WO2023284383A1

WO2023284383A1 - Electrochemical device and electronic device

Info

Publication number: WO2023284383A1
Application number: PCT/CN2022/091727
Authority: WO
Inventors: 周卫源; 戴志芳; 龙海; 张青文
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-07-13
Filing date: 2022-05-09
Publication date: 2023-01-19
Also published as: CN113675372A; CN113675372B

Abstract

An electrochemical device, comprising a winded cell and a shell for accommodating the cell, wherein the cell comprises a first electrode plate (100), a second electrode plate and a separator which are arranged in a stacked manner. The first electrode plate (100) comprises a current collector (110), wherein the current collector (110) comprises a first surface facing the interior of the cell and a second surface facing away from the interior of the cell; a tab (120) which is electrically connected to the current collector (110) and extends out of the current collector (110); and a first active substance layer (130) arranged on the first surface of the current collector (110). The first active substance layer (130) comprises a main body coating (131) and an edge coating (132); in a first direction, the edge coating (132) is located on a side, which faces the tab (120), of the main body coating (131) and is adjacent to or partially overlapped with the main body coating (131); and in a second direction, the main body coating (131) and the edge coating (132) extend in a strip shape, and the length of the edge coating (132) is larger than that of the main body coating (131). The electrochemical device has the advantages of a high energy density and relatively high electrical properties.

Description

Electrochemical devices and electronic devices

Cross References to Related Applications

This application claims the priority of the Chinese patent application 202110789954.5 entitled "Electrochemical Devices and Electronic Devices" filed on July 13, 2021, the entire content of which is incorporated herein by reference.

technical field

The embodiments of the present application relate to the technical field of batteries, and in particular, to an electrochemical device and an electronic device.

Background technique

The electrochemical device has a battery cell and a casing for containing the battery cell. The battery cell generally includes a stacked pole piece and a diaphragm. The pole piece has a current collector and an active material layer disposed on the surface of the current collector. In the coating process of producing an electrochemical device, as shown in Figure 1, an active material layer 11 is set on a metal foil 12, and the area where the active material layer 11 is located at the edge of the metal foil 12 will be affected by surface energy and gravity. The outer expansion causes the edge of the pole piece to form a thinned region 13, the thickness of the thinned region 13 is smaller than the thickness of the middle region 14, and the width of the thinned region is larger, which will cause the electrochemical device to precipitate lithium and reduce the energy of the electrochemical device. density. And as shown in Figure 2, due to the shrinkage of the slurry in the coating process, after the slurry is solidified to form a diaphragm, the corner 15 will be formed in the head and tail regions of the diaphragm. Since the corner 15 is relatively large, it will cause Lithium separation in the electrochemical device will also reduce the energy density of the electrochemical device, thereby affecting the performance of the electrochemical device.

application content

In order to solve the above technical problems, embodiments of the present application provide an electrochemical device with better performance and an electronic device using the electrochemical device.

According to one aspect of the present application, the present application provides an electrochemical device, which includes an electric core and a casing for accommodating the electric core. The electric core includes a wound first pole piece, a second pole piece, and a and the diaphragm between the second pole piece. Wherein, the first pole piece includes a current collector, and the current collector includes a first surface facing the inside of the battery core and a second surface away from the inside of the battery core; the tab is electrically connected to the current collector and protrudes from the current collector; the first The active material layer is disposed on the first surface and includes a main coating and an edge coating. Along the first direction, the edge coating is located on the side of the main coating facing the tab, and is adjacent to or partially overlapped with the main coating, Along the second direction, the main coating and the edge coating are extended in a strip shape, and the length of the edge coating is longer than the length of the main coating. The first direction is the direction in which the tab extends out of the current collector, and the second direction is the first The winding direction of the pole piece; the second active material layer is arranged on the second surface.

In the present application, a relatively long edge coating is arranged on the edge of the main body coating, which increases the thickness of the edge area of the active material layer, reduces the angular position of the active material layer at the head and tail of the pole piece, and improves the electrochemical device. energy density, and reduces the risk of lithium precipitation.

In some embodiments of the present application, along the second direction, the winding starting end of the first pole piece includes a single-sided area, the first surface located in the single-sided area is only provided with an edge coating, and the second surface located in the single-sided area is provided with an edge coating. The surface is provided with a second active material layer. The setting of the single-sided area can avoid the problems of increasing the thickness of the battery cell and reducing the energy density at the starting end of the winding due to double-sided coating.

In some embodiments of the present application, along the second direction, the winding starting end of the first pole piece further includes an empty foil area, and the empty foil area is closer to the head of the winding starting end of the first pole piece than the single-sided area The first surface located in the empty foil area is only provided with an edge coating, and the second surface located in the empty foil area is an empty current collector. The setting of the empty foil area improves the problem of coiling on one side of the pole piece during the winding process, thereby facilitating the winding of the pole piece.

In some embodiments of the present application, the second active material layer includes a main part and an edge part, and along the first direction, the edge part is located on the side of the main part facing the tab, and is adjacent to or partially overlapped with the main part; In the second direction, the main body portion and the edge portion extend in a strip shape. In this way, the second active material layer can play a role similar to that of the first active material layer, and jointly weaken the influence of the weakened area and the angular position on the energy density of the battery cell.

In some embodiments of the present application, the ratio of the thickness of the edge coating to the thickness of the main coating is k, 0.8≦k≦1.2.

In some embodiments of the present application, the thickness of the edge coating is 50-150 μm, and/or the width of the edge coating is 1-20 mm.

In some embodiments of the present application, the tab and the current collector are integrally formed.

In some embodiments of the present application, the first pole piece is an anode pole piece.

In some embodiments of the present application, both the main body coating and the edge coating include an anode active material and a binder, and the anode active material includes artificial graphite, natural graphite, graphene, carbon nanotubes, mesocarbon microspheres, soft At least one of carbon, hard carbon, silicon carbon, silicon alloy, silicon crystal, lithium titanate, and tin oxide; binders include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated rubber, polyurethane, and styrene-butadiene rubber , polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, sodium alginate at least one.

According to another aspect of the present application, the present application provides an electronic device, including the above-mentioned electrochemical device, and the electrochemical device is used to supply power to the electronic device.

The above-mentioned electrochemical device and electronic device have an edge coating on the edge of the main coating of the active material layer. Compared with the traditional electrochemical device, on the one hand, it weakens the active material layer in the slurry state. The outer expansion increases the thickness of the edge region of the active material layer, thereby improving the energy density of the electrochemical device; The contraction at the head and tail of the pole piece in the material state reduces the angular position of the active material layer at the head and tail of the pole piece, thereby increasing the energy density of the electrochemical device. In addition, due to the increase in the thickness of the edge region of the active material layer, and in the plate hot pressing process of the electrochemical device, compared with the existing electrochemical device, the multilayer pole pieces are stacked more tightly in the edge region, reducing the ion transmission path, Reduce the possibility of lithium analysis.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the accompanying drawings that need to be used in the embodiments of the present application. Obviously, the accompanying drawings described below are only some embodiments of the present application. Those of ordinary skill in the art can also obtain other drawings based on the accompanying drawings on the premise of not paying creative efforts.

1 is a cross-sectional view of a pole piece of an electrochemical device in the prior art in a coating process;

Fig. 2 is a schematic structural view of the pole piece of the prior art electrochemical device in the coating process;

Fig. 3 is a schematic structural diagram of a first pole piece according to an embodiment of the present application;

Fig. 4 is a sectional view of the first pole piece of the embodiment shown in Fig. 3;

5 is a schematic structural diagram of the intermediate state of the first pole piece in the coating process according to an embodiment of the present application;

Fig. 6 is a schematic structural view of the first pole piece before cutting according to an embodiment of the present application;

Fig. 7 is a schematic structural diagram of a first pole piece according to an embodiment of the present application;

Fig. 8 is a sectional view of the first pole piece of the embodiment shown in Fig. 7;

Fig. 9 is a schematic structural diagram of a first pole piece according to an embodiment of the present application;

Fig. 10 is a sectional view of the first pole piece of the embodiment shown in Fig. 9;

Fig. 11 is a schematic structural diagram of a first pole piece according to an embodiment of the present application;

Fig. 12 is a sectional view of the first pole piece of the embodiment shown in Fig. 11;

Fig. 13 is a cross-sectional view of the first pole piece according to an embodiment of the present application;

Fig. 14 is a data comparison diagram of the pole piece thickness of Example 1 of the present application and Comparative Example 1;

FIG. 15 is a data comparison chart of the cell thickness of Example 1 and Comparative Example 1 of the present application.

detailed description

In order to facilitate the understanding of the present invention, the present invention will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that when an element is said to be "fixed" to another element, it may be directly on the other element, or there may be one or more intervening elements therebetween. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or one or more intervening elements may be present therebetween. The terms "vertical", "horizontal", "left", "right" and similar expressions are used in this specification for the purpose of description only.

Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used in the description of the present invention in this specification are only for the purpose of describing specific embodiments, and are not used to limit the present invention. The term "and/or" used in this specification includes any and all combinations of one or more of the associated listed items.

The electrochemical device includes an electric core and a case for accommodating the electric core. Wherein, the electric core includes a first pole piece, a second pole piece, and a diaphragm located between the first pole piece and the second pole piece, and the first pole piece, the diaphragm, and the second pole piece are wound in one roll Wound around the surface as the center to form a wound battery.

As shown in FIGS. 3 and 4 , the first pole piece 100 includes a current collector 110 , a tab 120 electrically connected to the current collector 110 , and a first active material layer 130 disposed on the first surface of the current collector 110 . The second active material layer 140 on the second surface of the current collector 110 and the tab 120 protrude from the current collector 110 along the first direction. Wherein, the first surface refers to the surface of the current collector 110 facing the inside of the battery cell, that is, the surface facing the above-mentioned winding surface is the first surface; the second surface refers to the surface of the current collector 110 facing away from the inside of the battery cell.

Wherein, the first active material layer 130 includes a main coating 131 and an edge coating 132, the edge coating 132 is located on the side of the main coating 131 facing the tab 120 along the first direction, and is adjacent to the main coating 131 or partially overlap. It should be understood that, along the thickness direction of the first pole piece 100 , the overlapping area can be the edge coating 132 superimposed on the main coating 131 , or the main coating 131 superimposed on the edge coating 132 . Along the second direction, the main coating 131 and the edge coating 132 extend in a strip shape, and the length of the edge coating 132 is longer than that of the main coating 131 along the second direction. As shown in Figure 3, the main coating 131 and the edge coating 132 are strip-shaped rectangles, and extend parallel to each other along the second direction, the length of the edge coating 132 is greater than the length of the main coating 131, that is, At the end of a pole piece 100 , the end of the edge coating 132 will exceed the end of the main coating 131 , and the end of the first active material layer 130 on the first pole piece 100 is uneven. Wherein, the first direction is the direction in which the tab 120 protrudes from the current collector 110, and the second direction is the winding direction of the first pole piece 100. It can also be understood that when the first pole piece 100 is strip-shaped, the second pole piece One direction is the width direction of the first pole piece 100 , and the second direction is the length direction of the first pole piece 100 .

FIG. 5 shows the morphology of the first pole piece 100 during the coating process. In the coating process, the slurry of the main coating 131 and the slurry of the edge coating 132 are respectively injected into the corresponding feeding system, and coated on the surface of the metal foil 200 simultaneously through the coating die. And, according to the length design requirements of the pole piece, by adjusting the parameters of the coating machine, controlling the feeding system or the working state of the coating die, the edge coating 132 slurry can be continuously coated without interruption, and the main coating 131 slurry can be continuously coated. Intermittent coating. Thus, after the above coating process, the intermediate state of the first pole piece 100 as shown in FIG. 5 can be obtained. As shown in FIG. 5, after the coating process, the first surface of the metal foil 200 is coated with the slurry of the first active material layer 130, and the second surface is coated with the slurry of the second active material layer 140 (not shown in the figure). As shown), the two edges of the metal foil 200 along the first direction are blank metal foils, which are not coated with the slurry of the first active material layer 130 and the slurry of the second active material layer 140 . After the coating process is completed, after drying, cold pressing and other processes, the intermediate shape of the first pole piece 100 shown in Figure 5 is die-cut and divided into tabs and strips, and the above-mentioned two edge regions are formed by laser die-cutting. A plurality of tabs 120 are divided from the middle of the main body coating along the second direction to obtain the shape of the first pole piece 100 before cutting as shown in FIG. 6 . After die-cutting the lugs and slitting, the first pole piece 100 shown in FIG. 6 is cut along the first direction to obtain the first pole piece 100 shown in FIG. 7 . In some embodiments, along the first direction, cutting can be carried out from the joint of the main coating 131 and the blank metal foil formed by the gap coating 132 (ie, the end of the main coating 131 ), so as to obtain different rolls Around the start and end. In some other embodiments, along the first direction, the blank metal foil formed by gap coating can be cut from the center line, so as to obtain the same winding start end and head and tail ends.

Because in the coating process, while coating the main body coating 131 slurry, the edge coating 132 slurry is also coated on the edge of the main body coating 131 slurry, the existence of the edge coating 132 slurry is very important for the main body coating. The expansion of the slurry of the layer 131 plays a certain blocking effect, thereby alleviating the thinning of the edge area of the active material layer caused by the expansion of the slurry of the main coating 131, which is conducive to increasing the thickness of the edge area of the active material layer. The energy density of the electrochemical device is improved. And, because edge coating 132 slurry is coated continuously and main body coating 131 slurry is gap coating, due to the existence of edge coating 132 slurry, can weaken main coating 131 slurry state when the pole piece head and The shrinkage of the tail reduces the angular position of the active material layer at the head and tail of the pole piece, thereby increasing the energy density of the electrochemical device. In addition, due to the increase in the thickness of the edge region of the active material layer, the stacking of multi-layer pole pieces is more compact than that of the existing chemical device during the flat plate hot pressing process of the electrochemical device, which reduces the ion transmission path and reduces the The possibility of lithium analysis occurs.

In the above embodiments, the current collector 110 and the tab 120 are integrally formed by die-cutting, and there are multiple tabs 120 . It should be understood that, along the second direction, the distance between the tabs 120 can also be set according to the width of the battery core and the number of winding layers, and the number of tabs 120 can also be set as a single.

As shown in FIGS. 7 and 8 , in some embodiments of the present application, the winding starting end of the first pole piece 100 includes a single-sided region 101 . In this application, the winding starting end of the first pole piece refers to the part from the head of the pole piece to the beginning of the double-sided area 102 of the pole piece according to the winding direction, and the double-sided area 102 refers to the current collector 110 The surface of each is provided with an active material layer. Specifically, in the single-sided region 101 , only the edge coating 132 is provided on the first surface of the current collector 110 without the main coating 131 , and the second active material layer 140 is provided on the second surface of the current collector 110 . By setting the single-sided area 101 and only setting the edge coating 132 on the first surface of the single-sided area 101, it can not only solve the problem that the head of the battery cell is thinner than the middle of the battery core, but also can avoid the winding starting end due to double-sided The problem of increased cell thickness and reduced energy density caused by coating.

As shown in Fig. 9 and Fig. 10, in some embodiments of the present application, along the second direction, the winding starting end of the first pole piece 100 also includes an empty foil area 103, and the empty foil area 103 is compared with the single-sided area 101 The head closer to the winding start end of the first pole piece 100 . Specifically, in the empty foil area 103, only the edge coating 132 is provided on the first surface of the current collector 110, and the main coating 131 is not provided, and the second active material layer 140, that is, the second active material layer 140 of the current collector 110 is not provided on the second surface of the current collector 110. The second surface of is an empty current collector. By setting the empty foil area 103 at the starting end of the winding, and the empty foil area 103 is also provided with an edge coating, it can not only solve the problem that the head of the cell is thinner than the middle of the cell, but also improve the first pole in the winding process. The winding problem of the single-side region 101 of the sheet 100 is eliminated, thereby facilitating the winding of the first pole piece 100 .

As shown in Figure 11 and Figure 12, in some embodiments of the present application, along the second direction, the winding starting end of the first pole piece 100 also includes an empty foil area 103, and the empty foil area 103 is compared with the single-sided area 101 The head closer to the winding start end of the first pole piece 100 . Specifically, in the empty foil area 103, the first active material layer 130 is not provided on the first surface of the current collector 110, that is, the main coating 131 and the edge coating 132 are not provided on the first surface, and the second surface of the current collector 110 is not provided. The second active material layer 140, that is, the second surface is an empty current collector. By setting the empty foil area 103 at the starting end of the winding, the empty foil area 103 is not provided with an active coating, which can improve the rolling problem of the single-sided area 101 of the first pole piece 100 in the winding process, thereby benefiting the first pole piece. 100's of winding.

In the above-mentioned embodiment, the edge coating 132 slurry is coated continuously, therefore, the edge coating 132 on the first pole piece 100 is continuously and uninterruptedly distributed. In some other embodiments, the edge coating 132 slurry can also be coated in gaps, so that the edge coating 132 on the first pole piece 100 is distributed in a dotted line, that is, the edge coating 132 on the first pole piece 100 is multi-segment , set at intervals from each other. Wherein, the lengths of each segment of the edge coating distributed in a dotted line shape can be the same or different, and the distance between two adjacent segments can be the same or different. In this way, it can be arranged on wound electric cores, some of the wound layers have an edge coating, and some of the wound layers do not have an edge coating. Specifically, one winding layer is provided with an edge coating, and the adjacent winding layer is not provided with an edge coating. In this way, on the one hand, the influence of the thinned area and angular position on the energy density of the cell can be weakened, and on the other hand, the thickness of the end of the cell can be controlled by controlling the number of layers of the edge coating on the wound cell.

In some embodiments of the present application, the thickness of the edge coating is greater than or equal to the thickness of the main coating. Specifically, in some embodiments, the ratio of the thickness of the edge coating to the thickness of the main coating is k, and k ranges from 0.8 to 1.2. For example, the ratio of the thickness of the edge coating to the thickness of the main coating is 0.8, 0.9, 1, 1.01, 1.03, 1.05, 1.07, 1.09, 1.11, 1.13, 1.15, 1.17, 1.19, 1.2 or any two of the above values. range of composition. Setting the ratio of the thickness of the edge coating to the thickness of the main coating within the above range, on the one hand, is beneficial to the edge area of the pole piece without a thinning area, which is conducive to improving the energy density of the battery cell and reducing the risk of lithium precipitation ; On the other hand, the end of the cell will not be uneven due to the thick coating on the edge of the pole piece, which will bring difficulties to the packaging.

In some embodiments of the present application, the thickness of the edge coating is 50-150 μm, for example, in some embodiments, the thickness of the edge coating is 70-130 μm; in some embodiments, the thickness of the edge coating is is 90-110 μm; in some embodiments, the thickness of the edge coating is 60 μm, 80 μm, 100 μm, 120 μm or a range composed of any two values above.

In some embodiments of the present application, the width of the edge coating is 1-20 mm, for example, in some embodiments, the width in the edge coating is 5-15 mm; in some embodiments, the width in the edge coating 8-10mm; in some embodiments, the width of the edge coating is 2mm, 4mm, 6mm, 8mm, 10mm, 12mm, 14mm, 16mm, 18mm, 20mm or a range composed of any two of the above values.

It should be understood that the thickness of the edge coating can be set according to the thickness of the main coating, and the width of the edge coating can be set according to the width of the main coating. By adjusting the thickness and width of the edge coating to reduce the edge thinning of the active material layer and the angular position of the active material layer at the head and tail of the pole piece, so as to achieve an increase in energy density and reduce the risk of lithium separation on the pole piece .

In some embodiments of the present application, the first pole piece is an anode pole piece, and correspondingly, the current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or a composite current collector Wait. The first active material layer is an anode active material layer, including an anode active material and a binder, that is, both the main coating layer and the edge coating include an anode active material and a binder. Wherein, the composition of the main coating can be the same as that of the edge coating, or it can be different. In some embodiments, the composition of the body coating is different from the composition of the edge coating, for example, the gram volume of the anode active material of the body coating is less than the gram volume of the anode active material material of the edge coating, thereby improving the dynamics of the edge of the pole piece Chemical performance, prevent edge lithium precipitation. For another example, the type or amount of the main coating binder is different from that of the edge coating, so that the bonding force between the main coating and the current collector is greater than that between the edge coating and the current collector. Adhesion, so as to prevent the edge coating from easily expanding or falling off from the current collector, and improve the safety performance of the cell.

In some embodiments of the present application, the anode active material includes artificial graphite, natural graphite, graphene, carbon nanotube, mesocarbon microsphere, soft carbon, hard carbon, silicon carbon, silicon alloy, silicon crystal, lithium titanate , at least one of tin oxide.

In some embodiments of the present application, the binder includes polyvinylidene fluoride, polytetrafluoroethylene, fluorinated rubber, polyurethane, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, alginic acid at least one of sodium.

In some embodiments of the present application, according to the dispersibility requirements of the active material layer slurry, the main body coating and/or the edge coating also include a thickener, and the thickener includes carboxymethyl cellulose, hydroxypropyl cellulose , at least one of hydroxypropyl methylcellulose.

In some embodiments of the present application, according to the conductivity requirements of the pole piece, the main body coating and/or the edge coating also include a conductive agent, and the conductive agent may include carbon-based materials (for example, natural graphite, artificial graphite, carbon black, etc.) , acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives ) at least one of.

In some embodiments of the present application, the first pole piece may also be a cathode pole piece, and correspondingly, the current collector may include aluminum foil, aluminum alloy foil, or a composite current collector. The first active material layer is a cathode active material layer, including a cathode active material and a binder, that is, both the main coating layer and the edge coating include a cathode active material and a binder. The cathode active material layer may also include thickeners and/or conductive agents according to dispersibility and/or conductivity needs.

In some embodiments of the present application, the cathode active material includes lithium iron phosphide, lithium iron manganese phosphide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide At least one of lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and lithium iron phosphate.

It should be understood that the selection of binders, thickeners, and conductive agents in the cathode active material layer may be the same as or different from the corresponding materials in the above-mentioned anode active material layer.

In some embodiments of the present application, the second active material layer 140 is integrally coated with the second active material layer slurry, that is, the second active material layer 140 does not distinguish between the main coating and the edge coating. In this way, in the case that the first active material layer 130 satisfies the performance design requirements, designing the second active material layer 140 in this way can simplify the coating process and reduce the production cost.

In some embodiments of the present application, the second active material layer 140 may also adopt a coating process similar to that of the first active material layer 130 , so as to form a coating structure similar to that of the first active material layer 130 . As shown in FIG. 13 , the second active material layer 140 also includes a main body portion 141 and an edge portion 142. Along the first direction, the edge portion 142 is located on the side of the main body portion facing the tab 120, and is adjacent to or adjacent to the main body portion 141. partially overlap. Preferably, the main body portion 141 of the second active material layer 140 has the same structure (such as thickness, width) and material (such as material composition, performance parameters) of the main coating layer 131 of the first active material layer 130 in any of the above methods, The structure and material of the edge portion 142 of the second active material layer 140 are the same as those of the edge coating layer 132 of the first active material layer 130 in any of the above embodiments, and will not be repeated here. In this way, the second active material layer on the second surface of the current collector can weaken the influence of the thinned area and angular position on the energy density of the cell through the setting of the edge, thereby improving the energy density of the cell together with the first active material layer on the first surface. energy density.

In some embodiments of the present application, the electrochemical device includes a lithium ion battery, but the application is not limited thereto. In some embodiments, the electrochemical device may also include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte and an electrolytic solution, and the electrolytic solution includes a lithium salt and a non-aqueous solvent. The lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB or lithium difluoroborate. For example, LiPF6 is chosen for lithium salt because of its high ionic conductivity and improved cycle characteristics.

In some embodiments of the present application, the electrochemical device includes a housing for accommodating the wound battery in the above embodiment. In some embodiments, the housing may be an aluminum-plastic film, which includes a nylon layer, an aluminum foil layer and PP layer. In some other embodiments, the shell can also be an insulated steel shell, aluminum shell, plastic shell, or the like.

Embodiments of the present application also provide an electronic device including the above electrochemical device. The electronic device in the embodiment of the present application is not particularly limited, and it may be used in any electronic device known in the prior art. In some embodiments, electronic devices may include, but are not limited to, notebook computers, pen-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, Lighting appliances, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.

Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

The first pole piece preparation process of embodiment 1 is as follows:

Mix the anode active material graphite, binder styrene-butadiene rubber, and thickener carboxymethyl cellulose in a mass ratio of 96:3:1, add water and stir to obtain a main coating with a solid content of 45% and a viscosity of 4500mPa.s Slurry; mix the anode active material graphite, binder styrene-butadiene rubber, and thickener carboxymethyl cellulose in a mass ratio of 98:1:1, add water and stir to obtain a slurry with a solid content of 48.4% and a viscosity of 7200mPa.s Edge coating slurry.

Inject the prepared main coating slurry and edge coating slurry into the corresponding feeding system respectively, and adjust the coating machine according to the parameters such as coating weight, coating width and coating length, in which the main coating is intermittently coated Cloth, continuous coating of the edge coating, the main coating slurry and the edge coating slurry are simultaneously coated on one side surface of the copper foil with a thickness of 6 microns, and the other side surface of the copper foil. And according to the parameter settings such as compaction density and cold pressing thickness, start cold pressing to obtain the intermediate state of the compacted pole piece. The parameters of the intermediate state pole piece are shown in Table 1.

Then carry out die-cutting tabs and slitting to obtain the shape of the pole piece before cutting, test the thickness data of the pole piece in the shape before cutting, and start from the edge of the pole piece along the first direction (the width direction of the pole piece) side) continuously measure the thickness of the pole piece every 2mm towards the middle of the pole piece. And measure the angular size of the head and tail of the pole piece before cutting (corresponding to the winding start and end of the pole piece). The relevant test results are shown in Figure 2.

Then, the pre-cut pole piece is cut, and the prepared negative pole piece and separator are stacked and wound to obtain a wound battery. Then test the thickness change data of the wound cell in the first direction. Specifically, 18 point values are continuously measured at intervals of 1 mm from the head of the battery cell (the side where the tab is released) to the tail of the battery cell (the side where the tab is not released). The above test results are shown in Table 4.

The first pole piece preparation process of comparative example 1 is as follows:

The difference from Example 1 is that only one kind of slurry for the anode active material layer is prepared: mix the anode active material graphite, binder styrene-butadiene rubber, and thickener carboxymethyl cellulose in a mass ratio of 96:3:1 , add water and stir to obtain a coating slurry with a solid content of 45% and a viscosity of 4500mPa.s; during coating, the anode active material layer slurry is intermittently mopped on the surface of the copper foil. All the other preparation processes are the same as in Example 1.

For the thickness of the pole piece, the following test method can be used: take a pole piece sample with a length of 100mm, and cut 4 width sections as 4 sample points. For a certain section, along the width direction of the pole piece, at an interval of 2 mm, from the edge of the pole piece to the middle of the pole piece, use a multi-meter thickness gauge to test the thickness of the pole piece at each position point, so as to obtain 11 positions of the section The pole piece thickness value of the point, then the coating thickness value=(pole piece thickness-current collector thickness)/2.

The size of the corner can be tested by the following method: intercept the pole piece sample containing the corner (the head and tail of the pole piece), take a CCD shot at the corner, and carry out circular fitting on the corner by the computer, and the fitting The radius R of the circle is the size of the corner.

Table 1: Various parameters of the intermediate pole piece

涂层类别Coating category	涂布重量g/1540.25mm ² Coating weight g/1540.25mm ²	涂膜宽度mmCoating film width mm	压实密度g/ccCompaction densityg/cc	冷压后厚度umThickness after cold pressing um
主体涂层Body Coating	0.1420.142	8181	1.711.71	113.8113.8
边缘涂层edge coating	0.1480.148	55	1.711.71	116.1116.1

Table 2: Thickness test results of pole pieces before cutting

It can be seen from Table 2 and Figure 14 that along the first direction, the thickness of the edge of the pole piece on the tab side of the pole piece of Example 1 is significantly greater than that of Comparative Example 1. Generally, the thickness of the pole piece gradually increases from the pole piece edge to the pole piece middle, and when the thickness change is continuously small (such as the difference is not more than 3 microns), it can be considered to have transitioned to the normal thickness area of the pole piece, while from the pole piece edge The region where the difference to the smaller thickness change first occurs is considered to be the thinned region of the pole piece. Therefore, from Table 2, the width of the thinned region of Comparative Example 1 is greater than 10 mm, while the width of the thinned region of Example 1 is 6 mm, and the width of the thinned region of Example 1 is significantly smaller than the width of the thinned region of Comparative Example 1 , so it has obvious improvement effect on the energy density of the electrochemical device with the first pole piece.

Table 3: Thickness test results of pole pieces before cutting

组别group	数据量The amount of data	头部角位均值mean head angle	尾部角位均值tail angle mean
对比例1Comparative example 1	183183	4.2mm±0.5mm4.2mm±0.5mm	3.8mm±0.4mm3.8mm±0.4mm
实施例1Example 1	204204	2.6mm±0.5mm2.6mm±0.5mm	2.4mm±0.4mm2.4mm±0.4mm

As can be seen from Table 3, compared with Comparative Example 1, Example 1 has a smaller test value at the head and tail angle of the pole piece. It can be seen that the angle of Example 1 is significantly improved. Therefore, for the first pole piece The energy density of the electrochemical device also has a relatively obvious improvement effect.

Table 4: Thickness test results of wound cells

It can be seen from Table 4 and Figure 15 that along the first direction, the thickness of the battery cell in Example 1 at the head of the battery cell (outside the tab side) is significantly greater than that of the battery cell of Comparative Example 1, and the battery cell of Example 1 has a larger thickness than the battery cell of Example 1. The core head transitions to the tail (non-tab side), and the thickness of the cell does not change much, so the possibility of lithium precipitation in the electrochemical device with the first pole piece can be significantly reduced.

It should be noted that preferred embodiments of the present invention are provided in the description of the present invention and the accompanying drawings, but the present invention can be realized in many different forms, and are not limited to the embodiments described in the description. These embodiments are not intended as additional limitations on the content of the present invention, and the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive. Moreover, the above-mentioned technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as the scope of the description of the present invention; further, for those of ordinary skill in the art, improvements or changes can be made according to the above description , and all these improvements and transformations should belong to the scope of protection of the appended claims of the present invention.

Claims

An electrochemical device, comprising an electric core and a casing for accommodating the electric core, the electric core includes a first pole piece wound and arranged, a second pole piece and a pole piece located between the first pole piece and the second pole piece The diaphragm, characterized in that the first pole piece comprises:

a current collector, comprising a first surface facing the interior of the battery core and a second surface facing away from the interior of the battery core;

The tab is electrically connected to the current collector and protrudes from the current collector;

The first active material layer is disposed on the first surface; the first active material layer includes a main coating and an edge coating, and along a first direction, the edge coating is located on the main coating toward the pole one side of the ear, and is adjacent to or partially overlapped with the main coating; along the second direction, the main coating and the edge coating are extended in a belt shape, and the length of the edge coating is longer than the the length of the main body coating; the first direction is the direction in which the tab protrudes from the current collector, and the second direction is the winding direction of the first pole piece; and,

The second active material layer is arranged on the second surface.
The electrochemical device according to claim 1, wherein the winding starting end of the first pole piece includes a single-sided area, and the first surface located in the single-sided area is only provided with the edge coating, The second active material layer is provided on the second surface located in the single-sided region.
The electrochemical device according to claim 2, wherein the winding start end of the first pole piece further includes an empty foil area, and the empty foil area is closer to the first pole piece than the single-sided area. At the head of the winding starting end of the pole piece, only the edge coating is provided on the first surface located in the empty foil area, and the second surface located in the empty foil area is an empty current collector.
The electrochemical device according to claim 1, wherein the second active material layer comprises a main body and an edge, and along the first direction, the edge is located on the main body toward the tab One side of the main body part is adjacent to or partially overlapped with the main part; along the second direction, the main part and the edge part extend in a belt shape.
The electrochemical device according to claim 1, wherein the ratio of the thickness of the edge coating to the thickness of the main coating is k, 0.8≤k≤1.2.
The electrochemical device according to claim 1, characterized in that the thickness of the edge coating is 50-150 μm, and/or the width of the edge coating is 1-20 mm.
The electrochemical device according to claim 1, wherein the tab is formed integrally with the current collector.
The electrochemical device according to claim 1, wherein the first pole piece is an anode pole piece.
The electrochemical device according to claim 8, wherein both the main body coating and the edge coating comprise an anode active material and a binding agent, and the anode active material comprises artificial graphite, natural graphite, graphene , carbon nanotubes, mesocarbon microspheres, soft carbon, hard carbon, silicon carbon, silicon alloys, silicon crystals, lithium titanate, tin oxide; the binder includes polyvinylidene fluoride, At least one of polytetrafluoroethylene, fluorinated rubber, polyurethane, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, and sodium alginate.
An electronic device, characterized by comprising the electrochemical device according to any one of claims 1-9, and the electrochemical device is used to supply power to the electronic device.