6；0≤1-x-y≤0.2，M表示掺杂元素，可选地包括Al、Cu、Mg、Zn、Ni、Ti、V、Zr、Co、Ga、Sn、Sb、Nb和Ge中的至少一种；
    和/或，所述正极材料的结构通式为LiNiaCobN(1-a-b)O2，式中，N可选地包括Mn、Zr、Al、B、Ta、Mo、W、Nb、Sb、La中的至少一种，其中，0.35≤a<1.0，0≤b≤0.35，0≤1-a-b≤0.35。
  16. 如权利要求1至15中任一项所述的补锂极片，其中，所述至少两活性层中的正极活性材料相同。
  17. 如权利要求16所述的补锂极片，其中，所述补锂极片的活性层中还包括导电剂和粘结剂，所 述导电剂包括石墨、碳纳米管、纳米纤维、炭黑和石墨烯中的至少一种；
    所述粘结剂包括聚丙烯、聚乙烯、聚偏氟乙烯、偏氟乙烯-六氟丙烯、聚四氟乙烯和聚六氟丙烯中的至少一种。
  18. 一种补锂极片的制备方法，其中，包括以下步骤：
    在集流体上涂布至少两层包括造孔剂的浆料，烘干、冷压后得到补锂极片，其中，至少两层包括造孔剂的浆料形成至少两层活性层，一所述活性层设置在所述集流体上，另一所述活性层设置在一所述活性层背离所述集流体的一侧，另一所述活性层中的孔隙率大于一所述活性层中的孔隙率。
  19. 如权利要求18所述的补锂极片的制备方法，其中，另一所述活性层中的造孔剂形成的孔隙率大于一所述活性层中的造孔剂形成的孔隙率。
  20. 如权利要求18或19所述的补锂极片的制备方法，其中，所述造孔剂包括自牺牲锂盐。
  21. 一种电池，其中，包括：负极极片、正极极片、隔离膜及电解液，其中所述正极极片为如权利要求1至17中任一项所述的补锂极片。
  22. 一种用电设备，其中，所述用电设备包括权利要求21所述的电池。
PCT/CN2023/112008 2022-11-17 2023-08-09 补锂极片及其制备方法、以及包含该补锂极片的电池和用电设备 WO2024103858A1 (zh)

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CN116111042A (zh) * 2023-04-11 2023-05-12 宁德新能源科技有限公司 正极极片、二次电池和电子装置
CN116789191B (zh) * 2023-07-25 2024-01-12 宁德时代新能源科技股份有限公司 补钠材料及其制备方法、正极极片、电极组件、电池和用电装置
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