CN114156487A - Pole piece and lithium ion battery - Google Patents

Pole piece and lithium ion battery Download PDF

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Publication number
CN114156487A
CN114156487A CN202111434303.0A CN202111434303A CN114156487A CN 114156487 A CN114156487 A CN 114156487A CN 202111434303 A CN202111434303 A CN 202111434303A CN 114156487 A CN114156487 A CN 114156487A
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China
Prior art keywords
pole piece
protective layer
carbide
mass
nitride
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CN202111434303.0A
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Chinese (zh)
Inventor
张健
彭冲
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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Priority to CN202111434303.0A priority Critical patent/CN114156487A/en
Publication of CN114156487A publication Critical patent/CN114156487A/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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2200/00—Safety devices for primary or secondary batteries
    • 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)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Composite Materials (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The invention provides a pole piece and a lithium ion battery. The invention provides a pole piece, which comprises a substrate, wherein the substrate comprises a current collector and a protective layer arranged on the surface of the current collector, and an active substance layer is also arranged on the protective layer; the protective layer comprises 62-96% of inactive materials, 0.1-8% of conductive agents and 3-30% of binders in percentage by mass, the inactive materials comprise inorganic particles and carbon layers coated on the surfaces of the inorganic particles, and the mass of the carbon layers is less than 10% of that of the inorganic particles. The pole piece provided by the invention can solve the problem that the safety and the electrical property of the lithium ion battery cannot be considered at the same time.

Description

Pole piece and lithium ion battery
Technical Field
The invention relates to a pole piece and a lithium ion battery, and relates to the technical field of lithium ion batteries.
Background
The lithium ion battery has the advantages of high platform voltage, high energy density, no memory effect, long service life and the like, and is widely applied to the fields of smart phones, notebook computers, Bluetooth, wearable equipment and the like. However, in some extreme cases, for example, when the lithium ion battery is subjected to mechanical damage, such as needle stick, heavy impact, etc., an internal short circuit occurs, and a large amount of heat is released in a short time, so that the lithium ion battery is subjected to fire and failure, and has a great safety hazard.
The protective layer is arranged on the surface of the current collector, so that the safety of the lithium ion battery is improved, and the electrical property of the lithium ion battery is reduced, so that more and more attention is paid to the safety and the electrical property of the lithium ion battery.
Disclosure of Invention
The invention provides a pole piece which is used for solving the problem that the safety and the electrical property of a lithium ion battery cannot be considered at the same time.
The invention also provides a lithium ion battery which has better safety and electrical property.
The invention provides a pole piece, which comprises a substrate, wherein the substrate comprises a current collector and a protective layer arranged on the surface of the current collector, and an active substance layer is also arranged on the protective layer;
the protective layer comprises 62-96% of inactive materials, 0.1-8% of conductive agents and 3-30% of binders in percentage by mass, the inactive materials comprise inorganic particles and carbon layers coated on the surfaces of the inorganic particles, and the mass of the carbon layers is less than 10% of that of the inorganic particles.
According to an embodiment of the present invention, the mass of the carbon layer is 0.5% to 5% of the mass of the inorganic particles.
According to an embodiment of the invention, the inorganic particles comprise one or more of oxides, carbides, nitrides, inorganic salts.
According to an embodiment of the present invention, the oxide is selected from one or more of alumina, titania, magnesia, zirconia, antimony oxysulfide, barium oxide, manganese oxide, silica, iron oxide, and ferroferric oxide; the carbide comprises metal carbide and/or non-metal carbide, the metal carbide comprises one or more of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide and tungsten carbide, and the non-metal carbide comprises boron carbide and/or silicon carbide; the nitride comprises a metal nitride and/or a non-metal nitride, the metal nitride comprises one or more of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride and tantalum nitride, and the non-metal nitride comprises at least one of boron nitride, phosphorus pentanitride and silicon tetranitride; the inorganic salt comprises a carbonate and/or a sulfate.
According to an embodiment of the present invention, the carbon layer has a thickness of 1 to 100 nm.
According to an embodiment of the present invention, the inactive material has D50 ≦ 2 μm and D90 ≦ 5 μm.
According to an embodiment of the invention, the inactive material has a D50 of 0.05-0.5 μm and a D90 of 1-3 μm.
According to an embodiment of the present invention, the relationship between D50 of the inactive material and the thickness H1 of the protective layer satisfies H1 ≧ 2 XD 50.
According to an embodiment of the invention, the relation between the thickness H1 of the protective layer and the thickness H2 of the active material layer satisfies H1/H2 ≦ 1/5.
In a second aspect, the invention provides a lithium ion battery, which includes any of the above pole pieces.
The implementation of the invention has at least the following advantages:
1. the pole piece provided by the invention comprises the protective layer, and the mass fractions of the components in the protective layer are controlled, and the carbon-coated inorganic particles are selected, so that the safety of the lithium ion battery can be effectively improved, particularly, the probability of fire failure of the lithium ion battery is reduced when mechanical abuse occurs, the through-nail test passing rate of the lithium ion battery is improved, the electrical property of the lithium ion battery is basically not influenced, and the problem that the safety and the electrical property of the lithium ion battery cannot be considered simultaneously is solved.
2. The lithium ion battery provided by the invention has better safety and electrical property.
Drawings
Fig. 1 is a schematic structural diagram of a pole piece according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a pole piece according to another embodiment of the present invention.
Description of reference numerals:
100-a current collector;
200-a protective layer;
300-active substance layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a pole piece, which comprises a substrate, wherein the substrate comprises a current collector and a protective layer arranged on the surface of the current collector, and an active substance layer is also arranged on the protective layer;
the protective layer comprises 62-96% of inactive materials, 0.1-8% of conductive agents and 3-30% of binders in percentage by mass, the inactive materials comprise inorganic particles and carbon layers coated on the surfaces of the inorganic particles, and the mass of the carbon layers is less than 10% of that of the inorganic particles.
The invention provides a pole piece, which comprises a substrate, wherein the substrate comprises a current collector and a protective layer arranged on the surface of the current collector, and an active material layer is further arranged on the protective layer, for example, fig. 1 is a schematic structural diagram of the pole piece provided by an embodiment of the invention, fig. 2 is a schematic structural diagram of the pole piece provided by a further embodiment of the invention, as shown in fig. 1-2, the pole piece comprises a current collector 100, the current collector 100 is a base metal for attaching other materials such as a protective layer material, an active material and the like in the pole piece, and comprises two surfaces, specifically an upper surface and a lower surface, for attaching other materials such as a protective layer material, an active material and the like, the protective layer 200 is arranged on the upper surface of the current collector 100, an active material layer 300 is arranged on the protective layer 200, the length of the active material layer 300 can be greater than, equal to or less than the length of the protective layer 200, that is the active material layer 300 can be arranged on the upper surface of the protective layer 200 away from the current collector 100 (as shown in fig. 1), the active material layer 300 may be divided into two parts, the first part is located on the upper surface of the protection layer 200 away from the current collector, the second part is located on the upper surface of the current collector (see fig. 2) where the protection layer is not disposed, fig. 1-2 show the arrangement of the protection layer and the active material layer on the upper surface of the current collector, the arrangement of the other surface of the current collector 100 may be the same as or different from the upper surface, for example, the protection layer 200 and the active material layer 300 may be disposed on the lower surface of the current collector 100, or only the active material layer 300 may be disposed, but at least one of the two surfaces of the current collector 100 should be provided with the protection layer, and those skilled in the art may perform the arrangement according to actual needs, which the present invention is not limited further.
In order to ensure that the electrical property of the lithium ion battery is not affected basically, the invention selects the inactive material as the main component of the protective layer, the inactive material refers to the material which does not participate in the electrochemical reaction (the function of the active material layer of the pole piece is opposite), the influence of the protective layer on the cycle stability of the lithium ion battery can be reduced, and the electrical property of the lithium ion battery is considered; the inactive material is used as a main component of the protective layer 200 and also plays a role of supporting the protective layer, when the content of the inactive material is too low, the structural stability of the protective layer is poor, and the protective layer is damaged by the action of the active material layer in the subsequent active material layer coating process or is pressed and dispersed by pressure in the pole piece rolling process, so that the mass percentage of the inactive material is not lower than 62%; it can be understood that the protective layer 200 includes a binder and a conductive agent in addition to the inactive material, the binder is used for binding the inactive material, the conductive agent and other components together to form a coating, and binding the protective layer and the current collector together, so as to improve the stability of the protective layer and the binding force between the protective layer and the current collector, thereby improving the stability and safety of the pole piece, when the content of the binder is too low, the binder cannot perform a binding function, and is not favorable for the protective layer to be well adhered to the current collector, and when the content of the binder is too high, the pole piece is easily embrittled, the compaction density is reduced, and the energy density of the lithium ion battery is affected; the conductive agent can construct an electronic conductive network, particularly when the protective layer is positioned between the current collector and the active substance layer, the conductive agent can be used as an electronic path for connecting the current collector and the active substance layer, the function of the current collector is favorably exerted, the performance of the pole piece such as the multiplying power is improved, if the content of the conductive agent is too low, the conductive performance of the protective layer is insufficient, the electrical performance of the pole piece is influenced, if the content of the conductive agent is too high, the protective function of the protective layer on the pole piece is also influenced to a certain extent, when an internal short circuit occurs, the protective layer has higher conductivity, and the contact with the pole piece with the other polarity can cause severe heat generation at a short circuit point and thermal runaway, so that in order to consider the safety and the electrical performance of the lithium ion battery, the protective layer comprises 62-96% of a non-active material, 0.1-8% of the conductive agent and 3-30% of a binder by mass percentage, the total mass of the protective layer is 100%, the mass of the non-active material is 62% -96% of the total mass of the protective layer, the mass of the conductive agent is 0.1% -8% of the total mass of the protective layer, and the mass of the binder is 3% -30% of the total mass of the protective layer; meanwhile, the inventor finds that the conductivity of the protective layer cannot be effectively ensured only by the conductive network constructed by the conductive agent, in order to ensure that the electrical property of the lithium ion battery is not influenced, the invention selects the carbon-coated inorganic particles as the inactive material, the carbon layer coated on the surface of the inorganic particles ensures that the inorganic particles have conductivity, and the conductive agent in the protective layer is matched to construct a more comprehensive conductive network, so that the problem of local conductivity loss caused by uneven conductive agents is avoided, the conductivity of the protective layer is improved, and the electrical property of the lithium ion battery is ensured, and it can be understood that the conductivity of the inactive material is improved along with the improvement of the carbon coating amount, but the excessively high carbon coating amount is not beneficial to the safety performance of the battery, and in order to consider the safety and the electrical property of the lithium ion battery, the mass of the carbon layer is less than 10 percent of the mass of the inorganic particles, the carbon coating process is a conventional process in the art and the present invention is not described herein. The pole piece provided by the invention comprises the protective layer, and the mass fractions of the components in the protective layer are controlled, and the carbon-coated inorganic particles are selected, so that the safety of the lithium ion battery can be effectively improved, particularly, the probability of fire failure of the lithium ion battery is reduced when mechanical abuse occurs, the through-nail test passing rate of the lithium ion battery is improved, the electrical property of the lithium ion battery is basically not influenced, and the problem that the safety and the electrical property of the lithium ion battery cannot be considered simultaneously is solved.
In order to further take the safety and the electrical property of the lithium ion battery into consideration, the mass of the carbon layer is 0.5-5% of the mass of the inorganic particles.
In some embodiments, the inorganic particles comprise one or more of an oxide, a carbide, a nitride, an inorganic salt;
further, the oxide is selected from at least one of alumina, titanium oxide, magnesium oxide, zirconia, antimony oxysulfide, barium oxide, manganese oxide, silicon oxide, iron oxide and ferroferric oxide; the carbide comprises a metal carbide and/or a non-metal carbide, the metal carbide comprises at least one of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide and tungsten carbide, and the non-metal carbide comprises boron carbide and/or silicon carbide; the nitride comprises a metal nitride and/or a non-metal nitride, the metal nitride comprises at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride and tantalum nitride, and the non-metal nitride comprises at least one of boron nitride, phosphorus pentanitride and silicon tetranitride; the inorganic salt comprises a carbonate and/or a sulfate.
The material of the carbon layer and the coating method can be performed according to the conventional techniques in the art, for example, the inorganic particles are mixed with glucose solution, hydrothermally treated at a high temperature (150-.
The ratio of inorganic particles to glucose can be reasonably selected by one skilled in the art to ensure that the mass of the carbon layer is less than 10% of the mass of the inorganic particles, and in one embodiment, the carbon layer has a thickness of 1-100 nm.
Research shows that when at least two layers of inactive materials are arranged on the plane vertical to the current collector in the protective layer, the protective effect of the protective layer can be further improved, so that the relation between the D50 of the inactive materials and the thickness H1 of the protective layer satisfies that H1 is more than or equal to 2 xD 50, D50 is the particle size distribution of volume reference, the inactive materials reach the particle size accumulated by 50% of volume from the small particle size side, the thickness H1 of the protective layer is the distance value from the surface of the current collector provided with the protective layer to the surface of the protective layer away from the protective layer in the direction vertical to the current collector, when the two layers satisfy that H1 is more than or equal to 2 xD 50, the protective layer is favorably enabled to be evenly distributed with at least two inactive materials in the thickness direction (direction vertical to the surface of the current collector), which corresponds to that the inactive materials are at least two layers on the plane vertical to the current collector, thereby improving the protective effect of the protective layer, the safety of the lithium ion battery is improved.
In order to further improve the safety of the lithium ion battery, an inactive material with a small particle size can be adopted, specifically, the D50 of the inactive material is less than or equal to 2 microns, and the D90 of the inactive material is less than or equal to 5 microns, the inactive material with the particle size range is not easy to fall off from the surface of a current collector in the nail piercing process, the stability and the safety of a pole piece are further improved, further, the D50 of the inactive material is 0.05-0.5 microns, and the D90 is 1-3 microns. D50 is a particle diameter at which the volume accumulation of the inactive material reaches 50% from the small particle diameter side in the volume-based particle diameter distribution; d90 is a particle size at which the volume of the inactive material reaches 90% cumulatively with the volume from the small particle size side in the volume-based particle size distribution.
The binder and the conductive agent in the protective layer may be conventional materials in the art, for example, the binder includes one or more of polyvinylidene fluoride (PVDF), carboxylic acid modified polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), Polyacrylonitrile (PAN), polyacrylates, Polyimide (PI), wherein the carboxylic acid modified PVDF includes acrylic acid modified PVDF; the conductive agent comprises one or more of conductive carbon black, acetylene black, graphite, graphene, carbon nanotubes and carbon nanofibers, and a person skilled in the art can select a suitable material, mix the material with a non-active material to obtain a protective layer slurry, coat the protective layer slurry on the surface of the current collector, and obtain a protective layer after drying.
The active material layer comprises an active material for performing an electrochemical reaction to provide capacity for the lithium ion battery, the protective layer does not provide capacity per se, but the weight and the volume of the lithium ion battery are increased to cause loss on the energy density of the lithium ion battery, in order to further avoid the influence of the protective layer on the energy density of the lithium ion battery, the thickness H1 of the protective layer is controlled to be a lower level compared with the thickness H2 of the active material layer, and specifically, the relation between the thickness H1 of the protective layer and the thickness H2 of the active material layer satisfies H1/H2 ≦ 1/5.
In the invention, the pole piece can be a positive pole piece or a negative pole piece, when the pole piece is the positive pole piece, the pole piece comprises a positive pole current collector, a protective layer and a positive pole active substance layer, and when the pole piece is the negative pole piece, the pole piece comprises a negative pole current collector, a protective layer and a negative pole active substance layer, wherein the positive pole current collector can be an aluminum foil formed by taking aluminum as a main component, or a composite current collector formed by laminating the aluminum foil and other materials (such as polymer materials and the like), or a composite current collector comprising the aluminum foil and a conductive carbon layer coated on the surface of the aluminum foil and the like, wherein the mass content of aluminum in the aluminum foil is generally not lower than 95%; the negative electrode current collector may be a copper foil or a nickel foil.
When the electrode sheet is a positive electrode sheet, the active material in the positive electrode active material layer is a positive electrode active material, such as a positive electrode active material for providing lithium ions, specifically including a lithium positive electrode composite metal oxide (i.e., an inorganic material containing lithium), such as lithium cobaltate (LiCoO)2) Lithium nickelate (LiNiO)2) Lithium manganate (LiMn)2O4) Lithium iron phosphate (LiFePO)4) Or ternary material, which may have the chemical formula LiNixCoyMnzO2And x + y + z is 1. When the electrode plate is a negative electrode plate, the active material is a negative electrode active material, and the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads (MCMB), silicon-carbon composites, silicon oxide, lithium titanate, and lithium metal.
The active material layer further includes a binder and a conductive agent, which function as the binder and the conductive agent in the protective layer, and the binder and the conductive agent are selected as described above, and the conductive agent and the binder in the protective layer and the active material layer may be the same or different.
In addition, when the electrode sheet is a negative electrode sheet, the negative active material layer may further include a dispersant including sodium carboxymethylcellulose or the like.
Research shows that when the lithium ion battery is in internal short circuit, various short circuit modes exist, and the internal short circuit caused by the contact of the positive electrode current collector and the negative electrode sheet is the most dangerous mode, so that the electrode sheet can be a positive electrode sheet, namely, the protective layer is arranged on the surface of the positive electrode current collector, and the negative electrode sheet is not provided with the protective layer.
The pole piece provided by the invention further comprises a pole lug, and the arrangement position of the pole lug can be the arrangement position of the pole lug which is conventional in the field, for example, the pole lug can be arranged at the end part or the middle part of the pole piece. When the pole piece is a positive pole piece, the positive pole tab can be an aluminum foil; when the pole piece is a negative pole piece, the negative pole tab can be a nickel foil.
The pole piece provided by the invention can be prepared by a coating method and other conventional methods in the field, and in specific implementation, the raw materials of the protective layer can be dispersed in a solvent, uniformly stirred to prepare protective layer slurry, then the protective layer slurry is coated on the surface of a current collector, and a protective layer is formed after drying; dispersing the raw materials of the active substance layer in a solvent, uniformly stirring to prepare active substance layer slurry, coating the active substance layer slurry on the surface of the protective layer far away from the current collector or the region of the surface of the current collector without the protective layer, drying, rolling and other processes to form the active substance layer, and then putting the tab on the surface of the current collector to obtain the pole piece.
In conclusion, the pole piece provided by the invention comprises the protective layer, the safety of the lithium ion battery can be effectively improved by controlling the mass fractions of the components in the protective layer and selecting the carbon-coated inorganic particles, particularly, the probability of ignition and failure of the lithium ion battery is reduced when mechanical abuse occurs, the through-nail test passing rate of the lithium ion battery is improved, the electrical property of the lithium ion battery is basically not influenced, and the problem that the safety and the electrical property of the lithium ion battery cannot be considered at the same time is solved.
In a second aspect, the invention provides a lithium ion battery, which includes any of the above pole pieces.
The invention provides a lithium ion battery, which comprises the pole piece provided by the first aspect of the invention, when the pole piece is a positive pole piece, the lithium ion battery can be prepared by adopting a conventional technical means together with a conventional negative pole piece, a diaphragm and electrolyte, wherein the diaphragm comprises one or more of Polyethylene (PE), polypropylene (PP) and polyimide, the electrolyte comprises carbonates, carboxylic ester solvents, lithium salts and proper additives, in the preparation process, the positive pole piece, the negative pole piece and an isolating membrane are sequentially wound or stacked into a battery cell, then the battery cell is packaged by using a packaging material such as an aluminum plastic membrane and injected with the electrolyte, and the lithium ion battery is prepared through charging and discharging. The lithium ion battery provided by the invention has better safety and electrical property.
The invention is further illustrated below with reference to specific examples:
example 1
The pole piece that this embodiment provided is positive plate, including the mass flow body aluminium foil, be located the protective layer on the mass flow body surface, be located the positive pole active material layer that the protective layer kept away from the mass flow body surface, wherein:
the protective layer comprises 62 parts by mass of an inactive material, 30 parts by mass of acrylic acid modified PVDF and 8 parts by mass of carbon black, wherein the inactive material is carbon-coated alumina, the mass of the carbon layer is 0.5% of the mass of the alumina, the mass of the inactive material D10 is 0.02 μm, the mass of the inactive material D50 is 0.3 μm, the mass of the inactive material D90 is 2 μm, and the thickness of the protective layer H1 is 2 μm;
the positive electrode active material layer includes 96 parts by mass of a positive electrode active material LCO, 2 parts by mass of a binder PVDF, and 2 parts by mass of a conductive agent carbon black, and the thickness H2 of the positive electrode active material layer is 40 μm.
The preparation method of the pole piece provided by the embodiment comprises the following steps: mixing alumina, acrylic acid modified PVDF and carbon black according to a certain mass part, dispersing in a solvent NMP, uniformly stirring to prepare a protective layer slurry, coating the protective layer slurry on the surface of an aluminum foil, and drying to obtain a protective layer; mixing LCO, PVDF and carbon black according to a certain mass part, dispersing the mixture in NMP solvent, uniformly stirring to prepare anode active material layer slurry, coating the anode active material layer slurry on the surface of a protective layer far away from a current collector, drying to obtain an anode active material layer, and rolling to obtain an anode sheet.
Example 2
The electrode sheet provided in this example can be referred to example 1 except that the protective layer includes 70 parts by mass of the inactive material, 25 parts by mass of the acrylic-modified PVDF, and 5 parts by mass of carbon black.
Example 3
The electrode sheet provided in this example can be referred to example 1 except that the protective layer includes 80 parts by mass of the inactive material, 15 parts by mass of the acrylic-modified PVDF, and 5 parts by mass of carbon black.
Example 4
The electrode sheet provided in this example can be referred to example 1 except that the protective layer includes 90 parts by mass of the inactive material, 8 parts by mass of the acrylic-modified PVDF, and 2 parts by mass of the carbon black.
Example 5
The electrode sheet provided in this example can be referred to example 1 except that the protective layer includes 96 parts by mass of the inactive material, 3.9 parts by mass of the acrylic-modified PVDF, and 0.1 parts by mass of the carbon black.
Example 6
The electrode sheet provided in this example can be referred to example 1 except that the protective layer includes 96 parts by mass of the inactive material, 3 parts by mass of the acrylic-modified PVDF, and 1 part by mass of carbon black.
Example 7
The electrode sheet provided in this example can be referred to example 4, except that the mass of the carbon layer in the inactive material is 1% of the mass of the alumina.
Example 8
The electrode sheet provided in this example can be referred to example 4, except that in the inactive material, the mass of the carbon layer is 2% of the mass of the alumina.
Example 9
The electrode sheet provided in this example can be referred to example 4, except that the mass of the carbon layer in the inactive material is 3% of the mass of the alumina.
Example 10
The electrode sheet provided in this example can be referred to example 4, except that the mass of the carbon layer in the inactive material is 4% of the mass of the alumina.
Example 11
The electrode sheet provided in this example can be referred to example 4, except that in the inactive material, the mass of the carbon layer is 5% of the mass of the alumina.
Comparative example 1
The electrode sheet provided in this comparative example can be referred to example 1 except that the protective layer includes 50 parts by mass of the inactive material, 45 parts by mass of the acrylic-modified PVDF, and 5 parts by mass of carbon black.
Comparative example 2
The electrode sheet provided in this comparative example can be referred to example 1 except that the protective layer includes 62 parts by mass of the inactive material, 20 parts by mass of the acrylic-modified PVDF, and 18 parts by mass of the carbon black.
Comparative example 3
The electrode sheet provided in this comparative example can be referred to example 1 except that the protective layer includes 92 parts by mass of the inactive material, 2 parts by mass of the acrylic-modified PVDF, and 6 parts by mass of the carbon black.
Comparative example 4
The electrode sheet provided in this comparative example can be referred to example 1 except that the protective layer includes 92 parts by mass of the inactive material and 8 parts by mass of the acrylic-modified PVDF.
Comparative example 5
The pole piece provided by this comparative example does not include a protective layer.
Comparative example 6
The electrode sheet provided in this comparative example can be referred to example 4, except that the inactive material is alumina.
Comparative example 7
The electrode sheet provided in this comparative example can be referred to example 4 except that the mass of the carbon layer in the inactive material is 10% of the mass of the alumina.
The positive plate provided in examples 1 to 11 and comparative examples 1 to 7 was matched with a negative plate and a diaphragm to prepare a bare cell, the bare cell was encapsulated with an aluminum-plastic film, a certain amount of electrolyte was injected, the seal was sealed, and a lithium ion battery was prepared by formation, wherein the negative plate included a negative current collector copper foil and a negative active layer, and the negative active layer included 96 parts by mass of artificial graphite, 1.5 parts by mass of styrene-butadiene rubber, 1.5 parts by mass of sodium carboxymethylcellulose, and 1 part by mass of carbon black.
The lithium ion batteries provided in examples 1-11 and comparative examples 1-7 were then tested for safety and electrical performance, the results of which are shown in table 1, and the test methods were as follows:
(1) nail penetration test
Taking 10 lithium ion batteries of each example (comparative example), placing the fully charged batteries on a through-nail testing device, starting the device, enabling a nail (with the diameter of 3mm) to penetrate into the center position of the batteries at a speed of 130mm/s, perpendicular to the plane of the batteries, stopping for 10min, withdrawing, regarding the batteries as passing batteries without fire, and counting the number of the passing lithium ion batteries.
(2) Rate capability test
Discharging the battery to 3.0V at a rate of 0.5C, standing for 5min, charging the battery to an upper limit voltage at a rate of 0.5C, then charging at constant voltage, and cutting off the current to 0.02C. After standing for 5min, the battery is discharged to 3.0V at a rate of 0.2C, and the capacity is C0. After standing for 5min, the battery was charged to the upper limit voltage at a rate of 0.5C, and then charged at constant voltage with a current cutoff of 0.02C. After standing for 5min, the battery is discharged to 3.0V at a rate of 0.5C, and the capacity is C1. The C1/C0 is the discharge capacity ratio of 0.5C/0.2C, and is used for evaluating the rate discharge capacity.
(3) Lithium ion battery energy density testing
The energy density ED of the lithium ion battery is equal to E/V, where E is the discharge energy of the battery, and the test method is to fully charge the battery, then discharge the battery at 0.2C to 3.0V, and the discharge energy is E. And V is the volume of the battery and is obtained by measuring the length, the width and the height.
Energy density loss rate Δ ED is the energy density ED of the lithium ion battery of comparative example 55Energy density ED of lithium ion battery of corresponding example (comparative example)nDifference of (1)/energy density ED of lithium ion battery of comparative example 55I.e. Δ ED ═ (ED)5-EDn)/ED5。
TABLE 1
Figure BDA0003381065310000121
The provision of a protective layer helps to improve the safety of the lithium ion battery, but with a different degree of loss in energy density compared to the data provided in comparative example 5; according to the data provided by examples 1-6 and comparative examples 1-4, controlling the mass fraction of each component in the protective layer within the range provided by the invention is helpful for balancing the safety and electrical properties of the lithium ion battery; it can be seen from the data provided in examples 7-11 and comparative example 6 that the use of carbon-coated inorganic particles contributes to the improvement of rate performance of the lithium ion battery, and from the data provided in examples 7-11 and comparative example 7, when the carbon coating amount on the surface of the inorganic particles exceeds 10%, the safety performance of the lithium ion battery is significantly reduced.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. The pole piece is characterized by comprising a substrate, wherein the substrate comprises a current collector and a protective layer arranged on the surface of the current collector, and an active substance layer is also arranged on the protective layer;
the protective layer comprises 62-96% of inactive materials, 0.1-8% of conductive agents and 3-30% of binders in percentage by mass, the inactive materials comprise inorganic particles and carbon layers coated on the surfaces of the inorganic particles, and the mass of the carbon layers is less than 10% of that of the inorganic particles.
2. The pole piece of claim 1, wherein the mass of the carbon layer is 0.5-5% of the mass of the inorganic particles.
3. The pole piece of claim 1 or 2, wherein the inorganic particles comprise one or more of oxides, carbides, nitrides, inorganic salts.
4. The pole piece of claim 3, wherein the oxide is selected from one or more of alumina, titania, magnesia, zirconia, antimony oxysulfide, barium oxide, manganese oxide, silica, iron oxide, and ferroferric oxide; the carbide comprises metal carbide and/or non-metal carbide, the metal carbide comprises one or more of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide and tungsten carbide, and the non-metal carbide comprises boron carbide and/or silicon carbide; the nitride comprises a metal nitride and/or a non-metal nitride, the metal nitride comprises one or more of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride and tantalum nitride, and the non-metal nitride comprises at least one of boron nitride, phosphorus pentanitride and silicon tetranitride; the inorganic salt comprises a carbonate and/or a sulfate.
5. The pole piece of claim 1, wherein the carbon layer has a thickness of 1-100 nm.
6. The pole piece of claim 1, wherein the inactive material has a D50 ≦ 2 μm and a D90 ≦ 5 μm.
7. The pole piece of claim 1 or 6, wherein the inactive material has a D50 of 0.05-0.5 μm and a D90 of 1-3 μm.
8. The pole piece of claim 1, wherein the relationship between the thickness H1 of the protective layer and the D50 of the inactive material satisfies H1 ≥ 2 XD 50.
9. The pole piece of claim 1 or 8, wherein the thickness of the protective layer H1 is in relation to the thickness of the active material layer H2, such that H1/H2 ≦ 1/5.
10. A lithium ion battery comprising a pole piece according to any one of claims 1 to 9.
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