Battery electrode assembly and battery

Abstract

This invention relates to the field of battery technology and discloses a battery electrode assembly and a battery, including a core, which consists of a positive electrode sheet, a first separator, a negative electrode sheet, and a second separator layer stacked and wound in a winding direction in sequence, and an empty foil area extending from the end of the negative electrode sheet. The empty foil area includes at least a first end and a second end. The first end is connected to the negative electrode sheet and has a corrugated protrusion. The second end has a first groove. The corrugated protrusion and the first groove cooperate to connect the first end and the second end. This invention designs the length of the empty foil area so that it forms an overlapping area after winding. The corrugated protrusion and the groove in this area are hot-pressed together to form a mechanical lock, which does not rely on chemical adhesives or interfacial friction. The locking force does not decrease during battery cycling, achieving reliable fixation of the end of the core while occupying little space and eliminating the need for tape pasting.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to battery electrode assemblies and batteries. Background Technology

[0002] In recent years, with the increasing awareness of environmental protection, the new energy vehicle industry has flourished. Wound square lithium-ion batteries are widely used in the field of new energy vehicles due to their advantages such as compact structure, high energy density and high manufacturing efficiency. The typical manufacturing process of this type of battery is to stack the positive electrode, separator and negative electrode in sequence and then wind them around a square winding needle to form a cell. After winding, the end of the cell lacks effective constraint, which makes it easy to have defects such as looseness and warping. This directly affects the yield of subsequent packaging processes and can cause lithium plating or even internal short circuits due to electrode misalignment during battery charge and discharge cycles.

[0003] To solve this problem, the mainstream solution in this field has long been to attach termination tape to the outermost part of the battery cell, such as: Chinese patent publication number CN221727188U discloses a square wound cell structure and battery, including a flat portion, a first arc portion and a second arc portion located on opposite sides of the flat portion, the first arc portion having a core tail end, the distance between the core tail end along the outer surface of the first arc portion and the flat portion being L, the square wound cell structure satisfies: L > 2mm, which has the advantages of improving energy density and safety performance.

[0004] Chinese Patent Publication No. CN218101398U discloses a wound cell structure for a square lithium battery, including a core body. The core body adopts a square structure and includes a negative electrode sheet, a separator, and a positive electrode sheet that are sequentially attached and wound. The free ends of the negative electrode sheet and the positive electrode sheet are attached to one of the narrow sides of the core body. It has the advantage of improving the winding end of the core body by tying the free ends of both the positive and negative electrode sheets to the narrow side of the core body.

[0005] There are several inherent drawbacks to using adhesive tape: First, the pressure-sensitive adhesive of the tape will swell and soften under long-term immersion in the electrolyte, resulting in an exponential decrease in adhesion and eventual loosening at the end of the cycle. Second, the low thermal conductivity of the area covered by the tape creates localized hot spots, accelerating battery degradation. Third, the edges of the tape are prone to becoming lithium-ion enrichment areas, leading to lithium plating. Fourth, the tape application process increases equipment investment and production cycle time, and carries the risk of misalignment.

[0006] In recent years, a few researchers have attempted to replace adhesive tape through structural improvements. For example, Chinese Patent Publication No. CN113422004B discloses a battery and battery electrode sheets, as well as a method and apparatus for their manufacture. The battery includes a rolling device for rolling and compacting the coated electrode sheets, a die-cutting device for cutting the rolled electrode sheets into conductive electrode tabs using a die-cutting machine, and a slitting device for slitting the die-cut electrode sheets into the required sizes. This method has the advantages of improving the bonding effect between the battery electrode sheets and the separator during the cell production process using an adhesive-free separator and preventing slippage between the battery electrode sheets and the separator.

[0007] It is evident that existing technologies have long focused on improving the materials and bonding processes of adhesive tapes, or optimizing embossing patterns to increase the coefficient of friction. In existing technologies, the tape fixing scheme solves the initial fixing problem at the end of the core through chemical adhesive force. However, due to the long-term stability of the adhesive in the electrolyte environment, embossing delays the loosening of the end by increasing the interfacial friction, but this friction decreases with the increase of the number of cycles. None of the above solutions can provide a mechanical constraint that does not rely on chemical adhesives and does not decrease with cycles. It is against this technical background that the present invention proposes a novel fixing method based on the self-locking of the empty foil of the negative electrode sheet. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a battery electrode assembly and a battery, solving the problem that the battery cells in existing battery electrode assemblies become loose and curl up at the end after winding.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a battery electrode assembly and a battery, including... The core is composed of a positive electrode sheet, a first diaphragm, a negative electrode sheet, and a second diaphragm that are sequentially stacked and wound along the winding direction. An empty foil area extends from the end of the negative electrode plate. The empty foil area includes at least a first end and a second end. The first end is connected to the negative electrode plate and is provided with a corrugated protrusion. The second end is provided with a first groove. The corrugated protrusion and the first groove cooperate to connect the first end and the second end. The tabs are connected to the winding core.

[0010] Furthermore, the corrugated protrusions and the first groove extend perpendicular to the winding direction and are fitted together by hot pressing.

[0011] Furthermore, a second groove is formed on the empty foil area. The second groove is located outside the overlapping area of ​​the first end and the second end, and the extension direction of the second groove is parallel to the winding direction.

[0012] Furthermore, a first ridge is provided on the empty foil area. The first ridge is located on the side surface of the empty foil area near the core and outside the overlapping area at the second end of the empty foil area.

[0013] Furthermore, the starting section of the empty foil area is provided with an insulating transition coating, which is in contact with the winding core. The thickness of the insulating transition coating decreases to zero along the winding direction and is sloped.

[0014] Furthermore, the insulating transition coating is composed of boehmite.

[0015] Furthermore, the core uses a positive electrode sheet as the starting layer for winding, and the stacked structure of the core from the inside out consists of a positive electrode sheet, a first layer of separator, a negative electrode sheet, and a second layer of separator.

[0016] A battery comprising a battery electrode assembly.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention designs the length of the empty foil section so that the first end and the second end form an overlapping area after winding. The corrugated protrusions and grooves set in this area are hot-pressed together to form a permanent mechanical lock. It does not rely on chemical adhesives or interface friction. The locking force does not decrease during battery cycling, which solves the problem of tape aging and failure. It achieves reliable fixation of the end of the core while occupying little space.

[0018] (2) The empty foil area of ​​the present invention is made of copper foil material of negative electrode sheet without coating of negative electrode active material, and has a heat dissipation groove. Its thermal conductivity is far better than that of tape, avoiding the risk of local hot spots and edge lithium plating in the area covered by tape.

[0019] (3) The self-locking structure of the present invention is completed simultaneously with the hot pressing process of the battery cell, eliminating the need for a separate adhesive application process and simplifying the production process. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall appearance of the present invention; Figure 2 This is a schematic diagram of the structure of the empty foil section of the present invention; Figure 3 This is a schematic diagram of the structure of the first edge of the present invention; Figure 4 This is a schematic diagram of the corrugated protrusion structure of the present invention; Figure 5 This is a schematic diagram of the structure of the corrugated protrusion facing the first groove before hot pressing in this invention; Figure 6 This is a schematic diagram of the structure of the corrugated protrusion engaging with the first groove after hot pressing according to the present invention.

[0021] In the picture: 100. Roll core; 200, Empty foil area; 210, First groove; 220, First ridge; 230, Insulating transition coating; 240, Corrugated protrusion; 250, Second groove. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] To address the problem of loosening and curling at the end of the battery cell in the prior art after winding the electrode assembly, this invention provides a technical solution. Please refer to [link / reference needed]. Figures 1-6 The battery electrode assembly includes The core 100 is composed of a positive electrode sheet, a first separator, a negative electrode sheet, and a second separator, which are sequentially stacked and wound along the winding direction. An empty foil area 200 extends from the end of the negative electrode sheet. The empty foil area 200 includes at least a first end and a second end. The first end is connected to the negative electrode sheet and is provided with a corrugated protrusion 240. The second end is provided with a first groove 210. The corrugated protrusion 240 and the first groove 210 cooperate to connect the first end and the second end.

[0024] The tab is connected to the core 100.

[0025] Specifically, in the process of coating the negative electrode sheet with the negative electrode active material, by precisely controlling the gap of the extrusion coating die, a predetermined length of uncoated area is reserved at the end of the negative electrode sheet. After coating and drying, this area is the exposed copper foil, forming the empty foil area 200. The length of the empty foil area 200 is determined according to the outermost circumference of the core 100 and the overlap allowance. After the last turn of winding the core 100, the negative electrode sheet is located outside the positive electrode sheet, and the outer side of the negative electrode sheet is only covered by the second layer of diaphragm. At this point, the winding continues, and the empty foil area 200 wraps around the outermost ring of the battery cell 100 from the outside. Since the length of the empty foil area 200 is longer than the circumference of the outermost ring, after the second end has completed one round of wrapping, there is still a part of its length that exceeds the first end, naturally covering the first end of the first end. The empty foil area 200 is fixed by the cooperation of the corrugated protrusions 240 and the first groove 210 provided on the first and second ends, preventing the battery cell 100 from loosening and lifting at the end after winding is completed.

[0026] To ensure the locking mechanism is securely fixed and easy to manufacture, as a preferred embodiment of the present invention, refer to... Figures 3-6The corrugated protrusions 240 and the first groove 210 extend perpendicular to the winding direction and are interlocked by hot pressing.

[0027] Specifically, a cold press roller with a corrugated pattern is used to press corrugated protrusions 240 onto the overlapping area surface at the first end of the empty foil section 200. At the corresponding position at the second end of the empty foil section, a first groove 210 that can be engaged after plastic deformation is pressed out. The corrugated protrusions 240 and the first groove 210 extend perpendicular to the winding direction, which can effectively resist sliding along the winding axis. At the same time, the continuous corrugated structure also provides radial constraint. The corrugated protrusions are softened by heat through hot pressing and undergo plastic deformation after being pressed into the first groove 210 under pressure. The corrugated protrusions 240 flow toward the lateral opening at the bottom of the first groove 210 to form an interference fit and complete the locking process.

[0028] It should be noted that by providing a corrugated protrusion 240 at the first end of the empty foil area 200 and a first groove 210 at the second end of the empty foil area 200, the corrugated protrusion 240 faces away from the diaphragm during hot pressing, preventing puncture of the diaphragm. In addition, in the original process, when hot pressing the core 100 to increase the adhesion between the diaphragm and the electrode, the hot pressing locking process of the corrugated protrusion 240 and the first groove 210 can be carried out simultaneously, simplifying the process.

[0029] To prevent the empty foil section 200 from covering the outermost edge of the core 100, which would affect battery heat dissipation and electrolyte wetting, as a preferred embodiment of the present invention, refer to... Figures 3-5 A second groove 250 is provided on the empty foil area 200. The second groove 250 is located outside the overlapping area of ​​the first end and the second end. The extension direction of the second groove 250 is parallel to the winding direction.

[0030] Specifically, multiple second grooves 250 are cut along the length of the empty foil area 200 using laser cutting. After winding, these second grooves 250 form heat escape channels from the inside of the core 100 to the outside, and also serve as flow channels for electrolyte to flow from the outside to the inside. During the laser cutting process, the groove wall is heated to form a heat-affected hardening layer, which improves the strength of the groove wall and prevents bending and breakage.

[0031] To prevent the empty foil section 200 from easily breaking at the winding bend, as a preferred embodiment of the present invention, refer to... Figure 3 The empty foil area 200 is provided with a first ridge 220, which is located on the side surface of the empty foil area 200 near the core 100, and is located outside the overlapping area of ​​the second end of the empty foil area 200.

[0032] Specifically, when the empty foil section 200 is wound, it is stretched on the outside and compressed on the inside of the bending part, which makes it very easy to crack or even break at the stress concentration point. The first ridge 220 transforms the planar stress mode into a three-dimensional stress mode, which greatly increases the moment of inertia of the section. This disperses the tensile and compressive stress during bending to the sidewall of the convex ridge, which significantly suppresses the local fracture of the copper foil and improves the bending stiffness. In addition, the empty foil section 200 forms a gap between the contact surface with the core 100 through the first ridge 220. This gap serves as a microchannel for gas and electrolyte, which is conducive to the heat dissipation inside the core 100 and provides a buffer space for the volume expansion of the electrode.

[0033] To address the problem that a step exists between the starting section of the empty foil 200 and the negative electrode plate, potentially causing the separator to puncture and contact the cross-section of the positive electrode plate after winding, leading to a short circuit, as a preferred embodiment of the present invention, refer to... Figures 2-3 The starting section of the empty foil section 200 is provided with an insulating transition coating 230. The insulating transition coating 230 is in contact with the core 100. The thickness of the insulating transition coating 230 decreases to zero along the winding direction and is in the shape of a slope.

[0034] The insulating transition coating 230 is composed of boehmite.

[0035] Specifically, in the process of coating the negative electrode with an active material coating, at the end of the coating process, while gradually closing the coating die head, another coating die head is opened to spray boehmite slurry. By controlling the linear increase of the die head gap, the output of boehmite slurry is gradually reduced, forming a slope-shaped insulating transition coating 230. When winding the empty foil area 200, the insulating transition coating 230 contacts the cross-section of the positive electrode and the separator at the junction, blocking the electronic path between the empty foil area 200 and the cross-section of the positive electrode and preventing short circuit. On the other hand, the slope-shaped transition eliminates sharp steps and prevents physical puncture of the separator.

[0036] In order to ensure that the empty foil section 200 is located on the outermost side, as a preferred embodiment of the present invention, refer to... Figure 3 The core 100 uses the positive electrode sheet as the starting layer for winding. The stacked structure of the core 100, from the inside out, consists of the positive electrode sheet, the first separator, the negative electrode sheet, and the second separator.

[0037] Specifically, before winding, the positive electrode sheet is placed at the bottom to contact the winding needle. The first layer of separator is stacked on the positive electrode sheet, the negative electrode sheet is stacked on the first layer of separator, and the second layer of separator is stacked on the negative electrode sheet. The winding needle is started and the winding is carried out in the set direction so that each layer of material is wound in sequence. By controlling the winding speed and tension, the negative electrode sheet is located outside the positive electrode sheet and inside the second layer of separator when the winding is finished, so that the empty foil area 200 on the negative electrode sheet can be wound to cover the core 100.

[0038] It should be noted that by setting the empty foil area 200 as an uncoated negative electrode, since the material of the negative electrode is copper foil, it can ensure that the empty foil area 200 is stable and reliable throughout the entire battery life cycle without the occurrence of lithium plating reaction.

[0039] A type of battery, reference Figures 1-6 This includes the battery electrode components mentioned above.

[0040] Working principle: In the negative electrode coating process, by precisely controlling the gap of the extrusion coating die, a predetermined length of uncoated area is reserved at the end. After drying, this area forms a bare copper foil, i.e., the empty foil area 200. At the end of the active material coating, the coating die is gradually closed while another die is opened to spray boehmite slurry. By linearly increasing the die gap, the slurry output gradually decreases, forming a sloped insulating transition coating 230. A cold press roller with a corrugated pattern is used to press corrugated protrusions 240 on the surface of the overlapping area at the beginning section, i.e., the first end, of the empty foil area 200, and a first groove 210 is pressed at the corresponding position at the second end. Both the first groove 210 and the first groove 40 extend perpendicular to the winding direction. Multiple second grooves 250 are then laser-cut along the length of the empty foil area 200, avoiding the overlapping area between the first and second ends. The groove walls are heated to form a heat-affected hardening layer. A first ridge 220 is cold-pressed on the side of the empty foil area 200 near the core, outside the overlapping area, perpendicular to the winding direction. The positive electrode is placed at the bottom layer to contact the winding needle. The first separator, negative electrode, and second separator are then stacked sequentially. The winding needle is started, and winding proceeds in the set direction, allowing each layer of material to wrap around the other. By controlling the winding speed and tension, a tight fit between the layers is ensured. After winding, the negative electrode sheet is located at the outermost end section. The empty foil area 200 wraps around the outermost ring of the core at least once. Since the length of the empty foil area 200 is greater than the circumference of the outermost ring, its second end still has a portion of its length exceeding the first end after completing one wrap, covering the first end and forming an overlapping area. At this time, the first groove 210 of the second end and the corrugated protrusion 240 of the first end are vertically opposite each other. The wound core 100 is sent into a hot press. The corrugated protrusion 240 softens under heat, the yield stress decreases, and it is pressed into the first groove 210 to undergo plastic deformation, flowing laterally towards the bottom of the first groove 210, forming a flow... The corrugated protrusion 240 is permanently fitted into the first groove 210, locking the first end and the second end together. The first ridge 220 provides bending stiffness to prevent the copper foil from breaking at the corner. The insulating transition coating 230 is in close contact with the core after being pressed, blocking the short circuit path. After the core 100 is hot-pressed, the electrode tabs are welded to form an electrode assembly. Electrolyte is injected and conventional processes such as formation, aging, and capacity testing are carried out. The microchannel formed by the second groove 250 accelerates the electrolyte wetting and provides a path for heat to escape during charge and discharge cycles. The empty foil area 200 remains locked throughout the entire battery life cycle without the need for termination tape.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A battery electrode assembly, characterized in that: include The core (100) is composed of a positive electrode sheet, a first diaphragm, a negative electrode sheet and a second diaphragm that are stacked in sequence and wound along the winding direction; An empty foil section (200) extends from the end of the negative electrode plate. The empty foil section (200) includes at least a first end and a second end. The first end is connected to the negative electrode plate and is provided with a corrugated protrusion (240). The second end is provided with a first groove (210). The corrugated protrusion (240) and the first groove (210) cooperate to connect the first end and the second end. The tab is connected to the core (100).

2. The battery electrode assembly according to claim 1, characterized in that: The empty foil section (200) is a negative electrode sheet without a negative electrode active material, and its length along the winding direction is longer than the circumference of the outermost ring of the core (100).

3. The battery electrode assembly according to claim 2, characterized in that: The corrugated protrusions (240) and the first groove (210) extend perpendicular to the winding direction and are joined together by hot pressing.

4. The battery electrode assembly according to claim 3, characterized in that: The empty foil section (200) has a second groove (250) located outside the overlapping area of ​​the first end and the second end, and the extension direction of the second groove (250) is parallel to the winding direction.

5. The battery electrode assembly according to claim 4, characterized in that: The empty foil area (200) is provided with a first edge (220), which is located on the side surface of the empty foil area (200) near the core (100) and outside the overlapping area of ​​the second end of the empty foil area (200).

6. The battery electrode assembly according to claim 5, characterized in that: The starting section of the empty foil section (200) is provided with an insulating transition coating (230). The insulating transition coating (230) is in contact with the core (100). The thickness of the insulating transition coating (230) decreases to zero along the winding direction and is in the shape of a slope.

7. The battery electrode assembly according to claim 6, characterized in that: The insulating transition coating (230) is composed of boehmite.

8. The battery electrode assembly according to claim 7, characterized in that: The core (100) uses the positive electrode sheet as the starting layer for winding. The stacked structure of the core (100) from the inside out consists of the positive electrode sheet, the first layer of separator, the negative electrode sheet, and the second layer of separator.

9. A battery, characterized in that: Includes the battery electrode assembly as described in any one of claims 1 to 8.

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