CN111785925A - Pole piece, application and low-temperature-rise safety lithium ion battery containing pole piece - Google Patents

Pole piece, application and low-temperature-rise safety lithium ion battery containing pole piece Download PDF

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Publication number
CN111785925A
CN111785925A CN202010802351.XA CN202010802351A CN111785925A CN 111785925 A CN111785925 A CN 111785925A CN 202010802351 A CN202010802351 A CN 202010802351A CN 111785925 A CN111785925 A CN 111785925A
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pole piece
conductive
coating
active
current collector
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CN111785925B (en
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郑彦俊
暴旭
马华
何伟
从长杰
王驰伟
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Tianjin EV Energies Co Ltd
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Tianjin EV Energies Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0585—Construction or manufacture of accumulators having only flat construction elements, i.e. flat positive electrodes, flat negative electrodes and flat separators
    • H—ELECTRICITY
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    • 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
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/61—Types of temperature control
    • H01M10/613—Cooling or keeping cold
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/61—Types of temperature control
    • H01M10/617—Types of temperature control for achieving uniformity or desired distribution of temperature
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/65—Means for temperature control structurally associated with the cells
    • H01M10/653—Means for temperature control structurally associated with the cells characterised by electrically insulating or thermally conductive materials
    • 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
    • H01M10/60—Heating or cooling; Temperature control
    • H01M10/65—Means for temperature control structurally associated with the cells
    • H01M10/654—Means for temperature control structurally associated with the cells located inside the innermost case of the cells, e.g. mandrels, electrodes or electrolytes
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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    • 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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

The invention provides a pole piece, application thereof and a low-temperature-rise safety lithium ion battery containing the pole piece, wherein the pole piece comprises a current collector, and at least two layers of active coatings and at least one layer of high-efficiency conductive PTC (positive temperature coefficient) film are fixedly arranged on two opposite surfaces of the current collector; the active coating and the high-efficiency conductive PTC film are arranged at intervals from the inside to the outside from the surface of the current collector, and the active coating is arranged on the outermost side; the electric conductivity of the outermost active coating is smaller than that of the rest active coatings, and/or the active material of the outermost active coating adopts the active material with high thermal stability. The pole piece has more uniform internal temperature distribution, reduces the temperature rise of the battery in conventional use or internal short circuit, and can slow down thermal runaway so as to improve the safety of the lithium ion battery.

Description

Pole piece, application and low-temperature-rise safety lithium ion battery containing pole piece
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a pole piece, application of the pole piece and a low-temperature-rise safety lithium ion battery containing the pole piece.
Background
With the continuous progress of science and technology, lithium ion batteries are gradually applied to many fields, from portable electronic products to electric vehicles, energy storage power supplies, aviation fields and the like. But lithium ion batteries also present a non-negligible safety risk. According to the report, the accidents of combustion and explosion of mobile phones due to the poor lithium ion batteries are reported, the mobile phones relate to well-known companies such as samsung, apple and the like, and certain events cause the recall of products; there are also many reports of the occurrence of combustion and explosion of lithium ion battery electric vehicles, including known electric vehicle enterprises such as biddi, yulai, tesla, and the like. The most major and serious safety risk faced by lithium ion batteries is thermal runaway. The triggering and diffusion of thermal runaway are closely related to internal short circuit, and if the internal short circuit current is large, the temperature of a short circuit point rises to cause thermal runaway; in other causes that cause thermal runaway, internal short circuit is also a key growth factor, for example, when overcharge causes thermal runaway, the initial temperature of starting rises, once the diaphragm destruction temperature is reached, internal short circuit can be generated, once the internal short circuit occurs, electric energy can be rapidly released near an internal short circuit point, the generated heat can promote the acceleration shrinkage and melting of the battery diaphragm, the melting and damaging of the diaphragm further increases the short circuit area and reduces the resistance of the short circuit point, thereby accelerating the release of the electric energy and exacerbating the thermal runaway. The occurrence of internal short circuit can be classified into 2 cases, one case is that the lithium ion battery is subjected to external strong abuse, such as severe overcharge, strong shock impact, severe extrusion deformation, fire burning or penetration by foreign matters; in another situation, during normal working cycle of the battery, under relatively mild service conditions, due to lithium dendrites, iron deposition, metal burrs, current collector cracking caused by cyclic stress and the like, under the disturbance action of temperature and pressure, the occurrence of micro-short-circuit internal short-circuit with small contact area is certainly avoided as much as possible. The known technology reduces the probability of internal short circuit by reducing the thermal shrinkage rate of the separator, strictly controlling the process to avoid the generation of metal burrs, ensuring a sufficient amount of negative electrode, and reducing the charge rate at low temperature to avoid the generation of lithium dendrites. In order to avoid internal short circuits caused by thermal contraction of the battery separator at high temperatures, it is known to produce a layer of heat-resistant ceramic powder between the separator and the electrodes to improve the high-temperature safety of the battery. A common way is to attach ceramic powder by means of coating to both sides of the membrane, the membrane thus treated being called ceramic coated membrane or ccm (ceramic coated membrane).
Despite the above-described known techniques, the current state of the art has not been able to reduce the probability of internal short circuits and thermal runaway occurrences below a negligible level. After the internal short circuit, especially the micro short circuit, occurs, thermal runaway is not necessarily caused, and the non-thermal runaway type internal short circuit macroscopically shows that the self-discharge rate of the battery is increased, and in the battery pack, the imbalance among the battery cells is intensified. If an internal short circuit cannot be avoided, we would like it to be embodied as a mild self-discharge rate rise, rather than a thermal runaway. The risk of thermal runaway can be avoided or reduced if, in a given internal short circuit situation, the current of the internal short circuit can be reduced.
Disclosure of Invention
In view of this, the present invention is directed to provide a pole piece to overcome the defects of the prior art, wherein the internal temperature distribution is more uniform, the temperature rise of the battery in normal use or internal short circuit is reduced, and thermal runaway can be slowed down to improve the safety of the lithium ion battery.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a pole piece comprises a current collector, wherein at least two layers of active coatings and at least one layer of high-efficiency conductive PTC film are fixedly arranged on two opposite surfaces of the current collector; the active coating and the high-efficiency conductive PTC film are arranged at intervals from the inside to the outside from the surface of the current collector, and the active coating is arranged on the outermost side; the electric conductivity of the outermost active coating is smaller than that of the rest active coatings, and/or the active material of the outermost active coating adopts the active material with high thermal stability.
Furthermore, the tail ends of all the high-efficiency conductive PTC films are bonded with the surface of the current collector.
Furthermore, the thickness of all the high-efficiency conductive PTC films is 0.1-5 μm.
Further, the current collector is an aluminum foil.
Further, the high-efficiency conductive PTC film is a mixture coating of a first conductive agent and a polymer;
preferably, the first conductive agent is a conductive inorganic substance or a conductive polymer having a delocalized large pi-bond characteristic.
More preferably, the first conductive agent is one or more of carbon nanotubes, graphene, conductive graphite, conductive carbon black, polyacetylene, polyaniline, polyphenylene ethylene, polydiyne, polydianiline and derivatives thereof, polytriphenylamine and derivatives thereof, polypyrrole and derivatives thereof, polythiophene and derivatives thereof, polyfluorene and derivatives thereof, and polyphenylene oxide.
Preferably, the polymer is one or more of polyaniline modified polyethylene wax, polyethylene-vinyl acetate, polytetrafluoroethylene, polystyrene, polyolefin, polyvinyl chloride and epoxy resin.
Furthermore, the composition of the high-efficiency conductive PTC film also comprises a first binder, and the weight ratio of the first conductive agent, the polymer and the first binder is (95-40): (5-55): (0.01-5).
Further, the forming mode of all the high-efficiency conductive PTC films and the outermost layer of the active coating is one of gravure printing, screen printing, extrusion coating, chemical vapor deposition and magnetron sputtering.
Further, all the active coatings are coating layers of a mixture of an active material, a second conductive agent and a second binder.
Preferably, the active material is one or more of lithium nickel cobalt manganese oxide, lithium cobaltate, lithium manganate, lithium iron phosphate and lithium manganese phosphate.
Preferably, the second conductive agent is one or more of conductive carbon black, carbon nanotubes and graphene.
Preferably, the second binder is one or more of polytetrafluoroethylene, polyimide, polypropionic acid and polyacrylonitrile.
Preferably, the content of the conductive agent in the outermost active coating layer is less than that in the remaining active coating layers.
Preferably, the active material with high thermal stability is one or more of lithium iron phosphate and derivatives thereof and lithium manganate.
The invention also relates to the application of the pole piece as a positive pole piece in a battery.
The invention also aims to provide a low-temperature-rise safety lithium ion battery, which has the characteristics of low temperature rise and high safety by applying the pole piece.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a low-temperature-rise safety lithium ion battery comprises a positive pole piece, a diaphragm and a negative pole piece, wherein the positive pole piece is the pole piece.
Compared with the prior art, the pole piece has the following advantages:
the pole piece has the advantages that the internal temperature distribution is more uniform, the temperature rise of the battery in conventional use or internal short circuit is reduced, and the thermal runaway is slowed down, so that the safety of the lithium ion battery is improved (the conventional battery cell does not have the technical advantages, and the thermal runaway is easier to occur in the short time in the occurrence process). In particular, the advantages of the invention are represented by:
(1) the presence of a highly conductive PTC film can, on the one hand, make the current density distribution within the coating more uniform in the vicinity of the conductive film, reducing uneven polarization and uneven heating, and on the other hand, when the internal temperature rises above the threshold temperature of the PTC material, its resistance rapidly increases, impairing electron transport.
(2) Each layer of high-efficiency conductive PTC film is bonded with the current collector in parallel, so that ohmic polarization of the coating layer in the direction perpendicular to the current collector can be reduced, current and heat can be conducted, and partial heat can be transmitted to the lug when the internal temperature rises.
(3) The outermost coating reduces the conductivity or/and uses the active material with high thermal stability, so that when the internal short circuit occurs, on one hand, the short circuit current can be reduced to reduce heat generation, and on the other hand, the active material with high thermal stability can absorb more heat to slow down thermal runaway.
(4) The temperature rise of the lithium ion battery during charging and discharging and the temperature rise of the internal short circuit can be obviously reduced (in the subsequent embodiment, the multiplying power discharging temperature rise and the uniformity of the battery cell using the lithium ion battery are better than those of the comparative example, and the temperature rise of a needling test (internal short circuit model) is lower than that of the comparative example).
Compared with the prior art, the low-temperature-rise safety lithium ion battery has the same advantages as the pole piece, and the description is omitted.
Drawings
FIG. 1 is a schematic structural view of a positive electrode tab of example 1;
FIG. 2 is a schematic structural view of a positive electrode tab of example 2;
FIG. 3 is a schematic structural view of a positive electrode tab of example 3;
FIG. 4 is a schematic structural view of the positive electrode sheet of comparative example 2;
fig. 5 is a schematic view of a partial structure of a cell in embodiment 1;
fig. 6 is a schematic view of a partial structure of a cell in embodiment 2;
fig. 7 is a schematic view of a partial structure of a cell in embodiment 3;
fig. 8 is a schematic diagram of a partial structure of a cell in comparative example 1 and comparative example 3;
fig. 9 is a partial structure diagram of a cell of comparative example 2.
Reference numerals:
1-a first current collector; 2-a first reactive coating; 3-a first highly efficient conductive PTC film; 4-a second reactive coating; 5-a second highly efficient conductive PTC film; 6-a third reactive coating; 7-a third highly conductive PTC film; 8-a fourth reactive coating; 9-positive pole piece; 10-a negative pole piece; 11-a separator; 12-a second current collector; 13-negative electrode slurry coating; and 14-coating of positive electrode slurry.
Detailed Description
Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional chemical reagents; the experimental methods are conventional methods unless otherwise specified.
The noun explains: PTC materials are materials whose resistivity increases with increasing temperature.
A pole piece comprises a current collector, wherein at least two layers of active coatings and at least one layer of high-efficiency conductive PTC film are fixedly arranged on two opposite surfaces of the current collector; the active coating and the high-efficiency conductive PTC film are arranged from the surface of the current collector at intervals from inside to outside, and the outermost side of the active coating is the active coating. Wherein, the current collector can adopt aluminum foil.
The tail ends of all the high-efficiency conductive PTC films are bonded with the surface of the current collector in parallel, so that current and heat can be conducted, and partial heat can be transmitted to the lug when the internal temperature is increased.
Wherein the thickness of all the high-efficiency conductive PTC films is 0.1-5 μm.
Wherein, the high-efficiency conductive PTC film is a mixture coating of a first conductive agent and a polymer, wherein the weight ratio of the first conductive agent to the polymer is (95-50): (5-50). Preferably, the first conductive agent is not limited to a conductive inorganic substance or a conductive polymer with delocalized large pi-bond characteristics, wherein the conductive inorganic substance is not limited to one or a combination of several of carbon nanotubes, graphene, conductive graphite, conductive carbon black and the like, and the conductive polymer is not limited to one or a combination of several of polyacetylene, polyaniline, polyphenylene ethylene, polydiyne, polydianiline and derivatives thereof, polytriphenylamine and derivatives thereof, polypyrrole and derivatives thereof, polythiophene and derivatives thereof, polyfluorene and derivatives thereof, and polyparaphenylene. Preferably, the polymer material is not limited to polyaniline-modified polyethylene wax (PANI-PEW), polyethylene-vinyl acetate (EVA), Polytetrafluoroethylene (PTFE), polystyrene, polyolefin, polyvinyl chloride, epoxy resin, or a combination thereof. According to the requirement, for example, when the conductive agent in the first conductive agent has no adhesiveness, the composition of the high-efficiency conductive PTC film also comprises a first binder, and the weight ratio of the first conductive agent, the polymer and the first binder is (95-40): 5-55): 0.01-5.
In the invention, all the high-efficiency conductive PTC films and the outermost active coating are formed in one of gravure printing, screen printing, extrusion coating, chemical vapor deposition and magnetron sputtering.
In the invention, all the active coatings are the mixture coatings of the active substance, the second conductive agent and the second binder, and if the pole piece is a positive pole piece, the active coatings are the coatings of positive pole slurry. Preferably, the active material is not limited to one or a combination of several of materials with lithium ion extraction functions, such as nickel cobalt lithium manganate, lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese phosphate and the like; the second conductive agent is not limited to one or a combination of several of materials with high electronic conductivity such as conductive carbon black, carbon nanotubes, graphene and the like; the second binder is not limited to one or a combination of several of high molecular compounds having an adhesive effect, such as polytetrafluoroethylene, polyimide, polypropionic acid, polyacrylonitrile, and the like.
In the invention, the outermost active coating reduces the conductivity (preferably, reduces the content of the second conductive agent in the formula), or uses the active substance with high thermal stability, or uses the two factors simultaneously, so that when the internal short circuit occurs, on one hand, the short-circuit current can be reduced to reduce heat generation, and on the other hand, the active substance with high thermal stability can absorb more heat to slow down thermal runaway. The active material having high thermal stability is not limited to lithium iron phosphate and its derivatives (e.g., lithium manganese iron phosphate, lithium cobalt iron phosphate, lithium manganese cobalt iron phosphate, etc.), lithium manganate, and the like.
The pole piece can be used for producing batteries, and particularly can be used as a positive pole piece for producing batteries.
A low-temperature-rise safety lithium ion battery comprises a positive pole piece, a diaphragm and a negative pole piece, wherein the positive pole piece is the pole piece. The negative pole piece can be a conventional negative pole piece, and comprises negative pole slurry and a negative pole current collector, wherein the negative pole current collector can adopt copper foil, and the negative pole slurry consists of an active substance, a conductive agent and a binder. The active material is not limited to graphite materials, silicon-based materials, lithium titanate and other materials with a lithium ion intercalation function; the conductive agent is not limited to materials having high electron conductivity such as conductive carbon black, carbon nanotubes, graphene, and the like; the binder is not limited to a polymer compound having an adhesive action such as carboxymethyl cellulose, styrene-butadiene rubber, polyimide, polypropionic acid, polyacrylonitrile, or the like. The separator may be a PE separator.
The present invention will be described in detail with reference to the following examples and accompanying drawings.
Example 1
As shown in fig. 1, the pole piece includes first mass flow body 1, and 1 upper surface and the lower surface of first mass flow body are equipped with first active coating 2, and the cladding of 2 outer surfaces of first active coating has first high-efficient electrically conductive PTC membrane 3, and first high-efficient electrically conductive PTC membrane 3 keeps away from first mass flow body 1 one side be equipped with second active coating 4 on the surface, and first high-efficient electrically conductive PTC membrane 3 is terminal all to be fixed with the mass flow body bonding. The pole piece is a positive pole piece. The first current collector 1 is an aluminum foil current collector.
1) Manufacturing a positive pole piece (namely a positive pole piece) with the composite coating:
a. pouring N-methyl-2-pyrrolidone into a positive active material NCM622, a conductive agent 1(SP), a conductive agent 2(CNTs) and a binder (PVDF) according to a weight ratio of 96:1:1:2, mixing and stirring uniformly to prepare positive slurry A with a solid content of 75%;
b. pouring N-methyl-2-pyrrolidone into a positive active material NCM622, a conductive agent 1(SP), a conductive agent 2(CNTs) and a binder (PVDF) according to the weight ratio of 97.5:0.3:0.2:2, mixing and uniformly stirring to obtain positive slurry B with the solid content of 75%;
c. pouring N-methyl-2-pyrrolidone into a conductive agent 1 (CNTs-carbon nano tubes), a conductive agent 2 (GNs-graphene), a polymer (polyaniline modified polyethylene wax-PANI-PEW) and a binder (PVDF) according to the weight ratio of 42:42:15:1, mixing, stirring and dispersing uniformly to obtain a high-efficiency conductive PTC slurry C with the solid content of 8.0%;
d. coating the positive electrode slurry A on the upper surface and the lower surface of an aluminum foil current collector (namely a first current collector 1), and drying to obtain a coating with the total load of 30mg/cm2Forming a first active coating 2 to obtain a positive pole piece A;
d. coating the high-efficiency conductive PTC slurry C on the outer surface of a first active coating 2 on the positive pole piece A through a gravure roller to form a first high-efficiency conductive PTC film 3, and controlling the thickness of the first high-efficiency conductive PTC film 3 to be 1-3 mu m to obtain a composite positive pole piece B;
e. coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode plate B, wherein the total loading capacity of the dried coating is 40mg/cm2Forming a second active coating 4 to obtain a composite positive pole piece C;
f. and (3) rolling the composite positive pole piece C to the thickness of 125 μm to obtain a target positive pole piece 9, wherein the structure is shown in figure 1.
2) Manufacturing a conventional negative pole piece (namely a negative pole piece):
the negative electrode pole piece comprises a second current collector 12 and negative electrode slurry coatings 13 coated on the upper surface and the lower surface of the second current collector 12, wherein the second current collector 12 is a copper foil current collector.
a. Mixing a negative active material artificial graphite, a conductive agent (SP), a thickening agent carboxymethylcellulose sodium (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a weight ratio of 94.5: 1.5: 1.5: 2.5, adding water, stirring and mixing uniformly to obtain negative electrode slurry with the solid content of 50%;
b. coating the negative electrode slurry on the upper and lower surfaces of the copper foil current collector (i.e., the second current collector 12), and drying to obtain a total loading of the coating of 24mg/cm2Forming a negative electrode slurry coating 13 to obtain a negative electrode plate 10;
c. the negative pole piece 10 is rolled to a thickness of 155 μm.
Manufacturing the lithium ion battery:
a. the positive pole piece 9, the negative pole piece 10 and the PE diaphragm (namely the diaphragm 11) which are prepared by the process are made into a battery core in a winding or laminating mode, and the local structure of the battery core is shown in figure 5;
b. preparing an electrolyte: 1mol/LLIPF6, and the mass ratio of the solvent is EC (ethylene carbonate): DMC (dimethyl carbonate): EMC (methyl ethyl carbonate) ═ 5: 2: 3, 1 wt% VC (vinylene carbonate), 1 wt% FEC (fluoroethylene carbonate), 1 wt% 1,3-PS (1, 3-propane sultone);
c. and injecting the electrolyte into the prepared battery core, standing, pre-charging and carrying out related safety performance tests.
Example 2
As shown in fig. 2, the pole piece of this embodiment is also a positive pole piece, and the structure of the positive pole piece is basically the same as that of embodiment 1, except that: the cladding of 4 surface of second active coating has the second high-efficient PTC membrane 5 of leading, and the second is high-efficient to lead PTC membrane 5 and keep away from 1 side surface of first mass flow body and be equipped with third active coating 6, and the second is high-efficient leads the end of PTC membrane 5 also all to bond fixedly with first mass flow body 1.
1) Manufacturing a positive electrode composite coating pole piece (namely, a positive electrode pole piece) (the embodiment emphasizes the situation of reducing the content of the conductive agent):
a. pouring N-methyl-2-pyrrolidone into a positive active material NCM622, a conductive agent 1(SP), a conductive agent 2(CNTs) and a binder (PVDF) according to a weight ratio of 96:1:1:2, mixing and stirring uniformly to prepare positive slurry A with a solid content of 75%;
b. the anode active material LiFePO4Conductive agent 1(SP), conductive agent 2(CNTs), and adhesivePouring N-methyl-2-pyrrolidone into a binder (PVDF) according to the weight ratio of 96.8:0.4:0.8:2, mixing and uniformly stirring to obtain anode slurry B with the solid content of 65%;
c. pouring N-methyl-2-pyrrolidone into a conductive agent 1 (CNTs-carbon nano tubes), a conductive agent 2 (GNs-graphene), a polymer (EVA) and a binder (PVDF) according to the weight ratio of 43:43:9:5, mixing, stirring and dispersing uniformly to prepare a high-efficiency conductive PTC slurry C with the solid content of 8.0%;
d. coating the positive electrode slurry A on the upper surface and the lower surface of an aluminum foil current collector (namely a first current collector 1), and drying to obtain a coating with the total load of 15mg/cm2Forming a first active coating 2 to obtain a positive pole piece A;
e. coating the high-efficiency conductive PTC slurry C on the outer surface of a first active coating 2 on the positive pole piece A through a gravure roller to form a first high-efficiency conductive PTC film 3, and controlling the thickness of the first high-efficiency conductive PTC film 3 to be 1-3 mu m to obtain a composite positive pole piece B;
f. coating the positive electrode slurry A on the upper surface and the lower surface of the composite positive electrode sheet B, and drying to obtain a coating with the total load of 36mg/cm2Forming a second active coating 4 to obtain a composite positive pole piece C;
g. coating the high-efficiency conductive PTC slurry C on the outer surface of a second active coating 4 on the positive pole piece C through a gravure roller to form a second high-efficiency conductive PTC film 5, and controlling the thickness of the second high-efficiency conductive PTC film 5 to be 1-3 mu m to obtain a composite positive pole piece D;
h. coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode plate D, wherein the total loading capacity of the dried coating is 42mg/cm2Forming a third active coating 6 to obtain a composite positive pole piece E;
h. and (3) rolling the composite positive pole piece E to the thickness of 127 mu m to obtain a target positive pole piece 9, wherein the structure is shown in figure 2.
2) Manufacturing a conventional negative pole piece (namely a negative pole piece):
the structure of the negative electrode plate of this example is the same as that of example 1. The preparation method comprises the following steps:
a. mixing a negative active material artificial graphite, a conductive agent (SP), a thickening agent carboxymethylcellulose sodium (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a weight ratio of 94.5: 1.5: 1.5: 2.5, adding water, stirring and mixing uniformly to obtain negative electrode slurry with the solid content of 50%;
b. coating the negative electrode slurry on the upper and lower surfaces of the copper foil current collector (i.e., the second current collector 12), and drying to obtain a total loading of the coating of 24mg/cm2Forming a negative electrode slurry coating 13 to obtain a negative electrode plate 10;
c. the negative pole piece 10 is rolled to a thickness of 155 μm.
Manufacturing the lithium ion battery:
a. the positive pole piece 9, the negative pole piece 10 and the PE diaphragm (namely the diaphragm 11) which are prepared by the process are made into a battery core in a winding or laminating mode, and the local structure of the battery core is shown in figure 6;
b. preparing an electrolyte: 1mol/LLIPF6, and the mass ratio of the solvent is EC: DMC: EMC 5: 2: 3, 1 wt% VC, 1 wt% FEC, 1 wt% 1, 3-PS;
c. and injecting the electrolyte into the prepared battery core, standing, pre-charging and carrying out related safety performance tests.
Comparative example 1
The positive pole piece comprises a first current collector 1, wherein the upper surface and the lower surface of the first current collector 1 are both provided with a positive slurry coating 14. The first current collector 1 is an aluminum foil current collector.
1) Manufacturing a positive pole piece:
a. pouring N-methyl-2-pyrrolidone into a positive active substance NCM622, a conductive agent 1(SP), a conductive agent 2(CNTs) and a binder (PVDF) according to a weight ratio of 96:1:1:2, mixing and uniformly stirring to obtain positive slurry with a solid content of 75%;
b. coating the anode slurry on the upper surface and the lower surface of an aluminum foil current collector, and drying to obtain a coating with a total load of 40mg/cm2Forming a positive electrode slurry coating 14 to obtain a positive electrode piece 9;
c. and rolling the thickness of the positive pole piece 9 to 125 mu m.
2) Manufacturing a negative pole piece:
the structure of the negative electrode tab 10 is the same as that of the negative electrode tab 10 of example 1. The preparation method comprises the following steps: a. mixing a negative active material artificial graphite, a conductive agent (SP), a thickening agent carboxymethylcellulose sodium (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a weight ratio of 94.5: 1.5: 1.5: 2.5, adding water, stirring and mixing uniformly to obtain negative electrode slurry with the solid content of 50%;
b. coating the negative electrode slurry on a copper foil current collector (namely, a second current collector 12), wherein the total loading of the dried coating is 24mg/cm2Forming a negative electrode slurry coating 13 to obtain a negative electrode plate 10;
c. and rolling the thickness of the negative pole piece to 155 mu m.
3) Manufacturing the lithium ion battery:
a. the positive pole piece 9, the negative pole piece 10 and the PE diaphragm (namely the diaphragm 11) which are prepared by the process are made into a battery core in a winding or laminating mode, and the local structure of the battery core is shown in figure 8;
b. preparing an electrolyte: 1mol/LLIPF6, and the mass ratio of the solvent is EC: DMC: EMC 5: 2: 3, 1 wt% VC, 1 wt% FEC, 1 wt% 1, 3-PS;
c. and injecting the electrolyte into the prepared battery core, standing, pre-charging and carrying out related performance tests.
Comparative example 2
The positive pole piece and the negative pole piece of the comparative example have the following structures:
as shown in fig. 4, the positive electrode plate includes a first current collector 1, the first current collector 1 is an aluminum foil, the upper surface and the lower surface of the first current collector 1 are both provided with a first high-efficiency conductive PTC film 3, and the surface of one side of the first high-efficiency conductive PTC film 3, which is far away from the first current collector 1, is both provided with a first active coating 2. The first current collector 1 and the first high-efficiency conductive PTC films 3 on both sides thereof constitute a primer current collector.
The structure of the negative electrode plate is the same as that of the negative electrode plate in example 1.
The preparation method of the positive pole piece and the negative pole piece comprises the following steps:
1) manufacturing a positive pole piece:
a. pouring N-methyl-2-pyrrolidone into a positive active substance NCM622, a conductive agent 1(SP), a conductive agent 2(CNTs) and a binder (PVDF) according to a weight ratio of 96:1:1:2, mixing and stirring uniformly to prepare positive slurry with a solid content of 75%;
b. pouring N-methyl-2-pyrrolidone into a conductive agent 1 (CNTs-carbon nano tubes), a conductive agent 2 (GNs-graphene), a polymer (polyaniline modified polyethylene wax-PANI-PEW) and a binder (PVDF) according to the weight ratio of 42:42:15:1, mixing, stirring and dispersing uniformly to obtain a high-efficiency conductive PTC slurry with the solid content of 8.0%;
c. coating the high-efficiency conductive PTC slurry on the upper surface and the lower surface of an aluminum foil (namely a first current collector 1) through a gravure roller to form a first high-efficiency conductive PTC film 3, and controlling the thickness of the first high-efficiency conductive PTC film 3 to be 1-3 mu m to obtain a bottom-coating current collector;
d. coating the positive electrode slurry on a bottom coating current collector, wherein the total load of the dried coating is 40mg/cm2Forming a first active coating 2 to obtain a composite positive pole piece;
e. and (3) rolling the composite positive pole piece to the thickness of 125 mu m to obtain the positive pole piece 9 of the comparative example, wherein the structure is shown in figure 4.
2) Manufacturing a conventional negative pole piece (namely a negative pole piece):
a. mixing a negative active material artificial graphite, a conductive agent (SP), a thickening agent carboxymethylcellulose sodium (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a weight ratio of 94.5: 1.5: 1.5: 2.5, adding water, stirring and mixing uniformly to obtain negative electrode slurry with the solid content of 50%;
b. coating the negative electrode slurry on a copper foil current collector, and drying to obtain a coating with a total load of 24mg/cm2Forming a negative electrode slurry coating 13 to obtain a negative electrode plate 10;
c. the negative pole piece 10 is rolled to a thickness of 155 μm.
Manufacturing the lithium ion battery:
a. the positive pole piece 9, the negative pole piece 10 and the PE diaphragm (namely the diaphragm 11) which are prepared by the process are made into a battery core in a winding or laminating mode, and the local structure of the battery core is shown in figure 9;
b. preparing an electrolyte: 1mol/LLIPF6, and the mass ratio of the solvent is EC: DMC: EMC 5: 2: 3, 1 wt% VC, 1 wt% FEC, 1 wt% 1, 3-PS;
c. and injecting the electrolyte into the prepared battery core, standing, pre-charging and carrying out related safety performance tests.
The batteries of example 1 and example 2, and the batteries of comparative example 1 and comparative example 2 were subjected to a 6C/4C/2C/1C rate discharge test at a temperature of 25 ℃, and the temperature rise under discharge and the temperature difference on the surface of the battery cell (infrared imaging temperature measurement) were recorded at different rates, and the results are shown in Table 1.
Table 1 results of rate discharge test for batteries of example 1, example 2, comparative example 1 and comparative example 2
Figure BDA0002627860350000141
Figure BDA0002627860350000151
As can be seen from table 1, the rate temperature rise and the temperature difference are significantly lower in examples 1 and 2 than in comparative examples 1 and 2. Meanwhile, by comparing the embodiment 1 with the comparative example 2, the invention places the high-efficiency conductive PTC film in the pole piece and is linked with the current collector through the leakage at the two ends, thereby not only conducting current, but also conducting the heat in the pole piece to the pole ear in time for heat dissipation; the above effects cannot be achieved by the highly efficient conductive PTC film on the surface of the current collector.
The 100% SOC cells of example 1, example 2 and comparative example 1, comparative example 2 were subjected to a needle punching test by the following method: a3 mm diameter high temperature resistant steel nail was used to penetrate the center of the cell vertically at a rate of 80mm/s (the steel needle stayed in the cell for 300s), and the test results are shown in Table 2:
table 2 test results of battery needling test of example 1, example 2, comparative example 1, and comparative example 2
Figure BDA0002627860350000152
Both example 1 and example 2 passed the needle prick test and the temperature rise was lower; comparative example 1 failed the needle prick test; comparative example 2 has 2/3 passing the needle test, but the temperature rise is higher, and the probability of thermal runaway will be greatly increased due to poor heat dissipation effect in the module.
Example 3
As shown in fig. 3, the pole piece of this embodiment is also a positive pole piece, and the mechanism of the positive pole piece is basically the same as that of embodiment 2, except that: the outer surface of the third active coating 6 is coated with a third high-efficiency conductive PTC film 7, the surface of one side of the third high-efficiency conductive PTC film 7, which is far away from the first current collector 1, is provided with a fourth active coating 8, and the tail end of the third high-efficiency conductive PTC film 7 is also fixedly bonded with the first current collector 1.
1) Manufacturing a positive pole piece (namely a positive pole piece) with the composite coating:
a. pouring N-methyl-2-pyrrolidone into a positive active material NCM811, a conductive agent 1(SP), a conductive agent 2(CNTs) and a binder (PVDF) according to the weight ratio of 96.9:0.8:0.8:1.5, mixing and stirring uniformly to prepare positive slurry A with the solid content of 75%;
b. pouring N-methyl-2-pyrrolidone into a positive active substance LMO, a conductive agent 1(SP) and a binder (PVDF) according to the weight ratio of 97.0:1.0:2.0, mixing and stirring uniformly to prepare positive slurry B with the solid content of 75%;
c. pouring N-methyl-2-pyrrolidone into a conductive agent 1 (CNTs-carbon nano tubes), a conductive agent 2 (GNs-graphene) and a Polymer (PTFE) according to the weight ratio of 46:46:8, mixing, stirring and dispersing uniformly to prepare a high-efficiency conductive PTC slurry C with the solid content of 8.0%;
d. coating the positive electrode slurry A on the upper surface and the lower surface of an aluminum foil current collector (namely a first current collector 1), and drying to obtain a coating with the total load of 9mg/cm2Forming a first active coating 2 to obtain a positive pole piece A;
e. coating the high-efficiency conductive PTC slurry C on the outer surface of a first active coating 2 on the positive pole piece A through a gravure roller to form a first high-efficiency conductive PTC film 3, and controlling the thickness of the first high-efficiency conductive PTC film 3 to be 1-3 mu m to obtain a composite positive pole piece B;
f. coating the positive electrode slurry A on the upper surface and the lower surface of the composite positive electrode sheet B, and drying to obtain a coating with a total load of 18mg/cm2Forming a second active coating 4 to obtain a composite positive pole piece C;
g. coating the high-efficiency conductive PTC slurry C on the outer surface of a second active coating 4 on the positive pole piece C through a gravure roller to form a second high-efficiency conductive PTC film 5, and controlling the thickness of the second high-efficiency conductive PTC film 5 to be 1-3 mu m to obtain a composite positive pole piece D;
h. coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode plate D, wherein the total loading capacity of the dried coating is 27mg/cm2Forming a third active coating 6 to obtain a composite positive pole piece E;
i. coating the high-efficiency conductive PTC slurry C on the outer surface of a third active coating 6 on the positive pole piece E through a gravure roller to form a third high-efficiency conductive PTC film 7, and controlling the thickness of the third high-efficiency conductive PTC film 7 to be 1-3 mu m to obtain a composite positive pole piece F;
j. coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode piece F, wherein the total loading capacity of the dried coating is 36mg/cm2Forming a fourth active coating 8 to obtain a composite positive pole piece G;
k. and (3) rolling the composite positive pole piece E to the thickness of 122 mu m to obtain the target positive pole piece 9, wherein the structure is shown in figure 3.
2) Manufacturing a conventional negative pole piece (namely a negative pole piece):
a. preparing negative active material artificial graphite, a conductive agent (SP), a thickening agent carboxymethylcellulose sodium (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a weight ratio of 95.5: 1.0: 1.3: 2.2, adding water, stirring and mixing uniformly to obtain negative electrode slurry with the solid content of 50%;
b. coating the negative electrode slurry on a copper foil current collector (namely, a second current collector 12), wherein the total loading of the dried coating is 22mg/cm2Forming a negative electrode slurry layer to obtain a negative electrode plate 10;
c. and rolling the thickness of the negative pole piece 10 to 145 mu m.
Manufacturing the lithium ion battery:
a. the positive pole piece 9, the negative pole piece 10 and the PE diaphragm (namely the diaphragm 11) which are prepared by the process are made into a battery core in a winding or laminating mode, and the local structure of the battery core is shown in figure 7;
b. preparing an electrolyte: 1mol/LLIPF6, and the mass ratio of the solvent is EC: DMC: EMC 5: 2: 3, 1 wt% VC, 1 wt% FEC, 1 wt% 1, 3-PS;
c. and injecting the electrolyte into the prepared battery core, standing, pre-charging and carrying out related safety performance tests.
Comparative example 3
The positive pole piece and the negative pole piece of the comparative example have the same structures as the positive pole piece and the negative pole piece of the comparative example 1 respectively, and the specific preparation method comprises the following steps:
1) manufacturing a positive pole piece:
a. pouring N-methyl-2-pyrrolidone into a positive active material NCM622, a conductive agent 1(SP), a conductive agent 2(CNTs) and a binder (PVDF) according to the weight ratio of 96.9:0.8:0.8:1.5, mixing and stirring uniformly to prepare positive slurry with the solid content of 75%;
b. coating the positive electrode slurry on an aluminum foil current collector (namely a first current collector 1), wherein the total loading of the dried coating is 36mg/cm2Forming a positive electrode slurry coating 14 to obtain a positive electrode piece 9;
c. the positive pole piece 9 is rolled to a thickness of 122 μm.
2) Manufacturing a negative pole piece:
a. preparing negative active material artificial graphite, a conductive agent (SP), a thickening agent carboxymethylcellulose sodium (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a weight ratio of 95.5: 1.0: 1.3: 2.2, adding water, stirring and mixing uniformly to obtain negative electrode slurry with the solid content of 50%;
b. coating the negative electrode slurry on a copper foil current collector (namely, a second current collector 12), wherein the total loading of the dried coating is 22mg/cm2Forming a negative electrode slurry coating 13 to obtain a negative electrode plate 10;
c. and rolling the thickness of the negative pole piece 10 to 145 mu m.
3) Manufacturing the lithium ion battery:
a. the positive pole piece 9, the negative pole piece 10 and the PE diaphragm (namely the diaphragm 11) which are prepared by the process are made into a battery core in a winding or laminating mode, and the local structure of the battery core is shown in figure 8;
b. preparing an electrolyte: 1mol/LLIPF6, and the mass ratio of the solvent is EC: DMC: EMC 5: 2: 3, 1 wt% VC, 1 wt% FEC, 1 wt% 1, 3-PS;
c. and injecting the electrolyte into the prepared battery core, standing, pre-charging and carrying out related performance tests.
The cells of example 3 and comparative example 3 were subjected to a 6C/4C/2C/1C rate discharge test at a temperature of 25 deg.C, and the temperature rise and surface temperature difference (infrared imaging thermometry) at different rates of discharge were recorded, and the results are shown in Table 3.
Table 3 results of rate discharge test of battery in example 3 and comparative example 3
Figure BDA0002627860350000191
As can be seen from table 3, the rate temperature rise of example 3 is significantly lower than that of comparative example 3.
The 100% SOC cells of example 3 and comparative example 2 were subjected to a needle punch test by the following method: a3 mm diameter refractory steel nail was used to penetrate the center of the cell vertically at a rate of 80mm/s (the steel needle stayed in the cell for 300s), and the test results are shown in Table 4:
table 4 test results of battery needle punching experiments of example 3 and comparative example 3
Figure BDA0002627860350000192
As can be seen from table 3, example 3 passed the needle prick test and the temperature rise of example 3 was lower; comparative example 2 failed the needle prick test.
It should be noted that, in the present invention, "first" and "second" in "first conductive agent", "first adhesive", "second conductive agent", "second adhesive", and the like are only used to distinguish different components, and the nature thereof is also conductive agent or adhesive; similarly, "first", "second", "third", and "fourth" in "first current collector", "first active coating", "first high-efficiency conductive PTC film", "second active coating", "second high-efficiency conductive PTC film", "third active coating", "third high-efficiency conductive PTC film", "fourth active coating", "second current collector", and the like are also to be interpreted as distinguishing the respective layers in the structure, and they are also "current collector", "active coating", and "high-efficiency conductive PTC film" in the respective structures per se.
In addition, each of the highly conductive PTC films of the present invention is substantially a "highly conductive PTC porous film" mainly because: according to the working principle of the lithium ion battery, the battery of the last embodiment can work, and the temperature rise and the cycle performance are superior to those of a comparative example, which shows that each high-efficiency conductive PTC film can permeate Li +, namely has a porous function, and the reduction of the temperature rise shows that the reduction of the ohmic resistance is due to the high-efficiency conduction of the film.
In conclusion, one or more layers of high-efficiency conductive PTC films are mixed in the coating, so that the difficulty in homogenizing and dispersing caused by the increase of the conductive agent is not influenced, and the high-efficiency conductive PTC porous films are adhered to the current collector, so that the current density near the conductive coating in the coating is more uniform, the heating is more uniform, and the conductive and heat-dissipation effects can be achieved; the electrochemical reaction current can be obviously reduced when the temperature is higher than the PTC material threshold value.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (10)

1. A pole piece, characterized by: the current collector comprises a current collector, wherein at least two active coatings and at least one high-efficiency conductive PTC film are fixedly arranged on two opposite surfaces of the current collector; the active coating and the high-efficiency conductive PTC film are arranged at intervals from the inside to the outside from the surface of the current collector, and the active coating is arranged on the outermost side; the electric conductivity of the outermost active coating is smaller than that of the rest active coatings, and/or the active material of the outermost active coating adopts the active material with high thermal stability.
2. The pole piece of claim 1, wherein: the tail ends of all the high-efficiency conductive PTC films are bonded with the surface of the current collector.
3. The pole piece of claim 1 or 2, wherein: the thickness of all the high-efficiency conductive PTC films is 0.1-5 mu m;
and/or the current collector is an aluminum foil.
4. The pole piece of any one of claims 1 to 3, wherein: the high-efficiency conductive PTC film is a mixture coating of a first conductive agent and a polymer;
preferably, the first conductive agent is a conductive inorganic substance or a conductive polymer having delocalized large pi-bond characteristics;
more preferably, the first conductive agent is one or more of carbon nanotubes, graphene, conductive graphite, conductive carbon black, polyacetylene, polyaniline, polyphenylene ethylene, polydiyne, polydianiline and derivatives thereof, polytriphenylamine and derivatives thereof, polypyrrole and derivatives thereof, polythiophene and derivatives thereof, polyfluorene and derivatives thereof, and poly-p-benzene;
preferably, the polymer is one or more of polyaniline modified polyethylene wax, polyethylene-vinyl acetate, polytetrafluoroethylene, polystyrene, polyolefin, polyvinyl chloride and epoxy resin.
5. The pole piece of claim 4, wherein: the high-efficiency conductive PTC film also comprises a first binder, and the weight ratio of the first conductive agent, the polymer and the first binder is (95-40): (5-55): (0.01-5).
6. The pole piece of any one of claims 1 to 5, wherein: all the high-efficiency conductive PTC films and the outermost active coating layer are formed in one of gravure printing, screen printing, extrusion coating, chemical vapor deposition and magnetron sputtering.
7. The pole piece of any one of claims 1 to 6, wherein: all the active coatings are mixture coatings of active substances, second conductive agents and second binders;
preferably, the active substance is one or more of lithium nickel cobalt manganese oxide, lithium cobaltate, lithium manganate, lithium iron phosphate and lithium manganese phosphate;
preferably, the second conductive agent is one or more of conductive carbon black, carbon nanotubes and graphene;
preferably, the second binder is one or more of polytetrafluoroethylene, polyimide, polypropionic acid and polyacrylonitrile.
8. The pole piece of claim 7, wherein: the content of the conductive agent in the active coating layer of the outermost layer is less than that of the conductive agent in the active coating layers of the rest layers;
preferably, the active material with high thermal stability is one or more of lithium iron phosphate and derivatives thereof and lithium manganate.
9. Use of a pole piece according to any one of claims 1 to 8 as a positive pole piece in a battery.
10. The utility model provides a low temperature rising security lithium ion battery, includes positive pole piece, diaphragm and negative pole piece, its characterized in that: the positive pole piece is the pole piece of any one of claims 1 to 8.
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