Iron-based current collector metal foil with edge passivation structure

Abstract

The present disclosure provides an iron-based current collector metal foil having an edge passivation structure, wherein in the thickness direction of the metal foil, the upper edge and the lower edge of the metal foil each forms an edge passivation angle with the side surface. The present disclosure forms a passivation angle structure in the thickness direction of the current collector or the pole piece, especially adopts an edge geometric design of a passivation angle of 95-120° and a passivation width of 10-50 μm, and further preferably a fillet or a quasi-fillet structure with a curvature radius of ≥50 μm, so as to reduce the risk of puncture and prevent short circuit, and at the same time improve the electrode interface stability.

Description

Technical Field

[0001] This disclosure belongs to the field of electrochemical energy storage device technology, specifically relating to a novel iron-based current collector metal foil with an edge passivation structure and an electrochemical device including the same. Background Technology

[0002] Electrochemical energy storage devices (such as lithium-ion batteries, sodium-ion batteries, and supercapacitors) are widely used in consumer electronics, electric vehicles, energy storage power stations, and other fields. Their performance is influenced by a variety of factors, including electrode structure, electrolyte composition, and current collector materials. The current collector, as a carrier of the positive or negative electrode active material, primarily functions to provide electron channels for electrode reactions, support and stabilize the active material layer structure, and improve the overall mechanical integrity and energy density of the electrode. The structural design and material selection of the current collector have a decisive impact on electrochemical performance, processability, and cell safety.

[0003] Currently, the most widely used current collector materials in commercial applications are aluminum foil (for the positive electrode) and copper foil (for the negative electrode). These metal foils typically possess good conductivity, low density, excellent ductility, and cost advantages, with thicknesses mostly ranging from 5 to 20 μm. However, aluminum and copper have low apparent elastic moduli (generally less than 5 GPa), limiting their structural support capabilities in high-energy-density, high-stack-density, or thin-layer devices. Especially during cell stacking, pressing, and winding processes, defects such as wrinkles, warping, or localized collapses are prone to occur, not only reducing the utilization efficiency of electrode active materials but also potentially causing reliability issues such as internal short circuits and capacity decay.

[0004] To improve the structural strength and heat resistance of current collectors, researchers have increasingly turned their attention to iron-based metal materials in recent years, such as stainless steel, iron-nickel alloys, and low-carbon steel. These materials typically possess higher mechanical modulus (approximately 100-200 GPa), good corrosion resistance, and electrical conductivity, making them suitable for energy storage systems with higher requirements for safety and mechanical strength, especially exhibiting good stability under high-temperature operating environments. For example, stainless steel foil, due to its high strength and rigidity, has great potential in high-energy-density battery cells, effectively suppressing electrode deformation and extending cycle life.

[0005] However, iron-based current collectors still face several technical challenges in practical applications: 1) Sharp edges can easily cause damage: During the cutting, stamping and other processing of iron-based metals, the edges are usually quite sharp, which can easily pierce the diaphragm, electrolyte membrane or electrode active layer, leading to potential electrochemical short circuits and posing a serious safety hazard. 2) Poor processing adaptability: High-rigidity materials may scratch adjacent electrodes or separators during the automated high-speed winding and stacking process of battery cells, reducing assembly yield and increasing manufacturing costs. 3) Insufficient flexibility limits device design: Iron-based materials have a large bending radius, making them difficult to bend and deform, which is not conducive to the construction of flexible or ultra-thin battery structures, and is also not conducive to matching with high viscoelastic coatings, affecting the consistency of electrode preparation. 4) Compatibility and interface stability need to be optimized: Iron-based metals have potential corrosion risks in some electrolyte systems, especially in high-voltage environments or fluorine-containing solvent systems, where their surfaces may react with active components to form a film layer with unfavorable interfaces.

[0006] Therefore, how to address the key challenges of sharp edges and poor processing flexibility in iron-based materials while retaining their high strength and stability has become an important research direction in the development of current collector materials for electrochemical energy storage devices. In particular, developing iron-based current collector structures with safe edge structure designs, good interface compatibility, and suitability for efficient mass production will provide crucial material support for the next generation of high-performance, high-safety energy storage devices. Utility Model Content

[0007] To overcome the shortcomings of the prior art, this disclosure provides an iron-based current collector metal foil with an edge passivation structure and an electrochemical device, which solves the above-mentioned technical problems through structural design and process innovation.

[0008] The iron-based current collector metal foil with edge passivation structure can combine the high strength advantage of iron-based materials with the problems of sharp edges, insufficient flexibility and poor processability, thereby improving its application safety, manufacturing efficiency and electrochemical stability in electrochemical energy storage devices (such as lithium-ion batteries, supercapacitors, etc.).

[0009] To achieve the above objectives, one aspect of this disclosure provides an iron-based current collector metal foil, characterized in that the metal foil has an edge passivation structure, wherein, in the thickness direction of the metal foil, the upper edge and the lower edge each form a passivation angle with the side surface.

[0010] The thickness of the metal foil is 5-30 mm.

[0011] The passivation angle of the edge passivation structure is 95-120 degrees. o The passivation width is 10-50mm.

[0012] Furthermore, the passivation angle of the edge passivation structure is 100-120 degrees. o The passivation width is 50mm.

[0013] In this disclosure, the passivation angle of the edge passivation structure refers to the included angle formed in the edge transition area after the metal foil edge has undergone passivation treatment. This angle reflects the degree to which the edge transitions from a sharp shape to a rounded or beveled shape. It is usually expressed in degrees ( o This indicates a larger blunting angle (e.g., 95-120 degrees). o This means that the edges are more rounded and the transition is gentler, which helps reduce the risk of scratching the diaphragm, electrodes or other electrodes; the larger the angle, the more obvious the passivation and the higher the safety.

[0014] Specifically, the iron-based current collector metal foil disclosed herein includes an upper edge and a lower edge in the thickness direction of the metal foil, wherein the upper edge and the lower edge form a first edge passivation angle and a second edge passivation angle with the side surface of the metal foil, respectively.

[0015] The first edge blunting angle and the second edge blunting angle can be the same or different.

[0016] In this disclosure, passivation width refers to the width of the structural buffer zone formed by the passivation treatment of the metal foil extending inward from the edge, i.e., the unfolded size of the passivation region in the plane of the foil. It is usually measured in micrometers (μm); the passivation width ranges from 10 to 50 μm; the larger the width, the more buffer space is provided, which reduces edge stress concentration and helps to improve processing adaptability and device mechanical integrity.

[0017] Specifically, the passivation width of this disclosure represents the size of the passivation transition structure (buffer area corresponding to the edge passivation angle) formed at the upper and lower edges of the iron-based current collector metal foil in the plane direction of the foil after edge passivation treatment, specifically the distance d extending from the original edge of the foil (the side when not passivated) into the interior of the foil (plane direction) (as shown in Figure 2).

[0018] The edge passivation structure may include rounded corners, near-rounded corners, chamfered corners, obtuse corners, and burr-free structures to avoid scratching the electrode or penetrating the diaphragm.

[0019] Furthermore, the average radius of curvature at the edge corners of the rounded or near-rounded structure can be greater than 50 μm. Even further, the average radius of curvature can be 70-200 μm.

[0020] Here, a near-rounded corner structure refers to a metal foil where, in the thickness direction, the edge corner area does not form a strictly mathematically rounded arc, but its overall outline visually and functionally resembles a rounded corner structure. That is, the edge corner can present a continuous curved transition without obvious sharp corners, bends, or abrupt acute angles. Furthermore, the radius of curvature can gradually or segmentally change in the edge transition area, with an average radius of curvature greater than 50 μm. In this case, compared to acute or right-angle structures, a near-rounded corner structure can effectively reduce the risks of stress concentration, mechanical scratches, and electrolyte retention.

[0021] The edge passivation structure disclosed herein can be formed by one of the following processes or any combination thereof: plasma passivation, laser melting, flame passivation, edge micro-bending treatment, micro-arc oxidation, electrochemical passivation, or mechanical edge grinding.

[0022] Preferably, the edge passivation structure of this disclosure can be formed by laser melting. By locally melting the edge material of the metal foil with a pulsed laser, the liquid metal flows and levels under the drive of surface tension, naturally forming an obtuse angle without the need for an additional passivation layer. The advantages of this process are that it is a non-contact processing, the heat-affected zone is less than 10 μm, it is suitable for ultra-thin foils (such as 5 μm), and it can be automated.

[0023] Preferably, the edge passivation structure of this disclosure can be formed by ultra-fine mechanical edge grinding. By combining nanoscale abrasives with soft abrasive pads and chemical mechanical polishing (CMP), the edge material of the metal foil is selectively removed, thereby forming a blunt angle. The advantage of this process is that it is an ultra-precision machining process with a surface roughness Ra ≤ 0.05 μm, making it suitable for mass production.

[0024] Preferably, the edge passivation structure of this disclosure can be formed by electrochemical passivation. Through anodic dissolution, the microscopic protrusions at the edge are preferentially removed to form a uniform obtuse angle, while simultaneously generating a passivation film. The thickness of this passivation film can be controlled as needed or removed subsequently. The advantages of this process are that it simultaneously achieves obtuseness and passivation, has low cost, and is suitable for complex shapes.

[0025] In addition, the iron-based current collector metal foil with edge passivation structure disclosed herein may further have corner passivation structure, which may include rounded corners, near-rounded corners, or obtuse corners.

[0026] In this disclosure, the corner passivation structure refers to the passivation angle formed between the horizontal right-angled side and the vertical right-angled side in the planar direction of the metal foil when the metal foil is unfolded into a rectangle.

[0027] Furthermore, the passivation angles of the corner passivation structure may include a first corner passivation angle, a second corner passivation angle, a third corner passivation angle, and a fourth corner passivation angle located at the four corners of the metal foil in the planar direction of the metal foil. These four corner passivation angles may be the same or different.

[0028] The corner obtuse angle disclosed herein differs from the definition of the edge obtuse angle above. Here, the corner obtuse angle refers to the angle formed between the transverse right-angled side and the longitudinal right-angled side in the planar direction of the metal foil.

[0029] Preferably, the corner passivation structure is obtained by mechanical grinding, and its passivation angle can be 100-120 degrees. o .

[0030] Furthermore, the iron-based material of the iron-based current collector metal foil can be selected from 304 stainless steel, 316 stainless steel or iron-nickel alloy.

[0031] Furthermore, the apparent elastic modulus of the iron-based current collector metal foil is 20-80 GPa.

[0032] Another aspect of this disclosure provides an electrochemical device characterized by comprising the iron-based current collector metal foil, the metal foil serving as a bipolar current collector structure in the electrochemical device. Beneficial effects

[0033] While existing technologies have reported the formation of passivation structures at the four corners of the current collector or electrode in the planar direction, technologies for forming passivation corner structures in the thickness direction of the current collector or electrode to reduce the risk of puncture and prevent short circuits have not yet been reported.

[0034] This disclosure provides an iron-based current collector metal foil with a passivated edge structure, which has undergone systematic optimization in terms of structure, material, and edge treatment, achieving the following significant technical effects: 1. Effectively improves edge safety and reduces puncture risk: By introducing rounded or near-rounded edge passivation structures into the edges of iron-based metal foils, the problem of sharp edges in traditional iron-based materials, which easily damage electrodes or penetrate diaphragms, is significantly alleviated. Compared to untreated edges, the puncture strength of passivated edges is reduced by more than 50%, significantly improving the structural integrity and safety of electrochemical devices.

[0035] 2. Optimize edge passivation geometry to improve stress buffering and electrolyte compatibility: Adopt an edge geometry design with a passivation angle of 95-120° and a passivation width of 10-50μm, and further optimize the rounded or near-rounded corner structure with a curvature radius ≥50μm to effectively reduce stress concentration and mechanical scratch risk, while avoiding electrolyte retention and accumulation at sharp corners, thus improving electrode interface stability.

[0036] 3. Innovative passivation process combination to improve edge processing consistency and industrial adaptability: The preferred passivation process is laser melting combined with mechanical edge grinding, which has both high precision forming and edge consistency. It can achieve μm-level edge curvature control on a large scale (curvature radius 70-200 μm), improve batch consistency and automation feasibility, and adapt to roll-to-roll process requirements. Attached Figure Description

[0037] Figure 1 A cross-sectional view along the thickness direction and a partially enlarged view at the edge of an iron-based current collector metal foil according to one embodiment of the present disclosure are schematically shown.

[0038] Figure 2 schematically shows a partial cross-sectional view in the thickness direction of iron-based current collector metal foils according to different embodiments of the present disclosure, wherein, Figure 2-1 It has rounded corners. Figure 2-2 The edges are other irregular structures. Figure 2-3 It has rounded corners.

[0039] Figure 3 The top view (left) and bottom view (right) of the iron-based current collector metal foil of this disclosure are schematically shown.

[0040] Figure 4 A top view of the iron-based current collector metal foil of this disclosure, including edge passivation structures and corner passivation structures, is schematically shown.

[0041] Explanation of reference numerals in the attached figures: 11: Current collector metal foil 12: Active material layer 111: First edge blunting angle 112: Second edge blunting angle 21: Obtuse angle of the first side angle 22: Obtuse angle of the second side angle 23: Obtuse angle of the third side angle 24: Obtuse angle of the fourth side angle Detailed Implementation

[0042] To more clearly illustrate the technical solutions of this disclosure, the following will describe this disclosure in further detail with reference to the accompanying drawings and specific embodiments.

[0043] Figure 1A cross-sectional view in the thickness direction and a partially enlarged view at the edge of an iron-based current collector metal foil according to one embodiment of the present disclosure are shown. The metal foil includes a current collector metal foil 11 and an active material layer 12 thereon. According to the partially enlarged view at the edge, a first edge passivation angle 111 is formed between the upper edge of the metal foil 11 and the right side surface, and a second edge passivation angle 112 is formed between the lower edge of the metal foil 11 and the right side surface.

[0044] Figure 2 shows a partial cross-sectional view of the iron-based current collector metal foil in the thickness direction according to different embodiments of the present disclosure. In the figure, 111 and 112 are the first edge passivation angle and the second edge passivation angle, respectively, d is the passivation width, and r1 and r2 are the radii of curvature of the first edge passivation angle 111 and the second edge passivation angle 112, respectively.

[0045] The first edge blunting angle 111 and the second edge blunting angle 112 are 95-120°. o The passivation width d is 10-50mm.

[0046] Preferably, the first edge blunting angle 111 and the second edge blunting angle 112 are 100-120°. o The passivation width d is 50mm.

[0047] Figure 2-1 In the middle, the first edge blunting angle 111 and the second edge blunting angle 112 are both rounded corner structures. Figure 2-2 In the above figure, the first edge blunting angle 111 is a rounded structure, and the second edge blunting angle 112 is a beveled structure. Figure 2-2 In the middle image, both the first edge blunting angle 111 and the second edge blunting angle 112 are oblique cut structures. The upper edge is connected to the right side via an upper oblique edge, and the lower edge is connected to the right side via a lower oblique edge. The oblique angle formed between the upper or lower oblique edge and the right side is the first edge blunting angle 111 and the second edge blunting angle 112, respectively, and this blunting angle is 100-120 degrees. o .

[0048] Figure 2-3 The first edge blunting angle 111 and the second edge blunting angle 112 are shown to be rounded corner structures with large radii of curvature (r1, r2).

[0049] Figure 3 The diagram shows a top view (left) and a bottom view (right) of an iron-based current collector metal foil 11 according to one embodiment of the present disclosure. The metal foil 11 has an active material layer 12. A total of eight edge passivation structures (e.g., ...) are formed at each of the four sides of the metal foil 11 with its upper and lower edges. Figure 3(The location is indicated by the dashed circle). The passivation angle and passivation width of these 8 edge passivation structures can be the same or different, but all are within a passivation angle of 95-120 degrees. o The passivation width is 10-50mm, and the radius of curvature is ≥50mm.

[0050] Figure 4 A top view of an iron-based current collector metal foil 11 according to another embodiment of the present disclosure is shown. The metal foil 11 has an active material layer 12 and further includes edge passivation structures. Specifically, a total of eight edge passivation structures (e.g., ...) are formed at each of the four sides of the metal foil 11 with respect to the upper and lower edges of the metal foil 11. Figure 4 (The location is indicated by the dashed circle). The passivation angle and passivation width of these 8 edge passivation structures can be the same or different, but all are within a passivation angle of 95-120 degrees. o The passivation width is 10-50mm, and the radius of curvature is ≥50mm. Furthermore, viewed from the planar direction of the metal foil 11, a first corner passivation angle 21, a second corner passivation angle 22, a third corner passivation angle 23, and a fourth corner passivation angle 24 are formed between the transverse right-angled side and the longitudinal right-angled side (e.g., ...). Figure 4 (The position indicated by the dashed ellipse). The obtuse angles of these four corners can be the same or different.

[0051] Example 1: Edge passivation structure of metal foil formed by laser melting Equipment: Pulsed fiber laser (1064nm) or ultraviolet laser (355nm), power 100-200W, spot diameter 50-100mm; argon gas protection device; deionized water rinsing equipment.

[0052] Process parameters: Power density: 1×10 6 -5×10 6 W / cm 2 (To avoid burning through) Pulse frequency: 50-100kHz Scanning speed: 500-1000 mm / s Defocusing amount: ±1mm Protective gas (argon) flow rate: 5-10 L / min Process steps: 1. Pre-scan to remove burrs, power 100-120W, spot diameter 50μm, scan once at a uniform speed along the edge of the foil to remove surface burrs; 2. Main scan forms an obtuse angle, power 150W, speed 800mm / s, spot diameter adjusted to 80μm (ensuring power density ≤5×10⁻⁶). 6W / cm²), forming an obtuse angle by scanning obliquely along the edge; 3. Post-treatment: Soak in 5% dilute hydrochloric acid solution for 5 minutes to remove the oxide layer, rinse with deionized water 3 times (30 seconds each time), and air dry at room temperature.

[0053] In this embodiment 1, after the 25mm thick 316L stainless steel foil is laser-melted, the passivation angle is 100° and the passivation width is 50mm.

[0054] Example 2: Forming an edge passivation structure for metal foil by mechanical edge grinding Equipment: Precision polishing machine, polyurethane abrasive pads (Shore hardness 30-50A), nano-SiO2 abrasive (particle size 50-200nm, divided into coarse polishing grade 100-200nm / fine polishing grade 50-100nm); polishing slurry circulation device.

[0055] Process parameters: Pressure: 0.1-0.5 N / cm 2 The 5mm foil uses 0.1N / cm 2 Speed: 20-50 rpm Abrasive concentration: 5-10wt% pH value: 9-11 Process steps: 1. Rough polishing: Fix a 25mm thick 316L stainless steel foil on the stage of the polishing machine, ensuring that the edges are exposed and without warping; use 100-200nm abrasive, pressure 0.3N / cm², rotation speed 50rpm, polishing fluid flow rate 5L / min, and processing time 2min. 2. Fine polishing: Replace with 50nm SiO2 abrasive + soft bevel layer (0.2mm thick), reduce pressure to 0.2N / cm², rotation speed 20rpm, polishing fluid flow rate 2L / min, processing time 3min; 3. Cleaning and drying: Ultrasonic cleaning with deionized water for 5 minutes, followed by drying with compressed air.

[0056] In this embodiment 2, after processing, the edge burrs of the 25mm thick 316L stainless steel foil were reduced from 5mm to 0.1mm, with no mechanical damage, and the resulting passivation angle was 110° and the passivation width was 30mm.

[0057] Example 3: Forming edge passivation structure of metal foil through electrochemical passivation Equipment: Electrolytic cell (polytetrafluoroethylene material), DC regulated power supply, platinum auxiliary electrode (area 10cm²), ultrasonic cleaner; Electrolyte: a mixture of phosphoric acid (85%) and sulfuric acid (94%) in a volume ratio of 2:1; 30 ml / L of glycerol was added (to inhibit excessive dissolution). Process parameters: Voltage: 15-20V Current density: 0.2-1 A / dm 2 Temperature: 60-70℃ Time: 3-5 minutes Edge dissolution depth: 1-3mm, forming a passivation angle of 100° and a passivation width of 30mm.

[0058] Process steps: 1. Pretreatment: Place the 25mm thick 316L stainless steel current collector in acetone, ultrasonically clean for 10 minutes, rinse with deionized water and air dry. 2. Electrochemical polishing: Using the above current collector as the anode and the platinum electrode as the cathode with an electrode spacing of 5 cm, immerse the electrode in the electrolyte (65℃), connect the power supply (voltage 18V, current density 0.8A / dm²), and process for 5 min; 3. Post-treatment: Immediately transfer to a 10% sodium carbonate solution for neutralization and cleaning for 5 minutes, then rinse with deionized water; alternatively, immerse in 3% dilute nitric acid for 30 seconds, then rinse again and air dry to remove the passivation film.

[0059] In this embodiment 3, the current density needs to be precisely controlled to avoid over-etching, and the voltage of the 5mm thick foil needs to be reduced to 10-15V.

Claims

1. A type of iron-based current collector metal foil, characterized in that, The metal foil has an edge passivation structure, wherein, in the thickness direction of the metal foil, the upper edge and the lower edge of the metal foil each form an edge passivation angle with the side surface.

2. The iron-based current collector metal foil according to claim 1, characterized in that, The thickness of the metal foil is 5-30 μm, and the edge passivation angle is 95-120°. o The passivation width is 10-50μm.

3. The iron-based current collector metal foil according to claim 2, characterized in that, The edge blunting angle is 100-120 degrees. o The passivation width is 50μm.

4. The iron-based current collector metal foil according to claim 1, characterized in that, The iron-based current collector metal foil includes an upper edge and a lower edge in the thickness direction of the metal foil, and the upper edge and the lower edge form a first edge passivation angle and a second edge passivation angle with the side surface of the metal foil, respectively.

5. The iron-based current collector metal foil according to claim 4, characterized in that, The first edge blunting angle and the second edge blunting angle may be the same or different.

6. The iron-based current collector metal foil according to claim 1, characterized in that, The edge blunting structure includes rounded corners, near-rounded corners, chamfered corners, obtuse corners, or burr-free structures.

7. The iron-based current collector metal foil according to claim 6, characterized in that, The rounded or near-rounded corner structure has an average radius of curvature greater than 50 μm at the edge corners.

8. The iron-based current collector metal foil according to claim 7, characterized in that, The average radius of curvature is 70-200 μm.

9. The iron-based current collector metal foil according to any one of claims 1 to 8, characterized in that, The iron-based current collector metal foil further has a corner passivation structure, which includes rounded corners, near-rounded corners, or obtuse corners.

10. The iron-based current collector metal foil according to claim 9, characterized in that, The passivation angle of the corner passivation structure is 100-120 degrees. o .

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