CN115498139A - Negative pole piece, secondary battery and electric equipment - Google Patents

Negative pole piece, secondary battery and electric equipment Download PDF

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Publication number
CN115498139A
CN115498139A CN202211052318.5A CN202211052318A CN115498139A CN 115498139 A CN115498139 A CN 115498139A CN 202211052318 A CN202211052318 A CN 202211052318A CN 115498139 A CN115498139 A CN 115498139A
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Prior art keywords
active layer
negative electrode
negative
active material
density
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Inventor
居小康
谭煜炫
黎盛才
胡梦
张耀
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Sunwoda Electric Vehicle Battery Co Ltd
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Sunwoda Electric Vehicle Battery 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
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Composite Materials (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The application discloses a negative pole piece, a secondary battery and electric equipment, wherein the negative pole piece comprises a current collector and a negative active layer arranged on at least one side of the current collector, and the negative active layer comprises a first active layer and a second active layer; the first active layer is positioned between the second active layer and the current collector; the first active layer includes a first negative active material including a metal phosphide; the second active layer includes a second negative active material including hard carbon. This application has set up the negative pole active layer respectively in at least one side of mass flow body to having injectd that first negative pole active material in the first active layer includes metal phosphide, the second negative pole active material in the second active layer includes hard carbon, can effectively improve sodium ion battery energy density, and maintain excellent quick charge performance and circulation stability.

Description

Negative pole piece, secondary battery and electric equipment
Technical Field
The application relates to the technical field of energy storage, in particular to a negative pole piece, a secondary battery and electric equipment.
Background
Under the background of emission reduction and energy development, electric vehicles and lithium ion batteries are rapidly developed. Meanwhile, due to the scarcity of the lithium source, the price of the raw materials at the upstream of the lithium ion battery is greatly increased, and the price of the lithium ion battery is further increased. Therefore, the industrialization of sodium ion batteries is coming into the public. Because the raw materials are wide, and the current collector of the negative electrode of the sodium ion battery can adopt cheaper aluminum foil instead of more expensive copper foil, the sodium ion battery has the advantage of low cost.
However, commercial graphite used for the negative electrode of the lithium ion battery is not suitable for the sodium ion battery. Currently, in the field of sodium ion batteries, hard carbon is more used as an anode active material. The hard carbon material has excellent kinetic properties, but its sodium storage capacity is low, which is one of the important reasons why the energy density of a sodium ion battery is not comparable to that of a lithium ion battery.
Therefore, in order to make the sodium ion battery have the characteristics of high kinetics, safety and high energy density at the same time, a new negative electrode plate must be developed.
Disclosure of Invention
The present application is directed to solving at least one of the problems in the prior art. Therefore, the application provides a negative electrode plate in a first aspect, which can effectively improve the energy density and the cycling stability of the sodium-ion battery.
The second aspect of the present application also provides a secondary battery.
The third aspect of the present application also provides an electric device.
The embodiment of the first aspect of the present application provides a negative electrode plate, which includes a current collector and a negative active layer disposed on at least one side of the current collector, where the negative active layer includes a first active layer and a second active layer; the first active layer is positioned between the second active layer and the current collector;
the first active layer includes a first negative active material including a metal phosphide;
the second active layer includes a second negative active material including hard carbon.
According to the negative pole piece of this application embodiment, have following beneficial effect at least:
this application has set up the negative pole active layer respectively in at least one side of mass flow body to having injectd first negative pole active material in the first active layer and including metal phosphorus phosphide, the second negative pole active material in the second active layer includes hard carbon, can be guaranteeing under the prerequisite of filling soon, effectively improve sodium ion battery energy density and circulation stability. The second active layer is made of hard carbon, so that the dynamic performance is better, the precipitation of metal sodium on the surface of the electrode can be effectively limited, the first active layer provides more gram volume volatilization, and the energy density is further improved. Since the first active layer is located between the second active layer and the current collector, the negative effect of metal phosphide on the precipitation of metal sodium is mitigated (sodium metal is precipitated only on the surface layer of the electrode).
According to some embodiments of the present application, a capacity ratio of the second active layer and the first active layer satisfies the following formula:
(in the second active layer, the second negative electrode active material in the second active layer in the mass percentage of the second negative electrode active material gram volume of the second active layer density)/(the first active layer in the mass percentage of the first negative electrode active material gram volume of the first active layer density) in the range of 1-5.
When the capacity ratio of the second active layer to the first active layer is 1 to 5, the energy density can be further improved on the premise of stable circulation.
According to some embodiments of the present application, the first negative active material has a gram capacity of 800 to 1200mAh/g; the gram capacity of the second negative electrode active material is 250-450 mAh/g. Therefore, the battery has better capacity and cycle performance.
According to some embodiments of the present application, the first active layer has an areal density of 0.94 to 8mg/cm 2 . Therefore, when the surface density of the first active layer is 0.94-8 mg/cm 2 When the surface density is lower than 0.94mg/cm, the battery has higher capacity 2 (ii) a The influence on the whole battery capacity is not significant, and the area density is not highHigher than 8mg/cm 2 The internal resistance of the battery increases and the capacity cycle retention rate decreases.
According to some embodiments of the present application, the second active layer has an areal density of 8.32 to 23mg/cm 2 . Therefore, the capacity retention rate is better.
The test method of the areal density is as follows:
weighing the base material with the known area S to obtain the mass M1 of the base material; weighing the electrode coated with the active material in the same area to obtain a mass M2; areal density = (M2-M1)/S.
According to some embodiments of the present application, the first active layer further comprises a first conductive agent, a first binder, and a first dispersant, the first active layer comprising, in mass percent based on the total mass of the first active layer:
Figure BDA0003824169530000021
according to some embodiments of the present application, the second active layer further comprises a second conductive agent, a second binder, and a second dispersant, and the second active layer comprises the following components in percentage by mass, based on the total mass of the second active layer:
Figure BDA0003824169530000022
according to some embodiments of the present application, the second negative active material comprises CaP 3 、CrP 2 、NiP 2 、VP 2 、CoP 2 、GaP、ZnP 4 At least one of (1).
According to some embodiments of the present application, a content of the first conductive agent in the first active layer is greater than a content of the second conductive agent in the second active layer. The conductivity of the metal phosphide is poor, and the electron conductivity can be properly improved and the circulation can be improved by introducing more conductive agents into the first active layer; while hard carbon has good conductivity, too much conductive agent has a negative effect on capacity.
According to some embodiments of the present application, the first binder and the second binder are independently selected from at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), or fluororubber. Thereby, the first adhesive and the second adhesive have a better bonding effect.
According to some embodiments of the present application, the first conductive agent and the second conductive agent are independently selected from at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, or carbon fiber. Therefore, the conductivity is better.
According to some embodiments of the present application, the first and second dispersing agents are independently selected from sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. Thereby, the first active layer and the second active layer are dispersed more uniformly.
According to some embodiments of the present application, the current collector comprises at least one of a copper foil, an aluminum foil, a copper mesh, an aluminum foil coated with a conductive carbon layer, a copper foil coated with a conductive carbon layer, a polymer film coated with aluminum, a polymer film coated with copper, a conductive polymer film, or a conductive film having corrosion stability when used in an electrolyte system.
According to some embodiments of the present application, the method for preparing the negative electrode sheet comprises the following steps:
s1, stirring a first negative electrode active material, a first conductive agent, a first binder and a first dispersing agent to obtain a first active layer; stirring a second negative electrode active material, a second conductive agent, a second binder and a second dispersing agent to obtain a second active layer;
and S2, coating the upper surface and the lower surface of the current collector by adopting a double-layer coating method, drying, rolling and cutting to obtain the negative pole piece.
The second aspect embodiment of the present application provides a secondary battery, which includes a positive electrode plate, an electrolyte, a diaphragm and the negative electrode plate as described above, wherein the diaphragm is between the positive electrode plate and the negative electrode plate, and the electrolyte is filled between the positive electrode plate and the negative electrode plate and soaks the diaphragm.
According to some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer formed on a surface of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of a sodium transition metal oxide, a polyanionic compound, or a prussian blue compound.
According to some embodiments of the present application, in the sodium transition metal oxide, the transition metal may be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr, and Ce. The sodium transition metal oxide being, for example, na x MO 2 Wherein M is one or more of Ti, V, mn, co, ni, fe, cr and Cu, 0<x≤1。
According to some embodiments of the present application, the polyanionic compound may be a compound having a sodium ion, a transition metal ion, and a tetrahedral type (YO) 4 ) n- A class of compounds of anionic units. The transition metal can be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce; y can be at least one of P, S and Si; n represents (YO) 4 ) n- A valence state of (c).
The polyanionic compound may have sodium ion, transition metal ion, tetrahedral (YO) 4 ) n- Anionic units and halogen anions. The transition metal can be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce; y may be at least one of P, S and Si, and n represents (YO) 4 ) n- A valence state of (c); the halogen may be at least one of F, cl and Br.
The polyanionic compound may also be of sodium ion, tetrahedral (YO) 4 ) n- Anion unit, polyhedral unit (ZO) y ) m+ And optionally a halide anion. Y may be at least one of P, S and Si, and n represents (YO) 4 ) n- The valence of (a); zRepresents a transition metal, and may be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce, and m represents (ZO) y ) m+ A valence state of (c); the halogen may be at least one of F, cl and Br.
The polyanionic compound being, for example, naFePO 4 、Na 3 V 2 (PO 4 ) 3 NaM 'PO4F (M' is one or more of V, fe, mn and Ni) and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y (0. Ltoreq. Y. Ltoreq.1).
The Prussian blue compound can be a compound with sodium ions, transition metal ions and cyanide ions (CN-). The transition metal may be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce. Prussian blue compounds are for example Na a Me b Me’ c (CN) 6 Wherein Me and Me' are at least one of Ni, cu, fe, mn, co and Zn respectively and independently, 0<a≤2，0<b<1，0<c<1。
According to some embodiments of the present application, the positive electrode active material layer may further include a conductive agent to improve conductive performance of the positive electrode. The type of the conductive agent is not particularly limited, and can be selected according to actual requirements. As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene, or carbon nanofibers.
According to some embodiments of the present application, the positive electrode active material layer may further include a binder to firmly bind the positive electrode active material and the optional conductive agent to the positive electrode current collector. The type of the binder is not particularly limited, and can be selected according to actual requirements. As an example, the binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), polyvinyl alcohol (PVA), ethylene-vinyl acetate copolymer (EVA), styrene Butadiene Rubber (SBR), carboxymethyl cellulose (CMC), sodium Alginate (SA), polymethacrylic acid (PMA), or carboxymethyl chitosan (CMCs).
According to some embodiments of the present application, the positive current collector employs a conductive carbon sheet, a metal foil, a carbon-coated metal foil, a porous metal plate or a composite current collector, wherein the conductive carbon material of the conductive carbon sheet may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphite, graphene or carbon nanofibers, and the metal materials of the metal foil, the carbon-coated metal foil and the porous metal plate may be independently selected from at least one of copper, aluminum, nickel and stainless steel. The composite current collector can be a composite current collector formed by compounding a metal foil and a polymer base film.
According to some embodiments of the present application, the separator may be any material suitable for a secondary battery separator in the art, for example, including but not limited to at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.
According to some embodiments of the present application, the electrolyte solution includes an organic solvent and an electrolyte sodium salt. For example, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, diethyl ether, diglyme, triglyme, tetraglyme, methyl tert-butyl ether; the electrolyte sodium salt comprises one or more of sodium hexafluorophosphate, sodium bifluorosulfonyl imide, sodium bistrifluoromethanesulfonyl imide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium difluorophosphate, sodium perchlorate and sodium chloride.
In an embodiment of the third aspect of the present application, an electric device is provided, and the electric device includes the secondary battery described above.
According to some embodiments of the application, the electric equipment comprises a mobile phone, a computer, a wearable device, a mobile power supply, an electric automobile, an energy storage device and the like.
Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the application.
Detailed Description
The following are specific examples of the present application and further describe the technical solutions of the present application in conjunction with the examples, but the present application is not limited to these examples.
Reagents, methods and equipment used in the application are conventional in the art, unless otherwise specified.
Example 1
Embodiment 1 provides a negative electrode sheet, and the preparation method thereof is as follows:
s1, selecting hard carbon with the gram capacity of 250mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active material layer adopts CoP with the gram capacity of 800mAh/g 2 94% of super P (conductive carbon black), 1.5% of sodium carboxymethylcellulose, 1.5% of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer of slurry and the first layer of slurry, and the density of the first active layer is 4.68mg/cm 2 Second active layer density 15mg/cm 2 (ii) a And (2) ensuring that the value of (the percentage of the second negative electrode active material of the second active layer to the gram volume of the second active layer to the second active layer density)/(the percentage of the first negative electrode active material of the first active layer to the gram volume of the first active layer to the first active layer density) is 1, and drying, rolling and slitting to obtain the negative electrode plate.
Example 2
Embodiment 2 also provides a negative electrode plate, and the preparation method is as follows:
s1, selecting hard carbon with the gram capacity of 250mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active layer adopts NiP with gram capacity of 1200mAh/g 2 94% of it and the balance 3% of super P (lead)Electrical carbon black), 1.5% cmc (sodium carboxymethylcellulose), 1.5% binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer slurry and the first layer slurry, and the density of the first active layer is 4.68mg/cm 2 Second active layer density 22.46mg/cm 2 (ii) a And ensuring that the value of (the percentage of the second negative active material of the second active layer per gram volume of the second active layer per gram density of the second active layer)/(the percentage of the first negative active material of the first active layer per gram volume of the first active layer per gram density of the first active layer) is 1, and drying, rolling and slitting to obtain the negative pole piece.
Example 3
Embodiment 3 also provides a negative electrode sheet, the preparation method is as follows:
s1, selecting hard carbon with the gram capacity of 450mAh/g as the second active layer, accounting for 94 percent, and the balance of 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare slurry of the first active layer; the first active layer adopts CoP with the gram capacity of 800mAh/g 2 94% of super P (conductive carbon black), 1.5% of CMC (sodium carboxymethyl cellulose), 1.5% of binder (styrene butadiene rubber), and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer of slurry and the first layer of slurry, and the density of the first active layer is 4.68mg/cm 2 Second active layer density 8.32mg/cm 2 (ii) a And (2) ensuring that the value of (the percentage of the second negative electrode active material of the second active layer to the gram volume of the second active layer to the second active layer density)/(the percentage of the first negative electrode active material of the first active layer to the gram volume of the first active layer to the first active layer density) is 1, and drying, rolling and slitting to obtain the negative electrode plate.
Example 4
Embodiment 4 also provides a negative electrode sheet, and the preparation method is as follows:
s1, the second active layer selects hard carbon with a gram capacity of 450mAh/g, the proportion of the hard carbon is 94 percent, and the rest isThe first active layer slurry was prepared by stirring 3% super P (conductive carbon black), 1.5% sodium carboxymethyl cellulose, 1.5% binder (styrene butadiene rubber), and deionized water as a solvent; the first active layer is made of NiP with the gram capacity of 1200mAh/g 2 94% of super P (conductive carbon black), 1.5% of CMC (sodium carboxymethyl cellulose), 1.5% of binder (styrene butadiene rubber), and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer slurry and the first layer slurry, and the density of the first active layer is 4.68mg/cm 2 The density of the second active layer was 12.48mg/cm 2 (ii) a And (2) ensuring that the value of (the percentage of the second negative electrode active material of the second active layer to the gram volume of the second active layer to the second active layer density)/(the percentage of the first negative electrode active material of the first active layer to the gram volume of the first active layer to the first active layer density) is 1, and drying, rolling and slitting to obtain the negative electrode plate.
Example 5
Embodiment 5 provides a negative electrode sheet, and the preparation method thereof is as follows:
s1, selecting hard carbon with the gram capacity of 250mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active material layer adopts CoP with the gram capacity of 800mAh/g 2 94% of super P (conductive carbon black), 1.5% of sodium carboxymethylcellulose, 1.5% of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer slurry and the first layer slurry, and the density of the first active layer is 3.13mg/cm 2 Second active layer density 10mg/cm 2 (ii) a Ensuring that the value of (the percentage of the second negative active material of the second active layer per gram volume of the second active layer per gram density of the second active layer)/(the percentage of the first negative active material of the first active layer per gram volume of the first active layer per gram density of the first active layer) is 1, drying, rolling and slitting to obtain the negative pole piece。
Example 6
Embodiment 6 provides a negative electrode sheet, and the preparation method thereof is as follows:
s1, selecting hard carbon with the gram capacity of 250mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active material layer adopts CoP with the gram capacity of 800mAh/g 2 94% of super P (conductive carbon black), 1.5% of sodium carboxymethylcellulose, 1.5% of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer slurry and the first layer slurry, and the density of the first active layer is 7.2mg/cm 2 Second active layer density 23mg/cm 2 (ii) a And (2) ensuring that the value of (the percentage of the second negative electrode active material of the second active layer to the gram volume of the second active layer to the second active layer density)/(the percentage of the first negative electrode active material of the first active layer to the gram volume of the first active layer to the first active layer density) is 1, and drying, rolling and slitting to obtain the negative electrode plate.
Example 7
Embodiment 7 also provides a negative electrode sheet, which is prepared by the following method:
s1, selecting hard carbon with the gram capacity of 450mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active layer is made of NiP with the gram capacity of 1200mAh/g 2 94% of super P (conductive carbon black), 1.5% of CMC (sodium carboxymethyl cellulose), 1.5% of binder (styrene butadiene rubber), and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer slurry and the first layer slurry, and the density of the first active layer is 1.56mg/cm 2 The density of the second active layer is 12.48mg/cm 2 (ii) a Guarantee (second)And (3) the value of the percentage of the second negative active material of the active layer, the gram volume of the second active layer, the gram density of the second active layer, and the percentage of the first negative active material of the first active layer, the gram volume of the first active layer, and the gram density of the first active layer) is 3, and the negative pole piece is obtained by drying, rolling and slitting.
Example 8
Embodiment 8 also provides a negative electrode sheet, the preparation method is as follows:
s1, selecting hard carbon with the gram capacity of 450mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active layer is made of NiP with the gram capacity of 1200mAh/g 2 94% of super P (conductive carbon black), 1.5% of CMC (sodium carboxymethyl cellulose), 1.5% of binder (styrene butadiene rubber), and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer of slurry and the first layer of slurry, and the density of the second active layer is 12.48mg/cm 2 The density of the first active layer is 0.936mg/cm 2 (ii) a And ensuring that the value of (the percentage of the second negative active material of the second active layer per gram volume of the second active layer per gram density of the second active layer)/(the percentage of the first negative active material of the first active layer per gram volume of the first active layer per gram density of the first active layer) is 5, and drying, rolling and slitting to obtain the negative pole piece.
Example 9
Example 9 also provides a negative electrode tab, the preparation method of which is as follows:
s1, selecting hard carbon with the gram capacity of 450mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active layer adopts NiP with gram capacity of 1200mAh/g 2 94% of super P (conductive carbon black), 1.5% of CMC (sodium carboxymethyl cellulose), 1.5% of binder (styrene butadiene rubber), and deionized water as solvent by stirringStirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer slurry and the first layer slurry, and the density of the second active layer is 12.48mg/cm 2 The density of the first active layer is 7.78mg/cm 2 (ii) a And ensuring that the value of (the percentage of the second negative electrode active material of the second active layer to the gram volume of the second active layer to the second active layer density)/(the percentage of the first negative electrode active material of the first active layer to the gram volume of the first active layer to the first active layer density) is 0.6, and drying, rolling and cutting to obtain the negative electrode plate.
Example 10
Embodiment 10 also provides a negative electrode sheet, and the preparation method is as follows:
s1, selecting hard carbon with the gram capacity of 450mAh/g as the second active layer, wherein the hard carbon accounts for 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare first active layer slurry; the first active layer is made of NiP with the gram capacity of 1200mAh/g 2 94% of super P (conductive carbon black), 1.5% of CMC (sodium carboxymethyl cellulose), 1.5% of binder (styrene butadiene rubber), and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer of slurry and the first layer of slurry, and the density of the second active layer is 12.48mg/cm 2 The density of the first active layer is 0.85mg/cm 2 (ii) a And ensuring that the value of (the percentage of the second negative active material of the second active layer per gram volume of the second active layer per gram density of the second active layer)/(the percentage of the first negative active material of the first active layer per gram volume of the first active layer per gram density of the first active layer) is 5.5, and drying, rolling and cutting to obtain the negative pole piece.
Example 11
Example 11 also provides a negative electrode sheet, which is prepared by the following method:
s1, selecting hard carbon with a gram capacity of 450mAh/g as the second active layer, accounting for 94 percent, and the balance being 3 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethylcellulose, 1.5 percent of binder (styrene butadiene rubber), solventDeionized water, and stirring to obtain a first active layer slurry; the first active layer is made of NiP with the gram capacity of 1200mAh/g 2 The percentage of the second active layer is 92 percent, the balance is 5 percent of super P (conductive carbon black), 1.5 percent of sodium carboxymethyl cellulose, 1.5 percent of binder (styrene butadiene rubber) and deionized water, and the second active layer slurry is prepared by stirring;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer slurry and the first layer slurry, and the density of the second active layer is 12.48mg/cm 2 The density of the first active layer is 1.59mg/cm 2 (ii) a And ensuring that the value of (the percentage of the second negative active material of the second active layer per gram volume of the second active layer per gram density of the second active layer)/(the percentage of the first negative active material of the first active layer per gram volume of the first active layer per gram density of the first active layer) is 3, and drying, rolling and slitting to obtain the negative pole piece.
Example 12
Embodiment 12 also provides a negative electrode sheet, the preparation method is as follows:
s1, selecting hard carbon with a gram capacity of 450mAh/g as a second active layer, accounting for 99.85 percent, and the balance being 0.05 percent of super P (conductive carbon black), 0.05 percent of sodium carboxymethyl cellulose, 0.05 percent of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to prepare slurry of the first active layer; the first active layer adopts NiP with gram capacity of 1200mAh/g 2 65% of super P (conductive carbon black), 5% of CMC (sodium carboxymethyl cellulose), 15% of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer of slurry and the first layer of slurry, and the density of the first active layer is 2.39mg/cm 2 The density of the second active layer was 12.48mg/cm 2 (ii) a And (the percentage of the second negative electrode active material of the second active layer to the gram volume of the second active layer to the second active layer density) is ensured to be 3, and the negative electrode pole piece is obtained by drying, rolling and slitting.
Example 13
Embodiment 13 also provides a negative electrode sheet, which is prepared by the following method:
s1, selecting hard carbon with a gram capacity of 450mAh/g as a second active layer, wherein the hard carbon accounts for 65 percent, and the balance is 15 percent of super P (conductive carbon black), 5 percent of sodium carboxymethylcellulose, 15 percent of binder (styrene butadiene rubber) and deionized water serving as a solvent, and stirring to prepare slurry of the first active layer; the first active layer adopts NiP with gram capacity of 1200mAh/g 2 99.85% of super P (conductive carbon black), 0.05% of CMC (sodium carboxymethyl cellulose), 0.05% of binder (styrene butadiene rubber) and deionized water as a solvent, and stirring to obtain a second active layer slurry;
s2, coating by using a double-layer coating machine, wherein the upper die head and the lower die head respectively correspond to the second layer of slurry and the first layer of slurry, and the density of the first active layer is 1.02mg/cm 2 The density of the second active layer is 12.48mg/cm 2 (ii) a And ensuring that the value of (the percentage of the second negative active material of the second active layer per gram volume of the second active layer per gram density of the second active layer)/(the percentage of the first negative active material of the first active layer per gram volume of the first active layer per gram density of the first active layer) is 3, and drying, rolling and slitting to obtain the negative pole piece.
Comparative example 1
Comparative example 1 provides a negative electrode sheet, which is prepared by the following steps:
s1, selecting the active material as 250mAh/g of hard carbon, the proportion of the hard carbon is 94 percent, and the balance is 3 percent of super P (conductive carbon black), 1.5 percent of CMC (sodium carboxymethyl cellulose), 1.5 percent of binder (styrene butadiene rubber) and deionized water, and stirring to prepare slurry;
s2, coating by using a double-layer coating machine, wherein the slurry obtained in the step 1 is adopted by an upper die head and a lower die head, and the total coating surface density is ensured to be 19.68mg/cm 2 (the total coating surface density is consistent with that of the embodiment 1), and drying, rolling and slitting are carried out to obtain the negative pole piece.
Comparative example 2
Comparative example 2 provides a negative electrode sheet, which is prepared by the following steps:
s1, selecting CoP with 800mAh/g as active material 2 94% of super P (conductive carbon black), 1.5% of sodium carboxymethylcellulose, and 1.5% of binderThe agent (styrene butadiene rubber) and the solvent are deionized water, and slurry is prepared by stirring;
s2, coating by using a double-layer coating machine, wherein the slurry obtained in the step 1 is adopted by an upper die head and a lower die head, and the total coating surface density is ensured to be 19.68mg/cm 2 (the total coating surface density is consistent with that of the embodiment 1), and drying, rolling and slitting are carried out to obtain the negative pole piece.
Performance testing
Preparing a sodium ion battery:
(1) Electrolyte solution: 1M NaPF 6 Dissolved in Ethylene Carbonate (EC): diethyl carbonate (DEC) =3:7, obtaining;
(2) A diaphragm: a PP film;
(3) The components of the positive pole piece are as follows: positive electrode Material (Na) 3 V 2 (PO 4 ) 2 F 3 96% by weight, a conductive agent (SP, 3% by weight); and uniformly mixing the binder (PVDF, 1 percent) in the N-methyl pyrrolidone to obtain the positive pole piece slurry. And coating the positive pole piece slurry on a positive current collector, and drying, rolling and slitting to obtain the positive pole piece.
(4) Sodium ion battery assembly
The negative electrode plate, the positive electrode plate, the separator, the structural member and the like prepared in examples 1 to 13 and comparative examples 1 to 2 were assembled, wound in the same number of layers, and subjected to injection, formation, aging, sealing and other processes to obtain a sodium ion battery.
Carrying out 0.5A current charge and discharge test on the obtained sodium ion battery by adopting a Xinwei power battery test system to obtain the battery capacity, and recording the battery capacity in a table 1; in addition, define 1C current = battery capacity; the higher the battery capacity, the higher the energy density;
charging the obtained sodium ion battery to an upper limit voltage by using a Xinwei power battery test system at 4C current, discharging to a lower limit voltage by using 1C current, and circularly charging and discharging for 10 times; then, the rechargeable battery is fully charged by 0.5A current, finally, the rechargeable battery is disassembled, the sodium precipitation condition on the surface of the negative electrode is observed, if sodium is precipitated, the fast charging is not supported, and the record is shown in the table 1;
the battery was charged with 2C current at constant current to the upper limit voltage, then was charged at constant voltage to 0.05C, and then was discharged with 1C current to the lower limit voltage, so that 25 ℃ cycling was performed, and the number of cycles at which the battery capacity had decayed to 80% of the initial capacity was recorded and recorded in Table 1.
TABLE 1 data for examples 1-13 and comparative examples 1-2
capacity/Ah Sodium evolution SOH at 25 ℃ cycle @80%
Example 1 3.05 Sodium is not separated out 1300
Example 2 4.57 Sodium is not separated out 1150
Example 3 3.05 Sodium is not separated out 1800
Example 4 4.51 Sodium is not separated out 1500
Example 5 2.83 Sodium is not separated out 1800
Example 6 4.68 Sodium is not separated out 1000
Example 7 3.03 Sodium is not separated out 1800
Example 8 2.84 Sodium is not separated out 1850
Example 9 6.09 Sodium is not separated out 850
Example 10 2.70 Sodium is not separated out 1500
Example 11 3.06 Sodium is not separated out 2200
Example 12 3.06 Sodium is not separated out 2200
Example 13 2.78 Sodium is not separated out 1500
Comparative example 1 2.00 Sodium is not separated out 2250
Comparative example 2 6.41 Severe sodium precipitation 150
As can be seen from the test results in table 1, in all of examples 1 to 4, the density of the first active layer was kept constant, and the value of the capacity ratio between the second layer and the first layer was fixed to 1, and it was found that the capacity fading in example 3 and example 4 was slow. When the surface density of the second active layer is larger, the composite electrode is thicker, so that the distance for transmitting sodium ions to the first active layer is longer, and the internal resistance is increased too fast and the attenuation is accelerated in the long-cycle process.
Examples 1,5,6 compare, and adjust the areal density design while maintaining the interlayer volume ratio fixed at 1 and the material selection unchanged. It can be seen that the larger the areal density, the higher the cell capacity, but the cycle decay is also accelerated.
Examples 4, 7 and 8 compare the effect of the difference in the second to first inter-layer capacity ratio (percent active material in the second active layer per gram capacity of the second active layer per gram density of the second active layer)/(percent active material in the first active layer per gram capacity of the first active layer per gram density of the first active layer) on the performance of the cell. The second and first interlayer volume ratios of examples 4, 7 and 8 were 1, 3 and 5, respectively, and the coating surface densities of the second active layers were kept uniform. It can be seen that when the capacity ratio between the layers is at a suitable value, for example, in this example 7, the overall performance of the battery can be better maintained. In comparison of examples 4 and 7, the areal density of the first active layer gradually decreased, the battery capacity showed a decreasing tendency, and the capacity retention rate showed an increasing tendency. Since the first active layer, although it may contribute more capacity, its conductivity deviates. The reduction in the density of the first active layer planes may reduce the internal resistance of the battery. However, when the areal density of the first active layer is further reduced, as in examples 7 and 8, the effect is not so great that a long cycle life of the battery can be ensured. However, when the difference in the capacity ratio between the second and first layers deviates from the predetermined range, for example, in examples 9 and 10. Either the capacity was much lower than in example 4 (example 10) or the cycling effect was not good (example 9).
Example 11 the performance of the battery was improved by optimizing the loading of the active material by adjusting the proportion of Super P (conductive carbon black). Because the first active material layer has poor conductivity. The introduction of more conductive carbon black in the first layer may suitably increase the electron conductivity, resulting in a slower cycle decay.
Examples 7, 12 and 13 change the formulation of the pole pieces. The first active layer of example 12 has more conductive agent than example 7, and optimizes the resistance, resulting in more excellent cycling stability. In the second active layer of example 13, the conductive agent was increased as compared with example 7. However, since the hard carbon has good conductivity, an excessive amount of conductive agent (inactive material) has a negative effect on the capacity.
The sodium ion battery obtained in comparative example 1 has the lowest capacity, and the metal phosphide negative electrode obtained in comparative example 2 has the highest capacity, but has poor conductivity, a chalking phenomenon on the surface, poor kinetics, extremely fast cycle decay and severe sodium precipitation.
The present invention is not limited to the above-described embodiments, and various changes can be made without departing from the spirit and scope of the present invention by those skilled in the art.

Claims (10)

1. The negative pole piece is characterized by comprising a current collector and a negative active layer arranged on at least one side of the current collector, wherein the negative active layer comprises a first active layer and a second active layer; the first active layer is positioned between the second active layer and the current collector;
the first active layer includes a first negative electrode active material including a metal phosphide;
the second active layer includes a second negative active material including hard carbon.
2. The negative electrode sheet of claim 1, wherein a capacity ratio of the second active layer to the first active layer satisfies the following formula:
(in the second active layer in the second negative electrode active material mass percentage of the second negative electrode active material gram volume of the second active material layer density)/(first active layer in the first negative electrode active material mass percentage of the first negative electrode active material gram volume of the first active layer density) in the range of 1 ~ 5.
3. The negative electrode tab of claim 1, wherein the first negative active material has a gram capacity of 800 to 1200mAh/g; the gram capacity of the second negative electrode active material is 250-450 mAh/g.
4. The negative electrode sheet according to any one of claims 1 to 3, wherein the first active layer has an areal density of 0.94 to 8mg/cm 2 The surface density of the second active layer is 8.32-23 mg/cm 2 。
5. The negative electrode sheet of claim 1, wherein the metal phosphide comprises CaP 3 、CrP 2 、NiP 2 、VP 2 、CoP 2 、GaP、ZnP 4 At least one of (a).
6. The negative electrode sheet of claim 1, wherein the first active layer further comprises a first conductive agent, the second active layer further comprises a second conductive agent, and the content of the first conductive agent in the first active layer is greater than the content of the second conductive agent in the second active layer.
7. The negative electrode tab of claim 6, wherein the first conductive agent and the second conductive agent each independently comprise at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, or carbon fiber.
8. The negative electrode sheet of claim 1, wherein the first binder and the second binder are independently selected from at least one of polyvinylidene fluoride, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, sulfonated EPDM, styrene-butadiene rubber, or fluororubber.
9. A secondary battery comprising a positive electrode sheet, an electrolyte, a separator and the negative electrode sheet according to any one of claims 1 to 8.
10. An electric device comprising the secondary battery according to claim 9.
CN202211052318.5A 2022-08-31 2022-08-31 Negative pole piece, secondary battery and electric equipment Pending CN115498139A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117293275A (en) * 2023-11-24 2023-12-26 天鹏锂能技术(淮安)有限公司 Sodium ion battery and negative electrode plate thereof

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117293275A (en) * 2023-11-24 2023-12-26 天鹏锂能技术(淮安)有限公司 Sodium ion battery and negative electrode plate thereof

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