Vanadium solid-state battery

Abstract

A vanadium solid battery capable of increasing capacity and reducing internal resistance is provided. [Solution] A vanadium solid state battery (10) includes a positive electrode (20) containing a positive electrode active material containing vanadium ions that change their oxidation state between pentavalent and tetravalent or cations containing vanadium that change their oxidation state between pentavalent and tetravalent through a redox reaction, a negative electrode (30) containing a negative electrode active material containing vanadium ions that change their oxidation state between divalent and trivalent or cations containing vanadium that change their oxidation state between divalent and trivalent through a redox reaction, a diaphragm (12) that separates the positive electrode (20) from the negative electrode (30) and allows hydrogen ions to pass through, and an electrolyte. The positive electrode (20) and the negative electrode (30) are supported by a carbon material, and the carbon material contained in at least one of the positive electrode (20) and the negative electrode (30) is porous carbon having an average pore diameter of 30 nm to 400 nm as measured by the BJH desorption method.

Description

[Technical Field]

[0001] The present invention relates to a vanadium solid state battery. [Background technology]

[0002] A vanadium redox flow battery, which uses vanadium as an active material, has been known as one type of secondary battery (Patent Document 1). A vanadium redox flow battery is a battery that can be charged and discharged by utilizing the oxidation-reduction reaction of the active material in an electrolyte solution.

[0003] In particular, vanadium redox flow batteries, which use divalent, trivalent, tetravalent, and pentavalent vanadium ions as the active material and circulate a sulfuric acid solution of vanadium stored in a tank between the cells, are used in the field of large-scale energy storage.

[0004] A vanadium redox flow battery consists of a positive electrode solution tank that contains the positive electrode solution, which is the active material on the positive electrode side; a negative electrode solution tank that contains the negative electrode solution, which is the active material on the negative electrode side; and a stack that performs charging and discharging. The positive electrode solution and negative electrode solution are circulated between the cell and the tank by a pump. The stack contains a positive electrode, a negative electrode, and an ion exchange membrane that separates them. The battery reaction equations in the positive electrode solution and the negative electrode solution are shown below as equations (1) and (2), respectively.

[0005] Positive electrode: VO 2+ (aq) + H2O ⇔ VO 2+ (aq)+e - +2H + ···(1)

[0006] Negative electrode: V 3+ (aq)+e - ⇔ V 2+ (aq) (2)

[0007] In the above equations (1) and (2), "⇔" indicates chemical equilibrium. Also, (aq) next to an ion means that the ion is in solution.

[0008] As a conventional vanadium redox flow battery, a static liquid vanadium redox battery is known (Patent Document 2), and a vanadium solid salt battery is also known (Patent Documents 3 and 4). Patent Document 4 discloses that when the average pore diameter of a carbon material measured by the BJH desorption method is 0.03 μm or less, particularly in the range of 0.065 to 0.0273 μm in the examples, the energy density is 1.2 to 87 Wh / L. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 4,786,567 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-216833 [Patent Document 3] International Publication No. WO2011 / 049103 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-194973 Summary of the Invention [Problem to be solved by the invention]

[0010] Vanadium solid state batteries are expected to become more widespread. However, in Patent Document 4, the average pore size of the carbon material is 0.03 μm or less, and the energy efficiency is relatively low. Therefore, there is a demand for high-capacity vanadium solid state batteries with low internal resistance and high energy efficiency. An object of the present disclosure is to provide a vanadium solid state battery that can achieve high capacity and reduced internal resistance. [Means for solving the problem]

[0011] The vanadium solid state battery (10) of the present disclosure is The battery includes a positive electrode (20) including a positive electrode active material containing vanadium ions whose oxidation state changes between pentavalent and tetravalent through an oxidation-reduction reaction or cations containing vanadium whose oxidation state changes between pentavalent and tetravalent through an oxidation-reduction reaction, a negative electrode (30) including a negative electrode active material containing vanadium ions whose oxidation state changes between divalent and trivalent through an oxidation-reduction reaction or cations containing vanadium whose oxidation state changes between divalent and trivalent through an oxidation-reduction reaction, a diaphragm (12) that separates the positive electrode (20) from the negative electrode (30) and allows hydrogen ions to pass through, and an electrolyte. The positive electrode (20) and the negative electrode (30) are supported by a carbon material, and the carbon material contained in at least one of the positive electrode (20) and the negative electrode (30) is porous carbon having an average pore diameter of 30 nm or more and 400 nm or less as measured by the BJH desorption method.

[0012] The carbon material may include porous carbon and non-porous carbon. The porous carbon may account for 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 100% by mass of 100% by mass of the carbon material. The carbon material supporting both the positive electrode (20) and the negative electrode (30) may be porous carbon having an average pore diameter of more than 30 nm and not more than 400 nm as measured by the BJH desorption method. The porous carbon may have a lower limit of the average pore diameter of 35 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, or 70 nm or more, and an upper limit of the average pore diameter of 360 nm or less, 300 nm or less, 260 nm or less, or 240 nm or less.

[0013] The volume resistivity of the carbon material of the vanadium solid state battery 10 may be 0.15 Ω·cm or less, 0.12 Ω·cm or less, 0.10 Ω·cm or less, 0.09 Ω·cm or less, 0.08 Ω·cm or less, 0.07 Ω·cm or less, 0.06 Ω·cm or less, 0.05 Ω·cm or less, or 0.04 Ω·cm or less. The volume resistivity is measured by a four-probe method with the carbon material compressed at 12.7 MPa.

[0014] The specific surface area of ​​the carbon material of the vanadium solid battery (10) is 50 m 2 / g or more 450m 2 / g or less. The lower limit of the specific surface area is 60 m 2 / g or more, 70m 2 / g or more, 80m 2 / g or more, 90m 2 / g or more, 100m 2 The upper limit of the specific surface area may be 420 m / g or more. 2 / g or less, 400m 2 / g or less, 380m 2 The specific surface area may be 1 / g or less. The specific surface area is measured by the BET method.

[0015] The bulk density of the carbon material of the vanadium solid state battery (10) is 1 g / cm 3 The upper limit of the bulk density may be 0.9 g / cm or less. 3 Below, 0.8g / cm 3 Below, 0.7g / cm 3 Below, 0.6g / cm 3 Below, 0.5g / cm 3 Below, 0.4g / cm 3 The bulk density may be less than or equal to material The bulk density of the carbon material is measured in a state where the material is compressed at 12.7 MPa.

[0016] The porosity of the carbon material of the vanadium solid state battery (10) may be 50% or more and 90% or less. The lower limit of the porosity may be 52% or more, 54% or more, 56% or more, 58% or more, or 60% or more. The upper limit of the porosity may be 80% or less, 75% or less, or 72% or less. The porosity is calculated using the specific gravities of the carbon material and binder used and the electrode volume.

[0017] The vanadium solid state battery (10) may have an energy density of 30 Wh / L or more. The lower limit of the energy density may be 32 Wh / L or more, 34 Wh / L or more, 36 Wh / L or more, 38 Wh / L or more, 40 Wh / L or more, 42 Wh / L or more, 44 Wh / L or more, 50 Wh / L or more, or 60 Wh / L or more. The energy density is calculated as follows. (1) Calculate the volume of the positive and negative electrodes. (2) The current value during battery discharge is set so that the output per electrode volume (Wa) is 600 W / L. (3) By discharging the battery, the time (T) that electricity can continue to flow at the set current value is calculated. The upper limit voltage during discharge was set to 1.61V and the lower limit voltage was set to 0.8V. (4) Energy density = Wa [W / L] × T (h)

[0018] In this specification, the term "vanadium solid-state battery" refers to all redox batteries that use vanadium, vanadium ions, ions containing vanadium, or compounds containing vanadium as the active material. Vanadium redox flow batteries, static vanadium redox batteries, and vanadium solid-state batteries are all included in the term "vanadium solid-state battery."

[0019] [Action and effect] (1) It is possible to achieve high output and reduced internal resistance in vanadium solid state batteries. (2) By using porous carbon with an average pore diameter of more than 30 nm and not more than 400 nm as the carbon material supporting the vanadium-containing active material, the energy density can be made higher than ever before. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a vanadium solid state battery. DETAILED DESCRIPTION OF THE INVENTION

[0021] (Embodiment 1) Figure 1 shows the configuration of a vanadium solid state battery 10. The vanadium solid state battery 10 includes a housing 11, a positive electrode 20, a negative electrode 30, and a diaphragm 12 provided within the housing 11. The positive electrode 20 and the negative electrode 30 are separated by the diaphragm 12. In Figure 1, from the left, the positive electrode 20, the diaphragm 12, and the negative electrode 30 are arranged.

[0022] The vanadium solid state battery 10 uses solid materials as the active materials of the positive electrode 20 and the negative electrode 30, so there is little concern about leakage. Furthermore, the vanadium solid state battery 10 has excellent safety and a high energy density because it uses solid materials as the active materials of the positive electrode 20 and the negative electrode 30. Note that in the vanadium solid state battery 10, the active materials do not necessarily all exist in a solid state, and the active materials may coexist in both a solid and a liquid state.

[0023] The housing 11 is not particularly limited and may be made of a non-conductive material, a resin, or a metal coated with a non-conductive material. The housing 11 is divided into left and right sections by a diaphragm 12.

[0024] The positive electrode 20 includes a first current collector 22 and a first electrode 24 . The first electrode 24 is configured to include a carbon material that supports a positive electrode active material. The positive electrode active material includes vanadium whose oxidation state changes between pentavalent and tetravalent through an oxidation-reduction reaction. Alternatively, the positive electrode active material includes vanadium ions whose oxidation state changes between pentavalent and tetravalent through an oxidation-reduction reaction. Alternatively, the positive electrode active material includes a cation containing vanadium whose oxidation state changes between pentavalent and tetravalent through an oxidation-reduction reaction. Alternatively, the positive electrode active material includes a solid vanadium salt containing vanadium whose oxidation state changes between pentavalent and tetravalent through a reduction-oxidation reaction. Alternatively, the positive electrode active material includes a complex salt containing vanadium whose oxidation state changes between pentavalent and tetravalent through a reduction-oxidation reaction.

[0025] Examples of positive electrode active materials that can be used in vanadium solid-state batteries include vanadium(IV) oxysulfate n-hydrate and vanadium(V) dioxysulfate n-hydrate. The positive electrode active material may be added to an electrolyte such as an aqueous sulfuric acid solution. In this embodiment, vanadium (IV) oxysulfate n-hydrate, which is the positive electrode active material, and an aqueous sulfuric acid solution (electrolyte) are impregnated into or supported on porous carbon.

[0026] The negative electrode 30 includes a second current collector 32 and a second electrode 34 . The second electrode 34 is configured to include a carbon material that supports a negative electrode active material. The negative electrode active material includes vanadium whose oxidation state changes between divalent and trivalent through a redox reaction. Alternatively, the negative electrode active material includes a cation containing vanadium whose oxidation state changes between divalent and trivalent through a redox reaction. Alternatively, the negative electrode active material includes a solid vanadium salt containing vanadium whose oxidation state changes between divalent and trivalent through a redox reaction. Alternatively, the negative electrode active material includes a complex salt containing vanadium whose oxidation state changes between divalent and trivalent through a redox reaction.

[0027] Examples of negative electrode active materials that can be used in vanadium solid state batteries include vanadium(II) sulfate n-hydrate and vanadium(III) sulfate n-hydrate. The negative electrode active material may be added to an electrolyte such as an aqueous sulfuric acid solution. In this embodiment, vanadium (III) sulfate n-hydrate, which is the negative electrode active material, and an aqueous sulfuric acid solution (electrolyte) are impregnated into or supported on porous carbon.

[0028] The reaction formula of the positive electrode active material during charge and discharge of the vanadium solid state battery is, for example, as shown in the following formula (3). Positive electrode: VOX2·nH2O(s) ⇔ VO2X·mH2O(s)+HX+H + +e - ···(3)

[0029] The reaction formula of the negative electrode active material during charging and discharging of the vanadium solid state battery is, for example, as shown in the following formula (4). Negative electrode: VX3·nH2O(s)+e - ⇔ 2VX2 mH2O(s) + X - ···(4)

[0030] In the above formulas (3) and (4), X represents a monovalent anion. In the above formulas (3) and (4), n can take on various values. For example, vanadium(IV) oxysulfate n-hydrate and vanadium(V) dioxysulfate n-hydrate do not necessarily have the same number of waters of hydration. The same is true for the chemical reaction formulas and substance names that appear below.

[0031] Examples of the carbon material that can be used for the first and second electrodes 24, 34 include carbon black, carbon fiber, carbon nanotubes, graphene, glassy carbon (registered trademark) powder, graphite powder, porous carbon powder, activated carbon, and / or carbon felt. Of these carbon materials, porous carbon powder is used in this embodiment. The first and second electrodes 24, 34 may have the same configuration or different configurations. Porous carbon refers to carbon that has a structure with many small holes, and has a pore diameter of 20 nm or more. In this embodiment, porous carbon with an average pore diameter of more than 30 nm is used.

[0032] The first and second current collectors 22, 32 are formed of a conductive material such as copper. Alternatively, the first and second current collectors 22, 32 are formed of a metal foil coated with, for example, conductive rubber, conductive resin, or DLC. The shape of the first and second current collectors 22, 32 is not particularly limited, but may be, for example, a flat plate. The surface of the first current collector 22 is in contact with the first electrode 24. The surface of the second current collector 32 is in contact with the second electrode 34. When the first and second current collectors 22 and 32 are made of copper, the copper surface may be coated with carbon to prevent corrosion. Alternatively, a graphite sheet may be attached to the copper surface to prevent corrosion. The first and second current collectors 22 and 32 may have the same configuration or different configurations.

[0033] The diaphragm 12 is, for example, an ion exchange membrane that can selectively pass hydrogen ions (protons). The diaphragm 12 may be, for example, a porous membrane. The diaphragm 12 is, for example, an ion exchange membrane such as Selemion Sx-050WK (registered trademark) (manufactured by AGC Engineering Co., Ltd.) or Nafion (registered trademark) (manufactured by DuPont Co., Ltd.), or alternatively, the diaphragm 12 is, for example, an ion exchange membrane such as Neosepta (registered trademark) (manufactured by Astom Corporation).

[0034] The battery is discharged by connecting an appropriate electrical resistance between the first current collector 22 and the second current collector 32. The battery is charged by applying a sufficient voltage between the first current collector 22 and the second current collector 32.

[0035] (Carbon material: porous carbon) The porous carbon has an average pore diameter of 30 nm or more and 400 nm or less as measured by the BJH desorption method. In this embodiment, the porous carbon accounts for 100% by mass of the carbon material. The porous carbon may have a lower limit of the average pore diameter of 35 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, or 70 nm or more, and an upper limit of the average pore diameter of 360 nm or less, 300 nm or less, 260 nm or less, or 240 nm or less. The average pore diameter obtained by the BJH desorption method can be calculated from the difference Δvij in the amount of adsorption (desorption) when the pressure is changed from relative pressure i to relative pressure j, and is calculated as the average diameter (nm) at each point x the differential pore surface area (m 2 / g) divided by the cumulative pore specific surface area.

[0036] The volume resistivity of the porous carbon may be 0.15 Ω·cm or less, 0.12 Ω·cm or less, 0.10 Ω·cm or less, 0.09 Ω·cm or less, 0.08 Ω·cm or less, 0.07 Ω·cm or less, 0.06 Ω·cm or less, 0.05 Ω·cm or less, or 0.04 Ω·cm or less. The volume resistivity is measured by the four-probe method when the porous carbon is compressed at 12.7 MPa.

[0037] The four-probe method for measuring volume resistivity is as follows. First, four needle-shaped electrodes are placed in a straight line on the sample, a constant current is passed between the two outer probes, and the potential difference between the two inner probes is measured to determine the resistance. Next, the volume resistivity is calculated by multiplying the determined resistance (R, unit: Ω) by the sample thickness t (cm) and the correction coefficient RCF (Resistivity Correction Factor).

[0038] The specific surface area of ​​the porous carbon is 50m 2 / g or more 450m 2 / g or less. The lower limit of the specific surface area is 60 m 2 / g or more, 70m 2 / g or more, 80m 2 / g or more, 90m 2 / g or more, 100m 2 The upper limit of the specific surface area may be 420 m / g or more. 2 / g or less, 400m 2 / g or less, 380m 2 The specific surface area may be 1 / g or less. The specific surface area is measured by the BET method.

[0039] The bulk density of the porous carbon is 1 g / cm 3 The upper limit of the bulk density may be 0.9 g / cm or less. 3 Below, 0.8g / cm 3 Below, 0.7g / cm 3 Below, 0.6g / cm 3 Below, 0.5g / cm 3 Below, 0.4g / cm 3 The bulk density may be less than or equal to materialThe bulk density of the carbon material is measured in a state where the material is compressed at 12.7 MPa.

[0040] The porosity of the porous carbon may be 50% or more and 90% or less. The lower limit of the porosity may be 52% or more, 54% or more, 56% or more, 58% or more, or 60% or more. The upper limit of the porosity may be 80% or less, 75% or less, or 72% or less. The porosity is calculated using the specific gravities of the carbon material and binder used and the electrode volume.

[0041] The energy density of the vanadium solid state battery 10 of this embodiment is 30 Wh / L or more. The lower limit of the energy density may be 32 Wh / L or more, 34 Wh / L or more, 36 Wh / L or more, 38 Wh / L or more, 40 Wh / L or more, 42 Wh / L or more, 44 Wh / L or more, 50 Wh / L or more, or 60 Wh / L or more. The energy density is calculated as follows. (1) Calculate the volume of the positive and negative electrodes. (2) The current value during battery discharge is set so that the output per electrode volume (Wa) is 600 W / L. (3) By discharging the battery, the time (T) that electricity can continue to flow at the set current value is calculated. The upper limit voltage during discharge was set to 1.61V and the lower limit voltage was set to 0.8V. (4) Energy density = Wa [W / L] × T (h)

[0042] (Manufacturing method) The first and second electrodes 24, 34 can be manufactured, for example, as follows. After kneading the carbon material and binder, the kneaded mixture is rolled to form a sheet. This sheet-like product is impregnated with an active material (including an electrolyte solution), dried, and punched into a predetermined shape. This allows the first and second electrodes 24, 34 to be manufactured. Examples of binders that can be used include PTFE, PVDF, fluorine-based binders, polyimide, polyamide, polyamideimide, rubber-based binders, acrylic binders, chlorine-based binders, and / or inorganic binders.

[0043] (Method of manufacturing solid active material) The method for producing a solid active material includes at least one of the following steps: preparing a solution (S1) containing tetravalent vanadium ions or vanadium-containing cations in a tetravalent state; drying the electrolytically reduced solution (S1) under reduced pressure to obtain a solid active material; electrolytically reducing or electrolytically oxidizing a solution (S2) containing tetravalent vanadium ions or vanadium-containing cations in a tetravalent state; placing the solution (S2) in an oxygen-containing environment; and drying the supernatant and sediment of the solution (S2).

[0044] (Example) Examples of the present invention will be specifically described below. In the examples, 14 types of porous carbon, designated A to N, were prepared. The following (1) to (7) were measured for the prepared 14 types of porous carbon.

[0045] (1) Volume resistivity [Ω cm] The volume resistivity of the porous carbon was measured in the processed state. (2) Bulk density [g / cm 3 ] The bulk density of the processed porous carbon was measured. (3) Specific surface area [m 2 / g] The specific surface area of ​​the porous carbon was measured. (4) Porosity [%] The porosity of the porous carbon was measured. (5) Average pore diameter [nm] The average pore diameter of the porous carbon was measured.

[0046] A vanadium solid salt battery was fabricated by the following procedure. First current collector 22 , second current collector 32 A combination of a graphite sheet (40 μm) and copper foil (40 μm) was used. The diaphragm 12 used was Neosepta (registered trademark) (manufactured by Astom Co., Ltd.). First electrode 24 , second electrode 34 is a mixture consisting of 85 mass% of 14 types of porous carbon A to N, 5 mass% of Ketjenblack powder ("EC600JD" manufactured by Ketjenblack International Co., Ltd.) as a conductive additive, and 10 mass% of polytetrafluoroethylene powder ("Teflon (registered trademark) 6J" manufactured by Mitsui DuPont Fluorochemicals Co., Ltd.) as a binder. For 100% by mass of this mixture, After adding 30% by mass of ethanol to the mixture and kneading, the mixture was extruded into a tape-like paste. The resulting tape was then passed through a roll twice to produce an electrode sheet with a thickness of 1.0 m. The sheet was then dried at 150°C for 1 hour to remove the ethanol. death Ta. The positive active material solution was prepared by dissolving vanadium(IV) oxide sulfate (VOSO4·nH2O) in a 2.2 M aqueous sulfuric acid solution to a concentration of 2.2 M. The negative active material solution was prepared by electrolytic reduction of the positive active material solution. As shown in FIG. 1, the positive electrode 20 is formed on a first current collector 22. Positive life First electrode impregnated with the substance solution 24 was installed. The negative electrode 30 is disposed on the second current collector 32. negative Second electrode impregnated with active material solution 34 was installed. The vanadium solid salt battery was fixed in a housing 11 with a diaphragm 12 sandwiched between a positive electrode 20 and a negative electrode 30 .

[0047] The discharge time [min] and energy density [Wh / L] of the fabricated vanadium solid salt battery 10 were measured.

[0048] The measured values ​​of (1) to (5) above are shown in Table 1. The measurement results of the discharge time and energy density of the battery are shown in Table 2.

[0049] [Table 1]

[0050] [Table 2]

[0051] As shown in Table 2, when the volume resistivity of the porous carbon is 0.15 Ω·cm or less, the energy density of the battery increases.

[0052] As shown in Table 2, when the bulk density of the porous carbon is 1 g / cm 3 below It can be seen that the energy density of the battery is high in this case.

[0053] As shown in Table 2, the specific surface area of ​​porous carbon is 50 m 2 / g or more, the energy density of the battery increases.

[0054] As shown in Table 2, the porosity of the porous carbon is 50%. End It can be seen that the energy density of the battery is high in this case.

[0055] As shown in Table 2, when the average pore diameter of the porous carbon exceeds 30 nm, the energy density of the battery increases.

[0056] (Another embodiment) (1) The vanadium solid battery is not limited to the above-described embodiment, and may be a vanadium redox flow battery, a static vanadium redox battery, a vanadium solid salt battery, or the like. (2) In the case of a redox flow battery, the cathode electrolyte 15 is filled on the cathode 20 side, and the anode electrolyte 16 is filled on the anode 30 side, and each electrolyte may be circulated through an inlet pipe, an outlet pipe, a liquid transfer pump, or the like connected to the casing 11. [Explanation of symbols]

[0057] 10. Vanadium solid-state battery 11. Housing 12 Bulkhead 20 positive electrode 22 First current collector 24 First electrode 30 negative electrode 32 Second current collector 34 Second electrode

Claims

1. A vanadium solid state battery comprising: a positive electrode including a positive electrode active material containing vanadium ions that change their oxidation state between pentavalent and tetravalent through an oxidation-reduction reaction or cations containing vanadium that change their oxidation state between pentavalent and tetravalent through an oxidation-reduction reaction; a negative electrode including a negative electrode active material containing vanadium ions that change their oxidation state between divalent and trivalent through an oxidation-reduction reaction or cations containing vanadium that change their oxidation state between divalent and trivalent through an oxidation-reduction reaction; a diaphragm that separates the positive electrode from the negative electrode and allows hydrogen ions to pass through; and an electrolyte; the positive electrode and the negative electrode are supported by a carbon material, and the carbon material contained in at least one of the positive electrode and the negative electrode is porous carbon having an average pore diameter measured by a BJH desorption method of more than 30 nm and not more than 400 nm; the porosity of the carbon material of the vanadium solid state battery is 50% or more and 90% or less; the volume resistivity of the carbon material of the vanadium solid state battery is 0.15 Ω cm or less; the specific surface area of ​​the carbon material of the vanadium solid state battery is 50 m 2 / g or more and 450 m 2 / g or less; A vanadium solid state battery, wherein the carbon material of the vanadium solid state battery has a bulk density of 1 g / cm 3 or less.

2. A vanadium solid state battery as described in claim 1, wherein the energy density of the vanadium solid state battery is 30 Wh / L or more.

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