CN113903917B

CN113903917B - Lithium ion battery and electric equipment

Info

Publication number: CN113903917B
Application number: CN202111101604.1A
Authority: CN
Inventors: 徐章林
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-09-18
Filing date: 2021-09-18
Publication date: 2023-03-31
Anticipated expiration: 2041-09-18
Also published as: CN113903917A

Abstract

The embodiment of the application relates to the technical field of energy storage, and particularly discloses an electrochemical device, electric equipment and a preparation method of a pole piece applied to the electrochemical device, wherein the electrochemical device comprises the pole piece, the pole piece comprises a current collector and an active material layer, the active material layer is arranged on the surface of the current collector and comprises an active material, a first binder and a second binder, the active material is wrapped by the first binder, and the first binder is wrapped by the second binder; the application also discloses a preparation method of the pole piece, the active material is wrapped by the first binder and the second binder, so that the side reaction between the active material on the current collector and the electrolyte can be reduced, the risk of internal short circuit of the electrochemical device at high temperature is reduced, and the influence on the whole battery system including the electrochemical device is reduced.

Description

Lithium ion battery and electric equipment

Technical Field

The embodiment of the application relates to the technical field of energy storage, in particular to an electrochemical device, electric equipment and a preparation method of a pole piece applied to the electrochemical device.

Background

In recent years, with the development of science and technology, lithium ion secondary batteries gradually occupy most markets of the battery industry by virtue of the advantages of high capacity, long cycle life, no memory effect, high energy density, cleanness, no pollution and the like, and are mostly applied to the fields of batteries, notebook computers and electric automobiles at present.

At present, the most common polymer lithium ion battery in the market is composed of a lithium-containing oxide positive electrode (composed of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium iron phosphate and the like), a negative electrode (any one or combination of more of natural graphite, artificial graphite, hard carbon, mesocarbon microbeads, lithium titanate, silicon carbon, silicon monoxide and the like), an organic electrolyte and a diaphragm. During the working process of the battery, lithium ions are de-intercalated on the positive electrode and the negative electrode to form a passage so as to achieve the purpose of charging and discharging the lithium ion battery. However, in the process of charging and discharging a lithium ion battery, there are not only reactions of deintercalation of lithium ions and redox of metal ions, but also many side reactions such as oxidative decomposition of an electrolyte, collapse of a positive electrode structure, decomposition and recombination of an SEI film and a CEI film on a material surface, reactions of an electrolyte and positive and negative electrode materials, and thermal decomposition reactions of a positive electrode material, and the like. Of course, in the normal operation process of the conventional lithium ion battery, the above side reactions occur to a lower degree, and the influence on the whole battery system including the electrochemical device is small.

In the process of implementing the present application, the applicant of the present application finds that: under the conditions of overcharge, high-temperature placement, heavy object impact and the like, the temperature in the lithium ion battery rises, so that the side reaction of an active material on a pole piece and an electrolyte is severe and serious, and the internal short circuit of the lithium ion battery easily causes safety accidents.

Disclosure of Invention

In view of the above problems, embodiments of the present application provide an electrochemical device, an electrical apparatus, and a method for manufacturing a pole piece applied to an electrochemical device, which overcome or partially solve the problems that the internal temperature of a battery rises due to overcharge, high-temperature placement, impact of a heavy object, and the like of a lithium ion battery, so that side reactions between an active material on the pole piece and an electrolyte are severe and serious, and a short circuit occurs inside the lithium ion battery, thereby causing a safety accident and the like.

According to an aspect of an embodiment of the present application, there is provided an electrochemical device including a pole piece including: the current collector and active material layer, the active material layer set up in the surface of current collector, the active material layer includes active material, first binder and second binder, first binder parcel active material, the second binder parcel first binder. The active material is wrapped by the first binder and the second binder, so that the side reaction between the active material on the current collector and the electrolyte can be reduced, the risk of internal short circuit of the electrochemical device at high temperature is reduced, the influence on the whole battery system including the electrochemical device is reduced, and the maintenance cost of the electrochemical device is reduced.

In an alternative form, the first binder is a water-soluble binder and the second binder is an oil-soluble binder. The active material is wrapped by the water-soluble binder and the oil-soluble binder, so that the side reaction between the pole piece and the electrolyte can be reduced, and the kinetics of the electrochemical device is not additionally lost.

In an alternative form, the first binder is an oil-soluble binder and the second binder is a water-soluble binder. No matter the active material is firstly wrapped by the oil-soluble adhesive and then wrapped by the water-soluble adhesive or is firstly wrapped by the water-soluble adhesive and then wrapped by the oil-soluble adhesive, the side reaction between the pole piece and the electrolyte can be reduced, and the kinetics of the electrochemical device is not additionally lost.

In an alternative mode, the first binder and the second binder are oil-soluble binders, so that even if the active material is wrapped by the oil-soluble binders and then wrapped by the oil-soluble binders, side reactions between the pole piece and the electrolyte can be reduced.

In an alternative form, the oil-soluble binder includes at least one of polyvinylidene fluoride and polyimide.

In an alternative form, the water-soluble binder includes at least one of styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylate, polytetrafluoroethylene, and polyallylamine.

In an alternative mode, the content of the second binder in the active material layer is gradually increased along the direction perpendicular to the surface of the current collector and outward from the surface of the current collector, even if the content of the second binder in the active material layer is not uniform along the direction perpendicular to the surface of the current collector, the side reaction between the pole piece and the electrolyte can be reduced, and the usage amount of the second binder can be reduced.

In an alternative form, the mass of the first binder is based on the mass of the active material

And/or the mass of the second binding agent is based on the mass of the active material>

. By reasonably setting the proportion of the first binder and/or the second binder in the active material, the protection of the active material by the first binder and/or the second binder can be realized, the side reaction between the active material and the electrolyte is reduced, and the exchange of active substances between the active material and the active material in another pole piece in the electrochemical device is not influenced by the use of the first binder and/or the second binder, for exampleFor example, the deintercalation of lithium ions is not affected by the use of the first binder and/or the second binder.

In an alternative form, the active material includes at least one of lithium cobaltate, lithium iron phosphate, lithium manganate, and a ternary material.

According to another aspect of embodiments of the present application, there is provided an electric device including the electrochemical device as described above.

According to another aspect of the embodiments of the present application, there is provided a method for manufacturing a pole piece, where the manufactured pole piece is applied to an electrochemical device, the method including the steps of: (a) Providing a first binder, a second binder, a conductive agent, an active material, a solvent, and a current collector; (b) Mixing and stirring the active material, the conductive agent and the first binder to form slurry, coating the slurry on the surface of the current collector in a roller coating mode, and drying to obtain the active material coated by the first binder; (c) And mixing the solvent and the second binder into a solution, coating the solution on the active material coated by the first binder in a roller coating or spraying manner, drying again, and rolling to obtain the pole piece. The solution formed by mixing the second binder and the solvent is coated on the active material coated by the first binder in a roll coating or spraying manner, so that the second binder permeates into the active material coated by the first binder, and a pole piece with the content of the second binder gradually increased in the active material layer along the direction perpendicular to the surface of the current collector and outward from the surface of the current collector is formed, and the side reaction between the pole piece and the electrolyte can be reduced, and the using amount of the second binder can also be reduced.

In an alternative form, step (c) is replaced with: (d) And mixing the solvent and the second binder into a solution, soaking the active material coated by the first binder into the solution, drying, and rolling to obtain the pole piece. Because the active material coated by the first binder is soaked in the solution formed by mixing the second binder and the solvent, the second binder can uniformly permeate into the active material coated by the first binder, and the side reaction between the pole piece and the electrolyte can be reduced.

The beneficial effects of the embodiment of the application are that: being different from the condition of prior art, this application embodiment is through the pole piece that is provided with current collector and active material layer, wherein, the active material layer set up in the surface of current collector, the active material layer includes active material, first binder and second binder, first binder cladding active material, the cladding of second binder under the circumstances such as electrochemical device overcharge, high temperature are placed, the heavy object is strikeed, even electrochemical device inside temperature risees, active material on the pole piece is protected by first binder and the layer upon layer parcel of second binder, will reduce the side reaction between active material and the electrolyte, reduces electrochemical device and takes place inside short circuit risk under high temperature, reduces the influence to whole battery system including electrochemical device.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.

FIG. 1 is a schematic diagram of one implementation of a pole piece provided by an embodiment of the present application;

FIG. 2 is a schematic diagram of another implementation of a pole piece provided in an embodiment of the present application;

FIG. 3 is a schematic view of the voltage and temperature during constant temperature holding at 124 ℃ and the furnace temperature of the electrochemical device provided in the comparative example;

FIG. 4 is a schematic diagram of the voltage and temperature of the electrochemical device during the constant temperature holding period at 124 ℃ and the furnace temperature in the first embodiment of the present application;

FIG. 5 is a schematic diagram of the voltage and temperature of the electrochemical device of the second embodiment of the present application during the constant temperature holding at 124 ℃ and the furnace temperature;

FIG. 6a is a scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in the comparative example before rolling;

fig. 6b is a scanning electron microscope image of the surface of the pole piece away from the current collector of the electrochemical device according to the first embodiment of the present application before rolling;

FIG. 7a is another SEM image of the surface of the electrode sheet away from the current collector of the electrochemical device in the comparative example before rolling;

fig. 7b is another sem image of the surface of the electrode sheet of the electrochemical device according to the first embodiment of the present application, away from the current collector, before rolling;

FIG. 8a is another SEM image of the surface of the electrode sheet away from the current collector of the electrochemical device in the comparative example after rolling;

fig. 8b is a scanning electron microscope image of the surface of the pole piece away from the current collector of the electrochemical device according to the first embodiment of the present application after rolling;

fig. 9a is another sem image of the surface of the pole piece away from the current collector of the electrochemical device in the comparative example after rolling;

fig. 9b is another sem image of the surface of the electrode sheet away from the current collector of the electrochemical device according to the first embodiment of the present disclosure after rolling;

fig. 10a is a scanning electron micrograph of a cross section of a pole piece of the electrochemical device in the comparative example taken in a direction perpendicular to the current collector;

fig. 10b is a scanning electron microscope image of a section of a pole piece of the electrochemical device in a direction perpendicular to a current collector in the fourth solution provided in the example of the present application;

fig. 10c is another sem image of a cross-section of the electrode sheet of the electrochemical device according to the fourth embodiment of the present disclosure, taken along a direction perpendicular to the current collector;

FIG. 11 is a schematic view of an electrochemical device provided in an embodiment of the present application;

FIG. 12 isbase:Sub>A cross-sectional view taken along line A-A of FIG. 11 according to an embodiment of the present application;

FIG. 13 is a flowchart of a method for manufacturing a pole piece according to an embodiment of the present disclosure;

fig. 14 is a flowchart of another method for manufacturing a pole piece according to an embodiment of the present disclosure.

Detailed Description

In order to facilitate an understanding of the present application, the present application is described in more detail below with reference to the accompanying drawings and specific embodiments. It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Example one

In the first embodiment, referring to fig. 1, a pole piece 10 includes a current collector 1 and an active material layer 2, where the active material layer 2 is disposed on a surface of the current collector 1.

For current collector 1 described above, in some embodiments, current collector 1 comprises aluminum foil.

With the above active material layer 2, the active material layer 2 includes an active material 21, a first binder 22, and a second binder 23, the first binder 22 wrapping the active material 21, and the second binder 23 wrapping the first binder 22. The active material 21 in the active material layer 2 is covered and protected by the first binder 22 and the second binder 23 layer by layer, so that the side reaction between the active material 21 on the pole piece 10 and the electrolyte can be reduced, the risk of internal short circuit of the electrochemical device at high temperature is reduced, the influence on the whole battery system including the electrochemical device is reduced, and the probability of internal short circuit of the lithium ion battery can be reduced.

For the active material 21, the active material 21 includes at least one of lithium iron phosphate, lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium manganese oxide.

With respect to the first binder 22 and the second binder 23, in some embodiments, the first binder 22 is a water-soluble binder and the second binder 23 is an oil-soluble binder, wherein the water-soluble binder encapsulates the active material 21 and the oil-soluble binder encapsulates the water-soluble binder to form the active material layer 2 in a "water-in-oil" form.

It is understood that the first binder 22 and the second binder 23 may be composed of other materials to constitute the active material layer 2 in different forms, such as: in some embodiments, the first binder 22 is an oil-soluble binder that encapsulates the active material 21, and the second binder 23 is a water-soluble binder that encapsulates the oil-soluble binder to form the active material layer 2 in an "oil-in-water" form, such as, for example: in some embodiments, the first binder 22 and the second binder 23 are both oil-soluble binders that encapsulate the active material 21, which is then further encapsulated by the oil-soluble binders to form the active material layer 2 in an "oil-in-oil" form.

Wherein, in some embodiments, the oil soluble binder comprises at least one of polyvinylidene fluoride and polyimide. In some embodiments, the water-soluble binder comprises at least one of styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylate, polytetrafluoroethylene, and polyallyl alcohol.

In some embodiments, the mass of the first binder 22 is based on the mass of the active material 21

And/or the mass of the second binder accounts for the activityQuality of material 21>

. By properly setting the proportion of the first binder 22 and/or the second binder 23 in the active material 21, the protection of the active material 21 by the first binder 22 and/or the second binder 23 can be achieved, the side reaction between the active material 21 and the electrolyte is reduced, and the exchange of the active material 2121 between the active material 21 and the active material 21 in another electrode sheet 10 in the electrochemical device is not influenced by the use of the first binder 22 and/or the second binder 23, for example, the deintercalation of lithium ions is not influenced by the use of the first binder 22 and/or the second binder 23.

It is noted that, in some embodiments, the first binder 22 and the active material 21 form a slurry, so as to form a state in which the first binder 22 wraps the active material 21, and specifically, refer to the fifth embodiment.

It should be noted that, in some embodiments, referring to fig. 1, the active material 21 wrapped by the first binder 22 is soaked in the solution formed by the second binder 23, so as to form the pole piece 10 in which the active material 21 wrapped by the first binder 22 is wrapped by the second binder 23, at this time, the content of the second binder 23 in the active material layer 2 is uniform along the direction L1 perpendicular to the surface of the current collector 1, so that the secondary reaction between the active material 21 and the electrolyte can be reduced because the active material 21 is wrapped by the first binder 22 and the second binder 23, and the secondary reaction between each part of the active material 21 wrapped by the first binder 22 and the electrolyte is reduced to a uniform extent along the direction L1 perpendicular to the surface of the current collector 1 because the content of the second binder 23 in the active material layer 2 is uniform along the direction L1 perpendicular to the surface of the current collector 1, so as to reduce damage to the pole piece including the whole electrochemical device 10.

Wherein, the surface of the current collector 1 is the active material layer 2 arranged on the surface of the current collector 1.

It is worth noting that in some embodiments, referring to fig. 2, the second binder 23 is coated on the active material 21 wrapped by the first binder 22, so as to form a gradually increasing content of the second binder 23 in the active material layer 2 along a direction L1 perpendicular to the surface of the current collector 1 and outward from the surface of the current collector 1. That is, the content of the second binder 23 in the active material layer 2 is not uniform along the direction L1 perpendicular to the surface of the current collector 1, however, even in the case of the pole piece 10 having such a structure, the side reaction between the pole piece 10 and the electrolyte can be reduced, and the amount of the second binder 23 used can be reduced, and the pole piece 10 provided by the embodiment of the present application is economical and environment-friendly.

For the convenience of the reader to understand the inventive concept of the present application, the following 8 specific pole pieces provided by the present application are listed as positive pole pieces to manufacture and form an electrochemical device for experiment, and specifically, the electrochemical device provided by the present application is scheme one, scheme two, scheme three, scheme four, scheme five, scheme six, scheme seven and scheme eight.

The electrode plate in the electrochemical device comprises a current collector and an active material layer, the active material layer comprises an active material, a first binder and a second binder, wherein the active material is wrapped by the first binder, and the first binder is wrapped by the second binder.

Wherein, the content of the second binder in the positive electrode sheet of the electrochemical device in the first to third aspects, and the fifth to eighth aspects is the same in the active material layer in the direction perpendicular to the surface of the current collector.

In the fourth aspect, the content of the second binder in the active material layer gradually increases in a direction perpendicular to the surface of the current collector and outward from the surface of the current collector.

The method comprises the following steps of taking 1 electrochemical device in the prior art as a comparative example, wherein a positive plate of the electrochemical device in the comparative example comprises a current collector and an active material layer, the active material layer comprises an active material and an oil-soluble binder, and the active material is wrapped by the oil-soluble binder.

Other structures of the electrochemical device in the first to eighth aspects and the comparative example, such as the structure and material of the negative electrode sheet and the separator, are the same.

And (3) carrying out performance test on the short circuit condition of the schemes I to eighth and the comparative examples, wherein the performance test process comprises the steps of firstly charging the electrochemical device at a constant current of 0.5 ℃ to the designed highest voltage of the electrochemical device, then charging at a constant voltage until the current reaches 0.02 ℃, then placing the fully charged electrochemical device in an oven at the normal temperature of 25 ℃, closing the door of the oven, heating the oven from 25 ℃ to 124 ℃ at a speed of 5 ℃/min, and keeping the temperature at the constant temperature of 124 ℃ for 1h, wherein the voltage and the temperature of the electrochemical device and the temperature (oven temperature) in the oven are tested in the whole process, if the voltage of the electrochemical device is greatly reduced, the short circuit occurs in the electrochemical device, the schemes I to eighth, the conditions of the comparative examples and the schemes I to eighth, and the results of the performance test carried out on the comparative examples are recorded in the following table 1.

TABLE 1

	Second adhesive	First adhesive	Internal short circuit condition of electrochemical device
				Comparative example	Is free of	Oil-soluble binder	124 ℃ with internal short circuit
Scheme one	Polyacrylic acid	Polyvinylidene fluoride	124 ℃ without internal short circuit
				Scheme two	Styrene butadiene rubber + polyacrylic acid	Polyvinylidene fluoride	124 ℃ without internal short circuit
Scheme three	Carboxymethyl cellulose	Polyvinylidene fluoride	124 ℃ without internal short circuit
				Scheme four	Polyacrylic acid	Polyvinylidene fluoride	124 ℃ without internal short circuit
Scheme five	Polyimide, polyimide resin composition and polyimide resin composition	Polyvinylidene fluoride	124 ℃ without internal short circuit
				Scheme six	Polyvinylidene fluoride	Polyacrylic acid	124 ℃ without internal short circuit
Scheme seven	Polyimide, polyimide resin composition and polyimide resin composition	Polyacrylic acid	124 ℃ without internal short circuit
				Scheme eight	Polyvinylidene fluoride	Styrene butadiene rubber	124 ℃ without internal short circuit

The electrochemical devices in the comparative example, the first and the second schemes were each subjected to the above-described performance test using 5 electrochemical devices, and data of the voltage and temperature of the electrochemical devices, and the temperature inside the oven (oven temperature) were recorded in fig. 3, fig. 4 and fig. 5 during the constant temperature holding at 124 ℃ for 1 hour.

From table 1, fig. 3, fig. 4 and fig. 5, during the constant temperature maintenance at 124 ℃, no short circuit occurred inside the electrochemical device including the pole piece provided in the example of the present application, whereas the comparative example occurred during the constant temperature maintenance at 124 ℃. Specifically, referring to fig. 3, the electrochemical device of the comparative example exhibited a sharp drop in voltage during the constant temperature holding at 124 ℃, indicating that the electrochemical device of the comparative example was internally short-circuited. Referring to fig. 4 and 5, the voltage of the electrochemical devices of the first and second embodiments is relatively stable during the constant temperature maintaining period at 124 ℃, which indicates that the electrochemical devices do not have an internal short circuit phenomenon during the constant temperature maintaining period at 124 ℃.

The positive electrode sheets in the electrochemical devices in examples and comparative examples were also observed for surface morphology and morphology of cut surfaces using a scanning electron microscope.

After the structure that the second binder coats the first binder and the first binder coats the active material is formed, the pole piece needs to be rolled to form a final pole piece.

Fig. 6a provides a scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in the comparative example before rolling, the magnification in fig. 6a is 5000 times, fig. 6b provides a scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in one of the schemes before rolling, and the magnification in fig. 6b is 5000 times. In fig. 6b, the film-like substance coated on the surface of the active material is polyacrylic acid. Since pvdf is transparent, it is not seen in fig. 6a and 6 b. Referring to fig. 6a and 6b, the active material in the first embodiment is coated with a second binder comprising polyacrylic acid.

Fig. 7a provides another scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in the comparative example before rolling, the magnification in fig. 7a is 10000 times, fig. 7b provides another scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in the first scheme before rolling, and the magnification in fig. 7b is 10000 times. Referring to fig. 7b, the film-like substance coated on the surface of the active material in fig. 7b is polyacrylic acid. Since pvdf is transparent, it is not seen in fig. 7a and 7 b. Referring to fig. 7a and 7b, it can also be seen that the active material in scheme one is coated with a second binder comprising polyacrylic acid.

Fig. 8a provides a scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in the comparative example after rolling, the magnification in fig. 8a is 5000 times, fig. 8b provides a scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in one of the schemes after rolling, and the magnification in fig. 8b is 5000 times. From fig. 8b, the film-like substance coated on the surface of the active material in fig. 8b is polyacrylic acid. Since pvdf is transparent, it is not seen in fig. 8a and 8 b. Referring to fig. 8a and 8b, after rolling, although the surface of the active material facing away from the current collector is relatively flat, the active material in the first embodiment is coated with a second binder including polyacrylic acid.

Fig. 9a provides another scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in the comparative example after rolling, the magnification in fig. 9a is 10000 times, fig. 9b provides another scanning electron micrograph of the surface of the pole piece away from the current collector of the electrochemical device in one of the schemes after rolling, and the magnification in fig. 9b is 10000 times. In fig. 9b, polyacrylic acid is the film-like substance coated on the surface of the active material in fig. 9 b. Since polyvinylidene fluoride is transparent, it is considered that polyvinylidene fluoride is not visible in fig. 9a and 9 b. Referring to fig. 9a and 9b, after rolling, although the surface of the active material facing away from the current collector is relatively flat, the active material in the first embodiment is coated with a second binder including polyacrylic acid.

Fig. 10a provides a scanning electron micrograph of a section of the pole piece of the electrochemical device in the comparative example taken in a direction perpendicular to the current collector, with a magnification of 1000 in fig. 10a, fig. 10b provides a scanning electron micrograph of a section of the pole piece of the electrochemical device in scheme four taken in a direction perpendicular to the current collector, and with a magnification of 1000 in fig. 10 b. Fig. 10c provides another sem image of a cross-section of the pole piece of the electrochemical device of scheme four taken along a direction perpendicular to the current collector, at a magnification of 5000 in fig. 10 c. Referring to fig. 10b and 10c, polyacrylic acid is the film-like substance coated on the surface of the active material in fig. 10 b. Since pvdf is transparent, it is not seen in fig. 10a, 10b, and 10 c. Referring to fig. 10a and 10b, the active material in scheme four is coated with a second binder comprising polyacrylic acid. The content of the second binder in the active material layer gradually increases from the region in the dashed oval frame in fig. 10b in the direction perpendicular to the current collector and outward from the current collector surface.

In the present embodiment, the pole piece 10 includes a current collector 1 and an active material layer 2, and the active material layer 2 is disposed on a surface of the current collector 1. The active material layer 2 comprises an active material 21, a first binder 22 and a second binder 23, the active material 21 is wrapped by the first binder 22, and the first binder 22 is wrapped by the second binder 23, so that the electrochemical device comprising the pole piece 10 is arranged, under the conditions of overcharge, high-temperature placement, heavy impact and the like, even if the internal temperature of the electrochemical device rises, the active material 21 on the pole piece 10 is wrapped and protected by the first binder 22 and the second binder 23 layer by layer, the side reaction between the active material 21 on the pole piece 10 and an electrolyte is reduced, the influence on the whole battery system including the electrochemical device is reduced, and the risk of internal short circuit at a high-temperature line in a lithium ion battery can be reduced.

Example two

Referring to fig. 11 and 12, a second embodiment of the present application provides an embodiment of an electrochemical device 100, where the electrochemical device 100 includes an electrochemical device casing 20, an electrolyte 30, two pole pieces 10, and a separator 40 located between the two pole pieces 10. Two pole pieces 10 and a separator 40 are located in the electrochemical device housing 20. The electrolyte 30 is filled in the electrochemical device case 20. At least one of the two pole pieces 10 is the pole piece 10 provided in the first embodiment, and the polarities of the two pole pieces 10 are opposite. For the function and structure of the pole piece 10, reference may be made to the first embodiment, and details are not repeated here.

EXAMPLE III

In a third embodiment of the present application, a battery pack is provided, where the battery pack includes at least one electrochemical device as described above, and the function and structure of the electrochemical device may refer to the second embodiment, which is not described herein again.

Example four

The application further provides an embodiment of an electric device, the electric device includes the battery pack in the third embodiment, and the function and structure of the battery pack may refer to the third embodiment, which is not described herein again.

EXAMPLE five

The fifth application provides a preparation method of a pole piece applied to an electrochemical device, please refer to fig. 13, the preparation method of the pole piece includes the following steps:

(a) A first binder, a second binder, a conductive agent, an active material, a solvent, and a current collector are provided.

The material of the first binder and the relationship between the mass of the first binder and the mass of the active material may be referred to in the first embodiment, and are not described herein again.

The material of the second binder and the relationship between the mass of the second binder and the mass of the active material may be referred to in the first embodiment, and are not described herein again.

The selection of the active material can also refer to the first embodiment, and will not be described herein.

The conductive agent is a conventional material in the preparation process of the pole piece, such as at least one of carbon black, acetylene black, carbon nanotubes, nanofibers and graphene.

The solvent is a substance that can form a solution with the second binder.

For the material of the current collector, reference may also be made to embodiment one, and details are not repeated herein.

(b) Mixing and stirring the active material, the conductive agent and the first binder to form slurry, coating the slurry on the surface of a current collector in a roll coating mode, and drying to obtain the active material coated by the first binder.

(c) And mixing the solvent and the second binder into a solution, uniformly coating the second binder solution on the active material coated by the first binder by using roller coating or spraying, drying again, and rolling to obtain the pole piece.

By the form, the situation that the content of the second binder in the active material layer is gradually increased along the direction which is vertical to the surface of the current collector and is outward from the surface of the current collector can be formed, namely, the content of the second binder in the active material layer is not uniform along the direction which is vertical to the surface of the current collector, however, even if the pole piece is of the structure, the side reaction between the pole piece and the electrolyte can be reduced, the using amount of the second binder can be reduced, and the pole piece provided by the embodiment of the application is economical and environment-friendly.

In some embodiments, referring to fig. 14, step (c) is replaced by step (d), in which the solvent and the second binder are mixed into a solution, the active material coated by the first binder is soaked in the solution, and then dried, and rolled to obtain the pole piece.

The content of the second binder in the active material layer is uniform in a direction perpendicular to the surface of the current collector, so that since the active material is wrapped with the first binder and the second binder, side reactions between the active material and the electrolyte can be reduced, and since the content of the second binder in the active material layer is uniform in a direction perpendicular to the surface of the current collector, the degree to which the side reactions between the respective portions of the active material wrapped with the first binder and the electrolyte are reduced is uniform in a direction perpendicular to the surface of the current collector, so that damage to the entirety of the electrochemical device including the pole piece can be reduced.

In an embodiment of the application, a preparation method of a pole piece comprises the steps of (a) providing a first binder, a second binder, a conductive agent, an active material, a solvent and a current collector; (b) Mixing and stirring an active material, a conductive agent and a first binder to form slurry, coating the slurry on the surface of a current collector in a roller coating mode, and drying to obtain the active material coated by the first binder; (c) The method comprises the steps of mixing a solvent and a second binder into a solution, coating the solution on an active material coated by a first binder in a roll coating or spraying manner, drying again, and rolling to obtain a pole piece, so that the active material in the pole piece is coated by the first binder and the second binder, and when the pole piece is applied to an electrochemical device, the side reaction between the active material and electrolyte in the electrochemical device can be reduced.

The above embodiments are merely examples, and not intended to limit the scope of the present application, and all modifications, equivalents, and flow charts using the contents of the specification and drawings of the present application, or those directly or indirectly applied to other related arts, are included in the scope of the present application.

Claims

1. A lithium ion battery comprising a pole piece, wherein the pole piece comprises:

a current collector;

the active material layer is arranged on the surface of the current collector and comprises an active material, a first binder and a second binder, the first binder wraps the active material completely, the second binder wraps the first binder, and the content of the second binder in the active material layer gradually increases along the direction which is vertical to the surface of the current collector and outwards from the surface of the current collector;

the first binder and the second binder satisfy one of the following conditions a, b, c:

a. the first binder is a water-soluble binder, and the second binder is an oil-soluble binder;

b. the first binder and the second binder are both oil-soluble binders;

c. the first binder is oil-soluble binder, and the second binder is water-soluble binder.

2. The lithium ion battery according to claim 1,

the oil-soluble binder includes at least one of polyvinylidene fluoride and polyimide.

3. The lithium ion battery of claim 1,

the water-soluble binder comprises at least one of styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polyacrylate, polytetrafluoroethylene and polypropylene glycol.

4. The lithium ion battery of claim 1,

the mass of the first binder accounts for the mass of the active material

。

5. An electrical consumer, characterized in that it comprises a lithium ion battery according to any of claims 1 to 4.

6. A method for preparing the lithium ion battery pole piece according to any one of claims 1 to 4, wherein the method comprises the following steps:

(a) Providing a first binder, a second binder, a conductive agent, an active material, a solvent, and a current collector;

(b) Mixing and stirring the active material, the conductive agent and the first binder to form slurry, coating the slurry on the surface of the current collector in a roller coating mode, and drying to obtain the active material completely coated by the first binder;

(c) Mixing the solvent and the second binder into a solution, coating the solution on the active material completely coated by the first binder in a roller coating or spraying manner, drying again, and rolling to obtain a pole piece;

or, replacing step (c) with:

(d) Mixing the solvent and the second binder into a solution, soaking the active material completely coated by the first binder in the solution, drying, and rolling to obtain a pole piece; the content of the second binder in the active material layer gradually increases along a direction perpendicular to the surface of the current collector and outward from the surface of the current collector;

wherein the first binder and the second binder satisfy one of the following conditions (1), (2), and (3):

(1) The first binder is a water-soluble binder, and the second binder is an oil-soluble binder;

(2) The first binder and the second binder are oil-soluble binders;

(3) The first binder is oil-soluble binder, and the second binder is water-soluble binder.