Secondary battery and electronic device

Abstract

A secondary battery and an electronic device, relating to the field of batteries. The secondary battery comprises a housing and electrode assemblies, the electrode assemblies are contained in the housing, the electrode assemblies are bent towards a first direction X, and the electrode assemblies include a first electrode assembly and a second electrode assembly which are arranged in the first direction X; the first electrode assembly comprises a first anode sheet, the first anode sheet comprises a first anode current collector and a first outer arc anode material layer and a first inner arc anode material layer which are arranged on the two sides of the first anode current collector in the first direction X, the first outer arc anode material layer comprises graphite, and the first inner arc anode material layer comprises hard carbon. The radian rebound phenomenon of a battery cell can be reduced, and the safety and reliability of the battery cell are improved.

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] With the increasing diversity of consumer electronics applications, especially the development of virtual reality technology, the demand for electrode assemblies compatible with head-mounted electronic devices is becoming increasingly urgent. Many well-known domestic and international companies have entered this field and have successfully launched a number of head-mounted virtual reality electronic products. Because the electrode assemblies in these head-mounted electronic products need to match the terminal battery compartment, they are typically designed with an arc-shaped electrode assembly. However, this arc-shaped electrode assembly can experience arc rebound during manufacturing and use, which can easily lead to black spots on the outermost layer of the electrode assembly, thus affecting the safety and reliability of the battery.

[0003] Summary of the Invention

[0004] In view of the above problems, the present application provides a secondary battery and an electronic device, which can reduce the curvature rebound phenomenon of the electrode assembly and improve the safety and reliability of the battery.

[0005] In a first aspect, the present application provides a secondary battery, comprising a housing and an electrode assembly, wherein the electrode assembly is accommodated in the housing, the electrode assembly is bent toward a first direction X, and the electrode assembly includes a first electrode assembly and a second electrode assembly arranged along the first direction X;

[0006] The first electrode assembly includes a first anode plate, the first anode plate includes a first anode current collector, and a first outer arc anode material layer and a first inner arc anode material layer arranged on both sides of the first anode current collector along the first direction X, the first outer arc anode material layer includes graphite, and the first inner arc anode material layer includes hard carbon.

[0007] In the technical solution of the embodiment of the present application, the electrode assembly is curved, and the first electrode assembly adopts a rebound difference design. Specifically, the anode material layers of the first anode pole piece located on the outer arc side and the inner arc side respectively adopt different carbon-based materials: the first outer arc anode material layer on the outer arc side contains graphite, which can be designed as an anode material layer with large rebound, and the first inner arc anode material layer on the inner arc side contains hard carbon, which can be designed as an anode material layer with small rebound. The accumulated shear stress of the first outer arc anode material layer with large rebound on the first inner arc anode material layer with small rebound can reduce the curvature rebound phenomenon of the electrode assembly. At the same time, the first outer arc anode material layer with large rebound can also supplement the outer arc space to reduce the slip and spacing between the pole pieces, improve the interface flatness of the electrode assembly, and improve the safety and reliability of the battery.

[0008] In any one or more optional embodiments above, the second electrode assembly includes a second anode plate, the second anode plate includes a second anode current collector, and a second outer arc anode material layer and a second inner arc anode material layer arranged on both sides of the second anode current collector along the first direction X, and the second inner arc anode material layer and the second outer arc anode material layer both include graphite.

[0009] In any one or more of the above optional embodiments, along the first direction X, the first electrode assembly is located on the outer arc side of the electrode assembly, and the second electrode assembly is located on the inner arc side of the electrode assembly. Compared to the first electrode assembly, the second electrode assembly located on the inner arc side experiences relatively less arc rebound. Therefore, the anode material layers of the second anode electrode sheet located on both the outer and inner arc sides can be made of the same graphite, thereby improving energy density.

[0010] In any one or more of the above optional embodiments, along the first direction X, the ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 3 to 1. The more layers of first anode plates using a rebound difference design, the thicker the first electrode assembly, the more conducive it is to reducing the curvature rebound of the electrode assembly; while the fewer layers of first anode plates using a rebound difference design, the thinner the first electrode assembly, the more conducive it is to improving the energy density of the electrode assembly and reducing the manufacturing cost. By controlling the thickness ratio of the first electrode assembly using a rebound difference design to the electrode assembly to 1 / 3 to 1, it is possible to better balance the control of the curvature rebound and energy density of the electrode assembly.

[0011] In any one or more optional embodiments above, the ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 2 to 4 / 5.

[0012] In any one or more optional embodiments above, the median particle size Dv50 of the graphite is 10 to 20 μm, and the median particle size Dv50 of the hard carbon is 2 to 10 μm.

[0013] In any one or more of the above optional embodiments, the graphite powder compaction density is 1.5 to 2.0 g / cm 3 The compacted density of the hard carbon powder is 0.5 to 1.5 g / cm 3 .

[0014] In any one or more optional embodiments above, the first outer arc anode material layer further comprises a binder, and the mass percentage of the graphite is 96-98% based on the mass of the first outer arc anode material layer; and / or

[0015] Based on the mass of the first outer arc anode material layer, the mass percentage of the binder is 1-2%.

[0016] In any one or more optional embodiments above, the first inner arc anode material layer further comprises a binder, and the mass percentage of the hard carbon is 96-98% based on the mass of the first inner arc anode material layer; and / or

[0017] Based on the mass of the first inner arc anode material layer, the mass percentage of the binder is 1-2%.

[0018] By adopting graphite and hard carbon as the anode materials respectively, it is possible to achieve control over the rebound difference of the anode material layer on the outer arc side and the inner arc side of the first anode pole piece.

[0019] In any one or more of the above optional embodiments, the relationship between the thickness A of the first outer arc anode material layer and the thickness B of the first inner arc anode material layer satisfies the following: B ≤ A ≤ 2B. A greater ratio of the thickness of the first outer arc anode material layer with greater rebound to the thickness of the first inner arc anode material layer with less rebound is more conducive to reducing the arc rebound of the electrode assembly; whereas a smaller ratio of the thickness of the first outer arc anode material layer with greater rebound to the thickness of the first inner arc anode material layer with less rebound is more conducive to improving the energy density of the electrode assembly.

[0020] In any one or more optional embodiments above, 1.3B≤A≤1.7B.

[0021] In any one or more of the above optional embodiments, the shell is a soft packaging bag.

[0022] In a second aspect, the present application provides an electronic device, which includes the secondary battery of the aforementioned embodiment.

[0023] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0025] FIG1 is a schematic structural diagram of an electrode assembly provided in an embodiment of the present application;

[0026] FIG2 is a schematic structural diagram of the first anode electrode provided in an embodiment of the present application.

[0027] Icons: 1000-electrode assembly; 1100-first electrode assembly; 1110-first anode plate; 1111-first anode current collector; 1112-first outer arc anode material layer; 1113-first inner arc anode material layer; 1120-cathode plate; 1130-isolation membrane; 1140-ear; 1200-second electrode assembly; 1210-second anode plate. DETAILED DESCRIPTION

[0028] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0030] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0031] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0033] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "thickness", "up", "down", "inside", and "outside" is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the embodiments of the present application.

[0034] In the description of the embodiments of this application, unless otherwise expressly specified or limited, technical terms such as "installation," "connection," and "fixation" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0035] At present, with the increasing diversification of application scenarios for consumer secondary batteries, especially the development of virtual reality technology, the demand for curved secondary batteries that match head-mounted electronic products is becoming increasingly strong. Currently, well-known domestic and international giants have entered this field and have successfully launched a number of head-mounted virtual reality electronic products.

[0036] Since the electrode assembly in this head-mounted electronic product needs to match the terminal battery compartment, it is usually designed to be an arc-shaped electrode assembly. However, this arc-shaped electrode assembly will experience arc rebound during manufacturing and use, which can easily lead to black spots on the outermost layer of the electrode assembly. The range of the black spots gradually decreases from the outer arc to the inner arc, thereby affecting the safety and reliability of the battery.

[0037] Specifically, during the manufacturing and use of curved electrode assemblies, it is generally required that they maintain a stable curvature to ensure smooth contact between the cathode and anode electrodes of the curved electrode assembly and to avoid interface problems caused by an increase in the spacing between the electrodes. During manufacturing, curved electrode assemblies are bent after a bending process. This causes the active material layers of the outer arcs of the cathode and anode electrodes to be stretched and the active material layers of the inner arcs to be squeezed. After the pressure is released, the cathode and anode electrodes will rebound in curvature. This phenomenon not only increases the spacing between the electrodes, leading to black spots, but also causes serious appearance problems, affecting the safety and reliability of the battery.

[0038] In order to reduce the curvature rebound phenomenon of the electrode assembly, currently methods such as pressurized shaping and increasing the diaphragm adhesive content and thickness can be used, but these methods will reduce production efficiency, increase production costs, and reduce energy density.

[0039] In order to effectively reduce the curvature rebound problem of the electrode assembly, a secondary battery can be designed. By performing differentiated rebound design on the electrode assembly at a specific position, the curvature rebound phenomenon of the electrode assembly can be reduced, the black spot problem can be reduced, and the safety and reliability of the battery can be improved.

[0040] An embodiment of the present application provides an electronic device, which can be any electronic device, such as a VR device, a mobile phone, a laptop computer, a video camera, a digital camera, an electric toy, an electric car, etc. The electronic device is provided with a secondary battery for providing electrical energy.

[0041] According to some embodiments of the present application, a secondary battery is provided. The secondary battery includes a housing and an electrode assembly 1000. The electrode assembly 1000 is accommodated in the housing. FIG1 is a schematic structural diagram of the electrode assembly 1000 provided in an embodiment of the present application. As shown in FIG1 , the electrode assembly 1000 is bent toward a first direction X. The electrode assembly 1000 includes a first electrode assembly 1100 and a second electrode assembly 1200 arranged along the first direction X.

[0042] The first electrode assembly 1100 includes at least one layer of a first anode plate 1110. Figure 2 is a schematic structural diagram of the first anode plate 1110 provided in an embodiment of the present application. As shown in Figure 2, the first anode plate 1110 includes a first anode current collector 1111, and a first outer arc anode material layer 1112 and a first inner arc anode material layer 1113 arranged on both sides of the first anode current collector 1111 along a first direction X. The first outer arc anode material layer 1112 includes graphite, and the first inner arc anode material layer 1113 includes hard carbon.

[0043] The electrode assembly 1000 is bent in the first direction X, which means that the electrode assembly 1000 is arched toward one side. The present application does not limit the degree of curvature of the electrode assembly 1000, which can be the same or different. For arc-shaped cells, electrode assemblies 1000 with the same degree of curvature at various locations are more common, so this article uses electrode assemblies 1000 with the same degree of curvature at various locations as an example. Those skilled in the art will understand that the present application's description of electrode assemblies 1000 with the same degree of curvature at various locations is merely a specific description of what can be achieved in this solution, and is not intended to limit the present invention. In other embodiments, the degree of curvature of the circularly curved electrode assembly 1000 may be different at various locations.

[0044] In the first anode electrode plate 1110, the first anode current collector 1111 has two surfaces opposite to each other in its own thickness direction, the first outer arc anode material layer 1112 is located on the outer arc surface of the first anode current collector 1111, and the first inner arc anode material layer 1113 is located on the inner arc surface of the first anode current collector 1111. The "outer arc" and "inner arc" are based on the positions in the bent state. The "outer arc" refers to the arched surface or position, and the "inner arc" refers to the concave surface or position.

[0045] The graphite in the embodiments of the present application may be natural graphite, artificial graphite, or modified graphite; the hard carbon may be resin carbon, organic polymer pyrolytic carbon, or carbon black.

[0046] In the first anode electrode 1110, different carbon-based materials are used to form the anode material layers on both sides of the first anode current collector 1111. The first outer arc anode material layer 1112 located on the outer arc side contains graphite and can be designed as an anode material layer with large rebound. The first inner arc anode material layer 1113 located on the inner arc contains hard carbon and can be designed as an anode material layer with small rebound. The first outer arc anode material layer 1112 may not contain hard carbon or only add a small amount of hard carbon, and the first inner arc anode material layer 1113 may not contain graphite or only add a small amount of graphite. In order to achieve the rebound difference, the graphite mass content of the first outer arc anode material layer 1112 is greater than the graphite mass content of the first inner arc anode material layer 1113, and the hard carbon mass content of the first outer arc anode material layer 1112 is less than the hard carbon mass content of the first inner arc anode material layer 1113, so that during the later use of the arc electrode assembly 1000, along the plane direction of the electrode piece, the first outer arc anode material layer 1112 generates shear stress on the first inner arc anode material layer 1113, thereby reducing the arc rebound; along the thickness direction of the electrode piece, the first outer arc anode material layer 1112 can also supplement the outer arc space to reduce the slip and spacing between the electrode pieces, improve the interface flatness of the electrode assembly 1000, and improve the safety and reliability of the battery.

[0047] According to some embodiments of the present application, the second electrode assembly 1200 includes a second anode electrode sheet 1210, which includes a second anode current collector, and a second outer-arc anode material layer and a second inner-arc anode material layer disposed on either side of the second anode current collector along a first direction X. The second inner-arc anode material layer and the second outer-arc anode material layer both include graphite. In some embodiments, the second inner-arc anode material layer and the second outer-arc anode material layer contain equal amounts of graphite.

[0048] In some embodiments, the first anode current collector 1111 and the second anode current collector can be any material suitable for use as a lithium-ion battery anode current collector in the art, specifically metal foil or a composite current collector. Optionally, the first anode current collector 1111 and the second anode current collector can each independently include: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0049] According to some embodiments of the present application, along the first direction X, the first electrode assembly 1100 is located on the outer arc side of the electrode assembly 1000 , and the second electrode assembly 1200 is located on the inner arc side of the electrode assembly 1000 .

[0050] According to some embodiments of the present application, along the first direction X, a ratio of the thickness of the first electrode assembly 1100 to the thickness of the electrode assembly 1000 is 1 / 3 to 1.

[0051] According to some embodiments of the present application, a ratio of the thickness of the first electrode assembly 1100 to the thickness of the electrode assembly 1000 is 1 / 2 to 4 / 5.

[0052] Illustratively, the thickness ratio of the first electrode assembly 1100 may be 1 / 3, 5 / 12, 1 / 2, 7 / 12, 2 / 3, 3 / 4, 4 / 5 or 1, etc., and may also be any value within the range of 1 / 6 to 3 / 4.

[0053] According to some embodiments of the present application, the median particle size Dv50 of graphite is 10 to 20 μm, and the median particle size Dv50 of hard carbon is 2 to 10 μm. For example, the median particle size Dv50 of graphite can be 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm, or any intermediate value between the above two values; the median particle size Dv50 of hard carbon can be 2 μm, 4 μm, 6 μm, 8 μm, or 10 μm, or any intermediate value between the above two values.

[0054] According to some embodiments of the present application, the compacted density of graphite powder is 1.5 to 2.0 g / cm 3 The compacted density of hard carbon powder is 0.5~1.5g / cm 3 For example, the graphite powder compaction density is 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 or 2.0g / cm 3 , or any intermediate value between the above two values; the compacted density of hard carbon powder is 0.5g / cm 3 , 0.7g / cm 3 、 1g / cm3 , 1.2g / cm 3 or 1.5g / cm 3 , or it can be an intermediate value between any of the above two values.

[0055] The median particle size Dv50 in the embodiments of the present application is measured using a laser particle size analyzer. The powder compaction density is measured in accordance with GB / T 24533-2009 "Graphite-based negative electrode materials for lithium-ion batteries," and is calculated using density = mass / volume.

[0056] According to some embodiments of the present application, the first outer arc anode material layer 1112 further includes a binder and a dispersant, and the first outer arc anode material layer 1112 satisfies at least one of the following conditions:

[0057] (1) Based on the mass of the first outer arc anode material layer 1112, the mass percentage of graphite is 96-98%; (2) Based on the mass of the first outer arc anode material layer 1112, the mass percentage of the binder is 1-2%; (3) Based on the mass of the first outer arc anode material layer 1112, the mass percentage of the dispersant is 1-2%.

[0058] According to some embodiments of the present application, the first inner arc anode material layer 1113 further includes a binder and a dispersant, and the first inner arc anode material layer 1113 satisfies at least one of the following conditions:

[0059] (1) Based on the mass of the first inner arc anode material layer 1113, the mass percentage of hard carbon is 96-98%; (2) Based on the mass of the first inner arc anode material layer 1113, the mass percentage of the binder is 1-2%; (3) Based on the mass of the first inner arc anode material layer 1113, the mass percentage of the dispersant is 1-2%.

[0060] According to some embodiments of the present application, the binders of the first outer arc anode material layer 1112 and the first inner arc anode material layer 1113 are independently selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, fluorinated rubber, polyurethane, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyvinyl alcohol, alginic acid, and sodium alginate;

[0061] And / or, the dispersants of the first outer arc anode material layer 1112 and the first inner arc anode material layer 1113 are independently selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0062] According to some embodiments of the present application, the relationship between the thickness A of the first outer arc anode material layer and the thickness B of the first inner arc anode material layer satisfies: B≤A≤2B. Optionally, 1.3B≤A≤1.7B.

[0063] For example, the value of A / B may be 1, 1.3, 1.5, 1.7 or 2, etc. It may also be any value within the range of 1 to 2.

[0064] According to some embodiments of the present application, the secondary battery also includes a cathode electrode 1120, an isolation film 1130, and a tab 1140. Each layer of anode electrode (first anode electrode 1110 or second anode electrode 1210) corresponds to a layer of cathode electrode 1120. The isolation film 1130 is used to separate the anode electrode and the cathode electrode 1120. The tab 1140 is connected to the electrode. Exemplarily, each electrode unit includes: 1 layer of anode electrode + 1 layer of cathode electrode 1120 + 2 layers of isolation film 1130.

[0065] According to some embodiments of the present application, the cathode electrode 1120 includes a cathode current collector and a cathode active material layer, and the cathode active material layer includes a cathode active material, a binder, and a conductive agent.

[0066] In some embodiments, the cathode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0067] In some embodiments, the cathode active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide, and lithium titanate.

[0068] In some embodiments, the binder comprises an adhesive polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder comprises at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0069] In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.

[0070] The present application has no particular limitation on the material and shape of the isolation film 1130 , which may be any material disclosed in the prior art.

[0071] In some embodiments, the isolation film 1130 includes a polymer or an inorganic material formed of a material that is stable to the electrolyte of the present application. For example, the isolation film 1130 may include a substrate layer and a surface treatment layer.

[0072] The substrate layer is a non-woven fabric, film, or composite film having a porous structure. The material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used.

[0073] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0074] According to some embodiments of the present application, the secondary battery also includes an electrolyte located in the shell, and the electrolyte includes an organic solution, specifically including a combination of one or more of ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate and methyl acetate, ethylene carbonate (EC), propylene carbonate (PC), and propylene carbonate.

[0075] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of an organic lithium salt and an inorganic lithium salt. Optionally, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), and lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB).

[0076] The housing can be used to encapsulate the electrode assembly 1000 and the electrolyte. According to some embodiments of the present application, the housing is a packaging bag, illustratively a soft bag. The soft bag can be made of plastic, specifically polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0077] According to some embodiments of the present application, the present application provides an electronic device, which includes a secondary battery according to any of the above solutions, and the secondary battery is used to provide power to the electronic device.

[0078] According to some embodiments of the present application, the present application provides a method for preparing a secondary battery according to any one of the above schemes, which comprises the following steps:

[0079] A first outer arc anode material layer and a first inner arc anode material layer are coated on both sides of the first anode current collector 1111 by using a die head extrusion single layer coating method to obtain a first anode pole piece 1110;

[0080] The first anode plates 1110 are stacked in sequence and bent using a bending process. As an embodiment, the processing of the electrode assembly 1000 is as follows: stirring - coating - cold pressing - slitting - lamination - bending - transfer welding - packaging - vacuum baking - liquid injection - standing - formation - exhaust - capacity - visual inspection. The bending process involves placing the straight stacked assembly in an arc-shaped fixture, standing at 50-90°C and 1-3 MPa pressure, and then bending the middle to form the arc-shaped electrode assembly 1000.

[0081] Next, one or more embodiments will be described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0082] Example

[0083] A secondary battery, the assembly process is as follows:

[0084] Preparation of anode electrode:

[0085] The anode material graphite, dispersant sodium carboxymethyl cellulose CMC, and binder styrene-butadiene rubber are mixed in a mass ratio of 97:1:2, and deionized water is added to obtain a first anode slurry with a solid content of 50% under the action of a vacuum mixer;

[0086] The anode material hard carbon, dispersant sodium carboxymethyl cellulose CMC, and binder styrene-butadiene rubber were mixed in a mass ratio of 97:1:2, deionized water was added, and a second anode slurry was obtained under the action of a vacuum mixer with a solid content of 50%.

[0087] The first anode slurry for forming the first outer arc anode material layer and the second anode slurry for forming the first inner arc anode material layer are uniformly coated on both sides of a first anode current collector copper foil having a thickness of 10 μm, dried at 110° C., cold pressed, cut, and bent to obtain a first anode electrode sheet;

[0088] The first anode slurry used to form the second outer arc anode material layer and the second inner arc anode material layer is evenly coated on both sides of the first anode current collector copper foil with a thickness of 10 μm, dried at 110° C., cold pressed, cut and bent to obtain the second anode pole piece.

[0089] Preparation of cathode electrode:

[0090] 96 wt% lithium cobalt oxide, 2 wt% superconducting carbon black, and 2 wt% binder polyvinylidene fluoride were mixed, and N-methylpyrrolidone was used as solvent. The cathode active slurry was mixed thoroughly with 0.3 g / 1540.25 mm 2 The coating amount is coated on both surfaces of a cathode current collector aluminum foil with a thickness of 9 μm and then dried to obtain a cathode active slurry layer; then cold pressing, cutting and bending are performed to obtain a cathode electrode sheet.

[0091] Preparation of electrode assembly:

[0092] The separator is made of PP (polypropylene) and has a thickness of 20μm. The first anode electrode piece, separator, cathode electrode piece, and separator are repeatedly stacked in sequence to form the first electrode assembly. The second anode electrode piece, separator, cathode electrode piece, and separator are repeatedly stacked in sequence to form the second electrode assembly. The first and second electrode assemblies are stacked, with a total of 24 electrode unit layers, and then the bending process is performed.

[0093] Preparation of secondary batteries:

[0094] The electrode assembly is placed in a housing, and an electrolyte is injected, followed by formation to obtain an electrochemical device. The solute in the electrolyte is 2 mol / L lithium hexafluorophosphate, and the solvent in the electrolyte is ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1.

[0095] Comparative Example 1

[0096] Except that the steps for preparing the anode electrode sheet are as follows, the rest are the same as those in the embodiment.

[0097] Preparation of anode electrode:

[0098] The anode material graphite (median particle size Dv50 is 15 μm, powder compaction density is 1.8 g / cm 3), dispersant sodium carboxymethyl cellulose CMC, binder styrene butadiene rubber according to the mass ratio of 97:1:2, add deionized water, under the action of a vacuum mixer to obtain an anode slurry with a solid content of 50%;

[0099] The anode slurry was coated on both sides of the anode current collector copper foil with a thickness of 10 μm. The thickness of the anode material layer formed by coating on each side was 65 μm. The anode sheet was obtained by drying at 110°C, cold pressing, cutting and bending.

[0100] The main parameters of each embodiment are shown in Table 1 below:

[0101] Table 1 Parameters of each embodiment

[0102] The secondary batteries provided in each embodiment and comparative example were subjected to a radian change rate test and a cycle capacity retention rate test. The test process is as follows:

[0103] Electrode assembly arc change rate test: ① Obtaining the initial arc radius: Before the secondary battery is cycled, use a 3D profilometer to scan the 3D structure of the electrode assembly surface, then average the scanned surface to obtain an arc line, fit three points on the arc line to obtain a standard arc line, and then read the arc radius a. ② Obtaining the arc radius after 800 cycles: After the secondary battery completes the cycle test, use a 3D profilometer to scan the 3D structure of the electrode assembly surface, then average the scanned surface to obtain an arc line, fit three points on the arc line to obtain a standard arc line, and then read the arc radius b. ③ Obtaining the arc radius change rate: The arc radius change rate of the electrode assembly 1000 is (b a) / a.

[0104] Secondary battery cycle capacity retention rate test: The secondary battery is charged at a constant current of 0.5C to the full charge voltage of the system, the constant voltage is increased to 0.05C, and the full discharge is performed to 3.0V under the condition of a constant current of 0.5C. This is one cycle, and a total of 800 cycles are performed. The cycle capacity retention rate test = discharge capacity in the Nth cycle mAh / initial discharge capacity in the first cycle mAh.

[0105] The test results are shown in Table 2:

[0106] Table 2 Test results

[0107] Combined with the results in Table 2, we can see that:

[0108] Compared with Comparative Example 1, the electrode assemblies of Examples 1 to 14 include a first electrode assembly and a second electrode assembly arranged along a first direction X. In the first anode plate of the first electrode assembly, the first outer arc anode material layer includes graphite, and the first inner arc anode material layer includes hard carbon, which can reduce the curvature rebound phenomenon of the electrode assembly and improve the cycle capacity retention rate of the battery.

[0109] According to Examples 1 to 14, in the second anode plate of the second electrode assembly, the second inner arc anode material layer and the second outer arc anode material layer both include graphite, which can reduce the curvature rebound phenomenon of the electrode assembly and improve the cycle capacity retention rate of the battery.

[0110] According to Examples 1 to 6, the ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 3 to 1, preferably 1 / 2 to 4 / 5, which can reduce the curvature rebound phenomenon of the electrode assembly and improve the cycle capacity retention rate of the battery.

[0111] According to Example 1, and Examples 7 to 12, the relationship between the thickness A of the first outer arc anode material layer and the thickness B of the first inner arc anode material layer satisfies A / B=1 to 2, preferably 1.3 to 1.7, which can reduce the curvature rebound phenomenon of the electrode assembly and improve the cycle capacity retention rate of the battery.

[0112] According to Example 1 and Examples 9-10, the median particle size Dv50 of the graphite is 10-20 μm, and the compacted density of the graphite powder is 1.5-2.0 g / cm 3 The median particle size Dv50 of hard carbon is 2-10 μm, and the compacted density of hard carbon powder is 0.5-1.5 g / cm 3 , which can reduce the curvature rebound phenomenon of the electrode assembly and improve the battery's cycle capacity retention rate.

[0113] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A secondary battery, characterized in that: The secondary battery includes a housing and an electrode assembly, wherein the electrode assembly is accommodated in the housing and is bent toward a first direction X. The electrode assembly includes a first electrode assembly and a second electrode assembly arranged along the first direction X. The first electrode assembly includes a first anode plate, the first anode plate includes a first anode current collector, and a first outer arc anode material layer and a first inner arc anode material layer arranged on both sides of the first anode current collector along the first direction X, the first outer arc anode material layer includes graphite, and the first inner arc anode material layer includes hard carbon.

2. The secondary battery according to claim 1, wherein The second electrode assembly includes a second anode plate, the second anode plate includes a second anode current collector, and a second outer arc anode material layer and a second inner arc anode material layer arranged on both sides of the second anode current collector along the first direction X, and the second inner arc anode material layer and the second outer arc anode material layer both include graphite.

3. The secondary battery according to claim 1, wherein Along the first direction X, the first electrode assembly is located on the outer arc side of the electrode assembly, and the second electrode assembly is located on the inner arc side of the electrode assembly.

4. The secondary battery according to claim 1, wherein Along the first direction X, a ratio of a thickness of the first electrode assembly to a thickness of the electrode assembly is 1 / 3 to 1.

5. The secondary battery according to claim 4, characterized in that The ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 2 to 4 / 5.

6. The secondary battery according to any one of claims 1 to 5, characterized in that The median particle size Dv50 of the graphite is 10 to 20 μm, and the median particle size Dv50 of the hard carbon is 2 to 10 μm.

7. The secondary battery according to any one of claims 1 to 5, characterized in that The graphite powder compaction density is 1.5 to 2.0 g / cm 3 The compacted density of the hard carbon powder is 0.5 to 1.5 g / cm 3 .

8. The secondary battery according to any one of claims 1 to 5, characterized in that The first outer arc anode material layer also includes a binder, Based on the mass of the first outer arc anode material layer, the mass percentage of the graphite is 96-98%; and / or Based on the mass of the first outer arc anode material layer, the mass percentage of the binder is 1-2%.

9. The secondary battery according to any one of claims 1 to 5, characterized in that The first inner arc anode material layer also includes a binder, Based on the mass of the first inner arc anode material layer, the mass percentage of the hard carbon is 96-98%; and / or Based on the mass of the first inner arc anode material layer, the mass percentage of the binder is 1-2%.

10. The secondary battery according to any one of claims 1 to 5, characterized in that The relationship between the thickness A of the first outer arc anode material layer and the thickness B of the first inner arc anode material layer satisfies: B≤A≤2B.

11. The secondary battery according to claim 10, wherein 1.3B≤A≤1.7B.

12. The secondary battery according to any one of claims 1 to 5, characterized in that The shell is a soft packaging bag.

13. An electronic device, characterized in that: The electronic device includes the secondary battery according to any one of claims 1 to 12.

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