Secondary battery and electronic device

Abstract

The invention discloses a secondary battery and an electronic device, and belongs to the technical field of batteries, the secondary battery is bent, and a first outer arc anode active material layer of a first anode strip of an outer arc side electrode assembly of the secondary battery is divided into two layers; the mass content of the binder in the inner layer of the first inner arc anode active material layer and the mass content of the binder in the outer layer of the first outer arc anode active material layer are larger than those of the binder in the outer layer, the content of the binder is in negative correlation with the rebound of the layers, and in use, the layer with relatively poor rebound resistance generates shear stress to the layer with relatively strong rebound resistance, so that the rebound resistance of the anode is improved. And the radian rebound resistance is effectively enhanced. The radian rebounding degree of the outer arc side of the bent electrode assembly is larger than that of the inner arc side of the bent electrode assembly, the electrode assembly with relatively high radian rebounding resistance is arranged on the outer arc side, the electrode assembly with relatively low radian rebounding resistance is arranged on the inner arc side, the radian rebounding difference of all the electrode assemblies in the bent electrode assembly is effectively reduced, and the electrode assembly is more stable and reliable. Therefore, the electrode assemblies are better attached, and the problem that the arc-shaped electrode assemblies are prone to radian rebound to generate black spots is solved.

Description

Secondary battery and electronic device 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] Currently, to accommodate various electronic device shapes, battery shapes are also changing accordingly. For example, batteries designed for curved electronic devices are often designed as curved batteries. However, curved batteries can experience deformation during use, such as curvature reduction and flattening. This can even lead to black spots on the electrode assembly, compromising the safety and reliability of the secondary battery. Therefore, a secondary battery that mitigates these curvature rebound and flattening issues is urgently needed.

[0003] Summary of the Invention

[0004] In view of the above problems, the present application provides a secondary battery and an electronic device to improve the problem that arc-shaped electrode assemblies are prone to arc rebound and thus cause black spots.

[0005] In a first aspect, the present application provides an electrode assembly. A secondary battery includes a shell and an electrode assembly, the electrode assembly being housed in the shell and bent toward a first direction X. The electrode assembly includes a first electrode assembly and a second electrode assembly stacked along the first direction X. The first electrode assembly includes a first anode sheet, the first anode sheet including a first outer arc anode active material layer, a first anode current collector, and a first inner arc anode active material layer stacked along the first direction X. The first outer arc anode active material layer includes a first active material layer and a second active material layer, the first active material layer being disposed between the second active material layer and the first anode current collector. The first active material layer includes a first binder, the second active material layer includes a second binder, the first inner arc anode active material layer includes a first inner arc binder, a mass content of the first binder in the first active material layer is greater than a mass content of the second binder in the second active material layer. The mass content of the first inner arc binder in the first inner arc anode active material layer is greater than a mass content of the second binder in the second active material layer. The second electrode assembly includes a second anode sheet, the second anode sheet including a second outer arc anode active material layer, a second anode current collector, and a second inner arc anode active material layer stacked along the first direction X.

[0006] In the above-mentioned implementation process, the first outer arc anode active material layer of the first anode sheet bent toward the first direction X in the first electrode assembly is divided into a first active material layer and a second active material layer in the direction from inside to outside, and the binder mass content in the first inner arc anode active material layer and the first active material layer is greater than the binder mass in the second active material layer, and the first inner arc anode active material layer and the first active material layer with high binder mass have relatively strong anti-rebound ability, and the second active material layer with low binder mass has relatively poor anti-rebound ability. During the use of the first anode sheet, the second active material layer with relatively poor anti-rebound ability generates shear stress against the first inner arc anode active material layer and the first active material layer with relatively strong anti-rebound ability. The generation of the shear stress can effectively enhance the anti-curvature rebound performance, thereby making the anti-curvature rebound ability of the first anode sheet stronger than the anti-curvature rebound ability of the second anode sheet. Among the multiple curved electrode assemblies, the electrode assembly located on the outer arc side is more likely to rebound to a greater extent than the electrode assembly located on the inner arc side. By setting the first electrode assembly with relatively strong anti-curvature rebound performance on the outer arc side of the curved electrode assembly and setting the second electrode assembly with relatively weak anti-curvature rebound performance on the inner arc side of the curved electrode assembly, the curvature rebound difference of each anode sheet in the curved electrode assembly is effectively reduced, thereby making the electrode assemblies fit better and improving the problem that the arc-shaped electrode assembly is prone to curvature rebound and thus the occurrence of black spots.

[0007] In one or more optional embodiments above, along the first direction X, a ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 6 to 3 / 4.

[0008] In the above implementation process, the thickness of the electrode assemblies is generally positively correlated with the number of electrode assemblies. A thicker first electrode assembly, which exhibits relatively strong resistance to arc rebound, is more conducive to reducing arc rebound in each layer of the anode sheets in the electrode assembly. Conversely, a thicker second electrode assembly, which exhibits relatively weaker resistance to arc rebound, is more conducive to increasing the energy density of the electrode assembly and reducing manufacturing costs. By controlling the thickness ratio of the first electrode assembly, which exhibits relatively strong resistance to arc rebound, to the electrode assembly within a range of 1 / 6 to 3 / 4, a better balance between controlling arc rebound in each layer of the anode sheets and the energy density of the electrode assembly can be achieved.

[0009] In one or more optional embodiments above, along the first direction X, a ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 4 to 3 / 4.

[0010] In the above implementation process, by controlling the thickness ratio of the first electrode assembly with relatively strong anti-curvature rebound performance to the electrode assembly to 1 / 4 to 3 / 4, it is possible to better balance the control of the curvature rebound of each layer of anode sheets and the energy density of the electrode assembly.

[0011] In one or more optional embodiments above, the relationship between the mass content W1 of the first binder in the first active material layer and the mass content W2 of the second binder in the second active material layer satisfies: 1.5≤W1 / W2≤3; and / or the relationship between the mass content N of the first inner arc binder in the first inner arc anode active material layer and the mass content W2 of the second binder in the second active material layer satisfies: 1.5≤N / W2≤3.

[0012] In the above implementation, controlling the relationship between the binder content of the first inner-arc anode active material layer, the first active material layer, and the second active material layer is, to a certain extent, equivalent to controlling the magnitude of the shear stress generated by the second active material layer (which has relatively poor anti-rebound capability) and the first inner-arc anode active material layer and the first active material layer (which has relatively strong anti-rebound capability). By controlling the binder mass content W1 of the first active material layer, the binder mass content N of the first inner-arc anode active material layer, and the binder mass content W2 of the second active material layer to satisfy 1.5≤W1 / W2≤3 and 1.5≤N / W2≤3, a favorable rebound force gradient difference is formed between the first active material layer, the first inner-arc anode active material layer, and the second active material layer. This, in turn, causes the second active material layer to generate a more appropriate shear stress on the first inner-arc anode active material layer and the first active material layer, further facilitating reduction of arc rebound.

[0013] In one or more optional embodiments above, 2≤W1 / W2≤2.5; and / or 2≤N / W2≤2.5.

[0014] In the above implementation process, by controlling the binder mass content W1 of the first active material layer, the binder mass content N of the first inner arc anode active material layer and the binder mass content W2 of the second active material layer to satisfy 2≤W1 / W2≤2.5 and 2≤N / W2≤2.5, the first active material layer, the first inner arc anode active material layer and the second active material layer form a better rebound force gradient difference, thereby making the second active material layer produce more suitable shear stress on the first inner arc anode active material layer and the first active material layer, which is more conducive to reducing the degree of curvature rebound.

[0015] In one or more optional embodiments above, the relationship between the thickness a1 of the first active material layer and the thickness A of the first outer arc anode active material layer satisfies: 0.45≤a1 / A≤0.95.

[0016] In the above implementation, controlling the thickness ratio of the first active material layer to the entire first outer-arc anode active material layer is, to a certain extent, equivalent to controlling the shear stress generated by the second active material layer, which has relatively poor rebound resistance, and the first inner-arc anode active material layer, which has relatively strong rebound resistance. By controlling the thickness a1 of the first active material layer and the thickness A of the first outer-arc anode active material layer to satisfy 0.45≤a1 / A≤0.95, the second active material layer can generate a relatively appropriate shear stress on the first inner-arc anode active material layer and the first active material layer when the first anode sheet is used as an electrode assembly.

[0017] In one or more of the above optional embodiments, 0.7≤a1 / A≤0.9.

[0018] In the above implementation process, by controlling the thickness a1 of the first active material layer and the thickness A of the first outer arc anode active material layer to satisfy 0.7≤a1 / A≤0.9, the second active material layer can generate more suitable shear stress on the first inner arc anode active material layer and the first active material layer when the first anode sheet is applied as an electrode assembly.

[0019] In one or more optional embodiments above, along the first direction X, a relationship between a thickness A of the first outer arc anode active material layer and a thickness B of the first inner arc anode active material layer satisfies: 1≤A / B≤2.

[0020] In the above implementation, controlling the thickness of the first inner-arc anode active material layer and the first outer-arc anode active material layer is, to a certain extent, equivalent to controlling the shear stress generated by the second active material layer, which has relatively poor rebound resistance, and the first inner-arc anode active material layer and the first active material layer, which has relatively strong rebound resistance. By controlling the thickness A of the first outer-arc anode active material layer and the thickness B of the first inner-arc anode active material layer to satisfy 1≤A / B≤2, the second active material layer can generate a relatively appropriate shear stress on the first inner-arc anode active material layer and the first active material layer when the first anode sheet is used as an electrode assembly.

[0021] In one or more of the above optional embodiments, 1.3≤A / B≤1.7.

[0022] In the above implementation process, by controlling the thickness A of the first outer arc anode active material layer and the thickness B of the first inner arc anode active material layer to satisfy 1.3≤A / B≤1.7, the second active material layer can generate more suitable shear stress on the first inner arc anode active material layer and the first active material layer when the first anode sheet is applied as an electrode assembly.

[0023] In one or more optional embodiments above, the mass content of the first binder in the first active material layer is 2% to 4%; and / or the mass content of the second binder in the second active material layer is 1% to 2%; and / or the mass content of the first inner arc binder in the first inner arc anode active material layer is 2% to 4%.

[0024] In the above implementation, controlling the binder content relationship between the first inner-arc anode active material layer, the first active material layer, and the second active material layer is, to a certain extent, equivalent to controlling the shear stress generated by the second active material layer (which has relatively poor rebound resistance) and the first inner-arc anode active material layer and the first active material layer (which has relatively strong rebound resistance). By controlling the mass of the first binder to 2% to 4% of the first active material layer, the mass of the second binder to 1% to 2% of the second active material layer, and the mass of the first inner-arc binder to 2% to 4% of the first inner-arc anode active material layer, the second active material layer can generate a relatively appropriate shear stress on the first inner-arc anode active material layer and the first active material layer when the first anode sheet is used as an electrode assembly.

[0025] In one or more optional embodiments above, the components of the first active material layer include, in parts by mass: 94 to 96 parts of the first anode active material, 2 to 4 parts of the first binder and 1 to 2 parts of the first dispersant; and / or the components of the second active material layer include, in parts by mass: 96 to 98 parts of the second anode active material, 1 to 2 parts of the second binder and 1 to 2 parts of the second dispersant; and / or the components of the first inner arc anode active material layer include, in parts by mass: 94 to 96 parts of the inner arc anode active material, 2 to 4 parts of the first inner arc binder and 1 to 2 parts of the inner arc dispersant.

[0026] In one or more optional embodiments above, the first anode active material, the second anode active material and the inner arc anode active material are independently selected from at least one of graphite, graphene, carbon nanotubes, soft carbon, hard carbon, silicon alloy, silicon crystal, and tin oxide; and / or

[0027] The first binder, the second binder and the first inner arc binder 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; and / or the first dispersant, the second dispersant and the inner arc dispersant are independently selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0028] In one or more optional embodiments above, the median particle size Dv50 of the first anode active material, the second anode active material and the inner arc anode active material is 10 to 20 μm respectively; and / or the powder compaction density of the first anode active material, the second anode active material and the inner arc anode active material is 1.5 to 2.0 g / cm 3 .

[0029] In one or more optional embodiments above, the first electrode assembly includes a plurality of first anode sheets, and along the first direction X, the mass content of the first binder in the first active material layer of the plurality of first anode sheets gradually decreases; and / or

[0030] Along the first direction X, the mass content of the first inner-arc binder in the inner-arc active material layers of the plurality of first anode sheets gradually decreases.

[0031] In the above embodiment, by gradually reducing the mass content of the binder in the first active material layer and the inner arc active material layer in the first electrode assembly, its anti-rebound ability is matched with the position of the electrode assembly in which it is located, thereby achieving better matching of the curvature rebound degree of each layer of the electrode assembly.

[0032] In one or more optional embodiments above, the difference in mass content of the binder in two adjacent first active material layers is 0.02% to 0.12%; and / or the difference in mass content of the binder in two adjacent inner arc active material layers is 0.02% to 0.12%.

[0033] In the above embodiment, by controlling the difference in the mass content of the binder between the first active material layer and the inner arc active material layer in the two adjacent first electrode assemblies to 0.02% to 0.12%, the anti-rebound ability is more in line with the position of the electrode assembly in which it is located, thereby achieving better matching of the curvature rebound degree of each layer of electrode assembly.

[0034] In one or more optional embodiments above, the central angle Q of the electrode assembly is 10° to 90°.

[0035] In one or more optional embodiments above, the second outer arc anode active material layer includes an outer arc binder, the second inner arc anode active material layer includes a second inner arc binder, and the mass content of the outer arc binder in the second outer arc anode active material layer and the mass content of the second inner arc binder in the second inner arc anode active material layer are equal to the mass content of the first inner arc binder in the first inner arc anode active material layer.

[0036] In one or more of the above optional embodiments, the shell is a packaging bag.

[0037] In a second aspect, the present application provides an electronic device, which includes the secondary battery provided in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0039] FIG1 is a schematic structural diagram of an electrode assembly provided in an embodiment of the present application;

[0040] FIG2 is a schematic structural diagram of the first anode sheet provided in an embodiment of the present application.

[0041] Figure markings: 1000-electrode assembly, 1100-first electrode assembly, 1110-first anode sheet, 1111-first anode current collector, 1112-first inner arc anode active material layer, 1113-first outer arc anode active material layer, 1113a-first active material layer, 1113b-second active material layer, 1120-cathode sheet, 1130-separation membrane, 1140-ear, 1200-second electrode assembly. DETAILED DESCRIPTION

[0042] 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.

[0043] 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.

[0044] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify 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 clearly and specifically defined.

[0045] 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.

[0046] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0047] In the description of the embodiments of the present application, the term “equal” means that two items are equal or approximately equal, that is, the difference between them does not exceed 5% of either item.

[0048] 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).

[0049] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0050] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0051] An embodiment of the present application provides an electronic device, which can be any electronic device, such as 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.

[0052] As the application scenarios of consumer secondary batteries become increasingly diverse, especially with the development of virtual reality technology, the demand for curved secondary batteries that match head-mounted devices 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 products. This has led to the need for the electrode components of secondary batteries to be designed in a curved shape to match the terminal battery compartment.

[0053] However, arc-shaped anode sheets are prone to arc rebound during manufacturing and consumer use, resulting in black spots on the outermost layer of the electrode assembly, thereby affecting the safety and reliability of the secondary battery.

[0054] Therefore, the inventor intends to provide an electrode assembly to improve the problem that arc-shaped electrode assemblies are prone to arc rebound and thus cause black spots.

[0055] The present application provides a secondary battery, which includes a shell and an electrode assembly. The electrode assembly is accommodated in the shell. FIG1 is a schematic structural diagram of the electrode assembly provided in the present application embodiment. As shown in FIG1 , 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; the first electrode assembly includes a first anode sheet. FIG2 is a schematic structural diagram of the first anode sheet provided in the present application embodiment. As shown in FIG2 , the first anode sheet includes a first outer arc anode active material layer, a first anode current collector, and a first inner arc anode active material layer stacked along the first direction X; the first outer arc anode active material layer includes a first active material layer and a second active material layer, and the first active material layer is arranged between the second active material layer and the first anode current collector; the first active material layer includes a first binder, and the second active material layer includes a second binder. agent, the first inner arc anode active material layer includes a first inner arc binder, the mass content of the first binder in the first active material layer is greater than the mass content of the second binder in the second active material layer; the mass content of the first inner arc binder in the first inner arc anode active material layer is greater than the mass content of the second binder in the second active material layer; the second electrode assembly includes a second anode sheet, the second anode sheet includes a second outer arc anode active material layer, a second anode current collector and a second inner arc anode active material layer stacked along a first direction X; the second outer arc anode active material layer includes an outer arc binder, the second inner arc anode active material layer includes a second inner arc binder, the mass content of the outer arc binder in the second outer arc anode active material layer and the mass content of the second inner arc binder in the second inner arc anode active material layer are equal to the mass content of the first inner arc binder in the first inner arc anode active material layer.

[0056] The electrode assembly being bent in the first direction X refers to a configuration in which both ends of the electrode assembly are tilted in the first direction X. In other words, it refers to a configuration in which the middle portion of the electrode assembly is arched in a direction opposite to the first direction X. The degree of curvature of the electrode assembly is not limited in this application and may be the same or different. Electrode assemblies having the same degree of curvature at all locations are more common, so this document uses an electrode assembly having the same degree of curvature at all locations as an example. Those skilled in the art will understand that the description herein of an electrode assembly having the same degree of curvature at all locations is merely a specific illustration 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 curved electrode assembly may be different at various locations.

[0057] The electrode assembly includes a pole piece, a separator, and a tab. The separator is positioned between the two pole pieces, which are also positioned between the two electrode assemblies. The tabs are connected to the pole pieces. In this embodiment, the electrode assembly is divided into a first electrode assembly and a second electrode assembly.

[0058] The anode current collector refers to a metal layer that collects the current generated by the anode active material to form a larger current output. The material of the anode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a polymer substrate covered with a conductive metal, etc.; wherein the conductive metal includes but is not limited to copper, nickel or titanium, and the material of the polymer substrate includes but is not limited to at least one of polyethylene, polypropylene, ethylene propylene copolymer, polyethylene terephthalate, polyethylene naphthalate and poly(p-phenylene terephthalamide).

[0059] The first outer arc anode active material layer, the first anode current collector and the first inner arc anode active material layer are stacked along the first direction X, which means that the first outer arc anode active material layer is arranged on the outer arc side of the first anode current collector, and the first inner arc anode active material layer is arranged on the inner arc side of the first anode current collector. The inner arc side of the first anode current collector refers to the concave side of the curved first anode sheet, and the outer arc side of the first anode collector refers to the arched side of the curved first anode sheet.

[0060] The binder refers to a substance that binds the anode active material to form the anode active material layer. The binder may include, but is not limited to, at least one of polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl pyrrolidone, polyethylene, polypropylene, epoxy resin, nylon, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral, water-based acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na). The binders in the first active material layer, the second active material layer, and the first inner arc anode active material layer may be the same or different. The choice of binder for each layer may be determined based on the actual conditions of the preparation process.

[0061] The mass content of the first binder in the first active material layer refers to the mass of the first binder in the first active material layer divided by the total mass of the first active material layer; the mass content of the second binder in the second active material layer refers to the mass of the second binder in the second active material layer divided by the total mass of the second active material layer; the mass content of the first inner-arc binder in the first inner-arc anode active material layer refers to the mass of the first inner-arc binder in the first inner-arc anode active material layer divided by the total mass of the first inner-arc anode active material layer; the mass content of the outer-arc binder in the second outer-arc anode active material layer refers to the mass of the outer-arc binder in the second outer-arc anode active material layer divided by the total mass of the second outer-arc anode active material layer; and the mass content of the second inner-arc binder in the second inner-arc anode active material layer refers to the mass of the second inner-arc binder in the second inner-arc anode active material layer divided by the total mass of the second inner-arc anode active material layer. During the preparation process, the binder content ratios in each layer and the comparison of the binder amounts between layers can be calculated and obtained by weighing. After obtaining the first anode sheet, the content ratio of the binder in each layer and the comparison of the amount of binder used between each layer can be obtained by testing Tg. The specific testing process is as follows: the first outer arc anode active material layer is peeled off from the first anode current collector, and a 10 μm thick material layer is taken on both sides as a sample. If the weight of the 10 μm thick material layer is greater than or equal to 100 g, 100 g is randomly taken for testing. If the weight of the 10 μm thick material layer is less than 100 g, samples can be taken from multiple first anode sheets until it is greater than 100 g, and 100 g is randomly taken for testing; then the glass transition temperature is measured using a thermogravimetric analyzer. (tg) test, respectively monitor the mass reduction of the samples removed from the two layers of the first outer arc anode active material layer, and obtain the binder content of the first active material layer and the second active material layer based on the sample mass reduction and the initial sample mass: binder content = sample mass reduction / initial sample mass. The temperature of the tg test can be determined based on the composition of the binder, that is, the tg test temperature is greater than the decomposition temperature of the binder. For example, when the binder is styrene-butadiene rubber (SBR), the test temperature is at least 400°C, and when the binder is carboxymethyl cellulose (CMC), the test temperature is at least 300°C. The composition of the binder can be determined by methods known in the art. For example, it can be determined by gas chromatography, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), and inductively coupled plasma optical emission spectrometry (ICP-OES).Similarly, the method provided above can be used to peel the first inner arc anode active material layer from the first anode current collector. If the weight is greater than or equal to 100g, 100g can be randomly selected for testing. If the weight is less than 100g, samples can be taken from multiple first anode sheets until the weight is greater than 100g, at which point 100g can be randomly selected for testing. After obtaining the sample, the tg test can be performed using the above method. After obtaining the second anode sheet, the proportion of the binder content in each layer and the amount of binder used between each layer can also be obtained by testing tg. The specific process can refer to the tg test of the first anode sheet.

[0062] In the secondary battery, the first outer arc anode active material layer of the first anode sheet bent toward the first direction X in the first electrode assembly is divided into a first active material layer and a second active material layer in the direction from the inside to the outside, and the binder mass content in the first inner arc anode active material layer and the first active material layer is greater than the binder mass in the second active material layer, and the first inner arc anode active material layer and the first active material layer with high binder mass have relatively strong anti-rebound capabilities, while the second active material layer with low binder mass has relatively poor anti-rebound capabilities. During use of the first anode sheet, the second active material layer with relatively poor anti-rebound capabilities generates shear stress against the first inner arc anode active material layer and the first active material layer with relatively strong anti-rebound capabilities. The generation of the shear stress can effectively enhance the anti-curvature rebound performance, thereby making the anti-curvature rebound capability of the first anode sheet stronger than that of the second anode sheet. Among the multiple curved electrode assemblies, the electrode assembly located on the outer arc side is more likely to rebound to a greater extent than the electrode assembly located on the inner arc side. By setting the first electrode assembly with relatively strong anti-curvature rebound performance on the outer arc side of the curved electrode assembly and setting the second electrode assembly with relatively weak anti-curvature rebound performance on the inner arc side of the curved electrode assembly, the curvature rebound difference of each electrode assembly in the curved electrode assembly is effectively reduced, thereby making the electrode assemblies fit better and improving the problem that the arc-shaped electrode assembly is prone to curvature rebound and thus the occurrence of black spots.

[0063] According to some embodiments of the present application, along the first direction X, the ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 6 to 3 / 4. Generally, the thickness of the electrode assembly is positively correlated with its number. The thicker the first electrode assembly with relatively strong anti-curvature rebound performance, the more conducive it is to reducing the curvature rebound of each layer of the anode sheet in the electrode assembly; while the thicker the second electrode assembly with relatively weak anti-curvature rebound performance, 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 with relatively strong anti-curvature rebound performance to the electrode assembly to 1 / 6 to 3 / 4 (to a certain extent, it can be equivalent to the proportion of the number of first electrode assemblies in multiple electrode assemblies), it is possible to better balance the control of the curvature rebound of each layer of the anode sheet and the energy density of the electrode assembly.

[0064] Furthermore, along the first direction X, the ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 4 to 3 / 4. By controlling the thickness ratio of the first electrode assembly, which has relatively strong anti-curvature rebound performance, to the electrode assembly to be 1 / 4 to 3 / 4 (which can be equivalent to the proportion of the first electrode assemblies in the multiple electrode assemblies to a certain extent), it is possible to better balance the control of the curvature rebound of each layer of the anode sheet and the energy density of the electrode assembly.

[0065] Illustratively, the thickness ratio of the first electrode assembly may be 1 / 6, 1 / 4, 1 / 3, 5 / 12, 1 / 2, 7 / 12, 2 / 3 or 3 / 4, etc., and may also be any value within the range of 1 / 6 to 3 / 4.

[0066] According to some embodiments of the present application, the relationship between the mass content W1 of the first binder in the first active material layer and the mass content W2 of the second binder in the second active material layer satisfies the following: 1.5≤W1 / W2≤3; and the relationship between the mass content N of the first inner-arc binder in the first inner-arc anode active material layer and the mass content W2 of the second binder in the second active material layer satisfies the following: 1.5≤N / W2≤3. Controlling the binder content relationship between the first inner-arc anode active material layer, the first active material layer, and the second active material layer is, to a certain extent, equivalent to controlling the shear stress generated by the second active material layer, which has relatively poor anti-rebound capability, and the first inner-arc anode active material layer and the first active material layer, which have relatively strong anti-rebound capability. By controlling the binder mass content W1 of the first active material layer, the binder mass content N of the first inner arc anode active material layer and the binder mass content W2 of the second active material layer to satisfy 1.5≤W1 / W2≤3 and 1.5≤N / W2≤3, a better rebound force gradient difference is formed among the first active material layer, the first inner arc anode active material layer and the second active material layer, thereby causing the second active material layer to produce a more appropriate shear stress on the first inner arc anode active material layer and the first active material layer, which is more conducive to reducing the degree of arc rebound.

[0067] Illustratively, the relationship between the mass content W1 of the first binder in the first active material layer and the mass content W2 of the second binder in the second active material layer may satisfy: W1=1.5×W2, W1=1.6×W2, W1=1.7×W2, W1=1.8×W2, W1=1.9×W2, W1=2×W2, W1=2.1×W2, W1=2.2×W2, W1=2.3×W2, W1=2.4×W2, W1=2.5×W2, W1=2.6×W2, W1=2.7×W2, W1=2.8×W2, W1=2.9×W2 or W1=3×W2, etc., which may also be any value satisfying the range of 1.5≤W1 / W2≤3. The relationship between the mass content N of the first inner arc binder in the first inner arc anode active material layer and the mass content W2 of the second binder in the second active material layer can satisfy: N=1.5×W2, N=1.6×W2, N=1.7×W2, N=1.8×W2, N=1.9×W2, N=2×W2, N=2.1×W2, N=2.2×W2, N=2.3×W2, N=2.4×W2, N=2.5×W2, N=2.6×W2, N=2.7×W2, N=2.8×W2, N=2.9×W2 or N=3×W2, etc., and it can also be any value within the range of 1.5≤N / W2≤3.

[0068] Furthermore, the relationship between the mass content W1 of the first binder in the first active material layer and the mass content W2 of the second binder in the second active material layer satisfies: 2≤W1 / W2≤2.5; and the relationship between the mass content N of the first inner-arc binder in the first inner-arc anode active material layer and the mass content W2 of the second binder in the second active material layer satisfies: 2≤N / W2≤2.5. By controlling the binder mass content W1 of the first active material layer, the binder mass content N of the first inner-arc anode active material layer, and the binder mass content W2 of the second active material layer to satisfy 2≤W1 / W2≤2.5 and 2≤N / W2≤2.5, a better rebound force gradient difference is formed between the first active material layer, the first inner-arc anode active material layer, and the second active material layer, thereby causing the second active material layer to generate more appropriate shear stress on the first inner-arc anode active material layer and the first active material layer, which is more conducive to reducing the degree of arc rebound.

[0069] According to some embodiments of the present application, the relationship between the thickness a1 of the first active material layer and the thickness A of the first outer arc anode active material layer satisfies the following: 0.45≤a1 / A≤0.95. Controlling the proportion of the first active material layer to the thickness of the entire first outer arc anode active material layer is, to a certain extent, equivalent to controlling the magnitude of the shear stress generated by the second active material layer, which has relatively poor anti-rebound ability, and the first inner arc anode active material layer, which has relatively strong anti-rebound ability. By controlling the thickness a1 of the first active material layer and the thickness A of the first outer arc anode active material layer to satisfy 0.45≤a1 / A≤0.95, the second active material layer can generate a more appropriate shear stress on the first inner arc anode active material layer and the first active material layer when the first anode sheet is applied as an electrode assembly.

[0070] Illustratively, the ratio a1 / A of the thickness a1 of the first active material layer and the thickness A of the first outer arc anode active material layer can be 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.95, etc., and can also be any value within the range of 0.45 to 0.95.

[0071] Furthermore, the relationship between the thickness a1 of the first active material layer and the thickness A of the first outer-arc anode active material layer satisfies the following: 0.7≤a1 / A≤0.9. By controlling the thickness a1 of the first active material layer and the thickness A of the first outer-arc anode active material layer to satisfy the following: 0.7≤a1 / A≤0.9, the second active material layer can generate a more appropriate shear stress on the first inner-arc anode active material layer and the first active material layer when the first anode sheet is used as an electrode assembly.

[0072] According to some embodiments of the present application, the relationship between the thickness A of the first outer-arc anode active material layer and the thickness B of the first inner-arc anode active material layer satisfies the following: 1≤A / B≤2. Controlling the thickness of the first inner-arc anode active material layer and the first outer-arc anode active material layer is, to a certain extent, equivalent to controlling the magnitude of the shear stress generated by the second active material layer, which has relatively poor rebound resistance, and the first inner-arc anode active material layer and the first active material layer, which has relatively strong rebound resistance. By controlling the thickness A of the first outer-arc anode active material layer and the thickness B of the first inner-arc anode active material layer to satisfy the following: 1≤A / B≤2, the second active material layer can generate a relatively suitable shear stress on the first inner-arc anode active material layer and the first active material layer when the first anode sheet is used as an electrode assembly.

[0073] Illustratively, the ratio A / B of the thickness A of the first outer arc anode active material layer to the thickness B of the first inner arc anode active material layer can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2, etc., and can also be any value within the range of 1 to 2.

[0074] Furthermore, the relationship between the thickness A of the first outer-arc anode active material layer and the thickness B of the first inner-arc anode active material layer satisfies the following: 1.3≤A / B≤1.7. By controlling the thickness A of the first outer-arc anode active material layer and the thickness B of the first inner-arc anode active material layer to satisfy the following: 1.3≤A / B≤1.7, the second active material layer can generate a more appropriate shear stress on the first inner-arc anode active material layer and the first active material layer when the first anode sheet is used as an electrode assembly.

[0075] After obtaining the first anode sheet, the thickness of the first outer arc anode active material layer and the thickness of the first inner arc anode active material layer can be obtained by the following method: performing a cross-sectional electron microscope scan on the first anode sheet, and measuring the thickness of the first outer arc anode active material layer and the thickness of the first inner arc anode active material layer through the obtained electron microscope scan image.

[0076] According to some embodiments of the present application, the first active material layer includes a first binder, the first binder comprising 2% to 4% by mass of the first active material layer; the second active material layer includes a second binder comprising 1% to 2% by mass of the second active material layer; and the first inner-arc anode active material layer includes the first inner-arc binder comprising 2% to 4% by mass of the first inner-arc anode active material layer. Controlling the binder content relationship between the first inner-arc anode active material layer, the first active material layer, and the second active material layer is, to a certain extent, equivalent to controlling the shear stress generated by the second active material layer, which has relatively poor rebound resistance, and the first inner-arc anode active material layer, which has relatively strong rebound resistance. By controlling the first binder mass to 2% to 4% of the first active material layer, the second binder mass to 1% to 2% of the second active material layer, and the first inner-arc binder mass to 2% to 4% of the first inner-arc anode active material layer, the second active material layer can generate a suitable shear stress on the first inner-arc anode active material layer and the first active material layer when the first anode sheet is used as an electrode assembly.

[0077] For example, the mass of the first binder in the first active material layer may account for 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9% or 4%, etc., and may also be any value within the range of 2% to 4%. The mass of the second binder in the second active material layer may account for 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%, etc., and may also be any value within the range of 1% to 2%. The mass of the first inner arc binder in the first inner arc anode active material layer can be 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9% or 4%, etc., and it can also be any value within the range of 2% to 4%.

[0078] According to some embodiments of the present application, the components of the first active material layer include, in parts by mass: 94 to 96 parts of the first anode active material, 2 to 4 parts of the first binder and 1 to 2 parts of the first dispersant; the components of the second active material layer include, in parts by mass: 96 to 98 parts of the second anode active material, 1 to 2 parts of the second binder and 1 to 2 parts of the second dispersant; the components of the first inner arc anode active material layer include, in parts by mass: 94 to 96 parts of the inner arc anode active material, 2 to 4 parts of the first inner arc binder and 1 to 2 parts of the inner arc dispersant.

[0079] For example, in the first active material layer, the weight fraction of the first anode active material can be 94 parts, 94.5 parts, 95 parts, 95.5 parts or 96 parts, etc., and can also be any value within the range of 94 to 96 parts; the weight fraction of the first binder can be 2 parts, 2.5 parts, 3 parts, 3.5 parts or 4 parts, etc., and can also be any value within the range of 2 to 4 parts; the weight fraction of the first dispersant can be 1 part, 1.5 parts or 2 parts, etc., and can also be any value within the range of 1 to 2 parts. In the second active material layer, the weight fraction of the second anode active material can be 96 parts, 96.5 parts, 97 parts, 97.5 parts or 98 parts, etc., and can also be any value within the range of 96 to 98 parts; the weight fraction of the first binder can be 1 part, 1.5 parts or 2 parts, etc., and can also be any value within the range of 1 to 2 parts; the weight fraction of the first dispersant can be 1 part, 1.5 parts or 2 parts, etc., and can also be any value within the range of 1 to 2 parts. In the first inner arc anode active material layer, the mass fraction of the inner arc anode active material can be 94 parts, 94.5 parts, 95 parts, 95.5 parts or 96 parts, etc., and it can also be any value within the range of 94 to 96 parts; the mass fraction of the first inner arc binder can be 2 parts, 2.5 parts, 3 parts, 3.5 parts or 4 parts, etc., and it can also be any value within the range of 2 to 4 parts; the mass fraction of the inner arc dispersant can be 1 part, 1.5 parts or 2 parts, etc., and it can also be any value within the range of 1 to 2 parts.

[0080] According to some embodiments of the present application, the first anode active material, the second anode active material and the inner arc anode active material are independently selected from at least one of graphite, graphene, carbon nanotubes, soft carbon, hard carbon, silicon alloy, silicon crystal, and tin oxide; the first binder, the second binder and the first inner arc binder 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; the first dispersant, the second dispersant and the inner arc dispersant are independently selected from at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0081] According to some embodiments of the present application, the median particle size Dv50 of the first anode active material, the second anode active material and the inner arc anode active material is 10 to 20 μm, respectively; the powder compaction density of the first anode active material, the second anode active material and the inner arc anode active material is 1.5 to 2.0 g / cm 3 .

[0082] The median particle size Dv50 is the particle size corresponding to 50% of the cumulative amount in the volume particle size cumulative distribution diagram. The volume particle size cumulative distribution diagram, also known as the differential distribution diagram of the particle size, is a curve drawn with the particle size as the horizontal coordinate and the differential distribution of the content at different particle sizes as the vertical coordinate. It can more accurately reflect the particle size distribution characteristics of the material particles. Among them, a laser particle size analyzer can be used to measure the volume particle size distribution of the material and draw an interval particle size distribution curve. When the median particle size of the active material in the active material layer of the electrode is measured, the active material layer can be removed and immersed in the solvent NMP to wash out the binder in the active material layer to obtain the powder material of the active material layer. After the powder material is dried, it is detected using a laser particle size analyzer with the model number Mastersizer3000 to obtain a volume particle size cumulative distribution diagram. The median particle size can be obtained based on the peak in the volume particle size cumulative distribution diagram.

[0083] For example, the median particle size Dv50 of the first anode active material, the second anode active material and the inner arc anode active material can be 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, 18.5 μm, 19 μm, 19.5 μm or 20 μm, etc., and can also be any value within the range of 10 to 20 μm. The powder compaction density of the first anode active material, the second anode active material and the inner arc anode active material can be 1.5 g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 or g / cm 3 etc., which can also be 1.5 to 2.0 g / cm 3 Any value in the range.

[0084] According to some embodiments of the present application, the first electrode assembly includes multiple first anode sheets, and along the first direction X, the mass content of the first binder in the first active material layer of the multiple first anode sheets gradually decreases; along the first direction X, the mass content of the first inner arc binder in the inner arc active material layer of the multiple first anode sheets gradually decreases.

[0085] The mass content of the binder in the multiple first active material layers and the multiple inner arc active material layers gradually decreases in a gradient that can be every layer or every few layers, for example, every 2 layers, every 3 layers, every 4 layers, etc., which are not listed here one by one. And in the process of gradually decreasing, the gradient can also change. In other words, the mass content of the binder in the multiple first active material layers and the multiple inner arc active material layers gradually decreases, or the mass content of the binder in the multiple first active material layers and the multiple inner arc active material layers gradually decreases in a step-like manner. It should be noted that in the process of gradually decreasing the multiple first active material layers and the multiple inner arc active material layers, the mass content of the binder in the multiple first active material layers and the multiple inner arc active material layers closest to the second anode assembly must be greater than the mass content of the binder in its second active material layer.

[0086] By gradually reducing the mass content of the binder in the first active material layer and the inner arc active material layer in the first electrode assembly, its anti-rebound ability is matched with its position in the electrode assembly, thereby achieving better matching of the curvature rebound degree of the first anode sheets of each layer of the electrode assembly.

[0087] Furthermore, the difference in binder mass content between two adjacent first active material layers is 0.02% to 0.12%, and the difference in binder mass content between two adjacent inner arc active material layers is 0.02% to 0.12%. By controlling the difference in binder mass content between the first active material layers and the inner arc active material layers in two adjacent first electrode assemblies to be 0.02% to 0.12%, their anti-rebound capabilities are more consistent with their positions in the electrode assemblies, thereby achieving better matching of the curvature rebound of the first anode sheets in each layer of the electrode assemblies.

[0088] According to some embodiments of the present application, the central angle Q of the electrode assembly is 10° to 90°. For example, the central angle Q of the electrode assembly can be 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85° or 920°, etc., and it can also be any value within the range of 10° to 90°.

[0089] According to some embodiments of the present application, the shell is a packaging bag. Specifically, the packaging bag can be selected from aluminum-plastic film.

[0090] After the above introduction to the materials and structure of the secondary battery, the preparation method of the secondary battery will be specifically introduced below.

[0091] A secondary battery, the assembly process is as follows:

[0092] Preparation of anode sheet:

[0093] Preparation of the first anode sheet:

[0094] Anode active material particles, a dispersant, and a binder are mixed, and an appropriate amount of deionized water is added and stirred thoroughly to obtain two anode active slurries with different binder contents. The anode active slurry with a high binder content is coated on one surface of a first anode current collector, and the anode active slurry with a high binder content is coated on the other surface of the first anode current collector. After drying, a high-binder active material layer is formed. The anode active slurry with a low binder content is coated on the surface of the high-binder active material layer, and then dried, cold pressed, cut, and bent to obtain a first anode sheet.

[0095] Preparation of the second anode sheet:

[0096] The anode active material particles, conductive agent, thickener, and binder are mixed, and an appropriate amount of deionized water is added and stirred thoroughly to obtain an anode active slurry. The anode active slurry is coated on both surfaces of the second anode current collector, dried, cold pressed, cut, and bent to obtain a second anode sheet.

[0097] Preparation of cathode sheet:

[0098] Cathode active material particles, a conductive agent, and a binder are mixed, and N-methylpyrrolidone is used as a solvent. The mixture is stirred thoroughly to form a cathode active slurry. The cathode active slurry is coated on both surfaces of the cathode current collector and dried to form a cathode active slurry layer. The cathode sheet is then cold-pressed, cut, and bent.

[0099] Preparation of electrode assembly:

[0100] The first anode sheet / the second anode sheet, the first separator, the cathode sheet and the second separator are repeatedly stacked in sequence to form the first electrode assembly / the second electrode assembly.

[0101] Preparation of secondary batteries:

[0102] The first electrode assembly and the second electrode assembly are stacked to form an electrode assembly with 24 electrode layers, which is then placed in a shell, injected with electrolyte, and then subjected to formation to obtain a secondary battery.

[0103] The present application is described in detail below through examples and comparative examples.

[0104] Examples and Comparative Examples

[0105] An electrochemical device, the assembly process is as follows:

[0106] Preparation of anode sheet:

[0107] Preparation of the first anode sheet:

[0108] A negative electrode active material, graphite particles, a dispersant, sodium carboxymethyl cellulose, and a binder, styrene-butadiene rubber, were mixed, and an appropriate amount of deionized water was added and thoroughly stirred to obtain two negative electrode active slurries with different binder contents. The negative electrode active slurry with a high binder content was coated on one surface of a 6-μm-thick copper foil, and the anode active slurry with a high binder content was coated on the other surface of the 6-μm-thick copper foil. After drying, a high-binder active material layer was formed. The negative electrode active slurry with a low binder content was coated on the surface of the high-binder active material layer, and then dried, cold pressed, cut, and bent to obtain a first anode sheet.

[0109] Preparation of the second anode sheet:

[0110] The anode active slurry with high binder content in the step of preparing the first anode sheet was prepared at 0.2 g / 1540.25 mm 2 After coating on both surfaces of a copper foil with a thickness of 6 μm, drying, cold pressing, cutting and bending are performed to obtain a second anode sheet.

[0111] Preparation of cathode sheet:

[0112] 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 mixture was stirred thoroughly to obtain the positive electrode active slurry. The positive electrode active slurry was prepared by mixing 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 positive electrode active slurry layer; then cold pressing, cutting, and bending are performed to obtain a cathode sheet.

[0113] Preparation of electrode assembly:

[0114] The separator is made of PP (polypropylene) and has a thickness of 20 μm. The first anode sheet / second anode sheet, the first separator, the cathode sheet, and the second separator are repeatedly stacked in sequence to form the first electrode assembly / second electrode assembly.

[0115] Preparation of secondary batteries:

[0116] The first electrode assembly and the second electrode assembly are stacked to form an electrode assembly, which is then placed in a housing, and an electrolyte is injected, followed by formation to obtain a secondary battery. The electrolyte contains 1 mol / L lithium hexafluorophosphate as the solute and 1:1 volume ratio of ethylene carbonate and dimethyl carbonate as the solvent.

[0117] The main parameter control of each embodiment is shown in the following table:

[0118] 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:

[0119] Electrode assembly 1000 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 1000 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 1000 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.

[0120] 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.

[0121] The results are shown in the following table:

[0122] As shown in the table above, the electrode assembly of the secondary battery produced using the method provided in the examples of this application has good anti-curvature rebound performance, with the curvature change rate being controllable to 2%. The secondary battery also has good cycle capacity retention, reaching 95%.

[0123] By comparing the data of Examples 1 to 6, it can be seen that as the proportion of the first electrode assemblies with stronger resistance to curvature rebound increases, the curvature change rate and the cycle capacity retention rate both show a trend of first getting better and then getting worse, and when the proportion of the first electrode assemblies is 1 / 6 to 3 / 4, the curvature change rate of the electrode assembly can be controlled below 5%, and the cycle capacity retention rate can be controlled above 90%. Furthermore, when the proportion of the first electrode assemblies is 1 / 4 to 3 / 4, the curvature change rate of the electrode assembly can be controlled below 4%, and the cycle capacity retention rate can be controlled above 91%.

[0124] By comparing the data of Example 4 and Examples 7 to 11, it can be seen that with the increase of the binder mass content ratio W1 / W2 of the first active material layer and the second active material layer, and the binder mass content ratio N / W2 of the first inner arc anode active material layer and the second active material layer, the curvature change rate and the cycle capacity retention rate both show a trend of first improving and then deteriorating, and when the values ​​of W1 / W2 and N / W2 are between 1.5 and 3, the curvature change rate of the electrode assembly can be controlled below 3%, and the cycle capacity retention rate can be controlled above 92%. Furthermore, when the values ​​of W1 / W2 and N / W2 are between 2 and 2.5, the curvature change rate of the electrode assembly can be controlled below 3%, and the cycle capacity retention rate can be controlled above 93%.

[0125] Comparison of the data from Example 4 and Examples 12 to 19 shows that as the thickness ratio a1 / A of the first active material layer to the first outer arc anode active material layer increases, the curvature change rate and cycle capacity retention rate both show a trend of first improving and then deteriorating. Furthermore, when the a1 / A value is between 0.45 and 0.95, the curvature change rate of the electrode assembly can be controlled below 5%, and the cycle capacity retention rate can be controlled above 90%. Furthermore, when the a1 / A value is between 0.7 and 0.9, the curvature change rate of the electrode assembly can be controlled below 3%, and the cycle capacity retention rate can be controlled above 93%.

[0126] Comparison of the data from Example 4 and Examples 20 to 25 shows that as the thickness ratio A / B of the first inner arc anode active material layer to the first outer arc anode active material layer increases, the curvature change rate and cycle capacity retention rate both show a trend of first improving and then deteriorating. Furthermore, when the A / B value is 1-2, the curvature change rate of the electrode assembly can be controlled below 4%, and the cycle capacity retention rate can be controlled above 93%. Furthermore, when the A / B value is 1.3-1.7, the curvature change rate of the electrode assembly can be controlled below 3%, and the cycle capacity retention rate can be controlled above 94%.

[0127] By comparing the data of Example 4 and Examples 26 to 28, it can be seen that gradually reducing the mass content of the binder in the first active material layer and the inner arc active material layer in the first electrode assembly can be more conducive to the curvature rebound of the electrode assembly and the cycle capacity retention rate of the battery. When the gradually decreasing gradient is 0.02% to 0.12%, the curvature change rate of the electrode assembly can be controlled below 2.5%, and the cycle capacity retention rate can be controlled above 93%.

[0128] The above are merely specific embodiments of the present application and are not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a housing and an electrode assembly. The electrode assembly is accommodated in the housing and is bent in a first direction X. The electrode assembly includes a first electrode assembly and a second electrode assembly stacked in the first direction X. The first electrode assembly includes a first anode sheet. The first anode sheet includes a first outer arc anode active material layer, a first anode current collector, and a first inner arc anode active material layer stacked in the first direction X. The first outer arc anode active material layer includes a first active material layer and a second active material layer. The first active material layer is disposed between the second active material layer and the first anode current collector. The first active material layer includes a first binder, the second active material layer includes a second binder, and the first inner arc anode active material layer includes a first inner arc binder. The mass content of the first binder in the first active material layer is greater than the mass content of the second binder in the second active material layer. The mass content of the first inner arc binder in the first inner arc anode active material layer is greater than the mass content of the second binder in the second active material layer. The second electrode assembly includes a second anode sheet. The second anode sheet includes a second outer arc anode active material layer, a second anode current collector, and a second inner arc anode active material layer stacked in the first direction X.

2. The secondary battery according to claim 1, characterized in that, Along the first direction X, the ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 6 to 3 / 4.

3. The secondary battery according to claim 2, characterized in that, Along the first direction X, the ratio of the thickness of the first electrode assembly to the thickness of the electrode assembly is 1 / 4 to 3 / 4.

4. The secondary battery according to any one of claims 1 to 3, characterized in that, The relationship between the mass content W1 of the first binder in the first active material layer and the mass content W2 of the second binder in the second active material layer satisfies: 1.5 ≤ W1 / W2 ≤ 3; and / or The relationship between the mass content N of the first inner arc binder in the first inner arc anode active material layer and the mass content W2 of the second binder in the second active material layer satisfies: 1.5 ≤ N / W2 ≤ 3.

5. The secondary battery according to claim 4, characterized in that, 2 ≤ W1 / W2 ≤ 2.5; and / or 2 ≤ N / W2 ≤ 2.

5.

6. The secondary battery according to any one of claims 1 to 3, characterized in that, The relationship between the thickness a1 of the first active material layer and the thickness A of the first outer arc anode active material layer satisfies: 0.45 ≤ a1 / A ≤ 0.

95.

7. The secondary battery according to claim 6, wherein 0.7 ≤ a1 / A ≤ 0.

9.

8. The secondary battery according to any one of claims 1 to 3, characterized in that, Along the first direction X, the relationship between the thickness A of the first outer arc anode active material layer and the thickness B of the first inner arc anode active material layer satisfies: 1 ≤ A / B ≤ 2.

9. The secondary battery according to claim 8, characterized in that, 1.3 ≤ A / B ≤ 1.

7.

10. The secondary battery according to any one of claims 1 to 3, characterized in that, The mass content W1 of the first binder in the first active material layer is 2% to 4%; and / or The mass content W2 of the second binder in the second active material layer is 1% to 2%; and / or The mass content N of the first inner arc binder in the first inner arc anode active material layer is 2% to 4%.

11. The secondary battery according to any one of claims 1 to 3, characterized in that, The first electrode assembly includes a plurality of the first anode sheets, and along the first direction X, the mass content of the first binder in the first active material layer of the plurality of the first anode sheets gradually decreases; and / or Along the first direction X, the mass content of the first inner arc binder in the first inner arc active material layer of the plurality of the first anode sheets gradually decreases.

12. The secondary battery according to claim 11, wherein, The difference in the mass content of the binder in the first active material layer between two adjacent first anode sheets is 0.02% to 0.12%; and / or The difference in the mass content of the binder in the inner arc active material layer between two adjacent first anode sheets is 0.02% to 0.12%.

13. The secondary battery according to any one of claims 1 to 3, characterized in that, The central angle Q of the electrode assembly is 10° to 90°.

14. The secondary battery according to claim 11, characterized in that, The second outer arc anode active material layer includes an outer arc binder, the second inner arc anode active material layer includes a second inner arc binder, and the mass content of the outer arc binder in the second outer arc anode active material layer and the mass content of the second inner arc binder in the second inner arc anode active material layer are equal to the mass content of the first inner arc binder in the first inner arc anode active material layer.

15. The secondary battery according to any one of claims 1 to 3, characterized in that, The housing is a packaging bag.

16. An electronic device, characterized in that, The electronic device includes a secondary battery according to any one of claims 1 to 15.

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