Vanadium electrolyte, method for preparing same, and secondary battery comprising same

Abstract

The present invention relates to a vanadium electrolyte, a method for preparing same, and a secondary battery comprising same. More specifically, the present invention relates to: a vanadium electrolyte into which carbon dioxide (CO2) is injected so as to suppress a hydrogen evolution reaction (HER) occurring during charging and discharging of the secondary battery; a method for preparing same; and a secondary battery comprising the vanadium electrolyte.

Description

Vanadium electrolyte, method for producing the same, and secondary battery comprising the same

[0001] The present invention relates to a vanadium electrolyte, a method for producing the same, and a secondary battery including the same, and more particularly, to a vanadium electrolyte injected with carbon dioxide (CO2) to suppress a hydrogen evolution reaction (HER) that occurs during charging and discharging of the secondary battery, a method for producing the same, and a secondary battery including the vanadium electrolyte.

[0002] Redox Flow Battery (RFB), a type of oxidation-reduction secondary battery, is an electrochemical storage device that stores electrical energy as chemical energy of the electrolyte by charging and discharging it through oxidation and reduction of the active material in the electrolyte, unlike conventional secondary batteries.

[0003] Meanwhile, the electrolyte of a redox secondary battery uses a substance having a redox couple. The electrolyte of the early redox secondary battery used redox couples of different substances for the positive and negative electrodes. However, there may be a problem in that the ionized substances cross over each other through the separator during charging and discharging, which reduces the capacity of the battery.

[0004] Accordingly, the use of vanadium in both the positive and negative electrodes was proposed as a method to alleviate the ion crossover phenomenon, and since the electrolyte containing vanadium ions ('vanadium electrolyte') is an aqueous electrolyte, it has been used until recently due to its advantages in that it not only has high safety against explosions when applied to secondary batteries, but also increases the lifespan of the batteries.

[0005] Vanadium electrolyte using vanadium ions as the active material has the longest lifespan when applied to redox secondary batteries and is advantageous in terms of large capacity. In addition, the electrolyte can be separated and reused through the electrochemical reaction of charging and discharging, which is advantageous in terms of cost.

[0006] The vanadium electrolyte used in the positive and negative electrodes requires a vanadium compound having an oxidation state of 4+ for the positive electrode and 3+ for the negative electrode, respectively, based on a fully discharged state. In addition, a vanadium compound having an oxidation state of 5+ for the positive electrode and 2+ for the negative electrode is required based on a fully charged state. Charge and discharge reactions occur as the oxidation state of the vanadium active material changes.

[0007] The anode and cathode are each anode oxidation-reduction couple (V 4+ / V 5+ ) and cathode oxidation-reduction couple (V 2+ / V 3+ ) is supplied with a dissolved electrolyte solution (electrolyte), which causes the following half-reactions.

[0008] Bipolar half-reaction: V 5+ + e- ←→ V 4+

[0009] Negative half-reaction: V 2+ ←→ V 3+ + e-

[0010] As a vanadium electrolyte, an electrolyte with a vanadium oxidation number of 3.50 (3.5+) that can be commonly used for the electrolyte supplied to the cathode and the electrolyte supplied to the anode has been used.

[0011] Meanwhile, in the negative electrode of a secondary battery using a vanadium electrolyte, the hydrogen evolution reaction (HER) inevitably occurs within the operating voltage range (1.1 to 1.6 V) to produce hydrogen (H2) gas. The hydrogen gas produced in this way consumes current and generates a voltage (V) between the electrode and the electrolyte. 2+ / V 3+) causes problems of interfering with the oxidation and reduction reactions. In addition, as the pressure of the electrolyte and the secondary battery containing it increases due to hydrogen gas, a considerable amount of effort and cost is required to improve durability against high pressure or to control safety issues such as explosion due to pressure increase, and there is also a limit to the usable voltage range. If there is a limit to the usable voltage range due to hydrogen gas generation, the energy capacity that can be stored per volume of electrolyte decreases, which causes problems of reduced efficiency such as increased cost of the secondary battery. Therefore, it is necessary to develop a method to suppress the hydrogen generation reaction that is a problem during charging and discharging of a secondary battery in a vanadium electrolyte.

[0012] The purpose of the present invention is to provide a vanadium electrolyte capable of suppressing a hydrogen generation reaction in a secondary battery using a vanadium electrolyte, an efficient method for producing the same, and a secondary battery including the vanadium electrolyte.

[0013] Another object of the present invention is to improve the efficiency and lifespan of a secondary battery including a vanadium electrolyte capable of suppressing a hydrogen generation reaction, increase the usable voltage range of the secondary battery, and significantly reduce or eliminate the risk of explosion due to hydrogen gas by using a vanadium electrolyte capable of suppressing a hydrogen generation reaction.

[0014] The objects of the present invention are not limited to the purposes mentioned above, and other purposes not mentioned will be clearly understood by those skilled in the art from the entire description of this specification.

[0015] In order to achieve the above task, according to the first aspect of the present invention,

[0016] A step of preparing an electrolyte containing vanadium ions and an acidic solution; and

[0017] A step of supplying carbon dioxide to the electrolyte;

[0018] A method for producing a vanadium electrolyte can be provided, wherein ΔP, which is the absolute value of the difference in partial pressure of dissolved gas (carbon dioxide) between the electrolyte after supplying carbon dioxide and the electrolyte before supplying carbon dioxide, is greater than 7 kPa.

[0019] The above ΔP can be 8 kPa to 30 kPa.

[0020] The step of supplying the carbon dioxide can be performed by injecting carbon dioxide gas into the electrolyte by bubbling it.

[0021] The step of supplying the carbon dioxide is performed by adding a compound that provides a carbonate to the electrolyte, and the compound that provides the carbonate may include at least one of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate.

[0022] The step of supplying the carbon dioxide is performed by adding a reducing agent that generates carbon dioxide gas to the electrolyte, and the reducing agent may include one or more of oxalic acid, ascorbic acid, methanol, ethanol, formaldehyde, and formic acid.

[0023] The step of supplying the above carbon dioxide can be performed by mixing dry ice into the electrolyte.

[0024] The above vanadium ions can be supplied by vanadium oxide including at least one of V2O5, VOSO4, V2O3, NH4VO3 and V2O4.

[0025] The above acid solution may contain one or more of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.

[0026] According to a second aspect of the present invention, a vanadium electrolyte prepared according to the method for preparing a vanadium electrolyte according to the first aspect can be provided.

[0027] According to a third aspect of the present invention, a vanadium ion battery,

[0028] The above vanadium ion battery comprises at least one vanadium ion battery unit cell,

[0029] The above vanadium ion battery unit cell is,

[0030] positive current collector;

[0031] A negative electrode current collector disposed spaced apart from the positive electrode current collector;

[0032] A separator disposed between the positive electrode current collector and the negative electrode current collector;

[0033] A cathode electrolyte receiving portion formed between the cathode current collector and the separator;

[0034] A negative electrode electrolyte receiving portion formed between the negative electrode current collector and the separator;

[0035] A positive electrode solid electrode disposed in the positive electrode electrolyte receiving portion and impregnated with the positive electrode electrolyte; and

[0036] A cathode solid electrode disposed in the cathode electrolyte receiving portion and impregnated with the cathode electrolyte;

[0037] An electrolyte containing vanadium ions is supplied as an anode electrolyte and a cathode electrolyte to each of the anode electrolyte receiving portion and the cathode electrolyte receiving portion,

[0038] The electrolyte containing the above vanadium ions may be manufactured according to the method for manufacturing the vanadium electrolyte of the first aspect.

[0039] The available voltage range of the above vanadium ion battery may be 1.1 to 1.75 V.

[0040] The above vanadium ion battery unit cell may further include a transition portion that connects the positive electrode electrolyte receiving portion and the negative electrode electrolyte receiving portion.

[0041] The positive electrode current collector may include a positive electrode metal current collector and a positive electrode carbon current collector, and the positive electrode current collector may include a negative electrode metal current collector and a negative electrode carbon current collector.

[0042] The vanadium electrolyte according to the present invention can suppress the hydrogen generation reaction even when applied to a secondary battery, thereby increasing the usable voltage range of the secondary battery and significantly reducing or eliminating the risk of pressure increase due to hydrogen gas generation and explosion caused thereby.

[0043] In addition, the present invention uses a vanadium electrolyte capable of suppressing hydrogen generation reaction, thereby solving problems related to current consumption due to hydrogen gas and inhibition of oxidation / reduction reactions.

[0044] Furthermore, a secondary battery using a vanadium electrolyte with suppressed hydrogen generation reaction manufactured according to the present invention can increase the storable energy capacity per volume of electrolyte and improve the efficiency and lifespan of the secondary battery.

[0045] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0046] Figure 1 is a flow chart showing a method for manufacturing a vanadium electrolyte according to one embodiment of the present invention.

[0047] FIG. 2 is an exploded perspective view of a vanadium ion battery unit cell according to one embodiment of the present invention.

[0048] FIG. 3 is a perspective view schematically illustrating the structure of a vanadium ion battery in which vanadium ion battery unit cells are stacked according to one embodiment of the present invention.

[0049] Figure 4 shows a measurement graph for confirming whether pressure is generated according to the amount of carbon dioxide treated in Example 1 and Comparative Examples 1 to 3 of the present invention.

[0050] Figure 5 shows a measurement graph for confirming whether pressure is generated according to the amount of carbon dioxide treated in Examples A to C and Comparative Examples A to C of the present invention.

[0051] The advantages and features of the present invention, and the methods for achieving them, will become clearer with reference to the embodiments described in detail below together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals designate like elements throughout the specification.

[0052] In describing this specification, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of this specification, the detailed description is omitted.

[0053] Although terms like "first" and "second" are used herein to describe various components, these components are not limited by these terms. These terms are used merely to distinguish one component from another, and unless otherwise specifically stated, a "first" component may also be a "second" component.

[0054] Throughout this specification, unless otherwise specifically stated, each component may be singular or plural.

[0055] In interpreting the components in this specification, even if there is no separate explicit description, it is interpreted to include the range of error.

[0056] In this specification, the phrase "any component is disposed "on (or below)" a component or "on (or below)" a component may mean not only that any component is disposed in contact with the upper surface (or lower surface) of said component, but also that another component may be interposed between said component and any component disposed on (or below) said component.

[0057] When it is described herein that any component is “connected,” “coupled,” or “connected” to another component, it should be understood that the components may be directly connected or connected to one another, but that other components may also be “interposed” between the components, or that each component may be “connected,” “coupled,” or “connected” through another component.

[0058] In this specification, when the words "includes," "contains," "has," "consists of," "arranges," and "provides" are used for a component, other parts may be added unless "only" is used. When a component is expressed in the singular, it includes cases where the plural is included unless specifically stated otherwise.

[0059] Throughout this specification, when we refer to "A and / or B", this means A, B, or A and B, unless otherwise stated, and when we refer to "C to D", this means C or more and D or less, unless otherwise stated.

[0060] Unless otherwise specified herein, any reference to a unit is interpreted as meaning “weight (wt).”

[0061] In this specification, unless otherwise specifically stated, “vanadium electrolyte” is interpreted to refer to the same thing as “electrolyte containing vanadium ions,” “electrolyte using (utilizing) vanadium ions,” “electrolyte containing vanadium oxide,” “electrolyte containing vanadium active material,” etc.

[0062] Hereinafter, the present invention will be described in more detail.

[0063] Referring to Figure 1, the method for manufacturing a vanadium electrolyte of the present invention is as follows:

[0064] A step of preparing an electrolyte containing vanadium ions and an acidic solution; and

[0065] A step of supplying carbon dioxide to the above electrolyte is included.

[0066] As described above, the inventors of the present invention experimentally discovered that the hydrogen evolution reaction (HER) occurring during charging and discharging of a secondary battery is suppressed when carbon dioxide is supplied to the electrolyte, thereby completing the present invention. This suppression effect of the HER is believed to be achieved when the hydrogen evolution reaction and the carbon dioxide reduction reaction (CO2 Reduction Reaction) within the electrolyte establish a competitive reaction relationship.

[0067] The above-described hydrogen evolution reaction suppression effect can be confirmed by supplying carbon dioxide to the electrolyte and checking whether pressure is generated. Furthermore, by resolving the pressure generation issue, the available voltage range during charging and discharging of secondary batteries can be significantly improved from the previous maximum of 1.60 V to 1.75 V. Consequently, by increasing the charging energy per unit volume of the secondary battery, the performance of the secondary battery can be improved, and safety can be secured by eliminating the risk of explosion.

[0068] In the present invention, the amount of carbon dioxide supplied to the electrolyte capable of achieving suppression of the hydrogen generation reaction was studied, and it was confirmed that the partial pressure of dissolved gas (carbon dioxide) in the electrolyte after carbon dioxide was supplied must exceed at least 7 kPa compared to the electrolyte before carbon dioxide was supplied.

[0069] In addition, as a result of the experiment in which the amount of carbon dioxide supplied was gradually increased so that the partial pressure of the increased carbon dioxide exceeded 7 kPa, the pressure generation due to hydrogen was well suppressed as the amount of carbon dioxide supplied increased, and there was an effect of increasing the charging energy of the secondary battery and the available voltage range during charging and discharging. However, it was confirmed that this effect converged after the amount of carbon dioxide supplied reached a certain level.

[0070] From this point of view, it is preferable that the absolute value of the difference in partial pressure of the dissolved gas (carbon dioxide) in the electrolyte after supplying carbon dioxide and in the electrolyte before supplying carbon dioxide, "ΔP", exceeds 7 kPa. That is, ΔP is the dissolved gas partial pressure in the electrolyte after supplying carbon dioxide minus the dissolved gas partial pressure in the electrolyte before supplying carbon dioxide, wherein the dissolved gas means dissolved carbon dioxide. The ΔP may be, for example, 8 kPa or more, for example, 9 kPa or more, for example, 12 kPa or more, for example, 15 kPa or more, for example, 20 kPa or more, for example, 24 kPa or more.

[0071] On the other hand, if the amount of carbon dioxide injected is excessive and ΔP exceeds 30 kPa, the amount of dissolved carbon dioxide gas in the electrolyte increases too much, which may cause problems when injecting the electrolyte after carbon dioxide treatment into the secondary battery. That is, an excessive amount of carbon dioxide gas may be injected into the secondary battery instead of the electrolyte, making it impossible to secure a sufficient supply of electrolyte, which may increase the defect rate during the production or operation of the secondary battery. From this point of view, ΔP may be 30 kPa or less, for example, 28 kPa or less, for example, 26 kPa or less, for example, 25 kPa or less.

[0072] According to the first method of supplying carbon dioxide in the present invention, the step of supplying carbon dioxide can be performed by injecting carbon dioxide gas into the electrolyte by bubbling it, and is a method of directly supplying the gas itself into the electrolyte.

[0073] When supplying carbon dioxide according to the first method, the supply flow rate and supply time of the injected carbon dioxide gas can be controlled, and for rapid diffusion of carbon dioxide, a stirring pipe can be inserted into the electrolyte and injected while rotating, and when a rod with pores is used for injection, the desired amount of carbon dioxide can be injected in a shorter time, thereby increasing process efficiency.

[0074] According to the second method of supplying carbon dioxide in the present invention, the step of supplying carbon dioxide may be performed by adding a compound that provides a carbonate to the electrolyte. The compound that provides a carbonate may include one or more of sodium carbonate, sodium bicarbonate, ammonium carbonate, and ammonium bicarbonate.

[0075] According to a third method of supplying carbon dioxide in the present invention, the step of supplying carbon dioxide may be performed by adding a reducing agent that generates carbon dioxide gas to an electrolyte. The reducing agent may include one or more of oxalic acid, ascorbic acid, methanol, ethanol, formaldehyde, and formic acid.

[0076] According to the fourth method of supplying carbon dioxide in the present invention, the step of supplying carbon dioxide may be performed by mixing dry ice into the electrolyte.

[0077] The electrolyte of the present invention preferably includes an acidic solution, which is an acidic aqueous solution containing vanadium ions and conducting current through ionization. The vanadium ions may be supplied by vanadium oxide containing at least one of V2O5, VOSO4, V2O3, NH4VO3, and V2O4, and the acidic solution may include at least one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.

[0078] As an electrolyte containing vanadium ions, it is common to use an electrolyte with a vanadium oxidation number of 3.50 (3.5+) that can be commonly used for the electrolyte supplied to the cathode and the electrolyte supplied to the anode.

[0079] Referring to FIGS. 2 and 3, a vanadium ion battery unit cell according to one embodiment of the present invention will be described in detail.

[0080] A vanadium ion battery unit cell (100) according to the present invention includes: a positive electrode current collector (130a); a negative electrode current collector (130b) disposed spaced apart from the positive electrode current collector; a separator (120) disposed between the positive electrode current collector (130a) and the negative electrode current collector (130b); a positive electrode electrolyte receiving portion (111a) formed between the positive electrode current collector (130a) and the separator (120); a negative electrode electrolyte receiving portion (111b) formed between the negative electrode current collector (130b) and the separator (120); a positive electrode solid electrode (150a) disposed in the positive electrode electrolyte receiving portion (111a) and impregnated with the positive electrode electrolyte; and a negative electrode solid electrode (150b) disposed in the negative electrode electrolyte receiving portion (111b) and impregnated with the negative electrode electrolyte.

[0081] The positive electrode current collector (130a) and the negative electrode current collector (130b) of the vanadium ion battery unit cell (100) can be manufactured by stacking metal current collectors (131a, 131b) and carbon current collectors (132a, 132b), respectively. The metal current collectors (131a, 131b) may be formed of a metal having high electrical conductivity (e.g., copper or aluminum) and may be connected to a busbar for electrically connecting each unit cell. The carbon current collectors (132a, 132b) may be formed of a material such as graphite, carbon, carbon plastic, etc. and may have high electrical conductivity and high acid resistance. The metal current collectors (131a, 131b) and carbon current collectors (132a, 132b) may be formed in a rectangular plate shape.

[0082] A vanadium ion battery unit cell (100) may include a frame (110) for providing a space for a positive electrolyte receiving portion (111a) and a negative electrolyte receiving portion (111b) while arranging a separator (120) between the positive electrode current collector (130a) and the negative electrode current collector (130b). The frame (110) may be attached to the carbon current collectors of the positive electrode current collector (130a) and the negative electrode current collector (130b) as a support, and due to this structure, a sealed structure may be formed, thereby ensuring the airtightness required for a vanadium ion battery.

[0083] In the present invention, the frame (110) may be a metal frame or a plastic frame, and according to one embodiment, may be a plastic frame. The plastic for forming the plastic frame may be a styrene-based plastic. Specific types of the plastic may be selected from polystyrene (PS), high impact polystyrene (HIPS), styrene acrylonitrile (AS), and acrylonitrile butadiene styrene (ABS), and preferably acrylonitrile butadiene styrene (ABS).

[0084] An electrolyte containing vanadium ions as the positive electrolyte and the negative electrolyte can be supplied to each of the positive electrolyte receiving portion (111a) and the negative electrolyte receiving portion (111b).

[0085] The positive solid electrode (150a) and the negative solid electrode (150b) may be respectively immersed in the positive electrolyte and the negative electrolyte and placed in the positive electrolyte receiving portion (111a) and the negative electrolyte receiving portion (111b). The positive solid electrode (150a) and the negative solid electrode (150b) may include carbon-based materials such as carbon or graphite felt, carbon cloth, carbon black, graphite powder, or graphene. The positive solid electrode (150a) may be in close contact with the positive current collector (130a) and the separator (120), and the negative solid electrode (150b) may be in close contact with the negative current collector (130b) and the separator (120).

[0086] According to one embodiment of the present invention, a vanadium ion battery unit cell (100) may include a transition portion (112) that connects the positive electrolyte receiving portion and the negative electrolyte receiving portion. The transition portion (112) may be formed on a frame (110).

[0087] The above transition portion (112) is intended to resolve the imbalance caused by the phenomenon of ionized substances (vanadium ions, ionized H2O, ions of acidic aqueous solution, etc.) crossing each other through the separator (120) during charging and discharging of the secondary battery.

[0088] More specifically, when charging and discharging are repeated, a phenomenon may occur in which the volume of the electrolyte contained in the positive electrolyte receiving portion (111a) and the negative electrolyte receiving portion (111b) changes. When charging a vanadium ion battery, water selectively moves from the positive electrolyte to the negative electrolyte through the separator due to the difference in osmotic pressure, thereby increasing the volume of the negative electrolyte. As water selectively moves from the positive electrolyte to the negative electrolyte through the separator until osmotic pressure equilibrium is achieved, the vanadium ion concentration of the negative electrode may decrease and the vanadium ion concentration of the positive electrode may increase.

[0089] In this way, as charging and discharging are repeated, an imbalance occurs in which the volumes of the negative and positive electrolytes change. Therefore, in the present invention, the electrolyte can move from a relatively larger electrolyte receiving portion to a smaller electrolyte receiving portion through the transition portion (112), thereby resolving the imbalance in the electrolyte volume.

[0090] The separator (120) of the vanadium ion battery unit cell (100) of the present invention may include a hydrocarbon-based separator including a cation-conducting hydrocarbon-based polymer. Nafion, which has been commonly used ®Since it is formed of a fluorine-based cation-conducting polymer, it has the disadvantage of being vulnerable to contamination of the secondary battery as it can leak halogen substances. In addition, since the vanadium ion battery (VIB) of the present invention has a sealed structure, it must have excellent mechanical strength to withstand the pressure generated while circulating on its own, have high stability to prevent irreversible and side reactions, and have excellent acid resistance even when immersed in an acidic electrolyte for a long time. Therefore, it is preferable to use a hydrocarbon-based separator.

[0091] The hydrocarbon-based separation membrane may be formed from the hydrocarbon-based polymer, or may be formed by coating the hydrocarbon-based polymer on a substrate. For example, the membrane may be coated by impregnating one or both sides of a porous substrate with a solution of the hydrocarbon-based polymer dissolved in a solvent, and then drying the solution.

[0092] The porous substrate may be selected to exhibit high tensile strength (e.g., 100 MPa or more) even with a thin thickness, and exhibit excellent hydrocarbon polymer impregnation properties and post-dry coating properties. For example, a porous membrane made of polypropylene (PP) or polyethylene (PE) may be selected, but is not necessarily limited thereto.

[0093] The above hydrocarbon polymer may include any one of a polyimide polymer, a polyetheretherketone polymer, a polyethersulfone polymer, and a polybenzimidazole polymer.

[0094] Referring to FIG. 3, the vanadium ion battery (1000) of the present invention can be manufactured by stacking a plurality of vanadium ion battery unit cells (100). The plurality of vanadium ion battery unit cells (100) can be electrically connected by a busbar (200). Some of the metal current collectors (131a, 131b) of the plurality of vanadium ion battery unit cells (100) can be electrically connected to the busbar (200) by a protrusion (100c).

[0095] A pair of endplates (300) are arranged at the top and bottom of a plurality of vanadium ion battery unit cells (100). The endplates (300) are made of a relatively strong insulating material or an insulated metal material.

[0096] The bus bar (200) transmits electricity generated in a plurality of unit cells (100) to the outside during discharge and transmits external electricity to the plurality of unit cells (100) during charging. The bus bar (200) can connect the plurality of unit cells (100) in parallel or series. The bus bar (200) can be arranged to cover one side of the plurality of unit cells (100) and one side of a pair of end plates (300).

[0097] Hereinafter, the present invention will be described in more detail by describing manufacturing examples and experimental examples. However, these are only examples of the present invention, and the present invention is not limited thereto.

[0098] Example 1

[0099] (1) Manufacturing of secondary battery unit cells

[0100] A unit cell of a secondary battery having a size of 99 mm × 99 mm was manufactured by stacking a first metal current collector - a first carbon current collector - a first solid electrode - a separator - a second solid electrode - a second carbon current collector - a second metal current collector in that order on a frame (ABS material, 15 mm) and then sealing it. The materials used in manufacturing the unit cell are as follows.

[0101] - First and second solid electrodes: carbon felt (thickness: 5 mm)

[0102] - First and second metal collectors: Aluminum collector (thickness: 0.2 mm)

[0103] - First and second carbon collectors: graphite sheet (thickness: 0.2 mm)

[0104] - Membrane: Polybenzimidazole-based membrane

[0105] The manufacturing method of the above separation membrane is as follows.

[0106] After adding m-PBI, a polybenzimidazole precursor, to dimethyl acetamide (DMAC), the solution was dissolved while stirring at 160°C and atmospheric pressure for 24 hours to produce a PBI solution with a maximum dissolution rate of 12 wt%. Then, a PE film (thickness: 20 μm) was impregnated into the PBI solution, and then dried with hot air at 50°C for 2 minutes to obtain a separator with a thickness of 27 μm.

[0107] (2) Pressure gauge leak test

[0108] By attaching a pressure gauge to the unit cell of the manufactured secondary battery and observing the internal pressure change, the presence of pressure was confirmed and a leak test was conducted. The leak test of the pressure gauge was performed through the following procedure. First, the pressure gauge was connected to the ball valve, and the total internal volume of the pressure gauge and the ball valve was designed to be 0.5 ml. Then, the pressure change was measured for 100 to 130 hours while maintaining the pressure at 40 kPa in a 30℃ environment. If the pressure change amount during this process is less than 0.02 kPa / h, it is determined that the leak test has been passed, and the pressure change of the unit cell was monitored in this manner.

[0109] (3) Electrolyte preparation process (carbon dioxide injection)

[0110] Vanadium electrolyte (1.7 M V 3.5+, 1.7 M sulfuric acid aqueous solution) was prepared, and CO₂ was injected into the electrolyte by bubbling using CO₂ compressed gas (purchased from Gascam Technology) stored in a steel gas container (bomb). At this time, the difference in the partial pressure of CO₂ gas before and after the injection of the CO₂ compressed gas was adjusted to 12 kPa. After that, 138 g (±2 g) of the prepared electrolyte was prepared by placing it in an appropriate container.

[0111] (4) Electrolyte injection process

[0112] After fixing the secondary battery unit cell manufactured according to the above (1) using a jig, a tube of a vacuum pump was connected to the secondary battery unit cell to create a vacuum state of -100 kPa inside the secondary battery unit cell. In order to inject the electrolyte manufactured according to the above (3) into the secondary battery unit cell, the electrolyte container was connected to the tube so that the electrolyte was injected into the secondary battery unit cell due to the vacuum state.

[0113] (5) Attaching a pressure gauge

[0114] A pressure gauge is attached to the electrolyte inlet to measure pressure. The pressure gauge used in the present invention is manufactured by Sensys, has a measurement pressure range of -100 kPa to 100 kPa, and an accuracy (display) of ±0.5% FS (full scale) (@25 ℃).

[0115] (6) Charge / discharge conditions

[0116] 1) Charge at a constant current of 1.6 A (1 C) at 25 ℃ until the target voltage of 1.75 V is reached.

[0117] 2) Check the available voltage range by discharging at a constant current until it reaches 1.1 V with a current of 1.6 A (1 C), which is the same as charging.

[0118] 3) Charge and discharge 1 to 100 cycles under the above conditions.

[0119] (7) Pressure generation evaluation

[0120] The pressure generation standard is based on the pressure during discharge of a secondary battery. If the pressure does not increase after 100 charge / discharge cycles compared to 1 cycle or is 0 kPa or lower, it is judged as "no pressure generated (indicated by 'X')".

[0121] (8) Measurement of charging energy

[0122] The charging energy per unit volume (Wh / L) was measured by multiplying the charging voltage measured at each measurement time (sampling time) by the charging current (1.0 C) while charging and discharging up to 100 times (cycles) under the charging and discharging conditions of the above (6).

[0123] (9) Measurement of voltage efficiency (VE)

[0124] The voltage efficiency value was measured according to the following equation (1).

[0125] - Equation (1): (Median value of discharge voltage) / (Median value of charge voltage) × 100 (%)

[0126] Comparative Examples 1 to 3

[0127] Except for not supplying CO2 compressed gas in (3) of the above Example 1, the same experiment was conducted and performed, but under the condition of (6), the target voltage during charging was increased as shown in Table 1 below, and the available voltage range during charging and discharging was measured.

[0128] In Table 1 below, ΔP of 0 (kPa) means that CO2 compressed gas was not supplied.

[0129] The results of Example 1 and Comparative Examples 1 to 3 are shown in Table 1 below, and a graph of the pressure measurement results for determining whether pressure was generated is shown in Fig. 4.

[0130] CO2 supply amount ΔP (kPa) VE (%) Voltage range (V) Charging energy (Wh / L) Pressure generation Example 11292.4 1.1~1.75 29.8X Comparative example 1092.5 1.1~1.75 29.3O Comparative example 2092.3 1.1~1.65 24.2O Comparative example 3092.6 1.1~1.60 20.6X

[0131] Referring to Table 1 and FIG. 4, it was found that when the electrolyte was treated by supplying carbon dioxide as in Example 1, no pressure was generated due to hydrogen gas generation even when charging up to a very high voltage of 1.75 V. In this way, it was confirmed that when the available voltage range is increased, the storable energy capacity per volume of electrolyte can increase, and further, there is an advantage of being able to eliminate hydrogen gas generation and the risk of explosion caused by it. On the other hand, when the electrolyte was used without supplying carbon dioxide as in Comparative Examples 1 to 3, it was confirmed that the pressure generation phenomenon due to hydrogen gas generation could be suppressed only when the available voltage was lowered to about 1.60 V. That is, when the charging voltage was increased to 1.75 V or 1.65 V as in Comparative Examples 1 and 2, the effect of suppressing pressure generation due to hydrogen gas generation could not be achieved.

[0132] Examples A to C and Comparative Examples A to C

[0133] In the conditions of (6) of the above Example 1, the maximum voltage during charging was changed to 1.65 V, and CO2 compressed gas was supplied in (3) above, but the gas partial pressure of the CO2 compressed gas was changed as shown in Table 2 below, and examples A to C and comparative examples A to C were each performed and tested in the same manner as in Example 1.

[0134] In Table 2 below, ΔP of 0 (kPa) means that CO2 compressed gas was not supplied.

[0135] The results of Examples A to C and Comparative Examples A to C are shown in Table 2 below, and the graph of the pressure measurement results for determining whether pressure was generated is shown in Fig. 5.

[0136] CO2 supply amount ΔP (kPa) VE (%) Voltage range (V) Charging energy (Wh / L) Pressure generation Comparative example A0 92.4 1.1~1.65 25.0 O Comparative example B5 92.6 1.1~1.65 25.0 O Comparative example C7 92.5 1.1~1.65 24.9 O Example A 9 92.3 1.1~1.65 25.2 X Example B 12 92.6 1.1~1.65 25.1 X Example C 24 92.3 1.1~1.65 25.4 X

[0137] Referring to Table 2 and Fig. 5 above, it can be confirmed that in a situation where the charging voltage range is the same at 1.1 to 1.65 V, the effect of suppressing pressure generation due to hydrogen gas generation can be achieved only when the gas partial pressure of the carbon dioxide injected during carbon dioxide treatment exceeds 7 kPa. In addition, since the voltage ranges during charging and discharging are the same for Examples A to C and Comparative Examples A to C, the values ​​of the charging energy are also almost the same or slightly increased for the Examples.

[0138] Although the embodiments of the present specification have been described in more detail with reference to the attached drawings, the present specification is not necessarily limited to these embodiments, and various modifications may be implemented without departing from the technical spirit of the present specification. Therefore, the embodiments disclosed in this specification are not intended to limit the technical spirit of the present specification, but to explain, and the scope of the technical spirit of the present specification is not limited by these embodiments. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. The scope of protection of this specification should be interpreted by the claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of rights of this specification.

Claims

1. A step of preparing an electrolyte containing vanadium ions and an acidic solution; and A step of supplying carbon dioxide to the electrolyte; The absolute value of the difference in partial pressure of dissolved gas (carbon dioxide) in the electrolyte before and after supplying carbon dioxide, ΔP, is greater than 7 kPa. Method for producing vanadium electrolyte.

2. In paragraph 1, The above ΔP is 8 kPa to 30 kPa, Method for producing vanadium electrolyte.

3. In paragraph 1, The step of supplying the carbon dioxide is performed by bubbling and injecting carbon dioxide gas into the electrolyte. Method for producing vanadium electrolyte.

4. In paragraph 1, The step of supplying the carbon dioxide is performed by adding a compound that provides carbonate to the electrolyte, The compound providing the above carbonate comprises at least one of sodium carbonate, sodium bicarbonate, ammonium carbonate and ammonium bicarbonate. Method for producing vanadium electrolyte.

5. In paragraph 1, The step of supplying the carbon dioxide is performed by adding a reducing agent that generates carbon dioxide gas to the electrolyte, The reducing agent comprises at least one of oxalic acid, ascorbic acid, methanol, ethanol, formaldehyde, and formic acid. Method for producing vanadium electrolyte.

6. In paragraph 1, The step of supplying the above carbon dioxide is performed by mixing dry ice into the electrolyte. Method for producing vanadium electrolyte.

7. In paragraph 1, The above vanadium ions are supplied by vanadium oxides including at least one of V2O5, VOSO4, V2O3, NH4VO3 and V2O4. Method for producing vanadium electrolyte.

8. In paragraph 1, The above acid solution contains at least one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Method for producing vanadium electrolyte.

9. A vanadium electrolyte manufactured according to the method for manufacturing a vanadium electrolyte according to any one of claims 1 to 8.

10. As a vanadium ion battery, The above vanadium ion battery comprises at least one vanadium ion battery unit cell, The above vanadium ion battery unit cell is, positive current collector; A negative electrode current collector disposed spaced apart from the positive electrode current collector; A separator disposed between the positive electrode current collector and the negative electrode current collector; A cathode electrolyte receiving portion formed between the cathode current collector and the separator; A negative electrode electrolyte receiving portion formed between the negative electrode current collector and the separator; A positive electrode solid electrode disposed in the positive electrode electrolyte receiving portion and impregnated with the positive electrode electrolyte; and A cathode solid electrode disposed in the cathode electrolyte receiving portion and impregnated with the cathode electrolyte; An electrolyte containing vanadium ions is supplied as an anode electrolyte and a cathode electrolyte to each of the anode electrolyte receiving portion and the cathode electrolyte receiving portion, The electrolyte containing the vanadium ion is a vanadium electrolyte prepared according to any one of claims 1 to 7. Vanadium ion battery.

11. In paragraph 10, The available voltage range is 1.1 to 1.75 V. Vanadium ion battery.

12. In paragraph 10, The above vanadium ion battery unit cell further includes a transition portion that connects the positive electrolyte receiving portion and the negative electrolyte receiving portion. Vanadium ion battery.

13. In paragraph 10, The above positive electrode current collector includes a positive electrode metal current collector and a positive electrode carbon current collector, The above positive electrode current collector includes a negative electrode metal current collector and a negative electrode carbon current collector. Vanadium ion battery.

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