Surface-modified anode for an aqueous zinc battery by plasma treatment and method for preparing the same

Abstract

The present invention relates to a negative electrode for an aqueous zinc battery whose surface is modified by plasma treatment and a method for manufacturing the same. More specifically, it relates to a negative electrode stabilization technology in which the surface of a zinc foil used as a negative electrode material is directly modified through a plasma process to remove surface contaminants and oxide layers, and to form a uniform nanoparticle layer on the surface. A zinc negative electrode treated by this process effectively suppresses dendrite growth, thereby improving Coulomb efficiency and lifespan characteristics, and thus enabling the realization of an aqueous zinc battery with improved performance, reliability, and stability.

Description

Technology Field

[0001] The present invention relates to a negative electrode for an aqueous zinc battery with a surface modified by plasma treatment and a method for manufacturing the same. More specifically, it relates to a technology for improving the performance of a battery by plasma treating the surface of a zinc metal foil, which is the negative electrode of an aqueous zinc battery, to flatten the surface and forming a uniform layer of nanoparticles on the surface to suppress dendrite growth. Background Technology

[0002] Aqueous zinc batteries are attracting attention in the fields of energy storage systems (ESS) and eco-friendly secondary batteries due to their advantages, such as high theoretical capacity, excellent safety, and relatively low manufacturing costs. In these aqueous zinc batteries, zinc foil is widely used as a negative electrode material, but it is known that problems such as dendrite growth and hydrogen evolution (HER) occur due to the repeated plating / skinning reaction of zinc during the charging and discharging process.

[0003] To address these problems, various technologies have been proposed in the past. For example, attempts have been reported to suppress dendrite growth by controlling the zinc grain structure or relieving internal stress through high-temperature heat treatment processes. However, such high-temperature heat treatment processes require temperatures exceeding several hundred degrees, resulting in high energy consumption; furthermore, there is a concern that excessive recrystallization or surface oxidation of zinc may actually degrade electrode performance. Additionally, high-temperature processes present limitations, such as difficulty in applying them to large-area zinc foils and increased process costs and manufacturing complexity.

[0004] Meanwhile, coating processes for forming protective or functional layers on the surface of zinc foil have also been widely studied. These coating processes aim to physically inhibit dendrite growth or mitigate direct contact with the electrolyte by coating the electrode surface using polymers, carbon, ceramics, or inorganic compounds. However, the coating layer may crack or peel during repeated plating and stripping processes, and there are limitations such as performance variations between electrodes due to non-uniformity of coating thickness. Furthermore, the coating process requires additional manufacturing steps and process control, which reduces productivity, and it is difficult to rule out the possibility of side reactions caused by residual solvents or chemicals.

[0005] As such, despite their respective advantages, conventional technologies simultaneously contain limitations such as energy consumption, process complexity, reduced long-term reliability, and difficulties in large-area application.

[0006] Therefore, regarding zinc foil used as the anode in aqueous zinc batteries, there is a need for research and development on a new approach that can simultaneously improve process efficiency and battery performance while overcoming the limitations of existing technology. Prior art literature

[0007] Korean Published Patent No. 10-2025-0059051, Korean Published Patent No. 10-2023-0080868, Korean Registered Patent No. 10-2872098 The problem to be solved

[0008] The objective of the present invention is to provide an efficient cathode stabilization technology for improving the performance and lifespan characteristics of aqueous zinc batteries. means of solving the problem

[0009] To achieve the above objective, the present invention provides a negative electrode for a water-based zinc battery, wherein the negative electrode comprises a sheet-shaped zinc (Zn) foil; at least one surface of the zinc foil is surface modified by argon (Ar) plasma treatment alone without including a separate coating process or chemical treatment process, so that a nanoparticle layer comprising zinc nanoparticles with an average particle size of 25 to 40 nm is formed on the surface of the metal foil, and the contact angle of the plasma-treated negative electrode is 15 to 30°.

[0010] In addition, the present invention provides a water-based zinc battery comprising: an anode; a cathode for the water-based zinc battery; a separator located between the anode and the cathode; and a water-based electrolyte.

[0011] In addition, the present invention provides a method for manufacturing a negative electrode for an aqueous zinc battery, comprising: (A) a step of preparing a zinc (Zn) foil on a sheet; and (B) a step of modifying the surface by irradiating at least one surface of the zinc foil with an argon (Ar) plasma under vacuum conditions; wherein a nanoparticle layer comprising zinc nanoparticles having an average particle size of 25 to 40 nm is formed on the surface of the zinc foil by step (B), and a separate coating process or chemical treatment process is not performed after step (B). Effects of the invention

[0012] The negative electrode for an aqueous zinc battery according to the present invention structurally suppresses short circuits and lifespan degradation caused by dendrite growth, which were problematic in conventional zinc batteries, thereby enabling the realization of an aqueous zinc battery with a long lifespan and high reliability.

[0013] In addition, the plasma treatment process according to the present invention is easily expandable to a large-area treatment method, thereby securing the advantage of being commercialized in various fields ranging from small energy storage devices (ESS) to large-scale power storage systems. Brief explanation of the drawing

[0014] Figure 1 is a schematic diagram illustrating the sequence of the plasma surface treatment process of the present invention. Figure 2 is an image showing the state of the chamber before and after plasma treatment. Figure 3 is an image showing the SEM analysis results of the zinc foil surface compared before and after plasma treatment. Figure 4 is an image showing the EDS analysis results of the zinc foil surface compared before and after plasma treatment. Figure 5 is a table and images showing the results of confocal microscopy analysis of the zinc foil surface before and after plasma treatment. Figure 6 is a table and images showing the results of atomic force microscopy analysis of the zinc foil surface before and after plasma treatment. Figure 7 is an image showing the contact angle analysis results of zinc foil compared before and after plasma treatment. Figure 8 is a graph showing the XPS analysis results of zinc foil compared before and after plasma treatment. Figure 9 is a graph showing the results of low-angle X-ray diffraction analysis of zinc foil compared before and after plasma treatment. Figure 10 is a microscopic image of a symmetric cell (Zn∥Zn) assembled with zinc foil before and after plasma treatment, analyzed by charging and discharging in real time. Figure 11 is an SEM image showing the surface of a symmetric cell (Zn∥Zn) assembled with zinc foil before and after plasma treatment, and the performance evaluated according to the current rate. Figure 12 is a graph showing the results of a performance evaluation analysis of a symmetric cell (Zn∥Zn) assembled with zinc foil, comparing the results before and after plasma treatment. Figure 13 is a graph showing the performance evaluation analysis results of a full cell (Zn∥V₂O₅) assembled with zinc foil, comparing the results before and after plasma treatment. Specific details for implementing the invention

[0015] The present invention will be described in detail below with reference to the drawings.

[0017] One aspect of the present invention relates to a large-area stabilization technology for zinc metal foil, which is a negative electrode material for an aqueous zinc battery, and more specifically, to a technology that modifies the surface of a zinc foil through a plasma surface treatment method to form a uniform surface and improves the Coulomb efficiency and cycle life of an aqueous zinc battery.

[0019] More specifically, the present invention can provide a negative electrode for a water-based zinc battery, wherein the negative electrode comprises a metal foil containing zinc (Zn), and at least one surface of the metal foil is surface modified by plasma treatment.

[0021] The plasma treatment process according to the present invention can significantly reduce surface roughness and flatten the surface of a metal foil by removing micro-sized protrusions and holes present on the surface of the metal foil and removing contaminants and oxidized parts.

[0022] In particular, a nanoparticle layer containing zinc nanoparticles can be formed on the surface of the metal foil by this plasma treatment process. The nanoparticles uniformly deposited on the surface of the metal foil induce uniform nucleation of zinc ions to inhibit dendrite growth and reduce surface corrosion, thereby suppressing hydrogen generation and byproduct formation, which can improve Coulomb efficiency. Through this, an aqueous zinc battery with significantly improved lifespan characteristics can be realized.

[0024] In addition, the average particle size of the nanoparticles may be 10 to 500 nm. Preferably, it may be 10 to 100 nm, more preferably 15 to 50 nm, and most preferably 20 to 40 nm. If the average particle size of the nanoparticles is less than 10 nm, particle aggregation or electrochemical instability may increase, and if it exceeds 500 nm, the nucleation homogenization effect may decrease, which is undesirable as it may reduce the dendrite inhibition effect.

[0026] In the present invention, the metal foil may be one or more selected from the group consisting of zinc foil, alloy foil containing zinc as a main component, and a metal substrate having a zinc layer formed thereon.

[0027] Most preferably, pure zinc foil can be used. Since zinc foil is composed of high-purity metallic zinc, it enables uniform electrochemical reactions without unnecessary side reactions and is the most desirable electrode material as it simultaneously satisfies high theoretical capacity, excellent electrical conductivity, and mechanical stability.

[0029] In the present invention, the shape of the metal foil may be one or more selected from the group consisting of plate-shaped, sheet-shaped, and roll-shaped.

[0030] Most preferably, a sheet-shaped metal foil can be used. Sheet-shaped metal foil, particularly zinc foil, may be the most desirable as it induces stable electrochemical reactions due to its excellent uniform thickness and surface uniformity, and possesses excellent processability and electrical conductivity.

[0032] In addition, in the present invention, the contact angle of the plasma-treated cathode may be 10 to 40°. More preferably, it may be 30° or less.

[0033] The cathode surface-treated by the plasma treatment process according to the present invention may have a hydrophilic surface with a contact angle of 40° or less, more preferably a super-hydrophilic surface with a contact angle of 30° or less. As a result, the wettability of the electrolyte is improved, and the reaction at the electrode-electrolyte interface proceeds uniformly, thereby effectively suppressing dendrite growth and improving the lifespan and stability of the battery.

[0035] Although not explicitly stated in the following examples, when the conditions of the aqueous zinc battery negative electrode material were varied, it was confirmed that, unlike other conditions, when all of the following conditions were satisfied, in addition to the effect of suppressing dendrite growth and improving battery performance, the following heterogeneous effects were additionally observed.

[0036] Specifically, a zinc foil cathode under the following conditions can alleviate local potential concentration at the electrode-electrolyte interface and effectively suppress hydrogen evolution (HER) reactions apart from dendrite growth inhibition. This can additionally provide heterogeneous effects such as changes in electrolyte composition and reduced bubble accumulation.

[0037] In addition, it eliminates the need for a separate low-current activation process or repetitive formation cycles during the initial charge and discharge phases, or can significantly shorten them. Consequently, this reduces the processing time required for battery manufacturing, lowers energy consumption, and provides the effect of improving manufacturing efficiency in mass production processes.

[0038] In addition, a highly hydrophilic zinc foil surface with a contact angle of 30° or less induces rapid and uniform infiltration of the electrolyte, and a layer of zinc nanoparticles on the surface can increase the electrolyte diffusion pathway through a micro-roughness structure. As a result, the electrolyte is rapidly supplied across the entire electrode surface immediately after battery assembly or during the initial operation phase, providing heterogeneous effects such as reduced voltage drop during initial charging and discharging and stabilized output characteristics.

[0039] Looking at the conditions, the metal foil is a sheet-shaped zinc foil, the contact angle of the plasma-treated cathode is 15 to 30°, and the nanoparticle layer containing zinc nanoparticles with an average particle size of 25 to 40 nm is formed on the surface of the metal foil by the plasma treatment.

[0041] Another aspect of the present invention relates to an aqueous zinc battery comprising a negative electrode according to the present invention.

[0042] Specifically, an aqueous zinc battery may include a positive electrode; a negative electrode plasma-treated according to the present invention; a separator located between the positive electrode and the negative electrode; and an aqueous electrolyte.

[0044] An aqueous zinc battery comprising a negative electrode according to the present invention may be composed of conventional materials used in the art and is not particularly limited.

[0045] The positive electrode of an aqueous zinc battery may include an active material capable of reversibly inserting and deinserting zinc ions. For example, vanadium oxide (V2O5, V6O 13 It may include one or more selected from the group consisting of , or hydrates thereof), manganese oxide (MnO2), Prussian blue compounds and organic cathode materials.

[0046] The separator of an aqueous zinc battery is a porous separator that allows the movement of ions while electrically separating the positive and negative electrodes, and may be one or more selected from the group consisting of, for example, glass fiber separators, cellulose-based separators and polyolefin-based separators.

[0047] The aqueous electrolyte of an aqueous zinc battery is an aqueous solution containing zinc salts, and may include one or more zinc salts selected from the group consisting of, for example, zinc sulfate (ZnSO4), zinc trifluoromethanesulfonate (Zn(CF3SO3)2) and zinc perchlorate (Zn(ClO4)2).

[0049] Another aspect of the present invention relates to a method for manufacturing a plasma-surface-treated negative electrode for an aqueous zinc battery.

[0050] Specifically, the method may include: (A) a step of preparing a metal foil containing zinc (Zn); and (B) a step of modifying the surface by irradiating at least one surface of the metal foil with plasma.

[0051] Through plasma treatment according to the manufacturing method of the present invention, contaminants and oxide layers on the cathode surface are removed or reduced, and the surface condition is homogenized, thereby achieving the effect of improving interfacial stability with the aqueous electrolyte.

[0053] In particular, the present invention can manufacture a negative electrode for an aqueous zinc battery using only plasma treatment, without including a separate coating process or chemical treatment process after step (B).

[0054] Here, 'separate coating process' may include processes such as coating, spraying, dip coating, electroplating, electrodeposition, deposition (PVD / CVD), and sol-gel coating performed to form a coating layer composed of polymers, carbon, ceramics, metals, metal oxides, etc., on the surface of a metal foil, and 'chemical treatment process' may include processes that change the surface composition using liquid reactants or chemicals, such as acid / base cleaning, chemical etching, redox treatment, wet reaction using surface modifiers, and chemical reaction for introducing functional groups. However, the above enumeration is merely an example and is not limited thereto.

[0056] According to the manufacturing method of the present invention, the surface of the negative electrode for an aqueous zinc battery can be modified solely by plasma treatment without performing an additional separate treatment process after the plasma irradiation corresponding to step (B). That is, the present invention is characterized by directly modifying the surface of the metal foil itself, rather than a method of imparting function through the formation of an additional coating layer or a wet chemical reaction.

[0057] By eliminating separate coating or chemical treatment processes in this manner, side reactions caused by coating layer peeling, thickness variations, or residual chemicals can be suppressed, and manufacturing reproducibility and productivity can be improved through the simplification of process steps. Furthermore, since the manufacturing method of the present invention can be performed under low temperature and low energy conditions, it can be easily applied to continuous or mass production processes for large-area metal foils.

[0058] Accordingly, the cathode according to the present invention can reduce process costs and manufacturing difficulty while maintaining interface stability with the aqueous electrolyte, thereby effectively improving the industrial applicability of aqueous zinc batteries.

[0060] Step (A) of the present invention is a step of preparing a metal foil used as a negative electrode material for an aqueous zinc battery, which can then be prepared by cutting it into a size suitable for battery assembly.

[0061] The metal foil may be, for example, a pure zinc foil, an alloy foil containing zinc as a main component, or a metal substrate with a zinc layer formed thereon, but most preferably, a pure zinc foil may be used. In addition, the shape of the metal foil may be plate-like, sheet-like, or roll-like, and most preferably, it may be in the form of a sheet.

[0062] In addition, if necessary, a cleaning and drying process can be selected and performed to remove foreign substances remaining on the surface prior to plasma treatment.

[0064] Step (B) of the present invention is a plasma surface treatment step, and the surface of a prepared metal foil can be modified using a plasma irradiation device commonly used in the field.

[0066] In the manufacturing method of the present invention, the plasma may be applied under atmospheric pressure or vacuum conditions. More preferably, it may be applied under vacuum conditions. Under vacuum plasma conditions, the average free path of the reactive species increases, enabling uniform activation across the entire surface of the metal foil, and since a stable nanoparticle layer can be formed without excessive etching or local damage, it may be particularly more suitable for surface modification.

[0068] In the manufacturing method of the present invention, the plasma may be one or more selected from the group consisting of oxygen plasma, nitrogen plasma, argon plasma, and a mixture thereof. More preferably, nitrogen or argon plasma, and most preferably argon plasma, may be applied.

[0069] Argon (Ar) plasma is most advantageous for forming a uniform zinc nanoparticle layer by stably modifying only the surface of the metal foil without unnecessary chemical reactions, while oxygen (O2) plasma may cause zinc to oxidize and form ZnO, and nitrogen (N2) plasma may be less effective than argon plasma, so argon plasma may be the most suitable for surface treatment.

[0070] According to one embodiment, through zinc target sputtering (Zn target sputtering) in which an argon plasma is applied under vacuum conditions, plasma ions are collided with a target Zn metal to emit Zn atoms or clusters, and the emitted Zn can form zinc (Zn) nuclei in the form of nanoparticles rather than a continuous film by attaching and condensing on the surface of a metal foil. These nanoparticles can be uniformly deposited on the surface of the foil to form the nanoparticle layer of the present invention.

[0072] In the manufacturing method of the present invention, the plasma treatment can be performed under conditions of an output of 10 to 500 W and a treatment time of 1 to 60 minutes. More preferably, it can be performed under conditions of 100 to 300 W and 10 to 55 minutes, and most preferably under conditions of 150 to 250 W and 30 to 50 minutes.

[0073] When the plasma treatment conditions are less than 10W and 1 minute, the plasma density is insufficient, so the removal of oxide layers and organic contaminants is insufficient, and thus the surface modification effect may be insufficient; when the conditions are more than 500W and 60 minutes, the non-uniformity of the surface structure may increase due to excessive sputtering or etching, which is undesirable.

[0075] In the manufacturing method of the present invention, the plasma treatment can be performed at 20 to 100°C. More preferably, it can be performed at 20 to 80°C, and most preferably at 25 to 40°C.

[0076] If plasma treatment is performed at a temperature below 20°C, the activation reaction rate by plasma may be reduced, resulting in insufficient surface modification effect, and if it exceeds 100°C, recrystallization or oxidation reaction of the zinc surface may be promoted, which may increase structural non-uniformity and is undesirable.

[0078] In addition, the manufacturing method of the present invention may further include, after step (B), step (C) applying the metal foil obtained in step (B) as the negative electrode of a water-based zinc battery.

[0079] The metal foil obtained in step (B) above can be directly applied as the negative electrode of a water-based zinc battery without any additional processing.

[0081] The surface-modified metal foil obtained after step (B) of the present invention can be applied as a negative electrode to a battery configured as a zinc symmetric cell (Zn∥Zn) or a zinc full cell (Zn∥anode), and can be combined with an aqueous electrolyte and a separator to form a battery. The plasma-treated negative electrode according to the present invention can improve reaction uniformity at the electrode-electrolyte interface and improve the stability of the zinc plating / stripping reaction and the electrochemical performance of the battery.

[0082] Accordingly, the manufacturing method of the present invention, which further includes the above step (C), can continuously perform the manufacturing of the cathode and the application to the battery, thereby improving process efficiency and providing the advantage of simultaneously ensuring the performance and reliability of the aqueous zinc battery.

[0084] Although not explicitly stated in the following examples, as a result of verifying with different plasma treatment process conditions, when all of the following conditions were satisfied—unlike other conditions—in addition to the effect of suppressing dendrite growth and improving Coulomb efficiency and lifespan characteristics, the following heterogeneous effects were additionally observed.

[0085] Specifically, the cathode plasma-treated according to the following conditions has its surface modified without involving reactive gases or high-temperature heat treatment, thereby preventing excessive changes in the original chemical composition of the zinc foil. Accordingly, oxidation or performance degradation during long-term storage of the cathode is suppressed, providing a heterogeneous effect of improved storage stability.

[0086] In addition, the ductility, flatness, and mechanical properties of the zinc foil are maintained by low-temperature plasma treatment conditions, thereby ensuring electrode handling and stacking process stability.

[0087] In addition, since rolling oil, organic contaminants, and adsorbed moisture are effectively removed during the vacuum plasma treatment process, a separate cleaning process becomes unnecessary or simplified, thereby providing a heterogeneous effect of improving the efficiency of the electrode manufacturing process.

[0088] Looking at the conditions, the plasma treatment may be characterized by applying argon plasma under vacuum conditions, with an output of 150 to 250 W, a treatment time of 30 to 50 minutes, and a temperature of 25 to 40°C.

[0090] Hereinafter, preferred embodiments are presented to aid in understanding the present invention. However, these embodiments are intended to explain the present invention more specifically, and the scope of the present invention is not limited by them. It will be obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention.

[0092] Examples

[0093] Example 1. Plasma surface treatment of zinc foil

[0094] After cutting the zinc foil into 10cm × 10cm pieces, it was placed into a chamber with vacuum conditions of 10 Pa. Argon gas was introduced into the chamber at a rate of 200 sccm, and an argon plasma was discharged while maintaining a pressure of approximately 20-30 Pa, and the process was carried out for 40 minutes under 200 W conditions. Afterward, the plasma-surfaced zinc foil was removed from the chamber and used as the negative electrode of an aqueous zinc battery.

[0096] Comparative Example 1. Untreated zinc foil

[0097] After cutting the zinc foil into 10cm × 10cm pieces, it was used as the negative electrode of a water-based zinc battery without any separate post-processing.

[0099] Experimental Example

[0100] Experimental Example 1. Surface stabilization by plasma treatment

[0101] In order to analyze the surface stabilization effect of a plasma-surface-treated zinc foil according to an embodiment of the present invention, the surface of the foil was analyzed using SEM, EDS, CLSM, and AFM.

[0103] Figure 3 is a scanning electron microscope (SEM) image of the zinc foil surface before and after plasma treatment.

[0104] Figure 4 is an image of the zinc foil surface analyzed by EDS before and after plasma treatment.

[0106] Referring to Figure 3, it can be seen that on the surface of the zinc foil before plasma treatment, micro-sized protrusions and holes, as well as some black carbon-based contaminants, are observed.

[0107] On the other hand, after plasma treatment, it can be confirmed that such protrusions, holes, and carbon-based contaminants are removed from the zinc foil surface, and nano-sized zinc particles are evenly formed on the foil surface.

[0109] Referring to the EDS-mapping results in Fig. 4, it can be seen that Zn, C, and O elements are evenly distributed on the surface of the zinc foil before and after plasma treatment, and among them, clusters of C and O elements concentrated in specific areas are observed on the surface of the foil before plasma treatment. This may refer to carbon-based contaminants observed in Fig. 3.

[0110] It can be confirmed that these cluster regions were significantly removed after plasma treatment. Through this, it can be verified that on the surface of the plasma-treated zinc foil, Zn, C, and O elements are uniformly distributed across the entire surface, and a stable Zn-based surface is formed without local aggregation.

[0112] Figure 5 shows images of the zinc foil surface analyzed by a confocal microscope (CLSM) before and after plasma treatment, and the results in a table.

[0113] Figure 6 shows images of the zinc foil surface analyzed by atomic force microscopy (AFM) before and after plasma treatment, and the results in a table.

[0115] In Figures 5 and 6, Ra (Average roughness) represents the average roughness, and Rq (RMS roughness) represents the mean squared roughness value.

[0117] Referring to Fig. 5, the confocal microscope image of the zinc foil before plasma treatment shows a wide distribution of colors including blue, green, yellow, and red, and it can be seen that there are some red regions with locally protruding peaks. In addition, it can be confirmed that the surface roughness is high because the surface height variation is large.

[0118] Confocal microscope images of the zinc foil after plasma treatment reveal that the range of color variation is small, centered mostly in green and light green, and that the overall height variation is minimal and uniform. This confirms that surface roughness has significantly decreased compared to before plasma treatment and that the surface of the zinc foil is flat and aligned.

[0120] Referring to Figure 6, it can be seen that the zinc foil before plasma treatment exhibits a relatively gentle uneven structure and has a surface at the level of a natural oxide film with a uniformly distributed fine grain structure.

[0121] After plasma treatment, the zinc foil forms a distinct nodular / hill-like morphology, and it can be observed that numerous fine peaks are formed, increasing surface relief and widening the 3D height distribution. Additionally, it can be seen that the average Ra value increased by approximately 54% from 2.133 nm to 3.291 nm, and the average Rq value increased by approximately 45% from 2.863 nm to 4.146 nm.

[0122] Through this, it can be confirmed that nano-sized zinc particles are uniformly deposited on the surface of the zinc foil by plasma treatment.

[0124] That is, according to the results of Experimental Example 1, it can be seen that protrusions, holes, and carbon-based contaminants present on the surface of the zinc foil are removed through the plasma treatment process, significantly reducing surface roughness, and that a uniform and stable surface layer is formed by the uniform deposition of zinc nanoparticles.

[0126] Experimental Example 2. Surface Energy Analysis According to Plasma Treatment

[0127] In order to analyze the change in surface energy of a plasma-surface-treated zinc foil according to an embodiment of the present invention, a contact angle measurement analysis was performed.

[0129] Figure 7 is an image showing the contact angle analysis results of zinc foil before and after plasma treatment.

[0131] Referring to Fig. 7, it can be seen that the contact angle of the zinc foil before plasma treatment is 93.74°, indicating a hydrophobic surface, low surface energy, and poor wettability. Through this, it can be confirmed that prior to plasma treatment, surface diffusion of the electrolyte, aqueous solution, and coating solution is restricted and the interfacial contact area is reduced.

[0132] After plasma treatment, the contact angle of the zinc foil is 21.26°, which is close to super-hydrophilic values ​​of 30° or less, and it can be observed that water droplets spread rapidly and surface energy increases sharply. Through this, it can be confirmed that the plasma-treated zinc foil increases the reaction active area and reduces interfacial resistance due to the immediate wetting of the aqueous-based electrolyte.

[0134] That is, according to the results of Experimental Example 2, a layer of zinc nanoparticles is formed on the surface of the zinc foil through the plasma treatment process, and as a result, the hydrophilicity of the zinc foil-based cathode is improved, the surface energy is increased, and the interfacial resistance is reduced.

[0136] Experimental Example 3. Chemical surface modification by plasma treatment

[0137] XPS and XRD analyses were performed to analyze the chemical surface modification of a plasma-surface-treated zinc foil according to an embodiment of the present invention.

[0139] Figure 8 is a graph showing the X-ray photoelectron spectroscopy (XPS) analysis results of zinc foil before and after plasma treatment.

[0141] Referring to Figure 8, it can be seen that the zinc foil before plasma treatment shows an oxidized Zn peak and a major peak (CC) of carbon-based contaminants.

[0142] After plasma treatment, the zinc foil shows a predominance of Zn-related peaks, confirming that oxidized zinc has been removed and a layer of zinc nanoparticles has been formed on the surface. Additionally, the decrease in peaks of contaminants such as CC / CH confirms that organic contaminants are removed by plasma treatment.

[0144] Figure 9 is a graph showing the results of low-angle X-ray diffraction (GIXRD) analysis of zinc foil before and after plasma treatment.

[0146] Referring to Fig. 9, the (002), (100), and (101) diffraction peaks of Zn(hcp) are observed both before and after plasma treatment, confirming that the basic crystal phase of the foil remains metallic Zn regardless of plasma treatment.

[0147] Meanwhile, a tendency for the full width at half maximum (FWHM) of the main diffraction peaks to increase (peak broadening) is observed after plasma treatment, which may suggest that as a layer of nanoparticles is formed on the surface of the zinc foil by plasma treatment, the grain size near the surface decreases and the crystallinity is reduced.

[0149] In other words, according to the results of Experimental Example 3, it can be seen that surface modification occurs through a plasma treatment process, which removes the oxide layer caused by oxidation on the surface of the zinc foil and forms a zinc nanoparticle layer. In addition, the zinc nanoparticle layer formed by plasma treatment can improve surface energy and interfacial reaction efficiency by refining the crystal grains near the surface and increasing the active surface.

[0151] Experimental Example 4. Performance Evaluation of Aqueous Zinc Battery

[0152] In order to evaluate the electrochemical performance of an aqueous zinc battery assembled with a plasma surface-treated zinc foil according to an embodiment of the present invention, capacity and lifespan analysis of a symmetric cell or a full cell by charging and discharging was performed.

[0154] A symmetric cell (Zn∥Zn) containing zinc foil before and after plasma treatment was assembled with a CR2032 coin cell structure. The aqueous electrolyte used was an aqueous solution of ZnSO₄ containing a zinc salt dissolved in deionized water at 1.0 M, and the separator used was a glass fiber separator with a diameter larger than that of the zinc electrode.

[0155] A first electrode, consisting of zinc foil before and after plasma treatment, was placed in the lower case, and a separator pre-wetted with an electrolyte was laminated on top of it. Subsequently, another second zinc electrode was placed on top of the separator. Afterward, a zinc symmetrical cell was assembled by sequentially laminating spacers and springs, sealing it with the upper case, and crimping. At this time, the electrolyte injection amount was 1 to 50 μL / cm² based on the electrode area. 2It was adjusted within the range, and all cells were manufactured with the same injection volume and the same injection conditions.

[0156] The fabricated symmetrical cells were tested after soaking for 0.5 to 12 hours after assembly to ensure sufficient wetting of the electrolyte and stabilization of the interface.

[0158] A full cell (Zn∥V₂O₅) containing zinc foil before and after plasma treatment was also assembled into a CR2032 coin cell structure and manufactured using the same method and conditions as the symmetric cell, except that a positive electrode containing vanadium oxide (V₂O₅) as the positive active material was placed on top of the separator.

[0160] Figure 10 is an image showing the results of real-time microscopic analysis during charging and discharging of a symmetric cell (Zn∥Zn) assembled with zinc foil before and after plasma treatment.

[0161] Figure 11 is an image of the surface of a symmetric cell (Zn∥Zn) assembled with zinc foil before and after plasma treatment, analyzed by scanning electron microscope after performance evaluation according to current rate.

[0163] Referring to Fig. 10, as the charging and discharging of the symmetrical cell are repeated, it can be observed that zinc is deposited locally on the uneven surface of the zinc electrode before surface treatment and dendrites are formed. On the other hand, it can be observed that zinc nanoparticles are uniformly deposited on the flattened, uniform surface of the plasma-surface-treated zinc electrode.

[0165] Referring to Fig. 11, it can be seen that the zinc electrode before surface treatment has a non-uniform surface, so as the current intensity increases, larger dendrites are formed.

[0166] On the other hand, as the plasma surface-treated zinc electrode induces the deposition of uniform zinc nanoparticles, it can be confirmed that uniform zinc deposition is maintained at various current intensities.

[0168] In other words, it can be seen that dendrite formation is effectively suppressed as a uniform layer of nanoparticles is formed on the surface of the plasma surface-treated zinc electrode.

[0170] Figure 12 is a graph showing the results of the electrochemical performance evaluation of a symmetric cell (Zn∥Zn) assembled with zinc foil before and after plasma treatment.

[0172] Referring to Fig. 12, it can be observed that the symmetric cell with zinc foil applied before plasma treatment exhibits behaviors in which the voltage fluctuation range increases rapidly or the signal becomes unstable compared to the beginning of the cycle, and after a certain number of cycles, a rapid voltage anomaly appears, causing the symmetric cell to die relatively quickly. Through this, it can be confirmed that the stability of the cell is degraded as the interfacial resistance increases rapidly due to local current concentration and dendrite growth caused by non-uniform Zn precipitation, or the accumulation of side reactions.

[0173] In contrast, it can be observed that the symmetrical cell with plasma-treated zinc foil exhibits small voltage fluctuations (overvoltage) under both low and high current conditions, and the increase in voltage amplitude is suppressed even as cycles progress, showing a tendency to maintain a stable lifespan over a long period. Through this, it can be confirmed that the voltage signal remains relatively constant during the plating / stripping process, thereby stabilizing the electrode-electrolyte interface.

[0175] Figure 13 is a graph showing the results of the electrochemical performance evaluation of a full cell (Zn∥V₂O₅) assembled with zinc foil before and after plasma treatment.

[0177] Referring to Fig. 13, it can be seen that the full cell with zinc foil applied as the cathode before plasma treatment shows a tendency for the discharge capacity to decrease rapidly and the Coulomb efficiency to also significantly decline as the cycle progresses. In particular, when charging and discharging are performed under various current density conditions, the voltage behavior becomes unstable and rapid degradation of life occurs frequently, which may suggest that the stability of the electrode-electrolyte interface is not sufficiently ensured.

[0178] On the other hand, it can be confirmed that the full cell with plasma-treated zinc foil applied as the cathode maintains a stable discharge capacity as the cycle progresses and shows a tendency for the capacity to decrease gradually even after long-term charging and discharging. In addition, it can be confirmed that the reversible reaction during the charging and discharging process proceeds efficiently by maintaining a high and stable Coulomb efficiency throughout the entire cycle range.

[0180] Therefore, it can be confirmed that the plasma surface-treated zinc cathode effectively induces dendrite formation and suppresses side reactions, thereby improving the long-term cycle life of the symmetric cell and improving the capacity retention rate and life characteristics of the full cell.

[0182] In other words, according to the results of Experimental Example 4, in an aqueous zinc battery in which a plasma surface-treated zinc foil is applied as the negative electrode, dendrite formation on the surface of the zinc negative electrode is effectively suppressed due to the surface treatment, thereby reducing irreversible reaction losses at the negative electrode and maintaining the electrochemical reaction balance with the positive electrode. Furthermore, it can be seen that the discharge capacity retention rate and Coulomb efficiency are improved, and the rapid decline in lifespan is suppressed even under various current density conditions.

[0184] In summary, the plasma treatment process for the surface of a negative electrode material for an aqueous zinc battery according to the present invention reduces the roughness of the negative electrode surface, removes contaminants and oxide layers, and induces the formation of a uniformly deposited nanoparticle layer, thereby effectively suppressing dendrite growth and improving the lifespan and stability of the battery.

[0185] Compared to conventional polishing or recrystallization processes, this surface treatment process can be performed under low-temperature conditions, consumes less energy, and is easy to apply to large areas; therefore, it can be highly competitive in the energy storage system (ESS) and eco-friendly secondary battery markets, where safety, low cost, and high output characteristics are required.

[0186] In addition, the plasma treatment process of the present invention offers the advantage of being easily applied to mass production without additional complex processes due to excellent compatibility with existing zinc electrode manufacturing processes, and can effectively improve the problem of reduced lifespan of existing zinc batteries caused by zinc dendrites.

Claims

Claim 1 A negative electrode for a water-based zinc battery, wherein the negative electrode comprises a sheet-shaped zinc (Zn) foil; at least one surface of the zinc foil is surface-modified by argon (Ar) plasma treatment, wherein a nanoparticle layer comprising zinc nanoparticles having an average particle size of 25 to 40 nm is formed on the surface of the zinc foil by the plasma treatment, and the contact angle of the plasma-treated negative electrode is 15 to 30°. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 A water-based zinc battery comprising: a positive electrode; a negative electrode according to claim 1; a separator located between the positive electrode and the negative electrode; and a water-based electrolyte. Claim 9 (A) a step of preparing a zinc (Zn) foil on a sheet; and (B) a step of modifying the surface by irradiating at least one surface of the zinc foil with an argon (Ar) plasma under vacuum conditions; wherein a nanoparticle layer comprising zinc nanoparticles having an average particle size of 25 to 40 nm is formed on the surface of the zinc foil by step (B), and a separate coating process or chemical treatment process is not performed after step (B). Claim 10 delete Claim 11 delete Claim 12 A method for manufacturing a negative electrode for an aqueous zinc battery, wherein, in claim 9, step (B) is characterized by irradiating plasma under conditions of an output of 10 to 500 W and a processing time of 1 to 60 minutes. Claim 13 A method for manufacturing a negative electrode for an aqueous zinc battery, wherein, in claim 9, step (B) is characterized by irradiating plasma at 20 to 100°C. Claim 14 A method for manufacturing a negative electrode for a water-based zinc battery, characterized in that, in claim 9, after step (B), (C) applying the metal foil obtained in step (B) as a negative electrode for a water-based zinc battery. Claim 15 A method for manufacturing a negative electrode for an aqueous zinc battery according to claim 9, wherein the plasma treatment of step (B) is performed by applying argon plasma under vacuum conditions, with an output of 150 to 250 W, a treatment time of 30 to 50 minutes, and a temperature of 25 to 40°C.

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