Secondary battery and electric device

Abstract

The present application relates to the technical field of energy storage, and in particular to a secondary battery and an electric device. The secondary battery comprises an electrode assembly; the electrode assembly comprises a first electrode sheet, a second electrode sheet, and a separator; and the separator is arranged between the first electrode sheet and the second electrode sheet. The first electrode sheet at the outermost side comprises first straight sections and first bent sections connected to each other; the first straight sections are located in a straight area; and the first bent sections are located in bent areas. Each first bent section comprises a first flattened portion and first raised portions; each first raised portion connects the first flattened portion and the corresponding first straight section; and a first interlayer gap is formed between the first raised portions and the second electrode sheet. Therefore, during expansion of the electrode assembly, the first interlayer gap is capable of buffering the tensile force on the first electrode sheet, thereby mitigating the problem of the electrode sheet breaking due to the tensile stress.

Description

Secondary batteries and electrical equipment Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and electrical equipment. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in small devices such as portable electronic devices, as well as medium and large devices such as battery packs or energy storage in hybrid and electric vehicles. With the rapid development of various commercial products, the requirements for the safety performance of rechargeable batteries are becoming increasingly stringent.

[0003] With the continuous pursuit of high energy density in wound battery cells, electrode designs are trending towards higher active material coating amounts, higher compaction densities, and thinner current collector thicknesses. This results in greater expansion and contraction of the active material during pressure application or cell charging and discharging, leading to increased electrode deformation and a higher risk of electrode breakage. To address these issues, it is indeed necessary to provide an improved secondary battery. Summary of the Invention

[0004] In view of this, this application provides a secondary battery and an electrical device that can improve the problem of electrode breakage.

[0005] In a first aspect, embodiments of this application provide a secondary battery, including an electrode assembly. The electrode assembly includes a first electrode, a second electrode, and a separator, with the separator disposed between the first and second electrodes. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The electrode assembly includes a straight region and a bent region, with the bent region connected to the straight region. The outermost ring of the first electrode includes a first straight segment and a first bent segment connected together. The first straight segment is located in the straight region, and the first bent segment is located in the bent region. The first bent segment includes a first flattened portion and a first raised portion, with the first raised portion connecting the first flattened portion and the first straight segment. A first interlayer gap exists between the first raised portion and the second electrode.

[0006] By providing a first interlayer gap between the first raised portion and the second electrode, the first interlayer gap can buffer the tensile force on the first electrode when the electrode assembly expands. This allows the first interlayer gap between the first raised portion and the second electrode to provide a margin for the expansion of the electrode assembly during charging, discharging, or collision, thus improving the problem of electrode breakage due to stretching.

[0007] In some embodiments, the first flattened portion and the first raised portion are formed by the first curved section being subjected to pressure along the extension direction of the first straight section. The pressed portion is the first flattened portion, and the unpressed portion is the first raised portion. The first raised portion is located between the first flattened portion and the first straight section.

[0008] In some embodiments, along the stacking direction of the electrode assembly, the maximum value of the first interlayer gap is s1, which satisfies 0.01mm < s1 ≤ 0.1mm.

[0009] By controlling the maximum value of the first interlayer gap between 0.01 mm and 0.1 mm, it is beneficial to increase the deformable space of the first interlayer gap and improve the problem of electrode breakage due to stretching.

[0010] In some embodiments, two first protrusions are provided, and the first protrusions are provided at both ends of the first flattened portion along the thickness direction of the electrode assembly.

[0011] By providing first raised portions at both ends of the first flattened portion along the thickness direction of the electrode assembly, the expansion margin of the electrode assembly is increased, thereby further improving the problem of electrode breakage due to stretching.

[0012] In some embodiments, a plane perpendicular to the width direction of the first electrode is defined as a first plane, the orthographic projection of the first flattened portion onto the first plane is a first straight line, the orthographic projection of the first straight segment onto the first plane is a second straight line, and the angle between the first straight line and the second straight line is θ, satisfying 70°≤θ≤110°.

[0013] The angle between the first and second straight lines is controlled between 70° and 110° to improve the ease of processing the first interlayer gap. If the angle between the first and second straight lines is less than 70° or greater than 110°, there is a problem that the first straight line is too inclined, making it difficult to form the first interlayer gap.

[0014] In some embodiments, the first line is perpendicular to the second line.

[0015] The first straight line is perpendicular to the second straight line, which is beneficial to simultaneously form the first raised part at both ends of the first flattened part along the thickness direction of the electrode assembly, thereby increasing the expansion margin of the electrode assembly and further improving the problem of electrode sheet breakage due to stretching.

[0016] In some embodiments, along the thickness direction of the electrode assembly, the length of the first flattened portion is h1, and the thickness of the electrode assembly is H, satisfying 0.05H≤h1≤0.8H.

[0017] Along the thickness direction of the electrode assembly, the ratio of the length of the first flattened portion to the thickness of the electrode assembly is controlled between 0.05 and 0.8, thus ensuring sufficient margin in the first interlayer gap for the stretching deformation of the electrode sheet. If the ratio of the length of the first flattened portion to the thickness of the electrode assembly is less than 0.05, the expansion margin provided by the first interlayer gap is insufficient, posing a risk of electrode breakage during electrode deformation. If the ratio of the length of the first flattened portion to the thickness of the electrode assembly is greater than 0.8, the deformation of the first bending section is excessive, leading to increased pressure on the inner electrode sheet from the first straight section, affecting the electrolyte flow rate and thus impacting the safety of the secondary battery.

[0018] In some embodiments, 0.25 ≤ h1 / H ≤ 0.6.

[0019] Along the thickness direction of the electrode assembly, the ratio of the length of the first flattened portion to the thickness of the electrode assembly is controlled between 0.25 and 0.6. The first interlayer gap has sufficient margin for the stretching deformation of the electrode sheet, and the pressure of the first straight section on the inner electrode sheet is within the design range, which is conducive to further improving the safety of the secondary battery.

[0020] In some embodiments, the second outer ring of the first electrode includes a second straight section and a second curved section connected together. The second straight section is located in a straight region, and the second curved section is located in a bending region. The second curved section includes a second flattened portion and a second raised portion. The second raised portion connects the second flattened portion and the second straight section, and there is a second interlayer gap between the second raised portion and the second electrode.

[0021] By having a second interlayer gap between the second raised portion and the second electrode, the second interlayer gap can buffer the tensile force on the first electrode when the electrode assembly expands. Thus, during charging, discharging or collision, the second interlayer gap between the second raised portion and the second electrode provides a margin for the expansion of the electrode assembly, improving the problem of electrode breakage due to stretching.

[0022] In some embodiments, along the stacking direction of the electrode assembly, the maximum value of the second interlayer gap is s2, which satisfies 0.01mm < s2 ≤ 0.09mm.

[0023] By controlling the maximum value of the second interlayer gap between 0.01 mm and 0.09 mm, it is beneficial to increase the deformable space of the second interlayer gap and improve the problem of electrode breakage due to stretching.

[0024] In some embodiments, the length of the second flattened portion along the thickness direction of the electrode assembly is h2, satisfying h2 < h1.

[0025] The second flattening part is located on the outermost ring of the first electrode sheet along the thickness direction of the electrode assembly. By controlling the length of the second flattening part to be less than the length of the first flattening part, the molding convenience of the second flattening part is improved.

[0026] In some embodiments, the secondary battery further includes a housing and tabs, the housing having a cavity in which an electrode assembly is housed, and the tabs being electrically connected to the electrode assembly and partially extending out of the housing.

[0027] The electrode assembly is housed within the cavity of the housing. The tabs are electrically connected to the electrode assembly and partially extend out of the housing, thereby protecting the electrode assembly through the housing and improving the safety of the secondary battery.

[0028] Secondly, embodiments of this application provide an electrical device including the secondary battery described in one or more of the above embodiments. Attached Figure Description

[0029] Figure 1 is a schematic diagram of the overall structure of the secondary battery in one embodiment of this application.

[0030] Figure 2 is a schematic diagram of the structure of a secondary battery after disassembly in one embodiment of this application.

[0031] Figure 3 is a schematic cross-sectional view of the electrode assembly before extrusion in one embodiment of this application.

[0032] Figure 4 is a schematic cross-sectional view of the electrode assembly after extrusion in one embodiment of this application.

[0033] Figure 5 is a schematic cross-sectional view of the electrode assembly before extrusion in another embodiment of this application.

[0034] Figure 6 is a schematic cross-sectional view of the electrode assembly after extrusion in another embodiment of this application.

[0035] Figure 7 is a schematic diagram of the structure of the electrical equipment in one embodiment of this application.

[0036] Key Component Symbol Explanation: 001 Secondary Battery; 100 Electrode Assembly; 110 First Electrode; 111 First Straight Section; 112 First Bending Section; 1121 First Flattened Section; 1122 First Raised Section; 1123 First Interlayer Gap; 113 Second Straight Section; 114 Second Bending Section; 1141 Second Flattened Section; 1142 Second Raised Section; 1143 Second Interlayer Gap; L1 First Straight Line; L2 Second Straight Line; 120 Second Electrode; 130 Separator; 140 Straight Region; 150 Bending Region; 200 Housing; 210 Cavity; 300 First Tab; 400 Second Tab; 002 Electrical Equipment Detailed Implementation

[0037] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0038] It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or may also have an intervening component. When a component is considered to be "placed" on another component, it can be directly placed on the other component or may also have an intervening component. The terms "top," "bottom," and similar expressions used in this article are for illustrative purposes only.

[0039] Unless otherwise stated, the term "multiple" as used herein refers to two or more.

[0040] The terms “first”, “second”, etc., are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implying the quantity, specific order, or primary and secondary relationship of the indicated technical features.

[0041] The term "perpendicular" is used to describe the ideal state between two components. In actual production or use, two components may exist in a state that is approximately perpendicular.

[0042] The term "parallel" is used to describe the ideal state between two components. In actual production or use, two components may exist in a state that is approximately parallel.

[0043] It should be noted that when a parameter is greater than, equal to or less than a certain endpoint value, it should be understood that the endpoint value is allowed to have a tolerance of ±5%.

[0044] It should be understood that the dimensions and thicknesses of the components shown in the accompanying drawings are for better understanding and more convenient description, and this application is not limited to the dimensions and thicknesses shown in the accompanying drawings.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0046] This application provides a secondary battery that can improve the problem of the first electrode breaking due to stretching during charging, discharging, or collision.

[0047] Embodiments of this application provide a secondary battery, including an electrode assembly. The electrode assembly includes a first electrode, a second electrode, and a separator, with the separator disposed between the first and second electrodes. The first electrode, the second electrode, and the separator are stacked and wound to form a wound structure. The electrode assembly includes a straight region and a bent region, with the bent region connected to the straight region. The outermost ring of the first electrode includes a first straight segment and a first bent segment connected together. The first straight segment is located in the straight region, and the first bent segment is located in the bent region. The first bent segment includes a first flattened portion and a first raised portion, with the first raised portion connecting the first flattened portion and the first straight segment. A first interlayer gap exists between the first raised portion and the second electrode.

[0048] By providing a first interlayer gap between the first raised portion and the second electrode, the first interlayer gap can buffer the tensile force on the first electrode when the electrode assembly expands. This allows the first interlayer gap between the first raised portion and the second electrode to provide a margin for the expansion of the electrode assembly during charging, discharging, or collision, thus improving the problem of electrode breakage due to stretching.

[0049] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the embodiments and features described below can be combined with each other.

[0050] Please refer to Figures 1 and 2. This application embodiment provides a secondary battery 001, which includes an electrode assembly 100 and a first tab 300 connected to the electrode assembly 100. The secondary battery 001 also includes a second tab 400 connected to the electrode assembly 100. The first tab 300 and the second tab 400 have different polarities.

[0051] In some embodiments, the secondary battery 001 further includes a housing 200 having a cavity 210, and the electrode assembly 100 is disposed within the cavity 210 of the housing 200. A portion of the first tab 300 extends out of the housing 200 and is used for electrical connection with an external structure. A portion of the second tab 400 extends out of the housing 200 and is used for electrical connection with an external structure.

[0052] In other embodiments, a first tab 300 is connected to a conductive first adapter (not shown), which extends out of the housing 200 and is used for electrical connection with an external structure. A second tab 400 is connected to a conductive second adapter (not shown), which extends out of the housing 200 and is used for electrical connection with an external structure.

[0053] In some embodiments, the housing 200 includes at least one of a steel housing, a resin housing, or an aluminum-plastic film. For example, when the secondary battery 001 is a hard-shell battery, the housing 200 includes a steel housing or a resin housing, and when the secondary battery 001 is a soft-pack battery, the housing 200 includes an aluminum-plastic film.

[0054] Please refer to Figures 2 and 3. The electrode assembly 100 includes a first electrode 110, a second electrode 120, and a diaphragm 130. The diaphragm 130 is disposed between the first electrode 110 and the second electrode 120. The first electrode 110, the second electrode 120, and the diaphragm 130 are stacked and wound to form a wound structure.

[0055] The electrode assembly 100 includes a straight region 140 and a bent region 150, with the bent region 150 connected to the straight region 140. The outermost ring of the first electrode 110 includes a first straight segment 111 and a first bent segment 112 connected to each other, with the first straight segment 111 located in the straight region 140 and the first bent segment 112 located in the bent region 150.

[0056] It is worth noting that the outermost ring of the first electrode 110 refers to the first turn of the first electrode 110 wound from the tail end of the first electrode 110 toward the winding start end along the winding direction of the electrode assembly 100.

[0057] Referring to Figures 3 and 4, the electrode assembly 100 is deformed by pressing it with pressure plates on both sides in the width direction. The first curved section 112 includes a first flattened portion 1121 and a first raised portion 1122. The first raised portion 1122 connects the first flattened portion 1121 and the first straight section 111. A first interlayer gap 1123 exists between the first raised portion 1122 and the second electrode 120.

[0058] By providing a first interlayer gap 1123 between the first raised portion 1122 and the second electrode 120, the first interlayer gap 1123 can buffer the tensile force on the first electrode 110 when the electrode assembly 100 expands. Thus, during charging, discharging or collision, the first interlayer gap 1123 between the first raised portion 1122 and the second electrode 120 provides a margin for the expansion of the electrode assembly 100, improving the problem of electrode breakage due to stretching.

[0059] In some embodiments, the first flattened portion 1121 and the first raised portion 1122 are formed by the first curved section 112 being subjected to pressure along the extending direction of the first straight section 111. The pressed portion is the first flattened portion 1121, and the unpressed portion is the first raised portion 1122. The first raised portion 1122 is located between the first flattened portion 1121 and the first straight section 111.

[0060] In some embodiments, along the stacking direction of the electrode assembly 100, the maximum value of the first interlayer gap 1123 is s1, satisfying 0.01mm < s1 ≤ 0.1mm. By controlling the maximum value of the first interlayer gap 1123 between 0.01mm and 0.1mm, it is beneficial to increase the deformable space of the first interlayer gap 1123 and improve the problem of electrode breakage due to stretching.

[0061] In some embodiments, the outermost straight segment 111 of the first electrode 110 is provided in two forms, and the two straight segments 111 are arranged facing each other along the thickness direction of the electrode assembly 100.

[0062] Two first raised portions 1122 are provided, one at each end of the first flattened portion 1121 along the thickness direction of the electrode assembly 100. By providing first raised portions 1122 at both ends of the first flattened portion 1121 along the thickness direction of the electrode assembly 100, the expansion margin of the electrode assembly 100 is increased, further improving the problem of electrode breakage due to stretching.

[0063] In some embodiments, the plane perpendicular to the width direction of the first electrode 110 is defined as the first plane, the orthographic projection of the first flattened portion 1121 onto the first plane is the first straight line L1, the orthographic projection of the first straight segment 111 onto the first plane is the second straight line L2, and the angle between the first straight line L1 and the second straight line L2 is θ, satisfying 70°≤θ≤110°.

[0064] The angle between the first straight line L1 and the second straight line L2 is controlled between 70° and 110° to improve the ease of processing the first interlayer gap 1123. If the angle between the first straight line L1 and the second straight line L2 is less than 70° or greater than 110°, there is a problem that the first straight line L1 is too inclined, which makes it difficult to form the first interlayer gap 1123.

[0065] In some embodiments, the angle θ between the first straight line L1 and the second straight line L2 is any one of 70°, 72°, 74°, 76°, 78°, 80°, 82°, 84°, 86°, 88°, 90°, 92°, 94°, 96°, 98°, 100°, 102°, 104°, 106°, 108°, and 110°.

[0066] The first straight line L1 is defined as the orthographic projection of the portion of the first flattened portion 1121 extending along the length of the first electrode 110 onto the first plane, meaning that some portions of the first flattened portion 1121 are allowed to deviate from the first straight line L1. Similarly, the second straight line L2 is defined as the orthographic projection of the portion of the first straight segment 111 extending along the length of the first electrode 110 onto the first plane, meaning that some portions of the first straight segment 111 are allowed to deviate from the second straight line L2.

[0067] Please refer to Figure 4. In some embodiments, the first straight line L1 is perpendicular to the second straight line L2, which is beneficial to simultaneously form the first raised portion 1122 at both ends of the first flattened portion 1121 along the thickness direction of the electrode assembly 100, thereby increasing the expansion margin of the electrode assembly 100 and further improving the problem of electrode sheet breakage due to stretching.

[0068] In some embodiments, along the thickness direction of the electrode assembly 100, the length of the first flattening portion 1121 is h1, and the thickness of the electrode assembly 100 is H, satisfying 0.05H≤h1≤0.8H.

[0069] Along the thickness direction of the electrode assembly 100, the ratio of the length of the first flattened portion 1121 to the thickness of the electrode assembly 100 is controlled between 0.05 and 0.8, thereby ensuring that the first interlayer gap 1123 has sufficient margin for the stretching deformation of the electrode sheet. If the ratio of the length of the first flattened portion 1121 to the thickness of the electrode assembly 100 is less than 0.05, the expansion margin provided by the first interlayer gap 1123 is insufficient, posing a risk of electrode sheet breakage during deformation. If the ratio of the length of the first flattened portion 1121 to the thickness of the electrode assembly 100 is greater than 0.8, the deformation of the first bent section 112 is excessive, leading to increased pressure on the inner electrode sheet from the first straight section 111, affecting the electrolyte flow rate, and thus impacting the safety of the secondary battery 001.

[0070] In one or more of the above embodiments, 0.25 ≤ h1 / H ≤ 0.6.

[0071] Along the thickness direction of the electrode assembly 100, the ratio of the length of the first flattened portion 1121 to the thickness of the electrode assembly 100 is controlled between 0.25 and 0.6. The first interlayer gap 1123 has sufficient margin for the stretching deformation of the electrode sheet, and the pressure of the first straight section 111 on the inner electrode sheet is within the design range, which is conducive to further improving the safety of the secondary battery 001.

[0072] In some embodiments, the value of h1 / H is any one of 0.25, 0.26, 0.27, 0.28, 0.29, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, and 0.6.

[0073] In some embodiments, the outermost ring of the first electrode 110 includes a second straight section 113 and a second curved section connected together, the second straight section 113 being located in the straight region 140 and the second curved section being located in the bending region 150.

[0074] It is worth noting that the second outer ring of the first electrode 110 refers to the second turn of the first electrode 110 wound from the tail end of the first electrode 110 toward the winding start end of the first electrode 110 along the winding direction of the electrode assembly 100.

[0075] The second curved section includes a second flattened portion 1141 and a second raised portion 1142. The second raised portion 1142 connects the second flattened portion 1141 and the second straight section 113. A second interlayer gap 1143 exists between the second raised portion 1142 and the second electrode 120.

[0076] By having a second interlayer gap 1143 between the second protrusion 1142 and the second electrode 120, the second interlayer gap 1143 can buffer the tensile force on the first electrode 110 when the electrode assembly 100 expands. Thus, during charging, discharging or collision, the second interlayer gap 1143 between the second protrusion 1142 and the second electrode 120 provides the electrode assembly 100 with room for expansion, improving the problem of electrode breakage due to stretching.

[0077] In some embodiments, along the stacking direction of the electrode assembly 100, the maximum value of the second interlayer gap 1143 is s2, satisfying 0.01mm < s2 ≤ 0.09mm. By controlling the maximum value of the second interlayer gap 1143 between 0.01mm and 0.09mm, it is beneficial to increase the deformable space of the second interlayer gap 1143 and improve the problem of electrode breakage due to stretching.

[0078] In some embodiments, the length of the second flattened portion 1141 along the thickness direction of the electrode assembly 100 is h2, satisfying h2 < h1. The second flattened portion 1141 is located on the sub-outer ring of the first electrode 110. By controlling the length of the second flattened portion 1141 to be less than the length of the first flattened portion 1121 along the thickness direction of the electrode assembly 100, the molding convenience of the second flattened portion 1141 is improved.

[0079] Referring to Figures 5 and 6, in some embodiments, the pressure plates on both sides of the electrode assembly 100 in the width direction are inclined and parallel. By using the two inclined pressure plates to compress the electrode assembly 100, the sides of the electrode assembly 100 are deformed. The angle θ between the first straight line L1 and the second straight line L2 is an obtuse angle, so that the shapes of the first raised portions 1122 at both ends of the first flattened portion 1121 along the thickness direction of the electrode assembly 100 are different. This results in different first interlayer gaps 1123 between the two first raised portions 1122 and the second electrode 120. This is beneficial for adjusting the size of the first interlayer gap 1123 according to the location of the weak area of ​​the first electrode 110 in the electrode assembly 100, further improving the problem of electrode breakage due to stretching.

[0080] In some embodiments, the angle θ between the first straight line L1 and the second straight line L2 is 100°.

[0081] Please refer to Figure 7. One embodiment of this application also provides an electrical device 002, which includes the secondary battery 001 in one or more of the above embodiments.

[0082] To verify the effect of the first flattening part 1121 on the charging cycle of the secondary battery 001, the following experiment was conducted:

[0083] Cyclic testing: Twenty secondary batteries (001) were used in each comparative and example group for testing. Each secondary battery (001) was 56mm long, 37mm wide, and 8mm thick. Each secondary battery (001) was placed in a 25°C environment and allowed to stand for 30 minutes. Then, it was charged and discharged according to the following steps: Charged at a constant current of 5C to 4.2V, then at a constant current of 4C to 4.3V, then at a constant current of 3C to 4.45V, then at a constant voltage of 4.45V to 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 3V, allowed to stand for 5 minutes. This constitutes one cycle. The above cyclic steps were repeated 1000 times. After the cyclic test, the capacity retention rate of each secondary battery (001) was calculated. The capacity retention rate is the ratio of the discharge capacity after 1000 cycles to the discharge capacity of the first cycle. Record the capacity retention rate of each comparative example and each set of examples after 1000 cycles of the 20 secondary batteries 001. A capacity retention rate greater than 80% is considered a pass. The cycle test pass rate is the ratio of the number of secondary batteries 001 that pass the test to the total number of tests.

[0084] The specific implementation of the secondary battery 001 in the embodiments and comparative examples will be described below.

[0085] Example 1:

[0086] The assembly process of a secondary battery 001 is as follows:

[0087] (1) Preparation of the anode electrode: Artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:1.5:2.5. Deionized water was added as a solvent to prepare an anode active material slurry with a weight percentage of 70 wt%, which was then stirred evenly. A 10 μm thick copper foil was used as the anode current collector. The anode active material slurry was uniformly coated onto one surface of the anode current collector along its thickness direction using a slot coater, leaving an empty foil area without an anode active material layer at one end of the anode current collector's width direction. The foil was dried at 110°C to obtain an anode electrode substrate with a single-sided anode active material layer. The above steps were then repeated on the other side of the anode current collector along its thickness direction, leaving an empty foil area without an anode active material layer at one end of the anode current collector's width direction, to obtain an anode electrode substrate with a double-sided anode active material layer, wherein the compaction of the anode active material layer was 1.70 g / cm³. 3 A single anode electrode is obtained by punching the anode electrode substrate using a mold and a die cutter, and the empty foil area where no anode active material layer is set forms the anode tab.

[0088] (2) Preparation of cathode electrode: Lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a cathode active material slurry with a solid content of 75 wt%, and the mixture was stirred evenly for later use. A 10 μm thick aluminum foil was used as the cathode current collector. The above cathode active material slurry was uniformly coated on one surface of the cathode current collector along its thickness direction using a slot coater. An empty foil area without a cathode active material layer was reserved at one end of the cathode current collector in the width direction. The foil was dried at 90°C to obtain a cathode electrode substrate with a cathode active material layer coated on one side. The above steps were then repeated on the other side of the cathode current collector along its thickness direction, with an empty foil area without a cathode active material layer reserved at one end of the cathode current collector in the width direction, to obtain a cathode electrode substrate with cathode active material layers coated on both sides. A single cathode electrode is obtained by punching the cathode electrode substrate using a mold and a die cutter, and the empty foil area where no cathode active material layer is set forms the cathode tab.

[0089] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L and an electrolyte conductivity of 8.0 S / m.

[0090] (4) Preparation of diaphragm 130: The diaphragm 130 adopts a three-layer structure with a thickness of 5 μm, which includes a first adhesive layer, a first substrate layer and a second adhesive layer stacked together. The first substrate layer is made of polyethylene (PE), and both the first adhesive layer and the second adhesive layer contain a first adhesive and boehmite.

[0091] (5) Electrode assembly 100 fabrication: A first electrode 110, a diaphragm 130, and a second electrode 120 are stacked along the first direction X to form a winding layer, which is then wound to form a winding structure. Pressure plates are used to press the electrode assembly 100 on both sides of its width direction, thereby deforming the sides of the electrode assembly 100. The first curved section 112 includes a first flattened portion 1121 and a first raised portion 1122. The first raised portion 1122 connects the first flattened portion 1121 with the first straight section 111, and a first interlayer gap 1123 exists between the first raised portion 1122 and the second electrode 120. The value of h1 is 0.4 mm, h1 / H = 0.05, and the angle θ between the first straight line L1 and the second straight line L2 is 90°.

[0092] (6) Assembly of electrode assembly 100: Place the punched aluminum-plastic film in the assembly fixture with the punched surface facing up, place the electrode assembly 100 in the punch, and apply external force to press it. Then cover the electrode assembly 100 with another punched aluminum-plastic film with the punched surface facing down, and heat seal the two aluminum-plastic films around their perimeter by hot pressing to obtain the assembled electrode assembly 100.

[0093] (7) Electrolyte injection and encapsulation: Electrolyte is injected into the assembled electrode assembly 100, and after vacuum encapsulation, standing, hot pressing formation, shaping and other processes, the secondary battery 001 is obtained.

[0094] Comparative Example 1: The difference from Example 1 is that the electrode assembly 100 is conventionally arranged, and pressure plates are not used to squeeze the electrode assembly 100 on both sides in the width direction of the electrode assembly 100.

[0095] Example 2: The difference from Example 1 is that the length h1 of the first flattening part 1121 is 2mm, and h1 / H = 0.25.

[0096] Example 3: The difference from Example 1 is that the length h1 of the first flattening part 1121 is 4.4 mm, and h1 / H = 0.55.

[0097] Example 4: The difference from Example 1 is that the length h1 of the first flattening part 1121 is 4.8 mm, and h1 / H = 0.6.

[0098] Example 5: The difference from Example 1 is that the length h1 of the first flattening part 1121 is 6.4 mm, and h1 / H = 0.8.

[0099] Example 6: The difference from Example 1 is that the length h1 of the first flattening part 1121 is 0.24 mm, and h1 / H = 0.03.

[0100] Example 7: The difference from Example 1 is that the length h1 of the first flattening part 1121 is 7.2 mm, and h1 / H = 0.9.

[0101] Example 8: The difference from Example 2 is that the angle θ between the first straight line L1 and the second straight line L2 is 70°.

[0102] Example 9: The difference from Example 2 is that the angle θ between the first straight line L1 and the second straight line L2 is 110°.

[0103] Example 10: The difference from Example 2 is that the angle θ between the first straight line L1 and the second straight line L2 is 60°.

[0104] Example 11: The difference from Example 2 is that the angle θ between the first straight line L1 and the second straight line L2 is 120°.

[0105] The main parameter controls and test results for each embodiment and comparative example are shown in Table 1:

[0106] Table 1 Note: " / " indicates that no value is taken.

[0107] In Comparative Example 1, the electrode assembly 100 is conventionally configured. During the process of being under pressure or charging and discharging the secondary battery 001, the active material expands and contracts more, and the electrode deformation increases, which makes the electrode prone to breakage.

[0108] In Example 1, compared to Comparative Example 1, by providing a first interlayer gap 1123 between the first raised portion 1122 and the second electrode 120, the first interlayer gap 1123 can buffer the tensile force on the first electrode 110 when the electrode assembly 100 expands. As a result, during charging, discharging or collision, the first interlayer gap 1123 between the first raised portion 1122 and the second electrode 120 provides a margin for the expansion of the electrode assembly 100, improving the problem of electrode breakage due to stretching. The pass rate of the cycle test is increased from 15% to 65%.

[0109] In Example 2, compared to Example 1, the length h1 of the first flattening portion 1121 is increased from 0.4 mm to 2 mm, thereby increasing the width of the first interlayer gap 1123, further increasing the allowance for the expansion of the electrode assembly 100, improving the problem of electrode breakage due to stretching, and increasing the cycle test pass rate from 65% to 95%.

[0110] Compared to Examples 3 to 7, in Example 2, the first straight section 111 exerts less pressure on the inner electrode, resulting in a higher electrolyte flow rate. Compared to Comparative Example 1, in Examples 3 to 7, the first interlayer gap 1123 between the first raised portion 1122 and the second electrode 120 provides ample space for the expansion of the electrode assembly 100, mitigating the problem of electrode breakage due to stretching and improving the cycle test pass rate.

[0111] As shown in Table 1, satisfying 0.05H≤h1≤0.8H allows the first interlayer gap 1123 to have sufficient margin for the stretching deformation of the electrode, thereby improving the problem of the first electrode 110 breaking due to stretching during charging, discharging or collision.

[0112] Compared to Examples 8 to 11, in Example 2, when the first straight line L1 is perpendicular to the second straight line L2, the pressure on the inner electrode sheet at both ends of the first flattening part 1121 is more uniform, which helps to improve the problem of electrode sheet breakage due to stretching and improve the pass rate of cycle test.

[0113] As shown in Table 1, satisfying 70°≤θ≤110° can improve the uniformity of the pressure on the inner electrode at both ends of the first flattening part 1121, thus mitigating the problem of electrode breakage due to stretching.

[0114] Furthermore, those skilled in the art can make various other corresponding changes and modifications based on the technical concept of this application, and all such changes and modifications should fall within the protection scope of the claims of this application.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly including a first electrode, a second electrode, and a separator, the separator being disposed between the first electrode and the second electrode, the first electrode, the second electrode, and the separator being stacked and wound to form a wound structure, characterized in that: The electrode assembly includes a flat region and a bent region, the bent region being connected to the flat region; the outermost ring of the first electrode includes a first flat segment and a first bent segment connected together, the first flat segment being located in the flat region and the first bent segment being located in the bent region; the first bent segment includes a first flattened portion and a first raised portion, the first raised portion connecting the first flattened portion and the first flat segment, and a first interlayer gap being present between the first raised portion and the second electrode.

2. The secondary battery as described in claim 1, characterized in that, The first flattened portion and the first raised portion are formed by the first curved section being subjected to pressure along the extending direction of the first straight section. The pressed portion is the first flattened portion, and the unpressed portion is the first raised portion. The first raised portion is located between the first flattened portion and the first straight section; and / or Along the stacking direction of the electrode assembly, the maximum value of the first interlayer gap is s1, where 0.01mm < s1 ≤ 0.1mm.

3. The secondary battery as described in claim 1, characterized in that, Two first raised portions are provided, and the first raised portions are provided at both ends of the first flattened portion along the thickness direction of the electrode assembly.

4. The secondary battery as described in claim 1, characterized in that, A plane perpendicular to the width direction of the first electrode is defined as the first plane. The orthographic projection of the first flattened portion onto the first plane is the first straight line. The orthographic projection of the first straight segment onto the first plane is the second straight line. The angle between the first straight line and the second straight line is θ, which satisfies 70°≤θ≤110°.

5. The secondary battery as described in claim 4, characterized in that, The first line is perpendicular to the second line.

6. The secondary battery as described in claim 1 or 5, characterized in that, Along the thickness direction of the electrode assembly, the length of the first flattened portion is h1, and the thickness of the electrode assembly is H, satisfying 0.05H≤h1≤0.8H.

7. The secondary battery as described in claim 6, characterized in that, 0.25≤h1 / H≤0.

6.

8. The secondary battery as described in claim 6, characterized in that, The second outer ring of the first electrode includes a second straight section and a second curved section connected together. The second straight section is located in the straight region, and the second curved section is located in the bending region. The second curved section includes a second flattened portion and a second raised portion. The second raised portion connects the second flattened portion and the second straight section. There is a second interlayer gap between the second raised portion and the second electrode.

9. The secondary battery as described in claim 8, characterized in that, Along the stacking direction of the electrode assembly, the maximum value of the second interlayer gap is s2, which satisfies 0.01mm < s2 ≤ 0.09mm.

10. The secondary battery as described in claim 8, characterized in that, Along the thickness direction of the electrode assembly, the length of the second flattened portion is h2, which satisfies h2 < h1.

11. The secondary battery as described in claim 1, characterized in that, The secondary battery also includes a housing and tabs. The housing has a cavity, the electrode assembly is housed in the cavity, and the tabs are electrically connected to the electrode assembly and partially extend out of the housing.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 11.

Images