CN113921753A - Positive plate, preparation method thereof and lithium ion battery - Google Patents

Positive plate, preparation method thereof and lithium ion battery Download PDF

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Publication number
CN113921753A
CN113921753A CN202010648323.7A CN202010648323A CN113921753A CN 113921753 A CN113921753 A CN 113921753A CN 202010648323 A CN202010648323 A CN 202010648323A CN 113921753 A CN113921753 A CN 113921753A
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active material
diffusion layer
porous diffusion
positive electrode
layer
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张柯
马永军
郭姿珠
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BYD Co Ltd
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BYD Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • 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
    • 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

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
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  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)
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Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a positive plate, a preparation method thereof and a lithium ion battery. The positive electrode sheet includes: the current collector, at least two active material layers and a porous diffusion layer, wherein the porous diffusion layer is arranged between two or more adjacent active material layers; wherein the thickness of the active material layer is greater than or equal to the thickness of the porous diffusion layer, and the porosity of the active material layer is less than or equal to the porosity of the porous diffusion layer. The positive plate can obtain a large-loading capacity positive plate without changing the overall compaction density, and the rate capability is not reduced.

Description

Positive plate, preparation method thereof and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a positive plate, a preparation method thereof and a lithium ion battery.
Background
At present, the advantages brought by the large-loading capacity positive electrode are obvious, and the active material proportion in the full battery can be obviously increased by increasing the loading capacity of the positive electrode, so that the energy density of a battery core is obviously increased.
However, under the prior art conditions, in order to realize high capacity, the positive electrode capacity is generally increased by thick coating, and thick coating has the problems of poor high rate performance, insufficient capacity and the like.
In view of the defect that the positive electrode sheet in the prior art can not satisfy the high rate performance and can also fully exert the capacity, the research and development of the positive electrode sheet which can satisfy the high rate performance and fully exert the capacity at the same time is of great significance.
Disclosure of Invention
The invention aims to overcome the defects of low rate performance and insufficient capacity in the prior art, and provides a positive plate, a preparation method thereof and a lithium ion battery.
In order to achieve the above object, a first aspect of the present invention provides a positive electrode sheet, wherein the positive electrode sheet includes: the current collector, at least two active material layers and a porous diffusion layer, wherein the porous diffusion layer is arranged between two or more adjacent active material layers; wherein the thickness of the active material layer is greater than or equal to the thickness of the porous diffusion layer, and the porosity of the active material layer is less than or equal to the porosity of the porous diffusion layer.
The invention provides a preparation method of the positive plate, wherein the method comprises the following steps: and arranging active material layers on the current collector, and arranging a porous diffusion layer between two or more adjacent active material layers to obtain the positive plate.
The third aspect of the invention provides a lithium ion battery, which comprises a positive plate, a negative plate and electrolyte, wherein the positive plate is the positive plate.
Compared with the prior art, the invention adopts the brand-new lithium ion battery positive plate which is easy for large-scale production by adopting the technical scheme. The structure of the positive plate has good ion diffusion performance, lithium ions can be effectively and rapidly diffused to the surface of the positive active material from bulk electrolyte and participate in embedding or separating under the condition of high-rate charge and discharge, the polarization phenomenon on the surface of the positive active material can be effectively relieved, the integral polarization impedance of the battery is further remarkably reduced, and the high-rate discharge capacity of the positive plate under a large loading capacity is remarkably enhanced. In addition, the thickness or the loading capacity of the positive plate can be improved by 2-10 times under the condition of maintaining the existing compaction density by using the existing production facilities. Meanwhile, the space utilization rate of the ion transmission pore channel can be greatly improved through reasonable and effective design. Thereby greatly improving the multiplying power performance under high compaction density.
In a word, the lithium battery positive plate can obtain a large-loading capacity positive plate without changing the overall compaction density, and the rate capability is not reduced.
Drawings
FIG. 1 is a schematic diagram of a positive electrode plate having a CECECECEC structure;
FIG. 2 is a schematic view showing the structure of a positive electrode sheet having a CECECECECEC structure with through holes.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The present invention provides, in a first aspect, a positive electrode sheet, wherein the positive electrode sheet includes: the current collector, at least two active material layers and a porous diffusion layer, wherein the porous diffusion layer is arranged between two or more adjacent active material layers; wherein the thickness of the active material layer is greater than or equal to the thickness of the porous diffusion layer, and the porosity of the active material layer is less than or equal to the porosity of the porous diffusion layer.
In the present invention, it should be noted that: the "active material layer" and the "porous diffusion layer" both refer to a single "active material layer" and a single "porous diffusion layer".
According to the present invention, the inventors of the present invention found that: in the prior art, lithium ions in the electrolyte are difficult to transmit to the active material close to the current collector in the thicker positive electrode layer, so that the active material of the positive electrode is difficult to exert the whole design capacity, and the phenomenon is more remarkable under the conditions of quick charge and high loading capacity. Based on this, the inventors of the present invention found through research that: the thin porous diffusion layer is introduced into the positive plate, and electrolyte ions can be stored and rapidly transmitted by the porous diffusion layer, so that the lithium ions can be effectively and rapidly diffused to the surface of the positive active material from bulk electrolyte and participate in embedding or separating, the polarization phenomenon on the surface of the positive active material can be effectively relieved, the integral polarization impedance of the battery is obviously reduced, and the high-rate discharge capacity of the positive plate under a large loading capacity is obviously enhanced. Further, the inventors of the present invention have found that when the thickness of the active material layer is greater than or equal to the thickness of the porous diffusion layer and the porosity of the active material layer is less than or equal to the porosity of the porous diffusion layer, a large loading of the positive electrode sheet can be obtained without reducing rate performance.
According to the present invention, as shown in fig. 1, fig. 1 is a schematic view of a positive electrode sheet of cececececec structure, which includes a current collector, at least two active material layers (denoted as "C"), and a porous diffusion layer (denoted as "E") disposed between adjacent two or more active material layers. Note that the "active layer" in fig. 1 is referred to as an "active material layer" in the present invention.
According to the present invention, it is preferable that the thickness ratio of the active material layer to the porous diffusion layer is (1-10): 1, more preferably (2-10): 1.
according to the present invention, the porosity ratio of the active material layer to the porous diffusion layer is 1: (1-5), preferably 1: (2-4).
According to the present invention, the thickness ratio of the active material layer to the porous diffusion layer is not preferably too large nor too small. This is because when the thickness ratio is too large, the porous diffusion layer is poor in the ability to diffuse and store ions, and is not favorable for the rate capability. When the thickness ratio is too small, the porous diffusion layer occupies too much of the total volume in the full cell without substantially contributing to capacity, thereby significantly reducing the volumetric energy density of the full cell.
According to the present invention, it is preferable that the thickness of the active material layer is 30 μm to 300 μm; the thickness of the porous diffusion layer is 100nm-30 μm; more preferably, the thickness of the active material layer is 50 μm to 100 μm; the thickness of the porous diffusion layer is 5-10 μm.
According to the present invention, it is preferable that the active material layer is attached to the surface of the current collector in the present invention, since the active material layer near the surface of the current collector can provide a transport path for lithium ions by the porous diffusion layer thereon, which has an advantage of further increasing the volumetric energy density.
According to the invention, the porosity of the porous diffusion layer is between 10 and 80%, preferably between 30 and 60%.
According to the invention, the pores in the porous diffusion layer have a pore diameter of 1.2nm to 10nm, preferably 2nm to 10 nm.
According to the invention, the skeleton material of the porous diffusion layer is different from the material of the active material layer, the skeleton material of the porous diffusion layer is a conductive carbon-based porous material, and preferably, the conductive carbon-based porous material is selected from one or more of graphene, graphene oxide, activated carbon, carbon nanotubes and conductive polymer materials. Wherein the conductive polymer material is selected from one or more of polyaniline, polyacetylene, poly-p-styrene, polypyrrole and polyphenylene sulfide.
In the present invention, when the framework material of the porous diffusion layer is a two-dimensional material, such as graphene, the average pore spacing refers to the average distance between a monoatomic layer (i.e., the spacing between two graphene monolayer films) and the nearest parallel monoatomic layer. The average distance can be derived from the theoretical monatomic layer density, the actual porous layer thickness, and the actual porous layer density.
In the present invention, when the framework material of the porous diffusion layer is a non-two-dimensional conductive porous material such as activated carbon, the average pore spacing is obtained from the nitrogen BET test.
According to the present invention, graphene generally means that there are sp between surface carbon atoms2Hybridized high-conductivity graphene is difficult to disperse. The graphene oxide generally refers to hydrophilic graphene with a large amount of OH, O and COOH groups on the surface, and is easy to disperse on a large scale to prepare hydrogel and porous membrane.
In the present invention, it is preferable that the material of the porous diffusion layer may include a positive electrode active material in addition to the skeleton material; more preferably, the material of the porous diffusion layer may further include a positive electrode active material, a first conductive additive, and a first binder, in addition to the framework material. In the present invention, it should be noted that, although the skeleton material itself is also conductive, the first conductive additive may be added to further enhance the conductivity when the positive electrode active material is added.
According to the present invention, the method for preparing the porous diffusion layer comprises: (1) under the condition of stirring, dissolving a conductive carbon-based porous material and a reducing agent in water, and adjusting the pH value to 8-11 by adopting hydrated ammonia water; (2) naturally cooling to room temperature, and filtering to obtain a mixed hydrogel film; (3) and coating the slurry of the mixed hydrogel film and the pore control solution on a release film, and peeling the release film after controlling drying and rolling to prepare the porous diffusion layer. Further, the porous diffusion layer (labeled "E") after being peeled off from the release film was transferred onto a positive electrode active material layer (labeled "C") to form CE.
In the present invention, the reducing agent is selected from unsymmetrical dimethylhydrazine and/or ascorbic acid.
In the present invention, the pore control solution includes a mixed liquid of one solvent or a plurality of solvents having different boiling points, such as a mixed solution of deionized water and acetone, a mixed solution of acetone and dimethyl carbonate, a mixed solution of N, N-dimethylformamide and dimethyl carbonate, and the like. Alternatively, the pore control solution comprises a solution, suspension, emulsion, or the like of one or more inorganic salts with a low boiling point solvent in which they are dispersible, e.g., a mixed liquid of lithium nitrate and acetone, a mixed liquid of lithium chloride and acetone, a mixed solution of lithium nitrate and N, N-dimethylformamide, or the like.
In the present invention, the pore control solution may further preferably comprise a mixed solution of any one of ionic liquids and a volatilizable solvent, for example, the ionic liquid may be 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) ionic liquid, which passes through a liquid phase so that the entire pore structure does not collapse upon freeze-drying.
In the invention, the pore control solution has the characteristic of selective volatilization, and the core of the function is that one or more components in the pore control solution can be selectively and mainly volatilized in the drying process, and at least one other component which is not easy to volatilize under the drying condition is left, so that the function of controlling the size of the ion transmission pore channel of the diffusion layer is achieved.
According to the present invention, the positive active material is various lithium-deintercalable positive active materials commonly used by those skilled in the art, for example, the positive active material is selected from LiCoO2、LiNiO2、LiCoxNi1-xO2(0≤x≤1)、LiCoxNi1-x-yAlyO2(0≤x≤1，0≤y≤1)、LiMn2O4、LiFexMnyMzO4(M is at least one of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn and Mo, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is equal to 1), Li1+xL1－y－zMyNzO2(L, M, N is at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S and B, -x is more than or equal to 0.1 and less than or equal to 0.2, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and y + z is more than or equal to 0 and less than or equal to 1), LiFePO4、Li3V2(PO4)3、Li3V3(PO4)3、LiVPO4F、Li2CuO2、Li5FeO4One or more of metal sulfides and oxides; wherein the metal sulfide is selected from V2S3、FeS、FeS2And LiMSx(M is at least one of transition metal elements such as Fe, Ni, Cu, Mo and the like, and x is more than or equal to 1 and less than or equal to 2.5); the oxide is selected from TiO2、Cr3O8、V2O5And MnO2One or more of (a).
According to the present invention, it is preferable that the particle diameter of the positive electrode active material is in the range of 100nm to 500 μm.
According to the present invention, the first conductive additive includes a common conductive agent, for example, the conductive additive is selected from one or more of acetylene black, graphene, carbon nanotubes, carbon fibers, and carbon black.
According to the present invention, the first binder is various positive electrode binders known to those skilled in the art, and may be selected from one or more of polythiophene, polypyrrole, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene, polyacrylamide, ethylene-propylene-diene copolymer resin, styrene butadiene rubber, polybutadiene, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, carboxypropyl cellulose, ethyl cellulose, polyethylene oxide, sodium carboxymethyl cellulose (CMC), and styrene butadiene latex (SBR), for example.
According to the present invention, the total volume of the porous diffusion layer is not more than 30 vol%, preferably 3 to 15 vol%, based on the total volume of the positive electrode sheet. This is because the porous diffusion layer is prepared without having lithium intercalation activity without adding an active material, which contributes less active capacity, and thus excessive addition of the porous diffusion layer leads to a reduction in volumetric energy density. Also, since the porous diffusion layer has the functions of storing lithium ions and rapidly conducting lithium ions, the total volume ratio thereof is not excessively low.
In the present invention, the positive electrode sheet has a repeating structural feature of at least two layers, which may be labeled "CE", but the outermost layer has a "CEC" structure. That is, a porous diffusion layer (designated as "E") is provided between two or more of the active material layers (designated as "C"), and the porous diffusion layer accounts for no more than 30 vol% of the total of the positive electrode sheet.
For example, when the porous diffusion layer E having a thickness of 10 μm is used, the thickness of the active material layer C is selected to be 100 μm, and a positive electrode sheet having a thickness of 210 μm can be obtained when it is compounded in a CEC structure. By calculation, the porous diffusion layer E was 4.77 vol% in total volume, and the selected active material layer C was 95.24 vol% in total volume.
For example, when the composite is carried out in a 5-layer CECECECECEC structure, a porous diffusion layer E having a thickness of 5 μm and an active material layer C having a thickness of 50 μm are selected, and a composite positive electrode layer having a thickness of 160 μm in total can be obtained. By calculation, the porous diffusion layer E was 6.25 vol% in total volume, and the selected active material layer C was 93.75 vol% in total volume.
In the present invention, the positive electrode active material layer includes various positive electrode active materials capable of intercalating and deintercalating lithium, a second conductive additive, and a second binder, which are commonly used by those skilled in the art.
In the present invention, the positive electrode active material layer is manufactured by a conventional manufacturing method: coating the slurry containing the positive active material capable of intercalating and deintercalating lithium, a second conductive additive, a second binder and a solvent on a current collector, drying, forming an active material layer on the current collector, and then performing rolling treatment at 0-5MPa to obtain a current collector-active material layer (marked as a current collector-C).
Wherein the second binder is a binder commonly used for positive electrodes, such as: a fluorine-containing resin and a polyolefin compound, wherein the fluorine-containing resin is polyvinylidene fluoride (PVDF) and/or Polytetrafluoroethylene (PTFE); the polyolefin compound is Styrene Butadiene Rubber (SBR).
Wherein the second conductive additive is a common positive electrode conductive agent, such as: acetylene black, carbon nanotubes, carbon fibers, carbon black, and the like. The content of the second binder is 0.01 to 10 weight percent (wt%), preferably 0.02 to 5 wt%, based on the weight of the positive electrode active material; the content of the second conductive additive is 0.1 to 20 wt%, preferably 1 to 10 wt%.
Wherein, the solvent can be one or more selected from N-methylpyrrolidone (NMP), water, ethanol and acetone; the solvent is generally used in an amount of 50 to 400 wt% based on the weight of the cathode active material.
According to the present invention, the positive electrode sheet further includes a through-hole penetrating the active material layer and the porous diffusion layer.
In the present invention, it is preferable that a through hole penetrates the active material layer and the porous diffusion layer in a direction perpendicular to the current collector.
According to the present invention, the purpose of introducing the through-holes is to improve the ionic current connection between the porous diffusion layers, so that the main ionic current between the porous diffusion layers does not need to pass through the positive electrode active material layer having a small porosity, but is mostly directly transmitted through the large through-holes. In addition, since the through hole also penetrates through the positive electrode active material layer, a part of a transmission channel is provided for the positive electrode active material layer at the same time, so that the rate performance is further enhanced.
According to the present invention, as shown in fig. 2, fig. 2 is a schematic view of a positive electrode sheet having a cecececececec structure with "vertical" through-holes, the positive electrode sheet including a current collector, at least two active material layers (denoted by "C"), and a porous diffusion layer (denoted by "E"), the porous diffusion layer being disposed between adjacent two or more active material layers, and through-holes penetrating the active material layers and the porous diffusion layer in a direction perpendicular to the current collector. Note that the "active layer" in fig. 2 is referred to as an "active material layer" in the present invention.
According to the invention, the total volume of the through holes is not more than 10 vol%, preferably 1-10 vol%, based on the total volume of the positive electrode sheet.
In the invention, the structure of the positive plate is provided with a through hole penetrating through the whole positive active material layer except the current collector and the porous diffusion layer, and the porous diffusion layer stores electrolyte and completes the rapid transmission of lithium ions in the horizontal direction; in the vertical direction, lithium ions are rapidly transferred into the porous diffusion layer near the surface of the current collector by the through holes that are perpendicular to the porous diffusion layer and penetrate the porous diffusion layer and the positive electrode active material layer, so that the lithium ions can be rapidly redistributed.
The porous diffusion layer and the through holes occupy smaller total volume of the positive plate, so that the overall energy density of the positive plate is not influenced. On the other hand, since the porous diffusion layer is porous, the porous diffusion layer can be used for storing an electrolyte and remarkably accelerating the lithium ion transport speed in the horizontal direction; the through holes can accelerate the transmission of lithium ions in the vertical direction, and then the lithium ions can be rapidly transmitted to the adjacent positive active material layer from the porous diffusion layer, so that the high-rate charge and discharge performance of the battery is improved, and the capacity of the positive active material is fully exerted; the positive plate still having good rate performance under large loading capacity and high compaction can be obtained, and the energy density of the battery is further improved.
According to the invention, the aperture of the through-hole is between 100nm and 100 μm. The average distance between the adjacent through holes is 10-100 times of the aperture size of the through holes. Preferably, the aperture of the through-hole is between 500nm and 50 μm. The average distance between the adjacent through holes is 10-30 times of the aperture size of the through holes. The aperture of the through hole has an important influence on the ion transmission capability in the vertical direction, and the larger the aperture of the through hole is, the larger the ion current can be transmitted, so that the ion transmission capability and the multiplying power performance are further improved. However, the aperture should not be too large, which would affect the mechanical properties of the entire pole piece. When the diameter of the through hole is too small, the ion transport cannot be effectively achieved. When the diameter of the through-hole is too large, the compaction density of the entire electrode is also reduced. Similarly, the average spacing between the through-holes is also important, and when the average spacing between the through-holes is small, the ion transport ability is enhanced, but the density of the electrodes is reduced, and the volumetric energy density is reduced instead. When the average distance between the through holes is too large, the lithium ion transport ability is not strong.
According to the invention, the thickness of the positive plate is 100-500 μm. Compared with the traditional positive pole layer with the thickness of 50 microns, the positive pole piece obtained by adopting the scheme can obviously increase the mass ratio and the volume ratio of the active substance in the full cell, can simultaneously improve the mass energy density and the volume energy density of the full cell, and simultaneously, because the introduced porous diffusion layer can play a role in rapidly transmitting ions, the rate capability of the obtained cell can still meet the charge and discharge requirements of more than 1C. If the charging and discharging requirements of more than 1C are not needed, the thickness of the positive electrode can be increased to more than 500 μm.
The invention provides a preparation method of the positive plate, wherein the method comprises the following steps: and arranging active material layers on the current collector, and arranging a porous diffusion layer between two or more adjacent active material layers to obtain the positive plate.
According to the present invention, the method further comprises providing through-holes in a direction perpendicular and/or oblique to the active material layer and the porous diffusion layer, wherein the number of the through-holes may be plural.
In the present invention, it is preferable that a through hole penetrates the active material layer and the porous diffusion layer in a direction perpendicular to the current collector.
In the invention, the preparation method of the positive plate comprises the following steps:
(1) coating the selected positive active material layer C on a (positive) current collector;
(2) then, hot-pressing a porous diffusion layer E on the positive active material layer C; after drying, coating another positive active material layer C on the porous diffusion layer E;
(3) CEC (i.e., current collector-positive active material layer-porous diffusion layer-positive active material layer (labeled: current collector-C-E-C)) was obtained after drying and rolling.
As a result, a multi-layered positive electrode sheet in which the respective layers are pressed together is obtained, forming the positive electrode sheet having ion transport channels of the present invention.
The invention provides a lithium ion battery, which comprises a positive plate, a negative plate and electrolyte, and is characterized in that the positive plate is the positive plate.
According to the invention, when a battery with higher requirement on rate performance, such as more than 1.5C (1.5C means charging with 1.5C charging and discharging current and constant voltage charging, and the exerted capacity of the battery is not less than 85% of the capacity measured by 0.1C charging and discharging current), is charged and discharged, the flow of lithium ions which are extracted or inserted in the positive electrode active material layer in unit time is higher, and the porous diffusion layer near the positive electrode active layer is correspondingly required to have more lithium ion storage and better lithium ion transmission capability. Therefore, at a high rate, the active material layer and the porous diffusion layer need to have smaller thicknesses to meet the larger lithium ion requirement of the active material layer, and the porous diffusion layer needs to have larger porosity to rapidly transfer lithium ions to relieve local electrolyte concentration polarization.
Similarly, when the rate performance requirement is small, such as below 1.5C, the ion current and ion storage capacity required for the positive electrode active material layer is small, and since the porous diffusion layer does not generally have lithium intercalation activity, lithium ions are transported therein in the form of solvated ions, contributing less capacity, and therefore, in order to achieve a higher energy density, a larger thickness ratio may be selected to increase the active material content ratio to achieve a higher volumetric energy density, and a larger porosity ratio may be selected to increase the compacted density of the full electrode to enhance the volumetric energy density.
According to the present invention, it is preferable that, for a battery having a rate capability of more than 1.5C, the ratio of the thickness of the active material layer to the porous diffusion layer is (2-5): 1; the ratio of the porosity of the active material layer to the porous diffusion layer is 1: (3-5); for cells having rate capability not greater than 1.5C, the ratio of the thickness of the active material layer to the porous diffusion layer is (5-10): 1; the ratio of the porosity of the active material layer to the porous diffusion layer is 1: (2-3).
According to the invention, the lithium ion battery can be obtained by injecting liquid after the anode and the cathode are combined.
According to the present invention, the anode includes an anode active material, a third conductive additive, and a third binder.
The negative electrode active material is various negative electrode active materials capable of absorbing and desorbing lithium, which are commonly used by those skilled in the art, and is preferably selected from one or more of carbon materials, tin alloys, silicon, tin, germanium, metallic lithium and lithium-indium alloys.
Wherein the carbon material is selected from one or more of non-graphitizing carbon, graphite and carbon. The carbon is one or more selected from pyrolytic carbon, coke, organic polymer sinter and active carbon obtained by high-temperature oxidation of polyacetylene polymer materials.
According to the present invention, the function of the third conductive additive contained in the negative electrode material layer is known to those skilled in the art as common general knowledge of those skilled in the art, and will not be described herein.
According to the present invention, preferably, the third binder is styrene-butadiene latex (SBR).
The present invention will be described in detail below by way of examples.
Example 1
This example is to illustrate a lithium ion battery prepared by the method of the present invention.
(1) Preparation of porous diffusion layer (E)
Mixing 1g of graphene oxide and 0.2g of unsymmetrical dimethylhydrazine, dissolving the mixture in 800mL of distilled water under a stirring state, adding 0.2g of 35% aqueous ammonia by mass into the mixed solution, and carrying out water bath reaction for 30min under stirring at 100 ℃; naturally cooling to room temperature, filtering to obtain a graphene oxide hydrogel film, and placing the graphene oxide hydrogel film on a release film; then soaking the mixed hydrogel film in a 10% lithium nitrate aqueous solution by mass for 12h, and replacing water in the hydrogel with a lithium nitrate solution containing 10% by mass; and finally, drying at 100 ℃ for 24h, washing the dried rapid ion diffusion layer with water, washing off lithium nitrate solid participating in drying in the pore channel, and drying again to obtain the graphene oxide supported rapid ion diffusion pore channel layer E.
The graphene oxide has good conductivity after being reduced by unsymmetrical dimethylhydrazine, namely, the obtained porous diffusion layer has the performance of conducting and ion conducting pore channels.
Wherein the porous diffusion layer E is attached to a release film for later use, wherein the thickness of the E layer is 10 μm, the average pore diameter is 1.2nm, and the porosity is 30%.
(2) Production of Positive electrode active Material layer (C)
9.3g of LiCoO, a positive electrode active material2(93%), 0.3g of PVDF (3%) as a binder, 0.2g of acetylene black (2%), and 0.2g of carbon nanotubes (2%) as a conductive agent were added to 15g of NMP (N-methylpyrrolidone) as a solvent, and then stirred in a stirrer to form a stable and uniform positive electrode slurry. The positive electrode slurry was uniformly and intermittently coated on the surface of an aluminum foil or a porous diffusion layer E (aluminum foil size: 160mm in width, 16 μm in thickness) after transfer hot pressing, and then dried at 120 ℃ and pressed into sheets by a roll press to obtain C or CEC. The thickness of the C layer was 50 μm and the porosity was 15%.
(3) Preparation of composite positive electrode layer
And placing the porous diffusion layer E attached to the release film on the dried active material layer C, and uncovering the release film after hot pressing at 92 ℃ and 1.2MPa in a face-to-face mode to obtain the CE anode film. And (3) continuously coating and drying another active material layer C on the surface of the CE positive electrode film according to the method in the step (2) to obtain the CEC positive electrode layer.
(3) Production of negative electrode active Material layer (A)
18.5g of negative active material artificial graphite (93%), 0.35g of binder CMC (3.5%) and 0.35g of binder SBR (3.5%) were added to 12g of xylene, and then stirred in a vacuum stirrer to form stable and uniform negative slurry. The slurry was uniformly coated intermittently on both sides of a copper foil (copper foil size: width 160mm, thickness 16 μm), then dried at 120 ℃, and cut into a negative electrode sheet a after being pressed into a sheet by a roll press.
(4) Preparation of CAEA CECA
And (3) cutting and aligning the CECs obtained in the steps (1) to (2) in a glove box, then using the A obtained in the step (3), placing a diaphragm between the CEC and the A, then using an aluminum plastic film, and injecting an electrolyte 1M LiPF6EC/DMC for vacuum sealing to obtain the lithium ion battery of the embodiment.
In the lithium ion battery, the thickness of the anode is 110 μm, and in a CEC structure, the thickness ratio of the first active material layer, the porous diffusion layer and the second active material layer is 5:1: 5; the ratio of the porosities of the first active material layer, the porous diffusion layer, and the second active material layer is 1:2: 1.
Example 2
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "1 g of graphene oxide" was modified to "0.5 g of graphene oxide", and the thickness of the rapid diffusion layer E after drying was changed so that the thickness of the rapid diffusion layer E was 5 μm.
In the lithium ion battery, the thickness of the anode is 105 μm, and in a CEC structure, the thickness ratio of the first active material layer, the porous diffusion layer and the second active material layer is 10:1: 10; the ratio of the porosities of the first active material layer, the porous diffusion layer, and the second active material layer is 1:2: 1.
Example 3
A lithium ion battery was prepared in the same manner as in example 1, except that: in step (1), the prepared positive electrode layer is rolled by using a metal needle array with the needle diameter of 25 μm and the average needle spacing of 1000 μm, so that the metal needle array penetrates through the positive electrode layer. And obtaining the positive electrode layer structure with vertical pore channels.
Example 4
A lithium ion battery was prepared in the same manner as in example 1, except that: in step (1), the prepared positive electrode layer is rolled by using a metal needle array with the needle diameter of 50 μm and the average needle spacing of 1000 μm, so that the metal needle array penetrates through the positive electrode layer. And obtaining the positive electrode layer structure with vertical pore channels.
Example 5
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "1 g of graphene oxide" is modified to "50 mg of graphene oxide", and the thickness of the rapid diffusion layer E is changed so that the thickness of the rapid diffusion layer E after drying is 500 nm.
In the lithium ion battery, in the step (2), the amount of the cathode auxiliary material is reduced to 1g so that the thickness of the cathode active material layer C is 5 μm, and in the CEC structure, the ratio of the thicknesses of the first active material layer, the porous diffusion layer and the second active material layer is 10:1: 10; the ratio of the porosities of the first active material layer, the porous diffusion layer, and the second active material layer is 1:2: 1.
Example 6
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), 3 active material layers C and 2 porous diffusion layers E were prepared, and a 170 μm thick composite electrode of CECEC structure was obtained after hot pressing.
Example 7
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), 1g of graphene oxide is modified into 0.2g of graphene oxide, and then a mixed solution of 10 vol% of 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF4) ionic liquid and water is used as an exchange solution of the hydrogel membrane, so that the hydrogel membrane contains 10 vol% of EmimBF4 liquid. Since the hydrogel contains more nonvolatile solvent at this time, the pore diameter thereof supported by the nonvolatile liquid after drying was more than 6 nm. The E layer has a thickness of 10 μm, an average pore diameter of 6nm and a porosity of 60% by volume.
In the lithium ion battery, the thickness of the anode is 110 μm, and in a CEC structure, the thickness ratio of the first active material layer, the porous diffusion layer and the second active material layer is 5:1: 5; the ratio of the porosities of the first active material layer, the porous diffusion layer, and the second active material layer is 1:4: 1.
Example 8
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "1 g of graphene oxide" was modified to "2 g of graphene oxide", and the thickness of the rapid diffusion layer was changed so that the thickness of the rapid diffusion layer E after drying was 30 μm.
In the lithium ion battery, the thickness of the anode is 130 μm, and in a CEC structure, the thickness ratio of the first active material layer, the porous diffusion layer and the second active material layer is 5:3: 5; the ratio of the porosities of the first active material layer, the porous diffusion layer, and the second active material layer is 1:2: 1.
Comparative example 1
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), the liquid in the hydrogel is not replaced with the mixed solution when the rapid diffusion layer E is prepared. Since there was no non-volatile solvent in the hydrogel at this time, the pore size was largely collapsed, and the porosity was 10 vol%.
In the lithium ion battery, the thickness of the anode is 110 μm, and in a CEC structure, the thickness ratio of the first active material layer, the porous diffusion layer and the second active material layer is 5:1: 5; the ratio of the porosities of the first active material layer, the porous diffusion layer, and the second active material layer was 3:2: 3.
Comparative example 2
A lithium ion battery was prepared in the same manner as in example 1, except that: the rapid diffusion layer E is not used, and a structure of superposing two active anode layers, namely a CC structure, is directly used.
Comparative example 3
A lithium ion battery was prepared in the same manner as in example 1, except that: in the step (1), "1 g of graphene oxide" was modified to "6 g of graphene oxide", and the thickness of the rapid diffusion layer was changed so that the thickness of the rapid diffusion layer E after drying was 70 μm.
In the lithium ion battery, the thickness of the anode is 170 mu m, and in a CEC structure, the thickness ratio of the first active material layer, the porous diffusion layer and the second active material layer is 5:7: 5; the ratio of the porosities of the first active material layer, the porous diffusion layer, and the second active material layer is 1:2: 1.
Test example
Battery performance testing
The full-cell lithium batteries obtained in examples 1 to 8 and comparative examples 1 to 3 were subjected to a cycle performance test of the batteries according to the following method:
28 batteries prepared in each example and each comparative example were used, and each of the batteries of the examples and the comparative examples was subjected to charge-discharge cycle tests at 0.1C, 0.5C, 1C, and 2C on a LAND CT 2001C secondary battery performance testing apparatus at 24-26 ℃.
The method comprises the following steps: standing for 10 min; constant current charging is carried out until 4.2V is cut off; standing for 10 min; constant current discharge to 1.5V, i.e. 1 cycle. The average value is obtained by repeating the step for 10 times, namely the capacity at the multiplying power is shown in table 1.
Meanwhile, when the battery capacity is lower than 80% of the first discharge capacity in the circulation process, the circulation is terminated, the circulation times are the circulation life of the battery, each group is averaged, and the data of the parameters and the average first discharge capacity of the battery are shown in table 2.
TABLE 1
Serial number 0.1C(*) 0.5C(*) 1C(*) 2C(*) Number of cycles
Example 1 789 771 763 732 670
Example 2 812 797 785 701 613
Example 3 831 815 789 776 765
Example 4 820 813 802 793 810
Example 5 705 701 697 695 860
Example 6 851 837 820 809 793
Example 7 832 803 791 781 790
Example 8 703 691 673 659 835
Comparative example 1 756 743 726 670 612
Comparative example 2 773 731 705 625 579
Comparative example 3 561 557 550 541 830
TABLE 2
Figure BDA0002573959200000171
Figure BDA0002573959200000181
As can be seen from the results of tables 1 and 2:
on the data of examples 1-4 and comparative example 2 it can be seen that: under the condition of not changing the integral compaction density, the lithium battery positive plate with large loading capacity can be obtained, and the rate performance is not reduced, namely, the mass energy density is increased, and the volume energy density is increased.
The higher cycle times in examples 1-5 illustrate that the porous diffusion layers and vias of the present invention can significantly improve the overall cycle times. In example 5, the rate performance was significantly improved when the porous diffusion layer and the active material layer were both thin, but the volumetric energy density was reduced when the proportion of the active material in the full cell was small.
Example 6 is a 170 μm thick composite electrode based on the CECEC structure obtained on the basis of example 1.
Example 7 uses an ionic liquid that acts to keep the entire pore structure from collapsing during freeze-drying through the liquid phase, which is advantageous compared to using solid lithium nitrate. Secondly, 10 vol% will give rise to a pore size of about 6nm, with a larger pore size being more conducive to lithium ion transport.
Example 8 is based on example 1, the porous diffusion layer is 3 times thicker, i.e., the ratio of the thicknesses of the first active material layer, the porous diffusion layer and the second active material layer is 5:3:5, and the ratio of the thicknesses is smaller than that of example 1, resulting in a reduction in volumetric energy density but better rate capability.
Comparative example 1 shows that when the average pore diameter of the porous diffusion layer is less than the lower limit of 1.2nm of the present invention, the volumetric energy density, rate capability and cycle number are significantly reduced.
Comparative example 2 shows that the effect is poor when a structure in which two active positive electrode layers are stacked, i.e., a CC structure, is directly used without using the rapid diffusion layer E.
Comparative example 3 shows that when the porous diffusion layer thickness is larger than the active material layer, i.e., when the range defined by the technical solution of the present invention is not exceeded, although the rate capability and the cycle are both good, the volumetric energy density is significantly reduced.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (16)

1. A positive electrode sheet, comprising: the current collector, at least two active material layers and a porous diffusion layer, wherein the porous diffusion layer is arranged between two or more adjacent active material layers; wherein the thickness of the active material layer is greater than or equal to the thickness of the porous diffusion layer, and the porosity of the active material layer is less than or equal to the porosity of the porous diffusion layer.
2. The positive electrode sheet according to claim 1, wherein the thickness ratio of the active material layer to the porous diffusion layer is (1-10): 1; the porosity ratio of the active material layer to the porous diffusion layer is 1: (1-5).
3. The positive electrode sheet according to claim 1 or 2, wherein the thickness of the active material layer is 30 μm to 300 μm; the thickness of the porous diffusion layer is 100nm-30 μm.
4. The positive electrode sheet according to claim 1 or 2, wherein the porosity of the porous diffusion layer is 10 to 80%, and the pore diameter of pores in the porous diffusion layer is 1.2nm to 10 nm.
5. The positive electrode sheet according to claim 1, wherein the total volume of the porous diffusion layer is not more than 30 vol%, based on the total volume of the positive electrode sheet.
6. The positive electrode sheet according to claim 1, wherein said positive electrode sheet further comprises through-holes penetrating said active material layer and said porous diffusion layer.
7. The positive electrode sheet according to claim 6, wherein the total volume of the through-holes is not more than 10% by volume based on the total volume of the positive electrode sheet.
8. The positive electrode sheet according to claim 6, wherein the through-holes have a pore diameter of 100nm to 100 μm, and the average pitch of adjacent through-holes is 10 to 100 times the pore diameter of the through-holes.
9. The positive electrode sheet according to claim 8, wherein the through-holes have a pore diameter of 500nm to 50 μm, and the average pitch of adjacent through-holes is 10 to 30 times the pore diameter of the through-holes.
10. The positive electrode sheet according to claim 1 or 2, wherein the skeleton material of the porous diffusion layer is a conductive carbon-based porous material.
11. The positive electrode sheet according to claim 10, wherein the conductive carbon-based porous material is selected from one or more of graphene, graphene oxide, activated carbon, carbon nanotubes, and a conductive polymer material.
12. The positive electrode sheet according to claim 1, wherein the thickness of the positive electrode sheet is 100 μm to 500 μm.
13. A method for producing a positive electrode sheet according to any one of claims 1 to 12, characterized by comprising: and arranging active material layers on the current collector, and arranging a porous diffusion layer between two or more adjacent active material layers to obtain the positive plate.
14. The method of claim 13, further comprising providing a plurality of through-holes in a direction perpendicular and/or oblique to the active material layer and the porous diffusion layer.
15. A lithium ion battery, comprising a positive plate, a negative plate and an electrolyte, wherein the positive plate is the positive plate of any one of claims 1 to 12.
16. The lithium ion battery of claim 15, wherein for a battery having a rate capability greater than 1.5C, the ratio of the thickness of the active material layer to the porous diffusion layer is (2-5): 1; the porosity ratio of the active material layer to the porous diffusion layer is 1: (3-5);
for cells with rate capability not greater than 1.5C, the ratio of the thickness of the active material layer to the porous diffusion layer is (5-10): 1; the porosity ratio of the active material layer to the porous diffusion layer is 1: (2-3).
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