JP5454265B2 - Pseudo capacitance capacitor - Google Patents

Description

  The present invention relates to a pseudo capacitance capacitor.

Conventionally, so-called electric double layer capacitors using electric double layer capacitance have been put to practical use as electrochemical capacitors, but development of pseudo capacitance capacitors using capacitance (pseudo capacitance) stored by the redox reaction of the active material. Various studies have also been conducted. The electric double layer capacitor has a low energy density (unit: Whkg ⁻¹ ), but can store and release charges instantaneously, and therefore has an extremely high output density (unit: Wkg ⁻¹ ). On the other hand, a pseudo-capacitor that can store charges by a redox reaction of an active material on an electrode has a higher energy density and a relatively higher output density than an electric double layer capacitor.

  In recent years, several pseudo-capacitance capacitors have been proposed which are designed to have a higher capacity using electrodes. For example, Patent Document 1 proposes to use an electrode in which ruthenium hydroxide hydrate is highly dispersed in a carbon electrode instead of ruthenium oxide. Patent Document 2 proposes to use an electrode in which a conductive polymer is mixed with manganese oxide, and Patent Document 3 proposes to use an electrode containing a manganese-zinc composite oxide.

JP 2000-36441 A Japanese Patent Laying-Open No. 2005-223089 JP 2009-182079 A

Incidentally, since the energy density W of the capacitor is generally expressed by W = 1/2 CV ² , in order to improve the energy density W, it is conceivable to improve the operating voltage V in addition to the improvement of the capacitance C. However, since the pseudo-capacitors of Patent Documents 1 to 3 use an aqueous electrolyte, they can be used only in a voltage range in which water does not cause electrolysis, and the operating voltage cannot be increased. There was a problem.

  The present invention has been made to solve such problems, and in a pseudo-capacitor using an aqueous electrolyte, it is possible to charge and discharge at an operating voltage exceeding the theoretical voltage of water electrolysis. Main purpose.

In order to achieve the above-described object, the present inventors have immersed a positive electrode containing MnO ₂ in an aqueous lithium hydroxide solution, immersed a negative electrode made of metal Li in a hydrophobic ionic liquid in which a lithium salt is dissolved, A pseudo-capacitance capacitor was prepared by separating an aqueous lithium oxide solution and a hydrophobic ionic liquid into two phases, and it was found that charge and discharge were possible at a voltage exceeding 3 V, and the present invention was completed.

That is, the first pseudo capacitance capacitor of the present invention is
A positive electrode containing a metal oxide immersed in an aqueous electrolyte containing lithium ions and capable of reversible redox change;
A negative electrode immersed in a non-aqueous electrolyte containing lithium ions and capable of absorbing and releasing lithium ions;
Including
The aqueous electrolytic solution and the non-aqueous electrolytic solution exist in a separated state or are separated by a lithium ion conductive solid electrolyte plate.

The second pseudo-capacitor of the present invention is
A positive electrode containing a metal oxide immersed in an aqueous electrolyte containing lithium ions and capable of reversible redox change;
A negative electrode capable of inserting and extracting lithium ions;
Including
The aqueous electrolyte and the negative electrode are separated by a solid electrolyte plate having lithium ion conductivity and water permeability.

  In the first or second pseudocapacitor of the present invention, reversible redox change of the metal oxide occurs on the positive electrode side, and charging and discharging are caused by a reaction in which lithium ions are occluded and released on the negative electrode side. . For this reason, a theoretically large capacity | capacitance is anticipated compared with an electrical double layer capacitor. Further, since water is present on the positive electrode side but not on the negative electrode side, charging and discharging can be performed with an operating voltage exceeding the theoretical voltage (about 1.2 V) of water electrolysis.

FIG. 3 is a cross-sectional view illustrating a configuration of an evaluation cell 10. Sectional drawing showing the structure of the evaluation cell 60. FIG. A photograph showing a state in which an aqueous electrolyte and a non-aqueous electrolyte are separated. The charge / discharge curve of Example 1. FIG. The cycle characteristic curve of Example 1. FIG. The charging / discharging curve of Example 4. The charge / discharge curve of Comparative Example 1.

  The first pseudo-capacitor of the present invention is immersed in an aqueous electrolyte containing lithium ions, immersed in a non-aqueous electrolyte containing a positive electrode containing a metal oxide capable of reversible redox change, and lithium ions, A negative electrode capable of inserting and extracting lithium ions, and the aqueous electrolyte solution and the non-aqueous electrolyte solution are separated or separated by a lithium ion conductive solid electrolyte plate Is. The second pseudo-capacitor of the present invention includes a positive electrode including a metal oxide that is immersed in an aqueous electrolyte containing lithium ions and capable of reversible redox change, and a negative electrode capable of inserting and extracting lithium ions. The aqueous electrolyte solution and the negative electrode are separated by a solid electrolyte plate having lithium ion conductivity and water permeability.

  In the first and second pseudocapacitors of the present invention, the positive electrode is a mixture of a metal oxide capable of reversible redox change, a conductive material, and a binder, and the mixture is formed using a molding apparatus. Applying and drying a paste-like positive electrode material on the surface of the current collector, which is formed by pressing the sheet into the surface of the current collector, or adding a suitable solvent to the mixture Correspondingly, it may be compressed and formed to increase the electrode density.

  Here, as the metal oxide capable of reversible redox change, for example, at least one metal selected from the group consisting of Ru, Mn, W, Co, Ni, Sn, Mo, In, Ti and V is used. The oxide of this is mentioned. Among these, an oxide of at least one metal selected from the group consisting of Ru, Mn, W and Co is preferable. Examples of the conductive material include graphite such as natural graphite (scale-like graphite, scale-like graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum). , Silver, gold, etc.) or a mixture of two or more thereof can be used. Among these, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. As a binder, it plays a role of anchoring carbon material particles and conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resins such as fluorine rubber, or polypropylene , Thermoplastic resins such as polyethylene, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Current collectors include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, and aluminum, copper, etc. for the purpose of improving adhesion, conductivity, and oxidation resistance. A surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and formed fiber group.

  In the first and second pseudocapacitance capacitors of the present invention, the negative electrode may be used after processing, for example, metallic lithium into an appropriate size as it is. Alternatively, a lithium compound (lithium alloy, lithium transition metal nitride, lithium transition metal oxide, etc.), a conductive material, and a binder are mixed, and the mixture is formed into a sheet using a molding device. Applying and drying on the surface of the current collector a paste-like positive electrode material that is formed by pressing on the surface or adding a suitable solvent to the mixture, and compressing it as necessary to increase the electrode density You may use what was formed. Alternatively, a carbon material may be used instead of the lithium compound.

  Here, examples of the lithium alloy include a lithium-aluminum alloy, a lithium-zinc alloy, a lithium-tin alloy, and a lithium-silicon alloy. Examples of the transition metal contained in the lithium transition metal nitride or the lithium transition metal oxide include Fe, Co, Ni, Cu, etc. Among these, Co is preferable. The carbon material is not particularly limited as long as it can intercalate lithium ions. For example, activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon Examples thereof include fibers. Of these, graphites such as natural graphite (scale-like graphite, scale-like graphite) and artificial graphite, and activated carbons having a high specific surface area are preferable. In addition, as the conductive material and the binder, those exemplified for the positive electrode can be used. The negative electrode current collector includes copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., as well as improved adhesion, conductivity and reduction resistance. For the purpose, for example, a copper surface treated with carbon, nickel, titanium, silver or the like can be used. For these, the surface can be oxidized. The shape of the current collector can be the same as that of the positive electrode.

  In the first and second pseudocapacitors of the present invention, examples of the aqueous electrolyte containing lithium ions include an aqueous solution in which lithium hydroxide or a lithium salt is dissolved. Examples of the lithium salt include lithium nitrate, lithium sulfate, and lithium acetate.

In the first pseudocapacitor of the present invention, examples of the non-aqueous electrolyte containing lithium ions include a non-aqueous electrolyte in which a lithium salt is dissolved. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSiF ₆ , LiAlF ₄ , LiSCN, Examples include LiClO ₄ , LiCl, LiF, LiBr, LiI, and LiAlCl ₄ . The lithium salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. Moreover, it is preferable that a non-aqueous electrolyte solution is hydrophobic. Examples of the hydrophobic nonaqueous electrolytic solution include a hydrophobic ionic liquid, and examples thereof include an ionic liquid having a counter anion of TFSI ((trifluoromethanesulfonyl) imide). Specifically, N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (abbreviation: PP13TFSI), 1-ethyl-3-methyl-imidazolium bis (trifluoromethanesulfonyl) imide (abbreviation: EMITFSI) N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide (abbreviation: TMPATFSI), N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) ) Imide and the like. Of these, PP13TFSI is preferred.

In the first and second pseudo-capacitors of the present invention, Li _{1 + X} Ti ₂ Si _x P ₃ -xO ₁₂ .AlPO ₄ (abbreviation: LICGC, OHARA glass) is used as the lithium ion conductive solid electrolyte plate. In addition to Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (abbreviation: LAGP), garnet-type oxides Li ₇ La ₃ Zr ₂ O ₁₂ , LiPON, and the like can be given. In the second pseudocapacitor of the present invention, when metallic lithium or a lithium alloy is used as the negative electrode, the negative electrode may be laminated on one surface of such a solid electrolyte plate by a film forming technique such as vapor deposition, sputtering, or CVD.

  The shape of the first and second pseudo-capacitance capacitors of the present invention is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Moreover, you may apply to the large sized thing etc. which are used for an electric vehicle etc.

  Now, a preferred embodiment of the present invention will be described. FIG. 1 is a cross-sectional view of an evaluation cell 10 which is an example of a first pseudocapacitor of the present invention, and FIG. 2 is a cross-sectional view of an evaluation cell 60 which is an example of a second pseudocapacitor of the present invention.

  In the evaluation cell 10, a resin-made cylindrical case 16 is disposed between a ring-like positive electrode side current collector 12 made of SUS and a disk-like negative electrode side current collector 14 made of SUS. The capacitor structure 20 is provided in the center hole 16a. The capacitor structure 20 includes a positive electrode 22 that closes the upper opening of the center hole 16a, a negative electrode 24 that is located on the negative electrode side current collector 14 and within the lower opening of the center hole 16a, and a step 16b in the middle stage of the center hole 16a. A solid electrolyte plate 26 held in the center hole 16a, a first liquid chamber 28 formed between the positive electrode 22 and the solid electrolyte plate 26 in the center hole 16a and filled with an aqueous electrolyte, and a negative electrode 24 in the center hole 16a. And a second liquid chamber 30 formed between the solid electrolyte plate 26 and filled with a non-aqueous electrolyte solution. The positive electrode 22 is an electrode containing a metal oxide capable of redox change, and the outer peripheral edge is sandwiched between the case 16 and the positive electrode side current collector 12. The negative electrode 24 is an electrode capable of inserting and extracting lithium ions, and an outer peripheral edge thereof is fixed on the negative electrode current collector 14. The solid electrolyte plate 26 plays a role of preventing lithium ions from conducting contact with the aqueous electrolyte and the negative electrode 24, and is pressed by a pressing ring 17 that also serves as a sealing material. The aqueous electrolytic solution is an aqueous solution containing lithium ions, and the non-aqueous electrolytic solution is preferably an organic solvent or ionic liquid that contains lithium ions and is hydrophobic and does not mix with water. If the aqueous electrolyte solution and the non-aqueous electrolyte solution are not mixed and separated, the solid electrolyte plate 26 may be omitted. Although not shown, the positive electrode side current collector 12 and the negative electrode side current collector 14 are pressed in directions approaching each other.

  According to this evaluation cell 10, since a reversible redox change of the metal oxide occurs on the positive electrode side, and lithium ions are occluded / released on the negative electrode side, charging and discharging are performed, compared with the electric double layer capacitor. Theoretically large capacity is expected. Further, since water is present on the positive electrode side but not on the negative electrode side, charging and discharging can be performed with an operating voltage exceeding the theoretical voltage (about 1.2 V) of water electrolysis.

  In the evaluation cell 60, the same components as those of the evaluation cell 10 are denoted by the same reference numerals, and the description thereof is omitted. In this evaluation cell 60, the negative electrode 24 is vapor-deposited and integrated on the back surface of the solid electrolyte plate 76. In addition, the second liquid chamber does not exist in the center hole 16 a, and the first liquid chamber 78 is formed between the positive electrode 22 and the solid electrolyte plate 76. The first liquid chamber 78 is filled with an aqueous electrolyte (an aqueous solution containing lithium ions). The solid electrolyte plate 76 plays a role of preventing the contact between the aqueous electrolyte and the negative electrode 24 in addition to the role of conducting lithium ions.

  Also in this evaluation cell 60, since reversible redox change of the metal oxide occurs on the positive electrode side, and lithium ions are occluded / released on the negative electrode side, charging and discharging are performed. Large capacity is expected. Further, since water is present on the positive electrode side but not on the negative electrode side, charging and discharging can be performed with an operating voltage exceeding the theoretical voltage (about 1.2 V) of water electrolysis.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

[Example 1]
As an evaluation cell of Example 1, a cell having a structure in which the solid electrolyte plate 26 is omitted from the evaluation cell 10 (see FIG. 1) was produced. A MnO ₂ electrode was used as the positive electrode 22, a metal Li electrode was used as the negative electrode 24, a 0.3M LiOH aqueous solution was used as the aqueous electrolyte, and 0.3M LiTFSI / PP13TFSI was used as the non-aqueous electrolyte. Moreover, the aqueous electrolyte solution and the non-aqueous electrolyte solution were put in the same container beforehand, and it was confirmed that both did not mix (refer FIG. 3).

The MnO ₂ electrode was produced as follows. First, 0.5 L of 0.5 M oxalic acid aqueous solution was dropped into 1 L of 0.25 M manganese acetate aqueous solution while stirring to prepare a manganese oxalate slurry. Then, it filtered, wash | cleaned, dried, and heat-processed at 270 degreeC, and obtained the manganese dioxide powder. The obtained powder was mixed with acetylene black and PVDF powder in a ratio of 75:15:10, kneaded in a mortar, formed into a sheet using a molding apparatus, and punched out with a punch to prepare a disk sheet having a diameter of 12 mm. Finally, this sheet was pressed against a stainless mesh to obtain a MnO ₂ electrode. Moreover, the metal Li electrode was produced as follows. That is, a Li metal plate (Honjo Metal) was punched out with a punch to obtain a metal sheet electrode in the form of a disk sheet having a diameter of 12 mm.

The evaluation cell of Example 1 was charged and discharged at a current density of 0.1 mA / cm ² as shown in Table 1. As shown in FIG. 4, linearity was maintained well up to 3.4 V. . Further, when charging up to 3.6 V, linearity was somewhat lost, but no particular problem was found. Thus, it was found that the operating voltage can be increased to about 3.4 to 3.6 V, which greatly exceeds the theoretical voltage (about 1.2 V) at which water causes electrolysis. Since the energy density W of the capacitor is generally expressed by W = 1/2 CV ² , it can be said that the energy density W of the evaluation cell of Example 1 is higher than that of a conventional pseudo-capacitor using an aqueous electrolyte. In addition, when charging / discharging at a current density of 0.1 mA / cm ² and a voltage of 3.4 V was repeated 12 times, as shown in FIG. 5, the characteristics hardly changed and good cycle characteristics were exhibited.

[Example 2]
As an evaluation cell of Example 2, a cell using a RuO ₂ electrode instead of the MnO ₂ electrode of the evaluation cell of Example 1 was prepared. The RuO ₂ electrode was produced as follows. First, 50 mL of ruthenium chloride aqueous solution (Ru20 g / L) is neutralized with 40 mL of ammonia water (10 mL / sec, dropwise) to prepare fine particles of ruthenium hydroxide (pH 7.7), and the resulting fine particles are washed. And dried to obtain ruthenium oxide powder. The obtained powder was mixed with acetylene black and PVDF powder in a ratio of 75:15:10, kneaded in a mortar, formed into a sheet using a molding apparatus, and punched out with a punch to prepare a disk sheet having a diameter of 12 mm. It was pressed against a stainless mesh to form a RuO ₂ electrode.

[Example 3]
As an evaluation cell of Example 3, an evaluation cell 10 (see FIG. 1) was produced. Here, a MnO ₂ electrode is used as the positive electrode 22, a LiCoN electrode is used as the negative electrode 24, LICGC (Ohara glass) is used as the solid electrolyte plate 26, a 0.3M LiOH aqueous solution is used as the aqueous electrolyte, and 0.3M LiTFSI / PP13TFSI is used as the non-aqueous electrolyte. did. The LiCoN electrode was produced as follows. First, Li ₃ N and metal Co were mixed at a predetermined ratio, the mixed powder was put into a crucible, and a reaction treatment was performed in a nitrogen atmosphere (700 ° C., 5 h). Thereafter, the obtained fired body was pulverized to obtain nitride particles. Using these nitride particles, nitride particles, acetylene black and PVDF powder were mixed, kneaded and formed into a sheet at a ratio of 85: 5: 10 and punched out with a punch to produce a disk sheet-like LiCoN electrode of φ12 mm. . These series of operations were performed in a glove box. LICGC also serves to prevent the aqueous electrolyte from coming into contact with the non-aqueous electrolyte or the negative electrode 24.

[Example 4]
As an evaluation cell of Example 4, an evaluation cell 60 (see FIG. 2) was produced. Here, a MnO ₂ electrode was used as the positive electrode 22, a vapor deposition Li electrode was used as the negative electrode 24, LICGC (Ohara Glass) was used as the solid electrolyte plate 76, and a 0.3 M LiOH aqueous solution was used as the aqueous electrolyte. The vapor deposition Li metal electrode was produced by vapor-depositing metal Li on one surface of the solid electrolyte plate 76 using a vapor deposition apparatus capable of performing vapor deposition in a glove box. LICGC also serves to prevent the aqueous electrolyte from contacting the negative electrode 24.

[Comparative Example 1]
As an evaluation cell of Comparative Example 1, the positive electrode and the negative electrode of the evaluation cell of Example 1 were MnO ₂ electrodes, and only the aqueous electrolyte solution (0.3 M LiOH aqueous solution) was used without using the non-aqueous electrolyte solution. The same evaluation cell as 1 was prepared.

As shown in Table 1, the evaluation cells of Examples 2 to 4 and Comparative Example 1 were charged and discharged at a current density of 0.1 mA / cm ² (in Example 4, 0.02 mA / cm ² ). As a result, in Examples 2 to 4, as in Example 1, good results were obtained up to a voltage of 3.4 V. FIG. 6 shows a charge / discharge curve of the evaluation cell of Example 4. On the other hand, in Comparative Example 1, charging / discharging was possible up to a voltage of about 1 V, but the charging curve was slightly rounded and characteristic degradation was observed. The state at that time is shown in FIG.

  The pseudo-capacitor of the present invention can be used as a power source for a hybrid vehicle or an electric vehicle, for example.

DESCRIPTION OF SYMBOLS 10 Evaluation cell, 12 Positive electrode side collector, 14 Negative electrode side collector, 16 Case, 16a Center hole, 16b Level difference, 20 Capacitor structure, 22 Positive electrode, 24 Negative electrode, 26 Solid electrolyte board, 28 1st liquid chamber, 30 Second liquid chamber, 60 evaluation cell, 76 solid electrolyte plate, 78 First liquid chamber

Claims (4)

A positive electrode containing a metal oxide immersed in an aqueous electrolyte containing lithium ions and capable of reversible redox change;
A negative electrode immersed in a non-aqueous electrolyte containing lithium ions and capable of absorbing and releasing lithium ions;
Including
The aqueous electrolyte and the non-aqueous electrolyte are present in a separated state or separated by a lithium ion conductive solid electrolyte plate,
Pseudo capacitance capacitor. The non-aqueous electrolyte is a hydrophobic ionic liquid,
The pseudo capacitance capacitor according to claim 1. A positive electrode containing a metal oxide immersed in an aqueous electrolyte containing lithium ions and capable of reversible redox change;
A negative electrode capable of inserting and extracting lithium ions;
Including
The aqueous electrolyte and the negative electrode are separated by a solid electrolyte plate having lithium ion conductivity and water permeability,
Pseudo capacitance capacitor. The metal oxide is ruthenium oxide, manganese oxide, tungsten oxide or cobalt oxide.
The pseudo-capacitor according to any one of claims 1 to 3.