WO2025116244A1 - NEGATIVE ELECTRODE FOR ZINC-ION BATTERY, COMPRISING PREDOMINANT β-PHASE POLYMER PROTECTIVE LAYER, METHOD FOR MANUFACTURING SAME, AND ZINC-ION BATTERY - Google Patents

Abstract

The present invention relates to a negative electrode for a zinc-ion battery, a method for manufacturing same, and a zinc-ion battery, the negative electrode comprising a polymer protective layer comprising a predominant β-phase polar polymer.

Description

Negative electrode for zinc-ion battery comprising polymer protective layer of dominant β-PHASE, method for producing same, and zinc-ion battery

The present invention relates to a negative electrode for a zinc-ion battery. In particular, it relates to a negative electrode for a zinc-ion battery comprising a polymer protective layer of a predominant β-phase, a method for producing the same, and a zinc-ion battery.

This application claims priority to Korean Patent Application No. 10-2023-0172644, filed on December 1, 2023, the entire contents of which are incorporated herein by reference.

Meanwhile, the present invention was supported by the following national research and development project.

Assignment ID: 2710004376

Assignment Number: RS-2024-00342112

Ministry Name: Ministry of Science and ICT

Project Management Agency Name: National Research Foundation of Korea

Research Project Name: Individual Basic Research (Ministry of Science and Technology)

Research Project Name: Implementation of High Energy Density Fiber-Type Power Source and Study on the Correlation between Faraday Reaction and Inductive Charge Separation for Self-Charging

Project implementation organization name: Gyeongsang National University

Research Period: 2024.05.01 ~ 2025.04.30

Environmental concerns and energy issues regarding the use of fossil fuels have led to increasing interest in using renewable energy sources such as solar and wind to generate electrical energy. However, the output of solar and wind is not regularly stable and constant due to unexpectedly diverse environmental and geographical conditions. In order to efficiently utilize variable renewable and clean energy, large-scale electrical energy storage (EES) systems that can achieve high energy/power density and excellent cycling stability are required.

As the most common energy storage device, lithium-ion batteries (LIBs) are proposed as a solution. However, the use of lithium has the disadvantages of low safety, limited supply, uneven distribution, and high cost. In this regard, rechargeable batteries, especially aqueous batteries based on earth-abundant aluminum (Al), magnesium (Mg), or zinc (Zn), are attracting attention because they use low-cost and safe aqueous electrolytes.

In particular, rechargeable aqueous zinc-ion batteries (AZIBs) have attracted great attention as a promising alternative for low-cost and safe energy storage systems. This is due to the natural abundance of zinc, the inherent safety of aqueous electrolytes, the high theoretical capacity of zinc metal, and the low cathode potential. However, zinc is thermodynamically unstable in weakly acidic aqueous electrolytes, and the zinc surface spontaneously experiences hydrogen evolution reaction and is prone to forming by-products in the ZnSO ₄ electrolyte. In addition, the non-uniform diffusion of zinc ions and the growth of zinc dendrites due to plating can cause a short circuit of the battery. Various methods have been introduced to overcome these problems, and among them, the method of introducing a protective layer is recognized as being convenient and effective.

Carbon materials, metal oxides, polymer materials, etc. are applied as protective layers, and in the case of polymer materials, polar polymer materials are particularly applied. However, research and development on a more effective polymer protective layer is needed to suppress zinc corrosion and hydrogen production reaction and prevent the uneven diffusion of zinc ions to suppress dendrite formation.

The present invention has been made to solve the above-described problems, and aims to provide a zinc-ion battery negative electrode including a polymer protective layer made of a predominant β-phase polar polymer, a method for manufacturing the same, and a zinc-ion battery.

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

A negative electrode for a zinc-ion battery according to the present invention comprises a zinc substrate and a predominantly β-phase polymer protective layer formed on the surface of the zinc substrate.

A method for manufacturing a negative electrode for a zinc-ion battery according to the present invention comprises the steps of: preparing a solution in which a polymer is completely dissolved in a solvent; adding one or more cationic additives selected from _the group consisting of ZnCl ₂ , Zn(CF ₃ SO ₃ ) ₂ , Zn(TFSI) _{2 ,} ZnO, Zn(NO 3 ) 2 6H ₂ O, Zn(NTF ₂ ) ₂ and ZnSO ₄ 7H ₂ O to the solution and then completely dissolving them to prepare a coating solution; applying the coating solution onto the surface of a zinc substrate washed with ethanol and then drying it to produce a polymer protective layer; and annealing the zinc substrate on which the polymer protective layer is produced to generate a predominant β-phase.

The present invention further includes a negative electrode for a zinc-ion battery manufactured by the above-mentioned manufacturing method.

The present invention further includes a zinc-ion battery including the above negative electrode.

According to the present invention as described above, when a predominant β-phase polymer protective layer is applied to the negative electrode of a zinc-ion battery, corrosion of zinc and hydrogen production reaction are suppressed, and non-uniform diffusion of zinc ions is prevented, so that dendrite formation can be suppressed very effectively.

In addition, the polymer protective layer of the present invention has a porosity of a certain level or higher, thereby improving wettability with an electrolyte, thereby improving the cycle performance of a zinc-ion battery and enhancing safety.

The effects of the present invention are not limited to those mentioned above, and also include other effects that are not explicitly mentioned but can be clearly understood by those skilled in the art from the description throughout the specification.

Figure 1 is a schematic diagram showing the manufacturing process and phase change of zinc cathodes of comparative examples and examples.

Figure 2 shows the results of experiments conducted to compare the surface structure and interface characteristics of zinc cathodes (related to Experimental Example 1).

Figure 3 shows the results of experiments conducted to compare the phase changes of zinc cathodes, particularly the change to the β phase (related to Experimental Example 2).

Figure 4 shows the results of experiments conducted to compare the chemical stability of zinc cathodes (related to Experimental Example 3).

Figure 5 shows the results of experiments conducted to compare the dendrite inhibition performance of zinc cathodes (related to Experimental Example 4).

Figure 6 shows the results of experiments conducted to compare the zinc ion diffusion capacity and energy storage capacity of zinc cathodes (related to Experimental Example 5).

Figure 7 shows the results of experiments conducted to compare the cycling stability (life characteristics) of zinc cathodes (related to Experimental Example 6).

Figure 8 shows the results of experiments conducted to compare the performance of batteries through power supply from zinc cathodes (related to Experimental Example 7).

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The advantages and features of the present invention, and the methods for achieving them, will become apparent with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and the present embodiments are provided only to make the disclosure of the present invention complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used in a meaning that can be commonly understood by a person of ordinary skill in the art to which the present invention belongs. In addition, terms defined in commonly used dictionaries shall not be ideally or excessively interpreted unless explicitly specifically defined. The terminology used in this specification is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, the singular also includes the plural unless specifically stated in the phrase.

The terms “comprises” and/or “comprising,” as used in the specification, do not exclude the presence or addition of one or more other components, steps, operations and/or elements.

The present invention relates to a negative electrode for a zinc-ion battery, and the present invention will be described in detail below.

A negative electrode for a zinc-ion battery according to the present invention comprises a zinc substrate and a predominant β-phase polymer protective layer formed on the surface of the zinc substrate.

As the zinc substrate, zinc foil, etc. can be used, and without particular limitation thereto, any zinc substrate that contains zinc and can be used as a current collector or negative electrode active material can be used.

It is preferable that the polymer forming the polymer protective layer be a polar polymer.

More specifically, polar polymers include polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyurethane, The polymer may be one or more of polyvinylidene fluoride (PU), polychloroprene, polyisoprene and polybutadiene. Among these, polyvinylidene fluoride (PVDF) may be particularly preferable.

The cathode of the present invention is characterized by a water contact angle of less than 70°, more specifically 10° to 60°, and even more specifically 10° to 55°. Here, the water contact angle specifically means the water contact angle targeting the surface of the polymer protective layer.

This is because the polymer protective layer formed on the surface of the zinc substrate has a porous structure and can preferably satisfy a porosity of 40 to 80%. More details on the porous structure are explained in Experimental Example 1.

Meanwhile, the cathode of the present invention is characterized in that the value of F(β) according to the following formula of the polymer protective layer formed on the surface of the zinc substrate is 70% or more. More specifically, it can satisfy 70% to 90%.

In the above equations, X _α and X _β represent the crystal percentages of the α phase and the β phase, respectively, K _α and K _β represent the absorption coefficients at individual wavenumbers, respectively, and A _α and A _β represent the absorbance values of the α phase and the β phase at 763 cm ^-1 and 839 cm ^-1 , respectively.

That is, the meaning of 'predominant β-phase' in the present invention may quantitatively mean that a large amount of β-phase exists in the polymer protective layer formed on the zinc substrate, and more specifically, it may mean that the F(β) value, which is the relative fraction of the β-phase in the polymer protective layer, is 70% or more. More detailed information about this is explained through Experimental Example 2.

This β phase has the highest polarity compared to other phases such as the α phase because all the heteroatoms are oriented in the same direction. When the β phase is dominant as the polymer protective layer of the zinc anode and has high polarity characteristics, the zinc ion movement can be uniformly diffused through the polymer protective layer, so it can be very effective in suppressing the formation of zinc dendrites.

Meanwhile, a method for manufacturing a zinc anode according to an embodiment of the present invention includes a step of preparing a solution in which a polymer is completely dissolved in a solvent, a step of adding one or more cationic additives selected from the group consisting of ZnCl ₂ , Zn(CF ₃ SO ₃ ) ₂ , Zn(TFSI) ₂ , ZnO, Zn( _{NO 3 ) 2 6H 2} O _, Zn(NTF ₂ ) ₂ , ZnBr 2 , Zn(ClO 3 ) 2 , Zn(CH ₃ CO ₂ ) ₂ 2H ₂ O, and ZnSO ₄ 7H ₂ O to the solution and then completely dissolving the solution to prepare a coating solution, a step of applying the coating solution onto the surface of a zinc substrate washed with ethanol and then drying it to produce a polymer protective layer, and a step of annealing the zinc substrate on which the polymer protective layer is produced to generate a predominant β-phase.

The polymer used is a polar polymer and the details are the same as those described above, so they are omitted.

The solvent used may be a polar solvent, and specifically may include one or more of N-methylformamide (NMF), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAc), dipropylene glycol monomethyl ether (DPM), sulfolane, N-methyl pyrrolidone (N-methyl-2-pyrrolidone, NMP), N-ethyl pyrrolidone (N-ethyl pyrrolidone), and dipropylene glycol monoethyl ether (DPE). Among these, N-methyl pyrrolidone (NMP) may be particularly preferable.

The cationic additive used may preferably be ZnSO ₄ 7H ₂ O.

The use of a cationic additive helps to promote the formation of β phase, thereby forming a polymer protective layer of a predominant β-phase. To explain this in more detail, for example, when ZnSO ₄ 7H ₂ O is used as a cationic additive, when ZnSO ₄ 7H ₂ O dissolves, it is divided into a zinc cation (Zn ²⁺ ) and anion of SO ₄ ^2- , and when the highly electronegative CF group of a polar polymer such as PVDF interacts with the zinc cation and rearranges in one direction, a predominant β-phase with high polarity is formed. In other words, the zinc cation due to the cationic additive ultimately induces the formation of the predominant β-phase.

It is preferable that these cationic additives are added in an amount of 10 to 40 wt% based on the polymer weight. If less than 10 wt% is added, it is difficult to promote the formation of β phase, and if more than 40 wt% is added, a problem of zinc precipitation may occur. More preferably, they can be added in an amount of 10 to 30 wt%.

Meanwhile, drying and annealing can be carried out simultaneously, and can be carried out by maintaining at a temperature of 50℃ to 70℃ for 3 to 9 hours and then slowly cooling. The temperature and maintenance time of drying and annealing, along with the use of cationic additives, are important factors in the formation of the dominant β phase, and the above range is the optimal condition.

The manufacturing method of the present invention described so far forms a polymer protective layer of β phase by integrating a simple ion-dipole interaction mechanism in a traditional heat treatment process, and further induces the formation of a more dominant β phase through the use of a cationic additive and the optimization of drying and annealing conditions. As a result, the polymer protective layer of the dominant β phase can ensure uniform zinc ion diffusion to suppress dendrite formation, and can suppress zinc corrosion and hydrogen production reaction by acting as a protective layer between the electrode and the electrolyte. In addition, the formation of a highly polar β phase and a porous structure improves the wettability of the electrolyte, thereby improving the cycle performance and enhancing the stability of the battery.

The present invention further includes a negative electrode for a zinc-ion battery manufactured by the above-described manufacturing method. The present invention further includes a zinc-ion battery including the above-described negative electrode.

Below, specific embodiments and experimental examples of the present invention are examined.

Example: Preparation of zinc cathode using cationic additives

PVDF, a polar polymer, was added at 210 mg in 10 ml of NMP (N-methyl 2-pyrolidone) so as to be 2 wt%, and stirred overnight to prepare a solution in which PVDF was completely dissolved in NMP. Thereafter, 42 mg of ZnSO ₄ 7H ₂ O as a cationic additive was added to the solution, and stirred at room temperature for 6 hours to completely dissolve ZnSO ₄ 7H ₂ O to prepare a coating solution. Thereafter, zinc foil with a diameter of 13 mm as a zinc substrate was washed with ethanol to remove oily residues or other contaminants that may be present on the surface. Thereafter, the prepared coating solution was applied to the washed zinc foil by drop coating, and then kept in an oven at 60°C for 6 hours. After slowly cooling, drying and annealing were performed at the same time to manufacture the final zinc anode.

Comparative Example: Manufacturing a Zinc Anode Without Using Cationic Additives

A zinc anode was manufactured in the same manner as in the previous example, except that a solution in which PVDF was completely dissolved in NMP was used as a coating solution and applied to a zinc foil without using a cationic additive.

In the drawings below, the zinc anode in the state of a zinc foil without forming a polymer protective layer is indicated as Bare Zn, the zinc anode of the comparative example manufactured previously is indicated as MBP@Zn or MBP film, and the zinc anode of the example is indicated as PBP@Zn or PBP film.

Figure 1 (a) is a schematic diagram showing the manufacturing process of a zinc anode in each of the examples and comparative examples, (b) is a schematic diagram showing the phase change of a polymer protective layer formed on the zinc anode of the comparative example, and (c) is a schematic diagram showing the phase change of a polymer protective layer formed on the zinc anode of the examples.

As shown in (b) of Fig. 1, the PVDF of the comparative example undergoes a phase change from the initial α-phase to the minor β-phase, and as shown in (c) of Fig. 1, the PVDF of the exemplary embodiment undergoes a phase change from the initial α-phase to the predominant β-phase.

In the following experiments, the experiments were conducted on a zinc anode in the form of a zinc foil without forming a polymer protective layer, a zinc anode of a comparative example manufactured previously (a zinc anode with a minor β-phase polymer protective layer formed by not using a cationic additive), and a zinc anode of an example (a zinc anode with a predominant β-phase polymer protective layer formed by using a cationic additive).

Experimental Example 1: Surface Structure and Interface Characteristics

Figures 2 (a) to (c) show the surface of each zinc anode observed using a scanning electron microscope (SEM), and (d) to (f) show the side views. (a) and (d) show the zinc anode without a polymer protective layer, (b) and (e) show the zinc anode of a comparative example, and (c) and (f) show the zinc anode of an embodiment.

As can be seen here, the zinc anode without a polymer protective layer has a smooth surface, and the side view confirms that there is no polymer protective layer. In the case of the zinc anode of the comparative example, interconnected micrometer hemispheres were observed on the surface, and the side view confirms that a polymer protective layer was formed, and its thickness is about 10 μm. In the case of the zinc anode of the example, unlike the previous zinc anodes, it was observed to have a porous structure in which various pores of 0.5 to 4 μm in size were distributed, and the side view confirms that a polymer protective layer was formed, and its thickness is about 10 μm.

In conclusion, the zinc anode of the present invention has a polymer protective layer having a porous structure in which various pores of 0.5 to 4 μm in size are distributed, and is formed on the surface with a thickness of about 10 μm. The reason why the polymer protective layer according to the present invention has porosity can be attributed to the Marangoni effect and the use of a cationic additive. More specifically, the porous structure is formed due to the difference in surface tension with the NMP solvent caused by H ₂ O present in the cationic additive.

Figures 2 (g) to (i) show the results of measuring the water contact angle of each zinc anode. (g) is the result of a zinc anode without a polymer protective layer, (h) is the result of a zinc anode of a comparative example, and (i) is the result of a zinc anode of an example.

As can be seen, the zinc cathode of the example shows the lowest contact angle, which can be understood to be due to the polymer protective layer having a porous structure.

In conclusion, the zinc anode of the present invention is characterized by having a low contact angle due to the formation of a polymer protective layer having a porous structure on the surface, and can satisfy a water contact angle of preferably less than 70°, more preferably 10° to 60°. This means that the characteristics with respect to the hydrophilic interface are improved, and consequently, when applied to an aqueous zinc ion battery, the interfacial characteristics (wettability) with an aqueous electrolyte can be improved. Through this, it has the effect of improving the cycle performance of the battery and enhancing safety.

Experimental Example 2: Conversion to β phase

Figure 3 (a) shows the results of measuring X-ray diffraction (XRD) patterns of the zinc anode of the comparative example and the zinc anode of the exemplary embodiment. More specifically, the measurements were performed using an X-ray diffractometer equipped with a Cu Kα radiation source.

As can be seen, a prominent peak was observed at 20.4° for both zinc cathodes, indicating successful conversion to the β phase.

Figures 3 (b) and (c) show the results of measuring the crystal phase of the zinc anode of the comparative example and the zinc anode of the exemplary embodiment. More specifically, the measurements were performed using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy.

As shown in (b) of Fig. 3, the β phase characteristic (839 cm ^-1 ) was observed for both zinc anodes. However, as shown in (c) of Fig. 3, the α phase characteristic (763 cm ^-1 ) was observed more for the zinc anode of the comparative example than for the zinc anode of the example. This means that a larger amount of α phase exists in the polymer protective layer of the zinc anode of the comparative example than in the polymer protective layer of the zinc anode of the example. In other words, it can be seen that the polymer protective layer of the zinc anode of the example achieved a more successful conversion to the β phase.

Figure 3 (d) shows the results of calculating the relative fraction of β phase, F(β), for the zinc anode of the comparative example and the zinc anode of the exemplary embodiment. Specifically, the α phase and the β phase were quantified from the characteristic absorption peaks of 763 cm ^-1 and 839 cm ^-1 using the Lambert-Beer law. More specifically, the calculation was performed using the following equation.

In the above equations, X _α and X _β represent the crystal percentages of the α phase and the β phase, respectively, K _α and K _β represent the absorption coefficients at individual wavenumbers, respectively, and A _α and A _β represent the absorbance values of the α phase and the β phase at 763 cm ^-1 and 839 cm ^-1 , respectively.

As a result calculated in this way, the F(β) of the zinc anode of the comparative example was 61.8%, and the F(β) of the zinc anode of the example was 74.2%. That is, it means that the content of the β phase is higher in the polymer protective layer of the zinc anode of the example, and it can preferably satisfy the F(β) value of 70% to 90%.

Figure 3 (e) shows the results of measuring the thermal behavior of the crystal phase for the zinc anode of the comparative example and the zinc anode of the exemplary embodiment. More specifically, it was investigated using differential scanning calorimetry (DSC).

As can be seen, the melting temperature of the zinc anode of the comparative example was observed to be about 170°C, and the melting temperature of the zinc anode of the example was observed to be about 167°C, confirming that a β-phase crystal phase existed in both polymer protective layers. In particular, it was confirmed that the melting temperature of the zinc anode of the example was more biased toward the β-phase crystal phase.

Figure 3 (f) shows the results of measuring the surface elemental composition and chemical state of the zinc anode of the comparative example and the zinc anode of the exemplary embodiment. More specifically, the analysis was performed using X-ray photoelectron spectroscopy (XPS).

As can be seen, both zinc anodes had distinct peaks at 285.8 eV and 290.5 eV, indicating the presence of CH ₂ and CF ₂ groups, respectively. Unlike the comparative example, the area of the CF ₂ species was reduced and asymmetric lines of CH ₂ and CF ₂ were observed in the results of the zinc anode of the example. This suggests that interfacial interactions occurred between the zinc cation (Zn ²⁺ ) and the CH ₂ /CF ₂ species of the PVDF. This is also supported by Fig. 3 (g), which shows a slight asymmetry in the center at 687.3 eV in the result of the high-resolution F1s spectrum. That is, these results imply that the zinc anode of the example has a polymer protective layer with a predominant β phase.

In conclusion, zinc (Zn) ion flux was uniformly distributed in the polymer protective layer formed on the zinc anode of the embodiment, which was promoted by the strong ion-dipole interaction between the zinc cation (Zn ²⁺ ) introduced by the cationic additive and the electronegative CF functional group. In addition, the diffusion path generated by the further aligned F atoms under the influence of the cationic additive can improve the movement of zinc ions (Zn), thereby increasing the overall energy storage capacity.

Experimental Example 3: Chemical Stability

Figures 4(a) to (c) show the results of observing the surface state of each zinc anode after immersing it in an electrolyte for 5 days. (a) shows a zinc anode without a polymer protective layer, (b) shows a zinc anode of a comparative example, and (c) shows a zinc anode of an example.

As can be seen, the by-products of corrosion by the electrolyte were almost absent in the zinc anode of the example. As a result, the zinc anode of the example exhibited excellent chemical stability in an aqueous electrolyte.

Figure 4 (d) shows the results of measuring the state of each zinc cathode after immersing it in the electrolyte for 5 days using XRD.

As can be seen, the peak corresponding to Zn ₄ SO ₄ (OH) ₆ 5H ₂ O, a by-product of corrosion, was found in the zinc anode without a polymer protective layer and the zinc anode of the comparative example, confirming that significant corrosion due to the electrolyte occurred. On the other hand, the corresponding peak was not found in the zinc anode of the example.

Figure 4 (e) shows the results of Tafel and Linear Sweep Voltammetry (LSV) tests performed using a three-electrode system configured with each zinc cathode as a working electrode, a Pt foil as a counter electrode, and Ag/AgCl as a reference electrode.

As can be seen therein, the corrosion potential values of each zinc anode were measured as -0.988 V (zinc anode without a polymer protective layer), -0.985 V (zinc anode of the comparative example), and -0.981 V (zinc anode of the exemplary example). The corrosion current was reduced when the polymer protective layer was present rather than when it was not, and in particular, the corrosion current value of the zinc anode of the exemplary example was the smallest, confirming that it most effectively suppressed the corrosion reaction. The corrosion current values of each zinc anode were measured as 1.061 mAcm ^-2 (zinc anode without a polymer protective layer), 0.757 mAcm ^-2 (zinc anode of the comparative example), and 0.679 mAcm ^-2 (zinc anode of the exemplary example).

Figure 4(f) shows the results of measuring the HER of each zinc cathode using LSV. The potential required to reach 20 mA was the lowest at -1.104 V for the zinc cathode of the example, indicating a decrease in hydrogen generation.

Figure 4 (g) shows the results showing that the corrosion resistance of the zinc anode is greatly improved by the introduction of the polymer protective layer, and the corrosion resistance of the zinc anode of the example is shown to be the best in both corrosion current value and HER value.

Experimental Example 4: Inhibition of Dendrites

Figures 5(a) to (c) show the surface measurements of the zinc anodes of the symmetrical cells manufactured using the respective zinc anodes while zinc plating for 30 minutes. The symmetrical cell used a glass fiber separator as a separator and an aqueous electrolyte consisting of 2 M ZnSO ₄ and 0.1 M MnSO ₄ as an electrolyte. (a) shows the zinc anode without a polymer protective layer, (b) shows the zinc anode of a comparative example, and (c) shows the zinc anode of an exemplary embodiment.

As can be seen, unlike the zinc anode of the comparative example and the zinc anode without a polymer protective layer, which has dendrites or protrusions formed on the surface over time, the zinc anode of the example can be seen to have a relatively uniform thickness of plating without visible dendrites or protrusions throughout the entire plating process.

Through this, it can be seen that the polymer protective layer of the zinc negative electrode of the embodiment most effectively suppresses the growth of dendrites, and by suppressing the growth of dendrites that cause side reactions between the electrode and electrolyte, etc., the safety and lifespan of the battery are improved as a result.

FIG. 5(d) shows the results of evaluating the stability of the zinc anode through a long-term galvanostatic cycle of the symmetric cell at a current density of 2 mAcm ^-2 . When the zinc anode without the polymer protective layer was used, the symmetric cell exhibited an initial overpotential of 82 mV, and the electrode potential was maintained stable for 50 hours after which a sudden voltage drop was detected. It can be assumed that this is due to an internal short circuit caused by the formation of dendrites. When the zinc anode of the comparative example was used, the symmetric cell exhibited an initial overpotential of 71 mV, maintained a stable potential for 245 hours, and eventually experienced a short circuit. On the other hand, when the zinc anode of the example was used, the symmetric cell exhibited the smallest initial overpotential of 52 mV, and showed excellent long-term stability without a short circuit even after 400 hours of plating/stripping.

Figure 5(e) shows the results of examining the critical current density of the symmetrical cell by gradually increasing the current density from 0.5 to 4 mAcm ^-2 for further evaluation. As can be seen here, in the case of using the zinc anode without the polymer protective layer, a short circuit was experienced after 20 hours due to the rapid change in current density, and in the case of using the zinc anode of the comparative example, the overpotential increased significantly as the current density increased, whereas in the case of using the zinc anode of the example, a slight and consistent overpotential was observed even at a current density of 4 mAcm ^-2 .

Fig. 5(f) shows the results showing the nucleation overpotential of zinc deposition at a current density of 2 mAcm ^-2 , respectively. As can be seen, the zinc anode of the example showed the lowest nucleation overpotential of about 27 mV. This indicates a significantly improved zinc nucleation process, and can be attributed to a significant increase in the number of active nucleation sites.

Figure 5(g) shows the CA curves obtained at fixed potentials, which provide insight into the diffusion behavior of zinc cations (Zn ²⁺ ) or adsorbed zinc atoms on the zinc surface. As shown in the results, for the zinc anode without a polymer protective layer, when an overpotential of -150 mV was applied, the current density continuously increased for more than 500 s, indicating a long-term uncontrolled 2D diffusion process. On the other hand, for the zinc anodes of the comparative examples and the examples, the zinc nucleation and 2D diffusion processes occurred within 76 s and 55 s, respectively, after which a stable and continuous 3D diffusion process appeared. This shows that the zinc cations (Zn ²⁺ ) adsorbed on the surface were locally reduced to Zn ⁰ by limited 2D surface diffusion.

Figures 5 (h) to (j) show the surface of each zinc anode, where (h) is a zinc anode without a polymer protective layer, (i) is a zinc anode of a comparative example, and (j) is a zinc anode of an example. It can be seen that the growth of dendrites is suppressed in the zinc anode of the example.

FIG. 5(k) is a schematic diagram schematically explaining the plating/stripping behavior of zinc and schematically showing the detailed modification mechanism achieved by the polymer protective layer according to the present invention.

As can be seen, the main factor for the inadequate zinc plating/stripping performance comes from the significant interfacial reaction between the uncontrolled electrochemical corrosion reaction of zinc and the chemical corrosion reaction of the electrolyte.

Experimental Example 5: Zinc ion diffusion and energy storage capacity

A two-electrode system was configured with each zinc cathode and MnO ₂ as the anode. The electrode slurry was prepared by mixing the active material (MnO ₂ ), conductive agent (Super-P), and binder (PVDF) in NMP at a weight ratio of 8:1:1, and mixing for 3 hours to ensure homogenization and uniformity. The prepared electrode slurry was applied onto a graphite foil used as a current collector using a doctor blade method, and the current collector was dried and heat-treated in an oven at 80°C for 12 hours. The electrochemical performance of the battery was tested as follows. Electrochemical impedance spectroscopy (EIS) was performed in the frequency range of 10 ⁵ to 10 ^-2 Hz. Cyclic voltammetry (CV) was performed between 1.0 and 1.9 V (vs. Zn/Zn ²⁺ ) at a scan rate of 0.2 mV s ^-1 . The rate performance was evaluated at various current densities in the range of 0.3 to 2.0 A g ^-1 for up to 10 cycles.

Figure 6 (a) shows the results of analyzing the EIS plot. As can be seen, the R _ct value was lower in the cases where the zinc anode of the comparative example and the zinc anode of the example were used than in the case of the zinc anode without the polymer protective layer. This can be understood as because the polymer protective layer promoted efficient electron transfer by suppressing corrosion of the zinc surface. In particular, the R _ct value was found to be the smallest in the case where the zinc anode of the example was used.

Fig. 6 (b) shows the results of measuring the Warburg impedance coefficient (σ _w ). Specifically, the Warburg impedance coefficient (σ _w ) and the Zn ion diffusion coefficient (D) are calculated using the following equations (2) and (3), respectively.

The Warburg impedance coefficient (σ _w ) showed values of 17.7, 15.1, and 9.9 Ωcm ² s ^-1/2 , respectively, for the zinc anode without a polymer protective layer, the zinc anode of the comparative example, and the zinc anode of the example. In addition, as shown in Fig. 6 (c), the ion diffusion coefficient (D) showed values of 0.71, 0.98, and 2.28x10 ^-17 cm ² s ^-1 , respectively, in the same order. Through this, it was found that the diffusion of zinc ions was most greatly improved in the case of the zinc anode of the example.

Fig. 6(d) shows the results of CV curves of the batteries based on each zinc cathode at 0.2 mVs ^-1 . The CV profiles were similar. When the zinc ion of the example was used, the CV curves showed a higher peak current response and a smaller polarization potential, confirming that it showed improved reaction activity.

This is further supported by Fig. 6(e), which shows a galvanostatic charge/discharge (GCD) curve. As shown, it was confirmed that the capacity of the zinc anode of the example was the highest at 255.7 mAhg ^-1 .

Figure 6(f) shows the results showing the rate performance at a current density range of 0.3 to 2.0 ^{A g -1} and a potential of 1.0 to 1.9 ^V. As can be seen, the case using the zinc anode of the example showed the best energy storage performance. Specifically, it showed high specific capacities of 258.5, 231.0, 205.2, 171.7, 137.3, 119.2, 108.1, and 97.7 mAh g ^-1 at current densities of 0.3, 0.5, 0.7, 1.0, 1.3, 1.5, 1.7, and 2.0 A g -1.

The reason why the zinc anode of the present invention has excellent energy storage capacity is largely because (1) the use of a cationic additive causes the polymer protective layer to have a predominant β phase, which promotes the alignment of F atoms and establishes a more organized diffusion path that enhances the movement of Zn ions, and (2) the improved electrode wettability due to the hydrophilic interface of the polymer protective layer and the formation of a porous surface through the Marangoni effect promote a more efficient electrode/electrolyte interface.

Furthermore, as shown in (g) of Fig. 6, the case using the zinc cathode of the embodiment (This work) showed the best results in speed performance, specific capacity, power, and energy density.

Experimental Example 6: Cycling Stability (Life Characteristics)

Figure 7 shows the results showing the cycling stability of batteries based on each zinc cathode. The batteries are the same as those manufactured in Experimental Example 5.

Fig. 7 (a) shows the results of cycling stability after 250 charge/discharge cycles at a current density of 0.5 A g ^-1 . As can be seen, the case using the zinc anode of the example showed the most improved cycling stability.

Figures 7 (b) to (d) show the results of observing the surface of each zinc anode after 250 charge/discharge cycles, where (b) is the case of a zinc anode without a polymer protective layer, (c) is the case of a zinc anode of a comparative example, and (d) is the case of a zinc anode of an example.

As shown in (b) to (d) of Fig. 7, in the case of the zinc anode without a polymer protective layer, it could be seen that the surface was covered with excessively large zinc flakes due to the formation of by-products. On the other hand, in the case of the zinc anodes of the comparative examples and examples, it could be seen that the growth and elution of by-products were suppressed.

Fig. 7(e) is a schematic diagram showing the appearance when each zinc cathode is in direct contact with an acid-based aqueous electrolyte. As shown therein, in the case where there is no polymer protective layer, zinc is gradually eluted during cycling due to direct contact with an acid-based aqueous electrolyte. On the other hand, in the case where a polymer protective layer is included, the polymer protective layer has the effect of preventing zinc eluted by blocking direct interaction with the electrolyte. Therefore, it can exhibit improved cycle life characteristics while maintaining low polarization.

Experimental Example 7: Battery Performance through Power Supply

Figure 8 shows the experimental results and graphs of the results of an experiment in which a pouch-type zinc-ion battery was manufactured using a zinc anode without a polymer protective layer and a zinc anode of an example, and the manufactured battery was used to connect a microcontroller and a liquid crystal display panel to supply power to a micro monitor.

As can be seen, both zinc cathodes supplied power, but the case using the zinc cathode of the example maintained a continuous power supply, demonstrating improved battery performance.

In conclusion, the present invention is to form a polymer protective layer having a predominant β-phase and a porous structure by using a cationic additive when forming a polymer protective layer on the surface of a zinc substrate. The zinc anode having the predominant β-phase and the porous polymer protective layer formed thereon has the following characteristics: 1) improved wettability with an aqueous electrolyte, thereby improving battery cycle performance; 2) improved energy storage capacity by creating a diffusion path to improve the movement of zinc ions; 3) excellent chemical stability, such as improved corrosion resistance by suppressing corrosion reactions and reducing hydrogen generation; 4) excellent battery safety and lifespan, such as improved zinc ion diffusion capacity, energy storage capacity, and cycling stability.

Although the embodiments of the present invention have been described with reference to the attached drawings, those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical idea or essential features thereof. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (13)

Zinc based; and Comprising a predominant β-phase polymer protective layer formed on the surface of the zinc substrate, Cathode for zinc-ion batteries. In the first paragraph, The porosity of the polymer protective layer is characterized by being 40 to 80%. Cathode for zinc-ion batteries. In the first paragraph, Characterized in that the water contact angle of the polymer protective layer is less than 70°. Cathode for zinc-ion batteries. In the first paragraph, The above polymer protective layer is characterized in that the value of F(β) according to the following formula is 70% or more. Cathode for zinc-ion battery;

(In the above formula, X _α and X _β represent the crystal percentages of the α phase and the β phase, respectively, K _α and K _β represent the absorption coefficients at individual wavenumbers, respectively, A _α and A _β represent the absorbance values of the α phase and the β phase at 763 cm ^-1 and 839 cm ^-1, respectively). In the first paragraph, The above polymer is characterized in that it is a polar polymer. Cathode for zinc-ion batteries. In paragraph 5, The above polar polymers are polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyurethane (PU), characterized by one or more of polychloroprene, polyisoprene and polybutadiene, Cathode for zinc-ion batteries. A step of preparing a solution in which a polymer is completely dissolved in a solvent; A step of preparing a coating solution by adding one or more cationic additives among ZnCl ₂ , Zn(CF ₃ SO ₃ ) ₂ , Zn(TFSI) ₂ , ZnO, Zn(NO ₃ ) ₂ 6H _{2 O ,} Zn(NTF ₂ ) 2, ZnBr ₂ , Zn(ClO 3 ) 2 , _Zn (CH ₃ CO ₂ ) ₂ 2H ₂ O, and ZnSO ₄ 7H ₂ O to the above solution and then completely dissolving it; A step of applying the coating solution to the surface of a zinc substrate washed with ethanol and then drying it to produce a polymer protective layer; and A step of annealing the zinc substrate on which the polymer protective layer is manufactured to generate a predominant β-phase, A method for manufacturing a negative electrode for a zinc-ion battery comprising a polymer protective layer. In Article 7, The cationic additive is characterized in that it is ZnSO ₄ 7H ₂ O. A method for manufacturing a negative electrode for a zinc-ion battery comprising a polymer protective layer. In Article 7, The cationic additive is characterized in that it is added in an amount of 10 to 40 wt% based on the polymer weight. A method for manufacturing a negative electrode for a zinc-ion battery comprising a polymer protective layer. In Article 7, The above polymers are polar polymers, such as polyvinylpyrrolidone (PVP), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polystyrene (PS), polymethyl methacrylate (PMMA), poly(n-butyl acrylate) (PBA), polyacrylonitrile (PAN), polyaniline (PANi), polyacrylic acid (PAA), polyester-amides (PEA), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), Characterized by one or more of polyurethane (PU), polychloroprene, polyisoprene and polybutadiene. A method for manufacturing a negative electrode for a zinc-ion battery comprising a polymer protective layer. In Article 7, The above drying and annealing are carried out simultaneously, and are characterized in that they are carried out by maintaining at a temperature of 50℃ to 70℃ for 3 to 9 hours and then cooling. A method for manufacturing a negative electrode for a zinc-ion battery comprising a polymer protective layer. A negative electrode for a zinc-ion battery, manufactured by any one of the manufacturing methods of claim 7. A zinc-ion battery comprising the negative electrode of claim 1 or 12.

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