KR102032184B1 - METAL FOIL SUPPORTED ELECTRODE AND Zn-Ni FLOW SECONDARY BATTERY COMPRISING THE SAME - Google Patents

Abstract

The present invention provides a thin positive electrode in which a metal foil is used as a positive electrode current collector and a positive electrode support in manufacturing a Zn-Ni flow battery, and a positive electrode material containing the positive electrode active material Ni (OH) ₂ is coated on at least one side or both sides thereof. And the metal foil support for the negative electrode and the gap between the positive electrode and the negative electrode is arranged very tightly compared to the prior art by integrating a large number of electrodes in the same volume compared to the prior art, the energy density (Wh / L) per unit volume is maintained at the conventional level In addition, it is possible to implement a Zn-Ni flow battery that can dramatically increase the power density (W / L) per unit volume.

Description

Metallic foil-supported thin anode, zinc-nickel flow cell comprising same TECHNICAL FOIL SUPPORTED ELECTRODE AND Zn-Ni FLOW SECONDARY BATTERY COMPRISING THE SAME

The present invention relates to a Zn-Ni flow battery comprising a metal foil support positive electrode and a negative electrode.

Due to the increase in energy demand and the use of fossil fuels around the world, environmental pollution due to CO ₂ emissions is a problem. Due to these problems, renewable energy, such as solar, wind, and fuel cells, has been in the spotlight, and recently, it is spreading and being used in real life, and its application is gradually expanding.

Since such renewable energy is greatly influenced by the location environment and natural conditions, the output fluctuates severely and thus it is impossible to continuously supply the energy, and the energy storage system is important because the time difference between the time of energy production and demand occurs.

In the case of surplus power or night load, positive power generation, compressed air energy storage, superconducting energy storage, flywheel storage, etc. may be applied, and large capacity secondary battery storage systems are selected for large-scale photovoltaic and wind farms. In particular, a large-capacity energy storage technology is important in the smart grid, the secondary battery that can respond quickly according to the system state is efficient for the electrical energy storage.

In the secondary battery for large-capacity power storage, the energy storage density should be high, and the flow battery is advantageous as the secondary battery having a high capacity and high efficiency that is most suitable for such characteristics.

As a flow battery, a Zn-Ni flow battery is mentioned. The charge / discharge reaction of the flow battery is as shown schematically in FIG. 1. More specifically, in the Zn-Ni flow battery, the following reaction occurs in the positive electrode and the negative electrode during the discharge reaction. As the electrolyte, for example, a strong alkaline aqueous solution containing KOH at a concentration of 6 to 10 M may be applied.

Anode _{reaction: 2NiOOH + 2H 2 O + 2e} - = 2Ni (OH) 2 + 2OH -, Eo = 0.490V

A negative electrode ^{reaction: Zn + 4OH - = Zn (} OH) 4 2 - + 2e -, Eo = -1.215V

Total reaction: Zn + 2KOH + 2H ₂ O + 2NiOOH = 2Ni (OH) ₂ + K ₂ Zn (OH) ₄ : V = 1.705 V

Such a Zn-Ni flow battery cross-arranges a positive electrode coated with a positive electrode material including a nickel compound of Ni (OH) ₂ as a positive electrode active material on a positive electrode current collector, and a negative electrode composed of a current collector at regular intervals, and between the positive electrode and negative electrode As a gap of, a strong alkaline aqueous solution having high OH ^- ion conductivity required for electrochemical reaction is circulated through a pump or a stirring device. Of Zn (OH) a negative electrode active material in the electrolyte solution in the cell production stage ^{₄₂ -} that is dissolved. Zn (OH) ₄ ^{2 -} dissolved in the electrolyte is precipitated as Zn in the negative electrode current collector during charging, and conversely, in discharging, Zn (OH) ₄ ^{2 -} is redissolved in the electrolyte as Zn (OH) ₄ ^{2 -} ions.

Current allowable current densities in Zn-Ni flow cells are as low as 10 mA / cm ² to 30 mA / cm ² . This is low compared to Li-ion battery as well as the competition V-RFB (Vanadium Redox Flow battery). Zn-Ni flow battery can be used for slow charge / discharge rate, for example, ESS operated at charge rate of 0.2 ~ 0.3C based on C-rate among long-cycle ESS applications, but it requires fast charge / discharge capability. There is a lack of competitiveness for more diverse ESS applications.

Current allowable current densities in Zn-Ni flow cells range from 10 mA / cm ² to 30 mA / cm ² . Therefore, it can be used for long-period ESS that is applied at low charge / discharge rate because the rated output and peak output per unit volume is low, but it is not competitive in the application that needs fast charge / discharge.

In the present invention, the energy density per unit volume (Wh / L) while maintaining the conventional level to implement a Zn-Ni flow battery that can dramatically increase the output density (W / L) per unit volume.

According to the present invention, in manufacturing a Zn-Ni flow battery, a thin metal foil is applied as a positive electrode current collector and a positive electrode support, and a positive electrode material including the positive electrode active material Ni (OH) ₂ is applied on at least one side or both sides thereof. By preparing a metal foil support for the positive electrode and the negative electrode and arranging the gaps between the positive electrode and the negative electrode very tightly compared to the prior art, by integrating a large number of electrodes in the same volume compared with the prior art, the energy density per unit volume (Wh / L) is maintained at a conventional level. It is possible to implement a Zn-Ni flow battery that can dramatically increase the power density (W / L) per unit volume while maintaining.

The Zn-Ni flow battery of the present invention includes a metal foil as a current collector and a support, and at least one surface of the metal foil includes a thin anode coated with a cathode material and a thin cathode including a metal foil as a current collector and a support. It is a Zn-Ni flow battery characterized in that the electrode density between the positive electrode and the thin cathode is reduced to improve the electrode density per unit volume to increase the output density per unit volume.

The thickness of the thin cathode may be 0.3 mm or less in total for the current collector and the positive electrode material.

The thickness of the thin cathode is the thickness of the negative electrode current collector, the thickness may be 0.2mm or less.

The electrode gap may be 0.5 mm or less.

The thin cathode is to use a stainless steel foil of 0.05 ~ 0.2mm as the current collector and support.

The current collector and support may include a Ni or Ni _{1- x} Co _x coating layer by plating or cladding on a surface thereof.

The coating layer preferably has a thickness of 5 ~ 30㎛.

The thin cathode may be one in which a cathode material containing Ni (OH) ₂ as a cathode active material is coated with a thickness of 0.1 mm or less on one or both surfaces of the metal foil support and the current collector.

The thin cathode may be a stainless steel foil of 0.05 ~ 0.2mm thickness.

The thin cathode preferably includes a coating layer of Ni, Cu, or Sn on the surface of the stainless foil by plating or cladding.

The present invention also provides a positive electrode support and a current collector of a metal foil and a positive electrode material including a positive electrode active material, a conductive material and a binder on at least one surface of the positive electrode current collector, and has a positive electrode thickness of 0.3 mm or less as a total of the positive electrode current collector and the positive electrode material. Provided is a thin cathode for a Zn-Ni flow battery.

The anode preferably has a thickness of 80 to 300㎛.

The positive electrode support and the current collector may be a metal foil having a thickness of 0.05 to 0.2 mm.

The positive electrode current collector may be a metal foil of nickel or nickel plated stainless steel.

According to the present invention, in manufacturing a Zn-Ni flow battery, a thin metal foil is applied as a positive electrode current collector and a positive electrode support, and a positive electrode material including the positive electrode active material Ni (OH) 2 is coated on at least one side or both sides thereof. By preparing a metal foil support for the positive electrode and the negative electrode and arranging the gaps between the positive electrode and the negative electrode very tightly compared to the prior art, by integrating a large number of electrodes in the same volume compared with the prior art, the energy density per unit volume (Wh / L) has been maintained It is possible to implement a Zn-Ni flow battery that can dramatically increase the power density (W / L) per unit volume while maintaining.

Therefore, the Zn-Ni flow battery according to the present invention is not only used for long-period-ESS that is operated at low charge / discharge speed, but also for high-power applications such as ESS with emergency power supply (UPS) and renewable energy peak shaving. It is expected to expand its use as a secondary battery in the ESS field that needs charging / discharging.

1 is a view schematically showing the concept of a Zn-Ni flow battery.
2 is a view schematically showing a process of manufacturing a metal foil support type positive electrode according to the present invention.
FIG. 3 conceptually illustrates the structure of the flow battery of the present invention using the metal foil support-type positive electrode of the present invention, and illustrates the concept of improving output as compared to the flow volume of the same volume shown in FIG. 1.

The present invention relates to a Zn-Ni flow cell. More specifically, by using a rigid metal foil as a positive electrode and a negative electrode current collector and a support, a thin positive electrode and a negative electrode having a thickness of the positive electrode active material reduced to a level of 50 to 300 μm are prepared, and the gap between the positive electrode and the negative electrode is made of the existing product. By reducing the level to about 3mm and increasing the number of electrodes per unit volume, the energy density per unit volume of the Zn-Ni flow cell's product is maintained at a conventional level while increasing the charge / discharge rate, that is, the Zn-Ni flow, which can increase the output per unit volume of the product. It is to provide a battery.

FIG. 1 schematically shows a structure of a general Zn-Ni flow battery. As can be seen from FIG. 1, a Zn-Ni flow cell includes a positive electrode, a negative electrode, and a flowing electrolyte based on a 6-10 M concentration of KOH aqueous solution between the positive electrode and the negative electrode.

When NiOOH is used as a cathode active material, a chemical reaction occurs as shown in Scheme 1 below.

Scheme 1

^{_{2NiOOH + 2H 2 O + 2e -}} = 2Ni (OH) 2 + 2OH -, E 0 = 0.490V

In addition, a chemical reaction of zinc occurs in the negative electrode as shown in Scheme 2 below.

Scheme 2

^{Zn + 4OH - = Zn (OH} ) 4 2 - + 2e -, E 0 = -1.215V

When the KOH aqueous solution is included in the electrolyte solution, the overall cell chemistry from the reaction schemes 1 and 2 is shown in Scheme 3 below.

Scheme 3

Zn + 2KOH + 2H ₂ O + 2NiOOH = 2Ni (OH) ₂ + K ₂ Zn (OH) ₄ , V = 1.705V

Referring to Reaction Schemes 1 to 3, during charging, Zn (OH) ₄ ^{2 -} ion, which is a negative electrode active material provided in a dissolved state in an electrolyte solution, is reduced and precipitated as Zn, and when discharged, Zn is again Zn (OH). ₄ ^{2 -} Becomes ions and dissolves in the electrolyte. On the other hand, NiOOH is changed to Ni (OH) ₂ during discharge. In contrast, during charging, the Ni (OH) ₂ is changed to NiOOH.

The cathode is coated with a cathode material on at least one surface of the cathode current collector and the cathode current collector. The cathode material includes a nickel compound, a conductive material, and a binder as the cathode active material. In this case, the nickel compound may be a powder having, for example, NiOOH, Ni (OH) _2, or the like. Such a nickel compound may exist in a state where NiOOH (after charge), Ni (OH) ₂ (after discharge) and NiOOH and Ni (OH) ₂ coexist (during charging and discharging) depending on the state of charge and discharge.

Meanwhile, in the present invention, the positive electrode means a state in which a positive electrode material composed of a positive electrode active material, a conductive material, and a binder is coated on a positive electrode current collector. The conductive material of the cathode material component serves to transfer electrons from Ni (OH) ₂ , which is a cathode active material, to a current collector. Carbon powder such as graphite, carbon black, and metal powder such as nickel powder may be used. Such conductive materials include nickel powder, carbon black, ketjen black, graphite, and the like, which may be used alone or in combination.

The nickel compound and the conductive material are applied to the surface of the current collector by a binder. The binder is not particularly limited, and for example, at least one fluorine resin selected from the group consisting of polytetra fluoro ethylene (PTEE) and polyvinylidene fluoride (PVDF) may be used.

As shown in Figure 2, the positive electrode of the present invention, after mixing the positive electrode material mixed with the Ni (OH) ₂ positive electrode active material, conductive material and binder with a solvent to form a slurry or paste, the positive electrode material slurry or positive electrode material paste It is possible to manufacture a positive electrode coated with a positive electrode material on the surface of the current collector by applying and drying / curing on the surface of the current collector.

The cathode material slurry or paste is not particularly limited as it can be formed by applying various methods such as screen printing, wet powder spray, bar coating, and tape casting.

The cathode material includes a cathode active material such as Ni (OH) ₂ , a conductive material, and a binder, which are 80 to 90% by volume of the cathode active material, 5 to 10% by volume of the conductive material, and 5 to 10% by volume of the binder. It is preferred to be configured. When the content of the conductive material is low, the conductivity is insufficient to secure the charge and discharge rate, but if excessively added, there is a disadvantage that the energy density per unit volume decreases. If the binder is also insufficient, anodic desorption occurs to reduce the long-term charge and discharge life, but when excessively added, the conductivity of the electrode decreases, resulting in a decrease in output and capacity.

In the positive electrode of the present invention, the positive electrode material is coated on the surface of the positive electrode current collector, and the positive electrode current collector is preferably 0.2 mm or less in thickness, more specifically, a metal foil (metal thin plate) in the range of 0.05 to 0.2 mm. Do. More preferably, it is preferable to use a 0.1 mm class thin plate. In the flow battery, since the electrolyte must flow between the anode and the cathode, each electrode must be able to stably maintain the shape of the electrode and the distance between the electrodes while the electrolyte flows.

In this case, the positive electrode current collector serves to stably maintain the distance and shape between the electrodes as well as the current collector. For this purpose, the current collector preferably has a thickness range as described above. That is, when the thickness of the current collector has a thickness of less than 0.05 mm, there is a fear that the shape of the electrode may not be maintained under the environment in which the electrolyte flows, and may be destroyed, resulting in contact between the positive electrode and the negative electrode, which may cause a short circuit of the battery.

On the other hand, when the thickness of the positive electrode current collector is thick outside the above range, it is suitable for maintaining the shape of the electrode as a flow battery, but the thickness of the entire electrode is increased to reduce the number of electrodes included in the battery per unit volume, This results in a decrease in battery capacity and also makes it impossible to exert high power.

The positive electrode current collector may be made of a material such as Ni or stainless steel plated with nickel. However, in the present invention, since the metal foil is used as the positive electrode current collector, the number of positive electrode current collectors included per unit volume of the battery increases. Therefore, it is more preferable to use a stainless steel foil having low cost and excellent rigidity as the cathode current collector of the present invention in terms of cost reduction. The stainless steel foil may include a Ni or Ni _{1 - x} Co _x coating layer by plating or cladding on a surface thereof.

The positive electrode is manufactured by applying the paste or slurry of the positive electrode material to the surface of such a positive electrode current collector. In the present invention, the thickness (or adhesion amount) of the positive electrode material applied to the surface of the positive electrode current collector is important, but by reducing the thickness or the adhesion amount, the distance of the positive electrode active material from the current collector is shortened, so that high output, that is, high speed charge and discharge is possible. . In this case, there may be a disadvantage in that the capacity (Ah / electrode) obtained from the electrode plate may be reduced when the same area is used. However, this may increase the number of electrodes by using the metal foil as a support, thereby increasing the capacity per unit volume. Can remain the same.

In general, Zn-Ni flow batteries use electrodes of 0.5 to 1.0 mm, and since these electrodes are disadvantageous for high output and high speed charging and discharging, their application is limited to long-period ESS that performs low-speed charging and discharging mainly in power storage devices. There are disadvantages. Therefore, in the present invention, the thickness of the anode is reduced to 300 µm or less, for example, 80 to 300 µm, 100 to 300 µm, and 150 to 300 µm, thereby greatly improving output density per unit area lower than that of Vanadium Redox Flow. Can be.

To this end, the present invention preferably forms a positive electrode material on the one side or both sides of the metal foil, which is the positive electrode support and the current collector, to a thickness of 0.1 mm or less, more preferably 0.03 to 0.1 mm, for example, 0.03 to 0.07 mm. Do.

For example, CUNY, a US leader in Zn-Ni flow battery products, uses a porous nickel sintered body as a positive electrode current collector and has a thickness of about 600 μm. In the present invention, as an example, by using a 0.1 mm thick metal foil as a positive electrode current collector, by applying a positive electrode material of 0.05 mm level on both sides thereof, it is thin to 200㎛ level that is 1/23 or less than the anode of the CUNY company An anode can be formed. As a result, the present invention can increase the effective area of the anode by about three times by integrating the anode three times per unit volume as compared with the conventional art, and the output per unit volume (W / L) can be improved accordingly.

In the Zn-Ni flow battery of the present invention, a negative electrode paired with the positive electrode may also use a metal foil of 0.2 mm or less, more preferably 0.05 to 0.2 mm, for example, 0.1 mm level, similarly to the positive electrode. The metal foil serves as a current collector and a support of the negative electrode, and is itself a thickness of the negative electrode.

As the metal foil of the negative electrode, for example, a material such as nickel and copper may be used, and a metal foil obtained by plating or cladding nickel, copper, or tin on the surface of the stainless steel foil may be used as the negative electrode current collector. For economics it is preferred to use stainless steel metal foils plated or clad with nickel, copper or tin.

The negative electrode of the present invention is composed of only the negative electrode current collector, the negative electrode active material is dissolved in the state of Zn (OH) ₄ ^2- ion. Is deposited on the entire ion is a negative electrode current collector, when the discharge is re-Zn Zn (OH) ₄ ^{2 - -} include Zn (OH) ₄ ² in the electrolyte during charging and soluble in the ionic liquid electrolyte. In the case of a KOH aqueous solution, required for the cell reaction of the OH ^- and provides a ^{sufficiently-in} Zn (OH) ions and a negative electrode active material ^_42.

The electrolytic solution ^₄₂ while continuously circulating with a pump or motor, Zn (OH) in the electrolyte ^-, (OH) ^- generation of the ion and the main ion dendritic zinc is Zn dendrite (dendrite) on the anode during charging by uniformly maintaining the concentration of And short circuits due to this can be prevented.

Through such a battery configuration of the present invention it is possible to significantly improve the current density per unit volume of the product, that is, the output per unit volume. In addition, when the electrode thickness is thin, the conduction path of the anode Ni (OH) ₂ is shortened, and thus the charge / discharge capacity is not reduced even at high C-rate, and the energy density per unit volume can be improved by reducing the content of the conductive material.

Meanwhile, the Zn-Ni flow battery uses a strong alkaline electrolyte based on a 6-10 M KOH aqueous solution electrolyte between a positive electrode and a negative electrode. The electrolyte serves as a passage through which zinc ions inside the battery move during charging or discharging.

Claims (14)

A metal or stainless steel foil of 0.05 to 0.2 mm including Ni or Ni _1-x Co _x coating layer is formed as a current collector and a support by plating or cladding on a surface thereof, and a cathode material is coated on at least one surface of the metal foil. Thin anode of 0.3 mm or less in total and positive electrode material; And
A thin negative electrode having a metal foil as a current collector and a support, and having a metal foil having a thickness of 0.2 mm or less;
Zn-Ni flow battery comprising a, wherein the electrode gap between the thin anode and thin cathode is 0.5mm or less, the electrode density per unit volume is improved to increase the output density per unit volume.
delete delete delete delete delete The Zn-Ni flow battery of claim 1, wherein the coating layer has a thickness of 5 to 30 μm.
The cathode according to any one of claims 1 to 7, wherein the thin cathode is formed by coating a cathode material having Ni (OH) ₂ as a cathode active material on one or both surfaces of the metal foil support and the current collector to a thickness of 0.1 mm or less. Zn-Ni flow battery.
The Zn-Ni flow battery of claim 1, wherein the thin cathode is a stainless steel foil having a thickness of 0.05 to 0.2 mm.
The Zn-Ni flow battery of claim 9, wherein the thin cathode includes a coating layer of Ni, Cu, or Sn on the surface of the stainless foil by plating or cladding.
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