CN114927643B - Negative electrode plate and preparation method and application thereof - Google Patents

Negative electrode plate and preparation method and application thereof Download PDF

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Publication number
CN114927643B
CN114927643B CN202210426192.7A CN202210426192A CN114927643B CN 114927643 B CN114927643 B CN 114927643B CN 202210426192 A CN202210426192 A CN 202210426192A CN 114927643 B CN114927643 B CN 114927643B
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negative electrode
electrode layer
binder
current collector
graphite
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CN114927643A (en
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李峥
冯玉川
沈志鹏
陈凯
何泓材
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Suzhou Qingtao New Energy S&T Co Ltd
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Suzhou Qingtao New Energy S&T Co Ltd
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Priority to PCT/CN2022/100402 priority patent/WO2023201871A1/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
    • H01M4/133—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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • 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)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Inorganic Chemistry (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention provides a negative pole piece, a preparation method and application thereof. The negative electrode plate comprises a current collector, a first negative electrode layer and a second negative electrode layer, and the first negative electrode layer is positioned between the current collector and the second negative electrode layer; wherein the negative electrode active material in the first negative electrode layer includes graphite and a silicon material, and the negative electrode active material in the second negative electrode layer includes graphite. According to the invention, the first negative electrode layer is arranged on one side of the negative electrode plate close to the current collector, and comprises graphite and silicon, so that the energy density of the whole negative electrode is improved, the capacity of the negative electrode is improved, and meanwhile, the second graphite negative electrode layer far away from one side of the current collector exists, so that the expansion of a silicon material is further inhibited, and the negative electrode plate is suitable for the existing commercial large-scale lithium ion battery system.

Description

Negative electrode plate and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a negative electrode plate, a preparation method and application thereof.
Background
Along with the large-scale commercial use of the lithium ion battery, the capacity, the cycle performance and the safety performance of the lithium ion battery are widely focused, wherein graphite is used as a material which is used for the negative electrode of the lithium ion battery earlier, and the graphite has good conductivity, high crystallinity and good lamellar structure and is suitable for Li + Is inserted/withdrawn. At present, a battery put into large-scale equipment such as an automobile and the like mostly uses graphite as a negative electrode material, so that the problem of low capacity exists, in order to improve the capacity performance of the battery, a technician proposes to use a silicon-carbon material to replace graphite as a negative electrode of a lithium ion battery, but the silicon-based material has the problem of easy expansion, the cycle life is poor, and the phenomenon that the negative electrode material collapses and falls off from a current collector after multiple cycles occurs. And now the related research of silicon carbon negative electrodes is mostly in laboratory stage,
CN101087021a discloses a preparation method of an artificial graphite negative electrode material for a lithium ion battery, which comprises the following steps: pulverizing coal-based or petroleum-based needle coke, preheating, adding modifier and catalyst, drying, granulating, and heat treating at 800-3000 deg.C for 1-48 hr to obtain graphite material with specific capacity of 350mAh/g and less than theoretical specific capacity of 370mAh/g.
CN105118974a discloses a silicon-based negative electrode material and a preparation method thereof, because electrostatic spinning equipment is introduced to blend the silicon material into carbon nanofibers, the problems of volume expansion of the silicon-carbon material and breakage of silicon-carbon particles are effectively solved, meanwhile, the later-stage regeneration phenomenon of an SEI film is effectively reduced, the mechanical strength of the negative electrode material is effectively improved by utilizing a nanofiber structure, and the problems of low efficiency and poor consistency of the electrostatic spinning equipment are solved, so that the silicon-based negative electrode material produced by the nanofiber mode is difficult to realize industrialized mass production. The patent provides a production process which is simple in preparation process and easy in mass production and conversion, and the artificial graphite and SiO-based silicon-carbon composite negative electrode material has high capacity, high multiplying power and high conductivity.
Therefore, how to increase the capacity of the graphite anode, reduce the expansion of the anode active material, and adapt to the existing commercial large-scale lithium ion battery system is a technical problem to be solved.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a negative electrode plate, and a preparation method and application thereof. According to the invention, the first negative electrode layer is arranged on one side of the negative electrode plate close to the current collector, and comprises graphite and silicon, so that the energy density of the whole negative electrode is improved, the capacity of the negative electrode is improved, and meanwhile, the second graphite negative electrode layer far away from one side of the current collector exists, so that the expansion of a silicon material is further inhibited, and the negative electrode plate is suitable for the existing commercial large-scale lithium ion battery system.
To achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a negative electrode tab, the negative electrode tab comprising a current collector, a first negative electrode layer, and a second negative electrode layer, the first negative electrode layer being located between the current collector and the second negative electrode layer;
wherein the negative electrode active material in the first negative electrode layer includes graphite and a silicon material, and the negative electrode active material in the second negative electrode layer includes graphite; the graphite in the first negative electrode layer is carbon-coated graphite;
The first negative electrode layer comprises a first binder and a first conductive agent; the first binder is a polyacrylonitrile binder.
The kind of the silicon anode active material is not particularly limited in the present invention, and any known silicon anode active material can be used in the present application without departing from the inventive concept of the present application; by way of illustrative example only, and not by way of any limitation of the scope of protection, silicon negative electrode active material materials include elemental silicon, silicon oxygen compounds, coated silicon-based materials, and the like.
The method and kind of carbon coating are not particularly limited in the present invention, and any known carbon coating method capable of improving electron conductance can be used in the present application without departing from the inventive concept of the present application; the conductivity of graphite electrons coated by carbon is obviously improved, and the problem that the overall internal resistance of the negative electrode layer is affected due to low electron conductivity of the first negative electrode layer is solved.
It is understood that polyacrylonitrile binder refers to a class of polymers that can be used as binders, such as, for example, LA132 and/or LA133 binders, obtained via free polymerization of the monomer acrylonitrile.
In the actual production process, even if a small amount of silicon oxide is added into the graphite negative electrode of the lithium ion battery, the silicon oxide expands in the charge and discharge process, so that the whole negative electrode layer is triggered to fall off from the current collector. Surprisingly, the use of the polyacrylonitrile-based binder can effectively inhibit the expansion of the silicon-oxygen compound, and the polyacrylonitrile-based binder has a stronger binding effect with the current collector than other binders, can effectively prevent the falling of the negative electrode layer, and can improve the cycle life of the battery.
Meanwhile, the high-tensile negative current collector is selected and matched with the polyacrylonitrile binder, so that the current collector can be ensured to adapt to the volume change of the silicon oxygen material.
The graphite provided by the invention is selected from one of natural graphite and artificial graphite. Further, the artificial graphite is selected from one of single-particle artificial graphite, secondary-particle artificial graphite, and a composite of single-particle artificial graphite and secondary-particle artificial graphite.
For a multilayer anode system, since the anode active material layer near the current collector is subjected to the binding force of the current collector to it, its expansion ratio is generally smaller than that of the anode active material layer on the side far from the current collector, and therefore the present invention selects to add a silicon material to the first anode layer near the current collector. Expansion due to the addition of silicon is avoided by the interaction of the negative electrode layer with the current collector.
In the invention, if the second negative electrode layer is not arranged in the negative electrode plate, the technical problem of unstable interface between the silicon oxygen material and the electrolyte can occur.
Preferably, the second anode layer includes a second binder and a second conductive agent therein.
Preferably, the second binder is an aqueous binder.
Preferably, the binding force between the first binder and the current collector is greater than the binding force between the second binder and the current collector.
In the present invention, the binder in the first negative electrode layer is selected to be of a type that is more strongly adhered to the current collector to further overcome the expansion of the first negative electrode layer due to the introduction of silicon. In contrast, since the pure graphite anode has little expansion, the second anode layer may continue to use conventional binders, such as conventional aqueous binders in the second anode layer that may be readily known to those skilled in the art, including, but not limited to, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, styrene butadiene rubber, or hydroxymethyl cellulose, and the like.
In the actual production process, even if a small amount of silicon oxide is added into the graphite negative electrode of the lithium ion battery, the silicon oxide expands in the charge and discharge process, so that the whole negative electrode layer is triggered to fall off from the current collector. Surprisingly, the use of the polyacrylonitrile-based binder can effectively inhibit the expansion of the silicon-oxygen compound, and the polyacrylonitrile-based binder has a stronger binding effect with the current collector than other binders, can effectively prevent the falling of the negative electrode layer, and can improve the cycle life of the battery.
Further preferably, the mass ratio of the binder in the second anode layer is larger than the mass ratio of the binder in the first anode layer.
Preferably, the mass ratio of the binder in the first negative electrode layer is 3 to 5wt%, for example, 3wt%, 4wt%, 5wt%, or the like.
Preferably, the mass ratio of the binder in the second negative electrode layer is 4 to 8wt%, for example, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, or the like.
Preferably, the current collector of the first negative electrode layer is made of a high tensile material, and the current collector is matched with the high expansion performance of the first negative electrode layer, so that the expansion of the first negative electrode layer caused by the introduction of silicon can be further resisted.
The tensile strength of the current collector is more than or equal to 350N/cm 2 For example 360N/cm 2 、380N/cm 2 、400N/cm 2 、450N/cm 2 、480N/cm 2 Or 500N/cm 2 Etc.
The invention selects the high tensile negative current collector, and can ensure that the current collector can adapt to the volume change of the silicon oxygen material by matching with the polyacrylonitrile binder.
Preferably, the mass of the silicon material in the first anode layer is 3 to 5% of the anode active material in the first anode layer.
In the invention, if the silicon oxygen material is added too much, the expansion rate of the anode material in the charge and discharge process is too high, the charge and discharge performance of the lithium battery is reduced, the cycle retention rate is greatly reduced, and if the addition amount is too little, the effect of increasing the battery capacity cannot be achieved.
In the invention, the graphite in the first negative electrode layer is carbon-coated graphite, so that the conductivity of the first negative electrode layer can be improved.
Preferably, the silicon material comprises a silicon oxygen material.
Preferably, the mass ratio of the first conductive agent in the first negative electrode layer is greater than the mass ratio of the second conductive agent in the second negative electrode layer.
Preferably, the first conductive agent includes any one or a combination of at least two of CNT, VGCF, super P, carbon black, acetylene black, or graphene.
Preferably, the CNT and/or VGCF accounts for 15 to 25wt% of the first conductive agent.
In the present invention, the choice of the second conductive agent includes, but is not limited to, carbon-based materials, powdered nickel or other metal particles or conductive polymers, for example, carbon-based materials may include carbon black, graphite, super p, acetylene black (such as KETCHENTM black or denketm black), carbon fibers and particles of nanotubes, graphene, and the like; the conductive polymer includes polyaniline, polythiophene, polyacetylene, polypyrrole, poly (3, 4-ethylenedioxythiophene) polysulfonastyrene, and the like.
In the invention, the mass ratio of the first conductive agent in the first anode layer is more than that of the conventional anode layer, so that the electron transmission in the charge and discharge process can be better realized, the decrease of the conductive performance of the anode layer caused by the addition of the silicon-oxygen material is prevented, and on the other hand, the electron transmission path is damaged caused by the expansion of the silicon-oxygen material, thereby influencing the electron transmission.
Preferably, the thickness of the first negative electrode layer is 5 to 40%, for example 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38% or 40% or the like, preferably 16 to 25%, of the thickness of the second negative electrode layer.
In the invention, the thickness of the first negative electrode layer is within the range of 16-25% of the thickness of the second negative electrode layer, so that the technical effects of improving the energy density and the cycle retention rate of the battery can be better realized, and if the thickness of the first negative electrode layer is too thick, the expansion coefficients of the two sides of the first negative electrode layer, which are close to the current collector, and the two sides, which are far away from the current collector, are different, the pole piece is easy to fall off, and the stripping between the first negative electrode layer and the second negative electrode layer is easy to cause, if the thickness of the first negative electrode layer is too small, the effect of improving the energy density is not obvious.
Preferably, the thickness of the first negative electrode layer is 16 to 55 μm, for example, 16 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, 53 μm, 55 μm or the like.
Preferably, the thickness of the second negative electrode layer is 170 to 210 μm, for example 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 195 μm, 200 μm, 205 μm, 210 μm or the like.
Preferably, the first negative electrode layer has a coating surface density of 30 to 50g/m 2 For example 30g/m 2 、33g/m 2 、35g/m 2 、38g/m 2 、40g/m 2 、43g/m 2 、45g/m 2 、48g/m 2 Or 50g/m 2 Etc.
Preferably, the second negative electrode layer has an areal density of 150 to 170g/m 2 For example 150g/m 2 、155g/m 2 、160g/m 2 、165g/m 2 Or 170g/m 2 Etc
In a second aspect, the present invention provides a method for preparing the negative electrode tab according to the first aspect, the method comprising:
and coating the slurry of the first negative electrode layer on the surface of the current collector to obtain a first negative electrode layer, and coating the slurry of the second negative electrode layer on the surface of the first negative electrode layer to obtain the negative electrode plate.
The preparation of the slurry of the first anode layer and the preparation of the slurry of the second anode layer are both conventional technical means.
Illustratively, the method of preparing the negative electrode layer slurry includes: the negative electrode active material, the binder, the solvent and the conductive agent are mixed to obtain a negative electrode layer slurry.
In a third aspect, the present invention also provides a lithium ion battery comprising a negative electrode tab according to the first aspect.
The lithium ion battery provided by the invention can be a liquid battery or a solid battery, and is not particularly limited.
When it is a liquid lithium ion battery, it comprises a negative electrode sheet, a positive electrode sheet, a separator and an electrolyte as described in the first aspect.
The positive electrode plate, the diaphragm and the electrolyte in the liquid lithium ion battery are all easily known and obtained by the person skilled in the art, namely, corresponding substances which can be assembled to obtain the complete lithium ion battery and the preparation method are all applicable.
When it is a solid state lithium ion battery, it comprises a negative electrode tab, a positive electrode tab and a solid state electrolyte layer as described in the first aspect.
The positive electrode plate and the solid electrolyte layer in the solid lithium ion battery are all easily known and obtained by the person skilled in the art, namely, the corresponding substances which can be assembled to obtain the complete lithium ion battery and the preparation method are both applicable.
Compared with the prior art, the invention has the following beneficial effects:
according to the negative electrode plate provided by the invention, the first negative electrode layer is arranged on one side close to the current collector, and graphite and silicon are simultaneously included in the first negative electrode layer, so that the energy density of the whole negative electrode is improved, the capacity of the negative electrode is improved, and the existence of the second graphite negative electrode layer on one side far away from the current collector further inhibits the expansion of a silicon material through the mutual matching of the current collector, the type and the using amount of a binder, the surface density and the thickness, and the synergistic effect is achieved, so that the first-circle expansion rate of the negative electrode material is reduced, the energy density of a traditional graphite-based negative electrode lithium battery is improved, the cycle life of the battery is prolonged, and the preparation method is simple and is suitable for the existing commercial large-scale lithium ion battery system without complex preparation steps. According to the battery provided by the invention, the gram capacity of the negative electrode at 0.33C can reach more than 375mAh/g, the expansion rate of the first ring of the negative electrode is less than 38%, the capacity retention rate after 500 circles of circulation can reach more than 85.8%, the thickness of the negative electrode layer is further adjusted, the gram capacity of the negative electrode at 0.33C can reach more than 375mAh/g after the silicon material accounts for the proportion and the cohesiveness of the first binder, the expansion rate of the first ring of the negative electrode is less than 30%, and the capacity retention rate after 500 circles of circulation can reach more than 93.4%.
Detailed Description
The technical scheme of the invention is further described by the following specific examples. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
The negative electrode for the lithium battery comprises a current collector and a first negative electrode layer and a second negative electrode layer which are arranged on the current collector, wherein the first negative electrode layer comprises 95-97wt% of graphite material coated by carbon and 3-5wt% of silicon oxide compound serving as active materials and comprises polyacrylonitrile binder serving as a first binder, and the second negative electrode layer adopts 100% of graphite serving as active material and comprises a second binder and a second conductive agent.
It is understood that the above percentages are in proportion to the anode active material rather than the anode layer, and that, for example, 95 to 97wt% means that the carbon-coated graphite material occupies 95 to 97wt% of the anode active material in the first anode layer.
Silicon is known to have a higher capacity but is limited in use due to its greater expansion properties; in the present application, the expansion performance of the first anode layer is effectively suppressed by means of the adhesion of the current collector to the first anode layer, and thus, even if a silicon anode active material with high expansion performance is added to the first anode layer, unexpected volume expansion of the anode layer as a whole is not caused. The problem of contradiction between the current expansion performance and the energy density is solved by arranging the multi-layer negative electrode.
The polyacrylonitrile binder mentioned in the present invention includes, but is not limited to, copolymers of monomeric acrylonitrile and simple variations of the copolymers thereof, such as polymers in which simple substitution of functional groups, change in the positions of functional groups, change in the number of functional groups and change in the number of monomers occur without changing the adhesive properties.
In one embodiment of the present application, the first negative electrode layer includes: the negative electrode comprises 90-97wt% of a negative electrode active material consisting of 95-97wt% of graphite material and 3-5wt% of silicon oxide, 3-5wt% of polyacrylonitrile binder in the first negative electrode layer, and 1-5wt% of a first conductive agent, more specifically, 15-20wt% of CNT and/or VGCF in the first conductive agent. When the proportion of each component satisfies the above range, the energy density of the graphite-based negative electrode lithium battery can be effectively improved, while the original excellent cycle retention rate of the lithium battery is not reduced, when the weight ratio of the silicon oxide in the first negative electrode layer active material is more than 5wt%, the expansion of the silicon oxide during charge and discharge is difficult to suppress, so that the performance of the battery is deteriorated, and when the weight ratio of the silicon oxide in the first negative electrode layer active material is less than 3wt%, the energy density of the lithium battery is not significantly improved.
Preferably, the first conductive agent includes at least one or both of CNT or VGCF. Compared with other conductive agents, the fibrous structures of the CNT and the VGCF have a certain length-diameter ratio, so that the silicon oxide can form a linear conductive channel in the first negative electrode layer when expanding, the transmission efficiency of lithium ions and electrons is improved, and the capacity performance and the cycle performance of the battery are ensured not to be deteriorated.
The specific types of CNT and VGCF are not particularly limited in the present application, and any known CNT, VGCF products having a relatively long jing ratio can be used in the present application without departing from the inventive concept of the present application, as an illustrative example, the aspect ratio of CNT and VGCF is >1000; preferably, the aspect ratio of CNT and VGCF is >2000.
In one embodiment of the present invention, the second anode layer includes: the second anode active material, 4 to 8wt% of a binder, and 1 to 5wt% of a second conductive agent, specifically, the second anode layer includes: graphite as the sole active material, 4-8 wt% of a binder, and 1-3wt% of a second conductive agent.
It is understood that the second anode active material may be a mixture of one or more anode active materials, but should have less expansion than the first anode layer; therefore, as a preferred embodiment, the second negative electrode active material is entirely composed of a graphite negative electrode active material.
As a preferred embodiment, the binding force of the first binder to the current collector is greater than that of the second binder, and the content of the binder in the second anode layer is greater than that of the binder in the first anode layer;
according to the invention, a negative electrode system with high binder content is adopted, and the first negative electrode layer and the current collector have stronger interaction through the adjustment of the binder content and the type, so that the problem of pole piece falling caused by silicon expansion is avoided. The content of the second binder is greater than the content of the first binder in the present invention based on the selection of the second anode layer away from the current collector. By increasing the binder content in the second anode layer, a "clamping" effect is formed on the first anode layer in conjunction with the current collector, further inhibiting expansion and structural changes of the first anode layer.
In one embodiment of the present invention, a projected area of the second anode layer on the current collector is equal to or larger than a projected area of the first anode on the current collector.
The graphite materials in the first negative electrode active material and the second negative electrode active material are not particularly limited in this application, and any known graphite material that can be used as a negative electrode active material can be used in this application without departing from the inventive concept of the present application, and the graphite material may be selected from one of natural graphite and artificial graphite by way of illustration only and not by way of any limitation of the scope of protection. Further, the artificial graphite is selected from one of single-particle artificial graphite, secondary-particle artificial graphite, and a composite of single-particle artificial graphite and secondary-particle artificial graphite.
According to the invention, the graphite in the first negative electrode layer is carbon-coated graphite, and the carbon-coated graphite is adopted to be beneficial to compensating for the reduction of the conductivity of the whole negative electrode layer caused by the addition of the silicon oxide, and simultaneously, when the silicon oxide expands, the conductive agent can form a conductive network, so that the phenomenon that a conductive path is damaged caused by the expansion of silicon is effectively avoided.
Carbon coating of graphite is known in the art, such as coating the graphite surface with a carbonaceous coating. The actual carbon coating method is not particularly limited, and any known carbon coating method or structure can be used in the present application without departing from the inventive concept of the present application.
According to the invention, the first negative electrode layer is arranged on one side of the negative electrode plate, which is close to the current collector, and comprises graphite and silicon, so that the energy density of the whole negative electrode is improved, the capacity of the negative electrode is improved, and meanwhile, the graphite negative electrode with smaller expansion is adopted on one side, which is far away from the current collector, so that the expansion of the first negative electrode layer is further restrained, and the negative electrode plate is suitable for the existing commercial large-scale lithium ion battery system.
In the present invention, there is an adhesive force between the anode layer and the current collector, and thus the expansion ratio of the anode active material layer on the side close to the current collector is generally smaller than that on the side far from the current collector, and thus the present invention selects to add a silicon material to the first anode layer close to the current collector. Expansion due to the addition of silicon is avoided by the interaction of the negative electrode layer with the current collector.
As a preferred embodiment, the current collector for the negative electrode is selected from current collectors having high tensile properties, and in some examples, may be copper foil; preferably, the tensile strength of the negative electrode current collector is 350N/cm or more 2 . For example 350N/cm 2 、400N/cm 2 、450N/cm 2 Etc.
The first negative electrode layer includes a first binder and a first conductive agent;
the first negative electrode layer includes a first binder and a first conductive agent;
the first binder is a polyacrylonitrile binder;
the first conductive agent comprises one or more of carbon black, super-P, CNT, VGCF, acetylene black and graphene.
In some embodiments, the first conductive agent comprises at least 15wt% to 25wt% CNT and/or VGCF.
The second negative electrode layer includes a second binder and a second conductive agent;
in the present invention, the binder in the first negative electrode layer is selected to be of a type that is more strongly adhered to the current collector to further overcome the expansion of the first negative electrode layer due to the introduction of silicon. In contrast, since the pure graphite anode has little expansion, the second anode layer may continue to use conventional binders, such as conventional aqueous binders in the second anode layer that may be readily known to those skilled in the art, including, but not limited to, polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylamide, styrene butadiene rubber, or hydroxymethyl cellulose, and the like.
In the present invention, the choice of the second conductive agent includes, but is not limited to, carbon-based materials, powdered nickel or other metal particles or conductive polymers, for example, carbon-based materials may include carbon black, graphite, super p, acetylene black (such as KETCHENTM black or denketm black), carbon fibers and particles of nanotubes, graphene, and the like; the conductive polymer includes polyaniline, polythiophene, polyacetylene, polypyrrole, poly (3, 4-ethylenedioxythiophene) polysulfonastyrene, and the like.
Preferably, the thickness of the first negative electrode layer is 5 to 40%, for example 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38% or 40% or the like, preferably 16 to 25%, of the thickness of the second negative electrode layer.
In the invention, the thickness of the first negative electrode layer is within the range of 16-25% of the thickness of the second negative electrode layer, so that the technical effects of improving the energy density and the cycle retention rate of the battery can be better realized, and if the thickness of the first negative electrode layer is too thick, the expansion coefficients of the two sides of the first negative electrode layer, which are close to the current collector, and the two sides, which are far away from the current collector, are different, the pole piece is easy to fall off, and the stripping between the first negative electrode layer and the second negative electrode layer is easy to cause, if the thickness of the first negative electrode layer is too small, the effect of improving the energy density is not obvious.
Preferably, the thickness of the first negative electrode layer is 16 to 55 μm, for example, 16 μm, 18 μm, 20 μm, 23 μm, 25 μm, 28 μm, 30 μm, 33 μm, 35 μm, 38 μm, 40 μm, 43 μm, 45 μm, 48 μm, 50 μm, 53 μm, 55 μm or the like.
Preferably, the thickness of the second negative electrode layer is 170 to 210 μm, for example 170 μm, 175 μm, 180 μm, 185 μm, 190 μm, 195 μm, 200 μm, 205 μm, 210 μm or the like.
In a second aspect, the present invention provides a method for preparing the negative electrode tab according to the first aspect, the method comprising:
and coating the slurry of the first negative electrode layer on the surface of the current collector to obtain a first negative electrode layer, and coating the slurry of the second negative electrode layer on the surface of the first negative electrode layer to obtain the negative electrode plate.
Preferably, the first negative electrode layer has an areal density of 30 to 50g/m 2 For example 30g/m 2 、35g/m 2 、40g/m 2 、45g/m 2 Or 50g/m 2 Etc.
Preferably, the second negative electrode layer has an areal density of 150 to 170g/m 2 For example 150g/m 2 、155g/m 2 、160g/m 2 、165g/m 2 Or 170g/m 2 Etc.;
the invention provides a lithium battery comprising the negative electrode.
The lithium battery comprises a positive electrode, a negative electrode and an electrolyte, and a battery shell with the structure.
The positive electrode includes a current collector and a positive electrode active material layer formed on the current collector;
The positive electrode current collector is not particularly restricted so long as it has conductivity without causing chemical changes in the battery. In particular, copper, stainless steel, aluminum, nickel, titanium, or a metal current collector surface-treated with carbon or other substances may be used.
The positive electrode current collector may generally have a thickness of 3 μm to 500 μm.
The positive electrode current collector may have fine irregularities formed on the surface thereof to improve the adhesion of the positive electrode active material. For example, positive electrode current collectors of various shapes such as films, sheets, foils, nets, porous bodies, foams and non-woven fabrics may be used.
The positive electrode active material layer may contain a positive electrode active material.
The positive electrode active material is a compound capable of reversibly intercalating and deintercalating lithium, and specifically may include a lithium transition metal composite oxide containing lithium and at least one other transition metal selected from the group consisting of nickel, cobalt, manganese, and aluminum; preferably, the transition metal may be lithium, nickel, cobalt, manganese, or the like.
More specifically, the lithium transition metal composite oxide may be a lithium manganese-based oxide (e.g., liMnO 2 、LiMn 2 O 4 Etc.), lithium cobalt-based oxides (e.g. LiCoO 2 Etc.), lithium nickel-based oxides (e.g., liNiO 2 Etc.), lithium nickel manganese-based oxides (e.g., liNi 1-y Mn y O 2 (wherein 0<y<1)、LiMn 2-z Ni z O 4 (wherein 0<z<2) Etc.), lithium nickel cobalt-based oxides (e.g., liNi 1- y1 Co y1 O 2 (wherein 0<y 1 <1) Etc.), lithium manganese cobalt-based oxides (e.g., liCo 1-y2 Mn y2 O 2 (wherein 0<y 2 <1)、LiMn 2-z1 Co z1 O 4 (wherein 0<z 1 <2) Etc.), lithium nickel manganese cobalt-based oxides (e.g., li (Ni) p Co q Mn r1 )O 2 (wherein 0<p<1，0<q<1，0<r1<1, p+q+r1=1), or lithium nickel cobalt transition metal (M) oxide (e.g., li (Ni) p2 Co q2 Mn r3 A S2 )O 2 (wherein M is selected from the group consisting of Al, fe, V, cr, ti, ta, mg and Mo, p 2 、q 2 、r 3 Sum s 2 Each being an atomic fraction of an independent element, and 0<p 2 <1、0<q 2 <1、0<r 3 <1、0<s 2 <1、p 2 +q 2 +r 3 +s 2 =1), etc.), and may contain any one or two or more compounds thereof. Of these, the lithium transition metal composite oxide may be LiCoO in terms of being capable of increasing the capacity and stability of the battery 2 、LiMnO 2 、LiNiO 2 Lithium nickel manganese cobalt oxide (e.g. Li (Ni) 0.6 Mn 0.2 Co 0.2 )O 2 、Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 、Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 Or LiNi 0.8 Mn 0.1 Co 0.1 )O 2 Etc. or lithium nickel cobalt aluminum oxide (e.g., li (Ni 0.8 Co 0.15 Al 0.05 )O 2 Etc.), etc. When considering the remarkable improvement effect obtained according to the control of the type and content ratio of the constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide may be Li (Ni 0.6 Mn 0.2 Co 0.2 )O 2 、Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 、Li(Ni 0.7 Mn 0.15 Co 0.15 )O 2 Or Li (Ni) 0.8 Mn 0.1 Co 0.1 )O 2 Etc., and any one or a mixture of two or more thereof may be used.
The amount of the positive electrode active material contained in the positive electrode active material layer may be 80wt% to 99wt%, preferably 92wt% to 98.5wt%.
The positive electrode active material layer may contain a positive electrode binder and/or a positive electrode conductive material in addition to the positive electrode active material described above.
The positive electrode binder is used to bind together the active material, the conductive material, and the current collector, and may include, in particular, at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.
The amount of the positive electrode binder contained in the positive electrode active material layer may be 1wt% to 20wt%, preferably 1.2wt% to 10wt%.
The conductive material is mainly used to assist and improve conductivity in the secondary battery, and is not particularly limited as long as it has conductivity without causing chemical changes. In particular, the conductive material may comprise graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes, such as carbon nanotubes; metal powders such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and polyphenylene derivatives, and may preferably contain carbon black in terms of improving conductivity.
The specific surface area of the positive electrode conductive material can be 80m 2 /g to 200m 2 /g, preferably 100m 2 /g to 150m 2 /g。
The amount of the positive electrode conductive material contained in the positive electrode active material layer may be 1wt% to 20wt%, preferably 1.2wt% to 10wt%.
The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 50 μm to 110 μm.
The positive electrode may be manufactured by coating a positive electrode slurry including a positive electrode active material and optionally a positive electrode binder, a positive electrode conductive material, and a solvent for forming a positive electrode slurry on a positive electrode current collector, followed by drying and rolling.
The solvent for forming the positive electrode slurry may contain an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in such an amount that a preferable viscosity is obtained when a positive electrode active material is contained and a positive electrode binder, a positive electrode conductive material, or the like is optionally contained. For example, the amount of the positive electrode slurry-forming solvent contained in the positive electrode slurry may be such that the concentration of the solid containing the positive electrode active material and optionally containing the positive electrode binder and the positive electrode conductive material is 50 to 95wt%, preferably 70 to 90wt%.
The type of electrolyte is not particularly limited in the present application, and any known electrolyte material can be used in the present application without departing from the inventive concept of the present application. As illustrative examples, the electrolyte may be a liquid electrolyte, a solid electrolyte, or a mixed form of a solid electrolyte and a liquid electrolyte.
When the electrolyte is liquid electrolyte, a separator should be further disposed in the battery system.
The separator serves the primary function of separating the negative and positive electrodes and providing a path for lithium ions to travel. Any separator may be used without particular limitation as long as it is a separator commonly used in secondary batteries. In particular, a separator having excellent electrolyte wettability and low resistance to ion movement in an electrolyte is preferable. Specifically, a porous polymer film, for example, a porous polymer film manufactured using a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or a laminated structure having two or more layers thereof may be used. Further, a typical porous nonwoven fabric, for example, a nonwoven fabric formed of glass fibers, polyethylene terephthalate fibers, or the like having a high melting point may be used. In addition, a coated separator including a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may be selectively used in a single-layer or multi-layer structure.
The electrolyte used in the present invention may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, or the like, which can be used for the production of a secondary battery, but is not limited thereto.
In particular, the electrolyte may include an organic solvent and a lithium salt.
Any organic solvent may be used without particular limitation as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ -butyrolactone, and epsilon-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene Carbonate (EC) and Propylene Carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (wherein R is a linear, branched or cyclic C2-C20 hydrocarbon group and may contain a double bond aromatic ring or ether linkage); amides such as dimethylformamide; dioxolanes, such as 1, 3-dioxolane; or sulfolane. Among the above solvents, a carbonate-based solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ion conductivity and high dielectric constant and a low-viscosity linear carbonate-based compound (e.g., ethylene carbonate, dimethyl carbonate or diethyl carbonate) which can increase charge/discharge performance of the battery is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.
Any compound can be used as the lithium salt withoutThere is a particular limitation as long as it can provide lithium ions used in the lithium secondary battery. Specifically, liPF 6 、LiClO 4 、LiAsF 6 、LiBF 4 、LiSbF6、LiAlO 4 、LiAlCl 4 、LiCF 3 SO 3 、LiC 4 F 9 SO 3 、LiN(C 2 F 5 SO 3 ) 2 、LiN(C 2 F 5 SO 2 ) 2 、LiN(CF 3 SO 2 ) 2 、LiCl、LiI、LiB(C 2 O 4 ) 2 Etc. may be used as the lithium salt. The lithium salt may be used in a concentration range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent performance, and lithium ions can be effectively moved.
As an embodiment, the electrolyte may be a solid state electrolyte, and the solid state electrolyte particles may comprise one or more polymeric components, oxide solid state electrolytes, sulfide solid state electrolytes, halide solid state electrolytes, borate solid state electrolytes, nitride solid state electrolytes, or hydride solid state electrolytes. When polymer particles are used, lithium salts should be used for rechecking. As an embodiment, the polymer-based component may comprise one or more polymeric materials selected from the group consisting of: polyethylene glycol, polyethylene oxide (PEO), poly (p-phenylene oxide) (PPO), poly (methyl methacrylate) (PMMA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyvinylidene fluoride co-hexafluoropropylene (PVDF-HFP), polyvinyl chloride (PVC), and combinations thereof. It will be appreciated that a high ionic conductivity of the polymeric material is advantageous for the performance of the overall solid state electrolyte material, and preferably the polymeric material should have an ionic conductivity of greater than or equal to 10-4S/cm.
As an embodiment, the oxide particles may comprise one or more garnet ceramics, LISICON-type oxides, NASICON-type oxides, and perovskite-type ceramics. As an illustrative example, the garnet ceramic may be selected from the group consisting of: li (Li) 6.5 La 3 Zr 1.75 Te 0.25 O 12 、Li 7 La 3 Zr 2 O 12 、Li 6.2 Ga 0.3 La 2.95 Rb 0.05 Zr 2 O 12 、Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 、Li 6.25 Al 0.25 La 3 Zr 2 O 12 、Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 、Li 6.75 La 3 Zr 1.75 Nb 0.25 O 12 And combinations thereof. The LISICON-type oxide may be selected from the group consisting of: li (Li) 14 Zn(GeO 4 ) 4 、Li 3+x (P 1-x Si x ) O4 (0 therein)<x<1)、Li 3+x Ge x V 1-x O 4 (wherein 0<x<1) And combinations thereof. NASICON type oxide can be formed from LiMM' (PO 4 ) 3 And a definition wherein M and M' are independently selected from Al, ge, ti, sn, hf, zr and La. Preferably, the NASICON-type oxide may be selected from the group comprising: li (Li) 1+x Al x Ge 2-x (PO 4 ) 3 (LAGP) (wherein 0.ltoreq.x.ltoreq.2), li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP) (where 0.ltoreq.x.ltoreq.2), li 1+x Y x Zr 2-x( PO 4 ) 3 (LYZP) (wherein 0.ltoreq.x.ltoreq.2), li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 、LiTi 2 (PO 4 ) 3 、LiGeTi(PO 4 ) 3 、LiGe 2 (PO 4 ) 3 、LiHf 2 (PO 4 ) 3 And combinations thereof. The one or more perovskite ceramics may be selected from the group comprising: li (Li) 3.3 La 0.53 TiO 3 、LiSr 1.65 Zr 1.3 Ta 1.7 O 9 、Li 2x-y Sr 1-x Ta y Zr 1-y O 3 (wherein x=0.75 y and 0.60<y<0.75)、Li 3/8 Sr 7/16 Nb 3/ 4 Zr 1/4 O 3 、Li 3x La (2/3-x) TiO 3 (wherein 0<x<0.25 To (3)And combinations thereof. Preferably, the one or more oxide-based materials may have a weight ratio of greater than or equal to about 10 -5 S/cm to less than or equal to about 10 -1 S/cm ionic conductivity.
The sulfide solid state electrolyte is selected from one or more sulfide-based materials from the group consisting of: li (Li) 2 S-P 2 S 5 、Li 2 S-P 2 S 5 MSx (wherein M is Si, ge and Sn and 0.ltoreq.x.ltoreq.2), li 3.4 Si 0.4 P 0.6 S 4 、Li 10 GeP 2 S 11.7 O 0.3 、Li 9.6 P 3 S 12 、Li 7 P 3 S 11 、Li 9 P 3 S 9 O 3 、Li 10.35 Si 1.35 P 1.65 S 12 、Li 9.81 Sn 0.81 P 2.19 S 12 、Li 10 (Si 0.5 Ge 0.5 )P 2 S 12 、Li(Ge 0.5 Sn 0.5 )P 2 S 12 、Li(Si 0.5 Sn 0.5 )PsS 12 、Li 10 GeP 2 S 12 (LGPS)、Li 6 PS 5 X (wherein X is Cl, br or I), li 7 P 2 S 8 I、Li 10.35 Ge 1.35 P 1.65 S 12 、Li 3.25 Ge 0.25 P 0.75 S 4 、Li 10 SnP 2 S 12 、Li 10 SiP 2 S 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、(1-x)P 2 S 5-x Li 2 S (wherein 0.5.ltoreq.x.ltoreq.0.7) and combinations thereof.
The halide solid state electrolyte may include one or more halide-based materials selected from the group consisting of: li (Li) 2 CdCl 4 、Li 2 MgCl 4 、Li 2 CdI 4 、Li 2 ZnI 4 、Li 3 OCl、LiI、Li 5 ZnI 4 、Li 3 OCl 1-x Brx (0 therein)<x<1) And combinations thereof.
The borate solid state electrolyte is selected from one or more borate-based materials comprising the group of: li (Li) 2 B 4 O 7 、Li 2 O-(B 2 O 3 )-(P 2 O 5) And combinations thereof.
The nitride solid state electrolyte may be selected from one or more nitride-based materials from the group consisting of: li (Li) 3 N、Li 7 PN 4 、LiSi 2 N 3 LiPON, and combinations thereof.
The hydride solid state electrolyte may be selected from one or more hydride-based materials from the group comprising: li (Li) 3 AlH 6 、LiBH 4 、LiBH 4 -LiX (wherein X is one of Cl, br and I), liNH 2 、Li 2 NH、LiBH 4 -LiNH 2 And combinations thereof.
As a particular embodiment, the solid electrolyte may be a quasi-solid electrolyte comprising a mixture of the nonaqueous liquid electrolyte solution detailed above and a solid electrolyte system, e.g., comprising one or more ionic liquids and one or more metal oxide particles (such as alumina (Al 2 O 3 ) And/or silicon dioxide (SiO) 2 ))。
Example 1
The present embodiment provides a negative electrode sheet, which is provided based on the above specific embodiment:
Wherein the thickness of the first negative electrode layer is 40 mu m, the thickness of the second negative electrode layer is 200 mu m, the first negative electrode layer is positioned between the current collector and the second negative electrode layer, and the thickness of the first negative electrode layer is 20% of the thickness of the second negative electrode layer;
the first negative electrode layer is made of SiO, carbon-coated artificial graphite, polyacrylonitrile and carbon nano tubes (the mass ratio of SiO to carbon-coated artificial graphite is 4:96), and the second negative electrode layer is made of artificial graphite, conductive carbon black and polyacrylic acid;
the preparation method of the negative electrode plate comprises the following steps:
(1) Weighing silicon oxide (SiO) and the carbon coating according to the mass ratio of 4:96Graphite, uniformly mixing to obtain a first mixed anode active material, mixing the first mixed anode active material, carbon nano tubes and polyacrylonitrile in a mass ratio of 90:6:4 with deionized dispersion to obtain a first anode layer slurry, and coating one side of the first anode layer slurry on copper foil (tensile strength is 350N/cm 2 ) Drying and rolling the surface to obtain a first negative electrode layer;
(2) Dispersing artificial graphite, conductive carbon black and polyacrylic acid in deionized water according to a mass ratio of 92:2:6 to obtain second negative electrode layer slurry, coating the second negative electrode layer slurry on the surface of the first negative electrode layer, and drying and rolling to obtain the negative electrode plate.
Example 2
The present embodiment provides a negative electrode sheet, which is provided based on the above specific embodiment:
the thickness of the first negative electrode layer is 30 mu m, the thickness of the second negative electrode layer is 180 mu m, the first negative electrode layer is positioned between the current collector and the second negative electrode layer, and the thickness of the first negative electrode layer is 16.7;
the first negative electrode layer is made of SiO, carbon coated artificial graphite, polyacrylonitrile and carbon fiber (the mass ratio of SiO to carbon coated artificial graphite is 3:97), and the second negative electrode layer is made of artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose;
the preparation method of the negative electrode plate comprises the following steps:
(1) Weighing silicon oxide (SiO) and graphite with a carbon coating layer according to a mass ratio of 3:97, uniformly mixing to obtain a first mixed anode active material, mixing the first mixed anode active material, a carbon nano tube and polyacrylonitrile in a mass ratio of 92:3:5 with deionized dispersion to obtain a first anode layer slurry, and coating one side of the first anode layer slurry on a copper foil (tensile strength is 350N/cm 2 ) Drying and rolling the surface to obtain a first negative electrode layer;
(2) Dispersing artificial graphite, conductive carbon black, styrene-butadiene rubber and sodium carboxymethylcellulose in deionized water according to a mass ratio of 92:2:3:3 to obtain second negative electrode layer slurry, coating the second negative electrode layer slurry on the surface of the first negative electrode layer, and drying and rolling to obtain the negative electrode plate.
Example 3
The present embodiment provides a negative electrode sheet, which is provided based on the above specific embodiment:
wherein the first negative electrode (thickness 52 μm, second negative electrode layer thickness 208 μm, first negative electrode layer between the current collector and the second negative electrode layer, first negative electrode layer thickness 1/4 of second negative electrode layer thickness;
the first negative electrode layer is made of SiO, carbon-coated artificial graphite, polyacrylonitrile and carbon nano tubes (the mass ratio of SiO to carbon-coated artificial graphite is 5:95), and the second negative electrode layer is made of artificial graphite, conductive carbon black and polyacrylic acid.
The remaining preparation remained the same as in parameter example 1.
Example 4
The difference between this example and example 1 is that the thickness of the first negative electrode layer in this example is 100 μm, and the thickness of the first negative electrode layer is 50% of the thickness of the second negative electrode layer.
The remaining preparation remained the same as in parameter example 1.
Example 5
The difference between this example and example 1 is that the mass ratio of SiO to carbon coated artificial graphite in this example is 8:92.
The remaining preparation methods and parameters were consistent with example 1.
Example 6
The difference between this example and example 1 is that the binder of the first negative electrode layer in this example is cmc+sbr.
The remaining preparation methods and parameters were consistent with example 1.
Comparative example 1
The difference between this comparative example and example 1 is that the negative electrode layer is only one layer in this comparative example, and the negative electrode active material is pure artificial graphite.
The preparation process and parameters were identical to those of step (2) in example 1.
Comparative example 2
The present comparative example differs from example 1 in that the negative electrode layer is only one layer in the present comparative example, and the negative electrode active material composition is the same as that of the first negative electrode layer in example 1.
The preparation process and parameters were identical to those of step (2) in example 1.
Preparation of a battery:
positive pole piece: weighing NCM811, polyvinylidene fluoride and conductive carbon black according to the mass ratio of 90:5:5, dispersing in NMP, preparing positive electrode slurry, coating the positive electrode slurry on the surface of an aluminum foil, drying, rolling to form a positive electrode plate, and die-cutting to form a corresponding shape.
Taking the negative electrode pieces provided in examples 1-6 and comparative examples 1-2 as negative electrodes, taking the prepared positive electrode piece as positive electrode, adopting a polyolefin diaphragm and ethylene carbonate as electrolyte, and adding LiCF into the electrolyte 3 SO 3 A battery was obtained.
The batteries provided in examples 1 to 6 and comparative examples 1 to 2 were subjected to electrochemical performance tests under the following conditions: the charge and discharge test was performed at 25℃with a constant current of 0.33C, and the results are shown in Table 1.
TABLE 1
As is clear from the data in examples 1 and 4, the excessive thickness of the first negative electrode layer affects the first-turn expansion ratio of the negative electrode, and the first-turn expansion ratio of the negative electrode increases, so that the capacity of the battery decreases and the cycle retention ratio decreases during continuous charge and discharge.
As is clear from the data in examples 1 and 5, the mass ratio of the silicon material in the first negative electrode layer is too large, which effectively increases the energy density of the battery, but also affects the initial expansion ratio of the negative electrode, resulting in a decrease in the cycle retention rate of the battery.
As is clear from the data in examples 1 and 6, when the binding force of the binder in the first negative electrode layer is equal to that in the second negative electrode layer, the initial expansion ratio increases, and the cycle performance of the battery is deteriorated.
As can be seen from the data results of example 1 and comparative example 1, the negative electrode provided by the invention has significantly improved capacity on the basis of maintaining a lower expansion rate and better cycle stability compared with a pure graphite negative electrode.
As is clear from the data results of example 1 and comparative example 2, the negative electrode provided by the present invention has higher capacity, significantly lower expansion rate and better cycle stability than the negative electrode structure using a single layer.
In summary, the first negative electrode layer is arranged on one side close to the current collector and comprises graphite and silicon, so that the energy density of the whole negative electrode is improved, the capacity of the negative electrode is improved, and the second graphite negative electrode layer on one side far away from the current collector further inhibits the expansion of a silicon material, so that the negative electrode plate is suitable for the existing commercial large-scale lithium ion battery system, and the preparation method is simple and does not need complex preparation steps. According to the battery provided by the invention, the gram capacity of the negative electrode at 0.33C can reach more than 375mAh/g, the expansion rate of the first ring of the negative electrode is less than 38%, the capacity retention rate after 500 circles of circulation can reach more than 85.8%, the thickness of the negative electrode layer is further adjusted, the gram capacity of the negative electrode at 0.33C can reach more than 375mAh/g after the silicon material accounts for the proportion and the cohesiveness of the first binder, the expansion rate of the first ring of the negative electrode is less than 30%, and the capacity retention rate after 500 circles of circulation can reach more than 93.4%.
While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.

Claims (14)

1. The negative electrode plate is characterized by comprising a current collector, a first negative electrode layer and a second negative electrode layer, wherein the first negative electrode layer is positioned between the current collector and the second negative electrode layer;
wherein the negative electrode active material in the first negative electrode layer includes graphite and a silicon material, and the negative electrode active material in the second negative electrode layer includes graphite; the graphite in the first negative electrode layer is carbon-coated graphite;
the first negative electrode layer comprises a first binder and a first conductive agent; the first binder is a polyacrylonitrile binder; the second negative electrode layer comprises a second binder and a second conductive agent; the binding force between the first binder and the current collector is larger than that between the second binder and the current collector; the mass ratio of the binder in the second negative electrode layer is larger than that of the binder in the first negative electrode layer; the mass of the silicon material in the first negative electrode layer is 3-5% of the mass of the negative electrode active material in the first negative electrode layer; the silicon material comprises a silicon oxygen material; the thickness of the first negative electrode layer is 5-40% of the thickness of the second negative electrode layer.
2. The negative electrode tab of claim 1, wherein the second binder is an aqueous binder.
3. The negative electrode tab of claim 1, wherein the mass ratio of the first conductive agent in the first negative electrode layer is greater than the mass ratio of the second conductive agent in the second negative electrode layer.
4. The negative electrode tab of claim 1, wherein the first conductive agent comprises any one or a combination of at least two of CNT, VGCF, carbon black, or graphene.
5. The negative electrode tab of claim 4, wherein the CNT and/or VGCF is present in the first conductive agent in a mass ratio of 15 to 25wt%.
6. The negative electrode tab of claim 1, wherein the mass ratio of the binder in the first negative electrode layer is 3-5 wt%.
7. The negative electrode tab of claim 1, wherein the mass ratio of the binder in the second negative electrode layer is 4-8 wt%.
8. The negative electrode tab of claim 1, wherein the current collector has a tensile strength of 350N/cm or more 2 。
9. The negative electrode tab of claim 1, wherein the thickness of the first negative electrode layer is 16-25% of the thickness of the second negative electrode layer.
10. The negative electrode tab of claim 1, wherein the first negative electrode layer has a thickness of 16-55 μm.
11. The negative electrode tab of claim 1, wherein the second negative electrode layer has a thickness of 170-210 μm.
12. The negative electrode tab of claim 1 wherein the first negative electrode layer has a coated areal density of 30 to 50g/m 2 。
13. A method of producing the negative electrode sheet according to any one of claims 1 to 12, comprising:
and coating the slurry of the first negative electrode layer on the surface of the current collector to obtain a first negative electrode layer, and coating the slurry of the second negative electrode layer on the surface of the first negative electrode layer to obtain the negative electrode plate.
14. A lithium ion battery comprising the negative electrode sheet according to any one of claims 1-12.
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