Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises an electrode assembly, wherein the electrode assembly comprises an anode sheet, the anode sheet comprising a current collector and an active layer disposed on at least one surface of the current collector, the surface density of the active layer ranging from 90 mg / 1540.25 mm2 to 180 mg / 1540.25 mm2, and the active layer being provided with a plurality of strip-shaped grooves. The secondary battery can improve the cycling performance and increase the energy density.

Description

Secondary batteries and electronic devices Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries are widely used in electric vehicles and consumer electronics due to their high energy density, high output power, and long cycle life. With technological advancements, the demand for the energy density of secondary batteries is increasing. The most direct and effective method for improving battery energy density in existing technologies involves increasing the surface density of the electrode film. However, while increasing the surface density of the battery can improve its energy density, it can also deteriorate its kinetic performance, leading to lithium plating and affecting its cycling performance.

[0003] Summary of the Invention

[0004] One purpose of the present application is to provide a secondary battery and an electronic device that can improve cycle performance while increasing energy density.

[0005] The first aspect of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising an anode electrode sheet, the anode electrode sheet comprising a current collector and an active layer disposed on at least one surface of the current collector, the surface density of the active layer being 90 mg / 1540.25 mm 2 ~180mg / 1540.25mm 2 , the active layer is provided with a plurality of strip-shaped grooves.

[0006] The secondary battery of this application has an active layer surface density of 90 mg / 1540.25 mm 2 ~180mg / 1540.25mm 2 , so that the active layer has an appropriate thickness and the secondary battery achieves high energy density. In addition, multiple strip-shaped grooves are set on the active layer to reserve space for electrolyte transmission, improving the electrolyte transmission capacity, improving the lithium precipitation problem caused by insufficient kinetics, and improving cycle performance.

[0007] According to some embodiments of the present application, the spacing between two adjacent strip-shaped grooves is 100μm to 2000μm. When the spacing is less than 100μm, the spacing is too small, making processing difficult, and reducing the bonding area between the electrode and the diaphragm, thereby reducing the bonding force and causing the electrode and diaphragm delamination problem. When the spacing is greater than 2000μm, the spacing is too large, and the effect of improving the electrolyte transport capacity is limited, and the effect of improving the cycle performance is limited.

[0008] According to some embodiments of the present application, the spacing between two adjacent strip-shaped grooves is 300 μm to 1000 μm, which has a good effect on improving the energy transmission of the electrolyte and significantly improves the cycle performance.

[0009] According to some embodiments of the present application, the spacing between two adjacent strip-shaped grooves is 500 μm to 800 μm, which has a better effect on improving the energy transmission of the electrolyte and significantly improves the cycle performance.

[0010] According to some embodiments of the present application, the thickness of the active layer is D1, the depth of the strip groove is D2, and 3% ≤ D2 / D1 ≤ 70%. When D2 / D1 < 3%, D2 is too small, and the improvement effect on cycle performance is limited; when D2 / D1 > 70%, D2 is too large, excessive etching may cause damage to the current collector, and may cause lithium deposition in the strip groove, with limited improvement effect on cycle performance. Furthermore, 8% ≤ D2 / D1 ≤ 70%.

[0011] According to some embodiments of the present application, 15%≤D2 / D1≤40%, which is more conducive to improving the cycle performance.

[0012] According to some embodiments of the present application, the secondary battery further includes a tab, the current collector includes a first edge and a second edge opposite to each other in a first direction, the tab extends out of the electrode assembly along the first direction through the first edge, and the strip-shaped groove is arranged perpendicular, parallel or inclined relative to the first edge.

[0013] According to some embodiments of the present application, the current collector includes a third edge and a fourth edge opposite to each other in a second direction perpendicular to the first direction, and a plurality of strip-shaped grooves are arranged from the third edge to the fourth edge.

[0014] According to some embodiments of the present application, the strip-shaped groove includes a first end located on one side of the first edge in the first direction, the active layer includes a first area corresponding to the pole ear in the first direction, and the distance between the first end of the strip-shaped groove located in the first area and the first edge is 0 to 3 mm, thereby reducing the risk of etching the pole ear when the strip-shaped groove is formed by etching.

[0015] According to some embodiments of the present application, the secondary battery has a notch, the electrode assembly is a laminated structure, the electrode assembly includes a first end face, a first side face, a second side face, a third side face, and a second end face connected in sequence, the first end face and the second end face are arranged opposite to each other in a first direction, the first side face, the second side face, and the third side face are located on the same side of the electrode assembly in a second direction perpendicular to the first direction, the first side face and the second side face are surrounded to form a notch, and the coating surface density of the active layer is greater than or equal to 130 mg / 1540.25 mm 2 .

[0016] According to some embodiments of the present application, the secondary battery is L-shaped.

[0017] According to some embodiments of the present application, in the second direction, the length of the electrode assembly is L1; in the first direction, the width of the electrode assembly is L2, and 1.0≤L1 / L2≤3.0.

[0018] According to some embodiments of the present application, 1.25≤L1 / L2≤3.0.

[0019] According to some embodiments of the present application, the compacted density of the active layer is greater than 1.72 g / cm 3 .

[0020] According to some embodiments of the present application, the electrode assembly further includes a diaphragm and a cathode electrode piece, the diaphragm is disposed between the anode electrode piece and the cathode electrode piece, and the peel strength between the diaphragm and the anode electrode piece is 5 to 15 N / m.

[0021] A second aspect of the present application provides an electronic device comprising any of the above-mentioned secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a schematic diagram of a secondary battery provided in one embodiment of the present application viewed along a third direction.

[0023] FIG2 is a schematic diagram of an electrode assembly provided in one embodiment of the present application observed along a first direction.

[0024] FIG3 is a schematic diagram of an anode electrode provided by one embodiment of the present application observed along a third direction.

[0025] FIG4 is a schematic cross-sectional view of an anode electrode sheet according to an embodiment of the present application.

[0026] FIG5 is a schematic diagram of an anode electrode provided in another embodiment of the present application observed along a third direction.

[0027] FIG6 is a schematic diagram of an anode electrode provided in another embodiment of the present application observed along a third direction.

[0028] FIG7 is a schematic cross-sectional view of a diaphragm provided in one embodiment of the present application.

[0029] Description of main component symbols

[0030] Secondary battery 100

[0031] Housing 10

[0032] Electrode assembly 20

[0033] Electrode terminal 30

[0034] Cathode tab 31

[0035] Anode tab 32

[0036] Notches 101, 210

[0037] First end wall 11

[0038] First side wall 12

[0039] Second side wall 13

[0040] The third side wall 14

[0041] Second end wall 15

[0042] Fourth side wall 16

[0043] Cathode plate 21

[0044] Anode plate 22

[0045] Diaphragm 23

[0046] Cathode current collector 211

[0047] Cathode active layer 212

[0048] Current collector 221

[0049] Active layer 222

[0050] First end surface 201

[0051] First side 202

[0052] Second side 203

[0053] The third side 204

[0054] Second end surface 205

[0055] Fourth side 206

[0056] First edge 221a

[0057] Second edge 221b

[0058] Strip groove 22a

[0059] First area 220

[0060] Third edge 221c

[0061] Fourth edge 221d

[0062] First end 22a1

[0063] Second end 22a2

[0064] Porous base membrane 231

[0065] Adhesive layer 232

[0066] First direction X

[0067] Second direction Y

[0068] The third direction Z

[0069] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0070] 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 of 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.

[0071] 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.

[0072] In addition, for the sake of brevity and clarity, the size or thickness of various components, layers may be amplified 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, or when element A is referred to as "connecting" to element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0073] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0074] 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.

[0075] It should be understood that although the terms first, second, third, etc. may 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 one 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 may be referred to as the second element, component, region, layer, or part without departing from the teachings of the exemplary embodiments.

[0076] Referring to Figure 1, an embodiment of the present application provides a secondary battery 100, comprising a housing 10, an electrode assembly 20, an electrolyte, and an electrode terminal 30. The electrode assembly 20 and the electrolyte are housed in the housing 10. The electrode terminal 30 is connected to the electrode assembly 20 and extends from one side of the housing 10 along a first direction X to connect to external components. In this application, the first direction X refers to the longitudinal direction of the secondary battery 100. In this embodiment, there are two electrode terminals 30, namely a cathode terminal and an anode terminal, and the two electrode terminals 30 are located on the same side of the secondary battery 100.

[0077] The secondary battery 100 can have a regular shape, such as a rectangle or a circle, or an irregular shape, such as a T-shape or an L-shape. In this embodiment, the secondary battery 100 is L-shaped. The secondary battery 100 has a recess 101. The recess 101 is used to accommodate external components to improve space utilization.

[0078] The housing 10 is generally L-shaped and includes a first end wall 11, a first side wall 12, a second side wall 13, a third side wall 14, a second end wall 15, and a fourth side wall 16, which are connected end to end. The electrode terminal 30 extends out of the housing 10 along the first direction X through the first end wall 11. The second end wall 15 and the first end wall 11 are arranged opposite each other in the first direction. The first side wall 12, the second side wall 13, and the third side wall 14 are located on the same side of the housing 10 in a second direction Y perpendicular to the first direction X, and the fourth side wall 16 and the third side wall 14 are arranged opposite each other in the second direction Y. The first side wall 12 and the second side wall 13 are arranged to form a recess 101. The housing 10 can be a packaging bag obtained by packaging with a packaging film (such as an aluminum-plastic film or a steel-plastic film), or it can be a metal housing, which is not limited in this application.

[0079] The electrode assembly 20 is generally L-shaped and includes a first end face 201, a first side face 202, a second side face 203, a third side face 204, a second end face 205, and a fourth side face 206, which are connected end to end. The secondary battery 100 also includes a cathode tab 31 (see FIG. 2 ) and an anode tab 32 (see FIG. 2 ). The cathode terminal is connected to the electrode assembly 20 via the cathode tab 31, and the anode terminal is connected to the electrode assembly 20 via the anode tab 32. The cathode tab 31 and the anode tab 32 extend out of the electrode assembly 20 along a first direction X through the first end face 201. The second end face 205 and the first end face 201 are opposite each other in the first direction. The first side face 202, the second side face 203, and the third side face 204 are located on the same side of the housing 10 in a second direction Y perpendicular to the first direction X, and the fourth side face 206 and the third side face 204 are opposite each other in the second direction Y. The first side face 202 and the second side face 203 enclose a recess 210. The shape of the notch 210 is substantially the same as that of the notch 101, and the notch 210 is disposed around the notch 101. In the case of an L-shaped secondary battery 100, the electrolyte tends to accumulate in the area surrounding the fourth side surface 206 of the electrode assembly 20, causing an increase in impedance in the local area and making lithium deposition more likely to occur on the side of the electrode assembly 20 where the fourth side surface 206 is located.

[0080] In the second direction Y, the distance between the third side surface 204 and the fourth side surface 206 is L1. In the first direction X, the distance between the first end surface 201 and the second end surface 205 is L2. In some embodiments, 1.0≤L1 / L2≤3.0. Preferably, 1.25≤L1 / L2≤3.0.

[0081] Referring to Figures 1 and 2, the electrode assembly 20 includes a cathode electrode sheet 21, an anode electrode sheet 22, and a separator 23 disposed between the cathode electrode sheet 21 and the anode electrode sheet 22. The cathode electrode sheet 21, the separator 23, and the anode electrode sheet 22 are stacked in sequence along a third direction Z to form a laminated structure. The first direction X, the second direction Y, and the third direction Z are mutually perpendicular. In other embodiments, the cathode electrode sheet 21, the separator 23, and the anode electrode sheet 22 are stacked along the third direction Z and then wound to form a wound structure.

[0082] The cathode electrode 21 includes a cathode current collector 211 and a cathode active layer 212 disposed on at least one surface of the cathode current collector 211. The cathode current collector 211 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. The cathode tab 31 is connected to the cathode current collector 211 and the corresponding electrode terminal 30. The cathode tab 31 may extend outward from one end of the cathode current collector 211, or the cathode tab 31 may be welded to the cathode current collector 211 and extend outside the electrode assembly 20. The cathode active layer 212 includes a cathode active material, which may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based materials, lithium nickel cobalt aluminum oxide, and combinations thereof.

[0083] In some embodiments, cathode active layer 212 further includes a binder and, optionally, a conductive agent. The binder can improve the bonding between active material particles and between the active material and the current collector. Examples of binders include, but are not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, and polyvinyl fluoride. The conductive agent can improve the conductivity of the electrode. Examples include, but are not limited to, graphite, carbon black, acetylene black, and metal powders.

[0084] The anode electrode 22 includes a current collector 221 and an active layer 222 disposed on at least one surface of the current collector 221. The current collector 221 includes at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Al, and combinations thereof. The anode tab 32 is connected to the current collector 221 and the corresponding electrode terminal 30. The anode tab 32 may extend outward from one end of the current collector 221, or the anode tab 32 may be welded to the current collector 221 and extend out of the electrode assembly 20. The active layer 222 includes an anode active material, which may include one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxides, silicon-carbon composites, lithium titanate, and metals capable of forming alloys with lithium.

[0085] In some embodiments, the active layer 222 further includes a binder and, optionally, a conductive agent. The binder can improve the bonding between the active material particles and between the active material and the current collector. Examples of binders include, but are not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, and polyvinyl fluoride. The conductive agent can improve the conductivity of the electrode. Examples include, but are not limited to, graphite, carbon black, acetylene black, and metal powders.

[0086] In some embodiments, the areal density of the active layer 222 is 90 mg / 1540.25 mm 2 ~180mg / 1540.25mm 2The surface density is the mass of the active layer per unit area on a single surface of the current collector. When the surface density of the active layer 222 is within the above range, it is beneficial for the secondary battery 100 to obtain a high energy density. When the surface density is less than 90 mg / 1540.25 mm 2 When the thickness of the active layer on one side of the current collector is too small, it is limited by the particle size of the active material, and there are problems such as processing scratches and cold pressing windows; when the surface density is greater than 180mg / 1540.25mm 2 When the active layer on one side of the current collector is too thick, lithium ion transport is difficult, the kinetics are too poor, and it cannot meet the requirements of secondary batteries. The high surface density will lead to poor wettability of the anode electrode 22, and the electrolyte cannot fully penetrate the anode active material, affecting the kinetic performance and easily causing lithium precipitation problems.

[0087] In some embodiments, the areal density of the active layer 222 is 130 mg / 1540.25 mm 2 ~180mg / 1540.25mm 2 In the case of an L-shaped secondary battery 100 , when the surface density of the active layer 222 is within the above range, lithium deposition is more likely to occur on the side of the electrode assembly 20 where the fourth side surface 206 is located.

[0088] In some embodiments, the active layer 222 has a compacted density greater than 1.72 g / cm 3 The compaction density is the ratio of the surface density of the active layer per unit area on a single surface of the current collector to its thickness. When the compaction density of the active layer 222 is within the above range, it is beneficial to obtain a high energy density. A high compaction density can lead to deterioration of dynamic performance and the risk of lithium plating.

[0089] Referring to Figure 3 , the current collector 221 includes a first edge 221a and a second edge 221b that are opposite to each other in a first direction X, and a third edge 221c and a fourth edge 221d that are opposite to each other in a second direction Y. The anode tab 32 extends out of the electrode assembly along the first direction X via the first edge 221a. The second direction Y is perpendicular to the first direction X. The active layer 222 is provided with a plurality of strip-shaped grooves 22a. The plurality of strip-shaped grooves 22a extend from the third edge 221c to the fourth edge 221d. In other words, the plurality of strip-shaped grooves 22a are distributed throughout the current collector 221. In other embodiments, the plurality of strip-shaped grooves 22a are distributed in a portion of the current collector 221, for example, only in the edge region of the current collector 221. The strip-shaped grooves 22a reserve space for electrolyte transport, improve electrolyte transport, mitigate lithium plating, and thus enhance cycling performance. The strip-shaped grooves 22a are formed by removing portions of the active layer 222. Any conventional technique may be used to remove a portion of the active layer 222 , for example, a laser etching process may be used to remove a portion of the active layer 222 to form the strip-shaped grooves 22 a .

[0090] Referring to Figure 3 , the strip-shaped groove 22a includes a first end 22a1 located on the first edge 221a side in the first direction X, and a second end 22a2 located on the second edge 221b side. The active layer 222 includes a first region 220 corresponding to the anode tab 32 in the first direction X. The first region 220 forms a first projected pattern along the third direction Z on the plane of the current collector 221, while the anode tab 32 forms a second projected pattern along the third direction Z on the plane of the current collector 221. Along the first direction X, two opposing sides of the first projected pattern in the second direction Y are aligned with two opposing sides of the second projected pattern in the second direction Y. In the first direction X, the minimum distance between the first end 22a1 of the strip-shaped groove 22a in the first region 220 and the first edge 221a is 0 to 3 mm. This reduces the risk of etching into the anode tab 32 during the etching process to form the strip-shaped groove 22a. In addition, the strip-shaped groove 22 a tends to penetrate the edge of the active layer 222 located at the first edge 221 a , so that the electrolyte can quickly enter the strip-shaped groove 22 a , which is beneficial to improving the transmission performance of the electrolyte.

[0091] In some embodiments, the minimum distance between the first end 22a1 of each strip-shaped groove 22a and the first edge 221a is 0 to 3 mm, and the minimum distance between the second end 22a2 of each strip-shaped groove 22a and the second edge 221b is 0 to 3 mm. In this way, each strip-shaped groove 22a tends to penetrate the active layer 222 in the first direction X, which is beneficial to improving the transmission performance of the electrolyte.

[0092] Please refer to Figure 3. A plurality of strip grooves 22a are arranged parallel to each other. When viewed along the third direction Z, the distance between two adjacent strip grooves 22a is D3. In this application, the distance D3 between two adjacent strip grooves 22a refers to the distance between the geometric center lines of the two adjacent strip grooves. In some embodiments, 100μm≤D3≤2000μm. When D3 is less than 100μm, D3 is too small, which is difficult to achieve due to the limitations of processing equipment (such as lasers), and the production efficiency is low. In addition, D3 is too small, which reduces the bonding area between the electrode and the diaphragm, reduces the bonding force, and causes the electrode diaphragm delamination problem. When D3 is greater than 2000μm, under the condition of a certain electrode area, the number of strip grooves is small, the effect of improving the electrolyte transmission capacity is limited, the effect of improving the lithium plating problem is limited, and the effect of improving the cycle performance is limited. Preferably, 300μm≤D3≤1000μm, which has a better effect on improving the electrolyte energy transmission, is more conducive to improving lithium plating, and significantly improves the cycle performance. Furthermore, 500 μm ≤ D3 ≤ 800 μm, which has a better effect on improving the energy transmission of the electrolyte and significantly improves the cycle performance.

[0093] Referring to Figure 4 , in the third direction Z, the depth of the strip-shaped groove 22a is D2, and the thickness of the active layer 222 is D1. In this application, the depth of the strip-shaped groove 22a refers to the distance between the deepest point of the strip-shaped groove 22a and the surface of the active layer 222. In some embodiments, 3% ≤ D2 / D1 ≤ 70%. When D2 / D1 < 3%, D2 is too small, and etching to form the strip-shaped groove 22a may result in poor etching, affecting electrolyte transport performance. Furthermore, a too small D2 has limited effect on improving kinetics. When D2 / D1 > 70%, D2 is too large, and excessive etching may damage the current collector 221. It may also cause the anode capacity to be less than the cathode capacity, leading to lithium plating at the location of the strip-shaped groove 22a. Preferably, 8% ≤ D2 / D1 ≤ 70%. More preferably, 15% ≤ D2 / D1 ≤ 40% is more conducive to improving cycling performance. It should be noted that in the present application, when the energy density remains unchanged, that is, when the mass loss of the active layer removed to form the strip grooves is fixed, the conditions that need to be met are obtained for the thickness D1 of the active layer, the depth D2 of the strip grooves, and the distance D3 between two adjacent strip grooves.

[0094] Referring to FIG3 , the strip-shaped groove 22a is disposed perpendicularly to the first edge 221a. Referring to FIG5 , in another embodiment, the strip-shaped groove 22a is disposed parallel to the first edge 221a. Referring to FIG6 , in another embodiment, the strip-shaped groove 22a is disposed obliquely relative to the first edge 221a, and the angle θ between the strip-shaped groove 22a and the first edge 221a satisfies 0°<θ<90°. Preferably, θ=45°, which further improves the lithium deposition effect.

[0095] Referring to FIG. 7 , in some embodiments, the diaphragm 23 includes a porous base film 231 and an adhesive layer 232 that are stacked. The adhesive layer 232 is disposed on the surface of the porous base film 231 facing the anode electrode and is bonded to its active layer. The adhesive layer 232 is bonded to the anode electrode to reduce the risk of delamination and misalignment between the diaphragm 23 and the anode electrode. The adhesive layer 232 can also be disposed on the surface of the porous base film 231 facing the cathode electrode and bonded to the cathode active layer to reduce the risk of delamination and misalignment between the diaphragm 23 and the cathode electrode. In other embodiments, the diaphragm 23 includes a binder, and the diaphragm 23 is bonded to the anode electrode and the cathode electrode.

[0096] In some embodiments, the porous base film 231 includes at least one of polyethylene terephthalate, polyethylene, polypropylene, phenolic resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, or polyurethane. In some embodiments, the adhesive layer 232 includes at least one of polymethyl methacrylate, polyacrylic acid, polyacrylic acid salt, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, or polyimide.

[0097] In some embodiments, the peel strength between the separator 23 and the anode electrode is 5 to 15 N / m.

[0098] One embodiment of the present application further provides an electronic device comprising any of the above-described secondary batteries. The electronic device 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 head-mounted stereo 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 lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0099] The performance of the secondary battery provided in this application is described below through specific examples and comparative examples.

[0100] Example 1

[0101] Preparation of the cathode electrode: The cathode active material (lithium cobalt oxide), conductive agent (conductive carbon black), and binder (polyvinylidene fluoride) are dissolved in N-methylpyrrolidone solution at a weight ratio of 97.5:1:1.5 to form a cathode slurry with a solid content of 75%. Using aluminum foil as a current collector, the cathode slurry is applied to the surface of the cathode current collector to form the cathode active layer. Anode electrodes are then cold pressed and cut.

[0102] Preparation of the anode pole piece: The anode active material (graphite), conductive agent (conductive carbon black), thickener (sodium carboxymethyl cellulose), and binder (styrene-butadiene rubber) are mixed in a mass ratio of 97.5:1:0.5:1, and then deionized water is added as a solvent and stirred evenly to obtain an anode slurry with a solid content of 50wt%. Copper foil is used as a current collector, and the anode slurry is coated on the surface of the anode current collector to obtain an anode active layer. Subsequently, the anode pole piece is obtained by cold pressing and cutting. A laser etching process is used to etch a plurality of strip grooves on the anode active layer. The plurality of strip grooves are distributed throughout the anode active layer, and the strip grooves are arranged parallel to the first edge of the anode current collector. The structure of the anode pole piece is shown in Figure 3.

[0103] Preparation of the diaphragm: A polyethylene film is used as the porous base film, and an adhesive layer is coated on the surface of the porous base film. The peel strength between the diaphragm and the electrode is 10N / m.

[0104] Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) are mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 and the organic solvent are mixed in a weight ratio of 8:92 to obtain an electrolyte.

[0105] Preparation of lithium-ion battery: The cathode electrode, separator, and anode electrode are stacked in sequence, with the separator positioned between the cathode and anode electrodes to obtain an electrode assembly; the electrode assembly is placed in an aluminum-plastic film packaging bag and hot-pressed at a preset pressure. After liquid injection and formation, a lithium-ion battery is obtained. The electrode assembly is 86 mm long and 43 mm wide, and the surface density of the single-sided anode active layer is 130 mg / 1540.25 mm 2 The thickness of the single-sided anode active layer is 60 μm.

[0106] Example 2-15

[0107] The difference from Example 1 lies in at least one of the following: the areal density of the anode active layer, the distance D3 between two adjacent strip-shaped grooves, the depth D2 of the strip-shaped grooves, and the ratio D2 / D1 of the thickness D1 of the anode active layer. In each example, the mass loss of the active layer removed to form the strip-shaped grooves was fixed at 1.5 wt%. See Table 1 for specific parameters.

[0108] Comparative Examples 1-4

[0109] The difference from Example 1 is that the anode active layer is not etched to form a plurality of strip-shaped grooves. Optionally, the surface density of the anode active layer is different.

[0110] The test methods for various parameters of this application are described below.

[0111] (1) Surface density test of anode active layer:

[0112] Take the anode electrode and punch it into an area of ​​1540.25mm 2 A small disc is placed on a plate, and then weighed using an electronic balance, recorded as W1; the anode active layer is scraped off, and only the weight of the disc substrate is measured, recorded as W2; the surface density of the single-sided anode active coating = (W1-W2) / 2.

[0113] (2) Test of the depth D2 of the strip grooves and the distance D3 between two adjacent strip grooves:

[0114] The cross section of the anode electrode is scanned using a CT device to measure the depth of the strip grooves and the distance between two adjacent strip grooves.

[0115] (3) Cycle capacity retention test:

[0116] When the surface density of the anode active layer is 90 mg / 1540.25 mm 2 When charging, use the following charging process:

[0117] (1) 4.8C constant current to 4.25V;

[0118] (2) 3.9C constant current to 4.25V;

[0119] (3) 3.1C constant current to 4.35V;

[0120] (4) 2C constant current to 4.48V;

[0121] (5) 1.6C constant current to 4.55V, constant voltage to 0.425C.

[0122] When the surface density of the anode active layer is 130 mg / 1540.25 mm 2 When charging, use the following charging process:

[0123] (1) 2.5C constant current to 4.25V, constant voltage to 2C;

[0124] (2) 2.0C constant current to 4.35V, constant voltage to 1.5C;

[0125] (3) 1.5C constant current to 4.45V, constant voltage to 1.2C;

[0126] (4) 0.8C constant current to 4.5V, constant voltage to 0.025C.

[0127] When the surface density of the anode active layer is 150-180 mg / 1540.25 mm 2 When charging, use the following charging process:

[0128] (1) 1.65C constant current to 4.10V, constant voltage to 1.55C cut-off;

[0129] (2) 1.55C constant current to 4.20V, constant voltage to 1.4C cut-off;

[0130] (3) 1.4C constant current to 4.24V, constant voltage to 1.1C cut-off;

[0131] (4) 1.1C constant current to 4.27V, constant voltage to 0.7C cut-off;

[0132] (5) 0.7C constant current to 4.30V, constant voltage to 0.4C cut-off;

[0133] (6) 0.4C constant current to 4.5V, constant voltage to C / 40 cutoff.

[0134] The above charge-discharge process constitutes one cycle. Record the discharge capacity after the first cycle as the initial discharge capacity. Repeat the above charge-discharge process 1000 times, and record the discharge capacity after 1000 cycles as the final discharge capacity. Capacity retention = final discharge capacity / initial discharge capacity × 100%.

[0135] Peel strength test:

[0136] According to GB / T2792-2014 "Test method for peel strength of adhesive tape", the peel strength between the diaphragm and the anode is tested using a high-speed rail tensile test machine. The test process is as follows: discharge the secondary battery to 0V, then disassemble the secondary battery, remove the diaphragm and the anode electrode bonded to it as a whole, and wipe the electrolyte on the surface with dust-free paper. Then cut into 5mm×5mm strip specimens. Along the length direction of the specimen, adhere the electrode side of the specimen to the steel plate with double-sided tape (Nitto 5000NS). Fix the steel plate to the corresponding position of the high-speed rail tensile test machine, pull up the other end of the diaphragm of the specimen that is not adhered to the electrode, and clamp the specimen in the chuck, wherein the pulled-up portion of the specimen is at an angle of 180° to the steel plate in space. The chuck pulls the specimen at a speed of 1±0.2mm / s. The average peel strength of the stable area is finally measured and recorded as the peel strength of the diaphragm, recorded as a, in N / m. Table 1 lists the parameters and evaluation results of each embodiment and comparative example.

[0137] Table 1

[0138] Comparison of Examples 1-15 and Comparative Examples 1-4 shows that when the surface density of the active layer is 90 mg / 1540.25 mm 2 ~180mg / 1540.25mm 2When multiple strip-shaped grooves are provided on the active layer, the cycle capacity retention rate can be significantly improved. This is because the strip-shaped grooves reserve space for electrolyte transmission, which improves the electrolyte transmission capacity, alleviates the lithium precipitation problem caused by insufficient kinetics, and improves the cycle performance.

[0139] Comparing Examples 1-12, it can be seen that when 3% ≤ D2 / D1 ≤ 70% and / or 100μm ≤ D3 ≤ 2000μm, it has a higher cycle capacity retention rate and significantly improves the cycle performance. In Example 12, D2 / D1> 70%, and D3> 2000μm. Although the cycle performance can be improved compared to the case where no strip grooves are set, the etching depth of the strip grooves is too large, resulting in lithium deposition in the strip grooves, so the effect of improving the cycle performance is the worst. In Examples 3-11, 8% ≤ D2 / D1 ≤ 70%, the cycle capacity retention rate reaches more than 70%. In Examples 4-9, 8% ≤ D2 / D1 ≤ 70% and / or 300μm ≤ D3 ≤ 1000μm are met, and the cycle capacity retention rate reaches more than 82%. In Examples 5-7, 500μm ≤ D3 ≤ 800μm, and the cycle capacity retention rate reaches more than 90%.

[0140] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the scope of rights of the present application. Therefore, equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A secondary battery comprising an electrode assembly, wherein the electrode assembly comprises an anode electrode sheet, wherein the anode electrode sheet comprises a current collector and an active layer disposed on at least one surface of the current collector, wherein: The surface density of the active layer is 90 mg / 1540.25 mm 2 ~180mg / 1540.25mm 2 , the active layer is provided with a plurality of strip-shaped grooves.

2. The secondary battery according to claim 1, wherein The distance between two adjacent strip-shaped grooves is 100 μm to 2000 μm.

3. The secondary battery according to claim 2, wherein The distance between two adjacent strip-shaped grooves is 300 μm to 1000 μm.

4. The secondary battery according to claim 3, wherein The distance between two adjacent strip-shaped grooves is 500 μm to 800 μm.

5. The secondary battery according to any one of claims 1 to 4, characterized in that: The thickness of the active layer is D1, the depth of the strip-shaped groove is D2, and 3%≤D2 / D1≤70%.

6. The secondary battery according to claim 5, wherein 8%≤D2 / D1≤70%.

7. The secondary battery according to claim 6, wherein 15%≤D2 / D1≤40%.

8. The secondary battery according to claim 1, wherein The secondary battery further includes a tab, the current collector includes a first edge and a second edge opposite to each other in a first direction, the tab extends out of the electrode assembly along the first direction through the first edge, and the strip-shaped groove is arranged perpendicular, parallel or inclined relative to the first edge.

9. The secondary battery according to claim 8, wherein The current collector includes a third edge and a fourth edge opposite to each other in a second direction perpendicular to the first direction, and the plurality of strip-shaped grooves are arranged from the third edge to the fourth edge.

10. The secondary battery according to claim 8, wherein The strip-shaped groove includes a first end located on one side of the first edge in the first direction, the active layer includes a first area corresponding to the tab in the first direction, and the distance between the first end of the strip-shaped groove located in the first area and the first edge is 0 to 3 mm.

11. The secondary battery according to claim 1, wherein The secondary battery has a notch, the electrode assembly is a laminated structure, the electrode assembly includes a first end face, a first side face, a second side face, a third side face, and a second end face connected in sequence, the first end face and the second end face are arranged opposite to each other in a first direction, the first side face, the second side face, and the third side face are located on the same side of the electrode assembly in a second direction perpendicular to the first direction, the first side face and the second side face are arranged to form the notch, and the coating surface density of the active layer is greater than or equal to 130 mg / 1540.25 mm 2 .

12. The secondary battery according to claim 11, wherein The secondary battery is L-shaped.

13. The secondary battery according to claim 12, wherein In the second direction, the length of the electrode assembly is L1; in the first direction, the width of the electrode assembly is L2, and 1.0≤L1 / L2≤3.

0.

14. The secondary battery according to claim 12, wherein 1.25≤L1 / L2≤3.

0.

15. The secondary battery according to claim 1, wherein The compaction density of the active layer is greater than 1.72 g / cm 3 .

16. The secondary battery according to claim 1, wherein The electrode assembly further includes a separator and a cathode electrode piece. The separator is disposed between the anode electrode piece and the cathode electrode piece. The peel strength between the separator and the anode electrode piece is 5 to 15 N / m.

17. An electronic device, wherein: The invention comprises the secondary battery according to any one of claims 1 to 16.

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