Electrode piece, electrode assembly and battery

Abstract

The utility model provides a pole piece, an electrode assembly and a battery. The pole piece comprises a current collector which comprises a current collector main body part and a tab part, the active material layer is arranged on the surface of the current collector main body part; the edge protection layer is arranged on the surface of the current collector, the edge protection layer is connected with the active material layer in the width direction, the edge protection layer extends outwards relative to the active material layer in the width direction, the edge protection layer comprises a gradually-thinned section, and the thickness of the gradually-thinned section is gradually reduced in the width direction. And the thickness of the gradually-thinned section is gradually thinned from one end, connected with the active material layer, of the gradually-thinned section to the other end of the gradually-thinned section.

Description

Technical Field

[0001] The present application relates to a pole piece, an electrode assembly and a battery. Background Art

[0002] A battery is a device that can convert chemical energy into electrical energy. The performance parameters of a battery mainly include electromotive force, capacity, specific energy and resistance. Using batteries as an energy source can obtain a current with stable voltage, stable current, long-term stable power supply, and little external influence. The battery has a simple structure, is easy to carry, and is easy to charge and discharge. It is not affected by external climate and temperature, and has stable and reliable performance. It plays a great role in all aspects of modern social life.

[0003] The pole piece of the battery generally includes a current collector and an active material. The current collector generally includes a current collector body and a pole ear protruding from the current collector body. The active material is generally coated on the surface of the current collector by a coating process. The process of forming the pole ear on the current collector generally adopts a die-cutting process. The die-cutting process, such as knife die-cutting or laser die-cutting, processes the pole ear of the pole piece. However, it is difficult to avoid defects such as metal burrs at the die-cutting position of the pole piece during the die-cutting process. Especially for the positive pole piece, since the width of the negative pole piece body is usually greater than the width of the positive pole piece body, the burrs on the edge of the positive pole piece assembled in the battery are easy to pierce the diaphragm and contact the negative pole piece, and the burrs on the edge of the negative pole piece may also pierce the diaphragm and contact the positive pole piece, thereby causing the risk of short circuit in the positive and negative pole pieces, seriously affecting the safety performance of the battery.

[0004] For the burr problem, in a comparative solution, such as Figure 1 As shown, the pole piece 1000 adopts a coating protection layer solution, and an active material layer 1002 is coated on the current collector 1001. In the width direction, one end of the active material layer 1002 extends outward to be coated with an edge protection layer 1003 of equal thickness, and die-cutting is performed from the position of the edge protection layer 1003 to reduce the generation of burrs during die-cutting, thereby reducing the risk of short circuit caused by the burrs. The edge protection layer contains insulating materials, such as ceramic particles, which have high resistance. After the burrs pierce the diaphragm, they will fall on the edge protection layer 1003. The edge protection layer can block the direct electrical contact between the positive pole piece and the negative pole piece, thereby reducing the risk of internal short circuit.

[0005] However, the inventors found in practice that Figure 1 The comparative scheme shown, taking lithium-ion batteries as an example, will have safety risks caused by lithium plating and problems of reduced battery capacity. The reason is probably that, after in-depth research by the inventors, Figure 1 The structure shown is only an ideal structure, and the actual structure is as follows Figure 2 As shown, the transition area where the active material layer 1002 of the positive electrode contacts the edge protection layer 1003 will form a mutual dissolution, for example, Figure 2 The first inter-soluble region 10041 and the second inter-soluble region 10042 are shown. The formation of the inter-soluble region will hinder the transmission of metal ions such as lithium ions, resulting in the easy precipitation of metals such as lithium in the contact transition region, which brings safety risks. In addition, the inter-soluble region will cause part of the positive electrode active material of the active material layer 1002 to be wrapped by the insulating material of the edge protection layer 1003, resulting in it being unable to participate in the battery reaction, thereby reducing the capacity of the battery.

[0006] Therefore, the art needs a pole piece, an electrode assembly and a battery to solve at least one of the above problems. Utility Model Content

[0007] The utility model aims to provide a pole piece.

[0008] Another object of the utility model is to provide an electrode assembly.

[0009] Another object of the utility model is to provide a battery.

[0010] According to the first aspect of the utility model, a pole piece includes a current collector, including a current collector body and a pole ear; an active material layer, arranged on the surface of the current collector body; an edge protection layer, arranged on the surface of the current collector, the edge protection layer is connected to the active material layer in the width direction, and the edge protection layer extends outward relative to the active material layer in the width direction, the edge protection layer includes a gradually thinning section, and in the width direction, the thickness of the gradually thinning section gradually thins from one end of the gradually thinning section connected to the active material layer to the other end.

[0011] The technical solution of the present application is to set a structure with a gradually thinning section of the edge protection layer. The protection layer with such a structure has a larger thickness and a larger slope in the part close to the active material, forming a buffer structure, which can effectively inhibit the substances in the protective layer from escaping to the active material layer to form mutual dissolution, thereby avoiding or reducing the formation of mutual dissolution zones, which may lead to safety risks caused by easy lithium precipitation, and avoiding or reducing the negative effect of reduced battery capacity caused by the active material being wrapped by the insulating material of the edge protection layer.

[0012] In one or more embodiments of the pole piece, the edge protection layer is composed of the gradually thinning section, the thickness of the outermost end of the edge protection layer in the width direction is substantially zero, and the cutting angle between the outermost end and the innermost end of the edge protection layer in the width direction and the connection position of the active material layer is 0.1° to 0.5°; or,

[0013] The edge protection layer also includes a constant thickness segment, which extends with constant thickness in the width direction, and the innermost end of the constant thickness segment in the width direction is directly connected to the outermost end of the gradually thinning segment in the width direction, and the gradually thinning segment is located on the surface of the collector body.

[0014] In one or more embodiments of the pole piece, the edge protection layer further comprises a constant thickness segment, and the thickness of the constant thickness segment is 3 μm to 7 μm.

[0015] In one or more embodiments of the pole piece, the edge protection layer is composed of the gradually thinning section, the first portion of the edge protection layer in the width direction is located at the collector ear portion, and the maximum thickness of the first portion is 6 μm to 14 μm.

[0016] In one or more embodiments of the pole piece, the first portion of the edge protection layer in the width direction is located at the collector ear portion, and the second portion in the width direction is located at the collector body portion, and the proportion of the width dimension occupied by the second portion is greater than or equal to the proportion of the width dimension occupied by the first portion.

[0017] In one or more embodiments of the pole piece, the first portion accounts for 30% to 50% of the width dimension, and the second portion accounts for 50% to 70% of the width dimension.

[0018] In one or more embodiments of the pole piece, a thickness difference between a maximum thickness value of the active material layer and a maximum thickness value of the edge protection layer is 50 μm to 70 μm.

[0019] According to the second aspect of the present invention, an electrode assembly includes a first pole piece, a second pole piece and a diaphragm, wherein the diaphragm is arranged between the first pole piece and the second pole piece, and the first pole piece is the pole piece described in the first aspect.

[0020] In one or more embodiments of the electrode assembly, the first pole piece is a positive pole piece, and the second pole piece is a negative pole piece.

[0021] A battery according to a third aspect of the utility model comprises the electrode assembly as described in the second aspect, and an electrolyte, wherein the electrolyte and the electrode assembly are accommodated in a chamber provided by a battery housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments. In the accompanying drawings, the same reference numerals always represent the same features. It should be noted that these drawings are only examples and are not drawn in proportion. They should not be used as a limitation on the actual scope of protection of the present invention. Among them:

[0023] Figure 1 A schematic diagram of an ideal partial structure of a pole piece for a comparative solution;

[0024] Figure 2 for Figure 1 The actual partial structure diagram of the pole piece of the comparative scheme shown;

[0025] Figure 3A as well as Figure 3B This is a schematic structural diagram of a pole piece according to the first embodiment of the present application;

[0026] Figure 4A as well as Figure 4B This is a schematic structural diagram of a pole piece according to a second embodiment of the present application;

[0027] Figure 5 It is a schematic structural diagram of the pole piece after die-cutting of the first embodiment or the second embodiment of the present application;

[0028] Figure 6 This is a schematic structural diagram of an electrode assembly according to an embodiment of the present application;

[0029] Figure 7 It is a schematic diagram of the structure of the electrode assembly winding according to one embodiment of the present application. DETAILED DESCRIPTION

[0030] Reference will now be made in detail to various embodiments of the present invention, examples of which are shown in the accompanying drawings and described below. Although the present invention will be described in conjunction with the exemplary embodiments, it should be appreciated that this specification is not intended to limit the present invention to those exemplary embodiments. On the contrary, the present invention is intended to cover not only these exemplary embodiments, but also various alternative forms, modified forms, equivalent forms and other embodiments that may be included within the spirit and scope of the present invention as defined by the appended claims.

[0031] In the following description, the orientation or positional relationship indicated by "upper", "lower", "inside", "outside" or other directional terms is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0032] In addition, although the terms used in this application are selected from well-known and commonly used terms, some of the terms mentioned in this application specification may be selected by the applicant at his or her discretion, and their detailed meanings are explained in the relevant parts of the description of this article. In addition, it is required to understand this application not only by the actual terms used, but also by the meaning implied by each term.

[0033] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment" and / or "an embodiment" means a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0034] Flowcharts are used in this application to illustrate the operations performed by the system according to the embodiments of the application. It should be understood that the preceding or following operations are not necessarily performed precisely in order. Other operations may also be added to these processes, or one or more operations may be removed from these processes.

[0035] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. However, the embodiments shown below are examples of current collectors, pole pieces and batteries for embodying the technical ideas of the present invention, and the current collectors, pole pieces and batteries of the present invention are not specifically the following contents. Furthermore, in order to facilitate the understanding of the scope of the claims, this specification assigns numbers corresponding to the components shown in the embodiments to the components shown in the "Claims" and "Contents of the Utility Model" columns. However, the components shown in the claims are by no means specified as the components of the embodiments. In particular, the size, material, shape, and relative configuration of the constituent components recorded in the embodiments, if there is no specific record, is not intended to limit the scope of the present invention to only this, but is only an illustrative example.

[0036] However, the size or positional relationship of the components shown in the drawings is sometimes exaggerated for the purpose of clear description. Furthermore, in the following description, for the same name and symbol, representing the same or homogeneous components, it is appropriate to omit their detailed description. Furthermore, the various elements constituting the utility model can be a form in which the same component constitutes multiple elements so that one component can serve as multiple elements. Conversely, it can also be realized by multiple components sharing the function of one component. In addition, in this specification, "on" is not limited to the case of being formed in contact with the upper surface, but also includes the case of being formed separately on the upper surface, and is also used to include the meaning of the existence of an intervening layer between layers.

[0037] To prevent the burrs on the edge of the pole piece from affecting the safety performance of the battery, you can use Figure 1 The structure of the comparison scheme shown is as follows Figure 1 As shown, the pole piece 1000 adopts a coating protection layer solution, and an active material layer 1002 is coated on the current collector 1001. In the width direction, one end of the active material layer 1002 extends outward to be coated with an edge protection layer 1003 of equal thickness, and die-cutting is performed from the position of the edge protection layer 1003 to reduce the generation of burrs during die-cutting, thereby reducing the risk of short circuit caused by the burrs. The edge protection layer contains insulating materials, such as ceramic particles, which have high resistance. After the burrs pierce the diaphragm, they will fall on the edge protection layer 1003. The edge protection layer can block the direct electrical contact between the positive pole piece and the negative pole piece, thereby reducing the risk of internal short circuit.

[0038] However, the inventors found in practice that Figure 1 The comparative scheme shown, taking lithium-ion batteries as an example, has the problem of safety risks caused by lithium plating and reduced battery capacity.

[0039] For the above problems, the inventors have conducted in-depth research and found that Figure 1 The structure shown is only an ideal structure, and the actual structure is as follows Figure 2 As shown, the transition area where the active material layer 1002 of the positive electrode contacts the edge protection layer 1003 will form a mutual dissolution, for example, Figure 2 The first inter-soluble region 10041 and the second inter-soluble region 10042 are shown. The formation of the inter-soluble region will hinder the transmission of lithium ions, causing the contact transition region to easily precipitate lithium, which brings safety risks. In addition, the inter-soluble region will cause part of the positive electrode active material of the active material layer 1002 to be wrapped by the insulating material of the edge protection layer 1003, making it unable to participate in the battery reaction, thereby reducing the capacity of the battery.

[0040] Based on the above research, the inventor has further studied and invented a pole piece. Figure 1 The edge protection layer 1003 shown in the figure, which is substantially of equal thickness extending in the width direction, is improved into a structure having a gradually thinning section, that is, the edge protection layer has a portion extending in a non-equal thickness in the width direction. The protection layer with such a structure has a larger thickness and a larger slope in the portion close to the active material, thereby forming a buffer structure, which can effectively inhibit the substances in the protective layer from escaping to the active material layer to form mutual dissolution, thereby minimizing or reducing the safety risks caused by easy lithium precipitation due to the formation of a mutual dissolution zone, and minimizing or reducing the negative effect of the active material being wrapped by the insulating material of the edge protection layer, resulting in a reduction in the capacity of the battery, thereby improving the safety and capacity of the electrode sheets, electrode assemblies and batteries.

[0041] The pole piece and electrode assembly of the battery of the present application can be used in batteries and electrical equipment containing batteries, but are not limited to batteries, including but not limited to secondary lithium-ion batteries, nickel-metal hydride batteries, nickel-chromium batteries, lead-acid batteries, polymer lithium-ion batteries, sodium batteries, etc. The electrical device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric vehicles, trains, ships, spacecraft, etc. Among them, electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles and spacecraft, etc. The electrical device can also be an energy storage system, such as large-scale commercial energy storage, microgrid energy storage, base station products, household uninterruptible power supply energy storage, etc.

[0042] The structure of a battery, such as a secondary lithium-ion battery, can be formed by winding a positive electrode sheet, a negative electrode sheet and a separator. Figure 7 The winding structure shown is used to form a battery cell with a wound structure. In some embodiments, the positive electrode sheet can adopt the electrode sheet 10, and the structure of the electrode sheet 10 will be described in detail in the following content. In addition, in some embodiments, a stacked structure of a positive electrode sheet, a negative electrode sheet and a diaphragm stack can also be used to form a stacked battery cell. The structure of the battery cell is not limited to the cross-section shown in the figure being similar to an ellipse (track shape) to form a battery cell with a square structure. For example, it can also be a battery cell with a cylindrical structure, and a battery cell with a soft package structure, etc., are not limited to this. In addition, the electrode assembly composed of the positive electrode sheet, the negative electrode sheet and the diaphragm needs to be integrated with the electrolyte, for example, immersed in a liquid electrolyte (i.e., an electrolyte), and the electrode assembly and the electrolyte are generally contained in the chamber provided by the battery casing. However, it is not limited to this. For example, the electrolyte can also be a solid electrolyte, and such a battery is generally referred to as a solid-state battery.

[0043] The length direction, width direction, and thickness direction that may appear in this article take the X direction, Y direction, and Z direction shown in the figure as an example.

[0044] refer to Figure 3A , Figure 3B as well as Figure 4A , Figure 4B As shown, Figure 3A , Figure 4A It is a schematic diagram of the local structure of the pole piece forming a plane in the width direction and thickness direction. Figure 3B , Figure 4BSchematic diagram of the structure of the pole piece in the length direction and the width direction. In some embodiments, the pole piece 10 includes a current collector 1, an active material layer 2 and an edge protection layer 3. The current collector 1 includes a current collector body 11 and a pole ear 12. Figure 5 As shown, the pole ear portion 12 generally protrudes from the current collector body 11, and the pole ear portion 12 is integrally connected to the current collector body 11. For example, the pole ear portion 12 is obtained on the basis of the current collector body 11 through a die-cutting process. The specific structure can be that the shape of the current collector body 11 is a rectangle, and the shape of the pole ear portion 12 is an isosceles trapezoid, but it is not limited to this. For example, the pole ear portion 12 can also be a rectangle or other structures. It can be understood that in FIG. 3A to FIG. 4B The drawings of the first embodiment and the second embodiment show the structure of the pole piece 10 before die-cutting, so the pole ear portion is not shown.

[0045] The meaning of the current collector 1 here is similar to the commonly used meaning in the art, that is, a structure or part for collecting current, which collects the current generated by the active material of the battery so as to form a larger current and output it to the outside through the pole ear portion 12. Similar to the comparative scheme, the current collector 1 can be as shown in the first embodiment, the current collector 1 is composed of a substrate, the substrate provides the current collector body 11 and the pole ear portion 12, and the active material layer 2 and the edge protection layer 3 are arranged on the surface of the substrate 111. It can be understood that the substrate can generally be a metal foil, such as copper foil, aluminum foil, etc., but is not limited to this, for example, it can also be a composite current collector including a polymer substrate and a metal layer. In addition, the current collector can also be composed of a substrate and a conductive coating, the substrate provides the current collector body 11 and the pole ear portion 12, the conductive coating is arranged on the surface of the substrate 111, and the active material layer 2 is arranged on the surface of the conductive coating. The conductive coating is an intermediate layer structure located between the substrate 111 and the active material layer 2, which can effectively improve the interface contact resistance between the current collecting unit and the active material, and can improve the bonding strength between the active material and the current collecting unit, and reduce the problem of active material peeling during the electrode cycle. The conductive coating can be, for example, a carbon coating layer, and the composition of the carbon coating layer can be one or more of conductive carbon black, nano-carbon fiber, graphite powder or carbon nanotubes, etc., to provide better static conductivity, collect the micro-current of the active material, thereby greatly reducing the contact resistance between the positive / negative active material and the current collector substrate, and can improve the adhesion between the two, reduce the amount of binder used, and thus significantly improve the overall performance of the battery. The thickness of the conductive coating is generally very thin, about 1μm, so even if a conductive coating is used, burrs are generally faced. In order to simplify the structure, the current collector 1 described below is composed of a substrate 111, and an aluminum foil material is used.

[0046] The active material layer 2 is disposed on the surface of the current collector body 11. Specifically, the active material can be coated on the current collector body 11 by a coating process, that is, the active material of the active material layer 2, for example, when the electrode 10 is a positive electrode, the active material is a positive electrode material, which can be one or more of lithium cobalt oxide, lithium iron phosphate, ternary material, and lithium manganese oxide, but is not limited thereto. Due to the fluidity of the slurry when the active material is coated, the active material generally extends outward in the width direction and forms a layer such as Figure 3A , Figure 4A The thinned area 21 shown, i.e., the thickness of the thinned area 21 is less than the thickness of the active material layer located in the main area 22 of the current collector main body 11, and the thickness generally decreases gradually outward along the width direction. The active material layer 2 here is entirely disposed on the surface of the main body 11 of the current collector 1, that is, the active material layer 2, whether in the thinned area 21 or the main area 22, is located in the main body of the current collector 1, and has no part located in the pole ear 12.

[0047] The edge protection layer 3 is a protection structure located at the edge of the current collector in the width direction. The structure is a layered structure. It is generally believed that the electrical properties of the edge protection layer 3 are insulators, but the possibility of being a semiconductor is not excluded. Figure 3A as well as Figure 4A As shown, the edge protection layer 3 is arranged on the surface of the current collector 1, and the edge protection layer 3 is directly connected to the active material layer 2 in the width direction, and the edge protection layer 3 extends outward relative to the active material layer 2 in the width direction, and the edge protection layer 3 includes a gradually thinning section 31, and in the width direction, the thickness of the gradually thinning section 31 gradually thins from one end 311 of the thickness gradually thinning section connecting the active material layer 2 to the other end 312. The meaning of "gradually thinning" here is to exclude the concept of step thinning, that is, the thinning of the thickness is along a certain slope, rather than 90° step thinning. The inside and outside in this application are relative to the entire pole piece, that is, the inner side or inner end is relatively close to the middle of the pole piece, and the outer side or outer end is relatively far from the middle of the pole piece.

[0048] The specific process may be to first apply the active material slurry to the current collector main body 11, then apply the slurry of the edge protection layer 3 to the current collector 1, and then dry, roll, die-cut, and slit the product to obtain a pole piece with a pole ear portion 12; or to apply the active material slurry and the slurry of the edge protection layer 3 at the same time. Examples of specific slurry formulations will be introduced later, but it can be understood that the components of the active material slurry and the slurry of the edge protection layer can refer to the common ratios in the prior art, and this application is not about the improvement of materials.

[0049] The beneficial effect achieved in this way is that the structure of the gradually thinning section 31 is set by the edge protection layer 3. The protection layer 3 with such a structure has a larger thickness and a larger slope in the part close to the active material, forming a buffer structure, which can effectively inhibit the material of the protection layer from escaping to the active material layer to form a mutual dissolution, thereby avoiding or reducing the formation of a mutual dissolution zone, which leads to the problem of easy lithium precipitation and safety risks, and avoiding or reducing the negative effect of the active material being wrapped by the insulating material of the edge protection layer, which leads to a reduction in the capacity of the battery. In addition, the inventors also found that the structure of unequal thickness formed by the gradually thinning section 31 makes the thickness of the protection layer on the side of the pole ear thinner, which can improve the tensile strength, avoid the breakage of the pole ear during rolling, and improve the yield rate of pole piece, pole piece assembly and battery production.

[0050] Preferably, in some embodiments, the edge protection layer 3 is provided with a specific structure of a gradually thinning section 31, which may be as follows: Figure 3A In the first embodiment shown, the edge protection layer 3 is composed of a gradually thinning section 31, that is, the thickness of the edge protection layer 3 at the outermost end in the width direction (i.e., the other end 312 mentioned above) is substantially zero, and the substantially zero here is not strictly zero, and may also include the thickness of a reasonable error and a very small amount of slurry residue caused by the coating equipment. The cutting angle a between the outermost end and the connection position between the innermost end of the edge protection layer in the width direction (i.e., the one end 311 mentioned above) and the active material layer 2 is 0.1° to 0.5°, and may be specifically 0.1°, 0.2°, 0.3°, 0.4°, or 0.5°. It can be understood that in the structure where the edge protection layer 3 extends outward from one end close to the active material layer 2 in the width direction, the cutting angle becomes smaller and smaller until the cutting angle is finally 0.1° to 0.5°. Although the cutting angle is small, the inventors have found that even with such a small cutting angle, the effect of preventing or reducing the miscible zone can be achieved, and the width of the edge protection layer can be larger under the condition of a certain thickness of the edge protection layer, so as to achieve an effective effect of preventing burrs. The beneficial effect of the first embodiment is that the coating process is continuous and easy to control, so that the yield rate is better.

[0051] Continue to refer FIG. 3A to FIG. 3B As shown, in some embodiments, for the first embodiment in which the edge protection layer 3 is composed of a gradually thinning section 31, the first portion 301 of the edge protection layer 3 in the width direction is located at the collector ear portion 12, and the maximum thickness of the first portion 301 is 6 μm to

[0052] 14μm, the beneficial effect is that the inventors found that if the maximum thickness of the first part 301 is less than 6μm, the edge protection layer 3 of the pole ear portion 12 far from the active material layer end is difficult to support the pole ear, and the edge shrinkage will occur during laser cutting, affecting the flatness of the die cutting. When the thickness is greater than 14μm, after rolling, the edge protection layer 3 on the pole ear near the active material layer end is thicker, resulting in a lower tensile strength of the pole ear here, and there is a risk of causing the pole ear to break.

[0053] The specific structure of the edge protection layer 3 with a gradually thinning section 31 can also be Figure 4A In the second embodiment shown, the edge protection layer 3 also includes a section of equal thickness 32, which extends with equal thickness in the width direction, and the innermost end 321 of the section of equal thickness 32 in the width direction is directly connected to the outermost end of the section of gradually decreasing thickness 31 in the width direction (i.e., the other end 312 mentioned above), and the section of gradually decreasing thickness 31 is located on the surface of the collector body 11. The beneficial effect of this is that the thickness of the section of gradually decreasing thickness 31 connecting with the active material layer 2 is larger, the slope is larger, the buffering effect is more obvious, and the protective layer slurry is more effectively inhibited from escaping to the active material slurry to form mutual dissolution. In addition, the edge protection layer 3 located at the pole ear portion 12 is a section of equal thickness 32, and the thickness of the section of equal thickness 32 can be thinner than the maximum thickness of the section of gradually decreasing thickness 31 located at the pole ear portion 12 in the first embodiment. Specifically, the thickness range of the section of equal thickness 32 is 3μm-7μm, so it can more effectively improve the tensile strength of the pole ear and alleviate the phenomenon of broken bands. In addition, although in theory Figure 5 In the perspective shown, the second embodiment is different from the first embodiment in Figure 5 There may be Figure 4B The dividing line 33 between the gradually thinning section 31 and the equal thickness section 32 is shown, but due to Figure 5 It is the structure after die cutting, and rolling is required before die cutting, so Figure 5 Generally, there is no visible boundary line 33 between the gradually decreasing thickness section 31 and the equal thickness section 32, so Figure 5 The die-cut structure of the pole piece of the first embodiment or the second embodiment can be reflected.

[0054] Continue to refer FIG. 3A to FIG. 4BAs shown, in some embodiments, the first part 301 of the width dimension of the edge protection layer 3 is located at the collector ear portion 12, and the second part 302 of the width dimension is located at the collector body portion 11. The proportion of the width dimension occupied by the second part 302 is greater than or equal to the proportion of the width dimension 301 occupied by the first part. The beneficial effect is that, on the basis of ensuring the effect of preventing lithium deposition and improving the capacity, the thickness of the protective layer in the ear portion 12 is reduced, the tensile strength of the ear can be improved, the band breaking phenomenon is alleviated, and the manufacturing yield rate is improved. Preferably, the inventor found that the proportion of the width dimension occupied by the first part 301 is 30% to 50%, and the proportion of the width dimension occupied by the second part 302 is 50% to 70%. In addition, the width of the edge protection layer 3 is 4mm to 6mm, and it is easier to carry out the coating process of the edge protection layer 3 within this width range to ensure the manufacturing yield rate.

[0055] Continue to refer FIG. 3A to FIG. 4B As shown, in some embodiments, the thickness difference between the maximum thickness value of the active material layer 2 and the maximum thickness value of the edge protection layer 3 is 50μm to 70μm. As shown in the figure, the thickness of the active material layer 2 is generally much greater than the edge protection layer 3. The maximum thickness value of the active material layer 2 here can be understood as the thickness of the main area 22 of the active material layer 2. The beneficial effect of this is that the inventors found that when the thickness difference is higher than 70μm, the thickness of the first part 301 of the edge protection layer 3 located at the pole ear portion 12 will be difficult to support the pole ear, and the edge will shrink during laser cutting, affecting the flatness of the die cutting. When the thickness difference is less than 50μm, the thickness of the edge protection layer 3 is relatively large, and the elongation is relatively large during rolling, which is higher than the elongation of the current collector. There is a risk that part of the protective layer is suspended and not attached to the current collector, resulting in leakage.

[0056] refer to Figure 6 As shown, the present application also includes an electrode assembly 100 of a battery, including a first electrode piece 101, a second electrode piece 102 and a diaphragm 103, wherein the diaphragm 103 is disposed between the first electrode piece 101 and the second electrode piece 102. Taking a secondary battery as an example, the first electrode piece 101 may be the electrode piece 10 described in the above embodiment, which is a positive electrode piece, and the second electrode piece 102 is a negative electrode piece, which may be an ordinary electrode piece, that is, a electrode piece structure without an edge protection layer 3 relative to the electrode piece 10. The beneficial effects of the electrode assembly 100 and the battery using the electrode piece 10 are as described above, thereby avoiding or reducing the formation of a miscible zone, resulting in the problem of easy lithium precipitation and bringing safety risks, and avoiding or reducing the negative effect of the active material being wrapped by the insulating material of the edge protection layer, resulting in a reduced capacity of the battery manufactured by the electrode assembly 100.

[0057] In order to more clearly describe the technical solution of this case, the specific steps and specific parameters for manufacturing the pole piece 100 according to the above embodiment are introduced below. It can be understood that the protection scope of this application is not limited to the specific steps and specific parameters recorded below.

[0058] Embodiment A:

[0059] The positive electrode sheet in this embodiment is prepared by steps (1) to (4):

[0060] Step (1): preparing a positive electrode slurry; using lithium iron phosphate (LiFePO4) as a positive electrode active material, carbon black (SP) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a solvent, stirring and mixing the above substances to form a positive electrode slurry, wherein the solid content of the slurry is 63%.

[0061] Step (2): 16.67% of polytetrafluoroethylene, 83.32% of boehmite particles and 0.01% of graphite are mixed, and N-methylpyrrolidone (NMP) is used as a solvent to form a slurry for an edge protection layer, wherein the solid content of the slurry is 63%.

[0062] Step (3): coating step: coating the positive electrode slurry on the surface of the aluminum foil to form a positive electrode active material layer with a thickness of 82 μm. Then, coating the slurry of the edge protection layer in step (2) on the position adjacent to the aluminum foil and the active material layer in the width direction to form an edge protection layer. The thickness of the edge protection layer near the thickest part of the positive electrode active material layer is 25 μm (the difference with the thickness of the active material layer is 57 μm), and the thickness gradually decreases along the width direction in a gradient manner, that is, the structure of the first embodiment mentioned above, with a width of 5 mm.

[0063] Step (4): The product obtained in step (3) is dried, rolled, die-cut, and slit to prepare a positive electrode sheet of a battery cell with a positive electrode tab.

[0064] Embodiment B:

[0065] The difference between this embodiment and the first embodiment is that 0.01% of graphite is replaced by 0.01% of carbon black. The effect of the embodiment B is similar to that of the embodiment A.

[0066] Comparative Example A:

[0067] Steps (1, 2) are the same as in Example A.

[0068] Step (3): coating step: coating the positive electrode slurry on the surface of the aluminum foil to form a positive electrode active material layer with a thickness of 82 μm. Adjusting the protective layer discharge port gasket and chamfer, coating the edge protection layer slurry in step (2) on the position adjacent to the aluminum foil and the active material layer in the width direction to form an edge protection layer. The thickness of the edge protection layer is kept uniform at 25 μm and the width is 5 mm.

[0069] Step (4) is the same as in Example 1.

[0070] In Comparative Example A, since the thickness of the edge protection layer is kept uniform at 25 μm, similar to Figure 1 The inventors found that the battery manufactured using comparative example A would have problems with lithium deposition and low capacity, and after rolling, the edge protection layer on the pole ear is thicker, resulting in a lower tensile strength of the pole ear here, which would cause the pole ear to break. The tensile strength test method can be: take a pole piece sample with a width of 5mm±0.1mm and an edge protection layer, take 3-5 strips in the MD direction, avoid the edge and the thickness measurement position, and ensure that the sample has no obvious defects. Set the tensile machine test gauge length to 50mm and the tensile speed to 20mm / min; confirm that the tensile machine chuck is smooth, clamp the two ends of the sample with a clamp, and ensure that the sample does not slip or skew; the specific reference standards can be: YB / T 4334-2013, GB / T 228-2010, GB / T 22638.10-2016.

[0071] Comparative Example B:

[0072] Steps (1, 2) are the same as in Example A.

[0073] Step (3): coating step: coating the positive electrode slurry on the surface of the aluminum foil to form a positive electrode active material layer with a thickness of 82 μm. Adjusting the protective layer discharge port gasket and chamfer, coating the edge protection layer slurry in step (2) on the position adjacent to the aluminum foil and the active material layer in the width direction to form an edge protection layer. The thickness of the edge protection layer near the thickest part of the positive electrode active material layer is 35 μm (the difference with the thickness of the active material layer is 47 μm), and the width is 5 mm.

[0074] Step (4) is the same as in Example 1.

[0075] In comparative example B, since the thickness of the edge protection layer is too large, the elongation during rolling is large, which is higher than the elongation of the current collector. Part of the edge protection layer is suspended in the air and is not attached to the current collector, resulting in leakage. The edge protection layer at the pole ear is thicker and has lower tensile strength, so it is easy to break during rolling.

[0076] Comparative Example C:

[0077] Steps (1, 2) are the same as in Example A;

[0078] Step (3): coating step: coating the positive electrode slurry on the surface of the aluminum foil to form a positive electrode active material layer with a thickness of 82 μm. Adjusting the protective layer discharge port gasket and chamfer, coating the edge protection layer slurry in step (2) on the position adjacent to the aluminum foil and the active material layer in the width direction to form an edge protection layer. The thickness of the edge protection layer close to the thickest part of the positive electrode active material layer is 10 μm (the difference with the thickness of the active material layer is 72 μm), and the width is 5 mm.

[0079] Step (4) is the same as in Example 1;

[0080] In Comparative Example C, since the thickness of the edge protection layer is too small, the thickness of the edge protection layer on the pole ear is overall too small, and it cannot support the pole ear. In addition, the edge will shrink during laser cutting, affecting the flatness of the die cutting.

[0081] In summary, the beneficial effects of the pole piece, electrode assembly and battery of the present application include, but are not limited to, a structure in which a gradually thinning section 31 is set by the edge protection layer 3. The protection layer 3 of such a structure has a larger thickness and a larger slope in the part close to the active material, forming a buffer structure, which can effectively inhibit the substances in the protection layer from escaping to the active material layer to form a mutual dissolution, thereby avoiding or reducing the formation of a mutual dissolution zone, which leads to the problem of easy lithium precipitation and safety risks, and avoiding or reducing the negative effect of the active material being wrapped by the insulating material of the edge protection layer, resulting in a reduced capacity of the battery. In addition, the inventors also found that the structure of unequal thickness formed by the gradually thinning section 31 makes the thickness of the protection layer on the side of the pole ear thinner, which can improve the tensile strength, avoid the breakage of the pole ear during rolling, and improve the yield rate of the pole piece, pole piece assembly and battery production.

[0082] Although the above disclosure discusses some application embodiments that are currently considered useful through various examples, it should be understood that such details are for illustrative purposes only, and the attached claims are not limited to the disclosed embodiments. On the contrary, the claims are intended to cover all modifications and equivalent combinations that are consistent with the essence and scope of the embodiments of the present application. Similarly, it should be noted that in order to simplify the description disclosed in this application, thereby helping to understand one or more application embodiments, in the above description of the embodiments of the present application, multiple features are sometimes merged into one embodiment, drawing or description thereof. However, this disclosure method does not mean that the features required by the object of the present application are more than the features mentioned in the claims. In fact, the features of the embodiment are less than all the features of the single embodiment disclosed above.

[0083] Although the utility model is disclosed as above with preferred embodiments, it is not intended to limit the utility model. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the utility model. Therefore, any modification, equivalent change and modification made to the above embodiments based on the technical essence of the utility model without departing from the content of the technical solution of the utility model shall fall within the protection scope defined by the claims of the utility model.

Claims

1. A pole piece, characterized in that: include: A current collector, comprising a current collector body and a pole ear portion; An active material layer is disposed on the surface of the current collector body; An edge protection layer is arranged on the surface of the current collector, the edge protection layer is connected to the active material layer in the width direction, and the edge protection layer extends outward relative to the active material layer in the width direction, and the edge protection layer includes a gradually thinning section, and in the width direction, the thickness of the gradually thinning section gradually thins from one end of the gradually thinning section connecting the active material layer to the other end.

2. The pole piece according to claim 1, characterized in that: The edge protection layer is composed of the gradually thinning sections, the thickness of the outermost end of the edge protection layer in the width direction is substantially zero, and the cutting angle between the outermost end and the innermost end of the edge protection layer in the width direction and the connection position with the active material layer is 0.1° to 0.5°; or, The edge protection layer also includes a constant thickness segment, which extends with constant thickness in the width direction, and the innermost end of the constant thickness segment in the width direction is directly connected to the outermost end of the gradually thinning segment in the width direction, and the gradually thinning segment is located on the surface of the collector body.

3. The pole piece according to claim 2, characterized in that: The edge protection layer further includes a section of equal thickness, and the thickness of the section of equal thickness is 3 μm to 7 μm.

4. The pole piece according to claim 2, characterized in that: The edge protection layer is composed of the gradually thinning sections, a first portion of the edge protection layer in the width direction is located at the collector ear portion, and a maximum thickness of the first portion is 6 μm to 14 μm.

5. The pole piece according to claim 1, characterized in that: The first portion of the edge protection layer in the width direction is located at the collector ear portion, and the second portion in the width direction is located at the collector body portion. The proportion of the width dimension occupied by the second portion is greater than or equal to the proportion of the width dimension occupied by the first portion.

6. The pole piece according to claim 5, characterized in that: The first portion occupies 30% to 50% of the width, and the second portion occupies 50% to 70% of the width.

7. The pole piece according to claim 1, characterized in that: The difference between the maximum thickness of the active material layer and the maximum thickness of the edge protection layer is 50 μm to 70 μm.

8. An electrode assembly, characterized in that: It comprises a first pole piece, a second pole piece and a diaphragm, wherein the diaphragm is arranged between the first pole piece and the second pole piece, and the first pole piece is the pole piece according to any one of claims 1-7.

9. The electrode assembly according to claim 8, characterized in that The first pole piece is a positive pole piece, and the second pole piece is a negative pole piece.

10. A battery comprising the electrode assembly according to claim 8 or 9, and an electrolyte, wherein the electrolyte and the electrode assembly are accommodated inside a chamber provided in a battery case.

Images