CN114497559A

CN114497559A - Electrochemical device and electricity utilization device

Info

Publication number: CN114497559A
Application number: CN202111624928.3A
Authority: CN
Inventors: 温兆冬
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-12-28
Filing date: 2021-12-28
Publication date: 2022-05-13

Abstract

The present invention relates to an electrochemical device and an electric device. The electrochemical device includes a pole piece, the pole piece including: a current collector; the bonding layer is arranged on the current collector, and the bonding strength between the bonding layer and the current collector is more than or equal to 38N/m; the active layer is arranged on the surface of the bonding layer, which is far away from the current collector, and contains active materials; the resistance layer is arranged on the surface of the active layer, which is far away from the bonding layer; wherein, the bending-resistant times of the pole piece are more than or equal to 4. The electrochemical device can improve the safety of the electrochemical device on the basis of ensuring better discharge rate.

Description

Electrochemical device and electricity utilization device

Technical Field

The invention relates to the technical field of batteries, in particular to an electrochemical device and an electric device.

Background

As the market demand for high energy density and fast charge batteries increases, the challenge of battery safety becomes more severe. The reports of smoke, fire and even explosion accidents of battery-using electric devices such as mobile phones, computers, electric vehicles, electric automobiles and the like are frequently repeated, so that serious hidden dangers are brought to the safety of users, and the safety of batteries is more and more valued by people. Research shows that some accident causes are that the battery is damaged by external force to cause internal short circuit, the temperature of the battery is increased due to Joule heat generated by the short circuit, the thermochemical reaction of electrode materials is accelerated, the battery is out of control due to heat when serious, and finally a safety accident is caused.

Currently, approaches for improving the safety of batteries such as lithium ion batteries and the like mostly reduce the risk of short circuits caused by surface contact. However, in practical applications of electrochemical devices such as batteries, short circuits are still discovered, which further causes thermal runaway of electrochemical devices such as batteries, thereby causing safety problems.

Disclosure of Invention

Accordingly, there is a need for an electrochemical device and an electric device capable of improving safety while ensuring a high discharge rate.

In a first aspect of the present invention, an electrochemical device is provided, which includes a pole piece, wherein the pole piece includes a current collector, a bonding layer, an active layer, and a resistance layer;

the bonding layer is arranged on the current collector, and the bonding strength between the bonding layer and the current collector is more than or equal to 38N/m;

the active layer is arranged on the surface, away from the current collector, of the bonding layer, and contains active materials;

the resistance layer is arranged on the surface of the active layer, which is far away from the bonding layer; and the bending resistant times of the pole piece are more than or equal to 4.

In some embodiments, the adhesive layer, the active layer and the resistive layer have thicknesses of 1% to 6%, 88% to 98% and 1% to 6%, respectively, in the total thickness of the adhesive layer, the active layer and the resistive layer.

In some of these embodiments, the resistance of the resistive layer is 80% to 98% of the total resistance of the pole piece.

In some of the embodiments, the bonding layer contains a first binder and a first conductive agent;

the first binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyacrylic acid, polyacrylate, polyacrylonitrile, sodium carboxymethylcellulose, styrene butadiene rubber, polyurethane, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan, and the mass content of the first binder in the bonding layer is 1-60%.

In some of these embodiments, the active layer comprises an active material, a second binder, and a second conductive agent;

the second binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyacrylic acid, polyacrylate, polyacrylonitrile, sodium carboxymethylcellulose, styrene butadiene rubber and polyurethane, and the mass content of the second binder in the active layer is more than 0% and less than or equal to 1%.

In some embodiments, the resistive layer includes an inorganic resistive material and a third binder, and the inorganic resistive material in the resistive layer is 93% to 97% by mass.

In some of these embodiments, the inorganic resistive material is selected from at least one of boehmite, alumina, magnesia, silica, titania, and magnesium hydroxide; and/or

The third binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyacrylic acid, polyacrylate, polyacrylonitrile, sodium carboxymethylcellulose, styrene butadiene rubber and polyurethane.

In some embodiments, the resistive layer further contains a third conductive agent, and a mass content of the third conductive agent in the resistive layer is greater than 0% and equal to or less than 4%.

In some of these embodiments, the active material in the active layer is a positive electrode active material or a negative electrode active material.

In a second aspect of the present invention, there is provided an electric device comprising the electrochemical device of the second aspect of the present invention.

According to the electrochemical device, the pole piece comprises the current collector, and the bonding layer, the active layer and the resistance layer which are stacked are sequentially formed on the surface of the current collector, so that the bonding strength between the bonding layer and the current collector and the overall bending resistance of the pole piece are optimized within a specific range. The electrochemical device is considered from at least three short circuit ways of short circuit participation of a current collector on the surface of a pole piece, electric core fracture short circuit and positive and negative contact short circuit, and further comprehensive control is realized from three dimensions of bonding strength, flexibility and resistance performance of the pole piece, so that the effect of each coating of the pole piece is synergistic, and further on the basis of ensuring the better discharge rate of the electrochemical device, the probability of short circuit occurrence is reduced, meanwhile, the passing rate of the electric core after external force damage is also improved, the firing probability is reduced, the danger degree after short circuit occurrence is further reduced, and therefore the safety of the electrochemical device is improved comprehensively.

Drawings

FIG. 1 is a schematic view of a pole piece structure of an electrochemical device according to an embodiment of the present invention;

FIG. 2 is a schematic view of a structure of a pole piece in an electrochemical device according to another embodiment of the present invention;

FIG. 3 is a SEM image of the cross section of the positive electrode sheet obtained in example 15;

fig. 4 is an SEM image of the positive electrode tab near the positive current collector area prepared in example 15;

FIG. 5 is an SEM image of the area of the resistive layer near the positive electrode sheet of example 15;

fig. 6 is an SEM image of the peeled surface of the positive electrode active layer of the positive electrode sheet obtained in example 15.

Description of the reference numerals:

10. pole pieces; 110. a current collector; 120. a bonding layer; 130. an active layer; 140. a resistive layer.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is to be understood that these embodiments are provided so that this disclosure will be thorough and complete.

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 invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

Based on the above technical problems, the skilled person of the present invention finds that if a resistive layer or a high adhesion layer is added to the pole piece structure of the pole piece, although the short circuit resistance of the diaphragm can be improved or the current collector can be prevented from participating in short circuit, these methods can only improve the short circuit caused by surface contact. The method has the advantage that the method cannot play a remarkable improvement role in the condition that the current collector with an exposed fracture is overlapped with electrode scraps due to the fact that the fracture and the electrode material scraps appear in the battery after the battery is damaged by external force. Practical application shows that dangerous short circuit points still can be generated at the moment, thermal runaway of the battery is caused, and safety problems are caused.

In order to solve the problem of how to improve the safety of electrochemical devices such as batteries on the basis of ensuring a good discharge rate, an embodiment of the present invention provides an electrochemical device. Referring to fig. 1, the electrochemical device includes a pole piece 10, where the pole piece 10 includes a current collector 110, a bonding layer 120, an active layer 130, and a resistance layer 140. The bonding layer 120 is arranged on the current collector 110, and the bonding strength between the bonding layer 120 and the current collector 110 is more than or equal to 38N/m. In some examples, the bond strength between the bonding layer 120 and the current collector 110 is ≧ 40N/m. The active layer 130 is disposed on a surface of the bonding layer 120 facing away from the current collector 110. The active layer 130 contains an active material. The resistive layer 140 is disposed on a surface of the active layer 130 facing away from the adhesive layer 120. Wherein, the bending-resistant times of the pole piece 10 are more than or equal to 4.

In the electrochemical device, the electrode sheet 10 includes the current collector 110, and the adhesive layer 120, the active layer 130 and the resistance layer 140 are sequentially formed on the surface of the current collector 110 in a stacked manner, and the adhesive strength between the adhesive layer 120 and the current collector 110 and the bending resistance of the entire electrode sheet 10 are optimized within a specific range. The electrochemical device is considered from at least three short circuit ways of short circuit participation of the current collector 110 on the surface of the pole piece 10, short circuit of a fracture of a cell fracture and short circuit of positive and negative electrode contact, and further comprehensive control of three dimensions of bonding strength, flexibility and resistance performance of the pole piece 10 is realized, so that the effect of each coating of the pole piece is synergistic, and further on the basis of ensuring better discharge rate of the electrochemical device, the probability of short circuit occurrence is reduced, meanwhile, the passing rate of the electrochemical device after external force damage is improved, the firing probability is reduced, further, the danger degree after short circuit occurrence is reduced, and therefore the safety of the electrochemical device is improved comprehensively.

In some embodiments, the thicknesses of the adhesive layer 120, the active layer 130 and the resistive layer 140 are 1% to 6%, 88% to 98% and 1% to 6%, respectively, of the total thickness of the adhesive layer 120, the active layer 130 and the resistive layer 140. Thus, the bonding strength between the bonding layer 120 and the current collector 110, the thickness ratio of each layer, and the bending resistance of the whole pole piece 10 are optimized within a specific range.

In some of these embodiments, the resistance of the resistive layer 140 is 80% to 98% of the total resistance of the pole piece 10. In this way, the adhesion strength between the adhesive layer 120 and the current collector 110, the resistance ratio of the resistance layer 140, and the bending resistance of the entire electrode sheet 10 are optimized within a specific range.

Further, in some examples, the adhesion strength between the adhesive layer 120 and the current collector 110, the thickness ratio of each layer, the resistance ratio of the resistive layer 140, and the bending resistance of the entire electrode sheet 10 may be optimized within the above specific ranges.

It is understood that the above-described electrode sheet 10 can be applied to a positive electrode sheet or a negative electrode sheet. In other words, the electrode plate 10 may be a positive electrode plate or a negative electrode plate.

It is understood that the adhesive layer 120, the active layer 130, and the resistive layer 140 each include a binder, and each binder is independently selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (ptfe), polypropylene (PP), polyacrylic acid (PAA), polyacrylate, polyacrylonitrile, sodium carboxymethyl cellulose, styrene butadiene rubber (sbr), polyurethane, sodium Polyacrylate (PAAs), Polyacrylamide (PAM), polyvinyl alcohol (PVA), Sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan.

Further, the adhesive layer 120 contains a first adhesive and a first conductive agent. The first binder is at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (ptfe), polypropylene (PP), polyacrylic acid (PAA), polyacrylate, polyacrylonitrile, sodium carboxymethylcellulose, styrene butadiene rubber, and polyurethane, and the mass content of the first binder in the adhesive layer 120 is 1% to 60%, and more preferably 3% to 60%.

Further, the first binder is at least one of polypropylene, polyacrylic acid, polyacrylate and polyacrylonitrile, and the mass content of the first binder in the adhesive layer 120 is 1% to 60%.

The first binder in the adhesive layer 120 is controlled to be higher in content or selected to have higher adhesive property, such as at least one of polypropylene, polyacrylic acid, polyacrylate and polyacrylonitrile, so as to meet the requirement of high adhesive strength with the current collector 110.

Further, the active layer 130 contains an active material, a second binder, and a second conductive agent. The second binder is at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (ptfe), polypropylene (PP), polyacrylic acid (PAA), polyacrylate, polyacrylonitrile, sodium carboxymethylcellulose, styrene butadiene rubber, and polyurethane, and the mass content of the second binder in the active layer 130 is greater than 0% and not more than 1%, and more preferably greater than 0% and not more than 0.5%.

Further, the second binder is at least one of polypropylene and polytetrafluoroethylene, and the mass content of the second binder in the active layer 130 is greater than 0% and not greater than 1%.

The content of the second binder in the active layer 130 is controlled to be lower or the binder with higher flexibility is selected, such as at least one of polypropylene and polytetrafluoroethylene, to meet the flexibility requirement of the pole piece.

Further, the resistive layer 140 contains an inorganic resistive material and a third binder. The mass content of the inorganic resistance material in the resistance layer 140 is 93% to 97%. The ratio of the inorganic resistive material in the resistive layer 140 is controlled, so that the resistive layer 140 satisfies the requirement of high resistance performance.

In the pole piece 10, the bonding layer 120, the active layer 130 and the resistance layer 140 are sequentially formed on the surface of the current collector 110 in a stacked manner, and the bonding layer 120 is formed by using the first binder with higher content or higher bonding performance, so that the bonding performance between the pole piece and the current collector 110 is enhanced, the pole piece is prevented from being damaged to expose the surface of the current collector 110, and thus dangerous short circuit, such as aluminum-negative short circuit, formed by exposing the current collector 110 on the surface can be prevented; the active material layer is formed by the second binder with lower content or higher flexibility and the active material, so that the active layer 130 is endowed with excellent flexibility, the deformation force of the pole piece for resisting external force damage is increased, the pole piece cracks caused by stress concentration and electrode scraps generated are reduced, and the dangerous short circuit caused by the lap joint of the scraps at the fracture after the electric core is fractured is avoided; the proportion of the inorganic resistance material in the resistance layer 140 is controlled to improve the short-circuit resistance of the pole piece, thereby reducing joule heat generated by the positive-negative short circuit, reducing the danger degree of the positive-negative short circuit, and avoiding thermal runaway of the battery core. On the basis, the thickness ratio of each coating is controlled simultaneously, and then the thickness ratio of each coating is controlled, so that the effect of each coating is synergistic, the probability of section short circuit is further reduced on the basis of improving the surface short circuit and ensuring better discharge rate, and the safety performance of the electrochemical device is improved.

The electrochemical device with the pole piece 10 can reduce the probability and the danger degree of short circuit caused by external force damage, and can obviously improve the safety performance of the electrochemical device.

Understandably, in the total thickness of the adhesive layer 120, the active layer 130 and the resistive layer 140, the thickness of the adhesive layer 120 and the resistive layer 140 may be 1%, 1.5%, 1.8%, 1.9%, 2%, 3%, 4%, 5% or 6%; the thickness of the active layer 130 may be 88%, 88.4%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%. Further, in the total thickness of the adhesive layer 120, the active layer 130 and the resistive layer 140, the thicknesses of the adhesive layer 120, the active layer 130 and the resistive layer 140 account for 1.9% to 5.8%, 88.4% to 96.2% and 1.9% to 5.8%, respectively.

Further, the thickness of the adhesive layer 120 is 1 to 3 μm, the thickness of the active layer 130 is 48 μm, and the thickness of the resistive layer 140 is 1 to 3 μm.

Further, in some examples, the adhesive layer 120 may contain one of an active material and an inorganic resistive material. It is understood that the active and inactive materials in the adhesive layer 120 may also be omitted.

It can be appreciated that the active layer 130 has better flexibility. In some embodiments, the active layer 130 satisfies the cold-pressed pole piece flexibility and enables the number of cracks occurring in the pole piece during bending to be greater than or equal to 4.

In some embodiments, the total resistance of the adhesive layer 120, the active layer 130, and the resistive layer 140 is 2 Ω to 16 Ω, and further 2 Ω to 15 Ω; the area of the corresponding pole piece is 1.54cm²The total thickness of the pole piece is 110 μm.

Further, in the total resistance of the pole piece 10, the resistance of the resistance layer 140 is 80% to 98% of the total resistance, and the sum of the resistances of the bonding layer 120 and the active layer 130 is 2% to 20% of the total resistance.

It is understood that the resistance of the resistive layer 140 is 80%, 81%, 83%, 85%, 88%, 90%, 92%, 93%, 95%, 96%, 97%, 98% of the total resistance of the pole piece 10.

Further, in the total resistance of the electrode sheet 10, the resistance of the resistance layer 140 is 90% to 98% of the total resistance, and the sum of the resistances of the bonding layer 120 and the active layer 130 is 2% to 10% of the total resistance.

Further, the resistance of the resistance layer 140 is 92% to 98% of the total resistance of the pole piece 10.

Each of the above-mentioned inorganic resistive materials is independently selected from at least one of boehmite, alumina, magnesia, silica, titania and magnesium hydroxide. These inorganic resistive materials, which have high resistance properties, are preferably used for the resistive layer 140.

Further, the resistive layer 140 may contain one of an active material and a conductive agent. It is understood that the active material and the conductive agent in the resistive layer 140 may also be omitted. Furthermore, if the resistive layer 140 contains a conductive agent, the mass content of the conductive agent in the resistive layer 140 can be controlled to be less than or equal to 4%. This ensures high resistance performance of the resistive layer 140.

In some embodiments, the electrochemical device comprises a positive electrode sheet and a negative electrode sheet. Wherein at least one of the positive pole piece and the negative pole piece adopts any pole piece of the invention. In other words, the electrode sheet may be at least one of a positive electrode sheet and a negative electrode sheet in an electrochemical device.

When the electrode plate 10 is a positive electrode plate, the active material mentioned above corresponds to a positive electrode active material, and each of the active materials is independently selected from at least one of lithium cobaltate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, lithium nickelate, lithium manganese oxide, and lithium nickel cobalt aluminate.

When the electrode sheet 10 is a negative electrode sheet, the above-mentioned active material corresponds to a negative electrode active material, and for example, it may be each independently selected from graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like.

It is understood that when only one of the positive electrode plate and the negative electrode plate adopts any of the electrode plates of the present invention, the other electrode plate can adopt a negative electrode plate with other structure, such as a negative electrode plate commonly used in the art. It can be understood that the pole piece with the structure can be adopted by both the positive pole piece and the negative pole piece.

In some of these embodiments, only the positive pole piece employs the pole pieces of the present invention described above. The negative electrode sheet may be a negative electrode sheet commonly used in the art, for example, the negative electrode sheet includes a negative electrode current collector and an active layer disposed on at least one surface of the negative electrode current collector, the active layer containing a negative electrode active material. And vice versa.

In some of the embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used.

Each of the above-mentioned conductive agents is independently selected from at least one of conductive carbon black, carbon nanotubes, carbon fibers, conductive graphite, graphene acetylene black, and ketjen black.

It is understood that the adhesive layer 120, the active layer 130, and the resistive layer 140 may be formed on one surface or both surfaces of the current collector 110. Referring to fig. 2, the bonding layer 120, the active layer 130 and the resistive layer 140 are stacked on two opposite surfaces of the electrode sheet 10.

In some embodiments, the electrochemical device further includes an electrolyte disposed between the positive electrode tab and the negative electrode tab. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece.

In some examples, the electrochemical device is a battery such as a lithium ion battery.

In some embodiments, a separator is also included in the electrochemical device. The diaphragm is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.

Further, the material of the separator may be at least one selected from the group consisting of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some of these embodiments, the electrolyte may be liquid, gel, or all solid. The kind of the electrolyte is not particularly limited in the present invention, and may be selected according to the need.

In some of these embodiments, the electrolyte includes an electrolyte salt and a solvent.

Further, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate.

Further, the solvent may be selected from at least one of ethylene carbonate, vinylene carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, propyl methyl carbonate, propyl ethyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

Further, the electrolyte may optionally include additives.

The invention further provides a preparation method of the pole piece, which comprises the following steps of S10-S30.

Step S10: the adhesive layer is formed on the current collector.

Step S20: an active layer is formed on a surface of the bonding layer facing away from the current collector.

Step S30: a resistive layer is formed on a surface of the active layer facing away from the adhesive layer.

It is understood that the adhesive layer, the active layer and the resistive layer can be formed by coating the respective pastes. Dispersing the component materials corresponding to each layer in a solvent (e.g., water or an organic solvent) to form a slurry; coating the slurry, and drying, cold pressing and the like.

It is understood that the coating described in the present invention includes, but is not limited to, print coating, knife coating, spin coating, or inkjet coating.

Further, the solvent may be selected from at least one of N-methylpyrrolidone (NMP), N-dimethylformamide, ethanol, ethylene glycol, methanol and isopropanol. It is understood that after each coating step, a drying step is also included.

Further, after the resistance layer is formed, the steps of cold pressing and baking the obtained pole piece are also included in sequence.

In another embodiment of the present invention, an electric device is provided, which includes the electrochemical device of the present invention.

Further, the powered device may be a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

In order to make the objects, technical solutions and advantages of the present invention more concise and clearer, the present invention is described with reference to the following specific embodiments, but the present invention is by no means limited to these embodiments. The following described examples are only preferred embodiments of the present invention, which can be used to describe the present invention and should not be construed as limiting the scope of the present invention. It should be understood that any modifications, equivalents, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

In order to better illustrate the invention, the following examples are given to further illustrate the invention. The following are specific examples.

Example 1

The aluminum foil is used as a positive current collector, a layer of slurry containing lithium iron phosphate is uniformly coated on the surface of the aluminum foil, the solvent-removing lithium iron phosphate slurry comprises 95 wt% of lithium iron phosphate (LFP), 3 wt% of polyvinylidene fluoride (PVDF) and 2 wt% of conductive carbon black (SP), and the bonding layer is prepared by drying at 85 ℃.

And continuously and uniformly coating a layer of lithium cobaltate slurry on the bonding layer, wherein the solvent-removing lithium cobaltate slurry comprises 98 wt% of Lithium Cobaltate (LCO), 0.5 wt% of polyvinylidene fluoride (PVDF) and 1.5 wt% of conductive carbon black (SP), and drying at 85 ℃ to obtain the active layer.

Continuously and uniformly coating a layer of alumina slurry on the active layer, wherein the alumina slurry except the solvent has the composition of 97 wt% of alumina (Al)₂O₃) And 3 wt% of polyvinylidene fluoride (PVDF), and drying at 85 ℃ to prepare a resistance layer and obtain the positive pole piece.

And then, carrying out cold pressing, slitting and cutting, and baking for 12h at 85 ℃ under a vacuum condition to prepare the positive pole piece (shown in figure 1). Wherein the thickness of the bonding layer is 1 μm, the thickness of the active layer is 48 μm, the thickness of the resistance layer is 1 μm, and the thickness ratio of the bonding layer, the active layer and the resistance layer is 1:48: 1.

Example 2

The same as example 1 except that: the composition (solvent removal) of the adhesive layer in example 2 was 94 wt% lithium iron phosphate (LFP), 4 wt% polyvinylidene fluoride (PVDF), and 2 wt% conductive carbon black (SP).

Example 3

The same as example 1 except that: the composition (except solvent) of the adhesive layer in example 3 was 97 wt% of lithium iron phosphate (LFP), 1 wt% of polypropylene (PP), and 2 wt% of conductive carbon black (SP).

Example 4

The same as example 1 except that: the composition (except solvent) of the adhesive layer in example 4 was 97 wt% lithium iron phosphate (LFP), 1 wt% polyacrylic acid (PAA), and 2 wt% conductive carbon black (SP).

Example 5

The same as example 1 except that: the composition (solvent removal) of the tie layer in example 5 was 60 wt% polyvinylidene fluoride (PVDF), 40 wt% conductive carbon black (SP).

Example 6

The same as example 1 except that: the composition (except solvent) of the active layer in example 6 was 97.5 wt% of Lithium Cobaltate (LCO), 1 wt% of polypropylene (PP), and 1.5 wt% of conductive carbon black (SP).

Example 7

The same as example 1 except that: the composition (except solvent) of the active layer in example 7 was 97.5 wt% of Lithium Cobaltate (LCO), 1 wt% of Polytetrafluoroethylene (PTFE), and 1.5 wt% of conductive carbon black (SP).

Example 8

The same as example 1 except that: the composition (except solvent) of the adhesive layer in example 8 was 97 wt% lithium iron phosphate (LFP), 1 wt% polyacrylic acid (PAA), and 2 wt% conductive carbon black (SP). The active layer comprises 97.5 wt% of Lithium Cobaltate (LCO), 1 wt% of Polytetrafluoroethylene (PTFE) and 1.5 wt% of conductive carbon black (SP).

Example 9

The same as example 1 except that: the composition (desolvation) of the resistive layer in example 9 was 95 wt% alumina (Al)₂O₃) 3 wt% polyvinylidene fluoride (PVDF), 2 wt% conductive carbon black (SP).

Example 10

The same as example 1 except that: examplesThe resistance layer in 10 had a composition (desolvation) of 93 wt% alumina (Al)₂O₃) 3 wt% polyvinylidene fluoride (PVDF), 4 wt% conductive carbon black (SP).

Example 11

Substantially the same as in example 1, except that: in example 11, the thickness of the resistive layer was 2 μm, and the thickness ratio of the adhesive layer, the active layer, and the resistive layer was 1:48: 2.

Example 12

The same as example 1 except that: in example 12, the thickness of the resistive layer was 3 μm, and the thickness ratio of the adhesive layer, the active layer, and the resistive layer was 1:48: 3.

Example 13

The same as example 1 except that: in example 13, the thickness of the adhesive layer was 2 μm, and the thickness ratio of the adhesive layer, the active layer, and the resistive layer was 2:48: 1.

Example 14

The same as example 1 except that: in example 14, the thickness of the adhesive layer was 3 μm, and the thickness ratio of the adhesive layer, the active layer, and the resistive layer was 3:48: 1.

Example 15

The same as example 1 except that: in example 15, the adhesive layer had a composition (desolvation) of 60 wt% of polyvinylidene fluoride (PVDF) and 40 wt% of conductive carbon black (SP), the active layer had a composition (desolvation) of 97.5 wt% of Lithium Cobaltate (LCO), 1 wt% of Polytetrafluoroethylene (PTFE) and 1.5 wt% of conductive carbon black (SP), the resistive layer had a thickness of 2 μm, and the thickness ratio of the adhesive layer, the active layer and the resistive layer was 1:48: 2.

Comparative example 1

The same as example 1 except that: the adhesive layer and the resistive layer in the positive electrode sheet of example 1 were omitted, and only the active layer was formed on the aluminum foil. The method comprises the following specific steps:

the aluminum foil is used as a positive current collector, a layer of lithium cobaltate slurry is uniformly coated on the surface of the aluminum foil, the solvent-removing lithium cobaltate slurry comprises 98 wt% of Lithium Cobaltate (LCO), 0.5 wt% of polyvinylidene fluoride (PVDF) and 1.5 wt% of conductive carbon black (SP), and the active layer is prepared by drying at 85 ℃. And then carrying out cold pressing, cutting into pieces and slitting on the single-layer membrane, and baking for 12 hours at 85 ℃ under a vacuum condition to prepare the positive pole piece. Wherein the thickness of the active layer is 48 μm.

Comparative example 2

Substantially the same as in example 1, except that: the resistive layer in the positive electrode sheet of example 1 was omitted, and only the adhesive layer and the active layer were formed on the aluminum foil. The method comprises the following specific steps:

And continuously and uniformly coating a layer of lithium cobaltate slurry on the bonding layer, wherein the lithium cobaltate slurry comprises 98 wt% of Lithium Cobaltate (LCO), 0.5 wt% of polyvinylidene fluoride (PVDF) and 1.5 wt% of conductive carbon black (SP), and drying at 85 ℃ to obtain the active layer.

And then, carrying out cold pressing, cutting into pieces and slitting, and baking for 12h at 85 ℃ under a vacuum condition to prepare the positive pole piece. Wherein the thickness of the bonding layer is 1 μm, the thickness of the active layer is 48 μm, and the thickness ratio of the bonding layer to the active layer is 1: 48.

Comparative example 3

Substantially the same as in example 1, except that: the adhesive layer in the positive electrode sheet of example 1 was omitted, and only the laminated active layer and resistive layer were formed on the aluminum foil. The method comprises the following specific steps:

the method comprises the steps of taking an aluminum foil as a positive current collector, uniformly coating a layer of lithium cobaltate slurry on the surface of the aluminum foil, wherein the lithium cobaltate slurry comprises 98 wt% of Lithium Cobaltate (LCO), 0.5 wt% of polyvinylidene fluoride (PVDF) and 1.5 wt% of conductive carbon black (SP), and drying at 85 ℃ to obtain the active layer.

And continuously and uniformly coating a layer of alumina slurry on the active layer, wherein the alumina slurry consists of 97 wt% of alumina (Al2O3) and 3 wt% of polyvinylidene fluoride (PVDF), and drying at 85 ℃ to prepare the resistance layer.

And then, carrying out cold pressing, cutting into pieces and slitting, and baking for 12h at 85 ℃ under a vacuum condition to prepare the positive pole piece. Wherein, the thickness of the active layer is 48 μm, the thickness of the resistance layer is 1 μm, and the thickness ratio of the active layer to the resistance layer is 48: 1.

Comparative example 4

The same as example 1 except that: the composition (except solvent) of the adhesive layer in comparative example 4 was 94 wt% of lithium iron phosphate (LFP), 1 wt% of polyvinylidene fluoride (PVDF), and 2 wt% of conductive carbon black (SP).

Comparative example 5

The same as example 1 except that: the composition (solvent removal) of the active layer in comparative example 5 was 97.5 wt% Lithium Cobaltate (LCO), 1 wt% polyvinylidene fluoride (PVDF), 1.5 wt% conductive carbon black (SP).

Comparative example 6

Substantially the same as in example 1, except that: in example 6, the thickness of the resistive layer was 4 μm, and the thickness ratio of the adhesive layer, the active layer, and the resistive layer was 1:48: 4.

Comparative example 7

The same as example 1 except that: in example 7, the thickness of the adhesive layer was 4 μm, and the thickness ratio of the adhesive layer, the active layer, and the resistive layer was 4:48: 1.

The steps of preparing the lithium ion battery by adopting the positive pole piece prepared in the embodiment 1-15 and the comparative example 1-7 are as follows:

the method comprises the steps of taking a copper foil as a negative current collector, uniformly coating a layer of graphite slurry on the surface of the copper foil, drying the copper foil at 85 ℃ by using a solvent-removing slurry which is a combination of 97.7 wt% of artificial graphite, 1.3 wt% of sodium carboxymethyl cellulose (CMC) and 1.0 wt% of Styrene Butadiene Rubber (SBR), and then carrying out cold pressing, cutting and slitting to prepare the negative pole piece.

Lithium salt LiPF₆And a nonaqueous organic solvent (ethylene carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Propyl Propionate (PP), Vinylene Carbonate (VC), in a mass ratio of 20:30:20:28:2, by mass: 92 as the electrolyte of the lithium ion battery.

And welding the electrode lugs on the positive electrode piece and the negative electrode piece, winding the positive electrode piece and the negative electrode piece, and separating the positive electrode piece and the negative electrode piece through a polyethylene diaphragm, so as to prepare a naked battery cell, wherein the naked battery cell is subjected to top side sealing, code spraying, vacuum drying, electrolyte injection, high-temperature standing, formation and capacity, and then the finished product lithium ion battery can be obtained.

Example 16

The copper foil is used as a negative current collector, a layer of conductive agent slurry is uniformly coated on the surface of the copper foil, the solvent removal slurry comprises 60 wt% of polyacrylic acid (PAA) and 40 wt% of conductive carbon black (SP), and the adhesive layer is prepared by drying at 85 ℃.

And continuously and uniformly coating a layer of graphite slurry on the bonding layer, wherein the solvent-removing graphite slurry comprises 98 wt% of artificial graphite, 1 wt% of Polytetrafluoroethylene (PTFE) and 1 wt% of conductive carbon black (SP), and drying at 85 ℃ to prepare the active layer.

Continuously and uniformly coating a layer of alumina slurry on the active layer, wherein the alumina slurry except the solvent has the composition of 98 wt% of alumina (Al)₂O₃) And 2 wt% of polyacrylic acid (PAA), and drying at 85 ℃ to prepare a resistance layer and obtain the negative pole piece.

And then, carrying out cold pressing, slitting and cutting, and baking for 12h at 85 ℃ under a vacuum condition to prepare the positive pole piece (as shown in figure 1). Wherein the thickness of the bonding layer is 1 μm, the thickness of the active layer is 59 μm, the thickness of the resistance layer is 1 μm, and the thickness ratio of the bonding layer, the active layer and the resistance layer is 1:59: 1.

Comparative example 8

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 (C), 1.3 wt% of sodium carboxymethyl cellulose (CMC) and 1.0 wt% of Styrene Butadiene Rubber (SBR), drying is carried out at 85 ℃, and then cold pressing, cutting and slitting are carried out to prepare a negative pole piece, wherein the thickness of a negative active layer is 59 mu m.

The steps for preparing the lithium ion battery by using the negative electrode plate prepared in example 16 and comparative example 8 are as follows:

lithium salt LiPF₆With non-aqueous organic solvents (ethylene carbonate (EC): diethyl carbonate (DEC): Propylene Carbonate (PC): Propylene Propionate (PP): carbonVinylene acetate (VC) ═ 20:30:20:28:2, mass ratio) by mass ratio of 8: 92 as the electrolyte of the lithium ion battery.

The aluminum foil is used as a positive current collector, a layer of lithium cobaltate slurry is uniformly coated on the surface of the aluminum foil, the solvent-removing lithium cobaltate slurry comprises 98 wt% of Lithium Cobaltate (LCO), 0.5 wt% of polyvinylidene fluoride (PVDF) and 1.5 wt% of conductive carbon black (SP), and the active layer is prepared by drying at 85 ℃. And then carrying out cold pressing, cutting into pieces and slitting on the single-layer membrane, and baking for 12 hours at 85 ℃ under a vacuum condition to prepare the positive pole piece.

Welding a tab of the positive pole piece and the negative pole piece, winding the positive pole piece and the negative pole piece, and separating the positive pole piece and the negative pole piece through a polyethylene diaphragm, so as to prepare a naked battery cell, wherein the naked battery cell is subjected to top side sealing, code spraying, vacuum drying, electrolyte injection, high-temperature standing, formation and capacity, and then a finished product lithium ion battery can be obtained.

The following are performance tests.

1. The pole piece flexibility test method comprises the following steps:

taking out the pole piece from the lithium ion battery, folding the pole piece along the length direction, opening to see whether the crease is transparent or not and cracks, unfolding the pole piece if the crease is not transparent, reversely folding the pole piece again, observing the position of the crease again, and repeatedly folding the pole piece until the crease is transparent and cracks appear. And representing the flexibility of the pole piece by the folding times corresponding to the cracks appearing at the crease position in the light transmission process.

2. The bonding strength test method of the bonding layer comprises the following steps:

taking out the pole piece from the lithium ion battery, taking a test sample with the width of 30mm and the length of 150mm by using a blade, and fixing the test sample on a test fixture of a high-speed rail tensile machine to test the bonding strength, wherein the peeling angle is 90 degrees, the tensile speed is 50mm/min, and the tensile displacement is 60 mm. When the peeling interface is the bonding layer and the current collector, the measured result is the bonding strength of the bonding layer and the current collector.

3. The membrane resistance test method comprises the following steps:

the positive electrode piece was taken out from the lithium ion battery (full charge state 100% SOC), and the cathode sheet resistance was measured with an IEST BER1300 sheet resistance tester under conditions of 0.35T pressure and 50s time.

4. Impact testing method:

fully charging the lithium ion battery, placing a fully charged core on a planar iron plate, and setting the diameter of the fully charged core to be equal to

A round bar with the length of at least 6cm is vertical to the sample (Tab position), a 9.1 plus or minus 0.1Kg heavy hammer is used for dropping in a vertical free state at a distance of 61 plus or minus 2.5cm from the intersection of the round bar and the sample to obtain the passing rate of the battery cell; and after the test is finished through the judgment standard, the battery cell does not catch fire or explode.

4. DC Rate test method:

and (3) placing the lithium ion battery in a constant temperature box at 25 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. The lithium ion battery reaching the constant temperature is charged with a constant current of 0.2C until the voltage is 4.45V, then charged with a constant voltage of 4.45V until the current is 0.025C, and discharged at 0.2C until the voltage is 3.0V, and the discharge capacity at 0.2C is recorded. Standing for 5 minutes, charging to a voltage of 4.45V at a constant current of 0.2C, then charging to a current of 0.025C at a constant voltage of 4.45V, discharging to a voltage of 3.0V at 3C, and recording the 3C discharge capacity.

DC Rate (3C/0.2C) means 3C discharge capacity/0.2C discharge capacity.

TABLE 1

TABLE 2

TABLE 3

In tables 1 to 3:

the thickness ratio is the thickness ratio of each layer outward from the surface of the current collector of the pole piece, for example, the thickness ratio of the bonding layer, the active layer and the resistance layer in example 1;

the flexibility of the pole piece is measured by the times of bending the cold-pressed pole piece until cracks appear;

the bonding strength refers to the bonding strength between the bonding layer and the current collector;

the full-charge diaphragm resistance of the pole piece refers to the overall resistance of the pole piece;

the adhesive layer + active layer full-charge sheet resistance refers to the resistance of the adhesive layer and/or the active layer on the positive electrode current collector except the resistance layer, and can be measured by adopting the method for measuring a sample of the electrode plate when the adhesive layer and/or the active layer are formed but the resistance layer is not formed;

the full-charge diaphragm resistance ratio of the resistance layer is 1- (bonding layer + active layer full-charge diaphragm resistance)/full-charge diaphragm resistance of the pole piece;

the cell pass rate is the pass rate of 10 tests.

Comparing the data in the table, the following conclusions can be drawn:

1. according to comparative examples 1 to 3 and example 1, the improvement of the safety against impact is limited only by improving the adhesion strength between the current collector and the diaphragm by the adhesive layer or improving the diaphragm resistance by the resistive layer. The adhesive layer can only protect the surface current collector from being exposed, but has no improvement effect on the short circuit of the anode-cathode diaphragm and the chip lap short circuit generated at the fracture, and the resistance layer can only improve the probability of the anode-cathode short circuit, but has no improvement effect on the reduction of the exposure of the current collector and the chip lap short circuit at the fracture. After the electric core is impacted, the electric core is cracked, and the mass layer on mass flow body surface can drop and expose the dangerous short circuit that the mass flow body formed the mass flow body and participated in, and positive pole and negative pole short circuit resistance reduce under the high pressure extrusion, easily cause electric core thermal runaway. In addition, the general pole piece is brittle and is easy to form a large amount of fragments at the fracture, and the fragments form short circuit lap joint with the fracture under the extrusion of the iron rod and can also cause the ignition failure of the battery core. Only by adopting the positive pole piece with the three-layer composite structure in the embodiment, the short-circuit probability and the short-circuit danger degree are reduced in all aspects, so that the passing rate of the battery cell can be obviously improved on the basis of higher discharge rate, and the safety performance of the battery cell is improved.

2. According to comparative example 4 and examples 1 to 5, it is known that the adhesive strength between the adhesive layer and the current collector can be improved by increasing the content of the adhesive in the adhesive layer or by using an adhesive (PP or PAA) having high adhesive property under the condition that other conditions are not changed. When the bonding strength is weak, the protective effect of the bonding layer on the current collector is weak, the high bonding layer still falls off in an impact test, the current collector is exposed, and dangerous short circuit such as aluminum-negative pole is formed to cause failure of the battery cell. Experimental data show that the battery cell passing rate can be obviously improved on the basis of higher discharge rate only when the bonding strength of the bonding layer and the current collector is more than or equal to 38N/m.

3. According to the comparative example 5 and the examples 1, 6 to 7, under the condition that other conditions are not changed, the softness of the pole piece can be improved by reducing the content of the binder in the active layer or adopting the binder (PP or PTFE) with high softness. When the softness of the pole piece is low, for example, in comparative example 5, the adopted binder has a high content, the pole piece is subjected to the action of impact force, and has no enough deformation to offset external force, so that stress concentration is easily formed, cracks are generated, the pole piece is broken into a large amount of scraps, dangerous short circuit lap joint is formed at the fracture of the battery cell, and ignition failure of the battery cell is caused. Experimental data shows that only when the cold-pressed pole piece is bent to the crack occurrence frequency not less than 4, the softness of the pole piece can obviously improve the safety performance of the battery cell on the basis of higher discharge rate, and the passing rate of the battery cell is improved.

Further, as can be seen from comparison of examples 6 to 8, the adhesive layer of example 8 used the adhesive (PAA) having high adhesive properties, and the active layer used the adhesive (PTFE) having high flexibility, which exhibited the highest discharge rate and highest cell passage rate, without changing other conditions.

4. According to the comparative example 6 and the examples 1 and 9 to 12, under the condition that other conditions are not changed, the content of the inorganic resistance material is increased or the thickness of the resistance layer is increased, so that the resistance of the pole piece can be improved. When the resistance of the pole piece is small, under the action of external force extrusion such as an iron bar, the resistance of the anode-cathode short circuit is small, and the resistance is equal to U according to P²and/R, the generated joule heat is high, and the battery core thermal runaway and the battery core ignition failure can be caused by the anode-cathode short circuit. Experimental data shows that the positive electrode-negative electrode short-circuit resistance is large enough to obviously improve the passing rate of the battery cell only when the diaphragm resistance is larger than or equal to 2 omega. However, if the resistance of the electrode sheet continues to increase, the cell safety is further improved, but when the resistance increases to a certain extent, the cell dynamic performance is rapidly deteriorated. The experimental data show that the resistance of the diaphragm needs to be less than or equal to 15 omega. In addition, the electron conduction in the battery is carried out in the thickness direction from the current collector, so that the bonding layer and the high-flexibility active material layer close to the current collector are not suitable for too large resistance, otherwise, the electron transmission is influenced, and the dynamic performance of the battery core is deteriorated. The resistance layer is positioned on the surface of the pole piece and can be used as a main contribution part of the resistance of the pole piece. The data show that the ratio of the resistance of the full charge diaphragm of the resistance layer is 80% to 98%, in other words, the ratio of the resistance of the bonding layer + the full charge diaphragm of the active layer is 3% to 20% which is a reasonable range.

5. It is understood from comparative example 7, examples 1, 11 and 12 that the ratio of the thickness of the resistance layer in the positive electrode sheet is not excessively high, and should be in the range of 1% to 6%. It can be seen from comparative example 7, examples 1, 13 and 14 that the thickness of the adhesive layer should not be too high in the pole piece, and should be in the range of 1% to 6%. Accordingly, the thickness of the active layer should be in the range of 88% to 98%. If the thickness of the bonding layer is too high, which exceeds 6%, the overall flexibility of the pole piece is reduced, and the safety performance of the battery cell is deteriorated. The thickness of the resistance layer is more than 6%, which may cause the resistance of the pole piece to exceed 15 Ω, and deteriorate the dynamic performance of the cell.

6. According to embodiments 15 and 16, the structure of each layer of the pole piece is optimized, so that the cell passing rate can be further improved, and the cell safety performance can be improved.

FIG. 3 shows a cross-sectional SEM image of the positive electrode sheet prepared in example 15; fig. 4 shows an SEM image of the area of the positive electrode sheet near the positive current collector prepared in example 15, and the adhesion strength of the current collector to the sheet was increased by increasing the binder content to 60%.

Fig. 5 shows an SEM image of the region of the positive electrode sheet near the resistive layer prepared in example 1, and the resistance of the positive electrode sheet is increased by using alumina as a high-resistance material and increasing the thickness of the resistive layer.

Fig. 6 is an SEM image showing the peeled surface of the active layer of the positive electrode sheet obtained in example 1, and the mesh-like structure of the positive electrode sheet can increase the deformation between the active materials and increase the ability of the sheet to plastically deform by using a highly flexible ptfe binder, thereby reducing the cracking and dusting of the sheet due to stress concentration. In addition, the net structure can improve ion channels to make up for the obstruction of ion migration caused by the outermost resistance layer.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims, and the description and the drawings can be used for explaining the contents of the claims.

Claims

1. An electrochemical device, comprising:

the electrode comprises a pole piece, a current collector, a bonding layer, an active layer and a resistance layer;

the resistance layer is arranged on the surface of the active layer, which is far away from the bonding layer;

and the bending resistant times of the pole piece are more than or equal to 4.

2. The electrochemical device according to claim 1, wherein the adhesive layer, the active layer and the resistive layer have a thickness of 1% to 6%, 88% to 98% and 1% to 6%, respectively, in a total thickness of the adhesive layer, the active layer and the resistive layer.

3. The electrochemical device of claim 1, wherein said resistive layer has a resistance of 80% to 98% of a total resistance of said pole piece.

4. The electrochemical device according to claim 1, wherein the adhesive layer contains a first binder and a first conductive agent;

5. The electrochemical device according to claim 1, wherein the active layer contains an active material, a second binder, and a second conductive agent;

6. The electrochemical device according to any one of claims 1 to 5, wherein the resistive layer contains an inorganic resistive material and a third binder, and a mass content of the inorganic resistive material in the resistive layer is 93% to 97%.

7. The electrochemical device according to claim 6, wherein said inorganic resistive material comprises at least one of boehmite, alumina, magnesia, silica, titania, and magnesium hydroxide; and/or

8. The electrochemical device according to any one of claims 1 to 5 and 7, wherein the resistive layer further contains a third conductive agent, and a mass content of the third conductive agent in the resistive layer is greater than 0% and not greater than 4%.

9. The electrochemical device according to any one of claims 1 to 5, 7,

the pole piece is at least one of a positive pole piece or a negative pole piece; when the pole piece is a positive pole piece, the active material in the active layer is a positive active material; and when the pole piece is a negative pole piece, the active material in the active layer is a negative active material.

10. An electric device comprising the electrochemical device according to any one of claims 1 to 9.