JP6176761B2 - Vanadium solid salt battery - Google Patents

Description

  The present invention relates to a vanadium battery using an electrolyte containing vanadium as an active material. In particular, the present invention relates to a vanadium solid salt battery containing a vanadium solid salt in a positive electrode and a negative electrode (hereinafter also referred to as “VSB (Vanadium Solid-Salt Battery)”).

  Secondary batteries are widely used not only in digital home appliances but also in electric vehicles and hybrid vehicles using motor power. Among such secondary batteries, a vanadium solid salt battery has been proposed (Patent Document 1). The vanadium solid salt battery of Patent Document 1 includes a positive electrode and a negative electrode in which a precipitate containing vanadium ions or vanadium-containing cations is supported on an electrode material such as carbon felt.

International Publication No. 2011/049103

  The vanadium solid salt battery of Patent Document 1 is desired to further improve battery performance. Here, the battery performance includes capacity maintenance rate, coulomb efficiency, and energy efficiency. Conventionally, studies have been made to improve the battery performance of the electrolyte flow type redox flow battery, but it has not been possible to improve the battery performance of the vanadium solid salt battery.

  This invention makes it a subject to provide the vanadium solid salt battery which improved the capacity | capacitance maintenance factor, the coulomb efficiency, and energy efficiency.

The present invention 1 includes vanadium solid salt containing vanadium ions and / or vanadium ions, an electrolytic solution, and a carbon material in a positive electrode and a negative electrode, and the carbon material of the positive electrode was determined by Raman spectroscopy. The R value is 1.10 or less, or a carbon material powder having a lattice spacing d (d002) measured by an X-ray powder method of 0.33 to 0.36 nm, and the vanadium solid salt of the positive electrode is Further, the present invention relates to a vanadium solid salt battery, wherein the content of the carbon material is 1 to 42% by mass.
Invention 2 includes sulfuric acid in the electrolytic solution, and the molar concentration of sulfuric acid in the electrolytic solution contained in the positive electrode vanadium solid salt is 0.34 to 0.80 mol / L, and is contained in the vanadium solid salt for negative electrode. The present invention relates to the vanadium solid salt battery according to the first aspect of the present invention, wherein the volume molar concentration of sulfuric acid in the electrolytic solution is 1.83 to 2.24 mol / L.
Invention 3 includes phosphoric acid or phosphate in the electrolytic solution, and the volume molar concentration of phosphoric acid or phosphate in the electrolytic solution contained in the positive electrode vanadium solid salt is 0.20 to 0.66 mol / L. The vanadium solid salt battery according to the first or second aspect of the invention, wherein the molar concentration of phosphoric acid or phosphate in the electrolyte contained in the negative electrode vanadium solid salt is 0.18 to 0.60 mol / L. .
In the present invention 4, the molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolyte contained in the vanadium solid salt for positive electrode is 1: 0.25 to 1: 1.94, and is included in the vanadium solid salt for negative electrode The present invention relates to the vanadium solid salt battery according to the third aspect of the present invention, wherein the molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolytic solution is 1: 0.082 to 1: 0.333.
This invention 5 is related with the vanadium solid salt battery in any one of this invention 1-4 which contains a binder in at least one of the vanadium solid salt for positive electrodes, and the vanadium solid salt for negative electrodes.
The present invention 6 is a vanadium solid salt composition for forming a vanadium solid salt for use in a vanadium solid salt battery, the vanadium solid salt composition for a positive electrode comprising vanadium oxide (IV) sulfate and an electrolytic solution. And a carbon material powder having an R value determined by Raman spectroscopy of 1.10 or less or a lattice spacing d (d002) measured by an X-ray powder method of 0.33 to 0.36 nm, It is related with the composition for vanadium solid salt whose content of vanadium oxide sulfate (IV) is 57.0-85.0 mass% with respect to 100 mass% of said compositions.
The present invention 7 is a vanadium solid salt composition for forming a vanadium solid salt used in a vanadium solid salt battery, wherein the vanadium solid salt composition for a negative electrode comprises vanadium (III) sulfate, an electrolytic solution, Carbon material powder having an R value determined by Raman spectroscopy of 1.10 or less or a lattice spacing d (d002) measured by X-ray powder method of 0.33 to 0.36 nm, It is related with the composition for vanadium solid salt whose content of vanadium (III) sulfate is 56.0-83.0 mass% with respect to 100 mass% of compositions.

  The present invention relates to a carbon material having an R value obtained by Raman spectroscopy of vanadium solid salt of 1.10 or less or a lattice spacing (d002) measured by X-ray powder method of 0.33 to 0.36 nm. By including a specific amount of powder, it is possible to maintain the balance of the redox state of vanadium ions or ions containing vanadium in the positive electrode and the negative electrode. The present invention can improve the capacity maintenance rate, coulomb efficiency, and energy efficiency of a vanadium solid salt battery by maintaining the balance of the redox state of vanadium ions or vanadium-containing ions in the positive electrode and the negative electrode.

It is a figure which shows schematic structure of the vanadium solid salt battery for a test. It is an X-ray diffraction spectrum of a vanadium solid salt containing different concentrations of phosphoric acid and sulfuric acid, measured at a diffraction angle of 2θ using CuKα rays as an X-ray source (wavelength λ = 0.15418 nm). It is a graph which shows the Raman spectrum by the Raman spectroscopy of Toka Black (TB). It is a graph which shows the Raman spectrum by the Raman spectroscopy of acetylene black (AB). It is a graph which shows the Raman spectrum by the Raman spectroscopy of ketjen black (KB). (A) XRD spectrum of Toka Black (Toka Black) is shown, (b) It is a figure which shows a half value width (FWHM). (A) XRD spectrum of acetylene black (Acetylene Black) is shown, (b) It is a figure which shows a half value width (FWHM). (A) The XRD spectrum of Ketjen Black (Ketjen Black) is shown, (b) It is a figure which shows a half value width (FWHM). The charging / discharging capacity | capacitance (capacity / mAh-voltage / V relationship) of the vanadium solid salt battery of an Example is shown, and the Coulomb efficiency by constant current charging / discharging is shown. The charge / discharge capacity | capacitance (capacity / mAh-voltage / V relationship) of the vanadium solid salt battery of a comparative example is shown, and the Coulomb efficiency by constant current charge / discharge is shown. The charging / discharging capacity | capacitance (capacity / mAh-voltage / V relationship) of the vanadium solid salt battery of an Example is shown, and the capacity | capacitance maintenance factor by constant current charging / discharging is shown. The charging / discharging capacity | capacitance (capacity / mAh-voltage / V relationship) of the vanadium solid salt battery of a comparative example is shown, and the capacity | capacitance maintenance factor by constant current charging / discharging is shown.

[Vanadium solid salt battery]
The vanadium solid salt battery includes vanadium solid salts containing vanadium ions and / or cations containing vanadium, an electrolytic solution, and a carbon material in the positive electrode and the negative electrode. The vanadium solid salt battery includes a diaphragm that partitions the positive electrode and the negative electrode. In addition, an extraction electrode is provided for each of the positive electrode and the negative electrode.

  FIG. 1 is a diagram showing a schematic configuration of a vanadium solid salt battery. The vanadium solid salt battery is not limited to the example shown in FIG.

  As shown in FIG. 1, a vanadium solid salt battery 1 includes a positive electrode 7 including a vanadium solid salt 2 for a positive electrode, a negative electrode 8 including a vanadium solid salt 3 for a negative electrode, a vanadium solid salt 2 for positive electrode, and a vanadium for negative electrode. And a diaphragm 4 that partitions the solid salt 3. The vanadium solid salt battery can be manufactured as follows.

  First, the positive electrode 7 of the vanadium solid salt battery 1 can be manufactured as follows. The positive electrode 7 of the vanadium solid salt battery 1 has the first current collector 5 placed on the first cell plate 11a constituting the cell. Next, the first mold 12 a is installed on the first current collector 5. Furthermore, the 1st formwork 12a is filled with the vanadium solid salt composition of the paste form which comprises the vanadium solid salt 2 for positive electrodes, and it is set as the vanadium solid salt 2 for positive electrodes.

  The positive electrode 7 includes a first extraction electrode 9 between the first current collector 5 and the first cell plate 11a.

  The negative electrode 8 of the vanadium solid salt battery 1 can be manufactured in the same manner as the positive electrode 7. First, the 2nd electrical power collector 6 is installed on the 2nd cell board 11b which comprises a cell. Next, the second mold 12 b is installed on the second current collector 6. Further, the paste-like vanadium solid salt composition constituting the negative electrode vanadium solid salt 3 is filled in the second mold 12 b to obtain the negative electrode vanadium solid salt 3.

  The negative electrode 8 includes a second extraction electrode 10 between the second current collector 6 and the second cell plate 11b.

  A vanadium solid salt battery 1 shown in FIG. 1 includes a diaphragm 4 sandwiched between a positive electrode vanadium solid salt 2 and a negative electrode vanadium solid salt 3, and surrounds the first cell plate 11a and the second cell plate 11b. Fix with a plurality of screws 13.

  In the vanadium solid salt battery, the following reaction occurs in the positive electrode and the negative electrode.

Positive electrode: VOX ₂ · nH ₂ O (s) ⇔VO ₂ X · nH ₂ O (s) + HX + H ⁺ + e ⁻ (3)

Negative electrode: VX ₃ · nH ₂ O (s) + e ⁻ ⇔2VX ₂ · nH ₂ O (s) + X ⁻ (4)

  In the reaction formula generated in the positive electrode and the negative electrode, X represents a monovalent anion. However, even if X is an m-valent anion, it may be understood that the coupling coefficient (1 / m) is considered. Here, “⇔” means equilibrium, but in the above formula, equilibrium means a state where the amount of change in the product of the reversible reaction matches the amount of change in the starting material. In the reaction formula, n indicates that various values can be taken.

  As one embodiment of the vanadium solid salt battery, the reaction at the positive electrode is shown below.

VOSO ₄ · nH ₂ O (s) ⇔VOSO ₄ · nH ₂ O (aq) ⇔VOSO ₄ (aq)
+ NH ₂ O (aq) (5)

(VO ₂ ) ₂ · SO ₄ · nH ₂ O (s) ⇔ (VO ₂ ) ₂ · SO ₄ · nH ₂ O (aq) ⇔
(VO ₂ ) ₂ SO ₄ (aq) + nH ₂ O (aq) (6)

_{^{VO 2+ (aq) + VO 2}} + (aq) ⇔V 2 O 3 3+ (aq) (7)

VO ²⁺ (aq) + SO ₄ ²⁻ (aq) ⇔VOSO ₄ (aq) (8)

_{^{2VO 2+ (aq) + SO 4}} 2- (aq) ⇔ (VO 2) 2 SO 4 (aq) (9)

  As an embodiment of the vanadium solid salt battery of the present invention, the reaction in the negative electrode is shown below.

V ₂ (SO ₄ ) ₃ · nH ₂ O (s) ⇔ V ₂ (SO ₄ ) ₃ · nH ₂ O (aq) ⇔
V ₂ (SO ₄ ) ₃ + nH ₂ O (aq) (10)

VSO ₄ · nH ₂ O (s) ⇔VSO ₄ · nH ₂ O (aq) ⇔VSO ₄ (aq)
+ NH ₂ O (aq) (11)

2V ³⁺ (aq) + 3SO ₄ ²⁻ ⇔V ₂ (SO ₄ ) ₃ (aq) (12)

[Vanadium solid salt]
The vanadium solid salt constituting the positive electrode or the negative electrode includes vanadium ions or cations containing vanadium, a carbon material, and an electrolytic solution. In this specification, vanadium ion or a compound containing a cation containing vanadium, a carbon material, and an electrolyte solution, which is in a solid state, is referred to as vanadium solid salt. Further, in this specification, a state before vanadium ion or a compound containing a cation containing vanadium, a carbon material, and an electrolytic solution and before becoming solid is referred to as a composition for vanadium solid salt. Here, the state before becoming solid is, for example, a state before mixing a vanadium ion or a compound containing a cation containing vanadium, a carbon material, and an electrolytic solution, mixing and pasting, etc. Including the previous state of solid state, such as the state of becoming.

  The carbon material is a carbon material powder having an R value obtained by Raman spectroscopy of 1.10 or less, or a lattice distance d (d002) measured by an X-ray powder method of 0.33 to 0.36 nm. is there.

Degree of graphitization of the carbon material, the intensity ratio of D band in general Raman spectrum obtained by Raman spectroscopy (1350 cm peak appearing in the vicinity of ^-1) and G band (peak appearing around 1580 cm ^-1) R It is represented by the value (R = I _D / I _G ). The G band reflects the planar structure (three-dimensional ordered structure) of sp ² bonded carbon of the carbon material. The D band reflects the disorder of the crystal. Further, a 2D band (a peak appearing in the vicinity of 2585 cm ⁻¹ ) may also exist in the Raman spectrum of the carbon material. The 2D band also reflects crystal turbulence. When the R value is small, the graphitization degree is high, that is, the crystallinity of the carbon material is high.

A carbon material having an R value determined by Raman spectroscopy of 1.10 or less and a relatively high degree of crystallinity has a sufficient bond between carbon atoms, and the ratio of the basal plane to the edge plane in the carbon laminate structure There are also many. Therefore, small amount of binding functional groups and capable of adsorbing oxygen and carbon, for example, in the positive electrode, the pentavalent vanadium oxide ion (VO ²⁺⁾ tetravalent vanadium oxide ion is charge state (VO 2 ^₊₎ The reduction (discharge) can be suppressed. In addition, for example, in the negative electrode, it is possible to prevent the charged divalent vanadium ion (V ²⁺ ) from being oxidized (discharged) to the trivalent vanadium ion (V ³⁺ ). When the R value obtained by Raman spectroscopy exceeds 1.10, the bonds between carbons are released, and the proportion of carbon that can be bonded to a functional group and carbon that can adsorb oxygen increases. The active material is oxidized and reduced by increasing the proportion of functional groups and oxygen involved in oxidation and reduction. For this reason, the reduction of pentavalent vanadium oxide ions in the charged state at the positive electrode and / or the oxidation of divalent vanadium ions in the charged state at the negative electrode cannot be suppressed, and the balance of the redox state in the battery is lost. . A battery in which the balance of the oxidation-reduction state is lost has a reduced battery capacity.

  The carbon material preferably has a high crystallinity. The carbon material has an R value determined by Raman spectroscopy of preferably 1.05 or less, more preferably 1.00 or less, still more preferably 0.80 or less, and particularly preferably 0.50 or less. It is. The lower limit of the R value obtained by Raman spectroscopy of the carbon material is not particularly limited as long as it is a measurable range, but is usually 0.10 or more.

The carbon material is a carbon material powder having a lattice interval d (d002) measured by the X-ray powder method of 0.33 to 0.36 nm.
The lattice spacing d (d002) measured by the X-ray powder method can be obtained from the peak derived from the c-axis (002) of the diffraction spectrum obtained by the X-ray powder method based on the Bragg equation (I).
d = λ / (2 × Sinθ _B ) (I)
(Where d is the lattice spacing d (d002), λ is the wavelength of 0.154 nm, and θ _B is the Bragg angle.)
A carbon material powder having a lattice spacing d measured by the X-ray powder method of 0.33 to 0.36 nm has a planar structure of sp ² -bonded carbon and is close to the structure of natural graphite showing a three-dimensional ordered structure, It indicates that the degree of crystallinity is high. An ideal natural graphite powder has a c-axis (002) plane lattice spacing d (d002) of 0.3354 nm, and the closer to this value, the higher the crystallinity of the carbon material powder.

When the lattice spacing d measured by the X-ray powder method is 0.33 to 0.36 nm, the crystal structure of the carbon material powder becomes a structure close to a three-dimensional regular structure and becomes a very stable structure. Alternatively, the redox state of vanadium ions or cations containing vanadium in the negative electrode can be balanced. When the lattice spacing d measured by the X-ray powder method is less than 0.33 or exceeds 0.36, the crystal structure of the carbon material powder is disturbed, and the vanadium ions or vanadium in the positive electrode or the negative electrode are included along with the disorder of the crystal structure. The balance of the cation redox state is lost, and the battery capacity is reduced.
A carbon material having a relatively high degree of crystallinity has a sufficient bond between carbon atoms, and the ratio of the basal plane to the edge surface in the carbon laminate structure is large. Therefore, the amount of functional groups that can be bonded to carbon and adsorbable oxygen is small. When the lattice spacing d (d002) is less than 0.33 nm or exceeds 0.36 nm, the bonds between carbons are released, and the proportion of carbon that can be bonded to a functional group and carbon that can adsorb oxygen increases. The active material is oxidized and reduced by increasing the proportion of functional groups and oxygen involved in oxidation and reduction.

  The R value obtained by Raman spectroscopy and the lattice spacing d measured by the X-ray powder method are both indices indicating the crystallinity of the carbon material powder. The R value obtained by Raman spectroscopy indicates the state of crystals on the surface of the carbon material powder. The lattice spacing d (d002) measured by the X-ray powder method indicates the state of crystals inside the carbon material powder. Due to the difference in these measurement methods, the carbon material powder has an R value obtained by Raman spectroscopy of 1.10 or less, or a lattice spacing d (d002) measured by the X-ray powder method is 0.33 to 0.33. A carbon material powder satisfying 0.36 nm is used.

  The carbon material is a carbon material powder having an R value obtained by Raman spectroscopy of 1.10 or less, or a lattice distance d (d002) measured by an X-ray powder method of 0.33 to 0.36 nm. If there are any, the type and the like are not particularly limited. Examples of the carbon material powder include natural graphite, graphitized carbon black, and acetylene black. Examples of commercially available graphitized carbon black include Talker Black # 3855, Talker Black # 3845, Talker Black # 3800 (manufactured by Tokai Carbon Co., Ltd.) and the like.

A carbon material is 1-42 mass% with respect to 100 mass% of vanadium solid salt, or 100 mass% of compositions for vanadium solid salt. The carbon material is preferably 2 to 41% by mass, more preferably 3 to 40% by mass, and further preferably 4 to 38% by mass with respect to 100% by mass of the vanadium solid salt or 100% by mass of the composition for vanadium solid salt. Most preferably, it is 5-35 mass%. When the content of the carbon material in the vanadium solid salt or the vanadium solid salt composition is less than 1% by mass, electrons (e ⁻ ) cannot be transmitted, and the capacity retention rate, the coulomb efficiency, and the energy efficiency Decreases. On the other hand, when the content of the carbon material in the vanadium solid salt exceeds 42% by mass, vanadium ions or cations containing vanadium contained in the vanadium solid salt decrease, and the battery capacity decreases.

The vanadium solid salt for positive electrode or the composition for vanadium solid salt for positive electrode preferably uses a compound containing a cation containing vanadium whose oxidation number changes between tetravalent and pentavalent. The cation containing tetravalent and pentavalent vanadium oxidation number changes _{^{between, VO 2+ (IV), VO}} 2 + (V) can be exemplified. Examples of the compound used for the positive electrode vanadium solid salt include vanadium oxide (IV) sulfate (VOSO ₄ .nH ₂ O) and vanadium oxide sulfate (V) ((VO ₂ ) ₂ SO ₄ .nH ₂ O). . n shows 0 or the integer of 1-6.

  Vanadium oxide sulfate (IV) is 57.0-85.0 mass% with respect to 100 mass% of vanadium solid salts for positive electrodes, or 100 mass% of vanadium solid salt compositions for positive electrodes. The content of vanadium oxide (IV) oxide is preferably 58.0 to 84.0% by mass, more preferably 100% by mass of the vanadium solid salt for positive electrode or 100% by mass of the composition for vanadium solid salt for positive electrode. Is 60.0-83.0 mass%, more preferably 62.0-82.0 mass%. When the content of vanadium oxide (IV) oxide is 57.0 to 85.0% by mass, the required battery capacity can be satisfied.

The vanadium solid salt for negative electrode or the composition for vanadium solid salt for negative electrode preferably uses a compound containing vanadium ions whose oxidation number varies between divalent and trivalent. Examples of the vanadium ion whose oxidation number changes between divalent and trivalent include V ²⁺ (II) and V ³⁺ (III). Examples of the vanadium compound used for the vanadium solid salt for the negative electrode include vanadium sulfate (II) (VSO ₄ · nH ₂ O) and vanadium sulfate (III) (V ₂ (SO ₄ ) ₃ · nH ₂ O). n shows 0 or the integer of 1-6.

  Vanadium sulfate (III) is 56.0-83.0 mass% with respect to 100 mass% of vanadium solid salt for negative electrodes, or 100 mass% of compositions for vanadium solid salts for negative electrodes. The content of vanadium sulfate (III) is preferably 57.0 to 82.0% by mass, more preferably 100% by mass of the vanadium solid salt for negative electrode or 100% by mass of the composition for vanadium solid salt for negative electrode, more preferably It is 60.0-81.0 mass%, More preferably, it is 62.0-80.5 mass%. When the content of vanadium sulfate (III) is 56.0 to 83.0% by mass, the required battery capacity can be satisfied.

  Vanadium solid salt contains electrolyte solution. The electrolytic solution is preferably 1 to 30% by mass, more preferably 2 to 25% by mass, and further preferably 3 to 20% by mass with respect to 100% by mass of the vanadium solid salt or 100% by mass of the composition for vanadium solid salt. is there. When the content of the electrolytic solution in the vanadium solid salt is 1 to 30% by mass, the required battery capacity can be satisfied and the cycle characteristics of the battery can be lengthened.

  The electrolytic solution contains sulfuric acid. As sulfuric acid, dilute sulfuric acid aqueous solution and / or concentrated sulfuric acid aqueous solution can be used. As the concentrated sulfuric acid, commercially available concentrated sulfuric acid having a mass percent concentration of 96 to 98% by mass can be used. Commercially available concentrated sulfuric acid usually has a molar concentration of 18 mol / L.

The volume molar concentration of sulfuric acid in the electrolyte contained in the positive electrode vanadium solid salt or the positive electrode vanadium solid salt composition is preferably 0.34 to 0.80 mol / L, more preferably 0.4 to 0.78 mol. / L, more preferably 0.45 to 0.76 mol / L, particularly preferably 0.50 to 0.75 mol / L.
The volume molar concentration of sulfuric acid in the electrolyte contained in the vanadium solid salt for negative electrode or the vanadium solid salt composition for negative electrode is preferably 1.83 to 2.24 mol / L, more preferably 1.80 to 2.23 mol. / L, more preferably 1.90 to 2.22 mol / L, and particularly preferably 1.97 to 2.20 mol / L.
The volume molar concentration of sulfuric acid in the electrolytic solution in the positive electrode is 0.34 to 0.80 mol / L, and the volume molar concentration of sulfuric acid in the electrolytic solution in the negative electrode is 1.83 to 2.24 mol / L. In addition to satisfying the battery capacity, the cycle characteristics can be lengthened.

The volume molar concentration of sulfuric acid contained in the electrolyte is different between the vanadium solid salt for positive electrode or the vanadium solid salt composition for positive electrode and the vanadium solid salt for negative electrode or the vanadium solid salt composition for negative electrode. This is because sometimes the movement of water from the negative electrode to the positive electrode is suppressed.
In the positive electrode, as shown in the formula (13), water is used in a reaction of oxidizing (charging) from tetravalent vanadium oxide ions to pentavalent vanadium ions.

VO ^{2+ _{(4-valent) + H 2 O⇔VO 2 + (}} 5 ^{valence) + 2H + + e - (} 13)

  When the positive electrode and the negative electrode have the same acid concentration in the initial state, the acid concentration of the positive electrode is relatively higher than that of the negative electrode during charging. As the acid concentration increases, water moves from the negative electrode to the positive electrode to maintain balance. The volume molar concentration of sulfuric acid in the electrolyte solution in the positive electrode and the volume molar concentration of sulfuric acid in the electrolyte solution in the negative electrode are different from each other in that the acid concentration of the positive electrode and the negative electrode is kept balanced even during charging. This is to suppress the movement of.

The electrolytic solution further contains phosphoric acid or phosphate. As phosphoric acid, orthophosphoric acid (H ₃ PO ₄ ) can be used. The phosphoric acid is not limited to orthophosphoric acid, and condensed phosphoric acid such as linear polyphosphoric acid or cyclic metaphosphoric acid may be used. Alternatively, phosphate may be used. As the phosphate, any of polyphosphate, metaphosphate and ultraphosphate may be used. When phosphoric acid or phosphate is contained in the electrolytic solution together with sulfuric acid, the crystal form of the vanadium solid salt is changed as compared with the case where only sulfuric acid is contained. For example, when an electrolytic solution containing sulfuric acid and phosphoric acid or phosphate is used as the positive electrode vanadium solid salt, the number of vanadium solid salt hydrates changes. From this, it is predicted that the crystal form has changed. Further, when an electrolytic solution containing sulfuric acid and phosphoric acid was used for the vanadium solid salt for the negative electrode, as shown in FIG. 2, it was measured by an X-ray diffraction method with an increase in the content of phosphoric acid in the electrolytic solution. It is predicted that the spectrum of vanadium sulfate (III) (V ₂ (SO ₄ ) ₃ .nH ₂ O) is in a broad state and the crystal form is changed. By including an electrolyte containing phosphoric acid or phosphate in the vanadium solid salt, the vanadium solid salt is prevented from becoming a stable crystalline form, and by being in an amorphous form, the electric power of the vanadium solid salt is prevented. The chemical reaction persists. In addition, the cycle characteristics are improved by maintaining the electrochemical reaction of the vanadium solid salt.

The volume molar concentration of phosphoric acid or phosphate in the electrolyte contained in the positive electrode vanadium solid salt or the positive electrode vanadium solid salt composition is preferably 0.20 to 0.66 mol / L, more preferably 0.8. It is 22-0.6 mol / L, More preferably, it is 0.24-0.55 mol / L, Most preferably, it is 0.25-0.46 mol / L.
The volume molar concentration of phosphoric acid or phosphate in the electrolyte contained in the vanadium solid salt for negative electrode or the vanadium solid salt composition for negative electrode is preferably 0.18 to 0.60 mol / L, more preferably 0.8. It is 20-0.55 mol / L, More preferably, it is 0.22-0.50 mol / L, Most preferably, it is 0.23-0.46 mol / L.

  The volume molar concentration of phosphoric acid or phosphate in the electrolytic solution in the positive electrode is 0.20 to 0.66 mol / L, and the volume molar concentration of phosphoric acid or phosphate in the electrolytic solution in the negative electrode is 0.18 to When it is 0.60 mol / L, the solid salt of the positive and negative electrodes is prevented from becoming a stable crystalline form, and the amorphous form is maintained, thereby continuing the electrochemical reaction of the vanadium solid salt. In addition, the cycle characteristics are improved by maintaining the electrochemical reaction of the vanadium solid salt.

  The molar ratio of phosphoric acid or phosphate (sulfuric acid: phosphoric acid or phosphate) to sulfuric acid in the electrolyte contained in the vanadium solid salt for positive electrode is preferably 1: 0.25 to 1: 1.94. More preferably, it is 1: 0.29 to 1: 1.50. More preferably, it is 1: 0.3-1: 1.2, Most preferably, it is 1: 0.33-1: 1.02. Electrochemistry in vanadium solid salt when molar ratio of phosphoric acid or phosphate to sulfuric acid contained in electrolyte contained in vanadium solid salt for positive electrode is in the range of 1: 0.25 to 1: 1.94 It is possible to form a good amorphous form that can sustain a typical reaction. When the molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolyte contained in the positive electrode vanadium solid salt is less than 1: 0.25, the vanadium solid salt can be prevented from becoming a stable crystal form. It is impossible to maintain the electrochemical reaction. If the molar ratio of phosphoric acid or phosphate to sulfuric acid contained in the positive electrode vanadium solid salt exceeds 1: 1.94, the abundance ratio of phosphoric acid increases and the initial capacity of the battery decreases.

  The molar ratio of phosphoric acid or phosphate to sulfuric acid (sulfuric acid: phosphoric acid or phosphate) in the electrolyte contained in the vanadium solid salt for negative electrode is preferably 1: 0.082 to 1: 0.333. More preferably, it is 1: 0.1 to 1: 0.234. When the molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolyte contained in the vanadium solid salt for negative electrode is in the range of 1: 0.082 to 1: 0.333, the electrochemical property in the vanadium solid salt It is possible to form a good amorphous form that can sustain the reaction. If the molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolyte contained in the negative electrode vanadium solid salt is less than 1: 0.082, the vanadium solid salt can be prevented from becoming a stable crystal form. It is impossible to maintain the electrochemical reaction. When the molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolyte contained in the vanadium solid salt for the negative electrode exceeds 1: 0.333, the abundance ratio of phosphoric acid or phosphate increases, and the initial capacity of the battery is increased. Decreases.

  The vanadium solid salt or the composition for vanadium solid salt may further contain a binder. As the binder, a fluorine-based binder, a rubber-based binder, or the like can be used. Fluorine binders include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (EFP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and ethylene / tetrafluoroethylene (ETFE). , Ethylene chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and the like. Examples of the rubber binder include styrene-butadiene rubber (SBR) and ethylene-propylene rubber (EPM). Among these, as the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and styrene-butadiene rubber (SBR) are preferable. A binder may be used individually by 1 type and may use 2 or more types together.

  In the vanadium solid salt or vanadium solid salt composition, the binder is preferably 0.1 to 20% by mass, more preferably 0.1 to 18% by mass, and still more preferably 0 to 100% by mass of the vanadium solid salt. 0.1 to 15% by mass, most preferably 0.1 to 10% by mass. In the vanadium solid salt composition, when the binder content is 0.1 to 20% by mass, the stability of the vanadium solid salt can be improved.

[Composition for vanadium solid salt and method for producing vanadium solid salt]
The composition for vanadium solid salt and the method for producing the vanadium solid salt are not particularly limited. As a vanadium solid salt composition and a method for producing a vanadium solid salt, for example, first, a carbon material powder and a compound containing vanadium ions or a cation containing vanadium are mixed, pulverized as necessary, and powdered. To obtain a mixture of Next, an electrolytic solution is put into the powdery mixture and mixed to obtain a paste-like composition for vanadium solid salt. Furthermore, a binder, other additives, and the like are added to and mixed with the paste-like vanadium solid salt composition as necessary. Thereafter, the paste-like composition for vanadium solid salt can be dried to obtain a vanadium solid salt. The paste-like composition for vanadium solid salt is dried at room temperature (about 20 ° C.) to 180 ° under atmospheric pressure (about 1.01 × 10 ⁵ Pa). When heating to room temperature or higher, for example, a hot plate or the like may be used. Further, the paste-like composition for vanadium solid salt may be dried in a vacuum state. The vacuum state means that the pressure is lower than the atmospheric pressure, and the degree of vacuum is preferably 1 × 10 ⁵ Pa or less. By a general-purpose means such as an aspirator or a vacuum pump, the pressure during drying can be dried in a vacuum state of about 1 × 10 ² Pa to 1 × 10 ⁵ Pa.

〔diaphragm〕
The vanadium solid salt battery includes a diaphragm that partitions a positive electrode and a negative electrode and that allows hydrogen ions (protons) to pass therethrough. Any membrane can be used as long as it can pass hydrogen ions (protons). As the diaphragm, a porous membrane, a nonwoven fabric, or an ion exchange membrane capable of selectively permeating hydrogen ions can be used. Examples of the porous membrane include a polyethylene microporous membrane (manufactured by Asahi Kasei Corporation). Moreover, NanoBase (made by Mitsubishi Paper Industries) etc. can be illustrated as a nonwoven fabric, for example. Examples of the ion exchange membrane include SELEMION (registered trademark) APS (manufactured by Asahi Glass), Neoceptor (registered trademark) CMX (manufactured by Astom).

[Current collector]
For the current collector, conductive rubber, graphite sheet, or the like can be used. The conductive rubber is preferably in the form of a sheet. Although the thickness of conductive rubber or the thickness of a graphite sheet is not specifically limited, Preferably it is 10-150 micrometers, More preferably, it is 20-120 micrometers, More preferably, it is 30-100 micrometers.

[Drawer electrode]
A metal foil can be used for the extraction electrode. Examples of the metal constituting the metal foil include copper, aluminum, silver, gold, nickel, and stainless steel having a low resistance. Among them, the metal foil is preferably an inexpensive copper foil or aluminum foil. Moreover, the thickness of metal foil becomes like this. Preferably it is 10-150 micrometers, More preferably, it is 20-120 micrometers, More preferably, it is 30-100 micrometers.

  As the vanadium solid salt battery, a combination of a current collector and an extraction electrode can be used. For example, a combination of conductive rubber and metal foil or a combination of graphite sheet and metal foil can be used. A combination of a conductive rubber and a metal foil or a combination of a graphite sheet and a metal foil can be suitably used because the resistance can be reduced. When metal is used for the plate constituting the cell, the extraction electrode can be omitted.

〔cell〕
The plate constituting the cell can be made of either conductive or insulating material. A metal plate is preferable as the conductive material. Examples of the metal constituting the metal plate include copper, aluminum, silver, gold, nickel, and stainless steel (SUS303, SUS314, SUS316L, etc.).
Examples of the insulating material include polyethylene, polypropylene, polyvinyl chloride, and engineering plastic.
An insulating material can be used for the mold forming the cell. Examples of the insulating material include polyethylene, polypropylene, polyvinyl chloride, and engineering plastic.

  The vanadium solid salt battery of the present invention contains a specific amount of carbon material powder in which the R value obtained by Raman spectroscopy or the lattice spacing d (d002) measured by the X-ray powder method is a specific value in the vanadium solid salt. Thus, the balance of the redox state of vanadium ions or cations containing vanadium in the positive electrode and the negative electrode can be maintained. By maintaining the balance of the redox state of vanadium ions or cations containing vanadium in the positive electrode and the negative electrode, the capacity retention rate, coulomb efficiency, and energy efficiency of the vanadium solid salt battery can be improved.

  Next, specific embodiments of the present invention will be described by way of examples, but the present invention is not limited to these examples.

(Carbon material powder)
With respect to the following carbon material powder, the R value and the lattice spacing d by the X-ray powder method were measured by Raman spectroscopy. 3 to 5 are No. 3 respectively. The Raman spectrum by the Raman spectroscopy of each carbon material powder of 1-3 is shown. FIGS. The (a) XRD spectrum by the X-ray powder method of each carbon material powder of 1-3 is shown, (b) A half value width (FWHM) is shown. No. Table 3 shows the R value of each of the material powders 1 to 3 by Raman spectroscopy and the lattice spacing d measured by the X-ray powder method.
No. 1: Graphitized carbon black (Toka Black # 3845, manufactured by Tokai Carbon Co., Ltd., arithmetic average particle size (volume cumulative average particle size determined by laser diffraction scattering method) 40 μm)
No. 2: Acetylene black (Denka Black HS-100, manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size 0.048 μm)
No. 3: Ketjen Black (Ketjen Black EC300J, manufactured by Lion Corporation, average particle size of 0.0395 μm)

[Raman spectroscopy]
Measurement by Raman spectroscopy was performed with the following apparatus and conditions.
[apparatus]
・ Laser Raman spectrophotometer NSR-3100 (manufactured by JASCO)
・ Two lasers (532nm, 785nm)
・ Two notch filters ・ Wavelength resolution 1cm ⁻¹ , depth resolution 1μm
Objective lens: x5, x20, x100
・ Automatic XYZ stage (step: 0.1 μm)
・ With polarization measurement attachment [Measurement method]
The sample is filled by letting the particles to be measured naturally fall into the measurement cell, and measurement is performed while rotating the measurement cell in a plane perpendicular to the laser light while irradiating the measurement cell with argon ion laser light. The measurement conditions are as follows.
Wavelength of argon ion laser light: 532 nm, 785 nm
Measurement range: 180 cm ^{−1 to} 3800 cm ⁻¹
Peak intensity measurement, peak half-width measurement: background processing, smoothing processing

[Raman R value]
Definition of the Raman R value in Raman spectrum obtained by Raman spectroscopy, the intensity _{I G} of the maximum peak in the vicinity of 1580 cm ^-1, 1360 cm intensity ratio of the maximum peak intensity _{I D} of around ^-1 _I D / _{I G} Is defined as a Raman R value.

[X-ray powder method]
Measurement by the X-ray powder method was performed with the following apparatus and conditions.
[apparatus]
・ X-ray diffractometer MiniFlex II (Rigaku)
X-ray source: CuKα ray (λ = 0.15148 nm)
-The diffraction intensity is measured every 0.02 [deg.] From 4 [deg.] / Min and 3 [deg.] To 90 [deg.] With the 2 [theta] method.
[Measuring method]
Each carbon material powder is placed in a square glass sample with a side of 20 mm on the bottom and a quartz glass sample cup with a depth of 0.1 mm. 1-No. An appropriate amount of the sample powder 3 was filled and filled with a spatula so that the height coincided with the quartz glass surface. This sample was measured with an X-ray diffractometer.
The lattice spacing d (d002) measured by the X-ray powder method was determined based on the Bragg equation (I) from the peak derived from the c-axis (002) of the diffraction spectrum obtained by the X-ray powder method.
d = λ / (2 × Sinθ _B ) (I)
(Where d is the lattice spacing d (d002), λ is the wavelength of 0.154 nm, and θ _B is the Bragg angle.)

  Table 1 shows graphite, no. 1 (graphitized carbon black (talker black)), No. 1 2 (acetylene black), No. 2 3 (Ketjen black) graphitization temperature, black angle, and lattice spacing d (d002) determined based on the formula (I) of black (Bragg).

Table 2 shows graphite (No.), No. 1 (graphitized carbon black (talker black)), No. 1 2 (acetylene black), No. 2 The graphitization temperature of 3 (Ketjen Black), the black angle, and the crystallite size t (nm) obtained from Scherr's formula (II) are shown.
t = (K × λ) / (B × cos θ _B ) (II)
(Where t is the crystal size (nm), K is a constant (in the case of graphite, K is 0.9), λ is the wavelength of 0.154 nm, and θ _B is the black angle. )

From the results shown in Table 1, no. 1 talker black and No. 1 The acetylene black of 2 is a carbon material powder having an R value obtained by Raman spectroscopy of 1.10 or less and a lattice spacing d (d002) measured by the X-ray powder method of 0.33 to 0.36 nm. It was confirmed that there was.
On the other hand, no. It can be confirmed that the ketjen black of No. 3 does not satisfy the numerical values of the R value obtained by Raman spectroscopy of 1.10 or less and the lattice spacing d measured by the X-ray powder method of 0.33 to 0.36 nm. It was.

(Example)
[Composition for paste-like vanadium solid salt for positive electrode]
Table 4 shows the composition of the vanadium solid salt battery composition for the positive electrode.
For the positive electrode, vanadium oxide (IV) (VOSO ₄ · nH ₂ O) 0.736 g (3.13 mmol) was used as a compound containing vanadium ion or a cation containing vanadium (hereinafter referred to as “vanadium compound”). Using. A mortar made of agate, graphitized carbon black is a carbon material in the formulation shown in Table 4 (Toka Black # 3845, manufactured by Tokai Carbon Co., Ltd.) were charged, further oxidized vanadium sulfate and _{(IV) (VOSO 4 · nH} 2 O) I put it in. In a mortar, vanadium oxide sulfate (IV) (VOSO ₄ · nH ₂ O) and graphitized carbon black were mixed and pulverized to obtain a powdery mixture. To the powdery mixture in the mortar, 1M sulfuric acid and 1M phosphoric acid were added in the formulation shown in Table 4, and kneaded in the mortar to obtain a paste-like composition for vanadium solid salt for the positive electrode.
The molar ratio of phosphoric acid to sulfuric acid contained in the solid salt for positive electrode (sulfuric acid: phosphoric acid) is converted to the molar ratio of sulfuric acid shown in Table 4 as 1. The molar ratio of phosphoric acid to sulfuric acid (sulfuric acid: phosphoric acid) Was 1: 1.02 (0.43: 0.44).
The volume molar concentration of sulfuric acid in the electrolyte contained in the positive electrode vanadium solid salt or the positive electrode vanadium solid salt battery composition shown in Table 4 is 0.5 mol / L.
The volume molar concentration of phosphoric acid in the electrolyte contained in the positive electrode vanadium solid salt or the positive electrode vanadium solid salt battery composition shown in Table 4 is 0.5 mol / L.

[Paste composition for vanadium solid salt for negative electrode]
Table 4 shows the composition of the vanadium solid salt battery composition for the negative electrode.
As the vanadium compound, 0.723 g (3.13 mmol) of vanadium sulfate (III) (V ₂ (SO ₄ ) ₃ .nH ₂ O) was used for the negative electrode. Vanadium (III) sulfate was produced as follows.
After vanadium oxide sulfate is dissolved in sulfuric acid, electrolytic reduction is performed to obtain a trivalent vanadium sulfate solution. This solution was dried under reduced pressure at 200 ° C. to obtain vanadium sulfate (III) (V ₂ (SO ₄ ) ₃ .nH ₂ O).
The obtained vanadium sulfate (III) (V ₂ (SO ₄ ) ₃ · nH ₂ O) and graphitized carbon black (Toka Black # 3845, manufactured by Tokai Carbon Co.) having the composition shown in Table 4 were pulverized together. It grind | pulverized with (commercially available coffee mill). Graphite carbon black and vanadium sulfate (III) are put into an agate mortar, and 1M sulfuric acid and 1M phosphoric acid are added in the composition shown in Table 4, kneaded in the mortar, and paste-like vanadium for the negative electrode. A composition for solid salt was obtained.
When the molar ratio of phosphoric acid to sulfuric acid (sulfuric acid: phosphoric acid) contained in the vanadium solid salt for negative electrode is converted to 1 as the molar number of sulfuric acid shown in Table 4, the molar ratio of phosphoric acid to sulfuric acid (sulfuric acid: phosphoric acid) Was 1: 0.23 (0.042 + 0.137: 0.042).
The volume molar concentration of sulfuric acid in the electrolytic solution contained in the negative electrode vanadium solid salt or the negative electrode vanadium solid salt battery composition shown in Table 4 is 1.99 mol / L.
The volume molar concentration of phosphoric acid in the electrolytic solution contained in the negative electrode vanadium solid salt or the negative electrode vanadium solid salt battery composition shown in Table 4 is 0.46 mol / L.

(Comparative example)
[Composition for paste-like vanadium solid salt for positive electrode]
As the carbon material powder, no. 3: Using ketjen black (Ketjen black EC300J, manufactured by Lion Corporation, average particle size 0.0395 μm), using 0.807 g (3.43 mmol) of vanadium oxide (IV) sulfate (VOSO ₄ · nH ₂ O) A vanadium solid salt composition for a positive electrode of a comparative example was produced in the same manner as in the example except that this was done. Table 5 shows the composition of the composition for vanadium solid salt for the positive electrode of the comparative example.
Regarding the molar ratio of phosphoric acid to sulfuric acid contained in the solid salt for positive electrode (sulfuric acid: phosphoric acid), when the molar number of sulfuric acid shown in Table 5 is converted to 1, the molar ratio of phosphoric acid to sulfuric acid (sulfuric acid: phosphoric acid) Was 1: 1.02 (0.43: 0.44).
The volume molar concentration of sulfuric acid in the electrolytic solution contained in the positive electrode vanadium solid salt or the positive electrode vanadium solid salt battery composition shown in Table 5 is 0.5 mol / L.
The volume molar concentration of phosphoric acid in the electrolyte contained in the positive electrode vanadium solid salt or the positive electrode vanadium solid salt battery composition shown in Table 5 is 0.5 mol / L.
[Paste-like vanadium solid salt composition for negative electrode]
As the carbon material powder, no. 3: Ketjen Black (Ketjen Black EC300J, manufactured by Lion, average particle size 0.0395 μm) was used, and vanadium sulfate (III) (V ₂ (SO ₄ ) ₃ .nH ₂ O) 0.792 g (1. A composition for a vanadium solid salt for a negative electrode of a comparative example was produced in the same manner as in the example except that 57 mmol) was used. Table 5 shows the composition of the vanadium solid salt composition for the negative electrode of the comparative example.
When the molar ratio of phosphoric acid to sulfuric acid contained in the vanadium solid salt for negative electrode (sulfuric acid: phosphoric acid) is converted to the number of moles of sulfuric acid shown in Table 5 as 1, the molar ratio of phosphoric acid to sulfuric acid (sulfuric acid: phosphoric acid) Was 1: 0.23 (0.042 + 0.137: 0.042).
The volume molar concentration of sulfuric acid in the electrolytic solution contained in the negative electrode vanadium solid salt or the negative electrode vanadium solid salt battery composition shown in Table 5 is 1.97 mol / L.
The volume molar concentration of phosphoric acid in the electrolytic solution contained in the negative electrode vanadium solid salt or the negative electrode vanadium solid salt battery composition shown in Table 5 is 0.46 mol / L.

The theoretical capacity of the positive electrode and the theoretical capacity of the negative electrode were calculated as follows, and the theoretical capacity of the battery was further calculated.
Theoretical capacity of the positive electrode: Number of moles of active material of the positive electrode × Faraday constant (c / mol) / (60 × 60) (i)
(Molar concentration of vanadium (number of moles of V) in vanadium solid salt battery composition for positive electrode: Example 3.13 mmol, Comparative example 3.43 mmol)
Theoretical capacity of the negative electrode: Number of moles of active material of the negative electrode × Faraday constant (c / mol) / (60 × 60) (ii)
(Molar concentration of vanadium (number of moles V) of vanadium solid salt battery composition for negative electrode: Example 3.13 mmol Comparative example 3.43 mmol)
The theoretical capacity of the battery: The numerical value of the smaller theoretical capacity of the positive electrode and theoretical capacity of the negative electrode (iii)
The theoretical capacity of the vanadium solid salt battery of the example was 84 mAh, and the theoretical capacity of the vanadium solid salt battery of the comparative example was 92 mAh.

[Vanadium solid salt battery]
The vanadium solid salt battery of the example was manufactured as follows.
As shown in FIG. 1, in the positive electrode 7, a first extraction electrode 9 was placed on a first cell plate 11a constituting the cell, and a first current collector 5 was placed thereon. Next, the first mold 12 a was installed on the first current collector 5. Furthermore, the 1st formwork 12a was filled with the vanadium solid salt composition for paste-like positive electrodes, and it was set as the vanadium solid salt 2 for positive electrodes.

  In the negative electrode 8 of the vanadium solid salt battery 1, first, the second extraction electrode 10 was placed on the second cell plate 11b constituting the cell, and the second current collector 6 was placed thereon. Next, the second mold 12 b was installed on the second current collector 6. Further, the paste-like vanadium solid salt composition constituting the negative electrode vanadium solid salt 3 was filled in the second mold 12b to obtain the negative electrode vanadium solid salt 3.

  The vanadium solid salt battery 1 has a diaphragm 4 sandwiched between a vanadium solid salt 2 for positive electrode and a vanadium solid salt 3 for negative electrode, and six screws around the first cell plate 11a and the second cell plate 11b. 13 was fixed evenly by tightening.

The material which comprises the vanadium solid salt battery 1 is as follows.
Cell plate: circular SUS (314) plate mold having a thickness of 3 mm and a diameter of 50 mm: Formwork current collector having a hole having a diameter of 20 mm in the center of a circular shape having a thickness of 1 mm and a diameter of 30 mm: thickness of 40 μm Graphite sheet (manufactured by Kaneka)
Extraction electrode: A copper foil having a thickness of 50 μm was used.
Diaphragm: Ion exchange membrane Neoceptor CMX (made by Astom)

[Coulomb efficiency]
About the vanadium solid salt battery of an Example and a comparative example, charging / discharging capacity | capacitance was measured using the charging / discharging measuring apparatus (TOSCAT-3500 (charge / discharge evaluation apparatus), the Toyo System Co., Ltd. make, battery cell normal temperature).
Number of cycles 1 and 2
Charging conditions: constant current (CC) charge 10mA (upper limit 1.6V)
Discharge condition: constant current (CC) discharge 10 mA (lower limit 0.8 V)
Number of cycles 3
Charging conditions: constant current (CC) charge 10mA (upper limit 1.65V)
Discharge condition: constant current (CC) discharge 10 mA (lower limit 0.8 V)
Number of cycles 4
Charging conditions: constant current (CC) charge 10mA (upper limit 1.7V)
Discharge condition: constant current (CC) discharge 10 mA (lower limit 0.8 V)
First, charging was started at a constant current (10 mA), and charging was completed (cut off) when the voltage reached the upper limit. Thereafter, discharge was started at a constant current (10 mA), and the time when the voltage reached 0.8 V was regarded as the completion of discharge (cut-off).
The energy efficiency was calculated from the charge / discharge capacity (mAh) in each cycle as follows. Coulomb efficiency was calculated as follows.
Coulomb efficiency (%) = discharge capacity (mAh) / charge capacity (mAh) in each cycle × 100

  9 and 10 show measurement results of charge capacity and discharge capacity in each cycle. Table 6 shows the discharge capacity (mAh), the charge capacity (mAh), and the Coulomb efficiency (%) calculated from the discharge capacity (mAh) and the charge capacity (mAh) in each cycle of the example. Table 7 lists the discharge capacity (mAh), the charge capacity (mAh), and the Coulomb efficiency (%) calculated from the discharge capacity (mAh) and the charge capacity (mAh) in each cycle of the comparative example.

  From the results shown in FIG. 9 and Table 6, the vanadium solid salt battery of the example (using graphitized carbon black) can obtain a Coulomb efficiency of nearly 100% even when the charge cut potential is increased to 1.7 V (number of cycles 4). ing. On the other hand, from the results shown in FIG. 10 and Table 7, the vanadium solid salt battery of the comparative example (using ketjen black) had low Coulomb efficiency. In addition, the vanadium solid salt battery of the comparative example (using ketjen black) exhibited capacity deterioration with the number of cycles up to the charge cut potential, 1.6 V, and 1.65 V. However, when the battery was charged to a charge cut potential of 1.7 V (number of cycles: 4), the discharge capacity increased rapidly, and the coulomb efficiency exceeded 100%.

[Capacity maintenance rate]
For the vanadium solid salt batteries of Examples and Comparative Examples, the initial discharge capacity was determined using a charge / discharge measuring device (model number / name: TOSCAT-3500 (charge / discharge evaluation device), manufactured by Toyo System Co., Ltd., battery cell at room temperature). It was measured. Subsequently, charge / discharge of 5 cycles was repeated on the same conditions, and the discharge capacity of the 5th cycle with respect to 100% of initial discharge capacity was made into the capacity maintenance rate.
Charging conditions: constant current (CC) charge 10mA (upper limit 1.7V)
Discharge condition: constant current (CC) discharge 10 mA (lower limit 0.8 V)
In FIG. 11, the result of the charge / discharge capacity | capacitance (capacity / mAh-voltage / V relationship) from the initial discharge capacity to 5 cycles of the vanadium solid salt battery of an Example is shown. The capacity retention rate after 5 cycles of the vanadium solid salt battery of the example was 91%.
FIG. 12 shows the results of charge / discharge capacity (capacity / mAh−voltage / V relationship) from the initial discharge capacity to 5 cycles of the vanadium solid salt battery of the comparative example. The capacity retention rate after 5 cycles of the vanadium solid salt battery of the comparative example was 60%.

[Energy efficiency (%)]
About the vanadium solid salt battery of an Example and a comparative example, Coulomb efficiency is measured using a charging / discharging measuring device (model number and name: TOSCAT-3500 (charging / discharging evaluation device), manufactured by Toyo System Co., Ltd., battery cell at room temperature). The amount of charge / discharge power (mWh) was measured under the same conditions as described above. The energy efficiency was calculated from the charge / discharge power amount (mWh) in each cycle as follows.
Energy efficiency (%) = discharge power amount (mWh) / charge power amount (mWh) × 100 in each cycle

  Table 8 describes the charging power amount (mWh), the discharging power amount (mWh), and the energy efficiency (%) calculated from the charging power amount (mWh) and the discharging power amount (mWh) in each cycle of the example. . Table 7 describes the amount of charge power (mWh), the amount of discharge power (mWh), and the energy efficiency (%) calculated from the amount of charge power (mWh) and the amount of discharge power (mWh) in each cycle of the comparative example. .

  As shown in FIG. 11, the capacity retention rate after 5 cycles of the vanadium solid salt battery of the example is 91%, whereas, as shown in FIG. 12, the vanadium solid salt battery of the comparative example after 5 cycles. The capacity retention rate was 60%. From this result, it was found that the capacity retention rate of the vanadium solid salt battery of the present invention was improved.

  From the results shown in Table 8, the vanadium solid salt batteries of Examples (using graphitized carbon black) have a charge cut potential of 1.6 V (cycle numbers 1 and 2), 1.65 V (cycle number 3), 1.7 V ( Even when the battery was charged up to the number of cycles 4), the energy efficiency exceeded 75%, and high energy efficiency was maintained. On the other hand, from the results shown in Table 9, the vanadium solid salt battery of the comparative example (using ketjen black) has energy efficiency at charge cut potentials of 1.6 V (cycle numbers 1 and 2) and 1.65 V (cycle numbers). It was below 60%.

  The vanadium solid salt battery of the example (using graphitized carbon black) seems to be able to withstand high voltage charge / discharge, which is due to the difference in the degree of graphitization due to the carbon treatment temperature. Among graphite carbon black and ketjen black, the graphite carbon black has a higher degree of graphitization (crystallinity), so the overvoltage of water electrolysis increased.

  The present invention includes a vanadium ion in a positive electrode and a negative electrode by containing a specific amount of carbon material powder having a specific value in the lattice spacing d measured by the R value and X-ray powder method determined by Raman spectroscopy in the vanadium solid salt. Alternatively, the balance of the redox state of the cation containing vanadium can be maintained. The present invention can improve the capacity retention rate, coulomb efficiency, and energy efficiency of a vanadium solid salt battery by maintaining the balance of the redox state of vanadium ions or cations containing vanadium in the positive electrode and the negative electrode. . Vanadium solid salt batteries are used not only in the large power storage field, but also in personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, electrical appliances, vehicles, wireless devices, mobile phones, etc. It can be widely used and is industrially useful.

DESCRIPTION OF SYMBOLS 1 Vanadium solid salt battery 2 Vanadium solid salt for positive electrodes 3 Vanadium solid salt for negative electrodes 4 Membrane 5 First current collector 6 Second current collector 7 Positive electrode 8 Negative electrode 9 First extraction electrode 10 Second extraction Electrode 11a First cell plate 11b Second cell plate 12a First mold 12b Second mold 13 Screw

Claims (5)

Vanadium ions and / or vanadium containing ions, an electrolyte, and a vanadium solid salt containing a carbon material are included in the positive electrode and the negative electrode,
The carbon material of the positive electrode has an R value obtained by Raman spectroscopy of 1.10 or less, or a lattice spacing d (d002) measured by an X-ray powder method of 0.33 to 0.36 nm. Carbon material powder,
The vanadium solid salt battery of the positive electrode has a carbon material content of 1 to 42% by mass.   The electrolytic solution contains sulfuric acid, and the volume molar concentration of sulfuric acid in the electrolytic solution contained in the positive electrode vanadium solid salt is 0.34 to 0.80 mol / L, and in the electrolytic solution contained in the negative electrode vanadium solid salt The vanadium solid salt battery according to claim 1, wherein the molar concentration of sulfuric acid is 1.83 to 2.24 mol / L.   The electrolyte contains phosphoric acid or phosphate, and the volume molar concentration of phosphoric acid or phosphate in the electrolyte contained in the positive electrode vanadium solid salt is 0.20 to 0.66 mol / L, The vanadium solid salt battery according to claim 1 or 2, wherein a volume molar concentration of phosphoric acid or a phosphate in the electrolyte contained in the vanadium solid salt is 0.18 to 0.60 mol / L. The molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolyte contained in the positive electrode vanadium solid salt is 1: 0.25 to 1: 1.94,
The vanadium solid salt battery according to claim 3, wherein the molar ratio of phosphoric acid or phosphate to sulfuric acid in the electrolyte contained in the negative electrode vanadium solid salt is 1: 0.082 to 1: 0.333.   The vanadium solid salt battery according to any one of claims 1 to 4, further comprising a binder in at least one of the positive electrode vanadium solid salt and the negative electrode vanadium solid salt.

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