Electrolyte containing vanadium ions, and redox secondary battery comprising same

Abstract

The present invention relates to an electrolyte containing vanadium ions, and a secondary battery comprising same, and, more specifically, to an electrolyte containing vanadium ions, the electrolyte having concentrations of vanadium ions and an acidic solution that are adjusted to be different in a cathode electrolyte and an anode electrolyte, which are used in a secondary battery using an electrolyte containing vanadium ions, so as to lower the self-discharge rate of a secondary battery, thereby enabling performance to be enhanced.

Description

Electrolyte containing vanadium ions and oxidation-reduction secondary battery containing the same

[0001] The present invention relates to an electrolyte containing vanadium ions and a redox secondary battery containing the same, and more particularly, to an electrolyte containing vanadium ions capable of improving performance by lowering the self-discharge rate of a secondary battery by differently controlling the concentrations of vanadium ions and acidic solutions of a positive electrode electrolyte and a negative electrode electrolyte used in a secondary battery using an electrolyte containing vanadium ions.

[0002] Unlike conventional secondary batteries, redox secondary batteries are electrochemical storage devices that store electrical energy as chemical energy of the electrolyte by charging and discharging it through oxidation and reduction of the active material in the electrolyte.

[0003] Meanwhile, the electrolyte of a redox secondary battery uses a substance having a redox couple. In the past, the electrolyte of a redox secondary battery was used by applying redox couples of different substances as a positive electrolyte and a negative electrolyte. However, there may be a problem in that the capacity of the battery is reduced due to a phenomenon in which ionized substances cross each other through a separator during charging and discharging.

[0004] Accordingly, the simultaneous use of vanadium as both a positive electrolyte and a negative electrolyte was proposed as a method for alleviating the ion crossover phenomenon, and since the electrolyte containing vanadium ions 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 ion electrolyte using vanadium ions as an 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 electrochemical reactions of charge and discharge, which is advantageous in terms of cost.

[0006] The electrolyte containing vanadium ions 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, and 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. The charge and discharge reaction occurs as the oxidation state of the vanadium active material changes, and in order for an accurate electrochemical reversible reaction to occur, it is required to manufacture the positive and negative electrolytes by matching the oxidation states of the vanadium ions.

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

[0010] Meanwhile, when charging a redox secondary battery, the divalent vanadium ions present in the negative electrolyte strongly attract H2O, causing water to selectively move from the positive electrolyte to the negative electrolyte through the separator, lowering the vanadium ion concentration in the negative electrode and increasing the vanadium ion concentration in the positive electrolyte. As a result, along with the movement of water, cations (protons) also move, causing problems such as self-discharge of the secondary battery and resulting energy loss.

[0011] Self-discharge is a phenomenon in which the energy stored in a battery is discharged over time, causing energy loss and lowering the performance of secondary batteries. Therefore, it is necessary to develop a technological solution that can suppress the self-discharge phenomenon.

[0012] The purpose of the present invention is to provide a positive electrode electrolyte and a negative electrode electrolyte in which the concentrations of vanadium ions and an acidic solution are controlled differently so as to suppress a self-discharge phenomenon that occurs when cations and water move from a positive electrode electrolyte to a negative electrode electrolyte through a separator during charging of a secondary battery, and a secondary battery including the same.

[0013] The object of the present invention is not limited to the above-mentioned purpose, and other objects not mentioned will be clearly understood by those skilled in the art from the description below.

[0014] In order to achieve the above object, according to one aspect of the present invention, there is provided a unit cell for a secondary battery, comprising: a positive electrode current collector; a negative electrode current collector; a separator disposed between the positive electrode current collector and the negative electrode current collector; a positive electrode electrolyte receiving portion formed between the positive electrode current collector and the separator; and a negative electrode electrolyte receiving portion formed between the negative electrode current collector and the separator, wherein a positive electrode electrolyte containing vanadium ions as an active material is supplied to the positive electrode electrolyte receiving portion, and a negative electrode electrolyte containing vanadium ions as an active material is supplied to the negative electrode electrolyte receiving portion, wherein the concentration of vanadium ions in the positive electrode electrolyte is higher by A % than a reference vanadium ion concentration, and the concentration of vanadium ions in the negative electrode electrolyte is lower by A % than a reference vanadium ion concentration, wherein A is a concentration deviation ratio with respect to a reference vanadium ion concentration and is 3 to 20, and the reference vanadium ion concentration is 1.5 M to 3.0 M.

[0015] The above positive electrode electrolyte and negative electrode electrolyte each contain an acidic solution.

[0016] The concentration of the acidic solution of the positive electrolyte is higher by B % than the concentration of the reference acidic solution, the concentration of the acidic solution of the negative electrolyte is lower by B % than the concentration of the reference acidic solution, and B is a concentration deviation ratio for the concentration of the reference acidic solution, which is 3 to 20, and the ion concentration of the reference acidic solution is 1.0 M to 10.0 M.

[0017] The above vanadium ions are supplied by vanadium oxide.

[0018] The above vanadium oxide may include one or more of V2O5, VOSO4, V2O3, NH4VO3, and V2O4.

[0019] The above acidic solution may contain one or more of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid.

[0020] The above-mentioned separator may include an ion-conducting polymer. The ion-conducting polymer may include at least one of a fluorine-based polymer and a hydrocarbon-based polymer.

[0021] The above hydrocarbon polymer may include at least one of a polyimide polymer, a polyetheretherketone polymer, a polyethersulfone polymer, and a polybenzimidazole polymer.

[0022] The above ion conductive polymer may be a hydrocarbon polymer or a fluorine polymer containing a sulfonic acid group.

[0023] The hydrocarbon polymer or fluorine polymer containing the above sulfonic acid group may include at least one of a perfluorosulfonic acid (PFSA) polymer, poly(styrene sulfonic acid) (PSSA), sulfonated poly(ether ether ketones) (SPEEK), sulfonated poly(ether sulfone) (SPES), sulfonated poly(aryl ether ketone) (SPAEK), sulfonated polybenzimidazole (SPBI), sulfonated poly(phenylen oxide) (SPPO), and sulfonated polyimide (SPI).

[0024] The volume of the cathode electrolyte receiving portion may be larger than the volume of the anode electrolyte receiving portion.

[0025] According to another aspect of the present invention, a secondary battery including a plurality of unit cells for a secondary battery according to an aspect of the present invention can be provided.

[0026] The electrolyte solution containing vanadium ions of the present invention can improve the self-discharge phenomenon and energy loss phenomenon caused by the movement of cations from the positive electrode to the negative electrode during charging of a secondary battery by differently controlling the concentration of vanadium ions and the concentration of an acidic solution in the positive electrode electrolyte supplied to the positive electrode and the negative electrode electrolyte supplied to the negative electrode, respectively.

[0027] 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 entire description of this specification.

[0028] FIG. 1 is an exploded perspective view of a vanadium ion battery unit cell according to one embodiment of the present invention.

[0029] FIG. 2 is a perspective view of a vanadium ion battery unit cell according to one embodiment of the present invention.

[0030] Figure 3 is a 3-3 cross-sectional view of the vanadium ion battery unit cell illustrated in Figure 2.

[0031] FIG. 4 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Throughout this specification, unless otherwise specifically stated, each component may be singular or plural.

[0036] In interpreting the components in this specification, even if there is no separate explicit description, it is interpreted to include the range of error.

[0037] 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.

[0038] 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.

[0039] In this specification, when a component is used as "includes," "has (has)," "consists of," "arranges," "provides," or "forms," ​​other parts may be added, unless "only" is used. When a component is expressed in the singular, it includes the plural unless otherwise explicitly stated.

[0040] 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.

[0041] Unless otherwise specified in this specification, any reference to a unit is interpreted to mean “weight.”

[0042] In this specification, unless otherwise specifically stated, “electrolyte containing vanadium ions” is interpreted to refer to the same thing as “vanadium ion electrolyte,” “electrolyte using (utilizing) vanadium ions,” “electrolyte containing vanadium oxide,” “vanadium electrolyte,” “electrolyte containing vanadium active material,” etc.

[0043] In this specification, “anode electrolyte” or “anolyte” means an electrolyte supplied to an anode, and the anode is driven by the supply of the anode electrolyte, and “cathode electrolyte” or “catholyte” means an electrolyte supplied to a cathode.

[0044]

[0045] The present invention will be described in detail below.

[0046] As the overall size of a redox flow battery using vanadium electrolyte has become very large due to the electrolyte storage tank and fluid pump for electrolyte flow of the existing redox flow battery (RFB), there have been limitations due to space constraints and design difficulty.

[0047] Accordingly, in the present invention, a Vanadium Ion Battery (VIB), which is a sealed oxidation-reduction secondary battery, was used, excluding an electrolyte tank and a fluid pump. Specifically, a unit cell including a positive electrode collector so that the internal portion of the battery can circulate without a pump; an anode collector arranged spaced apart from the positive electrode collector; and a separator arranged between the positive electrode collector and the negative electrode collector; was designed by stacking one or more of them, and as a result, compared to a conventional oxidation-reduction secondary battery, the power density can be improved by up to 2-50 times, and the stability of energy output can be increased.

[0048] A vanadium ion battery according to one embodiment of the present invention may include one or two or more vanadium ion battery unit cells, for example, three or more, and, for example, after being stacked in this manner, the stacked unit cells may be additionally electrically connected in parallel.

[0049] A vanadium ion battery unit cell is described in detail with reference to FIGS. 1 to 3.

[0050] 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); and a negative electrode electrolyte receiving portion (111b) formed between the negative electrode current collector (130b) and the separator (120).

[0051] 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.

[0052] A vanadium ion battery unit cell (100) may include a support (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 support (110) may be attached to the carbon current collectors of the positive electrode current collector (130a) and the negative electrode current collector (130b), and due to this structure, a sealed structure may be formed, thereby ensuring the airtightness required for a vanadium ion battery.

[0053] An electrolyte containing vanadium ions may be supplied as a positive electrolyte and a negative electrolyte to each of the positive electrolyte receiving portion (111a) and the negative electrolyte receiving portion (111b). The supplied electrolyte is an electrolyte containing vanadium ions according to one embodiment of the present invention described above, and may include vanadium ions having an oxidation number exceeding 3.50 and less than 4.00 and an acidic solution, and according to one embodiment, may include vanadium ions having an oxidation number exceeding 3.50 and less than 3.80.

[0054] 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 support (110).

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Meanwhile, when discharging a redox secondary battery using an electrolyte containing vanadium ions, water, vanadium ions, and anions contained in the acidic solution of the electrolyte (for example, HSO4 in the case of sulfuric acid) pass through the transition portion (112). - ) can move from the cathode electrolyte to the anode electrolyte, which may further aggravate the phenomenon of the vanadium concentration in the cathode electrolyte decreasing and the vanadium concentration in the anode electrolyte increasing.

[0059] In this way, in the vanadium ion battery (VIB) of the present invention, the phenomenon of vanadium concentration imbalance between the positive and negative electrolytes that occurs during charging and discharging can be resolved by applying an electrolyte containing vanadium ions according to one embodiment of the present invention.

[0060] Furthermore, as the charging and discharging of the vanadium ion battery is repeated, the charging energy is improved compared to when the conventional 3.50 valence vanadium ion electrolyte is used, which can result in increasing the efficiency and lifespan of the vanadium ion battery and reducing the volume of the vanadium ion battery.

[0061] Meanwhile, according to one embodiment of the present invention, the vanadium ion battery unit cell (100) may further include a positive electrode solid electrode (150a) disposed in the positive electrolyte receiving portion (111a) and impregnated with the positive electrolyte; and a negative electrode solid electrode (150b) disposed in the negative electrolyte receiving portion (111b) and impregnated with the negative electrolyte.

[0062] 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).

[0063]

[0064] Referring to FIG. 4, 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).

[0065] 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.

[0066] 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 a 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).

[0067] Meanwhile, the core of battery control is to improve battery performance by correcting various factors based on battery condition prediction. Generally, battery condition prediction refers to estimating the battery's current state of charge (SOC), state of life (SOL), and state of health (SOH) based on factors such as current battery voltage, temperature, and existing usage environment.

[0068] Vanadium-ion battery unit cells are often connected in multiples to form a vanadium-ion battery, increasing battery capacity rather than being used singly. In this case, the overall performance of the vanadium-ion battery is limited by the lowest-performing unit cell within the battery. Therefore, predictions for each vanadium-ion battery unit cell are crucial.

[0069] The self-discharge rate of a battery's unit cell is a critical factor in predicting its condition, and must be accurately predicted. A smaller absolute value of the self-discharge rate reduces the impact of deviations in the self-discharge rate prediction on battery condition. Consequently, this leads to more accurate predictions of the unit cell's condition, making it a crucial element in controlling the entire battery.

[0070] A high self-discharge rate means that the stored energy gradually disappears, which increases the rest time after charging and ultimately reduces the efficiency of the battery, which can cause major problems in the efficiency and capacity of large-capacity batteries (ESS).

[0071] Accordingly, the inventors of the present invention experimentally confirmed that the self-discharge rate of a secondary battery can be reduced by controlling the concentration of the positive and negative electrolytes containing vanadium ions in the positive and negative electrolytes, as a result of prior research, thereby completing the present invention.

[0072] According to one embodiment of the present invention, a secondary battery unit cell having a structure including: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; a positive electrode electrolyte receiving portion formed between the positive electrode and the separator; and a negative electrode electrolyte receiving portion formed between the negative electrode and the separator; wherein a positive electrode electrolyte containing vanadium ions as an active material is supplied to the positive electrode electrolyte receiving portion, and a negative electrode electrolyte containing vanadium ions as an active material is supplied to the negative electrode electrolyte receiving portion.

[0073] At this time, the concentration of vanadium ions in the positive electrolyte is characterized by being higher than the concentration of vanadium ions in the negative electrolyte. Specifically, the concentration of vanadium ions in the positive electrolyte can be adjusted to be A % higher than the reference vanadium ion concentration, and the concentration of vanadium ions in the negative electrolyte can be adjusted to be A % lower than the reference vanadium ion concentration. The A is a concentration deviation ratio with respect to the reference vanadium ion concentration, and may be, for example, 3 to 20, for example, 6 to 15, for example, 6 to 12. In addition, the reference vanadium ion concentration may be 1.5 M to 3.0 M, and for example, 1.7 M to 2.5 M. For example, when the standard vanadium ion concentration is 1.7 M and the concentration deviation ratio A is selected as 6, the concentration of the positive electrolyte is 1.802 M, which is 6% higher than 1.7 M, and when processed to significant figures, it is 1.80 M. In addition, the concentration of the negative electrolyte is 1.598 M, which is 6% lower than 1.7 M, and when processed to significant figures, it is 1.60 M, which is the same as that tested in Example 2 of the present invention.

[0074] The positive and negative electrolytes of the present invention each contain vanadium ions and an acidic solution. The vanadium ions may be supplied by vanadium oxide, and may include, for example, one or more selected from the group consisting of V2O5, VOSO4, V2O3, NH4VO3, and V2O4, but are not necessarily limited thereto, and may be selected according to electrolyte production conditions, production target volume, etc.

[0075] The acidic solution included in the vanadium electrolyte may include at least one selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and may be, for example, a sulfuric acid solution. As described above, the present invention controls the vanadium ion concentration of the positive electrolyte and the vanadium ion concentration of the negative electrolyte, and accordingly, the concentrations of the acidic solutions of the positive electrolyte and the negative electrolyte are also controlled differently.

[0076] Specifically, the concentration of the acidic solution of the positive electrolyte may be adjusted to be B % higher than the concentration of the reference acidic solution, and the concentration of the acidic solution of the negative electrolyte may be B % lower than the concentration of the reference acidic solution. The B is a concentration deviation ratio with respect to the concentration of the reference acidic solution, and may be, for example, 3 to 20, for example, 6 to 15, for example, 6 to 12. In addition, the concentration of the reference acidic solution may be 1.0 M to 10.0 M, and for example, 3.0 M to 5.0 M. According to one embodiment of the present invention, the deviation ratio B with respect to the concentration of the acidic solution may be the same as or different from the deviation ratio A with respect to the concentration of the vanadium ion, but is preferably the same.

[0077] The separator (120) of the present invention separates the positive current collector (130a) and the positive current collector (130b) while spatially dividing the negative electrolyte and positive electrolyte receiving portions (111a, 111b) and allows protons to move between the negative electrolyte and positive electrolyte. During discharge, protons pass through the separator and move from the negative electrolyte to the positive electrolyte, and during charge, they pass through the separator and move from the positive electrolyte to the negative electrolyte.

[0078] The separator may include an ion-conducting polymer, and more specifically, may be manufactured by being formed of an ion-conducting polymer or coated with a material including an ion-conducting polymer.

[0079] According to one embodiment of the present invention, the ion-conducting polymer may include at least one of a fluorine-based polymer or a hydrocarbon-based polymer, and the fluorine-based polymer or the hydrocarbon-based polymer may include an ion-conducting functional group including at least one selected from a sulfonic acid group, a carboxyl group, and a phosphoric acid group.

[0080] For example, the hydrocarbon polymer may include at least one of a polyimide polymer, a polyetheretherketone polymer, a polyethersulfone polymer, and a polybenzimidazole polymer.

[0081] For example, the ion conductive polymer containing a sulfonic acid group may include, but is not limited to, one or more of a perfluorosulfonic acid (PFSA) polymer, poly(styrene sulfonic acid) (PSSA), sulfonated poly(ether ether ketones) (SPEEK), sulfonated poly(ether sulfone) (SPES), sulfonated poly(aryl ether ketone) (SPAEK), sulfonated polybenzimidazole (SPBI), sulfonated poly(phenylen oxide) (SPPO), and sulfonated polyimide (SPI).

[0082] In addition, examples of the perfluorosulfonic acid polymer membrane may include Nafion (Dupont), Flemion (Ashahi Kasei), Fumasep (Fumatech), Ballard advanced (Ballard), Gore-Select (Gore), Aciplex (Asahi Glass), Aquivion (Solvay). According to one embodiment of the present invention, the volume of the negative electrode electrolyte receiving portion may be designed to be larger than the volume of the positive electrode electrolyte receiving portion. This is to minimize the imbalance due to the difference in the mole number of vanadium ions by making the total mole number of vanadium ions included in the positive electrode electrolyte and the negative electrode electrolyte the same, since the vanadium ion concentration of the positive electrode electrolyte is higher as described above, and the vanadium ion concentration of the negative electrode electrolyte is relatively lower. As the volume of the electrolyte receiving portion is varied in this way, the volume of the electrolyte received in the electrolyte receiving portion also varies.

[0083] For example, the volume of the cathode electrolyte receptacle can be designed to be, for example, 5 to 20% larger than the volume of the anode electrolyte receptacle, or, for example, 5 to 10% larger. The method for implementing such a design is not limited. For example, the position of the separator can be adjusted so that the volume of the cathode electrolyte receptacle is larger than that of the anode electrolyte receptacle. As another example, the cross-sectional area and thickness of the electrolyte receptacle can be adjusted to design a different volume.

[0084] According to one aspect of the present invention, the unit cell as described above may be used as one, but by designing by stacking a plurality of unit cells (two or more), the power density can be improved by up to 2-50 times compared to a conventional oxidation-reduction secondary battery, and the stability of energy output can be increased.

[0085] 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.

[0086] Preparation of positive and negative electrolytes of comparative example 1

[0087] Oxidation number is 3.50 (V 3.50+ ) was prepared, and the concentration of vanadium ions and sulfuric acid solution was 1.7 M, and the concentration of sulfuric acid ions was 4.2 M. These were used as the positive and negative electrolytes of Comparative Example 1, respectively.

[0088] Preparation of positive and negative electrolytes of Examples 1 to 7 and Comparative Example 2

[0089] As shown in Table 1 below, the reference electrolyte was heated to volatilize water so that the concentration of vanadium ions and the concentration of sulfate ions were 3%, 6%, 8%, 10%, 12%, 15%, 20%, and 25% higher than the reference electrolyte of Comparative Example 1, thereby preparing the positive electrode electrolytes of Examples 1 to 7 and Comparative Example 2, respectively.

[0090] In addition, water was added to the reference electrolyte so that the concentration of vanadium ions and the concentration of sulfate ions were 3%, 6%, 8%, 10%, 12%, 15%, 20%, and 25% lower than the reference electrolyte of Comparative Example 1, thereby preparing the negative electrolytes of Examples 1 to 7 and Comparative Example 2, respectively.

[0091] Preparation of positive and negative electrolytes of comparative example 3

[0092] As shown in Table 2 below, the oxidation number is 3.50 (V 3.50+) was prepared, and the concentration of vanadium ions and sulfuric acid solution was 2.5 M, and the concentration of sulfuric acid ions was 4.5 M. These were used as the positive and negative electrolytes of Comparative Example 3, respectively.

[0093] Preparation of positive and negative electrolytes of Examples 8 to 11 and Comparative Example 4

[0094] As shown in Table 2 below, the reference electrolyte was heated to volatilize water so that the concentration of vanadium ions and the concentration of sulfate ions were 5%, 10%, 15%, 20%, and 25% higher than the reference electrolyte of Comparative Example 3, thereby preparing the positive electrode electrolytes of Examples 8 to 11 and Comparative Example 4, respectively.

[0095] In addition, the cathode electrolytes of Examples 8 to 11 and Comparative Example 4 were prepared by adding water to the reference electrolyte so that the concentration of vanadium ions and the concentration of sulfate ions were 5%, 10%, 15%, 20%, and 25% lower than the reference electrolyte of Comparative Example 1, respectively.

[0096] Experimental example

[0097] Two current collectors were manufactured by stacking a carbon current collector (graphite composite, thickness: 0.2 mm) and a metal current collector (aluminum foil, thickness: 0.2 mm), and were used as a positive current collector and a negative current collector, respectively.

[0098] A cation exchange membrane (thickness: 20 μm, Standard Energy Co.) was manufactured by coating polyethylene (PE) as a substrate with a solution of m-PBI (poly[2,2-(m-phenylene)-5,5bibenzimidazole) dissolved in DMAC (dimethylacetamide) solvent, and this was used as a separation membrane (hereinafter referred to as 'PBI separation membrane').

[0099] After preparing a hollow square support, a positive electrode current collector and a negative electrode current collector were placed on both sides of the support, and the PBI separator was placed in the center of the support to form a positive electrode electrolyte receiving portion and a negative electrode electrolyte receiving portion while separating the positive electrode current collector and the negative electrode current collector. A transition portion connecting the positive electrode electrolyte receiving portion and the negative electrode electrolyte receiving portion was formed on the support, thereby manufacturing a vanadium ion battery unit cell.

[0100] For the vanadium ion battery unit cell manufactured as described above, the charge / discharge operation conditions were as follows: constant current charging was performed with a current of 1.0 C until the voltage reached 1.50 V, and constant current discharge was performed with the same current of 1.0 C during discharge until the voltage reached 1.10 V. The above charging and discharging conditions were repeated 3 times (cycles). In the 4th cycle, after constant current charging with a current of 1.0 C until 1.50 V, the cell was rested for a certain period of time, and the change in voltage per hour was measured to determine the self-discharge rate (mV / h). The 'certain period of time' refers to the time until the voltage decreases immediately after the 4th charge is completed, shows a slope (discharge rate = voltage / time), and the slope converges to 0. This is because immediately after charging is complete, there is unevenness in the distribution of ions within the battery cell, and as they reach equilibrium, the accurate self-discharge rate cannot be measured due to movement of ions, so the self-discharge rate can be accurately measured only after equilibrium is reached.

[0101] The self-discharge rate was measured in the same manner for Examples 1 to 11 and Comparative Examples 2 to 4, and is shown in Tables 1 and 2 below.

[0102] Concentration deviationAnolyte vanadium ion concentrationCatholyte vanadium ion concentrationAnolyte sulfate ion concentrationCatholyte sulfate ion concentrationSelf-discharge rate (mV / h)Comparative example 1-1.7 M1.7 M4.2 M4.2 M0.35Example 13 %1.75 M1.65 M4.32 M4.08 M0.16Example 26 %1.80 M1.60 M4.46 M3.95 M0.1Example 38 %1.83 M1.57 M4.53 M3.87 M0.05Example 410 %1.88 M1.53 M4.62 M3.78 M0.08Example 512 %1.91 M1.50 M4.71 M3.73 M0.1Example 615 %1.95 M1.45 M4.83 M3.57 M0.17 Example 720 %2.04 M1.36 M5.04 M3.36 M0.32 Comparative Example 225 %2.12 M1.27 M5.25 M3.15 M0.41

[0103] Concentration deviationAnolyte vanadium ion concentrationCatholyte vanadium ion concentrationAnolyte sulfate ion concentrationCatholyte sulfate ion concentrationSelf-discharge rate (mV / h)Comparative example 3-2.5 M2.5 M4.5 M4.5 M0.24Example 85 %2.62 M2.38 M4.72 M4.28 M0.19Example 910 %2.75 M2.25 M4.95 M4.05 M0.12Example 1015 %2.89 M2.11 M5.09 M4.03 M0.05Example 1120 %3.0 M2.0 M5.40 M3.60 M0.15Comparative example 425 %3.12 M1.88 M5.62 M3.38 M0.31

[0104] Referring to Tables 1 and 2 above, it can be confirmed that, compared to Comparative Examples 1 and 3 in which the vanadium ion concentration and sulfate ion concentration of the positive electrolyte and the vanadium ion concentration and sulfate ion concentration of the negative electrolyte are all the same, the self-discharge rate is reduced as the vanadium ion concentration of the positive electrolyte is set higher than the vanadium ion concentration of the negative electrolyte and the deviation in concentration increases.

[0105] Meanwhile, as the difference in the concentration of vanadium ions in the positive electrolyte and the concentration of vanadium ions in the negative electrolyte increased, the effect of reducing the self-discharge rate decreased, and as can be seen from Comparative Examples 2 and 4, it was confirmed that the self-discharge rate actually increased when the concentration difference increased to 25%.

[0106]

[0107] 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. Bipolar collector; Negative current collector; A separator disposed between the positive electrode collector and the negative electrode collector; A cathode electrolyte receiving portion formed between the cathode current collector and the separator; and Including a negative electrode electrolyte receiving portion formed between the negative electrode current collector and the separator; A positive electrolyte containing vanadium ions as an active material is supplied to the positive electrolyte receiving portion, and a negative electrolyte containing vanadium ions as an active material is supplied to the negative electrolyte receiving portion. The concentration of vanadium ions in the positive electrolyte is A % higher than the reference vanadium ion concentration, and the concentration of vanadium ions in the negative electrolyte is A % lower than the reference vanadium ion concentration. The above A is a concentration deviation ratio with respect to the standard vanadium ion concentration, and is 3 to 20, The above standard vanadium ion concentration is 1.5 M to 3.0 M. Unit cell for secondary batteries.

2. In paragraph 1, The above positive and negative electrolytes each contain an acidic solution. Unit cell for secondary batteries.

3. In paragraph 2, The concentration of the acidic solution of the positive electrolyte is B % higher than the concentration of the reference acidic solution, and the concentration of the acidic solution of the negative electrolyte is B % lower than the concentration of the reference acidic solution. The above B is a concentration deviation ratio for the standard acid solution concentration, and is 3 to 20, The ion concentration of the above standard acid solution is 1.0 M to 10.0 M. Unit cell for secondary batteries.

4. In paragraph 1, The above vanadium ions are supplied by vanadium oxide. Unit cell for secondary batteries.

5. In paragraph 4, The above vanadium oxide is V 2 O 5 , VOSO 4 , V 2 O 3 , NH 4 VO 3 and V 2 O 4 Containing one or more of the following: Unit cell for secondary batteries.

6. In paragraph 2, The above acidic solution contains at least one of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid. Unit cell for secondary batteries.

7. In paragraph 1, The above separator comprises an ion-conducting polymer. Unit cell for secondary batteries.

8. In paragraph 7, The above ion conductive polymer comprises at least one of a fluorine-based polymer or a hydrocarbon-based polymer. Unit cell for secondary batteries.

9. In paragraph 8, The above hydrocarbon polymer comprises at least one of a polyimide polymer, a polyetheretherketone polymer, a polyethersulfone polymer, and a polybenzimidazole polymer. Unit cell for secondary batteries.

10. In paragraph 8, A unit cell for a secondary battery, wherein the ion conductive polymer is a hydrocarbon polymer or a fluorine polymer containing a sulfonic acid group.

11. In paragraph 10, A secondary battery unit cell, wherein the hydrocarbon polymer or fluorine polymer containing the sulfonic acid group is at least one of a perfluorosulfonic acid (PFSA) polymer, poly(styrene sulfonic acid) (PSSA), sulfonated poly(ether ether ketones) (SPEEK), sulfonated poly(ether sulfone) (SPES), sulfonated poly(aryl ether ketone) (SPAEK), sulfonated polybenzimidazole (SPBI), sulfonated poly(phenylen oxide) (SPPO), and sulfonated polyimide (SPI).

12. In paragraph 1, The volume of the cathode electrolyte receiving portion is larger than the volume of the anode electrolyte receiving portion. Unit cell for secondary batteries.

13. A secondary battery comprising a plurality of secondary battery unit cells according to any one of claims 1 to 12.

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