Battery cell and electric device

Abstract

The application belongs to the technical field of battery preparation, and particularly relates to a battery cell and an electric device. The battery cell comprises a positive electrode sheet, a diaphragm and a negative electrode sheet, and is formed into a battery cell through winding. The negative electrode sheet comprises a negative electrode current collector, a first coating layer and a second coating layer. The second coating layer is arranged on at least one surface of the negative electrode current collector, and the first coating layer is arranged between the negative electrode current collector and the second coating layer. The first coating layer comprises a graphite material. The second coating layer comprises a silicon-based material. The negative electrode sheet comprises a first flat area and first arc areas located at two ends of the first flat area. The surface of the second coating layer located at the first arc areas is provided with a protrusion, and the protrusion comprises a silicon-based material. The application adopts a double-layer design to arrange a silicon-containing coating layer on the surface of the second coating layer of the negative electrode sheet, so that the expansion and shrinkage generated in the charging and discharging process of the silicon negative electrode can be solved. The protrusion arranged on the second coating layer can reduce the stress in the expansion or shrinkage process, improve the lithium precipitation problem of the arc area and relieve the expansion.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery preparation, and particularly relates to a battery cell and an electric device. BACKGROUND

[0002] Silicon negative electrodes bring significant advantages in lithium-ion batteries, mainly in high energy density and longer battery life. Silicon negative electrode materials have higher theoretical specific capacity than traditional graphite negative electrodes, can store more lithium ions, thereby improving the overall energy density of the battery. Silicon negative electrodes can provide longer battery life without changing the volume. In addition, the energy density of silicon negative electrodes can also enhance the performance of devices without increasing the weight of the battery, significantly improving the endurance of electric vehicles and portable electronic devices.

[0003] Although silicon negative electrodes have significant advantages in improving the energy density of lithium-ion batteries, they will experience significant volume expansion and contraction during charging and discharging, leading to unstable battery performance, which seriously restricts the widespread application of silicon negative electrodes. At the same time, the winding structure battery also has the problem of lithium precipitation at the circular arc due to the large stress, and the greater the expansion, the worse the circular arc lithium precipitation problem. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the problems of the prior art, such as the serious volume expansion and contraction of silicon negative electrodes during charging and discharging, and the lithium precipitation at the circular arc of the winding battery, thereby providing a battery cell and an electric device.

[0005] To this end, the present application provides the following technical solutions.

[0006] The present application provides a battery cell, which comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, and is formed by winding; the negative electrode sheet comprises a negative electrode current collector, a first coating layer and a second coating layer; the second coating layer is arranged on at least one surface of the negative electrode current collector, and the first coating layer is arranged between the negative electrode current collector and the second coating layer; the first coating layer comprises a graphite material; the second coating layer comprises a silicon-based material; the negative electrode sheet comprises a first flat area and first circular arc areas located at both ends of the first flat area, and the surface of the second coating layer located in the first circular arc area is provided with a protrusion, and the protrusion comprises a silicon-based material.

[0007] Further, the mass content of the silicon-based material is x based on the total mass of the second coating layer, and x satisfies: 25wt%≤x≤100wt%;

[0008] The number of protrusions within a 0.1mmx0.1mm area of the surface of the second coating layer located in the first circular arc area is n, and n satisfies: 8≤n≤15;

[0009] n and x satisfy relationship 1:

[0010]

[0011] Further, the height of the protrusion is not less than 3 μm.

[0012] Further, the first coating layer comprises first graphite particles and second graphite particles.

[0013] Optionally, the median particle size Dv50 of the second graphite particles is greater than the median particle size Dv50 of the first graphite particles.

[0014] Optionally, the median particle size Dv50 of the first graphite particles is 5 μm-10 μm, and the median particle size Dv50 of the second graphite particles is 11 μm-16 μm.

[0015] Further, the silicon-based material comprises silicon-carbon particles, and the silicon-carbon particles have an average sphericity of 0.5-1; and / or,

[0016] The second coating layer further comprises a graphite material.

[0017] Further, the OI value of the graphite in the first coating layer located in the first arc region is less than the OI value of the graphite in the first coating layer located in the first flat region; and / or,

[0018] The OI value of the graphite in the first coating layer located in the first arc region is 4-14; and / or,

[0019] The OI value of the graphite in the first coating layer located in the first flat region is 12-24.

[0020] Further, the positive electrode tab comprises a second flat region and second arc regions located at both ends of the second flat region, and the positive electrode tab located in the second arc region is provided with a groove.

[0021] Further, the weight loss rate of the positive electrode tab located in the second arc region is s, and s satisfies: 1%≤s≤10%;

[0022] The mass content of the silicon-based material is x, and x satisfies: 25wt%≤x≤100wt%, based on the total mass of the second coating layer;

[0023] s and x satisfy relationship 2:

[0024] Relationship 2.

[0025] Further, the number of grooves within a 0.1 mm x 0.1 mm area of the positive electrode tab located in the second arc region is not less than 5; and / or,

[0026] a depth of the groove is 3-30 μm; and / or,

[0027] s and x satisfy relationship 3:

[0028] relationship 3

[0029] The application provides a kind of electric equipment, including above-mentioned electric core.

[0030] The technical scheme of the application has the following advantages:

[0031] 1. The electric core provided by the application, the electric core includes a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, and is formed by winding to form the electric core;The negative electrode sheet includes a negative electrode current collector, a first coating layer and a second coating layer;The second coating layer is arranged on at least one surface of the negative electrode current collector, and the first coating layer is arranged between the negative electrode current collector and the second coating layer;The first coating layer contains graphite material;The second coating layer contains silicon-based material;The negative electrode sheet includes a first flat area and a first circular arc area located at both ends of the first flat area, and the surface of the second coating layer located in the first circular arc area is provided with a protrusion, and the protrusion contains silicon-based material.The application adopts double-layer design to set the silicon-containing coating layer on the surface of the second coating layer of the negative electrode sheet, which can solve the expansion and shrinkage of the silicon negative electrode during charging and discharging, but due to the lack of buffer of the silicon particles on the surface of the second coating layer, the lithium precipitation problem of the winding battery circular arc will be aggravated, the application sets a protrusion on the second coating layer, and the protrusion contains silicon particles, which can provide more buffer area, reduce the stress in the expansion or shrinkage process, improve the lithium precipitation problem of the circular arc area and relieve the expansion. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0033] Figure 1 It is a structural schematic diagram of the electric core of the application;

[0034] Reference signs:

[0035] 1-flat area; 2-circular arc area. DETAILED DESCRIPTION

[0036] The following examples are provided to better enable those skilled in the art to further understand the application, and are not intended to limit the scope of the application, and are not intended to limit the contents and protection scope of the application, and any person who obtains any product same or similar to the application under the enlightenment of the application or combines the application with other prior art features falls within the protection scope of the application.

[0037] The specific experimental steps or conditions not indicated in the examples can be carried out according to the conventional experimental steps or conditions described in the literature in the art. The reagents or instruments not indicated by the manufacturer are conventional reagent products that can be obtained by purchase.

[0038] Silicon negative electrode has a significant advantage in improving the energy density of lithium ion batteries, but it undergoes significant volume expansion and contraction during charging and discharging, resulting in unstable battery performance. The stress at the arc of the wound battery is large, and the separator located at the arc is compressed, resulting in problems such as decreased porosity and insufficient electrolyte retention, which leads to lithium precipitation. The greater volume expansion of the silicon negative electrode makes the lithium precipitation problem even more significant.

[0039] To solve the problem of expansion and contraction of the silicon negative electrode, a silicon-based material is provided in the second coating layer of the negative electrode tab, but due to the lack of buffering of the silicon-based material on the surface of the negative electrode tab, the volume expansion will further exacerbate the arc lithium precipitation problem of the wound battery. In order to balance the reduction of the volume expansion and contraction of the silicon negative electrode and the arc lithium precipitation problem, the present application provides the following technical solutions.

[0040] In a first aspect, the present application provides an electric core, comprising a positive electrode tab, a negative electrode tab and a separator provided between the positive electrode tab and the negative electrode tab, which is wound to form the electric core; the negative electrode tab comprises a negative electrode current collector, a first coating layer and a second coating layer; the second coating layer is provided on at least one surface of the negative electrode current collector, and the first coating layer is provided between the negative electrode current collector and the second coating layer; the first coating layer comprises a graphite material; the second coating layer comprises a silicon-based material; the negative electrode tab comprises a first flat area and a first arc area located at both ends of the first flat area, and the surface of the second coating layer located in the first arc area is provided with a protrusion, and the protrusion comprises a silicon-based material.

[0041] The coating in the negative electrode sheet of the battery cell in the application adopts a double-layer design. The first coating containing graphite material is arranged on the surface of the negative current collector, and the second coating containing silicon-based material is arranged on the surface of the first coating. The expansion force of the silicon in the second coating is used to inhibit the expansion of the graphite in the first coating, so that the silicon-based material is concentrated in the second coating, the interaction between the silicon-based material and the graphite material is reduced, the influence range of the large volume expansion of the silicon-based material on the graphite is reduced, and thus the overall expansion of the battery is reduced. The greater the expansion, the more serious the lithium precipitation. The negative electrode sheet with the special design in the application can reduce the expansion and avoid the problem of lithium precipitation from the source. The protrusions are arranged on the surface of the second coating. The protrusions include silicon-based material, achieve the purpose of creating space in the circular arc area, reduce the stress in the circular arc area, make the stress in the circular arc area more evenly distributed, and the protrusions in the circular arc area provide a buffer area, reduce the stress of the shell in the expansion or contraction process, and are beneficial to the infiltration of the electrolyte, thereby improving the problem of lithium precipitation in the circular arc area and relieving the expansion in the circular arc area, and also reducing the phenomenon that the expansion causes the lithium precipitation to be intensified.

[0042] It should be explained that when the battery is wound, as shown in Figure 1 , the negative electrode sheet forms a flat area 1 and a circular arc area 2.

[0043] In an alternative embodiment, the mass content of the silicon-based material is x based on the total mass of the second coating, and x satisfies: 25wt%≤x≤100wt%;

[0044] The number of protrusions in the area of 0.1mm×0.1mm on the surface of the second coating in the first circular arc area is n, and n satisfies: 8≤n≤15;

[0045] n and x satisfy the relationship formula 1:

[0046]

[0047] The more the content of the silicon-based material in the second coating layer is, the greater the stress on the tab in the circular arc area is, and the tab is prone to swelling and lithium precipitation. The number of the protrusions in the second coating layer of the circular arc area can achieve the purpose of creating space, reduce the stress in the circular arc area, and make the stress evenly distributed in the area. The protrusions provide a buffer area, reduce the stress in the swelling or shrinking process, are conducive to the infiltration of the electrolyte, improve the lithium precipitation in the circular arc area, and relieve the swelling. Further, the higher the content of the silicon-based material in the second coating layer is, the greater the swelling is, the greater the stress on the tab in the circular arc area is, and the more serious the lithium precipitation in the circular arc area is. Therefore, the inventor of the present application finds that by regulating the number of the protrusions in the second coating layer and the content of the silicon-based material in the second coating layer to satisfy 8-60, the energy density can be ensured, and the problems such as swelling and lithium precipitation in the circular arc area can be relieved. Exemplarily, n is 8, 9, 10, 11, 12, 13, 14, 15, or within a range composed of any two of the above values. x is 25wt%, 35wt%, 45wt%, 55wt%, 65wt%, 75wt%, 85wt%, 95wt%, 100wt%, or within a range composed of any two of the above values. The ratio of n to x is 8, 10, 15, 25, 30, 35, 40, 45, 50, 55, 60, or within a range composed of any two of the above values.

[0048] In an alternative embodiment, the height of the protrusions is not less than 3 μm. It should be noted that the protrusion is a protruding part of the second coating layer surface higher than the surrounding area. The heights of the protrusions in the second coating layer can be the same or different. The height and number of the protrusions are tested by a method known in the art, and one is listed here: a laser microscope. Exemplarily, the height of the protrusions can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any value within a range composed of any two of the above values.

[0049] It should be noted that the number of the protrusions is obtained by a method known in the art. One is listed here: a negative electrode tab at the circular arc area with an area of 0.1 mm x 0.1 mm is taken, a laser side thickness microscope is used to observe the surface of the tab, the number of the protrusions with a height of ≥3 μm is observed, and the number of the protrusions is obtained. The content of the silicon-based material in the second coating layer is obtained by a method known in the art.

[0050] In an alternative embodiment, the first coating layer comprises first graphite particles and second graphite particles.

[0051] Optionally, the median particle size Dv50 of the second graphite particles is greater than the median particle size Dv50 of the first graphite particles.

[0052] Optionally, the first graphite particles have a median particle size Dv50 of 5-10 μm, and the second graphite particles have a median particle size Dv50 of 11-16 μm. Controlling the median particle size of the graphite particles helps to alleviate the swelling. For example, the first graphite particles have a median particle size Dv50 of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or within a range defined by any two of the above values. The second graphite particles have a median particle size Dv50 of 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, or within a range defined by any two of the above values.

[0053] In an optional embodiment, the silicon-based material comprises silicon-carbon particles having an average sphericity of 0.5-1; optionally, the silicon-carbon particles have an average sphericity of 0.85-1. A negative electrode material with high sphericity can more fully utilize the active material during the charge and discharge process, improving the cycle stability and rate performance of the battery. The spherical particles have better wettability in the electrolyte, and can more effectively contact and react with the electrolyte. Higher sphericity can uniformly disperse the mechanical stress during the volume expansion of the particles, so that the particles are not easily broken, thereby improving the cycle retention rate of the battery. For example, the silicon-carbon particles have an average sphericity of 0.5, 0.6, 0.7, 0.8, 0.9, 1, or within a range defined by any two of the above values.

[0054] The average sphericity of the silicon-carbon particles is obtained by testing using a method known in the art. For example, the method for testing the average sphericity of the silicon-based particles comprises the following steps: first, disassemble the lithium ion battery, remove the negative electrode sheet, and soak and rinse the negative electrode sheet with dimethyl carbonate solvent to remove the lithium salt and electrolyte solvent on the negative electrode sheet. After drying, the cross section of the negative electrode sheet is obtained by argon ion cutting. In the backscattering mode of the scanning electron microscope, the silicon-based particles have a brighter contrast and the graphite particles are darker, so the image of each bright particle in the SEM backscattering mode photo of the negative electrode sheet at a certain magnification (e.g., 2500 times) can be calculated by image processing software (e.g., Image Pro Plus) to obtain the perimeter and area of each silicon-based particle. The perimeter equivalent radius r1 and the area equivalent radius r2 of each particle are calculated, and then the sphericity b of each particle is calculated as r2 / r1. The sphericity of each particle is then averaged by quantity to obtain the average sphericity of the silicon-based particles in the cross section of the negative electrode sheet.

[0055] It should be noted that the specific surface area of the silicon-carbon particles is 0.5-10 m 2 / g, Dv10 is 3-6 μm, Dv50 is 6-20 μm, and Dv90 is 12-25 μm. The larger specific surface area of the silicon-carbon particles can increase the contact area between the negative electrode material and the electrolyte, and more active sites can participate in the electrode reaction, thereby improving the electrochemical activity of the battery. The specific surface area, Dv10, Dv50, and Dv90 of the silicon-carbon particles are obtained by testing using methods known in the art. One method for testing the specific surface area is as follows: a BET specific surface area tester is used for testing. The method for testing Dv50 is as follows: after the battery is discharged, the negative electrode is removed, the residual electrolyte of the negative electrode is washed with a solvent, and then the negative electrode is placed in deionized water for ultrasonic treatment for 10 s. The powder is shaken off and dried. The powder is placed in a muffle furnace and calcined at 500°C for 2 h. The particle size of the calcined powder is measured to obtain Dv50. For example, the specific surface area of the silicon-carbon particles is 0.5 m 2 / g, 1.5 m 2 / g, 2.5 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, or within a range defined by any two of the above values. The Dv50 of the silicon-carbon particles is 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or within a range defined by any two of the above values.

[0056] In an alternative embodiment, the second coating further comprises a graphite material. It should be noted that the present application includes a technical solution in which the second coating does not contain a graphite material.

[0057] In an alternative embodiment, the OI value of the graphite in the first coating located in the first arc region is less than the OI value of the graphite in the first coating located in the first flat region; and / or,

[0058] The OI value of the graphite in the first coating located in the first arc region is 4-14; and / or,

[0059] The OI value of the graphite in the first coating located in the first flat area is 12-24. The present application can improve the lithium intercalation kinetics of the negative electrode sheet by reducing the OI value of the first coating, further inhibit the lithium precipitation in the circular arc area, and reduce the expansion. For example, the OI value of the graphite in the first coating located in the first circular arc area is 4, 8, 10, 12, 14, or within a range formed by any two of the above values. The OI value of the graphite in the first coating located in the first flat area is 12, 14, 16, 18, 20, 22, 24, or within a range formed by any two of the above values. The OI value of the graphite is obtained by testing using a method known in the art. Here, one of the methods is to obtain the OI value of the graphite by using an X-ray diffraction (XRD) technique.

[0060] In an alternative embodiment, the thickness of the first coating is 5 μm-30 μm, and the thickness of the second coating is 5 μm-50 μm. For example, the thickness of the first coating is 5 μm, 8 μm, 13 μm, 15 μm, 18 μm, 21 μm, 24 μm, 27 μm, 30 μm, or within a range formed by any two of the above values. The thickness of the second coating is 5 μm, 8 μm, 13 μm, 15 μm, 18 μm, 21 μm, 24 μm, 27 μm, 30 μm, 33 μm, 35 μm, 38 μm, 41 μm, 44 μm, 47 μm, 50 μm, or within a range formed by any two of the above values.

[0061] In an alternative embodiment, the first coating and / or the second coating further comprises at least one of a conductive agent and a binder. The conductive agent comprises at least one of carbon black, carbon nanotubes, etc. The binder comprises at least one of an SBR binder, a PAA binder, etc. The conductive agent and the binder are used in a conventional amount in the art. The negative current collector is made of a material known to those skilled in the art, for example, the negative current collector is a copper foil, etc.

[0062] In an alternative embodiment, the positive electrode sheet comprises a second flat area and second circular arc areas located at both ends of the second flat area, and the positive electrode sheet located in the second circular arc area is provided with a groove.

[0063] In an alternative embodiment, the weight loss rate of the positive electrode sheet located in the second circular arc area is s, and s satisfies: 1%≤s≤10%;

[0064] The mass content of the silicon-based material is x based on the total mass of the second coating, and x satisfies: 25wt%≤x≤100wt%;

[0065] s and x satisfy the following relationship 2:

[0066]

[0067] The weight loss rate of the positive electrode tab in the arc region is related to the setting mode of the groove. The positive electrode tab located in the second arc region is provided with a groove, and the more the number of the groove, the higher the weight loss rate of the positive electrode tab. The higher the content of the silicon-based material in the second coating layer of the negative electrode tab, the stress after the expansion of the silicon is concentrated in the second coating layer of the negative electrode tab, and the stress on the arc region is further increased. The weight loss rate of the positive electrode tab located in the second arc region is controlled to be 1%-10%, which on one hand reserves more electrolyte to infiltrate the positive electrode tab in the arc region, and on the other hand can improve the local NP ratio and increase the energy density of the battery. Wherein, NP is the ratio of the negative electrode capacity to the positive electrode capacity, and the calculation formula is as follows:

[0068]

[0069] Unit area capacity = areal density x active material gram capacity x active material mass proportion in active material layer

[0070] For example, the weight loss rate of the positive electrode tab located in the second arc region is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or within the range formed by any two of the above values. The weight loss rate of the positive electrode tab is obtained by testing with a method known in the art.

[0071] In an alternative embodiment, the number of grooves within 0.1mmx0.1mm area of the positive electrode tab located in the second arc region is not less than 5; and / or,

[0072] The depth of the groove is 3-30μm; and / or,

[0073] s and x satisfy the relationship formula 3:

[0074]

[0075] The larger the size of the groove, the greater the weight loss rate of the positive electrode tab. The number and depth of the groove controlled by the present application can make the positive electrode tab meet the specific weight loss rate requirement. It should be noted that the groove structure on the positive electrode tab is made by a method known in the art, such as laser pore forming technology. The present application does not make specific requirements for the shape of the groove, and common shapes in the art can be used, such as cylinder, cuboid, arc, T-shaped, etc.

[0076] In an alternative embodiment, the positive electrode tab comprises a positive electrode current collector and a positive electrode coating layer arranged on at least one surface of the positive electrode current collector; the positive electrode coating layer comprises a positive electrode active material;

[0077] The positive electrode active material layer is a conventional structure in the art, and the raw materials are selected from conventional raw materials in the art, such as at least one of lithium nickelate, lithium titanate, lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganate. The positive electrode coating further includes at least one of a conductive agent and a binder. The conductive agent includes at least one of carbon black, carbon nanotubes, conductive graphite, and graphene; and the binder includes at least one of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymer, polyimide, butadiene styrene rubber, and phenylpropyl rubber. It should be noted that the positive electrode active material, the conductive agent, and the binder are formulated according to the conventional ratio in the art. The positive electrode current collector is made of a material known to those skilled in the art, such as an aluminum foil.

[0078] In an alternative embodiment, the battery further includes an electrolyte; the electrolyte is an organic solvent system, and the organic solvent includes at least one of acetonitrile, tetrahydrofuran, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, propyl propionate, ethyl propionate, propyl acetate, ethyl acetate, methyl ethyl carbonate, and dimethyl sulfoxide. The density M of the electrolyte is 1.1-1.3 g / cm 3 , and the conductivity p is 8.5-9.5 ms / cm. Alternatively, propylene sulfite (PS) has excellent high-temperature performance, and the content of propylene sulfite (PS) in the electrolyte is 0.3-5%. The battery is assembled using an electrolyte known in the art, which is not specifically limited in the present application. The electrolyte further includes an additive, and the additive includes at least one of sodium difluorophosphate, sodium bisoxalate borate, tris(trimethylsilyl) borate, vinylene carbonate, and succindinitrile. The electrolyte further includes at least one of a sodium salt and a lithium salt; both the sodium salt and the lithium salt are selected from the known types in the art. As an example, the sodium salt includes at least one of NaPF6, NaBF4, NaClO4, NaAsF6, and NaCF3SO3; and the lithium salt includes at least one of LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3.

[0079] In an alternative embodiment, the battery further includes a separator; the separator includes a substrate layer and a ceramic layer disposed on at least one surface of the substrate layer. The separator further includes a rubberized layer; the rubberized layer is disposed on the surface of the substrate layer and / or the ceramic layer.

[0080] It should be noted that the materials of the substrate layer, the ceramic layer, and the rubberized layer are selected from the known types in the art. For example, the material of the substrate layer includes at least one of a woven film, a non-woven film, a polyolefin film, and a separator paper, and the polyolefin film includes at least one of polyethylene, polypropylene, polyethylene, and polypropylene.

[0081] The ceramic layer comprises ceramic particles and a binder, the ceramic particles comprise one or more of boehmite (γ-AlOOH), alumina (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2), and the particle size Dv50 of the ceramic particles is 0.1-2.5 μm. The binder comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of vinylidene fluoride-trichloroethylene, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, a polyacrylic acid salt, polyvinylpyrrolidone, a polyvinyl ether, styrene-butadiene rubber, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0082] The adhesive layer comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of vinylidene fluoride-trichloroethylene, polyvinyl acetate, polyvinyl alcohol, polyethylene oxide, polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, a polyacrylic acid salt, polyvinylpyrrolidone, a polyvinyl ether, styrene-butadiene rubber, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0083] In a second aspect, the present application provides a power-using device comprising the above-mentioned battery cell.

[0084] Embodiment 1

[0085] The present embodiment provides a preparation method of a battery, comprising:

[0086] Preparation of the positive electrode tab: mix the positive electrode active material, SP, and PVDF according to a mass ratio of 97.6:1.4:1, and add NMP, stir uniformly, and prepare a positive electrode slurry; wherein the positive electrode active material comprises lithium cobaltate (LCO) and Li2NiO2, the amount of Li2NiO2 is 1wt% of the weight of LCO, and the doping amount of Y in LCO is 700 ppm. The positive electrode slurry is coated on both surfaces of an aluminum foil, the initial tensile strength of the aluminum foil used is 290 MPa, and after baking and rolling, a positive electrode tab with a thickness of 80 μm is obtained, the positive electrode tab has one fixed-size slot, and the aluminum tab is welded in the slot by laser or ultrasonic welding to obtain a positive electrode tab with an aluminum tab.

[0087] The negative electrode sheet: graphite, SP, CMC-Na, SBR are mixed according to the mass ratio of 97:0.4:0.1:2.5 to prepare a first negative electrode slurry. The silicon-doped carbon negative active material, SP, CMC-Li, PAA are mixed according to the mass ratio of 97:0.4:0.1:2.5, and deionized water is added to prepare a second negative electrode slurry. The first negative electrode slurry is coated on the surface of the current collector copper foil, and the second negative electrode slurry is coated on the surface of the first negative electrode slurry. After baking and rolling, a negative electrode sheet with a thickness of 95 μm is obtained. The negative electrode sheet is laser-wired on the surface, the wire depth h is 20 μm, and the edge is reserved 0.5 mm to obtain the negative electrode sheet.

[0088] The positive and negative electrode sheets are cut and sheeted, and then wound with the separator to obtain the core, wherein the separator comprises a base layer (the base layer material is PP) and a ceramic layer arranged on one side of the base layer. A glue coating layer is arranged on the other side of the base layer and the surface of the ceramic layer. The thickness of the ceramic layer is 2 μm, the ceramic particles are boehmite, and the particle size of the ceramic particles is 200 nm. The thickness of the glue coating layer is 2 μm. The material of the glue coating layer in contact with the negative electrode sheet comprises SBR and PAA, and the material of the glue coating layer in contact with the positive electrode sheet comprises PVDF. During winding, the ceramic layer is attached to the negative electrode sheet. Then, the lithium ion battery is obtained through packaging, baking, liquid injection, formation, two-sealing, sorting and OCV. The electrolyte comprises EC and DMC in a mass ratio of 1:1, and further comprises FEC and LiFP6. The content of FEC in the electrolyte is 15 wt%, and the concentration of LiFP6 is 1M. After winding, the positive electrode sheet and the negative electrode sheet each comprise a flat area and a circular arc area.

[0089] The particle size of the graphite particles in the first coating layer, the OI value of the flat area and the circular arc area, the thickness of the first coating layer, the thickness of the second coating layer, the number n of protrusions on the surface of the second coating layer, the content x of the silicon-based material (the silicon-based material is a silicon-carbon particle) in the second coating layer, the sphericity of the silicon-carbon particle, and the median particle size Dv50 of the silicon-carbon particle are shown in Table 1. The weight loss rate s of the circular arc area of the positive electrode sheet is shown in Table 1.

[0090] Examples 2-24

[0091] Example 2-24 provides a battery, which is basically the same as the examples, and the differences are shown in Table 1.

[0092] Comparative Example 1

[0093] The present comparative example provides a battery, which is basically the same as the examples, and the difference is that the surface of the second coating layer does not contain protrusions.

[0094] The parameters of the examples and comparative examples are shown in Table 1.

[0095] Table 1: Parameters of Examples and Comparative Examples

[0096]

[0097]

[0098] Test Example

[0099] The present test example provides battery performance tests of each embodiment and comparative example, specifically including:

[0100] Whether lithium is precipitated: after the battery is charged, the battery is disassembled, and whether lithium is precipitated in the battery is observed. No lithium precipitation is determined to be no lithium precipitation. The severity of lithium precipitation is determined by the ratio of the lithium precipitation area in the lithium precipitation area to the total area of the negative electrode plate (the ratio is represented by M). When M≤5%, it is determined to be slight lithium precipitation; when 5%<M<10%, it is determined to be lithium precipitation; and when M≥10%, it is determined to be severe lithium precipitation.

[0101] Test method of battery cycle life: at 45°C constant room, 3C constant current and constant voltage to the upper limit voltage, 0.05C cut-off, 10min standing, and then 0.5C discharge to 3.0V, the expansion rate and capacity retention rate of the battery after 300 cycles are obtained, and the calculation formula is as follows:

[0102]

[0103] Test method of weight loss rate of positive circular arc punching: disassemble the battery, and test the mass before and after punching to calculate the weight loss rate according to the area of the punched area.

[0104] Test method of graphite OI value: based on X-ray diffraction (XRD) technology. Specifically including: disassemble the battery to obtain the negative electrode plate. The active material in the coating is made into a thin film sample or a powder sample, and the sample is scanned using an XRD diffractometer to obtain the X-ray diffraction pattern of the graphite material. The OI value is obtained by the ratio of the peak intensity of the (004) crystal plane to the peak intensity of the (110) crystal plane.

[0105] Height and number of protrusions: take the negative electrode plate with an area of 0.1mmx0.1mm at the circular arc, and observe the surface of the plate using a laser side thickness microscope to observe the number of protrusions with a height≥3μm, and obtain the number of protrusions. Among them, the protruding part higher than the surrounding area by 3μm is defined as a protrusion, that is, the height t of the protrusion≥3μm.

[0106] Test method of median particle size Dv50: after the battery is discharged, it is disassembled, and the negative electrode plate is taken out. After the residual electrolyte of the negative electrode plate is washed with a solvent, it is placed in deionized water for ultrasonic treatment for 10s. After the negative electrode plate is taken out, the powder is shaken off and dried. It is placed in a muffle furnace and calcined at 500°C for 2h. The particle size of the calcined powder is measured to obtain Dv50.

[0107] The test method of the content x of the silicon-based material in the second coating active material: scrape the powder on the negative electrode sheet, weigh and record as a, place the powder in a muffle furnace, calcine at 800℃ for 10h, weigh after calcination and record as b, calculate the ash content c by the following formula, then calculate the mass content d of the silicon element in the negative electrode active material by the following formula, and calculate the mass content x of the silicon-based material in the second coating active material by the following formula:

[0108]

[0109]

[0110] The thicknesses of the first coating and the second coating are tested by the cross-section SEM image of the negative electrode sheet of the battery.

[0111] Table 2: Test results of each example

[0112]

[0113]

[0114] From the above results, the coating of the negative electrode sheet of the application adopts a double-layer design, and a protrusion is provided on the surface of the second coating, the protrusion comprising a silicon-based material, which can reduce the stress in the circular arc area, make the stress more evenly distributed in the circular arc area, reduce the shell stress during the expansion or contraction process, facilitate the infiltration of electrolyte, improve the lithium precipitation problem in the circular arc area, relieve the expansion, and help to improve the cycle performance of the battery.

[0115] Obviously, the above examples are merely examples for clarity and do not limit the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. It is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the scope of protection of the application.

Claims

1. An electric cell, characterized by, The battery cell comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, and is formed by winding; the negative electrode sheet comprises a negative electrode current collector, a first coating layer and a second coating layer; the second coating layer is arranged on at least one surface of the negative electrode current collector, and the first coating layer is arranged between the negative electrode current collector and the second coating layer; the first coating layer comprises a graphite material; the second coating layer comprises a silicon-based material; the negative electrode sheet comprises a first flat area and a first arc area located at both ends of the first flat area, and the surface of the second coating layer located at the first arc area is provided with a protrusion, and the protrusion comprises a silicon-based material; The mass content of the silicon-based material is x, and x satisfies 25wt%≤x≤100wt% based on the total mass of the second coating layer; The number of protrusions within an area of 0.1mm×0.1mm on the surface of the second coating layer located at the first arc area is n, and n satisfies 8≤n≤15; The silicon-based material comprises silicon-carbon particles, and the average sphericity of the silicon-carbon particles is 0.5-1; The graphite OI value in the first coating layer located at the first arc area is 4-14.

2. The electric cell of claim 1, wherein, n and x satisfy relationship formula 1: Relationship 1.

3. The electric cell of claim 1, wherein, The height of the protrusion is not less than 3μm.

4. The electric cell of claim 1, wherein, The first coating layer comprises first graphite particles and second graphite particles.

5. The electric cell of claim 4, wherein, The median particle size Dv50 of the second graphite particles is greater than the median particle size Dv50 of the first graphite particles.

6. The electric cell of claim 5, wherein, The median particle size Dv50 of the first graphite particles is 5μm-10μm, and the median particle size Dv50 of the second graphite particles is 11μm-16μm.

7. The electric cell of claim 1, wherein, The second coating layer further comprises a graphite material.

8. The electric cell of claim 1, wherein, The graphite OI value in the first coating layer located at the first arc area is less than the graphite OI value in the first coating layer located at the first flat area; and / or, The graphite OI value in the first coating layer located at the first flat area is 12-24.

9. The electric cell of claim 1, wherein, The positive electrode sheet comprises a second flat area and a second arc area located at both ends of the second flat area, and the positive electrode sheet located at the second arc area is provided with a groove.

10. The electric cell of claim 9, wherein, The weight loss rate of the positive electrode sheet located at the second arc area is s, and s satisfies 1%≤s≤10%; The mass content of the silicon-based material is x, and x satisfies 25wt%≤x≤100wt% based on the total mass of the second coating layer; s and x satisfy relationship formula 2: Relationship 2.

11. The cell of claim 9 or 10, wherein, The number of grooves within an area of 0.1mm×0.1mm on the positive electrode sheet located at the second arc area is not less than 5; and / or, The depth of the groove is 3-30μm; and / or, s and x satisfy relationship formula 3: Relationship 3.

12. An electrical device, characterized by The battery cell comprises a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, and is formed by winding; the negative electrode sheet comprises a negative electrode current collector, a first coating layer and a second coating layer; the second coating layer is arranged on at least one surface of the negative electrode current collector, and the first coating layer is arranged between the negative electrode current collector and the second coating layer; the first coating layer comprises a graphite material; the second coating layer comprises a silicon-based material; the negative electrode sheet comprises a first flat area and a first arc area located at both ends of the first flat area, and the surface of the second coating layer located at the first arc area is provided with a protrusion, and the protrusion comprises a silicon-based material;

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