A shallow-embossed low-aspect-ratio sodium storage cavity current collector

Abstract

The application discloses a shallow-embossed low-aspect-ratio sodium storage cavity current collector, and relates to the technical field of negative electrode-free sodium metal battery current collectors. The application discloses a shallow-embossed low-aspect-ratio sodium storage cavity current collector, and relates to the technical field of negative electrode-free sodium metal battery current collectors. The application discloses a shallow-embossed low-aspect-ratio sodium storage cavity current collector, and relates to the technical field of negative electrode-free sodium metal battery current collectors.

Description

Technical Field

[0001] This application relates to a shallowly imprinted, low aspect ratio sodium storage cavity current collector, and is related to the field of current collector technology for negative electrode-free sodium metal batteries. Background Technology

[0002] In a negative electrode-less sodium metal battery, no sodium source is pre-placed on the negative electrode side; sodium deposition / stripping occurs directly on the aluminum foil surface. Besides interfacial chemistry, how the deposition space is pre-defined in a "lightweight, continuously conductive, and rollable" manner is also a core issue determining cycle stability.

[0003] Most of the currently disclosed improvement routes focus on adding carbon layers, sodium-loving particles, alloy layers, or three-dimensional porous frameworks. While these routes can provide deposition space, they are often accompanied by engineering problems such as large surface area, numerous additional processes, poor welding and flatness, and complex tab region treatment.

[0004] For example, the published patent WO2022267503A1 employs a technical solution that involves setting an external step and establishing a matching relationship between the thickness of the external step coating and the capacity of the positive electrode surface. Another approach is to use through-holes, porous current collectors, or three-dimensional skeletons, as seen in published patents CN108950570A and CN112599784A. These approaches focus on corroding porous layers, sintering porous bodies from powder, or using three-dimensional skeletons to accommodate space. While these solutions can improve the corresponding problems to some extent, their protection focus is mostly still on deep holes, through-holes, external space layers, or three-dimensional skeletons. They still present engineering problems such as large surface area, numerous additional processes, poor welding and flatness, and complex treatment of the tab area. Summary of the Invention

[0005] The first objective of this application is to form a low aspect ratio sodium storage cavity through shallow imprinting without introducing through-holes, forming a deeply corroded porous layer, or adding a thick three-dimensional skeleton, thereby providing a controlled local containment space for sodium deposition.

[0006] The technical solution adopted in this application is as follows: A shallow-imprinted low aspect ratio sodium storage cavity current collector includes an aluminum foil substrate, and a plurality of shallow-imprinted low aspect ratio sodium storage cavities are formed on at least one side surface of the aluminum foil substrate.

[0007] The shallow imprinted low aspect ratio sodium storage cavity described in this application refers to the sodium storage cavity with a low aspect ratio formed on an aluminum foil substrate by mechanical shallow imprinting, and the surface of the aluminum foil substrate simultaneously retains a continuous non-imprinted planar area.

[0008] The innovative mechanism of this application is as follows: a low aspect ratio sodium storage cavity is formed on an aluminum foil substrate by mechanical shallow imprinting, while retaining a continuous non-imprinted planar area; compared with the existing technology that uses deep etching porous layers, through holes, additional three-dimensional carbon fiber skeletons and high aspect ratio deep trench routes: this application provides local sodium storage space while maintaining the continuous conductivity and planar processing of aluminum foil; alleviates thickness fluctuations and disordered protrusion of the separator direction during deposition / stripping; retains the planar compatibility of the tab area and the welding area; and avoids the degradation of the general "micro-pit / micro-groove" route into a rough surface or deep hole structure.

[0009] Further settings are as follows: The aluminum foil substrate has a thickness of 6-20 μm, preferably 8-16 μm.

[0010] The shallow-imprinted, low-aspect-ratio sodium storage cavity has the following characteristics: cavity depth is 0.8-8.0 μm, preferably 1.5-6.0 μm; equivalent cavity opening width is 4-28 μm, preferably 6-20 μm; cavity aspect ratio is 0.04-0.35; and cavity volume per unit area is 0.006-0.080 mm². 3 / cm 2 .

[0011] The cavity does not penetrate the thickness of the aluminum foil and does not form a through-hole structure.

[0012] The aluminum foil substrate has a cavity area accounting for 15%-55%, preferably 20%-45%, and a non-imprinted planar area accounting for 45%-85%.

[0013] The tab welding area is located in the non-imprinted plane area, and the width of the tab welding area is 1.0-4.0mm.

[0014] The beneficial effects of this application are as follows: (1) The sodium storage space in this application is formed by mechanical shallow imprinting of the aluminum foil body, rather than by corrosion, hollowing, powder sintering or adding a three-dimensional skeleton. The process is simple and the cost is low.

[0015] (2) The cavity formed by mechanical shallow imprinting is a shallow cavity with a low aspect ratio, while retaining a continuous planar area. The tab welding area retains the non-imprinted planar edge to accommodate winding, stacking and welding.

[0016] (3) By controlling the cavity volume per unit area, the area ratio of the cavity region and the width of the reserved plane, the feasibility of the project is guaranteed, while also having excellent physical and electrochemical properties. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the shallow-imprinted, low-aspect-ratio sodium storage cavity current collector of this application.

[0018] Figure 1 In the middle: 1 is the aluminum foil substrate; 2 is the low aspect ratio sodium storage cavity; 3 is the non-imprinted planar area; 4 is the electrode tab welding area.

[0019] Figure 2 This is a schematic diagram of the cross-section of the sodium storage cavity current collector with shallow imprinting and low aspect ratio in this application.

[0020] Figure 3 The image shows a SEM image of the shallow imprinted low aspect ratio sodium storage cavity current collector prepared in Example 1.

[0021] Figure 4 This is a comparison chart of the first charge-discharge curves of the battery cell prepared using the current collector in Example 1 and the battery cell prepared using Comparative Example 1. Detailed Implementation

[0022] The present application will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] Regarding raw materials and equipment: Unless otherwise specified, the raw materials and equipment used in the embodiments are all existing technologies or commercially available products in the field.

[0024] Product characterization and testing: For cavity depth, equivalent opening width, cavity area ratio, and cavity volume per unit area, three-dimensional morphology characterization was performed using laser confocal microscopy and white light profilometry. For each sample, no less than 5 fields of view and no less than 50 cavities were randomly selected for statistical analysis. The cavity volume per unit area was obtained by integrating the three-dimensional morphology.

[0025] The aspect ratio of the cavity is calculated based on the ratio of the average depth of the cavity to the equivalent width of the opening; and the cross-sectional SEM is used to verify the typical cavity profile.

[0026] Regarding the thickness reduction rate after embossing: a micrometer was used to measure the thickness of the sample before and after embossing at different locations.

[0027] For warpage: the maximum height off the surface of a 100mm spline is used for evaluation.

[0028] For weld compatibility: Welding was performed under the same tab and ultrasonic welding process conditions. The integrity of the weld area was evaluated by weld spot micrographs and peel strength tests, where peel strength was expressed in N / mm.

[0029] For electrochemical performance: A sodium metal full cell without a negative electrode was assembled using the same positive electrode, separator, and electrolyte. In the example presented here, the positive electrode has an areal capacity of 1.8 mAh / cm². 2The cathode is a polyanionic polymer (PAP) electrode with a polyolefin separator. The electrolyte is a 1.0 M NaPF6-diethylene glycol dimethyl ether solution. The initial coulombic efficiency was obtained through formation testing, followed by cycling at 25°C for 1000 cycles and at 45°C for 500 cycles. Test conditions: 0.5C charging, 1C discharging, charging cutoff voltage 3.5V, discharging cutoff voltage 1.5V.

[0030] The following provides a detailed description of the structure and manufacturing process of the shallow imprinted low aspect ratio sodium storage cavity current collector of this application.

[0031] like Figure 1 As shown, the basic structure of a shallow-imprinted low aspect ratio sodium storage cavity current collector of this application includes an aluminum foil substrate 1, a low aspect ratio sodium storage cavity 2 is formed on the aluminum foil substrate 1 by mechanical shallow imprinting, and the surface of the aluminum foil substrate 1 simultaneously retains a continuous non-imprinted planar area 3.

[0032] The thickness of the aluminum foil substrate 1 is 6-20 μm, preferably 8-16 μm.

[0033] The low aspect ratio sodium storage cavity 2 has the following characteristics: cavity depth is 0.8-8.0 μm, preferably 1.5-6.0 μm; equivalent cavity opening width is 4-28 μm, preferably 6-20 μm; aspect ratio is 0.04-0.35; and cavity volume per unit area is 0.006-0.080 mm². 3 / cm 2 .

[0034] The low aspect ratio sodium storage cavity does not penetrate the thickness of the aluminum foil substrate 1 and does not form a through-hole structure.

[0035] The aluminum foil substrate has a low aspect ratio sodium storage cavity area accounting for 15%-55% of the area, preferably 20%-45%; and a non-imprinted planar area accounting for 45%-85% of the area.

[0036] The tab welding area 4 is located within the non-imprinted plane area 3, and the width of the tab welding area 4 is 1.0-4.0mm.

[0037] The following description, in conjunction with different production processes, further illustrates the shallow imprinted low aspect ratio sodium storage cavity current collector and its performance in this application.

[0038] Example 1

[0039] A manufacturing process for a shallow-imprinted, low-aspect-ratio sodium storage cavity current collector is described below: A single pass shallow imprinting is performed on an 11μm thick aluminum foil substrate 1 using an imprinting roller with a shallow cup-shaped texture to form regularly distributed low aspect ratio sodium storage cavities 2, while retaining continuous non-imprinted planar areas 3 and tab welding areas 4.

[0040] The resulting shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector: The cavity has a depth of 2.4 μm, an equivalent opening width of 15.8 μm, an aspect ratio of 0.15, a cavity area ratio of 24%, and a cavity volume per unit area of ​​0.012 mm². 3 / cm 2 The width of the electrode welding area 4 is 2.0 mm.

[0041] Product morphology confirmation: The SEM morphology of the shallow imprinted low aspect ratio sodium storage cavity current collector prepared in Example 1 is as follows: Figure 3 As shown: the cavity is a shallow cavity with a dispersed distribution, and the aluminum foil substrate still maintains a continuous planar conductive structure.

[0042] Examples 2-14 To investigate the effects of different cavity sizes, cavity area ratios, cavity volume per unit area, and electrode welding area width on current collector performance, experiments were conducted in Examples 2-14 as shown in Table 1, and compared with Comparative Examples 1-4.

[0043] Table 1 .

[0044] Performance testing: For the current collectors prepared in the examples and comparative examples shown in Table 1, tests were conducted on aspects such as thickness reduction rate after imprinting, warpage, peel strength, and electrochemical performance according to the aforementioned testing methods. The test results are shown in Table 2. Table 2 .

[0045] analyze: As can be seen from Examples 1-6, when the cavity depth is between 1.5 and 6.0 μm and the cavity aspect ratio is maintained between 0.08 and 0.30, the first-cycle coulombic efficiency and high-temperature cycling performance are both superior. In Comparative Example 2, the cavity depth is only 0.7 μm, which can maintain good flatness and weldability, but the initial deposition control capability is limited due to insufficient reserved space. In Comparative Example 3, the cavity depth reaches 8.6 μm and the cavity aspect ratio reaches 0.51. Although it has a large volume space, the warpage increases and the weld peel strength decreases, indicating that excessively deep structures are not conducive to engineering applications.

[0046] As can be seen from Examples 7-10 and Comparative Example 4, when the area ratio of the cavity region is between 20% and 45%, a better balance can be achieved between the sodium storage space and the continuous planar region. When the area ratio is too low, the space that can be accommodated per unit area is insufficient; when the area ratio is too high and the reserved planar edge is too narrow, the integrity and flatness of the welding area are significantly reduced.

[0047] As can be seen from Examples 11-12, when the aluminum foil thickness is in the range of 8-16 μm, the embossing formability, flatness, and electrochemical performance can be balanced. Examples 13-14 further show that when the width of the plane edge of the tab welding area is in the range of 1.5-3.0 mm, the ultrasonic welding peel strength is high and the cycle performance is stable.

[0048] Figure 3 The comparison of the first-cycle charge-discharge curves of Example 1 and Comparative Example 1 further illustrates that after setting up a shallow imprinted sodium storage cavity with a low aspect ratio, the first-cycle deposition / stripping process is more stable and the polarization is smaller, which is consistent with the first-cycle coulombic efficiency improvement results in Table 2.

[0049] In summary, this application improves the interface stability and cycle performance of a negative electrode-free sodium metal battery by forming a shallowly imprinted, low aspect ratio sodium storage cavity on the aluminum foil body while retaining the continuous planar area and the planar edge of the tab welding area.

Claims

1. A shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector, comprising an aluminum foil substrate, characterized in that: Multiple shallowly imprinted, low aspect ratio sodium storage cavities are formed on at least one side of the aluminum foil substrate.

2. The shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 1, characterized in that: The shallow imprinted low aspect ratio sodium storage cavity refers to the sodium storage cavity with a low aspect ratio formed on an aluminum foil substrate by mechanical shallow imprinting, while the surface of the aluminum foil substrate simultaneously retains a continuous non-imprinted planar area.

3. The shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 1, characterized in that: The thickness of the aluminum foil substrate is 6-20 μm.

4. The shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 3, characterized in that: The thickness of the aluminum foil substrate is 8-16 μm.

5. The shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 1, characterized in that: The shallow-imprinted, low-aspect-ratio sodium storage cavity has the following characteristics: cavity depth of 0.8-8.0 μm, equivalent cavity opening width of 4-28 μm, cavity aspect ratio of 0.04-0.35, and cavity volume per unit area of ​​0.006-0.080 mm². 3 / cm 2 .

6. The shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 5, characterized in that: The shallow-imprinted, low-aspect-ratio sodium storage cavity has a cavity depth of 1.5-6.0 μm and an equivalent width of 6-20 μm for the cavity opening.

7. The shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 1, characterized in that: The cavity does not penetrate the thickness of the aluminum foil and does not form a through-hole structure.

8. The shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 1, characterized in that: The aluminum foil substrate has a cavity area accounting for 15%-55% of the total area and a non-imprinted planar area accounting for 45%-85% of the total area.

9. A shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 1, characterized in that: The cavity area of ​​the aluminum foil substrate accounts for 20%-45%.

10. A shallow-imprinted, low-aspect-ratio sodium-storage cavity current collector according to claim 2, characterized in that: The tab welding area is located in the non-imprinted plane area, and the width of the tab welding area is 1.0-4.0mm.

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