Electrochemical device and electronic device

Abstract

An electrochemical device and an electronic device. The first pole piece of the electrochemical device comprises a current collector, a tab and an active material layer, the current collector comprises a first end, a second end arranged opposite to the first end, a third end and a fourth end arranged opposite to the third end. The tab and the current collector are integrally formed and extend out of the third end. The active material layer is arranged on the first surface of the current collector. The active material layer is composed of a main body area and an edge area which are connected in the first direction, and the main body area and the edge area extend from the first end to the second end. The thickness of the edge area is smaller than that of the main body area. The edge area comprises a first edge and a second edge which are oppositely arranged in the first direction, and the second edge is connected to the main body area. A connection point is arranged between the first edge and the first surface. And the included angle between the tangent line passing through the connecting point and the first surface is 45-90 degrees, so that the energy density of the electrochemical device can be improved or the lithium precipitation risk can be reduced.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an electrochemical device and an electronic device having the electrochemical device. Background Art

[0002] With the popularity of consumer electronic products such as laptops, mobile phones, handheld game consoles, tablets, mobile power supplies and drones, people's requirements for electrochemical devices (e.g., lithium-ion batteries) are becoming increasingly stringent.

[0003] However, in the prior art, the anode and cathode coating uses a gasket extrusion coating method. During coating, the thickness of the solid-liquid interface gradually changes due to the effect of gravity, forming a thinned area at the edge, resulting in the energy density of the electrochemical device still not being effectively guaranteed. Summary of the Invention

[0004] In order to solve the above deficiencies in the prior art, there is a need for an electrochemical device and an electronic device including the electrochemical device.

[0005] In a first aspect, the present application provides an electrochemical device comprising an electrode assembly. The electrode assembly comprises a first electrode plate, a second electrode plate, and a separator disposed between the first and second electrode plates. The first electrode plate comprises a first current collector, a first tab, and a first active material layer. The first current collector comprises a first surface. The first current collector further comprises a first end and a second end disposed opposite the first end along a third direction. The first current collector further comprises a third end and a fourth end disposed opposite the third end along the first direction. The third end is connected between the first and second ends, and the fourth end is connected between the first and second ends. The first tab is integrally formed with the first current collector and extends beyond the third end along the first direction. The first active material layer is disposed on the first surface. The first active material layer comprises a main region and an edge region connected along a first direction. Both the main region and the edge region extend from the first end to the second end. In the first direction, the edge region is closer to the third end than the main region. In the second direction, the thickness of the edge region is less than that of the main region. The second direction is the thickness direction of the first electrode plate, and the first, second, and third directions are perpendicular to each other. When viewed from the second direction, the edge region includes a first edge and a second edge disposed opposite each other along the first direction, with the second edge connected to the main body region. On a cross section defined by the first and second directions, a connection point is defined between the first edge and the first surface. An angle α is defined between a tangent line passing through the connection point and the first surface, with a value of 45°≤α≤90°.

[0006] By limiting the angle between the tangent line passing through the connection point and the first surface to a preset range, this application helps increase the active material content per unit area in the edge region. Therefore, on the one hand, the active material in the edge region can provide more lithium ions, which helps to increase the energy density of the electrochemical device. On the other hand, when the first electrode is a negative electrode, the edge region can provide more active material to embed lithium ions released from the positive electrode, thereby reducing the risk of lithium plating and improving the safety of the electrochemical device.

[0007] Based on the first aspect, in some possible implementations, 60° ≤ α ≤ 85°. This can further increase the active material content per unit area in the edge region, thereby further improving the energy density of the electrochemical device. When the first electrode is a negative electrode, the risk of lithium plating can be further reduced, thereby improving the safety of the electrochemical device.

[0008] Based on the first aspect, in some possible implementations, the ratio of the coating weight per unit area of ​​the edge area to the coating weight per unit area of ​​the main area is R, 95%≤R<100%. In particular, along the direction from the edge area to the main area, a test point is taken every 50 µm on the first active material layer, and the position where the thickness increase rate of two adjacent test points is less than 1% is the dividing point between the edge area and the main area. By limiting the ratio of the coating weight per unit area of ​​the edge area to the coating weight per unit area of ​​the main area, the active material content per unit area of ​​the edge area can be further increased, thereby further increasing the energy density of the electrochemical device. When the first electrode is a negative electrode, the risk of lithium plating can be further reduced, thereby providing the safety of the electrochemical device.

[0009] Based on the first aspect, in some possible implementations, 98%≤R<100%, thereby further increasing the active material content per unit area in the edge region.

[0010] Based on the first aspect, in some possible implementations, the first active material layer includes an active material and a binder. The first active material is the same in the main region and the edge region, and the binder is the same in the main region and the edge region. Therefore, the main region and the edge region can be simultaneously coated on the first current collector with the same active slurry, saving coating steps.

[0011] Based on the first aspect, in some possible implementations, the first electrode is a negative electrode, and the active material includes at least one of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, a silicon-carbon composite, silicon oxide, a lithium-tin alloy, a lithium-tin-oxygen alloy, metallic tin, tin oxide, lithium titanate, a lithium-aluminum alloy, or metallic lithium. By configuring the first electrode as a negative electrode, the edge region can provide more active material to embed lithium ions released from the positive electrode, thereby reducing the risk of lithium plating and improving the safety of the electrochemical device.

[0012] Based on the first aspect, in some possible implementations, the first electrode is a positive electrode, and the active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, a lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate. Therefore, the active material in the edge region can provide more lithium ions, thereby facilitating improved energy density of the electrochemical device.

[0013] Based on the first aspect, in some possible implementations, the first pole piece further includes an insulating layer disposed on the first surface, the insulating layer comprising inorganic particles. The insulating layer extends from the first end to the second end. Along the first direction, the insulating layer is closer to the third end than to the edge region. The insulating layer is adjacent to or at least partially overlaps the edge region. The provision of the insulating layer can reduce the risk of burrs on the first pole piece piercing the diaphragm and causing a contact short circuit, or reduce the risk of a short circuit caused by shrinkage of the separator at high temperatures, thereby further improving the safety of the electrochemical device.

[0014] Based on the first aspect, in some possible implementations, the number of the first pole tabs is at least two, thereby reducing the internal resistance of the first pole piece and improving the charge and discharge rate of the first pole piece.

[0015] A second aspect of the present application provides an electronic device comprising a storage compartment and the aforementioned electrochemical device. The electrochemical device is disposed within the storage compartment. The electronic device is powered by the electrochemical device, and the energy density of the electrochemical device is improved. When the first electrode is a negative electrode, the risk of lithium plating from the first electrode is reduced, thereby improving the safety of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic structural diagram of an electrochemical device provided in one embodiment of the present application.

[0017] Figure 2 Schematic diagrams of the structures of electrochemical devices provided in some other embodiments.

[0018] Figure 3 In some embodiments Figure 1 Schematic diagram of the first pole piece of the electrode assembly shown.

[0019] Figure 4 for Figure 3 The cross-sectional view of the first pole piece is shown along IV-IV.

[0020] Figure 5 In some other embodiments Figure 1 Schematic diagram of the first pole piece of the electrode assembly shown.

[0021] Figure 6 for Figure 5 The cross-sectional view of the first pole piece along line VI-VI is shown.

[0022] Figure 7 In other embodiments Figure 1 Schematic diagram of the first pole piece of the electrode assembly shown.

[0023] Figure 8 for Figure 7 The cross-sectional view of the first pole piece is shown along IV-IV.

[0024] Figure 9 A schematic structural diagram of an electronic device provided in one embodiment of the present application.

[0025] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0027] Below, embodiments of the present application will be described in detail. However, the present application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided to make the present application thorough and detailed for those skilled in the art.

[0028] In addition, for the sake of brevity and clarity, the size or thickness of various components or layers may be exaggerated in the accompanying drawings. Throughout the text, the same numerical value refers to the same element. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more related enumerated items. In addition, it should be understood that when element A is referred to as "connecting" element B, element A can be directly connected to element B, or there may be an intermediate element C and element A and element B can be indirectly connected to each other.

[0029] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0030] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of the described features, values, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0031] Spatial related terms, such as "on" etc., can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as "above" or "on" other elements or features will be oriented "below" or "below" other elements or features. Therefore, the exemplary term "on" can include the direction above and below. It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or parts, these elements, components, regions, layers and / or parts should not be limited by these terms. These terms are used to distinguish an element, component, region, layer or part from another element, component, region, layer or part. Therefore, the first element, component, region, layer or part discussed below can be referred to as the second element, component, region, layer or part, without departing from the teachings of the exemplary embodiments.

[0032] See also Figure 1 In one embodiment of the present application, an electrochemical device 100 is provided, comprising a housing 10 , an electrode assembly 20 , and an electrolyte (not shown). The electrode assembly 20 and the electrolyte are located within the housing 10 .

[0033] The electrode assembly 20 includes a first electrode sheet 21, a second electrode sheet 22, and a separator 23 disposed between the first electrode sheet 21 and the second electrode sheet 22. The first electrode sheet 21 includes a first current collector 210, a first electrode tab 211, and a first active material layer 212. The first current collector 210 includes a first surface 210A and a second surface 210B disposed opposite to each other, and the first active material layer 212 is disposed on the first surface 210A and the second surface 210B, respectively. The second electrode sheet 22 includes a second current collector 220, a second electrode tab 221, and a second active material layer 222. The second current collector 220 includes a third surface 220A and a fourth surface 220B disposed opposite to each other, and the second active material layer 222 is disposed on the third surface 220A and the fourth surface 220B, respectively. In some embodiments, the electrode assembly 20 is a laminated structure, that is, the first electrode sheet 21, the separator 23, and the second electrode sheet 22 are stacked. Please refer to Figure 2In other embodiments, the electrode assembly 20 may also be a wound structure.

[0034] The first electrode tab 211 is integrally connected to the first current collector 210. For example, the first electrode tab 211 can be formed by cutting the first current collector 210. The second electrode tab 221 is integrally connected to the second current collector 220. For example, the second electrode tab 221 can be formed by cutting the second current collector 220. The first electrode tab 211 and the second electrode tab 221 extend from the first current collector 210 and the second current collector 220, respectively, and are used to connect to external components (not shown). In some embodiments, there are at least two first electrode tabs 211. Providing at least two first electrode tabs 211 can prevent excessive current concentration in the first electrode sheet 21, reduce the internal resistance of the first electrode sheet 21, and thus improve the charge and discharge rate of the first electrode sheet 21. The housing 10 can be a packaging bag encapsulated with a packaging film (such as an aluminum-plastic film). The first electrode tab 211 and the second electrode tab 221 both extend from the interior of the housing 10. In other embodiments, the electrochemical device 100 can also be a steel-cased battery, an aluminum-cased battery, or the like.

[0035] The first electrode sheet 21 can be a positive electrode sheet, and the second electrode sheet 22 can be a negative electrode sheet. Accordingly, the first current collector 210 is a positive electrode current collector, and the first active material layer 212 is a positive electrode active material layer; the second current collector 220 is a negative electrode current collector, and the second active material layer 222 is a negative electrode active material layer. In other embodiments, the first electrode sheet 21 can also be a negative electrode sheet, and the second electrode sheet 22 can be a positive electrode sheet.

[0036] The positive electrode current collector may be made of aluminum foil or nickel foil, and the negative electrode current collector may be made of copper foil, nickel foil or a carbon-based current collector.

[0037] The positive electrode active material layer includes a positive electrode active material, which includes a compound (i.e., a lithiated intercalation compound) that reversibly intercalates and deintercalates active ions (such as lithium ions, sodium ions, etc., with lithium ions being used as an example below). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide, such as at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, a lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate.

[0038] The positive electrode active material layer may also include a binder to bind the active material particles to facilitate film formation and improve the bonding strength between the positive electrode active material layer and the positive electrode current collector. In some embodiments, the binder may include, but is not limited to, at least one of polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, polyacrylonitrile, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0039] The positive electrode active material layer may further include a conductive agent, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0040] The negative electrode active material layer includes a negative electrode active material, which can be a negative electrode active material that can reversibly deintercalate active ions, such as natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, silicon oxide, lithium-tin alloy, lithium-tin-oxygen alloy, metallic tin, tin oxide, lithium titanate, lithium-aluminum alloy or metallic lithium.

[0041] The negative electrode active material layer may also include a binder, which is used to bind the negative electrode active particles to facilitate film formation and improve the bonding strength between the negative electrode active material layer and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, polyacrylonitrile, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0042] The negative electrode active material layer may further include a conductive agent, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include but are not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, or any combination thereof. Metal-based materials may include but are not limited to metal powders or metal fibers, such as copper, nickel, aluminum, or silver. The conductive polymer may be a polyphenylene derivative.

[0043] A three-dimensional coordinate system is defined by a first direction X, a second direction Y, and a third direction Z that are perpendicular to each other. The first direction X is the direction in which the first electrode tab 211 extends out of the first current collector 210 , and the second direction Y is the thickness direction of the electrode assembly 20 .

[0044] See also Figure 3 and Figure 4 The first current collector 210 includes a first end 2101, a second end 2102, a third end 2103, and a fourth end 2104. The first end 2101 and the second end 2102 are disposed opposite each other along a third direction Z, and the third end 2103 and the fourth end 2104 are disposed opposite each other along a first direction X. The third end 2103 is connected between the first end 2101 and the second end 2102, and the fourth end 2104 is connected between the first end 2101 and the second end 2102. The first electrode tab 211 extends from the third end 2103 along the first direction X. When viewed from the second direction Y, the first electrode tab 211 is connected to the third end 2103.

[0045] The first active material layer 212 consists of a main region 2121 and an edge region 2122, which are connected along a first direction X. The main region 2121 extends from the first end 2101 to the second end 2102 of the first current collector 210, while the edge region 2122 also extends from the first end 2101 to the second end 2102 of the first current collector 210. Furthermore, along the first direction X, the edge region 2122 is closer to the third end 2103 of the first current collector 210 than the main region 2121. In some embodiments, the first active material layer 212 includes an active material and a binder. The active material in the main region 2121 and the edge region 2122 are of the same type, and the binder in the main region 2121 and the edge region 2122 are of the same type. In this way, the main region 2121 and the edge region 2122 can be simultaneously coated on the first current collector 210 using the same active slurry, saving coating steps.

[0046] It should be understood that the fact that both the main region 2121 and the edge region 2122 extend from the first end 2101 to the second end 2102 does not necessarily mean that the first surface 210A covers both the main region 2121 and the edge region 2122 from the first end 2101 to the second end 2102. Portions of the first surface 210A may still be free of active material. For example, when the electrode assembly 20 is in a wound structure, a portion of the first surface 210A near the first end 2101 may be free of active material, or a portion of the first surface 210A near the second end 2102 may be free of active material. Furthermore, "adjacent" means that the contacting regions of the main region 2121 and the edge region 2122 do not overlap, i.e., the orthographic projection of the main region 2121 in the second direction Y does not overlap with the orthographic projection of the edge region 2122 in the second direction Y.

[0047] like Figure 4 As shown, when viewed from the second direction Y, the edge region 2122 includes a first edge 2122A and a second edge 2122B that are oppositely disposed along the first direction X. For example, when the edge region 2122 is rectangular when viewed from the second direction Y, the first edge 2122A and the second edge 2122B are respectively two sides of the edge region 2122 that are oppositely disposed along the first direction X. The second edge 2122B is connected to the main body region 2121. In a cross section defined by the first direction X and the second direction Y, a connection point C is defined between the first edge 2122A and the first surface 210A. The angle α between the tangent line L passing through the connection point C and the first surface 210A is 45°≤α≤90°. The angle α refers to the acute angle or right angle formed between the tangent line L and the first surface 210A.

[0048] In an embodiment of the present application, the test steps for α may include: 1) discharging the electrochemical device 100 to 0 SOC% at a test temperature of 25°C, and disassembling to obtain the first electrode piece 21; 2) making a cross-section parallel to the first direction X and the second direction Y on the first electrode piece 21 to obtain a test sample; 3) under an optical microscope, measuring the angle between the tangent L passing through the connection point C in the test sample and the first surface 210A, with the opening direction of the angle toward the main body area 2121, and the measured angle is the α value.

[0049] In the embodiment of the present application, the boundary point between the main region 2121 and the edge region 2122 (i.e., the first edge 2122A) can be determined by the following methods: 1) discharging the electrochemical device 100 to 0 SOC% at a test temperature of 25°C, disassembling to obtain the first electrode piece 21; 2) making a cross section parallel to the first direction X and the second direction Y on the first electrode piece 21 to obtain a test sample; 3) under an optical microscope, determining a test point on the first active material layer 212 every 50 μm along the direction from the edge region 2122 to the main region 2121, and the test points are marked as P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, P23, P24, P25, P26, P27, P28, P29, P30, P31, P32, P33, P34, P35, P36, P37, P38, P39, P40, P41, P42, P43, P44, P45, P46, P47, P58, P59, P60, P61, P71, P72, P73, P74, P85, P96, P10, P11 x Correspondingly, the thickness values ​​of the first active material layer 212 are sequentially recorded as T1, T2, T3, T4, T5, T6, T x Etc., define T1 as the thickness value at the edge position P1 of the first active material layer 212, that is, the test value at the 0 micron position. Similarly, T2 is the test value at the 50 micron position P2, T3 is the test value at the 100 micron position P3, etc. Among them, the thickness of the first active material layer 212 refers to the distance from the surface of the first active material layer 212 away from the first current collector 210 to the first surface 210A, that is, the thickness of the first active material layer 212 on a single side of the first pole piece 21. Then calculate the thickness increase rate at each position, that is, the thickness increase rate K1 at position P2 = (T2-T1) / T1, the thickness increase rate K2 at position P3 = (T3-T2) / T2, the thickness increase rate K3 at position P4 = (T4-T3) / T3, P x Thickness increase rate K at position x-1 =(T x -T x-1 ) / T x-1 , etc. The position where the thickness increase rate is less than 1% is defined as the boundary point P between the main area 2121 and the edge area 2122 x The width W1 of the edge area 2122 is the dividing point P x The distance from the first edge 2122A, the thickness t1 of the edge region 2122 is the distance including the dividing point P x The average thickness value of all the previous test points, that is, t1=(T1+T2+T3+……+T x-2 +T x-1 +T x ) / (x), the width W2 of the main region 2121 is the difference between the total width of the first active material layer 212 and W1, and the thickness t2 of the main region 2121 is the thickness value T at the dividing point. x .

[0050] Typically, the electrode preparation process includes slurry preparation, electrode coating, and electrode rolling. When the active slurry, prepared from active materials, is applied to the current collector surface via extrusion coating, the slurry, mostly in a liquid state and fluid, is subject to surface energy and gravity, resulting in less active material at the edges of the current collector surface. This results in the active material layer at the edges being thinner than in the central region, forming a common thin zone. This reduced active material content in the thin zone reduces energy density. Furthermore, if the negative electrode's active material layer forms a thin zone, during charge and discharge, while the positive electrode releases the same number of lithium ions per unit area, the thin zone per unit area of ​​the negative electrode, containing less active material, cannot fully incorporate these ions. This results in excess lithium ions accumulating on the surface of the thin zone, where they deposit and form lithium dendrites. These dendrites can puncture the separator, leading to direct contact between the negative and positive electrodes and an electrochemical short circuit, thus reducing safety.

[0051] In the present application, the first active material layer 212 is composed of a main region 2121 and an edge region 2122. A connection point C is defined between a first edge 2122A of the edge region 2122 and the first surface 210A. By limiting the angle α between the tangent line L passing through the connection point C and the first surface 210A to within a predetermined range, the active material content per unit area of ​​the edge region 2122 is increased. Therefore, on the one hand, the active material in the edge region 2122 can provide more lithium ions, which is beneficial for improving the energy density of the electrochemical device 100. On the other hand, when the first electrode 21 is a negative electrode, the edge region 2122 can provide more active material to embed lithium ions released from the positive electrode, thereby reducing the risk of lithium plating and improving the safety of the electrochemical device 100. It is understood that to further increase the energy density of the electrochemical device 100 or reduce the risk of lithium plating, the first active material layer 212 on the second surface 210B can also be configured to have a similar structure.

[0052] In some embodiments, the angle α can be set to 60°≤α≤85°. This can further increase the active material content per unit area of ​​the edge region 2122. On the one hand, the active material in the edge region 2122 can provide more lithium ions, further improving the energy density of the electrochemical device 100. On the other hand, when the first electrode 21 is a negative electrode, the risk of lithium plating can be further reduced, thereby improving the safety of the electrochemical device 100.

[0053] In some embodiments, the ratio of the coating weight per unit area of ​​the edge region 2122 to the coating weight per unit area of ​​the main region 2121 is R, and 95%≤R<100%. In this way, the active material content per unit area of ​​the edge region 2122 can be further increased. Optionally, 98%≤R<100% can be set. In this embodiment, when the first electrode 21 is a negative electrode, the coating weight per unit area of ​​the edge region 2122 is 128 mg / 1540.25 mm 2 Up to 160 mg / 1540.25 mm 2 The coating weight per unit area of ​​the main area 2121 is 122 mg / 1540.25 mm 2 Up to 160 mg / 1540.25 mm 2 When the first electrode 21 is a positive electrode, the coating weight per unit area of ​​the edge region 2122 is 263 mg / 1540.25 mm 2 to 337 mg / 1540.25 mm 2 The coating weight per unit area of ​​the main body area 2121 is 250 mg / 1540.25 mm 2 to 337 mg / 1540.25 mm 2 .

[0054] In an embodiment of the present application, the coating weight per unit area of ​​the edge region 2122 can be measured by the following method: 1) at a test temperature of 25°C, the electrochemical device 100 is discharged to 0 SOC%, the first electrode 21 is disassembled to obtain the first electrode 21, and the electrode is cleaned with dimethyl carbonate (DMC) and then dried; 2) a double-sided film with an area of ​​S is punched out from the edge region 2122 of the first electrode 21 as a test sample, the weight of which is recorded as W1, the active material of the sample is washed away with solvent N-methylpyrrolidone (NMP), and the weight of the first current collector 210 is weighed after drying, which is recorded as W0; the coating weight per unit area of ​​the edge region 2122 is calculated by the following formula: W = [(W1-W0)] / 2S.

[0055] See also Figure 5 and Figure 6 In some embodiments, the first pole piece 21 further includes an insulating layer 30 disposed on the first surface 210A. The insulating layer 30 extends from the first end 2101 to the second end 2102. Along the first direction X, the insulating layer 30 is closer to the third end 2103 than the edge area 2122. The insulating layer 30 is adjacent to or at least partially overlaps the edge area 2122. By providing the insulating layer 30, the risk of burrs of the first pole piece 21 (the above-mentioned burrs may be generated during the cutting process, but this application does not limit this) piercing the isolation membrane 23 and causing contact short circuits can be reduced, and the risk of contact short circuits caused by shrinkage of the isolation membrane 23 at high temperatures can also be reduced.

[0056] It should be understood that "partial overlap" in the present application means that in the thickness direction of the first pole piece 21, that is, the second direction Y, there is an overlapping area between the projection of the edge area 2122 and the projection of the insulating layer 30, that is, in the area where the edge area 2122 contacts the insulating layer 30, the edge portion of the insulating layer 30 covers the edge area 2122.

[0057] like Figure 7 and Figure 8 As shown, in some embodiments, an insulating layer 30 is also provided on a portion of the surface of the first electrode tab 211. Specifically, the insulating layer 30 is provided on the end of the first electrode tab 211 connected to the first current collector 210, while the insulating layer 30 is not provided on the end of the first electrode tab 211 facing away from the first current collector 210. The first electrode tab 211 without the insulating layer 30 can extend out of the housing 10 to electrically connect to external components. By providing the insulating layer 30 on a portion of the surface of the first electrode tab 211, the risk of burrs generated during the cutting process of the first electrode tab 211 piercing the separator 23 and causing a short circuit can be reduced.

[0058] In some embodiments, the insulating layer 30 includes inorganic particles and polymers, the inorganic particles include at least one of aluminum oxide, silicon dioxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium dioxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate, and the polymer includes at least one of polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, styrene-butadiene rubber, polyvinyl alcohol, polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, water-based acrylic resin, carboxymethyl cellulose or sodium carboxymethyl cellulose.

[0059] In some embodiments, the second electrode piece 22 can have a structure similar to that of the first electrode piece 21, and a detailed description thereof will not be repeated here. By also providing the second electrode piece 22 with an edge region similar to that of the first electrode piece 21, the active material content per unit area of ​​the edge region can be increased, which is beneficial for improving the energy density of the electrochemical device 100. Furthermore, the risk of lithium plating can be reduced, thereby improving the safety of the electrochemical device 100.

[0060] Although lithium-ion batteries are used as examples above, the electrochemical device 100 of the present application also includes other devices capable of generating electrochemical reactions. Specifically, the electrochemical device 100 includes primary batteries, secondary batteries, fuel cells, solar cells, and capacitors (e.g., supercapacitors). Alternatively, the electrochemical device 100 may be a lithium secondary battery, including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, and lithium ion polymer secondary batteries.

[0061] See also Figure 9 The present application also provides an electronic device 1 comprising a storage compartment 101 and an electrochemical device 100 disposed within the storage compartment 101. The electronic device 1 supplies power to a load (not shown) via the electrochemical device 100, and the energy density of the electrochemical device 100 is improved. When the first electrode 21 is a negative electrode, the risk of lithium plating from the first electrode 21 is reduced, thereby improving the safety of the electrochemical device 100. The electronic device 1 of the present application may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, lighting fixtures, toys, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0062] The present application is described in detail below through specific examples and comparative examples. Herein, the present application is described using an electrochemical device 100 as a lithium-ion secondary battery, a first electrode 21 as a positive electrode, and a second electrode 22 as a negative electrode, as an example. The present application is described in conjunction with specific preparation processes and testing methods. Those skilled in the art will understand that the preparation methods described herein are merely examples, and any other suitable preparation methods are within the scope of the present application.

[0063] Examples 1-7 Positive electrode sheet preparation: Lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone (NMP) solvent at a mass ratio of 96.5:1.5:2.0 to form a positive electrode active slurry. Aluminum foil is used as the positive electrode current collector. Adhesive tape is affixed to the aluminum foil according to the electrode sheet width design requirements. Furthermore, a gravure primer is formed by gravure printing according to the design requirements. The positive electrode active slurry is then applied to the positive electrode current collector with the adhesive tape and gravure primer. The more slurry applied to the adhesive tape (the area of ​​the slurry applied to the adhesive tape accounts for greater than 0 and less than or equal to 100% in Examples 1-6), the larger the angle α formed on the electrode sheet. After drying to remove the solvent (NMP), the positive electrode sheet is obtained through stripping, dust removal, cold pressing, tab forming, and cutting.

[0064] Negative electrode sheet preparation: Graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are dissolved in deionized water at a mass ratio of 96.5:1.0:1.0:1.5. The mixture is stirred in a vacuum mixer until uniform, creating a negative electrode active slurry. Copper foil is used as the negative electrode current collector, and the design requires gravure printing to form a gravure primer. The negative electrode active slurry is then applied to the gravure-primed negative electrode current collector. After drying to remove the solvent (deionized water), the negative electrode sheet is produced through cold pressing, electrode sheet slitting, and welding of the negative electrode tabs.

[0065] Preparation of electrolyte: In a dry argon atmosphere, first mix the organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) at a mass ratio of EC:EMC:DEC=30:50:20, then add lithium hexafluorophosphate (LiPF6) to the organic solvent, dissolve it and mix it evenly to obtain an electrolyte with a lithium salt concentration of 1.15M.

[0066] Battery preparation: A polyethylene (PE) separator is placed between the positive electrode and the negative electrode, and the electrode assembly is obtained by winding. The electrode assembly is placed in a packaging bag, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a lithium-ion secondary battery is obtained.

[0067] Examples 8-14 The difference from Example 1 lies in the preparation method of the positive electrode sheet and the negative electrode sheet.

[0068] To prepare the positive electrode sheet, lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1.5:2.0 to form a positive electrode active slurry. Aluminum foil is used as the positive electrode current collector, and a gravure primer is formed through gravure printing. The negative electrode active slurry is then applied to the gravure-primed positive electrode current collector. After drying to remove the solvent, the positive electrode sheet is completed through cold pressing, electrode sheet slitting, and welding of the positive electrode tabs.

[0069] To prepare the negative electrode sheet, graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are dissolved in deionized water at a mass ratio of 96.5:1.0:1.0:1.5. The mixture is stirred in a vacuum mixer until uniform, creating the negative electrode active slurry. Copper foil is used as the negative electrode current collector. Adhesive tape is applied to the copper foil according to the designed width of the electrode sheet. Furthermore, the design requires gravure printing to form a gravure primer. The negative electrode active slurry is then applied to the negative electrode current collector with the adhesive tape and gravure primer. The more slurry applied to the adhesive tape, the larger the angle α formed on the electrode sheet. After drying to remove the solvent (deionized water), the negative electrode sheet is produced through debonding, dust removal, cold pressing, tab forming, and cutting.

[0070] Examples 15-16 The difference from Example 1 is that when preparing the negative electrode sheet, graphite, conductive carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are dissolved in deionized water at a mass ratio of 96.5:1.0:1.0:1.5 and stirred in a vacuum mixer until the mixture is homogeneous to obtain a negative electrode active slurry. Copper foil is used as the negative electrode current collector, and adhesive tape is affixed to the copper foil according to the design width of the electrode sheet. Furthermore, the design requires forming a gravure primer by gravure printing. The negative electrode active slurry is then applied to the negative electrode current collector with adhesive tape and gravure primer. After drying to remove the solvent (deionized water), the negative electrode sheet is obtained through the following steps: stripping, dust removal, cold pressing, tab forming, and cutting.

[0071] Comparative Example 1-2 The difference from Example 1 is that, when preparing the positive electrode sheet, aluminum foil is used as the positive electrode current collector, and a gravure primer is formed by gravure printing according to the design requirements; then the positive electrode active slurry is coated on the positive electrode current collector with the gravure primer, and after drying to remove the solvent (deionized water), the positive electrode sheet is obtained by cold pressing, stripping the electrode sheet, and welding the positive electrode tabs.

[0072] 100 secondary batteries of each embodiment and comparative example were taken for energy density and lithium deposition tests, and the test results are recorded in Table 3.

[0073] The energy density test procedure involves placing the battery in a constant temperature chamber at 25°C ± 2°C, charging it at 0.7C to 4.35V with a cut-off current of 0.025C, and discharging it at 0.2C to 3.0V to obtain the battery capacity, which is then divided by the battery volume to obtain the energy density. The energy density of 100 secondary batteries is then averaged.

[0074] The lithium deposition test steps include: placing the battery in a constant temperature box at 25℃±2℃ for 2 hours, charging it at a constant current of 3C to 4.4V, then charging it at a constant voltage of 4.4V to 0.02C and letting it rest for 15 minutes; then discharging it at a constant current of 0.5C to 3.0V. This is one lithium deposition test cycle. After repeating the above lithium deposition test cycle 100 times, the battery is discharged at a constant current of 0.5C to 3.0V. After that, the battery is disassembled and the surface of the active material layer of the negative electrode is inspected for lithium deposition. If there is a gray area, it is lithium deposition; if there is no gray area, it is not lithium deposition. Then, the proportion of lithium deposition in 100 secondary batteries is counted.

[0075] Table 1 Among them, after the positive electrode sheets or negative electrode sheets of each embodiment in Table 1 are divided into strips, an angle of approximately 90 degrees can be formed on the electrode sheets.

[0076] As shown in Table 1, compared to Comparative Example 1, the included angles of the positive electrode tabs in Examples 1-7 satisfy the following conditions: 45° ≤ α ≤ 90°. Consequently, the active material content in the edge region of the positive electrode tabs is increased, providing more lithium ions and improving the energy density of the secondary battery. Specifically, the included angles of the positive electrode tabs in Examples 3-6 satisfy the following conditions: 60° ≤ α ≤ 85°, further improving the energy density of the secondary battery.

[0077] Compared with Comparative Example 2, the angle of the negative electrode sheets in Examples 8-14 satisfies: 45°≤α≤85°, so the active material content in the edge area of ​​the negative electrode sheets is increased, providing more accommodation space for the embedding of lithium ions. Therefore, the negative electrode sheets do not have the problem of lithium plating, thereby improving the safety of the secondary battery.

[0078] In Examples 15-16, the angles between the positive and negative electrodes satisfy the following condition: 45°≤α≤90°. Therefore, the energy density of the secondary battery can be improved. At the same time, the negative electrode does not have the problem of lithium plating, so that the secondary battery can have both high energy density and safety performance.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. An electrochemical device, comprising an electrode assembly, wherein the electrode assembly comprises a first electrode piece, a second electrode piece, and a separator disposed between the first electrode piece and the second electrode piece, wherein: The first pole piece includes: a first current collector including a first surface, the first current collector further including a first end and a second end disposed opposite to the first end along a third direction; the first current collector further including a third end and a fourth end disposed opposite to each other along the first direction, the third end connected between the first end and the second end, and the fourth end connected between the first end and the second end; a first electrode tab, integrally formed with the first current collector and extending out of the third end along the first direction; and a first active material layer disposed on the first surface, the first active material layer comprising a main region and an edge region connected along the first direction, the main region and the edge region both extending from the first end to the second end, the edge region being closer to the third end than the main region along the first direction, the edge region being thinner than the main region along the second direction, the second direction being the thickness direction of the first electrode sheet, and the first direction, the second direction, and the third direction being perpendicular to each other; Observed from the second direction, the edge area includes a first edge and a second edge arranged opposite to each other along the first direction, the second edge is connected to the main area, and on the cross-section defined by the first direction and the second direction, there is a connection point between the first edge and the first surface, and the angle between the tangent passing through the connection point and the first surface is α, 45°≤α≤90°.

2. The electrochemical device according to claim 1, wherein 60°≤α≤85°。 3. The electrochemical device according to claim 1, wherein The ratio of the coating weight per unit area of ​​the edge area to the coating weight per unit area of ​​the main body area is R, and 95%≤R<100%.

4. The electrochemical device according to claim 3, wherein 98%≤R<100%。 5. The electrochemical device according to claim 1, wherein The first active material layer includes an active material and a binder. The active material in the main body region and the edge region are of the same type. The binder in the main body region and the edge region are of the same type.

6. The electrochemical device according to claim 5, wherein The first electrode is a negative electrode, and the active material includes at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, silicon oxide, lithium-tin alloy, lithium-tin-oxygen alloy, metallic tin, tin oxide, lithium titanate, lithium-aluminum alloy or metallic lithium.

7. The electrochemical device according to claim 5, wherein The first electrode is a positive electrode, and the active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

8. The electrochemical device according to claim 7, wherein The first pole piece also includes an insulating layer arranged on the first surface, the insulating layer contains inorganic particles, and the insulating layer extends from the first end to the second end. Along the first direction, the insulating layer is closer to the third end than the edge area, and the insulating layer is adjacent to or at least partially overlaps with the edge area.

9. The electrochemical device according to claim 1, wherein The number of the first electrode tabs is at least two.

10. An electronic device comprising a storage compartment, wherein: The electronic device further comprises the electrochemical device according to any one of claims 1 to 9, wherein the electrochemical device is disposed in the containing chamber.

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