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CN114464778A - Method for preparing negative pole piece, negative pole piece and secondary battery - Google Patents

Method for preparing negative pole piece, negative pole piece and secondary battery Download PDF

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Publication number
CN114464778A
CN114464778A CN202210054240.4A CN202210054240A CN114464778A CN 114464778 A CN114464778 A CN 114464778A CN 202210054240 A CN202210054240 A CN 202210054240A CN 114464778 A CN114464778 A CN 114464778A
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China
Prior art keywords
lithium
negative pole
pole piece
negative electrode
film layer
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CN202210054240.4A
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Chinese (zh)
Inventor
张强
岳昕阳
闫崇
李泽珩
姚雨星
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Tsinghua University
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Tsinghua University
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Priority to CN202210054240.4A priority Critical patent/CN114464778A/en
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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
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/043—Processes of manufacture in general involving compressing or compaction
    • H01M4/0435—Rolling or calendering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The application discloses a method for preparing a negative pole piece, the negative pole piece and a secondary battery. The method comprises the following steps: providing an initial negative pole piece, wherein the initial negative pole piece comprises a negative current collector and a negative film layer arranged on at least one surface of the negative current collector; the method comprises the following steps of preparing a lithium-containing negative pole piece, wherein a lithium-containing layer for supplementing active lithium is arranged on the surface of a negative pole film layer, so that the lithium-containing negative pole piece is obtained; and the step for carrying out pre-lithiation reaction comprises the step of applying 25-55 MPa of pressure to the lithium-containing negative pole piece in an electrolyte containing lithium ions so as to obtain the pre-lithiated negative pole piece. The active lithium lost due to the formation of the SEI film can be supplemented, and the first coulombic efficiency and the cycle performance of the secondary battery can be improved.

Description

Method for preparing negative pole piece, negative pole piece and secondary battery
Technical Field
The application belongs to the technical field of secondary batteries, and particularly relates to a method for preparing a negative pole piece, the negative pole piece and the secondary battery.
Background
In recent years, as secondary batteries are applied and popularized in industries such as various electronic products and new energy vehicles, their energy density has been receiving more and more attention. However, in the first charging process of the secondary battery, a Solid Electrolyte Interface (SEI) film is inevitably formed on the surface of the negative active material, which causes irreversible consumption of active ions, thus resulting in irreversible capacity loss of the secondary battery being difficult to eliminate, and presenting a challenge to increase of energy density of the secondary battery.
Disclosure of Invention
A first aspect of the present application provides a method for preparing a negative electrode tab of a secondary battery, the method comprising:
providing an initial negative pole piece, wherein the initial negative pole piece comprises a negative current collector and a negative pole film layer arranged on at least one surface of the negative current collector;
the method comprises the following steps of preparing a lithium-containing negative pole piece, wherein a lithium-containing layer for supplementing active lithium is arranged on the surface of a negative pole film layer, so that the lithium-containing negative pole piece is obtained;
and the step for carrying out pre-lithiation reaction comprises the step of applying 25-55 MPa of pressure to the lithium-containing negative pole piece in an electrolyte containing lithium ions so as to obtain the pre-lithiated negative pole piece.
According to the method for preparing the negative pole piece of the secondary battery, the lithium-containing layer is arranged on the surface of the negative pole film layer, and then pressure is applied to the negative pole piece placed in the electrolyte containing lithium ions, so that the pre-lithiated negative pole piece is obtained. According to the negative pole piece prepared by the method, the lithium-containing layer has higher conversion rate, so that active lithium lost due to the formation of an SEI (solid electrolyte interphase) film can be supplemented, and the first coulombic efficiency and the cycle performance of the secondary battery can be improved. In addition, the negative pole piece prepared by the method is simple in structure and convenient to prepare, and industrial production of the negative pole piece is facilitated.
In an alternative embodiment of the method of the present application, providing an initial negative electrode tab comprises:
providing negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material, a conductive agent and a binder, and based on the total mass of solids in the negative electrode slurry, the mass proportion of the negative electrode active material is 88-92 wt%, the mass proportion of the conductive agent is 4-6 wt%, and the mass proportion of the binder is 4-6 wt%;
the step for preparing the initial negative pole piece comprises the steps of coating the negative pole slurry on at least one surface of a negative pole current collector, and drying and cold pressing to obtain the initial negative pole piece.
In an alternative embodiment of the method of the present application, the profile arithmetic mean deviation Ra of the negative electrode film layer1Satisfies the following conditions: ra of 0.3 mu m or less1Less than or equal to 1.2 mu m, and the porosity of the negative electrode film layer is 5-50%.
In an alternative embodiment of the method of the present application, a lithium-containing layer for supplementing active lithium is provided on a surface of the negative electrode film layer, and includes:
and arranging a lithium-containing layer for supplementing active lithium on the surface of the negative electrode film layer in a physical mode, wherein the physical mode comprises at least one of blade coating, spraying, layer pressing, magnetron sputtering and vacuum evaporation.
In an alternative embodiment of the method of the present application, the lithium-containing negative electrode sheet has an arithmetic mean difference Ra in profile2Satisfies the following conditions: ra of 0.01 mu m2≤2μm。
In an alternative embodiment of the method of the present application, the step for performing a prelithiation reaction comprises:
after obtaining the lithium-containing negative pole piece, transferring the lithium-containing negative pole piece into an electrolyte containing lithium ions within 0-1440 min, preferably 0-30 min;
and applying 25-55 MPa of pressure to the lithium-containing negative pole piece to obtain the pre-lithiated negative pole piece.
In an optional embodiment of the method, applying a pressure of 25 to 55MPa to the lithium-containing negative electrode plate in an electrolyte containing lithium ions comprises:
and arranging metal pressure plates on two opposite surfaces in the thickness direction of the lithium-containing negative pole piece, and applying 25-55 MPa pressure to the lithium-containing negative pole piece through the metal pressure plates.
In an alternative embodiment of the method of the present application, a wire is connected between the metal pressure plates.
In an alternative embodiment of the method of the present application, the ratio of the active lithium capacity per unit area of the negative electrode film layer to the active lithium capacity per unit area of the lithium-containing layer is 1:0.1 to 1: 0.5.
A second aspect of the present application provides a negative electrode sheet obtained by a method according to any of the embodiments of the first aspect of the present application.
The negative pole piece according to the second aspect of the application is applied to the secondary battery, and the first coulomb efficiency and the cycle performance of the secondary battery can be improved. In addition, the negative pole piece of this application simple structure, the preparation of being convenient for is favorable to realizing the industrial production of this negative pole piece.
A third aspect of the present application provides a secondary battery comprising a negative electrode tab according to the second aspect of the present application.
The secondary battery provided by the third aspect of the application comprises the negative pole piece according to the second aspect of the application, and has high first coulombic efficiency and good cycle performance.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present application, and it is obvious for a person skilled in the art to obtain other drawings based on the drawings without any creative effort.
Fig. 1 is a schematic view of a pre-lithiation reaction performed in an embodiment of the present application.
Detailed Description
In order to make the purpose, technical solution and advantageous technical effects of the present invention clearer, the present invention is further described in detail with reference to the following embodiments. It should be understood that the embodiments described in this specification are only for the purpose of explaining the present application and are not intended to limit the present application.
For the sake of brevity, only some numerical ranges are explicitly disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Also, although not explicitly recited, each point or individual value between endpoints of a range is encompassed within the range. Thus, each point or individual value can form a range not explicitly recited as its own lower or upper limit in combination with any other point or individual value or in combination with other lower or upper limits.
In the description herein, when a composition is described as containing, comprising, or including a particular component, or when a process is described as containing, comprising, or including a particular process step, it is contemplated that the composition of the present application also consists essentially of, or consists of, the component, and that the process of the present application also consists essentially of, or consists of, the process step.
The use of the terms "comprising," "including," "containing," and "having" are generally to be construed as open-ended and non-limiting unless otherwise expressly specified.
In the description herein, it is to be noted that, unless otherwise specified, "above" and "below" are inclusive, and "a plurality" of "one or more" means two or more.
The above summary of the present application is not intended to describe each disclosed embodiment or every implementation of the present application. The following description more particularly exemplifies illustrative embodiments. At various points throughout this application, guidance is provided through a list of embodiments that can be used in various combinations. In each instance, the list is merely a representative group and should not be construed as exhaustive.
As described in the background art, the SEI film formed on the surface of the negative active material is an important factor causing irreversible capacity loss of the secondary battery. The silicon-based negative electrode material (3579 mAh/g) with extremely high theoretical specific capacity has larger volume expansion during first charging, so that the secondary battery generates a serious irreversible capacity loss phenomenon during first charging, and further the first coulombic efficiency is reduced and the cycle performance is poor. However, the formation of the SEI film is inevitable during the electrochemical reaction. Therefore, in order to more fully utilize the theoretical capacity of the negative electrode active material, it is very important to develop an appropriate prelithiation method to compensate for the capacity loss of the secondary battery.
As one of the prelithiation methods for improving the initial coulombic efficiency of the battery, the lithium-containing layer is covered on the surface of the negative electrode to carry out prelithiation reaction on the negative electrode, so that a solid electrolyte film is formed on the surface of the negative electrode in advance or extra lithium ion capacity is prestored in the negative electrode structure, and the initial coulombic efficiency and the reversible cycle capacity of the lithium ion battery can be obviously improved. For example, in a patent publication No. CN110828778A, a sandwich-structured pre-lithiation negative electrode and a lithium ion battery are disclosed, in which a protective layer is covered on the surface of the negative electrode by a magnetron sputtering method, then a lithium-containing layer is deposited on the protective layer by a vacuum thermal evaporation method, and finally another protective layer is covered on the surface of the lithium-containing layer by a magnetron sputtering method, so as to form a pre-lithiation electrode to implement a contact pre-lithiation reaction. However, this method still has difficulty in achieving accurate control of the contact prelithiation process and promotion of industrialization.
Based on this, the inventors have conducted intensive studies with the intention of providing a simple negative contact prelithiation method suitable for industrial production, thereby effectively improving the energy density of a secondary battery.
In view of this, the present application provides, in a first aspect, a method for preparing a negative electrode tab of a secondary battery, the method comprising:
step S10, providing an initial negative electrode sheet, where the initial negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector.
The method further comprises a step S20 of preparing a lithium-containing negative electrode plate, wherein the step comprises the step of arranging a lithium-containing layer for supplementing active lithium on the surface of the negative electrode film layer, so that the lithium-containing negative electrode plate is obtained.
The composition of the lithium-containing layer is not particularly limited as long as active lithium can be provided. In some embodiments, the lithium-containing layer may satisfy: the potential at which lithium in the lithium-containing layer is oxidized to form lithium ions may be 0.5V to 0V with respect to the potential of metallic lithium. Specifically, the lithium-containing layer may include at least one of metallic lithium and a lithium alloy, and more specifically, the lithium alloy may be an alloy including metallic Li and at least one of Ag, Au, Sn, Si, Bi, Al, Mg, In.
The method further comprises a step S30 of carrying out a pre-lithiation reaction, wherein the step comprises applying 25-55 MPa of pressure to the lithium-containing negative pole piece in an electrolyte containing lithium ions, so that the pre-lithiated negative pole piece is obtained.
The electrolyte may include an electrolyte used in a lithium ion battery, and for example, the electrolyte may include an electrolyte prepared from raw materials such as an organic solvent, an electrolyte lithium salt, and necessary additives at a certain ratio under certain conditions.
Without intending to be bound by any theory or explanation, the inventors have found that applying a pressure of a magnitude within the above range to the lithium-containing negative electrode tab can ensure effective contact of the lithium-containing layer and the negative electrode film layer. Specifically, in the prelithiation process, the contact interface between the lithium-containing layer and the negative electrode film layer is a reaction interface, and along with the dissolution of the lithium-containing layer and the growth of the SEI film, the structure of the contact interface decays, so that the reaction cannot be effectively performed. The lithium-containing negative pole piece is applied with pressure with proper magnitude, so that the effective contact of the lithium-containing layer and the negative pole film layer can be ensured, the conversion rate of the lithium-containing layer in the pre-lithiation process is improved, the irreversible capacity loss generated in the first circulation process of the secondary battery can be effectively compensated, and the first coulomb efficiency and the circulation performance of the secondary battery are improved.
According to the method for preparing the negative pole piece of the secondary battery, the lithium-containing layer is arranged on the surface of the negative pole film layer, and then pressure is applied to the negative pole piece placed in the electrolyte containing lithium ions, so that the pre-lithiated negative pole piece is obtained. According to the negative pole piece prepared by the method, the lithium-containing layer has higher conversion rate, so that active lithium lost due to the formation of an SEI (solid electrolyte interphase) film can be supplemented, and the first coulombic efficiency and the cycle performance of the secondary battery can be improved. In addition, the negative pole piece prepared by the method is simple in structure and convenient to prepare, and industrial production of the negative pole piece is facilitated.
Providing an initial negative electrode tab in some embodiments may include the following steps of providing a negative electrode slurry and for preparing an initial negative electrode tab.
Providing negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material, a conductive agent and a binder, and based on the total mass of solids in the negative electrode slurry, the mass proportion of the negative electrode active material is 88-92 wt%, the mass proportion of the conductive agent is 4-6 wt%, and the mass proportion of the binder is 4-6 wt%.
The step for preparing the initial negative pole piece comprises the steps of coating the negative pole slurry on at least one surface of a negative pole current collector, and drying and cold pressing to obtain the initial negative pole piece.
The types of the negative electrode active material, the conductive agent, and the binder are not particularly limited in the present application. As one example, the negative active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. As one example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As one example, the binder may include at least one of Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), Polyacrylamide (PAM), polyvinyl alcohol (PVA), Sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
The proportion of the components of the negative electrode slurry is within the range, so that the negative electrode pole piece has good conductivity and high energy density, and the secondary battery has good cycle performance, long cycle life and high energy density.
In some embodiments, the profile arithmetic mean difference Ra of the negative electrode film layer1Can satisfy the following conditions: ra of 0.3 mu m or less1Less than or equal to 1.2 mu m, and the porosity of the negative electrode film layer can be 5-50%.
The arithmetic mean difference in profile can be measured by methods known in the art, for example by a non-contact surface roughness meter or atomic force microscope. The porosity can be measured by methods known in the art, for example by a porosimeter.
Without intending to be bound by any theory or explanation, the inventors found that when the contour arithmetic mean difference of the negative electrode film layer is within the above range, the lithium-containing layer is favorably adhered to the surface of the negative electrode film layer closely, and the effective contact surface of the two phases is higher, thereby being favorable for improving the conversion rate of the lithium-containing layer.
In some embodiments, providing a lithium-containing layer for supplementing active lithium on a surface of the negative electrode film layer may include:
and arranging a lithium-containing layer for supplementing active lithium on the surface of the negative electrode film layer in a physical mode, wherein the physical mode comprises at least one of blade coating, spraying, layer pressing, magnetron sputtering and vacuum evaporation.
Without intending to be bound by any theory or explanation, the inventors have discovered that physically disposing the lithium-containing layer on the surface of the negative electrode film layer facilitates formation of a suitable contact interface between the negative electrode film layer and the lithium-containing layer, thereby facilitating the prelithiation process. The lithium-containing layer is arranged on the surface of the negative electrode film layer in a physical mode, so that the lithium-containing layer can be ensured to have higher conversion rate, and the effect of lithium supplement through pre-lithiation is improved. In addition, compared with other methods, the physical mode is more matched with an industrial manufacturing mode, and industrial production of the negative pole piece is facilitated.
In some embodiments, the profile arithmetic mean deviation Ra of the lithium-containing negative electrode sheet2Can satisfy the following conditions: ra of 0.01 mu m2≤2μm。
Without intending to be bound by any theory or explanation, the inventors found that the contour arithmetic mean difference of the lithium-containing negative electrode sheet can reflect the contact state between the lithium-containing layer and the negative electrode film layer to some extent. When the contour arithmetic mean difference of the lithium-containing negative pole piece is in the range, the lithium-containing layer is tightly contacted with the negative pole film layer, and the matching degree of the space geometric structures of the two phases is high, which is beneficial to the smooth operation of the pre-lithiation reaction. By controlling the contour arithmetic mean difference of the lithium-containing negative pole piece to be within the proper range, the prepared negative pole piece is applied to the secondary battery, and the first coulombic efficiency and the cycle performance of the secondary battery can be effectively improved.
In some embodiments, the step for performing a prelithiation reaction may comprise:
after obtaining the lithium-containing negative pole piece, transferring the lithium-containing negative pole piece into an electrolyte containing lithium ions within 5-1440 min, preferably within 5-30 min;
and applying 25-55 MPa of pressure to the lithium-containing negative pole piece to obtain the pre-lithiated negative pole piece.
Without intending to be limited by any theory or explanation, the inventor finds that transferring the lithium-containing negative electrode plate into the electrolyte containing lithium ions within 0-1440 min, and applying pressure to the lithium-containing negative electrode plate can avoid lithium loss caused by long-time placement, such as ambient etching, lithium loss caused by side reaction between the negative electrode film layer and the lithium-containing layer, and the like, so that the lithium-containing layer can have higher conversion rate, and further the secondary battery has higher first coulombic efficiency and good cycle performance.
In some embodiments, applying a pressure of 25 to 55MPa to the lithium-containing negative electrode sheet in an electrolyte containing lithium ions may include:
and arranging metal pressure plates on two opposite surfaces in the thickness direction of the lithium-containing negative pole piece, and applying 25-55 MPa pressure to the lithium-containing negative pole piece through the metal pressure plates.
The pressure applied by the metal pressure plate to the lithium-containing negative electrode plate can be a pressure with a constant magnitude.
In some embodiments, as shown in fig. 1, wires may be connected between the metal pressure plates.
Without being bound by any theory or explanation, the inventors have discovered that connecting a wire between metal pressure plates allows electrons to pass from an external circuit, thereby promoting the conversion of the lithium-containing layer and the pre-lithiation reaction.
In some embodiments, a ratio of an active lithium capacity per unit area of the negative electrode film layer to an active lithium capacity per unit area of the lithium-containing layer may be 1:0.1 to 1: 0.5.
Without being bound by any theory or explanation, the inventors found that the ratio of the active lithium capacity per unit area of the negative electrode film layer to the active lithium capacity per unit area of the lithium-containing layer is within the above range, and that ineffective prelithiation reaction (i.e., supplemented capacity much higher than that to be supplemented) can be avoided while active lithium lost by the formation of the SEI film is effectively supplemented, thereby enabling the secondary battery to have higher energy density and lower manufacturing cost while improving the first coulombic efficiency and cycle performance of the secondary battery.
The ratio of the active lithium capacity per unit area of the negative electrode film layer to the active lithium capacity per unit area of the lithium-containing layer may be controlled in various ways, and specifically, may be controlled by the ratio of the mass of the negative electrode active material in the negative electrode film layer to the mass of the lithium-containing layer, or by the ratio of the thickness of the negative electrode film layer to the thickness of the lithium-containing layer.
A second aspect of the present application provides a negative electrode tab obtained according to the method of any embodiment of the first aspect of the present application.
The negative pole piece according to the second aspect of the application is applied to the secondary battery, and the first coulomb efficiency and the cycle performance of the secondary battery can be improved. In addition, the negative pole piece of this application simple structure, the preparation of being convenient for is favorable to realizing the industrial production of this negative pole piece.
In a third aspect, the present application provides a secondary battery comprising a negative electrode sheet according to the second aspect of the present application
The secondary battery provided by the third aspect of the application comprises the negative pole piece according to the second aspect of the application, and has high first coulombic efficiency and good cycle performance.
Examples
The present disclosure is more particularly described in the following examples that are intended as illustrative only, since various modifications and changes within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are on a weight basis, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the equipment used in the examples is commercially available.
Test section
In the following examples, the porosity of the negative electrode film layer was measured by a mercury porosimeter (instrument). The specific test method is as follows:
the pole piece to be measured is placed in a mercury porosimeter, mercury is pressed into the pores of the porous body by using a certain pressure to overcome the resistance of the capillary tube, and when the pressure applied to the mercury in the pole piece to be measured is increased from atmospheric pressure to the pressure limit of the mercury porosimeter, the volume of the part of the capillary tube can be measured according to the volume change of the mercury in the stem of the dilatometer.
Arithmetic mean deviation Ra of profile of negative electrode film layer1And the profile arithmetic mean difference Ra of the lithium-containing negative pole piece2Measured by an interferometric coaxial 3D displacement gauge (instrument). The specific test method is as follows:
placing the electrode to be measured under the lens of the measuring instrument to capture the surface roughness information of the sample, thereby obtaining the arithmetic mean deviation Ra of the profile of the negative electrode film layer1And the profile arithmetic mean difference Ra of the lithium-containing negative pole piece2。
Example 1
Uniformly mixing 90 wt% of graphite, 5 wt% of conductive carbon black and 5 wt% of PVDF in an N-methyl pyrrolidone solvent by taking the total mass of solids in the negative electrode slurry as 100 wt% to form viscous negative electrode slurry;
uniformly coating the negative electrode slurry on a copper foil current collector, then placing the copper foil current collector in a vacuum drying oven, and drying for 24 hours at 80 ℃ to obtain a dried negative electrode piece;
after the negative pole piece is subjected to rolling treatment, cutting the negative pole piece into a certain size to obtain an initial negative pole piece, and placing the initial negative pole piece in a vacuum drying oven for storage, wherein the porosity of a negative pole film layer is 30%, and the arithmetic mean deviation Ra of the outline is10.5 μm;
compounding a lithium-containing layer on the surface of a negative electrode film layer of the initial negative electrode pole piece in a physical mode to obtain the lithium-containing negative electrode pole piece, wherein the ratio (marked as A) of the active lithium capacity per unit area of the negative electrode film layer to the active lithium capacity per unit area of the lithium-containing layer is 1:0.15, and the arithmetic mean difference Ra of the outline of the lithium-containing negative electrode pole piece is2The thickness was controlled to 0.3. mu.m.
And transferring the lithium-containing negative pole piece into an electrolyte containing lithium ions, wherein the time T from the formation of the lithium-containing negative pole piece to the transfer of the lithium-containing negative pole piece into the electrolyte is 1min, and applying constant pressure P with a certain size to the lithium-containing negative pole piece to obtain the pre-lithiated negative pole piece.
Examples 2 to 9
The preparation process of the negative electrode plate was the same as in example 1, with the changes that: the porosity and Ra of the negative electrode film layer are adjusted1、Ra2T and F.
Examples 10 to 12
The preparation process of the negative electrode plate was the same as in example 1, with the changes that: the porosity and Ra of the negative electrode film layer are adjusted1、Ra2T and F, and the initial negative pole piece was prepared by the following procedure:
uniformly mixing 90 wt% of silica/graphite composite material, 5 wt% of conductive carbon black, 3 wt% of sodium carboxymethylcellulose (CMC) and 2 wt% of Styrene Butadiene Rubber (SBR) in deionized water to form viscous negative electrode slurry, wherein the total mass of solids in the negative electrode slurry is 100 wt%;
uniformly coating the negative electrode slurry on a copper foil current collector, then placing the copper foil current collector in a vacuum drying oven, and drying for 24 hours at 70 ℃ to obtain a dry negative electrode piece;
and after the negative pole piece is subjected to rolling treatment, cutting the negative pole piece into a certain size to obtain an initial negative pole piece, and placing the initial negative pole piece in a vacuum drying oven for storage.
Comparative example 1
The preparation process of the negative electrode plate was the same as in example 1, with the changes that: no pressure was applied to the lithium-containing negative electrode piece.
Comparative example 2
The preparation process of the negative electrode plate was the same as in example 1, with the changes that: the electrolyte containing lithium ions is replaced with an electrolyte not containing lithium ions.
The preparation parameters of examples 1 to 12 and comparative examples 1 to 2 are detailed in Table 1.
Table 1: preparation parameters of examples 1 to 12 and comparative examples 1 to 2
Figure BDA0003475556030000111
Half-cells were prepared using the negative electrode sheets of examples 1 to 12 and comparative examples 1 to 2, and the following performance tests were performed, and the obtained test results are shown in table 2.
[ first coulomb efficiency test ]
And assembling the pre-lithiated negative electrode, the metal lithium sheet electrode and the diaphragm into a half cell at 25 ℃, and adding a lithium ion electrolyte. Discharging the battery to 0.01V at constant current with the multiplying power of 0.1C, and standing for 10 min; and then charging to 2.0V at a constant current of 0.1C, recording the charge-discharge capacity, and calculating the first coulombic efficiency.
First coulombic efficiency-discharge capacity (negative electrode lithium intercalation capacity)/charge capacity (negative electrode lithium deintercalation capacity) × 100%
[ test for conversion to lithium-containing layer ]
And assembling the pre-lithiated negative electrode, the metal lithium sheet electrode and the diaphragm into a half cell at 25 ℃, and adding a lithium ion electrolyte. The cell was constant current charged to 2.0V at a rate of 0.1C, the charge capacity was recorded, and the conversion of the lithium-containing layer was calculated.
Conversion rate of lithium-containing layer (first charge capacity (negative electrode lithium removal capacity)/(lithium-containing layer mass 3860mAh/g)
[ 100-cycle Capacity Retention Rate test ]
And assembling the pre-lithiated cathode, the lithium iron phosphate anode and the diaphragm into a half-cell at 25 ℃, and adding a lithium ion electrolyte. Charging the battery to 3.6V with constant current at a rate of 0.5C, standing for 10min, and discharging to 2.5V with constant current at 0.5C, which is the discharge capacity recorded in a cyclic charge-discharge process, namely the initial capacity C0. For the same one as aboveRepeating the above cyclic charge and discharge process, and recording the discharge capacity C of the battery after the 100 th cycle100Then, the cycle capacity retention rate is C for 100 cycles100/C0*100％。
Table 2: test results of examples 1 to 12 and comparative examples 1 to 2
Serial number First coulombic efficiency Conversion rate of lithium-containing layer Retention ratio of 100 cycles
Example 1 99％ 40％ 85％
Example 2 101％ 60％ 92％
Example 3 104％ 73％ 95％
Example 4 115％ 73％ 97％
Example 5 109％ 53％ 90％
Example 6 105％ 40％ 85％
Example 7 97％ 25％ 86％
Example 8 106％ 65％ 96％
Example 9 109％ 80％ 98％
Example 10 89％ 20％ 84％
Example 11 99％ 70％ 91％
Example 12 101％ 80％ 94％
Comparative example 1 85％ 14％ 72％
Comparative example 2 79％ 5％ 46％
As can be seen from tables 1 and 2, the lithium-containing layer of the negative electrode sheet prepared by the method of the present application has a high conversion rate, that is, the lost active lithium can be effectively replenished. Therefore, when the negative electrode plates of embodiments 1 to 12 are applied to a secondary battery, the first coulomb efficiency and the capacity retention rate of the secondary battery can be obviously improved.
On the other hand, comparative example 1 does not perform pressure treatment on the lithium-containing negative electrode sheet, and comparative example 2 does not place the lithium-containing negative electrode sheet in the electrolyte containing lithium ions, and the conversion rate of the lithium-containing layer is far lower than that in examples 1 to 12. The negative electrode plates of comparative examples 1 and 2 are applied to secondary batteries, and the effect of improving the first coulombic efficiency and capacity retention rate is not obvious.
While the invention has been described with reference to specific embodiments, the scope of the invention is not limited thereto, and those skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (11)

1. A method for preparing a negative electrode tab of a secondary battery, comprising:
providing an initial negative pole piece, wherein the initial negative pole piece comprises a negative pole current collector and a negative pole film layer arranged on at least one surface of the negative pole current collector;
the method comprises the following steps of preparing a lithium-containing negative pole piece, wherein a lithium-containing layer for supplementing active lithium is arranged on the surface of a negative pole film layer, so that the lithium-containing negative pole piece is obtained;
and the step for carrying out pre-lithiation reaction comprises the step of applying 25-55 MPa of pressure to the lithium-containing negative pole piece in an electrolyte containing lithium ions so as to obtain the pre-lithiated negative pole piece.
2. The method of claim 1, wherein the providing an initial negative pole piece comprises:
providing negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material, a conductive agent and a binder, and based on the total mass of solids in the negative electrode slurry, the mass proportion of the negative electrode active material is 88-92 wt%, the mass proportion of the conductive agent is 4-6 wt%, and the mass proportion of the binder is 4-6 wt%;
and the step for preparing the initial negative pole piece comprises the steps of coating the negative pole slurry on at least one surface of the negative pole current collector, and drying and cold pressing to obtain the initial negative pole piece.
3. The method of claim 1 or 2, wherein the negative electrode film layer has an arithmetical mean deviation of contours Ra1Satisfies the following conditions: ra of 0.3 mu m or less1Less than or equal to 1.2 mu m, and the porosity of the negative electrode film layer is 5-50%.
4. The method of claim 1, wherein the providing of the lithium-containing layer for supplementing active lithium on the surface of the negative electrode film layer comprises:
and arranging a lithium-containing layer for supplementing active lithium on the surface of the negative electrode film layer in a physical mode, wherein the physical mode comprises at least one of blade coating, spraying, laminating, magnetron sputtering and vacuum evaporation.
5. The method of claim 1 or 4, wherein the lithium-containing negative pole piece has an arithmetical mean deviation of profile Ra2Satisfies the following conditions: ra of 0.01 mu m2≤2μm。
6. The method of claim 1, wherein the step for performing a prelithiation reaction comprises:
after the lithium-containing negative pole piece is obtained, transferring the lithium-containing negative pole piece into the electrolyte containing lithium ions within 0-1440 min, preferably within 0-30 min;
and applying 25-55 MPa of pressure to the lithium-containing negative pole piece to obtain the pre-lithiated negative pole piece.
7. The method of claim 1, wherein the applying a pressure of 25-55 MPa to the lithium-containing negative electrode sheet in an electrolyte containing lithium ions comprises:
and arranging metal pressure plates on two opposite surfaces in the thickness direction of the lithium-containing negative pole piece, and applying 25-55 MPa pressure to the lithium-containing negative pole piece through the metal pressure plates.
8. The method of claim 7, wherein a wire is connected between the metal pressure plates.
9. The method of claim 1, wherein a ratio of an active lithium capacity per unit area of the negative electrode film layer to an active lithium capacity per unit area of the lithium-containing layer is 1:0.1 to 1: 0.5.
10. A negative electrode sheet obtained by the method of any one of claims 1 to 9.
11. A secondary battery comprising the negative electrode sheet of claim 10.
CN202210054240.4A 2022-01-18 2022-01-18 Method for preparing negative pole piece, negative pole piece and secondary battery Pending CN114464778A (en)

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