CN111785925B - Pole piece and application, low-temperature elevated safety lithium-ion battery containing the pole piece - Google Patents

Abstract

The invention provides a pole piece and application thereof, and a low-temperature-rise high-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 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 surface of the current collector from inside to outside, and the outermost side is the active coating; the conductivity of the active coating of the outermost layer is smaller than that of the other active coatings, and/or the active material of the active coating of the outermost layer adopts active material with high thermal stability. The pole piece disclosed by the invention has the advantages that the internal temperature distribution is more uniform, the temperature rise of the battery in normal use or internal short circuit is reduced, and the thermal runaway can be slowed down, so that the safety of the lithium ion battery is improved.

Description

Pole piece and application, low-temperature elevated safety lithium-ion battery containing the pole piece

technical field

The invention belongs to the field of lithium-ion batteries, and in particular relates to a pole piece and its application, and a low-temperature rising safe lithium-ion battery containing the pole piece.

Background technique

With the continuous advancement 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, etc. But lithium-ion batteries also have safety risks that cannot be ignored. According to reports, there have been many accidents of mobile phones burning and exploding due to bad lithium-ion batteries, involving well-known companies such as Samsung and Apple, and some incidents have led to product recalls; Well-known electric car companies such as BYD, NIO, and Tesla. The primary and most serious safety risk faced by Li-ion batteries is thermal runaway. The trigger and spread of thermal runaway are closely related to internal short circuit. If the internal short circuit current is large, the temperature of the short circuit point will rise and cause thermal runaway; among other causes of thermal runaway, internal short circuit is also a key contributing factor, such as when overcharging causes Thermal runaway, the initial temperature rises, and once it reaches the diaphragm destruction temperature, an internal short circuit will occur. Once an internal short circuit occurs, the electric energy may be released quickly near the internal short circuit point, and the heat generated will accelerate the shrinkage and melting of the battery diaphragm. The melting damage further increases the short-circuit area and reduces the resistance of the short-circuit point, thus accelerating the release of electric energy and exacerbating thermal runaway. The occurrence of internal short circuit can be divided into two types. One is that the lithium-ion battery is subjected to strong external abuse, such as severe overcharge, strong vibration, severe extrusion deformation, fire, or pierced by foreign objects; the other is In the normal working cycle of the battery, under relatively mild conditions of use, due to lithium dendrites, iron deposition, metal burrs, and current collector cracking caused by cyclic stress, contact points are generated under the disturbance of temperature and pressure. Micro-short-circuit internal short-circuits with a small area must of course be avoided as much as possible. Known technologies reduce the probability of internal short circuits by reducing the thermal shrinkage rate of the separator, strictly controlling the process to avoid the generation of metal burrs, ensuring sufficient negative electrodes, and reducing the charging rate at low temperatures to avoid the generation of lithium dendrites. In order to avoid the internal short circuit caused by the heat shrinkage of the battery separator at high temperature, a known technology is to make a heat-resistant ceramic powder layer between the separator and the electrodes to improve the high temperature safety of the battery. A commonly used method is to attach ceramic powder to both sides of the diaphragm by coating, and the diaphragm treated in this way is called a ceramic coated diaphragm or CCM (Ceramic Coated Membrane).

Although the above-mentioned known technologies are adopted, the current technical level is still unable to reduce the probability of internal short circuit and thermal runaway to a negligible level. The internal short circuit, especially the micro short circuit, does not necessarily lead to thermal runaway. The non-thermal runaway internal short circuit is manifested as an increase in the self-discharge rate of the battery macroscopically. In the battery pack, it is reflected in the imbalance between the battery cells. . If the internal short circuit cannot be avoided, we hope that it will be manifested as a mild self-discharge rate increase rather than thermal runaway. If the current of the internal short circuit can be reduced under a given internal short circuit situation, the risk of thermal runaway can be avoided or reduced.

Contents of the invention

In view of this, the present invention aims to propose a pole piece to overcome the defects of the prior art. The internal temperature distribution is more uniform, the temperature rise of the battery is reduced in conventional use or internal short circuit, and the thermal runaway can be slowed down to improve the safety of lithium-ion batteries. sex.

In order to achieve the above object, technical solution of the present invention is achieved in that way:

A pole piece, comprising a current collector, at least two layers of active coatings and at least one layer of high-efficiency conductive PTC film are fixedly arranged on the opposite surfaces of the current collector; the active coating and the high-efficiency conductive PTC film start from the surface of the current collector It is arranged at intervals from the inside to the outside, and the outermost side is an active coating; the conductivity of the outermost active coating is smaller than that of the remaining active coatings, and/or, the outermost active coating has a As the active material, an active material with high thermal stability is used.

Further, the ends of all high-efficiency conductive PTC films are bonded to the surface of the current collector.

Further, the thickness of all high-efficiency conductive PTC films is 0.1-5 μm.

Further, the current collector is aluminum foil.

Further, the high-efficiency conductive PTC film is a mixture coating of the first conductive agent and polymer;

Preferably, the first conductive agent is a conductive inorganic material or a conductive polymer with the characteristics of delocalized large π bonds.

More preferably, the first conductive agent is carbon nanotubes, graphene, conductive graphite, conductive carbon black, polyacetylene, polyaniline, polyphenylene, polyphenylene vinylene, polydiyne, polydianiline and derivatives thereof, One or more of polytriphenylamine and its derivatives, polypyrrole and its derivatives, polythiophene and its derivatives, polyfluorene and its derivatives, polyparaphenylene.

Preferably, the polymer is one or more of polyaniline-modified polyethylene wax, polyethylene-vinyl acetate, polytetrafluoroethylene, polystyrene, polyolefin, polyvinyl chloride, and epoxy resin.

Further, the composition of the high-efficiency conductive PTC film also includes the 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, all highly efficient conductive PTC films and the outermost active coating are formed by one of gravure printing, screen printing, extrusion coating, chemical vapor deposition, and magnetron sputtering.

Further, all the active coatings are mixture coatings of the active material, the second conductive agent and the second binder.

Preferably, the active material is one or more of nickel-cobalt lithium manganese oxide, lithium cobalt oxide, 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 the content of the conductive agent in the active coating layers of the remaining layers.

Preferably, the active material with high thermal stability is one or more of lithium iron phosphate and its derivatives, and lithium manganate.

The present invention also relates to the application of the pole piece as the positive pole piece in batteries.

Another object of the present invention is to propose a low-temperature rise safety lithium-ion battery, which has the characteristics of low temperature rise and high safety, using the above-mentioned pole piece.

In order to achieve the above object, technical solution of the present invention is achieved in that way:

A lithium-ion battery with elevated safety at low temperature comprises a positive pole piece, a diaphragm and a negative pole piece, and the positive pole piece is the above pole piece.

Compared with the prior art, the pole piece of the present invention has the following advantages:

The pole piece of the present invention has a more uniform internal temperature distribution, lowers the temperature rise of the battery in conventional use or internal short circuit, and slows down thermal runaway so as to improve the safety of lithium-ion batteries (the existing conventional batteries do not have the above technical advantages. more prone to thermal runaway when internal short-circuits occur). Specifically, the advantages of the present invention are reflected in:

(1) The existence of highly efficient conductive PTC film can make the current density distribution in the vicinity of the conductive film inside the coating more uniform on the one hand, reduce uneven polarization and uneven heating, on the other hand, when the internal temperature rises beyond the threshold of the PTC material When the temperature is high, its resistance increases rapidly and the electron transport is weakened.

(2) Each layer of high-efficiency conductive PTC film is bonded in parallel with the current collector, which can reduce the ohmic polarization of the coating perpendicular to the direction of the current collector. It can not only conduct current but also conduct heat. The increase in internal temperature can transfer part of the heat to the pole. ear.

(3) The outermost coating reduces the electrical conductivity or/and uses an active material with high thermal stability. When an internal short circuit occurs, it can reduce the short-circuit current and reduce heat generation on the one hand. On the other hand, the active material with high thermal stability can Absorb more heat to slow down thermal runaway.

(4) It can significantly reduce the temperature rise of lithium-ion battery charge and discharge and the temperature rise of internal short circuit (in the following examples, the electric core using the invention is better than the comparison example in the rate discharge temperature rise and its uniformity, and the acupuncture test ( The temperature rise of the internal short circuit model) is also lower than that of the comparative example).

The low-temperature elevated safety lithium-ion battery has the same advantages as the above-mentioned pole piece over the prior art, and will not be repeated here.

Description of drawings

Fig. 1 is the structural representation of embodiment 1 positive pole piece;

Fig. 2 is the schematic structural representation of embodiment 2 positive pole piece;

Fig. 3 is the schematic structural representation of embodiment 3 positive pole piece;

Fig. 4 is the structural schematic diagram of comparative example 2 positive electrode sheet;

Fig. 5 is a schematic diagram of the local structure of the battery cell in embodiment 1;

Fig. 6 is a schematic diagram of the local structure of the cell in Embodiment 2;

Fig. 7 is a schematic diagram of the local structure of the battery cell in embodiment 3;

Fig. 8 is a schematic diagram of the local structure of the cells of Comparative Example 1 and Comparative Example 3;

FIG. 9 is a schematic diagram of a partial structure of a cell in Comparative Example 2. FIG.

Reference signs:

1-the first current collector; 2-the first active coating; 3-the first high-efficiency conductive PTC film; 4-the second active coating; 5-the second high-efficiency conductive PTC film; 6-the third active coating; 7 -The third high-efficiency conductive PTC film; 8-the fourth active coating; 9-positive pole piece; 10-negative pole piece; 11-diaphragm; 12-second current collector; 13-negative slurry coating; 14-positive pole Slurry coating.

Detailed ways

Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples are conventional chemical reagents unless otherwise specified; the experimental methods are conventional methods unless otherwise specified.

Explanation of terms: PTC material is a material whose resistivity increases with temperature.

A pole piece, comprising a current collector, at least two layers of active coatings and at least one layer of high-efficiency conductive PTC film are fixedly arranged on the opposite surfaces of the current collector; the active coating and the high-efficiency conductive PTC film start from the surface of the current collector It is arranged at intervals from the inside to the outside, and the outermost side is an active coating. Wherein, aluminum foil can be used as the current collector.

Among them, the ends of all high-efficiency conductive PTC films are bonded in parallel with the surface of the current collector, which can not only conduct current but also conduct heat, and the internal temperature rise can transfer part of the heat to the tab.

Wherein, the thickness of all highly efficient conductive PTC films is 0.1-5 μm.

Wherein, the high-efficiency conductive PTC film is a mixture coating of the first conductive agent and 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 conductive inorganic substances or conductive polymers with delocalized large π bond characteristics, wherein the conductive inorganic substances are not limited to one or the other of carbon nanotubes, graphene, conductive graphite, conductive carbon black, etc. A combination of several, conductive polymers are not limited to polyacetylene, polyaniline, polyphenylene, polyphenylene vinylene, polydiyne, polydiphenylamine and its derivatives, polytriphenylamine and its derivatives, polypyrrole and its derivatives One or a combination of polythiophene and its derivatives, polyfluorene and its derivatives, 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, One or several combinations of epoxy resins. According to needs, for example, when the conductive agent in the first conductive agent does not have adhesiveness, the composition of the high-efficiency conductive PTC film also includes the first binder. At this time, the first conductive agent, the polymer and the first binder The weight ratio of the three is (95-40):(5-55):(0.01-5).

In the present invention, all high-efficiency conductive PTC films and the outermost active coating are formed by one of gravure printing, screen printing, extrusion coating, chemical vapor deposition, and magnetron sputtering.

In the present invention, all active coatings are mixture coatings of active material, second conductive agent and second binder. If the pole piece is a positive pole piece, it is essentially a coating of positive electrode slurry. Preferably, the active material is not limited to one or a combination of materials with lithium ion extraction functions such as nickel-cobalt lithium manganese oxide, lithium cobalt oxide, lithium manganate, lithium iron phosphate, lithium manganese phosphate; the second conductive agent It is not limited to one or a combination of materials with high electronic conductivity such as conductive carbon black, carbon nanotubes, and graphene; the second binder is not limited to polytetrafluoroethylene, polyimide, polypropylene One or a combination of polymer compounds with adhesive properties such as acid and polyacrylonitrile.

In the present invention, the outermost active coating reduces the electrical conductivity (preferably, reducing the second conductive agent content in the formula) or uses an active material with high thermal stability, or uses both factors at the same time. When an internal short circuit occurs, on the one hand it can reduce Small short-circuit current reduces heat generation. On the other hand, active materials with high thermal stability can absorb more heat to slow down thermal runaway. Among them, the active material with high thermal stability is not limited to lithium iron phosphate and its derivatives (such as lithium manganese iron phosphate, lithium cobalt iron phosphate, lithium manganese cobalt iron phosphate, etc.), lithium manganate and the like.

The pole piece in the present invention can be used in battery production, especially as a positive pole piece for battery production.

A lithium-ion battery with elevated safety at low temperature comprises a positive pole piece, a diaphragm and a negative pole piece, and the positive pole piece is the above pole piece. The negative electrode sheet can be a conventional negative electrode sheet. The negative electrode sheet includes a negative electrode slurry and a negative electrode collector. The negative electrode collector can be made of copper foil. The negative electrode slurry is composed of an active material, a conductive agent and a binder. Active materials are not limited to graphite materials, silicon-based materials, lithium titanate and other materials with lithium ion intercalation functions; conductive agents are not limited to conductive carbon black, carbon nanotubes, graphene and other materials with high electronic conductivity; bonding The agent is not limited to carboxymethyl cellulose, styrene-butadiene rubber, polyimide, polypropionic acid, polyacrylonitrile and other polymer compounds with bonding effect. The diaphragm can use PE diaphragm.

The present invention will be described in detail below in conjunction with the embodiments and accompanying drawings.

Example 1

As shown in Figure 1, the pole piece includes a first current collector 1, the upper surface and the lower surface of the first current collector 1 are provided with a first active coating 2, and the outer surface of the first active coating 2 is coated with a first high-efficiency conductive coating. PTC film 3, the surface of the first high-efficiency conductive PTC film 3 away from the first current collector 1 is provided with a second active coating 4, and the ends of the first high-efficiency conductive PTC film 3 are bonded and fixed to the current collector. The pole piece is a positive pole piece. The first current collector 1 is an aluminum foil current collector.

1) Production of the positive electrode composite coating pole piece (that is, the positive pole piece):

a. Pour positive active material NCM622, conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 96:1:1:2, Mix and stir evenly to prepare positive electrode slurry A with a solid content of 75%;

b. Pour positive electrode active material NCM622, conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 97.5:0.3:0.2:2, Mix and stir evenly to prepare positive electrode slurry B with a solid content of 75%;

c. Conductive agent 1 (CNTs-carbon nanotube), conductive agent 2 (GNs-graphene), polymer (polyaniline modified polyethylene wax-PANI-PEW), binder (PVDF) by weight ratio 42: 42:15:1, pour N-methyl-2-pyrrolidone, mix, stir and disperse evenly, and obtain a high-efficiency conductive PTC slurry C with a solid content of 8.0%;

d. Coat the positive electrode slurry A on the upper and lower surfaces of the aluminum foil current collector (that is, the first current collector 1), and after drying, the total loading of the coating is 30 mg/cm ² to form the first active coating 2. Obtain positive pole piece A;

d. Coating the high-efficiency conductive PTC slurry C on the outer surface of the first active coating 2 on the positive electrode sheet A by gravure roller to form the first high-efficiency conductive PTC film 3, and control the thickness of the first high-efficiency conductive PTC film 3 at 1 μm ~3μm, to obtain the composite positive electrode piece B;

e. Coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode sheet B, the total loading of the coating after drying is 40 mg/cm ² , forming the second active coating 4, and obtaining the composite positive electrode sheet C ;

f. Roll the composite positive electrode piece C to a thickness of 125 μm to obtain the target positive electrode piece 9 , the structure of which is shown in FIG. 1 .

2) Production of negative conventional pole piece (that is, negative pole piece):

The negative electrode sheet includes a second current collector 12 and a negative electrode slurry coating 13 coated on the upper and lower surfaces of the second current collector 12 , wherein the second current collector 12 is a copper foil current collector.

a. Negative electrode active material artificial graphite, conductive agent (SP), thickener sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber (SBR) in a weight ratio of 94.5:1.5:1.5:2.5, add water Stir and mix evenly to obtain a negative electrode slurry with a 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), the total loading of the coating after drying is 24 mg/cm ² to form the negative electrode slurry coating 13 , to obtain the negative electrode sheet 10;

c. Rolling the negative pole piece 10 to a thickness of 155 μm.

Lithium-ion battery production:

a. The positive pole piece 9, the negative pole piece 10 and the PE diaphragm (that is, the diaphragm 11) prepared by the above process are made into a battery core by winding or laminating, and the local structure of the battery core is shown in Figure 5;

b. configuration electrolyte: 1mol/LLiPF6, the solvent mass ratio is EC (ethylene carbonate): DMC (dimethyl carbonate): EMC (ethyl methyl carbonate) = 5: 2: 3, 1wt% VC (ethylene carbonate vinyl ester), 1wt% FEC (fluoroethylene carbonate), 1wt% 1,3-PS (1,3-propane sultone);

c. Inject the above-mentioned electrolyte into the prepared battery core, let it stand still, pre-charge and form, and conduct related safety performance tests.

Example 2

As shown in Figure 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 Example 1, except that the outer surface of the second active coating 4 is covered with a second high-efficiency conductive PTC The membrane 5 and the second high-efficiency conductive PTC film 5 are provided with a third active coating 6 on the surface away from the first current collector 1 , and the ends of the second high-efficiency conductive PTC film 5 are also bonded and fixed to the first current collector 1 .

1) Fabrication of the positive electrode composite coating pole piece (that is, the positive pole piece) (this embodiment emphasizes the situation of reducing the content of the conductive agent):

a. Pour positive active material NCM622, conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 96:1:1:2, Mix and stir evenly to prepare positive electrode slurry A with a solid content of 75%;

b. Pour positive electrode active material LiFePO ₄ , conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) in a weight ratio of 96.8:0.4:0.8:2 into N-methyl-2-pyrrolidone , mixed and stirred uniformly to prepare positive electrode slurry B with a solid content of 65%;

c. Conductive agent 1 (CNTs-carbon nanotubes), conductive agent 2 (GNs-graphene), polymer (EVA), binder (PVDF) in a weight ratio of 43:43:9:5, pour N- Methyl-2-pyrrolidone, mixing, stirring and dispersing evenly to obtain a high-efficiency conductive PTC slurry C with a solid content of 8.0%;

d. Coat the positive electrode slurry A on the upper and lower surfaces of the aluminum foil current collector (that is, the first current collector 1), and after drying, the total loading of the coating is 15 mg/cm ² to form the first active coating 2. Obtain positive pole piece A;

e. The high-efficiency conductive PTC slurry C is coated on the outer surface of the first active coating 2 on the positive electrode sheet A by a gravure roll to form the first high-efficiency conductive PTC film 3, and the thickness of the first high-efficiency conductive PTC film 3 is controlled at 1 μm ~3μm, to obtain the composite positive electrode piece B;

f. Coating the positive electrode slurry A on the upper surface and the lower surface of the composite positive electrode sheet B, the total loading of the coating after drying is 36 mg/cm ² to form the second active coating 4, and obtain the composite positive electrode sheet C ;

g. the high-efficiency conductive PTC slurry C is coated on the outer surface of the second active coating 4 on the positive pole piece C by gravure roll to form the second high-efficiency conductive PTC film 5, and the thickness of the second high-efficiency conductive PTC film 5 is controlled at 1 μm ～3μm, the composite positive electrode sheet D was obtained;

h. Coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode sheet D, after drying, the total loading of the coating is 42 mg/cm ² to form the third active coating 6, and obtain the composite positive electrode sheet E ;

h. Roll the composite positive pole piece E to a thickness of 127 μm to obtain the target positive pole piece 9 , the structure of which is shown in FIG. 2 .

2) Production of negative conventional pole piece (that is, negative pole piece):

The structure of the negative pole piece of this embodiment is the same as that of the negative pole piece of Embodiment 1. Its specific preparation method is as follows:

a. Negative electrode active material artificial graphite, conductive agent (SP), thickener sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber (SBR) in a weight ratio of 94.5:1.5:1.5:2.5, add water Stir and mix evenly to obtain a negative electrode slurry with a 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), the total loading of the coating after drying is 24 mg/cm ² to form the negative electrode slurry coating 13 , to obtain the negative electrode sheet 10;

c. Rolling the negative pole piece 10 to a thickness of 155 μm.

Lithium-ion battery production:

a. The positive pole piece 9, the negative pole piece 10 and the PE diaphragm (that is, the diaphragm 11) prepared by the above process are made into a battery core by winding or laminating, and the local structure of the battery core is shown in Figure 6;

b. Configure the electrolyte: 1mol/LLiPF6, the solvent mass ratio is EC:DMC:EMC=5:2:3, 1wt% VC, 1wt% FEC, 1wt% 1,3-PS;

c. Inject the above-mentioned electrolyte into the prepared battery core, let it stand still, pre-charge and form, and conduct related safety performance tests.

Comparative example 1

The positive electrode sheet includes a first current collector 1 , and the upper surface and the lower surface of the first current collector 1 are provided with a positive electrode slurry coating 14 . The first current collector 1 is an aluminum foil current collector.

1) Production of positive pole piece:

a. Pour positive active material NCM622, conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 96:1:1:2, Mix and stir evenly to obtain a positive electrode slurry with a solid content of 75%;

b. Coating the positive electrode slurry on the upper surface and the lower surface of the aluminum foil current collector, the total loading of the coating after drying is 40 mg/cm ² , forming the positive electrode slurry coating 14, and obtaining the positive electrode sheet 9;

c. Rolling the positive pole piece 9 to a thickness of 125 μm.

2) Production of negative pole piece:

The structure of the negative electrode sheet 10 is the same as that of the negative electrode sheet 10 in the first embodiment. Its specific preparation method is as follows: a. Negative electrode active material artificial graphite, conductive agent (SP), thickener sodium carboxymethylcellulose (CMC) and binding agent styrene-butadiene rubber (SBR) are by weight 94.5:1.5: 1.5:2.5, add water and stir to mix evenly to obtain a negative electrode slurry with a solid content of 50%;

b. Coating the negative electrode slurry on the copper foil current collector (that is, the second current collector 12), the total loading of the coating after drying is 24 mg/cm ² , forming the negative electrode slurry coating 13, and obtaining the negative electrode sheet 10 ;

c. Roll the thickness of the negative pole piece to 155μm.

3) Production of lithium-ion batteries:

a. The positive pole piece 9, the negative pole piece 10 and the PE diaphragm (that is, the diaphragm 11) prepared by the above process are made into a battery core by winding or laminating, and the local structure of the battery core is shown in Figure 8;

b. Configure the electrolyte: 1mol/LLiPF6, the solvent mass ratio is EC:DMC:EMC=5:2:3, 1wt% VC, 1wt% FEC, 1wt% 1,3-PS;

c. Inject the above-mentioned electrolyte into the prepared battery core, let it stand still, pre-charge and form, and then conduct relevant performance tests.

Comparative example 2

The structures of the positive pole piece and the negative pole piece of this comparative example are as follows:

As shown in Figure 4, the positive electrode sheet includes a first current collector 1, the first current collector 1 is aluminum foil, and the first high-efficiency conductive PTC film 3 is provided on the upper and lower surfaces of the first current collector 1, and the first high-efficiency The surface of the conductive PTC film 3 away from the first current collector 1 is provided with a first active coating 2 . The first current collector 1 and the first high-efficiency conductive PTC film 3 on both sides thereof constitute an undercoated current collector.

The structure of the negative pole piece is the same as that of the negative pole piece in Example 1.

The preparation method of concrete positive pole piece and negative pole piece is as follows:

1) Production of positive pole piece:

a. Pour positive active material NCM622, conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 96:1:1:2, Mix and stir evenly to prepare positive electrode slurry with a solid content of 75%;

b. Conductive agent 1 (CNTs-carbon nanotube), conductive agent 2 (GNs-graphene), polymer (polyaniline modified polyethylene wax-PANI-PEW), binder (PVDF) by weight ratio 42: 42:15:1, pour N-methyl-2-pyrrolidone, mix, stir and disperse evenly, and obtain a high-efficiency conductive PTC slurry with a solid content of 8.0%;

c. The high-efficiency conductive PTC slurry is coated on the upper surface and the lower surface of the aluminum foil (that is, the first current collector 1) by a gravure roll to form the first high-efficiency conductive PTC film 3, and the thickness of the first high-efficiency conductive PTC film 3 is controlled at 1 μm ~ 3 μm, to obtain the undercoat current collector;

d. Coating the positive electrode slurry on the base coating current collector, the total loading of the coating after drying is 40 mg/cm ² , forming the first active coating layer 2, and obtaining the composite positive electrode sheet;

e. Roll the composite positive electrode sheet to a thickness of 125 μm to obtain the positive electrode sheet 9 of this comparative example, the structure of which is shown in FIG. 4 .

2) Production of negative conventional pole piece (that is, negative pole piece):

a. Negative electrode active material artificial graphite, conductive agent (SP), thickener sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber (SBR) in a weight ratio of 94.5:1.5:1.5:2.5, add water Stir and mix evenly to obtain a negative electrode slurry with a solid content of 50%;

b. Coating the negative electrode slurry on the copper foil current collector, the total loading capacity of the coating after drying is 24mg/cm ² , forming the negative electrode slurry coating 13, and obtaining the negative electrode sheet 10;

c. Rolling the negative pole piece 10 to a thickness of 155 μm.

Lithium-ion battery production:

a. The positive pole piece 9, the negative pole piece 10 and the PE diaphragm (that is, the diaphragm 11) prepared by the above process are made into a battery core by winding or laminating, and the local structure of the battery core is shown in Figure 9;

b. Configure the electrolyte: 1mol/LLiPF6, the solvent mass ratio is EC:DMC:EMC=5:2:3, 1wt% VC, 1wt% FEC, 1wt% 1,3-PS;

c. Inject the above-mentioned electrolyte into the prepared battery core, let it stand still, pre-charge and form, and conduct related safety performance tests.

The batteries of Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 were subjected to 6C/4C/2C/1C rate discharge tests at a temperature of 25°C, and the temperature rise and battery life under different rate discharges were recorded. Core surface temperature difference (infrared imaging temperature measurement), the recorded results are shown in Table 1.

Table 1 Example 1, Example 2, Comparative Example 1, Comparative Example 2 battery rate discharge test results

It can be seen from Table 1 that the rate temperature rise and temperature difference of Example 1 and Example 2 are significantly lower than those of Comparative Example 1 and Comparative Example 2. At the same time, through the comparison of Example 1 and Comparative Example 2, the present invention puts the high-efficiency conductive PTC film inside the pole piece and connects it with the current collector through the leakage at both ends, which can not only conduct current, but also conduct heat inside the pole piece in time To dissipate heat from the tabs; the high-efficiency conductive PTC film on the surface of the current collector cannot achieve the above functions.

The 100% SOC batteries of Example 1, Example 2 and Comparative Example 1 and Comparative Example 2 were subjected to acupuncture experiments. The test method was: use a high-temperature-resistant steel nail with a diameter of 3 mm to vertically penetrate the battery at a speed of 80 mm/s. The center of the core (the steel needle stays in the battery for 300s), the test results are shown in Table 2:

Table 2 Example 1, Example 2, Comparative Example 1, Comparative Example 2 battery acupuncture test results

Embodiment 1 and embodiment 2 all pass acupuncture test, and temperature rise is lower; Comparative example 1 does not pass acupuncture test; Comparative example 2 has 2/3 to pass acupuncture test, but temperature rise is higher, as in mold Due to the poor heat dissipation effect in the group, the probability of thermal runaway will be greatly increased.

Example 3

As shown in Figure 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 Example 2, except that the outer surface of the third active coating 6 is coated with a third highly efficient conductive PTC The film 7 and the third high-efficiency conductive PTC film 7 are provided with a fourth active coating 8 on the side away from the first current collector 1 , and the ends of the third high-efficiency conductive PTC film 7 are also bonded and fixed to the first current collector 1 .

1) Production of the positive electrode composite coating pole piece (that is, the positive pole piece):

a. Pour positive active material NCM811, conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 96.9:0.8:0.8:1.5, Mix and stir evenly to prepare positive electrode slurry A with a solid content of 75%;

b. Pour positive electrode active material LMO, conductive agent 1 (SP), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 97.0:1.0:2.0, mix and stir evenly, and obtain a solid content 75% positive electrode slurry B;

c. Conductive agent 1 (CNTs-carbon nanotubes), conductive agent 2 (GNs-graphene), polymer (PTFE) in a weight ratio of 46:46:8, pour N-methyl-2-pyrrolidone, mix, Stir and disperse evenly to prepare a high-efficiency conductive PTC slurry C with a solid content of 8.0%;

d. Coat the positive electrode slurry A on the upper and lower surfaces of the aluminum foil current collector (that is, the first current collector 1), and after drying, the total loading of the coating is 9 mg/cm ² to form the first active coating 2. Obtain positive pole piece A;

e. The high-efficiency conductive PTC slurry C is coated on the outer surface of the first active coating 2 on the positive electrode sheet A by a gravure roll to form the first high-efficiency conductive PTC film 3, and the thickness of the first high-efficiency conductive PTC film 3 is controlled at 1 μm ~3μm, to obtain the composite positive electrode piece B;

f. Coating the positive electrode slurry A on the upper surface and the lower surface of the composite positive electrode sheet B, the total loading of the coating after drying is 18 mg/cm ² to form the second active coating 4, and obtain the composite positive electrode sheet C ;

g. the high-efficiency conductive PTC slurry C is coated on the outer surface of the second active coating 4 on the positive pole piece C by gravure roll to form the second high-efficiency conductive PTC film 5, and the thickness of the second high-efficiency conductive PTC film 5 is controlled at 1 μm ～3μm, the composite positive electrode sheet D was obtained;

h. Coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode sheet D, after drying, the total loading of the coating is 27 mg/cm ² to form the third active coating 6, and obtain the composite positive electrode sheet E ;

i. The high-efficiency conductive PTC slurry C is coated on the outer surface of the third active coating 6 on the positive electrode sheet E by a gravure roll to form the third high-efficiency conductive PTC film 7, and the thickness of the third high-efficiency conductive PTC film 7 is controlled at 1 μm ~3μm, to obtain the composite positive electrode sheet F;

j. Coating the positive electrode slurry B on the upper surface and the lower surface of the composite positive electrode sheet F, the total loading of the coating after drying is 36 mg/cm ² , forming the fourth active coating layer 8, and obtaining the composite positive electrode sheet G ;

k. Roll the composite positive pole piece E to a thickness of 122 μm to obtain the target positive pole piece 9 , the structure of which is shown in FIG. 3 .

2) Production of negative conventional pole piece (that is, negative pole piece):

a. Negative electrode active material artificial graphite, conductive agent (SP), thickener sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber (SBR) in a weight ratio of 95.5:1.0:1.3:2.2, add water Stir and mix evenly to obtain a negative electrode slurry with a solid content of 50%;

b. Coating the negative electrode slurry on the copper foil current collector (that is, the second current collector 12), the total loading of the coating after drying is 22 mg/cm ² , forming a negative electrode slurry layer, and obtaining the negative electrode sheet 10;

c. Rolling the negative pole piece 10 to a thickness of 145 μm.

Lithium-ion battery production:

a. The positive pole piece 9, the negative pole piece 10 and the PE diaphragm (that is, the diaphragm 11) prepared by the above process are made into a battery core by winding or stacking, and the local structure of the battery core is shown in Figure 7;

b. Configure the electrolyte: 1mol/LLiPF6, the solvent mass ratio is EC:DMC:EMC=5:2:3, 1wt% VC, 1wt% FEC, 1wt% 1,3-PS;

c. Inject the above-mentioned electrolyte into the prepared battery core, let it stand still, pre-charge and form, and conduct related safety performance tests.

Comparative example 3

The structure of the positive pole piece and the negative pole piece of this comparative example is the same as that of the positive pole piece and the negative pole piece of Comparative Example 1 respectively, and its specific preparation method is as follows:

1) Production of positive pole piece:

a. Pour positive electrode active material NCM622, conductive agent 1 (SP), conductive agent 2 (CNTs), and binder (PVDF) into N-methyl-2-pyrrolidone in a weight ratio of 96.9:0.8:0.8:1.5, Mix and stir evenly to prepare positive electrode slurry with a solid content of 75%;

b. Coating the positive electrode slurry on the aluminum foil current collector (that is, the first current collector 1), the total loading of the coating after drying is 36 mg/cm ² , forming the positive electrode slurry coating 14, and obtaining the positive electrode sheet 9;

c. Rolling the positive pole piece 9 to a thickness of 122 μm.

2) Production of negative pole piece:

a. Negative electrode active material artificial graphite, conductive agent (SP), thickener sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber (SBR) in a weight ratio of 95.5:1.0:1.3:2.2, add water Stir and mix evenly to obtain a negative electrode slurry with a solid content of 50%;

b. Coating the negative electrode slurry on the copper foil current collector (that is, the second current collector 12), the total loading of the coating after drying is 22 mg/cm ² , forming the negative electrode slurry coating 13, and obtaining the negative electrode sheet 10 ;

c. Rolling the negative pole piece 10 to a thickness of 145 μm.

3) Production of lithium-ion batteries:

a. The positive pole piece 9, the negative pole piece 10 and the PE diaphragm (that is, the diaphragm 11) prepared by the above process are made into a battery core by winding or laminating, and the local structure of the battery core is shown in Figure 8;

b. Configure the electrolyte: 1mol/LLiPF6, the solvent mass ratio is EC:DMC:EMC=5:2:3, 1wt% VC, 1wt% FEC, 1wt% 1,3-PS;

c. Inject the above-mentioned electrolyte into the prepared battery core, let it stand still, pre-charge and form, and then conduct relevant performance tests.

The batteries of Example 3 and Comparative Example 3 were subjected to 6C/4C/2C/1C rate discharge tests at a temperature of 25°C, and the temperature rise and surface temperature difference under different rate discharges were recorded (infrared imaging temperature measurement), Record the results as in Table 3.

Table 3 embodiment 3 and comparative example 3 battery rate discharge test results

It can be seen from Table 3 that the rate temperature rise of Example 3 is significantly lower than that of Comparative Example 3.

The 100% SOC batteries of Example 3 and Comparative Example 2 were subjected to acupuncture experiments. The test method was: use a high-temperature-resistant steel nail with a diameter of 3 mm to penetrate the center of the battery cell vertically at a speed of 80 mm/s (the steel needle stays on the 300s in the battery), the test results are shown in Table 4:

Table 4 Example 3 and Comparative Example 3 battery acupuncture test results

As can be seen from Table 3, Example 3 passed the acupuncture test, and the temperature rise of Example 3 was low; Comparative Example 2 failed the acupuncture test.

It should be noted that the "first" and "second" in the "first conductive agent", "first binder", "second conductive agent", "second binder" in the present invention are only In order to distinguish and illustrate different components, its essence is still a conductive agent or a binder; similarly, "the first current collector", "the first active coating", "the first high-efficiency conductive PTC film", and "the second active coating" , "Second Efficient Conductive PTC Film", "Third Active Coating", "Third Efficient Conductive PTC Film", "Fourth Active Coating", "Second Current Collector", etc. "First", " The second", "third", and "fourth" are also for the purpose of distinguishing and explaining the various layers in the structure, which are essentially "collectors", "active coatings", and "high-efficiency conductive PTC films" in their respective structures. ".

In addition, each high-efficiency conductive PTC film in the present invention is essentially a "high-efficiency conductive PTC porous film". The ratio shows that each high-efficiency conductive PTC film in the present invention can pass through Li+, that is, it has a porous function, and the decrease in temperature rise shows that the decrease in ohmic resistance is due to the high-efficiency conduction of the film.

In summary, in the present invention, adopting one or more layers of high-efficiency conductive PTC film inside the coating will not affect the difficulty of homogenate dispersion caused by the increase of conductive agent on the one hand, and on the other hand, the high-efficiency conductive PTC porous film Existing and bonding with the current collector, the current density near the conductive coating inside the coating can be more uniform, the heat generation can be more uniform, and it can also play the role of conduction and heat dissipation; when the temperature is higher than the threshold of the PTC material, the electrochemical reaction current can be significantly reduced .

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (12)

1. A pole piece, characterized in that: the solar cell comprises a first current collector, wherein first active coatings are arranged on the upper surface and the lower surface of the first current collector, a first efficient conductive PTC film is coated on the outer surface of the first active coating, a second active coating is arranged on the surface of one side, far away from the first current collector, of the first efficient conductive PTC film, a second efficient conductive PTC film is coated on the surface of the second active coating, a third active coating is arranged on the surface of one side, far away from the first current collector, of the second efficient conductive PTC film, the tail ends of the first efficient conductive PTC film are all fixedly adhered to the current collector, the tail ends of the second efficient conductive PTC film are also fixedly adhered to the first current collector, the pole piece is an anode pole piece, and the first current collector is an aluminum foil current collector;

wherein, the conductivity of the active coating of the outermost layer is smaller than that of the other active coatings, and the active material of the active coating of the outermost layer adopts the active material with high thermal stability;

the forming mode of all the high-efficiency conductive PTC films and the active coating of the outermost layer is one of gravure printing, screen printing, extrusion coating, chemical vapor deposition and magnetron sputtering;

the high-efficiency conductive PTC film is a mixture coating of a first conductive agent and a polymer, wherein the polymer is one or more of polyaniline modified polyethylene wax, polyethylene-vinyl acetate, polytetrafluoroethylene, polystyrene, polyolefin, polyvinyl chloride and epoxy resin;

the high-efficiency conductive PTC film also comprises a first adhesive, wherein the weight ratio of the first conductive agent to the polymer to the first adhesive is (95-40) (5-55) (0.01-5);

the first binder is PVDF.

2. A pole piece according to claim 1, characterized in that: the thickness of all the high-efficiency conductive PTC films is 0.1-5 mu m;

and/or the current collector is aluminum foil.

3. A pole piece according to claim 1 or 2, characterized in that: the first conductive agent is a conductive inorganic or conductive polymer having delocalized large pi-bond characteristics.

4. A pole piece according to claim 1 or 2, characterized in that: the first conductive agent is one or more of carbon nano tube, graphene, conductive graphite, conductive carbon black, polyacetylene, polyaniline, polyphenylene ethylene, polydiacetylene, polydianiline and derivatives thereof, polytrianiline and derivatives thereof, polypyrrole and derivatives thereof, polythiophene and derivatives thereof, polyfluorene and derivatives thereof, and polyparaphenylene.

5. A pole piece according to claim 1 or 2, characterized in that: all active coatings are coatings of a mixture of active material, second conductive agent and second binder.

6. A pole piece according to claim 5, characterized in that: the active substance is one or more of nickel cobalt lithium manganate, lithium cobaltate, lithium manganate, lithium iron phosphate and lithium manganese phosphate.

7. A pole piece according to claim 5, characterized in that: the second conductive agent is one or more of conductive carbon black, carbon nano tube and graphene.

8. A pole piece according to claim 5, characterized in that: the second binder is one or more of polytetrafluoroethylene, polyimide, poly-propionic acid and polyacrylonitrile.

9. A pole piece according to claim 5, characterized in that: the content of the conductive agent in the active coating of the outermost layer is smaller than the content of the conductive agent in the active coating of each other layer.

10. A pole piece according to claim 1, characterized in that: the active substance with high thermal stability is one or more of lithium iron phosphate, derivatives thereof and lithium manganate.

11. Use of a pole piece according to any of claims 1 to 10 as positive pole piece in a battery.

12. The utility model provides a low temperature rise high security lithium ion battery, includes positive pole piece, diaphragm and negative pole piece, its characterized in that: the positive electrode sheet is the sheet according to any one of claims 1 to 10.

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