Laminated cushion foil, preparation method of laminated cushion foil and application of laminated cushion foil in electrode foil coiling and sintering process

Abstract

The invention discloses a laminated cushion foil, a preparation method of the laminated cushion foil and application of the laminated cushion foil in an electrode foil coiling and sintering process. The preparation method comprises the following steps: (1) carrying out hydrothermal treatment on an aluminum foil to obtain an aluminum foil with a boehmite film; and (2) adding a carbon precursor layer on the surface of the aluminum foil with the boehmite film to obtain the laminated cushion foil. According to the invention, the binding force between the boehmite film and the aluminum foil substrate is strong, and during high-temperature sintering, gamma-AlOOH is dehydrated and converted into a boehmite conversion film; the conversion film can be used as a perfect anti-sticking isolating layer, active carbon atoms generated by thermal decomposition of an external carbon source can be guided to the surface of an aluminum foil substrate by primary micropores in the film, and the active carbon atoms can react with the aluminum foil substrate to generate a nanoscale AlC strengthening phase, so that a gradient functional layer with enhanced performance is formed on the surface of the aluminum foil; the gradient functional layer can remarkably improve the surface hardness and strength of the aluminum foil, so that the obtained laminated cushion foil has excellent creep resistance.

Description

Technical Field

[0001] This invention belongs to the field of capacitor technology, specifically relating to a laminated foil, its preparation method, and its application in the electrode foil roll-and-sintering process. Background Technology

[0002] The general manufacturing process of sintered electrode foil is as follows: aluminum powder or aluminum powder slurry is first coated on the surface of aluminum foil substrate, and then dried, sintered and formed to obtain sintered electrode foil. In the prior art, during sintering, the electrode foil is rolled up and multiple foil rolls are placed in a sintering furnace for joint sintering, such as CN117900480A.

[0003] To prevent adhesion between the layers of the foil roll, existing technologies propose a scheme where the electrode foil and the laminated foil are wound together during winding, with the laminated foil providing isolation between the layers of the electrode foil. Examples include CN115274304B and CN120748937A.

[0004] The laminated foils used in the prior art are usually high-purity aluminum foils. However, pure aluminum has a low recrystallization temperature. At a sintering temperature of 550-650℃, its grains grow rapidly, and its yield strength drops sharply to one-tenth or even less than that at room temperature. At this time, under the action of the electrode foil's own gravity and sintering shrinkage stress, the softened laminated foil will undergo significant plastic deformation and creep, and cannot effectively support the electrode foil. Summary of the Invention

[0005] The purpose of this invention is to provide a laminated foil, its preparation method, and its application in the electrode foil roll sintering process. This laminated foil has strong creep resistance and is not easily deformed during high-temperature sintering.

[0006] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows: This invention first provides a method for preparing a laminated foil, the method comprising the following steps: (1) Aluminum foil is subjected to hydrothermal treatment to obtain aluminum foil with boehmite film; (2) A carbon precursor layer is added to the surface of the aluminum foil with boehmite film to obtain the laminated pad foil.

[0007] In this invention, a boehmite (γ-AlOOH) film is first grown in situ on the surface of aluminum foil. This boehmite film has a strong adhesion to the aluminum foil substrate. When the laminated pad foil and the coated foil are wound alternately into a foil roll and sintered at high temperature, the γ-AlOOH will dehydrate and transform into a hard, stable boehmite conversion film (γ-Al2O3 or α-Al2O3) with a large number of native micropores. On the one hand, it can serve as a perfect anti-adhesion isolation layer to prevent adhesion between the laminated pad foil and the coated foil, thereby improving production yield. On the other hand, the native micropores allow this anti-adhesion isolation layer to also act as a medium to guide the active carbon atoms generated by the thermal decomposition of external carbon sources to the surface of the aluminum foil substrate. These active carbon atoms will react with the aluminum foil substrate to generate a nanoscale Al4C3 reinforcing phase, thereby forming a performance-enhancing gradient functional layer on the surface of the aluminum foil. This gradient functional layer can significantly improve the surface hardness and strength of the aluminum foil, giving the obtained laminated pad foil excellent creep resistance. Moreover, the carbon content on the surface of the laminated foil varies in a gradient, which avoids stress concentration caused by sudden changes in performance and makes the interface between the foil and the sintered foil more stable and reliable during thermal cycling.

[0008] In this invention, the boehmite conversion and the thermal decomposition of the carbon source both occur during the high-temperature sintering process. This high-temperature sintering step can occur simultaneously with the high-temperature sintering process after the coated foil is wound into a foil roll, or it can be performed before winding into a foil roll. This invention does not require either of these steps. From the perspective of saving procedures and costs, it is obviously better to eliminate the separate high-temperature sintering step.

[0009] Preferably, in step (1) of the above preparation method, the hydrothermal treatment is: placing the aluminum foil in deionized water at 90-100℃ and pH 6-10 and boiling it for 1-30 minutes.

[0010] Preferably, in step (1) and step (2) of the above preparation method, the carbon source is selected from at least one of organic carbon materials and nano carbon materials.

[0011] The organic carbon material is selected from at least one of sucrose, phenolic resin, and polyacrylonitrile; the nano carbon material is selected from at least one of graphene and carbon nanotubes.

[0012] When organic carbon materials are selected, step (2) of the above preparation method includes: 1) Dissolve the organic carbon material in a solvent to prepare an organic carbon precursor solution; 2) The organic carbon precursor solution is applied to the surface of the aluminum foil with the boehmite film by dip coating or spraying. 3) The carbon precursor layer is formed after low-temperature pre-curing.

[0013] Preferably, the concentration of the organic carbon precursor solution is 5-30 wt%; and the pre-curing temperature is 100-200℃.

[0014] When nano-carbon materials are selected, step (2) of the above preparation method includes: 1) The nano-carbon material is dispersed in a solvent to obtain a nano-carbon material dispersion with a concentration of 0.05-5 wt%; 2) The nano-carbon material dispersion is coated onto the surface of the aluminum foil with the boehmite film, and after drying, the carbon precursor layer is formed.

[0015] The present invention also provides a laminated foil, which is prepared by the above-described preparation method.

[0016] The present invention also provides the application of the above-mentioned laminated pad foil in the electrode foil roll sintering process, the application including: winding the coated foil and the laminated pad foil alternately to form a foil roll, and then performing high-temperature sintering.

[0017] Because the laminated pad foil of the present invention has excellent creep resistance, it can effectively support the coated foil in the foil roll.

[0018] Compared with the prior art, the beneficial effects of the present invention are reflected in: This invention first grows a boehmite (γ-AlOOH) film in situ on the surface of aluminum foil. This boehmite film has strong adhesion to the aluminum foil substrate. When the laminated pad foil and coated foil are wound alternately into a roll and sintered at high temperature, the γ-AlOOH dehydrates and transforms into a hard, stable boehmite conversion film (γ-Al2O3 or α-Al2O3) with numerous native micropores. On one hand, this serves as a perfect anti-adhesion barrier layer, preventing adhesion between the laminated pad foil and coated foil, thus improving production yield. On the other hand, the native micropores allow this anti-adhesion barrier layer to also act as a medium... The active carbon atoms generated by the thermal decomposition of an external carbon source are guided to the surface of the aluminum foil substrate. These active carbon atoms react with the aluminum foil substrate to generate a nanoscale Al4C3 reinforcing phase, thereby forming a performance-enhancing gradient functional layer on the aluminum foil surface. This gradient functional layer can significantly improve the surface hardness and strength of the aluminum foil, giving the resulting laminated pad foil excellent creep resistance and effectively supporting the coated foil. Moreover, the carbon content on the surface of the laminated pad foil changes in a gradient, which avoids stress concentration caused by abrupt performance changes, making the interface between the pad foil and the sintered foil more stable and reliable during thermal cycling. Detailed Implementation

[0019] The following examples illustrate the technical solution of the present invention in a more detailed manner.

[0020] Example 1 This embodiment describes a laminated foil, the preparation method of which includes the following steps: (1) Aluminum foil is subjected to hydrothermal treatment to obtain aluminum foil with boehmite film; Specifically, a high-purity aluminum foil (1xxx series, purity ≥99.99%, background carbon content <0.002%) with a thickness of 0.20 mm was selected. The high-purity aluminum foil was placed in water with pH 10 (adjusted with ammonia) and 98°C and boiled for 15 minutes to obtain an aluminum foil with a boehmite film (thickness of about 300 nm). (2) A carbon precursor layer is added to the surface of the aluminum foil with boehmite film to obtain the laminated pad foil of this embodiment; Specifically, aluminum foil with a boehmite film is immersed in a 5 wt% sucrose solution, dip coating is performed (that is, the aluminum foil is pulled out of the sucrose solution to form a liquid film on the surface of the aluminum foil), and then pre-cured at 150°C to form a carbon precursor layer with a thickness of about 50 nm.

[0021] Example 2 This embodiment is a multilayer foil, the preparation method of which is basically the same as that of Example 1, except that: a 15% sucrose solution is used in step (2); the thickness of the carbon precursor layer obtained is about 200 nm.

[0022] Example 3 This embodiment is a laminated foil, and its preparation method is basically the same as that of Example 1, except that: a 30% sucrose solution is used in step (2); the thickness of the carbon precursor layer obtained is about 1 μm.

[0023] Examples 4-6 This embodiment is a laminated foil, and its preparation method is basically the same as that of embodiment 1. The difference is that the phenolic resin solutions used in step (2) are 5wt%, 10wt%, and 15wt%, respectively.

[0024] Examples 7-9 This embodiment is a laminated foil, and its preparation method is basically the same as that of Example 1. The difference is that in step (2), 5wt%, 10wt%, and 15wt% polyacrylonitrile solutions are used respectively.

[0025] Examples 10-12 This embodiment is a multilayer foil, the preparation method of which is basically the same as that of Example 1, except that: in step (2), 0.1wt%, 0.5wt%, and 1.5wt% graphene dispersions are used respectively; after spraying, it is dried at 80°C.

[0026] Examples 13-15 This embodiment is a laminated foil, and its preparation method is basically the same as that of Example 10. The difference is that the carbon nanotube dispersions used in step (2) are 0.1wt%, 0.5wt%, and 1.5wt%, respectively.

[0027] Comparative Example 1 This comparative example is a laminated foil, the preparation method of which is basically the same as that of Example 1, except that step (2) is not included.

[0028] The laminated foils prepared in Examples 1-15 and Comparative Example 1 were wound into foil rolls with the coated foils from the same batch, and then placed in a sintering furnace for sintering under argon protection at a temperature of 580°C for 2 hours. After sintering, the properties of the sintered foils (i.e., the sintered coated foils) were tested, and the test results are shown in Table 1.

[0029] Table 1 Note: Resistance increase rate refers to the resistance increase rate of the sintered foil relative to its aluminum foil substrate.

[0030] As can be seen from Table 1, compared with Comparative Example 1 (unmodified pure aluminum foil), Example 1, through surface carbonization modification, achieved: 1. Significantly improved high-temperature softening resistance: The high-temperature hardness retention rate increased from 25% to 45%, an improvement of 80%. This proves that even with milder modification conditions, carbon-reinforcing phases can be effectively introduced to pin grain boundaries and suppress grain growth and softening at high temperatures.

[0031] 2. Significantly improved contact interface stability: The resistance increase rate decreased from >300% to 80%, a reduction of over 73%. This indicates that the carbon-modified layer effectively mitigated the interface contact deterioration caused by aluminum foil softening and creep during sintering, thus avoiding a catastrophic increase in contact resistance.

[0032] 3. Basic performance is maintained: The room temperature conductivity (61.8% IACS) and bending resistance (480 times) are very close to those of pure aluminum foil (63.0% IACS, >500 times), indicating that the modification process improves high-temperature performance while hardly damaging the inherent high conductivity and excellent flexibility of aluminum foil.

[0033] In summary, Example 1 successfully verified the basic feasibility and effectiveness of the technical route of this invention, achieving a preliminary balance between high-temperature performance and basic performance. It represents the performance starting point at a relatively low degree of modification within the scope of this invention. Further performance leaps can be achieved through process optimization (such as increasing carbon content and selecting nano-carbon materials), as shown in Examples 2 and 11, providing optional solutions for different application needs. This fully embodies the core idea of ​​this invention: achieving designable performance through controllable surface carbon deposition.

Claims

1. A method for preparing a laminated foil, characterized in that, Includes the following steps: (1) Aluminum foil is subjected to hydrothermal treatment to obtain aluminum foil with boehmite film; (2) A carbon precursor layer is added to the surface of the aluminum foil with boehmite film to obtain the laminated pad foil.

2. The preparation method according to claim 1, characterized in that, In step (1), the hydrothermal treatment is to boil the aluminum foil in deionized water at 90-100℃ and pH 6-10 for 1-30 minutes.

3. The preparation method according to claim 1, characterized in that, In step (2), the carbon source is selected from at least one of organic carbon materials and nano carbon materials.

4. The preparation method according to claim 1, characterized in that, The organic carbon material is selected from at least one of sucrose, phenolic resin, and polyacrylonitrile.

5. The preparation method according to claim 4, characterized in that, Step (2) includes: 1) Dissolve the organic carbon material in a solvent to prepare an organic carbon precursor solution; 2) The organic carbon precursor solution is applied to the surface of the aluminum foil with the boehmite film by dip coating or spraying. 3) The carbon precursor layer is formed after low-temperature pre-curing.

6. The preparation method according to claim 5, characterized in that, The concentration of the organic carbon precursor solution is 5-30 wt%; the pre-curing temperature is 100-200℃.

7. The preparation method according to claim 3, characterized in that, The nano-carbon material is selected from at least one of graphene and carbon nanotubes.

8. The preparation method according to claim 7, characterized in that, Step (2) includes: 1) The nano-carbon material is dispersed in a solvent to obtain a nano-carbon material dispersion with a concentration of 0.05-5 wt%; 2) The nano-carbon material dispersion is coated onto the surface of the aluminum foil with the boehmite film, and after drying, the carbon precursor layer is formed.

9. A laminated foil, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the laminated pad foil as described in claim 9 in the electrode foil roll sintering process, characterized in that, include: The coated foil and the stacked pad foil are wound alternately to form a foil roll, which is then sintered at high temperature.

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