Pole piece winding structure for improving R-angle lithium extraction and battery cell manufacturing method

Abstract

The application relates to a structure and a manufacturing method of improving R-angle lithium precipitation of a pole piece, and belongs to the technical field of lithium batteries. The structure comprises a positive pole piece, a negative pole piece and a diaphragm, and the features are that the electrode coating of the positive pole piece and the negative pole piece are discontinuous designs, and a non-coating area with the same width as the pole piece is formed. In the manufacturing method, the non-coating area is completely corresponding to the R-angle area formed by the winding of the battery through accurate control of the winding process; thus, at the R-angle, the electrical connection between the adjacent coating areas is only realized through the current collector, the local current density and the lithium ion flux of the area are effectively reduced, and the risk of lithium dendrite precipitation is fundamentally inhibited. The application starts from the electrode structure design, realizes the active optimization of the weak link of the battery through the combination of partition coating and winding alignment, and provides an effective scheme for improving the safety and the cycle life of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to an electrode structure, and more particularly to an electrode winding structure for improving lithium plating at the R-angle and a method for manufacturing battery cells, belonging to the field of battery cell pouch technology. Background Technology

[0002] Lithium-ion batteries, as energy storage devices with high energy density and long cycle life, have been widely used in new energy vehicles, energy storage systems, and consumer electronics. However, in the manufacturing process of wound cells, the R-corner region formed by the bending of the electrode sheets (i.e., the corner of the cell) is always a high-incidence area for lithium plating, which seriously restricts the safety performance and cycle stability of the battery. The causes of lithium plating are complex and can be mainly summarized into the following three aspects: First, insufficient matching accuracy of the positive and negative electrode sizes leads to the negative electrode not being able to completely cover the active region of the positive electrode R-corner, causing a local imbalance in lithium ion insertion / extraction kinetics; Second, inaccurate control of the spacing between the electrode sheets during winding results in poor adhesion between the separator and the electrode sheets, obstructing the ion transport path and exacerbating the polarization effect; Third, continuous coverage of adjacent negative electrode coatings leads to an increase in the conductivity resistance of the current collector, resulting in excessively high local current density, which further induces lithium dendrite precipitation.

[0003] To alleviate these problems, existing technologies mostly employ passive improvement strategies. For example, simply increasing the size of the negative electrode (i.e., increasing the overhang region) can improve the N / P ratio in the R-corner region, but this reduces the battery's energy density and cannot fundamentally improve ion transport efficiency. Another approach is to optimize interface stability by adjusting the electrolyte formulation (such as adding film-forming additives like VC and FEC), but this has limited effectiveness and increases process costs.

[0004] In addition, some patents propose structural improvements, such as the utility model patent with authorization announcement number CN222126605U, which improves the local N / P ratio by inserting a support member into the inner ring of the wound cell to increase the radius of curvature of the R-angle. However, this method requires the introduction of additional components, increasing the complexity of the process, and there are potential risks to the long-term interface stability between the support member and the electrode.

[0005] Overall, existing technologies have not yet solved the technical problem of how to achieve precise control of the radius (R-corner) region of the entire winding cell while ensuring process feasibility. Therefore, there is an urgent need in this field for an integrated solution that can collaboratively address the lithium plating problem at the R-corner from multiple dimensions, including electrode structure design, conductive path optimization, and interface bonding control. Summary of the Invention

[0006] To address the aforementioned problems, in a first aspect, the present invention provides an electrode winding structure for improving R-angle lithium deposition.

[0007] The technical solution is as follows:

[0008] An electrode winding structure for improving lithium plating at the R-angle includes a positive electrode, a negative electrode, and a separator stacked in sequence; the positive and negative electrodes include a current collector and an electrode coating composited on the current collector; the electrode coatings of the positive and negative electrodes are discontinuous, thereby forming uncoated regions between adjacent coated regions; in the stacked structure formed by winding, the uncoated regions correspond in position to the R-angle of the electrode, such that adjacent coated regions of the electrode are electrically connected only through the current collector; the width of the uncoated regions is the same as the width of the electrode body.

[0009] This invention provides an innovative solution to the lithium deposition problem in the radius (R-corner) region of wound battery cells based on electrode structure design. This invention is not a simple fix for existing passive improvement strategies (such as simply increasing the negative electrode size or adding electrolyte additives), but rather based on a profound understanding of the root causes of lithium deposition in the R-corner of wound battery cells (local imbalance of lithium-ion insertion / extraction kinetics, obstructed ion transport paths, and excessively high local current density). Through proactive structural design and precise process control, it achieves precise regulation of the electrochemical microenvironment of the electrode winding structure, especially the R-corner region. Its fundamental goal is to suppress lithium dendrite deposition at its source, while ensuring process feasibility and high energy density, thereby comprehensively improving the battery's safety performance and cycle stability.

[0010] Background technology has clearly pointed out that the radius-of-field (R-corner) region of wound-type battery cells is a high-incidence area for lithium plating, the root cause of which lies in the local bottleneck of ion / electron transport caused by the winding geometry. Existing technologies mostly adopt "post-hoc remedial" or "local compromise" strategies. For example, increasing the negative electrode overhang can improve the local N / P ratio but sacrifices energy density, or introducing external supports to increase the radius of curvature but increases process complexity and interface risks. Overall, existing solutions have failed to systematically and synergistically solve the multiple kinetic constraints in the R-corner region.

[0011] The electrode winding structure of this invention is a fundamental solution to the aforementioned systemic problems. It transforms cell design from a continuous model of "complete electrode coverage" into a precise control model of "selective conductivity and ion transport".

[0012] Firstly, the design of discontinuous coatings and the active control of current density in the R-corner region.

[0013] The core innovation of this invention lies in preparing discontinuous electrode coatings on the current collectors of the positive and negative electrodes, thereby forming uncoated regions that run longitudinally across the width of the electrode between adjacent coated areas. The technical logic is to precisely control the position of the uncoated regions so that they perfectly correspond to the radius (R-corner) region of the battery cell after winding. The ingenuity of this design is that when the R-corner region corresponds to the uncoated portion of the current collector, electron conduction in that region can be maintained by the current collector itself, but the active material (i.e., the site of electrochemical reactions) is actively removed. Its direct technical effect is to fundamentally eliminate the demand for excessive local lithium-ion insertion / extraction at the R-corner caused by coating coverage, significantly reducing the local current density in that region. Since the driving force for lithium dendrite deposition is positively correlated with the local current density, this design fundamentally suppresses the tendency for lithium deposition at the R-corner from a thermodynamic and kinetic perspective, thereby directly improving the battery's safety margin.

[0014] Secondly, the size matching and spacing of the electrodes are optimized to achieve uniformity of the ion transport path throughout the entire ring.

[0015] Building upon the discontinuous coating design, this invention further optimizes the dimensional relationship between the positive and negative electrodes (the positive electrode coating area is 2-4 mm wider than the negative electrode coating area) and the winding arrangement spacing based on a mathematical model (the recursive relationship between am and bn). The technical logic is to construct a precise design framework coupled with multiple physics fields. Making the positive electrode coating wider than the negative electrode coating ensures that the negative electrode can completely cover the positive electrode in the flat area of ​​the core (i.e., with sufficient overhang), preventing edge lithium deposition. Furthermore, by precisely controlling the relative winding position of each electrode layer using the mathematical model (am, bn), it ensures that any R-corner area can accurately "fall" into the preset uncoated window during winding, achieving perfect reproduction of the design intent across the entire core. Simultaneously, the precise arrangement spacing (±0.1 mm) and tension control (5-15 N) ensure a tight and uniform fit between the separator and the electrode, reducing additional resistance to ion transport caused by interfacial gaps and further mitigating the polarization effect in the R-corner area.

[0016] Thirdly, optimization of the continuous conductive path and local resistance of the current collector.

[0017] In the uncoated region corresponding to the radius (R-angle), adjacent coated regions are electrically connected only through the current collector. The technical logic lies in utilizing the excellent electronic conductivity and uniform thickness of the current collector (usually copper foil) to provide a low-resistance, uniform lateral conduction path for the current. The technical effect is that it avoids the problem of significantly increased electronic conduction resistance caused by coating curvature, uneven thickness, and variations in conductive agent distribution at the radius (R-angle) of traditional continuous coatings. By directly "bridging" the active coating regions on both sides with the current collector, it ensures smooth electron transport even under complex radius (R-angle) geometry, avoiding local overpotential increases caused by electron transport bottlenecks, thereby synergistically suppressing lithium plating.

[0018] As a preferred embodiment of the above technical solution, the coating area of ​​the positive electrode sheet is 2-4 mm wider than the coating area of ​​the positive electrode sheet.

[0019] This size difference is a fine-tuning of the traditional "negative electrode covering the positive electrode" principle. It ensures that in the flat section of the cell, the active area of ​​the negative electrode completely covers the active area of ​​the positive electrode, preventing edge lithium deposition caused by misalignment, which is the foundation for ensuring the overall cell safety. At the same time, this difference is controlled within a small range (2~4mm), minimizing the negative impact on energy density.

[0020] As a preferred embodiment of the above technical solution, the spacing 'a' between the positive electrode plates is... m and the spacing b between the negative electrode plates n The following relationship must be satisfied:

[0021] a m =δ 负 +6δ 隔 +mk+X;

[0022] b n =δ 负 +6δ 隔 +nK;

[0023] K=δ 正 +δ 负 +2δ 隔；

[0024] Where n and m represent the number of electrode layers, which are positive integers, and n = m + 2; δ 负 δ represents the thickness of the negative electrode. 正 δ represents the thickness of the positive electrode. 隔 Where X is the membrane thickness, and K = δ is the width difference between the negative and positive electrodes. 正 +δ 负 +2δ 隔；

[0025] Where n and m represent the number of electrode layers, which are positive integers, and n = m + 2; δ 负 δ represents the thickness of the negative electrode.正 δ represents the thickness of the positive electrode. 隔 X represents the membrane thickness, and X represents the width difference between the negative and positive electrode plates.

[0026] This mathematical model dynamically calculates the theoretical spacing for different numbers of layers (m, n) based on the physical thicknesses (δpositive, δnegative, δseparator) of the electrode and separator. Its effect is to achieve precise prediction and control of the electrode's spatial position during winding, ensuring that the radius (R) angle is precisely aligned with the uncoated area regardless of the winding layer. This is key to transforming the design concept of discontinuous coatings into repeatable, manufacturable products, guaranteeing the consistency and reliability of the solution.

[0027] As a preferred embodiment of the above technical solution, the diaphragm is made of polyethylene, polypropylene, or a composite material of polyethylene and polypropylene, and has a thickness of 10~25μm.

[0028] The use of mature and reliable diaphragm materials ensures basic safety and mechanical strength. The thickness range of 10~25μm guarantees ion conductivity while providing necessary mechanical support and isolation for the winding structure, which is the basis for achieving compact winding and precise arrangement.

[0029] As a preferred embodiment of the above technical solution, the thickness of the negative electrode is 60~120μm, and the thickness of the positive electrode is 80~150μm.

[0030] As a preferred embodiment of the above technical solution, the active material of the positive electrode is one of lithium iron phosphate, ternary materials, or lithium cobalt oxide.

[0031] As a preferred embodiment of the above technical solution, the active material of the negative electrode sheet is one of artificial graphite, natural graphite, or silicon-carbon composite material.

[0032] Secondly, the present invention provides a method for manufacturing a battery cell.

[0033] The technical solution is as follows:

[0034] A method for manufacturing a battery cell includes the following steps:

[0035] S1. Electrode preparation: Prepare the positive electrode and negative electrode as described above;

[0036] S2. Electrode arrangement: The negative electrode, separator, positive electrode and separator are arranged and wound in sequence to form a wound stacked structure core.

[0037] S3. Cell assembly: The core is loaded into the housing, electrolyte is injected, and the cell is manufactured through sealing, formation and capacity testing processes.

[0038] As a preferred embodiment of the above technical solution, in step S1, the uncoated area is reserved on the electrode sheet by intermittent coating or laser scraping process.

[0039] Gap coating is a mature and efficient large-scale coating technology that easily achieves precise shaping of uncoated areas; laser coating offers greater flexibility and precision, making it suitable for more complex or adjustable pattern designs. These two process routes provide feasible manufacturing methods with high compatibility with existing production lines for the implementation of the solution.

[0040] As a preferred embodiment of the above technical solution, in step S2, the arrangement accuracy during winding is controlled within ±0.1mm, and the winding tension is controlled within 5~15N.

[0041] In summary, the present invention has the following beneficial effects:

[0042] 1. Fundamental improvement in lithium plating suppression and safety performance: Through a unique discontinuous coating design, the electrochemical activity of the R-corner region is precisely "shielded," significantly reducing the lithium-ion flux and local current density at the source, and fundamentally suppressing the nucleation and growth of lithium dendrites; combined with optimized electrode arrangement and interface control, the ion / electron transport environment in the R-corner region is systematically improved, significantly enhancing the safety performance of the battery, especially high-energy-density batteries, under harsh conditions such as fast charging and low temperature.

[0043] 2. Synergistic optimization of energy density and cycle life: Compared with the solution of simply increasing the overhang of the negative electrode, this method effectively solves the problem of lithium plating at the R-angle while sacrificing the area of ​​the active region of the electrode by a small margin (limited to the designed uncoated strip), thus maximizing the preservation of the battery's mass energy density and volumetric energy density. At the same time, since lithium plating is effectively suppressed, the problems of SEI film damage and continuous loss of active lithium on the negative electrode surface are alleviated, which is expected to significantly extend the cycle life of the battery.

[0044] 3. Balance between process feasibility and manufacturing cost: The core structural improvement of the solution is mainly achieved through the patterned design of the electrode coating process, without the need to introduce additional components (such as support components) or increase the complexity of winding or assembly; gap coating or laser scraping are existing or integrable mature technologies, and the process modification cost is relatively controllable.

[0045] 4. Design flexibility and adaptability: The width, position, and size difference between the positive and negative electrodes of the uncoated area can be flexibly adjusted and optimized according to different cell models, winding turns, and active material systems, making the solution widely adaptable and enabling customized design of cells for different application scenarios.

[0046] 5. In summary, the improved electrode winding structure and manufacturing method for lithium plating at the R-angle of this invention starts from the weak point (R-angle) of the wound cell failure. By combining the electrode structure design concept of "functional partitioning" with the manufacturing process of "precise alignment", it achieves active intervention and optimization of the local electrochemical microenvironment. This solution transcends the traditional ideas of "local coverage remedy" or "external mechanical correction" and evolves into an integrated solution endogenous to electrode design. It not only provides a new and effective technical path to overcome the long-standing problem of lithium plating in wound cells, but also provides a key innovative design idea for realizing the next generation of lithium-ion batteries with high safety, long life and high energy density. It has important theoretical value and broad prospects for industrial application. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the electrode winding structure of the present invention;

[0048] Figure 2 This is a schematic diagram of the positive electrode structure of the present invention;

[0049] Figure 3 This is a schematic diagram of the negative electrode structure of the present invention;

[0050] In the diagram, the component names represented by each number are as follows:

[0051] 100 - Positive electrode, 200 - Negative electrode, 300 - Separator. Detailed Implementation

[0052] The present invention will be further explained and described below with reference to the accompanying drawings.

[0053] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims, will be protected by patent law.

[0054] An improved R-angle lithium plating electrode winding structure and its fabrication method are disclosed, with the following specific implementation steps:

[0055] 1. Electrode preparation

[0056] Positive electrode preparation: Active material lithium iron phosphate (LiFePO4), conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 90:5:5. An appropriate amount of N-methylpyrrolidone (NMP) solvent is added, and the mixture is stirred at high speed to form a uniform positive electrode slurry. The slurry is coated onto a 12μm thick aluminum foil current collector using a gap coating process. The spacing am between the coated area and the uncoated area is precisely controlled according to the design value. After coating, the material is dried and rolled to achieve a positive electrode coating thickness of 100μm (total thickness including the current collector δpositive ≈ 112μm). A die-cutting process is then performed to obtain a positive electrode sheet with a width of 150mm and periodic uncoated areas. The structure of the obtained positive electrode sheet 100 can be referenced. Figure 2 As shown, Am indicates the width of the coated area, am indicates the distance between the uncoated areas of adjacent coated areas, and m is a positive integer.

[0057] Negative electrode preparation: Active material artificial graphite, conductive agent conductive carbon black (Super P), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are mixed in a mass ratio of 95:2:1:2. Deionized water solvent is added, and the mixture is stirred at high speed to form a uniform negative electrode slurry. A combination of gap coating and laser scraping is used to coat the slurry onto an 8μm thick copper foil current collector. The spacing bm between the coated and uncoated areas (uncoated areas) is precisely controlled according to the design value, and the uncoated areas are precisely pre-reserved at predetermined positions using laser scraping. After coating, the material is dried and rolled to achieve a negative electrode coating thickness of 80μm (total thickness including the current collector δnegative ≈ 88μm). A die-cutting process is then performed to obtain a negative electrode with a width of 154mm and periodic uncoated areas corresponding to the positive electrode. The structure of the resulting negative electrode 200 can be referenced. Figure 3 As shown, Bn+2 indicates the width of the coating area (e.g., Figure 3 As shown, bn indicates the spacing between uncoated areas between adjacent coated areas, where n is a positive integer (from...). Figure 3 It can be seen that n = m + 2).

[0058] Separator preparation: Select polyethylene-polypropylene (PE-PP) composite separator 300 with a thickness of 16μm (δ separator = 16μm).

[0059] 2. Calculation and setting of winding parameters

[0060] Based on the provided spacing calculation formula and given electrode structure parameters (δpositive = 100μm, δnegative = 80μm, δgap = 16μm, width difference between negative and positive electrodes X = 4mm, number of electrode layers n = 12, m = 10), calculate the key winding parameters:

[0061] Calculate the constant K: K = δpositive + δnegative + 2δseparation = 100 + 80 + 2×16 = 212μm = 0.212mm;

[0062] Calculate the spacing between the positive electrode plates, such as:

[0063] a 12 :a 12 = (δnegative + 6δseparation + mK) / 1000 + X = (80 + 6×16 + 12×212) / 1000 + 4 = (80+96+2544) / 1000 + 4 = 2.72 + 4 = 6.720mm;

[0064] Calculate the spacing between the negative electrode plates, such as:

[0065] b 10 :b 10 = [δnegative + 6δinterval + (n-1)K] / 1000 = [80 + 6×16 + (10-1)×212] / 1000 = (80+96+1908) / 1000 = 2.084mm;

[0066] The calculated a m b n As input parameters for the winding process.

[0067] 3. Cell winding and assembly

[0068] like Figure 1 As shown, the prepared negative electrode 200, separator 300, positive electrode 100, and separator 300 are precisely arranged in sequence on a winding machine. The winding program is started, and the winding tension is controlled at 10N to ensure that the arrangement spacing between the electrode and the separator strictly conforms to the calculated values ​​am and bn, and the winding alignment accuracy is controlled within ±0.1mm. After winding, a core with a specific stacked structure is formed. The core is inspected to confirm that the uncoated areas of each electrode layer precisely correspond to the R-corner areas of the cell after winding.

[0069] The core is inserted into a prefabricated aluminum-plastic film housing, and after vacuum baking to remove moisture, a 1.0 mol / L LiPF6 carbonate-based electrolyte is injected at a dew point below -40°C. Standard processes such as encapsulation, settling, formation (activated by low-current charge-discharge), and capacity testing are then performed to complete the assembly of the pouch cell.

[0070] 4. Performance Testing and Effect Verification

[0071] The prepared battery cell was subjected to a 1C charge-discharge cycle test. The test results showed that the cell retained a capacity of 93.2% after 500 cycles. Upon disassembly and observation of the cycled cell, the surface of its radius (R-corner) region was smooth, with no obvious signs of lithium dendrite precipitation or deposition. This indicates that the electrode structure and winding method provided in this embodiment effectively balance the lithium-ion flow and current density in the radius (R-corner) region, significantly suppressing lithium deposition reactions at this location, thereby greatly improving the long-term cycle stability of the battery cell.

Claims

1. An electrode winding structure for improving lithium plating at the R-angle, comprising a positive electrode (100), a negative electrode (200), and a separator (300) stacked in sequence; wherein the positive electrode (100) and the negative electrode (200) comprise a current collector and an electrode coating composited on the current collector; characterized in that: The electrode coatings of the positive electrode (100) and the negative electrode (200) are discontinuous, thus forming uncoated areas between adjacent coated areas; In the stacked structure formed by winding, the uncoated area corresponds to the R-angle of the electrode in position, so that the coated areas of the adjacent electrodes are electrically connected only through the current collector; the width of the uncoated area is the same as the width of the electrode body.

2. The electrode winding structure for improving R-angle lithium plating according to claim 1, characterized in that: The coating area of ​​the positive electrode (100) is 2-4 mm wider than the coating area of ​​the positive electrode (100).

3. The electrode winding structure for improving R-angle lithium deposition according to claim 1, characterized in that, Positive electrode spacing a m and the spacing b between the negative electrode plates n The following relationship must be satisfied: a m =d 负 +6d 隔 +mk+X; b n =d 负 +6d 隔 +nK; K=δ 正 +d 负 +2d 隔； Where n and m represent the number of electrode layers, which are positive integers, and n = m + 2; δ 负 δ represents the thickness of the negative electrode. 正 δ represents the thickness of the positive electrode. 隔 X represents the membrane thickness, and X represents the width difference between the negative and positive electrode plates.

4. The electrode winding structure for improving R-angle lithium plating according to claim 1, characterized in that: The diaphragm (300) is made of polyethylene, polypropylene, or a composite material of polyethylene and polypropylene, and has a thickness of 10~25μm.

5. The electrode winding structure for improving R-angle lithium plating according to claim 1, characterized in that: The thickness of the negative electrode (200) is 60~120μm, and the thickness of the positive electrode (100) is 80~150μm.

6. The electrode winding structure for improving R-angle lithium plating according to claim 1, characterized in that, The active material of the positive electrode (100) is one of lithium iron phosphate, ternary materials or lithium cobalt oxide.

7. The electrode winding structure for improving R-angle lithium plating according to claim 1, characterized in that, The active material of the negative electrode (200) is one of artificial graphite, natural graphite or silicon-carbon composite material.

8. A method for manufacturing a battery cell, comprising the following steps: S1. Electrode preparation: Prepare the positive electrode (100) and negative electrode (200) as described in any one of claims 1 to 7 respectively. S2. Electrode arrangement: The negative electrode (200), separator (300), positive electrode (100), and separator (300) are arranged and wound in sequence to form a wound stacked structure core. S3. Cell assembly: The core is loaded into the housing, electrolyte is injected, and the cell is manufactured through sealing, formation and capacity testing processes.

9. A method for manufacturing a battery cell according to claim 8, characterized in that: In step S1, the uncoated area is reserved on the electrode sheet by gap coating or laser scraping process.

10. A method for manufacturing a battery cell according to claim 8, characterized in that: In step S2, the arrangement accuracy during winding is controlled within ±0.1mm, and the winding tension is controlled within 5~15N.

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