battery

Abstract

The application provides a battery. The battery comprises a negative electrode sheet, a separator and a positive electrode sheet forming a roll electrode body and an electrolyte. In the roll direction, the starting end of the separator at least partially adheres to the part of the starting end of the negative electrode sheet to form a separator starting end composite area. The separator comprises a base film and a coating layer arranged on the base film, and the coating layer comprises a nitrogen-containing compound. The positive electrode current collector at the first positive electrode bending section is provided with micropores, and the number of micropores is N / mm 2 . The electrolyte comprises lithium bis(trifluoromethylsulfonyl)imide, and the mass percentage of lithium bis(trifluoromethylsulfonyl)imide in the electrolyte is C based on the total mass of the electrolyte. N satisfies: 450 / mm2≤N≤2000 / mm2, and C satisfies: 1wt%≤C≤12wt%. The numerical relationship between N and C satisfies: 0.000005≤C / N≤0.00027.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a battery. Background Technology

[0002] Lithium-ion batteries (e.g., lithium-ion pouch batteries) are high-energy rechargeable batteries that operate by moving lithium ions between the positive and negative electrodes to achieve the charging and discharging process.

[0003] In related technologies, the reliability of lithium-ion battery cell structure needs to be improved in order to further enhance the battery's electrical performance and safety. Summary of the Invention

[0004] In view of this, embodiments of this application provide a battery to improve battery performance and safety of use.

[0005] Embodiments of this application provide a battery comprising a wound electrode body formed by stacking and winding a negative electrode, a separator, and a positive electrode, a housing containing the wound electrode body, and an electrolyte filled in the housing. The wound electrode body includes a flat portion and curved portions located on both sides of the flat portion. The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector. In the innermost ring of the wound electrode body, the negative electrode includes a first straight negative electrode section located in the flat portion and a first bent negative electrode section located in the curved portion. The first straight negative electrode section and the first bent negative electrode section are connected, and the end of the first straight negative electrode section away from the first bent negative electrode section is the starting end of the negative electrode. The positive electrode includes a first straight positive electrode section located in a flat portion and a first bent positive electrode section located in a curved portion. The first straight positive electrode section and the first bent positive electrode section are connected. The end of the first straight positive electrode section away from the first bent positive electrode section is the starting end of the positive electrode. Along the width direction of the battery, the starting end of the negative electrode is positioned towards the first bent positive electrode section. Along the winding direction, the starting end of the separator extends beyond the starting end of the negative electrode, and the portion of the starting end of the separator extending beyond the starting end of the negative electrode is at least partially bonded together to form a separator starting end composite region. The separator includes a base film and a coating disposed on the base film, the coating including a nitrogen-containing compound. The positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector. Along the winding direction, micropores are provided on the positive current collector located in the first bent positive electrode section, the number of micropores being N / mm. 2 The electrolyte includes lithium bis(trifluoromethanesulfonyl)imide. Based on the total mass of the electrolyte, the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is C. N satisfies: 450 particles / mm² ≤ N ≤ 2000 particles / mm², and C satisfies: 1 wt% ≤ C ≤ 12 wt%. The numerical relationship between N and C satisfies: 0.000005 ≤ C / N ≤ 0.00027.

[0006] Optionally, in some embodiments, the length of the composite region at the initiation end of the diaphragm is L, and the nitrogen-containing compound D v50 The condition L satisfies: 500 ≤ L / D v50 ≤50000; and / or, the length of the composite region at the diaphragm initiation end is L, 0.5 mm ≤ L ≤ 10 mm, preferably 0.5 mm ≤ L ≤ 5 mm; and / or, the particle size Dv50 of the nitrogen-containing compound satisfies: 0.1 μm ≤ Dv50 ≤ 3 μm, preferably 0.1 μm ≤ Dv50 ≤ 1 μm. μm; and / or, the nitrogen-containing compound includes at least one of melamine cyanurate, melamine polyphosphate, melamine thiocyanate, melamine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, melamine chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, and 2-amino-4,6-methoxy-1,3,5-triazine.

[0007] Optionally, in some embodiments, the maximum Feret diameter D of each micropore satisfies: 0.5 μm ≤ D ≤ 4 μm; and / or, the pore depth h1 of the micropore satisfies: 0.5 μm ≤ h1 ≤ 5 μm; and / or, the pore depth h1 of the micropore is less than or equal to the thickness of the positive electrode current collector.

[0008] Optionally, in some embodiments, at least a portion of the diaphragm initiation end composite region is provided with a plurality of recesses. Preferably, the area S1 of the plurality of recesses and the area S of the diaphragm initiation end composite region satisfy: 0.1 ≤ S1 / S ≤ 0.9.

[0009] Optionally, in some embodiments, along the winding direction, the minimum distance between the edge of the recess closest to the starting end of the negative electrode and the starting end of the negative electrode is d, where d ≥ 1 mm; and / or Multiple recesses are formed on the coating or on the coating and at least part of the base film. Preferably, the maximum size of the orthographic projection of a single recess along the thickness direction of the composite region at the starting end of the diaphragm is 0.1 mm to 1.5 mm, and / or the number of recesses on the composite region at the starting end of the diaphragm is 1 / mm. 2 ~4 pieces / mm 2 .

[0010] Optionally, in some embodiments, the positive active layer of the first positive electrode bending section facing the winding center is provided with a thinning region, and the thickness h2 of the positive active layer in the thinning region and the thickness h3 of the remaining positive active layers satisfy: 0.05≤h2 / h3≤0.95, and the composite region at the beginning of the separator is at least partially disposed opposite to the thinning region; preferably, a first insulating layer is bonded to the inner surface of the first positive electrode bending section; more preferably, the first insulating layer at least covers the thinning region, and even more preferably, along the winding direction, the end of the composite region at the beginning of the separator away from the beginning of the negative electrode does not extend beyond the two ends of the first insulating layer.

[0011] Optionally, in some embodiments, the positive electrode active layer includes a positive electrode active material, which includes a lithium cobalt oxide substrate and a coating layer covering at least a portion of the surface of the lithium cobalt oxide substrate; preferably, the average thickness of the coating layer is 5 nm to 500 nm, and / or the coating layer includes at least one of Al, Mg, Zr, Ti, Y, La and Zn elements.

[0012] Optionally, in some embodiments, the negative electrode active layer comprises a silicon-based material, which includes at least one of silicon-carbon or silicon-oxygen materials. The particle size Dv50 of the silicon-based material is 5 μm to 15 μm, and the span value of the silicon-based material is 0.2 to 2. The span value is the ratio of the difference between Dv90 and Dv10 of the silicon-based material to Dv50 of the silicon-based material. Dv represents the cumulative volume percentile of the silicon-carbon material. The Dv10, Dv50, and Dv90 of the silicon-based particles refer to the particle sizes that, in ascending order of particle size, correspond to the 10%, 50%, and 90% of the cumulative volume distribution of the silicon-carbon material, respectively; and / or, the sphericity of the silicon-based material is 0.6 to 0.98.

[0013] Optionally, in some embodiments, at least a portion of the tail section of the negative electrode sheet is bonded to the separators on both sides to form a first composite region, and at least a portion of the tail section of the separator extending beyond the tail section of the negative electrode sheet is bonded to form a second composite region along the winding direction. The dimension A of the first composite region along the winding direction is 1 mm to 20 mm; and / or, the dimension B of the second composite region along the winding direction is 2 mm to 15 mm.

[0014] Optionally, in some embodiments, the separator further includes an adhesive layer disposed on the coating. The adhesive layer comprises polymer particles, including one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-modified polyvinylidene fluoride-hexafluoropropylene and its copolymers, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol and its copolymerized modified polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, waterborne polyurethane, ethylene-vinyl acetate copolymer, and multi-component acrylic copolymers. Preferably, in the composite region at the beginning of the separator, the coverage of the adhesive layer per unit area on the separator is M1, and the coverage of the adhesive layer per unit area on the separator located at the battery bend is M2. The difference between M1 and M2 satisfies: 3% ≤ (M1-M2) ≤ 15%, and / or, in the composite region at the beginning of the separator, the thickness of the adhesive layer is h4, and the thickness of the adhesive layer located at the battery bend is h5. h4 and h5 satisfy: 0.1 μm ≤ (h5-h4) ≤ 0.5 μm.

[0015] According to the technical solution of this application, the portion of the separator's starting end extending beyond the starting end of the negative electrode sheet is bonded together to form a separator starting end composite region. This avoids internal short circuits caused by the separator's starting end folding, thus improving battery safety performance. The separator starting end composite region is at least partially oriented towards the first positive electrode bending section, which can slightly increase the bending radius of the first positive electrode bending section and provide support, reducing the risk of breakage due to excessive bending. However, the accumulation of the separator starting end composite region inside the battery will adsorb a large amount of electrolyte. Under high-temperature cycling, the positive electrode active material undergoes structural transformation, with increased lattice distortion, increasing the risk of metal ion dissolution in the positive electrode active material. This leads to side reactions between metal ions and the electrolyte, resulting in increased heat generation and deteriorating the battery's high-temperature cycling performance. A nitrogen-containing compound is placed on the surface of the separator. Nitrogen atoms have high electronegativity, and nitrogen-containing groups have lone pairs of electrons with strong coordination ability. It can dissolve or swell in trace amounts in the electrolyte and form stable coordination bonds with metal ions dissolved from the positive electrode. This inhibits the dissolution of metal ions from the positive electrode active material, improves the stability of the positive electrode material, and reduces side reactions at high temperatures. This ensures the high-temperature cycle performance of the battery while avoiding the folding of the separator at the beginning and supporting the bending section of the first positive electrode.

[0016] Then, micropores are provided on the positive current collector located in the first positive electrode bending section, and the number of micropores N is controlled to satisfy: 450 micropores / mm² ≤ N ≤ 2000 micropores / mm². The presence of an appropriate number of micropores can release and buffer stress during bending, improve deformation capacity, thereby further reducing the bending stress of the positive current collector in the first positive electrode bending section and improving the problem of fracture in the first positive electrode bending section.

[0017] The large anionic structure of LiTFSI in the electrolyte can reduce the solvation degree of lithium ions and decrease migration resistance, thereby improving the migration rate of lithium ions and enhancing the rate performance of the battery. On the other hand, LiTFSI in the electrolyte is insensitive to moisture inside the battery. Unlike other lithium salts (e.g., lithium hexafluorophosphate), it does not readily react with trace amounts of water in the electrolyte to produce hydrofluoric acid. Hydrofluoric acid is more likely to corrode and damage the structure of the cathode material, leading to the dissolution of metal ions from the cathode material. Adding a certain amount of LiTFSI to the electrolyte can reduce the generation of hydrofluoric acid in the battery, further suppressing the risk of metal ion dissolution from the cathode active material.

[0018] However, because the recombination region at the membrane initiation end is located close to the first positive electrode bending section, it adsorbs and stores a large amount of electrolyte in this region, resulting in a higher concentration of TFSI in the LiTFSI electrolyte. ﹣ After the anions diffuse from the electrolyte to the surface of the positive electrode aluminum foil, they are easily adsorbed at high-energy active sites on the surface of the positive electrode current collector (e.g., aluminum foil) at defects or mechanical damage sites (e.g., the micropores of the aforementioned positive electrode current collector aluminum foil). They then react with the Al2O3 passivation film on the positive electrode current collector aluminum foil to generate soluble macromolecular composite anions [Al(TFSI)]. x ] 3－x This leads to the destruction of the passivation film. After the Al2O3 passivation film is destroyed, the exposed metallic aluminum is oxidized to Al at a high potential. 3+ This leads to the continuous dissolution of the positive electrode current collector, forming large pores and damaging the structural integrity of the positive electrode current collector. As a result, during battery cycling, especially during high-temperature cycling, LiTFSI exacerbates the corrosion of the positive electrode current collector in the first positive electrode bending section, increasing the risk of positive electrode sheet breakage in this area and short circuits inside the battery.

[0019] Controlling the LiTFSI content (C) in the electrolyte to the condition 1 wt% ≤ C ≤ 12 wt% can improve the battery's rate performance. Too low a content will not improve rate performance, while too high a content significantly enhances the interaction between cations and anions, causing a sharp increase in electrolyte viscosity. The increased ion migration resistance due to high viscosity will offset or even exceed the conductivity gain from the increased ion quantity, leading to a decrease in ionic conductivity and thus worsening the battery's rate performance. It will also exacerbate corrosion of the current collector, increasing the risk of breakage at the first positive electrode bending section. Furthermore, controlling the number of micropores on the positive electrode current collector at the first positive electrode bending section within a specific range relative to the LiTFSI content can balance battery rate performance with reducing corrosion of the current collector at the first positive electrode bending section, thereby mitigating the risk of breakage at the first positive electrode bending section. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the drawings only show some embodiments of this application and should not be considered as a limitation of the scope. It should also be understood that the same or similar reference numerals are used in the drawings to represent the same or similar elements. Furthermore, it should be understood that the drawings are merely schematic, and the dimensions and scale of the elements in the drawings are not necessarily precise.

[0021] Figure 1 This is a schematic diagram of the structure of a wound electrode body according to an embodiment of this application.

[0022] Figure 2 yes Figure 1 A magnified view of a section at point C.

[0023] Figure 3 This is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of this application.

[0024] Figure 4 This is a schematic diagram of the negative electrode sheet and separator according to an embodiment of this application.

[0025] Figure 5 yes Figure 4 A magnified view of a section at point D.

[0026] Figure 6 yes Figure 5 Top view.

[0027] Figure 7 yes Figure 5 Another top view.

[0028] Figure 8 yes Figure 4 A magnified view of a section at point E in the middle.

[0029] Figure 9 yes Figure 8 Top view.

[0030] Figure 10 This is a schematic diagram of the structure of a diaphragm according to an embodiment of this application.

[0031] Figure 11 This is a schematic diagram of the structure of a battery according to an embodiment of this application.

[0032] Figure 12 This is another structural schematic diagram of a battery according to one embodiment of this application.

[0033] Figure label: 1000, battery; 100. Winded electrode body; 101. Flat portion; 102. Bending portion; 11. Positive electrode sheet; 111. Positive electrode current collector; 112. Positive electrode active layer; 113. First positive electrode straight section; 114. First positive electrode bent section; 116. Thinning region; 117. Positive electrode empty foil region; 118. Positive electrode single-sided coating region; 12. Negative electrode sheet; 121. Negative electrode current collector; 122. Negative electrode active layer; 123. First negative electrode straight section; 124. First negative electrode bent section; 13. Separator; 131. Base layer; 132. Coating layer; 133. Adhesive layer; 134. Separator starting end composite region; 135. Recess; 136. First composite region; 137. Second composite region; 14. First insulating layer; 15. Second insulating layer; 200. Shell. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0035] Improving battery energy density is a continuous goal in the battery industry. To achieve this, the battery structure needs to be modified to reduce the space occupied by electrode components. Simultaneously, new materials are required to match the battery structure, thereby improving battery reliability.

[0036] The following is for reference. Figures 1 to 12 The present application provides an example description of the battery provided in the embodiments.

[0037] It should be noted that the winding direction mentioned in the text is the direction indicated by R in the figure.

[0038] refer to Figures 1 to 12This application provides a battery 1000, which includes a wound electrode body formed by stacking and winding a negative electrode 12, a separator 13, and a positive electrode 11, a housing containing the wound electrode body, and an electrolyte filled in the housing. The wound electrode body includes a flat portion 101 and curved portions 102 located on both sides of the flat portion 101. The negative electrode 12 includes a negative current collector 121 and a negative active layer 122 disposed on the negative current collector 121. In the innermost circle of the wound electrode body, the negative electrode 12 includes a first negative straight section 123 located in the flat portion 101 and a first negative bent section 124 located in the curved portion 102. The first negative straight section 123 and the first negative bent section 124 are connected, and the end of the first negative straight section 123 away from the first negative bent section 124 is the winding start end of the negative electrode 12. The positive electrode 11 includes a first positive electrode straight section 113 located in the flat portion 101 and a first positive electrode bent section 114 located in the bent portion 102. The first positive electrode straight section 113 and the first positive electrode bent section 114 are connected. The end of the first positive electrode straight section 113 away from the first positive electrode bent section 114 is the winding start end of the positive electrode 11. Along the width direction of the battery 1000, the start end of the negative electrode 12 is arranged towards the first positive electrode bent section 114, that is, the wound electrode body is an interlocking wound electrode body.

[0039] Along the winding direction, the starting end of the separator 13 extends beyond the starting end of the negative electrode 12, and the portion of the starting end of the separator 13 extending beyond the starting end of the negative electrode 12 is at least partially bonded together to form a separator starting end composite region 134. The separator 13 includes a base film 131 and a coating 132 disposed on the base film 131, the coating 132 comprising a nitrogen-containing compound. The positive electrode 11 includes a positive current collector 111 and a positive active layer 112 disposed on the positive current collector 111. Along the winding direction, micropores are provided on the positive current collector 111 located in the first positive electrode bending section 114, the number of micropores being N / mm. 2The electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide. Based on the total mass of the electrolyte, the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte, denoted as C, satisfies the following: 450 cells / mm² ≤ N ≤ 2000 cells / mm², for example, 450, 500, 600, 800, 1000, 1200, 1400, 1600, 1800, or 2000 cells / mm². C satisfies the following: 1 wt% ≤ C ≤ 12 wt%, for example, 1.5 wt%, 2 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, or 12 wt%. The numerical relationship between N and C satisfies: 0.000005 ≤ C / N ≤ 0.00027, for example, 0.000008, 0.00001, 0.000015, 0.000018, 0.00020, 0.00022, 0.00025 or 0.00027.

[0040] According to the technical solution of this application, the portion of the starting end of the separator 13 extending beyond the starting end of the negative electrode 12 is bonded together to form a separator starting end composite region 134. This avoids internal short circuits caused by the folding of the starting end of the separator 13, thus improving the safety performance of the battery 1000. The separator starting end composite region 134 is at least partially oriented towards the first positive electrode bending section 114, which can slightly increase the bending radius of the first positive electrode bending section 114 and provide support for the first positive electrode bending section 114, reducing the risk of breakage of the first positive electrode bending section 114 due to excessive bending. However, the separator starting end composite region 134, when accumulated inside the battery 1000, will adsorb a large amount of electrolyte. Under high-temperature cycling, the positive electrode active material of the battery 1000 will undergo structural transformation, with increased lattice distortion, increasing the risk of metal ion dissolution in the positive electrode active material. This leads to side reactions between metal ions and the electrolyte, resulting in increased heat generation and deteriorating the high-temperature cycling performance of the battery 1000. A nitrogen-containing compound is disposed on the surface of the separator 13. Nitrogen atoms have high electronegativity, and nitrogen-containing groups have lone pairs of electrons with strong coordination ability. It can dissolve or swell in the electrolyte in small amounts and form stable coordination bonds with metal ions dissolved from the positive electrode, inhibiting the dissolution of metal ions in the positive electrode active material, improving the stability of the positive electrode material, thereby reducing side reactions at high temperatures. While avoiding the folding of the starting end of the separator 13 and supporting the first positive electrode bending section 114, the high-temperature cycle performance of the battery 1000 is guaranteed.

[0041] Then, micropores are provided on the positive current collector 111 located in the first positive electrode bending section 114, and the number of micropores N is controlled to satisfy: 450 micropores / mm² ≤ N ≤ 2000 micropores / mm². The presence of an appropriate number of micropores can release and buffer stress during bending, improve deformation capacity, thereby further reducing the bending stress of the positive current collector 111 in the first positive electrode bending section 114 and improving the problem of breakage of the first positive electrode bending section 114.

[0042] The large anionic structure of LiTFSI in the electrolyte can reduce the solvation degree of lithium ions and decrease migration resistance, thereby improving the migration rate of lithium ions and enhancing the 1000-rate performance of the battery. On the other hand, LiTFSI in the electrolyte is insensitive to moisture inside the battery. Unlike other lithium salts (e.g., lithium hexafluorophosphate), it does not readily react with trace amounts of water in the electrolyte to produce hydrofluoric acid. Hydrofluoric acid is more likely to corrode and damage the structure of the cathode material, leading to the dissolution of metal ions from the cathode material. Adding a certain amount of LiTFSI to the electrolyte can reduce the generation of hydrofluoric acid in the battery, further suppressing the risk of metal ion dissolution from the cathode active material.

[0043] However, because the membrane initiation recombination region 134 is located close to the first positive electrode bending section 114, the membrane initiation recombination region 134 adsorbs and stores a large amount of electrolyte in this region, and the TFSI in the LiTFSI in the electrolyte... ﹣ After the anions diffuse from the electrolyte to the surface of the positive electrode aluminum foil, they readily adsorb at high-energy active sites on the surface of the positive electrode current collector 111 (e.g., aluminum foil) at defects or mechanical damage sites (e.g., the micropores of the aforementioned positive electrode current collector 111 aluminum foil). These sites react with the Al2O3 passivation film on the positive electrode current collector 111 aluminum foil to generate soluble macromolecular composite anions [Al(TFSI)]. x ] 3－x This leads to the destruction of the passivation film. After the Al2O3 passivation film is destroyed, the exposed metallic aluminum is oxidized to Al at a high potential. 3+ This causes the positive current collector 111 to be continuously dissolved, forming large pores and damaging the structural integrity of the positive current collector 111. As a result, during the battery 1000 cycling process, especially during the high-temperature cycling process of the battery 1000, LiTFSI intensifies the corrosion of the positive current collector 111 of the first positive electrode bending section 114, increasing the risk of breakage of the positive electrode sheet 11 in this area and short circuit inside the battery 1000.

[0044] Controlling the LiTFSI content C in the electrolyte to satisfy 1 wt% ≤ C ≤ 12 wt% can improve the rate performance of the battery 1000. If the content is too low, it will not improve the rate performance of the battery 1000. If the content is too high, the interaction between the cations and anions will be significantly enhanced, and the viscosity of the electrolyte will increase sharply. The increased ion migration resistance due to high viscosity will offset or even exceed the conductivity gain brought by the increased ion quantity, leading to a decrease in ionic conductivity and thus worsening the rate performance of the battery 1000. It will also exacerbate the corrosion of the current collector, increasing the risk of breakage of the first positive electrode bending section 114. Furthermore, controlling the number of micropores on the positive current collector 111 of the first positive electrode bending section 114 within a specific range with the LiTFSI content can balance the rate performance of the battery 1000 while reducing its corrosion effect on the positive current collector 111 of the first positive electrode bending section 114, thus reducing the risk of breakage of the first positive electrode bending section 114.

[0045] By way of example only, the negative electrode current collector 121 can be a strip of metal foil, and its active material layer can contain a negative electrode active material that can reversibly absorb and release charge carriers, binders, dispersants and various additives.

[0046] By way of example only, the metal foil mentioned in the negative electrode 12 above can be copper foil.

[0047] As examples, the diaphragm 13 can be a porous strip made of resin composed of polyolefin resins such as polyethylene and polypropylene. Of course, it is also conceivable that other materials can be used to construct the diaphragm 13, and this application does not limit or impose any special requirements on this.

[0048] By way of example only, the positive current collector 111 can be a strip of metal foil. For example, the metal foil of the positive current collector 111 can be aluminum foil.

[0049] Along the winding direction, the positive electrode 11 includes multiple positive electrode bending sections and multiple positive electrode straight sections, which are arranged alternately. After winding, the positive electrode bending sections are located in the curved portion 102 of the wound electrode body, and the positive electrode straight sections are located in the flat portion 101 of the wound electrode body.

[0050] Similarly, along the winding direction, the negative electrode 12 includes multiple negative electrode bending sections and multiple negative electrode straight sections, which are arranged alternately. After winding, the negative electrode bending sections are located in the curved portion 102 of the wound electrode body, and the negative electrode straight sections are located in the flat portion 101 of the wound electrode body.

[0051] In this application, the test method for the number of micropores per unit area on the positive electrode current collector 111 of the first bending section is described below. After discharging the battery 1000 to 0 SOC%, the battery 1000 is disassembled, and a sample of approximately 3mm × 3mm (adjustable as needed) area on the positive electrode sheet 11 located on the first positive electrode bending section 114 is cut out. The positive electrode active layer 112 is removed by ultrasonic cleaning (using DMC solution). The positive electrode current collector 111 sample is then dried by baking. The positive electrode current collector 111 sample is then observed under an electron scanning microscope at 5000x to 10000x (adjustable as needed). The number of micropores on the surface of the positive electrode current collector 111 sample is recorded using image analysis software, and the maximum Feret diameter D of the micropores is calculated by measurement. In the image analysis software, the maximum Feret diameter D specifically refers to the maximum distance between any two edges of the micropore in a two-dimensional projection (such as a microscope image).

[0052] The obtained positive electrode current collector 111 sample is cut along the thickness direction of the positive electrode current collector 111. Then, the positive electrode current collector 111 sample is magnified 5000x to 10000x (adjustable as needed) under an electron scanning microscope to observe and measure the depth of the micropores.

[0053] It should be noted that methods such as laser, electrochemical etching, and chemical etching can be used to pre-treat the surface of specific areas of the positive electrode current collector, thereby controlling the number, depth, diameter, and other parameters of the micropores on the surface of those specific areas to meet the structural requirements of the positive electrode current collector in this application. Specifically, the control methods can include adjusting parameters such as laser pulse width, frequency, etching time, and the composition and concentration of the etching solution to regulate the number N, maximum Feretta diameter D, and depth of the micropores on the positive electrode current collector in the first positive electrode bending section.

[0054] In some embodiments, the length of the membrane initiation composite region 134 is L, and the particle size of the nitrogen-containing compound is D. v50 The condition L satisfies: 500 ≤ L / D v50 ≤50000, for example, 500, 1000, 3000, 5000, 8000, 10000, 15000, 20000, 30000, 40000, or 50000. This makes the D of nitrogen-containing compounds... v50The size of the nitrogen compound is matched with the size of the nitrogen (L). This avoids situations where L is too large and the Dv50 of the nitrogen compound is too small, resulting in excessive accumulation and adsorption of electrolyte in the composite region 134 at the beginning of the separator at the first positive electrode bend 114. Alternatively, if the particle size of the nitrogen compound is too small, its absorption capacity with the electrolyte decreases, preventing it from undergoing micro-dissolution or swelling. This leads to insufficient coordination ability with dissolved ions in the positive electrode material, failing to effectively alleviate the problem of deteriorated high-temperature cycle performance of the battery 1000 due to side reactions between the dissolved metal ions in the positive electrode active material and the electrolyte. On the other hand, if L is too small and the Dv50 of the nitrogen compound is too large, the separator 13 cannot be effectively prevented from folding. Furthermore, if the size of the nitrogen compound is too large, the flatness of the coating 132 on the surface of the separator 13 will be poor, affecting the adhesion stability of the composite region 134 at the beginning of the separator and further increasing the risk of internal short circuits caused by the folding of the separator 13.

[0055] In some embodiments, the length of the composite region 134 at the starting end of the separator is L, 0.5 mm ≤ L ≤ 10 mm, for example, 0.5 mm, 0.8 mm, 1 mm, 1.5 mm, 2 mm, 4 mm, 6 mm, 8 mm or 10 mm. Preferably, 0.5 mm ≤ L ≤ 5 mm, for example, 0.5 mm, 0.8 mm, 1.2 mm, 1.7 mm, 2.1 mm, 3.5 mm, 4.2 mm, 4.7 mm or 5 mm. This avoids L being too large, causing excessive accumulation at the starting end of the separator 13 in the first positive electrode bending section 114, thereby adsorbing too much electrolyte and exacerbating the side reaction between the dissolution of metal ions in the positive electrode active material and the electrolyte. Alternatively, if L is too small, it cannot effectively prevent the separator 13 from folding.

[0056] In some embodiments, the Dv50 of the nitrogen-containing compound satisfies: 0.1 μm ≤ Dv50 ≤ 3 μm, for example, 0.3 μm, 0.5 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.8 μm, or 3 μm. Preferably, 0.1 μm ≤ Dv50 ≤ 1 μm, for example, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, or 1 μm. This avoids the nitrogen-containing compound having an excessively small Dv50, resulting in insufficient dissolution or swelling in the electrolyte, which would fail to effectively mitigate the side reactions between the dissolution of metal ions in the positive electrode active material and the electrolyte. At the same time, the excessive size of the nitrogen-containing compound Dv50 is prevented, which would result in poor flatness of the coating 132 on the separator 13, affecting the bonding stability of the composite region 134 at the beginning of the separator, and further increasing the risk of separator 13 folding during battery 1000 cycling.

[0057] In this application, the length L of the diaphragm initiation end composite region 134 can be measured by disassembling the battery 1000 after discharging it to 0 SOC%, and then measuring the length L of the diaphragm initiation end composite region 134 with vernier calipers.

[0058] In this application, the particle size Dv50 of the nitrogen-containing compound on the diaphragm 13 refers to the particle size value corresponding to 50% of the cumulative volume on the cumulative distribution curve from small to large in the volume-based particle size distribution, which can be measured by a laser particle size analyzer.

[0059] In some embodiments, the nitrogen-containing compound includes at least one of melamine cyanurate, melamine polyphosphate, melamine thiocyanate, melamine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, melamine chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, and 2-amino-4,6-methoxy-1,3,5-triazine.

[0060] In some embodiments, the maximum Feret diameter D of each micropore satisfies: 0.5 μm ≤ D ≤ 4 μm, for example, 0.7 μm, 0.9 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, or 4 μm. By controlling the maximum Feret diameter D of the micropores on the positive current collector 111 of the first positive electrode bending section 114, it is possible to avoid the micropores being too small, which would not effectively buffer and release stress, thus failing to reduce bending stress and reduce the risk of breakage of the first positive electrode bending section 114; or the micropores being too large, which would significantly weaken the strength and current carrying capacity of the positive current collector 111 in that area, making the first positive electrode bending section 114 more prone to breakage or deteriorating the rate performance of the battery 1000. Meanwhile, when the maximum Feret diameter D of each micropore is within the above range, it can also ensure that the positive active layer 112 of the first positive electrode bending section 114 and the positive current collector 111 form a more firmly bonded area, improve the overall structural stability of the positive active layer 112, and reduce the risk of the positive active layer 112 falling off after the first positive electrode bending section 114 is bent.

[0061] In some embodiments, the pore depth h1 of the micropore satisfies: 0.5 μm ≤ h1 ≤ 5 μm, for example 0.7 μm, 0.9 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4 μm, 4.2 μm, 4.4 μm, 4.4 μm, 4.6 μm, 4.8 μm, or 5.0 μm.

[0062] By controlling the depth of the micropores on the positive current collector 111 of the first positive electrode bending section 114, the depth of the micropores can be avoided from being too small, thus effectively buffering and releasing stress, thereby effectively improving the deformation capacity of this area and preventing cracking in this area. Alternatively, if the depth of the micropores is too large, it will significantly weaken the strength and flow capacity of the positive current collector 111 in this area. At the same time, when the pore depth h is within the above-mentioned range, the interlocking ability between the positive active layer 112 and the positive current collector 111 of the first positive electrode bending section 114 can also be enhanced, reducing the risk of the positive active layer 112 falling off after the first positive electrode bending section 114 is bent.

[0063] In some embodiments, at least a portion of the diaphragm initiation composite region 134 is provided with a plurality of recesses 135. This not only increases the composite strength of the diaphragm initiation composite region 134, further improving the prevention of folding in the diaphragm initiation composite region 134, but also causes localized micropore closure due to compression of the micropores in the diaphragm 13 of the diaphragm initiation composite region 134. This reduces the porosity of the diaphragm 13 in the diaphragm initiation composite region 134, thereby reducing the amount of electrolyte absorbed and retained in the diaphragm initiation composite region 134. This avoids the problem of decreased high-temperature cycle performance caused by increased side reactions between metal ions in the positive electrode active material and the electrolyte due to increased dissolution at high temperatures, thus improving the high-temperature performance of the battery 1000.

[0064] Preferably, the area S1 of the plurality of recesses 135 and the area S of the composite region 134 at the beginning of the separator satisfy the following condition: 0.1 ≤ S1 / S ≤ 0.9, for example, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9. This avoids the situation where too few recesses 135 can fail to effectively improve the composite strength of the separator 13, thus failing to effectively improve the folding of the separator 13 or effectively reduce the volume of micropores in the composite region 134 at the beginning of the separator. Simultaneously, it prevents the area S1 of the plurality of recesses 135 from being too large, resulting in a lower overall strength of the composite region 134 at the beginning of the separator, which could lead to the entire composite region 134 breaking, resulting in insufficient coverage of the positive and negative electrodes and increasing the risk of a short circuit in the battery 1000.

[0065] In some examples, the recess 135 is a blind hole or a through hole. In some examples, the orthographic projection of the recess 135 along the thickness direction of the composite region 134 at the starting end of the diaphragm is a square, a circle, or other irregular polygon.

[0066] In some embodiments, along the winding direction, the minimum distance between the edge of the recess 135 closest to the starting end of the negative electrode 12 and the starting end of the negative electrode 12 is d, where d ≥ 1 mm, for example, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, or 1.6 mm. By controlling the minimum distance between the edge of the recess 135 closest to the starting end of the negative electrode 12 and the starting end of the negative electrode 12, the safety of the battery 1000 can be improved. This prevents the negative electrode from expanding during subsequent cycles and rupturing the composite region 134 at the starting end of the separator at the recess 135, thus causing a large-area rupture of the separator 13 from that location, exposing the negative electrode 12 and leading to a short circuit.

[0067] In some embodiments, a plurality of recesses 135 are formed on the coating 132 and at least a portion of the base film 131 to ensure the bonding strength of the diaphragm initiation bonding region 134. In one example, the maximum size of the orthographic projection of the recess 135 along the thickness direction of the diaphragm initiation bonding region 134 is 0.1 mm to 1.5 mm, for example, 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.4 mm, or 1.5 mm. The number of recesses 135 on the diaphragm initiation bonding region 134 is 1 per mm. 2 ~4 pieces / mm 2 For example, 1 per mm 2 2 per mm 2 3 per mm 2 Or 4 per mm 2 .

[0068] In some embodiments, a thinning region 116 is provided on the positive electrode active layer 112 on the side of the first positive electrode bending section facing the winding center to reduce the stress of the positive electrode sheet 11 during bending. This prevents the outer positive electrode active layer 112 in this region from being overstretched and generating microcracks, or the inner positive electrode active layer 112 from being over-compressed and causing the active material to peel off from the positive electrode current collector 111, resulting in powder shedding, which in turn leads to local capacity loss and reduced cycle life. At the same time, it facilitates the penetration of electrolyte into this region, preventing local liquid shortage. The thickness h2 of the positive electrode active layer 112 in the thinning region 116 and the thickness h3 of the remaining positive electrode active layers 112 satisfy: 0.05 ≤ h2 / h3 ≤ 0.95, for example, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9 or 0.95. This avoids excessive thinning leading to a decrease in the battery 1000 capacity, or insufficient thinning failing to effectively relieve stress and improve deformation capacity, thus balancing the battery 1000 capacity and stress relief. The diaphragm initiation composite region 134 is at least partially disposed opposite to the thinning region 116, so that the diaphragm initiation composite region 134 can be stacked on the thinning region 116 to provide support for it, reducing the risk of the thinning region 116 breaking due to excessive bending.

[0069] In one example, a first insulating layer 14 (e.g., adhesive tape) is adhered to the inner surface of the first positive electrode bending section. The adhesive tape insulation on the inner surface of the first positive electrode bending section prevents the starting end of the negative electrode sheet 12 from piercing the separator 13 and directly contacting the positive electrode active layer 112. It also prevents the positive electrode active layer 112, which is located in the thinning region 116, from detaching and migrating into the interior of the battery 1000, thus preventing a short circuit and improving the safety of the battery 1000.

[0070] In one example, the first insulating layer 14 at least covers the thinning region 116, which on the one hand ensures comprehensive protection of the thinning region 116 and reduces the occurrence of powder shedding from the positive electrode active layer 112 thereon, and on the other hand ensures that the first insulating layer 14 is stably set and does not fall off.

[0071] In one example, the first insulating layer 14 may allow metal ions to pass through in order to increase the energy density of the battery 1000.

[0072] In one example, along the winding direction, the end of the separator start-end composite region 134 away from the start end of the negative electrode 12 does not extend beyond both ends of the first insulating layer 14. This prevents excessive stacking of the separator 13 between the start end of the innermost negative electrode 12 and the first positive electrode arc end and the first positive electrode straight section 113, which would hinder ion transport and cause lithium plating in that region.

[0073] In some embodiments, the positive electrode active layer 112 includes a positive electrode active material, which includes a lithium cobalt oxide substrate and a coating layer covering at least a portion of the surface of the lithium cobalt oxide substrate. Coating the surface of the positive electrode active material with a dense and uniform coating layer, such as a metal oxide, can improve the structural stability of the positive electrode active material, reduce the risk of metal ion dissolution at high temperatures, and thereby improve the high-temperature performance of the battery.

[0074] In one example, the average thickness of the coating layer is 5 nm to 500 nm, for example, 10 nm, 30 nm, 50 nm, 70 nm, 90 nm, 110 nm, 140 nm, 170 nm, 200 nm, 240 nm, 280 nm, 320 nm, 360 nm, 400 nm, 440 nm, 480 nm, or 500 nm. By controlling the average thickness of the coating layer, it is possible to avoid the situation where the average thickness is too thin and therefore fails to provide effective protection, or where the average thickness is too thick and increases the migration resistance of lithium ions, thus affecting the electrical performance of the battery.

[0075] In one example, the coating layer includes at least one of the elements Al, Mg, Zr, Ti, Y, La, and Zn.

[0076] For example, the positive electrode active layer 112 may contain a positive electrode active material capable of reversibly absorbing and releasing charge carriers. Furthermore, it may further include conductive materials, binders, and various additives. By way of example only, the metal foil mentioned here may be aluminum foil; the positive electrode active material may also include lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, lithium iron phosphate, and other lithium transition metal composite oxides; the conductive material may be carbon-based materials such as acetylene black or conductive carbon black; and the binder may be polyvinylidene fluoride, etc.

[0077] In some embodiments, the negative electrode active layer 122 comprises a silicon-based material, which includes at least one of silicon-carbon or silicon-oxygen materials, to improve the energy density of the battery 1000. The Dv50 of the silicon-based material is 5 μm to 15 μm, for example, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, 12 μm, 14 μm, 15 μm. The span value of the silicon-based material is 0.2 to 2, for example, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8 or 2. In some embodiments, the sphericity of the silicon-based material is 0.6 to 0.98, for example, 0.6, 0.7, 0.8, 0.9 or 0.98. By controlling the particle size, particle size distribution uniformity and sphericity of the silicon-based material, the expansion of the negative electrode during charging and discharging can be better reduced, thereby improving the problem of breakage of the first positive electrode bending section 114 caused by expansion. Other components in the negative electrode active layer 122 are set in accordance with conventional settings in the art and will not be described in detail here.

[0078] If the particle size of silicon-based materials is too small, the specific surface area will increase, leading to increased side reactions between the materials and the electrolyte. If the particle size is too large, the lithium-ion diffusion distance will increase, resulting in decreased kinetics. Insufficient sphericity in silicon-based materials leads to stress concentration, making the SEI film prone to rupture, and its volume expansion is greater compared to silicon-based materials with higher sphericity. Furthermore, the uneven force experienced during expansion makes silicon-based materials more susceptible to localized fracture. A span value of 0.2 to 2 for silicon-based materials can improve their anisotropic expansion and reduce the occurrence of localized structural damage.

[0079] The span value is the ratio of the difference between Dv90 and Dv10 of silicon-based materials to Dv50 of silicon-based materials. Here, Dv represents the cumulative volume percentile of silicon-carbon materials. Dv10, Dv50, and Dv90 of silicon-based materials refer to the particle sizes that correspond to the 10%, 50%, and 90% of the cumulative volume particle size distribution of silicon-carbon materials, arranged from smallest to largest. Dv10, Dv50, and Dv90 of silicon-based materials can be measured by a laser particle size analyzer.

[0080] In this application, the sphericity of silicon-based materials can be tested using methods conventional in the art. For example, using image processing software (e.g., Image Pro Plus), at least 10 silicon-based material particles are selected from a scanning electron microscope (SEM) image of the silicon-based material at a certain magnification (e.g., 2500x), and the perimeter and area of ​​each particle are measured. The perimeter equivalent radius r1 and area equivalent radius r2 of each particle are calculated respectively. The sphericity is r2 / r1, and the average of all test values ​​is taken to obtain the sphericity of the silicon-based material.

[0081] In some embodiments, the tail section of the negative electrode 12 is at least partially bonded to the separators 13 on both sides to form a first composite region 136, and along the winding direction, the portion of the tail section of the separator 13 extending beyond the tail section of the negative electrode 12 is at least partially bonded to form a second composite region 137. Providing the first composite region 136 and the second composite region 137 at the tail section of the negative electrode 12 effectively prevents the separator 13 located at the tail section of the negative electrode 12 from folding during winding, thus preventing a short circuit between the positive and negative electrodes and improving the safety of the battery 1000. The tail section of the negative electrode 12 refers to the negative electrode 12 closest to the outermost part of the wound electrode body of the battery 1000.

[0082] In one example, the dimension A of the first composite region 136 along the winding direction is 1 mm to 20 mm, for example, 1 mm, 3 mm, 5 mm, 7 mm, 10 mm, 12 mm, 15 mm, 17 mm, 19 mm or 20 mm. This avoids the first composite region 136 being too small to effectively bond, preventing the expansion stress from accumulating layer by layer, which could cause the separator 13 to fold, or the composite region being too large so that the expansion stress at the tail end of the negative electrode sheet 12 cannot be effectively released when the battery 1000 is charging and discharging, resulting in poor deformation ability of the tail end of the negative electrode sheet 12 and causing damage to the negative electrode active layer 122 or excessive stretching of the separator 13. In one example, the dimension B of the second composite region 137 along the winding direction is 2 mm to 15 mm, for example, 2 mm, 3 mm, 5 mm, 7 mm, 10 mm, 12 mm, 14 mm or 15 mm, to avoid the second composite region 137 being too small to effectively combine and reduce the risk of the separator 13 flipping, or too large to cause an increase in the overall ineffective volume of the battery 1000 and a decrease in energy density.

[0083] In some embodiments, the positive electrode sheet 11 is provided with a positive electrode empty foil region 117, and the positive electrode sheet 11 includes a positive electrode single-sided coating region 118 located on the outermost side of the wound electrode body. The positive electrode single-sided coating region 118 and the positive electrode empty foil region 117 are connected sequentially along the winding direction. A second insulating layer 15 (e.g., an adhesive tape layer) is provided at the junction of the positive electrode active layer 112 of the positive electrode single-sided coating region 118 and the positive electrode empty foil region 117. The portion of the second insulating layer 15 covering the positive electrode active layer 112 is located within the first composite region 136 along the thickness direction of the battery 1000.

[0084] Because the second insulating layer 15 at the tail end of the positive electrode 11 has a certain thickness on the surface of the positive electrode active layer 112, the steps formed at the junction of the positive electrode single-sided coating area 118 and the positive electrode empty foil area 117 overlap to some extent. This can easily lead to poor contact between the positive electrode active layer 112 and the corresponding negative electrode active layer 122 near this area, thereby causing lithium deposition on the negative electrode at the edge of the second insulating layer 15. By placing the portion of the positive electrode active layer 112 at the junction of the positive electrode single-sided coating area 118 and the positive electrode empty foil area 117 covered by the second insulating layer 15 within the first composite area 136, the close contact between the separator 13 and the negative electrode 12 within the first composite area 136 helps to reduce the distance between the positive and negative electrode active layers 122, thereby improving the situation of lithium deposition on the negative electrode near the edge of the second insulating layer 15.

[0085] In some embodiments, along the winding direction, the second insulating layer 15 covers the positive electrode active coating 132 in a size of 0.5 mm to 5 mm. In some embodiments, along the width direction of the wound electrode body, the distance E between the end of the second composite region 137 near the tail section of the negative electrode 12 and the end of the tail section of the negative electrode 12 is 0.05 mm to 0.5 mm. In some embodiments, along the width direction of the wound electrode body, the distance F between the end of the diaphragm starting end composite region 134 near the starting end of the negative electrode 12 and the starting end of the negative electrode 12 is 0.05 mm to 0.5 mm.

[0086] The distance between the end of the second composite region 137 of the separator 13 near the end of the negative electrode 12 and the end of the negative electrode 12, and the distance between the end of the composite region 134 of the separator near the beginning of the negative electrode 12 and the beginning of the negative electrode 12, can ensure the protective effect of the separator 13 on the negative electrode 12 and avoid the aforementioned distances E and F being too large. When the separator 13 is locally hot-pressed and bonded, its active coating on the edge of the end of the negative electrode 12 and the edge of the beginning of the negative electrode 12 is... The compressive stress generated by layer 132 can easily cause powder to fall off its edge coating 132, triggering a micro-short circuit inside the battery 1000, resulting in excessively fast voltage drop and rapid capacity decay of the battery 1000. Alternatively, if the distance is too small, the composite area of ​​separator 13 may not be able to fix the electrode when the distance is too large. If the edge of separator 13 is still prone to folding or relative slippage between separator 13 and negative electrode 12, the exposed negative electrode 12 may be prone to short-circuiting with positive electrode 11, affecting the safety of battery 1000.

[0087] In some embodiments, the diaphragm 13 further includes an adhesive layer 133 disposed on the coating 132. The adhesive layer 133 comprises polymer particles, including one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene modified polyvinylidene fluoride and its copolymers, polyacrylonitrile, polymethyl methacrylate, polyacrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol and its copolymerized polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, waterborne polyurethane, ethylene-vinyl acetate copolymer, and multi-component acrylic copolymers. The adhesive layer 133 on the diaphragm 13 helps to improve the adhesion strength between the diaphragm 13 and the electrode, such as the negative electrode 12, and further prevents the diaphragm 13 from shifting or folding.

[0088] In one example, in the initial composite region 134 of the separator, the coverage rate of the adhesive layer 133 per unit area of ​​the separator 13 is M1, and the coverage rate of the adhesive layer 133 per unit area of ​​the separator 13 located at the bend 102 of the battery 1000 is M2. The difference between M1 and M2 satisfies: 3% ≤ (M1 - M2) ≤ 15%, for example, 3%, 4%, 6%, 8%, 10%, 12%, 14%, or 15%. Thus, the large coverage rate of the adhesive layer 133 per unit area of ​​the separator 13 in the initial composite region 134 makes the composite more robust, further reducing the likelihood of separator 13 folding. By setting a relatively small coverage of the adhesive layer 133 of the separator 13 per unit area located in the bent portion 102 of the battery 1000, more microspaces can be formed between the adhesive layers 133. This allows for the absorption and bearing of the expansion stress generated by the negative electrode, reducing the risk of breakage of the electrode in the bent portion 102 of the battery 1000 during cycling, especially the first positive electrode bending section 114, thereby reducing the risk of short circuits in the battery 1000. Furthermore, controlling the difference between the two within the aforementioned range can improve the problem of localized electrode breakage while reducing separator 13 folding. It also avoids the problem of poor adhesion between the separator 13 and the electrode in different areas of the battery 1000 when the coverage of the separator 13 varies too much, which would increase the lithium-ion migration distance, reduce the rate performance of the battery 1000, and even lead to localized lithium plating.

[0089] In one example, at the starting end composite region 134 of the separator, the thickness of the adhesive layer 133 is h4, and the thickness of the adhesive layer 133 on the separator 13 located at the bending portion 102 of the battery 1000 is h5. h4 and h5 satisfy: 0.1 μm ≤ (h5 - h4) ≤ 0.5 μm, for example, 0.15 μm, 0.2 μm, 0.3 μm, 0.4 μm or 0.5 μm.

[0090] This reduces the thickness of the composite region 134 at the beginning of the separator, improves the flatness of this region, and thus reduces the electrolyte retention capacity of the separator 13 in the composite region 134. This prevents excessive electrolyte accumulation in this region, which could increase the risk of metal ion dissolution from the positive electrode active material at high temperatures and lead to more side reactions with the electrolyte, thereby improving the high-temperature cycle performance of the battery 1000. Simultaneously, appropriately increasing the gap between the positive and negative electrodes in the bend 102 improves the local breakage problem of the first positive electrode bending section 114 of the bend 102. It also avoids that excessively increasing the gap would increase the lithium-ion migration distance, reduce the rate performance of the battery 1000, or even lead to localized lithium plating.

[0091] In some embodiments, the battery 1000 further includes a housing in which wound electrode bodies are housed.

[0092] It is understood that the battery 1000 in this application can be Figure 11 The square-shell battery 1000 shown can also be Figure 12 The pouch cell 1000 shown is an example.

[0093] Secondly, this application provides an electrical device that includes the aforementioned battery 1000. Exemplarily, this electrical device can be a charging device or a power-consuming device. For example, the electrical device can be a pure electric vehicle, a hybrid electric vehicle, a range-extended electric vehicle, or a drone, etc.

[0094] The battery 1000 provided according to the embodiments of this application has the corresponding effects of the battery 1000 described above, as detailed above, and will not be repeated here.

[0095] It should be understood that the term "comprising" and its variations used in the embodiments of this application are open-ended, meaning "including but not limited to". The term "according to" means "at least partially according to". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least another embodiment". The term "a plurality of" means "more than one", which implies covering two, three or more cases.

[0096] It should be understood that although terms such as "first" or "second" may be used in embodiments of this application to describe various elements, such as the first positive electrode active layer 112 and the second positive electrode active layer 112, these elements are not defined by these terms, which are only used to distinguish one element from another.

[0097] The scope of protection of the embodiments of this application is not limited to the above embodiments. Any variations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be included within the scope of protection of the embodiments of this application. Therefore, the scope of protection of the embodiments of this application should be determined by the scope of the claims.

[0098] The present application is described in detail below with reference to specific embodiments, which are used to understand rather than limit the present application.

[0099] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Unless otherwise specified, the processing procedures and techniques involved are conventional technical methods.

[0100] Example 1 Preparation of negative electrode sheet 12: Negative electrode active material (i.e., negative electrode active material, graphite and silicon-carbon material), sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black are dispersed in deionized water (or water) at a mass percentage of 58 (graphite): 35 (silicon-carbon composite): 2.5: 1.5: 3, and mixed evenly to obtain a slurry. The prepared negative electrode slurry is uniformly coated onto a 6 μm thick copper foil of negative electrode current collector 121, dried at 100°C, and then rolled and slit to obtain negative electrode sheet 12. The negative electrode active material is a graphite and silicon-carbon composite material. In the negative electrode active layer 122, the silicon content A is 15 wt%. The silicon content in the negative electrode active layer 122 is varied by controlling the proportion of silicon-carbon composite material in the negative electrode active material and the silicon content in the silicon-carbon composite material. The silicon-carbon material has a Dv50 of 7 μm, a span value of 1.2, and a sphericity of 0.92.

[0101] Preparation of positive electrode sheet 11: Lithium cobalt oxide (aluminum-doped lithium cobalt oxide with a coating thickness of 50 nm, the coating being alumina), polyvinylidene fluoride (PVDF) binder, and carbon black conductive agent are mixed in a mass percentage ratio of 97.2:1.8:1. An appropriate amount of N-methylpyrrolidone is added as a solvent, and the mixture is stirred until homogeneous, forming a uniformly dispersed electrode slurry. The prepared positive electrode slurry is uniformly coated onto an 8 μm thick aluminum foil current collector 111, and then rolled and slit to form the positive electrode sheet 11. The tail of the positive electrode sheet 11 is the positive electrode empty foil region 117. The number of micropores per unit area on the positive electrode current collector 111 in the first positive electrode bending section 114 is N = 800 pores / mm². The maximum Ferete diameter D of the micropores in the first positive electrode bending section 114 is 2 μm, and the pore depth h1 is 3 μm.

[0102] Then, following a conventional winding structure, the positive electrode 11, negative electrode 12, and separator 13 are fabricated into a wound electrode body. The tail end of the negative electrode 12 is combined with the separators 13 on both sides to form a first composite region 136. Along the winding direction, the portion of the separator 13 extending beyond the tail end of the negative electrode 12 is combined to form a second composite region 137. The dimensions of the first composite region 136 are A = 8 mm, and the dimensions of the second composite region 137 are B = 5 mm. The portion of the starting end of the separator 13 extending beyond the starting end of the negative electrode 12 is bonded together to form a separator starting end composite region 134. The length of the separator starting end composite region 134 is L = 4.5 mm. The electrolyte contains lithium bis(trifluoromethanesulfonyl)imide, with a mass percentage C = 8 wt% and a C / N (numerical ratio) = 0.0001. It should be noted that C / N is a unitless numerical comparison. The nitrogen-containing compound in the coating 132 of the diaphragm 13 is melamine cyanurate, with a Dv50 of 0.8 μm. v50 The numerical relationship between L and D v50 =5625. It should be noted that the unit of L is millimeters (mm), while the unit of Dv50 is micrometers (μm). The two need to be converted in units before calculating the ratio.

[0103] Electrolyte preparation: In an argon-filled glove box (moisture < 1 ppm, oxygen < 1 ppm), a mixed solvent of propylene carbonate and ethyl propionate in a 1:1 mass ratio was stirred until homogeneous. Then, 8 wt% LITFSI, 7 wt% lithium hexafluorophosphate (LiPF6), 3 wt% 1,3,6-hexanetrionitrile, 15 wt% fluoroethylene carbonate, and 2 wt% 1,3-propanesulfonate lactone were added. After homogeneity, the electrolyte was tested for moisture and free acid and found to be within acceptable limits. The total mass percentage of propylene carbonate and ethyl propionate was 65 wt%.

[0104] The content of LITFSI in the electrolyte can be changed by adjusting the content of lithium hexafluorophosphate (LiPF6) in the electrolyte and the content of propylene carbonate and ethyl propionate in the mixed solvent.

[0105] Then, the wound electrode body 10 is housed in the casing and manufactured into a battery 1000 through steps such as encapsulation, liquid injection, formation, secondary sealing, and capacity testing. The area S1 of the plurality of recesses 135 in the separator initiation end composite region 134 satisfies the condition that S1 / S = 0.5 with respect to the area S of the separator initiation end composite region 134. The maximum size of the orthographic projection of the recesses 135 along the thickness direction of the separator initiation end composite region 134 is 0.3 mm, and the number of recesses 135 per unit area of ​​the separator initiation end composite region 134 is 3 / mm. 2The thickness h2 of the positive electrode active layer 112 in the thinning region 116 and the thickness h3 of the remaining positive electrode active layers 112 satisfy: h2 / h3=0.3.

[0106] The adhesive layer 133 is made of polymethyl methacrylate. The coverage of the adhesive layer 133 per unit area on the separator 13 in the composite region 134 at the starting end of the separator is M1, and the coverage of the adhesive layer 133 per unit area on the separator 13 in the bending portion 102 of the battery 1000 is M2, where (M1-M2)=5%. In the composite region 134 at the starting end of the separator, the thickness of the adhesive layer 133 is h4, and in the bending portion 102, the thickness of the adhesive layer 133 is h5, where (h5-h4)=0.3 μm.

[0107] Example 2 The procedure was carried out in accordance with Example 1, except that C = 12 wt% and N = 450 pieces / mm. 2 C / N = 0.000266. L = 0.5 mm. The maximum size of the orthographic projection of the recess 135 along the thickness direction of the diaphragm initiation end composite region 134 is 1.5 mm. The number of recesses 135 per unit area of ​​the diaphragm initiation end composite region 134 is 1 / mm. 2 D of nitrogen-containing compounds v50 =1 μm, L / D v50 =500. The maximum Feret diameter of the micropores D = 4 μm. h2 / h3 = 0.05, the coating thickness is 500 nm, and the coating is magnesium oxide. The D of the silicon-based material... v50 =5 μm, sphericity is 0.6, span value is 0.2. The length A of the first composite region 136 is 1 mm, the length B of the second composite region 137 is 2 mm, (M1-M2)=3%, (h5-h4)=0.1 μm.

[0108] Example 3 The procedure was carried out in accordance with Example 1, except that C = 1 wt% and N = 2000 pieces / mm. 2 C / N = 0.000005. L = 5 mm. The maximum size of the orthographic projection of the recess 135 along the thickness direction of the diaphragm initiation end composite region 134 is 1.5 mm. The number of recesses 135 per unit area of ​​the diaphragm initiation end composite region 134 is 1 / mm. 2 D of nitrogen-containing compounds v50 =1μm, L / D v50 =50000. Maximum Feret diameter of micropores D = 0.5 μm. h2 / h3 = 0.95, coating thickness is 5 nm, coating is zirconium oxide. D of silicon-based material v50=15 μm, sphericity is 0.98, span value is 2. The length A of the first composite region 136 is 20 mm, the length B of the second composite region 137 is 15 mm, (M1-M2)=15%, (h5-h4)=0.5 μm.

[0109] Example 4 The procedure was carried out in accordance with Example 1, except that the nitrogen-containing compound was melamine, and the nitrogen-containing compound D... v50 =3 μm, L / D v50 =2000. h2 / h3=0.95, the thickness of the coating layer is 5 nm.

[0110] Example 5 The procedure was carried out in accordance with Example 1, except that L = 0.3 mm and L / D were used. v50 =375.

[0111] Example 6 The procedure was carried out in accordance with Example 1, except that L = 1.2 mm and L / D... v50 =15000.

[0112] Example 7 The procedure was carried out in accordance with Example 1, except that the nitrogen-containing compound D... v50 =0.05 μm, L / D v50 =90000.

[0113] Example 8 The procedure was carried out in accordance with Example 1, except that the nitrogen-containing compound D... v50 =43 μm, L / D v50 =1125.

[0114] Example 9 The procedure was carried out in accordance with Example 1, except that the maximum Ferete diameter of the micropores was D = 0.03 μm.

[0115] Example 10 The procedure was carried out in accordance with Example 1, except that the maximum Ferete diameter of the micropores was D = 5 μm.

[0116] Example 11 The procedure was carried out in accordance with Example 1, except that the depth of the micropores was h1 = 0.3 μm.

[0117] Example 12 The procedure was carried out in accordance with Example 1, except that the depth of the micropores was h1 = 7 μm.

[0118] Example 13 The procedure was carried out with reference to Example 1, except that (M1-M2) = 2%.

[0119] Example 14 The procedure was carried out with reference to Example 1, except that (M1-M2) = 17%.

[0120] Example 15 The procedure was carried out in accordance with Example 1, except that (h5-h4) = 0.05 μm.

[0121] Example 16 The procedure was carried out in accordance with Example 1, except that (h5-h4) = 0.7 μm.

[0122] Comparative Example 1 The experiment was carried out with reference to Example 1, except that C = 0.6 wt% and C / N = 0.000075.

[0123] Comparative Example 2 The procedure was carried out with reference to Example 1, except that C = 14 wt% and C / N = 0.000175.

[0124] Comparative Example 3 The procedure was carried out in accordance with Example 1, except that N = 400 pieces / mm² and C / N = 0.002.

[0125] Comparative Example 4 The procedure was carried out in accordance with Example 1, except that N = 2500 pieces / mm² and C / N = 0.000032.

[0126] Comparative Example 5 The experiment was conducted in accordance with Example 1, except that C = 0.7 wt%, N = 2000 pieces / mm², and C / N = 0.0000035.

[0127] Comparative Example 6 The procedure was carried out with reference to Example 1, except that C = 12 wt%, N = 350 pieces / mm², and C / N = 0.00034.

[0128] Relevant performance testing methods 1. 45℃ high-temperature cycling test method: Battery 1000 was left to stand in a constant temperature chamber of 45℃±3℃ for 2 hours, at 2.8 C (2.8 (Nominal capacity) constant current charging to 4.2V, then charged at 1.9C (1.9) The battery (nominal capacity) is charged to 4.53 V using constant current and constant voltage, cut off at 0.05 C, allowed to stand for 10 minutes, and then discharged to 3.0 V at 0.7 C. Under these conditions, the battery is cycled 500 times. The discharge capacity of the battery 1000 when fully charged on the 500th cycle is measured as C1, and the discharge capacity of the battery 1000 when fully charged on the first cycle is measured as C0. C1 / C0 is the capacity retention rate after 500 cycles, which is the high-temperature cycle performance of the battery 1000.

[0129] 2. Ratio performance testing method: The batteries 1000 obtained in the examples and comparative examples were placed in a constant temperature chamber at 25℃±3℃ for 2 hours. The fully charged battery 1000 was then discharged at 0.5C to the lower limit voltage of 3.0 V, and placed for 10 minutes. The initial discharge capacity Q0 was recorded. The battery 1000 was then fully charged at a constant current of 3C, with a cutoff current of 0.02C. It was then discharged at a constant current of 0.5C, and the discharge capacity Q1 was recorded. Therefore, the discharge capacity retention rate at 3C = Q1 / Q0 × 100%.

[0130] 3. Short circuit occurrence rate test method: After the wound electrode bodies obtained in the examples and comparative examples were fabricated, the high voltage withstand capability of the positive and negative terminals of the electrode body was tested using an insulation resistance tester (test voltage 100 V, test time 2.5 s, test pressure 0.1 MPa~0.3 MPa). If the test resistance < 25 MPa, it was determined that a short circuit had occurred in the wound electrode body. The number of short circuits N1 of batteries 1000 in each example and comparative example and the total number N of batteries 1000 tested (total number of batteries 1000 tested: 500) were recorded. N1 / N 100% means the battery has a short circuit rate of 1000%.

[0131] 4. Test method for the breakage of the first bend of the positive terminal after 1000 battery cycles: After undergoing 500 cycles at 45°C, the batteries 1000 obtained in the examples and comparative examples were left to stand for 10 hours. Then, the batteries 1000 were fully charged and placed in a CT scanner for scanning. After the test, CT analysis software was used to observe whether cracks or breaks occurred in the first positive electrode bending section 114 of the battery 1000 in the thickness direction (plane) and the winding direction (cross-section). It should be noted that the presence of cracks or breaks in the first positive electrode bending section 114 of the battery 1000 constituted a test failure. Each group tested a total of 20 batteries 1000; 1 / 20 indicates that one of the 20 tested batteries 1000 had a broken first positive electrode bending section 114.

[0132] Table 1 shows the test results.

[0133] Table 1

Claims

1. A battery, characterized in that, include: A wound electrode body is formed by stacking and winding a negative electrode, a separator, and a positive electrode, and a housing containing the wound electrode body, and an electrolyte filled in the housing. The wound electrode body includes a flat portion and curved portions located on both sides of the flat portion. The negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector. In the innermost ring of the wound electrode body, the negative electrode includes a first straight negative electrode section located in the flat portion and a first bent negative electrode section located in the curved portion. The first straight negative electrode section and the first bent negative electrode section are connected. The end of the first straight negative electrode section away from the first bent negative electrode section is the starting end of the negative electrode. The positive electrode includes a first straight positive electrode section located in the flat portion and a first bent positive electrode section located in the curved portion. The positive electrode straight section and the first positive electrode bent section are connected. The end of the first positive electrode straight section away from the first positive electrode bent section is the starting end of the positive electrode sheet. Along the width direction of the battery, the starting end of the negative electrode sheet is positioned towards the first positive electrode bent section. Along the winding direction, the starting end of the separator extends beyond the starting end of the negative electrode sheet, and the portion of the starting end of the separator extending beyond the starting end of the negative electrode sheet is at least partially bonded together to form a separator starting end composite region. The separator includes a base film and a coating disposed on the base film, the coating including a nitrogen-containing compound. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on the positive electrode current collector. Along the winding direction, micropores are provided on the positive electrode current collector located in the first positive electrode bent section, the number of micropores being N / mm. 2 The electrolyte comprises lithium bis(trifluoromethanesulfonyl)imide. Based on the total mass of the electrolyte, the mass percentage of lithium bis(trifluoromethanesulfonyl)imide in the electrolyte is C. The nitrogen (N) satisfies: 450 particles / mm² ≤ N ≤ 2000 particles / mm², and the C satisfies: 1 wt% ≤ C ≤ 12 wt%. The numerical relationship between N and C satisfies: 0.000005 ≤ C / N ≤ 0.00027.

2. The battery according to claim 1, characterized in that, The length of the composite region at the starting end of the diaphragm is L, and the D of the nitrogen-containing compound is... v50 The condition L satisfies: 500 ≤ L / D v50 ≤50000; and / or The length of the composite region at the starting end of the diaphragm is L, 0.5 mm ≤ L ≤ 10 mm, preferably 0.5 mm ≤ L ≤ 5 mm; and / or The particle size Dv50 of the nitrogen-containing compound satisfies: 0.1 μm ≤ Dv50 ≤ 3 μm, preferably, 0.1 μm ≤ Dv50 ≤ 1 μm; and / or The nitrogen-containing compound includes at least one of melamine cyanurate, melamine polyphosphate, melamine thiocyanate, melamine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, melamine chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, and 2-amino-4,6-methoxy-1,3,5-triazine.

3. The battery according to claim 1, characterized in that, The maximum Feret diameter D of each of the micropores satisfies: 0.5 μm ≤ D ≤ 4 μm; and / or, the pore depth h1 of the micropores satisfies: 0.5 μm ≤ h1 ≤ 5 μm; and / or, The pore depth h1 of the micropore is less than or equal to the thickness of the positive electrode current collector.

4. The battery according to claim 1, characterized in that, The composite region at the starting end of the diaphragm is provided with multiple recesses in at least a portion of its area; preferably... The area S1 of the plurality of recesses and the area S of the composite region at the starting end of the diaphragm satisfy the condition: 0.1≤S1 / S≤0.

9.

5. The battery according to claim 4, characterized in that, Along the winding direction, the minimum distance between the edge of the recess closest to the starting end of the negative electrode sheet and the starting end of the negative electrode sheet is d, where d ≥ 1 mm; and / or The plurality of recesses are formed on the coating or on the coating and at least a portion of the base film, preferably, The maximum size of the orthographic projection of a single recess along the thickness direction of the composite region at the starting end of the diaphragm is 0.1 mm to 1.5 mm, and / or the number of recesses on the composite region at the starting end of the diaphragm is 1 per mm. 2 ~4 pieces / mm 2 .

6. The battery according to claim 1, characterized in that, The positive electrode active layer on the side of the first positive electrode bending section facing the winding center has a thinning region. The thickness h2 of the positive electrode active layer in the thinning region and the thickness h3 of the remaining positive electrode active layers satisfy: 0.05 ≤ h2 / h3 ≤ 0.

95. The composite region at the starting end of the separator is at least partially opposite to the thinning region. Preferably, A first insulating layer is bonded to the inner surface of the first positive electrode bending section; more preferably, the first insulating layer at least covers the thinned area; even more preferably, Along the winding direction, the end of the diaphragm starting end composite region away from the starting end of the negative electrode sheet does not extend beyond the two ends of the first insulating layer.

7. The battery according to claim 1, characterized in that, The positive electrode active layer includes a positive electrode active material, which includes a lithium cobalt oxide substrate and a coating layer covering at least a portion of the surface of the lithium cobalt oxide substrate; preferably, The average thickness of the coating layer is 5 nm to 500 nm, and / or The coating layer includes at least one of the elements Al, Mg, Zr, Ti, Y, La and Zn.

8. The battery according to claim 1, characterized in that, The negative electrode active layer comprises a silicon-based material, which includes at least one of silicon-carbon or silicon-oxygen materials. The silicon-based material has a Dv50 of 5 μm to 15 μm and a span value of 0.2 to 2. The span value is the ratio of the difference between Dv90 and Dv10 of the silicon-based material to Dv50. Here, Dv represents the cumulative volume percentile of the silicon-carbon material. Dv10, Dv50, and Dv90 of the silicon-based material refer to the particle sizes that, arranged from smallest to largest, represent the cumulative volume distribution of the silicon-carbon material at 10%, 50%, and 90% of the total volume, respectively. The sphericity of the silicon-based material is 0.6 to 0.

98.

9. The battery according to claim 1, characterized in that, The tail section of the negative electrode sheet is at least partially bonded to the separators on both sides to form a first composite region, and along the winding direction, at least a portion of the tail section of the separator that extends beyond the tail section of the negative electrode sheet is bonded to form a second composite region. The dimension A of the first composite region along the winding direction is 1 mm to 20 mm; and / or, The dimension B of the second composite region along the winding direction is 2 mm to 15 mm.

10. The battery according to any one of claims 1 to 9, characterized in that, The diaphragm further includes an adhesive layer disposed on the coating. The adhesive layer comprises polymer particles, which include one or more of the following: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), PTFE-hexafluoropropylene modified polyvinylidene fluoride and its copolymers, polyacrylonitrile, polymethyl methacrylate (PMMA), polyacrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol and its copolymerized polyvinyl alcohol, polyvinyl acetate, polyacrylamide, phenolic resin, epoxy resin, waterborne polyurethane, ethylene-vinyl acetate copolymer, and multi-component acrylic copolymers; preferably. In the composite region at the starting end of the diaphragm, the coverage rate of the adhesive layer on the diaphragm per unit area is M1, and the coverage rate of the adhesive layer on the diaphragm per unit area at the curved portion is M2. The difference between M1 and M2 satisfies: 3% ≤ (M1 - M2) ≤ 15%, and / or In the composite region at the starting end of the diaphragm, the thickness of the adhesive layer is h4, and the thickness of the adhesive layer on the diaphragm located at the bend is h5. The thicknesses h4 and h5 satisfy: 0.1 μm ≤ (h5 - h4) ≤ 0.5 μm.

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