Patent Application
20230282806
This application claims priority to and the benefit of Korean Patent Applications No. 2022-0066926, filed on May 31, 2022 and No. 2022-0026488, filed on Mar. 2, 2022, the disclosure of which is incorporated herein by reference in its entirety.
The present invention relates to a secondary battery, and more particularly to a zinc metal battery.
In recent years, as portable wireless devices such as portable phones and portable computers have been made lighter and more functional, a lot of research has been conducted on secondary batteries used as driving power sources of them. Examples of the secondary batteries include a nickel cadmium battery, a nickel hydride battery, a nickel zinc battery, and a lithium secondary battery. Among them, lithium secondary batteries are widely used in the field of advanced electronic devices because they are rechargeable, have high operating voltage, and have high energy density per unit weight.
Meanwhile, as various technologies for wearable electronic devices beyond the flexible electronic devices have recently been developed, the demand for secondary batteries that operate with materials with high stability and no risk of explosion is also increasing. In relation to this, zinc secondary batteries have the advantages of being more stable than other secondary batteries, eco-friendly, less toxic, and more economical than other alkali metal secondary batteries. Currently, research on zinc secondary batteries using zinc metal as an electrode material is being actively conducted.
An electrolyte of a general zinc secondary battery uses an aqueous solvent having high ionic conductivity and low fire risk. However, there is a limitation in the voltage range in which charging and discharging of the battery is performed, and there is a problem in that the probability of occurrence of zinc dendrites is high due to high ionic conductivity compared to organic solvents.
The present invention is directed to provide an anode including a protective layer and a zinc metal battery including the same for suppressing the growth of zinc dendrites on the anode when an aqueous electrolyte is used.
The technical tasks of the present invention are not limited to the technical tasks mentioned above, and other technical tasks not mentioned will be clearly understood by those skilled in the art from the following description.
In order to solve the above tasks, one aspect of the present invention is to provide an anode for zinc metal battery comprising a zinc metal film containing zinc metal, and a protective layer formed on the surface of the zinc metal film.
In ToF-SIMS analysis, PO−, HPO−, ZnPO− and ZnHPO− peaks can be detected from the protective layer.
The protective layer may include zinc phosphate.
The protective layer may have an orthorhombic structure as a crystal structure, and a space group thereof may be Pnma.
The protective layer may have a thickness of 5 to 15 nm.
In order to solve the above tasks, another aspect of the present invention provides a method for manufacturing an anode for a zinc metal battery comprising immersing zinc metal in an aqueous phosphate solution, and subjecting it to ultrasonic treatment to form a protective layer.
The ultrasonic treatment time may be 1 to 30 minutes, and may be 5 to 15 minutes in detail.
In order to solve the above tasks, another aspect of the present invention is to provide a zinc metal battery comprising an anode including a zinc metal film containing zinc metal and a protective layer formed on the surface of the zinc metal film, a cathode containing a cathode active material, and an aqueous electrolyte disposed between the anode and the cathode and containing a zinc salt.
The cathode active material may include alkali metal vanadium oxide or vanadium oxide.
The alkali metal vanadium oxide may be MxV3O8, M may be an alkali metal, and x may be 0.8 to 2.2.
The alkali metal vanadium oxide may include at least one selected from LiV3O8, NaV3O8 and K2V3O8.
The vanadium oxide may include at least one selected from VO2(B), V2O3 and V2O5.
The zinc salt may include at least one selected from ZnSO4, Zn(NO3)2, Zn(CH3CO2)2, Zn(CF3SO3)2, ZnCl2, and Zn(ClO4)2.
The aqueous electrolyte may have a pH of 3 to 7.
According to the present invention described above, an anode for a zinc metal battery according to the present invention includes a zinc metal film and a protective layer such as zinc phosphate formed on a surface of the zinc metal film, and the protective layer coats the outermost surface of the zinc metal film to prevent direct contact of zinc metal with an aqueous electrolyte. Therefore, there is an effect of helping uniform growth of zinc dendrites formed during plating/stripping of zinc ions during the charging and discharging process of the battery and preventing a short circuit of the battery.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee. The above and other objects, features, and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the adhered drawings, in which:
Since the present invention may have various changes and various forms, specific embodiments are illustrated in the drawings and described in detail in the description. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals have been used for like elements throughout the description of each figure.
Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning.
Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail.
Zinc Metal Battery
The zinc metal battery according to an embodiment of the present invention includes an anode 10 including zinc metal film 11 and a protective layer 13 formed on a surface of the zinc metal film 11; a cathode 20 including a cathode active material; and an aqueous electrolyte 30 disposed between the anode 10 and the cathode 20 and containing a zinc salt.
Anode
Referring to
The standard electrode potential of zinc (Zn2++2e−→Zn) is −0.76 V (vs. SHE), and the theoretical mass specific capacity of zinc is 412 mAh/g. Zinc metal is one of the possible candidate materials as an anode material for batteries that require high capacity in a limited volume. In addition, since the zinc metal is considerably cheaper than lithium metal, it is possible to solve the problem of unstable supply of lithium metal, and since it has a lower reactivity than lithium metal, a relatively stable battery can be provided.
The zinc metal film 11 is a layer containing zinc metal, and may be a pure zinc metal film or a zinc alloy layer. The zinc alloy can be alloy of zinc and other metals.
The anode 10 may have the pure zinc metal film or the zinc alloy layer in the form of a foil or flake, and having a thickness of 100 μm to 1000 μm, for example, 200 μm to 500 μm, but is not limited thereto.
The anode 10 may include a protective layer 13 formed on the surface of the zinc metal film 11.
The protective layer 13 may include zinc phosphate. Specifically, the protective layer 13 may be zinc phosphate of hopeite, have an orthorhombic structure as a crystal structure, and may have a space group of Pnma.
In ToF-SIMS analysis, PO−, HPO−, ZnPO−, and ZnHPO− peaks may be detected from the protective layer 13.
In addition, the protective layer 13 may be formed through the reaction of Chemical Formula 1 below:
3Zn+2H3PO4+4H2O→Zn3(PO4)2·4H2O+3H2 [Chemical Formula 1]
The protective layer 13 may include zinc phosphate (Zn3(PO4)2·4H2O) formed by reacting zinc metal with phosphoric acid. Specifically, the protective layer 13 may be formed by immersing the zinc metal film in a phosphoric acid aqueous solution and performing ultrasonic treatment at room temperature for 1 to 30 minutes, for example, 10 minutes. In addition, the protective layer 13 may be formed on one surface of the zinc metal film, specifically, at least one surface immersed and contacted with the phosphoric acid aqueous solution. Thus, the anode 10 may include the zinc metal film 11 containing zinc metal, and the protective layer 13 formed on at least one surface of the zinc metal film 11 in contact with the outside, specifically the protective layer 13 may includes zinc phosphate.
When the anode 10 including the protective layer 13 is assembled into a battery, direct contact of zinc metal with the electrolyte can be prevented. In the case of a zinc secondary battery using zinc metal as an electrode, a side reaction by an electrochemical reaction, for example, an electrolysis reaction of water contained in the aqueous solvent can be generated due to a potential difference while driving of the secondary battery. Due to the electrolysis reaction of the water-based solvent, hydrogen gas, zinc hydroxide, or zinc oxide may be generated, and these side reactions may cause a problem in durability of the battery. However, since the zinc metal battery including the anode including the zinc phosphate layer of the present invention prevents direct contact between the electrode and the electrolyte to limit the aforementioned side reactions, the stability of the battery can be improved.
In addition, since the anode including the protective layer 13 may serve to help the uniform growth of zinc dendrites formed during the charging and discharging process of the battery, there is an effect of preventing a short circuit during plating/stripping of zinc ions within the charging and discharging process and improving cycle characteristics.
The concentration of the aqueous phosphoric acid solution may be 50 to 100 wt %, specifically 70 to 90 wt %. In one embodiment, the concentration of the aqueous phosphoric acid solution may be 85 wt %, but is not limited thereto.
The protective layer 13 may have a thickness of 5 to 15 nm. When the thickness of the protective layer is less than 5 nm, sharp and irregular zinc dendrites may be formed as zinc ions are plated on/stripped from the zinc metal used as the anode during the cycle process, thereby not only occurring a short circuit of the battery but also accelerating the deterioration of the battery by formation of dead zinc. On the other hand, when the thickness of the protective layer is greater than 15 nm, the ability to conduct zinc ions to the zinc metal film is reduced, which may hinder the charging and discharging rate of the battery. When the protective layer has a thickness within the above range, it is possible to suppress the generation of dead zinc and zinc dendrites during the cycle process in which zinc ions are plated/stripped, and also the shape of the formed zinc dendrites can be regular and evenly distributed over the entire surface of the electrode, the surface of the zinc metal can be protected and the lifespan of the battery can be improved. Specifically, the thickness of the protective layer may be 7 to 12 nm, more specifically 8 to 11 nm, and more specifically 9 to 10 nm. In one embodiment, the thickness of the protective layer may be 9.5 nm, but is not limited thereto.
Cathode
A cathode for a zinc metal battery according to the present invention may be one in which a slurry containing a cathode active material, a binder, and a conductive material is formed on a current collector.
The cathode active material may include an alkali metal vanadium oxide or a vanadium oxide.
The alkali metal vanadium oxide may be MxV3O8, M may be an alkali metal, and x may be 0.8 to 2.2.
The alkali metal vanadium oxide may include at least one selected from LiV3O8, NaV3O8 and K2V3O8. In one embodiment, the alkali metal vanadium oxide may be NaV3O8, but is not limited thereto.
The vanadium oxide may include at least one selected from VO2(B), V2O3 and V2O5. In particular, since zinc ion (Zn2+), which is a divalent ion, is used as a charge carrier, it is preferable to use a vanadium-based cathode active material having a wide range of oxidation numbers from 2 to 5. In addition, since its crystal lattice size is large, insertion and desorption of zinc ions (Zn2+) may be facilitated during charging and discharging of the battery.
The conductive material may be used without limitation as long as it is generally usable in the art, for example artificial graphite, natural graphite, carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, carbon nanofibers, carbon nanotubes, metal fibers, or mixtures thereof can be used. In one embodiment, the conductive material may be a mixture of ketjen black and super Pin a mass ratio of 1:1, but is not limited thereto.
The binder may be used without limitation as long as it is generally usable in the art, for example, polyvinylidene fluoride (PVdF), polyhexafluoropropylene-polyvinylidene fluoride copolymer (PVdF/HFP), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyvinylpyridine, alkylated polyethylene oxide, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoroethylene (PTFE), polyvinyl chloride, polyacrylonitrile, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluoro rubber, ethylene-propylene-diene monomer (EPDM), sulfonated ethylene-propylene-diene monomer, carboxymethylcellulose (CMC), sodium carboxymethylcellulose, regenerated cellulose, starch, hydroxypropyl cellulose, tetrafluoroethylene, or a mixture thereof may be used. In one embodiment, the binder may include sodium carboxymethyl cellulose, but is not limited thereto.
The solvent for forming the slurry containing the active material of the cathode, the binder, and the conductive material may include an aqueous solvent such as water, ethanol, isopropyl alcohol (IPA), or organic solvent such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, and these solvents may be used alone or in combination of two or more. In one embodiment, the solvent may be water, but is not limited thereto. The amount of the solvent used may be adjusted so as to dissolve and disperse the active material, the binder, and the conductive material, and to have an appropriate viscosity of the slurry in consideration of the coating thickness and manufacturing yield.
The active material of the cathode, the binder, and the conductive material may be mixed in a certain ratio to form the slurry having appropriate viscosity and processability. The ratio of the active material, the binder, and the conductive material may be 8:1:1 in terms of mass ratio, but is not limited thereto.
The cathode may be formed on a current collector layer to a thickness of 50 to 200 μm, specifically, to a thickness of 80 to 120 μm. In one embodiment, the cathode may be formed on the current collector layer to a thickness of 100 μm, but is not limited thereto.
Separator
A separator may be disposed between the anode and the cathode to electrically insulate the electrodes. In addition, the separator is sufficiently impregnated with the aqueous electrolyte, and the porous interior thereof may allow zinc ions to move from the anode to the cathode and from the cathode to the anode.
The separator may be a conventional porous polymer film used as a separator, for example, polyolefin based porous polymer film including ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/methacrylate copolymer, or polyvinyl alcohol, which may be used alone or in a laminated form. Alternatively, the separator may be a conventional porous nonwoven fabric formed from, for example, glass fiber, carboxymethyl cellulose, polyethylene terephthalate fiber, etc. In one embodiment, the separator may be a glass fiber membrane having a thickness of 10 to 500 μm, but is not limited thereto.
Aqueous Electrolyte
The zinc metal battery of the present invention may refer to a battery utilizing zinc ions as a charge transfer material. In other words, the zinc metal battery may include an aqueous electrolyte containing an aqueous solvent and a zinc salt to enable intercalation and deintercalation of zinc ions.
The aqueous solvent may be water.
The zinc salt may be a water-soluble salt that can generate zinc ions when dissolved in water. For example, the zinc salt may include at least one or more selected from ZnSO4, Zn(NO3)2, Zn(CH3CO2)2, Zn(CF3SO3)2, ZnCl2 and Zn(ClO4)2. In one embodiment, the zinc salt may be ZnSO4, but is not limited thereto.
The molar concentration of the aqueous electrolyte may be 0.1 to 2 M, and in one embodiment, it may be 1 M.
The pH of the aqueous electrolyte may be 3 to 7, specifically, 4 to 5, and in one embodiment, the pH of the electrolyte may be 4.03. If the pH of the aqueous electrolyte is less than 3, there may be a problem of causing corrosion of the electrode due to the strong acidic component. On the other hand, when the pH of the aqueous electrolyte exceeds 7, there may be a problem in that the ionic conductivity decreases due to the small amount of the ion transport material in the electrolyte.
By using an aqueous electrolyte, a battery including it can have high ionic conductivity. In addition, it is advantageous in terms of stability, and the process and manufacturing cost may also be inexpensive.
Hereinafter, in order to explain the present invention in more detail, preferred experimental examples according to the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms.
First, a zinc metal film was surface treated to prepare an anode having a zinc phosphate layer as a protective layer on a surface of the zinc metal film. The zinc metal film having holes with a diameter of 16 mm was immersed in 10 ml of an 85 wt % phosphoric acid (H3PO4) aqueous solution, and ultrasonic treatment was performed for 10 minutes. During the sonication process, a large amount of hydrogen gas bubbles was generated while the surface of the zinc metal reacted with phosphoric acid. The reaction-completed zinc metal film was taken out, and phosphoric acid remaining on the surface was removed using distilled water and ethanol immediately, and then dried in an oven at 60° C. for 1 hour. As a result, an anode having zinc phosphate coated on the surface of the zinc metal film was formed.
A symmetrical cell including the anodes prepared in Preparation Example as the working electrode and the counter electrode, a separator and an electrolyte between the working electrode and the counter electrode was prepared. A 1 M aqueous solution of ZnSO4 was used as the electrolyte, and glass fiber membrane is used as the separator. The symmetric cell was assembled into an R2032 coin type battery by sequentially stacking the working electrode, the glass fiber separator, and the counter electrode. Then, the electrolyte was injected into the coin cell. All manufacturing processes were carried out inside the glove box.
A zinc metal battery was manufactured in the same manner as in Manufacturing Example 1, except that the anode prepared in Preparation Example was used as the counter electrode and a cathode containing NaV3O8 as a cathode active material was used instead of the working electrode.
A symmetrical cell was manufactured in the same manner as in Manufacturing Example 1, except that untreated zinc metal was used as the working electrode and the counter electrode.
A zinc metal battery was manufactured in the same manner as in Manufacturing Example 2, except that untreated zinc metal was used as an anode.
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ToF-SIMS (Time-of-flight secondary ion mass spectrometry) analysis is an analysis method to obtain chemical components and surface structures by analyzing the time-of-flight of cations or anions emitted from the surface of a sample by colliding primary ions with the surface.
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Referring to 13a and 13b, when zinc metal is used as an electrode of a symmetrical cell, irregular-shaped zinc dendrites and/or dead zinc, and fibers torn from the separator are observed on the surface of the anode, wherein the anode was obtained by separating the cell after the charge/discharge cycle test is completed. Furthermore, a large amount of dead zinc can be observed on the surface of the front and rear surfaces of the separator obtained from the cell after the charge/discharge test. Similar to the results shown in
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The embodiments of the present invention disclosed in this specification and drawings are only presented as specific examples to aid understanding, and are not intended to limit the scope of the present invention. In addition to the embodiments disclosed herein, it is obvious to those skilled in the art that other modified examples based on the technical idea of the present invention can be implemented.
10: anode, 11: zinc metal film, 13: protective layer, 20: cathode, 30: aqueous electrolyte
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0026488 | Mar 2022 | KR | national |
| 10-2022-0066926 | May 2022 | KR | national |
