KR20220023081A - Zn anode with β-Polyvinylidene fluoride coating and aqueous Zn-ion batterie including the same - Google Patents

Abstract

The present invention relates to a zinc negative electrode having a beta-polyvinylidene fluoride coating layer and an aqueous zinc ion battery including the negative electrode. The zinc negative electrode having a beta-polyvinylidene fluoride coating layer of the present invention can further improve structural stability, electrochemical performance, and charge/discharge capacity of a secondary battery.

Description

A zinc anode with a beta-polyvinylidene fluoride coating layer formed thereon and an aqueous zinc ion battery including the anode {Zn anode with β-Polyvinylidene fluoride coating and aqueous Zn-ion battery including the same}

The present invention relates to a zinc negative electrode having a beta-polyvinylidene fluoride (β-PVDF) coating layer formed thereon and an aqueous zinc ion battery including the negative electrode. The zinc negative electrode with the beta-polyvinylidene fluoride coating layer of the present invention can further improve structural stability, electrochemical performance and charge/discharge capacity of a secondary battery.

A secondary battery refers to a battery that can be used repeatedly because it can be charged as well as discharged. In a typical lithium secondary battery among secondary batteries, lithium ions contained in the positive electrode active material move to the negative electrode through the electrolyte, and then are inserted into the layered structure of the negative electrode active material (charging). It works through the principle of returning to the positive pole (discharge). These lithium secondary batteries are currently commercialized and used as small power sources for mobile phones and notebook computers, and are expected to be used as large power sources for hybrid vehicles, and the demand is expected to increase. However, since the composite metal oxide mainly used as a cathode active material in a lithium secondary battery contains a rare metal element such as lithium, there is a concern that it may not be able to meet the increase in demand. Accordingly, although research on a sodium secondary battery using abundant supply and cheap sodium as a cathode active material is being conducted, the sodium battery system still has complex stability problems and environmental problems.

On the other hand, as various technologies for wearable electronic devices have recently been developed beyond flexible, demand for secondary batteries that do not have a risk of explosion and are operated with materials with high stability is increasing. In contrast, an aqueous zinc ion battery (AZIB) has higher stability than other secondary batteries, is eco-friendly, has less toxicity, and is economical compared to other alkali metals. In such a water-based zinc secondary battery, the zinc anode is dissolved in an alkali solution, and the elution and precipitation of zinc are repeated during the charge/discharge reaction. Due to this, the shape of the electrode plate changes according to the progress of the charge/discharge reaction, and the eluted zinc does not precipitate uniformly during charging but grows into a dendritic form, and the dendrite zinc penetrates the separator to cause a short circuit of the battery. Therefore, there is a disadvantage in that the battery life is short.

In order to solve this problem, the following techniques have been proposed. First, in Japanese Patent Laid-Open No. 1985-185372, a nickel/zinc secondary battery in which oxides and hydrates of In and Ti are added to a zinc electrode so as to maintain a high energy density in order to increase the number of times of charging and discharging of a nickel/zinc secondary battery. is disclosed about Japanese Patent Laid-Open No. 1987-108467 discloses an alkaline zinc battery in which indium metal, indium oxide, and thallium are added to a zinc electrode in order to increase the number of charging and discharging of the alkaline zinc battery, and germanium ions are added to the electrolyte solution. is disclosed about Japanese Patent Laid-Open No. 1986-061366 discloses an alkaline zinc battery in which an inert, non-conductive organic compound is added to a zinc electrode in order to prevent deformation of the zinc electrode plate and increase the number of charging and discharging in an alkaline zinc battery. . In addition, PCT/US2004/026859 describes a method for manufacturing a nickel/zinc secondary battery in which a separator layer is used to prevent dendrites from forming on the negative electrode of a nickel/zinc secondary battery and borate and fluoride are included in potassium hydroxide electrolyte. is starting Furthermore, US Patent No. 6,649,305 points out that the conductivity of zinc oxide is very low as a problem, and proposes the use of a conductive ceramic as a method of improving this problem.

1. Japanese Patent Laid-Open No. 1985-185372 2. Japanese Patent Laid-Open No. 1987-108467 3. International Patent Application PCT/US2004/026859 4. US Patent No. 6,649,305

In a zinc secondary battery, as the charge/discharge cycle by the dissolution and precipitation reaction of zinc proceeds, the shape of the zinc negative electrode changes, and the growth of charge/discharge zinc dendrites occurs, which penetrates the separator and contacts the positive electrode, causing a short circuit. This will shorten the lifespan. The growth of such zinc dendrites, that is, zinc dendrites, is one of the important causes of shortening the lifespan of secondary batteries.

Accordingly, the inventors of the present inventors made diligent efforts to increase the lifespan of a secondary battery by inhibiting the growth of zinc dendrites generated in the negative electrode of a zinc secondary battery. As a result, a ferroelectric polymer, beta-polyvinylidene (β-Polyvinylidene) fluoride, β-PVDF), the formation of zinc dendrites is improved, and after confirming that a zinc secondary battery with improved charge/discharge stability can be manufactured, the present invention has been completed.

An object of the present invention is to provide a negative electrode for an aqueous zinc secondary battery, characterized in that a beta-polyvinylidene fluoride (β-PVDF) coating layer is formed on the surface of a zinc metal negative electrode.

The present invention also comprises the steps of (A) applying a polyvinylidene fluoride (PVDF)-based polymer solution dissolved in a solvent on zinc metal; and (B) evaporating the solvent from the PVDF-based polymer solution applied on the zinc metal.

The present invention also relates to an anode; a cathode in which a beta-polyvinylidene fluoride (β-PVDF) coating layer is formed on a surface of a zinc metal anode; and an aqueous electrolyte disposed between the positive electrode and the negative electrode.

The negative electrode for a zinc secondary battery with a β-PVDF coating layer of the present invention has higher structural stability, electrochemical performance, and charging/discharging capacity of the secondary battery compared to the case of using a bare zinc negative electrode or a zinc negative electrode with an α-PVDF coating layer. can be improved Specifically, a very low overpotential (400mV) was maintained even after 2000 hours of operation in a symmetrical battery including a zinc secondary battery negative electrode with a β-PVDF coating layer formed, and the capacity during 4000 cycles of charging and discharging was also observed in full cell performance measurement. was found to be stable.

1 shows the XRD patterns of β-PVDF according to Example 1 and α-PVDF according to Comparative Example 1. FIG.
2 is a result of evaluating stripping/plating behavior and cycling stability of a symmetrical battery including PVDF @ Zn according to Example 1, α-PVDF@Zn according to Comparative Example 1, and bare Zn according to Comparative Example 2 indicates
3 shows the characteristics of PVDF @ Zn according to Example 1, α-PVDF@Zn according to Comparative Example 1, and bare Zn negative electrode according to Comparative Example 2 after 500 charge/discharge cycling.
4 shows the electrochemical performance evaluation results in a full-cell including PVDF @ Zn according to Example 1, α-PVDF@Zn according to Comparative Example 1, and bare Zn according to Comparative Example 2. FIG.

Aha, a negative electrode for a water-based zinc secondary battery, characterized in that a coating layer of beta-polyvinylidene fluoride (β-PVDF) is formed on the surface of a zinc metal negative electrode according to a specific embodiment of the present invention. do. However, this is presented as an example of the invention, thereby not limiting the scope of the invention, it is apparent to those skilled in the art that various modifications to the embodiment are possible within the scope of the invention.

Throughout this specification, unless otherwise specified, "including" or "containing" refers to including any component (or component) without particular limitation, and excludes the addition of other components (or components). cannot be construed as

According to the first embodiment,

An object of the present invention is to provide a negative electrode for an aqueous zinc secondary battery, characterized in that a beta-polyvinylidene fluoride (β-PVDF) coating layer is formed on the surface of a zinc metal negative electrode.

In the negative electrode for an aqueous zinc secondary battery according to the present invention, the beta-polyvinylidene fluoride coating layer has a thickness of 0.05 to 10 μm.

According to the second embodiment,

the present invention

(A) applying a polyvinylidene fluoride (PVDF)-based polymer solution dissolved in a solvent on zinc metal; and

(B) To provide a method of manufacturing a negative electrode for a water-based zinc secondary battery having a β-PVDF coating layer, comprising the step of evaporating the solvent from the PVDF-based polymer solution applied on the zinc metal.

In the method for manufacturing a negative electrode for an aqueous electrolyte lithium secondary battery according to the present invention, the solvent is dimethylformamide (DMF), dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), It is characterized in that at least one selected from hexamethylphosphoamide (HMPA), acetone and 2-butanone.

In the method for manufacturing a negative electrode for an aqueous electrolyte lithium secondary battery according to the present invention, the polyvinylidene fluoride-based polymer is a ferroelectric polymer. The ferroelectric polymer is characterized in that it is a PVDF homopolymer or P(VDF-TrFE), which is a copolymer of PVDF and trifluoroethylene (TrFE).

In the method for manufacturing a negative electrode for an aqueous electrolyte lithium secondary battery according to the present invention, the method for applying the PVDF-based polymer solution is vacuum deposition including thermal evaporation method, spin coating, roll coating ( roll coating), spray coating or printing.

In the method for manufacturing a negative electrode for an aqueous electrolyte lithium secondary battery according to the present invention, the step (B) is characterized in that it is performed at 55 to 65 ℃ for 50 nabi 100 minutes. Preferably, the step (B) is characterized in that it is carried out at 60 ℃ for 90 minutes.

According to the third embodiment,

the present invention

(A) anode;

(B) an anode having a beta-polyvinylidene fluoride (β-Polyvinylidene fluoride, β-PVDF) coating layer formed on a surface of a zinc metal anode; and

(C) to provide an aqueous zinc secondary battery including an aqueous electrolyte disposed between the positive electrode and the negative electrode.

In the aqueous zinc secondary battery according to the present invention, the secondary battery is characterized in that it further comprises a separator between the positive electrode and the negative electrode.

In the aqueous zinc secondary battery according to the present invention, the aqueous electrolyte is characterized in that it contains an aqueous solvent and a metal salt. The aqueous solvent may be water. The metal salt may be ZnSO ₄ , Zn(NO ₃ ) ₂ , Zn(CF ₃ SO ₃ ) ₂ , and mixtures thereof.

In the negative electrode for a zinc secondary battery having a β-PVDF coating layer of the present invention, the Zn stripping/plating process is controlled by the β-PVDF coating layer, so that corrosion can be suppressed. Therefore, the negative electrode for a zinc secondary battery with a β-PVDF coating layer improves the structural stability of the negative electrode, the electrochemical performance of the secondary battery, and the charging/discharging capacity compared to the case of using a bare zinc negative electrode or a zinc negative electrode with an α-PVDF coating layer. can do it

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.

<Example>

Example 1. Preparation of β-PVDF @ Zn Anode

10 wt% of PVDF (Sigma-Aldrich, Mw ~ 534,000) was added to N,N-dimethylacetamide (DMAc, 99%, Sigma-Aldrich) solvent and dissolved by magnetic stirring for 12 hours. The Zn foils were washed by sonication in acetone, isopropyl alcohol and deionized water and then dried with compressed air. The PVDF solution was spin-coated on a Zn foil (diameter 12 mm) at a constant speed of 5000 rpm for 30 seconds. Then, the solvent was slowly evaporated at 60° C. for 90 minutes on a hot plate in a closed system to prepare a β-PVDF coated Zn anode.

Comparative Example 1. Preparation of α-PVDF-coated Zn anode

After spin-coating the PVDF solution on the Zn foil in the same manner as in Example 1, the solvent was rapidly evaporated at 90° C. for 60 minutes in an open environment to prepare an α-PVDF-coated Zn anode.

Comparative Example 2. bare Zn cathode

Zn foil not coated with PVDF was used.

<Experimental example>

Experimental Example 1. Characterization of PVDF @ Zn cathode

The X-ray diffraction (XRD) patterns of β-PVDF according to Example 1 and α-PVDF according to Comparative Example 1 were analyzed using a Rigaku D/MAX-2200 X-ray diffractometer with Cu Kα radiation (λ = 0.15406 nm). was used to confirm. The crystalline phase was further analyzed using Fourier transform infrared spectroscopy (FTIR) (Vertex 70, Bruker, Germany).

As a result, the top surface of the β-PVDF coating layer according to Example 1 appeared in the form of nanometer-sized hemispheres interconnected with each other, and the thickness of the coating layer was measured to be ~10 μm. The XRD 2θ of the β-PVDF coating layer according to Example 1 showed a peak at 20.8, and the XRD 2θ of the α-PVDF coating layer according to Comparative Example 1 showed peaks at 17.6, 18.3 and 19.9, and according to Example 1 The FTIR bands of the β-PVDF coating layer showed peaks at 510, 840, 1062, 1227 and 1400 cm ^-1 , and the FTIR bands of the α-PVDF coating layer according to Comparative Example 1 were 530, 614, 764, 795, 873, 976, A peak appeared at 1176, 1380 cm ^-1 (FIG. 1). Therefore, it was confirmed that the β-PVDF coating layer according to Example 1 and the α-PVDF coating layer according to Comparative Example 1 were stably formed on the Zn foil.

Experimental Example 2. Performance characteristics in a symmetrical battery including PVDF @ Zn negative electrode

A symmetrical full-cell was prepared using a CR2032 coin cell and the stripping/plating behavior and cycling stability of the battery were observed. The symmetrical full-cell was composed of two β-PVDF@Zn foils according to Example 1 and 2M ZnSO ₄ aqueous solution combined with a glass fiber separator. On the other hand, a symmetrical battery including the α-PVDF@Zn foil according to Comparative Example 1 and the bare Zn foil according to Comparative Example 2 was also prepared. The batteries were subjected to galvanostatic charge/discharge cycling at various current densities with various areal capacities in a WBCS battery cycler (WBCS3000, WonATech).

As a result, when the area capacity is 0.05 mAh cm ^-2 when cycling at 0.25 mA cm ^-2 , the β-PVDF @ Zn symmetric full-cell exhibited an initial overpotential of 79 mV, and the overpotential is the end of the first stage. Zn stripping/plating was advantageously reversible in β-PVDF @ Zn by showing a continuously low overpotential of 40 mV in the subsequent cycle. Moreover, the α-PVDF @ Zn symmetric full-cell and the bare Zn symmetric full-cell showed unstable cycling performance after about 1300 and 350 hours, respectively, whereas the β-PVDF @ Zn symmetric full-cell showed an unstable cycling performance of 80mV. It was confirmed to have excellent long-term stripping/plating stability by working well even when stripping/plating exceeds 2000 hours with insignificant polarization (FIG. 2).

Experimental Example 3. Confirmation of characteristics of PVDF @ Zn cathode after 500 charge/discharge cycling

Morphology of bare Zn, α-PVDF @ Zn, and β-PVDF @ Zn electrodes was confirmed after 500 stripping/plating cycles. Bare Zn before cycling had a dense and glossy surface, but after cycling, gigantic Zn flakes were formed with some grains growing up to ~10 μm with sharp edges due to irregular Zn deposition/dissolution. Even in the case of α-PVDF@Zn, small Zn flakes were found to form sporadically after 500 cycles. On the other hand, in the case of β-PVDF @ Zn, the outer top surface still maintained a smooth and compact shape after 500 cycles. It was confirmed to have (Fig. 3)

Experimental Example 4. Performance characteristics in full-cell including PVDF @ Zn anode

To prepare a V ₂ O ₅ /C positive electrode, the obtained V ₂ O ₅ /C powder (active material), acetylene black and PVDF were mixed in N-methylpyrrolidone (NMP) in a weight ratio of 70:15:15 mixed together. Additional NMP was then dropped into the mixture under constant magnetic stirring to produce a well-dispersed coating slurry. The slurry was cast on titanium foil by adopting a doctor blade method and finally vacuum dried at 60° C. overnight. In coin cells with 2 M ZnSO ₄ aqueous electrolyte, respectively V ₂ O ₅ /C Anode, glass fiber separator and β-PVDF@Zn | V ₂ O ₅ /C, α-PVDF@Zn | V ₂ O ₅ /C and bare Zn | A V ₂ O ₅ full-cell battery was prepared. Full cell cyclic voltammetry (CV) measurements were performed at 0.4 and 1.6V (vs. Zn / Zn ²⁺ ) with a scan rate of 0.2 mV s ⁻¹ using ZIVE MP1 (WonATech). Cyclic performance was measured at a current density of 1 Ag ^-1 . In addition, rate performance was measured by applying various current rates of 0.1, 1, 2, 4, 8 Ag ^-1 . Specific charge and discharge capacities in the full cell were calculated based on the mass of the active positive electrode material. To investigate the Zn nucleation behavior, Zn|Cu half-cells were assembled with pristine, α-PVDF and β-PVDF-coated Cu as working electrodes and Zn foil as counter electrodes.

As a result, in the initial cycle, two redox peaks were well observed at ~0.59/0.78, and then a much duller reduction/oxidation peak pair branching from 0.9V to 1.1V in each cell appeared (Fig. 4a). However, after 3 cycles, all peaks of this profile appeared to converge at almost identical positions (0.59/0.78 and 0.89/1.14, respectively) corresponding to the two-step intercalation/deintercalation process of Zn ²⁺ ( Fig. 4b). Constant current charge/discharge analysis result, β-PVDF @ Zn | The first discharge capacity of the V ₂ O ₅ /C battery is 256 mAh g ^-1 , with α-PVDF @ Zn | V ₂ O ₅ / C and bare Zn | It was confirmed that the discharge capacities of the V ₂ O ₅ /C batteries, respectively, of 196 mAh g ^-1 and 185 mAh g ^-1 , were overwhelmed, and surprisingly, β-PVDF @ Zn | The discharge/charge profile curve of the V ₂ O ₅ / C battery showed surprising cyclic stability while maintaining its original shape even after 20 cycles with a slight increase in capacity (269mAh g ^-1 ). In addition, the batteries using the β-PVDF @ Zn cathode exhibited discharge capacities of 276, 267, 253, 220 and 154 mAh g ^-1 at current densities of 0.1, 1, 2, 4 and 8A g ^-1 , respectively, Then, even when the current density was suddenly dropped to 1A g ⁻¹ , it was confirmed that the discharge capacity immediately returned to 265 mAh g ⁻¹ even after 20 cycles during each period of increasing the current rate ( FIG. 4c ). Finally, as a result of evaluating the long-term cycling life at a current rate of 1A g ^-1 , the discharge capacity of the β-PVDF @ Zn cells started up to 252 mAh g ^-1 , whereas the bare and α-PVDF @ Zn cells were 150 and 150 mAh g -1 , respectively. decreased to 175 mAh g ^-1 , and in particular, the α-PVDF @ Zn battery had a sharp drop in discharge capacity after 200 cycles, and the bare Zn battery showed an overwhelming sink at 50 to 25 mAh g ^-1 after 800 cycles, eventually leading to 1200 cycles. It was confirmed that the discharge capacity disappears as the meeting cycle approaches. However, the discharge capacity of the β-PVDF @ Zn battery according to the present invention was gradually decreased, and it was found to have a discharge capacity of about 60 mAh g ⁻¹ steadily without damage to the battery even after 2000 cycles ( FIG. 4d ). Therefore, it has been proven that, when the zinc anode is coated with β-PVDF, the battery speed and charge/discharge performance can be significantly improved, and thus, AZIB with a long lifespan can be manufactured.

As described above in detail a specific part of the content of the present invention, for those of ordinary skill in the art, it is clear that this specific description is only a preferred embodiment, and the scope of the present invention is not limited thereby. something to do. Accordingly, it is intended that the substantial scope of the present invention be defined by the appended claims and their equivalents.

Claims (10)

A negative electrode for a water-based zinc secondary battery, characterized in that a beta-polyvinylidene fluoride (β-PVDF) coating layer is formed on the surface of the zinc metal negative electrode.
The method of claim 1,
The beta-polyvinylidene fluoride coating layer has a thickness of 0.05 to 10 μm, characterized in that it is an anode for a water-based zinc secondary battery.
(A) applying a polyvinylidene fluoride (PVDF)-based polymer solution dissolved in a solvent on zinc metal; and
(B) A method of manufacturing a negative electrode for an aqueous zinc secondary battery having a β-PVDF coating layer, comprising the step of evaporating the solvent from the PVDF-based polymer solution applied on the zinc metal.
4. The method of claim 3,
The solvent is from dimethylformamide (DMF), dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), hexamethylphosphoamide (HMPA), acetone and 2-butanone. The method, characterized in that one or more selected.
4. The method of claim 3,
The method, characterized in that the ferroelectric polymer is P(VDF-TrFE), which is a PVDF homopolymer or a copolymer of PVDF and trifluoroethylene (TrFE).
4. The method of claim 3,
The method for applying the PVDF-based polymer solution is vacuum deposition including a thermal evaporation method, spin coating, roll coating, spray coating, or printing. characterized in that the method.
4. The method of claim 3,
The method, characterized in that the step (B) is carried out at 55 to 65 ℃ 50 for 100 minutes.
8. The method of claim 7,
The method, characterized in that the step (B) is carried out at 60 ℃ for 90 minutes.
(A) anode;
(B) an anode manufactured by the method according to any one of claims 3 to 8; and
(C) an aqueous zinc secondary battery comprising an aqueous electrolyte disposed between the positive electrode and the negative electrode.
10. The method of claim 9,
The secondary battery is characterized in that it further comprises a separator between the positive electrode and the negative electrode, a water-based zinc secondary battery.

Images