Anode for aqueous secondary battery comprising polymer protective film, method for manufacturing same, and aqueous secondary battery comprising same

Abstract

The present invention relates to a negative electrode for a water-based secondary battery comprising: a zinc metal film; and a water-based polymer protective film formed on at least one surface of the zinc metal film; a method for manufacturing the same; and a water-based secondary battery comprising the same. The negative electrode for an aqueous secondary battery according to the present invention can suppress side reactions and suppress dendrite formation on the surface of the negative electrode by minimizing contact between the zinc electrode and the aqueous electrolyte, and can improve the lifespan characteristics of the aqueous secondary battery.

Description

Technology Field

[0001] The present invention relates to a negative electrode for an aqueous secondary battery comprising a polymer protective film, a method for manufacturing the same, and an aqueous secondary battery comprising the same. Background Technology

[0003] Recently, as interest in renewable energy grows due to the push for low-carbon green growth driven by resource depletion and environmental pollution, energy storage system technology is simultaneously gaining prominence. In particular, lithium-ion rechargeable batteries are experiencing increasing demand in the electronics and automotive industries due to their advantages in high energy density and very high available voltage in the field of energy storage devices.

[0004] However, lithium-ion rechargeable batteries pose a risk of explosion because they use flammable electrolytes. As various technologies for wearable electronic devices are developed beyond flexible ones, there is an increasing demand for rechargeable batteries that operate with materials that are safe and do not pose a risk of explosion.

[0005] In this regard, aqueous zinc-ion secondary batteries containing a zinc anode are attracting attention as a power source for various wearable electronic devices because they have high stability compared to other secondary batteries, as they use a water-based aqueous electrolyte and thus have no risk of explosion, are eco-friendly, less toxic, and are more economical than other alkali metals.

[0006] However, zinc cathodes have the disadvantage of a short lifespan due to dendrites formed on the surface of the zinc cathode and side reactions with the aqueous electrolyte when charging and discharging continue.

[0007] Therefore, there is a need for technology that can minimize dendrite formation and side reactions of the zinc anode during charging and discharging in a zinc-ion secondary battery system containing an aqueous electrolyte. The problem to be solved

[0009] The object of the present invention is to provide a negative electrode for an aqueous secondary battery comprising a zinc metal film; and a polymer protective film formed on at least one surface of the zinc metal film.

[0010] In addition, another object of the present invention provides a method for manufacturing a negative electrode for an aqueous secondary battery, comprising the step of forming a polymer protective film on at least one surface of a zinc metal film.

[0011] In addition, another object of the present invention provides a method for manufacturing a negative electrode for a water-based secondary battery comprising: a negative electrode for a water-based secondary battery; a positive electrode; and a water-based electrolyte.

[0013] The problems that the present invention aims to solve are not limited to the problem(s) mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0015] To achieve the above objective, the present invention provides a negative electrode for a water-based secondary battery comprising: a zinc metal film; and a water-based polymer protective film formed on at least one surface of the zinc metal film.

[0016] The above water-based polymer may be polyacrylic acid.

[0017] The molecular weight of the above polyacrylic acid may be 1,000 to 500,000 g / mol.

[0018] The thickness of the above water-based polymer protective film may be 50 to 500 nm.

[0019] In addition, the present invention provides a method for manufacturing a negative electrode for a water-based secondary battery, comprising: (a) a step of preparing a zinc metal film; and (b) a step of forming a water-based polymer protective film on at least one surface of the zinc metal film.

[0020] The above step (a) may be a step of preparing a surface-treated zinc metal film by treating a zinc metal film with oxygen plasma.

[0021] Step (b) above may be a step of forming a water-based polymer protective film by coating a water-based polymer solution on at least one surface of the zinc metal film using spin-coating.

[0022] The spin coating above may be performed at 2,000 to 4,000 rpm.

[0023] The above method for manufacturing a negative electrode for a water-based secondary battery may further include (c) a step of heat-treating a water-based polymer protective film formed on at least one surface of a zinc metal film.

[0024] In addition, the present invention provides a water-based secondary battery comprising: a negative electrode for the water-based secondary battery; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and a water-based electrolyte.

[0025] The above aqueous electrolyte may include one or more metal salts selected from the group consisting of zinc sulfate (ZnSO4), zinc chloride (Zn(Cl2) and zinc triplate (Zn(CF3SO3)2).

[0026] The above aqueous electrolyte may have a molar concentration of the metal salt of 1 to 5 M.

[0027] The above anode may include manganese oxide (MnO2), vanadium oxide (V2O5), and lithium iron phosphate (LiFePO4). Effects of the invention

[0029] The negative electrode for an aqueous secondary battery according to the present invention includes a polymer protective film to minimize contact between the zinc electrode and the aqueous electrolyte, thereby suppressing side reactions.

[0030] In addition, the negative electrode for an aqueous secondary battery according to the present invention includes a polymer protective film, which can suppress the formation of dendrites on the surface of the negative electrode, thereby improving the lifespan characteristics of the aqueous secondary battery.

[0031] In addition, the polymer protective film included in the negative electrode for the aqueous secondary battery of the present invention uses a hydrophilic polymer, making it an eco-friendly material that is safe for microorganisms and completely free of toxicity or irritation. This allows for the manufacture of an environmentally friendly aqueous secondary battery negative electrode compared to other secondary batteries that use highly toxic chemicals.

[0033] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0035] Figure 1 shows a schematic diagram of a method for manufacturing a zinc electrode according to one embodiment of the present invention. Figure 2 is the result of confirming the wettability of a zinc electrode prepared according to Example 3 of the present invention and a zinc electrode prepared according to Comparative Example 1. Figure 3 is an SEM image for confirming the surface shape of a zinc electrode when a zinc electrode prepared according to Example 3 of the present invention and a zinc electrode prepared according to Comparative Example 1 are brought into contact with an electrolyte. Figure 4 is infrared spectrometer data for observing structural changes on the surface of a zinc electrode after contacting a zinc electrode prepared according to Example 3 of the present invention and a zinc electrode prepared according to Comparative Example 1 with an electrolyte. Figure 5 shows a schematic diagram of the zinc electrode effect depending on whether plasma treatment is present or not when manufacturing a zinc electrode according to Example 3 of the present invention. FIG. 6 shows the results of a symmetric cell including a zinc electrode prepared according to Example 3 of the present invention and a zinc electrode prepared according to Comparative Example 1, where FIG. 6a is 4 mA / cm² 2 , 1mAh / cm 2 This is data for zinc deposition and desorption, and Fig. 6b is 4 mA / cm 2 , 4mAh / cm 2This shows the data for depositing and desorbing zinc. FIG. 7 shows the change in the electrode surface after repeating charge and discharge 50 times in a symmetric cell comprising a zinc electrode prepared according to Example 3 of the present invention and a zinc electrode prepared according to Comparative Example 1, where FIG. 7a and FIG. 7b are SEM images of the zinc electrode prepared according to Comparative Example 1 before and after 50 charge and discharge cycles, and FIG. 7c and FIG. 7d are SEM images of the zinc electrode prepared according to Example 3 before and after 50 charge and discharge cycles. Figure 8 is the result of evaluating current density according to the change in polymer molecular weight of the aqueous polymer protective film included in the zinc electrode prepared according to Examples 1 to 3 of the present invention. Figure 9 shows the results of the lifespan characteristics of a complete cell manufactured including a zinc electrode manufactured according to Example 3 of the present invention and a zinc electrode manufactured according to Comparative Example 1. Specific details for implementing the invention

[0036] It should be noted that in the following description, only the parts necessary for understanding the embodiments of the present invention are described, and the description of other parts may be omitted to the extent that it does not detract from the gist of the present invention.

[0037] The terms and words used in the specification and claims described below should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Accordingly, the embodiments described in this specification and the configurations illustrated in the drawings are merely preferred embodiments of the invention and do not represent all aspects of the technical spirit of the invention; therefore, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0039] The present invention will be described in detail below.

[0040] In one embodiment of the present invention, a negative electrode for a water-based secondary battery is provided, comprising: a zinc metal film; and a water-based polymer protective film formed on at least one surface of the zinc metal film.

[0041] In one embodiment, the zinc metal film may represent a zinc electrode or a zinc cathode.

[0042] In one embodiment, the zinc metal film may be zinc metal or a zinc alloy. The zinc alloy includes an element capable of alloying with zinc, and, for example, the element may be one or more selected from Si, Sn, Ni, Cu, Ti, Fe, Mg, Ca, Sr, Sb, Pb, and Al.

[0043] The zinc metal film may be in the form of a sheet or a foil. Additionally, the zinc metal film may be in the form of zinc metal or a zinc alloy deposited or coated on a current collector by a dry process, or in the form of particulate metal and alloy deposited or coated by a wet process, etc.

[0044] The above zinc metal film may further include a current collector on one side that is not in contact with the water-based polymer protective film. For example, the zinc metal film may be a cathode, and in this case, a cathode current collector may be used.

[0045] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and may be selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and the alloy may be an aluminum-cadmium alloy, and in addition, calcined carbon, a non-conductive polymer surface-treated with a conductive material, or a conductive polymer may be used. For example, a copper foil may be used as the negative electrode current collector.

[0046] In one embodiment, the water-based polymer protective film may be formed on at least one surface of the zinc metal film.

[0047] In a water-based zinc secondary battery, when the zinc metal film is included as an electrode, contact between the zinc electrode and the water electrolyte is minimized, thereby suppressing side reactions. In addition, when charging and discharging the water-based zinc secondary battery, uniform electrodeposition of zinc is induced to suppress the occurrence of overvoltage, thereby preventing cell short circuits and improving the lifespan characteristics of the battery.

[0048] Polyacrylic acid may be used as the aqueous polymer for forming the above-mentioned aqueous polymer protective film. When polyacrylic acid is used as the above-mentioned aqueous polymer, it contains carboxylic acid functional groups, which improves the wettability of the electrolyte and ensures a uniform zinc concentration on the surface, enabling stable operation for a long period of time.

[0049] The molecular weight of the above polyacrylic acid may be 1,000 to 500,000 g / mol, and to achieve low overpotential and dendrite-efficient dendrite suppression when the zinc cathode is driven, polyacrylic acid having a molecular weight of, for example, 5,000 to 240,000 g / mol may be used.

[0050] The thickness of the above water-based polymer protective film may be 50 to 500 nm, specifically 100 to 300 nm. When the thickness of the water-based polymer protective film is formed within the above range, uniform electrodeposition of zinc can be induced, thereby suppressing the growth of zinc dendrites.

[0052] In addition, in one embodiment of the present invention, a method for manufacturing a negative electrode for a water-based secondary battery is provided, comprising: (a) a step of preparing a zinc metal film; and (b) a step of forming a water-based polymer protective film on at least one surface of the zinc metal film.

[0053] In one embodiment, step (a) may be a step of preparing a surface-treated zinc metal film by treating a zinc metal film with oxygen plasma.

[0054] The above zinc metal film is identical to the zinc metal film described above, and any details that overlap with those explained in the above zinc metal film are not explained again.

[0055] When the above zinc metal film is treated with oxygen plasma, the surface of the zinc metal film is oxidized, and due to step (c) described later, the aqueous polymer and the surface of the zinc metal film are bonded, thereby improving the cohesive force between the aqueous polymer and the zinc metal film. As a result, wettability to the aqueous electrolyte can be improved.

[0056] In one embodiment, step (b) may be a step of forming a water-based polymer protective film by coating a water-based polymer solution on at least one surface of the zinc metal film using spin-coating.

[0057] The above-mentioned water-based polymer protective film is identical to the water-based polymer protective film described above, and any details that overlap with those explained in the above-mentioned water-based polymer protective film are not explained again.

[0058] The spin coating above may be performed at 2,000 to 4,000 rpm, and to uniformly coat the polymer protective film, spin coating may be performed at, for example, 3,000 rpm.

[0059] In one embodiment, after step (b), the method may further include step (c) of heat-treating a water-based polymer protective film formed on at least one surface of the zinc metal film.

[0060] The above heat treatment can be performed at 70 to 90°C, and in terms of strengthening the dehydration reaction between the oxidized zinc surface and the water-based polymer protective film and the cohesion between the protective film and the zinc cathode, for example, it can be performed at 70 to 80°C.

[0061] In addition, in one embodiment of the present invention, a water-based secondary battery is provided, comprising: a negative electrode for the water-based secondary battery; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and a water-based electrolyte.

[0062] The above-mentioned negative electrode may be the negative electrode for the above-mentioned aqueous zinc secondary battery, and the above-mentioned negative electrode may have an aqueous polymer protective film formed on the surface facing the positive electrode.

[0063] As described above, the negative electrode for the aqueous secondary battery includes an aqueous polymer protective film on at least one surface of the zinc metal film, which can reduce the interfacial resistance between the aqueous electrolyte and the zinc negative electrode surface, and the negative electrode surface is modified to reduce the initial overvoltage when zinc ions grow on the negative electrode surface, and efficiently facilitates the diffusion of zinc to suppress dendrite formation, and the dendrites grow in a soft elliptical shape unlike conventional ones, thereby improving the lifespan of the aqueous zinc secondary battery.

[0064] The above aqueous electrolyte may include one or more metal salts selected from the group consisting of zinc sulfate (ZnSO4), zinc chloride (Zn(Cl2) and zinc triplate (Zn(CF3SO3)2), and zinc sulfate (ZnSO4) may be used in terms of acidity that allows for stable operation without causing precipitation of zinc ions or significant corrosion.

[0065] The above aqueous electrolyte may have a molar concentration of the metal salt of 1 to 5 M, and for the purpose of evenly depositing zinc on the surface, for example, one with a concentration of 2 M may be used.

[0066] The above anode may include manganese oxide (MnO2), vanadium oxide (V2O5), and lithium iron phosphate (LiFePO4).

[0067] Since the above-described aqueous secondary battery includes the negative electrode for the aqueous secondary battery described above, stability is improved, and electrochemical performance such as charge / discharge life characteristics and rate characteristics is enhanced.

[0068] Unlike lithium-ion rechargeable batteries, the aforementioned aqueous secondary battery is a safe battery system that utilizes an aqueous electrolyte without a risk of ignition. Furthermore, it is an eco-friendly battery because the components used in it are made of non-toxic materials. In other words, since the battery components are non-toxic and pose no risk of ignition, it is suitable as a power source for wearable medical devices, bio-implantable batteries, and the like.

[0069] In addition, the above-mentioned aqueous secondary battery allows for cell assembly in an atmospheric environment, which has the effect of reducing process costs.

[0070] In addition, it is suitable for medium to large-scale energy storage devices because it has battery components that are inexpensive compared to the cost of lithium-ion rechargeable batteries.

[0072] The above description explains the technical concept of the present invention using one embodiment, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments described in this invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

[0073] <Example>

[0074] Example 1

[0075] A zinc electrode was prepared by punching a zinc foil (ThermoFisher, Zinc foil, 7440-66-6) with a thickness of 0.25 mm into a 16 mm circle and a thickness of 0.25 mm. The zinc electrode was ultrasonically cleaned with acetone, isopropyl alcohol, and ethanol in that order for 15 minutes each. Afterward, the solvent was removed using an air gun, and the zinc electrode was dried in a 70°C oven for 2 hours. The dried zinc electrode was then surface-treated using oxygen plasma at 150 W for 3 minutes.

[0076] A polyacrylic acid solution was prepared by mixing and dispersing 1% by weight of 5,000 g / mol polyacrylic acid in 100% by weight of water. The polyacrylic acid solution was spin-coated at a speed of 3,000 rpm onto the surface-treated zinc electrode to form a polyacrylic acid film on the zinc electrode. Subsequently, the zinc electrode with the formed polyacrylic acid film was dried on an 80°C hot plate to produce a zinc electrode with a 200 nm polyacrylic acid film (Fig. 1).

[0078] Example 2

[0079] A zinc electrode was prepared using the same method and conditions as in Example 1, except that 100,000 g / mol of polyacrylic acid was used instead of 5,000 g / mol of polyacrylic acid in Example 1.

[0081] Example 3

[0082] A zinc electrode was prepared using the same method and conditions as in Example 1, except that 240,000 g / mol of polyacrylic acid was used instead of 5,000 g / mol of polyacrylic acid in Example 1.

[0084] Example 4

[0085] A zinc electrode was prepared using the same method and conditions as in Example 1, except that a dried zinc electrode without surface treatment was used instead of the dried zinc metal film in Example 1 which was surface-treated at 150 W for 3 minutes using oxygen plasma.

[0086] <Comparative Example>

[0087] Comparative Example 1

[0088] A zinc electrode was prepared by punching a zinc foil (ThermoFisher, Zinc foil, 7440-66-6) with a thickness of 0.25 mm into a 12 mm circle and a thickness of 0.25 mm.

[0090] <Experimental Example>

[0091] Experimental Example 1: Evaluation of Electrolyte Wetness

[0092] 20 μL of 2 M ZnSO4 electrolyte was dropped onto a zinc electrode prepared according to Example 3 (hereinafter referred to as "Zn@PAA") and a zinc electrode prepared according to Comparative Example 1 (hereinafter referred to as "Bare Zn"), and the contact angle was measured using a contact angle measuring instrument (SL200, USA), and the results are shown in FIG. 2.

[0093] Since the wettability of the electrolyte on the electrode surface of a secondary battery affects interfacial resistance, better wettability can influence the improvement of the secondary battery's performance.

[0094] Referring to FIG. 2, the one prepared according to Example 3 Zn@PAA is 84.88 It was confirmed that wettability was improved by more than 2.5 times compared to Bare Zn prepared according to Comparative Example 1, which exhibited a contact angle of 29.5°, by exhibiting a contact angle of °.

[0095] Experimental Example 2: Surface Analysis Due to Electrolyte Contact

[0096] Zn@PAA prepared according to Example 3 and Bare Zn prepared according to Comparative Example 1, respectively, were each immersed in 10 ml of 2 M ZnSO4 electrolyte for 20 days, and the surface morphology was confirmed by SEM, and the results are shown in Figure 3.

[0097] Referring to Fig. 3, it can be seen that sharp dendrites were formed in the bare Zn prepared according to Comparative Example 1. On the other hand, it can be seen that the Zn@PAA prepared according to Example 3 had round dendrites formed, which is different from the shape of bare Zn, indicating that the aqueous polymer influences the dendrite formation mechanism of zinc. These results suggest that the aqueous polymer protective film can solve the problem of short circuits with the electrodes caused by the formation of sharp dendrites during the charging and discharging of aqueous zinc secondary batteries.

[0098] Experimental Example 3: Confirmation of electrode surface structure due to electrolyte contact

[0099] After immersing each of the Zn@PAA prepared according to Example 3 and the Bare Zn prepared according to Comparative Example 1 in 10 ml of 2 M ZnSO4 electrolyte for 20 days, the structural changes on the surface of the zinc electrode were confirmed using an infrared spectrometer (FT-IR), and the results are shown in Figure 4.

[0100] Referring to Fig. 4, it can be seen that the polyacrylic acid of the zinc electrode (Zn@PAA) coated with a polyacrylic acid protective film exists on the electrode surface without the aqueous electrolyte dissolving.

[0101] Experimental Example 4: Confirmation of effects depending on the presence or absence of a polymer protective film after plasma treatment

[0102] Figure 5 shows a schematic diagram of the predicted effect of the dendrite shape on the surface of the zinc electrode according to the presence or absence of a water-based polymer protective film after plasma treatment.

[0103] Referring to Fig. 5, when a water-based polymer protective film is introduced, a zinc surface can be stably formed.

[0104] Experimental Example 5: Verification of lifespan characteristics

[0105] Zn@PAA prepared according to Example 3 and Bare Zn prepared according to Comparative Example 1 were each prepared as 2032-coin cell type using a GF / C separator and a 2M ZnSO4 electrolyte, and electrochemical evaluation was performed. The lifetime characteristics of the zinc electrode were confirmed through zinc||zinc symmetric cell evaluation, and the results are shown in Fig. 6.

[0106] Referring to Fig. 6, it can be confirmed through a symmetric cell test that the zinc electrode with a water-based polymer protective film has superior lifespan characteristics compared to a zinc electrode without a water-based polymer protective film (~200 cycles -> over 1000 cycles).

[0107] In addition, Zn@PAA prepared according to Example 3 and Bare Zn prepared according to Comparative Example 1 were each prepared into a complete cell (LFP||Zn) using a GF / C separator, a 2M ZnSO4 electrolyte, and a lithium iron phosphate cathode, and charge-discharge evaluations were performed. The life characteristics of the zinc electrode were confirmed through the charge-discharge evaluation of the LFP||Zn complete cell, and the results are shown in Fig. 9.

[0108] Referring to Fig. 9, it can be seen that the lifespan characteristics are much better in the case of a zinc electrode with a water-based polymer protective film formed (~200 cycles -> 500 cycles or more).

[0109] Experimental Example 6: Surface Analysis of a Symmetric Cell According to Charging and Discharging

[0110] Zn@PAA prepared according to Example 3 and Bare Zn prepared according to Comparative Example 1 were each prepared as 2032-coin cell type using a GF / C separator and a 2M ZnSO4 electrolyte, and electrochemical evaluation was performed. The electrode surface was examined by SEM after 50 charge-discharge cycles using a zinc||zinc symmetry cell evaluation. The results are shown in Fig. 7; specifically, Figs. 7a and 7b are SEM images of the zinc electrode prepared according to Comparative Example 1 before and after 50 charge-discharge cycles, and Figs. 7c and 7d are SEM images of the zinc electrode prepared according to Example 3 before and after 50 charge-discharge cycles.

[0111] Referring to Fig. 7, it can be seen that sharp dendrite structures grew indiscriminately on bare Zn (Figs. 7a and 7b), and that the zinc electrode coated with a water-based polymer protective film (Zn@PAA) showed that the formation of zinc dendrites was suppressed (Figs. 7c and 7d).

[0112] Experimental Example 7: Evaluation of Current Density According to Change in Molecular Weight of Aqueous Polymer

[0113] Each zinc electrode prepared according to Examples 1 to 3 was prepared as a 2032-coin cell type using a GF / C separator and a 2M ZnSO4 electrolyte, and an electrochemical evaluation was performed. The current density was evaluated after 50 charge-discharge cycles using a zinc||zinc symmetric cell evaluation, and the results are shown in Figure 8.

[0114] Referring to Fig. 8, in order to verify the electrochemical lifetime characteristics according to the low resistance and current density that occur when zinc is initially deposited, an evaluation of current density according to changes in the molecular weight of the aqueous polymer was performed, and it was confirmed that the zinc electrode prepared according to Example 3 (polyacrylic acid molecular weight: 240,000 g / mol) most efficiently suppresses indiscriminate dendrite growth.

[0116] Although the present invention has been described above with reference to embodiments, the present invention is not limited by the embodiments disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention were not explicitly described while describing the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized.

Claims

Claim 1 A negative electrode for an aqueous secondary battery, comprising: a zinc metal film surface-treated by oxygen plasma treatment; and a protective film made of polyacrylic acid formed on at least one surface of the surface-treated zinc metal film, wherein the molecular weight of the polyacrylic acid is 5,000 to 240,000 g / mol. Claim 2 delete Claim 3 delete Claim 4 A negative electrode for a water-based secondary battery according to claim 1, wherein the thickness of the protective film is 50 to 500 nm. Claim 5 (a) a step of preparing a surface-treated zinc metal film by oxygen plasma treatment; (b) a step of forming a protective film made of polyacrylic acid on at least one surface of the surface-treated zinc metal film using a polyacrylic acid solution containing polyacrylic acid; and (c) a step of heat-treating the protective film made of polyacrylic acid formed on at least one surface of the surface-treated zinc metal film, wherein the molecular weight of the polyacrylic acid is 5,000 to 240,000 g / mol. Claim 6 delete Claim 7 A method for manufacturing a negative electrode for an aqueous secondary battery, wherein in claim 5, step (b) is a step of forming a protective film made of polyacrylic acid by coating a polyacrylic acid solution on at least one surface of the zinc metal film using spin-coating. Claim 8 A method for manufacturing a negative electrode for an aqueous secondary battery according to claim 7, wherein the spin coating is performed at 2,000 to 4,000 rpm. Claim 9 delete Claim 10 A water-based secondary battery comprising: a negative electrode for a water-based secondary battery according to claim 1; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and a water-based electrolyte. Claim 11 A water-based secondary battery according to claim 10, wherein the water-based electrolyte comprises one or more metal salts selected from the group consisting of zinc sulfate (ZnSO4), zinc chloride (Zn(Cl2) and zinc triplate (Zn(CF3SO3)2). Claim 12 In claim 11, the aqueous electrolyte is an aqueous secondary battery in which the molar concentration of the metal salt is 1 to 5 M. Claim 13 In claim 10, the above-mentioned positive electrode is a water-based secondary battery comprising lithium iron phosphate (LiFePO4).

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