KR102539660B1 - 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 anode having a beta-polyvinylidene fluoride coating layer and an aqueous zinc ion battery including the anode. The zinc anode having 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.

Description

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

The present invention relates to a zinc anode having a β-polyvinylidene fluoride (β-PVDF) coating layer and an aqueous zinc ion battery including the anode. The zinc anode having 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.

The secondary battery refers to a battery that can be used repeatedly as it can be charged as well as discharged. In a typical lithium secondary battery among secondary batteries, lithium ions included in the positive electrode active material move to the negative electrode through the electrolyte and are then inserted into the layered structure of the negative electrode active material (charging). It works through the principle of returning to the anode (discharge). These lithium secondary batteries are currently commercialized and used as small power sources such as mobile phones and notebook computers, and are expected to be used as large power sources such as hybrid vehicles, and demand for them is expected to increase. However, since composite metal oxides, which are mainly used as cathode active materials in lithium secondary batteries, contain rare metal elements such as lithium, there is a concern that they may not be able to meet the increasing demand. Accordingly, studies on sodium secondary batteries using abundant and cheap sodium as a cathode active material are being conducted, but sodium battery systems still have complex safety and environmental problems.

On the other hand, as various technologies for wearable electronic devices have recently been developed beyond flexible (flexible), there is also an increasing demand for secondary batteries that are operated with materials that have no risk of explosion and have high stability. In contrast, an aqueous zinc ion battery (AZIB) has advantages in that it has higher stability than other secondary batteries, is environmentally friendly, has less toxicity, and is economical compared to other alkali metals. In such an aqueous zinc secondary battery, the zinc negative electrode is dissolved in an alkaline solution, and zinc elution and precipitation are repeated during charging and discharging reactions. As a result, the shape of the electrode plate changes as the charge/discharge reaction proceeds, and the eluted zinc does not precipitate uniformly during charging and grows as a dendrite, and the dendrite zinc penetrates the separator, causing a problem of short circuiting the battery. The downside is that the battery life is short.

In order to solve this problem, the following techniques have been proposed. First, Japanese Patent Publication No. 1985-185372 discloses a nickel/zinc secondary battery in which oxides and hydrates of In and Ti are added to a zinc electrode so as to maintain high energy density in order to increase the number of charge/discharge cycles of the nickel/zinc secondary battery. are initiating about Japanese Laid-Open Patent Publication No. 1987-108467 discloses an alkali 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 an alkaline zinc battery, and germanium ions are added to an electrolyte solution. are initiating about Japanese Patent Laid-open Publication No. 1986-061366 discloses an alkali 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 charge/discharge cycles in the alkali 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 the formation of dendrites on the negative electrode of the nickel/zinc secondary battery and borate and fluoride are included in the potassium hydroxide electrolyte. are 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 Publication 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 dissolution and precipitation of zinc progresses, the shape of the zinc negative electrode changes, and dendrites of charge/discharge zinc occur, breaking through the separator and contacting the positive electrode, resulting in a short circuit. This will result in a shortened 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 present inventors have made diligent efforts to increase the lifespan of a secondary battery by suppressing the growth of zinc dendrites generated in the negative electrode of a zinc secondary battery, and as a result, beta-polyvinylidene fluoride (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 β-polyvinylidene fluoride (β-PVDF) coating layer is formed on the surface of a zinc metal negative electrode.

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

The present invention also provides an anode; A negative electrode having a β-Polyvinylidene fluoride (β-PVDF) coating layer formed on the surface of a zinc metal negative electrode; And an object of the present invention is to provide an aqueous zinc secondary battery comprising 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 of the negative electrode, electrochemical performance and charge / discharge capacity of the secondary battery than when using a bare zinc negative electrode or a zinc negative electrode with an α-PVDF coating layer. can improve Specifically, a very low overpotential (400mV) was maintained even after 2000 hours of operation in a symmetrical battery including a negative electrode for a zinc secondary battery on which a β-PVDF coating layer was formed, and in full cell performance measurement, the capacity during charge and discharge of 4000 cycles It was found to be stable.

1 shows XRD patterns of β-PVDF according to Example 1 and α-PVDF according to Comparative Example 1.
2 is a result of evaluating stripping/plating behavior and cycling stability of batteries in symmetrical cells 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 a bare Zn negative electrode according to Comparative Example 2 after 500 cycles of charging and discharging.
4 shows 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.

Aha, the negative electrode for an aqueous zinc secondary battery, characterized in that a β-Polyvinylidene fluoride (β-PVDF) coating layer is formed on the surface of a zinc metal negative electrode according to a specific embodiment of the present invention, will be described in detail. do. However, this is presented as an example of the invention, whereby the scope of the invention is not limited, and it is obvious to those skilled in the art that various modifications to the embodiments are possible within the scope of the invention.

Throughout this specification, unless otherwise specified, "include" or "include" refers to including a certain component (or component) without particular limitation, and excludes the addition of other components (or components). cannot be interpreted 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 β-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 onto zinc metal; and

(B) It is intended to provide 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.

In the method of manufacturing an anode 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 hexamethylphosphoramide (HMPA), acetone and 2-butanone.

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

In the method of manufacturing an anode for an aqueous electrolyte lithium secondary battery according to the present invention, the method of applying the PVDF-based polymer solution is a vacuum deposition method including a 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 ° C. for 100 minutes at 50 ° C. Preferably, the step (B) is performed at 60° C. for 90 minutes.

According to the third embodiment,

the present invention

(A) anode;

(B) a negative electrode having a β-Polyvinylidene fluoride (β-PVDF) coating layer formed on the surface of a zinc metal negative electrode; and

(C) It is intended 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 the β-PVDF coating layer of the present invention, corrosion can be suppressed because the Zn stripping/plating process is controlled by the β-PVDF coating layer. 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 charge/discharge capacity compared to the case of using a bare zinc negative electrode or a zinc negative electrode with an α-PVDF coating layer. can make 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 cathode

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 foil was cleaned by sonication in acetone, isopropyl alcohol and deionized water and then dried with compressed air. The PVDF-dissolved solution was spin-coated on a Zn foil (12 mm in diameter) at a constant speed of 5000 rpm for 30 seconds. Then, the β-PVDF-coated Zn cathode was prepared by slowly evaporating the solvent at 60° C. for 90 min on a hot plate in a closed system.

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 quickly evaporated at 90° C. for 60 minutes in an open environment to prepare an α-PVDF coated Zn cathode.

Comparative Example 2. bare Zn cathode

Zn foils not coated with PVDF were used.

<Experimental example>

Experimental Example 1. Confirmation of characteristics of PVDF @ Zn cathode

The X-ray diffraction (XRD) patterns of the β-PVDF according to Example 1 and the α-PVDF according to Comparative Example 1 were measured using a Rigaku D/MAX-2200 X-ray diffractometer with Cu Kα radiation (λ = 0.15406 nm). confirmed using 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. 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, Peaks appeared at 1176 and 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 Symmetrical Battery Containing PVDF @ Zn Cathode

A symmetrical full-cell was fabricated using a CR2032 coin cell and the stripping/plating behavior and cycling stability of the battery were observed. A symmetrical full-cell was composed of two β-PVDF@Zn foils according to Example 1 combined with a glass fiber separator and a 2M ZnSO ₄ aqueous solution. Meanwhile, a symmetric 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 cells were subjected to galvanostatic charge/discharge cycling at various current densities with different areal capacities in a WBCS battery cycler (WBCS3000, WonATech).

As a result, when the areal capacity is 0.05 mAh cm ^-2 when cycling at 0.25 mA cm ^-2 , the β-PVDF @ Zn symmetrical full-cell exhibits an initial overpotential of 79mV, which is It was confirmed that the Zn stripping/plating is advantageously reversible in β-PVDF @ Zn, as it rapidly decreased to ~ 48 mV and showed a continuously low overpotential of 40 mV in subsequent cycles. Moreover, the α-PVDF @ Zn symmetric full-cell and the bare Zn symmetric full-cell showed unstable cycling performance after about 1300 hours and 350 hours, respectively, while the β-PVDF @ Zn symmetric full-cell showed constant cycling performance of 80 mV. It was confirmed that it works well even when stripping/plating exceeds 2000 hours with a slight polarization and has excellent long-term stripping/plating stability (Fig. 2).

Experimental Example 3. Confirmation of characteristics of PVDF @ Zn cathode after 500 cycles of charging and discharging

The morphology of bare Zn, α-PVDF @ Zn and β-PVDF @ Zn electrodes was confirmed after 500 stripping/plating cycles. The bare Zn before cycling had a dense and glossy surface, but after cycling, huge Zn flakes with sharp edges and some grains growing up to ~10 μm were formed due to irregular Zn deposition/dissolution. Even for α-PVDF@Zn, small Zn flakes were found to be sporadically formed after 500 cycles. On the other hand, in the case of β-PVDF @ Zn, the outer top surface was found to still maintain a smooth and compact shape even after 500 cycles, and even in the case of the Zn foil with the β-PVDF coating removed, it was found to have a smooth and flat surface even though there were some cracks. It was confirmed to have (Fig. 3)

Experimental Example 4. Performance characteristics in full-cell containing PVDF @ Zn cathode

To prepare a V ₂ O ₅ /C positive electrode, N-methylpyrrolidone (NMP) was mixed with the obtained V ₂ O ₅ /C powder (active material), acetylene black and PVDF in a weight ratio of 70:15:15. mixed together. Then, additional NMP was dropped into the mixture under constant magnetic stirring to create a well-dispersed coating slurry. The slurry was cast on titanium foil by employing 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 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 manufactured. Full cell cyclic voltammetry (CV) measurements were performed at 0.4 and 1.6V (vs. Zn / Zn ²⁺ ) at a scan rate of 0.2mV s ^-1 using a 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, and 8 Ag ^-1 . The specific charge and discharge capacities in a full cell were calculated based on the mass of the active cathode material. To investigate the Zn nucleation behavior, a Zn|Cu half-cell was assembled with pristine, α-PVDF and β-PVDF coated Cu as the working electrode and Zn foil as the counter electrode.

As a result, after two redox peaks were well observed at ~0.59/0.78 for the initial cycle, a much duller reduction/oxidation peak pair diverging from 0.9 V to 1.1 V appeared in each cell (Fig. 4a). However, after 3 cycles, all peaks of these profiles were found to converge at almost the same position (0.59/0.78 and 0.89/1.14, respectively), corresponding to the two-step intercalation/deintercalation process of Zn ²⁺ ( Fig. 4b). As a result of constant current charge/discharge analysis, 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 found to overwhelm the discharge capacities of 196 mAh g ^-1 and 185 mAh g ^-1 of the V ₂ O ₅ /C battery, respectively, and surprisingly, β-PVDF @ Zn | The discharge/charge profile curve of the V ₂ O ₅ /C battery maintained its original shape even after 20 cycles with a slight increase in capacity (269mAh g ^-1 ), showing remarkable cyclic stability. In addition, the battery 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 8 A g ^-1 , respectively, Even when the current density was then suddenly dropped to 1 A g ^-1 , 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, evaluation of the long-term cycling life at a current rate of 1 A g ⁻¹ showed that the discharge capacity of the β-PVDF @ Zn cell started with a maximum of 252 mAh g ⁻¹ , whereas the bare and α-PVDF @ Zn cells reached 150 and 150 mAh g −1 , respectively. 175 mAh g ^-1 , in particular, the α-PVDF @ Zn battery showed 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 reaching 1200 It was confirmed that the discharge capacity disappeared as the cycle approached. However, the discharge capacity of the β-PVDF @ Zn battery according to the present invention gradually decreased, and even after 2000 cycles, the battery was consistently shown to have a discharge capacity of about 60 mAh g ⁻¹ without damage ( FIG. 4d ). Therefore, it has been proven that when the zinc anode is coated with β-PVDF, the speed and charge/discharge performance of the battery can be significantly improved, and thus AZIB with a long lifespan can be manufactured.

Having described specific parts of the present invention in detail above, it is clear that these specific descriptions are only preferred embodiments for those skilled in the art, and the scope of the present invention is not limited thereby. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (10)

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

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