A battery

Abstract

This invention provides a battery comprising: a negative electrode sheet including a negative electrode current collector and a negative electrode active layer located on at least one surface of the negative electrode current collector, the negative electrode active layer including a second coating and a first coating located between the negative electrode current collector and the second coating, the first coating including silicon-carbon and the second coating including graphite; a separator including a base film and a ceramic layer located on at least one surface of the base film, the ceramic layer including a ceramic material; wherein the average particle size D3 of the graphite in the second coating and the average particle size D of the ceramic material are... 31 Satisfying 3≤D3 / D 31 ≤350; the thickness H of the ceramic layer 31 Satisfying 0.5μm≤H 31 ≤6μm. This invention can alleviate the expansion of the negative electrode, reduce the risk of electrode breakage, and simultaneously improve the energy density and cycle stability of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical devices, in particular to a battery. BACKGROUND

[0002] A battery is a common electrochemical device and is widely used. The energy density (i.e. the energy that can be stored per unit volume or per unit mass) of a battery is a key performance indicator. In the prior art, a scheme for improving the energy density of a battery includes using a silicon-doped negative electrode material in a negative electrode sheet, which can effectively improve the energy density of the battery. However, during the charging and discharging process of the battery, the silicon-doped negative electrode sheet using the silicon-doped negative electrode material is prone to serious swelling, which causes the negative electrode sheet to have a large extension and is likely to cause the negative electrode sheet to break, resulting in failure of the battery. Therefore, how to improve the energy density (capacity) of the battery while avoiding the breakage of the electrode sheet and reducing the swelling rate of the battery is a technical problem that needs to be solved in the field. SUMMARY

[0003] The present application provides a battery that can alleviate the swelling of the negative electrode sheet, reduce the risk of breakage of the electrode sheet, and reduce the swelling rate of the battery and improve the capacity of the battery, thereby effectively overcoming the defects in the prior art.

[0004] The present application provides a battery, comprising: a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a second coating layer and a first coating layer located between the negative electrode current collector and the second coating layer, the first coating layer comprising a first active material, the first active material comprising a silicon-carbon material, and the second coating layer comprising a second active material, the second active material comprising a second graphite; a separator, comprising a base film and a ceramic layer located on at least one side surface of the base film, the ceramic layer comprising a ceramic material; the average particle size D3 of the second graphite in the second coating layer, the average particle size D 31 satisfies 3≤D3 / D 31 ≤350, and the thickness H 31 of the ceramic layer satisfies 0.5μm≤H 31 ≤6μm.

[0005] According to an embodiment of the present application, 4≤D3 / D 31 ≤70; and / or, 5μm≤D3≤22μm; and / or, 50nm≤D 31≤2 μm; and / or, the first active material further comprises a first graphite; preferably, an average particle size D2 of the first graphite in the first coating is greater than an average particle size D3 of the second graphite in the second coating, preferably 0.3≤D3 / D2≤1; preferably, a maximum particle size D1 of the silicon-carbon material in the first coating and the average particle size D2 of the first graphite in the first coating satisfy 0.5≤D1 / D2≤1.5; preferably, 5 μm≤D1≤20 μm.

[0006] According to an embodiment of the present application, the battery further comprises an electrolyte, the electrolyte comprising a sulfonate; preferably, a mass percentage content e of the sulfonate in the electrolyte and a tensile strength S1 of the negative current collector satisfy S1 / e≥550, preferably 550≤S1 / e≤60000, a unit of S1 being in MPa; preferably, the tensile strength S1 of the negative current collector is ≥400 MPa; preferably, the mass percentage content e of the sulfonate in the electrolyte is 0.1%~20%; preferably, the sulfonate comprises 1,3-propane sultone and / or 1,3-propene sultone.

[0007] According to an embodiment of the present application, a thickness H 10 of the negative current collector, a tensile strength S1 of the negative current collector, and a mass ratio X of the silicon-carbon material to graphite in the negative active layer satisfy H 10 ×S1 / X≥1600, preferably 1600≤(H 10 ×S1) / X≤660000, a unit of S1 being in MPa, a unit of H 10 being in μm; preferably, 3 μm≤H 10 ≤12 μm; preferably 1%≤X≤50%.

[0008] According to an embodiment of the present application, the ceramic layer is located on a side surface of the base film facing the negative sheet; and / or, the battery further comprises a positive sheet, the separator is located between the positive sheet and the negative sheet; an adhesive force between the separator and the positive sheet is greater than an adhesive force between the separator and the negative sheet.

[0009] According to an embodiment of the present application, the battery further comprises a positive sheet, the positive sheet comprising a positive active material, the positive active material containing yttrium element; preferably, the first coating further comprises graphite, 400≤y / X≤200000, y being a content of yttrium in the positive active layer, a unit of y being in ppm, X being a mass ratio of the silicon-carbon material to graphite in the negative active layer; preferably, 100 ppm≤y≤2000 ppm.

[0010] According to an embodiment of the present application, the battery further comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, and a positive electrode active layer located on at least one side surface of the positive electrode current collector;H 20 X S2 / X≥600, preferably 600≤(H 20 X S2) / X≤300000,H 20 H is the thickness of the positive electrode current collector, in units of μm, S2 is the tensile strength of the positive electrode current collector, in units of MPa, and X is the mass ratio of the silicon-carbon material to graphite in the negative electrode active layer; preferably, 5 μm≤H 20 ≤20 μm; preferably, 50 MPa≤S2≤300 MPa.

[0011] According to an embodiment of the present application, the first coating further comprises first graphite; and / or, the mass ratio X of the silicon-carbon to graphite in the negative electrode active layer and the mass percentage a of silicon element in the silicon-carbon material satisfy 0.35%≤a×X≤35%; and / or, the mass percentage a of silicon element in the silicon-carbon material is 35% to 70%; and / or, the content of silicon element in the silicon-carbon material decreases from the center of the silicon-carbon particle to the edge of the silicon-carbon particle; and / or, the mass ratio of the silicon-carbon to graphite in the negative electrode active layer is 1% to 50%, preferably 4% to 30%.

[0012] According to an embodiment of the present application, the surface of the second coating is provided with recesses; preferably, the width of the recesses is 50 μm to 160 μm; preferably, the depth of the recesses is 3 μm to 40 μm; preferably, the interval of the recesses is 0.3 to 3 mm.

[0013] According to an embodiment of the present application, the negative electrode sheet comprises a negative electrode tab; the negative electrode active layer comprises a main body area, a first recessed area, and a second recessed area between the main body area and the first recessed area, and the negative electrode tab is located in the first recessed area; the battery further comprises a tab adhesive paper, the tab adhesive paper comprising a first connecting portion located on the side of the negative electrode tab away from the negative electrode current collector, and a second connecting portion located on the side of the first recessed area away from the negative electrode current collector, and the side surface of the second connecting portion away from the negative electrode current collector does not exceed the side surface of the main body area away from the negative electrode current collector.

[0014] The battery provided by this invention incorporates silicon-carbon material into the first coating near the negative electrode current collector (i.e., the lower layer near the negative electrode current collector in the double coating of the negative electrode sheet). Utilizing the shallow charge-discharge effect of silicon particles, side reactions on the surface of the silicon-carbon particles are reduced, and the expansion of the silicon-carbon particles is decreased. This improves energy density while mitigating the significant elongation (or expansion) of the negative electrode sheet (silicon-doped negative electrode) caused by silicon-carbon particle expansion, thus improving the electrode breakage problem. Simultaneously, a ceramic separator is used, and the average particle size D3 of graphite in the second coating and the thickness H of the ceramic layer are synergistically controlled. 31 The average particle size D of ceramic materials 31 Make it satisfy 3≤D3 / D 31 ≤350, 0.5μm≤H 31 With a thickness of ≤6μm, the positive electrode coating (paste) can be bound by the separator, reducing the risk of electrode breakage. This approach can improve the battery's energy density (capacity) and cycle stability, while also reducing the battery expansion rate and preventing battery failure caused by electrode breakage. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the projection structure of the first coating on the first current collector according to an embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of the projection structure of the first coating on the first current collector according to another embodiment of the present invention;

[0017] Figure 3 This is a schematic cross-sectional view of the first electrode sheet according to an embodiment of the present invention;

[0018] Figure 4 Electron micrographs of silicon-carbon materials used in some embodiments in backscattered electron mode (BSE mode);

[0019] Figure 5 This is a schematic diagram of a negative electrode sheet structure with tab adhesive paper on the surface of the negative electrode tab in one embodiment of the present invention;

[0020] Figure 6 This is a schematic diagram of the stacked structure of the negative electrode, separator, and positive electrode according to an embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1; negative electrode sheet; 11; negative electrode current collector; 12; negative electrode active coating; 121; first coating; 122; second coating; 123; first recessed area; 124; second recessed area; 125; third recessed area; 126; fourth recessed area; 127; main body area; 101; first side; 102; second side; 13; recess; 130; recess group; 14; negative electrode tab; 2; tab adhesive paper; 21; first connecting part; 22; second connecting part; 3; separator; 31; ceramic layer; 32; base film; 4; positive electrode sheet; 41; positive electrode current collector; 42; : Positive electrode active layer; W1: Width of the first recessed region and the width of the third recessed region; W2: Width of the tab adhesive paper; W3: Width of the groove; L: Width of the recess; △L: Spacing between two adjacent recesses; h: Depth of the recess; △L1: Distance between the recess closest to the outer edge of the first side of the second coating and the outer edge of the first side of the second coating; △L2: Distance between the recess closest to the outer edge of the second side of the second coating and the outer edge of the second side of the second coating; w: Distance between the recesses in two adjacent recess groups in the second direction c; b: First direction; c: Second direction; d: Third direction. Detailed Implementation

[0022] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention provides a battery, such as... Figures 1 to 6 As shown, the battery includes: a negative electrode 1, including a negative electrode current collector 11, and a negative electrode active layer 12 located on at least one side surface of the negative electrode current collector 11. The negative electrode active layer 12 includes a second coating layer 122 and a first coating layer 121 located between the negative electrode current collector 11 and the second coating layer 122. The first coating layer 121 includes a first active material, which includes a silicon-carbon material. The second coating layer 122 includes a second active material, which includes a second graphite. A separator 3 includes a base film 32 and a ceramic layer 31 located on the side of the base film 32 facing the negative electrode 1. The ceramic layer 31 includes a ceramic material. The average particle size D3 of the second graphite in the second coating layer 122 and the average particle size D of the ceramic material are also specified. 31 Satisfy: 3≤D³ / D 31 ≤350, thickness H of ceramic layer 31 31 Satisfying 0.5μm≤H 31 ≤6μm.

[0024] According to the inventor's research and analysis, the lithium intercalation potential of silicon-carbon materials is higher than that of graphite. During charging, graphite particles preferentially complete lithium intercalation, followed by silicon-carbon material particles, achieving the effect of shallow charging and discharging of silicon-carbon material particles. In this embodiment of the invention, silicon-carbon material is added to the first coating 121 near the negative electrode current collector 11 (that is, the lower layer near the negative electrode current collector 11 in the double coating of the negative electrode sheet 1), and the average particle size D3 of graphite and the thickness H of ceramic layer 31 in the second coating 122 are synergistically controlled. 31 The average particle size D of ceramic materials 31 Make it satisfy 3≤D3 / D 31 ≤350, 0.5μm≤H 31 With a particle size ≤6μm, this battery system allows silicon-carbon particles (i.e., silicon-carbon materials) to exhibit shallow charge and discharge characteristics, reducing side reactions on the surface of silicon-carbon particles and minimizing particle expansion. This, in turn, improves energy density while mitigating the significant elongation (or expansion) of the negative electrode (silicon-doped negative electrode) 1 caused by silicon-carbon particle expansion, preventing electrode breakage and battery failure. Simultaneously, a ceramic separator 3 (i.e., at least one side of the base film 32 of the separator 3 has a ceramic layer 31) is used, and the average particle size D3 of the graphite in the second coating 122 and the average particle size D of the ceramic material in the ceramic layer 31 are synergistically controlled. 31 and the thickness H of the ceramic layer 31 31 Meeting the above requirements can reduce the risk of electrode breakage by restricting the extension of the electrode coating through the separator 3, and reduce the battery expansion rate, while improving the battery capacity and cycle stability, and avoiding battery failure caused by electrode breakage.

[0025] If the ceramic layer 31 in the diaphragm 3 is too thin (H) 31 <0.5μm), then compared with the average particle size D3 of graphite in the second coating 122 and the average particle size D of ceramic material in the ceramic layer 31. 31 Poor adaptability hinders the effective function of the diaphragm in confining the electrode coating's extension. Furthermore, if the ceramic layer 31 is too thick (H... 31 If the diameter is greater than 6μm, it will occupy more space and affect the energy density of the battery. Therefore, by co-controlling 3≤D3 / D 31 ≤350, 0.5μm≤H 31 With a thickness of ≤6μm, the risk of electrode short circuits can be reduced, and the battery expansion rate can be decreased, while also improving battery capacity and cycle stability.

[0026] For example, the thickness H of the ceramic layer 31 31It can be a range of 0.5μm, 1μm, 1.5μm, 1.8μm, 2μm, 2.2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm or any two of them.

[0027] For example, D3 / D 31 It can be a range consisting of 3, 4, 7, 10, 25, 55, 65, 70, 90, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 335, 350, or any two of them.

[0028] In some embodiments, 4≤D3 / D 31 ≤70 helps to further reduce the risk of electrode breakage and suppress battery expansion rate, while maintaining a high battery capacity.

[0029] In some embodiments, 5μm ≤ D3 ≤ 22μm, where D3 is, for example, a range of 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, 20μm, 22μm, or any two of these. In the aforementioned anode system with a double-layer coating, the ratio 3 ≤ D3 / D is controlled to... 31 ≤350, 0.5μm≤H 31 Based on ≤6μm, by further controlling 5μm≤D3≤22μm, it is more conducive to the capacity of the second coating 122, thereby improving the battery capacity. At the same time, it works in conjunction with the first coating 121 and the separator 3 to reduce the risk of electrode breakage and lower the battery expansion rate.

[0030] In some embodiments, 50nm≤D 31 ≤2μm, D 31 For example, within the range of 50nm, 100nm, 150nm, 180nm, 190nm, 200nm, 210nm, 220nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 1.3μm, 1.5μm, 1.8μm, 2μm, or any combination thereof, under the aforementioned negative electrode system with a double-layer coating, while controlling 3≤D3 / D... 31 ≤350, 0.5μm≤H 31 Based on ≤6μm, further control of 50nm≤D 31 With a thickness of ≤2μm, it is beneficial to further ensure the function of the ceramic layer 31, and to assist in binding the electrode extension through the separator 3, thereby reducing the risk of electrode breakage, while maintaining a high energy density of the battery and improving the battery's capacity and other performance.

[0031] In some specific embodiments, the average particle size D of the ceramic material31 The ceramic layer 31 can have an average particle size D

[0032] Specifically, the ceramic material in the ceramic layer 31 can include one or more of alumina, boehmite, magnesium oxide, magnesium hydroxide, titanium oxide, barium sulfate, and calcium sulfate.

[0033] According to the research of the inventors, the present application mainly achieves the effects of reducing the risk of electrode fracture, inhibiting battery swelling, improving battery capacity and cycle stability, etc. by controlling the average particle size D 31 of the ceramic layer 31 to be matched with the particle size D3 of the second graphite, satisfying 3≤D3 / D 31 ≤350, and cooperatively matching 0.5μm≤H 31 ≤6μm. The above-mentioned ceramic materials can all be suitable for achieving the effects in the ceramic layer 31. Further controlling 50nm≤D 31 ≤2μm is conducive to further ensuring the function of the ceramic layer 31, assisting in restraining the electrode extension through the separator 3, reducing the risk of electrode fracture, and at the same time, maintaining a relatively high energy density of the battery and improving the capacity of the battery.

[0034] In addition, the ceramic layer 31 also includes a binder, which is used to bond the ceramic material particles and can improve the adhesion between the ceramic layer 31 and the film layer such as the base film 32. The binder in the ceramic layer 31 can include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polymethyl methacrylate (PMMA).

[0035] In some embodiments, the mass percentage content of the ceramic material in the ceramic layer 31 (i.e., the ratio of the mass of the ceramic material to the total mass of the ceramic layer 31) can be 50% to 99.8%, such as 50%, 60%, 70%, 80%, 83%, 85%, 88%, 90%, 93%, 95%, 97%, 99.5%, 99.8%, or a range consisting of any two of them.

[0036] Specifically, the negative active layer 12 includes a negative active material, the first coating layer 121 and the second coating layer 122 each includes a negative active material, the negative active material in the first coating layer 121 is referred to as a first active material, the negative active material in the second coating layer 122 is referred to as a second active material, the first active material in the first coating layer 121 includes a silicon-carbon material, and the second active material in the second coating layer 122 includes a second graphite (the graphite in the second coating layer 122 is referred to as a second graphite), wherein the second coating layer 122 can not include a silicon-based material such as silicon-carbon, that is, the content of the silicon-based material such as silicon-carbon in the second coating layer 122 is substantially 0.

[0037] In addition, the first active material in the first coating layer 121 further includes a first graphite (the graphite in the second coating layer 122 is referred to as a second graphite), which is beneficial to further reduce the expansion rate of the battery and improve the cycle life and other performances of the battery.

[0038] In some embodiments, the average particle size (Dv50) D2 of the first graphite in the first coating layer 121 is greater than the average particle size (Dv50) D3 of the second graphite in the second coating layer 122, and preferably 0.3 < D3 / D2 < 1, for example, D3 / D2 can be 0.31, 0.35, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range formed by any two of them, in this way, the first graphite in the first coating layer 121 has a relatively larger particle size, and in the above-mentioned negative electrode system with a double-layer coating, by further synergistically regulating the average particle size D3 of the second graphite in the second coating layer 122 and the average particle size D2 of the first graphite in the first coating layer 121 to satisfy the above-mentioned relationship, the first coating layer 121 and the second coating layer 122 are more suitable for each other, and the function of the negative active layer 12 is further taken into account, and the expansion problem of the negative active layer 12 is reduced, thereby further reducing the cycle expansion rate of the battery while maintaining a high capacity of the battery, and reducing the risk of electrode fracture.

[0039] In some embodiments, the average maximum particle size D1 of the silicon-carbon material in the first coating layer 121 and the average particle size (Dv50) D2 of the first graphite in the first coating layer 121 satisfy 0.5 ≤ D1 / D2 ≤ 1.5, for example, D1 / D2 can be 0.5, 0.6, 0.7, 0.9, 1.0, 1.1, 1.3, 1.4, 1.5 or a range formed by any two of them, and in the above-mentioned negative electrode system with a double-layer coating, by further synergistically regulating the average maximum particle size D1 of the silicon-carbon material in the first coating layer 121 and the average particle size D2 of the first graphite in the first coating layer 121 to satisfy the above-mentioned relationship, the silicon-carbon material is introduced into the first coating layer 121 to improve the energy density of the negative electrode sheet 1 while further inhibiting the expansion of the negative electrode sheet 1, reducing the cycle expansion rate of the battery, and reducing the risk of electrode fracture.

[0040] In some embodiments, 5 pm≤D1≤20 pm, D1 is for example 5 pm, 8 pm, 10 pm, 13 pm, 15 pm, 18 pm, 20 pm, or a range between any two of them.

[0041] The average maximum particle size D1 of the silicon-carbon material in the first coating layer 121 can be tested by the following process: cutting the negative electrode sheet 1 using argon ions to obtain a cross-sectional morphology, measuring the maximum size of the silicon-carbon particles seen in 3-5 cross-sections under 1K times, taking the average value to obtain the average maximum particle size D1 of the silicon-carbon material (i.e. the silicon-carbon particles).

[0042] In the embodiments of the present application, the average particle size of the material (such as the average particle size D2 of the first graphite, the average particle size D3 of the second graphite, the average particle size D 31 of the ceramic material, etc.) can be measured by conventional methods in the art, for example by a laser particle size analyzer or by electron microscopy such as scanning electron microscopy (SEM) and statistical analysis.

[0043] In particular, when testing the average particle size D2 of the first graphite in the first coating layer 121, the first coating layer 121 can be scraped off from the negative electrode sheet 1, the obtained first coating layer 121 material is dispersed in a solvent such as water, and is uniformly dispersed by ultrasonic treatment (specifically, ultrasonic treatment for at least 2 min) to remove the binder and other components on the surface of the particles in the first coating layer 121 material, and then the particle size Dv50 of the particles is tested by a laser particle size analyzer, which is the average particle size D2 of the first graphite in the first coating layer 121.

[0044] In addition, when testing the average particle size D3 of the second graphite in the second coating layer 122, the second coating layer 122 can be scraped off from the negative electrode sheet 1, the obtained second coating layer 122 material is dispersed in a solvent such as water, and is uniformly dispersed by ultrasonic treatment (specifically, ultrasonic treatment for at least 2 min) to remove the binder and other components on the surface of the particles in the second coating layer 122 material, and then the particle size Dv50 of the particles is tested by a laser particle size analyzer, which is the average particle size D3 of the second graphite in the second coating layer 122.

[0045] In addition, when testing the average particle size D 31 of the ceramic material in the ceramic layer 31 of the separator 3, the ceramic layer 31 of the separator 3 can be scanned by SEM to test the particle size (diameter) of the ceramic material therein and obtain the average value by statistical analysis, which is the average particle size D 31 of the ceramic material. 31

[0046] ​In the embodiment of the present application, the battery comprises a battery cell, a shell encapsulating the battery cell, and an electrolyte, the battery cell comprises a positive electrode sheet 4, a negative electrode sheet 1, and a diaphragm 3 between the positive electrode sheet 4 and the negative electrode sheet 1, and the electrolyte is injected into the shell to soak the battery cell.

[0047] Specifically, the electrolyte comprises a solvent, a solute, and an additive, and the electrolyte can be a non-aqueous electrolyte, wherein the solvent can comprise an organic solvent, and specifically can comprise a carbonate solvent, such as one or more of ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), propylene carbonate (PC), and propyl propionate (PP); the additive can comprise one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), and sulfonate; and the solute can comprise a lithium salt, and the lithium salt can comprise one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0048] Specifically, the sulfonate can comprise 1,3-propane sulfonate (PS) and / or 1,3-propylene sulfonate (PST), both of which can be used as a high-temperature film-forming additive to improve the high-temperature cycle performance of the battery, and are suitable for the above-mentioned negative electrode system with double-layer coating, further inhibit the swelling of the battery, and improve the capacity and cycle stability of the battery.

[0049] In some embodiments, the above-mentioned electrolyte comprises sulfonate (such as PS and / or PST), which is more suitable for the above-mentioned negative electrode sheet 1 with the first coating 121 and the second coating 122 and the ceramic diaphragm 3, further reduces the cycle swelling rate of the battery, improves the capacity of the battery, and reduces the risk of short circuit of the electrode sheet.

[0050] The inventors found in the research that the mass percentage content e of sulfonate in the electrolyte and the tensile strength S1 of the negative current collector 11 can satisfy S1 / e≥550, preferably 550≤S1 / e≤60000, the unit of S1 is MPa, by synergistically controlling the mass percentage content e of sulfonate in the electrolyte and the tensile strength S1 of the negative current collector 11 in the above range, the problems of deformation of the negative plate 1 and fracture of the positive plate 4 can be effectively avoided, the reason is that the high-temperature film-forming additive (sulfonate) has a certain corrosion effect on the negative current collector 11 (such as copper foil), which can greatly reduce the strength of the negative current collector 11 (such as copper foil) after formation, so that the corroded negative current collector 11 loses the binding force to the negative coating (pasted paste) due to insufficient strength, resulting in easy deformation of the negative plate 1, and the deformed negative plate 1 will cause extrusion to the positive plate 4, thereby causing the fracture of the positive plate 4, and in the above negative electrode system with double-layer coating, by further synergistically controlling the content e of sulfonate in the electrolyte and the tensile strength S1 of the negative current collector 11, so as to satisfy the above range, it is more conducive to avoiding the problems of deformation of the negative plate 1 and fracture of the positive plate 4, while taking into account the better high-temperature cycle performance of the battery.

[0051] Further, the tensile strength S1 of the above negative current collector 11 is ≥400 MPa, preferably for example S1 can be 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa, 1000 MPa or a range composed of any two of them, which is conducive to better reducing the risk of fracture of the negative plate 1 and the positive plate 4.

[0052] In some embodiments, 200Mpa≤S1≤700Mpa, further can be 400Mpa≤S1≤700Mpa.

[0053] Further, the mass percentage content e of sulfonate in the above electrolyte can be 0.1%~20%, for example 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 10%, 15%, 20% or a range composed of any two of them, which is conducive to better taking into account the better high-temperature cycle performance and avoiding the problems of fracture of the negative plate 1 and the positive plate 4.

[0054] In some embodiments, the thickness H of the negative current collector 11 10 , the tensile strength S1 of the negative current collector 11, and the mass ratio of the silicon-carbon material in the negative active layer 12 to the graphite in the negative active layer 12 (i.e. the silicon doping amount of the negative active layer 12) X satisfy (H 10 ×S1) / X≥1600, preferably 1600≤(H 10X*Si1) / X≤660000, the unit of Si1 is MPa, which can effectively avoid the problem of breaking of the negative sheet 1, and the reason is that: with the increase of the amount of silicon X, the expansion range of the negative coating during the charging and discharging process is larger, the ductility of the negative sheet 1 is larger, and the negative sheet 1 is more prone to breakage. By increasing the tensile strength Si1 (such as maximum tensile force) of the negative current collector 11 (such as copper foil), the above problem of easy breaking of the negative sheet 1 can be effectively avoided, and at the same time, the thickness of the negative current collector 11 (such as copper foil) can be increased to increase the maximum tensile force it can withstand, which is more conducive to avoiding the above problem of easy breaking of the negative sheet 1. Therefore, in the above negative electrode system with a double-layer coating, silicon-carbon material is introduced into the first coating 121, and 3≤D3 / D 31 ≤350, 0.5μm≤H 31 ≤6μm, on this basis, by synergistically regulating the thickness H 10 of the negative current collector 11, the tensile strength Si1 of the negative current collector 11, and the amount of silicon X to satisfy the above range, the problem of breaking of the negative sheet 1 can be further avoided.

[0055] For example, when the graphite in the negative active layer 12 exists in the first coating 121 and the second coating 122, or the negative active layer 12 is composed of the first coating 121 and the second coating 122, the amount of silicon X = the mass of the silicon-carbon material in the first coating 121 / (the mass of the first graphite in the first coating 121 + the mass of the second graphite in the second coating 122).

[0056] For example, (H 10 *Si1) / X can be 1600, 2000, 2500, 5000, 10000, 100000, 500000, 660000, or a range consisting of any two of them.

[0057] In some embodiments, 3μm≤H 10 ≤12μm, H 10 For example, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, or a range consisting of any two of them.

[0058] In the embodiments of the present application, the separator 3 is located between the positive sheet 4 and the negative sheet 1, and the separator 3 is adhered to the positive sheet 4 and the negative sheet 1 respectively (i.e. one side of the separator 3 is adhered to the positive sheet 4, and the other side is adhered to the negative sheet 1). In specific implementation, the positive sheet 4, the separator 3 and the negative sheet 1 can be placed in turn and then hot-pressed to integrate them.

[0059] Specifically, the battery cell can be a jelly-roll battery cell (a roll cell), i.e., the positive electrode sheet 4 and the negative electrode sheet 1 each have a jelly-roll structure. The positive electrode sheet 4 includes a plurality of first straight sections and a first bending section connected between adjacent two first straight sections, the number of the first bending section is usually at least one, and specifically can be multiple, the positive electrode sheet 4 is bent through the first bending section, thereby forming a jelly-roll structure; the negative electrode sheet 1 includes a plurality of second straight sections and a second bending section connected between adjacent two second straight sections, the number of the second bending section is usually at least one, and specifically can be multiple, the negative electrode sheet 1 is bent through the second bending section, thereby forming a jelly-roll structure.

[0060] In a specific implementation, the positive electrode sheet 4, the separator 3 and the negative electrode sheet 1 are sequentially placed, and then the formed laminated structure (as shown in Figure 6 ) is rolled, and then hot-pressed to integrate the positive electrode sheet 4, the separator 3 and the negative electrode sheet 1, thereby forming a jelly-roll battery cell.

[0061] In general, the surface of the separator 3 is provided with a glue coating layer, the glue coating layer is a surface layer of the separator 3 (for either side surface of the base film 32, when the ceramic layer 31 is provided, the glue coating layer is provided on the surface of the ceramic layer 31 (i.e., the ceramic layer 31 is located between the base film 32 and the glue coating layer), and when the ceramic layer 31 is not provided, the glue coating layer is provided on the surface of the base film 32), and the separator 3 is bonded to the positive and negative electrode sheets 1 through the glue coating layer on the surface thereof.

[0062] In the embodiment of the present application, as shown in Figure 6 , the ceramic layer 31 of the separator 3 can be located on the side of the base film 32 facing the negative electrode sheet 1, and no ceramic layer 31 is provided on the side of the base film 32 facing the positive electrode sheet 4, i.e., the separator 3 used is a single-side ceramic separator 3, and specifically can be a single-side ceramic double-side glue coating separator 3 (i.e., the opposite two sides of the separator 3 are each provided with a glue coating layer).

[0063] In the embodiment of the present application, the base film 32 can be a polypropylene (PP) separator 3, a polyethylene (PE) separator 3, a polypropylene / polyethylene (PP / PE) double-layer composite film, a polyimide electrostatic spinning separator 33 (PI), a polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite film, or a cellulose non-woven fabric separator 3, etc.

[0064] In some embodiments, the adhesion between the diaphragm 3 and the positive electrode sheet 4 is greater than the adhesion between the diaphragm 3 and the negative electrode sheet 1, which can effectively reduce the risk of fracture of the positive electrode sheet 4. The reason is that, during the expansion-shrinkage process of the battery during charging and discharging, the current collector (positive current collector or negative current collector 11) exerts a binding force on the positive electrode coating or negative electrode coating (coated paste), and the current collector will stretch and extend with the coated paste. Generally, the tensile strength of the diaphragm 3 > the strength of the negative current collector 11 (such as copper foil) > the strength of the positive current collector (such as aluminum foil). Therefore, during the expansion-shrinkage process of the battery during charging and discharging, the positive electrode sheet 4 is more likely to break. However, in the battery system of the embodiments of the present application, the negative active layer 12 of the negative electrode sheet 1 includes a first coating layer 121 and a second coating layer 122, and the particle size D3 of the second graphite in the second coating layer 122 of the negative electrode sheet 1 and the average particle size D of the ceramic material in the ceramic layer 31 of the diaphragm 3 are cooperatively controlled. 31 The thickness H of the ceramic layer 31 31 satisfies 3≤D3 / D 31 ≤350, 0.5μm≤H 31 ≤6μm. On this basis, by making the adhesion between the diaphragm 3 and the positive electrode sheet 4 greater than the adhesion between the diaphragm 3 and the negative electrode sheet 1, the diaphragm 3 assists in binding the positive electrode coating (coated paste) to extend, thereby reducing the risk of fracture of the positive electrode sheet 4. This is conducive to further improving the capacity and cycle stability of the battery, and avoiding problems such as battery failure caused by fracture of the electrode sheet.

[0065] The positive electrode sheet 4 further includes a positive current collector (such as an aluminum foil) 41 and a positive active layer (positive electrode coating) 42 located on at least one side surface of the positive current collector. The positive active layer 42 includes a positive active material, a conductive agent, and a binder. The positive active material can include conventional positive active materials in the art, such as positive lithium-containing active materials, for example, at least one of lithium cobaltate, lithium manganate, lithium nickelate, ternary material, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, and lithium-rich manganese-based material. The ternary material can include nickel cobalt lithium manganate and / or nickel cobalt lithium aluminate, etc. The chemical formula of lithium cobaltate is generally Li f Co g Al j M i O2, where 0.95≤f≤1.1 (for example, 0.95≤f≤1.05), 0.94≤g≤0.985, 0.01≤j≤0.04, 0.005≤i≤0.02, and M is a metal element other than aluminum, which can specifically include a transition metal element, such as one or more of Mg, Ti, Zr, Y, La, Mn, Ni, Fe, etc.

[0066] According to further research of the inventor, due to the high lithium intercalation potential of silicon-carbon, the negative electrode potential increases, and under the condition of a certain voltage, the positive electrode potential also increases, that is, under the same voltage system, a material with higher voltage stability needs to be used for the positive electrode. Therefore, in the embodiment of the present application, the negative active layer 12 of the negative electrode sheet 1 comprises a first coating layer 121 and a second coating layer 122, and the particle size D3 of the second graphite in the second coating layer 122 of the negative electrode sheet 1 and the thickness H of the ceramic layer 31 of the separator 3 are synergistically controlled 31 , the average particle size D of the ceramic material 31 satisfies 3≤D3 / D 31 ≤350, 0.5μm≤H 31 ≤6μm, and on this basis, by doping yttrium element (Y) in the positive active material, the positive active layer contains yttrium element (Y), and under the same voltage system, the yttrium element doping can stabilize the lattice structure of the core of the positive active material (such as lithium cobaltate, LCO), thereby improving the cycle stability of the positive active material (such as lithium cobaltate) at a higher voltage and a higher temperature, and also improving the rate performance of the battery.

[0067] In some embodiments, the first coating layer 121 also comprises first graphite, 400≤y / X≤200000, y is the yttrium doping amount in the positive active layer, the yttrium doping amount is the concentration of yttrium element in the standard solution measured according to the test method in GBT 30902-2014, the specific test process can be seen in the test method part of the specific embodiments below, the unit of y is ppm, and X is the silicon doping amount of the negative active layer 12. By synergistically controlling the yttrium doping amount in the positive active layer and the silicon doping amount X of the negative active layer 12 to satisfy the above relationship range, it is beneficial to better improve the energy density, cycle stability, rate performance and the like of the battery. For example, y / X can be 400, 600, 1000, 5000, 10000, 50000, 100000, 200000 or a range formed by any two of them.

[0068] In some embodiments, 100ppm≤y≤2000ppm, for example, y is 100ppm, 300ppm, 500ppm, 800ppm, 1000ppm, 1300ppm, 1500ppm, 1800ppm, 2000ppm or a range formed by any two of them.

[0069] The inventor found through research that during the charging and discharging process, the silicon-doped negative electrode will undergo a severe expansion-contraction process, forming a extrusion stress on the positive electrode sheet 4. In order to avoid the fracture of the positive electrode sheet 4, the thickness H 20 of the positive current collector, the tensile strength S2 of the positive current collector, and the silicon doping amount X of the negative active layer 12 satisfy (H 20 ×S2) / X≥600, preferably 600≤(H20 X S2) / X≤300000, which can effectively avoid the fracture of the positive electrode sheet, and improve the capacity and cycle life of the battery.

[0070] For example, (H 20 X S2) / X can be 600, 1000, 5000, 10000, 50000, 100000, 150000, 200000, 250000, 300000, or a range consisting of any two of them.

[0071] In some embodiments, 50Mpa≤S2≤300Mpa, S2 is, for example, 50MPa, 100MPa, 150MPa, 200MPa, 250MPa, 300MPa, or a range consisting of any two of them.

[0072] In some embodiments, 5μm≤H 20 ≤20μm, H 20 may be 5μm, 6μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, or a range consisting of any two of them.

[0073] In some embodiments, the silicon content X of the negative electrode active layer 12 and the mass percentage a of silicon in the silicon carbon satisfy 0.35%≤a×X≤35%, which helps to better reduce the risk of fracture of the negative electrode sheet 1 and the positive electrode sheet 4 while taking into account the higher energy density. For example, a×X can be 0.35%, 0.5%, 1%, 10%, 15%, 20%, 25%, 35%, or a range consisting of any two of them.

[0074] In some embodiments, the mass percentage a of silicon in the above-mentioned silicon carbon is 35% to 70%, for example, 35%, 40%, 50%, 60%, 70%, or a range consisting of any two of them. Relatively speaking, the low-silicon material has a lower silicon content, so the expansion rate of the low-silicon material is low, and more silicon carbon material can be added to the negative electrode sheet 1, which helps to improve the capacity and cycle performance of the negative electrode sheet 1.

[0075] In some embodiments, the content of silicon in the above-mentioned silicon carbon (silicon carbon material particles) decreases in the direction from the center of the silicon carbon to the edge of the silicon carbon, that is, the content of silicon in the central part of the silicon carbon particles is greater than the content of silicon in the surface part of the silicon carbon particles. By using this silicon carbon material, it is beneficial to improve the rate charging performance, while reducing the particle expansion, which helps to better reduce the risk of sheet fracture.

[0076] Specifically, Figure 4The electron microscope image of the silicon-carbon (low-silicon material particle) of an embodiment under a backscattered electron mode (BSE mode) shows that the main component of the black part is carbon and the main component of the white part is silicon, and that there are regions with different substrate (contrast) inside the silicon-carbon material (low-silicon material particle), and the silicon content is high at the edge (surface part) of the silicon-carbon particle and low at the middle (central part).

[0077] The silicon-carbon material described above can be obtained by a method conventional in the art, for example, commercially available or self-made by a method conventional in the art. For example, the silicon-carbon material described above, in which the content of silicon element decreases from the center of the silicon-carbon to the edge of the silicon-carbon, can include a core and a carbon coating layer existing on the surface of the core, the core including a porous carbon substrate and silicon elements dispersed in the porous carbon substrate, and the silicon elements can be particularly dispersed inside the pores of the porous carbon substrate.

[0078] In some embodiments, the amount of silicon doping X can be 1% to 50%, for example, 1%, 10%, 20%, 30%, 40%, 50%, or a range formed by any two of them, and preferably 4% to 30%.

[0079] As shown in Figures 1 to 3 , the surface of the second coating layer 122 of the negative electrode sheet 1 is provided with a recess 13, which is beneficial to further improve the electrochemical performance and safety performance of the battery. The reason is that when the surface of the second coating layer 122 is provided with the recess 13, it is beneficial to guide the electrolyte, so that the electrolyte can be more fully soaked into the battery cell, thereby improving the electrolyte storage capacity of the battery cell, improving the migration ability of active ions such as lithium ions, improving the electrical conductivity, and reducing the pressure drop and the risk of short circuit.

[0080] In some embodiments, the width L of the recess 13 is 50 μm to 160 μm, for example, 50 μm, 80 μm, 100 μm, 150 μm, 160 μm, or a range formed by any two of them.

[0081] Specifically, the surface of the second coating layer 122 can be provided with one recess 13 (i.e., the recess 13 is continuously arranged on the surface of the second coating layer 122), or, as shown in Figures 1 to 3 , the surface of the second coating layer 122 is provided with at least two recesses 13, which can be distributed along the first direction b (as shown in Figure 2 ), or along the second direction c, or part of the recesses 13 are distributed along the first direction b and part of the recesses 13 are distributed along the second direction c (as shown in Figure 1 ).

[0082] As shown in Figures 1 to 3As shown, at least some of the recesses 13 are distributed along the first direction b. Two adjacent recesses 13 in the first direction b are separated by the second coating 122. The distance between two adjacent recesses 13 in the first direction b (i.e., the distance between two adjacent recesses 13 in the first direction b) ΔL > 0.

[0083] Specifically, the surface of the second coating 122 may include at least one set of recesses 130, each set of recesses 130 including at least two recesses 13 distributed along the first direction b. When the number of recesses 130 is at least two (i.e. the surface of the second coating 122 includes at least two sets of recesses 130), these recesses 130 are distributed along the second direction c.

[0084] For example, such as Figure 1 As shown, the surface of the second coating 122 includes two sets of recesses 130, which are distributed along the second direction c. In each set of recesses 130, one edge of the recess 13 in the length direction is substantially flush with one edge of the second coating 122 in the width direction; or, as shown... Figure 2 As shown, the surface of the second coating 122 has a set of recesses 130, wherein the length of the recesses 13 in the second direction c is substantially equal to the width of the second coating 122.

[0085] In some embodiments, in two adjacent recess groups 130, the distance w between the recess 13 in one recess group 130 and the recess 13 in the other recess group 130 in the second direction c basically satisfies the following relationship: the width of the first coating = the length of the recess 13 in one recess group 130 in the second direction c + the length of the recess 13 in the other recess group 130 in the second direction c + w.

[0086] Among the two adjacent recess groups 130, the recess 13 in one recess group 130 and the recess 13 in the other recess group 130 that is closest to the recess 13 can be connected or not connected. When the two recesses 13 are connected, the gap (distance in the second direction c) w between the two recesses 13 is basically equal to 0.

[0087] Continue to refer to Figures 1 to 3 The spacing ΔL between two adjacent recesses 13 in the first direction b is greater than 0. The second coating 122 has a first side 101 and a second side 102 opposite to each other in the first direction b. The distance between the recess 13 closest to the outer edge of the first side 101 of the second coating 122 and the outer edge of the first side 101 of the second coating 122 is denoted as ΔL1, and the distance between the recess 13 closest to the outer edge of the second side 102 of the second coating 122 and the outer edge of the second side 102 of the second coating 122 is denoted as ΔL2, such that the recesses 13 are arranged at a spacing ΔL across the entire surface of the second coating 122.

[0088] The interval AL of two adjacent recesses 13 in the first direction b refers to the distance between the two adjacent recesses 13 in the first direction b, which is also the interval of the two adjacent recesses 13 in each recess group 130.

[0089] In some embodiments, the interval AL of two adjacent recesses 13 in the first direction b is 0.3-3 mm, for example 0.3 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, or a range formed by any two of them.

[0090] With reference to Figures 1 to 3 , the width direction of the recesses 13 is substantially parallel to the first direction b, and the length direction (extending direction) of the recesses 13 is substantially perpendicular to the first direction b.

[0091] Specifically, the recesses 13 can be in the shape of holes or grooves, and preferably the recesses 13 are linear grooves, i.e., the projection of the recesses 13 on the negative current collector 11 is in the shape of a strip (as shown in Figure 1 and Figure 2 , and specifically can be in the shape of a rectangle (as shown in Figure 2 or other regular or irregular shapes.

[0092] With reference to Figure 1 and Figure 2 , when the surface of the second coating layer 122 is provided with at least two recesses 13, each recess 13 is a linear groove, and the projection of each recess 13 on the negative current collector 11 is substantially in the shape of a rectangle. The length direction (extending direction) of the recesses 13 is substantially parallel to each other, and specifically can be parallel to the second direction c. The width direction of the recesses 13 is substantially parallel, and can be substantially parallel to the first direction b.

[0093] In the embodiments of the present application, the laser can be used to form recesses 13 with predetermined shapes and thicknesses, widths, lengths, and intervals on the surface of the negative active coating 12. For example, the recesses 13 (linear grooves) can be formed on the surface of the second coating layer 122 by laser scribing. The thickness and other parameters of the recesses 13 can be adjusted by adjusting the laser intensity and other parameters. These adjustment methods are conventional operations in the art and will not be described in detail.

[0094] Specifically, the first direction b and the second direction c intersect, and specifically can be perpendicular to each other. As shown in Figure 1 and Figure 2 , the second direction c, the length direction of the recesses 13, the width direction of the second coating layer 122, the width direction of the negative current collector 11, and the width direction of the negative plate 1 are substantially parallel to each other. The first direction b, the width direction of the recesses 13, the length direction of the second coating layer 122, the length direction of the negative current collector 11, and the length direction of the negative plate 1 are substantially parallel to each other.

[0095] In addition, as shown inFigure 3 As shown, the recess 13 extends from the surface of the second coating layer 122 to the interior of the second coating layer 122, and the depth direction of the recess 13 can be substantially parallel to the third direction d, the thickness direction of the second coating layer 122, the thickness direction of the negative current collector 11, the thickness direction of the negative sheet 1, and the thickness direction of the separator 3 are parallel to each other.

[0096] Generally, as shown, Figure 3 As shown, the depth h of the recess 13 is less than the thickness of the second coating layer 122, that is, the recess 13 does not penetrate the second coating layer 122 in the thickness direction of the second coating layer 122, that is, the second coating layer 122 exists between the recess 13 and the negative current collector 11.

[0097] In some embodiments, the depth h of the recess 13 is 3-40 μm, for example, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, or a range consisting of any two of them.

[0098] In addition, the negative sheet 1 also includes a negative tab 14, and the battery also includes a tab gum paper 2 connected to the negative tab, which can be embedded on the negative sheet 1, which is beneficial to reduce the thickness of the negative sheet 1 and further improve the energy density and other properties of the battery. Specifically, the negative active layer 12 on at least one side surface of the negative current collector 11 is provided with a slot, the negative tab 14 is arranged at the slot, and the tab gum paper 2 is arranged on the side of the negative tab 14 away from the negative current collector 11 and embedded in the slot.

[0099] In some specific embodiments, as shown, Figure 5 As shown, in the negative active layer 12 on one side (hereinafter referred to as the third side) of the negative current collector 11, the slot includes a main body area 127, a first recess area (tab slot) 123, and a second recess area 124 between the main body area 127 and the first recess area 123, and the negative tab 14 is arranged in the first recess area 123; the tab gum paper 2 includes a first connecting part 21 on the side of the negative tab 14 away from the negative current collector 11, and a second connecting part 22 on the side of the first recess area 123 away from the negative current collector 11, and the side surface of the second connecting part 22 away from the negative current collector 11 does not exceed the side surface of the main body area 127 away from the negative current collector 11.

[0100] Specifically, the first recess area 123 substantially does not exist negative active layer 12, that is, the first recess area 123 exposes the surface of the negative current collector 11, and the negative tab 14 can be welded on the negative current collector exposed by the first recess area 123. The second recess area 124 exists negative active layer 12, and the depth of the second recess area 124 is less than the depth of the first recess area 123.

[0101] In addition, the width W2 of the tab adhesive paper 2 is greater than the width W1 of the first recessed area 123, the width of the groove is greater than the width of the tab adhesive paper 2 (the width of the groove is basically equal to the sum of the width W1 of the first recessed area 123 and the width of the second recessed area 124), the depth of the second recessed area 124 is greater than or equal to the thickness of the tab adhesive paper, and the depth of the deepest part of the groove (which is also the depth of the first recessed area 123) is less than the thickness of the negative electrode active layer 12.

[0102] In some embodiments, the width W1 of the first recessed area 123 can be 6 to 15 mm, the width W2 of the tab adhesive paper 2 can be 7 to 20 mm, the width W3 of the groove can be 8 to 25 mm, and the depth of the groove can be greater than or equal to 5 μm, for example, about 20 μm, so as to satisfy the tab adhesive paper being embedded in the groove.

[0103] In addition, such as Figure 5 As shown, in the negative electrode active layer 12 on the other side (hereinafter referred to as the fourth side) of the negative electrode current collector 11, there are also grooves corresponding to the grooves on the third side surface. That is, the projections of the grooves on the fourth side surface and the grooves on the third side surface onto the negative electrode current collector 11 at least partially overlap, and generally basically completely overlap. The grooves on the fourth side surface include a third recessed area 125 corresponding to the first recessed area 123 and a fourth recessed area 126 corresponding to the second recessed area 124.

[0104] In this embodiment of the invention, the battery can be a lithium-ion battery.

[0105] In this embodiment of the invention, any negative electrode coating (such as the first coating 121 or the second coating 122) may further include a conductive agent and a binder.

[0106] Specifically, the binder in the positive electrode active layer and the negative electrode coating (such as the first coating 121 or the second coating 122) can be a conventional adhesive material in the art, such as one or more of polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile (PAN), polyacrylate, polyacrylic acid (PAA), polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene and styrene-butadiene rubber (SBR), and the polyacrylate may include lithium polyacrylate and / or sodium polyacrylate, etc.

[0107] In this embodiment of the invention, the conductive agent in the positive electrode active layer and the negative electrode coating can be a conventional binder material in the art, such as one or more of carbon nanotubes (carbon nanotubes), carbon black (SP), acetylene black, graphene, and conductive graphite.

[0108] In addition, the negative electrode coating can further include a thickening agent, which can include a carboxymethyl cellulose (CMC)-based thickening agent, such as including carboxymethyl cellulose and / or a carboxymethyl cellulose salt, such as including carboxymethyl cellulose lithium (CMC-Li) and / or carboxymethyl cellulose sodium (CMC-Na), etc.

[0109] Generally, for any negative electrode coating (e.g., the first coating 121 or the second coating 122), the mass fraction of the negative active material can be 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 95%, 99%, or a range between any two of them, the mass fraction of the conductive agent can be 0.3% to 12%, such as 0.3%, 0.5%, 1%, 3%, 5%, 8%, 10%, 12%, or a range between any two of them, the mass fraction of the binder can be 0% to 15%, such as 0, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 9%, 10%, 12%, 15%, or a range between any two of them, and the mass fraction of the thickening agent can be 0.05% to 3%, such as 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or a range between any two of them, but not limited thereto, based on the total mass of the negative electrode coating (negative active material layer).

[0110] In addition, the mass fraction of the positive active material can be 70% to 99%, such as 70%, 75%, 80%, 85%, 90%, 95%, 99%, or a range between any two of them, the mass fraction of the conductive agent can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 9%, 10%, 12%, 15%, or a range between any two of them, and the mass fraction of the binder can be 0.5% to 15%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 7%, 9%, 10%, 12%, 15%, or a range between any two of them, but not limited thereto, based on the total mass of the positive electrode active layer (positive active material layer).

[0111] In the embodiment of the present application, the positive electrode sheet 4 can be prepared by a conventional method in the art such as coating method. For example, the preparation process of the positive electrode sheet 4 can include: placing positive electrode active material, conductive agent, and binder and other materials in a solvent to prepare a positive electrode slurry, the solvent used can include, for example, N-methyl pyrrolidone (NMP), then coating the positive electrode slurry on at least one surface of the positive electrode current collector, and after drying, rolling and other processes, forming a positive electrode active material layer on at least one surface of the positive electrode current collector to prepare the positive electrode sheet 4; wherein during the coating process, a groove (slot position) exposing the surface of the positive electrode current collector is reserved at a predetermined position of the positive electrode current collector, and after the positive electrode active material layer is formed by coating, drying, rolling and other processes, the positive electrode tab is welded at the slot position by laser or ultrasonic welding (the positive electrode tab is welded with the positive electrode current collector).

[0112] In the embodiment of the present application, the negative electrode coating layer can be formed on the surface of the negative electrode current collector by a conventional method in the art such as coating method, and then the negative electrode coating layer surface is wired by laser to prepare the negative electrode sheet 1. For example, the process of the negative electrode sheet 1 can include: placing negative electrode active material, conductive agent, and binder and other materials in a solvent to prepare a negative electrode slurry, the solvent used can include, for example, water (such as deionized water), then coating the negative electrode slurry on the surface of the negative electrode current collector, and after drying, rolling and other processes, forming a negative electrode active layer on the surface of the negative electrode current collector; then, a recess 13 is formed in a predetermined area on the surface of the negative electrode active material layer by laser drilling to prepare the negative electrode sheet 1; wherein during the coating process, a groove (slot position) exposing the surface of the negative electrode current collector is reserved at a predetermined position of the negative electrode current collector, and after the negative electrode active material layer is formed by coating, drying, rolling and other processes, and the recess 13 is formed on the surface of the negative electrode active material layer by laser wiring and other methods, the negative electrode tab is welded at the slot position by laser or ultrasonic welding (the negative electrode tab is welded with the positive electrode current collector) to prepare the negative electrode sheet 1.

[0113] In the embodiment of the present application, a conventional laser drilling machine in the art is used for laser wiring.

[0114] In the embodiment of the present application, the battery can be prepared according to a conventional method in the art. For example, after the positive electrode sheet 4 and the negative electrode sheet 1 are cut and sheeted, the positive electrode sheet 4, the separator 3, and the negative electrode sheet 1 are sequentially stacked and hot-pressed into one, and then wound to form a winding core, wherein the ceramic layer of the separator 3 faces the negative electrode sheet 1 during winding, and then a shell is packaged, and after processes such as liquid injection (injecting electrolyte into the shell), formation, capacity, two-sealing, sorting, and OCV (testing open circuit voltage), the battery is prepared. These steps / processes are all conventional operations in the art, and the present application does not make special limitations on them, and they will not be described in detail.

[0115] The present application will be further described through specific examples.

[0116] Example 1

[0117] 1. Preparation of positive electrode sheet

[0118] The positive electrode active material (lithium cobalt oxide LCO), SP, and PVDF are mixed in a mass ratio of 97.6:1.4:1, and NMP is added, and the mixture is stirred uniformly to prepare a positive electrode slurry; wherein the yttrium content y in the lithium cobalt oxide LCO is 700 ppm; the positive electrode slurry is coated on both surfaces of an aluminum foil with a thickness of 8 μm, the initial tensile strength of the aluminum foil is 290 MPa, and after baking and rolling, the positive electrode active material layer is formed on both surfaces of the aluminum foil, and a positive electrode sheet with a thickness of about 80 μm is obtained;

[0119] wherein a slot position exposing the surface of the aluminum foil is reserved at the preset tab position of the aluminum foil, and after the positive electrode active material layer is formed, the positive electrode tab is welded in the slot position by laser or ultrasonic welding (i.e., the positive electrode tab and the aluminum foil exposed through the slot position are welded), and the positive electrode sheet is prepared.

[0120] 2. Preparation of negative electrode sheet

[0121] (1) The first negative electrode active material, SP, CMC-Li, and PAA are mixed in a mass ratio of 97:0.4:0.1:2.5, and deionized water is added to prepare a first negative electrode slurry; wherein the first active material includes a first graphite and a silicon-carbon material, and the silicon content in the silicon-carbon particles increases from the center of the silicon-carbon to the edge of the silicon-carbon (the electron microscope image of the silicon-carbon in the backscattered electron mode (BSE mode) is shown in Figure 4 );

[0122] (2) The second negative electrode active material, SP, CMC-Li, and PAA are mixed in a mass ratio of 97:0.4:0.1:2.5, and deionized water is added to prepare a second negative electrode slurry; wherein the second active material is a second graphite;

[0123] (3) The first negative electrode slurry and the second negative electrode slurry are simultaneously coated on both surfaces of a carbon-coated copper foil with a thickness of 4 μm by a double-layer coating method (when coating, the extrusion head for coating the second negative electrode slurry is located above the extrusion head for coating the first negative electrode slurry, so that the first coating layer formed by the first negative electrode slurry is located between the carbon-coated copper foil and the second coating layer formed by the second negative electrode slurry), and after baking and rolling, a negative electrode active layer (including the second coating layer and the first coating layer located between the carbon-coated copper foil and the second coating layer) is formed on both surfaces of the carbon-coated copper foil;

[0124] wherein a slot position exposing the surface of the aluminum foil is reserved at the preset tab position of the aluminum foil, and after the positive electrode active material layer is formed, the positive electrode tab is welded in the slot position by laser or ultrasonic welding (i.e., the positive electrode tab and the aluminum foil exposed through the slot position are welded), and the positive electrode sheet is prepared.Figure 5 (This will not be elaborated further), wherein the width of the groove W3 = 13mm, the width of the tab adhesive paper W2 = 12mm, the width of the first recessed area 123 W1 = 9mm, the thickness of the tab adhesive paper is 12μm, and the depth of the groove is 20μm.

[0125] (4) Using a laser, linear grooves (i.e., recesses, which do not penetrate the negative electrode active material layer) are formed on the surface of the negative electrode active material layer on each side. The spacing between the recesses is ΔL = 1.5 mm, the width of the recess is L = 100 μm, and the depth of the recess is h = 20 μm, thus producing a negative electrode sheet with a thickness of approximately 100 μm (see schematic diagram of the negative electrode sheet). Figure 1 and Figure 3 As shown, it will not be repeated here.

[0126] 3. Battery manufacturing

[0127] The positive and negative electrode sheets are cut according to a predetermined shape and size. Then, the positive electrode sheet, separator, and negative electrode sheet are placed in sequence, wound, and hot-pressed together to form a core. The separator includes a base film, a ceramic layer on the side of the base film facing the negative electrode sheet, a coating layer on the side of the ceramic layer facing the negative electrode sheet, and a coating layer on the side of the base film facing the positive electrode sheet. The thickness of the coating layer on each side is approximately 1 μm, and the material of the coating layer is PVDF. The thickness of the base film is 5 μm, and the thickness of the ceramic layer is H. 31 The average particle size D of the ceramic material is 2 μm. 31 The thickness is 200 nm, and the ceramic layer is composed of ceramic particles (boehmite) and a third binder (PVDF) in a mass ratio of 99.5:0.5.

[0128] Then, the core is packaged with aluminum-plastic film, and then successively baked, injected with electrolyte, formed, second sealed, sorted and OCV and other processes to obtain a lithium-ion battery with a thickness of 5.285mm; wherein, the lithium salt in the electrolyte is LiPF6 with a concentration of 1mol / L, and the electrolyte contains PS with a mass percentage e of 5%.

[0129] Examples 2 to 32, and Comparative Examples 1 to 2: The differences from Example 1 are as follows: the average maximum particle size D1 of the silicon-carbon particles, the graphite particle size D2 in the bottom layer (first coating), the graphite particle size D3 in the top layer (second coating), the ratio of D1 to D2, the ratio of D3 to D2, and the average particle size D of the ceramic material. 31 D3 / D 31 Thickness H of ceramic layer 31 The mass percentage of sulfonate esters in the electrolyte (e), the tensile strength of the carbon-coated copper foil (S1), S1 / e, the silicon doping content (X) of the negative electrode active layer, and the thickness of the carbon-coated copper foil (H). 10 H 10×S1 / X, yttrium doping amount y, y / X, aluminum foil thickness H 20 tensile strength S2 of the aluminum foil, H 20 ×S2 / X, or the silicon element content a in silicon carbon, a×X, and the like, see Tables 1 and 2 for details, and the other conditions are the same as shown in Tables 1 and 2.

[0130] Example 30: The difference from Example 1 is that the ceramic layer of the separator is located on the side of the base film facing the positive electrode sheet, and no ceramic layer is arranged on the side of the base film facing the positive electrode sheet, and the other conditions are the same as in Example 1.

[0131] The negative electrode sheets and batteries of each example and comparative example were tested by the following methods, respectively:

[0132] (1) The test method for battery capacity is as follows: in a 25°C constant temperature room, use 0.2C constant current and constant voltage to charge to the upper limit voltage of the battery, then constant voltage charging, cutoff current 0.02C, stand for 10min, then discharge to 3.0V with 0.2C, the battery capacity is measured and shown in Table 3;

[0133] (2) The expansion rate of the battery after 500 cycles: in a 45°C constant temperature room, charge to 4.25V with 4C constant current, then charge to 4.35V with 3C constant current, then charge to the upper limit voltage with 2C constant current, constant voltage charging to the cutoff current 0.05C, stand for 10min, then discharge to 3.0V with 1C, after 500 cycles, the battery cycle expansion rate is measured and shown in Table 3;

[0134] (3) The fracture rate of the electrode sheet: in a 45°C constant room, 1C constant current and constant voltage to the upper limit voltage, 0.05C cutoff, stand for 10min, then 0.5C discharge to 3.0V, after 600T cycles, disassemble the battery, and observe whether the positive electrode sheet is broken; according to the process, a total of 100pcs batteries are tested, and the fracture rate of the electrode sheet (the proportion of the number of batteries with broken positive electrode sheets to 100 batteries) is calculated, and the results are shown in Table 3.

[0135] (4) The yttrium doping amount y in the positive active layer: after discharging the battery to 0% SOC, disassemble and take out the positive electrode sheet, soak in dimethyl carbonate (DMC) solvent for 12h, then rinse with DMC to remove the lithium salt attached to the electrode sheet, calcine in a 400°C high temperature furnace under air atmosphere for 2h, rub off the positive electrode powder, and measure the concentration of aluminum element in the standard solution by inductively coupled plasma (ICP) according to the test method in GBT 30902-2014, which is the yttrium doping amount y in the positive active layer, with unit of ppm;

[0136] (5) Tensile strength of carbon-coated copper foil in the battery: after discharging the battery to 0% SOC, the negative electrode sheet was taken out, soaked in dimethyl carbonate (DMC) solvent for 12 h, then washed with DMC to remove the lithium salt attached to the negative electrode sheet, then the negative active layer was washed off from the negative electrode sheet with deionized water to obtain an intact copper foil, which was dried and then cut into a sample to be tested with a width of 15 mm and a length of more than 50 mm using a knife; a WD-D3 electronic universal testing machine (accuracy of 0.5 level, accuracy of ±1% of the indicated value) was used to set the gauge length to 50 mm and the speed to 50 mm / min, and the tensile test was performed on the sample to be tested to measure the tensile strength;

[0137] (6) Tensile strength of aluminum foil in the battery: after discharging the battery to 0% SOC, the positive electrode sheet was taken out, soaked in dimethyl carbonate (DMC) solvent for 12 h, then washed with DMC to remove the lithium salt attached to the positive electrode sheet, and the tail empty foil of the roll core or the positive active layer was wiped with CMC to obtain an intact and undamaged aluminum foil, which was dried and then cut into a sample to be tested with a width of 15 mm and a length of more than 50 mm using a knife; a WD-D3 electronic universal testing machine (accuracy of 0.5 level, accuracy of ±1% of the indicated value) was used to set the gauge length to 50 mm and the speed to 10 mm / min, and the tensile test was performed on the sample to be tested to measure the tensile strength of the aluminum foil.

[0138] Table 1 Battery-related parameters

[0139]

[0140]

[0141] Table 2 Battery-related parameters

[0142]

[0143]

[0144] Table 3 Performance test results

[0145] Example Pole piece fracture rate Cycle expansion rate Capacity Example 1 0％ 9％ 4980 Example 2 9％ 14％ 5000 Example 3 0％ 9％ 4950 Example 4 12％ 11％ 4900 Example 5 0％ 9％ 4990 Example 6 0％ 12％ 4990 Example 7 8％ 11％ 4980 Example 8 0％ 9％ 4990 Example 9 1％ 10％ 4990 Example 10 35％ 9％ 4980 Example 11 0％ 9％ 4980 Example 12 0％ 9％ 4980 Example 13 0％ 12％ 4980 Example 14 25％ 9％ 5200 Example 15 0％ 9％ 5200 Example 16 0％ 9％ 4900 Example 17 0％ 9％ 4900 Example 18 0％ 9％ 4900 Example 19 0％ 9％ 4900 Example 20 0％ 9％ 5200 Example 21 0％ 14％ 5200 Example 22 38％ 9％ 5200 Example 23 0％ 9％ 4900 Example 24 0％ 9％ 4800 Example 25 10％ 9％ 5200 Example 26 0％ 9％ 4980 Example 27 0％ 9％ 4980 Example 28 5％ 9％ 5200 Example 29 0％ 17％ 4980 Example 30 16％ 11％ 4980 Example 31 0％ 10.5％ 4965 Example 32 0％ 8.5％ 4970 Comparative Example 1 45％ 11％ 4990 Comparative Example 2 100％ 15％ 4970

[0146] As can be seen from Tables 1, 2 and 3, compared with Comparative Examples 1-2, Examples 1-32 31 , the average particle size D 31 of the ceramic material 31≤350, the electrode sheet breakage can be effectively inhibited, and the battery cycle expansion rate can be reduced, and the battery capacity can be improved, especially in Example 1, Example 3, Example 5, Example 6, Example 8, Example 9, Example 12, Example 16, Example 19, Example 23, Example 26, and Example 28, the electrode sheet breakage rate can be relatively more significantly reduced (not more than 5%, mostly 0%), the battery cycle expansion rate can be reduced (not more than 12%), and the battery capacity can be maintained, thereby further illustrating that, when 4≤D3 / D 31 ≤70, 0.5≤D1 / D2≤1.5, 0.3≤D3 / D2≤1, S1≥400MPa, 550≤S1 / e≤60000, 1600≤H 10 ×S1 / X≤660000, 100ppm≤y≤2000ppm, 400≤y / X≤200000, 600≤H 20 ×S2 / X≤300000, 0.35%≤a×X≤35%, 35%≤a≤70% are met, the electrode sheet breakage risk can be further reduced, the battery expansion can be inhibited, and the high battery capacity and other performances can be maintained.

[0147] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery, characterized by, Comprise: a negative electrode sheet comprising a negative electrode current collector and a negative electrode active layer located on at least one side surface of the negative electrode current collector, the negative electrode active layer comprising a second coating layer and a first coating layer located between the negative electrode current collector and the second coating layer, the first coating layer comprising a first active material, the first active material comprising a silicon-carbon material, the second coating layer comprising a second active material, the second active material comprising a second graphite; a separator comprising a base film and a ceramic layer located on at least one side surface of the base film, the ceramic layer comprising a ceramic material; the average particle size D3 of the second graphite in the second coating, the average particle size D 31 satisfies: 3 < D3 / D 31 ≤ 350; The thickness H of the ceramic layer 31 satisfies 0.5 pm ≤ H 31 ≤ 6 pm.

2. The battery according to claim 1, wherein 4 < D3 / D 31 ≤ 70; and / or, 5 pm ≤ D3 ≤ 22 pm; and / or, 50 nm < D < 200 nm 31 ≤ 2 μm; and / or, the first active material further comprises a first graphite.

3. The battery according to claim 2, wherein an average particle size D2 of the first graphite in the first coating layer is greater than an average particle size D3 of the second graphite in the second coating layer; and / or, a maximum particle size D1 of the silicon-carbon material in the first coating layer and the average particle size D2 of the first graphite in the first coating layer satisfy 0.5 ≤ D1 / D2 ≤ 1.5; and / or, the maximum particle size D1 of the silicon-carbon material in the first coating layer satisfies 5 pm ≤ D1 ≤ 20 pm.

4. The battery of claim 3, wherein, 0.3 ≤ D3 / D2 ≤ 1.

5. The battery of claim 1, wherein, The battery further comprises an electrolyte, the electrolyte comprising a sulfonate.

6. The battery according to claim 5, wherein a mass percentage content e of the sulfonate in the electrolyte and a tensile strength S1 of the negative electrode current collector satisfy S1 / e ≥ 550, a unit of S1 being MPa; and / or, the tensile strength S1 of the negative electrode current collector is ≥ 400 MPa; and / or, the mass percentage content e of the sulfonate in the electrolyte is 0.1% to 20%; and / or, the sulfonate comprises 1,3-propane sultone and / or 1,3-propene sultone.

7. The battery of claim 6, wherein, 550 ≤ S1 / e ≤ 60000.

8. The battery of claim 1, wherein, a thickness H of the negative electrode current collector 10 , a tensile strength S1 of the negative electrode current collector, and a mass ratio X of the silicon-carbon material to graphite in the negative electrode active layer satisfy H 10 × S1 / X ≥ 1600, the unit of S1 is MPa, and the unit of H 10 is μm.

9. The battery according to claim 8, wherein 1600 ≤ (H 10 × S1) / X ≤ 660000; and / or 3 pm < H 10 ≤ 12 pm; and / or, 1% ≤ X ≤ 50%.

10. The battery according to claim 1, wherein the ceramic layer is located on a side surface of the base film facing the negative electrode sheet; and / or, the battery further comprises a positive electrode sheet, the separator is located between the positive electrode sheet and the negative electrode sheet; an adhesion between the separator and the positive electrode sheet is greater than an adhesion between the separator and the negative electrode sheet.

11. The battery of claim 1, wherein, The battery further comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material, the positive electrode active material containing a yttrium element.

12. The battery according to claim 11, wherein the first coating layer further comprises a graphite, 400 ≤ y / X ≤ 200000, y being a content of yttrium in the positive electrode active layer, a unit of y being ppm, X being a mass ratio of the silicon-carbon material to the graphite in the negative electrode active layer; and / or, the content of yttrium y in the positive electrode active layer satisfies 100 ppm ≤ y ≤ 2000 ppm.

13. The battery of claim 1, wherein, The battery further comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active layer on at least one side surface of the positive electrode current collector; H 20 X S2 / X ≥ 600, H 20 is the thickness of the positive current collector in units of pm, S2 is the tensile strength of the positive current collector in units of MPa, and X is the mass ratio of the silicon-carbon material to graphite in the negative active layer.

14. The battery of claim 13, wherein, 600 ≤ (H 20 × S2) / X ≤ 300,000; and / or 5 pm < H 20 ≤ 20 pm; and / or 50 Mpa≤S2≤300 Mpa.

15. The battery of claim 1, wherein, The first coating further comprises a first graphite; and / or the mass ratio X of the silicon-carbon material to the graphite in the negative electrode active layer and the mass percentage content a of silicon element in the silicon-carbon material satisfy 0.35%≤a×X≤35%; and / or the mass percentage content a of silicon element in the silicon-carbon material is 35%~70%; and / or the content of silicon element in the silicon-carbon material decreases from the center of the silicon-carbon particle to the edge of the silicon-carbon particle; and / or the mass ratio of the silicon-carbon material to the graphite in the negative electrode active layer is 1%~50%.

16. The battery of claim 15, wherein, The mass ratio of the silicon-carbon material to the graphite in the negative electrode active layer is 4%~30%.

17. The battery of any one of claims 1-16, wherein, The surface of the second coating is provided with a recess.

18. The battery of claim 17, wherein, The width of the recess is 50μm~160μm; and / or the depth of the recess is 3μm~40μm; and / or the interval of the recesses is 0.3~3mm.

19. The battery of any one of claims 1-16, wherein, The negative electrode sheet comprises a negative electrode tab; The negative electrode active layer comprises a main body area, a first recessed area, and a second recessed area between the main body area and the first recessed area, and the negative electrode tab is arranged in the first recessed area; The battery further comprises a tab adhesive paper, the tab adhesive paper comprising a first connecting part on the side of the negative electrode tab away from the negative electrode current collector, and a second connecting part on the side of the first recessed area away from the negative electrode current collector, and the side surface of the second connecting part away from the negative electrode current collector does not exceed the side surface of the main body area away from the negative electrode current collector.

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