Winding-type pole group, battery cell, and manufacturing method of winding-type pole group

Abstract

The application belongs to the technical field of lithium batteries, and particularly relates to a winding type pole group, a battery cell and a manufacturing method of the winding type pole group, which comprises a positive electrode sheet, a negative electrode sheet and a separator, and the core part of the winding type pole group is provided with a directional expansion adhesive tape, which can swell under electrolyte immersion to provide internal supporting force for the core part of the pole group. By arranging the directional expansion adhesive tape which can swell in electrolyte in the core part of the winding type pole group, the internal supporting force is generated by the swelling of the adhesive tape after liquid injection, the gap caused by the cold pressure rebound and the weak thermal pressure bonding of the core part of the pole group is effectively compensated, the electrolyte is absorbed and stored by the adhesive tape, the core part liquid deficiency problem is relieved, and the interface defects such as electrode sheet wrinkles, black spots and lithium precipitation are significantly inhibited.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method for manufacturing a wound electrode assembly, a battery cell, and a wound electrode assembly. Background Technology

[0002] Lithium-ion batteries have been widely used in consumer electronics, electric vehicles, and energy storage due to their high specific energy, long cycle life, suitable cost, and mature manufacturing processes. Based on cell structure, lithium-ion batteries are mainly divided into two types: wound and laminated. Among them, wound cells occupy a larger market share due to their mature manufacturing process and high production efficiency.

[0003] The typical manufacturing process for wound battery cells includes: electrode winding, cold pressing, hot pressing, and welding encapsulation. In the cold pressing process, the electrode assembly remains relatively flat under pressure, but after the pressure is released, the positive and negative electrodes and the separator exhibit elastic rebound, resulting in gaps in the electrode core. In the hot pressing process, the electrode assembly is pressed while heated, and the separator adhesive layer bonds the electrodes to the separator. However, the temperature of the electrode core is lower than the outer surface, making the bonding in this area the weakest. Due to the rebound tendency and weak bonding force of the core, when the cell is charged and discharged, the positive and negative electrodes undergo volume changes, and the stress-induced strain tends to concentrate in the electrode core, frequently resulting in electrode wrinkles, black spots, and lithium plating in production practice. Furthermore, after electrolyte filling, excess electrolyte often exists in the gaps between the electrode assembly and the casing. With charge and discharge cycles, the electrolyte is gradually consumed, and the excess electrolyte can be used for replenishment. However, the electrode core area is difficult to replenish with electrolyte, leading to electrolyte deficiency and further exacerbating performance degradation. The aforementioned problems not only affect the performance stability of individual battery cells, but also cause poor consistency in mass production, especially affecting the yield of battery pack assembly in electric vehicles and energy storage applications.

[0004] To address the aforementioned shortcomings of wound battery cells, several improvement solutions have been proposed. For example, patent CN119029335A discloses a wound core for wound batteries, an anti-expansion wound battery, and a manufacturing method. It improves battery life by sealing the wound core body with a binding structure wrapped around its surface. Patent CN118073668A discloses a segmented winding method, a wound core, and a wound battery. This method reduces internal stress and improves hot-pressing shaping and flatness by cutting the electrode sheets at least once during the winding process. Patent CN121394598A discloses a wound battery cell, a battery, and a vehicle, which sets an active layer only in the straight sections of the inner winding layer assembly to avoid short circuits caused by the active layer detaching from the curved sections. The patent with publication number CN121319801A proposes a high-expansion tape for cylindrical batteries and its preparation method, which combines an expandable base film layer, an adhesive layer and a flame-retardant coating to improve problems such as vibration displacement and electrolyte utilization in cylindrical batteries.

[0005] However, the above solutions either require changes to the electrode structure, the introduction of a cutting process, or are only applicable to cylindrical batteries, and none of them fundamentally solve the interface problems such as wrinkles, black spots, and lithium plating caused by springback, weak bonding, and low electrolyte levels in the core of prismatic wound cells. Therefore, it is still necessary to propose a solution that is simple in structure, has good process compatibility, and can effectively improve the performance of the core of wound cells. Summary of the Invention

[0006] The purpose of this invention is to provide a wound electrode assembly, a battery cell, and a method for manufacturing the wound electrode assembly, aiming to solve the problems of electrode wrinkles, black spots, lithium plating, and poor performance consistency caused by cold pressing springback, weak hot pressing bonding, and difficulty in replenishing electrolyte in the manufacturing and use of existing wound lithium-ion battery cells.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a wound electrode assembly, including a positive electrode sheet, a negative electrode sheet and a separator. The core of the wound electrode assembly is provided with a directional expansion tape, which can swell when immersed in electrolyte to provide internal support force in the core of the electrode assembly.

[0008] Preferably, the directional expansion tape includes an expandable substrate and an adhesive layer disposed on the expandable substrate; after being immersed in a commercial electrolyte, the expandable substrate has an expansion rate of 150% to 400% in the thickness direction.

[0009] Preferably, the thickness of the expandable substrate is 10–40 μm, and the thickness of the adhesive layer is 5–15 μm.

[0010] Preferably, the number of turns of the directional expansion tape wound in the core of the wound electrode assembly is an integer multiple of 0.5.

[0011] Preferably, the directional expansion tape has one winding in the core of the wound electrode assembly.

[0012] Preferably, the positive electrode sheet includes a positive electrode active material layer, wherein the positive electrode active material is selected from at least one of lithium iron phosphate, nickel cobalt manganese ternary materials, nickel cobalt aluminum ternary materials, lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide; the negative electrode sheet includes a negative electrode active material layer, wherein the negative electrode active material is selected from at least one of carbon materials, silicon materials, and tin materials, or a composite thereof.

[0013] Preferably, the diaphragm is selected from one of the following: polypropylene diaphragm, polyethylene diaphragm, polypropylene and polyethylene composite diaphragm, polypropylene diaphragm with ceramic and / or adhesive coating, polyethylene diaphragm with ceramic and / or adhesive coating, and polypropylene and polyethylene composite diaphragm with ceramic and / or adhesive coating.

[0014] The present invention also discloses a wound battery cell, comprising the aforementioned wound electrode assembly, a battery casing encapsulating the wound electrode assembly, and an electrolyte.

[0015] This invention also discloses a method for manufacturing a wound electrode assembly, comprising the following steps: (1) Make the diaphragm wind the first predetermined number of turns on the winding needle; (2) Attach the directional expansion tape to the diaphragm, and cut it after wrapping it a second predetermined number of times; (3) Insert the negative electrode and the positive electrode in sequence and wind them until the set length is reached, then cut the electrode. (4) Except at the cut point of the negative electrode sheet, the diaphragm is rolled up three predetermined turns, then the diaphragm is cut and the termination tape is attached to obtain a wound electrode assembly with directional expansion tape in the core.

[0016] Preferably, the first predetermined number of laps is 1 lap, the second predetermined number of laps is 1 lap, and the third predetermined number of laps is 1.5 laps.

[0017] The beneficial effects of this invention are as follows: By setting a directional expansion tape that can swell in electrolyte in the core of the wound electrode assembly, the tape swells after electrolyte injection to generate internal support force, effectively compensating for the gaps in the core of the electrode assembly caused by cold-pressed springback and hot-pressed weak bonding. At the same time, the tape absorbs and stores electrolyte, alleviating the problem of electrolyte deficiency in the core, thereby significantly suppressing interface defects such as electrode wrinkles, black spots and lithium plating, improving the capacity consistency and cycle stability of the battery cell. Moreover, this structure does not require changes to the electrode coating or the introduction of a cutting process, and has good compatibility with existing winding processes, providing a reliable solution for the design and mass production of long-life, high-consistency wound battery cells. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the wound pole assembly provided in an embodiment of the present invention; Figure 2 A schematic diagram of a conventional wound pole assembly provided for comparison; Figure 3 This is a comparison diagram of the discharge capacity distribution of the battery cells prepared in the embodiments of the present invention and the comparative examples; Figure 4 This is a comparison chart of the cycle capacity retention rates of battery cells obtained in the embodiments and comparative examples of the present invention; In the diagram: 1. Directional expansion tape; 2. Negative electrode; 3. Positive electrode; 4. Separator. Detailed Implementation

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixed connection," and "fixed connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] This invention provides a wound electrode assembly and a wound battery cell containing the electrode assembly. The core improvement of this wound electrode assembly lies in the placement of a directional expansion tape 1 at the core of the electrode assembly (i.e., near the starting end of winding). The directional expansion tape undergoes controllable swelling along its thickness direction when immersed in electrolyte, thereby generating a continuous radial inward support force in the core of the electrode assembly. This compensates for the gaps caused by the weak bonding during cold pressing and rebound, and hot pressing. Simultaneously, the tape absorbs and retains some electrolyte, alleviating the problem of electrolyte deficiency in the core. By optimizing parameters such as the tape's expansion rate, thickness, and number of winding turns, precise control of core stress and electrolyte retention can be achieved for battery cells of different specifications.

[0023] The directional expansion tape of this invention comprises an expandable substrate and an adhesive layer disposed on the substrate. After immersion in commercial lithium-ion battery electrolyte, the expansion rate of the expandable substrate in the thickness direction is preferably 150% to 400%. Too low an expansion rate results in insufficient internal support, while too high an expansion rate may cause excessive stress in the electrode core. The thickness of the expandable substrate is preferably 10 to 40 μm, and the thickness of the adhesive layer is preferably 5 to 15 μm. The adhesive layer is used to fix the tape to the separator or electrode sheet, ensuring accurate positioning during winding.

[0024] The wound electrode assembly of the present invention can be prepared by the following steps: (1) Make the diaphragm 4 loosely wound on the winding needle for the first predetermined number of turns, usually 1 turn, to form a smooth winding start; (2) Attach the directional expansion tape to the diaphragm, and cut it after winding it a second predetermined number of turns; the number of turns of the tape is generally an integer multiple of 0.5, preferably 1 turn; (3) Insert the negative electrode 2 and the positive electrode 3 in sequence and wind them in a conventional manner until the set length is reached, then cut the electrode. (4) Outside the cut point of the negative electrode sheet, roll the diaphragm loosely for a third predetermined number of turns, usually 1.5 turns, then cut the diaphragm and attach the termination tape to obtain a wound electrode assembly with directional expansion tape in the core.

[0025] The above method does not require additional cutting or spacing coating of the electrode sheets and is highly compatible with existing winding production lines.

[0026] The prepared wound electrode assembly is inserted into a battery casing (which can be an aluminum casing, a steel casing, or an aluminum-plastic film), electrolyte is injected, and after conventional processes such as encapsulation and formation, the finished battery cell is obtained. The electrolyte can be a combination of conventional carbonate solvents and lithium salts in the art, such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and lithium hexafluorophosphate (LiPF6).

[0027] To verify the technical effect of the present invention, the inventors conducted comparative experiments on embodiments and comparative examples using a 2714897 type square aluminum shell battery cell as a carrier.

[0028] Example (1) Cell design: The 2714897 type square aluminum shell cell is used. The positive electrode active material is lithium iron phosphate, and the positive electrode mass ratio is lithium iron phosphate: conductive carbon black: binder (PVDF) = 98:0.9:1.1. The positive electrode coating amount is 45.5 mg / cm³. 2 The negative electrode active material is artificial graphite, with a mass ratio of artificial graphite: conductive carbon black: binder (SBR): thickener (CMC) = 96:1:2:1. The negative electrode coating amount is 21.1 mg / cm². 2 .

[0029] (2) Preparation of positive electrode sheet: 80,000 g of lithium iron phosphate, 14,966 g of PVDF slurry (898 g of effective material), 735 g of conductive carbon black and 15,584 g of solvent NMP are stirred and dispersed evenly, coated on 12 μm carbon-coated aluminum foil according to the designed coating amount, and obtained positive electrode sheet by drying, rolling and laser cutting.

[0030] (3) Preparation of negative electrode sheet: 50,000 g of artificial graphite, 521 g of conductive carbon black, 2604 g of SBR slurry (1042 g of effective material), 34,722 g of CMC slurry (521 g of effective material) and 12,150 g of deionized water are mixed to form a slurry, coated on a 5 μm copper foil according to the designed coating amount, and then dried, rolled and laser-cut to obtain the negative electrode sheet.

[0031] (4) Electrode winding: Wind according to the following steps (see Appendix) Figure 1 ): The diaphragm is rolled once in the loop on the winding needle; Apply the directional expansion tape (expandable substrate thickness 25 μm, adhesive layer thickness 10 μm, thickness expansion rate in electrolyte 300%) to the diaphragm, and cut it after wrapping it once. Insert the negative and positive electrodes in sequence and wind them until the set length is reached, then cut the electrode sheet. Except for the negative electrode cut-off point, roll the diaphragm 1.5 turns loosely, then cut it and apply termination tape.

[0032] (5) Cell assembly: The wound electrode assembly is inserted into a square aluminum shell, and an electrolyte containing 1 mol / L LiPF6 EC / DMC / EMC (volume ratio 1:1:1) is injected. After encapsulation and formation, the finished cell is obtained.

[0033] (6) Performance testing: Discharge capacity test: At 25℃, charge at 1C to 3.65V, charge at constant voltage to 0.05C cutoff, let stand for 10 min, discharge at 1C to 2V, and calculate the discharge capacity.

[0034] Cyclic performance test: Perform charge and discharge cycles according to the above procedure, record the discharge capacity for each cycle, and calculate the capacity retention rate.

[0035] Comparative Example The only difference between the comparative example and the embodiment is that no directional expansion tape is added during the winding process; that is, the winding is performed using conventional methods (see Appendix). Figure 2 All other materials, parameters, and test conditions are exactly the same as in the example.

[0036] Discharge capacity tests were conducted on 100 cells each from the examples and comparative examples. The results are shown in the appendix. Figure 3 As shown, the discharge capacity distribution of the embodiment is significantly more concentrated and the standard deviation is smaller, indicating that its capacity consistency is better than that of the comparative example.

[0037] The comparison results of cycle capacity retention are attached. Figure 4As shown, after 500 cycles, the capacity retention rate of the embodiment remained above 91%, while that of the comparative embodiment dropped below 90%, and the capacity decay curve of each cycle in the embodiment was smoother. This indicates that by setting directional expansion tape in the core, interface degradation such as electrode wrinkles, black spots, and lithium plating was effectively suppressed, significantly improving the cycle stability of the cell.

[0038] Based on the actual cell design requirements, those skilled in the art can adjust the following parameters appropriately: The number of turns of the directional expansion tape can be selected as 0.5 turns, 1.5 turns, or 2 turns, or an integer multiple of 0.5. The thickness of the expandable substrate can be selected in the range of 10 to 40 μm, and the expansion rate can be selected in the range of 150% to 400%. The positive and negative electrode active materials, the type of separator, and the composition of the electrolyte can be adjusted according to the target cell system. As long as the above-mentioned directional expansion tape is set in the core of the electrode assembly, the technical effects of improving the core interface problem, enhancing consistency, and increasing cycle life can be achieved.

[0039] In summary, this invention effectively solves the long-standing problems of core wrinkles, black spots, lithium plating, and electrolyte deficiency in wound battery cells through a simple and easily industrialized structural improvement, significantly improving the performance consistency and cycle stability of the battery cells, and has high practical value and application prospects.

[0040] For those skilled in the art, various improvements and modifications can be made without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. A jelly-roll type electrode group comprising a positive electrode sheet, a negative electrode sheet, and a separator, characterized by, The core of the wound electrode assembly is provided with a directional expansion tape, which can swell when immersed in electrolyte to provide internal support in the core of the electrode assembly.

2. The wound pack of claim 1, wherein The directional expansion tape includes an expandable substrate and an adhesive layer disposed on the expandable substrate; after being immersed in a commercial electrolyte, the expandable substrate has an expansion rate of 150% to 400% in the thickness direction.

3. The wound pack of claim 2, wherein, The thickness of the expandable substrate is 10–40 μm, and the thickness of the adhesive layer is 5–15 μm.

4. The wound pack of claim 1, wherein, The number of turns of the directional expansion tape wound in the core of the wound electrode assembly is an integer multiple of 0.

5.

5. The wound pole assembly according to claim 4, characterized in that, The directional expansion tape has one winding in the core of the wound electrode assembly.

6. The wound pole assembly according to claim 1, characterized in that, The positive electrode includes a positive active material layer, wherein the positive active material is selected from at least one of lithium iron phosphate, nickel cobalt manganese ternary materials, nickel cobalt aluminum ternary materials, lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide; the negative electrode includes a negative active material layer, wherein the negative active material is selected from at least one of carbon materials, silicon materials, and tin materials, or a composite thereof.

7. The wound pole assembly according to claim 1, characterized in that, The diaphragm is selected from one of the following: polypropylene diaphragm, polyethylene diaphragm, polypropylene and polyethylene composite diaphragm, polypropylene diaphragm with ceramic and / or adhesive coating, polyethylene diaphragm with ceramic and / or adhesive coating, and polypropylene and polyethylene composite diaphragm with ceramic and / or adhesive coating.

8. A wound battery cell, characterized in that, It includes a wound electrode assembly as described in any one of claims 1 to 7, a battery casing encapsulating the wound electrode assembly, and an electrolyte.

9. A method for manufacturing a wound electrode assembly, characterized in that, Includes the following steps: (1) Make the diaphragm wind the first predetermined number of turns on the winding needle; (2) Attach the directional expansion tape to the diaphragm, and cut it after wrapping it a second predetermined number of turns; (3) Insert the negative electrode and the positive electrode in sequence and wind them until the set length is reached, then cut the electrode. (4) Except at the cut point of the negative electrode sheet, the diaphragm is rolled up three predetermined turns, then the diaphragm is cut and the termination tape is attached to obtain a wound electrode assembly with directional expansion tape in the core.

10. The manufacturing method according to claim 9, characterized in that, The first predetermined number of laps is 1 lap, the second predetermined number of laps is 1 lap, and the third predetermined number of laps is 1.5 laps.

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