JP2012221885A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new power storage device using anions as carriers.SOLUTION: The power storage device comprises a positive electrode, a negative electrode including a composite of a nitrogen-containing organic polymer supporting anions and a Si sheet having a basic skeleton composed of a chain of six-membered rings of silicon atoms, and an ion conducting medium intervening between the positive electrode and the negative electrode and conducting anions, and is charged and discharged by migration of anions. In the negative electrode, the composite may contain a nitrogen-containing organic polymer having a branched structure. In addition, the negative electrode may contain polyethylenimine as the nitrogen-containing organic polymer.

Description

  The present invention relates to an electricity storage device.

Conventionally, as an electricity storage device, a secondary electrochemical cell using an anion charge carrier that can be accommodated by a positive electrode and a negative electrode containing an anion host material, CF as a positive electrode, a metal such as La as a negative electrode, and F ⁻ as an anion. The one to be used has been proposed (see, for example, Patent Document 1).

Special table 2009-529222

  However, in the electricity storage device of Patent Document 1 described above, an anion-supporting material is used for the positive electrode and a metal is used for the negative electrode, discharge is the negative electrode, and charging is a battery system in which a chemical reaction proceeds at the positive electrode. Therefore, problems may occur in cycle characteristics and rate characteristics, and the development of new power storage devices has been desired.

  This invention is made | formed in view of such a subject, and it aims at providing the novel electrical storage device which uses an anion as a carrier.

  As a result of diligent research to achieve the above-described object, the present inventors have found that when an anion is supported on a nitrogen-containing organic polymer and combined with an Si sheet, charging and discharging can be performed using the anion as a carrier, The present invention has been completed.

  That is, the electricity storage device of the present invention comprises a composite comprising a positive electrode, a nitrogen-containing organic polymer supporting an anion, and a Si sheet having a basic skeleton having a structure in which a plurality of six-membered rings composed of silicon atoms are connected. And an ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts the anion, and is charged and discharged by movement of the anion.

  The electricity storage device of the present invention can be charged and discharged using anions as carriers. The reason why such an effect is obtained is not clear, but is presumed as follows. For example, in an electricity storage device in which a composite is manufactured using a carbon material for the positive electrode and polyethyleneimine for the negative electrode, the negative electrode reaction can be represented by the following formula (1), and the positive electrode reaction can be represented by the following formula (2). . In charging, the anion supported on the negative electrode moves to the positive electrode, and in discharging, the anion held on the positive electrode moves again to the negative electrode. As described above, it is presumed that the anion as a carrier moves and acts as an electricity storage device.

The schematic diagram which shows the operation | movement principle of the electrical storage device of this invention. The schematic diagram which shows an example of the composite_body | complex of Si sheet | seat and nitrogen-containing organic polymer. The schematic diagram of layered polysilane containing a Si sheet. IR spectrum of the complex. The X-ray-diffraction measurement result of a composite_body | complex. The electron microscope (SEM) photograph of a composite_body | complex. The EDX measurement result of a composite_body | complex. 2 is a charge / discharge curve of the electricity storage device of Example 1. FIG.

  The electricity storage device of the present invention includes a composite comprising a composite of a positive electrode, a nitrogen-containing organic polymer supporting an anion, and a Si sheet having a basic skeleton composed of a plurality of six-membered rings composed of silicon atoms. And an ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts anions, and is charged and discharged by movement of the anions. FIG. 1 is a schematic view showing the operating principle of the electricity storage device of the present invention. In FIG. 1, a carbon material is used for the positive electrode, a cation is represented as A, an anion is represented as B, polyethyleneimine is illustrated as a nitrogen-containing organic polymer, and tetrafluoroboric acid is illustrated as an example. Note that m, n, and x in the figure are arbitrary numbers. In this electricity storage device, anions are occluded in the negative electrode during discharging, and anions are released from the negative electrode during charging. Specifically, for example, during discharge, anions bind to the nitrogen site of the nitrogen-containing organic polymer and the negative electrode active material is oxidized, and during charging, the anion is detached from the nitrogen site of the nitrogen-containing organic polymer and the negative electrode active material becomes It is considered to be reduced. At this time, a reserve-type reaction may be generated, or a capacitance due to the electric double layer may be generated. In this electricity storage device, it is considered that anions are released from the positive electrode during discharging and occluded in the positive electrode during charging.

  In the electricity storage device of the present invention, the positive electrode is prepared by, for example, mixing a positive electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like positive electrode material on the surface of the current collector. However, it may be compressed to increase the electrode density as necessary. The positive electrode active material is not particularly limited as long as it can occlude and release anions, and examples thereof include carbon materials and metal oxides. Examples of the carbon material include graphite, carbon black, activated carbon, and the like, and those containing graphite as a main component are preferable. Here, “having graphite as a main component” means that graphite is contained in an amount of 50% or more, preferably 90% or more, more preferably 95% or more. If it is such, it may contain amorphous carbon and may contain other active materials. Examples of graphite include natural graphite (scale-like graphite, scale-like graphite), artificial graphite, and the like, but artificial graphite is preferable in that the potential of the electricity storage device can be further increased and the energy density can be increased. . Furthermore, it is preferable to use artificial graphite activated with alkali, since the interlayer of graphite expands and ions easily enter and exit, and output characteristics are improved. Specifically, alkali activation can be performed by adding an alkali such as Na or K to graphite and treating the graphite at a high temperature of 600 ° C. to 1000 ° C. in an inert atmosphere. Use of a carbon material as the positive electrode active material is preferable because it easily absorbs and releases anions reversibly.

  The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the electrode performance. A mixture of one or more of black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) can be used. Among these, as the conductive material, carbon black and acetylene black are preferable from the viewpoints of electron conductivity and coatability. The binder serves to bind the active material particles and the conductive material particles. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorine-containing resin 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. Examples of the solvent for dispersing the active material, the conductive material, and the binder include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylaminopropylamine. Organic solvents such as ethylene oxide and tetrahydrofuran can be used. Moreover, a dispersing agent, a thickener, etc. may be added to water, and an active material may be slurried with latex, such as SBR. As the thickener, for example, polysaccharides such as carboxymethyl cellulose and methyl cellulose can be used alone or as a mixture of two or more. Examples of the application method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, and the like, and any of these can be used to obtain an arbitrary thickness and shape. Current collectors of the positive electrode include aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, etc., as well as aluminum and titanium for the purpose of improving adhesion, conductivity and oxidation resistance. What processed the surface of copper etc. with carbon, nickel, titanium, silver, etc. 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. The thickness of the current collector is, for example, 1 to 500 μm.

In the electricity storage device of the present invention, the negative electrode is, for example, a mixture of a negative electrode active material, a conductive material, and a binder, and an appropriate solvent is added to form a paste electrode mixture on the surface of the current collector. It may be dried and compressed to increase the electrode density as necessary. The negative electrode active material includes a complex in which a nitrogen-containing organic polymer supporting an anion and a Si sheet having a basic skeleton with a structure in which a plurality of six-membered rings composed of silicon atoms are connected. FIG. 2 is a schematic view showing an example of a composite of a Si sheet and a nitrogen-containing organic polymer. Note that m and n in the figure are arbitrary numbers. As shown in FIG. 2, the composite may have a structure in which a nitrogen-containing organic polymer and a Si sheet are bonded. Further, it may have a structure in which an anion is bonded to nitrogen of the nitrogen-containing organic polymer. The nitrogen-containing organic polymer is not particularly limited as long as it contains nitrogen in the material, and examples thereof include polyaniline, polypyrrole, polypyridine, polyethyleneimine, etc. Among these, polyethyleneimine is preferable from the viewpoint of the occlusion density of anions. . The nitrogen-containing organic polymer preferably has a site capable of supporting an anion and capable of reacting with the Si sheet (for example, —OH, —NHR, —CR ¹ = CR ^2, etc.). R, R ¹ , and R ² are functional groups, and examples thereof include a chain-like (which may be linear or branched) hydrocarbon group or a cyclic hydrocarbon group. The “nitrogen-containing organic polymer carrying an anion” may be a nitrogen-containing organic polymer doped with an anion or an anion-doped polymer. Further, the nitrogen-containing organic polymer may have a double bond or may not have a double bond. The charge during charging can be balanced by the Si sheet. The molecular weight of the nitrogen-containing organic polymer is not particularly limited, but is preferably in the range of 2,000 to 100,000. The type of anion to be supported is not particularly limited, and examples thereof include halogen, chalcogen, tetrafluoroboric acid, hexafluorophosphoric acid, trifluoromethanesulfonic acid, bis (trifluoromethanesulfonic acid) imide, etc. From the viewpoint of mobility during discharge, tetrafluoroboric acid (BF ₄ ⁻ ) is more preferable. The nitrogen-containing organic polymer is preferably one that is hardly solubilized in the ion conductive medium (solvent). The slightly solubilizing treatment is not particularly limited as long as the solubility of the nitrogen-containing organic polymer in the ion conductive medium can be reduced, and examples thereof include thermal decomposition by heat treatment of the polymer and condensation by a crosslinking agent. A condensation treatment with a crosslinking agent is more preferred. That is, the nitrogen-containing polymer preferably has a branched structure. In addition, when performing heat processing as a poorly soluble process, it is good also as what is performed in the temperature range of 100 to 500 degreeC, for example.

The composite contained in the negative electrode may be obtained, for example, by mixing and reacting layered polysilane (Si ₆ H ₆ ) and a nitrogen-containing organic polymer. The reaction method may be any kind of chemical reaction (eg, alkoxylation, amination, hydrosilylation, etc.), liquid phase, solid phase, and the like. In this composite, for example, the laminated structure of the layered polysilane may disappear, that is, the Si sheet structure included in the layered polysilane may be fixed in a random state. FIG. 3 is a schematic view of a layered polysilane composed of a plurality of Si sheets. As shown in FIG. 3, the layered polysilane is a sheet structure having a basic skeleton with a structure in which a plurality of six-membered rings composed of silicon atoms are continuous. The layered polysilane can be obtained by treating calcium disilicide with concentrated hydrochloric acid at -30 ° C. In this layered polysilane, hydrogen is preferably bonded to a silicon atom, but a part thereof may be another element, a functional group, or the like. When the layered polysilane and the nitrogen-containing organic polymer are mixed and reacted, they may be mixed with an organic solvent such as N, N-dimethylformamide (DMF) or acetone. This is because the dispersibility of the layered polysilane can be further improved. This organic solvent is preferably an anhydride. This is because layered polysilane easily reacts with water. In this way, a complex can be obtained.

  As the conductive material, binder, solvent and the like used for the negative electrode, 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.

  As the ionic conduction medium of the electricity storage device of the present invention, those capable of conducting anions can be used, and non-aqueous electrolytes and non-aqueous gel electrolytes containing a supporting salt can be used. The ion conductive medium may contain an organic solvent such as an ionic liquid or a carbonate, and preferably contains an anion of the same type as that supported on the nitrogen-containing organic polymer contained in the negative electrode active material. In addition, if a carbonate-based organic solvent is included, freezing at low temperatures can be prevented, and low-temperature characteristics such as output characteristics at low temperatures can be improved. In addition, if a carbonate-based organic solvent is added, the viscosity can be reduced to improve the output characteristics. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, and methyl-t-. Chain carbonates such as butyl carbonate, di-i-propyl carbonate, t-butyl-i-propyl carbonate, cyclic esters such as γ-butyllactone and γ-valerolactone, methyl formate, methyl acetate, ethyl acetate, butyric acid Chain esters such as methyl, ethers such as dimethoxyethane, ethoxymethoxyethane and diethoxyethane, nitriles such as acetonitrile and benzonitrile, tetrahydrofuran, Examples include furans such as methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Among these, the combination of cyclic carbonates and chain carbonates is preferable.

The ionic liquid is a salt of a cation and an anion melted at room temperature, and examples of the cation include imidazolium, ammonium, choline, pyridinium, piperidinium and the like. Examples of imidazolium include 1- (hydroxyethyl) -3-methylimidazolium and 1-methyl-3-octylimidazolium, and examples of ammonium include N, N-dimethylammonium and tetrabutylammonium. Examples of pyridinium include 1-butyl-3-methylpyridinium and 1-butylpyridinium, and examples of piperidinium include 1-ethyl-1-methylpiperidinium. As the anion, TFSI ^- and BETI ^- other imide anion, such _{^{as, BF 4 -, ClO 4 -}} , PF 6 -, Br -, Cl -, F - inorganic anions and the like. Among these, if the anion is tetrafluoroborate, the power storage device can be further reduced in weight. If the anion is TFSI ⁻ , the charge / discharge characteristics can be further enhanced. Specific examples of the anion as BF ₄ ⁻ include diethylmethyl (2 methoxyethyl) ammonium and BF ₄ . Specific examples of the anion used as TFSI include N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (abbreviation: PP13TFSI), 1-ethyl-3-methyl-imidazolium bis (trifluoro) (Romethanesulfonyl) imide (abbreviation: EMITFSI), N, N, N-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide (abbreviation: TMPATFSI), N, N-diethyl-N-methyl-N- (2- And methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide. Of these, PP13TFSI is preferred. When the ionic liquid and the organic solvent are mixed and used, the concentration of the ionic liquid is preferably 0.5 M or more and 2.0 M or less.

The supporting salt contained in the electricity storage device of the present invention is, for example, 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, LiClO ₄ , LiCl, LiF, LiBr, LiI, LiAlCl _{4 and the} like. Among these, from the group consisting of inorganic salts such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , and organic salts such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. It is preferable from the viewpoint of electrical characteristics to use a combination of one or two or more selected salts. The supporting salt preferably has a concentration in the non-aqueous electrolyte of 0.5 mol / L or more and 2.0 mol / L or less, and more preferably 0.7 mol / L or more and 1.5 mol / L or less. When the concentration of the supporting salt is 0.5 mol / L or more, a sufficient current density can be obtained, and when it is 2.0 mol / L or less, the electrolytic solution can be more stabilized. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte.

The electricity storage device of the present invention may include a separator between the negative electrode and the positive electrode. The separator is not particularly limited as long as it is a composition that can withstand the use range of the electricity storage device. For example, glass fiber glass filters, polypropylene nonwoven fabrics, polymer nonwoven fabrics such as polyphenylene sulfide nonwoven fabrics, polyethylene and polypropylene, etc. A thin microporous film of an olefin resin can be mentioned. Among these, a glass filter has good wettability with an electrolytic solution such as a BF ₄ -based ionic liquid, and can smoothly move the anion. These may be used alone or in combination.

  The shape of the electricity storage device 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.

  In the electricity storage device of the present embodiment described in detail above, the negative electrode contains a complex in which the nitrogen-containing organic polymer supporting an anion and the Si sheet are combined, and can be charged and discharged by the movement of the anion. In addition, since the electricity storage device of the present invention is an electricity storage device using anions as carriers, the occurrence of a short circuit due to overload can be significantly reduced as compared with, for example, a Li ion battery. Furthermore, since the electricity storage system takes in and out anions in a capacitor-like manner, high output is expected. The capacity can be easily changed depending on the amount supported on the nitrogen-containing organic polymer and the anion used, and a high-capacity electricity storage device can be constructed. Furthermore, since all the configured electrodes are stable in the atmosphere, the manufacturing process is very easy. Moreover, it is considered that the processing at the time of disposal of the battery can be easily performed if a metal and a metal oxide material are not used as the constituent elements of the electrode.

  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.

  Below, the example which produced the electrical storage device of this invention concretely is demonstrated as an Example.

[Example 1]
First, layered polysilane (Si ₆ H ₆ ) used for synthesis of the composite was synthesized as follows. In this synthesis, 3 g of calcium disilicide (CaSi ₂ ) was added to 100 ml of concentrated hydrochloric acid cooled to −30 ° C., and allowed to stand in a dark room at −30 ° C. for 1 week. This treatment turned the black calcium disilicide to yellow. The yellow solid was filtered under pressure in an Ar atmosphere, washed with degassed hydrochloric acid (−30 ° C.), washed with degassed HF (hydrogen fluoride) aqueous solution (−30 ° C.), and further degassed acetone (−30 The layered polysilane was synthesized by washing at 110 ° C. overnight under reduced pressure. The synthesized layered polysilane was used for the synthesis of the following examples. The chemical reaction formula for the synthesis of this layered polysilane is shown in Formula (3).

(Chemical formula 3)
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂ (3)

1.0 g of a 50% aqueous solution of polyethyleneimine was set at 0 ° C. in an ice bath, and 1.558 g of tetrafluoroboric acid (HBF ₄ ) was slowly added dropwise. This was warmed to room temperature and stirred for 18 hours. The water from the resulting mixture by vacuum removal BF ₄ ^- was obtained nitrogen-containing organic polymers which is carried. Next, the synthesized layered polysilane 50mg and the BF ₄ ^- carrying nitrogen-containing organic polymers 75mg and the N under an inert atmosphere, N- dimethylformamide (DMF) was added, 60 ° C., 18 h, the mixture was heated with stirring. DMF was removed from the obtained mixture under vacuum, and then heated at 110 ° C. for 30 minutes to obtain 120 mg of the Si sheet / nitrogen-containing organic polymer composite of Example 1.

[IR spectrum measurement]
FIG. 4 is an IR spectrum of the composite of Example 1. The IR spectrum was measured by the KBr method using an IR measuring device (Magna 760 type Fourier infrared spectrometer manufactured by Nicorey). In the IR spectrum shown in FIG. 4, the stretching vibration of the Si—N bond was observed at 925 cm ⁻¹ , indicating that this material is a material compounded by the Si—N bond. Moreover, since there exist Si-H bond and N-H bond, it was shown that not all the reaction points reacted. The stretching vibration of the N ⁺ -H bond derived from ammonium carrying an anion is also observed at 3200 cm ⁻¹ , suggesting that the anion is carried.

[X-ray diffraction measurement]
FIG. 5 shows the result of X-ray diffraction measurement of the composite of Example 1. X-ray diffraction was performed by RINT-TTR manufactured by Rigaku Corporation using CuKα rays as a radiation source. As shown in FIG. 5, when the XRD of the obtained composite was measured, it showed an amorphous structure, and a diffraction peak (001) derived from a layered structure unique to layered polysilane could not be confirmed. From the above, it was suggested that the Si sheet was randomly fixed in the nitrogen-containing organic polymer.

[Electron microscope (SEM) observation]
An SEM image of the Si sheet / nitrogen-containing organic polymer composite was observed. SEM observation was performed using HITACHI S-3600N. 6 is an electron microscope (SEM) photograph of the composite of Example 1. FIG. As shown in FIG. 6, since the plate-like structure can be confirmed, it was confirmed that the structure of the Si sheet itself was maintained. Further, during SEM observation, EDX composition analysis of the Si sheet / nitrogen-containing organic polymer composite was performed. FIG. 7 shows EDX measurement results of the composite of Example 1. In the EDX composition analysis, in addition to silicon derived from Si sheet and nitrogen derived from nitrogen-containing organic polymer, anion-derived fluorine was observed. From the above, it was confirmed that the synthesis of the Si sheet / anion-supporting nitrogen-containing organic polymer composite was successful.

[Production of electricity storage device]
The negative electrode by mixing 7 mg of the Si sheet / anion-supporting nitrogen-containing organic polymer composite of Example 1, 2.5 mg of activated carbon (ECP), and 0.5 mg of polytetrafluoroethylene (PTFE) and pressing the mixture against the mesh as the current collector It was. The positive electrode was produced by applying 20 mg of graphite to a binder on an aluminum foil as a current collector and heat-treating it. The electrolyte used was LiBF ₄ as a supporting salt, dissolved in propylene carbonate and adjusted to a concentration of 1 mol / L. A glass filter was used as the separator. The produced cell was used as the electricity storage device of Example 1. FIG. 8 is a charge / discharge curve of the electricity storage device of Example 1. As shown in FIG. 8, the electricity storage device of Example 1 was charged and discharged, and the capacity was stabilized as the cycle was repeated. The charge after 20 cycles was 400 mAh / g per active material, and the discharge was 120 mAh / g. The capacity was shown. This charging / discharging was presumed to be carried out by the negative electrode reaction of formula (1) and the positive electrode reaction of formula (2). Thus, a novel electricity storage device using an anion could be developed.

Claims (3)

A positive electrode;
A negative electrode including a composite of a nitrogen-containing organic polymer supporting an anion and a Si sheet having a basic skeleton having a structure in which a plurality of six-membered rings composed of silicon atoms are linked;
An ion conductive medium that is interposed between the positive electrode and the negative electrode and conducts the anion,
An electricity storage device that is charged and discharged by the movement of anions.   The electricity storage device according to claim 1, wherein the negative electrode includes the nitrogen-containing organic polymer in which the composite has a branched structure.   The electricity storage device according to claim 1, wherein the negative electrode contains polyethyleneimine as the nitrogen-containing organic polymer.