Battery cell and electric equipment

Abstract

The invention provides a battery cell and electric equipment, an electrode assembly of the battery cell is of a winding type structure, the electrode assembly comprises a negative pole piece, the elongation at break of the negative pole piece is X0 in the winding direction of the electrode assembly, the elongation of the negative pole piece is X1 in the extending direction of the winding axis of the electrode assembly, and the elongation of the negative pole piece is X2 in the thickness direction of the electrode assembly. The expansion rate of the electrode assembly is X2, and 0 < = X0-(X1 + X2) < = 2%; the risk that the negative plate expands and fractures when the battery cell is fully charged can be reduced, the safety performance of the battery cell is improved, the capacity loss of the battery cell can also be reduced, and the production cost of the battery cell can also be controlled.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a battery cell and an electrical device. Background Art

[0002] Battery cells are widely used in portable electronic devices, electric vehicles, electric tools, drones, energy storage devices, etc. As the application environment and conditions become more and more complex, higher requirements are placed on the safety performance of battery cells. Summary of the invention

[0003] The embodiments of the present application provide a battery cell and an electrical device to improve the safety performance of the battery cell.

[0004] In a first aspect, an embodiment of the present application provides a battery cell, the battery cell comprising a housing and an electrode assembly; the electrode assembly is accommodated in the housing, the electrode assembly is a winding structure, the electrode assembly comprises a negative electrode sheet, along the winding direction of the electrode assembly, the elongation at break of the negative electrode sheet is X0, along the extension direction of the winding axis of the electrode assembly, the elongation of the negative electrode sheet is X1, along the thickness direction of the electrode assembly, the expansion rate of the electrode assembly is X2, satisfying: 0≤X0-(X1+X2)≤2%; wherein, when the battery cell is in a fully charged state, the length of the negative electrode sheet along the extension direction of the winding axis of the electrode assembly is X 11 The dimension of the electrode assembly along its thickness direction is X 21 When the battery cell is fully charged, the length of the negative electrode sheet along the extension direction of the winding axis of the electrode assembly is X 12 The dimension of the electrode assembly along its thickness direction is X 22 The dimension of the electrode assembly along its width direction is b, X1=(X 11 -X 12 ) / X 12 , X2=(X 21 -X 22 ) / b, the extension direction of the winding axis of the electrode assembly, the thickness direction of the electrode assembly and the width direction of the electrode assembly are perpendicular to each other.

[0005] According to the battery cell of the embodiment of the present application, if X0-(X1+X2)<0, when the battery cell is in a fully charged state, the negative electrode sheet is prone to expansion and fracture, resulting in capacity loss and burrs generated after the negative electrode sheet breaks, which can easily cause safety problems; if X0-(X1+X2)>2%, when the battery cell is fully charged, the risk of the negative electrode sheet breaking is low, but the production cost increases. Therefore, 0≤X0-(X1+X2)≤2% can reduce the risk of expansion and fracture of the negative electrode sheet when the battery cell is fully charged, improve the safety performance of the battery cell, reduce and reduce the capacity loss of the battery cell, and control the production cost of the battery cell.

[0006] In some embodiments of the first aspect of the present application, 0.4%≤X0-(X1+X2)≤1.5%.

[0007] In one or more of the above optional embodiments, when X0-(X1+X2)≥0.4%, the risk of the negative electrode plate expanding and breaking after the number of battery cell cycles increases can be reduced, thereby further improving the safety performance of the battery cell and extending the service life of the battery cell; when X0-(X1+X2)≤1.5%, it is beneficial to control the production cost of the battery cell within a reasonable range. Therefore, 0.4%≤X0-(X1+X2)≤1.5%, which can further reduce the risk of the negative electrode plate expanding and breaking after the number of battery cell cycles increases, thereby further improving the safety performance of the battery cell and extending the service life of the battery cell, and can also control the production cost of the battery cell.

[0008] In some embodiments of the first aspect of the present application, the negative electrode plate includes a negative electrode active material, and the negative electrode active material includes silicon.

[0009] In one or more of the above optional embodiments, the negative electrode active material includes silicon, which is beneficial for the battery cell to have advantages such as high energy density, low cost, and environmental protection.

[0010] In some embodiments of the first aspect of the present application, the weight percentage of the silicon in the negative electrode active material is C, 0<C<100%.

[0011] In one or more of the above optional embodiments, the weight percentage of silicon in the negative electrode active material is greater than 0 and less than 100%, which is beneficial for the battery cell to have advantages such as high energy density and environmental protection, and can further control the cost of the battery cell.

[0012] In some embodiments of the first aspect of the present application, 15%≤C≤80%.

[0013] In one or more of the above optional embodiments, the weight percentage of silicon in the negative electrode active material is greater than or equal to 15%, so that the battery cell has a higher energy density, and the weight percentage of silicon in the negative electrode active material is less than or equal to 80%, which is conducive to further controlling the cost of the battery cell.

[0014] In some embodiments of the first aspect of the present application, the negative electrode active material further includes graphite.

[0015] In one or more of the above optional embodiments, the negative electrode active material also includes graphite, which is beneficial to improving the stability of the battery cell.

[0016] In some embodiments of the first aspect of the present application, the number of the electrode assemblies is N, a receiving space is formed inside the housing, and a size of the receiving space along the thickness direction of the electrode assembly is H, wherein N≥2, 0.5H / N≤X 22 ≤1.5H / N.

[0017] In one or more of the above optional embodiments, X 22 ≥0.5H / N, the battery cell has a larger capacity, X 22 When ≤1.5H / N, the risk of expansion and fracture of the negative electrode sheet due to excessive thickness of the electrode assembly is avoided, thereby improving the safety performance of the battery cell.

[0018] In some embodiments of the first aspect of the present application, the battery cell includes a plurality of the electrode assemblies, and the plurality of the electrode assemblies are stacked along a thickness direction of the electrode assembly; the number of the electrode assemblies does not exceed four.

[0019] In one or more of the above optional embodiments, the battery cell includes multiple electrode assemblies. When the capacity of the battery cell is constant, compared with the case where the battery cell includes one electrode assembly, the battery cell in this solution includes multiple electrode assemblies, and the thickness of each electrode assembly can be smaller. The smaller the thickness of the electrode assembly, the lower the risk of the negative electrode sheet of the electrode assembly breaking, thereby making the safety performance of the battery cell better. The number of electrode assemblies does not exceed four, which can reduce the complexity of the process, improve production efficiency and reduce production costs.

[0020] In some embodiments of the first aspect of the present application, a receiving space is formed inside the shell, and a dimension of the receiving space along the thickness direction of the electrode assembly is H, 5mm≤H≤20mm.

[0021] In one or more of the above optional embodiments, when H≥5mm, the internal space of the outer shell of the battery cell is larger, which is conducive to the battery cell having a higher energy density and also makes the processing of the outer shell easier; when H≤20mm, the processing difficulty and production cost of the battery cell are reduced.

[0022] In some embodiments of the first aspect of the present application, 6mm≤H≤15mm.

[0023] In one or more of the above optional embodiments, when H≥6mm, the internal space of the battery cell shell is larger, which is conducive to the battery cell having a higher energy density and also makes the processing of the shell easier; when H≤15mm, the processing difficulty and production cost of the battery cell are further reduced.

[0024] In some embodiments of the first aspect of the present application, 2.5 mm ≤ X 22 ≤10mm.

[0025] In one or more of the above optional embodiments, the thickness of the electrode assembly is greater than or equal to 2.5 mm, which is conducive to the electrode assembly having a higher capacity and facilitating the production and processing of the electrode assembly; the thickness of the electrode assembly is less than or equal to 10 mm, which reduces the risk of expansion and fracture of the negative electrode plate when the battery cell is fully charged, thereby improving the safety of the battery cell.

[0026] In some embodiments of the first aspect of the present application, 3 mm ≤ X 22 ≤7.5mm.

[0027] In one or more of the above optional embodiments, the thickness of the electrode assembly is greater than or equal to 3 mm, which is conducive to the electrode assembly having a higher capacity and facilitating the production and processing of the electrode assembly; the thickness of the electrode assembly is less than or equal to 7.5 mm, which further reduces the risk of expansion and fracture of the negative electrode plate when the battery cell is fully charged, thereby further improving the safety of the battery cell.

[0028] In a second aspect, an embodiment of the present application provides an electrical device, comprising a battery cell provided by any of the above embodiments.

[0029] In one or more of the above optional embodiments, the battery cell provided by any of the above embodiments has good safety, which is beneficial to improving the power safety of electrical equipment powered by the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope.

[0031] Figure 1 A cross-sectional view of a battery cell provided in some embodiments of the present application;

[0032] Figure 2 A schematic diagram of the structure of an electrode assembly in a fully charged state provided in some embodiments of the present application;

[0033] Figure 3 A schematic diagram of the structure of an electrode assembly in a fully charged state provided in some embodiments of the present application;

[0034] Figure 4 A schematic diagram of an unfolded negative electrode sheet after it has not expanded provided in some embodiments of the present application;

[0035] Figure 5 This is a schematic diagram of the expanded negative electrode sheet after unfolding provided in some embodiments of the present application.

[0036] Icon: 100-battery cell; 10-housing; 11-first wall; 12-second wall; 20-electrode assembly; 21-negative electrode sheet; 22-positive electrode sheet; 23-separation membrane; X-winding direction of electrode assembly; X'-length direction of negative electrode sheet; Y-extension direction of winding axis of electrode assembly; Y'-width direction of negative electrode sheet; Z-width direction of electrode assembly; K-thickness direction of electrode assembly; A1-straight area; A2-bending area; Q-accommodating space. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0039] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0040] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0041] In the description of the embodiments of the present application, it should be noted that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the application is usually placed when in use, or the orientation or positional relationship commonly understood by those skilled in the art, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0042] In the description of the embodiments of the present application, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0043] At present, judging from the development of the market situation, the application of battery cells is becoming more and more extensive. Battery cells are widely used in electric vehicles such as electric bicycles, electric motorcycles, electric vehicles, as well as electric tools, drones, energy storage equipment and other fields. With the continuous expansion of the application field of battery cells, the market demand is also constantly expanding, and the requirements for battery cell performance are becoming higher and higher.

[0044] The battery cells include wound cells and laminated cells. The electrode assembly of the wound cell is a wound structure. For the wound electrode assembly, the negative electrode plate will expand during the cycle. The expansion degree of the negative electrode plate is different for different types of wound cells: for example, the thickness change rate of the graphite negative electrode in the fully charged and fully discharged states is 5% to 10%, and the expansion rate of the pure Si negative electrode is even more than 100%. The expansion rate of the composite negative electrode of graphite and silicon is between the two pure materials.

[0045] The expansion of the negative electrode sheet will pull the sheet, causing deformation of the negative electrode sheet in the length and width directions. At the same time, for the winding structure, the negative electrode sheet expands and the thickness of the negative electrode sheet increases, resulting in extrusion at the winding corners (bending areas) of the electrode assembly, which further pulls the negative electrode sheet in the main position (straight area). After the negative electrode sheet in the main position is pulled, the elongation at break of the negative electrode sheet itself is exceeded, and the negative electrode sheet will break. On the one hand, the fracture may lead to capacity loss, and on the other hand, the burrs on the sheet at the fracture position may cause safety risks. The thicker the battery cell, the higher the risk of the negative electrode sheet breaking.

[0046] Based on the above considerations, in order to alleviate the problem of the negative electrode sheet being broken due to the expansion of the negative electrode sheet, an embodiment of the present application provides a battery cell, wherein the electrode assembly of the battery cell is a winding structure, the electrode assembly includes a negative electrode sheet, and along the winding direction of the electrode assembly, the fracture elongation of the negative electrode sheet is X0, along the extension direction of the winding axis of the electrode assembly, the elongation of the negative electrode sheet is X1, and along the thickness direction of the electrode assembly, the expansion rate of the electrode assembly is X2, satisfying: 0≤X0-(X1+X2)≤2%; wherein, when the battery cell is in a fully charged state, the length of the negative electrode sheet along the extension direction of the winding axis of the electrode assembly is X 11 The dimension of the electrode assembly along its thickness direction is X 21 When the battery cell is fully discharged, the length of the negative electrode sheet along the extension direction of the winding axis of the electrode assembly is X12 The dimension of the electrode assembly along its thickness direction is X 22 The dimension of the electrode assembly along its width direction is b, X1=(X 11 -X 12 ) / X 12 , X2=(X 21 -X 22 ) / b, the extension direction of the winding axis of the electrode assembly, the thickness direction of the electrode assembly and the width direction of the electrode assembly are perpendicular to each other.

[0047] If X0-(X1+X2)<0, when the battery cell is in a fully charged state, the negative electrode sheet is prone to expansion and fracture, resulting in capacity loss and burrs generated after the negative electrode sheet breaks, which can easily cause safety problems; if X0-(X1+X2)>2%, when the battery cell is fully charged, the risk of the negative electrode sheet 21 breaking is low, but the production cost increases. Therefore, 0≤X0-(X1+X2)≤2% can not only reduce the risk of expansion and fracture of the negative electrode sheet when the battery cell is fully charged, improve the safety performance of the battery cell, but also reduce and reduce the capacity loss of the battery cell, and also control the production cost of the battery cell.

[0048] The battery cell disclosed in the embodiment of the present application can be used in, but not limited to, electric two-wheeled vehicles, electric tools, drones, energy storage devices and other electrical equipment. The battery cell with the working condition of the present application can also be used as a power supply system for electrical equipment, which is conducive to improving the safety performance of the battery cell.

[0049] The embodiment of the present application provides an electric device using a battery cell as a power source, and the electric device may be, but is not limited to, electronic equipment, electric tools, electric vehicles, drones, and energy storage devices. Among them, electronic equipment may include mobile phones, tablets, laptops, etc., electric tools may include electric drills, electric saws, etc., and electric vehicles may include electric cars, electric motorcycles, electric bicycles, etc.

[0050] like Figure 1-Figure 5 As shown, the embodiment of the present application provides a battery cell 100, the battery cell 100 includes a shell 10 and an electrode assembly 20; the electrode assembly 20 is accommodated in the shell 10, the electrode assembly 20 is a winding structure, the electrode assembly 20 includes a negative electrode sheet 21, along the winding direction X of the electrode assembly, the elongation at break of the negative electrode sheet 21 is X0, along the extension direction Y of the winding axis of the electrode assembly, the elongation of the negative electrode sheet 21 is X1, along the thickness direction K of the electrode assembly, the expansion rate of the electrode assembly 20 is X2, satisfying: 0≤X0-(X1+X2)≤2%; wherein, when the battery cell 100 is in a fully charged state, the length of the negative electrode sheet 21 along the extension direction Y of the winding axis of the electrode assembly is X 11 The dimension of the electrode assembly 20 along its thickness direction is X 21When the battery cell 100 is fully charged, the length of the negative electrode sheet 21 along the extension direction Y of the winding axis of the electrode assembly is X 12 The dimension of the electrode assembly 20 along its thickness direction is X 22 The dimension of the electrode assembly 20 along its width direction is b, X1=(X 11 -X 12 ) / X 12 , X2=(X 21 -X 22 ) / b, the extension direction Y of the winding axis of the electrode assembly, the thickness direction K of the electrode assembly and the width direction Z of the electrode assembly are perpendicular to each other.

[0051] If X0-(X1+X2)<0, when the battery cell 100 is in a fully charged state, the negative electrode sheet 21 is prone to expansion and fracture, resulting in capacity loss and burrs generated after the negative electrode sheet 21 breaks, which can easily cause safety problems; if X0-(X1+X2)>2%, when the battery cell 100 is fully charged, the risk of the negative electrode sheet 21 breaking is low, but the production cost increases. Therefore, 0≤X0-(X1+X2)≤2% can reduce the risk of expansion and fracture of the negative electrode sheet when the battery cell 100 is fully charged, improve the safety performance of the battery cell 100, reduce and reduce the capacity loss of the battery cell 100, and control the production cost of the battery cell 100.

[0052] The housing 10 forms a storage space Q. The storage space Q can be used to store the electrode assembly 20, electrolyte, etc. The housing 10 can be a hard shell, for example, the housing 10 is a steel shell or an aluminum shell, forming a steel shell battery cell 100 or an aluminum shell battery cell 100. The housing 10 can also be formed of a softer material, for example, the housing 10 is an aluminum-plastic film or a steel-plastic film, forming a soft-pack battery cell 100.

[0053] The electrode assembly 20 further includes a positive electrode sheet 22 and a separator 23 . The negative electrode sheet 21 , the separator 23 and the positive electrode sheet 22 are stacked and wound to form a wound electrode assembly 20 .

[0054] The positive electrode sheet 22 includes a positive current collector and a positive active material layer, and the positive active material layer is provided on at least one side of the positive current collector. For the lithium-ion battery cell 100, the material of the positive current collector can be aluminum. The positive active material layer can be lithium cobalt oxide, lithium iron phosphate, ternary lithium or lithium manganese oxide, etc. The positive current collector can be a composite current collector or a non-composite current collector.

[0055] The negative electrode sheet 21 includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is disposed on at least one side of the negative electrode current collector. For the lithium-ion battery cell 100, the negative electrode current collector may be made of copper, and the negative electrode active material may be carbon or silicon, etc. The negative electrode current collector may be a composite current collector or a non-composite current collector.

[0056] In some embodiments, the negative electrode plate 21 includes a negative electrode active material, and the negative electrode active material includes silicon. The negative electrode active material includes silicon, which is conducive to the battery cell 100 having advantages such as high energy density, low cost, and environmental protection.

[0057] In some embodiments, the weight percentage of silicon in the negative electrode active material is C, 0<C<100%.

[0058] The weight percentage of silicon in the negative electrode active material is less than 100%, that is, the negative electrode active material also includes other substances, such as a binder, graphite, etc. Exemplarily, the weight percentage C of silicon in the negative electrode active material is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.

[0059] The weight percentage of silicon in the negative electrode active material is greater than 0 and less than 100%, which is beneficial for the battery cell 100 to have advantages such as high energy density and environmental protection, and can further control the cost of the battery cell 100.

[0060] In some embodiments, 15%≤C≤80%.

[0061] Illustratively, C may be 15%, 25%, 35%, 45%, 55%, 65%, 75%, 80%, etc.

[0062] The weight percentage of silicon in the negative electrode active material is greater than or equal to 15%, so that the battery cell 100 has a higher energy density. The weight percentage of silicon in the negative electrode active material is less than or equal to 80%, which is beneficial to further control the cost of the battery cell 100.

[0063] The silicon content in the negative electrode plate 21 can be tested by ICP-AES. The specific testing method is: take the electrode material (ie, negative electrode active material) on the negative electrode current collector side of the negative electrode plate 21, and weigh its mass as M 负 , M 负 In volume V 负 The solution was digested in a hydrofluoric acid solution and the silicon concentration in the solution was tested by ICP-AES (inductively coupled atomic emission spectroscopy). 负 , calculate the total mass m of silicon using the concentration and solution volume 负 =n 负 *V 负 , then the average silicon content of the electrode material on this side is m 负 / M 负 .

[0064] In some embodiments, the negative electrode active material further includes graphite. The negative electrode active material further includes graphite, which is beneficial to improving the stability of the battery cell 100.

[0065] The separator 23 insulates and separates the positive electrode sheet 22 and the negative electrode sheet 21 to reduce the risk of short circuit of the battery cell 100. The material of the separator 23 may include PP (polypropylene) or PE (polyethylene).

[0066] like Figure 2 , Figure 3 As shown, the electrode assembly 20 includes a straight area A1 and two bending areas A2. Along the first direction, the two bending areas A2 are respectively connected to the two ends of the straight area A1. The straight area A1 is the main body of the electrode assembly 20, and the bending area A2 is the corner of the electrode assembly 20. The first direction is the width direction Z of the electrode assembly.

[0067] The expansion of the negative electrode sheet 21 pulls the negative electrode sheet 21, which will cause the negative electrode sheet 21 to deform in both the winding direction X of the electrode assembly and the width direction of the negative electrode sheet 21. When expanded, the elongation of the negative electrode sheet 21 in its width direction is close to the elongation in the winding direction X of the electrode assembly. One reason for the breakage of the negative electrode sheet 21 is the elongation of the negative electrode sheet 21 along the winding direction X of the electrode assembly when it expands. Since when the negative electrode sheet 21 is in a wound state, the elongation of the negative electrode sheet 21 in its width direction is easier to measure than the elongation of the negative electrode sheet 21 in the winding direction X of the electrode assembly, the elongation of the negative electrode sheet 21 in the winding direction X of the electrode assembly can be replaced by obtaining the elongation of the negative electrode sheet 21 in its width direction.

[0068] The winding axis direction of the electrode assembly 20 corresponds to the width direction of the unfolded negative electrode sheet 21. The winding direction X of the electrode assembly corresponds to the length direction of the unfolded negative electrode sheet 21.

[0069] Elongation at break refers to the ratio of the elongation length before and after stretching to the length before stretching when the material is stretched to break, usually expressed as a percentage. The elongation at break of the negative electrode is a common indicator to characterize the ability of the negative electrode sheet 21 to resist deformation without breaking. The elongation at break of the negative electrode sheet 21 is the ratio of the elongation length before and after stretching to the length before stretching when the negative electrode sheet 21 is stretched to break. The test method for the elongation at break of the negative electrode sheet 21 can be as follows:

[0070] Test method: Cut the negative electrode sheet 21 into strips with a width of a and a length >10mm (the length is recorded as L), fix one end to the lower end of the tensile testing machine and the other end to the upper end of the tensile testing machine, keep the two ends in the same vertical plane, set the tensile testing machine speed to 50mm / min, the length of the negative electrode sheet 21 when it is broken is L', record the stretching amount ΔL=L'-L when the negative electrode breaks, then the copper foil strength X0=ΔL / L.

[0071] The elongation at break of the negative electrode plate 21 is mainly related to the material of the negative electrode current collector, and commonly used negative electrode current collectors include copper foil, polymer-copper layer composite current collector, etc. Generally speaking, the elongation at break of the polymer-copper layer composite current collector is greater than the elongation at break of the copper foil.

[0072] The fully charged state of the battery cell 100 means that the battery cell 100 is charged to the upper limit voltage. The fully charged test process of the battery cell 100 of the present application can be: the battery cell is charged to 4.25V with a specified current (such as 0.2C) at a constant current, and then charged to 0.02C at a constant voltage. The upper limit voltage of the battery cell 100 of different systems is different, and the upper limit voltage of the battery cell 100 can refer to the rated upper limit voltage of the battery cell 100.

[0073] The fully discharged state of the battery cell 100 means that the battery cell 100 is discharged to the lower limit voltage. The fully discharged test process of the battery cell 100 can be: the battery cell is discharged to 2.5V at a constant current with a specified current (such as 0.2C). The lower limit voltage of the battery cell 100 of different systems is different, and the lower limit voltage of the battery cell 100 can refer to the rated lower limit voltage of the battery cell 100.

[0074] X0-(X1+X2) can be 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, etc.

[0075] In some embodiments, 0.4%≤X0-(X1+X2)≤1.5%.

[0076] Illustratively, X0-(X1+X2) may be 0.4%, 0.45%, 0.55%, 0.65%, 0.75%, 0.85%, 0.95%, 1.05%, 1.15%, 1.25%, 1.35%, 1.45%, 1.5%, etc.

[0077] 0.4%≤X0-(X1+X2) can reduce the risk of expansion and fracture of the negative electrode plate 21 after the number of cycles of the battery cell 100 increases, thereby further improving the safety performance of the battery cell 100 and extending the service life of the battery cell 100; X0-(X1+X2)≤1.5% is beneficial to controlling the production cost of the battery cell 100 within a reasonable range. Therefore, 0.4%≤X0-(X1+X2)≤1.5% can further reduce the risk of expansion and fracture of the negative electrode plate 21 after the number of cycles of the battery cell 100 increases, thereby further improving the safety performance of the battery cell 100 and extending the service life of the battery cell 100, and can also control the production cost of the battery cell 100.

[0078] In some embodiments, the battery cell 100 includes a plurality of electrode assemblies 20 , and the plurality of electrode assemblies 20 are stacked along a thickness direction K of the electrode assembly.

[0079] A plurality refers to a number of two or more, for example, the battery cell 100 includes three electrode assemblies 20, four electrode assemblies 20, five electrode assemblies 20, six electrode assemblies 20, and the like.

[0080] The battery cell 100 includes a plurality of electrode assemblies 20. When the capacity of the battery cell 100 is constant, compared with the case where the battery cell 100 includes one electrode assembly 20, in this solution, the battery cell 100 includes a plurality of electrode assemblies 20, and the thickness of each electrode assembly 20 can be smaller. The smaller the thickness of the electrode assembly 20, the lower the risk of the negative electrode of the electrode assembly 20 being broken, thereby making the safety performance of the battery cell 100 better.

[0081] In some embodiments, the number of electrode assemblies 20 is no more than four. For example, the number of electrode assemblies 20 may be two, three, or four. The number of electrode assemblies 20 is no more than four, which can reduce the complexity of the process, improve production efficiency, and reduce production costs.

[0082] In some embodiments, a receiving space Q is formed inside the housing 10 , and a size of the receiving space Q along a thickness direction K of the electrode assembly is H, 5 mm≤H≤20 mm.

[0083] Along the thickness direction K of the electrode assembly, the outer shell 10 has a first wall 11 and a second wall 12 opposite to each other, and the dimension H of the accommodating space Q along the thickness direction K of the electrode assembly is the distance between the inner surface of the first wall 11 and the inner surface of the second wall 12 along the thickness direction K of the electrode assembly.

[0084] Exemplarily, H may be 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm, etc.

[0085] 5mm≤H, the internal space of the shell 10 of the battery cell 100 is larger, which is conducive to the battery cell 100 having a higher energy density and also makes the processing of the shell 10 easier; H≤20mm, reducing the processing difficulty and production cost of the battery cell 100.

[0086] In some embodiments, 6 mm ≤ H ≤ 15 mm.

[0087] Illustratively, H may be 6 mm, 6.5 mm, 7.5 mm, 8.5 mm, 9.5 mm, 10.5 mm, 11.5 mm, 12.5 mm, 13.5 mm, 14.5 mm, 15 mm, etc.

[0088] 6mm≤H, the internal space of the shell 10 of the battery cell 100 is larger, which is conducive to the battery cell 100 having a higher energy density and also makes the processing of the shell 10 easier; H≤15mm, further reducing the processing difficulty and production cost of the battery cell 100.

[0089] In some embodiments, the number of electrode assemblies 20 is N, and a receiving space Q is formed inside the housing 10. The size of the receiving space Q along the thickness direction K of the electrode assembly is H, wherein N≥2, 0.5H / N≤X 22 ≤1.5H / N.

[0090] 0.5H / N≤X 22 , so that the battery cell 100 has a larger capacity, X 22 ≤1.5H / N, thereby preventing the electrode assembly 20 from being too thick and increasing the risk of the negative electrode plate 21 expanding and breaking, thereby improving the safety performance of the battery cell 100.

[0091] like Figure 3 As shown, in some embodiments, 2.5 mm ≤ X 22 ≤10mm.

[0092] For example, X 22 It can be 2.5mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, etc.

[0093] The thickness of the electrode assembly 20 is greater than or equal to 2.5 mm, which is conducive to the electrode assembly 20 having a higher capacity and is convenient for the production and processing of the electrode assembly 20; the thickness of the electrode assembly 20 is less than or equal to 10 mm, which reduces the risk of expansion and fracture of the negative electrode plate 21 when the battery cell 100 is fully charged, thereby improving the safety of the battery cell 100.

[0094] In some embodiments, 3 mm ≤ X 22 ≤7.5mm.

[0095] For example, X 22 It can be 3mm, 3.5mm, 4.5mm, 5.5mm, 6.5mm, 7.5mm, etc.

[0096] The thickness of the electrode assembly 20 is greater than or equal to 3 mm, which is conducive to the electrode assembly 20 having a higher capacity and facilitating the production and processing of the electrode assembly 20; the thickness of the electrode assembly 20 is less than or equal to 7.5 mm, which further reduces the risk of expansion and fracture of the negative electrode plate 21 when the battery cell 100 is fully charged, thereby further improving the safety of the battery cell 100.

[0097] The embodiment of the present application further provides an electric device, the electric device comprising the battery cell 100 provided by any of the above embodiments. The battery cell 100 is used to provide electric energy to the electric device.

[0098] The battery cell 100 provided in any of the above embodiments has good safety, which is beneficial to improving the power safety of the electrical equipment powered by the battery cell 100.

[0099] By comparing and testing the fracture performance of the negative electrode sheet 21 of the battery cell 100 provided in the embodiment of the present invention, the data in Table 1 were obtained. The battery cell 100 in the embodiment and the battery cell 100 in the comparative example have the same parameters and structures except the parameters in Table 1.

[0100] X 11 , X 21 Measurement: The battery cell 100 prepared in each embodiment and comparative example was charged at a constant current of 0.2C to 4.25V, and then charged at a constant voltage of 4.25V to 0.02C cut-off, and the battery cell was disassembled after standing for 15 minutes; the thickness X of each electrode assembly when fully charged was measured with a ruler 21 and the length X of the negative electrode sheet in each electrode assembly along the extension direction of its winding axis (i.e., the width direction of the negative electrode sheet after unfolding) 11 .

[0101] X 12 , X 22 Measurement: The battery cell 100 prepared in each embodiment and comparative example was charged to 4.25V at a constant current of 0.2C, then charged to 0.02C at a constant voltage of 4.25V, left standing for 15 minutes, then discharged to 2.5V at a constant current of 0.2C, left standing for 15 minutes, and then the battery cell was disassembled; the thickness X of each electrode assembly after full discharge was measured with a ruler 22 and the length X of the negative electrode sheet in each electrode assembly along the extension direction of its winding axis (i.e., the width direction of the negative electrode sheet after unfolding) 12 .

[0102] Table 1

[0103]

[0104]

[0105] From Table 1, we can see that:

[0106] (1) By comparing Example 1 with Comparative Example 1, it can be seen that when the size of the accommodating space Q of the outer shell 10 of the battery cell 100 along the thickness direction K of the electrode assembly is the same and the capacity of the battery cell 100 is constant, the battery cell 100 in Example 1 includes two electrode assemblies 20. Compared with the battery cell 100 in Comparative Example 1 including one electrode assembly 20, the thickness of the single electrode assembly 20 in Example 1 is smaller, and the negative electrode sheet 21 is not broken in the fully charged state; By comparing Example 3 with Comparative Example 2, it can be seen that when the size of the accommodating space Q of the outer shell 10 of the battery cell 100 along the thickness direction K of the electrode assembly is the same and the capacity of the battery cell 100 is constant, the battery cell 100 in Example 3 includes three electrode assemblies 20. Compared with the battery cell 100 in Comparative Example 2 including one electrode assembly 20, the thickness of the single electrode assembly 20 in Example 3 is smaller, and the negative electrode sheet 21 is not broken in the fully charged state; In summary, by reducing the thickness of the single electrode assembly 20, it is beneficial to reduce the risk of expansion and fracture of the negative electrode sheet 21 and improve the safety performance of the battery cell 100.

[0107] (2) By comparing Example 2 and Comparative Example 2, it can be seen that, when the size of the accommodating space Q of the shell 10 of the battery cell 100 along the thickness direction K of the electrode assembly is the same and the capacity of the battery cell 100 is constant, the battery cell 100 in Example 2 includes two electrode assemblies 20. Compared with the battery cell 100 in Comparative Example 2 including one electrode assembly 20, the thickness of the single electrode assembly 20 in Example 2 is smaller and the width is larger, and the negative electrode plate 21 is not broken in the fully charged state.

[0108] By comparing Example 6 and Comparative Example 2, it can be seen that when the size of the accommodating space Q of the shell 10 of the battery cell 100 along the thickness direction K of the electrode assembly is the same and the capacity of the battery cell 100 is constant, the battery cell 100 in Example 2 includes two electrode assemblies 20. Compared with the battery cell 100 in Comparative Example 2 including one electrode assembly 20, the thickness of the single electrode assembly 20 in Example 2 is smaller and the width is larger, and the negative electrode plate 21 is not broken in the fully charged state.

[0109] By comparing Example 8 and Comparative Example 2, it can be seen that when the size of the accommodating space Q of the shell 10 of the battery cell 100 along the thickness direction K of the electrode assembly is the same and the capacity of the battery cell 100 is constant, the battery cell 100 in Example 8 includes two electrode assemblies 20 with different thicknesses. Compared with the battery cell 100 in Comparative Example 2 including one electrode assembly 20, the thickness of the single electrode assembly 20 in Example 8 is smaller, and the negative electrode plate 21 is not broken in the fully charged state.

[0110] Therefore, by reducing the thickness of the electrode assembly 20 and increasing the width of the electrode assembly 20 , the risk of expansion and fracture of the negative electrode plate 21 can be reduced, thereby improving the safety performance of the battery cell 100 .

[0111] (3) Comparing Example 4 with Example 2, Example 4 increases the thickness of the current collector of the negative electrode sheet 21 relative to Example 2, so that the elongation of the negative electrode sheet 21 in the winding direction X of the electrode assembly and the extension direction Y of the winding axis of the electrode assembly in Example 4 is lower than that in Example 2. Therefore, increasing the thickness of the negative electrode current collector is beneficial to reducing the expansion, which is the elongation of the negative electrode sheet 21 in the winding direction X of the electrode assembly and the extension direction Y of the winding axis of the electrode assembly, thereby reducing the risk of breakage of the negative electrode sheet 21.

[0112] (4) Comparing Example 4 and Example 5, the current collector of the negative electrode plate 21 in Example 5 adopts a copper foil-polymer composite current collector, while the current collector of the negative electrode plate 21 in Example 4 adopts a copper foil current collector, so that the elongation at break of the negative electrode plate 21 in Example 5 is larger than that in Example 4. Therefore, the use of the composite current collector for the negative electrode plate 21 is beneficial to increase the elongation at break of the negative electrode plate 21, thereby reducing the risk of the negative electrode plate 21 breaking.

[0113] (5) By comparing Example 2, Example 6 and Example 7, it can be seen that when the number of electrode assemblies 20 in the battery cell 100 is the same as the thickness of the electrode assemblies 20, the larger the width of the electrode assembly 20, the larger X0-(X1+X2), and the lower the risk of the negative electrode plate 21 breaking.

[0114] (6) By comparing Example 9 with Example 5, it can be seen that, when the size of the accommodating space Q of the shell 10 of the battery cell 100 along the thickness direction K of the electrode assembly is the same and the capacity of the battery cell 100 is constant, Example 9 further increases the number of electrode assemblies 20 relative to Example 5, reduces the thickness of a single electrode assembly 20, and the negative electrode sheet 21 is not broken. However, Example 5 can already meet the requirements, so there is no need to further split it into three electrode assemblies 20 on the basis of Example 5 to further reduce the thickness of a single electrode assembly 20.

[0115] Table 2

[0116]

[0117]

[0118] It can be seen from Table 2, combined with Comparative Example 3, Example 10-Example 21, that when X0-(X1+X2) is -0.1% and 0, the negative electrode sheet 21 is broken after the battery cell 100 is fully charged, and when X0-(X1+X2) is 0.1%, 0.3%, 0.4%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, the negative electrode sheet 21 is not broken when the battery cell 100 is fully charged. Therefore, when X0-(X1+X2)≥0, the negative electrode sheet 21 is not broken when the battery cell 100 is in a fully charged state. As X0-(X1+X2) increases, the energy density of the battery cell 100 gradually decreases. When X0-(X1+X2) is 2.5%, the energy density of the battery cell 100 is lower than when X0-(X1+X2) is 0.1%, 0.3%, 0.4%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, and 2%. Therefore, 0≤X0-(X1+X2)≤2% can reduce the risk of expansion and fracture of the negative electrode sheet when the battery cell 100 is fully charged, improve the safety performance of the battery cell 100, reduce the capacity loss of the battery cell 100, and make the battery cell 100 have a better energy density.

[0119] Please continue to refer to Table 2. When X0-(X1+X2) is 0.1% and 0.3%, the negative electrode sheet 21 of the battery cell 100 does not break when it is fully charged. However, after the battery cell 100 is cycled a certain number of times, the negative electrode sheet 21 will break, resulting in a reduction in the service life of the battery cell 100. When X0-(X1+X2) is 0.4%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, and 2.5%, the negative electrode sheet 21 does not break when the battery cell 100 is fully charged and as the number of cycles of the battery cell 100 increases. Therefore, 0.4%≤X0-(X1+X2) can reduce the risk of expansion and fracture of the negative electrode sheet 21 after the number of cycles of the battery cell 100 increases, thereby further improving the safety performance of the battery cell 100 and extending the service life of the battery cell 100. The battery cell 100 when X0-(X1+X2) is 0.8%, 1%, 1.2%, and 1.5% has a better energy density than the battery cell 100 when X0-(X1+X2) is 1.8% and 2%. Therefore, 0.4%≤X0-(X1+X2)≤1.5%, which can further reduce the risk of expansion and fracture of the negative electrode plate 21 after the number of cycles of the battery cell 100 increases, thereby further improving the safety performance of the battery cell 100 and extending the service life of the battery cell 100, and also has a better energy density.

[0120] Cyclic tests were performed on Examples 22 to 26 to obtain the data in Table 3. The dimensions of the accommodation spaces Q of the housings 10 of the battery cells 100 of the examples in Table 3 along the thickness direction K of the electrode assembly are the same, and the capacities of the battery cells 100 are the same.

[0121] Table 3

[0122]

[0123] As shown in Table 3, by comparing Example 22 and Example 23 to Example 26, it can be seen that when the size of the accommodation space Q of the shell 10 of the battery cell 100 along the thickness direction K of the electrode assembly is the same and the capacity of the battery cell 100 is constant, the battery cell 100 in Example 23, Example 24, Example 25, and Example 26 includes two electrode assemblies 20, three electrode assemblies 20, four electrode assemblies 20, and five electrode assemblies 20, respectively. Compared with the battery cell 100 in Example 22 including only one electrode assembly 20, the thickness of each electrode assembly 20 in Example 23 to Example 26 is smaller, X0-(X1+X2) is larger, and the risk of expansion and fracture of the negative electrode sheet 21 of the battery cell 100 in the fully charged state is lower, and Example 23 to Example 25 have a higher energy density than Example 26. Therefore, when the accommodation space Q is constant, by increasing the number of electrode assemblies 20 and reducing the thickness of the electrode assembly 20, it is beneficial to reduce the risk of expansion and fracture of the negative electrode sheet 21, improve the safety performance of the battery cell 100, and ensure the energy density of the battery cell 100.

[0124] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A battery cell, characterized in that: include: shell; An electrode assembly is contained in the housing, the electrode assembly is a wound structure, the electrode assembly includes a negative electrode sheet, along the winding direction of the electrode assembly, the elongation at break of the negative electrode sheet is X0, along the extension direction of the winding axis of the electrode assembly, the elongation of the negative electrode sheet is X1, along the thickness direction of the electrode assembly, the expansion rate of the electrode assembly is X2, and the following conditions are satisfied: 0≤X0-(X1+X2)≤2%; Wherein, when the battery cell is in a fully charged state, the length of the negative electrode sheet along the extension direction of the winding axis of the electrode assembly is X 11 The dimension of the electrode assembly along its thickness direction is X 21 When the battery cell is fully charged, the length of the negative electrode sheet along the extension direction of the winding axis of the electrode assembly is X 12 The dimension of the electrode assembly along its thickness direction is X 22 The dimension of the electrode assembly along its width direction is b, X1=(X 11 -X 12 ) / X 12 , X2=(X 21 -X 22 ) / b, the extension direction of the winding axis of the electrode assembly, the thickness direction of the electrode assembly and the width direction of the electrode assembly are perpendicular to each other.

2. The battery cell according to claim 1, characterized in that: 0.4%≤X0-(X1+X2)≤1.5%.

3. The battery cell according to claim 1, characterized in that: The negative electrode plate includes a negative electrode active material, and the negative electrode active material includes silicon.

4. The battery cell according to claim 3, characterized in that: The weight percentage of silicon in the negative electrode active material is C, 0<C<100%.

5. The battery cell according to claim 4, characterized in that: 15％≤C≤80％。 6. The battery cell according to claim 3, characterized in that: The negative electrode active material further includes graphite.

7. The battery cell according to claim 1, characterized in that: The number of the electrode assemblies is N, and a receiving space is formed inside the housing. The size of the receiving space along the thickness direction of the electrode assembly is H, wherein N≥2, 0.5H / N≤X 22 ≤1.5H / N.

8. The battery cell according to claim 7, characterized in that: The battery core includes a plurality of the electrode assemblies, and the plurality of the electrode assemblies are stacked along a thickness direction of the electrode assemblies; the number of the electrode assemblies does not exceed four.

9. The battery cell according to claim 1, characterized in that: A containing space is formed inside the shell, and a dimension of the containing space along the thickness direction of the electrode assembly is H, 5mm≤H≤20mm.

10. The battery cell according to claim 9, characterized in that: 6mm≤H≤15mm.

11. The battery cell according to claim 1, characterized in that: 2.5mm≤X 22 ≤10mm。 12. The battery cell according to claim 11, characterized in that: 3mm≤X 22 ≤7.5mm。 13. An electrical equipment, characterized in that: Comprising the battery cell according to any one of claims 1-12.

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