Composite pole piece and preparation method thereof, battery cell and preparation method thereof, and battery

Abstract

The embodiment of the present application relates to a composite electrode sheet and a preparation method thereof, a battery cell and a preparation method thereof, and a battery, wherein the composite electrode sheet comprises: a base film, the base film having a first surface and a second surface opposite to each other, the first surface and the second surface respectively comprising at least one negative electrode region, at least one diaphragm region and at least one positive electrode region, the diaphragm region being located between adjacent negative electrode regions and positive electrode regions, the negative electrode region and the positive electrode region located on the first surface respectively corresponding to the negative electrode region and the positive electrode region located on the second surface; a negative electrode sheet, located on the negative electrode region, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector; a positive electrode sheet, located on the positive electrode region, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector. In this way, the composite electrode sheet can be Z-folded to form a battery cell, which can improve the stacking efficiency and enhance the safety performance and cycle performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a composite pole piece and a preparation method thereof, a battery cell and a preparation method thereof, and a battery. Background Art

[0002] The battery cell is usually made by a winding process or a folding process. In the winding process, first, the positive active material and the negative active material are coated on the positive current collector and the negative current collector respectively to prepare the positive electrode sheet and the negative electrode sheet. Secondly, the positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, and the separator is located between the positive electrode sheet and the negative electrode sheet. Then, the battery cell is obtained by winding. In the folding process, the specific method for preparing the positive electrode sheet and the negative electrode sheet is similar to the winding process. After the preparation of the positive electrode sheet and the negative electrode sheet is completed, a slitting step is required to cut the positive electrode sheet and the negative electrode sheet into multiple independent small pieces, and then the positive electrode sheet and the negative electrode sheet are respectively inserted into the Z-folded separator at intervals, so that the separator is located between the positive electrode sheet and the negative electrode sheet, thereby obtaining a battery cell.

[0003] The cells formed by the winding process have greater tension on the semicircular edges (also called corners) on both sides of the cells, which are prone to lithium deposition. In addition, the corners are prone to expansion and deformation during the charging and discharging process, which has a significant impact on the electrochemical performance and safety performance of the battery. Compared with the winding process, the advantage of the folding process is that it avoids the adverse effects caused by the corners during the charging and discharging process and increases the electrochemical stability of the lithium-ion battery cycle. However, the current folding process is complicated to operate and has low production efficiency, resulting in high manufacturing costs. Summary of the invention

[0004] In view of this, the embodiments of the present application provide a composite electrode and a method for preparing the same, a battery cell and a method for preparing the same, and a battery to solve at least one problem existing in the background technology.

[0005] In a first aspect, an embodiment of the present application provides a composite pole piece, comprising:

[0006] A base film, the base film having a first surface and a second surface opposite to each other, the first surface and the second surface respectively including at least one negative electrode region, at least one separator region and at least one positive electrode region, the separator region is located between the adjacent negative electrode region and the positive electrode region, the negative electrode region and the positive electrode region located on the first surface respectively correspond to the negative electrode region and the positive electrode region located on the second surface;

[0007] A negative electrode plate, located on the negative electrode region, the negative electrode plate comprising a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector;

[0008] A positive electrode plate is located on the positive electrode region, and the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector.

[0009] In conjunction with the first aspect of the present application, in an optional embodiment, the negative electrode current collector is directly located on the surface of the base film, and the negative electrode active material layer is located on the surface of the negative electrode current collector on the side away from the base film; and / or,

[0010] The positive electrode current collector is directly located on the surface of the base film, and the positive electrode active material layer is located on the surface of the positive electrode current collector on a side away from the base film.

[0011] In conjunction with the first aspect of the present application, in an optional embodiment, the base film, the negative electrode current collector and the positive electrode current collector in the composite electrode sheet meet at least one of the following characteristics (1) to (9):

[0012] (1) The width of the base film is 130 mm to 150 mm;

[0013] (2) The thickness of the base film is 4.5 μm to 9 μm;

[0014] (3) The material of the base film includes a polymer material;

[0015] (4) In the length direction of the base film, the size of the positive electrode current collector is 40 mm to 60 mm, and the size of the negative electrode current collector is 40 mm to 60 mm;

[0016] (5) In the width direction of the base film, the size of the positive electrode collector is 116 mm to 126 mm, and the size of the negative electrode collector is 116 mm to 126 mm;

[0017] (6) In the length direction of the base film, the size of the diaphragm region is larger than the size of the positive electrode current collector and the negative electrode current collector, and the difference between the size of the diaphragm region and the size of the positive electrode current collector and / or the negative electrode current collector is 1 mm to 3 mm;

[0018] (7) The negative electrode current collector and the positive electrode current collector are staggered in the width direction of the base film, the negative electrode current collector is close to one side edge of the base film, and the positive electrode current collector is close to the other side edge of the base film;

[0019] (8) The materials of the negative electrode current collector and the positive electrode current collector both include aluminum;

[0020] (9) The base film includes a polyvinylidene fluoride coating and a ceramic coating sequentially stacked on the diaphragm region.

[0021] In conjunction with the first aspect of the present application, in an optional embodiment, the negative electrode active material layer and the positive electrode active material layer in the composite electrode sheet satisfy at least one of the following features (1) to (7):

[0022] (1) In the length direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer;

[0023] (2) In the width direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer;

[0024] (3) In the length direction of the base film, the negative electrode active material layer is located in the middle of the corresponding negative electrode current collector;

[0025] (4) In the length direction of the base film, the positive electrode active material layer is located in the middle of the corresponding positive electrode current collector;

[0026] (5) The central axes of the negative electrode active material layer and the positive electrode active material layer in the length direction of the base film are on a straight line;

[0027] (6) The compaction density of the negative electrode active material layer is 0.9 g / cm 3 ~0.96g / cm 3 ;

[0028] (7) The compaction density of the positive electrode active material layer is 3.0 g / cm 3 ~3.2g / cm 3 .

[0029] In a second aspect, an embodiment of the present application provides a method for preparing a composite electrode, the method comprising:

[0030] Providing a base film, the base film having a first surface and a second surface opposite to each other, the first surface and the second surface respectively including at least one negative electrode region, at least one separator region and at least one positive electrode region, the separator region is located between the adjacent negative electrode region and the positive electrode region, the negative electrode region and the positive electrode region located on the first surface respectively correspond to the negative electrode region and the positive electrode region located on the second surface;

[0031] forming a negative electrode current collector on the negative electrode region by using a first process;

[0032] forming a positive electrode current collector on the positive electrode region by using a second process;

[0033] A negative electrode active material layer and a positive electrode active material layer are formed on the negative electrode collector and the positive electrode collector, respectively.

[0034] In conjunction with the second aspect of the present application, in an optional embodiment, the negative electrode current collector and the positive electrode current collector are formed to meet at least one of the following characteristics (1) to (7):

[0035] (1) In the length direction of the base film, the size of the positive electrode current collector is 40 mm to 60 mm, and the size of the negative electrode current collector is 40 mm to 60 mm;

[0036] (2) In the width direction of the base film, the size of the positive electrode current collector is 116 mm to 126 mm, and the size of the negative electrode current collector is 116 mm to 126 mm;

[0037] (3) In the length direction of the base film, the size of the diaphragm region is larger than the size of the positive electrode current collector and the negative electrode current collector, and the difference between the size of the diaphragm region and the size of the positive electrode current collector and / or the negative electrode current collector is 1 mm to 3 mm;

[0038] (4) The negative electrode current collector and the positive electrode current collector are staggered in the width direction of the base film, with the negative electrode current collector close to one side edge of the base film and the positive electrode current collector close to the other side edge of the base film;

[0039] (5) The materials of the negative electrode current collector and the positive electrode current collector both include aluminum;

[0040] (6) The first process includes at least one of magnetron sputtering, water electroplating, evaporation, and chemical vapor deposition;

[0041] (7) The second process includes at least one of magnetron sputtering, water electroplating, evaporation, and chemical vapor deposition.

[0042] In conjunction with the second aspect of the present application, in an optional embodiment, the negative electrode active material layer and the positive electrode active material layer are formed to meet at least one of the following characteristics (1) to (7):

[0043] (1) In the length direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer;

[0044] (2) In the width direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer;

[0045] (3) In the length direction of the base film, the negative electrode active material layer is located in the middle of the corresponding negative electrode current collector;

[0046] (4) In the length direction of the base film, the positive electrode active material layer is located in the middle of the corresponding positive electrode current collector;

[0047] (5) The central axes of the negative electrode active material layer and the positive electrode active material layer in the length direction of the base film are on a straight line;

[0048] (6) The compaction density of the negative electrode active material layer is 0.9 g / cm 3 ~0.96g / cm 3 ;

[0049] (7) The compaction density of the positive electrode active material layer is 3.0 g / cm 3 ~3.2g / cm 3 .

[0050] In a third aspect, an embodiment of the present application provides a method for preparing a battery cell, the method comprising:

[0051] Providing a composite pole piece as described in any one of the first aspects or a composite pole piece prepared by the preparation method as described in any one of the second aspects;

[0052] The base film is folded in a Z shape, and portions of the base film located in the diaphragm region close to the negative electrode region and close to the positive electrode region form bending portions, so that the diaphragm region located on the first surface covers the negative electrode collector and / or the positive electrode collector located on the first surface, and the diaphragm region located on the second surface covers the negative electrode collector and / or the positive electrode collector located on the second surface.

[0053] In a fourth aspect, an embodiment of the present application provides a battery cell, which is prepared using the battery cell preparation method described in the third aspect.

[0054] In a fifth aspect, an embodiment of the present application provides a battery, comprising a battery cell prepared by the preparation method described in the third aspect or comprising the battery cell described in the fourth aspect.

[0055] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0056] The composite electrode sheet and its preparation method, battery cell and its preparation method and battery provided in the embodiments of the present application, the composite electrode sheet includes: a base film, the base film has a first surface and a second surface relative to each other, the first surface and the second surface respectively include at least one negative electrode region, at least one diaphragm region and at least one positive electrode region, the diaphragm region is located between adjacent negative electrode regions and positive electrode regions, the negative electrode region and the positive electrode region located on the first surface respectively correspond to the negative electrode region and the positive electrode region located on the second surface; a negative electrode sheet, located on the negative electrode region, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector; a positive electrode sheet, located on the positive electrode region, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector. In the embodiment of the present application, the negative electrode sheet and the positive electrode sheet are respectively located on the negative electrode region and the positive electrode region of the base film, so that the base film and the positive electrode sheet and the negative electrode sheet form an integrated structure. The diaphragm region is located between the adjacent negative electrode region and the positive electrode region, and the negative electrode region and the positive electrode region located on the first surface correspond to the negative electrode region and the positive electrode region located on the second surface, respectively, so that the positive electrode sheet and the negative electrode sheet are closely arranged, and the composite electrode sheet can be directly Z-folded to form a battery cell, thereby improving the stacking efficiency, saving materials, and thus reducing costs. Compared with the battery cell formed by the winding process, the problem of easy lithium deposition at the corners of the battery cell can be avoided, and the battery cell formed by the Z-shaped folding of the composite electrode sheet is more compact, which can reduce the battery resistance, improve the energy density, safety performance and cycle performance.

[0057] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0059] Figure 1 A top view of a composite pole piece provided in an embodiment of the present application;

[0060] Figure 2 For along Figure 1 Vertical section along line AA;

[0061] Figure 3 A schematic diagram of a process for preparing a composite electrode provided in an embodiment of the present application;

[0062] Figure 4 A side view of a base film provided in an embodiment of the present application;

[0063] Figures 5 to 7A top view of the composite electrode provided in an embodiment of the present application during the preparation process;

[0064] Figure 8 A schematic diagram of a process for preparing a battery cell provided in an embodiment of the present application;

[0065] Fig. 9 A schematic diagram of the cross-sectional structure of a battery cell provided in an embodiment of the present application. DETAILED DESCRIPTION

[0066] In order to make the technical scheme and beneficial effects of the present invention more obvious and easy to understand, the following is described in detail by combining the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0067] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features known in the art are not described; that is, all features of the actual embodiments are not described here, and well-known functions and steps are not described in detail.

[0068] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present application. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0069] In order to thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below, but in addition to these detailed descriptions, the present application may also have other implementation methods.

[0070] Unless otherwise defined, technical and scientific terms used in this application have the same meanings as those in the technical field to which this application belongs.

[0071] If no specific techniques or conditions are specified in the following examples, the conventional techniques or conditions described in the literature in the art, or the conditions recommended by the product instructions and the manufacturer are generally used. The numerical ranges in the following examples all include the endpoint values.

[0072] The present application embodiment provides a composite electrode. Figure 1 and Figure 2 , the composite pole piece comprises:

[0073] A base film 100, the base film 100 has a first surface 101 and a second surface 102 opposite to each other, the first surface 101 and the second surface 102 respectively include at least one negative electrode region 201, at least one separator region 202 and at least one positive electrode region 203, the separator region 202 is located between adjacent negative electrode regions 201 and positive electrode regions 203, and the negative electrode region 201 and the positive electrode region 203 located on the first surface 101 correspond to the negative electrode region 201 and the positive electrode region 203 located on the second surface 102, respectively;

[0074] A negative electrode sheet 300 is located on the negative electrode region 201 , and the negative electrode sheet 300 includes a negative electrode current collector 301 and a negative electrode active material layer 302 located on at least one side surface of the negative electrode current collector 301 ;

[0075] The positive electrode sheet 400 is located on the positive electrode region 203 . The positive electrode sheet 400 includes a positive electrode current collector 401 and a positive electrode active material layer 402 located on at least one side surface of the positive electrode current collector 401 .

[0076] In the embodiment of the present application, the negative electrode sheet 300 and the positive electrode sheet 400 are respectively located on the negative electrode region 201 and the positive electrode region 203 of the base film 100, so that the base film 100 and the positive electrode sheet 400 and the negative electrode sheet 300 form an integrated structure. The diaphragm region 202 is located between the adjacent negative electrode region 201 and the positive electrode region 203, and the negative electrode region 201 and the positive electrode region 203 located on the first surface 101 correspond to the negative electrode region 201 and the positive electrode region 203 located on the second surface 102, respectively. The positive electrode sheet 400 and the negative electrode sheet 300 are arranged closely, and the composite electrode sheet can be directly Z-folded to form a battery cell, thereby improving the stacking efficiency, saving materials, and thus reducing costs. Compared with the battery cell formed by the winding process, the problem of easy lithium deposition at the corners of the battery cell can be avoided. Moreover, the battery cell formed by the Z-folding of the composite electrode sheet is compact, which can reduce the battery resistance, improve the energy density, safety performance and cycle performance.

[0077] It should be noted that if Figure 2As shown, in the embodiment of the present application, the negative electrode region 201 and the positive electrode region 203 located on the first surface 101 correspond to the negative electrode region 201 and the positive electrode region 203 located on the second surface 102, respectively. It can be understood that in the thickness direction of the base film 100, that is, Figure 2 In the third direction, the vertical projections of the negative electrode region 201 located on the first surface 101 and the negative electrode region 201 located on the second surface 102 at least partially overlap, and the vertical projections of the positive electrode region 203 located on the first surface 101 and the positive electrode region 203 located on the second surface 102 at least partially overlap. Since the diaphragm region 202 is located between the adjacent negative electrode region 201 and positive electrode region 203, in the third direction, the vertical projections of the diaphragm region 202 located on the first surface 101 and the diaphragm region 202 located on the second surface 102 at least partially overlap.

[0078] In some specific embodiments, in the third direction, the vertical projections of the negative electrode region 201 located on the first surface 101 and the negative electrode region 201 located on the second surface 102 overlap, the vertical projections of the positive electrode region 203 located on the first surface 101 and the positive electrode region 203 located on the second surface 102 overlap, and the vertical projections of the diaphragm region 202 located on the first surface 101 and the diaphragm region 202 located on the second surface 102 overlap. In this way, the area of ​​the base film 100 can be more fully utilized, so that the arrangement of the pole pieces is more compact, thereby improving the energy density of the battery, and the negative electrode region 201, the diaphragm region 202 and the positive electrode region 203 of the first surface 101 are respectively opposite to the negative electrode region 201, the diaphragm region 202 and the positive electrode region 203 of the second surface 102, which can make the process of folding the composite pole piece to form a battery cell simpler, and the structure of the formed battery cell is more regular and stable, and the performance is better.

[0079] In some embodiments, the negative electrode active material layer 302 may be located on two opposite surfaces of the negative electrode current collector 301. This can further improve the energy density of the battery. Figure 2 As shown, the negative electrode current collector 301 can be directly located on the surface of the base film 100, and the negative electrode active material layer 302 is located on the surface of the negative electrode current collector 301 away from the base film 100. In this way, the negative electrode current collector 301 can be directly formed on the base film 100, and the bonding force between the negative electrode plate 300 and the base film 100 can be enhanced, thereby greatly reducing the risk of the negative electrode plate 300 and the base film 100 falling off, thereby further improving the cycle performance and safety performance of the battery.

[0080] In some embodiments, the positive electrode active material layer 402 may be located on two opposite surfaces of the positive electrode current collector 401. This can further improve the energy density of the battery. Figure 2As shown, the positive electrode current collector 401 can be directly located on the surface of the base film 100, and the positive electrode active material layer 402 is located on the surface of the positive electrode current collector 401 away from the base film 100. In this way, the positive electrode current collector 401 can be directly formed on the base film 100, and the bonding force between the positive electrode sheet 400 and the base film 100 can be enhanced, thereby greatly reducing the risk of the positive electrode sheet 400 and the base film 100 falling off, thereby further improving the cycle performance and safety performance of the battery.

[0081] In the embodiment of the present application, the base film 100 at the negative electrode region 201 and the positive electrode region 203 respectively serves as a carrier of the negative electrode plate 300 and the positive electrode plate 400, and the base film 100 at the diaphragm region 202 serves as a diaphragm. When the composite electrode plate is Z-folded to form a battery cell, the base film 100 as a diaphragm is located between the positive electrode plate 400 and the negative electrode plate 300 to play an insulating role. Exemplarily, the material of the base film 100 may include a polymer material, for example, one or more of polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyimide (PI), etc. In a specific embodiment, the material of the base film 100 includes polypropylene.

[0082] In the present application embodiment, Figure 1 As shown, in the length direction of the base film 100, that is, Figure 1 In the first direction of the substrate 100, the number of the negative electrode region 201, the separator region 202 and the positive electrode region 203 can be set according to actual needs, and the length of the corresponding base film 100 can be set according to actual needs. Figure 1 In the second direction of the substrate 100, the width of the substrate 100 can be set according to the size of the required battery cell. In some specific embodiments, the width of the substrate 100 can be 130 mm to 150 mm, for example, 130 mm, 140 mm, 150 mm, or any value between any two of the above ranges. In this way, the battery cell formed by the composite electrode sheet can have a suitable size and capacity. In a specific embodiment, the width of the substrate 100 is 132 mm.

[0083] The thickness of the base film 100 affects the mechanical strength, safety, energy density and battery cycle performance of the battery. In some specific embodiments, the thickness of the base film 100 can be 4.5 μm to 9 μm, for example, 4.5 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or any value between any two of the above ranges. In this way, the formed battery cell can have a suitable size and have higher mechanical properties and cycle performance. In a specific embodiment, the thickness of the base film 100 is 6 μm.

[0084] In the first direction, the positive electrode current collector 401 and the negative electrode current collector 301 may have the same size or different sizes. In some specific embodiments, the positive electrode current collector 401 and the negative electrode current collector 301 have the same size in the first direction. This can make the structure of the battery cell formed by the composite electrode sheet more regular and stable, and have better performance.

[0085] For example, in the first direction, the size of the positive current collector 401 may be 40 mm to 60 mm, and the size of the negative current collector 301 may be 40 mm to 60 mm. In a specific embodiment, the size of the positive current collector 401 and the negative current collector 301 in the first direction are both 52 mm.

[0086] In the second direction, the positive electrode current collector 401 and the negative electrode current collector 301 may have the same size or different sizes. In some specific embodiments, the positive electrode current collector 401 and the negative electrode current collector 301 have the same size in the second direction. This can make the structure of the battery cell formed by the composite electrode sheet more regular and stable, and have better performance.

[0087] For example, in the second direction, the size of the positive current collector 401 may be 116 mm to 126 mm, and the size of the negative current collector 301 may be 116 mm to 126 mm. In a specific embodiment, the size of the positive current collector 401 and the negative current collector 301 in the second direction are both 120 mm.

[0088] As mentioned above, in the embodiment of the present application, when the composite pole piece is Z-folded to form a battery cell, the base film 100 as a separator is located between the positive pole piece 400 and the negative pole piece 300, and plays an insulating role. Then, the bending position of the composite pole piece is located at both ends of the separator region 202 close to the negative electrode region 201 and the positive electrode region 203. When the size of the separator region 202 in the first direction is small, the separator region 202 cannot cover the positive pole piece 400 and the negative pole piece 300 well after folding. When the size of the separator is large, the area utilization of the base film 100 is not sufficient, which affects the energy density of the battery cell. Therefore, in some specific embodiments, the size of the separator region 202 in the first direction may be larger than the size of the positive current collector 401 and the negative current collector 301, and the difference between the size of the separator region 202 and the size of the positive current collector 401 and / or the negative current collector 301 may be 1mm~3mm. In this way, the separator region 202 in the battery cell formed by the composite electrode sheet can better cover the positive electrode sheet 400 and the negative electrode sheet 300, and reserve a suitable space for the folding of the composite electrode sheet, while fully utilizing the area of ​​the base film 100, facilitating the folding of the composite electrode sheet, and the energy density, cycle performance and safety performance of the formed battery cell are higher. In a specific embodiment, in the first direction, the difference between the size of the separator region 202 and the size of the positive current collector 401 and the negative current collector 301 is 2 mm.

[0089] Please refer to Figure 1 In the actual preparation of the composite electrode sheet, the negative electrode current collector 301 and the positive electrode current collector 401 may not be coated with active materials on the two sides (two sides extending in the first direction) of the base film 100, and may be used as the negative electrode tab 303 and the positive electrode tab 403. Therefore, in some embodiments, the negative electrode current collector 301 and the positive electrode current collector 401 may be staggered in the second direction, with the negative electrode current collector 301 close to one side edge of the base film 100 and the positive electrode current collector 401 close to the other side edge of the base film 100. In this way, the negative electrode tab 303 and the positive electrode tab 403 can be distributed on opposite sides, increasing the distance between the positive and negative tabs, reducing the risk of short circuit, and making it easier to connect the positive and negative electrodes of the battery cell. In addition, in the actual process, it is necessary to cut off part of the base film 100 from the two sides in the width direction of the base film 100 to form the negative electrode tab 303 and the positive electrode tab 403. Therefore, the negative electrode collector 301 and the positive electrode collector 401 are staggered in the second direction, which can avoid part of the positive electrode collector 401 and part of the negative electrode current collector 301 being cut off together, thereby avoiding material waste and saving costs.

[0090] In addition, please continue to refer to Figure 1In the second direction, the side of the base film 100 away from the negative electrode tab 303 exceeds the negative electrode current collector 301, and the side of the base film 100 away from the positive electrode tab 403 exceeds the positive electrode current collector 401. In this way, the base film 100 can better wrap the positive electrode tab 400 and the negative electrode tab 300 in the battery cell formed by the composite electrode sheet. Even if the edges of the composite electrode sheet are misaligned to a certain extent during the lamination process, the cathode and the anode can be prevented from contacting and short-circuiting. Specifically, the size of the positive electrode tab 403 in the second direction can be 6mm~15mm, the size of the negative electrode tab 303 in the second direction can be 6mm~15mm, the size of the base film 100 in the second direction beyond the negative electrode current collector 301 can be 2mm~4mm, and the size of the base film 100 in the second direction beyond the positive electrode current collector 401 can be 2mm~4mm.

[0091] In some embodiments, the materials of the negative electrode current collector 301 and the positive electrode current collector 401 may both include aluminum. In sodium ion batteries, since sodium ions do not form alloys with aluminum during the charge and discharge process, the material of the negative electrode current collector 301 may include aluminum, and the material of the negative electrode current collector 301 includes aluminum relative to the material of the negative electrode current collector 301 including copper, which can save costs. Exemplarily, the negative electrode current collector 301 and the positive electrode current collector 401 may both include aluminum foil. Of course, the embodiment of the present application does not exclude the situation where the negative electrode current collector 301 includes copper and the positive electrode current collector 401 includes aluminum, so it can be applied to more types of batteries.

[0092] In some embodiments, please refer to Figure 1 and Figure 2 , the base film 100 may include a polyvinylidene fluoride coating layer 103 and a ceramic coating layer 104 sequentially stacked on the diaphragm region 202 .

[0093] In the embodiment of the present application, the base film 100 at the diaphragm region 202 serves as the diaphragm in the battery cell, and the polyvinylidene fluoride coating 103 and the ceramic coating 104 on the diaphragm region 202 can enhance the thermal stability, mechanical strength and wettability of the diaphragm to the electrolyte, thereby further improving the performance of the battery.

[0094] It should be noted that the polyvinylidene fluoride coating 103 and the ceramic coating 104 in the embodiment of the present application may cover the entire area of ​​the diaphragm area 202, or may cover a part of the diaphragm area 202. The diaphragm area 202 covered by the polyvinylidene fluoride coating 103 and the ceramic coating 104 may be referred to as an effective diaphragm area, where the effective area may be understood as being located between the positive electrode sheet 400 and the negative electrode sheet 300, and having an insulating effect. The diaphragm area 202 not covered by the polyvinylidene fluoride coating 103 and the ceramic coating 104 may be referred to as a bending area. When the composite electrode sheet is subsequently folded into a Z-shape to form a battery cell, the bending position may be in the bending area. The polyvinylidene fluoride coating 103 and the ceramic coating 104 are not provided on the bending area, which can save materials on the one hand and facilitate the folding process on the other hand.

[0095] Exemplarily, the material of the ceramic coating 104 may include one or more of aluminum oxide, boehmite, zirconium oxide, silicon oxide, magnesium oxide, titanium oxide, zinc oxide, calcium oxide, barium sulfate, aluminum hydroxide, magnesium hydroxide, silicon nitride, boron nitride, aluminum nitride, and silicon carbide. The thickness of the polyvinylidene fluoride coating 103 may be 2 μm to 4 μm. The thickness of the ceramic coating 104 may be 2 μm to 4 μm. In a specific embodiment, the material of the ceramic coating 104 includes aluminum oxide, the thickness of the polyvinylidene fluoride coating 103 is 3 μm, and the thickness of the ceramic coating 104 is 3 μm.

[0096] Please refer to Figure 1 and Figure 2 In the embodiment of the present application, the negative electrode active material layer 302 and the positive electrode active material layer 402 are respectively located on the surface of the negative electrode collector 301 and the positive electrode collector 401 , thereby forming the negative electrode sheet 300 and the positive electrode sheet 400 .

[0097] In the design of the battery, the length and width of the negative electrode plate 300 usually exceed the length and width of the positive electrode plate 400, and the area where the negative electrode plate 300 exceeds the positive electrode plate 400 can be called the overhang area. This design can effectively reduce the risk of lithium deposition at the edge of the negative electrode plate 300 during charging.

[0098] In some embodiments, in the first direction, the size of the negative electrode active material layer 302 may be larger than the size of the positive electrode active material layer 402. This allows the negative electrode active material layer 302 to better cover the positive electrode active material layer 402, thereby effectively reducing the risk of lithium deposition at the edge of the negative electrode plate 300 during charging.

[0099] In some embodiments, in the second direction, the size of the negative electrode active material layer 302 may be larger than the size of the positive electrode active material layer 402. This allows the negative electrode active material layer 302 to better cover the positive electrode active material layer 402, thereby further reducing the risk of lithium deposition at the edge of the negative electrode plate 300 during charging.

[0100] In some embodiments, in the first direction, the negative electrode active material layer 302 may be located in the middle of the corresponding negative electrode current collector 301. This makes it easy for the negative electrode active material layer 302 and the positive electrode active material layer 402 to correspond better in the battery cell formed by the composite electrode sheet, and the area of ​​the overlapped area of ​​the vertical projection of the negative electrode active material layer 302 and the positive electrode active material layer 402 in the thickness direction of the base film 100 is larger, thereby further improving the cycle performance and safety performance of the battery.

[0101] In some embodiments, in the first direction, the positive electrode active material layer 402 may be located in the middle of the corresponding positive electrode current collector 401. This makes it easy for the negative electrode active material layer 302 and the positive electrode active material layer 402 to correspond better in the battery cell formed by the composite electrode sheet, and the area of ​​the overlapped area of ​​the vertical projection of the negative electrode active material layer 302 and the positive electrode active material layer 402 in the thickness direction of the base film 100 is larger, thereby further improving the cycle performance and safety performance of the battery.

[0102] In some embodiments, the central axes of the negative electrode active material layer 302 and the positive electrode active material layer 402 in the first direction are in a straight line. This makes it easier for the negative electrode active material layer 302 and the positive electrode active material layer 402 to correspond better in the battery cell formed by the composite electrode sheet, and the area of ​​the overlapped area of ​​the vertical projection of the negative electrode active material layer 302 and the positive electrode active material layer 402 in the thickness direction of the base film 100 is further increased, thereby further improving the cycle performance and safety performance of the battery.

[0103] In some embodiments, the compaction density of the negative electrode active material layer 302 may be 0.9 g / cm 3 ~0.96g / cm 3 This can make the battery's energy density higher.

[0104] In some embodiments, the compaction density of the positive electrode active material layer 402 may be 3.0 g / cm 3 ~3.2g / cm 3 This can make the battery's energy density higher.

[0105] In some specific embodiments, in the first direction, the size of the positive electrode current collector 401 can be the same as the size of the negative electrode current collector 301, the size of the negative electrode active material layer 302 can be the same as the size of the negative electrode current collector 301, the size of the positive electrode active material layer 402 can be smaller than the size of the positive electrode current collector 401, and in the second direction, the size of the negative electrode active material layer 302 can be larger than the size of the positive electrode active material layer 402. In this way, the area of ​​the negative electrode current collector 301 can be utilized to a greater extent, thereby improving the energy density of the battery, and at the same time ensuring that the negative electrode active material layer 302 in the battery cell formed by the composite electrode sheet can better cover the positive electrode active material layer 402, so as to better reduce the risk of lithium deposition at the edge of the negative electrode sheet 300 during charging.

[0106] Based on this, the present application also provides a method for preparing a composite electrode. Figure 3 The method for preparing the composite pole piece provided in the embodiment of the present application comprises:

[0107] Step S1: providing a base film, the base film having a first surface and a second surface opposite to each other, the first surface and the second surface respectively including at least one negative electrode region, at least one separator region and at least one positive electrode region, the separator region is located between adjacent negative electrode regions and positive electrode regions, and the negative electrode region and the positive electrode region located on the first surface correspond to the negative electrode region and the positive electrode region located on the second surface respectively;

[0108] Step S2: forming a negative electrode current collector on the negative electrode region by using the first process;

[0109] Step S3: forming a positive electrode current collector on the positive electrode region using a second process;

[0110] Step S4: forming a negative electrode active material layer and a positive electrode active material layer on the negative electrode current collector and the positive electrode current collector respectively.

[0111] It can be understood that in the above method, the negative electrode current collector and the positive electrode current collector are directly formed on the base film, and the positive electrode current collector and the negative electrode current collector form an integrated structure with the base film, and the bonding force between the two is strong. Then, a negative electrode active material layer is formed on the negative electrode current collector to obtain a negative electrode sheet, and a positive electrode active material layer is formed on the positive electrode current collector to obtain a positive electrode sheet, so that the positive electrode sheet and the negative electrode sheet form an integrated structure with the base film. Therefore, the risk of the positive electrode sheet and the negative electrode sheet falling off from the base film can be greatly reduced, thereby improving the cycle performance and safety performance of the battery. In addition, by arranging the diaphragm area between adjacent negative and positive electrode areas and the negative and positive electrode areas on the first surface corresponding to the negative and positive electrode areas on the second surface respectively, the formed positive and negative electrode sheets are arranged closely, and the prepared composite electrode sheets can be directly Z-folded to form battery cells, thereby improving the stacking efficiency, saving materials, and thus reducing costs. Compared with battery cells formed by a winding process, the problem of easy lithium deposition at the corners of the battery cells can be avoided, and the battery cells formed by the Z-folding of the composite electrode sheets are more compact, which can reduce battery resistance, improve energy density, safety performance and cycle performance.

[0112] It should also be understood that, although the steps in the above flowchart are shown in sequence as indicated by the arrows, these steps are not necessarily performed in the order indicated by the arrows. Moreover, at least a portion of the steps in the above flowchart may include multiple steps or multiple stages, and these steps or stages are not necessarily performed at the same time or performed in sequence.

[0113] Next, combine Figures 4 to 6 , the preparation method of the composite electrode provided in the embodiment of the present application and its beneficial effects are further described in detail.

[0114] First, please refer to Figure 4 and Figure 5 , perform step S1, provide a base film 100, the base film 100 has a first surface 101 and a second surface 102 relative to each other, the first surface 101 and the second surface 102 respectively include at least one negative electrode region 201, at least one diaphragm region 202 and at least one positive electrode region 203, the diaphragm region 202 is located between adjacent negative electrode regions 201 and positive electrode regions 203, the negative electrode region 201 and the positive electrode region 203 located on the first surface 101 correspond to the negative electrode region 201 and the positive electrode region 203 located on the second surface 102, respectively.

[0115] In the embodiment of the present application, the base film 100 at the positive electrode region 203 and the negative electrode region 201 serves as a carrier of the positive electrode sheet 400 and the negative electrode sheet 300, and the base film 100 at the diaphragm region 202 serves as a diaphragm. When the composite electrode sheet is folded in a Z shape to form a battery cell, the base film 100 serving as a diaphragm is located between the positive electrode sheet 400 and the negative electrode sheet 300, thereby playing an insulating role.

[0116] Next, please refer to Figure 6 , executing step S2, forming a negative electrode current collector 301 on the negative electrode region 201 using a first process.

[0117] In some embodiments, the first process may include at least one of magnetron sputtering, water electroplating, evaporation, and chemical vapor deposition, wherein the material of the negative electrode current collector 301 may include copper and / or aluminum. In the first direction, the size of the negative electrode current collector 301 may be 40 mm to 60 mm. In the second direction, the size of the negative electrode current collector 301 may be 116 mm to 126 mm.

[0118] Next, please continue to refer to Figure 6 , execute step S3, and form a positive electrode current collector 401 on the positive electrode region 203 using a second process.

[0119] In some embodiments, the second process may include at least one of magnetron sputtering, water electroplating, evaporation, and chemical vapor deposition, wherein the material of the positive electrode current collector 401 may include aluminum. In the first direction, the size of the positive electrode current collector 401 may be 40 mm to 60 mm. In the second direction, the size of the positive electrode current collector 401 may be 116 mm to 126 mm.

[0120] In some specific embodiments, the first process and the second process may be the same, so that the negative electrode current collector 301 and the positive electrode current collector 401 may be formed by the same process, thereby simplifying the preparation process.

[0121] In some specific embodiments, the negative electrode current collector 301 and the positive electrode current collector 401 and the material may both include aluminum, so that the negative electrode current collector 301 and the positive electrode current collector 401 can be formed simultaneously in a one-step process, further simplifying the preparation process. Moreover, in the embodiment of the present application, the negative electrode region 201 and the positive electrode region 203 are separated by the diaphragm region 202. When the negative electrode current collector 301 and the positive electrode current collector 401 are formed in a one-step process, the process window is large, which can further reduce the process difficulty.

[0122] In some embodiments, in the first direction, the size of the diaphragm region 202 may be larger than the size of the positive current collector 401 and the negative current collector 301, and the difference between the size of the diaphragm region 202 and the size of the positive current collector 401 and / or the negative current collector 301 is 1 mm to 3 mm. In this way, the diaphragm region 202 in the battery cell prepared with the composite electrode sheet can better cover the positive electrode sheet 400 and the negative electrode sheet 300, and reserve a suitable space for the folding of the composite electrode sheet, while fully utilizing the area of ​​the base film 100, facilitating the folding of the composite electrode sheet, and the energy density, cycle performance and safety performance of the formed battery cell are higher.

[0123] In some embodiments, please refer to Figure 6 , the negative electrode current collector 301 and the positive electrode current collector 401 can be staggered in the second direction, the negative electrode current collector 301 is close to one side edge of the base film 100, and the positive electrode current collector 401 is close to the other side edge of the base film 100. In this way, it is convenient to form a negative electrode tab and a positive electrode tab respectively with part of the negative electrode current collector 301 close to one side edge of the base film 100 and part of the positive electrode current collector 401 close to the other side edge of the base film 100, and the formed negative electrode tab and positive electrode tab are distributed on opposite sides, which can increase the distance between the positive and negative tabs and reduce the risk of short circuit on the one hand, and facilitate the connection of the positive and negative electrodes of the battery cell on the other hand.

[0124] In some specific embodiments, the distance between the sides of the negative electrode current collector 301 and the positive electrode current collector 401 close to the same side edge of the base film 100 may be 6 mm to 19 mm.

[0125] In some embodiments, please refer to Figure 6 The method for preparing the composite electrode sheet may further include: sequentially forming a polyvinylidene fluoride coating 103 and a ceramic coating 104 on the diaphragm region 202. The base film 100 of the diaphragm region 202 includes the polyvinylidene fluoride coating 103 and the ceramic coating 104, which can improve the thermal stability, mechanical strength and wettability of the base film 100 to the electrolyte.

[0126] In the embodiment of the present application, the order of forming the negative electrode current collector 301 , forming the positive electrode current collector 401 , and forming the polyvinylidene fluoride coating 103 and the ceramic coating 104 is not limited and can be adjusted according to the actual process.

[0127] Finally, please refer to Figure 7 , executing step S4 , forming the negative electrode active material layer 302 and the positive electrode active material layer 402 on the negative electrode current collector 301 and the positive electrode current collector 401 , respectively.

[0128] In some embodiments, executing step S4 may include the following steps:

[0129] S41: preparing negative electrode slurry and positive electrode slurry;

[0130] S42: coating the negative electrode slurry and the positive electrode slurry on the negative electrode current collector 301 and the positive electrode current collector 401 respectively, and drying to obtain the negative electrode active material layer 302 and the positive electrode active material layer 402;

[0131] S43 : The negative electrode active material layer 302 and the positive electrode active material layer 402 are roll-pressed respectively.

[0132] In step S41, preparing the negative electrode slurry may include: mixing the negative electrode active material, the conductive agent and the binder, adding deionized water, and stirring to form a uniform and stable negative electrode slurry, wherein the mass ratio of the negative electrode active material, the conductive agent and the binder may be (92~98): (0~4): (0~6). Exemplarily, the negative electrode active material may include at least one of graphite, hard carbon, soft carbon, and graphene. The conductive agent may include at least one of conductive carbon black, acetylene black, carbon nanotubes, and carbon fibers. The binder may include at least one of polyvinylidene fluoride, styrene butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, and polyacrylate.

[0133] In step S41, preparing the positive electrode slurry may include: mixing the positive electrode active material, the conductive agent and the binder, adding N-methylpyrrolidone, and stirring to form a uniform and stable positive electrode slurry, wherein the mass ratio of the positive electrode active material, the conductive agent and the binder may be (91.5~97): (0~3): (2~6). Exemplarily, the positive electrode active material may include at least one of Prussian blue, layered metal oxides, and phosphates. The conductive agent may include at least one of conductive carbon black, acetylene black, and carbon nanotubes. The binder may include at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyacrylonitrile, and polyacrylate.

[0134] In step S42, coating the negative electrode slurry and the positive electrode slurry on the negative electrode current collector 301 and the positive electrode current collector 401 respectively may include: coating the negative electrode slurry and the positive electrode slurry on the negative electrode current collector 301 and the positive electrode current collector 401 by transfer coating. Exemplarily, the size of the positive electrode slurry in the first direction may be 40 mm to 48 mm, and the size in the second direction may be 92 mm to 100 mm. The surface density of the coated positive electrode slurry may be 0.00013 g / mm 2 ~0.00026g / mm 2 The size of the negative electrode slurry in the first direction may be 44 mm to 52 mm, and the size in the second direction may be 96 mm to 108 mm. The surface density of the coated negative electrode slurry may be 0.000065 g / mm 2 ~0.000097g / mm 2 .

[0135] In some specific embodiments, in the first direction, the size of the negative electrode slurry is larger than the size of the positive electrode slurry, so that the size of the formed negative electrode active material layer 302 in the first direction is larger than the size of the positive electrode active material layer 402. Specifically, in the first direction, the difference between the size of the negative electrode slurry and the size of the positive electrode slurry can be 4mm~6mm. In this way, the energy density of the battery and the risk of lithium deposition at the edge of the negative electrode plate 300 during charging can be taken into account.

[0136] In some specific embodiments, in the second direction, the size of the negative electrode slurry is larger than the size of the positive electrode slurry, so that the size of the formed negative electrode active material layer 302 in the second direction is larger than the size of the positive electrode active material layer 402. Specifically, in the second direction, the difference between the size of the negative electrode slurry and the size of the positive electrode slurry can be 4mm~6mm. In this way, the energy density of the battery and the risk of lithium deposition at the edge of the negative electrode plate 300 during charging can be taken into account.

[0137] In the case where the composite electrode sheet includes multiple negative electrode sheets 300 and multiple positive electrode sheets 400, the electrode sheets located at both ends of the composite electrode sheet can both be negative electrode sheets 300. In step S43, the negative electrode active material layer 302 is rolled, which can be in the first direction, in which the first electrode sheet, the third electrode sheet, ..., the 2n+1th electrode sheet are rolled in sequence. The positive electrode active material layer 402 is rolled, which can be in the first direction, in which the second electrode sheet, the fourth electrode sheet, ..., the 2nth electrode sheet are rolled in sequence, where n is an integer greater than or equal to 1.

[0138] In some specific embodiments, the compaction density of the negative electrode active material layer 302 in the final composite electrode sheet can be 0.9 g / cm 3 ~0.96g / cm 3 This can make the battery's energy density higher.

[0139] In some specific embodiments, the compaction density of the positive electrode active material layer 402 in the final composite electrode sheet can be 3.0 g / cm 3 ~3.2g / cm 3 This can make the battery's energy density higher.

[0140] In some embodiments, in the first direction, the negative electrode active material layer 302 is located in the middle of the corresponding negative electrode current collector 301. And / or, the positive electrode active material layer 402 is located in the middle of the corresponding positive electrode current collector 401. And / or, the central axes of the negative electrode active material layer 302 and the positive electrode active material layer 402 in the first direction are in a straight line. This makes it easy for the negative electrode active material layer 302 and the positive electrode active material layer 402 to better correspond to each other in the battery cell formed by the composite electrode sheet, and the area of ​​the overlapped area of ​​the vertical projection of the negative electrode active material layer 302 and the positive electrode active material layer 402 in the thickness direction of the base film 100 is larger, thereby further improving the cycle performance and safety performance of the battery.

[0141] In some embodiments, please refer to Figure 1 The method for preparing the composite electrode sheet may further include: laser die-cutting the rolled composite electrode sheet to form a positive electrode tab 403 and a negative electrode tab 303 .

[0142] For example, part of the base film 100 may be cut inward from both sides in the width direction of the base film 100 to expose part of the sides of the positive electrode collector 401 and part of the negative electrode collector 301, expose the positive electrode collector 401 on the side as the positive electrode tab 403, and expose the negative electrode collector 301 on the side as the negative electrode tab 303. In some specific embodiments, the size of the positive electrode tab 403 in the second direction may be 6 mm to 15 mm, and the size of the negative electrode tab 303 in the second direction may be 6 mm to 15 mm.

[0143] In some embodiments, after the composite pole piece is laser die-cut, the side edges of the base film 100 extend beyond the side edges of the positive current collector 401 and the negative current collector 301. This can better ensure that in the battery cell formed by the composite pole piece, the base film 100 can better wrap the positive pole piece 400 and the negative pole piece 300. Even if the edges of the composite pole piece are misaligned during the stacking process, a short circuit between the cathode and the anode can be avoided.

[0144] Based on this, the present application also provides a method for preparing a battery cell, please refer to Figure 8 The method for preparing the composite pole piece provided in the embodiment of the present application comprises:

[0145] Step S21: providing a composite electrode sheet as described in any of the above embodiments or a composite electrode sheet prepared by the preparation method described in any of the above embodiments;

[0146] Step S22: Fold the base film in a Z shape, and form bending portions in the base film located in the diaphragm area close to the negative electrode area and the positive electrode area, so that the diaphragm area located on the first surface covers the negative electrode collector and / or the positive electrode collector located on the first surface, and the diaphragm area located on the second surface covers the negative electrode collector and / or the positive electrode collector located on the second surface.

[0147] In the embodiment of the present application, by directly Z-folding the composite pole piece described in the above embodiment to form a battery cell, the stacking efficiency can be effectively improved, materials can be saved, and costs can be reduced. Compared with the battery cell formed by the winding process, the problem of easy lithium deposition at the corner of the battery cell can be avoided. Moreover, the battery cell formed by Z-folding the composite pole piece is more compact, which can reduce battery resistance, improve energy density, safety performance and cycle performance. In addition, since the positive pole piece 400 and the negative pole piece 300 in the composite pole piece are an integrated structure with the base film 100, the risk of the positive pole piece 400 and the negative pole piece 300 falling off from the base film 100 can be greatly reduced, thereby further improving the cycle performance and safety performance of the battery.

[0148] Please refer to Fig. 9 The Z-folding of the composite electrode sheet in the embodiment of the present application can be understood as taking the negative electrode sheet 300, the diaphragm (the base film 100 of the diaphragm region 202), and the positive electrode sheet 400 as a single unit, and folding them alternately clockwise and counterclockwise in sequence to form a battery cell, and the bending portion 500 is formed between the adjacent negative electrode sheet 300 and the diaphragm and the adjacent positive electrode sheet 400 and the diaphragm. In actual operation, the last folded electrode sheet can be the negative electrode sheet 300, and the base film 100 wraps the entire battery cell.

[0149] Based on this, an embodiment of the present application further provides a battery cell, which is prepared using the battery cell preparation method described in any of the above embodiments.

[0150] Based on this, an embodiment of the present application further provides a battery, including a battery cell prepared by the battery cell preparation method described in any of the above embodiments or the battery cell described in the above embodiments.

[0151] In some embodiments, the battery is a secondary battery, and the secondary battery may be a lithium ion secondary battery or a sodium ion secondary battery.

[0152] The technical solution of the present application is further described below in combination with a plurality of embodiments and comparative examples. Example 1

[0153] The preparation of the composite electrode in this embodiment includes the following steps:

[0154] Step S101: providing a polypropylene base film, wherein the base film has a thickness of 6 μm and a width of 132 mm, and the first surface and the second surface opposite to each other of the base film respectively include a negative electrode region, a separator region and a positive electrode region, the separator region is located between adjacent negative electrode regions and positive electrode regions, and the negative electrode region and the positive electrode region located on the first surface correspond to the negative electrode region and the positive electrode region located on the second surface respectively;

[0155] Step S102: sequentially coating a polyvinylidene fluoride coating and an alumina ceramic coating on the diaphragm region of the first surface and the second surface of the base film, wherein the thickness of the polyvinylidene fluoride coating and the alumina ceramic coating are both 3 μm;

[0156] Step S103: A magnetron sputtering process is used to form an aluminum foil layer on the negative electrode region and the positive electrode region of the first surface and the second surface of the base film, the aluminum foil layer located in the negative electrode region is used as the negative electrode current collector, and the aluminum foil layer located in the positive electrode region is used as the positive electrode current collector, wherein the length of the positive electrode current collector and the negative electrode current collector are both 52 mm, and the width is both 120 mm. In the length direction of the base film, the size of the diaphragm region is larger than the size of the positive electrode current collector and the negative electrode current collector, and the difference L between the size of the diaphragm region and the size of the positive electrode current collector and the negative electrode current collector is 误差 2mm;

[0157] Step S104: coating the negative electrode slurry and the positive electrode slurry on the negative electrode current collector and the positive electrode current collector on the first surface and the second surface of the base film respectively, and forming the negative electrode active material layer and the positive electrode active material layer after drying, wherein the preparation process of the positive electrode slurry is to mix the Prussian blue positive electrode active material, the conductive carbon black and the polyvinylidene fluoride (PVDF) in a mass ratio of 96.5:1.5:2, and then add N-methylpyrrolidone, stir to form a uniform and stable positive electrode slurry, and the size L of the positive electrode slurry in the length direction of the base film is 正浆 The width of the positive electrode slurry in the base film is W. 正浆 The surface density of the coating is 0.00019g / mm 2 (0.3g / 1540.25mm 2 The preparation process of the negative electrode slurry is to mix hard carbon, conductive carbon black, carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 97:0.6:1:1.4, add deionized water, and stir to form a uniform and stable negative electrode slurry. The size L of the negative electrode slurry in the length direction of the base film is 正浆 The dimension W of the negative electrode slurry in the width direction of the base film is 50 mm. 负浆 The surface density of the coating is 0.000078g / mm 2 (0.12g / 1540.25mm 2 );

[0158] Step S105: Roll-press the negative electrode active material layer and the positive electrode active material layer respectively. After rolling, the compaction density of the negative electrode active material layer is 0.94 g / cm 3 The compaction density of the positive electrode active material layer is 3.1 g / cm 3 ;

[0159] Step S106: laser die-cut the sides of the rolled composite electrode sheet to form positive electrode tabs and negative electrode tabs, wherein the dimensions of the positive electrode tabs and negative electrode tabs in the width direction of the base film are both 10 mm, and the width of the base film exceeds the dimensions of the positive electrode collector and the negative electrode collector by 3 mm. Example 2

[0160] The preparation of the composite electrode in this embodiment is basically the same as that in embodiment 1, except that: L in step S103 误差 is 1 mm, and W in step S104 正浆 102mm, W 负浆 It is 106mm. Example 3

[0161] The preparation of the composite electrode in this embodiment is basically the same as that in Embodiment 1, except that: 负浆 It is 106mm. Example 4

[0162] The preparation of the composite electrode in this embodiment is basically the same as that in embodiment 1, except that: L in step S103 误差 is 3 mm, and W in step S104 正浆 98mm, W 负浆 It is 106mm. Example 5

[0163] The preparation of the composite electrode in this embodiment is basically the same as that in Embodiment 1, except that: 正浆 It is 98mm. Example 6

[0164] The preparation of the composite electrode in this embodiment is basically the same as that in Embodiment 1, except that: 正浆 98mm, W 负浆 It is 102mm. Example 7

[0165] The preparation of the composite electrode in this embodiment is basically the same as that in embodiment 1, except that: L in step S103 误差 is 1 mm, and W in step S104 正浆 101mm, W 负浆 It is 105mm. Example 8

[0166] The preparation of the composite electrode in this embodiment is basically the same as that in embodiment 1, except that: L in step S103 误差 is 3 mm, and W in step S104 正浆 It is 99mm. Example 9

[0167] The preparation of the composite electrode in this embodiment is basically the same as that in Embodiment 1, except that: 正浆 It is 101mm. Example 10

[0168] The preparation of the composite electrode in this embodiment is basically the same as that in embodiment 1, except that: L in step S103 误差 is 0 mm, W in step S104 正浆 97mm, W 负浆 It is 105mm.

[0169] The composite electrode sheets obtained in the above embodiments are prepared into batteries, and the preparation of the batteries includes the following steps:

[0170] First, the composite pole piece obtained in each of the above embodiments is Z-folded, and the base film near the negative electrode region and the positive electrode region in the diaphragm region is formed into a bending portion, so that the diaphragm region located on the first surface covers the negative electrode current collector and the positive electrode current collector located on the first surface, and the diaphragm region located on the second surface covers the negative electrode current collector and the positive electrode current collector located on the second surface, thereby obtaining a battery cell. Then, the electrolyte is injected into the dried battery cell, and a sodium ion soft-pack battery is obtained after formation and volume separation, wherein the electrolyte is a solution of LiPF6 dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a volume ratio of 1.4:0.8:0.4, and the concentration of the electrolyte is 1.2 mol / L.

[0171] Comparative Example 1

[0172] Step S201: preparing positive electrode slurry and negative electrode slurry, wherein the preparation method of the positive electrode slurry and the negative electrode slurry is the same as the preparation method of the positive electrode slurry and the negative electrode slurry in step S104 of the above embodiment 1;

[0173] Step S202: Continuously apply the positive electrode slurry to the aluminum foil current collector by transfer coating, and dry it to obtain a positive electrode sheet. Continuously apply the negative electrode slurry to the aluminum foil current collector by transfer coating, and dry it to obtain a negative electrode sheet;

[0174] Step S203: coating a polyvinylidene fluoride coating and an alumina ceramic coating in sequence on a polypropylene base film having a thickness of 6 μm to form a diaphragm, wherein the thickness of the polyvinylidene fluoride coating and the alumina ceramic coating are both 3 μm;

[0175] Step S204: stacking the positive electrode sheets, the separator and the negative electrode sheets in sequence to obtain a battery cell, injecting the electrolyte into the dried battery cell, and obtaining a sodium ion soft-pack battery after formation and capacity separation, wherein the electrolyte is the same as the electrolyte in the above-mentioned battery.

[0176] Comparative Example 2

[0177] Step S301: preparing positive electrode slurry and negative electrode slurry, wherein the preparation method of the positive electrode slurry and the negative electrode slurry is the same as the preparation method of the positive electrode slurry and the negative electrode slurry in step S104 of the above embodiment 1;

[0178] Step S302: Continuously apply the positive electrode slurry to the aluminum foil current collector by transfer coating, and dry it to obtain a positive electrode sheet. Continuously apply the negative electrode slurry to the aluminum foil current collector by transfer coating, and dry it to obtain a negative electrode sheet;

[0179] Step S303: coating a polyvinylidene fluoride coating and an alumina ceramic coating in sequence on a polypropylene base film having a thickness of 6 μm to form a diaphragm, wherein the thickness of the polyvinylidene fluoride coating and the alumina ceramic coating are both 3 μm;

[0180] Step S304: After stacking the positive electrode sheet, the separator and the negative electrode sheet in order, winding them to obtain a battery cell, injecting the electrolyte into the dry battery cell, and obtaining a sodium ion soft-pack battery after formation and capacity separation, wherein the electrolyte is the same as the electrolyte in the above-mentioned battery.

[0181] The cycle performance and safety performance of the batteries prepared from the composite pole pieces obtained in the above embodiments and the batteries prepared in the comparative examples were tested. The test method is as follows:

[0182] (1) Cycle performance test: In a 25°C incubator, charge the battery to 4.2V at a constant current rate of 0.33C, charge the battery at a constant voltage of 4.2V until the current reaches 0.05C, let it stand for 30 minutes, then discharge the battery to 2.5V at a constant current of 0.33C, let it stand, and cycle the battery for three cycles. The capacity of the last cycle is the actual capacity C0 of the battery. Charge and discharge the battery at 1C / 1C, compare the capacity of each cycle with the capacity of the first cycle, and obtain the cycle capacity retention rate. Record the number of cycles corresponding to the capacity retention rate of 80%.

[0183] (2) Safety performance test: Use C0 to conduct an overcharge test on the battery, charge it to 150% SOC (State of Charge), and observe the battery status. The battery status is determined by the following criteria: good (battery cell has no obvious abnormality), better (battery cell is swollen), fair (battery cell smokes but does not catch fire), and poor (battery cell catches fire or explodes).

[0184] The test results are shown in Table 1.

[0185] Table 1

[0186]

[0187] From the data of Examples 1 to 10 in Table 1 and the data of Comparative Examples 1 and 2, it can be seen that the cycle performance and safety performance of the battery in the examples of the present application are significantly better than those of the batteries in Comparative Examples 1 and 2. This is because the positive electrode sheet and the negative electrode sheet in the present application form an integrated structure with the base film, and the bonding force with the base film is strong, so the risk of the positive electrode sheet and the negative electrode sheet falling off from the base film can be greatly reduced, and the expansion of the battery during the cycle can be better suppressed, thereby improving the cycle performance and safety performance of the battery. Moreover, the battery cell formed by direct Z-shaped folding of the composite electrode sheet in the present application is more compact, and the active ion migration distance is relatively short, which can reduce the battery resistance, and further improve the energy density, safety performance and cycle performance.

[0188] In Comparative Example 1, the battery cell is prepared in a conventional lamination method, and the positive electrode sheet, separator and negative electrode sheet are stacked one by one. The prepared battery will have expansion of the electrode sheet during the cycle, which makes the contact between the positive and negative electrodes worse and the cycle performance is reduced. In Comparative Example 2, the battery cell is prepared in a conventional winding method. Compared with the lamination method, the prepared battery cell will have corners. Sodium precipitation and black spots will appear at the corners during the cycle, resulting in poor cycle performance. In addition, the current collector of the battery in Comparative Examples 1 and 2 uses a conventional aluminum foil current collector. The battery is overcharged and the battery produces gas, which directly leads to contact between the positive and negative electrodes, and the safety performance is poor. In this application, since there is a layer of polymer material film in the middle of the current collector located on the two opposite surfaces of the base film, when the battery is overcharged, the middle base film will melt and separate the positive and negative electrodes. At the same time, the base film itself is non-conductive, which can control the short-circuit current from increasing, and reduce the risk of fire and explosion, so the safety performance is better.

[0189] It should be noted that the composite electrode embodiments, composite electrode preparation method embodiments, battery cell embodiments, battery cell preparation method embodiments and battery embodiments provided in the present application belong to the same concept; the technical features in the technical solutions recorded in the embodiments can be arbitrarily combined without conflict.

[0190] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations included in the claims. Various modifications and changes may be made on the basis of the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A composite pole piece, characterized in that: include: A base film, the base film having a first surface and a second surface opposite to each other, the first surface and the second surface respectively including at least one negative electrode region, at least one separator region and at least one positive electrode region, the separator region is located between the adjacent negative electrode region and the positive electrode region, the negative electrode region and the positive electrode region located on the first surface respectively correspond to the negative electrode region and the positive electrode region located on the second surface; A negative electrode sheet, located on the negative electrode region, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer located on at least one side surface of the negative electrode current collector; the negative electrode current collector is directly located on the surface of the base film, and the negative electrode active material layer is located on the side surface of the negative electrode current collector away from the base film; A positive electrode sheet, located on the positive electrode region, comprising a positive electrode current collector and a positive electrode active material layer located on at least one side surface of the positive electrode current collector; the positive electrode current collector is directly located on the surface of the base film, and the positive electrode active material layer is located on a side surface of the positive electrode current collector away from the base film; The negative electrode collector and the positive electrode collector are staggered in the width direction of the base film, the negative electrode collector is close to one side edge of the base film, and the positive electrode collector is close to the other side edge of the base film; a portion of the base film is cut inward from both sides in the width direction of the base film to expose a portion of the side of the negative electrode collector close to the one side edge and a portion of the side of the positive electrode collector close to the other side edge, the positive electrode collector on the side is exposed as a positive electrode tab, and the negative electrode collector on the side is exposed as a negative electrode tab.

2. The composite pole piece according to claim 1, characterized in that: The base film, the negative electrode current collector and the positive electrode current collector in the composite electrode sheet satisfy at least one of the following characteristics (1) to (8): (1) The width of the base film is 130 mm to 150 mm; (2) The thickness of the base film is 4.5 μm to 9 μm; (3) The material of the base film includes a polymer material; (4) In the length direction of the base film, the size of the positive electrode current collector is 40 mm to 60 mm, and the size of the negative electrode current collector is 40 mm to 60 mm; (5) In the width direction of the base film, the size of the positive electrode collector is 116 mm to 126 mm, and the size of the negative electrode collector is 116 mm to 126 mm; (6) In the length direction of the base film, the size of the diaphragm region is larger than the size of the positive electrode current collector and the negative electrode current collector, and the difference between the size of the diaphragm region and the size of the positive electrode current collector and / or the negative electrode current collector is 1 mm to 3 mm; (7) The materials of the negative electrode current collector and the positive electrode current collector both include aluminum; (8) The base film includes a polyvinylidene fluoride coating and a ceramic coating sequentially stacked on the diaphragm region.

3. The composite pole piece according to claim 1, characterized in that: The negative electrode active material layer and the positive electrode active material layer in the composite electrode sheet satisfy at least one of the following characteristics (1) to (7): (1) In the length direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer; (2) In the width direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer; (3) In the length direction of the base film, the negative electrode active material layer is located in the middle of the corresponding negative electrode current collector; (4) In the length direction of the base film, the positive electrode active material layer is located in the middle of the corresponding positive electrode current collector; (5) The central axes of the negative electrode active material layer and the positive electrode active material layer in the length direction of the base film are on a straight line; (6) The compaction density of the negative electrode active material layer is 0.9 g / cm 3 ~0.96g / cm 3 ; (7) The compaction density of the positive electrode active material layer is 3.0 g / cm 3 ~3.2g / cm 3 .

4. A method for preparing a composite electrode, characterized in that: The method comprises: Providing a base film, the base film having a first surface and a second surface opposite to each other, the first surface and the second surface respectively including at least one negative electrode region, at least one separator region and at least one positive electrode region, the separator region is located between the adjacent negative electrode region and the positive electrode region, the negative electrode region and the positive electrode region located on the first surface respectively correspond to the negative electrode region and the positive electrode region located on the second surface; forming a negative electrode current collector on the negative electrode region by using a first process; forming a positive electrode current collector on the positive electrode region by using a second process; The negative electrode current collector and the positive electrode current collector are staggered in the width direction of the base film, the negative electrode current collector is close to one side edge of the base film, and the positive electrode current collector is close to the other side edge of the base film; Cutting part of the base film inward from both sides in the width direction of the base film to expose part of the side of the negative electrode current collector close to the one side edge and part of the side of the positive electrode current collector close to the other side edge, exposing the positive electrode current collector on the side as the positive electrode tab, and exposing the negative electrode current collector on the side as the negative electrode tab; A negative electrode active material layer and a positive electrode active material layer are formed on the negative electrode collector and the positive electrode collector, respectively.

5. The method for preparing a composite pole piece according to claim 4, characterized in that: The negative electrode current collector and the positive electrode current collector are formed to satisfy at least one of the following characteristics (1) to (6): (1) In the length direction of the base film, the size of the positive electrode current collector is 40 mm to 60 mm, and the size of the negative electrode current collector is 40 mm to 60 mm; (2) In the width direction of the base film, the size of the positive electrode current collector is 116 mm to 126 mm, and the size of the negative electrode current collector is 116 mm to 126 mm; (3) In the length direction of the base film, the size of the diaphragm region is larger than the size of the positive electrode current collector and the negative electrode current collector, and the difference between the size of the diaphragm region and the size of the positive electrode current collector and / or the negative electrode current collector is 1 mm to 3 mm; (4) The materials of the negative electrode current collector and the positive electrode current collector both include aluminum; (5) The first process includes at least one of magnetron sputtering, water electroplating, evaporation, and chemical vapor deposition; (6) The second process includes at least one of magnetron sputtering, water electroplating, evaporation, and chemical vapor deposition.

6. The method for preparing a composite pole piece according to claim 4, characterized in that: The negative electrode active material layer and the positive electrode active material layer are formed to satisfy at least one of the following characteristics (1) to (7): (1) In the length direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer; (2) In the width direction of the base film, the size of the negative electrode active material layer is larger than the size of the positive electrode active material layer; (3) In the length direction of the base film, the negative electrode active material layer is located in the middle of the corresponding negative electrode current collector; (4) In the length direction of the base film, the positive electrode active material layer is located in the middle of the corresponding positive electrode current collector; (5) The central axes of the negative electrode active material layer and the positive electrode active material layer in the length direction of the base film are on a straight line; (6) The compaction density of the negative electrode active material layer is 0.9 g / cm 3 ~0.96g / cm 3 ; (7) The compaction density of the positive electrode active material layer is 3.0 g / cm 3 ~3.2g / cm 3 .

7. A method for preparing a battery cell, characterized in that: The method comprises: Providing a composite pole piece according to any one of claims 1 to 3 or a composite pole piece prepared by the preparation method according to any one of claims 4 to 6; The base film is folded in a Z shape, and portions of the base film located in the diaphragm region close to the negative electrode region and close to the positive electrode region form bending portions, so that the diaphragm region located on the first surface covers the negative electrode collector and / or the positive electrode collector located on the first surface, and the diaphragm region located on the second surface covers the negative electrode collector and / or the positive electrode collector located on the second surface.

8. A battery cell, characterized in that: The battery is prepared by the method for preparing the battery cell according to claim 7.

9. A battery, characterized in that: A battery cell comprising the preparation method described in claim 7 or a battery cell comprising the battery cell described in claim 8.

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