JP5245864B2 - Power storage device - Google Patents

Description

  The present invention relates to an electricity storage device.

Conventionally, as an electricity storage device, an electric double layer capacitor having a BET specific surface area of 10 to 300 m ² / g, an interlayer distance of 0.3354 nm to 0.3390 nm, and a large capacitance has been proposed (for example, , See Patent Document 1). In this electricity storage device, when the positive electrode is an electrode containing graphite, the negative electrode is lithium metal, and LiPF ₆ is an electrolyte, a sudden rise region and a relatively moderate voltage around 4.6 V with respect to lithium metal. The charge / discharge curve has a changing region (also referred to as a plateau region), and can have an electric capacity of 25 mAh / g at 4.8V. In general, an electric double layer capacitor or the like undergoes a voltage change linearly due to charge / discharge, so that the capacity increases when a plateau region exists. In addition, as such an electric storage device, non-porous charcoal having a developed multi-layer graphene layer having an interlayer distance in the range of 0.355 nm to 0.360 nm, such as needle coke or infusibilized pitch, is used as an electrode active material. An electric double layer capacitor having an electrode contained as a substance has been proposed (see, for example, Patent Document 2). In this electricity storage device, for example, cations such as 1-ethyl-3-methylimidazolium intercalate into the multilayer graphene layer, whereby the energy density can be further increased. In addition, as such an electricity storage device, an electric double layer capacitor has been proposed in which electrostatic capacitance is increased by producing a dividing electrode using microcrystalline carbon having an interlayer distance of 0.360 nm to 0.385 nm. (For example, see Patent Document 3).

Japanese Patent Laying-Open No. 2005-294780 (FIG. 7) JP 2004-289130 A JP 11-317333 A

  However, in the electricity storage device of Patent Document 1 described above, the plateau region is as high as 4.6 V or more on the basis of lithium metal, and the effect of increasing the electric capacity is greatly limited because the plateau region is closer to the decomposition start voltage of the electrolyte at 4.6 V or more. There was a problem that would have been. Moreover, in the electrical storage device of the above-mentioned patent document 2, a capacity | capacitance improvement is aimed at by intercalating a cation by the negative electrode side, and the capacity | capacitance improvement by the positive electrode side is not considered. Further, in the electric storage device of Patent Document 2, the second and subsequent charge / discharge cycles are not considered. Furthermore, even in the first charge / discharge, there are some that do not show a plateau region, and the capacity improvement has not been sufficient yet. In addition, although the multilayer graphene layer whose interlayer distance is 0.354 nm is also described, charging / discharging performance is not described and is unknown. Moreover, in the electrical storage device of the above-mentioned patent document 3, the plateau region disappeared in the second charge / discharge cycle, and the capacity improvement was not yet sufficient.

  This invention is made | formed in view of such a subject, and it aims at providing the electrical storage device which can raise the capacity | capacitance in a charging / discharging cycle more.

  As a result of earnest research to achieve the above-described object, the inventors of the present invention have provided, in the electricity storage device, a carbon material having a layered graphite structure having a face spacing of 0.340 nm or more and 0.354 nm or less on the positive electrode. Then, it has been found that the capacity in the charge / discharge cycle can be further increased, and the present invention has been completed.

That is, the electricity storage device of the present invention is
A negative electrode,
A positive electrode comprising a carbon material having a layered graphite structure with a face spacing of 0.340 nm or more and 0.354 nm or less;
An electrolyte interposed between the negative electrode and the positive electrode;
It is equipped with.

  The electricity storage device of the present invention can further increase the capacity in the charge / discharge cycle. The reason why such an effect is obtained is not clear, but is presumed as follows. For example, it is conceivable that the voltage developed in the plateau region described above is determined by the energy required to increase the interlayer distance of the layered graphite structure. And, in a carbon material having a layered graphite structure with an interplanar spacing of 0.340 nm or more and 0.354 nm or less, the interlayer distance is in an appropriate range. For example, in the positive electrode, anions easily enter between layers of the layered graphite structure and are relatively low. It is inferred that a plateau region appears in the voltage region, and this is more easily maintained even during repeated charge / discharge cycles. Thus, it is assumed that the capacity in the charge / discharge cycle can be increased. Further, according to the electricity storage device of the present invention, when the electricity storage device has a configuration in which lithium is dissolved in a non-aqueous electrolyte, the charging voltage can be suppressed to a range of, for example, 4.6 V or less, Restrictions such as the decomposition start voltage of the electrolytic solution can be suppressed, and the capacity in the charge / discharge cycle can be further increased.

It is explanatory drawing of the evaluation cell. It is a charging / discharging curve of the 5th cycle of each evaluation cell. It is explanatory drawing which shows the relationship of the bending point of the charging voltage with respect to a surface space | interval.

  An electricity storage device of the present invention includes a negative electrode, a positive electrode including a carbon material having a layered graphite structure with a surface interval of 0.340 nm to 0.354 nm, an electrolyte interposed between the negative electrode and the positive electrode, It has. In the electricity storage device of the present invention, although not particularly limited, the electrolyte may include an anion and a cation, and the negative electrode may store electricity by one or more of cation adsorption, intercalation, or electrochemical reaction. That is, the electricity storage device of the present invention may be configured as, for example, a lithium ion capacitor using lithium ions, or may be configured as an electric double layer capacitor.

The positive electrode of the electricity storage device of the present invention includes a carbon material having a layered graphite structure with a surface spacing of 0.340 nm or more and 0.354 nm or less. When the interplanar spacing of the carbon material having a layered graphite structure is in the range of 0.340 nm to 0.354 nm, for example, anions tend to easily insert and desorb between the layers of the layered graphite. In this range, a region where the voltage changes relatively slowly (plateau region) appears in a region of relatively low voltage in the charge / discharge curve, which is preferable. More preferably, the spacing is 0.342 nm or more and 0.353 nm or less. As the carbon material having a layered graphite structure, for example, a material having hexabenzocoronene as a basic skeleton is preferable. In this way, it is easy to make the range of the above-mentioned surface interval. The carbon material having hexabenzocoronene as a basic skeleton preferably has 42 to 144 carbon atoms, and more preferably 96 or less carbon atoms. When the number of carbon atoms is in the range of 42 or more and 144 or less, a decrease in the number of sites into which anions can be inserted can be suppressed, which is preferable. Such a carbon material is preferably any graphene compound represented by the general formulas (1) to (7). Here, in the formula, R ^{1 to} R ¹⁷⁴ are each independently a hydrogen atom, a halogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, a heterocyclic group, an alkoxy group, an aryloxy group, or a cyano group. Selected from the group consisting of a group, an acyl group, a perfluoroaryl group, and a perfluoroalkyl group. In this specification, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, a heterocyclic group, an alkoxy group, and an aryloxy group have at least one hydrogen atom as a halogen atom (particularly a fluorine atom) or a cyano group. And those substituted with a substituent such as. Note that the carbon material having hexabenzocoronene as a basic skeleton refers to a compound containing a hexabenzocoronene portion in the structural formula. Also, carbon number of a portion excluding the R ¹ to R ¹⁷⁴ of the graphene compounds of general formula (1) to (7), respectively 42 pieces, 72, 60, 78, 54 pieces, 78 pieces, 114 It is a piece.

  Here, examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The alkyl group preferably has 1 to 6 carbon atoms. For example, methyl group, ethyl group, n-propyl group, isopropyl group, cyclopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert- A butyl group, an n-pentyl group, a cyclopentyl group, an n-hexyl group, a cyclohexyl group and the like can be mentioned. Examples of the alkenyl group include a vinyl group, an allyl group, a butenyl group, a styryl group, a cyclopropenyl group, a cyclopentenyl group, and a cyclohexenyl group. Examples of the alkynyl group include an ethynyl group, a propargyl group, and a phenylacetinyl group. Examples of the aryl group include phenyl group, 2,6-xylyl group, mesityl group, duryl group, biphenyl group, terphenyl group, naphthyl group, anthryl group, pyrenyl group, toluyl group, anisyl group, fluorophenyl group, diphenylamino. Examples thereof include a phenyl group, a dimethylaminophenyl group, a diethylaminophenyl group, and a phenanthrenyl group. Examples of the aralkyl group include an ethynyl group, a propargyl group, and a phenylacetinyl group. Examples of the heterocyclic group include a furyl group, a thienyl group, a pyrrolyl group, a pyridyl group, a benzothienyl group, and a quinolyl group. Examples of the alkoxy group include a methoxy group, an ethoxy group, an isopropoxy group, and a tert-butoxy group. Examples of the aryloxy group include those in which the aryl group exemplified above is bonded to an oxygen atom. Examples of the acyl group include formyl group, acetyl group, propionyl group, isopropionyl group, butyryl group, and pivaloyl group. Examples of the perfluoroaryl group include a pentafluorophenyl group, a nonafluorobiphenyl group, and a heptafluoronaphthyl group. Examples of the perfluoroalkyl group include a trifluoromethyl group and a pentafluoroethyl group.

Of the graphene compounds represented by the general formula (1), those in which R ^{1 to} R ¹⁸ are all hydrogen atoms can be synthesized by, for example, the route represented by the following formula. That is, the compound (11) and the compound (12) are heated at a molar ratio of 1: 1 using diphenyl ether or the like as a solvent to obtain the compound (13), and then dichloromethane or the like as a solvent to the compound (13) in a nitromethane solution of iron chloride. Can be added to obtain the graphene compound represented by the general formula (1). Here, although the exemplified for the case of all R ¹ to R ¹⁸ hydrogen atoms, when part or all of R ¹ to R ¹⁸ are such as an alkyl group, the compound according to R ¹ ~R ¹⁸ (11 ) And (12) may be appropriately set.

Of the graphene compounds represented by the general formula (2), those in which R ^{19 to} R ⁴⁴ are all hydrogen atoms can be synthesized, for example, by the route represented by the following formula. That is, the compound (21) and the compound (22) are heated at a molar ratio of 1: 2 using diphenyl ether or the like as a solvent to obtain the compound (23), and then dichloromethane or the like as a solvent to the compound (23) in a nitromethane solution of iron chloride. Is added, the graphene compound represented by the general formula (2) can be obtained. Here, although the exemplified for the case of all R ¹⁹ to R ⁴⁴ hydrogen atoms, when part or all of R ¹⁹ to R ⁴⁴ are such as an alkyl group, the compound according to R ¹⁹ ~R ⁴⁴ (21 ) And (22) may be appropriately set.

Of the graphene compounds represented by the general formula (3), those in which R ^{45 to} R ⁶⁶ are all hydrogen atoms can be synthesized, for example, by the route represented by the following formula. That is, first, compound (31) and compound (32) are heated at a molar ratio of 1: 1 using diphenyl ether or the like as a solvent to obtain compound (33). Thereafter, the compound (33) is reacted with tetrabutylammonium fluoride using THF or the like as a solvent to obtain the compound (34). Then, the compound (34) and the compound (32) are heated at a molar ratio of 1: 1 using diphenyl ether or the like as a solvent to obtain a compound (35), and then dichloromethane or the like as a solvent to the compound (35) in a nitromethane solution of iron chloride. Can be added to obtain the graphene compound represented by the general formula (3). Here, although the exemplified case R ⁴⁵ to R ⁶⁶ are all hydrogen atoms, when part or all of R ⁴⁵ to R ⁶⁶ are such as an alkyl group, the compound according to R ⁴⁵ ~R ⁶⁶ (31 ) And (32) may be appropriately set.

  Note that the graphene compounds represented by the general formulas (4) to (7) can also be synthesized according to these routes.

  The positive electrode of the electricity storage device of the present invention is, for example, a mixture of the carbon material, a conductive material, and a binder, and a paste-like positive electrode material added with an appropriate solvent is applied to the surface of the current collector and dried. If necessary, it may be compressed to increase the electrode density. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode. For example, graphite such as natural graphite (scale-like graphite, scale-like graphite) or artificial graphite, acetylene black, carbon black, What mixed 1 type (s) or 2 or more types, such as ketjen 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, a polytetrafluoroethylene (PTFE), a polyvinylidene fluoride (PVDF), a 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. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the solvent for dispersing the carbon 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 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.

  For the negative electrode of the electricity storage device of the present invention, for example, a negative electrode active material capable of containing an alkali metal, an alkali metal alloy, or an alkali metal may be used. In this case, the electricity storage device is an alkaline ion capacitor. Examples of the alkali metal include lithium, sodium, and potassium, among which lithium is more preferable. Examples of the negative electrode active material that can contain an alkali metal include carbonaceous materials capable of inserting and extracting lithium, metal oxides such as lithium titanate, and conductive polymers. The carbonaceous material is not particularly limited, and examples thereof include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Of these, graphites such as artificial graphite and natural graphite have an operating potential close to that of metallic lithium, can be charged and discharged at a high operating voltage, and suppresses self-discharge when a lithium salt is used as an electrolyte salt. In addition, it is preferable because the irreversible capacity during charging can be reduced. Alternatively, the negative electrode of the electricity storage device of the present invention may include a high specific surface area material capable of adsorbing cations. In this case, the electricity storage device is an electric double layer capacitor. Examples of the high specific surface area material include activated carbon. The negative electrode of the electricity storage device of the present invention is, for example, a mixture of a negative electrode active material or a high specific surface area material, a conductive material and a binder, and an appropriate solvent added to form a paste-like negative electrode material. It may be applied and dried on the surface of the body, and may be compressed to increase the electrode density as necessary. 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.

The electrolyte of the electricity storage device of the present invention is not particularly limited, but includes an electrolyte containing a supporting salt, a polar organic solvent containing a supporting salt, a non-aqueous electrolyte such as an ionic liquid, a gel electrolyte, a solid electrolyte, etc. Can be used. As the supporting salt, those used in various batteries can be used. Examples of those containing lithium 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, LiClO 4, LiCl, LiF, LiBr, LiI, and the like LiAlCl _4. 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 includes a quaternary ammonium salt containing an alkyl having 2 to 10 carbon atoms, such as (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , ( _{C 4 H 9) 4 NBF 4} , it can be used _{(C 2 H 5) 4 NPF} 6, (C 2 H 5) 3 (CH 3) NPF 6, and _{(C 4 H 9) 4 NPF} 6.

  Examples of the solvent for the electrolytic solution include non-aqueous solvents. Examples of the non-aqueous solvent include carbonates, esters, ethers, nitriles, hydrofurans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, as carbonates, cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, butylene carbonate, chloroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, 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, Chain esters such as methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane; nitriles such as acetonitrile and benzonitrile; And hydrofurans such as lan, methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Further, the ionic liquid is not particularly limited, but 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide, 1-ethyl-3-butylimidazolium tetrafluoroborate, diethyl-methyl -Methoxyethylammonium tetrafluoroborate, methyl-propyl-pyrrolidinium-bistrifluoromethanesulfonylimide and the like can be used. Among these, the combination of cyclic carbonates and chain carbonates is preferable. According to this combination, not only the cycle characteristics representing the battery characteristics in repeated charge and discharge are excellent, but also the viscosity of the electrolyte, the electric capacity of the obtained battery, the battery output, etc. should be balanced. it can. The supporting salt preferably has a concentration in the non-aqueous electrolyte of 0.1 mol / L to 5 mol / L, and more preferably 0.8 mol / L to 5 mol / L. If the concentration of the supporting salt is 0.1 mol / L or more, a sufficient current density can be obtained, and if it is 5 mol / L or less, the electrolytic solution can be made more stable. Moreover, you may add flame retardants, such as a phosphorus type and a halogen type, to this non-aqueous electrolyte.

  Further, a solid ion conductive polymer can be used instead of the electrolytic solution. As the ion conductive polymer, for example, a polymer gel composed of a polymer such as acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, and polyvinylidene fluoride and a supporting salt can be used. Further, an ion conductive polymer and a non-aqueous electrolyte can be used in combination.

  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 usage range of the electricity storage device. For example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or an olefin resin such as polyethylene or polypropylene is used. A microporous film is mentioned. 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. A specific example of manufacturing an electricity storage device will be described. FIG. 1 is a configuration diagram illustrating an example of the configuration of an electricity storage device 10, in which an upper stage is a cross-sectional view before assembly of the electricity storage device 10, and a lower stage is a cross-sectional view after assembly of the electricity storage device 10. In assembling the electricity storage device 10, first, a negative electrode 16, a separator 18, and a positive electrode 20 are laminated in this order in a cavity 14 provided in the center of the upper surface of a stainless steel cylindrical substrate 12 having a thread groove on the outer peripheral surface. To do. Next, after injecting a non-aqueous electrolyte into the cavity 14, an insulating ring 29 is inserted, and then a conductive cylinder 24 liquid-tightly fixed in the hole of the insulating ring 22 is disposed on the positive electrode 20. A conductive cup-shaped lid 26 is screwed into the cylindrical base 12. Further, an insulating resin ring 27 is arranged on the cylinder 24, and a pressure bolt 25 having a through hole 25a is screwed into a screw groove carved in an inner peripheral surface of an opening 26a provided at the center of the upper surface of the lid 26, The negative electrode 16, the separator 18, and the positive electrode 20 are pressed and adhered. In this way, the electricity storage device 10 can be manufactured. Since the cylinder 24 is positioned below the upper surface of the ring 22 and is in contact with the lid 26 via the insulating resin ring 27, the lid 26 and the cylinder 24 are in an electrically non-contact state. In addition, since the packing 28 is disposed around the cavity 14, the electrolyte injected into the cavity 14 does not leak to the outside. In the electricity storage device 10, the lid 26, the pressure bolt 25, and the cylindrical base 12 are integrated with the negative electrode 16, so that the whole is on the negative electrode side, and the column 24 is integrated with the positive electrode 20 and insulated from the negative electrode 16. Therefore, it becomes the positive electrode side.

  According to the electricity storage device of this embodiment described in detail above, the capacity in the charge / discharge cycle can be further increased. The reason for this is that in a carbon material having a layered graphite structure with an interplanar spacing of 0.340 nm or more and 0.354 nm or less, the interlayer distance is in an appropriate range. For example, in the positive electrode, anions easily enter between layers of the layered graphite structure. It is assumed that a plateau region (region where the voltage changes relatively slowly) appears in a relatively low voltage region, and this is more easily maintained even during repeated charge / discharge cycles. Thus, it is assumed that the capacity in the charge / discharge cycle can be increased. In addition, according to the electricity storage device of the present invention, when the electricity storage device has a configuration in which lithium is dissolved in a non-aqueous electrolyte, the charging voltage is suppressed to a relatively low range (for example, a range of 4.6 V or less). It is possible to suppress the restrictions such as the decomposition start voltage of the non-aqueous electrolyte, and to fully utilize the plateau region, thereby further increasing the capacity in the charge / discharge cycle.

  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.

[Example 1]
(Synthesis of hexabenzocoronene)
1.10 g of hexaphenylbenzene was dissolved in 500 mL of dichloromethane, and nitrogen was blown for 5 minutes. To this solution, a solution prepared by dissolving 6.30 g of anhydrous iron chloride (FeCl ₃ ) in 72 mL of nitromethane was added dropwise under a nitrogen atmosphere and stirred at room temperature for 30 minutes. 500 mL of methanol was added, and the generated precipitate was filtered. The precipitate was stirred in 50 mL of 10 wt% aqueous ammonia and filtered. Further, it was washed with 50 mL of water and 50 mL of dichloromethane, and vacuum-dried to obtain 470 mg of hexabenzocoronene as an orange powder. This structure was confirmed as follows. That is, molecular ions were confirmed by MALDI-MS measurement combining a matrix assisted laser desorption ionization (MALDI) and a mass spectrometer (MS) (M ⁺ = 522), and the structure was confirmed. . Further, X-ray diffractometry of the obtained hexabenzocoronene was performed using CuKα rays with an X-ray diffractometer (RINT2200 manufactured by Rigaku) in the range of 2θ of 10 ° to 60 °. From the 2θ value (°) of the obtained diffraction peak, the inter-plane distance of this hexabenzocoronene was determined to be 0.342 nm.

(Production of evaluation cell)
The above-mentioned hexabenzocoronene as an active material, carbon (ECP600JD, manufactured by Lion Corporation) as a conductive auxiliary agent, and polytetrafluoroethylene (PTFE) as a binder are kneaded until they are in a bowl shape and dried to produce a positive electrode material. did. The mixing ratio of HBC: carbon: PTFE was 70:20:10 by weight. The negative electrode was a lithium metal plate having a thickness of 0.4 mm and a diameter of 18 mm, and the separator was porous polyethylene (manufactured by Tonen Functional Membrane). Moreover, ethylene carbonate and diethyl carbonate in a volume ratio (3: 7) and to prepare those obtained by dissolving LiPF ₆ in 1M in mixed solvent so that, which was used as a nonaqueous electrolyte. And the cell of FIG. 1 was produced using this positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte. The charge / discharge behavior was evaluated by constant current driving with a positive electrode material weight of 3 mg, an electrode area of 1.3 cm ² , a voltage range of 2.5 V to 4.7 V, and 1 mA.

[Example 2]
An evaluation cell obtained through the same steps as in Example 1 except that hexabenzocoronene was changed to dihexylhexabenzocoronene (HBCC62) was used as Example 2. Dihexylhexabenzocoronene is a compound in which R ² and R ¹¹ in the above general formula (1) are hexyl groups (6 carbon atoms) and the others are hydrogen. When X-ray diffraction measurement was performed in the same manner as in Example 1, the inter-plane distance of this dihexyl hexabenzocoronene was 0.353 nm.

[Comparative Example 1]
Comparative Example 1 was an evaluation cell obtained through the same steps as in Example 1 except that hexabenzocoronene was graphite (KS6 manufactured by TIMREX). When X-ray diffraction measurement was performed in the same manner as in Example 1, the interplanar distance of this graphite was 0.335 nm. In Comparative Example 1, the voltage range was 3V-5V, and the charge / discharge behavior was evaluated.

[Comparative Example 2]
An evaluation cell obtained through the same steps as in Example 1 except that hexabenzocoronene was changed to graphene oxide was used as Comparative Example 2. This graphene oxide was synthesized according to the method described in H. Jeong, et.al., J. Amer. Chem. Soc., 130, 1362 (2008). Specifically, 20 g of fuming nitric acid and 10 g of potassium chlorate were mixed with 1 g of graphite at room temperature and stirred for 24 hours. This was washed and filtered to obtain graphene oxide. The surface interval by X-ray diffraction of this dried product was 0.58 nm. In Comparative Example 2, the voltage range was set to 2.5 V to 4.5 V, and the charge / discharge behavior was evaluated.

(Experimental result)
The measurement results of each sample are shown in Table 1 and FIGS. Table 1 shows the interplanar spacing (nm) of each sample by X-ray diffraction, the bending voltage (V) during charging, and the charge / discharge capacity (mAh / g) at the fifth cycle. FIG. 2 is a charge / discharge curve at the fifth cycle of each evaluation cell. FIG. 3 is an explanatory diagram showing the relationship of the inflection point (V) of the charging voltage with respect to the surface spacing (nm). As shown in FIG. 2, in Comparative Example 1, the inflection point is at 4.6V close to the decomposition start voltage (for example, 5.0V) of the nonaqueous electrolyte, and the plateau region is in the voltage region of 4.6V or higher. I understood it. This result supports the same experimental result as JP 2005-294780 (Patent Document 1). In Comparative Example 2, the surface separation was as large as 0.58 nm, no clear plateau region was shown, and the capacity was low. On the other hand, Examples 1 and 2 have a bending point in the vicinity of 4.0 V at the time of charging and discharging even at the 5th cycle, have a plateau region in a voltage range lower than that of Comparative Example 1, and non-aqueous electrolysis. It has been found that even when the decomposition start voltage of the liquid is taken into consideration, the plateau region is used more effectively, and a larger capacity can be obtained even though the voltage is lower than that of Comparative Example 1. Further, as shown in FIG. 3, it was found that, for example, in order for the bending point at the time of charging to be 4.0 V or less, it is necessary that the surface interval be 0.340 nm or more. On the other hand, it was also found that the inflection point of the charge / discharge curve is not clear when the interplanar spacing is 0.354 nm or more. Thus, it was found that the carbon material having a layered graphite structure preferably has a plane spacing of 0.340 nm or more and 0.354 nm or less, and more preferably 0.342 nm or more and 0.353 nm or less.

  The capacitance per active material weight was calculated from the slope of the plateau region in FIG. This capacitance was 330 F / g in Example 1 and 200 F / g in Example 2. Moreover, the electrostatic capacitance calculated | required from the minimum inclination of the comparative example 2 was 72 F / g. In an electric double layer capacitor using a non-porous carbon material with a developed multi-layer graphene layer having an interlayer distance in the range of 0.350 to 0.380 nm as disclosed in JP-A-2004-289130 as an electrode active material, 40 is required in the first cycle. It is ˜80 F / g, and at the 10th cycle when the characteristics are stabilized, the capacitance remains at 50 F / g or less. The value of an electric double layer capacitor using a carbon material having an interlayer distance of 0.365 to 0.385 nm described in JP-A-11-317333 is 28.5 F / ml per unit volume. Even if it is assumed to be 0.5 of 1/4 of the value, it becomes a value of 60 F / g or less. Thus, it has been found that the electrostatic capacity of the electricity storage device of the present invention is extremely large.

DESCRIPTION OF SYMBOLS 10 Power storage device, 12 Cylindrical base | substrate, 14 Cavity, 16 Negative electrode, 18 Separator, 20 Positive electrode, 22 Ring, 24 Cylinder, 25 Pressure bolt, 25a Through-hole, 26 Lid, 26a Opening, 27 Insulating resin ring, 28 Packing, 29 Insulation ring.

Claims (4)

A negative electrode,
A positive electrode provided with a carbon material having a layered graphite structure having an interplanar spacing of 0.340 nm or more and 0.354 nm or less as a positive electrode active material ;
E Bei and a electrolyte interposed between the negative electrode and the positive electrode,
The capacitance per mass of the positive electrode active material is 200 F / g or more,
Power storage device.   The electricity storage device according to claim 1, wherein the positive electrode includes the carbon material having hexabenzocoronene as a basic skeleton.   The power storage device according to claim 2, wherein the positive electrode includes the carbon material including at least one of hexabenzocoronene and dihexylhexabenzocoronene.   The bending voltage in the charging curve at a current density of 0.33 A / g is Li ⁺ The electrical storage device of any one of Claims 1-3 which is 4.0V or less on the basis of / Li.

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