Current collectors and their surface modification methods and applications

Abstract

This invention provides a current collector and its surface modification method and application. The surface modification method includes: sequentially subjecting an initial current collector to ultraviolet cleaning, plasma activation, plasma modification, and curing to obtain a surface-modified current collector; wherein the initial current collector includes aluminum foil; the discharge power of plasma modification is greater than the discharge power of plasma activation; the discharge power of plasma modification is 200~400W; and the time interval between plasma activation and ultraviolet cleaning is ≤10min. The surface modification method of this invention, through the synergistic effect of ultraviolet cleaning, plasma grading treatment, and curing, can effectively remove impurities such as oil stains from the surface of current collectors such as aluminum foil, and construct a rough hydrophilic interface, thereby achieving a simultaneous and significant improvement in the surface hydrophilicity and peel strength of current collectors used in sodium-ion batteries, without the need for the use of highly corrosive chemical reagents throughout the process.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a current collector and its surface modification method and application. Background Technology

[0002] Aluminum foil current collectors, with their core advantages of high conductivity, excellent mechanical strength, good chemical stability, and cost-effectiveness, have been widely used in the positive and negative electrode current collector fields of new energy storage devices such as lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries. However, traditional aluminum foil still has significant shortcomings in practical applications: its inert hydrophobic surface results in weak interfacial bonding with electrode active materials and binders, easily leading to active material shedding during charge and discharge, thus affecting the cycle stability of the battery. Simultaneously, aluminum foil lacks sufficient corrosion resistance in some electrolyte systems, and long-term use may lead to surface oxidation and peeling. It is worth noting that the electrolyte systems of lithium-ion batteries and sodium-ion batteries are fundamentally different, resulting in significantly different requirements for the hydrophilicity of aluminum foil. The radius of sodium ions is larger than that of lithium ions, making it more difficult for the electrolyte in sodium-ion battery systems to wet the aluminum foil surface, thus imposing more stringent requirements on the hydrophilicity of the current collector. The hydrophilicity of traditional aluminum foil cannot meet the performance requirements of both battery systems simultaneously. Therefore, there is an urgent need to develop modified aluminum foil specifically for sodium-ion batteries, and to solve the compatibility problem between traditional aluminum foil and sodium-ion battery systems through modification technologies such as surface hydrophilicity control and enhanced interfacial bonding.

[0003] Currently, surface modification methods for aluminum foil current collectors in sodium-ion batteries are mainly divided into chemical modification and physical modification. While chemical modification can improve the hydrophilicity of the aluminum foil surface to some extent, it suffers from complex processes, environmental pollution from chemical reagents, and corrosion of the aluminum foil substrate leading to decreased mechanical strength and uneven modification effects, making it difficult to simultaneously improve peel strength. Furthermore, chemical modification requires subsequent wastewater treatment, increasing production energy consumption and costs. Additionally, chemical residues may affect the electrochemical performance of the battery, making it unsuitable for the high-end modification requirements of battery current collectors. Physical modification methods, such as mechanical polishing and ultraviolet irradiation, have limited modification effects and easily damage the aluminum foil surface, disrupting its smoothness and leading to uneven coating, which in turn affects battery consistency.

[0004] Therefore, there is a need to develop a current collector modification method that is process-controllable, environmentally friendly, leaves no chemical residues, and can simultaneously improve the hydrophilicity and peel strength of sodium-ion battery current collectors, while also meeting the requirements of sodium-ion battery cathode coating processes. Summary of the Invention

[0005] The main objective of this invention is to provide a current collector and its surface modification method and application, in order to solve the problems of poor modification effect and difficulty in simultaneously improving hydrophilicity and peel strength in the surface modification methods of current collectors in the prior art.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for surface modification of a current collector is provided, the method comprising: sequentially subjecting an initial current collector to ultraviolet cleaning, plasma activation, plasma modification, and curing to obtain a surface-modified current collector; wherein the initial current collector comprises aluminum foil; the discharge power of plasma modification is greater than the discharge power of plasma activation; the discharge power of plasma modification is 200~400W; and the time interval between plasma activation and ultraviolet cleaning is ≤10min.

[0007] Furthermore, the above-mentioned surface modification method also includes: pre-treating the initial current collector to obtain a pre-treated current collector; sequentially performing ultraviolet cleaning, plasma activation, plasma modification, and curing on the pre-treated current collector to obtain a surface-modified current collector; wherein, the surface pre-treatment process includes sequential pre-cleaning and drying; pre-cleaning the initial current collector with a pre-cleaning solution, which is a mixed solution of anhydrous ethanol and distilled water; the volume ratio of anhydrous ethanol to distilled water is 1:1~2, and the temperature of the pre-cleaning solution is 25~35℃; ultrasonication is performed during the pre-cleaning process, with an ultrasonic power of 200~300W; the pre-cleaning time is 15~30min; the drying temperature is 50~80℃, the drying vacuum degree is -0.08~-0.1MPa, and the drying time is 10~20min.

[0008] Furthermore, the ultraviolet cleaning process includes: placing the surface-pretreated current collector in an ultraviolet cleaning device equipped with an ultraviolet lamp; adjusting the vertical distance between the surface-pretreated current collector and the ultraviolet lamp to 8-20mm; turning on the ultraviolet lamp; and using ultraviolet light with a wavelength of 185-254nm to perform ultraviolet cleaning on the surface-pretreated current collector to obtain an ultraviolet-cleaned current collector; when the ultraviolet lamp is a dual-wavelength ultraviolet lamp, the wavelengths of the ultraviolet light from the dual-wavelength ultraviolet lamp are 185nm and 254nm; and / or, the power of ultraviolet cleaning is 80-150W, and the ultraviolet cleaning time is 20-60min.

[0009] Further, the plasma activation process includes: placing the UV-cleaned current collector into the reaction chamber of a plasma processing device, which includes a plasma spray gun and a plasma generator; adjusting the vertical distance between the UV-cleaned current collector and the plasma spray gun to 5-15 mm; evacuating to a vacuum level of 100-1000 Pa; introducing a mixed gas into the reaction chamber; turning on the plasma generator; and performing plasma activation on the UV-cleaned current collector to obtain a plasma-activated current collector; wherein the mixed gas includes a first gas and a second gas; the first gas is argon and / or nitrogen; the second gas is oxygen and / or carbon dioxide; the flow rate of the mixed gas is 10-50 sccm; and the volume ratio of the first gas to the second gas is 5-10:1.

[0010] Furthermore, the plasma activation discharge power is 50~200W, the plasma activation frequency is 13.56~27.12MHz, and the plasma activation time is 30~120s.

[0011] Furthermore, the discharge power of plasma modification is 250~350W, the processing frequency of plasma modification is 27.12~40.68MHz, and the processing time of plasma modification is 60~300s.

[0012] Furthermore, the curing temperature is 25~40℃, the relative humidity is 40~60%, and the curing time is 2~6h.

[0013] Furthermore, the initial current collector has a thickness of 10~50μm and a purity of ≥99.7%.

[0014] According to another aspect of the invention, a current collector is provided, which is prepared by the surface modification method described above.

[0015] According to another aspect of the present invention, there is provided an application of a current collector in a battery, the current collector being the aforementioned current collector.

[0016] By applying the technical solution of this invention, the surface modification method of this application, through the synergistic effect of ultraviolet cleaning, plasma classification treatment, and curing, can effectively remove impurities such as oil stains from the surface of current collectors such as aluminum foil, and construct a rough hydrophilic interface. This achieves a simultaneous and significant improvement in the hydrophilicity and peel strength of the current collector surface for sodium-ion batteries, without the need for highly corrosive chemical reagents throughout the process. Specifically, ultraviolet cleaning utilizes the decomposition effect of high-energy ultraviolet photons to effectively remove organic contaminants from the surface of the current collector, while simultaneously introducing a small number of hydrophilic functional groups to the surface, thereby improving the hydrophilicity of the current collector. Ultraviolet cleaning does not damage the substrate, causes no secondary pollution, and does not affect the electrochemical performance of sodium-ion batteries. However, if ultraviolet cleaning is used alone, it can only remove surface contaminants and slightly improve hydrophilicity, but cannot change the microstructure of the current collector surface, thus making it difficult to improve its peel strength. Furthermore, the long-term effectiveness of the modification is poor, failing to meet the requirements of long-term charge-discharge cycles for sodium-ion batteries. Although UV cleaning technology has been widely used for surface cleaning of semiconductors and optical devices, and plasma treatment is also used for metal surface activation, in the field of aluminum foil current collectors for sodium-ion batteries, the two have never been used together to synergistically improve hydrophilicity and peel strength. The fundamental reasons are: (1) The industry generally believes that UV cleaning only has a "cleaning" function. Its ability to introduce functional groups on the aluminum foil surface is weak and its effect is short-lived, which cannot meet the stringent requirements of battery-grade materials for interface stability; (2) Although plasma treatment can enhance surface roughness and polarity, its high-energy particles can easily cause local overheating of aluminum foil or uneven oxide layer. When used alone, the peel strength improvement is limited; (3) More importantly, if the two are simply used in series, the traditional understanding is that the active oxygen species (such as ozone and ·OH) generated by UV will rapidly decay or be adsorbed by the environment within a few minutes, and cannot form an effective synergy with the subsequent plasma treatment. This "time window failure" understanding has long hindered the application exploration of this combination. This application, by precisely controlling the time interval between UV cleaning and plasma activation within the aforementioned range, successfully introduces the physical etching and functional group enhancement effects of plasma-based graded treatment within the "active window" before the UV-activated layer decays. This achieves precise spatiotemporal coupling of "chemical activation" and "physical anchoring," thereby simultaneously improving hydrophilicity and peel strength. In other words, this application achieves a modification effect of "1+1>2." Single-step plasma treatment has advantages such as being green and environmentally friendly, operating at room temperature, and leaving no chemical residue. However, it suffers from problems such as limited process complexity, insufficient modification depth, limited improvement in hydrophilicity and peel strength, and unsatisfactory treatment results, making it difficult to meet the stringent requirements of high-rate and long-cycle sodium-ion batteries.Therefore, this application employs a plasma-stage treatment process, namely plasma activation and plasma modification. The discharge power of plasma modification is controlled to be greater than that of plasma activation. This allows for the activation of the current collector surface with a lower discharge power, initially introducing polar functional groups and enhancing its surface energy, laying the foundation for subsequent deep modification. Subsequently, high-power plasma modification (200-400W) achieves deeper ion bombardment and free radical reactions on the current collector surface. This significantly increases the density of hydrophilic functional groups such as hydroxyl and carboxyl groups and induces the formation of a nanoscale rough structure, thereby synergistically enhancing the surface hydrophilicity of the current collector and the adhesion of the coating. Finally, the modified layer structure is stabilized through curing to prevent functional group failure. In summary, the surface modification method of this application is simple, environmentally friendly, leaves no chemical residue, and exhibits good stability. The surface-modified current collector obtained can solve the problems of poor slurry wetting and easy coating peeling during the coating process. The modification effect is stable and long-lasting, thus better adapting to the coating process requirements of sodium-ion batteries. This is conducive to achieving the high-rate and long-cycle performance goals of sodium-ion batteries, and also provides a green and efficient technical solution for interface optimization of current collectors used in sodium-ion batteries. In addition, the surface modification method of this application does not require large-scale modification of existing production lines, making it easy to achieve industrial-scale application. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0018] As analyzed in the background section of this application, the surface modification methods for current collectors in the prior art have problems such as poor modification effect and difficulty in simultaneously improving hydrophilicity and peel strength. In order to solve the above problems, this application provides a current collector and its surface modification method and application.

[0019] In a typical embodiment of this application, a surface modification method for a current collector is provided. The surface modification method includes: sequentially subjecting an initial current collector to ultraviolet cleaning, plasma activation, plasma modification, and curing to obtain a surface-modified current collector; wherein the initial current collector includes aluminum foil; the discharge power of plasma modification is greater than the discharge power of plasma activation; the discharge power of plasma modification is 200~400W; and the time interval between plasma activation and ultraviolet cleaning is ≤10min, preferably 3~6min.

[0020] The surface modification method of this application, through the synergistic effect of ultraviolet cleaning, plasma classification treatment, and curing, can effectively remove impurities such as oil stains from the surface of current collectors, such as aluminum foil, and construct a rough hydrophilic interface. This achieves a simultaneous and significant improvement in the hydrophilicity and peel strength of the current collector surface for sodium-ion batteries, all without the need for highly corrosive chemical reagents. Specifically, ultraviolet cleaning utilizes the decomposition effect of high-energy ultraviolet photons to effectively remove organic contaminants from the current collector surface, while simultaneously introducing a small number of hydrophilic functional groups to the surface, thereby improving the hydrophilicity of the current collector. Ultraviolet cleaning does not damage the substrate, causes no secondary pollution, and does not affect the electrochemical performance of sodium-ion batteries. However, if ultraviolet cleaning is used alone, it can only remove surface contaminants and slightly improve hydrophilicity, but cannot change the microstructure of the current collector surface, thus making it difficult to improve its peel strength. Furthermore, the long-term effectiveness of the modification is poor, failing to meet the long-term charge-discharge requirements of sodium-ion batteries. Although UV cleaning technology has been widely used for surface cleaning of semiconductors and optical devices, and plasma treatment is also used for metal surface activation, in the field of aluminum foil current collectors for sodium-ion batteries, the two have never been used together to synergistically improve hydrophilicity and peel strength. The fundamental reasons are: (1) The industry generally believes that UV cleaning only has a "cleaning" function. Its ability to introduce functional groups on the aluminum foil surface is weak and its effect is short-lived, which cannot meet the stringent requirements of battery-grade materials for interface stability; (2) Although plasma treatment can enhance surface roughness and polarity, its high-energy particles can easily cause local overheating of aluminum foil or uneven oxide layer. When used alone, the peel strength improvement is limited; (3) More importantly, if the two are simply used in series, the traditional understanding is that the active oxygen species (such as ozone and ·OH) generated by UV will rapidly decay or be adsorbed by the environment within a few minutes, and cannot form an effective synergy with the subsequent plasma treatment. This "time window failure" understanding has long hindered the application exploration of this combination. This application, by precisely controlling the time interval between UV cleaning and plasma activation within the aforementioned range, successfully introduces the physical etching and functional group enhancement effects of plasma-based graded treatment within the "active window" before the UV-activated layer decays. This achieves precise spatiotemporal coupling of "chemical activation" and "physical anchoring," thereby simultaneously improving hydrophilicity and peel strength. In other words, this application achieves a modification effect of "1+1>2." Single-step plasma treatment has advantages such as being green and environmentally friendly, operating at room temperature, and leaving no chemical residue. However, it suffers from problems such as limited process complexity, insufficient modification depth, limited improvement in hydrophilicity and peel strength, and unsatisfactory treatment results, making it difficult to meet the stringent requirements of high-rate and long-cycle sodium-ion batteries.Therefore, this application employs a plasma-stage treatment process, namely plasma activation and plasma modification. The discharge power of plasma modification is controlled to be greater than that of plasma activation. This allows for the activation of the current collector surface with a lower discharge power, initially introducing polar functional groups and enhancing its surface energy, laying the foundation for subsequent deep modification. Subsequently, high-power plasma modification (200-400W) achieves deeper ion bombardment and free radical reactions on the current collector surface. This significantly increases the density of hydrophilic functional groups such as hydroxyl and carboxyl groups and induces the formation of a nanoscale rough structure, thereby synergistically enhancing the surface hydrophilicity of the current collector and the adhesion of the coating. Finally, the modified layer structure is stabilized through curing to prevent functional group failure. In summary, the surface modification method of this application is simple, environmentally friendly, leaves no chemical residue, and exhibits good stability. The surface-modified current collector obtained can solve the problems of poor slurry wetting and easy coating peeling during the coating process. The modification effect is stable and long-lasting, thus better adapting to the coating process requirements of sodium-ion batteries. This is conducive to achieving the high-rate and long-cycle performance goals of sodium-ion batteries, and also provides a green and efficient technical solution for interface optimization of current collectors used in sodium-ion batteries. In addition, the surface modification method of this application does not require large-scale modification of existing production lines, making it easy to achieve industrial-scale application.

[0021] In one embodiment of this application, the surface modification method further includes: pre-treating the initial current collector to obtain a pre-treated current collector; sequentially performing ultraviolet cleaning, plasma activation, plasma modification, and curing on the pre-treated current collector to obtain a surface-modified current collector; wherein the surface pre-treatment process includes sequential pre-cleaning and drying; pre-cleaning the initial current collector with a pre-cleaning solution, the pre-cleaning solution being a mixed solution of anhydrous ethanol and distilled water; the volume ratio of anhydrous ethanol to distilled water being 1:1~2, and the temperature of the pre-cleaning solution being 25~35℃; performing ultrasound during the pre-cleaning process, the ultrasound power being 200~300W; the pre-cleaning time being 15~30min; the drying temperature being 50~80℃, the drying vacuum degree being -0.08~-0.1MPa, and the drying time being 10~20min.

[0022] Pre-treating the initial current collector with the aforementioned surface treatment helps to remove adsorbed organic oil and loose oxides from the aluminum foil surface. Simultaneously, drying under the aforementioned conditions helps to remove surface moisture and volatile impurities, thereby improving the surface cleanliness and uniformity of the current collector. This provides a clean and uniformly active substrate for subsequent UV cleaning and plasma treatment. Preferably, the type and temperature of the pre-cleaning solution, as well as the ultrasonic power, are within the aforementioned ranges to improve the cleaning effect.

[0023] In one embodiment of this application, the ultraviolet cleaning process includes: placing the surface-pretreated current collector in an ultraviolet cleaning device, the ultraviolet cleaning device having an ultraviolet lamp, adjusting the vertical distance between the surface-pretreated current collector and the ultraviolet lamp to 8~20mm, preferably 12~16mm, turning on the ultraviolet lamp, and using ultraviolet light with a wavelength of 185~254nm to perform ultraviolet cleaning on the surface-pretreated current collector to obtain an ultraviolet-cleaned current collector; when the ultraviolet lamp is a dual-wavelength ultraviolet lamp, the wavelengths of the ultraviolet light from the dual-wavelength ultraviolet lamp are 185nm and 254nm; and / or, the power of ultraviolet cleaning is 80~150W, preferably 100~120W, and the ultraviolet cleaning time is 20~60min, preferably 30~45min.

[0024] Preferably controlling the vertical distance between the initial current collector and the UV lamp, and using UV light with a wavelength of 185~254nm for irradiation, helps to efficiently decompose organic pollutants on the current collector surface and stably introduce hydrophilic functional groups. 185nm UV light can excite oxygen in the air to generate highly reactive ozone, deeply oxidizing and removing surface grease and residual organic matter; 254nm UV light can promote the formation of polar functional groups such as CO and C=O on the surface. The two work synergistically to improve the surface energy and wettability of the current collector. Preferably controlling the vertical distance between the initial current collector and the UV lamp within the above range helps to ensure that the UV light intensity is evenly distributed on the surface of the current collector, reducing incomplete cleaning due to energy attenuation caused by excessive distance, or localized overheating and surface damage caused by excessively close distance. Using a dual-wavelength composite light source (185nm and 254nm) for the UV lamps and controlling the power and time of UV cleaning within the aforementioned range helps to achieve precise matching between energy input and reaction kinetics. This reduces fluctuations in the effect of subsequent plasma modification caused by insufficient processing power and time, and also reduces the risk of excessive surface oxide layer thickness or structural damage due to over-processing. This provides a stable and uniform active substrate for subsequent high-power plasma modification. The UV cleaning conditions, combined with the time interval between UV cleaning and plasma activation, help to better introduce the physical etching and functional group enhancement effects of plasma-based graded treatment within the "active window" before the UV-activated layer decays, thereby further improving the hydrophilicity and peel strength of the current collector.

[0025] In one embodiment of this application, the plasma activation process includes: placing the UV-cleaned current collector in the reaction chamber of a plasma processing device, the plasma processing device including a plasma spray gun and a plasma generator; adjusting the vertical distance between the UV-cleaned current collector and the plasma spray gun to 5-15 mm, preferably 8-12 mm; evacuating to a vacuum degree of 100-1000 Pa; introducing a mixed gas into the reaction chamber; turning on the plasma generator; and performing plasma activation on the UV-cleaned current collector to obtain a plasma-activated current collector; wherein the mixed gas includes a first gas and a second gas; the first gas is argon and / or nitrogen; the second gas is oxygen and / or carbon dioxide; the flow rate of the mixed gas is 10-50 sccm; and the volume ratio of the first gas to the second gas is 5-10:1.

[0026] By placing the UV-cleaned current collector in a reaction chamber equipped with a plasma spray gun, and precisely controlling its vertical distance from the plasma spray gun and maintaining the vacuum level within the chamber within the aforementioned range, followed by the introduction of a mixed gas of the aforementioned types and flow rates, the surface of the UV-cleaned current collector is gently and selectively activated, promoting the formation of oxygen-containing polar functional groups (such as hydroxyl and carboxyl groups), thereby enhancing the hydrophilicity of the current collector surface and providing a good foundation for subsequent high-power plasma modification. Preferably, the first gas is a combination of argon and nitrogen in a volume ratio of 1 to 2:1, and the second gas (reactant gas) is oxygen.

[0027] In one embodiment of this application, the discharge power of plasma activation is 50~200W, preferably 100~150W, the frequency of plasma activation is 13.56~27.12MHz, and the time of plasma activation is 30~120s, preferably 60~90s.

[0028] Preferably, the discharge power, frequency, and time of plasma activation are within the above range, which helps to gently introduce hydrophilic functional groups such as hydroxyl and carboxyl groups without damaging the current collector matrix, and remove residual contaminants on its surface, so that the current collector surface changes from an inert hydrophobic state to a high-energy active state.

[0029] In one embodiment of this application, the discharge power of plasma modification is 250~350W, the processing frequency of plasma modification is 27.12~40.68MHz, preferably 30~35MHz, and the processing time of plasma modification is 60~300s, preferably 120~240s.

[0030] After plasma activation, the cavity pressure and flow rate of the mixed gas in the plasma treatment equipment are kept constant, and plasma modification continues. Preferably, the discharge power, frequency, and time of plasma modification are within the aforementioned ranges. This facilitates the in-situ construction of a micron-nano composite rough structure on the surface of the activated current collector through high-energy ion bombardment, thereby achieving a dual enhancement mechanism of "chemical bonding + mechanical interlocking" between the active material and the current collector. The two-stage treatment of plasma activation and plasma modification forms a gradient coupling in terms of time and energy, which helps to reduce the problems of excessive surface oxidation, functional group destruction, and substrate damage caused by direct high-power treatment. This simultaneously achieves hydrophilicity, improves the adhesion of the active material, and minimizes damage to the current collector.

[0031] The discharge power of plasma modification is 100-200W higher than that of plasma activation, which helps to achieve precise etching and anchoring of the micro-nano-scale rough structure on the surface without destroying the introduced hydrophilic functional groups, thereby synergistically improving the peel strength and hydrophilic stability.

[0032] In one embodiment of this application, the curing temperature is 25~40℃, the curing relative humidity is 40~60%, and the curing time is 2~6h.

[0033] After plasma modification, the plasma generator is turned off, and mixed gas is continuously introduced until the gas pressure in the reaction chamber returns to normal. The current collector is then removed and placed in a constant temperature and humidity chamber for curing. Preferably controlling the curing temperature, relative humidity, and time within the aforementioned ranges helps the hydrophilic functional groups introduced by the synergistic plasma treatment and UV cleaning to complete molecular rearrangement and hydrogen bond network construction, thereby achieving thermodynamic stability of the surface chemical state. Simultaneously, appropriate water molecule intercalation promotes microstructure relaxation, eliminates plasma-induced surface stress, and blocks the adsorption of environmental pollutants to active sites, thus improving the long-term stability of the modification effect.

[0034] In one embodiment of this application, the thickness of the initial current collector is 10~50μm, and the purity of the initial current collector is ≥99.7%.

[0035] Optimizing the initial current collector's thickness and purity within the aforementioned range helps it possess sufficient mechanical strength under high-energy plasma to resist the risk of local perforation and deformation. Simultaneously, the extremely low impurity content significantly improves the uniformity of the surface reaction and the efficiency of active site generation. This thickness range avoids structural failure caused by thermal stress concentration in thin materials during high-power processing, while ensuring that the plasma-modified layer can fully penetrate into the surface microstructure. Optimizing the initial current collector's purity within the aforementioned range helps to effectively suppress the interference of metal impurities such as iron and copper on functional groups such as oxygen and nitrogen, thereby simultaneously optimizing surface hydrophilicity and the active bonding interface. Ultimately, this significantly improves the peel strength between the current collector and the active material, providing a reliable guarantee for the interface stability of sodium-ion batteries under high-rate cycling.

[0036] In another typical embodiment of this application, a current collector is provided, which is prepared by the surface modification method described above.

[0037] The current collector prepared by the above surface modification method can reduce the surface contact angle to below 15°, increase the peel strength by more than 80%, exhibit excellent hydrophilicity, strong adhesion to active materials, and no damage to the substrate. This effectively improves the interfacial compatibility between the current collector and the active materials of sodium-ion batteries, reduces interfacial impedance, and thus enhances battery performance. (Image: Current collector after surface modification)

[0038] In another typical embodiment of this application, an application of a current collector in a battery is provided, wherein the current collector is the aforementioned current collector.

[0039] The current collector of this application can improve the long cycle performance, cycle life and safety performance of the battery, and is especially suitable for sodium-ion battery systems.

[0040] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0041] Example 1

[0042] 1) Surface pretreatment: Industrial pure aluminum foil with a thickness of 20 μm and a purity of 99.8% was selected as the initial current collector. A mixed solution of anhydrous ethanol and distilled water (volume ratio 1:1.5) was used for ultrasonic pre-cleaning at 30℃ and 250W for 20 min. Subsequently, it was placed in a vacuum drying oven and dried at 60℃ and a vacuum of -0.09MPa for 15 min to obtain the surface-pretreated current collector.

[0043] 2) UV cleaning: Place the surface pretreated current collector into the UV cleaning equipment, adjust the vertical distance between the surface pretreated current collector and the UV lamp (dual wavelength 185nm+254nm) to 14mm, turn on the UV lamp, and perform UV cleaning on the surface pretreated current collector. Set the power to 110W and the time to 35min to obtain the UV-cleaned current collector.

[0044] 3) Plasma Activation: After UV cleaning, the UV-cleaned current collector is placed into the reaction chamber of the plasma treatment equipment for plasma activation within 8 minutes to obtain a plasma-activated current collector. Specifically, the vertical distance between the UV-cleaned current collector and the plasma nozzle is adjusted to 10 mm, and a vacuum of 500 Pa is evacuated. A mixture of argon (first gas) and oxygen (second gas) is introduced into the reaction chamber at a volume ratio of 8:1 and a flow rate of 30 sccm. After stabilization, the plasma generator is turned on to activate the UV-cleaned current collector. The discharge power is set to 120 W, the frequency to 13.56 MHz, and the time to 80 s to complete the plasma activation.

[0045] 4) Plasma modification: After plasma activation, keep the cavity pressure and the flow rate of the mixed gas constant, adjust the discharge power to 300W, the frequency to 27.12MHz, and the time to 180s to complete the plasma modification and obtain the plasma-modified current collector.

[0046] 5) Curing: After plasma modification is completed, the plasma generator is turned off, and the mixed gas is continued to be introduced to atmospheric pressure. The plasma-modified current collector is taken out and placed in a constant temperature and humidity chamber. It is cured for 3.5 hours at 32℃ and 55% relative humidity to obtain the surface-modified current collector.

[0047] Example 2

[0048] 1) Surface pretreatment: A 10μm thick, 99.7% pure industrial-grade aluminum foil was selected as the initial current collector. A mixed solution of anhydrous ethanol and distilled water (volume ratio 1:1) was used for ultrasonic pre-cleaning at 25℃ and 200W for 15 minutes. Subsequently, it was placed in a vacuum drying oven and dried at 50℃ and a vacuum of -0.08MPa for 10 minutes to obtain the pretreated current collector.

[0049] 2) UV cleaning: Place the surface pretreated current collector into the UV cleaning equipment, adjust the vertical distance between the surface pretreated current collector and the UV lamp (dual wavelength 185nm+254nm) to 12mm, turn on the UV lamp, and perform UV cleaning on the surface pretreated current collector. Set the power to 100W and the time to 30min to obtain the UV-cleaned current collector.

[0050] 3) Plasma Activation: After UV cleaning, the UV-cleaned current collector is placed into the reaction chamber of the plasma treatment equipment for plasma activation within 6 minutes to obtain a plasma-activated current collector. Specifically, the vertical distance between the UV-cleaned current collector and the plasma nozzle is adjusted to 8 mm, and a vacuum of 300 Pa is evacuated. A mixture of nitrogen (first gas) and oxygen (second gas) is introduced into the reaction chamber at a volume ratio of 5:1 and a flow rate of 10 sccm. After stabilization, the plasma generator is activated to perform plasma activation on the UV-cleaned current collector. The discharge power is set to 100 W, the frequency to 27.12 MHz, and the time to 60 s to complete the plasma activation.

[0051] 4) Plasma modification: After plasma activation, keep the cavity pressure and the flow rate of the mixed gas constant, adjust the discharge power to 250W, the frequency to 33.9MHz, and the time to 120s to complete the plasma modification and obtain the plasma-modified current collector.

[0052] 5) Curing: After plasma modification is completed, the plasma generator is turned off, and the mixed gas is continued to be introduced to atmospheric pressure. The plasma-modified current collector is taken out and placed in a constant temperature and humidity chamber. It is cured for 3 hours at 30℃ and 50% relative humidity to obtain the surface-modified current collector.

[0053] Example 3

[0054] 1) Surface pretreatment: Industrial pure aluminum foil with a thickness of 50 μm and a purity of 99.9% was selected as the initial current collector. A mixed solution of anhydrous ethanol and distilled water (volume ratio 1:2) was used for ultrasonic pre-cleaning at 35℃ and 300W for 15 min. Subsequently, it was placed in a vacuum drying oven and dried at 80℃ and a vacuum degree of -0.1MPa for 10 min to obtain the surface-pretreated current collector.

[0055] 2) UV cleaning: Place the surface pretreated current collector into the UV cleaning equipment, adjust the vertical distance between the surface pretreated current collector and the UV lamp (dual wavelength 185nm+254nm) to 16mm, turn on the UV lamp, and perform UV cleaning on the surface pretreated current collector. Set the power to 120W and the time to 45min to obtain the UV-cleaned current collector.

[0056] 3) Plasma Activation: After UV cleaning, the UV-cleaned current collector is placed into the reaction chamber of the plasma treatment equipment for plasma activation within 10 minutes to obtain a plasma-activated current collector. Specifically, the vertical distance between the UV-cleaned current collector and the plasma nozzle is adjusted to 12 mm, and a vacuum of 800 Pa is evacuated. A mixture of a first gas (argon and nitrogen in a 1:1 volume ratio) and a second gas (oxygen) is introduced into the reaction chamber, with a volume ratio of 8:1 and a flow rate of 50 sccm. After stabilization, the plasma generator is turned on to activate the UV-cleaned current collector. The discharge power is set to 150 W, the frequency to 13.56 MHz, and the time to 90 s to complete the plasma activation.

[0057] 4) Plasma modification: After plasma activation, keep the cavity pressure and the flow rate of the mixed gas constant, adjust the discharge power to 350W, the frequency to 40.68MHz, and the time to 240s to complete the plasma modification and obtain the plasma-modified current collector.

[0058] 5) Curing: After plasma modification is completed, the plasma generator is turned off, and the mixed gas is continued to be introduced to atmospheric pressure. The plasma-modified current collector is taken out and placed in a constant temperature and humidity chamber. It is cured for 4 hours at 35℃ and 60% relative humidity to obtain the surface-modified current collector.

[0059] Example 4

[0060] The difference from Example 1 is that the vertical distance between the current collector and the UV lamp after surface pretreatment is 12mm, the power of UV cleaning is 120W, the UV cleaning time is 30min, and after UV cleaning is completed, the UV-cleaned current collector is placed into the reaction chamber of the plasma treatment equipment for plasma activation within 5min, and finally the surface-modified current collector is obtained.

[0061] Example 5

[0062] The difference from Example 1 is that the vertical distance between the current collector and the ultraviolet lamp after surface pretreatment is 25mm, the ultraviolet light wavelength of the ultraviolet lamp is 185nm, the power of ultraviolet cleaning is 60W, the ultraviolet cleaning time is 90min, and after ultraviolet cleaning is completed, the ultraviolet-cleaned current collector is placed into the reaction chamber of the plasma treatment equipment within 10min for plasma activation, and finally the surface-modified current collector is obtained.

[0063] Example 6

[0064] The difference from Example 1 is that the plasma activation discharge power is 100W, the plasma activation frequency is 20.25MHz, and the plasma activation time is 90s, finally obtaining the surface-modified current collector.

[0065] Example 7

[0066] The difference from Example 1 is that the plasma activation discharge power is 30W, the plasma activation frequency is 10.15MHz, and the plasma activation time is 150s, finally obtaining the surface-modified current collector.

[0067] Example 8

[0068] The difference from Example 1 is that the discharge power of plasma modification is 350W, the processing frequency of plasma modification is 40.68MHz, and the processing time of plasma modification is 120s, finally obtaining the surface-modified current collector.

[0069] Example 9

[0070] The difference from Example 1 is that the discharge power of plasma modification is 400W, the processing frequency of plasma modification is 45.25MHz, and the processing time of plasma modification is 30s, finally obtaining the surface-modified current collector.

[0071] Example 10

[0072] The difference from Example 1 is that the discharge power of plasma activation is 150W, and the discharge power of plasma modification is 250W. The discharge power of plasma modification is 100W higher than that of plasma activation, and the surface-modified current collector is finally obtained.

[0073] Example 11

[0074] The difference from Example 1 is that the discharge power of plasma activation is 200W, and the discharge power of plasma modification is 250W. The discharge power of plasma modification is 50W higher than that of plasma activation, and the surface-modified current collector is finally obtained.

[0075] Example 12

[0076] The difference from Example 1 is that the curing temperature is 35°C, the curing relative humidity is 50%, and the curing time is 3 hours, resulting in a surface-modified current collector.

[0077] Example 13

[0078] The difference from Example 1 is that the curing temperature is 45°C, the curing relative humidity is 30%, and the curing time is 1 hour, finally obtaining the surface-modified current collector.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that the initial current collector industrial pure aluminum foil was placed in a 5% sodium hydroxide solution and etched at 60°C for 10 minutes. After being taken out, it was rinsed with distilled water and vacuum dried to obtain the surface-modified current collector.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that UV cleaning is not performed to obtain the surface-modified current collector.

[0083] Comparative Example 3

[0084] The difference from Example 1 is that plasma activation and plasma modification are not performed to obtain a surface-modified current collector.

[0085] Comparative Example 4

[0086] The difference from Example 1 is that plasma activation is not performed, the discharge power of plasma modification is 450W, and the surface-modified current collector is finally obtained.

[0087] Comparative Example 5

[0088] The difference from Example 1 is that the discharge power of plasma activation is 200W, and the discharge power of plasma modification is 150W, ultimately resulting in a surface-modified current collector.

[0089] Comparative Example 6

[0090] The difference from Example 1 is that after UV cleaning for 15 minutes, the UV-cleaned current collector is placed in the reaction chamber of the plasma treatment equipment for plasma activation, and finally the surface-modified current collector is obtained.

[0091] Test method:

[0092] Contact angle test of current collector: The current collector after surface modification was tested using a contact angle tester.

[0093] Peel strength test between surface-modified current collector and positive electrode active layer: The peel strength of the tape coated with positive electrode current collector at 90° was tested using a tensile testing machine.

[0094] The test results are shown in Table 1.

[0095] Table 1

[0096]

[0097] As shown above, Comparative Example 1, using existing chemical etching methods for surface modification, resulted in slight corrosion marks on the aluminum foil surface, a 12.3% decrease in mechanical strength, and the generation of a large amount of alkaline wastewater, polluting the environment. When used as a current collector in the fabrication of sodium-ion batteries, after 500 1C charge-discharge cycles, the capacity retention was only 68.7%, and the battery's internal resistance increased abnormally, indicating a problem with chemical residues affecting the battery's electrochemical performance.

[0098] Comparative Example 2, which did not undergo UV cleaning, suffered from insufficient surface cleanliness, a lack of initial active sites, difficulty in fully utilizing plasma treatment, inadequate surface hydrophilic modification, low introduction of functional groups, weak adhesion between the coating and the current collector, limited improvement in peel strength, and a tendency for interfacial debonding during cycling.

[0099] Comparative Example 3, without plasma activation and modification, exhibits low surface polarity and poor wettability of the current collector, making it prone to phenomena such as pinholes and foil exposure during slurry coating. The coating adhesion is extremely poor, and the interfacial impedance is high, resulting in a significant deterioration in the battery's rate performance and cycle stability.

[0100] Comparative Example 4 did not undergo plasma activation, and the discharge power of plasma modification was relatively high. Direct bombardment by high-energy plasma could easily cause excessive etching and local thermal damage to the aluminum foil surface, resulting in uneven oxide layer and increased structural defects. Although it had a certain hydrophilic effect, its mechanical properties were damaged, its interface stability was poor, and long-term cycling could easily cause the coating to peel off.

[0101] In Comparative Example 5, the discharge power of plasma activation was higher than that of plasma modification, and the discharge power of plasma modification was lower. This resulted in excessive surface activation and insufficient deep modification, uneven distribution of functional groups, shallow modified layer with poor stability, short-lasting improvement in hydrophilicity, and failure to achieve optimal peel strength, thus failing to meet the requirements for long-term interfacial bonding.

[0102] In Comparative Example 6, the time interval between plasma activation and UV cleaning exceeded 10 minutes. The active sites and oxygen-containing functional groups generated by UV activation rapidly decayed and became inactive, failing to form an effective spatiotemporal synergy with subsequent plasma treatment. The interface coupling effect disappeared, and the improvement in hydrophilicity and peel strength was significantly reduced. The modification effect was close to that of a single treatment, making it difficult to achieve a synergistic effect of 1+1>2.

[0103] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0104] The surface modification method of this application, through the synergistic effect of ultraviolet cleaning, plasma classification treatment, and curing, can effectively remove impurities such as oil stains from the surface of current collectors, such as aluminum foil, and construct a rough hydrophilic interface. This achieves a simultaneous and significant improvement in the hydrophilicity and peel strength of the current collector surface for sodium-ion batteries, all without the need for highly corrosive chemical reagents. Specifically, ultraviolet cleaning utilizes the decomposition effect of high-energy ultraviolet photons to effectively remove organic contaminants from the current collector surface, while simultaneously introducing a small number of hydrophilic functional groups to the surface, thereby improving the hydrophilicity of the current collector. Ultraviolet cleaning does not damage the substrate, causes no secondary pollution, and does not affect the electrochemical performance of sodium-ion batteries. However, if ultraviolet cleaning is used alone, it can only remove surface contaminants and slightly improve hydrophilicity, but cannot change the microstructure of the current collector surface, thus making it difficult to improve its peel strength. Furthermore, the long-term effectiveness of the modification is poor, failing to meet the long-term charge-discharge requirements of sodium-ion batteries. Although UV cleaning technology has been widely used for surface cleaning of semiconductors and optical devices, and plasma treatment is also used for metal surface activation, in the field of aluminum foil current collectors for sodium-ion batteries, the two have never been used together to synergistically improve hydrophilicity and peel strength. The fundamental reasons are: (1) The industry generally believes that UV cleaning only has a "cleaning" function. Its ability to introduce functional groups on the aluminum foil surface is weak and its effect is short-lived, which cannot meet the stringent requirements of battery-grade materials for interface stability; (2) Although plasma treatment can enhance surface roughness and polarity, its high-energy particles can easily cause local overheating of aluminum foil or uneven oxide layer. When used alone, the peel strength improvement is limited; (3) More importantly, if the two are simply used in series, the traditional understanding is that the active oxygen species (such as ozone and ·OH) generated by UV will rapidly decay or be adsorbed by the environment within a few minutes, and cannot form an effective synergy with the subsequent plasma treatment. This "time window failure" understanding has long hindered the application exploration of this combination. This application, by precisely controlling the time interval between UV cleaning and plasma activation within the aforementioned range, successfully introduces the physical etching and functional group enhancement effects of plasma-based graded treatment within the "active window" before the UV-activated layer decays. This achieves precise spatiotemporal coupling of "chemical activation" and "physical anchoring," thereby simultaneously improving hydrophilicity and peel strength. In other words, this application achieves a modification effect of "1+1>2." Single-step plasma treatment has advantages such as being green and environmentally friendly, operating at room temperature, and leaving no chemical residue. However, it suffers from problems such as limited process complexity, insufficient modification depth, limited improvement in hydrophilicity and peel strength, and unsatisfactory treatment results, making it difficult to meet the stringent requirements of high-rate and long-cycle sodium-ion batteries.Therefore, this application employs a plasma-stage treatment process, namely plasma activation and plasma modification. The discharge power of plasma modification is controlled to be greater than that of plasma activation. This allows for the activation of the current collector surface with a lower discharge power, initially introducing polar functional groups and enhancing its surface energy, laying the foundation for subsequent deep modification. Subsequently, high-power plasma modification (200-400W) achieves deeper ion bombardment and free radical reactions on the current collector surface. This significantly increases the density of hydrophilic functional groups such as hydroxyl and carboxyl groups and induces the formation of a nanoscale rough structure, thereby synergistically enhancing the surface hydrophilicity of the current collector and the adhesion of the coating. Finally, the modified layer structure is stabilized through curing to prevent functional group failure. In summary, the surface modification method of this application is simple, environmentally friendly, leaves no chemical residue, and exhibits good stability. The surface-modified current collector obtained can solve the problems of poor slurry wetting and easy coating peeling during the coating process. The modification effect is stable and long-lasting, thus better adapting to the coating process requirements of sodium-ion batteries. This is conducive to achieving the high-rate and long-cycle performance goals of sodium-ion batteries, and also provides a green and efficient technical solution for interface optimization of current collectors used in sodium-ion batteries. In addition, the surface modification method of this application does not require large-scale modification of existing production lines, making it easy to achieve industrial-scale application.

[0105] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for surface modification of a current collector, characterized in that, The surface modification method includes: sequentially performing ultraviolet cleaning, plasma activation, plasma modification and curing on the initial current collector to obtain a surface-modified current collector; Wherein, the initial current collector includes aluminum foil; the discharge power of the plasma modification is greater than the discharge power of the plasma activation; the discharge power of the plasma modification is 200~400W; The time interval between plasma activation and ultraviolet cleaning is ≤10 min.

2. The surface modification method according to claim 1, characterized in that, The surface modification method further includes: pre-treating the initial current collector to obtain a pre-treated current collector; and sequentially performing ultraviolet cleaning, plasma activation, plasma modification, and curing on the pre-treated current collector to obtain the surface-modified current collector. The surface pretreatment process includes sequential pre-cleaning and drying; The initial current collector is pre-cleaned using a pre-cleaning solution, which is a mixture of anhydrous ethanol and distilled water; the volume ratio of anhydrous ethanol to distilled water is 1:1~2, and the temperature of the pre-cleaning solution is 25~35℃; ultrasonication is performed during the pre-cleaning process, and the ultrasonic power is 200~300W; the pre-cleaning time is 15~30min. The drying temperature is 50~80℃, the drying vacuum degree is -0.08~-0.1MPa, and the drying time is 10~20min.

3. The surface modification method according to claim 2, characterized in that, The ultraviolet cleaning process includes: placing the surface-pretreated current collector in an ultraviolet cleaning device, the ultraviolet cleaning device having an ultraviolet lamp tube, adjusting the vertical distance between the surface-pretreated current collector and the ultraviolet lamp tube to 8~20mm, turning on the ultraviolet lamp tube, and using ultraviolet light with a wavelength of 185~254nm to perform ultraviolet cleaning on the surface-pretreated current collector to obtain an ultraviolet-cleaned current collector; When the ultraviolet lamp is a dual-wavelength ultraviolet lamp, the wavelengths of the ultraviolet light emitted by the dual-wavelength ultraviolet lamp are 185nm and 254nm. And / or, the power of the ultraviolet cleaning is 80~150W, and the ultraviolet cleaning time is 20~60min.

4. The surface modification method according to claim 3, characterized in that, The plasma activation process includes: placing the UV-cleaned current collector in the reaction chamber of a plasma processing device, which includes a plasma spray gun and a plasma generator; adjusting the vertical distance between the UV-cleaned current collector and the plasma spray gun to 5-15 mm; evacuating to a vacuum level of 100-1000 Pa; introducing a mixed gas into the reaction chamber; turning on the plasma generator; and performing plasma activation on the UV-cleaned current collector to obtain a plasma-activated current collector. The mixed gas comprises a first gas and a second gas; the first gas is argon and / or nitrogen; the second gas is oxygen and / or carbon dioxide; the flow rate of the mixed gas is 10~50 sccm, and the volume ratio of the first gas to the second gas is 5~10:

1.

5. The surface modification method according to any one of claims 1 to 4, characterized in that, The plasma activation discharge power is 50~200W, the plasma activation frequency is 13.56~27.12MHz, and the plasma activation time is 30~120s.

6. The surface modification method according to any one of claims 1 to 4, characterized in that, The discharge power of the plasma modification is 250~350W, the processing frequency of the plasma modification is 27.12~40.68MHz, and the processing time of the plasma modification is 60~300s.

7. The surface modification method according to any one of claims 1 to 4, characterized in that, The curing temperature is 25~40℃, the curing relative humidity is 40~60%, and the curing time is 2~6h.

8. The surface modification method according to any one of claims 1 to 4, characterized in that, The initial current collector has a thickness of 10~50μm and a purity of ≥99.7%.

9. A current collector, characterized in that, The current collector is prepared by the surface modification method according to any one of claims 1 to 8.

10. An application of a current collector in a battery, characterized in that, The current collector is the current collector as described in claim 9.

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