WO2024085273A1

WO2024085273A1 - Zinc-bromine supercapattery

Info

Publication number: WO2024085273A1
Application number: PCT/KR2022/015965
Authority: WO
Inventors: 이주혁; 김완영; 안제헌; 곽정권
Original assignee: 주식회사 코스모스랩
Priority date: 2022-10-18
Filing date: 2022-10-19
Publication date: 2024-04-25
Also published as: KR102577084B1

Abstract

The present invention relates to a zinc-bromine supercapacitor. The zinc-bromine supercapacitor according to one embodiment of the present invention may comprise first and second carbon electrodes having micropores; and an electrolyte solution containing an aqueous solvent and a Zn-Br redox couple.

Description

Zinc-bromine supercapacitor

The present invention relates to a zinc-bromine supercapacitor, and more specifically, to a zinc-bromine supercapacitor with high energy density and power density and excellent lifespan characteristics.

Around the world, there is a growing demand for the introduction of new energy such as solar and wind power generation as a measure against global warming. However, in order to compensate for the irregular characteristics of renewable energy, in which power is produced intermittently and under certain conditions, secondary batteries with a power storage function are receiving great attention.

Among various secondary batteries, it has the highest energy density (over 250 Wh/kg & 650 Wh/L) and driving voltage (over 3.2 V), and not only has excellent cycle life (over 3000 cycles), but also has an advanced long-term manufacturing process. Lithium-ion batteries, which are easy to commercialize, are widely used. However, due to the disadvantage of lithium-ion batteries using flammable materials, frequent fire accidents occur in ESS, electric vehicles, small devices, etc. This is because the temperature rise caused by the battery short-circuit encourages ignition of the flammable organic electrolyte. Therefore, in order to change the global ecosystem centered on the use of renewable energy-based power, next-generation secondary battery technology with high stability and high performance is required.

In line with this trend, energy storage systems using aqueous electrolytes are receiving great attention from academia and industry around the world. In particular, water-based secondary batteries using zinc and bromine have excellent material price competitiveness, have a high charging voltage of over 1.8 V, and have an energy density of 85 Wh/kg, which is similar to that of lead acid batteries (40 Wh/kg) and vanadium flow batteries. It is receiving a lot of attention as it is superior to (300 Wh/kg). In particular, zinc metal and halide-based bromine, which are abundant and inexpensive elements on Earth, have a much more fluid raw material production network and supply chain compared to lithium-ion batteries.

However, compared to lithium-ion batteries, the theoretical energy density of aqueous zinc-bromine batteries is low, so it is difficult to develop as a technology targeting various consumers and devices without an intrinsic electrochemical solution at the cell level that can improve this. It has limitations. In particular, the quantitative target values of 300 Wh/kg (energy density), 8,500 W/kg (output), and Water-based battery technology that can achieve less than $90/kWh (manufacturing cost) is needed.

[Prior art literature]

[Patent Document]

Korean Patent No. 10-1862368

Korean Patent No. 10-2255426

[Non-patent literature]

Brian Evanko et al: "Stackable bipolar pouch cells with corrosionresistant current collectors enable high-power aqueous electrochemical energy storage" (14 June 2018, Energy & Environmental Science)

A zinc bromine ‘supercapattery’ system combining triple functions of capacitive, pseudocapacitive and battery-type charge storage (Materials Horizons, 2020)

The present invention seeks to provide a zinc-bromine supercapacitor with high energy density and power density and excellent lifespan characteristics.

One embodiment of the present invention includes first and second carbon electrodes having micropores; and an electrolyte solution containing an aqueous solvent and a Zn/Br redox couple.

The micropores may include micro pores, meso pores, and macro pores.

The first and second carbon electrodes may include one or more carbon materials selected from the group consisting of activated carbon, graphite, hard carbon, and porous carbon materials.

The first and second carbon electrodes may include activated carbon with an average particle size of 1 to 10 ㎛ and a porosity of 80% or more.

The first and second carbon electrodes may include 60 to 90 parts by weight of the carbon body, 5 to 20 parts by weight of the conductive material, and 5 to 20 parts by weight of the binder.

The first and second carbon electrodes may be formed on a carbon body current collector.

In the first and second carbon electrodes, Zn ²⁺ and Br ^- are adsorbed and desorbed in micropores to form an electric double layer (EDLC), a non-Faraday reaction, and Zn ²⁺ and Br are formed on the microsurface of the electrode. ^- A reaction in which ions undergo underpotential deposition and a Faradaic reaction in which Zn ²⁺ and Br ^- ions are deposited on the surface of the electrode can be performed.

The electrolyte solution may contain ZnBr ₂ (Zinc bromide), hydrobromic acid, acids other than hydrobromic acid, bromine complexing agents, and other additives.

The zinc-bromine supercapacitor according to one embodiment of the present invention is a compound word of battery and supercapacitor, and is an electrochemical energy storage device that combines the advantages of batteries and supercapacitors.

The supercapacitor according to one embodiment of the present invention is based on an aqueous electrolyte containing a Zn/Br redox couple, is non-flammable, and uses a carbon electrode with a fine pore structure to form an electric double layer (EDLC, Electric) of the capacitor. Capacity based on double layer capacitor, pseudo-capacitor, and battery principles can all be implemented.

1 is a cross-sectional view schematically showing a zinc-bromine supercapacitor according to an embodiment of the present invention.

Figure 2 is a graph showing the coverage (θ) of the material adsorbed (electrosoprtion) on the surface and the change in pseudocapacitance (C _ø ) according to voltage.

Figure 3 is a graph showing cyclic voltammetry (CV) curve characteristics combining the EDLC response and pseudocapacitance response at the electrode.

Figure 4 shows the results of a charge/discharge test at a constant current state of the zinc-bromine supercapacitor according to the above manufacturing example.

Figure 5 shows the Coulombic efficiency measurement results of the zinc-bromine supercapacitor according to the above manufacturing example.

Figure 6 shows the results of a voltage curve experiment of a zinc-bromine supercapacitor according to the above manufacturing example.

Figure 7 is a schematic diagram of a voltage curve according to charge/discharge current density.

Hereinafter, implementation examples and examples of the present invention will be described in detail so that those skilled in the art can easily practice it. However, the present invention may be implemented in various different forms and is not limited to the implementation examples and examples described herein.

The terms used in this application are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, terms such as “comprise” or “have” are intended to designate the presence of features, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features or steps. , it should be understood that it does not exclude in advance the possibility of the existence or addition of operations, components, parts, or combinations thereof.

Additionally, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by a person of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and unless clearly defined in the present application, should not be interpreted in an ideal or excessively formal sense. No.

The present invention relates to a zinc-bromine supercapacitor and a method of driving the same.

In this specification, ‘supercapacitor’ is a compound word of battery and supercapacitor, and can be understood as an electrochemical energy storage device that combines the advantages of batteries and supercapacitors.

The supercapacitor according to an embodiment of the present invention is based on an aqueous electrolyte containing a Zn/Br redox couple, and uses a carbon electrode with a micropore structure to form an electric double layer capacitor (EDLC). ), pseudo-capacitor, and battery principle-based capacity can all be implemented.

The supercapacitor according to one embodiment of the present invention applies carbon electrodes with micropores to both the anode and cathode, so that Zn ²⁺ and Br ^- can implement three types of electrochemical charging and discharging at the carbon electrode interface, respectively. It was designed.

Specifically, the reaction in which Zn ²⁺ and Br ^- adsorb and desorb to the micropores of the carbon electrode to form an electric double layer (electric double layer capacitance, EDLC), and the low potential of Zn ²⁺ and Br ^- ions generated on the microsurface of the electrode. Underpotential deposition reaction, pseudocapacitance, and deposition reaction of Zn ²⁺ and Br ^- ions generated on the surface of the electrode may be performed. In particular, the pseudocapacitance reaction is a principle that is not utilized in existing batteries. This is explained in more detail below.

1 is a cross-sectional view schematically showing a zinc-bromine supercapacitor according to an embodiment of the present invention. Referring to FIG. 1, it may include a first electrode 221 and a second electrode 222, a separator 240 disposed between the first and second electrodes, and an electrolyte solution. Figure 1 illustrates a unit cell of a zinc-bromine supercapacitor. The zinc-bromine supercapacitor may be implemented by stacking one or more unit cells. The unit cells can be stacked to form small batteries such as pouch, cylindrical, or square shapes.

According to one embodiment of the present invention, the first carbon electrode and the second carbon electrode may have polarities opposite to each other. For example, the first electrode 221 formed on the first current collector 211 may be an anode. , and the second electrode 222 formed on the second current collector 212 may be a negative electrode.

The materials of the first carbon electrode and the second carbon electrode are not particularly limited, and materials commonly used in the art can be used. It is not limited thereto, but for example, a carbon body, etc. can be used. According to one embodiment of the present invention, the electrode may have micropores. More specifically, it may have micro pores, meso pores, and macro pores.

In the present invention, the average size of micropores may be 2 nm or less, the average size of mesopores may be 2 to 50 nm, and the average size of macropores may be 50 nm or more.

According to one embodiment of the present invention, the electrode may be formed to have a thickness of 5 to 300 ㎛ to provide an active site. Specifically, the cathode may be formed to a thickness of 5 to 100 ㎛, and the anode may be formed to a thickness of 50 to 300 ㎛. In addition, the specific surface area of the electrode is preferably formed to be large, and is not limited thereto, but may be, for example, 500 to 3,000 m ² /g.

According to one embodiment of the present invention, the carbon body may be activated carbon, graphite, hard carbon, or porous carbon material. The porous carbon material is not limited to this, but carbon felt, carbon cloth, or carbon paper may be used. Specifically, activated carbon can be used, and activated carbon with an average particle size of 1 to 10 ㎛ can be used, and activated carbon with a porosity of 80% or more can be used.

Additionally, the carbon electrode may additionally include a conductive material, binder, etc. The conductive material is not limited to this, but for example, carbon-based conductive materials such as carbon black, carbon fiber, carbon nanotubes, or graphite can be used. The carbon black is not limited thereto, but for example, acetylene black, Ketjen black, Super P, channel black, furnace black, lamp black, or thermal black can be used. The graphite may be natural graphite or artificial graphite.

The conductive material can be used in an amount of 5 to 20 parts by weight, specifically 5 to 10 parts by weight, based on 100 parts by weight of the carbon electrode. If the content is less than 5 parts by weight, the electrical conductivity of the electrode is low and there is a risk of deteriorating the performance of the supercapacitor. In addition, conductive materials are prone to agglomeration due to the fine particle size, and uniform distribution is difficult. Accordingly, if it exceeds 20 parts by weight, capacity may be reduced in some areas, and resistance characteristics may increase in other areas.

The binder is not limited to this, but for example, carboxymethyl cellulose, styrene butadiene rubber, polyvinylidene fluoride, or polytetrafluoroethylene may be used. .

The binder may be used in an amount of 5 to 20 parts by weight, specifically 5 to 10 parts by weight, based on 100 parts by weight of the carbon electrode. If the content is less than 5 parts by weight, there is a risk that it may not function as a binding agent between the active material and the conductive material or as a binding agent to the current collector. If it exceeds 20 parts by weight, internal resistance characteristics may increase, capacity may decrease, and the amount of activated carbon filled may decrease, causing damage to the capacitor. There is a risk of deteriorating performance.

The reaction performed at the electrode according to one embodiment of the present invention is as follows.

Taking Zn ²⁺ of the cathode as an example, following a charging reaction based on the EDLC principle in which zinc cations are adsorbed to the electrode, the pseudocapacitance capacity can be expressed as equation (1) below. When Zn ²⁺ cations are adsorbed onto the carbon electrode (M), they are adsorbed on the electrode surface according to the electron exchange reaction as shown in Equation (1).

[Equation 1]

Assuming that this adsorption process ideally follows a Langmuir type electrosorption isotherm, it can be expressed as Equation (2) below. C _Zn2+ is the concentration of Zn ²⁺ , θ is the degree of adsorption of MZn _ads on the electrode surface, K is the reaction rate constant, F is Faraday's constant, R is the ideal gas constant, V is the electrode potential, and T is the temperature.

[Equation 2]

By substituting the above equation (2) into the Nernst equation that describes the existing electrochemical redox reaction, conversion is possible as shown in equation (3). E represents the equilibrium potential and E ⁰ represents the reference potential.

[Equation 3]

Therefore, assuming that the charge required for adsorption of MZn _ads as a single layer on the surface of the electrode is q, the pseudocapacitance (capacitance of pseudocapacitance (C _ø )) can be expressed as in equation (4) below.

[Equation 4]

As shown in Equation (4) above, the pseudocapacitance capacity not only indicates that the maximum capacity can be realized when θ = 0.5 (when MZn _ads occupy 50% of the electrode surface area), but also indicates that the maximum capacity can be achieved when θ = 0.5. It is proven that the potential and the ions electrosorbed on the surface have a functional proportional relationship with the pseudocapacitance capacity.

FIG. 2 is a graph showing the coverage (θ) of the electrosorbed material on the surface according to Equation 4 above, and the change in pseudocapacitance (C _ø ) according to voltage.

As shown in Figure 3, it is possible to implement additional capacity in addition to Faraday reaction (battery driving principle) through capacity due to EDLC and pseudocapacitance reaction.

According to one embodiment of the present invention, the first and second carbon electrodes may be formed on the carbon body

current collectors

211 and 212. The carbon body current collector may refer to a current collector made only of carbon body without other materials mixed.

The supercapacitor according to one embodiment of the present invention may use an acidic aqueous electrolyte, but if a metal current collector is used, side reactions, chemical corrosion, and electrochemical corrosion may occur.

The carbon body current collector may have lower electrical conductivity than the metal current collector, but side reactions with the acidic aqueous electrolyte solution do not occur and corrosion does not progress, so lifespan characteristics can be improved.

The carbon body is not limited thereto, and may be, for example, graphite foil, carbon cloth, carbon paper, or a mixture thereof.

The carbon body current collector may have an electrical conductivity of 1.38×10 ⁷ to 3.49×10 ⁷ S/m, specifically 2.46×10 ⁷ to 3.49×10 ⁷ S/m.

The carbon body current collector can enable charging and discharging at an appropriate current density without increasing the transfer resistance of the carbon electrode.

The carbon body current collector does not contain any other material other than the carbon body, so it has higher electrical conductivity than the carbon electrode, and can have a strength sufficient to be applied to the coating process of the electrode material.

When using a carbon body as a current collector, the specific surface area characteristics are not considered, and it can function as a current collector even with a small thickness.

The carbon body current collector may have a thickness of 10 to 50 ㎛. Specifically, it may be 20 to 30 ㎛. If the thickness is less than 10 ㎛, it may be difficult to apply to the electrode formation process, and if it exceeds 50 ㎛, the thickness of the current collector may be too thick, causing difficulties in the process, or the energy density of the cell may be significantly lowered.

When mixing a polymer, etc. with a carbon body to use it as a current collector, a porous structure may be formed through the mixing process. Due to this porous structure, strength may decrease, resistance may increase, and electrolyte may be absorbed. there is.

However, the carbon body current collector according to one embodiment of the present invention is not mixed with other materials and has excellent electrical conductivity. In addition, it is hydrophobic and has no pores on the surface, so it has excellent strength and may not absorb electrolytes.

According to one embodiment of the present invention, the electrolyte solution may include an aqueous solvent (water) and a Zn/Br redox couple. According to one embodiment of the present invention, the aqueous electrolyte solution may be acidic and the pH may be 2 or less.

Additionally, according to one embodiment of the present invention, the electrolyte solution may further include bromonic acid, an acidic substance other than bromous acid, a bromine complexing agent, and other additives.

The bromine complexing agent may include quaternary ammonium bromide. It is not limited thereto, but for example, pyridinium bromide substituted with 1 or more alkyl groups having 1 to 10 carbon atoms, imidazolium bromide substituted with 1 or more alkyl groups having 1 to 10 carbon atoms, or 1 -Ethyl-1-methylpyrrolidinium bromide, etc. can be used.

The bromous acid (HBr) is an acidic substance, which serves to lower the pH of the electrolyte and increases the content of bromine ions (Br ^- ) through ionization, thereby improving the charge/discharge efficiency of the zinc-bromine battery.

Acidic substances other than hydrobromic acid (HBr) are not limited thereto, but include, for example, a strong acid with a pH of 2.0 or less or -1.0 to 2.0, specifically hydrochloric acid, nitric acid, sulfuric acid, hydroiodide acid, or two types thereof. A mixture of the above can be used.

Additionally, other additives may include Na ₂ SO ₄ , NaCl, etc.

The separator 140 performs the main functions of separating the positive and negative electrolytes during charging or discharging, preventing internal short circuits during charging or discharging, and containing the electrolyte. The material of the separator 140 is not particularly limited, and may be, for example, a polyolefin film containing polyethylene or polypropylene, polyvinyl chloride, cellulose, polyester, or a fibrous nonwoven fabric containing polypropylene.

Hereinafter, the present invention will be described in more detail through examples according to one embodiment of the present invention, but these examples do not limit the scope of the present invention.

[Example]

Manufacturing example

A carbon electrode prepared by mixing 80 parts by weight of activated carbon with an average particle size of 1 to 10 ㎛ and a porosity of 80% or more, 10 parts by weight of a conductive material, and 10 parts by weight of a binder was composed of an anode and a cathode. Graphite foil was used as the current collector, and an aqueous electrolyte containing ZnBr ₂ (Zinc bromide) was used as the electrolyte.

evaluation

Figure 4 shows the results of a charge/discharge test at a constant current state of the zinc-bromine supercapacitor according to the above manufacturing example. Referring to Figure 4, unlike the zinc-bromine supercapacitor, when charging, the charging voltage instantaneously shows 1.82V, which is the theoretical charge potential shown by zinc bromine batteries classified as existing secondary batteries. It can be seen that charging follows a linear rise section from 1.7V to 1.85V and charging under a certain voltage after reaching a voltage of 1.7V or more and 1.85V or less.

It can be seen that the linear voltage rise section before 1.82V during the first 500 seconds of charging is a mixed potential section caused by the charging reactions (Capacitive reaction, Pseudocapacitive reaction, Faradic reaction) of the supercapacitor, pseudocapacitor, and battery occurring simultaneously.

[Reaction equation based on representative pseudocapacitor reaction]

Anode: Zn ²⁺ + AC + 2e ^- → Zn@AC

Cathode: 3Br ^- + AC → Br ^- @AC +2e ^-

[Reaction formula based on Faradaic reaction]

Anode: xZn ²⁺ + Zn@AC + 2e ^- → Zn _x @AC

Cathode: Br ₃ ^- + Br ₃ ^- @AC → Br _3x ^- @AC + 2e ^-

It can be seen that 1.82V is maintained for about 3000 seconds after the initial 500 seconds of charging. In this section, the concentration is polarized between the electrode interface and the electrolyte, and local battery reactions mainly occur at the electrode interface due to mass transfer resistance.

When discharging, a dissolution reaction of the active material occurs similar to the battery discharge reaction.

Anode: Zn _x @AC → xZn ²⁺ + Zn@AC + 2e ^-

Cathode: Br _3x ^- @AC + 2e ^- → Br ₃ ^- +Br ₃ ^- @AC

After the active material desorption reaction, adsorption ion desorption reaction occurs similar to the discharge reaction of pseudocapacitors and supercapacitors, and discharge occurs sequentially.

Anode: Zn@AC → Zn ²⁺ + AC + 2e ^-

Cathode: Br ^- @AC + 2e ^- → 3Br ^- +AC

Figure 5 shows the Coulombic efficiency measurement results of the zinc-bromine supercapacitor according to the above manufacturing example. Referring to FIG. 5, it can be seen that the zinc-bromine supercapacitor according to an embodiment of the present invention is a completely new energy storage system that can be actually implemented for about 25 cycles.

Figure 6 shows the results of a voltage curve experiment of a zinc-bromine supercapacitor according to the above manufacturing example. Figure 6(a) is the result of a voltage curve experiment of charging and discharging at a charge and discharge current density of 0.5 mA cm ^-2 , and Figure 6(b) is the result of a voltage curve experiment of charge and discharge at a charge and discharge current density of 10 mA cm ^-2 , Figure 6(c) is the result of a voltage curve experiment performed at a charge/discharge current density of 40 mA cm ^-2 . Figure 7 is a schematic diagram of a voltage curve according to charge/discharge current density.

In fact, in order for active material ions to penetrate into the carbon electrode of a three-dimensional structure and cause a redox reaction, it is necessary to analyze it by considering the diffusion length according to the charge and discharge speed. As shown in equation (5) below, the diffusion length to reach the electrode from the electrolyte inside the three-dimensional structure is a term that takes into account diffusion time (t _d ) and diffusion coefficient (D). It can be assumed that the value is much larger than .

[Equation 5]

In particular, as the charge/discharge current density increases, concentration polarization occurs due to the limit of the diffusion coefficient (D) inside the three-dimensional structure electrode, resulting in an overvoltage phenomenon due to limiting current density. do.

As shown in FIGS. 6(a) to 6(c), as the charge/discharge current density increases, the charge voltage increases to 0.8, 1.2, and 1.9V. In other words, it appears that a situation has arisen in which only a portion of the surface of the outermost electrode is involved in charging and discharging, rather than utilizing the entire surface area of the electrode. Due to the rapid charge/discharge current density, concentration polarization occurs within the electrode, resulting in the zinc cations and bromide anions not being able to utilize the interface of the electrode as a reaction area.

Therefore, in order to realize the full theoretical capacity of the supercapacitor, it is very important to select driving conditions according to the appropriate charging and discharging current density that do not cause concentration polarization, and it is also important to improve the supercapacitor technology both theoretically and experimentally. This actual current density has been proven to be freely adjustable and implementable through variables.

The above description is merely an illustrative explanation of the technical idea of the present embodiment, and those skilled in the art will be able to make various modifications and variations without departing from the essential characteristics of the present embodiment. Accordingly, the present embodiments are not intended to limit the technical idea of the present embodiment, but rather to explain it, and the scope of the technical idea of the present embodiment is not limited by these examples. The scope of protection of this embodiment should be interpreted in accordance with the claims below, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of rights of this embodiment.

[Explanation of symbols]

211, 212: The whole house

221, 222: Carbon electrode

240: Separator

Claims

First and second carbon electrodes having micropores; and

An electrolyte solution containing an aqueous solvent and a Zn/Br redox couple;

Zinc-bromine supercapacitor containing.
According to paragraph 1,

The micropores include micro pores, meso pores, and macro pores.
According to paragraph 1,

The first and second carbon electrodes are a zinc-bromine supercapacitor comprising at least one carbon material selected from the group consisting of activated carbon, graphite, hard carbon, and porous carbon materials.
According to paragraph 1,

The first and second carbon electrodes include activated carbon having an average particle size of 1 to 10 ㎛ and a porosity of 80% or more.
According to paragraph 1,

The first and second carbon electrodes include 60 to 90 parts by weight of carbon body, 5 to 20 parts by weight of conductive material, and 5 to 20 parts by weight of binder.
According to paragraph 1,

The first and second carbon electrodes are zinc-bromine supercapacitors formed on a carbon body current collector.
According to paragraph 1,

In the first and second carbon electrodes, Zn 2+ and Br - adsorb and desorb in micropores to form an electric double layer, and Zn 2+ and Br - ions form an underpotential deposition on the microscopic surface of the electrode. A zinc-bromine supercapacitor in which a Faradaic reaction is carried out, in which Zn 2+ and Br - ions are deposited on the surface of the electrode.
According to paragraph 1,

The electrolyte is a zinc-bromine supercapacitor containing ZnBr 2 (Zinc bromide), hydrobromic acid, acids other than hydrobromic acid, bromine complexing agent, and other additives.