Battery and electric device

Abstract

The invention discloses a battery and an electric device. The battery comprises an outer package, an electrode assembly and electrolyte, the electrode assembly comprises an isolating membrane and a plurality of pole pieces, the pole pieces and the isolating membrane are wound for multiple circles to form an electrode main body, and the electrode main body comprises a straight part and corner parts arranged at the two opposite ends of the straight part; the pole piece is provided with a plurality of first convex parts arranged corresponding to the corner parts, the height of the first convex parts is Hm (mu m) along the thickness direction of the pole piece, and Hm is more than or equal to 20 and less than or equal to 80; the electrolyte comprises lithium difluorophosphate, based on the total weight of the electrolyte, the weight percentage of the lithium difluorophosphate is E (%), and E is more than or equal to 0.01 and less than or equal to 3.00. According to the invention, the content E of the lithium difluorophosphate is matched with the height Hm of the first convex part, so that a solid electrolyte interface film formed by the lithium difluorophosphate on a pole piece interface, especially the first convex part, has a good improvement effect on the circulation of lithium ions on the basis of meeting the improvement of the electrolyte infiltration effect; and the 1s direct-current impedance of the battery at 20% SOC can be further reduced.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a battery and an electrical device using the same. Background Art

[0002] Currently, a large number of secondary battery electrode assemblies adopt a winding structure. For a wound electrode assembly, hot pressing is required after winding, and the electrode assembly needs to be fixed after being placed in an outer package. In this case, it is not easy for the electrolyte to enter the interior of the wound electrode assembly, and abnormal conditions such as insufficient electrolyte and poor electrolyte infiltration are likely to occur, ultimately leading to deterioration of the electrode interface of the electrode assembly, affecting the battery cycle performance, and even lithium deposition, affecting battery safety. Summary of the Invention

[0003] The inventors found that there is extrusion between the layers of the electrode assembly, resulting in insufficient electrolyte and poor infiltration between the layers of the electrode assembly, and it is easy to cause interface deterioration.

[0004] The embodiments of the present application provide a battery and an electrical device using the same, which can improve the problem of poor electrolyte infiltration.

[0005] In a first aspect, the embodiments of the present application provide a battery, including an outer package, an electrode assembly, and an electrolyte. The electrode assembly is disposed in the inner space of the outer package, and the electrolyte fills the inner space of the outer package;

[0006] The electrode assembly includes a separator and multiple electrode sheets. The separator is disposed between two electrode sheets with opposite polarities, and the electrode sheets and the separator are wound multiple times to form an electrode body. The electrode body includes a flat part and corner parts disposed at opposite ends of the flat part; multiple first protrusions are provided at the corner parts of the electrode sheets. Along the thickness direction of the electrode sheets, the height of the first protrusions is Hm (μm), and Hm satisfies: 20 ≤ Hm ≤ 80;

[0007] The electrolyte includes lithium difluorophosphate. Based on the total weight of the electrolyte, the weight percentage content of lithium difluorophosphate is E (%), and E satisfies: 0.01 ≤ E ≤ 3.00.

[0008] Based on the above embodiments, the content E of lithium difluorophosphate is matched with the height Hm of the first protrusions, so that the solid electrolyte interface film formed by lithium difluorophosphate at the electrode interface has a good improvement effect on the lithium ion circulation at the first protrusions, thereby achieving the improvement of the electrode interface problem and simultaneously reducing the DC impedance value of the battery at 20% of the capacity.

[0009] In some embodiments, the battery satisfies: 0.01 ≤ E ≤ 1.8, 20 ≤ Hm ≤ 40.

[0010] In some embodiments, the electrolyte further includes ethylene glycol bis(2-cyanoethyl) ether. Based on the total weight of the electrolyte, the weight percentage of ethylene glycol bis(2-cyanoethyl) ether is F(%), and F satisfies: 0.1 ≤ F ≤ 2.5.

[0011] Based on the above embodiments, ethylene glycol bis(2-cyanoethyl) ether can assist lithium difluorophosphate in forming a stable solid electrolyte interface film at the cathode electrode interface, improve the problem of uneven formation of the solid electrolyte interface film caused by the presence of protrusions, and the solid electrolyte interface film can also inhibit the occurrence of side reactions at the electrode interface at low temperatures, improve the low-temperature discharge performance and intermittent cycle performance of the battery, and at the same time reduce the gas generation during long cycles of the battery.

[0012] In some embodiments, the battery satisfies: 0.1 ≤ F ≤ 1.8, 20 ≤ Hm ≤ 60.

[0013] In some embodiments, the battery satisfies: 0.3 ≤ F ≤ 1.2, 20 ≤ Hm ≤ 40.

[0014] In some embodiments, the viscosity of the electrolyte is A (mpa.s), and the battery satisfies: 4.0 ≤ A ≤ 7.0.

[0015] Based on the above embodiments, by matching the viscosity A of the electrolyte with the height of the first protrusion, a suitable spacing is provided between the electrode and the separator, which helps to improve the wetting rate of the electrolyte and facilitates the selection of the content of lithium difluorophosphate within a suitable range, so that a solid electrolyte interface film with a suitable thickness is formed at the cathode electrode interface.

[0016] In some embodiments, the battery satisfies: 5 ≤ A ≤ 6.5, 20 ≤ Hm ≤ 40.

[0017] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and tetraethylammonium tetrafluoroborate.

[0018] In some embodiments, the electrolyte further includes a lithium salt, and the lithium salt includes lithium difluorooxalate borate. Based on the total weight of the electrolyte, the weight percentage of lithium difluorooxalate borate is K(%), and K satisfies: 3.0 ≤ K ≤ 10.0.

[0019] Based on the above embodiments, by adding lithium difluoro(oxalato)borate to the electrolyte, lithium difluoro(oxalato)borate can play an effect of inhibiting gas generation and improve the hot box performance. At the same time, it has good high-voltage stability, a wide operating temperature range, and a small ion migration resistance at -20°C. By selecting the height Hm of the first convex portion, on the basis of improving the infiltration effect of the electrolyte into the active material layer, by selecting the weight percentage content K of lithium difluoro(oxalato)borate in the range of 3.0 ≤ K ≤ 10.0, the application of lithium difluoro(oxalato)borate in the electrolyte can be promoted.

[0020] In some embodiments, the battery satisfies: 3.0 ≤ K ≤ 8.0, 20 ≤ Hm ≤ 60.

[0021] In some embodiments, the electrode has a plurality of second convex portions corresponding to the flat portion. Along the thickness direction of the electrode, the height of the second convex portion is Hn (μm); the diameter of the inner surface of the first convex portion is Rm (mm), and the diameter of the inner surface of the second convex portion is Rn (mm); the battery satisfies at least one of the following conditions:

[0022] (1) 5 ≤ Hn ≤ 40;

[0023] (2) 1.25 ≤ Hm / Hn ≤ 5;

[0024] (3) 0.3 ≤ Rm ≤ 10;

[0025] (4) Rm = Rn.

[0026] In some embodiments, the electrode includes a current collector and an active material layer provided on the surface of the current collector. The active material layer includes carbon nanotubes, and the length of the carbon nanotubes is L (μm), and L satisfies: 0.2 ≤ L ≤ 5.

[0027] Based on the above embodiments, the length of the carbon nanotubes is appropriate, so that the active material layer at the first convex portion and the second convex portion has good morphological stability, and abnormal conditions such as cracks and chipping are not likely to occur. In addition, it also has the effects of improving the electronic conductivity of the electrode and improving the floating charge of the battery at 45°C.

[0028] In some embodiments, the diameter of the carbon nanotubes is D1 (nm), and D1 satisfies: 5 ≤ D1 ≤ 18.

[0029] Based on the above embodiments, the diameter D1 of the carbon nanotubes is appropriate, and it has the effects of reducing the interfacial side reactions in the electrode, improving the cycle performance, and improving the hot box performance of the battery.

[0030] In a second aspect, an electrical device provided by an embodiment of the present application includes a housing and the battery as described above, and the battery is disposed in the internal space of the housing.

[0031] Based on the battery and the electrical device according to the embodiments of the present application, by selecting to add lithium difluorophosphate in the electrolyte and selecting the weight percentage content E of lithium difluorophosphate to satisfy 0.01≤E≤3.00, lithium difluorophosphate can improve the ion mobility in the lithium salt, and at the same time, a relatively thin solid electrolyte interface film is uniformly formed on the surface of the positive electrode active material layer, capturing gas molecules at the interface between the electrolyte and the electrode sheet, reducing the interface side reaction, thereby improving the fast charging performance and the charge-discharge cycle performance of the battery. At the same time, the content E of lithium difluorophosphate is matched with the height Hm of the first convex portion, and on the basis of satisfying the improvement of the electrolyte infiltration effect, the solid electrolyte interface film has a good improvement effect on the lithium ion mobility especially at the first convex portion, and can slow down the 1s DC impedance of the battery at 20% SOC. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0033] Figure 1 It is a schematic front view structural diagram of a pole piece in an unfolded state according to an embodiment of the present application;

[0034] Figure 2 It is a schematic cross-sectional structural diagram of an electrode assembly according to an embodiment of the present application;

[0035] Figure 3 It is a schematic partial cross-sectional structural diagram of a pole piece with a convex portion according to an embodiment of the present application;

[0036] Figure 4 It is a schematic front view structural diagram of a pole piece with an end clearance area according to an embodiment of the present application.

[0037] Reference numerals:

[0038] 20, electrode body; 21, straight section; 22, corner section; 100, tab; 40, tab assembly; 50, separator;

[0039] 300, pole piece; 311, convex portion; 301, first convex portion;

[0040] 410, positive electrode pole piece; 420, negative electrode pole piece;

[0041] 310, convex point area; 320, tab area; 330, end clearance area 330; 331, head clearance area; 332, tail clearance area; 341, edge clearance area;

[0042] X, length direction; Y, width direction; Z, thickness direction. Detailed implementation manners

[0043] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0044] The inventors found that for the electrode assembly inside the secondary battery adopting a winding structure, after the electrode sheets and the separator of the electrode assembly are alternately laminated and wound, the electrode assembly needs to be hot-pressed. There is internal stress inside the electrode assembly, resulting in poor electrolyte wettability. Moreover, during the charge and discharge process, the electrode assembly will expand, and the interlayer extrusion of the electrode assembly will be further aggravated, resulting in insufficient electrolyte and poor wetting. Eventually, the interface at the weak position deteriorates, and even lithium deposition occurs. To solve the above problems, it is necessary to create a gap between the battery layers. Currently, there are the following methods to create a gap: (1) The method of sticking adhesive tape at specific positions on the electrode sheet. By sticking the adhesive tape to support and form a gap. This method currently improves the wetting ability, but due to the presence of the adhesive tape occupying the thickness, the thickness of the electrode assembly increases, and there is a certain loss in the energy density of the battery; (2) The method of coating soluble chemical substances. By evenly coating some glue soluble in the electrolyte on the electrode sheet to form a gap, but the improvement effect is limited, and there are other side effects on the battery performance; (3) The method of thickening the separator. The ability of the separator to store the electrolyte is enhanced, and the wetting effect on the electrolyte is improved to some extent, but this method will thicken the battery and greatly reduce the energy density.

[0045] The inventors also found that by processing protrusions on the electrode sheet, the protrusions play a supporting role during the winding process, forming a gap between the electrode sheets of the electrode assembly, thereby improving the transmission ability of the electrolyte inside the electrode assembly and improving the cycle performance of the battery. Based on this, the embodiments of the present application provide a battery and an electrical device using the same, and design the protrusions on the electrode sheet and the electrolyte to effectively improve the poor electrolyte wetting effect and improve the electrode sheet interface problem.

[0046] The battery provided by the embodiment of the present application includes an outer package and an electrode assembly disposed in the inner space of the outer package, and further includes an electrolyte filled in the inner space of the outer package. The electrode assembly includes two electrode sheets with opposite polarities and a separator. As Figure 1 shown, it is a schematic front view structure diagram of the electrode sheet 300 in an unfolded state according to an embodiment of the present application. The electrode sheet 300 has a length direction X, a width direction Y, and a thickness direction Z that are perpendicular to each other in pairs. The length direction X, the width direction Y, and the thickness direction Z of the two electrode sheets 300 with opposite polarities of the electrode assembly are the same. As Figure 2As shown, the separator 50 is disposed in the thickness direction Z of the electrode plate 300 between two electrode plates 300 with opposite polarities. One of the two electrode plates 300 with opposite polarities is the positive electrode plate 410, and the other is the negative electrode plate 420. The separator 50 has insulation to separate the positive electrode plate 410 and the negative electrode plate 420 to prevent short - circuiting between the positive electrode plate 410 and the negative electrode plate 420.

[0047] As Figure 2 shown, the separator 50 and the two electrode plates 300 are wound multiple times along the length direction X of the electrode plate 300 to form the electrode body 20. The length direction X of the electrode plate 300 is the winding direction of the electrode plate 300. The electrode body 20 is flat. The electrode body 20 includes a straight part 201 and two corner parts 202. The two corner parts 202 are disposed at opposite ends of the straight part 201. Specifically, each turn of the electrode plate 300 of the electrode body 20 includes two straight segments 21 and two corner segments 22. The two straight segments 21 are arranged side by side in a direction perpendicular to the plane of the straight segment 21, and the two corner segments 22 are arranged opposite to each other along the plane of the straight segment 21. That is, the two straight segments 21 and the two corner segments 22 are connected end to end in sequence. The electrode body 20 has a finishing end, and the finishing end is formed by a part of the straight segment 21 of the outermost turn of the electrode plate 300. All the straight segments 21, the finishing end, and the separator 50 sandwiched between adjacent two straight segments 21, which are stacked in a direction perpendicular to the plane of the straight segment 21, together form the straight part 201; all the corner segments 22 on the same side of the straight segment 21 and the separator 50 sandwiched between adjacent two corner segments 22, which are arranged in a direction parallel to the plane of the straight segment 21, together form the corner part 202.

[0048] At least one of the positive electrode plate 410 and the negative electrode plate 420 has a convex part 311. Specifically, the electrode plate 300 includes a current collector and an active material layer. The active material layer and the current collector are stacked in the thickness direction Z of the electrode plate 300, and the active material layer is disposed on the surface of the current collector. The convex part 311 is formed by a part of the current collector and a part of the active material layer protruding toward the same side of the electrode plate 300 in the thickness direction Z of the electrode plate 300. The electrolyte serves as a channel for providing ion transmission. It enters the battery through the liquid injection process and continuously infiltrates the inside of the battery under the drive of gravity and capillary force. In the embodiment of the present application, by providing the convex part 311, support is provided for the separator 50, so that there is a gap between the separator 50 and the electrode plate 300, improving the electrolyte infiltration effect.

[0049] The electrolyte generally includes multiple components, mainly including three categories: lithium salts, non-aqueous organic solvents, and additives. These components affect the viscosity, ionic conductivity, and density of the electrolyte, and thus affect the ion transport performance of the electrolyte. By combining the components of the electrolyte with the convex portions 311 of the electrode sheet 300 in the embodiments of the present application, the infiltration process of the electrolyte can be accelerated, the infiltration effect of the electrolyte can be improved, the ion transport ability of the electrolyte can be improved, and thus the high-current cycling performance of the battery can be improved, the dynamics of the battery can be improved, and the DC impedance value of the battery can be reduced.

[0050] The electrode sheet 300 has a plurality of first convex portions 301 corresponding to the corner portions 202, as Figure 3 shown. Along the thickness direction Z of the electrode sheet 300, the height of the first convex portion 301 is Hm (μm), and Hm satisfies: 20 ≤ Hm ≤ 80. For example, Hm can be 20 μm, 25 μm, 34 μm, 54 μm, 66 μm, 70 μm, 80 μm, or any range between the two. Since the corner portion 202 is a high-incidence area where extrusion is likely to occur between the layers of the electrode main body 20, by providing the corner portion 202 with the first convex portions 301, stable support can be provided for the separator 50 of the corner portion 202, and thus the infiltration effect of the electrolyte in the corner portion 202 can be improved. Among them, the electrolyte further includes lithium difluorophosphate. Based on the total weight of the electrolyte, the weight percentage content of lithium difluorophosphate is E (%), and E satisfies: 0.01 ≤ E ≤ 3.00. For example, E can be 0.01%, 0.10%, 0.15%, 2.11%, 2.45%, 2.68%, 3.00%, or any range between the two. By selecting the weight percentage content E of lithium difluorophosphate in the electrolyte within the above range, lithium difluorophosphate can improve the ion mobility in the lithium salt, and at the same time, a relatively thin solid electrolyte interface film can be uniformly formed on the surface of the positive active material layer, capturing gas molecules at the interface between the electrolyte and the electrode sheet 300, reducing the interfacial side reaction, and thus improving the charge and discharge cycling performance of the battery. At the same time, since the first convex portion 301 is prone to damage due to extrusion, and the formed solid electrolyte interface film is relatively thin, the content E of lithium difluorophosphate is matched with the height Hm of the first convex portion, so that the solid electrolyte interface film has a good improvement effect on the lithium ion mobility, especially at the first convex portion 301, and can slow down the 1s DC impedance of the battery at 20% SOC (State of Charge). Among them, when Hm is lower than 20 μm or higher than 80 μm, the improvement of the lithium difluorophosphate combined with the first convex portion 301 on the cycling performance of the battery is limited. When the weight percentage content E of lithium difluorophosphate is higher than 3.00%, problems such as high electrolyte viscosity and lithium ion enrichment at the interface of the electrode sheet 300 will also occur.

[0051] Preferably, the battery satisfies: 0.01 ≤ E ≤ 1.8, 20 ≤ Hm ≤ 40. When combining the content E of lithium difluorophosphate with the height Hm of the first convex portion 301, the electrolyte can have a more appropriate viscosity and ion transport ability, so as to better improve the electrolyte infiltration effect and the fast charging performance of the battery.

[0052] In some embodiments, the electrolyte further includes ethylene glycol bis(2-cyanoethyl) ether. Based on the total weight of the electrolyte, the weight percentage content of ethylene glycol bis(2-cyanoethyl) ether is F(%), and F satisfies: 0.1 ≤ F ≤ 2.5. For example, F can be 0.10%, 0.15%, 0.58%, 1.22%, 1.68%, 2.23%, 2.50% or any range between the above two. By selecting that the electrolyte further includes ethylene glycol bis(2-cyanoethyl) ether, ethylene glycol bis(2-cyanoethyl) ether can assist lithium difluorophosphate to form a stable solid electrolyte interface film at the interface of the positive electrode sheet 410, and improve the problem of uneven formation of the solid electrolyte interface film caused by the presence of the convex portion 311. Moreover, the solid electrolyte interface film can also inhibit the occurrence of side reactions at the interface of the electrode sheet 300 at low temperatures, improve the low-temperature discharge performance and intermittent cycle performance of the battery, and at the same time reduce the gas generation amount during long cycles of the battery.

[0053] In some embodiments, the battery satisfies: 0.1 ≤ F ≤ 1.8, 20 ≤ Hm ≤ 60. By selecting the weight percentage content F of ethylene glycol bis(2-cyanoethyl) ether to match the height of the first convex portion 301, when the first convex portion 301 at the corner portion 202 has a higher height, ethylene glycol bis(2-cyanoethyl) ether can well play the role of improving the stability of the solid electrolyte interface film, and improve the low-temperature high-rate discharge performance and charge-discharge cycle performance of the battery. Preferably, the battery satisfies: 0.3 ≤ F ≤ 1.2, 20 ≤ Hm ≤ 40. In this range, ethylene glycol bis(2-cyanoethyl) ether can better stabilize the problem of uneven solid electrolyte interface film caused by the presence of the convex portion 311, and assist lithium difluorophosphate to form a more stable solid electrolyte interface film at the interface of the positive electrode sheet 410.

[0054] In some embodiments, the viscosity of the electrolyte is A (mPa·s), and the battery satisfies: 4.0 ≤ A ≤ 7.0, 20 ≤ Hm ≤ 80. For example, A can be 4.0 mPa·s, 4.6 mPa·s, 5.0 mPa·s, 5.3 mPa·s, 6.8 mPa·s, 7.0 mPa·s or any range between the above two values. By selecting the viscosity A of the electrolyte within the above range, on the basis of the good wetting effect of the electrolyte, it is convenient to select the content of lithium difluorophosphate within a suitable range, so that a solid electrolyte interface film with a suitable thickness is formed at the interface of the positive electrode sheet 410. By matching the viscosity A of the electrolyte with the height of the first convex portion 301, a suitable spacing is provided between the electrode sheet 300 and the separator 50, which helps to improve the wetting rate of the electrolyte. Preferably, the battery satisfies: 5 ≤ A ≤ 6.5, 20 ≤ Hm ≤ 40.

[0055] In some embodiments, the lithium salt in the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and lithium tetrafluoroborate.

[0056] The presence of lithium difluorooxalate borate can achieve the effects of inhibiting the high-temperature decomposition of lithium salts and gas generation, improving the hot box performance. At the same time, it has good high-voltage stability, a wide operating temperature range, and low ion migration resistance at -20°C. However, due to the low solubility of lithium difluorooxalate borate in the electrolyte, it is easy to cause the wetting effect of the electrolyte to deteriorate, and it is difficult for lithium difluorooxalate borate to be widely used in the electrolyte. In the embodiments of the present application, a convex portion 311 is provided on the electrode sheet 300 to provide a suitable gap between the electrode sheet 300 and the separator 50, which can improve the wetting effect of the electrolyte entering the active material layer and promote the application of lithium difluorooxalate borate in the electrolyte. Among them, when the lithium salt includes lithium difluorooxalate borate, based on the total weight of the electrolyte, the weight percentage content of lithium difluorooxalate borate is K (%), and K satisfies: 3.0 ≤ K ≤ 10.0. For example, K can be 3.00%, 3.55%, 3.69%, 5.22%, 6.68%, 8.89%, 10.00% or any range between the above two values. By selecting lithium difluorooxalate borate within the above range, the electrolyte can have a good wetting effect. Preferably, the battery satisfies: 3.0 ≤ K ≤ 9.0, 20 ≤ Hm ≤ 60, and lithium difluorooxalate borate can be fully dissolved in the electrolyte and make the electrolyte have a suitable wetting effect.

[0057] In some embodiments, the electrode tab 300 has a plurality of second protrusions 302 corresponding to the flat portion 201. Along the thickness direction of the electrode tab 300, the height of the second protrusion 302 is Hn (μm), and Hn satisfies: 5 ≤ Hn ≤ 40. For example, Hn can be 5μm, 10μm, 15μm, 25μm, 35μm, 40μm, or any range between the above two values. By selecting the height of the second protrusion 302 within the above range, the second protrusion 302 has a good supporting effect on the flat portion 201 of the electrode body 20. Among them, the height Hm of the first protrusion 301 and the height Hn of the second protrusion 302 satisfy: 1.5 ≤ Hm / Hn ≤ 5, so that the ratio of the height Hm of the first protrusion 301 to the height Hn of the second protrusion 302 is appropriate, providing better support for the flat portion 201 and the corner portion 202 of the electrode body 20 respectively, and improving the wetting effect of the electrolyte.

[0058] In some embodiments, the diameter of the inner surface of the first protrusion 301 is Rm (mm), and Rm satisfies: 0.3 ≤ Rm ≤ 10. For example, Rm can be 0.3mm, 10mm, 15mm, 25mm, 35mm, 40mm, or any range between the above two values. By selecting the diameter Rm of the inner surface of the first protrusion 301 to satisfy the range of the above conditional formula, it is convenient to match the height of the first protrusion 301, so that the first protrusion 301 of the electrode tab 300 has an appropriate elongation rate and an appropriate sharpness, and the first protrusion 301 has good support stability, which helps to form a uniform solid electrolyte interface film at the first protrusion 301. In some embodiments, the diameter of the inner surface of the second protrusion 302 is Rn (mm), and Rm = Rn. Similarly, it helps to form a uniform solid electrolyte interface film at the second protrusion 302. If the first protrusion 301 or the second protrusion 302 is an irregular shape, the equivalent diameter is used, that is, the distance between the two farthest points.

[0059] In the embodiments of the present application, when the electrode tab 300 has a first convex portion 301 and a second convex portion 302, optionally, all the convex portions 311 of the same electrode tab 300 protrude toward the same side of the electrode tab 300 in the thickness direction Z of the electrode tab 300. For example, the first convex portion 301 provided on the straight section 21 and the second convex portion 302 provided on the corner section 22 both protrude toward the side of the winding center of the electrode body 20; or, the first convex portion 301 provided on the straight section 21 and the second convex portion 302 provided on the corner section 22 both protrude toward the side away from the winding center of the electrode body 20. Optionally, some of the convex portions 311 of the same electrode tab 300 protrude toward one side of the electrode tab 300 in the thickness direction Z of the electrode tab 300, and the other part of the convex portions 311 protrude toward the other side of the electrode tab 300 in the thickness direction Z of the electrode tab 300. For example, the first convex portion 301 provided on the straight section 21 protrudes toward the side of the winding center of the electrode body 20, and the second convex portion 302 provided on the corner section 22 protrudes toward the side away from the winding center of the electrode body 20; or, the first convex portion 301 provided on the straight section 21 protrudes toward the side away from the winding center of the electrode body 20, and the second convex portion 302 provided on the corner section 22 protrudes toward the side of the winding center of the electrode body 20.

[0060] The above is only an exemplary introduction, and the present application does not limit the orientation of the convex portions 311 of each electrode tab 300, and specific selection can be made according to actual needs.

[0061] In some embodiments, the active material layer of the electrode tab 300 includes a conductive agent, the conductive agent includes carbon nanotubes, and the length of the carbon nanotubes is L (μm), and L satisfies: 0.2 ≤ L ≤ 5. For example, L can be 0.3μm, 10μm, 15μm, 25μm, 35μm, 40μm or any range between the above two. By selecting that the active material layer further includes carbon nanotubes, the high-temperature impedance of the electrode tab 300 can be improved, and the high-temperature charge and discharge rate performance of the battery can be improved. Among them, by selecting the length L of the carbon nanotubes within the above range, the length of the carbon nanotubes is appropriate, so that the active material layer at the first convex portion 301 and the second convex portion 302 has good morphological stability, and abnormal conditions such as cracks and chipping are not likely to occur, and it also has the effects of improving the electronic conductivity of the electrode tab and improving the 45°C floating charge of the battery.

[0062] In some embodiments, the diameter of the carbon nanotubes is D1 (nm), and D1 satisfies: 5 ≤ D1 ≤ 18. For example, D1 can be 5nm, 6nm, 8nm, 10nm, 12nm, 15nm, 18nm or any range between the above two. By selecting the diameter D1 of the carbon nanotubes within the above range, it has the effects of reducing the interfacial side reactions in the electrode tab, improving the cycle performance, and improving the thermal box performance of the battery.

[0063] In some embodiments, the surface of the active material layer facing away from the current collector forms a first surface. The convex portion 311 is disposed in the bump region of the first surface, and the bump region is defined by bump boundary lines. The convex portion 311 of the bump region may be located in the inner region defined by the bump boundary lines, or the convex portion 311 may be inscribed in the bump boundary lines. The first surface further includes an end clearance region 330 and an edge clearance region 341. The end clearance region 330 is connected to the end of the bump region in the length direction X of the electrode tab 300 and extends to the edge of the electrode tab 300. The edge clearance region 341 is disposed on one side of the bump region in the width direction Y of the electrode tab 300 and extends to the edge of the electrode tab 300. No convex portion 311 is provided in the edge clearance region 341 and the end clearance region 330. After the two electrode tabs 300 and the separator 50 are wound, the surfaces of the electrode tab 300 corresponding to the edge clearance region 341 and the end clearance region 330 may be spaced apart from the separator 50. The end clearance region 330 includes a head clearance region 331 and a tail clearance region 332. In the electrode body 20, the head clearance region 331 of the electrode tab 300 is located in the innermost layer, and the tail clearance region 332 of the electrode tab 300 is located in the outermost layer.

[0064] In the embodiments of the present application, the current collector of the negative electrode tab 420 is a negative current collector, the active material layer is a negative active material layer, the current collector of the positive electrode tab 410 is a positive current collector, and the active material layer is a positive active material layer. There are no particular limitations on the materials of the positive active material, the positive current collector, the negative active material, and the negative current collector in the embodiments of the present application. All kinds of materials known to those skilled in the art that can be used as the positive active material, the positive current collector, the negative active material, and the negative current collector are applicable to the present application.

[0065] Exemplarily, the negative current collector may be at least one of copper foil, aluminum foil, nickel foil, or a carbon-based current collector; the thickness of the negative current collector may be 1 μm to 200 μm. The negative active material layer may be disposed on one surface or two opposite surfaces of the negative current collector. Further, in the thickness direction Z of the negative electrode tab 420, the negative active material layer may be coated only on a partial region of the negative current collector. Exemplarily, the thickness of the negative active material layer may be 10 μm to 500 μm.

[0066] Exemplarily, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of lithium metal, natural graphite, artificial graphite, or a silicon-based material. The silicon-based material includes at least one of silicon, silicon oxide, silicon carbide, or silicon alloy. The negative electrode active material layer may further include a conductive agent. Exemplarily, the conductive agent in the negative electrode active material layer may include at least one of carbon black, acetylene black, Ketjen black, flake graphite, graphene, carbon fiber, or carbon nanotube in addition to carbon nanotubes. Among them, the negative electrode active material layer may further include a binder, and the binder may include at least one of carboxymethyl cellulose CMC, polyacrylate, polyacrylic ester, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0067] Exemplarily, the positive electrode current collector may be made of aluminum foil. Of course, other positive electrode current collectors commonly used in the art may also be used, and the thickness of the positive electrode current collector may be 1 μm to 200 μm. The positive electrode active material layer may be provided on one surface or two opposite surfaces of the positive electrode current collector. Further, in the thickness direction Z of the positive electrode plate 410, the positive electrode active material layer may be coated only on a partial area of the positive electrode current collector, and the thickness of the positive electrode active material layer may be 10 μm to 500 μm.

[0068] Exemplarily, the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y M y O2, LiNi 1-y M y O2, LiMn 2-y M y O4, LiNi x Co y Mn z M 1-x-y-z O2, where M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, or Ti, and 0 ≤ y ≤ 1, 0 ≤ x ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1. The positive electrode active material layer further includes a conductive agent. Exemplarily, the conductive agent in the positive electrode active material layer may include at least one of conductive carbon black, acetylene black, Ketjen black, flake graphite, graphene, or carbon fiber in addition to carbon nanotubes. Among them, the positive electrode active material layer may further include a binder, and the binder may include at least one of a copolymer of vinylidene fluoride - hexafluoropropylene, styrene - acrylate copolymer, styrene - butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylate salt, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0069] There is no particular limitation on the separator 50 in the embodiments of the present application, and various materials known to those skilled in the art that can be used as the separator 50 are applicable to the present application. Exemplarily, the separator 50 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits and can improve the stability of the electrode assembly through the shut-off effect. The thickness of the separator 50 is in the range of about 3 μm to 500 μm. The positive electrode tab and the negative electrode tab are made of a metal conductive material.

[0070] In the embodiments of the present application, the battery further includes a positive electrode tab and a negative electrode tab. The positive electrode tab is provided on the positive electrode plate 410, and the negative electrode tab is provided on the negative electrode plate 420. There is no particular limitation on the positive electrode tab, the negative electrode tab, and the protective glue in the embodiments of the present application, and various materials known to those skilled in the art that can be used as the positive electrode tab, the negative electrode tab, and the protective glue are applicable to the present application.

[0071] The electrolyte in the embodiments of the present application further includes a non-aqueous organic solvent. There is no particular limitation on the non-aqueous organic solvent in the embodiments of the present application, and various materials known to those skilled in the art that can be used as the non-aqueous organic solvent are applicable to the present application. Exemplarily, the non-aqueous organic solvent may include at least one of a carboxylic acid ester compound, an ether compound, or other organic solvents. The above-mentioned carbonate compound may include at least one of a chain carbonate compound and a cyclic carbonate compound. The above-mentioned chain carbonate compound may include at least one of dipropyl carbonate (DPC) or ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate compound may include at least one of butylene carbonate (BC) or vinylene ethylene carbonate (VEC). The above-mentioned carboxylic acid ester compound may include at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The above-mentioned ether compound may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvents may include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate ester. The present application has no particular limitation on the weight percentage of the non-aqueous organic solvent in the electrolyte, as long as the object of the present application can be achieved. For example, based on the total mass of the electrolyte, the weight percentage of the non-aqueous organic solvent is 10% to 70%.

[0072] The packaging bag of the battery in this application is not particularly limited and can be a packaging bag well-known in the art, as long as it can achieve the purpose of this application.

[0073] This application does not particularly limit the type of battery, which can include any device that undergoes an electrochemical reaction. In this application, the battery can include but is not limited to: lithium metal batteries, lithium-ion batteries, lithium polymer batteries, or lithium-ion polymer batteries, etc.

[0074] The preparation process of the battery in this application is well-known to those skilled in the art, and this application has no special limitations. For example, it can include but is not limited to the following steps: after installing the positive electrode tab on the positive electrode plate 410 and the negative electrode tab on the negative electrode plate 420, stack the positive electrode plate 410, the separator 50, and the negative electrode plate 420 in sequence, and perform operations such as winding and folding as needed to obtain a wound electrode assembly. Place the electrode assembly into a packaging bag, inject electrolyte into the packaging bag and seal it to obtain a battery; or stack the positive electrode plate 410, the separator 50, and the negative electrode plate 420 in sequence, and then fix the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly. Place the electrode assembly into a packaging bag, inject electrolyte into the packaging bag and seal it to obtain a battery.

[0075] The battery of this application can be used in electrical devices. This application does not particularly limit the type of electrical device, which can be any electrical device known in the prior art. In some embodiments, the electrical device can include but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, hand-held cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium-ion capacitors, etc.

[0076] Taking a lithium-ion battery as an example and in combination with specific embodiments, the present application will be further elaborated below. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0077] The following methods are used to test the performance of lithium-ion batteries in the embodiments and comparative examples of this application:

[0078] (1) Test method for cycle capacity retention rate of 25°C / 45°C 1.5C charge / 0.5C discharge

[0079] In an environment of 25°C / 45°C, the lithium-ion battery is charged at a constant current of 1.5C until the full charge voltage (the maximum voltage of the lithium-ion battery design is 4.53V), then charged at a constant voltage at the maximum voltage until the current is 0.02C, and then discharged at a constant current of 0.5C until the final voltage is 3.0V. Record the discharge capacity of the first cycle. Then repeat the above steps for charge and discharge cycles, and record the discharge capacity of the lithium-ion battery for each charge and discharge cycle.

[0080] The cycle capacity retention rate of 25°C / 45°C 1.5C charge / 0.5C discharge = (discharge capacity of the Nth cycle / discharge capacity of the first cycle) × 100%.

[0081] The number of cycles with a 25°C / 45°C 0.5C cycle capacity ≤ 80% is: the number of charge and discharge cycles when the cycle capacity retention rate is 80%.

[0082] (2) Test method for the height H of the convex part 311

[0083] Use a scanning electron microscope (SEM) measurement method to measure the electrode sheet. Place the electrode sheet sample in the scanning electron microscope and obtain a high-resolution image of the bump through electron beam scanning. In the SEM image, an image processing software can be used to draw a measurement line along the height direction of the bump, and calculate the height of the bump based on the pixel information of the image and the known magnification. Similarly, in the SEM image, measure the diameter of the bump through the image processing software, and obtain the height H of the convex part by taking the average value of the diameters of three adjacent bumps at three positions.

[0084] It can also be obtained by measuring with a VR series shape profile measuring microscope.

[0085] (3) Test method for electrolyte viscosity

[0086] Place the electrolyte sample in a beaker and test the electrolyte viscosity with a viscosity tester at 25°C.

[0087] (4) Test scheme for the 20% SOC 1s DCR (Direct Current Resistance) value of a fresh battery

[0088] The fully charged battery is left to stand for 1 hour, discharged at a current of 0.2C to the target 20% SOC, left to stand for 1 min, and then discharged at 1C for 1s. Record the change in the battery terminal voltage within 1 second after applying the current. Use the formula to calculate the direct current resistance of the battery, R = ΔV / I, where ΔV is the voltage change within 1s before and after applying the current, and I is the applied current.

[0089] (5) Test scheme for the -20°C 0.2C discharge capacity retention rate (%)

[0090] Take 5 lithium-ion batteries from each group and charge them in an environment of 25°C. Perform constant current and constant voltage charging at a charging current of 1C until the upper limit voltage. Then, let the fully charged lithium-ion batteries stand for 1h in environments of 25°C and -20°C respectively, and then perform constant current discharge at a discharge current of 0.2C until the cut-off voltage, and obtain the discharge capacity DR of the lithium-ion battery at 25°C and the discharge capacity DL at -20°C respectively. Among them, the upper limit voltage for charging the lithium-ion battery is 4.53V, and the cut-off voltage for discharging is 3V.

[0091] Low-temperature capacity retention rate (%) = DL / DR×100%.

[0092] When the low-temperature capacity retention rate is lower, it indicates that the low-temperature charge and discharge performance of the lithium-ion battery is worse; when the low-temperature capacity retention rate is higher, it indicates that the low-temperature charge and discharge performance of the lithium-ion battery is better.

[0093] (6) Test plan for gas production

[0094] Use a gas analyzer or a gas collection device to measure the amount of gas released by the battery. The operation method is as follows: Ensure that the equipment is calibrated to improve the measurement accuracy. Place the battery in a test container and start recording the initial gas amount. Use the charge and discharge cycle method in the cycle capacity retention rate test method of 25°C 1.5C charging / 0.5C discharging in test item (1) to perform 800 charge and discharge cycles, and then measure the gas amount of the battery.

[0095] Battery gas production = gas amount after test - initial gas amount.

[0096] (7) Test plan for 134°C hot box pass rate (%, test 10ea)

[0097] Take 10 lithium-ion batteries from each group and charge them in an environment of 25°C. Perform constant current and constant voltage charging at a charging current of 1C until the upper limit voltage. Then, place the fully charged lithium-ion batteries in a hot box. When the temperature of the hot box reaches 134°C, let them stand for 1h, and record the battery voltage and equipment temperature data during the process. After 1h, if the battery does not catch fire, it is judged to pass the test.

[0098] Pass rate (%) = number of batteries passing the test / 10×100%.

[0099] The higher the pass rate, the better the battery hot box performance.

[0100] (8) Test plan for the longest time without gas production during 45°C floating charge

[0101] Control the temperature of the test environment at 45°C. An incubator or environmental chamber can be used to maintain this temperature. Connect the battery to the floating charge power supply, ensure the connection is correct and the contact is good. Start CV at 4.53V, record the start time, and monitor the voltage, current, temperature, and thickness of the battery every day. Pay attention to observe whether there are any abnormal phenomena in the battery, such as overheating, leakage, or gas generation.

[0102] Thickness expansion rate = Test thickness / Initial thickness * 100% - 1.

[0103] Record the date when obvious gas generation is observed and the thickness expansion rate > 10% in days.

[0104] (9) Test plan for the electronic conductivity of the electrode

[0105] Use a four-probe tester or other suitable conductivity testing equipment. The operation method is as follows: Calibrate the equipment to ensure the accuracy of the measurement, and ensure that the temperature and humidity of the test environment are between 20°C - 25°C. Place the sample on the test equipment and ensure good contact between the probes and the sample surface. Apply a known current and calculate the conductivity by measuring the voltage drop. For the four-probe method, the conductivity can be calculated by the following formula: σ = I / V * t / W. Where σ is the electronic conductivity, I is the current, V is the voltage drop, t is the sample thickness, and W is the sample width.

[0106] (10) Test plan for the K value

[0107] After the battery is produced, use an open-circuit voltage tester to measure the open-circuit voltage OCV1 of the battery first. After an interval of 48 hours, measure the open-circuit voltage OCV2 of the battery again. K value = (OCV1 - OCV2) mv / 48h.

[0108] The K value can characterize the self-discharge performance of the battery. When the K value is larger, it means that the battery discharges quickly, that is, the battery's power drops quickly when it is in a static state. When the K value is smaller, it means that the battery discharges slowly and the battery has good stability, that is, the battery's power drops slowly when it is in a static state.

[0109] (11) Measurement of electrolyte components

[0110] Use a GC-MS gas chromatography-mass spectrometry combined with the internal standard method for testing.

[0111] Example 1-1

[0112] (1) Preparation of the positive electrode 410

[0113] Mix the positive active material LiCoO2, the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride (PVDF, Mw = 7×10 6)Mix in a mass ratio of 97.5:1:1.5, add N-methylpyrrolidone (NMP) as a solvent, and stir evenly under a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. Uniformly coat the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, dry it at 85 °C, and cold press it to obtain a positive electrode plate 410 with a single-sided coated positive electrode active material layer having a thickness of 50 μm. Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode plate 410 with a double-sided coated positive electrode active material layer. After cutting, a positive electrode plate 410 with a specification of 74 mm × 851 mm is obtained for use, and the tap density of the positive electrode active material layer is 4.23 g / cm 3 。

[0114] (2) Preparation of negative electrode plate 420

[0115] Mix artificial graphite as the negative electrode active material, conductive carbon black (Super P) as the negative electrode conductive agent, carboxymethyl cellulose (CMC-Na, Mw = 7×10 5 ) as the thickening agent, and styrene-butadiene rubber (SBR, Mw = 5×10 6 ) as the negative electrode binder in a mass ratio of 97.5:1:0.5:1, then add deionized water as a solvent, and stir evenly under a vacuum mixer to obtain a negative electrode slurry with a solid content of 50 wt%. Uniformly coat the negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 8 μm, dry it at 85 °C, and cold press it to obtain a negative electrode plate 420 with a single-sided coated negative electrode active material layer having a thickness of 60 μm. Then, repeat the above steps on the other surface of the copper foil to obtain a negative electrode plate 420 with a double-sided coated negative electrode active material layer. After cutting, a negative electrode plate 420 with a specification of 76 mm × 867 mm is obtained for use, and the tap density of the negative electrode active material layer is 1.77 g / cm 3 。

[0116] (3) Preparation of separator 50

[0117] Use a polyethylene (PE) porous membrane with a thickness of 5 μm.

[0118] (4) Preparation of electrolyte

[0119] In a glove box under an argon atmosphere with a water content of less than 10 ppm, mix ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a mass ratio of 1:1:2 to obtain a basic solvent, and then dissolve lithium hexafluorophosphate (LiPF6), lithium difluorophosphate, and ethylene glycol bis(2-cyanoethyl) ether in the above basic solvent to obtain an electrolyte.

[0120] Among them, based on the total mass of the electrolyte, the weight percentage content K of LiPF6 is 8.0%, the weight percentage content E of lithium difluorophosphate is 0.01%, the weight percentage content F of ethylene glycol bis(2-cyanoethyl) ether is 0.1%, and the viscosity A of the electrolyte is 5.5 mPa·s.

[0121] (5) Assembly of the lithium-ion battery

[0122] The positive electrode tab, the aluminum tab, is installed in the edge clearance area 341 of the positive electrode plate 410 by means of rolling. The protective glue is pasted on the edge area of the positive electrode plate 410. The negative electrode nickel tab is installed in the edge clearance area 341 of the negative electrode plate 420 by means of rolling.

[0123] The positive electrode plate 410 with the positive electrode tab, the separator 50, and the negative electrode plate 420 with the negative electrode tab are stacked in sequence. The separator 50 is placed between the positive electrode plate 410 and the negative electrode plate 420 to play a role in isolation, and then wound to obtain the electrode body 20. The electrode assembly is placed in an outer packaging aluminum-plastic film, dried in a vacuum oven at 85°C for 12 h to remove moisture, then the electrolyte is injected, and after vacuum packaging, standing, formation (constant current charging at 0.2°C to 3.5 V, and then constant current charging at 1C to 3.9 V), capacity measurement, degassing, trimming and other processes, the lithium-ion battery is obtained.

[0124] In Example 1-1, the negative electrode plate 420 has a first convex portion 301 and a second convex portion 302. The convex portion 311 is rolled out on the negative electrode plate 420 by means of rolling, and the Figure 4 shown electrode plate 300 is used as the negative electrode plate 420.

[0125] In Examples 1-2 to 1-15 and Comparative Examples 1-1 to 1-6, except that the height Hm of the first convex portion 301 is adjusted according to Table 1 during the preparation of the negative electrode plate 420, and the weight percentage content E of lithium difluorophosphate is adjusted according to Table 1 during the preparation of the electrolyte, the rest is the same as that in Example 1-1. Among them, the electrolyte in Comparative Example 1-6 does not contain lithium difluorophosphate.

[0126] The parameters of the lithium-ion batteries in Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-6 and the performance test results of the lithium-ion batteries are shown in Table 1.

[0127] Table 1

[0128]

[0129] Among them, the larger the number of charge-discharge cycles and the smaller the DCR value of the battery at 20% SOC for 1 s, the better the performance of the battery.

[0130] It can be seen from Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-6 in Table 1 that by selecting the height Hm of the first convex portion of the electrode tab to satisfy 20 ≤ Hm ≤ 80, and selecting the weight percentage content E of lithium difluorophosphate in the electrolyte to satisfy 0.01 ≤ E ≤ 3.00, lithium difluorophosphate can improve the ion fluidity in the lithium salt, reduce the interfacial side reaction, thereby improving the charge-discharge cycle performance of the battery and slowing down the 1s DC impedance of the battery at 20% SOC. Among them, when Hm is lower than 20 μm or higher than 80 μm, the improvement of the fast charging performance of the battery by lithium difluorophosphate combined with the first convex portion 301 is limited. When the weight percentage content E of lithium difluorophosphate is higher than 3.00%, problems such as high electrolyte viscosity and lithium ion enrichment at the interface of the electrode tab 300 will also occur.

[0131] It can be seen from Examples 1-1 to 1-6 that Hm satisfies 20 ≤ Hm ≤ 40, and it can be seen from Examples 1-7 to 1-15 that E satisfies 0.01 ≤ E ≤ 3.00, which can make the electrolyte have a more appropriate viscosity and ion transport ability, so as to better improve the electrolyte infiltration effect, and further improve the charge-discharge cycle performance of the lithium ion battery, and make the DCR value of the lithium ion battery at 20% SOC for 1s smaller.

[0132] Examples 2-1 to 2-18 are the same as Example 1-3 except that in the preparation of the negative electrode tab 420, the height Hm of the first convex portion 301 is adjusted according to Table 2, and in the preparation of the electrolyte, the weight percentage content F of ethylene glycol bis(2-cyanoethyl) ether is adjusted according to Table 2.

[0133] The parameters of the lithium ion batteries and the performance test results of the lithium ion batteries in Examples 2-1 to 2-18 are shown in Table 2.

[0134] Table 2

[0135]

[0136] It can be seen from Examples 2-1 to 2-14 and Example 1-3 in Table 2 that by selecting the weight percentage content F of ethylene glycol bis(2-cyanoethyl) ether to satisfy 0.1 ≤ F ≤ 1., and selecting the height Hm of the first convex portion 301 to satisfy 20 ≤ Hm ≤ 80, with Hm and F matching, when the first convex portion 301 at the corner portion 202 has a higher height, ethylene glycol bis(2-cyanoethyl) ether can play a good role in improving the stability of the solid electrolyte interface film, improving the low-temperature high-rate discharge performance and intermittent cycle performance of the battery, and at the same time reducing the gas generation amount during long-term cycling of the battery.

[0137] It can be seen from Examples 2-1 to 2-8 that F satisfies 0.1 ≤ F ≤ 1.8, and it can be seen from Examples 2-9 to 2-14 that Hm satisfies 20 ≤ Hm ≤ 60. Ethylene glycol bis(2-cyanoethyl) ether can better stabilize the problem of uneven solid electrolyte interface film caused by the presence of the convex portion 311, assist lithium difluorophosphate to form a more stable solid electrolyte interface film at the interface of the positive electrode sheet 410, so as to improve the low-temperature high-rate discharge performance and charge-discharge cycle performance of the battery.

[0138] Examples 3-1 to 3-13 are the same as Example 1-3 except that in the preparation of the negative electrode sheet 420, the height Hm of the first convex portion 301 is adjusted as shown in Table 3, and in the preparation of the electrolyte, the viscosity A of the electrolyte is adjusted as shown in Table 3.

[0139] The parameters of the lithium-ion batteries of Examples 3-1 to 3-13 and the performance test results of the lithium-ion batteries are shown in Table 3.

[0140] Table 3

[0141]

[0142] It can be seen from Examples 3-1 to 3-13 and Example 1-3 in Table 3 that by selecting the viscosity A of the electrolyte to satisfy 4.0 ≤ A ≤ 7.0 and the height Hm of the first convex portion to satisfy 20 ≤ Hm ≤ 80, by matching the viscosity A of the electrolyte with the height Hm of the first convex portion 301, a suitable spacing is provided between the electrode sheet 300 and the separator 50, which helps to improve the infiltration rate of the electrolyte and facilitates the selection of the content of lithium difluorophosphate within a suitable range, so that a solid electrolyte interface film with a suitable thickness is formed at the interface of the positive electrode sheet 410 by lithium difluorophosphate, which can effectively improve the low-temperature high-rate discharge performance and charge-discharge cycle performance of the lithium-ion battery, as well as improve the passing rate of the high-temperature hot box test of the battery.

[0143] It can be seen from Examples 3-1 to 3-7 and Example 1-3 that by further selecting the viscosity A of the electrolyte to satisfy 5.0 ≤ A ≤ 6.5 and the height Hm of the first convex portion to satisfy 20 ≤ Hm ≤ 40, the various performances of the lithium-ion battery can be further improved.

[0144] Examples 4-1 to 4-13 are the same as Example 3-1 except that in the preparation of the negative electrode sheet 420, the height Hm of the first convex portion 301 is adjusted as shown in Table 4, and in the preparation of the electrolyte, the type of lithium salt is adjusted or the weight percentage content K of lithium difluorooxalate borate is adjusted as shown in Table 4.

[0145] The parameters of the lithium-ion batteries of Examples 4-1 to 4-13 and the performance test results of the lithium-ion batteries are shown in Table 4.

[0146] Table 4

[0147]

[0148] As can be seen from Examples 4-1 to 4-4 and Example 3-1 in Table 4, the lithium salt in the electrolyte is selected from lithium hexafluorophosphate, lithium perchlorate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide or lithium tetrafluoroborate, and the low-temperature high-rate discharge performance, charge-discharge cycle performance and passing rate of the high-temperature hot box test of the lithium-ion battery are all good.

[0149] As can be seen from Examples 4-4 to 4-13 in Table 4, when the electrolyte includes lithium difluorooxalate borate, the weight percentage content K of lithium difluorooxalate borate satisfies 3.0 ≤ K ≤ 10.0, and lithium difluorooxalate borate can be dissolved in the electrolyte and cooperate with the height Hm of the first convex portion to satisfy 20 ≤ Hm ≤ 80, so that there is a suitable gap between the electrode sheet 300 and the separator 50, which can improve the infiltration effect of the electrolyte into the active material layer, enable lithium difluorooxalate borate to be applied in the electrolyte, and further achieve the effect of improving the hot box performance of the lithium-ion battery and can improve the low-temperature high-rate discharge performance of the lithium-ion battery.

[0150] Examples 5-1 to 5-10 are the same as Example 3-1 except that in the preparation of the negative electrode sheet 420, carbon nanotubes are used to replace conductive carbon black as shown in Table 5, and the length L of the carbon nanotubes and the diameter D1 of the carbon nanotubes are adjusted.

[0151] The parameters of the lithium-ion batteries of Examples 5-1 to 5-10 and the performance test results of the lithium-ion batteries are shown in Table 5.

[0152] Table 5

[0153]

[0154]

[0155] As can be seen from Examples 5-1 to 5-5 and Example 3-1 in Table 5, the height Hn of the second convex portion 302 satisfies 5 ≤ Hn ≤ 40, and satisfies 1.5 ≤ Hm / Hn ≤ 5. The ratio of the height Hm of the first convex portion 301 to the height Hn of the second convex portion 302 is appropriate, providing better support for the straight portion 201 and the corner portion 202 of the electrode body 20 respectively, improving the infiltration effect of the electrolyte, and helping to form a uniform solid electrolyte interface film at the first convex portion 301, so that the various performances of the lithium-ion battery can be improved.

[0156] As can be seen from Examples 5-6 to 5-11 in Table 5, by selecting the diameter Rm of the inner surface of the first convex portion 301 to satisfy 0.3 ≤ Rm ≤ 10, it is convenient to match the height Hm of the first convex portion 301, so that the first convex portion 301 of the electrode tab 300 has an appropriate elongation rate and an appropriate sharpness, and the first convex portion 301 has good support stability, which helps to form a uniform solid electrolyte interface film at the first convex portion 301, thereby improving the performance of the lithium-ion battery.

[0157] As can be seen from Examples 5-12 to 5-17 in Table 5, by selecting the length L of the carbon nanotubes to satisfy 0.2 ≤ L ≤ 5, the length of the carbon nanotubes is appropriate, so that the active material layers at the first convex portion 301 and the second convex portion 302 have good morphological stability, and abnormal conditions such as cracks and chipping are not likely to occur, and it also has the effects of improving the electronic conductivity of the electrode tab and improving the floating charge of the lithium-ion battery at 45°C.

[0158] As can be seen from Examples 5-18 to 5-25 in Table 5, by selecting the diameter D1 of the carbon nanotubes to satisfy 5 ≤ D1 ≤ 18, the interfacial side reactions in the electrode tab can be reduced, achieving the effects of improving the charge-discharge cycle performance of the lithium-ion battery and improving the battery hot box performance.

[0159] In the attached drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components; in the description of this application, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the attached drawings, and are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and cannot be understood as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0160] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of this application should be included in the protection scope of this application.

Claims

1. A battery, characterized in that: The invention comprises an outer package, an electrode assembly and an electrolyte, wherein the electrode assembly is arranged in the inner space of the outer package, and the electrolyte fills the inner space of the outer package; The electrode assembly comprises a separator and a plurality of pole pieces, wherein the separator is arranged between two pole pieces with opposite polarities, and the pole piece and the separator are wound multiple times to form an electrode body, wherein the electrode body comprises a straight portion and corner portions arranged at opposite ends of the straight portion; the corner portions of the pole pieces are provided with a plurality of first protrusions, and along the thickness direction of the pole pieces, the height of the first protrusions is Hm (μm), and Hm satisfies: 20≤Hm≤80; The electrolyte includes lithium difluorophosphate. Based on the total weight of the electrolyte, the weight percentage of the lithium difluorophosphate is E (%), and E satisfies: 0.01≤E≤3.

00.

2. The battery according to claim 1, characterized in that The battery satisfies: 0.01≤E≤1.8, 20≤Hm≤40.

3. The battery according to claim 1, characterized in that The electrolyte further comprises ethylene glycol bis(2-cyanoethyl) ether. Based on the total weight of the electrolyte, the weight percentage of the ethylene glycol bis(2-cyanoethyl) ether is F(%), and F satisfies: 0.1≤F≤2.

5.

4. The battery according to claim 3, characterized in that The battery satisfies: 0.1≤F≤1.8, 20≤Hm≤60.

5. The battery according to claim 4, characterized in that The battery satisfies: 0.3≤F≤1.2, 20≤Hm≤40.

6. The battery according to claim 1, characterized in that The viscosity of the electrolyte is A (mpa.s), and the battery satisfies: 4.0≤A≤7.

0.

7. The battery according to claim 1, characterized in that The battery meets the following requirements: 5≤A≤6.5, 20≤Hm≤40.

8. The battery according to claim 1, characterized in that The electrolyte further comprises a lithium salt, and the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium difluorooxalatoborate, lithium bis(fluorosulfonyl)imide and lithium tetrafluoroborate.

9. The battery according to claim 1, characterized in that The electrolyte further includes a lithium salt, and the lithium salt includes lithium difluorooxalatoborate. Based on the total weight of the electrolyte, the weight percentage of the lithium difluorooxalatoborate is K (%), and K satisfies: 3.0≤K≤10.

0.

10. The battery according to claim 9, characterized in that The battery satisfies: 3.0≤K≤8.0, 20≤Hm≤60.

11. The battery according to any one of claims 1 to 10, characterized in that The pole piece has a plurality of second protrusions arranged corresponding to the straight portion, and along the thickness direction of the pole piece, the height of the second protrusion is Hn (μm); the diameter of the inner surface of the first protrusion is Rm (mm), and the diameter of the inner surface of the second protrusion is Rn (mm); the battery satisfies at least one of the following conditions: (1) 5 ≤ Hn ≤ 40; (2) 1.25 ≤ Hm / Hn ≤ 5; (3) 0.3 ≤ Rm ≤ 10; (4)Rm=Rn.

12. The battery according to any one of claims 1 to 11, characterized in that The pole piece includes a current collector and an active material layer disposed on the surface of the current collector. The active material layer includes carbon nanotubes. The length of the carbon nanotubes is L (μm), and L satisfies: 0.2≤L≤5.

13. The battery according to claim 12, characterized in that The diameter of the carbon nanotube is D1 (nm), and D1 satisfies: 5≤D1≤18.

14. An electrical device, characterized in that: include: shell; and, The battery according to any one of claims 1 to 13, wherein the battery is arranged in the internal space of the shell.

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