CN211879509U

CN211879509U - Electrode pole piece, electrochemical device and electronic device comprising same

Info

Publication number: CN211879509U
Application number: CN202020464623.5U
Authority: CN
Inventors: 李保章
Original assignee: Ningde Amperex Technology Ltd; Dongguan Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd; Dongguan Amperex Technology Ltd
Priority date: 2020-04-02
Filing date: 2020-04-02
Publication date: 2020-11-06
Anticipated expiration: 2030-04-02

Abstract

The application relates to an electrode plate, an electrochemical device and an electronic device comprising the same. This electrode sheet includes: the current collector, the first active material layer, the second active material layer and the insulating layer. The current collector includes a first surface, the first active material layer includes a first active material, and the second active material layer includes a second active material. The first active material layer is arranged between the current collector and the second active material layer and covers a first part of the first surface of the current collector, the insulating layer covers a second part, different from the first part, of the first surface of the current collector, in the length direction of the electrode pole piece, the first active material layer comprises a first end and a second end, the insulating layer comprises a third end and a fourth end, and the first end and the third end are mutually stacked to form an overlapping part. The current collector of the electrode plate can be covered by a layer with high resistivity, and the safety performance of an electrochemical device and an electronic device is improved.

Description

Electrode pole piece, electrochemical device and electronic device comprising same

Technical Field

The present application relates to the field of energy storage technologies, and in particular, to an electrode sheet, an electrochemical device, and an electronic device including the electrochemical device.

Background

Electrochemical devices (e.g., lithium ion batteries) have entered our daily lives with technological advances and increased environmental demands. With the great popularization of lithium ion batteries, the safety problem caused by the fact that the lithium ion battery is punctured by external force occasionally occurs at a user end, the safety performance of the lithium ion battery is more and more emphasized by people, and particularly, continuous fermentation of some mobile phone explosion events causes new requirements on the safety performance of the lithium ion battery by users, after-sales terminals and lithium ion battery manufacturers.

At present, methods for improving the safety performance of lithium ion batteries, such as increasing the content of binders in the positive active material layer and thickening the ceramic coating on the surface of the isolating membrane, are all at the expense of the energy density of the lithium ion batteries. Therefore, it is urgently needed to provide a technical means capable of significantly improving the safety performance of the lithium ion battery under the condition of higher energy density.

SUMMERY OF THE UTILITY MODEL

The present application provides an electrode pad, an electrochemical device, and an electronic device including the electrochemical device in an attempt to solve at least one of the problems existing in the related art to at least some extent.

According to an aspect of the present application, some embodiments of the present application provide an electrode tab, including: the current collector, the first active material layer, the second active material layer and the insulating layer. The current collector includes a first surface, the first active material layer includes a first active material, and the second active material layer includes a second active material. The first active material layer is arranged between the current collector and the second active material layer and covers a first part of the first surface of the current collector, the insulating layer covers a second part, different from the first part, of the first surface of the current collector, in the length direction of the electrode pole piece, the first active material layer comprises a first end and a second end, the insulating layer comprises a third end and a fourth end, and the first end and the third end are mutually stacked to form an overlapping part.

According to an aspect of the present application, some embodiments of the present application provide an electrochemical device including a positive electrode sheet, a separator, and a negative electrode sheet, wherein the positive electrode sheet and/or the negative electrode sheet is the electrode sheet described above.

According to another aspect of the present application, some embodiments of the present application provide an electronic device comprising the electrochemical device described above.

The electrochemical device adopts the electrode pole piece with the structure of the double active material layers, the insulating layer is arranged on the part of the empty current collector which is not covered by the active material layers, the insulating layer and the first active material layers are overlapped to completely cover the current collector, and therefore short circuit between the electrode pole pieces is prevented when the electrochemical device is impacted by external force or punctured, and the safety performance of the electrochemical device and the electronic device is improved.

Additional layers and other advantages of the embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the embodiments of the present application.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the drawings can be obtained from the structures illustrated in these drawings without the need for inventive work.

Fig. 1 is a schematic structural diagram of an electrode sheet in which an insulating layer covers a first active material layer according to an embodiment of the present application.

Fig. 2 is a schematic structural diagram of an electrode sheet in which an insulating layer covers a first active material layer according to an embodiment of the present application (a second active material layer is flush with the edge of a current collector in the length direction).

Fig. 3 is a schematic view of the structure of an electrode sheet in which an insulating layer covers a first active material layer according to an embodiment of the present application (a second active material layer partially covers an overlapping portion).

Fig. 4 is a schematic structural view of an electrode sheet in which a first active material layer covers an insulating layer according to an embodiment of the present application.

Fig. 5 is a schematic structural view of an electrode sheet in which a first active material layer covers an insulating layer according to an embodiment of the present application (a second active material layer is flush with the edge of a current collector in the length direction).

Fig. 6 is a schematic view showing the structure of an electrode sheet in which a first active material layer covers an insulating layer (a second active material layer partially covers an overlapping portion) in an example of the present application.

Fig. 7 is a schematic structural view of an electrode sheet according to an embodiment of the present application (active material layer structure on the second surface of the current collector).

Fig. 8 is a schematic structural view of the positive electrode tab of example 1.

Fig. 9 is a schematic structural view of the positive electrode tab of example 7.

Fig. 10 is a schematic structural view of the positive electrode tab of example 8.

Fig. 11 is a schematic structural view of the positive electrode tab of example 9.

Fig. 12 is a schematic structural view of the positive electrode tab of example 11.

Fig. 13 is a schematic structural view of the positive electrode tab of example 12.

Fig. 14 is a schematic structural view of the positive electrode tab of example 13.

Detailed Description

Embodiments of the present application will be described in detail below. Throughout the specification, the same or similar components and components having the same or similar functions are denoted by like reference numerals. The embodiments described herein with respect to the figures are illustrative in nature, are diagrammatic in nature, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

In this specification, unless specified or limited otherwise, relative terms such as: terms of "central," "longitudinal," "lateral," "front," "rear," "right," "left," "inner," "outer," "lower," "upper," "horizontal," "vertical," "above," "below," "top," "bottom," and derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described in the discussion or as shown in the drawing figures. These relative terms are for convenience of description only and do not require that the present application be constructed or operated in a particular orientation.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

Moreover, for convenience in description, "first," "second," "third," etc. may be used herein to distinguish between different elements of a figure or series of figures. Unless specifically specified or limited, "first," "second," "third," and the like are not intended to describe corresponding components.

In electrochemical devices (e.g., lithium ion batteries), when impacted or punctured by an external force, four short circuit modes typically occur: positive electrode active material layer-negative electrode active material layer, positive electrode active material layer-negative electrode current collector, positive electrode current collector-negative electrode active material layer. Of these four short-circuit modes, the short-circuit mode of the positive electrode collector-negative electrode active material layer and the negative electrode collector-positive electrode active material layer is the most dangerous of the four short-circuit modes because the short-circuit power when these two short-circuit modes occur is relatively large.

The embodiment of the application provides an electrode plate adopting a double-active-material-layer structure, wherein a first active material layer and a second active material layer covering the first active material layer are arranged on a part covered by the active material layer on a current collector, and an insulating layer is arranged on an empty current collector part not covered by the first active material layer. The electrode pole piece can effectively improve the resistance of the surface of the current collector when being damaged due to external force by adjusting the combination mode of the first active material layer and the insulating layer so as to improve the safety performance of the electrochemical device in corresponding tests (nail penetration or heavy object impact).

The electrochemical device comprises a positive pole piece, a negative pole piece, an isolating membrane, electrolyte and the like. The positive pole piece and the negative pole piece both comprise a current collector, an active substance layer and the like. The current collector includes a portion not covered with the active material layer (also referred to as an empty current collector portion) in addition to a portion covered with the active material layer. For example, when the electrode assembly of the electrochemical device is wound, the empty current collector portion thereof includes an outer layer portion of the electrode assembly and an inner layer tab welding portion of the electrode assembly.

In the active material layer covering portion, a first active material layer may be provided at a position close to the current collector and a second active material layer may be provided at a position far from the surface of the current collector in a dual active material layer structure. Compared with the first active material layer, the second active material layer can have higher energy density, and when collision or puncture occurs, the first active material layer can increase the contact resistance between the current collector and other contacts, so that the current collector is protected. However, during the nail penetration test, the empty current collector part on the current collector can directly contact with the nail, thereby causing a possible short circuit condition. For example, the positive electrode collector can be electrically connected to the negative electrode active material layer through the nail, thereby forming a short circuit pattern of positive electrode collector-negative electrode active material layer or positive electrode collector-nail-negative electrode active material layer. Therefore, the current collector in the electrode plate can be effectively protected by arranging the insulating layer on the empty current collector region, and a short circuit mode of the positive current collector-negative active material layer or the negative current collector-positive active material layer is avoided, wherein the coverage degree of the insulating layer on the empty current collector part of the current collector is higher, and the effect of avoiding short circuit is more obvious. The utility model provides an overlap portion among the electrode sheet piles up and cover the mass flow body that can avoid both junctions through above-mentioned insulating layer and first active material layer each other and exposes to ensure the insulating layer to the coverage of mass flow body, and improve electrode sheet's security performance.

Fig. 1-3 are schematic structural views of electrode pads according to some embodiments of the present application, in which an insulating layer covers a first active material layer in an overlapping portion of the electrode pad. The electrode pole piece can be a positive pole piece or a negative pole piece. As shown in fig. 1 to 3, the electrode sheet includes a current collector 101, a first active material layer 102, a second active material layer 103, and an insulating layer 104. The first active material layer 102 is disposed between the current collector 101 and the second active material layer 103 and covers a first portion on one surface of the current collector 101, the insulating layer 104 covers a second portion of the first surface of the current collector 101 different from the first portion, the first active material layer 102 includes a first end 102a and a second end 102b, the insulating layer 104 includes a third end 104b and a fourth end 104a, and the first end 102a and the third end 104b are stacked on each other to form an overlapping portion 105 in a length direction of the electrode tab. The insulating layer 104 and the first active material layer 102 do not have any gap in the longitudinal direction of the electrode sheet, and the current collector 101 is not easily exposed even when subjected to external impact or puncture.

In some embodiments, the distance between the edge of the first end 102a of the first active material layer 102 in the length direction of the electrode tab and the edge of the third end 104b of the insulating layer 104 in the length direction of the electrode tab is less than or equal to 20 mm. That is, the length of the overlapping portion 105 of the first active material layer 102 and the insulating layer 104 in the longitudinal direction of the electrode tab is 20mm or less. In some embodiments, the length of the overlapping portion 105 of the first active material layer 102 and the insulating layer 104 in the length direction of the electrode tab is 5.0mm to 20 mm. In other embodiments, the length of the overlapping portion 105 of the first active material layer 102 and the insulating layer 104 in the length direction of the electrode pad is approximately, for example, 0.5mm, 1.0mm, 2.5mm, 5.0mm, 10.0mm, 15.0mm, 20.0mm, or a range consisting of any two of these values.

In some embodiments, as shown in fig. 1-3, the first end 102a is disposed between the third end 104b and the current collector 101 in the thickness direction of the electrode tab. The process tolerance required for covering the third end 104b of the insulating layer 104 on the first end 102a of the first active material layer 102 in the overlapping portion 105 is low, and the time and cost required for manufacturing can be reduced.

In some embodiments, the second active material layer includes a fifth end 103a in the length direction of the electrode pad, the fifth end 103a being proximate to the overlap portion 105. As shown in fig. 1, the second active material layer 103 can extend from the overlapping portion 105 in the longitudinal direction of the electrode tab and cover a part of the insulating layer 104, so that the edge of the first end 102a of the first active material layer 102 in the longitudinal direction of the electrode tab is located between the edge of the third end 104b in the longitudinal direction of the electrode tab and the edge of the fifth end 103a in the longitudinal direction of the electrode tab.

In some embodiments, in the electrode tab length direction, the distance between the edge of the first end 102a of the first active material layer 102 in the electrode tab length direction and the edge of the fifth end 103a of the second active material layer 103 in the electrode tab length direction is less than or equal to 3 mm. In some embodiments, the length of the second active material layer 103 covering the extension of the insulating layer 104 in the length direction of the electrode tab is less than or equal to 3 mm.

In some embodiments, as shown in fig. 2, the edge of the fifth end 103a of the second active material layer 103 in the length direction of the electrode tab is flush with the edge of the third end 104b of the insulating layer 104 in the length direction of the electrode tab.

In some embodiments, as shown in fig. 3, the edge of the fifth end 103a of the second active material layer 103 in the length direction of the electrode tab is located between the edge of the first end 102a of the first active material layer 102 in the length direction of the electrode tab and the edge of the third end 104b of the insulating layer 104 in the length direction of the electrode tab.

In some embodiments, the second active material layer 103 entirely covers the first active material layer 102 except for the overlapping portion 105. Taking a lithium ion battery as an example, after the exposed portion of the first active material layer 102 except the overlapping portion 105 causes lithium ions in the exposed portion to be extracted, the corresponding electrode pole piece of the other polarity does not have an active material for inserting lithium ions, the extracted lithium ions form lithium metal particles on the current collector (e.g., negative electrode current collector) of the other polarity, and the cycle number of the lithium ion battery increases, so that the lithium metal particle pits appear on the surface of the negative electrode pole piece, and the capacity of the lithium ion battery (electrochemical device) is reduced.

In some embodiments, the length of the second active material layer 103 is greater than the length of the first active material layer 102 excluding the overlapping portion 105 in the length direction of the electrode pad. In some embodiments, the length of the second active material layer 103 minus the length of the portion of the first active material layer 102 excluding the overlapping portion 105 is less than or equal to 4 mm.

Fig. 4-6 are schematic structural views of electrode pads according to some embodiments of the present application, wherein an insulating layer covers a first active material layer in an overlapping portion of the electrode pads. As shown in fig. 4 to 6, the third end 104b is disposed between the first end 102a and the current collector 101 in the thickness direction of the electrode tab. As shown in fig. 4, the second active material layer 103 can extend from the overlapping portion 105 in the longitudinal direction of the electrode tab and cover a part of the insulating layer 104, so that the edge of the first end 102a of the first active material layer 102 in the longitudinal direction of the electrode tab is located between the edge of the third end 104b in the longitudinal direction of the electrode tab and the edge of the fifth end 103a in the longitudinal direction of the electrode tab. Since the insulating layer 104 has a better insulating effect than the first active material layer 102, when the electrode sheet is impacted by a nail or a heavy object, the insulating layer 104 covered by the first active material layer 102 in the overlapping portion 105 of the electrode sheet shown in fig. 4 can perform better insulating isolation on the current collector 101, and thus has higher safety performance. Meanwhile, since the fifth end 103a of the second active material layer 103 covers the end of the first end 102a of the first active material layer 102, the first end 102a is difficult to fall off under an external force of a nail penetration or an impact, which is a destructive force, so that the current collector 101 does not leak, and the electrode assembly thereof is safer.

In some embodiments, as shown in fig. 5, the edge of the fifth end 103a of the second active material layer 103 in the length direction of the electrode tab is flush with the edge of the third end 104b of the insulating layer 104 in the length direction of the electrode tab.

In some embodiments, as shown in fig. 6, the edge of the fifth end 103a of the second active material layer 103 in the length direction of the electrode tab is located between the edge of the first end 102a of the first active material layer 102 in the length direction of the electrode tab and the edge of the third end 104b of the insulating layer 104 in the length direction of the electrode tab.

Fig. 7 is a schematic structural diagram of an electrode sheet according to other embodiments of the present application, where the electrode sheet further includes a third active material layer 106 and a fourth active material layer 107, and the current collector 101 further includes a second surface. The third active material layer 106 is disposed between the current collector 101 and the fourth active material layer 107 and covers the second surface of the current collector. In some embodiments, the third active material layer 106 has the same composition as the first active material layer 102, the fourth active material layer 107 has the same composition as the second active material layer 103, and the content of the active material of the third active material layer 106 is smaller than the content of the active material of the fourth active material layer 107.

As shown in fig. 7, in some embodiments, the third active material layer 106 includes a sixth end 106a in the length direction of the electrode tab, the sixth end 106a is proximate to the overlapping portion 105, and the edge of the sixth end 106a in the length direction of the electrode tab is located between the edge of the first end 102a in the length direction of the electrode tab and the edge of the fourth end 104a in the length direction of the electrode tab.

In some embodiments, the fourth active material layer 107 includes a seventh end 107a in the length direction of the electrode pad, the seventh end 107a is proximate to the overlap portion 105, and the seventh end 107a exceeds the sixth end 106a in the length direction of the electrode pad.

It is to be understood that, without departing from the spirit of the present application, it is possible to provide an insulating layer forming an overlapping portion with the active material layer at either end of the electrode sheet according to actual needs, for example, an insulating layer at an empty current collector portion where both ends (in the length direction of the positive electrode sheet) of both surfaces of the positive electrode current collector are joined to the positive electrode active material layer, or an insulating layer on one surface of the positive electrode current collector, without being limited thereto.

In some embodiments, the first active material has a particle diameter (Dv50, average particle diameter) reaching 50% by volume accumulation from the small particle diameter side in a range of 0.2 μm to 15 μm in a volume-based particle size distribution, while the first active material has a particle diameter (Dv90) reaching 90% by volume accumulation from the small particle diameter side in a range of 40 μm or less in a volume-based particle size distribution. When the first active material has a smaller Dv90, higher coverage and adhesion to the current collector 101 can be achieved. In some embodiments, the average particle size of the second active material (Dv 50): the first active material has an average particle diameter (Dv50) of 1: 1-40: 1. the smaller the particles of the first active material are, the thinner the thickness of the first active material layer can be made. For the measurement of the active substance particle size, the measurement can be carried out by means of a malvern particle size tester: dispersing the active substance in dispersant (ethanol or acetone, or other surfactant), and performing ultrasonic treatment for 30min, adding the sample into Malvern particle size tester, and starting the test.

In some embodiments, the thickness of the first active material layer 102 is 0.1 μm to 20 μm. In other embodiments, the thickness of the first active material layer 102 is 0.5 μm to 15 μm. In other embodiments, the thickness of the first active material layer 102 is 2 μm to 8 μm. In particular, the thickness of the first active material layer is not less than the particle size Dv90 of the first active material in order to ensure coverage of the first active material layer.

In some embodiments, the thickness of the insulating layer 104 is less than or equal to the sum of the thickness of the first active material layer 102 and the thickness of the second active material layer 103. In some embodiments, the thickness of the insulating layer 104 is greater than 0.1 μm to achieve a certain insulating effect. In other embodiments, the insulating layer 104 has a thickness of 1 μm to 30 μm. In other embodiments, the insulating layer 104 has a thickness of 5 μm to 15 μm.

In some embodiments, the density of the insulating layer 104 in the overlapping portion 105 is 60% to 90% of its density not in the overlapping portion. In some embodiments, the length of the first active material layer at the overlapping portion is less than the length of the non-overlapping portion, and the density of the first active material layer at the overlapping portion is similar to the density at the non-overlapping portion.

According to some embodiments of the present application, the insulating layer includes inorganic particles and/or polymers, and a suitable dispersant may also be added, including, but not limited to, ethanol or acetone, or other surfactants. The inorganic particles are selected from the group consisting of aluminum oxide, silicon dioxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium dioxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, barium sulfate, and combinations thereof; the polymer is selected from the group consisting of homopolymers of vinylidene fluoride, copolymers of hexafluoropropylene, polystyrene, polyphenylacetylene, sodium polyvinyl acid, potassium polyvinyl acid, polymethyl methacrylate, polyethylene, polypropylene, polytetrafluoroethylene, and combinations thereof.

In some embodiments, the electrode sheet is a positive electrode sheet, wherein the first active material and the second active material are each independently selected from the group consisting of lithium cobaltate, lithium iron phosphate, lithium manganese phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadyl phosphate, sodium vanadyl phosphate, lithium vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganese, lithium rich manganese based materials, lithium nickel cobalt aluminate, lithium titanate, and combinations thereof.

In some embodiments, the electrode sheet is a negative electrode sheet, wherein the first active material and the second active material are each independently selected from the group consisting of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon, silica compounds, silicon-carbon composites, tin alloys, niobium titanate, lithium titanate, and combinations thereof.

In some embodiments, first active material layer 102 and second active material layer 103 further comprise a binder including, but not limited to, one of polyvinylidene fluoride, copolymers of vinylidene fluoride-hexafluoropropylene, polyamides, polyacrylonitriles, polyacrylates, polyacrylic acids, polyacrylates, sodium carboxymethylcellulose, polyvinylpyrollidinone, polyvinyl ethers, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene butadiene rubber, and combinations thereof. The binder allows better adhesion of the active material layer to the current collector on the one hand, and on the other hand, the binder content is increased, the compacted density of the first active material layer 102 is lower, the binder content of the first active material layer 102 is 1.5% to 6% by total weight of the first active material layer 102, and the binder content of the second active material layer 103 is 0.5% to 4% by total weight of the second active material layer 103.

In some embodiments, the first active material layer 12 and the second active material layer 13 may further contain a certain amount of a conductive agent. The conductive agent includes, but is not limited to, one of carbon nanotubes, conductive carbon black, acetylene black, graphene, ketjen black, and carbon fibers, and combinations thereof. The content of the conductive agent in the first active material layer is 0.5% to 5% by total weight of the first active material layer, and the content of the conductive agent in the second active material layer is 0.5% to 5% by total weight of the second active material layer.

Further, some other treatment may be performed on the first active material layer 102 or the second active material layer 103, or some treatment may be performed on the current collector 101, such as roughness treatment, heat treatment, etc., and the action principle or action effect thereof may be to enhance the adhesion to the current collector, which is included in the scope of the present application, although not described in detail in the present application.

In some embodiments, the electrode plate is used as a positive electrode plate, the positive current collector thereof may be an aluminum foil or a nickel foil, the electrode plate is used as a negative electrode plate, and the negative current collector thereof may be a copper foil or a nickel foil, however, other positive current collectors and negative current collectors commonly used in the art may be used.

It is to be understood that the preparation method of the electrode sheet of the present application may adopt any suitable preparation method in the art without departing from the spirit of the present application, and is not limited thereto.

Some embodiments of the present application further provide an electrochemical device, including a positive electrode plate, a separator, and a negative electrode plate, wherein at least one of the positive electrode plate and the negative electrode plate is the electrode plate in the above embodiments.

In some embodiments, the release film includes, but is not limited to, at least one selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid. For example, the polyethylene includes at least one component selected from the group consisting of high density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect.

The surface of the separation film may further include a porous layer disposed on at least one surface of the separation film, the porous layer including inorganic particles selected from alumina (Al) and a binder₂O₃) Silicon oxide (SiO)₂) Magnesium oxide (MgO), titanium oxide (TiO)₂) Hafnium oxide (HfO)₂) Tin oxide (SnO)₂) Cerium oxide (CeO)₂) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)₂) Yttrium oxide (Y)₂O₃) Silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

The porous layer can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the positive pole piece or the negative pole piece.

The electrochemical device of the present application further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent.

In some embodiments herein, the lithium salt is selected from LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆One or more of LiBOB and lithium difluoroborate. For example, the lithium salt is LiPF₆Since it can give high ionic conductivity and improve cycle characteristics.

The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of the above chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), Propyl Propionate (PP), and combinations thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

Examples of the above carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, and combinations thereof.

Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

Examples of such other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

It is to be understood that the method of manufacturing the electrochemical device of the present application may employ any suitable method of manufacturing in the art without departing from the spirit of the present application, and is not limited thereto. In some embodiments, the electrochemical device employed is prepared as follows: and (3) winding or stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence to form an electrode assembly, then putting the electrode assembly into an aluminum plastic film, injecting electrolyte, forming and packaging to obtain the lithium ion battery.

Although some of the above exemplary embodiments are illustrated as lithium ion batteries, it will be understood by those skilled in the art after reading this application that specific examples of electrochemical devices of the present application can include all kinds of primary or secondary batteries without departing from the spirit of the present application. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Some embodiments of the present application further provide an electronic device comprising the electrochemical device of the embodiments of the present application.

The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, an electronic cigarette, an electronic vapor device, a wireless headset, a sweeping robot, an unmanned airplane, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large-sized household battery and a lithium ion capacitor, and the like.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Some specific examples and comparative examples are listed below and subjected to a battery capacity test, a battery nail penetration test, and a weight impact test, respectively, to better illustrate the present application. Those skilled in the art will appreciate that the preparation methods described herein are merely exemplary examples and that any other suitable preparation method is within the scope of the present application.

Test method

1.1 Battery Capacity test:

standing the formed lithium ion battery (electrochemical device) in an environment of 25 +/-3 ℃ for 30 minutes, charging the lithium ion battery to 4.4V (rated voltage) at a constant current of 0.5C, then stopping charging until the current reaches 0.05C, and placing the lithium ion battery to be tested for 30 minutes. And then discharging the lithium ion battery to 3.0V by 0.2C current, and placing the lithium ion battery to be tested for 30 minutes. And finally, taking and placing the electric capacity as the actual battery capacity of the lithium ion battery.

The lithium ion battery volumetric energy density is the actual battery capacity/(length × width × thickness of the lithium ion battery).

1.2 Battery nail penetration test:

10 lithium ion batteries after being formed into blocks are charged to a voltage of 4.4V at a constant current of 0.5C at normal temperature (25 +/-3 ℃), and further charged to a current of 0.05C at a constant voltage of 4.4V, so that the lithium ion batteries are in a full charge state of 4.4V. And then carrying out a nail penetration experiment on the lithium ion battery under the normal temperature condition, adopting a nail (steel nail, the material is carbon steel, the taper is 16.5mm, the total length of the steel nail is 100mm) with the diameter of 2.5mm, penetrating the nail at the nail penetration speed of 30mm/s, and observing whether the lithium ion battery produces smoke, fires or explodes or not on the basis that the taper of the steel nail penetrates through the lithium ion battery. And if not, the lithium ion battery is judged to pass the nail penetration test.

1.3 weight impact test

10 lithium ion batteries after being formed into blocks are charged to a voltage of 4.4V at a constant current of 0.5C at normal temperature (25 +/-3 ℃), and further charged to a current of 0.05C at a constant voltage of 4.4V, so that the lithium ion batteries are in a full charge state of 4.4V. Then, a weight impact experiment is carried out on the lithium ion battery under the normal temperature condition, an impact piece (bar material, the total weight is 9.1kg) with the diameter of 15.8mm is adopted, the impact piece is dropped at the position which is 61cm away from the lithium ion battery to impact the lithium ion battery, and whether the lithium ion battery produces smoke, fires or explodes is observed. And if not, the lithium ion battery is judged to pass the weight impact test.

Example 1

An aluminum foil is used as a positive electrode current collector, and a layer of first positive electrode active material layer slurry is uniformly coated on one surface of the aluminum foil and comprises a first positive electrode active material (wherein the granularity of lithium iron phosphate is Dv 50: 3 μm, and Dv 90: 10 μm). The first positive electrode active material layer slurry is composed of 95.8 wt% of lithium iron phosphate, 2.8 wt% of polyvinylidene fluoride and 1.4 wt% of conductive carbon black, and is dried at the temperature of 85 ℃ to form a first positive electrode active material layer; then coating a layer of insulating layer slurry on the empty current collector part connected with the first positive electrode active material layer and the part on the first positive electrode active material layer along one end of the positive electrode piece in the length direction, wherein the insulating layer slurry comprises 98 wt% of alumina and 2 wt% of polyvinylidene fluoride, and drying at 85 ℃ to form an insulating layer with the thickness of 10 mu m, wherein the length of the overlapping part formed by covering the first positive electrode active material layer by the insulating layer in the length direction of the positive electrode piece is 2 mm; then, continuously coating a layer of second positive electrode active material layer slurry on the dried first positive electrode active material layer, wherein the second positive electrode active material layer slurry consists of 97.8 wt% of lithium cobaltate (the granularity of the lithium cobaltate is Dv 50: 13 μm, Dv 90: 38 μm), 0.8 wt% of polyvinylidene fluoride and 1.4 wt% of conductive carbon black, and drying at 85 ℃ to form a second positive electrode active material layer, wherein in the length direction of the positive electrode piece, the fifth end edge of the second positive electrode active material layer is positioned on the non-overlapping part of the insulating layer (namely, extends beyond the first end edge of the first positive electrode active material layer), and the length of the second positive electrode active material layer extending beyond the overlapping part is 1 mm; preparing a third positive electrode active material layer and a fourth positive electrode active material layer on the other surface of the positive electrode current collector according to a graph 8, wherein the composition of the third positive electrode active material layer is the same as that of the first active material layer, the composition of the second positive electrode active material layer is the same as that of the fourth positive electrode active material layer, then carrying out cold pressing on the positive electrode piece, wherein the cold pressing pressure is 60T, the cold pressing speed is 40m/min, and after cutting and slitting, drying for 4 hours under the vacuum condition of 85 ℃ to prepare the positive electrode piece. Wherein the first positive electrode active material layer and the third active material layer have a thickness of 8 μm, the insulating layer has a thickness of 10 μm, and the second positive electrode active material layer and the fourth active material layer have a thickness of 50 μm. Fig. 8 is a schematic structural diagram of the positive electrode tab of example 1, and please refer to fig. 8 for the arrangement relationship of the positive electrode current collector 201, the first positive electrode active material layer 202, the second positive electrode active material layer 203 and the insulating layer 204 in the positive electrode tab of example 1.

The copper foil is used as a negative current collector, a layer of graphite slurry is uniformly coated on the surface of the copper foil, the slurry is composed of 97.7 wt% of artificial graphite, 1.3 wt% of sodium carboxymethyl cellulose and 1.0 wt% of styrene butadiene rubber, the artificial graphite, the 1.3 wt% of sodium carboxymethyl cellulose and the 1.0 wt% of styrene butadiene rubber are dried at 85 ℃, and then cold pressing, cutting into pieces and slitting are carried out, so that the negative pole piece is prepared.

Lithium salt LiPF₆And a nonaqueous organic solvent (ethylene carbonate: diethyl carbonate: propylene carbonate: propyl propionate: vinylene carbonate: 20:30:20:28:2, mass ratio) in a mass ratio of 8: 92 as the electrolyte of the lithium ion battery.

And winding the positive pole piece and the negative pole piece, and separating the positive pole piece and the negative pole piece by a polyethylene isolating film to prepare a wound electrode assembly, and then putting the wound electrode assembly into a shell and injecting electrolyte. And carrying out vacuum packaging, standing, formation, shaping and other processes to obtain the finished product of the lithium ion battery.

Examples 2 to 6

The same preparation method as that of example 1, except that the lengths of the overlapping portions of the first positive electrode active material layer and the insulating layer in the length direction of the positive electrode sheet in examples 2 to 6 are different, refer to table 1 specifically.

Example 7

The same as in example 1 except that in example 7, in the length direction of the positive electrode sheet, the fifth end edge of the second positive electrode active material layer was located on the overlapping portion (i.e., between the first end edge of the first positive electrode active material layer and the third end edge of the insulating layer), and the length of the overlapping portion covered with the second positive electrode active material layer was 1 mm. Fig. 9 is a schematic structural diagram of the positive electrode tab of example 7, and please refer to fig. 9 for an arrangement relationship of the positive electrode current collector 301, the first positive electrode active material layer 302, the second positive electrode active material layer 303 and the insulating layer 304 in the positive electrode tab of example 7.

Example 8

The same as in example 1 except that in example 8, the fifth end edge of the second positive electrode active material layer was flush with the third end edge of the insulating layer in the length direction of the positive electrode tab (i.e., the second positive electrode active material layer overlapped with the overlapping portion), and the second positive electrode active material layer was spaced from the overlapping portion by a distance of 0 mm. Fig. 10 is a schematic structural diagram of the positive electrode tab of example 8, and please refer to fig. 10 for an arrangement relationship of the positive electrode collector 401, the first positive electrode active material layer 402, the second positive electrode active material layer 403, and the insulating layer 404 in the positive electrode tab of example 8.

Example 9

The preparation method is the same as that of the embodiment 1, except that in the embodiment 9, a layer of insulating layer slurry is uniformly coated on the surface of the aluminum foil; and then coating a layer of first positive electrode active material layer slurry on the empty current collector part and the part on the insulating layer, wherein one end of the positive electrode plate in the length direction is connected with the insulating layer, the length of an overlapped part formed by the first positive electrode active material layer covering the insulating layer in the length direction of the positive electrode plate is 2mm, the thickness of the first positive electrode active material layer is 10 microns, and the thickness of the insulating layer is 8 microns. Fig. 11 is a schematic structural diagram of the positive electrode tab of example 9, and please refer to fig. 11 for an arrangement relationship of the positive electrode collector 501, the first positive electrode active material layer 502, the second positive electrode active material layer 503 and the insulating layer 504 in the positive electrode tab of example 9.

Example 10

The same procedure as in example 9 was repeated, except that in example 10, the length of the second positive electrode active material layer extending beyond the overlapping portion in the longitudinal direction of the positive electrode tab was 3 mm.

Example 11

The same preparation method as in example 9 was repeated, except that in example 11, the fifth end edge of the second positive electrode active material layer was located on the overlapped portion (i.e., between the first end edge of the first positive electrode active material layer and the third end edge of the insulating layer) in the length direction of the positive electrode tab, and the length of the overlapped portion covered with the second positive electrode active material layer was 1 mm. Fig. 12 is a schematic structural diagram of the positive electrode tab of example 11, and please refer to fig. 12 for an arrangement relationship of the positive electrode collector 601, the first positive electrode active material layer 602, the second positive electrode active material layer 603, and the insulating layer 604 in the positive electrode tab of example 11.

Example 12

The same production method as in example 9 was conducted except that in example 12, the fifth end edge of the second positive electrode active material layer was flush with the third end edge of the insulating layer in the length direction of the positive electrode sheet (i.e., the second positive electrode active material layer overlapped with the overlapping portion), and the second positive electrode active material layer was spaced from the overlapping portion by a distance of 0 mm. Fig. 13 is a schematic structural diagram of the positive electrode tab of example 12, and please refer to fig. 13 for an arrangement relationship of the positive electrode collector 701, the first positive electrode active material layer 702, the second positive electrode active material layer 703 and the insulating layer 704 in the positive electrode tab of example 12.

Example 13

The same preparation method as that of example 1 was followed except that an insulating layer structure similar to that of example 1 was provided on both side surfaces of the positive electrode collector in example 13. Fig. 14 is a schematic structural diagram of the positive electrode tab of example 13, and please refer to fig. 14 for the arrangement relationship among the positive electrode current collector 801, the first positive electrode active material layer 802, the second positive electrode active material layer 803, and the insulating layer 804 in the positive electrode tab of example 13.

Comparative example 1

The same preparation method as that of example 1 except that in comparative example 1, insulating layer slurry was applied to a position spaced 3mm apart from the first positive electrode active material layer at one end in the length direction of the positive electrode tab, wherein the distance between the third end of the insulating layer after formation and the first end of the first positive electrode active material layer was 3 mm; and then continuously coating a layer of second positive electrode active material layer slurry on the dried first positive electrode active material layer and the part of the empty current collector part at the interval between the first positive electrode active material layer and the insulating layer, and drying to form a second positive electrode active material layer, wherein in the length direction of the positive electrode piece, the fifth end edge of the second positive electrode active material layer is positioned on the empty current collector part at the interval between the first positive electrode active material layer and the insulating layer, and the distance between the fifth end edge and the insulating layer is 2 mm.

After the lithium ion battery finished products of the above examples and comparative examples are finished, the capacity, thickness, width and length of the finished products are recorded to determine the volume energy density of the lithium ion battery. Then, the lithium ion battery finished products of the above examples and comparative examples were subjected to a battery capacity test, a battery nail penetration test, and a weight impact test.

Experimental parameters and measurement results for the respective examples and comparative examples are shown in table 1 below.

TABLE 1

As shown in table 1 above, the overlapping portion that this application's electrode piece set up the overlap can effectual promotion piercing pin percent of pass and the heavy object impact rate of pass of heavy object impact test through first active material layer and insulating layer, and then increases electrochemical device's security performance to there is not much influence to its energy density basically.

As is clear from comparison of comparative example 1 and example 1, when there is a gap between the insulating layer and the first active material layer, the weight impact passage rate of the lithium ion battery is greatly reduced, and the nail penetration rate of the lithium ion battery is slightly reduced. For example, in the lithium ion battery of comparative example 1, since the positive electrode current collector which is not protected by the layer having a high resistivity is present between the insulating layer and the first positive electrode active material layer, the positive electrode current collector is likely to contact the negative electrode active material layer when being impacted by a heavy object, and causes a short circuit in the lithium ion battery.

As can be seen from comparative examples 1 to 6, as the overlapping portion of the insulating layer and the first active material layer is enlarged, the weight impact passage rate of the lithium ion battery is also increased. However, the enlargement of the overlapping portion also causes a reduction in the energy density of the lithium ion battery.

As can be seen from comparison of examples 1, 7 and 8, the arrangement relationship between the second active material layer and the first active material layer and the insulating layer has a certain effect on the weight impact passage rate of the lithium ion battery, and when the second active material layer extends to cover the overlapping portion and/or exceeds the overlapping portion, the lithium ion battery has a higher weight impact passage rate. In addition, the extension and covering of the second active material layer on the overlapping portion or the insulating layer can slightly increase the energy density of the lithium ion battery.

As is clear from comparison between example 1 and example 9, covering the insulating layer with the first positive electrode active material layer in the overlapping portion can have a high weight impact passage rate. Meanwhile, as can be seen from comparative examples 9 to 12, when the fifth end of the second positive electrode active material layer covers the end portion of the first end of the first positive electrode active material layer, the first end 102a is less likely to come off, and thus the nail penetration rate and the weight impact rate are better.

Through the comparison of the above embodiments, it can be clearly understood that the electrode sheet of the present application can effectively improve the safety performance of the electrochemical device thereof, and reduce the influence on the energy density.

Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrode sheet, comprising:

a current collector comprising a first surface;

a first active material layer including a first active material;

a second active material layer including a second active material; and

an insulating layer;

wherein the first active material layer is disposed between the current collector and the second active material layer and covers a first portion of the first surface of the current collector, the insulating layer covers a second portion of the first surface of the current collector different from the first portion, the first active material layer includes a first end and a second end, the insulating layer includes a third end and a fourth end, and the first end and the third end are stacked on each other to form an overlapping portion in a length direction of the electrode tab.

2. The electrode tab of claim 1 wherein the distance between the edge of the first end in the length direction of the electrode tab and the edge of the third end in the length direction of the electrode tab is less than or equal to 20 mm.

3. The electrode tab of claim 1, wherein the first end is disposed between the third end and the current collector in a thickness direction of the electrode tab.

4. The electrode tab of claim 1, wherein the third end is disposed between the first end and the current collector in a thickness direction of the electrode tab.

5. The electrode pad of any one of claims 1-4, wherein the second active material layer comprises a fifth end in the length direction of the electrode pad.

6. The electrode pole piece according to claim 5, wherein the edge of the fifth end in the length direction of the electrode pole piece is flush with the edge of the third end in the length direction of the electrode pole piece.

7. The electrode pole piece according to claim 5, wherein the edge of the fifth end in the length direction of the electrode pole piece is located between the edge of the first end in the length direction of the electrode pole piece and the edge of the third end in the length direction of the electrode pole piece.

8. The electrode pole piece according to claim 5, wherein the edge of the first end in the length direction of the electrode pole piece is located between the edge of the third end in the length direction of the electrode pole piece and the edge of the fifth end in the length direction of the electrode pole piece.

9. The electrode tab of claim 8 wherein the distance between the edge of the first end in the length direction of the electrode tab and the edge of the fifth end in the length direction of the electrode tab is less than or equal to 3 mm.

10. The electrode tab of claim 1, further comprising a third active material layer and a fourth active material layer, wherein the current collector further comprises a second surface, and wherein the third active material layer is disposed between the current collector and the fourth active material layer and covers the second surface of the current collector.

11. The electrode tab of claim 10, wherein the third active material layer comprises a sixth end in the length direction of the electrode tab, and the edge of the sixth end in the length direction of the electrode tab is located between the edge of the first end in the length direction of the electrode tab and the edge of the fourth end in the length direction of the electrode tab.

12. The electrode tab according to claim 11, wherein the fourth active material layer includes a seventh end in a length direction of the electrode tab, the seventh end exceeding the sixth end in the length direction of the electrode tab.

13. The electrode tab of claim 1, wherein the density of the insulating layer in the overlapping portion is 60% to 90% of the density of the insulating layer not in the overlapping portion.

14. The electrode sheet according to claim 1, wherein the first active material and the second active material are each independently lithium cobaltate, lithium iron phosphate, lithium manganese phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadyl phosphate, sodium vanadyl phosphate, lithium vanadyl vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganese, lithium rich manganese based material, lithium nickel cobalt aluminate, or lithium titanate.

15. The electrode sheet according to claim 1, wherein the first active material and the second active material are each independently artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon-oxygen compounds, silicon-carbon composites, tin alloys, niobium titanate, or lithium titanate.

16. The electrode sheet of claim 1, wherein the first active material layer and the second active material layer each further comprise a binder and a conductive agent, the binder being polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, or styrene-butadiene rubber, and

the conductive agent is carbon nano tube, conductive carbon black, acetylene black, graphene, ketjen black or carbon fiber.

17. The electrode sheet according to claim 1, wherein the insulating layer comprises inorganic particles and/or polymers, wherein the inorganic particles are aluminum oxide, silicon dioxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium dioxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate,

the polymer is a homopolymer of vinylidene fluoride, a copolymer of hexafluoropropylene, polystyrene, polyphenylacetylene, sodium polyvinyl acid, potassium polyvinyl acid, polymethyl methacrylate, polyethylene, polypropylene or polytetrafluoroethylene.

18. An electrochemical device comprising a positive electrode plate, a separator and a negative electrode plate, wherein the positive electrode plate and/or the negative electrode plate is the electrode plate of claims 1 to 17.

19. An electronic device comprising the electrochemical device according to claim 18.