Battery pole piece, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery pole piece, a preparation method thereof and a battery. The provided battery pole piece comprises a current collector, the first coating is arranged on the surface of at least one side of the current collector along the thickness direction; the second coatings are arranged on the surface of at least one side of the current collector in the thickness direction, and the second coatings are arranged at the two ends of the first coating in the first direction; the first direction represents the width direction of the battery pole piece; the first coating comprises a first binder, and the second coating comprises a second binder; the mass content of the first binder in the first coating is U1, the mass content of the second binder in the second coating is U2, and U1 and U2 meet the condition that U1 is larger than or equal to U2; the thickness of the first coating is H1, the thickness of the second coating is H2, and H1 and H2 meet the condition that H1 / H2 is larger than or equal to 2 and smaller than or equal to 10. According to the invention, the problem of thick edge of the pole piece can be effectively solved without thinning the edge of the pole piece, the space waste caused by thinning can be reduced, and the machinability and reliability of the pole piece can be improved.

Description

Technical Field

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

[0002] In the production process of batteries such as lithium-ion batteries, the slit extrusion coating method is usually used to produce electrode sheets. The slit extrusion coating system mainly consists of a feeding system, a coating mechanism, a drying system, etc. The slurry is provided by the feeding system, enters the inner cavity of the die head, and then the slurry is extruded through the slit of the die head to form a coating on the moving substrate. Generally, due to the fluid characteristics of the slurry, a half-moon shape is easily formed at the starting point, the ending point, and both side edges of the coating. The morphology of the sudden increase in thickness at the edge of the electrode sheet is called the "thick edge" phenomenon (as Figure 1 shown). As the winding length increases, after thousands of layers of electrode sheets are stacked, the thickness at the edge is significantly higher than that in the normal area, which will cause the electrode sheet to be damaged and broken, and normal production cannot be carried out.

[0003] In the related art, in order to solve the thick edge phenomenon of the electrode sheet, a gasket is set in the die head. In this way, when extrusion coating is carried out, the chamfer is mainly set by the gasket in the die head to change the morphology of the slurry when it exits the die head, so as to thin the edge of the coating, and the thickness of the edge of the electrode sheet is less than the thickness in the middle of the electrode sheet (as Figure 2 shown), thereby avoiding the occurrence of the thick edge phenomenon. However, this method of setting a gasket in the die head has poor control accuracy, resulting in large fluctuations in the slurry in the thinned area of the electrode sheet, so that the width and depth of the thinned area cannot meet the requirements, and finally the thick edge problem cannot be effectively solved.

[0004] In addition, the thinning treatment of the edge of the electrode sheet in the related art will also cause the following problems: (1) Excessive thinning of the negative electrode sheet is likely to cause lithium deposition at the edge position, and the lithium dendrites may pierce the separator, resulting in a short circuit, which poses a safety problem; (2) The edge thickness is lower than the middle thickness. After the electrode sheet is roll-pressed, the edge and the middle are not uniformly rolled, resulting in wavy edges or snake shapes, which affects the accurate alignment during the winding of the battery cell, and the consistency of the battery cell is poor. Even the electrode sheet is wrinkled, affecting the production yield; (3) The edge thickness is lower than the middle thickness, which affects the adhesion between the electrode sheet and the separator, and the edge gap is large, increasing the lithium ion transmission distance, resulting in lithium deposition problems in the thinned area; (4) Thinning the edge of the positive electrode sheet will cause capacity loss and reduce the energy density of the battery.

[0005] Therefore, there is an urgent need to provide a battery electrode sheet and a preparation method thereof to solve the defects existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, the present invention provides a battery electrode, a preparation method thereof, and a battery, which are beneficial to improving the processability and reliability of the battery electrode and can avoid or reduce the thick edge problem at the edge of the electrode.

[0007] To solve the above technical problems, the present application is implemented as follows:

[0008] According to one aspect of the present application, the present application provides a battery electrode, which includes:

[0009] A current collector;

[0010] A first coating disposed on at least one surface of the current collector along the thickness direction;

[0011] A second coating disposed on at least one surface of the current collector along the thickness direction, and the second coating is disposed at both ends of the first coating along a first direction; the first direction represents the width direction of the battery electrode;

[0012] The first coating contains a first binder, and the second coating contains a second binder; the mass content of the first binder in the first coating is U1, the mass content of the second binder in the second coating is U2, and U1 and U2 satisfy: U1≥U2;

[0013] The thickness of the first coating is H1, the thickness of the second coating is H2, and H1 and H2 satisfy the following relational expression: 2≤H1 / H2≤10.

[0014] In some embodiments, the first coating and the second coating satisfy at least one of the following features (1) to (6):

[0015] (1) U1 is 3% to 10%; and / or, U2 is 1% to 5%; (2) H2 is 10 μm to 50 μm; and / or, H1 is 50 μm to 200 μm; (3) The width of the first coating is 80 mm to 300 mm; (4) The width of the second coating is 4 mm to 10 mm; (5) An overlapping area is formed between the first coating and the second coating, and the width of the overlapping area is 0.5 mm to 3 mm; (6) The first coating and the second coating have the same length.

[0016] In some embodiments, the first coating further includes a first active material and a first conductive agent; the second coating further includes a second active material and a second conductive agent.

[0017] In some of these embodiments, in the first coating, the mass ratio of the first active material, the first conductive agent, and the first binder is (89 to 96):(1 to 3):(3 to 10).

[0018] In some of these embodiments, in the second coating, the mass ratio of the second active material, the second conductive agent, and the second binder is (92 to 98):(1 to 3):(1 to 5).

[0019] In some of these embodiments, the battery electrode sheet satisfies at least one of the following characteristics (1) to (4):

[0020] (1) When the battery electrode sheet is a positive electrode sheet, the first active material and the second active material both include at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, lithium nickel cobaltate, lithium iron phosphate, or ternary material; (2) When the battery electrode sheet is a negative electrode sheet, the first active material and the second active material both include at least one of artificial graphite, natural graphite, silicon-carbon graphite, silicon-oxygen graphite, or silicon; (3) The first conductive agent and the second conductive agent both include at least one of conductive graphite, conductive carbon black, carbon fiber, carbon nanotube, graphene, or graphene oxide; (4) The first binder and the second binder both include at least one of hydroxymethyl cellulose, polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyethylene oxide, polyester, polyamide, or polycarbonate.

[0021] In some of these embodiments, the current collector includes at least one of a metal foil or a composite current collector; the composite current collector includes a polymer substrate layer and a conductive layer provided on at least one surface of the polymer substrate layer along the thickness direction.

[0022] In some of these embodiments, the metal foil includes at least one of aluminum foil, copper foil, nickel foil, or stainless steel foil.

[0023] In some of these embodiments, the conductive layer includes at least one of a conductive resin, conductive carbon powder, or a metal layer.

[0024] According to another aspect of the present application, the present application provides a method for preparing a battery electrode sheet, the method comprising:

[0025] Coating a first slurry on at least one surface of the current collector along the thickness direction to obtain a wet film of the first coating;

[0026] Coating a second slurry along both ends of the wet film of the first coating in a first direction to obtain a wet film of the second coating; the first direction represents the width direction of the battery electrode sheet;

[0027] After drying, a first coating and a second coating are formed on the surface of the current collector, and the second coating is provided at both ends of the first coating along a first direction to obtain a battery electrode sheet;

[0028] Wherein, the solid content of the first slurry is S1, the solid content of the second slurry is S2, and S1 and S2 satisfy the following relational expression: 2 ≤ S1 / S2 ≤ 10;

[0029] The thickness of the first coating is H1, the thickness of the second coating is H2, and H1 and H2 satisfy the following relational expression: 2 ≤ H1 / H2 ≤ 10.

[0030] In some embodiments, the preparation of the first coating and the second coating satisfies at least one of the following features (1) to (6):

[0031] (1) The thickness of the wet film of the first coating is 60 μm to 200 μm; (2) The thickness of the wet film of the second coating is 12 μm to 80 μm; (3) S1 is 50% to 80%; and / or, S2 is 8% to 40%; (4) The first slurry contains a first binder, and the second slurry contains a second binder; the mass content of the first binder in the first slurry is U1, and the mass content of the second binder in the second slurry is U2, and U1 and U2 satisfy: U1 ≥ U2; optionally, U1 is 3% to 10%; and / or, U2 is 1% to 5%; (5) H2 is 10 μm to 50 μm; and / or, H1 is 50 μm to 200 μm; (6) The viscosity of the first slurry is 2000 mPa·s to 20000 mPa·s; and / or, the viscosity of the second slurry is 2000 mPa·s to 20000 mPa·s.

[0032] In some embodiments, the second slurry includes a surfactant.

[0033] In some embodiments, when the battery electrode sheet is a positive electrode sheet, the surfactant includes at least one of butyl acetate, ethyl acetate, acetone, or methyl ethyl ketone.

[0034] In some embodiments, when the battery electrode sheet is a negative electrode sheet, the surfactant includes at least one of ethanol, butanol, or styrene.

[0035] In some embodiments, the surface tension of the first slurry is Z1, the surface tension of the second slurry is Z2, and Z1 and Z2 satisfy the following relational expression: 2 ≤ Z1 / Z2 ≤ 4.

[0036] In some of these embodiments, Z1 is 40 to 120 mN / m; and / or, Z2 is 20 to 30 mN / m.

[0037] In some of these embodiments, the preparation of the first slurry includes: dissolving a first active material, a first conductive agent, and a first binder in a solvent and mixing them evenly to obtain the first slurry; the preparation of the second slurry includes: dissolving a second active material, a second conductive agent, a second binder, and a surfactant in a solvent and mixing them evenly to obtain the second slurry.

[0038] In some of these embodiments, in the first slurry, the mass ratio of the first active material, the first conductive agent, and the first binder is (89 to 96):(1 to 3):(3 to 10).

[0039] In some of these embodiments, in the second slurry, the mass ratio of the second active material, the second conductive agent, the second binder, and the surfactant is (92 to 98):(1 to 3):(1 to 5):(0.1 to 5).

[0040] According to another aspect of the present application, the present application provides a battery, which includes a battery electrode sheet, and the battery electrode sheet is the aforementioned battery electrode sheet or a battery electrode sheet prepared according to the aforementioned preparation method.

[0041] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0042] In this application, the provided battery electrode includes a current collector, a first coating and a second coating disposed on the current collector. The second coating is disposed at edge positions opposite to each other in the width direction of the first coating, and the content of the second binder in the second coating does not exceed the content of the first binder in the first coating. The thickness of the first coating is greater than the thickness of the second coating. Thus, by controlling the ratio of the content and thickness of the binders in the first coating and the second coating within the above range, it is helpful to adjust the drying rates of the two coatings during the preparation process. For example, during the drying process of the battery electrode, when the first slurry used to prepare the first coating has completed solvent evaporation and meets the drying requirements, the second slurry has not completed solvent evaporation and is still in a wet state. The surface tension in the edge region will be smaller than that in the middle region of the electrode, and the wet slurry at the edge will move towards the middle region of the electrode under the action of the surface tension, thereby preventing the first slurry from flowing towards the edge and forming a thick edge. Furthermore, through the above solution, it is possible to effectively alleviate the problem of thick edges at the electrode edge without thinning the electrode edge, reduce the space waste caused by thinning, and at the same time is beneficial to improving the battery energy density; it can also prevent the lithium plating problem caused by excessive thinning of the battery electrode, reducing safety risks; it can make the thickness of the electrode edge and the main body more uniform, improving the processability and reliability of the electrode.

[0043] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. Brief Description of the Drawings

[0044] Figure 1 Schematic diagram of a battery electrode structure provided by the prior art shown;

[0045] Figure 2 Another schematic diagram of a battery electrode structure provided by the prior art shown;

[0046] Figure 3 Top view schematic diagram of a battery electrode provided by an embodiment of the present invention shown;

[0047] Figure 4 Side view schematic diagram of a battery electrode provided by an embodiment of the present invention shown.

[0048] Description of the reference numerals:

[0049] 10 - Coating; 11 - Main body area; 12 - Thinning area;

[0050] 101 - First coating;

[0051] 102 - Second coating;

[0052] 103 - Current collector. Detailed Description of the Embodiments

[0053] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments of the present application are only used to illustrate the present application and not to limit the scope of the present application.

[0054] In the ranges and values disclosed herein, the endpoints and any value are not limited to the exact range or value. These ranges and values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0055] If there is no special indication, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. If there is no special indication, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0056] If there is no special indication, all steps of the present application can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0057] If there is no special indication, the "including" and "comprising" mentioned in the present application mean open-ended, and can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0058] As analyzed in the background art, related prior arts, such as Figure 1As shown, a coating 10 is provided on the current collector 103. During the preparation process of the electrode in the battery, the morphology of the sudden increase in thickness at the edge of the coating 10 on the electrode is called the "thick edge" phenomenon. Through research, in the extrusion coating process, the main reasons for the thick edge phenomenon of the electrode include the following: (1) The slurry is extruded from the die head to the foil, and the slurry overflows to both sides of the edge; (2) After the slurry exits the die head, it is dragged along with the movement of the substrate, so that the slurry flows towards the tail of the coating, forming a thick edge; (3) During the drying process of the slurry, the solvent evaporation rate at the edge position of the coating is faster than that at the middle position. The edge dries first, causing the undried slurry in the middle to flow towards the edge and form a thick edge. This thick edge phenomenon easily leads to damage or breakage of the electrode, and then makes normal production impossible. In response to this "thick edge" problem, most of the existing improvement methods adopt the method of setting a thinning area through thinning treatment as shown in Figure 2 As shown, Figure 2 In, the coating provided on the current collector 103 is divided into a main body area 11 and a thinning area 12. However, the thinning treatment is likely to cause problems such as lithium deposition, or affect the production yield, or reduce the battery energy density, etc.

[0059] In view of this, through a large amount of research, the inventors of this application have proposed new improvement ideas from the electrode structure and process aspects. By improving the electrode structure or the preparation process of the electrode, it is used to alleviate the thick edge problem at the edge of the electrode coating, and avoid problems such as lithium deposition or reduction of the battery energy density, thereby improving the electrochemical performance of the battery. Next, this application will be described in detail.

[0060] [Electrode]

[0061] Referring to Figures 3 to 4 As shown, in some embodiments, the present application provides a battery electrode, which includes: a current collector 103, and a first coating 101 and a second coating 102 provided on the current collector 103.

[0062] Among them, the first coating 101 is provided on at least one surface of the current collector 103 along the thickness direction; the second coating 102 is provided on at least one surface of the current collector 103 along the thickness direction, and the second coating 102 is provided at both ends of the first coating 101 along the first direction; the first direction represents the width direction of the battery electrode.

[0063] In the present application, the electrode includes a current collector 103, a first coating 101 and a second coating 102. Among them, both the first coating 101 and the second coating 102 are provided on at least one surface of the current collector 103 along the thickness direction, and the second coating 102 is provided at both ends of the first coating 101 in the width direction, that is, the second coating 102 is provided at the opposite edge positions in the width direction of the first coating 101.

[0064] The statement "the first coating 101 and the second coating 102 are provided on at least one surface of the current collector 103 in the thickness direction" means that the first coating 101 and the second coating 102 can be provided on one surface of the current collector 103 in its own thickness direction, or can be provided on both surfaces of the current collector 103 in its own thickness direction. The "surface" here can be the entire area of the current collector 103 or a partial area of the current collector 103. This application has no special limitation on this, as long as the purpose of this application can be achieved.

[0065] As an example, the current collector 103 has two surfaces opposite to each other in its own thickness direction. The first coating 101 and the second coating 102 are provided on the two surfaces opposite to each other in the thickness direction of the current collector 103, and the second coating 102 is provided at the edge position opposite to the first coating 101 in the width direction. It can be understood that in other embodiments, the first coating 101 and the second coating 102 can also be stacked on any one of the two surfaces of the current collector 103.

[0066] In this application, the first coating 101 contains a first binder, and the second coating 102 contains a second binder; the mass content of the first binder in the first coating 101 is U1, and the mass content of the second binder in the second coating 102 is U2. U1 and U2 satisfy: U1≥U2. Preferably, U1>U2. That is, the binder content in the first coating 101 exceeds or is equal to the binder content in the second coating 102. Further preferably, the binder content in the first coating 101 is greater than the binder content in the second coating 102.

[0067] The types of the first binder in the first coating 101 and the second binder in the second coating 102 described above can be the same or different, and are preferably the same. For example, both the first coating 101 and the second coating 102 contain a binder. The main difference is that the binder contents in the first coating 101 and the second coating 102 are different.

[0068] In this application, the thickness of the first coating 101 is H1, and the thickness of the second coating 102 is H2. H1 and H2 satisfy the following relational expression: 2≤H1 / H2≤10. As an example, the value of H1 / H2 can be 2, 3, 4, 5, 6, 7, 8, 9, 10 or within the range composed of any two of the above values.

[0069] In this application, the first coating 101 can be formed by drying the first slurry after coating; the second coating 102 can be formed by drying the second slurry after coating.

[0070] In some preferred embodiments, the solid contents of the first slurry for forming the first coating 101 and the second slurry for forming the second coating 102 are different, and the solid content of the first slurry for forming the first coating 101 is higher than that of the second slurry for forming the second coating 102.

[0071] Preferably, the solid content of the first slurry for forming the first coating 101 is S1, and the solid content of the second slurry for forming the second coating 102 is S2. S1 and S2 satisfy the following relationship: 2 ≤ S1 / S2 ≤ 10. As an example, the value of S1 / S2 can be 2, 3, 4, 5, 6, 7, 8, 9, 10 or within the range composed of any two of the above values.

[0072] In the present application, by disposing the first coating 101 and the second coating 102 on at least one surface of the current collector 103, and making the second coating 102 located at the edge positions opposite to each other in the width direction of the first coating 101, and controlling the content of the binder in the first coating 101 and the second coating 102, the thickness of the first coating 101 and the second coating 102, or the solid contents of the first slurry for forming the first coating 101 and the second slurry for forming the second coating 102 within the above suitable ranges, the "thick edge" problem of the electrode can be alleviated. Specifically:

[0073] The viscosities of the first coating 101 and the second coating 102 are related to the content of the binder contained therein, or the viscosities of the first slurry for forming the first coating 101 and the second slurry for forming the second coating 102 are related to the relative contents of the binder and the solvent contained therein. In order to ensure the coating quality, it is necessary to control the viscosity of the slurry within a suitable range, so that by controlling the content of the binder in the first coating 101 and the second coating 102 within a suitable range, it is beneficial to make the solid content of the slurry within a suitable range, which helps to achieve a better coating effect. At the same time, the viscosity of the slurry is related to the relative contents of the binder and the solvent in the slurry. The higher the content of the binder and the lower the content of the solvent, the higher the viscosity of the slurry. By making the content of the first binder in the first coating 101 higher than the content of the second binder in the second coating 102, it is beneficial to regulate the relative viscosities or relative solid contents of the first slurry and the second slurry.

[0074] The solid content of the first slurry (i.e., the first slurry) used to form the first coating 101 is higher than that of the second slurry (i.e., the second slurry) used to form the second coating 102. The higher the solid content of the slurry, the lower the solvent content and the faster the drying rate. At the same time, the surface tension of the wet film is less than that of the dry film, and the slurry will flow from the area with lower surface tension to the area with higher surface tension under the action of surface tension. Furthermore, during the drying process of the electrode, when the first slurry completes solvent evaporation and meets the drying requirements, the second slurry has not completed solvent evaporation and is still in a wet state. The surface tension of the edge area will be less than that of the middle area of the electrode, and the wet slurry at the edge will move towards the middle area of the electrode under the action of surface tension, thus effectively preventing the first slurry from flowing towards the edge to form a thick edge and alleviating the existing "thick edge" problem.

[0075] It is also worth noting that the solid content of the slurry and the thickness of the coated layer, that is, the thicknesses of the first coating 101 and the second coating 102, jointly determine the drying rate. Specifically, the solid content of the slurry is directly proportional to the drying rate, and the coating thickness is inversely proportional to the drying rate. That is to say, the higher the solid content and the thinner the coating thickness, the greater the drying rate. In order to ensure that the second slurry is still in a wet state when the first slurry is completely dried, the ratio of the drying rate of the second slurry to that of the first slurry should be as large as possible. In this application, the drying rate of the first coating 101 is set as V1, and the drying rate of the second coating 102 is set as V2. Assume that V1 = K * S1 / H1, V2 = K * S2 / H2, where K is a constant independent of the properties of the slurry, S1 and S2 are the solid contents of the first slurry and the second slurry respectively, and H1 and H2 are the thicknesses of the first coating 101 and the second coating 102 respectively. Therefore, when S1 / S2 > H1 / H2, V1 > V2 can be satisfied. When V1 ≥ 2 * V2, that is, S1 / S2 ≥ 2, a better effect can be achieved. Although when V1 is much greater than V2, there is a more obvious improvement effect on the thick edge problem, too large a difference in solid content will cause a large amount of the second slurry to move towards the first slurry, affecting the thickness uniformity. On the other hand, if the solid content of the second slurry is too low, the coating quality will also deteriorate. Therefore, the ratio of S1 / S2 cannot be too large. Under the condition of satisfying 2 ≤ S1 / S2 ≤ 10 and 2 ≤ H1 / H2 ≤ 10, the drying rate V1 of the first coating 101 can be greater than the drying rate V2 of the second coating 102, and the thickness uniformity can be ensured, and the coating quality can be guaranteed.

[0076] Thus, based on the above settings, through the above solution, the present invention can effectively alleviate the problem of thick edges at the edges of the electrode sheets without thinning the edges of the electrode sheets, can also reduce the space waste caused by thinning, and is beneficial to improving the energy density of the battery. It can also prevent the problem of lithium deposition caused by excessive thinning of the battery electrode sheet (negative electrode sheet), and can reduce safety risks. In addition, it can effectively avoid problems such as capacity loss and purple spots on the electrode sheet caused by excessive thinning of the battery electrode sheet (positive electrode sheet). It can also effectively avoid problems such as waviness and serpentine of the electrode sheet, and improve the production yield of the battery. It can also make the thickness of the edge and the main body of the electrode sheet more uniform, and can improve the processability and reliability of the electrode sheet.

[0077] In an embodiment of the present invention, the battery electrode sheet is suitable for use in a battery. Specifically, the battery electrode sheet can be a positive electrode sheet or a negative electrode sheet. That is, the polarity of the battery electrode sheet can be positive or negative.

[0078] In some embodiments, the battery electrode sheet is a negative electrode sheet.

[0079] In other embodiments, the battery electrode sheet is a positive electrode sheet.

[0080] In some embodiments, the mass content U1 of the first binder in the first coating 101 is 3% to 10%; as an example, U1 can be any one of 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range value between any two of them.

[0081] The mass content U2 of the second binder in the second coating 102 is 1% to 5%; as an example, U2 can be any one of 1%, 2%, 3%, 4%, 5% or a range value between any two of them.

[0082] In some embodiments, the solid content S1 of the first slurry for forming the first coating 101 is 50% to 80%; as an example, S1 can be any one of 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range value between any two of them.

[0083] The solid content S2 of the second slurry for forming the second coating 102 is 8% to 40%; as an example, S2 can be any one of 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range value between any two of them.

[0084] It should be understood that the viscosity of the slurry is related to the relative contents of the binder and the solvent in the slurry. The higher the binder content and the lower the solvent content, the higher the viscosity of the slurry. To ensure the coating quality, the viscosity range of the slurry is generally about 2000 mPa·s to 20000 mPa·s. Usually, the coating effect is better in the range of 4000 mPa·s to 10000 mPa·s. To achieve the above viscosity range, the mass ratio U1 of the first binder in the first slurry is 3% to 10%, and the solid content S1 of the first slurry is 50% to 80%. The mass ratio U2 of the second binder in the second slurry is 1% to 5%, and the solid content S2 of the second slurry is 8% to 40%. Thus, by controlling the above U1 and U2, or the above S1 and S2 within appropriate ranges, the drying rate of the first slurry can be made greater than that of the second slurry, effectively alleviating the thick-edge problem of the electrode sheet, improving the thickness uniformity, and achieving a better coating effect.

[0085] It should be noted that the mass ratios of the binders and the solid contents in the first slurry and the second slurry are not absolute and need to be appropriately adjusted according to the slurry viscosity during the slurry preparation process to achieve a better coating effect.

[0086] In some embodiments, the thickness H2 of the second coating 102 is 10 μm to 50 μm; by way of example, H2 is any one of the point values of 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or the range value between any two of them.

[0087] The thickness H1 of the first coating 101 is 50 μm to 200 μm; by way of example, H1 is any one of the point values of 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm or the range value between any two of them.

[0088] In the present application, the thickness H1 of the first coating 101 can be the thickness of the conventional coating (or active material layer) in the electrode sheet. The thickness H2 of the second coating 102 needs to be less than the thickness of the first coating 101, and H1 and H2 need to satisfy: 2 ≤ H1 / H2 ≤ 10. Thus, by controlling H1 and H2 within the above ranges and combining the settings of the above S1 and S2, it helps to make the drying rate of the first slurry greater than that of the second slurry, effectively alleviating the thick-edge problem of the electrode sheet and improving the thickness uniformity.

[0089] In this application, the width of the first coating 101 can be determined according to the battery design size. For example, for a conventional square aluminum shell power battery, the width of the first coating 101 is generally above 80 mm. As an example, in some embodiments, the width of the first coating 101 is 80 mm to 300 mm; as an example, the width of the first coating 101 is any one of the point values of 80 mm, 90 mm, 100 mm, 120 mm, 150 mm, 180 mm, 200 mm, 250 mm, 300 mm or the range value between any two of them.

[0090] The width of the above-mentioned second coating 102 is 4 mm to 10 mm; as an example, the width of the second coating 102 is any one of the point values of 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or the range value between any two of them.

[0091] It should be understood that the thickness and width of the above-mentioned first coating 101 can adopt the thickness and width of a conventional coating, and can be selected and set according to the actual battery needs. The second coating 102 mainly plays the role of avoiding the thick edge of the electrode sheet and improving the thickness consistency. The thickness and width of the second coating 102 can be much smaller than those of the first coating 101. Thus, by controlling the thickness or width of the second coating 102 within the above range, it can not only effectively play the role of avoiding the thick edge of the electrode sheet and improving the thickness consistency, but also reduce the amount of the second coating 102 and lower the cost.

[0092] In some embodiments, the first coating 101 and the second coating 102 have the same length.

[0093] In some embodiments, an overlapping area is formed between the first coating 101 and the second coating 102, and the width of the overlapping area is 0.5 mm to 3 mm; as an example, the width of the overlapping area is any one of the point values of 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm or the range value between any two of them.

[0094] In this application, the second coating 102 is provided at the edge positions opposite to each other in the width direction of the first coating 101, and the second coating 102 and the first coating 101 can be lap-jointed, that is, an overlapping area can be formed between the two end edges in the width direction of the second coating 102 and the first coating 101. This is beneficial to improving the connection continuity between the first coating 101 and the second coating 102, and is more conducive to exerting the role of the second coating 102. When the drying rates of the first coating 101 and the second coating 102 are different, the wet slurry at the edge will move towards the middle area of the electrode sheet under the action of surface tension, thereby preventing the problem that the first slurry flows towards the edge to form a thick edge.

[0095] It should be noted that in this application, there may be no thinned area at the edge of the battery electrode sheet, and the thickness of the edge of the electrode sheet can be substantially the same as that of the middle area of the electrode sheet.

[0096] Optionally, when the battery electrode sheet is applied to a battery, the second coating 102 of the battery electrode sheet can be removed in subsequent processes. For example, the removal methods of the second coating 102 include but are not limited to laser cleaning, mechanical scraping, etc.

[0097] It should be understood that the above battery electrode sheet can also be connected or provided with a tab, such as connecting or providing a tab on at least one side edge of the current collector 103.

[0098] Optionally, after the electrode sheet coating is completed and after slitting and die-cutting, the second coating 102 can be removed. In this way, the second coating 102 only exists beside the tab, and only the first coating 101 is provided in the non-tab area (main body area). The second coating 102 is removed from the non-tab area, and at this time, the thickness of the electrode sheet in this area is substantially the same, and there is no thinned area.

[0099] In some embodiments, the first coating 101 further includes a first active material and a first conductive agent; that is, the first coating 101 includes a first active material, a first conductive agent, and a first binder.

[0100] The second coating 102 further includes a second active material and a second conductive agent; that is, the second coating 102 includes a second active material, a second conductive agent, and a second binder.

[0101] In this application, both the first coating 101 and the second coating 102 can include an active material, a conductive agent, and a binder. The types of the active material, the conductive agent, and the binder in the first coating 101 and the second coating 102 can be the same or different, and preferably the same. The main difference between the first coating 101 and the second coating 102 is that the amounts of the active material, the conductive agent, or the binder contained in the two can be slightly different, or the thickness and width of the first coating 101 and the second coating 102 are different, and the active material, the conductive agent, and the binder contained in the two preferably use the same type.

[0102] As an example, when the battery electrode sheet is a positive electrode sheet, the above-mentioned first active material and second active material are both positive electrode active materials. In some embodiments, the positive electrode active material includes, but is not limited to, at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, lithium nickel cobaltate, lithium iron phosphate, or ternary material; wherein, the ternary material can be lithium nickel cobalt manganate or lithium nickel cobalt aluminate.

[0103] However, this application is not limited to these positive electrode materials, and this application can also use other conventional materials that can be used as lithium battery positive electrode active materials. These positive electrode materials can be used alone or in combination of two or more.

[0104] When the battery electrode is a negative electrode, both the first active material and the second active material are negative active materials. In some embodiments, the negative active materials include, but are not limited to, at least one of artificial graphite, natural graphite, silicon-carbon graphite, silicon-oxygen graphite, or silicon (such as elemental silicon or silicon-containing alloys). Among them, silicon-carbon graphite can be a material containing graphite and nano-silicon, such as incorporating nano-silicon particles into artificial graphite to obtain silicon-carbon graphite. Silicon-oxygen graphite can be a material containing graphite and silicon monoxide, such as incorporating silicon monoxide into artificial graphite to obtain silicon-oxygen graphite.

[0105] However, the present application is not limited to these negative electrode materials. The present application can also use other conventional materials that can be used as negative active materials for lithium batteries. These negative electrode materials can be used alone or in combination of two or more.

[0106] When the battery electrode is a positive electrode and / or a negative electrode, the first conductive agent includes, but is not limited to, any one or a combination of at least two of conductive graphite, conductive carbon black, carbon fiber, carbon nanotube, graphene, or graphene oxide; among them, the above-mentioned conductive carbon black includes acetylene black, Ketjen black, etc. The second conductive agent includes, but is not limited to, any one or a combination of at least two of conductive graphite, conductive carbon black, carbon fiber, carbon nanotube, graphene, or graphene oxide; among them, the above-mentioned conductive carbon black includes acetylene black, Ketjen black, etc.

[0107] The above-mentioned first conductive agent and the second conductive agent can be of the same type or different types, and preferably the same type is adopted.

[0108] In addition, in other embodiments, any conductive agent known in the art that can be applied to the positive electrode or the negative electrode can also be used, and will not be listed one by one here.

[0109] When the battery electrode is a positive electrode and / or a negative electrode, the first binder includes, but is not limited to, any one or a combination of at least two of hydroxymethyl cellulose (or sodium carboxymethyl cellulose), polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyethylene oxide, polyester, polyamide, or polycarbonate. The second binder includes, but is not limited to, any one or a combination of at least two of hydroxymethyl cellulose (or sodium carboxymethyl cellulose), polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyethylene oxide, polyester, polyamide, or polycarbonate.

[0110] The above-mentioned first binder and the second binder can be of the same type or different types, and preferably the same type is adopted.

[0111] In addition, in other embodiments, any binder known in the art that can be applied to the positive electrode or the negative electrode can also be used, and will not be listed one by one here.

[0112] In some embodiments, in the first coating layer 101, the mass ratio of the first active material, the first conductive agent, and the first binder is (89-96):(1-3):(3-10). As an example, the mass ratio of the first active material, the first conductive agent, and the first binder in the first coating layer 101 can be any point value among 89:3:8, 90:3:7, 92:2:6, 93:2:5, 94:2:4, 95:1:4, 96:1:3 or the range value between any two of them.

[0113] In some embodiments, in the second coating layer 102, the mass ratio of the second active material, the second conductive agent, and the second binder is (92-98):(1-3):(1-5). As an example, the mass ratio of the second active material, the second conductive agent, and the second binder in the second coating layer 102 can be any point value among 92:3:5, 93:3:4, 94:3:3, 93:2:3.5, 96:2:3, 97:1:2, 98:1:1 or the range value between any two of them.

[0114] By making the ratios of the substances in the above-mentioned first coating layer 101 and the ratios of the substances in the second coating layer 102 within the above-mentioned appropriate ranges, it helps to regulate the viscosity of the slurry while ensuring the requirements of conductivity, adhesion, etc., alleviate the problem of thick edges of the electrode sheet, and improve the thickness uniformity of the electrode sheet.

[0115] It should be noted that in the battery electrode sheet, such as in the positive electrode sheet or the negative electrode sheet, the current collector 103, i.e., the positive current collector or the negative current collector, can be the current collector 103 conventionally used in the art, such as aluminum foil, copper foil, etc.

[0116] In some embodiments, the current collector 103 includes at least one of a metal foil or a composite current collector; the composite current collector includes a polymer substrate layer and a conductive layer provided on at least one surface of the polymer substrate layer along the thickness direction.

[0117] In some embodiments, the metal foil includes at least one of aluminum foil, copper foil, nickel foil, or stainless steel foil.

[0118] In some embodiments, the conductive layer includes at least one of a conductive resin, conductive carbon powder, or a metal layer.

[0119] In the above-mentioned battery electrode, a metal foil or a composite current collector can be used. For example, as the metal foil, generally, an aluminum foil is used as the positive current collector, and a copper foil is used as the negative current collector; the composite current collector includes a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The metal layer can be made of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc., and the polymer material substrate can be made of polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), etc.

[0120] In the above-mentioned battery electrode, the thickness of the current collector 103 is not limited in any way. As an example, the thickness of the current collector 103 is 3 μm to 500 μm, preferably 5 μm to 50 μm, more preferably 6 μm to 20 μm; for example, it can be 3 μm, 5 μm, 6 μm, 10 μm, 12 μm, 13 μm, 15 μm, 20 μm, 50 μm, 80 μm, 100 μm, 200 μm, 300 μm, 500 μm or within the range composed of any two of the above values.

[0121] Preferably, the thickness of the positive current collector is 13 μm, and the thickness of the negative current collector is 6 μm.

[0122] [Preparation method of battery electrode]

[0123] In some embodiments, the embodiments of the present application provide a preparation method of a battery electrode, and the method includes the following steps:

[0124] Coat a first slurry on at least one surface of the current collector 103 in the thickness direction to obtain a first coated wet film;

[0125] Coat a second slurry along both ends of the first coated wet film in a first direction to obtain a second coated wet film; the first direction represents the width direction of the battery electrode;

[0126] After drying, a first coating 101 and a second coating 102 are formed on the surface of the current collector 103. Both ends of the first coating 101 in the first direction are provided with the second coating 102 to obtain the battery electrode;

[0127] Wherein, the solid content of the first slurry is S1, the solid content of the second slurry is S2, and S1 and S2 satisfy the following relationship: 2 ≤ S1 / S2 ≤ 10; the thickness of the first coating 101 is H1, the thickness of the second coating 102 is H2, and H1 and H2 satisfy the following relationship: 2 ≤ H1 / H2 ≤ 10.

[0128] It should be understood that the "preparation method of the battery electrode" and the foregoing "battery electrode" are based on the same inventive concept. All the features and advantages described above for the "battery electrode" also apply to the "preparation method of the battery electrode", and will not be elaborated here one by one.

[0129] In the process of preparing the battery electrode sheet, the first slurry and the second slurry can be prepared separately first, and then coated on at least one surface of the current collector 103 by means of extrusion coating. The first slurry can be coated on the middle position of the surface of the current collector 103 to form a first wet coating film, and the second slurry can be coated on the positions near the edges of the surface of the current collector 103 and on both sides opposite to each other in the width direction of the first wet coating film to form a second wet coating film; then drying is carried out to obtain the battery electrode sheet.

[0130] In the above battery electrode sheet, the first coating 101 is formed by drying the first slurry after coating; the second coating 102 is formed by drying the second slurry after coating.

[0131] The above methods for preparing the first slurry and the second slurry can adopt conventional methods in the art. For example, each active material, conductive agent, binder and any other components are dispersed in a solvent and stirred evenly to form each slurry. It can be understood that in order to ensure the uniform mixing of the slurries, steps of respectively stirring each slurry are included before coating, and the stirring method can be stirring with a stirring paddle, or a method of synchronous stirring of a stirring paddle and a dispersing wheel, etc.

[0132] In some embodiments, the second slurry includes a surfactant.

[0133] In the present application, the first slurry may not contain a surfactant, while the second slurry needs to contain a surfactant. By adding a certain amount of surfactant to the second slurry, it can be used to reduce the surface tension of the second slurry, so that the surface tension of the first slurry is greater than that of the second slurry.

[0134] As an example, in some embodiments, the surface tension of the first slurry is Z1, and the surface tension of the second slurry is Z2. Z1 and Z2 satisfy the following relationship: 2 ≤ Z1 / Z2 ≤ 4. As an example, the value of Z1 / Z2 can be 2, 3, 4 or within the range composed of any two of the above values.

[0135] In some embodiments, Z1 is 40 to 120 mN / m; and / or, Z2 is 20 to 30 mN / m. As an example, Z1 can be 40 mN / m, 50 mN / m, 60 mN / m, 70 mN / m, 80 mN / m, 90 mN / m, 100 mN / m, 110 mN / m, 120 mN / m or within the range composed of any two of the above values. Z2 can be 20 mN / m, 22 mN / m, 24 mN / m, 25 mN / m, 28 mN / m, 30 mN / m or within the range composed of any two of the above values.

[0136] Thus, by adding a certain amount of surfactant to the second slurry and making the surface tension Z1 of the first slurry and the surface tension Z2 of the second slurry within the above range, or making Z1 and Z2 satisfy: 2 ≤ Z1 / Z2 ≤ 4, the problem of thick edges of the electrode sheet can be effectively alleviated. This is because the surface tension of the first slurry is greater than that of the second slurry. Therefore, during coating, the first slurry and the second slurry come into contact with each other, and a surface tension gradient is formed at the junction of the first slurry and the second slurry, and the gradient direction points from the first slurry to the second slurry. According to the Marangoni effect, the first slurry with a large surface tension has a pulling effect on the second slurry with a small surface tension, causing the second slurry to flow towards the first slurry. As the drying process proceeds, the second slurry flows towards the first slurry, and the edge position of the first slurry flows towards the middle position of the first slurry, thereby preventing the thick edge phenomenon caused by the wet slurry in the middle area moving towards the edge area.

[0137] In the present application, for different types of battery electrode sheets, the specific types of surfactants added may be different. For example, when the battery electrode sheet is a positive electrode sheet, the surfactant in the second slurry can be an ester or a ketone; when the battery electrode sheet is a negative electrode sheet, the surfactant in the second slurry can be an alcohol or a benzene and its derivative.

[0138] As an example, in some embodiments, when the battery electrode sheet is a positive electrode sheet, the surfactant includes, but is not limited to, any one or at least two combinations of butyl acetate, ethyl acetate, acetone, or methyl ethyl ketone.

[0139] In some embodiments, when the battery electrode sheet is a negative electrode sheet, the surfactant includes, but is not limited to, any one or at least two combinations of ethanol, butanol, or styrene.

[0140] Optionally, based on the mass of the electrode slurry without solvent being 100%, the mass ratio of the surfactant is 0.1% - 5%, for example, it can be any one of the point values of 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5% or the range value between any two of them.

[0141] It should be noted that during the preparation process of the battery electrode sheet, when a certain amount of surfactant is added to the second slurry, since most of the added surfactants are volatile substances, generally with a boiling point below 150°C, the finally prepared battery electrode sheet product may not contain surfactants or contain a small amount of residues. For example, a small amount of residues may remain for some surfactants with a higher boiling point (such as butanol, styrene, butyl acetate), while other surfactants will volatilize during high-temperature treatments such as drying.

[0142] Thus, through the above settings, on the one hand, the second slurry is provided in the edge area of the first slurry, and the second slurry plays a wetting role during the drying process, thereby preventing the occurrence of thick edge phenomenon. On the other hand, a certain amount of surfactant is added to the second slurry, so that part of the slurry in the second slurry and the edge area of the first slurry flows towards the middle area of the first slurry, which can further prevent the thick edge problem of the first coating 101.

[0143] In some embodiments, the preparation of the first slurry includes: dissolving the first active material, the first conductive agent, and the first binder in a solvent and mixing them evenly to obtain the first slurry.

[0144] As an example, the first active material, the first conductive agent, and the first binder can be evenly dispersed in an appropriate amount of solvent in a certain proportion and stirred evenly to form the first slurry. Among them, in the first slurry, the mass ratio of the first active material, the first conductive agent, and the first binder is (89-96):(1-3):(3-10).

[0145] In some embodiments, the preparation of the second slurry includes: dissolving the second active material, the second conductive agent, the second binder, and the surfactant in a solvent and mixing them evenly to obtain the second slurry.

[0146] As an example, the second active material, the second conductive agent, the second binder, and the surfactant can be evenly dispersed in an appropriate amount of solvent in a certain proportion and stirred evenly to form the first slurry. Among them, in the second slurry, the mass ratio of the second active material, the second conductive agent, the second binder, and the surfactant is (92-98):(1-3):(1-5):(0.1-5).

[0147] It should be noted that the specific type of the solvent in this embodiment is not limited, and a common solvent used in the field for preparing the positive electrode slurry or the negative electrode slurry composition can be used as the solvent. For example, N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, acetone, or water (such as deionized water) can be used alone or in combination of two or more. Considering the coating thickness of the slurry and the preparation yield, if the solvent can dissolve or disperse the active material, the conductive agent, and the binder, and can make its viscosity exhibit excellent thickness uniformity during the subsequent coating for preparing the positive electrode, the amount of the solvent used can be sufficient.

[0148] In some embodiments, the solid content S1 of the first slurry is 50%-80%. The solid content S2 of the second slurry is 8%-40%.

[0149] In some embodiments, the mass content U1 of the first binder in the first slurry is 3%-10%. The mass content U2 of the second binder in the second slurry is 1%-5%.

[0150] In some embodiments, during the preparation of the battery electrode sheet, a first coating wet film and a second coating wet film are first formed, wherein the thickness of the first coating wet film is 60 μm to 200 μm; the thickness of the second coating wet film is 12 μm to 80 μm.

[0151] In some embodiments, the thickness H2 of the second coating 102 is 10 μm to 50 μm. The thickness H1 of the first coating 101 is 50 μm to 200 μm

[0152] In some embodiments, the viscosity of the first slurry is 2000 mPa·s to 20000 mPa·s; and / or, the viscosity of the second slurry is 2000 mPa·s to 20000 mPa·s. Further, the viscosity of the first slurry can be 4000 mPa·s to 10000 mPa·s; and / or, the viscosity of the second slurry can be 4000 mPa·s to 10000 mPa·s. Within this viscosity range, the coating quality can be guaranteed and a better coating effect can be achieved.

[0153] Thus, by coating the second slurry with a lower solid content on the edge position of the surface of the current collector 103, the present invention can effectively alleviate the thick-edge problem at the edge of the electrode sheet, and adding a certain amount of surfactant to the second slurry can reduce the surface tension at the edge position of the first coating 101, thereby reducing the retraction effect of the slurry during the drying process of the electrode sheet and further improving the thick-edge problem at the edge of the electrode sheet. In this way, the thick-edge problem at the edge can be effectively solved without thinning the edge of the electrode sheet, which can reduce the space waste caused by thinning, and at the same time can effectively improve the energy density of the battery; it can make the thickness of the edge and the main body of the electrode sheet more uniform, and can improve the processability and reliability of the electrode sheet.

[0154] [Battery]

[0155] In some embodiments, the embodiments of the present application provide a battery, which includes a battery electrode sheet, and the battery electrode sheet is the aforementioned battery electrode sheet or the battery electrode sheet prepared according to the aforementioned preparation method.

[0156] The above battery can be a secondary battery or a primary battery, preferably a secondary battery. For example, the above battery can be a lithium-ion secondary battery, a lithium primary battery, a sodium-ion battery, a magnesium-ion battery, etc., but is not limited thereto. The battery structure of the present application includes but is not limited to a soft-pack lithium-ion battery, a square hard-shell battery or a cylindrical hard-shell battery, etc.

[0157] It should be noted that in the specific implementation manner, a lithium-ion battery is taken as an example of the secondary battery to explain the present application, but the battery of the present application is not limited to the lithium-ion battery.

[0158] The above battery electrode sheet provided by the present application can be a positive electrode sheet or a negative electrode sheet.

[0159] In some embodiments, the battery further includes an electrolyte and a separator membrane.

[0160] In the battery, the separator membrane separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. As the separator membrane, any separator membrane can be used without particular limitation as long as it is commonly used in lithium secondary batteries.

[0161] In the embodiments of the present application, the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used to manufacture lithium secondary batteries, but is not limited thereto.

[0162] Since the battery provided by the embodiments of the present invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be elaborated one by one here.

[0163] To better understand the present invention, the following will elaborate on the specific implementation process of the present invention in detail in specific implementation manners. The implementation manners described below are exemplary and are only used to explain the present application and cannot be construed as a limitation to the present application. For those technical or conditions not specified in the implementation manners, they shall be carried out according to the technologies or conditions described in the literature in the art or according to the product specifications.

[0164] Example 1

[0165] The preparation of the positive electrode sheet includes the following steps:

[0166] (1) Prepare the first slurry.

[0167] Dissolve lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) in a mass ratio of 91%:6%:3% in N-methylpyrrolidone (NMP) to make the first slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the first slurry is about 30%, that is, the solid content S1 of the first slurry is about 70%.

[0168] (2) Prepare the second slurry.

[0169] Dissolve lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) in a mass ratio of 94%:3%:3% in N-methylpyrrolidone (NMP) to make the second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry is about 70%, that is, the solid content S2 of the second slurry is about 30%.

[0170] (3) Prepare the positive electrode sheet.

[0171] The prepared first slurry and second slurry are respectively coated on the two opposite sides in the thickness direction of the current collector aluminum foil by means of extrusion coating. Among them, the first slurry is coated on the middle position of the aluminum foil surface to form a first coating wet film, and the second slurry is coated on the positions near the edges of the aluminum foil surface and on the two opposite sides in the width direction of the first coating wet film to form a second coating wet film. Among them, the thickness of the current collector aluminum foil is 13 μm and the width is 270 mm; the width of the first coating wet film is 250 mm, and the width of the second coating wet film is 3 mm.

[0172] Then, drying treatment is carried out, baking at 70 - 100 °C for 15 min. For example, taking a tunnel furnace with 7 sections of ovens as an example, hot air is used as the heat transfer medium to heat and dry the electrode sheet. The oven temperatures of the first section to the seventh section are 70 °C, 80 °C, 80 °C, 90 °C, 100 °C, 80 °C, and 75 °C respectively; after drying, a first coating and a second coating are respectively formed on the surface of the current collector aluminum foil to obtain a positive electrode sheet. Among them, the thickness of the first coating is about 122 μm (including the thickness of the aluminum foil), and the thickness of the second coating is 30 μm (including the thickness of the aluminum foil). That is, the thickness H1 of the first coating is 109 μm, and the thickness H2 of the second coating is 17 μm.

[0173] The surface density of the first coating is 0.2 g / m 2 , and the surface density of the second coating is 0.02 g / m 2 .

[0174] Example 2

[0175] The positive electrode sheet of Example 2 is prepared according to the preparation method of Example 1 above, and the difference is only that:

[0176] In the preparation of the second slurry, the positive electrode active material lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) according to the mass ratio: 92%:5%:3% to make the second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry is about 60%, that is, the solid content S2 of the second slurry is about 40%.

[0177] Example 3

[0178] The positive electrode sheet of Example 3 is prepared according to the preparation method of Example 1 above, and the difference is only that:

[0179] In the preparation of the second slurry, butyl acetate as a surfactant is added. Based on the mass of the electrode slurry without solvent being 100%, the mass proportion of butyl acetate is 2%.

[0180] Example 4

[0181] The positive electrode sheet of Example 4 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0182] In the preparation of the second slurry, butyl acetate as a surfactant was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of butyl acetate was 0.1%.

[0183] Example 5

[0184] The positive electrode sheet of Example 5 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0185] In the preparation of the second slurry, butyl acetate as a surfactant was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of butyl acetate was 5%.

[0186] Example 6

[0187] The positive electrode sheet of Example 6 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0188] In the preparation of the second slurry, acetone as a surfactant was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of acetone was 2%.

[0189] Example 7

[0190] The positive electrode sheet of Example 7 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0191] In the preparation of the second slurry, acetone as a surfactant was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of acetone was 0.1%.

[0192] Example 8

[0193] The positive electrode sheet of Example 8 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0194] In the preparation of the second slurry, acetone as a surfactant was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of acetone was 5%.

[0195] Example 9

[0196] The positive electrode sheet of Example 9 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0197] In the preparation of the second slurry, the cathode active material lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) according to a mass ratio of 98%:1%:1% to form the second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry is about 92%, that is, the solid content S2 of the second slurry is about 8%.

[0198] Example 10

[0199] The positive electrode sheet of Example 10 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0200] In the preparation of the second slurry, the cathode active material lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) according to a mass ratio of 93%:4%:3% to form the second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry is about 76%, that is, the solid content S2 of the second slurry is about 24%.

[0201] Example 11

[0202] The positive electrode sheet of Example 11 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0203] The thickness H1 of the first coating is 50 μm, and the thickness H2 of the second coating is 10 μm.

[0204] Example 12

[0205] The positive electrode sheet of Example 12 was prepared according to the preparation method of Example 1 above, with the only difference being that:

[0206] The thickness H1 of the first coating is 200 μm, and the thickness H2 of the second coating is 50 μm.

[0207] Example 13

[0208] The preparation of the negative electrode sheet includes the following steps:

[0209] (1) Prepare the first slurry.

[0210] The negative electrode active material (artificial graphite), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) according to a mass ratio of 91%:6%:3% to form the first slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the first slurry is about 30%, that is, the solid content S1 of the first slurry is about 70%.

[0211] (2) Prepare the second slurry.

[0212] The negative electrode active material (artificial graphite), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 94%:3%:3% to form a second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry is about 70%, that is, the solid content S1 of the first slurry is about 30%.

[0213] (3) Prepare the negative electrode plate.

[0214] The prepared first slurry and second slurry are respectively coated on the two opposite sides in the thickness direction of the current collector copper foil by extrusion coating. Among them, the first slurry is coated on the middle position of the copper foil surface to form a first coating wet film, and the second slurry is coated on the position close to the edge of the copper foil surface and on the two opposite sides in the width direction of the first coating wet film to form a second coating wet film. Among them, the thickness of the current collector copper foil is 13 μm and the width is 270 mm; the width of the first coating wet film is 250 mm, and the width of the second coating wet film is 3 mm.

[0215] Then, drying treatment is carried out, and it is baked at 70-100 °C for 15 min. For example, taking a tunnel furnace with 7 sections of ovens as an example, hot air is used as the heat transfer medium to heat and dry the electrode plate. The oven temperatures of the first section to the seventh section are 70 °C, 80 °C, 80 °C, 90 °C, 100 °C, 80 °C, and 75 °C respectively; after drying, a first coating and a second coating are respectively formed on the surface of the current collector copper foil to obtain the negative electrode plate. Among them, the thickness of the first coating is about 122 μm (including the copper foil thickness), and the thickness of the second coating is 30 μm (including the copper foil thickness). That is, the thickness H1 of the first coating is 109 μm, and the thickness H2 of the second coating is 17 μm.

[0216] The surface density of the first coating is 0.2 g / m 2 , and the surface density of the second coating is 0.02 g / m 2 .

[0217] Example 14

[0218] The negative electrode plate of Example 14 is prepared according to the preparation method of Example 13 above, and the difference is only that:

[0219] In the preparation of the second slurry, the negative electrode active material (artificial graphite), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 92%:5%:3% to form a second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry is about 60%, that is, the solid content S2 of the second slurry is about 40%.

[0220] Example 15

[0221] The negative electrode sheet of Example 15 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0222] In the preparation of the second slurry, surfactant ethanol was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of ethanol was 2%.

[0223] Example 16

[0224] The negative electrode sheet of Example 16 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0225] In the preparation of the second slurry, surfactant ethanol was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of ethanol was 0.1%.

[0226] Example 17

[0227] The negative electrode sheet of Example 17 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0228] In the preparation of the second slurry, surfactant ethanol was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of ethanol was 5%.

[0229] Example 18

[0230] The negative electrode sheet of Example 18 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0231] In the preparation of the second slurry, surfactant butanol was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of butanol was 2%.

[0232] Example 19

[0233] The negative electrode sheet of Example 19 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0234] In the preparation of the second slurry, surfactant butanol was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of butanol was 0.1%.

[0235] Example 20

[0236] The negative electrode sheet of Example 20 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0237] In the preparation of the second slurry, surfactant butanol was added. Based on the mass of the electrode slurry without solvent being 100%, the mass ratio of butanol was 5%.

[0238] Example 21

[0239] The negative electrode sheet of Example 21 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0240] In the preparation of the second slurry, artificial graphite as the negative active material, polyvinylidene fluoride (PVDF), and conductive carbon black (SP) were dissolved in N-methylpyrrolidone (NMP) according to a mass ratio of 98%:1%:1% to form the second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry was about 92%, that is, the solid content S2 of the second slurry was about 8%.

[0241] Example 22

[0242] The negative electrode sheet of Example 22 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0243] In the preparation of the second slurry, artificial graphite as the negative active material, polyvinylidene fluoride (PVDF), and conductive carbon black (SP) were dissolved in N-methylpyrrolidone (NMP) according to a mass ratio of 93%:4%:3% to form the second slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the second slurry was about 76%, that is, the solid content S2 of the second slurry was about 24%.

[0244] Example 23

[0245] The negative electrode sheet of Example 23 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0246] The thickness H1 of the first coating was 50 μm, and the thickness H2 of the second coating was 10 μm.

[0247] Example 24

[0248] The negative electrode sheet of Example 24 was prepared according to the preparation method of Example 13 above, with the only difference being that:

[0249] The thickness H1 of the first coating was 200 μm, and the thickness H2 of the second coating was 50 μm.

[0250] Comparative Example 1

[0251] The preparation of the positive electrode sheet includes the following steps:

[0252] (1) Prepare the first slurry.

[0253] The positive electrode active material lithium iron phosphate (LiFePO4), polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) according to a mass ratio of 91%:6%:3% to prepare a first slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the first slurry is about 30%, that is, the solid content S1 of the first slurry is about 70%.

[0254] (2) Prepare the positive electrode plate.

[0255] The prepared first slurry is coated on both sides of the current collector aluminum foil in the thickness direction by extrusion coating. The first slurry is coated at the middle position of the aluminum foil surface to form a first coating wet film. Among them, the thickness of the current collector aluminum foil is 13 μm and the width is 270 mm; the width of the first coating wet film is 250 mm.

[0256] Then, drying treatment is carried out. Bake at 70-100 °C for 15 min. For example, taking a tunnel furnace with 7 sections of ovens as an example, hot air is used as the heat transfer medium to heat and dry the electrode plate. The oven temperatures of the first to seventh sections are 70 °C, 80 °C, 80 °C, 90 °C, 100 °C, 80 °C, and 75 °C respectively; after drying, a first coating is formed on the surface of the current collector aluminum foil to obtain the positive electrode plate. Among them, the thickness of the first coating is about 122 μm (including the thickness of the aluminum foil), that is, the thickness H1 of the first coating is 109 μm.

[0257] The surface density of the first coating is 0.2 g / m 2 .

[0258] Comparative Example 2

[0259] The preparation of the negative electrode plate includes the following steps:

[0260] (1) Prepare the first slurry.

[0261] The negative electrode active material artificial graphite, polyvinylidene fluoride (PVDF), and conductive carbon black (SP) are dissolved in N-methylpyrrolidone (NMP) according to a mass ratio of 91%:6%:3% to prepare a first slurry. Among them, the proportion of N-methylpyrrolidone (NMP) in the total mass of the first slurry is about 30%, that is, the solid content S1 of the first slurry is about 70%.

[0262] (2) Prepare the negative electrode plate.

[0263] The prepared first slurry is coated on both sides of the current collector copper foil in the thickness direction by extrusion coating. The first slurry is coated at the middle position of the copper foil surface to form a first coating wet film. Among them, the thickness of the current collector copper foil is 13 μm and the width is 270 mm; the width of the first coating wet film is 250 mm.

[0264] Then, a drying process is carried out, baking at 70 - 100 °C for 15 min. For example, taking a tunnel furnace with 7 sections of ovens as an example, hot air is used as the heat transfer medium to heat and dry the electrode sheet. The oven temperatures of the first to seventh sections are 70 °C, 80 °C, 80 °C, 90 °C, 100 °C, 80 °C, and 75 °C respectively; after drying, a first coating is formed on the surface of the current collector copper foil to obtain the negative electrode sheet. Among them, the thickness of the first coating is about 122 μm (including the copper foil thickness), that is, the thickness H1 of the first coating is 109 μm.

[0265] The areal density of the first coating is 0.2 g / m 2 .

[0266] When formulating slurries with different solid contents in the above-mentioned examples and comparative examples, the viscosity can be adjusted by adjusting the content of the binder PVDF to meet the requirements of the coating for the slurry viscosity.

[0267] The main preparation parameters of the above-mentioned Examples 1 - 24 and Comparative Examples 1 - 2 are shown in Table 1 below.

[0268] Table 1

[0269]

[0270]

[0271]

[0272]

[0273] Performance Test

[0274] (1) The electrode sheets of the above-mentioned examples and comparative examples are subjected to electrode sheet thickness testing. The testing method includes:

[0275] Take a test electrode sheet with a length of about 100 mm, place the test electrode sheet on the test platform of the laser thickness gauge, and the laser thickness gauge will scan the test electrode sheet point by point along the width direction at a step of 0.1 mm along the edge of the electrode sheet to measure the thickness of the measured electrode sheet, and return the test point position and the measured transverse thickness of the measured electrode sheet at that place.

[0276] The test results are shown in Table 1.

[0277] In addition, through the thickness test of the pole pieces of each example and comparative example, it was also found that the edge thinning effect of the pole pieces in the examples of the present invention was significantly improved compared with the comparative examples; among them, there were slight bulges in the second coatings of Example 1 and Example 2, and neither the first coating 101 nor the second coating 102 in Example 3 had thick edges or bulges. In addition, due to the action of the surfactant added, the thickness of the edge region of the first coating 101 was more uniform with that of the middle region, and the thickness consistency was better.

[0278] (2) Test method for lithium plating on the pole piece

[0279] Coulombic efficiency test (CE): When lithium plating occurs, the lithium embedded in the negative electrode material will come into contact with the positive electrode material and be stripped during discharge. Irreversible lithium plating (dead lithium) will cause capacity loss and a decrease in Coulombic efficiency. By monitoring the change in Coulombic efficiency, the occurrence of lithium plating can be indirectly judged, and it is recorded whether lithium plating occurs in each example and comparative example.

[0280] (3) Test of capacity and cycle retention rate

[0281] Constant current charge and discharge test: The battery is charged and discharged at a constant current, and the change in the battery capacity is recorded; specifically including: 1. Under the test constant temperature environment condition of 25 °C, the battery is fully charged to the highest voltage (3.65 V); 2. Constant current charging: The battery is charged at a constant current of 0.5C until the set charging cut-off voltage (3.65 V) is reached; 3. Constant voltage charging: After reaching the cut-off voltage, it is switched to constant voltage charging, and the charging voltage is kept constant for 30 minutes to ensure that the battery is fully charged; 4. Standing: After charging is completed, the battery is allowed to stand for 15 min to ensure the stability inside the battery; 5. Constant current discharging: The battery is discharged at a constant current of 0.5C until the discharge cut-off voltage of 2.0 V is reached, and the current and discharge time during the discharge process are recorded. The battery capacity is calculated according to the formula "capacity = discharge current × discharge time"; 6. Data recording: The charging capacity and discharge capacity of each cycle, as well as the initial capacity of the battery are recorded. Initial Coulombic efficiency = initial discharge capacity / initial charging capacity * 100%.

[0282] Capacity retention rate (cycling performance) test: Under specific charge and discharge conditions, the battery is subjected to multiple charge and discharge cycles, and the capacity attenuation of the battery is recorded; specifically including: 1. Preparation stage: Ensure that the test environment temperature is constant (25 °C), and charge the battery to the highest voltage (3.65 V); 2. Charge: Charge the battery at a current of 2C until the set charge cut-off voltage (3.65 V) is reached; 3. Rest: After charging is completed, let the battery rest for 15 minutes to ensure stability inside the battery; 4. Discharge: Discharge the battery at 2C until the discharge cut-off voltage of 2.0 V is reached, record the current and discharge time during the discharge process, and calculate the battery capacity according to the formula "Capacity = Discharge current × Discharge time"; 5. Data recording: Record the charge capacity and discharge capacity of each cycle, as well as the number of cycles of the battery. Number of cycles: Test until the capacity decays to 80% of the initial capacity. After completing 1000 charge and discharge cycles, end the test. Capacity retention rate of the 1000th cycle = Discharge capacity of the 1000th cycle / Initial discharge capacity * 100%.

[0283] The test results are shown in Table 2.

[0284] Table 2

[0285]

[0286]

[0287] It can be seen from the data in Table 2 that compared with Comparative Examples 1-2, the negative electrode sheets and positive electrode sheets provided in Examples 1-24 of the present invention do not show lithium plating phenomenon, indicating that the solution of the present invention can prevent the lithium plating problem caused by excessive thinning of the battery electrode sheets. At the same time, compared with Comparative Examples 1-2, the batteries using the battery electrode sheets of Examples 1-24 of the present invention have higher capacity, higher first efficiency, and better cycle stability, improving the electrochemical performance of the battery electrode sheets.

[0288] The parts not detailed in the present invention are well-known technologies to those skilled in the art.

[0289] The basic principles of the present invention have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, advantages, effects, etc. mentioned in the present invention are only examples and not limitations, and it cannot be considered that these advantages, advantages, effects, etc. are essential for each embodiment of the present invention. In addition, the above-disclosed specific details are only for the purpose of illustration and easy understanding, and are not limitations. The above details do not limit the present invention to necessarily adopt the above specific details to implement.

[0290] It should be noted that the term "and / or" or " / " used in this article is merely a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. The singular forms of "a", "the", and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0291] In the specific embodiments and the claims, a list of items connected by the terms "at least one of", "at least one in", "at least one kind in", or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0292] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery pole piece, characterized in that: The battery pole piece comprises: current collector; A first coating layer is disposed on at least one side of the current collector along the thickness direction; A second coating layer is disposed on at least one side of the current collector along the thickness direction, and the second coating layer is disposed on both ends of the first coating layer along the first direction; the first direction represents the width direction of the battery electrode sheet; The first coating layer comprises a first binder, and the second coating layer comprises a second binder; the mass content of the first binder in the first coating layer is U1, and the mass content of the second binder in the second coating layer is U2, and U1 and U2 satisfy: U1≥U2; The thickness of the first coating layer is H1, the thickness of the second coating layer is H2, and H1 and H2 satisfy the following relationship: 2≤H1 / H2≤10.

2. The battery electrode according to claim 1, characterized in that: The first coating and the second coating satisfy at least one of the following features (1) to (6): (1) U1 is 3% to 10%; and / or U2 is 1% to 5%; (2) H2 is 10 μm to 50 μm; and / or H1 is 50 μm to 200 μm; (3) The width of the first coating is 80 mm to 300 mm; (4) The width of the second coating layer is 4 mm to 10 mm; (5) The first coating and the second coating form an overlapping area, and the width of the overlapping area is 0.5 mm to 3 mm; (6) The first coating layer and the second coating layer have the same length.

3. The battery pole piece according to claim 1, characterized in that: The first coating layer also includes a first active material and a first conductive agent; The second coating layer also includes a second active material and a second conductive agent; Optionally, in the first coating layer, the mass ratio of the first active material, the first conductive agent and the first binder is (89-96): (1-3): (3-10); Optionally, in the second coating layer, the mass ratio of the second active material, the second conductive agent and the second binder is (92-98): (1-3): (1-5).

4. The battery pole piece according to claim 3, characterized in that: The battery electrode sheet satisfies at least one of the following characteristics (1) to (4): (1) When the battery electrode is a positive electrode, the first active material and the second active material both include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt oxide, lithium iron phosphate or a ternary material; (2) When the battery electrode is a negative electrode, the first active material and the second active material both include at least one of artificial graphite, natural graphite, silicon-carbon graphite, silicon-oxygen graphite or silicon; (3) The first conductive agent and the second conductive agent both include at least one of conductive graphite, conductive carbon black, carbon fiber, carbon nanotube, graphene or graphene oxide; (4) The first binder and the second binder both include at least one of hydroxymethyl cellulose, polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, polyethylene oxide, polyester, polyamide or polycarbonate.

5. The battery electrode according to any one of claims 1 to 4, characterized in that: The current collector comprises at least one of a metal foil or a composite current collector; The composite current collector comprises a polymer substrate layer and a conductive layer disposed on at least one side of the polymer substrate layer along the thickness direction; Optionally, the metal foil includes at least one of aluminum foil, copper foil, nickel foil or stainless steel foil; Optionally, the conductive layer includes at least one of a conductive resin, a conductive carbon powder or a metal layer.

6. A method for preparing a battery electrode, characterized in that: The method comprises: Coating a first slurry on at least one side of the current collector along the thickness direction to obtain a first coating wet film; Coating a second slurry near both ends of the first coating wet film along a first direction to obtain a second coating wet film; the first direction represents the width direction of the battery electrode sheet; After drying, a first coating layer and a second coating layer are formed on the surface of the current collector, and the second coating layer is disposed at both ends of the first coating layer along the first direction, thereby obtaining a battery electrode sheet; The solid content of the first slurry is S1, the solid content of the second slurry is S2, and S1 and S2 satisfy the following relationship: 2≤S1 / S2≤10; The thickness of the first coating layer is H1, the thickness of the second coating layer is H2, and H1 and H2 satisfy the following relationship: 2≤H1 / H2≤10.

7. The method for preparing a battery pole piece according to claim 6, characterized in that: The first coating and the second coating are prepared to meet at least one of the following characteristics (1) to (6): (1) The thickness of the wet film of the first coating is 60 μm to 200 μm; (2) The thickness of the wet film of the second coating is 12 μm to 80 μm; (3) S1 is 50% to 80%; and / or S2 is 8% to 40%; (4) The first slurry contains a first binder, and the second slurry contains a second binder; the mass content of the first binder in the first slurry is U1, and the mass content of the second binder in the second slurry is U2, and U1 and U2 satisfy: U1≥U2; Optionally, U1 is 3% to 10%; and / or, U2 is 1% to 5%; (5) H2 is 10 μm to 50 μm; and / or H1 is 50 μm to 200 μm; (6) The viscosity of the first slurry is 2000mpa.s to 20000mpa.s; And / or, the viscosity of the second slurry is 2000mpa.s to 20000mpa.s.

8. The method for preparing a battery pole piece according to claim 6 or 7, characterized in that: The second slurry includes a surfactant; Optionally, when the battery pole piece is a positive pole piece, the surfactant includes at least one of butyl acetate, ethyl acetate, acetone or methyl ethyl ketone; Optionally, when the battery pole piece is a negative pole piece, the surfactant includes at least one of ethanol, butanol or styrene; Optionally, the surface tension of the first slurry is Z1, the surface tension of the second slurry is Z2, and Z1 and Z2 satisfy the following relationship: 2≤Z1 / Z2≤4; Optionally, the Z1 is 40 to 120 mN / m; and / or the Z2 is 20 to 30 mN / m.

9. The method for preparing a battery pole piece according to claim 8, characterized in that: The preparation of the first slurry includes: dissolving the first active material, the first conductive agent and the first binder in a solvent and mixing them uniformly to obtain the first slurry; The preparation of the second slurry includes: dissolving the second active material, the second conductive agent, the second binder and the surfactant in a solvent and mixing them uniformly to obtain the second slurry; Optionally, in the first slurry, the mass ratio of the first active material, the first conductive agent and the first binder is (89-96): (1-3): (3-10); Optionally, in the second slurry, the mass ratio of the second active material, the second conductive agent, the second binder and the surfactant is (92-98): (1-3): (1-5): (0.1-5).

10. A battery, comprising a battery pole piece, characterized in that: The battery pole piece is the battery pole piece according to any one of claims 1 to 5 or the battery pole piece prepared by the preparation method according to any one of claims 6 to 9.

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