WO2023046027A1 - 锂离子电池电极及其制备方法与锂离子电池 - Google Patents

锂离子电池电极及其制备方法与锂离子电池 Download PDF

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WO2023046027A1
WO2023046027A1 PCT/CN2022/120594 CN2022120594W WO2023046027A1 WO 2023046027 A1 WO2023046027 A1 WO 2023046027A1 CN 2022120594 W CN2022120594 W CN 2022120594W WO 2023046027 A1 WO2023046027 A1 WO 2023046027A1
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layer
electrode
pore
lithium
ion battery
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English (en)
French (fr)
Inventor
袁晓涛
许占
吴煊伟
叶涛
何科峰
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BYD Co Ltd
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BYD Co Ltd
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Priority to EP22872071.0A priority Critical patent/EP4345933A4/en
Priority to AU2022350417A priority patent/AU2022350417B2/en
Priority to KR1020247000234A priority patent/KR20240016426A/ko
Priority to JP2023578016A priority patent/JP2024531038A/ja
Publication of WO2023046027A1 publication Critical patent/WO2023046027A1/zh
Priority to US18/404,634 priority patent/US20240154121A1/en
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
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    • H01M4/00—Electrodes
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
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    • 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
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    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0585—Construction or manufacture of accumulators having only flat construction elements, i.e. flat positive electrodes, flat negative electrodes and flat separators
    • H—ELECTRICITY
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    • H01M4/043—Processes of manufacture in general involving compressing or compaction
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    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
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    • 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
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0416—Methods of deposition of the material involving impregnation with a solution, dispersion, paste or dry powder
    • 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 disclosure relates to the technical field of lithium-ion batteries, in particular, to a lithium-ion battery electrode, a preparation method thereof, and a lithium-ion battery.
  • Improving the areal density and compaction density of lithium-ion battery electrodes can effectively increase the energy density of lithium-ion batteries.
  • the tortuosity of the pores inside the electrode becomes larger, and the diffusion path of lithium ions inside the electrode becomes longer, which will lead to an increase in the impedance of the electrode. , thus affecting the kinetic performance of the electrode.
  • the purpose of the present disclosure is to solve the problems of unreasonable distribution of internal pore structure and poor kinetic performance of electrodes in existing lithium-ion battery electrodes, and provide a lithium-ion battery electrode, a preparation method thereof and a lithium-ion battery.
  • the present disclosure provides a lithium-ion battery electrode, the electrode includes a current collector and n layers of pole sheets stacked on the current collector, where n is an integer greater than 2;
  • the pole piece layer contains a pore-forming agent, and along the direction gradually away from the current collector, the content of the pore-forming agent in each layer of the pole piece layer gradually increases;
  • the pore-forming agent is selected from Electrolyte additives in a solid state.
  • the pole piece layer also contains an active material, relative to 100 parts by weight of the active material, along the direction gradually away from the current collector, the pore-forming agent in the pole piece layer of the first layer
  • the content of the pore-forming agent in the pole piece layer of the nth layer is 0 to 4 parts by weight
  • the content of the pore-forming agent in the pole piece layer of the nth layer is 1-10 parts by weight
  • the pore-forming agent in the pole piece layer of the second to n-1th layer is The content of the porogen is 1-10 parts by weight.
  • the pole piece layer of each layer has a pore structure, and the pore-forming agent is filled in at least part of the pore structure;
  • the porosity ⁇ i of the pore structure in the i-th layer of the pole piece layer is:
  • ⁇ i is the weight ratio of the pore former to the active material in the pole sheet layer of the i-th layer
  • ⁇ 1 is the true density of the active material, in units is g/cm 3
  • ⁇ 2 is the ultimate compacted density of the active material in g/cm 3
  • ⁇ 3 is the true density of the pore-forming agent in g/cm 3 .
  • the average porosity of the pore structure in the n-layer pole piece layer satisfies the following conditions:
  • d i is the thickness of the pole piece layer in the i-th layer, and the unit is ⁇ m.
  • the porosity of the pore structure in the two adjacent pole piece layers satisfies the following conditions:
  • ⁇ i+1 ⁇ i +( ⁇ n ⁇ 1 )/n.
  • the volume density of the pole piece layer in the first layer is 2.55g/cm 3 to 2.75g/cm 3
  • the volume density of the pole piece layer in the nth layer is 2.0g/cm 3 to 2.5g/cm 3
  • the bulk density of the second to n-1th layer of the pole piece is 2.0g/cm 3 to 2.70g/cm 3 .
  • the total thickness of the n pole piece layers is 20-200 ⁇ m.
  • n is an integer of 2-10.
  • n is an integer of 2-5.
  • the electrode layer of each layer also contains a conductive agent and a binder, relative to 100 parts by weight of the active material, the content of the conductive agent is 0.1 to 5 parts by weight, and the binder The content of is 0.5 ⁇ 5 parts by weight;
  • the active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate and lithium manganate;
  • the conductive agent is selected from at least one of carbon nanotubes, graphene, carbon black and carbon fibers;
  • the binder is selected from polyvinylidene fluoride and/or polytetrafluoroethylene;
  • the pore forming agent is at least one selected from lithium difluorooxalate borate, lithium bisfluoromethyldiamine, lithium borate, lithium tetraborate, lithium tetrafluoroborate, lithium nitrate and lithium chloride.
  • the pore forming agent is lithium difluorooxalate borate and/or lithium bisfluoromethyldiamine.
  • the present disclosure also provides a method for preparing the lithium-ion battery electrode described in any one of the above, the method comprising:
  • n-layer electrode sheets containing different contents of pore-forming agents are stacked and pressed sequentially on the current collector according to the order of the contents of the pore-forming agents from the least to the most, so as to obtain the lithium ion battery electrode.
  • the preparation method of the electrode sheet includes:
  • the fibrous material is hot-pressed to obtain the electrode sheet.
  • the present disclosure also provides a lithium ion battery, the lithium ion battery contains a porous electrode, and the porous electrode is soaked in an electrolyte by the lithium ion battery electrode described in any one of the above or the lithium ion battery electrode obtained by the above method after getting.
  • the lithium-ion battery electrode provided by the present disclosure contains a multi-layer electrode sheet layer with a gradually increasing pore-forming agent content, and the pore-forming agent is an electrolyte additive that is solid at room temperature, and the electrode is soaked in the electrolyte Afterwards, the pore-forming agent therein will be dissolved in the electrolyte, thereby forming an electrode with a gradient pore structure, which can provide a channel for the rapid diffusion of lithium ions inside the electrode, so that lithium ions have a better diffusion path. Therefore, the present disclosure The provided lithium ion battery electrode has good electrode kinetic performance.
  • Fig. 1 schematically shows a schematic diagram of the dissolution process of a pore forming agent in a single pole piece layer according to an embodiment of the present disclosure
  • Fig. 2 schematically shows the arrangement relationship of the multi-layer electrode sheet after the pore-forming agent is dissolved according to an embodiment of the present disclosure.
  • the first aspect of the present disclosure provides a lithium-ion battery electrode, which includes a current collector and n-layer pole sheet layers stacked on the current collector, where n is an integer greater than 2; wherein, in the pole piece layer Containing a pore-forming agent, the content of the pore-forming agent in each layer of the electrode layer gradually increases along the direction of gradually moving away from the current collector; the pore-forming agent is selected from electrolyte additives that are solid at room temperature.
  • the pore-forming agent contained in each pole piece layer can play a role in maintaining the internal pore structure of each pole piece layer during the preparation process of the electrode, so that the lithium-ion battery electrode has a good Pore structure; in addition, since the pore-forming agent is a solid electrolyte additive at room temperature, and along the direction gradually away from the current collector, the content of the pore-forming agent in each layer of the electrode layer gradually increases, so the electrode soaked in the electrolytic After being immersed in the liquid, the pore-forming agent in it will dissolve in the electrolyte, thereby forming an electrode with a gradient pore structure, which can provide a channel for the rapid diffusion of lithium ions inside the electrode, so that lithium ions have a better diffusion path. Therefore, The lithium ion battery electrode provided by the present disclosure has good electrode kinetic performance.
  • the lithium-ion battery electrode provided by the present disclosure has a smaller pore tortuosity, and has a higher gram capacity of the electrode, a lower impedance and a higher rate discharge retention rate.
  • Figure 1 schematically shows a schematic diagram of the dissolution process of the pore-forming agent in a single pole piece layer according to an embodiment of the present disclosure.
  • the pore-forming agent in the pole piece layer dissolves to form a pore structure .
  • FIG. 2 schematically shows the arrangement relationship of the multi-layer pole sheet after the pore-forming agent is dissolved according to an embodiment of the present disclosure, wherein the current collector is arranged below FIG. 2 .
  • the pole sheet layer may further contain active materials.
  • the relative amount of the active material and the pore-forming agent can be changed within a certain range, for example, relative to 100 parts by weight of the active material, along the direction gradually away from the current collector, the first The content of the pore-forming agent in the pole piece layer of the first layer can be 0-4 parts by weight, the content of the pore-forming agent in the pole piece layer of the n-th layer can be 1-10 parts by weight, and the second layer The content of the pore-forming agent in the pole sheet layer up to the (n-1)th layer may be 1-10 parts by weight.
  • the content of the pore-forming agent in the pole sheet layer of the first layer may be 0 to 0. 2 parts by weight
  • the content of the pore-forming agent in the pole piece layer of the nth layer can be 4 to 8 parts by weight
  • the content of the pore-forming agent in the pole piece layer of the second layer to the n-1th layer It may be 2 to 6 parts by weight.
  • the lithium-ion battery electrode has a more reasonable gradient pore structure after soaking in the electrolyte.
  • each pole piece layer has a pore structure, and the pore-forming agent is filled in at least part of the pore structure.
  • the porosity of the pore structure in each layer of the pole piece layer is determined by the content of the pore-forming agent, specifically, along the direction gradually away from the current collector, the i-th pole piece layer described in The porosity ⁇ i of the pore structure can be expressed as:
  • ⁇ i is the weight ratio of the pore former to the active material in the pole sheet layer of the i-th layer
  • ⁇ 1 is the true density of the active material, in units is g/cm 3
  • ⁇ 2 is the ultimate compacted density of the active material, in g/cm 3
  • ⁇ 3 is the true density of the pore-forming agent, in g/cm 3 .
  • the porosity ⁇ i of the pore structure in the electrode sheet layer of the i-th layer may be:
  • 3.6 is the true density of lithium iron phosphate, the unit is g/cm 3 ; 2.7 is the ultimate compacted density of lithium iron phosphate, the unit is g/cm 3 .
  • the porosity of all the pore structures in the n-layer pole piece layer can meet the following conditions:
  • d i is the thickness of the pole piece layer in the i-th layer, and the unit is ⁇ m, and 0.22 and 0.44 are respectively the maximum porosity when the lithium-ion battery electrode of the present disclosure has better electrode performance (such as volumetric energy density) and minimum porosity.
  • the porosity of the pore structure in the two adjacent pole piece layers can meet the following conditions:
  • ⁇ i+1 ⁇ i +( ⁇ n ⁇ 1 )/n.
  • the porosity distribution of the pore structure in each layer of the electrode layer is reasonable, and the porosity between any two adjacent layers of the electrode layer is uniformly transitioned, which can provide a better environment for the diffusion of lithium ions in the electrode. diffusion path.
  • the volume density of each pole piece layer can be changed within a certain range, for example, along the direction gradually away from the current collector, the volume density of the first pole piece layer can be 2.55g /cm 3 to 2.75g/cm 3 , the bulk density of the pole piece layer in the nth layer can be 2.0g/cm 3 to 2.5g/cm 3 , and the volume density of the pole piece layer in the second to n-1th layer The bulk density may be 2.0 g/cm 3 to 2.70 g/cm 3 .
  • the pole piece layer close to the current collector has a higher volume density than the middle layer and the uppermost pole piece layer, which can make the lithium-ion battery electrode as a whole have a higher level of volume density, thereby
  • the lithium-ion battery electrode has a higher energy density; in addition, the uppermost (electrode surface) pole sheet layer has a lower bulk density, so that the lithium-ion battery electrode surface has a larger porosity, which is conducive to Lithium ions diffuse into the interior of the electrode.
  • the total thickness of the n pole piece layers may vary within a certain range, for example, the total thickness of the n pole piece layers may be 20 ⁇ m ⁇ 200 ⁇ m.
  • each pole piece layer can be uniformly distributed, and the thickness of the pole piece layer with a specific porosity can also be increased or reduced as required.
  • the total number n of the pole piece layers can be varied within a certain range, for example, n can be an integer of 2-10, and according to some embodiments of the present disclosure, n is an integer of 2-5.
  • n can be an integer of 2-10, and according to some embodiments of the present disclosure, n is an integer of 2-5.
  • the larger the value of n the more uniform the gradient distribution of the pore structure inside the lithium-ion battery electrode, but as the value of n increases, the production efficiency of the electrode will also decrease. Therefore, it can be Choose an appropriate n value according to actual needs.
  • a conductive agent and a binder may also be contained in each pole sheet layer, and the content of the conductive agent may be 0.1 to 5 parts by weight relative to 100 parts by weight of the active material.
  • the content of the binder may be 0.5-5 parts by weight.
  • the active material, conductive agent, binder and pore-forming agent can be selected within a certain range, for example, the active material can be selected from at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate and lithium manganate ;
  • the conductive agent can be selected from at least one of carbon nanotubes, graphene, carbon black and carbon fiber;
  • the binder can be selected from polyvinylidene fluoride and/or polytetrafluoroethylene;
  • the pore-forming agent Can be selected from at least one of lithium difluorooxalate borate, lithium bisfluoromethyldiamine, lithium borate, lithium tetraborate, lithium tetrafluoroborate, lithium nitrate and lithium chloride, according to some embodiments of the present disclosure, the The pore forming agent is lithium difluorooxalate borate and/or lithium bisfluoromethyldiamine.
  • the second aspect of the present disclosure provides a method for preparing the lithium-ion battery electrode described in any one of the first aspect, the method includes: n-layer electrode sheets containing different contents of pore-forming agents according to the content of pore-forming agents from less to less The sequence at most is stacked and pressed on the current collector in order to obtain the lithium ion battery electrode.
  • the lithium ion battery electrode is obtained by directly combining multilayer electrode sheets with different contents of pore-forming agents and pressing them together. Electrode sheets with different contents of pore-forming agents can quickly obtain electrodes meeting different porosity requirements, which can provide more options for electrode design.
  • the preparation method of the electrode sheet includes: performing airflow pulverization and mixing the active material, the conductive agent, the binder and the pore forming agent to obtain a mixed material; after heating and melting the mixed material, performing electrospinning, A fibrous material is obtained; the fibrous material is hot-pressed to obtain the electrode sheet.
  • Electrode sheets with different contents of pore-forming agents are pre-prepared by dry-process electrodes, which is convenient for subsequent selection and adjustment.
  • the present disclosure also provides a lithium-ion battery, which contains a porous electrode, and the porous electrode is obtained by any one of the lithium-ion battery electrodes described in the first aspect or by using the method described in the second aspect Lithium-ion battery electrodes are obtained after soaking in electrolyte solution.
  • the present disclosure is further illustrated by the following examples, but the present disclosure is not limited thereby.
  • the raw materials, reagents, instruments and equipment involved in this example, unless otherwise specified, can be obtained through purchase.
  • the active material, conductive agent, binder and pore-forming agent are jet-milled and mixed to obtain a mixed material; then the mixed material is heated and melted, and then electrospun to obtain a fibrous material; finally, the fiber
  • the material is subjected to thermocompression molding to obtain the electrode sheet.
  • the lithium ion battery electrode is prepared by the following method:
  • the first layer of electrode sheet is pressed on the current collector (aluminum foil) by hot pressing, wherein the first layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black) and Binding agent (polytetrafluoroethylene), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts;
  • the thickness of first layer electrode sheet is 50 ⁇ m, wherein has Pore structure, after calculation, the porosity of the pore structure is 0.25;
  • the second layer of electrode sheets is pressed on the first layer of electrode sheets by hot pressing, and fusion treatment is carried out to obtain lithium ion battery electrodes, wherein the second layer of electrode sheets contains active materials (lithium iron phosphate), Conductive agent (carbon tube+carbon black), binder (polytetrafluoroethylene) and pore-forming agent (difluorooxalate lithium borate, true density 2.12g/cm 3 ), relative to 100 parts by weight of the active material, the conductive agent
  • the content of the binder is 1 part by weight, the content of the binder is 3 parts by weight, and the content of the pore-forming agent is 4 parts by weight;
  • the thickness of the second electrode sheet is 50 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pores In the structure, the porosity of the pore structure is calculated to be 0.294.
  • the lithium-ion battery electrode prepared in this embodiment has two layers of pole sheets. Along the direction gradually away from the current collector, the porosity of the pore structure in each layer of pole sheets gradually increases, the total thickness is 100 ⁇ m, and the average porosity ( According to the weighted average of upper and lower layer thickness) is 0.272.
  • the lithium ion battery electrode is prepared by the following method:
  • the first layer of electrode sheet is pressed on the current collector (aluminum foil) by hot pressing, wherein the first layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black) and Binding agent (polytetrafluoroethylene), with respect to the active material of 100 weight parts, the content of conducting agent is 1 weight part, and the content of binding agent is 3 weight parts;
  • the thickness of first layer electrode sheet is 33.3 ⁇ m, wherein It has a pore structure, and the porosity of the pore structure is calculated to be 0.25;
  • the second layer of electrode sheet is pressed on the first layer of electrode sheet by hot pressing method, wherein the second layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), adhesive Bonding agent (polytetrafluoroethylene) and pore-forming agent (lithium difluorooxalate borate), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts, pore-forming The content of the agent is 2 parts by weight; the thickness of the second electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.272;
  • the third layer of electrode sheet is pressed on the second layer of electrode sheet by hot pressing method, and fusion treatment is carried out to obtain lithium ion battery electrode, wherein, the third layer of electrode sheet contains active material (lithium iron phosphate), Conductive agent (carbon tube+carbon black), binding agent (polytetrafluoroethylene) and pore-forming agent (difluorooxalate lithium borate), relative to the active material of 100 weight parts, the content of conductive agent is 1 weight part, viscous The content of the binding agent is 3 parts by weight, and the content of the pore-forming agent is 4 parts by weight; the thickness of the third electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the pore The porosity of the structure is 0.294.
  • active material lithium iron phosphate
  • Conductive agent carbon tube+carbon black
  • binding agent polytetrafluoroethylene
  • pore-forming agent difluoroo
  • the lithium-ion battery electrode prepared in this example has three layers of pole sheets. Along the direction of gradually moving away from the current collector, the porosity of the pore structure in each layer of pole sheets gradually increases, with a total thickness of 100 ⁇ m and an average porosity of 100 ⁇ m. 0.272.
  • the lithium ion battery electrode is prepared by the following method:
  • the first layer of electrode sheet is pressed on the current collector (aluminum foil) by hot pressing, wherein the first layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black) and Binding agent (polytetrafluoroethylene), with respect to the active material of 100 weight parts, the content of conducting agent is 1 weight part, and the content of binding agent is 3 weight parts;
  • the thickness of first layer electrode sheet is 33.3 ⁇ m, wherein It has a pore structure, and the porosity of the pore structure is calculated to be 0.25;
  • the second layer of electrode sheet is pressed on the first layer of electrode sheet by hot pressing method, wherein the second layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), adhesive Bonding agent (polytetrafluoroethylene) and pore-forming agent (lithium difluorooxalate borate), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts, pore-forming The content of the agent is 4 parts by weight; the thickness of the second electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.294;
  • the third layer of electrode sheet is pressed on the second layer of electrode sheet by hot pressing method, and fusion treatment is carried out to obtain lithium ion battery electrode, wherein, the third layer of electrode sheet contains active material (lithium iron phosphate), Conductive agent (carbon tube+carbon black), binding agent (polytetrafluoroethylene) and pore-forming agent (difluorooxalate lithium borate), relative to the active material of 100 weight parts, the content of conductive agent is 1 weight part, viscous The content of the binding agent is 3 parts by weight, and the content of the pore-forming agent is 8 parts by weight; the thickness of the third electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the pore The porosity of the structure is 0.334.
  • active material lithium iron phosphate
  • Conductive agent carbon tube+carbon black
  • binding agent polytetrafluoroethylene
  • pore-forming agent difluoroo
  • the lithium-ion battery electrode prepared in this example has three layers of pole sheets. Along the direction of gradually moving away from the current collector, the porosity of the pore structure in each layer of pole sheets gradually increases, with a total thickness of 100 ⁇ m and an average porosity of 100 ⁇ m. 0.292.
  • the lithium ion battery electrode is prepared by the following method:
  • the first layer of electrode sheet is pressed on the current collector (aluminum foil) by hot pressing, wherein the first layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black) and Binding agent (polytetrafluoroethylene), with respect to the active material of 100 weight parts, the content of conducting agent is 1 weight part, and the content of binding agent is 3 weight parts;
  • the thickness of first layer electrode sheet is 25 ⁇ m, wherein has Pore structure, after calculation, the porosity of the pore structure is 0.25;
  • the second layer of electrode sheet is pressed on the first layer of electrode sheet by hot pressing method, wherein the second layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), adhesive Bonding agent (polytetrafluoroethylene) and pore-forming agent (lithium difluorooxalate borate), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts, pore-forming The content of the agent is 2 parts by weight; the thickness of the second electrode sheet is 25 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.272;
  • the third layer of electrode sheet is pressed on the second layer of electrode sheet by hot pressing method, wherein, the third layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), adhesive Bonding agent (polytetrafluoroethylene) and pore-forming agent (lithium difluorooxalate borate), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts, pore-forming The content of the agent is 4 parts by weight; the thickness of the third electrode sheet is 25 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure, and the porosity of the pore structure is calculated to be 0.294;
  • active material lithium iron phosphate
  • conductive agent carbon tube + carbon black
  • adhesive Bonding agent polytetrafluoroethylene
  • pore-forming agent lithium difluorooxalate borate
  • the fourth layer of electrode sheet is pressed on the third layer of electrode sheet by hot pressing method, and fusion treatment is carried out to obtain lithium ion battery electrode, wherein, the fourth layer of electrode sheet contains active material (lithium iron phosphate), Conductive agent (carbon tube+carbon black), binding agent (polytetrafluoroethylene) and pore-forming agent (difluorooxalate lithium borate), relative to the active material of 100 weight parts, the content of conductive agent is 1 weight part, viscous The content of the binding agent is 3 parts by weight, and the content of the pore-forming agent is 8 parts by weight; the thickness of the fourth electrode sheet is 25 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the pore structure The porosity is 0.334.
  • the lithium-ion battery electrode prepared in this example has four layers of pole sheets. Along the direction of gradually moving away from the current collector, the porosity of the pore structure in each layer of pole sheets gradually increases, with a total thickness of 100 ⁇ m and an average porosity of 100 ⁇ m. 0.287.
  • the lithium ion battery electrode is prepared by the following method:
  • the first layer of electrode sheet is pressed on the current collector (aluminum foil) by hot pressing, wherein the first layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), Binding agent (polytetrafluoroethylene) and pore forming agent (difluorooxalate lithium borate), with respect to the active material of 100 weight parts, the content of conducting agent is 1 weight part, and the content of binding agent is 3 weight parts, makes The content of the pore agent is 4 parts by weight; the thickness of the first electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.294;
  • the second layer of electrode sheet is pressed on the first layer of electrode sheet by hot pressing method, wherein the second layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), adhesive Bonding agent (polytetrafluoroethylene) and pore-forming agent (lithium difluorooxalate borate), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts, pore-forming The content of the agent is 8 parts by weight; the thickness of the second electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.334;
  • the third layer of electrode sheet is pressed on the second layer of electrode sheet by hot pressing method, and fusion treatment is carried out to obtain lithium ion battery electrode, wherein, the third layer of electrode sheet contains active material (lithium iron phosphate), Conductive agent (carbon tube+carbon black), binding agent (polytetrafluoroethylene) and pore-forming agent (difluorooxalate lithium borate), relative to the active material of 100 weight parts, the content of conductive agent is 1 weight part, viscous The content of the binding agent is 3 parts by weight, and the content of the pore-forming agent is 12 parts by weight; the thickness of the third electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the pore The porosity of the structure is 0.368.
  • active material lithium iron phosphate
  • Conductive agent carbon tube+carbon black
  • binding agent polytetrafluoroethylene
  • pore-forming agent difluoroo
  • the lithium-ion battery electrode prepared in this example has three layers of pole sheets. Along the direction of gradually moving away from the current collector, the porosity of the pore structure in each layer of pole sheets gradually increases, with a total thickness of 100 ⁇ m and an average porosity of 100 ⁇ m. 0.332.
  • the lithium ion battery electrode is prepared by the following method:
  • the single-layer electrode sheet is pressed on the current collector (aluminum foil) by hot pressing to obtain a lithium-ion battery electrode, wherein the single-layer electrode sheet contains an active material (lithium iron phosphate), a conductive agent (carbon tube+carbon black) and binding agent (polytetrafluoroethylene), relative to the active material of 100 weight parts, the content of conducting agent is 1 weight part, and the content of binding agent is 3 weight parts;
  • the thickness of described single-layer electrode sheet is 100 ⁇ m, which has a pore structure, and the porosity of the pore structure is calculated to be 0.25.
  • the lithium ion battery electrode is prepared by the following method:
  • the single-layer electrode sheet is pressed on the current collector (aluminum foil) by hot pressing to obtain a lithium-ion battery electrode, wherein the single-layer electrode sheet contains an active material (lithium iron phosphate), a conductive agent (carbon tube+carbon black), binding agent (polytetrafluoroethylene) and pore forming agent (lithium difluorooxalate borate), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts
  • the content of the pore-forming agent is 2 parts by weight; the thickness of the single-layer electrode sheet is 100 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.272.
  • the lithium ion battery electrode is prepared by the following method:
  • the first layer of electrode sheet is pressed on the current collector (aluminum foil) by hot pressing, wherein the first layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), Binding agent (polytetrafluoroethylene) and pore forming agent (difluorooxalate lithium borate), with respect to the active material of 100 weight parts, the content of conducting agent is 1 weight part, and the content of binding agent is 3 weight parts, makes The content of the pore agent is 4 parts by weight; the thickness of the first electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.294;
  • the second layer of electrode sheet is pressed on the first layer of electrode sheet by hot pressing method, wherein the second layer of electrode sheet contains active material (lithium iron phosphate), conductive agent (carbon tube + carbon black), adhesive Bonding agent (polytetrafluoroethylene) and pore-forming agent (lithium difluorooxalate borate), with respect to the active material of 100 weight parts, the content of conductive agent is 1 weight part, and the content of binding agent is 3 weight parts, pore-forming The content of the agent is 2 parts by weight; the thickness of the second electrode sheet is 33.3 ⁇ m, which has a pore structure, and the pore-forming agent is filled in at least part of the pore structure. After calculation, the porosity of the pore structure is 0.272;
  • the third layer of electrode sheet is pressed on the second layer of electrode sheet by hot pressing method, and fusion treatment is carried out to obtain lithium ion battery electrode, wherein, the third layer of electrode sheet contains active material (lithium iron phosphate), Conductive agent (carbon tube+carbon black) and binding agent (polytetrafluoroethylene), with respect to the active material of 100 weight parts, the content of conducting agent is 1 weight part, and the content of binding agent is 3 weight parts;
  • the third The thickness of the layered electrode sheet is 33.3 ⁇ m, which has a pore structure, and the porosity of the pore structure is calculated to be 0.25.
  • the lithium-ion battery electrode prepared in this comparative example has three layers of pole sheets. Along the direction gradually away from the current collector, the porosity of the pore structure in each layer of pole sheets gradually decreases, with a total thickness of 100 ⁇ m and an average porosity of 0.272.
  • the lithium ion battery electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were respectively used as positive electrodes, corresponding negative electrodes, and electrolytes to form lithium ion batteries, and the battery design capacity was 1.8Ah.
  • the preparation process of the negative electrode sheet is as follows: mix artificial graphite with conductive agent carbon black, thickener CMC, and binder SBR at a mass ratio of 96.4:1:1.2:1.4, add deionized water and stir under the action of a mixer to obtain a uniform negative electrode A slurry system, coating the slurry on the copper foil current collector, drying, rolling, and cutting to obtain the negative electrode sheet.
  • Preparation of electrolyte Mix organic solvents, which can be selected from one or more of cyclic carbonates, chain carbonates, and carboxylates, and then dissolve fully dried LiPF 6 in the mixed solvent, Prepare an electrolyte solution with a concentration of 1mol/L.
  • the tortuosity, gram capacity, capacity per unit area, internal resistance, and discharge capacity ratio of the positive electrode in each lithium ion battery were measured by conventional methods in the art.
  • Tortuosity measurement the pole piece is cut layer by layer through FIB-SEM and then the structure of the pole piece is reconstructed three-dimensionally, and the tortuosity of the pole piece can be obtained by software simulation;
  • Gram capacity measurement After the assembled battery is converted into capacity, it is charged to 3.8V at 0.33C constant current and constant voltage, and 0.05C is cut off, and then 0.33C is discharged to 2.0V to obtain the discharge capacity.
  • the discharge capacity is higher than the total dressing amount of the battery As a gram capacity, the unit is mAh/g;
  • Capacity per unit area The ratio of the above discharge capacity to the area of the total positive electrode sheet is taken as the capacity per unit area, unit mAh/cm 2 ;
  • Rate discharge capacity ratio 0.33C constant current and constant voltage charge to 3.8V, 0.05C cut off and then 0.2C discharge to 2.0V, then 0.33C constant current constant voltage charge to 3.8V, 0.05C cut off and 2C discharge to 2.0V, 2C
  • the ratio of the capacity obtained by discharge to the capacity obtained by 0.2C discharge is the ratio of the rate discharge capacity
  • Example 3 1.8
  • Example 4 1.8
  • Example 5 1.7 Comparative example 1 2.6 Comparative example 2 2.5 Comparative example 3 2.7
  • Example 2C/0.2C discharge ratio Example 1 0.941
  • Example 2 0.962 Example 3 0.983
  • Example 4 0.985
  • Example 5 0.985 Comparative example 1 0.875 Comparative example 2 0.898 Comparative example 3 0.872

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Abstract

公开了一种锂离子电池电极及其制备方法与锂离子电池，该电极包括集流体和层叠设置在集流体上的n层极片层，n为2以上的整数；其中，极片层中含有造孔剂，沿着逐渐远离集流体的方向，各层极片层中造孔剂的含量逐渐增多；造孔剂选自常温下呈固态的电解液添加剂。

Description

锂离子电池电极及其制备方法与锂离子电池
优先权信息
本公开请求于2021年09月24日向中国国家知识产权局提交的、专利申请号为202111122407.8、申请名称为“一种锂离子电池电极及其制备方法与锂离子电池”的中国专利申请的优先权，并且其全部内容通过引用结合在本公开中。
技术领域
本公开涉及锂离子电池技术领域，具体地，涉及一种锂离子电池电极及其制备方法与锂离子电池。
背景技术
提高锂离子电池电极的面密度和压实密度，能够有效提升锂离子电池的能量密度。但是，在提高电极面密度和压实密度的过程中，随着电极厚度的增加，电极内部的孔隙曲折度变大，锂离子在电极内部的扩散路径变长，这会导致电极的阻抗增大，从而影响电极的动力学性能。
为了提升电极的动力学性能，需要在电极内部构造合适的孔隙结构，为锂离子在电极内部的高速扩散提供通道。然而，现有的锂离子电池电极仍然存在内部孔隙结构分布不合理、电极动力学性能较差的问题。
公开内容
本公开的目的是解决现有的锂离子电池电极存在的内部孔隙结构分布不合理、电极动力学性能较差的问题，提供一种锂离子电池电极及其制备方法与锂离子电池。
为了实现上述目的，本公开提供一种锂离子电池电极，该电极包括集流体和层叠设置在所述集流体上的n层极片层，n为2以上的整数；
其中，所述极片层中含有造孔剂，沿着逐渐远离所述集流体的方向，各层所述极片层中所述造孔剂的含量逐渐增多；所述造孔剂选自常温下呈固态的电解液添加剂。
进一步地，所述极片层中还含有活性材料，相对于100重量份的所述活性材料，沿着逐渐远离所述集流体的方向，第1层所述极片层中所述造孔剂的含量为0～4重量份，第n层所述极片层中所述造孔剂的含量为1～10重量份，第2层至第n-1层所述极片层中所述造孔剂的含量为1～10重量份。
进一步地，各层所述极片层具有孔隙结构，所述造孔剂填充在至少部分所述孔隙结构 中；
沿着逐渐远离所述集流体的方向，第i层所述极片层中所述孔隙结构的孔隙率δ i为：
Figure PCTCN2022120594-appb-000001
其中，1≤i≤n，i为整数，ε i为第i层所述极片层中所述造孔剂与所述活性材料的重量比值，ρ 1为所述活性材料的真密度，单位为g/cm 3，ρ 2为活性材料的极限压实密度，单位为g/cm 3，ρ 3为所述造孔剂的真密度，单位为g/cm 3。
进一步地，在所述电极中，n层所述极片层中所述孔隙结构的平均孔隙率满足如下条件：
Figure PCTCN2022120594-appb-000002
其中，d i为第i层所述极片层的厚度，单位为μm。
进一步地，在所述电极中，相邻两层所述极片层中所述孔隙结构的孔隙率满足如下条件：
δ i+1＝δ i+(δ n-δ 1)/n。
进一步地，沿着逐渐远离所述集流体的方向，第1层所述极片层的体密度为2.55g/cm 3～2.75g/cm 3，第n层所述极片层的体密度为2.0g/cm 3～2.5g/cm 3，第2层至第n-1层所述极片层的体密度为2.0g/cm 3～2.70g/cm 3。
进一步地，在所述电极中，n层所述极片层的总厚度为20～200μm。
进一步地，n为2～10的整数。
进一步地，n为2～5的整数。
进一步地，在各层所述极片层中还含有导电剂和粘结剂，相对于100重量份的所述活性材料，所述导电剂的含量为0.1～5重量份，所述粘结剂的含量为0.5～5重量份；
所述活性材料选自锂镍钴锰氧、磷酸铁锂和锰酸锂中的至少一种；
所述导电剂选自碳纳米管、石墨烯、炭黑和碳纤维中的至少一种；
所述粘结剂选自聚偏氟乙烯和/或聚四氟乙烯；
所述造孔剂选自二氟草酸硼酸锂、双氟甲基二胺锂、硼酸锂、四硼酸锂、四氟硼酸锂、硝酸锂和氯化锂中的至少一种。
进一步地，所述造孔剂为二氟草酸硼酸锂和/或双氟甲基二胺锂。
本公开还提供一种制备上述任意一项所述的锂离子电池电极的方法，该方法包括：
将含有不同含量造孔剂的n层电极片按照造孔剂含量由少至多的顺序依次层叠压合在集流体上，得到所述锂离子电池电极。
进一步地，所述电极片的制备方法包括：
将活性材料、导电剂、粘结剂和造孔剂进行气流粉碎并混合，得到混合物料；
将所述混合物料加热熔融后，进行静电纺丝，得到纤维化物料；
将所述纤维化物料进行热压成型，得到所述电极片。
本公开还提供一种锂离子电池，所述锂离子电池中含有多孔电极，所述多孔电极由上述任意一项所述的锂离子电池电极或采用上述方法得到的锂离子电池电极经电解液浸泡后得到。
通过上述技术方案，本公开提供的锂离子电池电极中含有多层造孔剂含量逐渐增多的极片层，且造孔剂为常温下呈固态的电解液添加剂，在该电极浸泡在电解液中之后，其中的造孔剂会溶解在电解液中，从而形成具有梯度孔隙结构的电极，能够为锂离子在电极内部的快速扩散提供通道，使得锂离子具有较佳的扩散路径，因此，本公开提供的锂离子电池电极具有良好的电极动力学性能。
本公开的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本公开的实践了解到。
附图说明
附图是用来提供对本公开的进一步理解，并且构成说明书的一部分，与下面的具体实施方式一起用于解释本公开，但并不构成对本公开的限制。在附图中：
图1示意性示出了根据本公开实施例的单一极片层中造孔剂溶解过程示意图；
图2示意性示出了根据本公开实施例的造孔剂溶解后的多层极片层的排列关系示意图。
具体实施方式
以下结合附图对本公开的具体实施方式进行详细说明。应当理解的是，此处所描述的具体实施方式仅用于说明和解释本公开，并不用于限制本公开。
本公开的第一方面提供一种锂离子电池电极，该电极包括集流体和层叠设置在所述集流体上的n层极片层，n为2以上的整数；其中，所述极片层中含有造孔剂，沿着逐渐远离所述集流体的方向，各层所述极片层中所述造孔剂的含量逐渐增多；所述造孔剂选自常温下呈固态的电解液添加剂。
本公开提供的锂离子电池电极中，各极片层中含有的造孔剂能够在电极的制备过程中发挥维持各极片层内部孔隙结构的作用，从而使得所述锂离子电池电极具有良好的孔隙结构；此外，由于造孔剂为常温下呈固态的电解液添加剂，且沿着逐渐远离集流体的方向，各层极片层中造孔剂的含量逐渐增多，因此在该电极浸泡在电解液中后，其中的造孔剂会 溶解在电解液中，从而形成具有梯度孔隙结构的电极，能够为锂离子在电极内部的快速扩散提供通道，使得锂离子具有较佳的扩散路径，因此，本公开提供的锂离子电池电极具有良好的电极动力学性能。
进一步地，本公开提供的锂离子电池电极内部的孔隙曲折度较小，具有较高的电极克容量、较低的阻抗和较高的倍率放电保持率。
图1示意性示出了根据本公开实施例的单一极片层中造孔剂溶解过程示意图，如图1所示，经电解液浸泡后，极片层中的造孔剂溶解而形成孔隙结构。图2示意性示出了根据本公开实施例的造孔剂溶解后的多层极片层的排列关系示意图，其中，集流体设置在图2的下方。
根据本公开，所述极片层中还可以含有活性材料。在各层极片层中，活性材料与造孔剂的相对用量可以在一定的范围内变化，例如，相对于100重量份的所述活性材料，沿着逐渐远离所述集流体的方向，第1层所述极片层中所述造孔剂的含量可以为0～4重量份，第n层所述极片层中所述造孔剂的含量可以为1～10重量份，第2层至第n-1层所述极片层中所述造孔剂的含量可以为1～10重量份。
根据本公开的一些实施例，相对于100重量份的所述活性材料，沿着逐渐远离所述集流体的方向，第1层所述极片层中所述造孔剂的含量可以为0～2重量份，第n层所述极片层中所述造孔剂的含量可以为4～8重量份，第2层至第n-1层所述极片层中所述造孔剂的含量可以为2～6重量份。在该情况下，所述锂离子电池电极经电解液浸泡后具有更合理的梯度孔隙结构。
根据本公开，各层所述极片层具有孔隙结构，所述造孔剂填充在至少部分所述孔隙结构中。其中，各层所述极片层中所述孔隙结构的孔隙率由造孔剂的含量决定，具体地，沿着逐渐远离所述集流体的方向，第i层所述极片层中所述孔隙结构的孔隙率δ i可以为：
Figure PCTCN2022120594-appb-000003
其中，1≤i≤n，i为整数，ε i为第i层所述极片层中所述造孔剂与所述活性材料的重量比值，ρ 1为所述活性材料的真密度，单位为g/cm 3；ρ 2为活性材料的极限压实密度，单位为g/cm 3；ρ 3为所述造孔剂的真密度，单位为g/cm 3。
示例性地，当活性材料为磷酸铁锂时，第i层所述极片层中所述孔隙结构的孔隙率δ i可以为：
Figure PCTCN2022120594-appb-000004
其中，3.6是磷酸铁锂的真密度，单位为g/cm 3；2.7是磷酸铁锂的极限压实密度，单位 为g/cm 3。
根据本公开，为了进一步提高所述锂离子电池电极整体的压实密度，在所述电极中，n层所述极片层中所有所述孔隙结构的孔隙率可以满足如下条件：
Figure PCTCN2022120594-appb-000005
其中，d i为第i层所述极片层的厚度，单位为μm，0.22和0.44分别是使本公开的锂离子电池电极具有较好的电极性能(例如体积能量密度)时的最大孔隙率和最小孔隙率。
根据本公开，为了进一步提升所述锂离子电池电极中梯度孔隙结构的合理性，在所述电极中，相邻两层所述极片层中所述孔隙结构的孔隙率可以满足如下条件：
δ i+1＝δ i+(δ n-δ 1)/n。
在上述情况下，各层极片层中孔隙结构的孔隙率分布合理，且任意相邻两层极片层之间的孔隙率均匀过渡，这能够为锂离子在电极中的扩散提供较佳的扩散路径。
根据本公开，各层所述极片层的体密度可以在一定的范围内变化，例如，沿着逐渐远离所述集流体的方向，第1层所述极片层的体密度可以为2.55g/cm 3～2.75g/cm 3，第n层所述极片层的体密度可以为2.0g/cm 3～2.5g/cm 3，第2层至第n-1层所述极片层的体密度可以为2.0g/cm 3～2.70g/cm 3。
在本公开中，具体地，靠近集流体的极片层具有较中间层和最上层极片层更高的体密度，这能够使得所述锂离子电池电极整体具有较高水平的体密度，从而使得所述锂离子电池电极具有较高的能量密度；此外，最上层(电极表面)极片层具有较低的体密度，使得所述锂离子电池电极表面具有较大的孔隙率，从而有利于锂离子扩散进入电极内部。
根据本公开，在所述电极中，n层所述极片层的总厚度可以在一定的范围内变化，例如，n层所述极片层的总厚度可以为20μm～200μm。
在本公开中，具体地，可以使各层极片层的厚度均匀分布，也可以根据需要增大或缩小具有特定空隙率极片层的厚度。
根据本公开，所述极片层的总层数n可以在一定的范围内变化，例如，n可以为2～10的整数，根据本公开的一些实施例，n为2～5的整数。具体地，n的取值越大，所述锂离子电池电极内部的孔隙结构的梯度分布越均匀，但是随着n的取值的增大，电极的生产效率也会有所降低，因此，可以根据实际需要选择合适的n值。
根据本公开，在各层所述极片层中还可以含有导电剂和粘结剂，相对于100重量份的所述活性材料，所述导电剂的含量可以为0.1～5重量份，所述粘结剂的含量可以为0.5～5重量份。
所述活性材料、导电剂、粘结剂和造孔剂可以在一定的范围内选择，例如，所述活性 材料可以选自锂镍钴锰氧、磷酸铁锂和锰酸锂中的至少一种；所述导电剂可以选自碳纳米管、石墨烯、炭黑和碳纤维中的至少一种；所述粘结剂可以选自聚偏氟乙烯和/或聚四氟乙烯；所述造孔剂可以选自二氟草酸硼酸锂、双氟甲基二胺锂、硼酸锂、四硼酸锂、四氟硼酸锂、硝酸锂和氯化锂中的至少一种，根据本公开的一些实施例，所述造孔剂为二氟草酸硼酸锂和/或双氟甲基二胺锂。
本公开的第二方面提供一种制备第一方面中任意一项所述的锂离子电池电极的方法，该方法包括：将含有不同含量造孔剂的n层电极片按照造孔剂含量由少至多的顺序依次层叠压合在集流体上，得到所述锂离子电池电极。
本公开的方法中，直接将具有不同含量造孔剂的多层电极片组合后压合得到所述锂离子电池电极，组合方便快速，而且通过调整电极片中的造孔剂含量，或者更换具有不同含量造孔剂的电极片，能够快速得到符合不同孔隙率要求的电极，这可以使得电极设计具有更多选择。
进一步地，所述电极片的制备方法包括：将活性材料、导电剂、粘结剂和造孔剂进行气流粉碎并混合，得到混合物料；将所述混合物料加热熔融后，进行静电纺丝，得到纤维化物料；将所述纤维化物料进行热压成型，得到所述电极片。利用干法电极预先制备具有不同含量造孔剂的电极片，方便后续选择和调整。
本公开还提供一种锂离子电池，所述锂离子电池中含有多孔电极，所述多孔电极由第一方面中任意一项所述的锂离子电池电极或采用第二方面所述的方法得到的锂离子电池电极经电解液浸泡后得到。
下面通过实施例来进一步说明本公开，但是本公开并不因此而受到任何限制。本实施例中涉及的原料、试剂、仪器和设备，如无特殊说明，均可通过购买获得。
本公开实施例中涉及的电极片采用如下方法制备：
将活性材料、导电剂、粘结剂和造孔剂进行气流粉碎并混合，得到混合物料；然后将所述混合物料加热熔融后，再进行静电纺丝，得到纤维化物料；最后将所述纤维化物料进行热压成型，得到所述电极片。通过调整造孔剂的添加量并重复上述操作以获得含有不同含量造孔剂的电极片。
实施例1
采用如下方法制备锂离子电池电极：
(1)利用热压法将第一层电极片压合在集流体(铝箔)上，其中，第一层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)和粘结剂(聚四氟乙烯)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份；第一层电极片的厚 度为50μm，其中具有孔隙结构，经计算，孔隙结构的孔隙率为0.25；
(2)利用热压法将第二层电极片压合在第一层电极片上，并进行融合处理，得到锂离子电池电极，其中，第二层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂，真密度2.12g/cm 3)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为4重量份；第二层电极片的厚度为50μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.294。
本实施例制备得到的锂离子电池电极具有二层极片层，沿着逐渐远离集流体的方向，各层极片层中孔隙结构的孔隙率逐渐增大，总厚度为100μm，平均孔隙率(根据上下层厚度加权平均得到)为0.272。
实施例2
采用如下方法制备锂离子电池电极：
(1)利用热压法将第一层电极片压合在集流体(铝箔)上，其中，第一层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)和粘结剂(聚四氟乙烯)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份；第一层电极片的厚度为33.3μm，其中具有孔隙结构，经计算，孔隙结构的孔隙率为0.25；
(2)利用热压法将第二层电极片压合在第一层电极片上，其中，第二层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为2重量份；第二层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.272；
(3)利用热压法将第三层电极片压合在第二层电极片上，并进行融合处理，得到锂离子电池电极，其中，第三层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为4重量份；第三层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.294。
本实施例制备得到的锂离子电池电极具有三层极片层，沿着逐渐远离集流体的方向，各层极片层中孔隙结构的孔隙率逐渐增大，总厚度为100μm，平均孔隙率为0.272。
实施例3
采用如下方法制备锂离子电池电极：
(1)利用热压法将第一层电极片压合在集流体(铝箔)上，其中，第一层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)和粘结剂(聚四氟乙烯)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份；第一层电极片的厚度为33.3μm，其中具有孔隙结构，经计算，孔隙结构的孔隙率为0.25；
(2)利用热压法将第二层电极片压合在第一层电极片上，其中，第二层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为4重量份；第二层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.294；
(3)利用热压法将第三层电极片压合在第二层电极片上，并进行融合处理，得到锂离子电池电极，其中，第三层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为8重量份；第三层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.334。
本实施例制备得到的锂离子电池电极具有三层极片层，沿着逐渐远离集流体的方向，各层极片层中孔隙结构的孔隙率逐渐增大，总厚度为100μm，平均孔隙率为0.292。
实施例4
采用如下方法制备锂离子电池电极：
(1)利用热压法将第一层电极片压合在集流体(铝箔)上，其中，第一层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)和粘结剂(聚四氟乙烯)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份；第一层电极片的厚度为25μm，其中具有孔隙结构，经计算，孔隙结构的孔隙率为0.25；
(2)利用热压法将第二层电极片压合在第一层电极片上，其中，第二层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为2重量份；第二层电极片的厚度为25μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.272；
(3)利用热压法将第三层电极片压合在第二层电极片上，其中，第三层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸 硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为4重量份；第三层电极片的厚度为25μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.294；
(4)利用热压法将第四层电极片压合在第三层电极片上，并进行融合处理，得到锂离子电池电极，其中，第四层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为8重量份；第四层电极片的厚度为25μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.334。
本实施例制备得到的锂离子电池电极具有四层极片层，沿着逐渐远离集流体的方向，各层极片层中孔隙结构的孔隙率逐渐增大，总厚度为100μm，平均孔隙率为0.287。
实施例5
采用如下方法制备锂离子电池电极：
(1)利用热压法将第一层电极片压合在集流体(铝箔)上，其中，第一层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为4重量份；第一层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.294；
(2)利用热压法将第二层电极片压合在第一层电极片上，其中，第二层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为8重量份；第二层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.334；
(3)利用热压法将第三层电极片压合在第二层电极片上，并进行融合处理，得到锂离子电池电极，其中，第三层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为12重量份；第三层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.368。
本实施例制备得到的锂离子电池电极具有三层极片层，沿着逐渐远离集流体的方向，各层极片层中孔隙结构的孔隙率逐渐增大，总厚度为100μm，平均孔隙率为0.332。
对比例1
采用如下方法制备锂离子电池电极：
利用热压法将单层电极片压合在集流体(铝箔)上，得到锂离子电池电极，其中，所述单层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)和粘结剂(聚四氟乙烯)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份；所述单层电极片的厚度为100μm，其中具有孔隙结构，经计算，孔隙结构的孔隙率为0.25。
对比例2
采用如下方法制备锂离子电池电极：
利用热压法将单层电极片压合在集流体(铝箔)上，得到锂离子电池电极，其中，所述单层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为2重量份；所述单层电极片的厚度为100μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.272。
对比例3
采用如下方法制备锂离子电池电极：
(1)利用热压法将第一层电极片压合在集流体(铝箔)上，其中，第一层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为4重量份；第一层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.294；
(2)利用热压法将第二层电极片压合在第一层电极片上，其中，第二层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)、粘结剂(聚四氟乙烯)和造孔剂(二氟草酸硼酸锂)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份，造孔剂的含量为2重量份；第二层电极片的厚度为33.3μm，其中具有孔隙结构，造孔剂填充在至少部分孔隙结构中，经计算，孔隙结构的孔隙率为0.272；
(3)利用热压法将第三层电极片压合在第二层电极片上，并进行融合处理，得到锂离子电池电极，其中，第三层电极片中含有活性材料(磷酸铁锂)、导电剂(碳管+炭黑)和粘结剂(聚四氟乙烯)，相对于100重量份的活性材料，导电剂的含量为1重量份，粘结剂的含量为3重量份；第三层电极片的厚度为33.3μm，其中具有孔隙结构，经计算，孔隙结 构的孔隙率为0.25。
本对比例制备得到的锂离子电池电极具有三层极片层，沿着逐渐远离集流体的方向，各层极片层中孔隙结构的孔隙率逐渐减小，总厚度为100μm，平均孔隙率为0.272。
测试例
分别将实施例1至5和对比例1至3中制备的锂离子电池电极作为正极与对应的负极、电解液组装成锂离子电池，电池设计容量为1.8Ah。
负极片的制备过程如下：将人造石墨与导电剂炭黑、增稠剂CMC、粘结剂SBR按质量比96.4:1:1.2:1.4混合，加入去离子水在搅拌机作用下搅拌得到均匀的负极浆料体系，将浆料涂覆在铜箔集流体上，经过烘干、辊压、裁切得到负极片。
电解液的制备：将有机溶剂混合，这些有机溶剂可以选自环状碳酸酯、链状碳酸酯、羧酸酯中的一种或几种，然后将充分干燥的LiPF 6溶解于混合溶剂中，配制成浓度为1mol/L的电解液。
利用本领域内的常规方法，对各锂离子电池中的正极的迂曲度、克容量、单位面积容量、内阻和放电容量比率进行测量。
迂曲度测量：通过FIB-SEM对极片进行逐层切割然后对极片结构进行三维重构，利用软件模拟可以得到极片的迂曲度；
克容量测量：组装成的电池经过化成分容之后，以0.33C恒流恒压充电至3.8V,0.05C截止，然后0.33C放电至2.0V得到放电容量，放电容量比上电池总的敷料量作为克容量，单位mAh/g；
单位面积容量：上述放电容量与总的正极片的面积比值作为单位面积容量，单位mAh/cm 2；
内阻：将电池调至50％SOC,静置2h,记录电压V1，以1.5C放电30s,记录电压V2，(V1-V2)/1.5C即可得到阻抗值；
倍率放电容量比率：0.33C恒流恒压充电至3.8V,0.05C截止然后0.2C放电至2.0V，然后0.33C恒流恒压充电至3.8V,0.05C截止然后2C放电至2.0V,2C放电得到的容量与0.2C放电得到的容量比值即为倍率放电容量的比率；
测量结果如表1至表4所示。
表1
  迂曲度
实施例1 2.1
实施例2 1.9
实施例3 1.8
实施例4 1.8
实施例5 1.7
对比例1 2.6
对比例2 2.5
对比例3 2.7
由表1可以看出，实施例1-5的锂离子电池正极具有较低的迂曲度。
表2
Figure PCTCN2022120594-appb-000006
由表2可以看出，实施例1-5的锂离子电池正极具有较高的克容量和单位面积容量，且随着孔隙率的提高，克容量逐渐增高，但是单位面积容量呈先上升后下降的趋势。
表3
实施例 DCIR(mΩ)
实施例1 51.9
实施例2 50.5
实施例3 48.1
实施例4 47.1
实施例5 52
对比例1 60.9
对比例2 58.2
对比例3 59.6
由表3可以看出，实施例1-5的锂离子电池正极具有较低的阻抗。
表4
实施例 2C/0.2C放电比率
实施例1 0.941
实施例2 0.962
实施例3 0.983
实施例4 0.985
实施例5 0.985
对比例1 0.875
对比例2 0.898
对比例3 0.872
由表4可以看出，实施例1-5的锂离子电池正极具有较高的倍率放电保持率。
由表1-4数据可知，实施例1-5的锂离子电池正极具有较低的迂曲度和阻抗、较高的克容量、单位面积容量和倍率放电保持率，从而表明本公开的锂离子电池电极具有良好的电极动力学性能。
上面结合附图对本申请的实施例进行了描述，但是本申请并不局限于上述的具体实施方式，上述的具体实施方式仅仅是示意性的，而不是限制性的，本领域的普通技术人员在本申请的启示下，在不脱离本申请宗旨和权利要求所保护的范围情况下，还可做出很多形式，均属于本申请的保护之内。

Claims (14)

  1. 一种锂离子电池电极，其中，所述锂离子电池电极包括集流体和层叠设置在所述集流体上的n层极片层，n为2以上的整数；
    其中，所述极片层中含有造孔剂，沿着逐渐远离所述集流体的方向，各层所述极片层中所述造孔剂的含量逐渐增多；所述造孔剂选自常温下呈固态的电解液添加剂。
  2. 根据权利要求1所述的电极，其中，所述极片层中还含有活性材料，相对于100重量份的所述活性材料，沿着逐渐远离所述集流体的方向，第1层所述极片层中所述造孔剂的含量为0～4重量份，第n层所述极片层中所述造孔剂的含量为1～10重量份，第2层至第n-1层所述极片层中所述造孔剂的含量为1～10重量份。
  3. 根据权利要求1或2所述的电极，其中，各层所述极片层具有孔隙结构，所述造孔剂填充在至少部分所述孔隙结构中；
    沿着逐渐远离所述集流体的方向，第i层所述极片层中所述孔隙结构的孔隙率δ i为：
    Figure PCTCN2022120594-appb-100001
    其中，1≤i≤n，i为整数，ε i为第i层所述极片层中所述造孔剂与所述活性材料的重量比值，ρ 1为所述活性材料的真密度，单位为g/cm 3，ρ 2为活性材料的极限压实密度，单位为g/cm 3，ρ 3为所述造孔剂的真密度，单位为g/cm 3。
  4. 根据权利要求1～3中任意一项所述的电极，其中，在所述电极中，n层所述极片层中所述孔隙结构的平均孔隙率满足如下条件：
    Figure PCTCN2022120594-appb-100002
    其中，d i为第i层所述极片层的厚度，单位为μm。
  5. 根据权利要求1～4中任意一项所述的电极，其中，在所述电极中，相邻两层所述极片层中所述孔隙结构的孔隙率满足如下条件：
    δ i+1＝δ i+(δ n-δ 1)/n。
  6. 根据权利要求1～5中任意一项所述的电极，其中，沿着逐渐远离所述集流体的方向，第1层所述极片层的体密度为2.55g/cm 3～2.75g/cm 3，第n层所述极片层的体密度为2.0g/cm 3～2.5g/cm 3，第2层至第n-1层所述极片层的体密度为2.0g/cm 3～2.70g/cm 3。
  7. 根据权利要求1～6中任意一项所述的电极，其中，在所述电极中，n层所述极片层的总厚度为20μm～200μm。
  8. 根据权利要求1～7中任意一项所述的电极，其中，n为2～10的整数。
  9. 根据权利要求1～8中任意一项所述的电极，其中，n为2～5的整数。
  10. 根据权利要求1～9中任意一项所述的电极，其中，各层所述极片层中还含有导电剂和粘结剂，相对于100重量份的所述活性材料，所述导电剂的含量为0.1～5重量份，所述粘结剂的含量为0.5～5重量份；
    所述活性材料选自锂镍钴锰氧、磷酸铁锂和锰酸锂中的至少一种；
    所述导电剂选自碳纳米管、石墨烯、炭黑和碳纤维中的至少一种；
    所述粘结剂选自聚偏氟乙烯和/或聚四氟乙烯；
    所述造孔剂选自二氟草酸硼酸锂、双氟甲基二胺锂、硼酸锂、四硼酸锂、四氟硼酸锂、硝酸锂和氯化锂中的至少一种。
  11. 根据权利要求1～10中任意一项所述的电极，其中，所述造孔剂为二氟草酸硼酸锂和/或双氟甲基二胺锂。
  12. 一种制备权利要求1～11中任意一项所述的锂离子电池电极的方法，其中，包括：
    将含有不同含量造孔剂的n层电极片按照造孔剂含量由少至多的顺序依次层叠压合在集流体上，得到所述锂离子电池电极。
  13. 根据权利要求12所述的方法，其中，所述电极片采用下列方法制备得到：
    将活性材料、导电剂、粘结剂和造孔剂进行气流粉碎并混合，得到混合物料；
    将所述混合物料加热熔融后，进行静电纺丝，得到纤维化物料；
    将所述纤维化物料进行热压成型，得到所述电极片。
  14. 一种锂离子电池，其中，所述锂离子电池中含有多孔电极，所述多孔电极由权利要求1～11中任意一项所述的锂离子电池电极或采用权利要求12或13所述的方法得到的锂离子电池电极经电解液浸泡后得到。
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