JP5440003B2 - Electric storage device and method for manufacturing electrode active material - Google Patents

Description

  The present invention relates to an electricity storage device and a method for producing an electrode active material.

Conventionally, as an electricity storage device, a high-capacity battery is expected to use sulfur having an extremely high theoretical capacity density of 1672 Ah / kg as an electrode active material. The basic structure of an electricity storage device using sulfur is relatively simple, using a mixture of sulfur, a conductive additive carbon and a binder for the positive electrode, using metallic Li or a material containing it for the negative electrode, and LiPF for the electrolyte. An ether-based organic electrolyte in which a supporting salt such as ₆ is dissolved is used. In electricity storage devices, the solubility of the positive electrode active material sulfur and the reaction product polysulfide ions in the electrolyte is high, so the capacity is reduced due to their elution and reaction with the negative electrode (hereinafter also referred to as the shuttle effect). A decrease in charge / discharge efficiency is a problem. As a prevention method for this, for example, in Patent Document 1, carbon and sulfur are the main constituent elements, disulfide is bonded to the carbon chain, and the weight ratio of sulfur is increased as much as possible to increase the capacity and capacity retention rate in the charge / discharge cycle. Improvements have been proposed. Patent Document 2 proposes a polysulfurized carbon having a sulfur ratio of 67% by weight or more and a total of carbon and sulfur of 95% by weight or more as an active material and further improved cycle characteristics. Non-Patent Document 1 proposes a ladder polymer in which the main chain of conductive polyaniline is connected by disulfide. Non-Patent Document 2 proposes a method for immobilizing sulfur by reacting polyacrylonitrile, which is a linear polymer not containing aromatics, with sulfur, and then cyclizing the carbon chain. Yes.

JP 2002-154815 A JP 2003-123758 A

Journal of Electrochemical Society 144, L173, 1997 Journal of Electroanalytical Chemistry 572, 121-128, 2004

  However, when single sulfur is used, two electrons are exchanged during redox, whereas in the electric storage devices described in Patent Documents 1 and 2 and Non-Patent Documents 1 and 2, sulfur is combined with carbon. For this reason, only one electron is transferred during oxidation-reduction, and the capacity may be reduced. In addition, there is a problem that the capacity per unit weight is reduced because a portion not directly related to the redox reaction, that is, energy storage, such as a carbon chain increases. For example, in Patent Documents 1 and 2, an attempt is made to further increase the sulfur component, to form a sulfide bond between sulfurs, and to increase the sulfur component that is not bonded to carbon. As in the case of using simple sulfur, it was considered that a problem of dissolution of the active material occurred, causing a decrease in charge / discharge efficiency and a decrease in capacity during cycling. Further, in Non-Patent Document 1, in poly (2,2′-dithiodianiline), the theoretical capacity is 330 Ah / kg even when the redox of the polyaniline part is used, and the experimental capacity is 270 Ah / kg per active material. The theoretical capacity of sulfur alone is 1672 Ah / kg, which is significantly lower than 670 Ah / kg in the case of a 50 wt% sulfur positive electrode. Non-Patent Document 2 states that a high-capacity material can be produced. However, the sulfur concentration is the best with only 35% by weight. This is because 15% by weight of nitrogen which cannot be combined with sulfur is contained, and therefore the capacity is not sufficient.

  This invention is made | formed in view of such a subject, and it aims at providing the manufacturing method of the electrical storage device and electrode active material which can improve cycling characteristics and a capacity | capacitance more in the thing containing sulfur. .

  As a result of diligent research to achieve the above-described object, the present inventors have found that when a polycyclic aromatic compound having a thiophene structure in the skeleton synthesized so as not to generate excessive sulfur is used as an active material, cycle characteristics are obtained. In addition, the present inventors have found that the capacity can be further increased and have completed the present invention.

That is, the electricity storage device of the present invention is
A polycyclic aromatic compound having carbon and sulfur as main components and a sulfur content of more than 38% by weight and 70% by weight or less and having a thiophene structure in the skeleton is used as an electrode active material.

The method for producing the electrode active material of the present invention includes:
A manufacturing method for manufacturing an electrode active material used for an electrode of an electricity storage device,
By mixing at least one of an aliphatic polymer compound having a straight chain structure and a polymer compound having a thiophene structure with sulfur, heating in an inert atmosphere, and removing excess sulfur, the inside of the skeleton A production step of producing a polycyclic aromatic compound having a thiophene structure in
Is included.

  The manufacturing method of the electricity storage device and the electrode active material of the present invention can further improve cycle characteristics and capacity. The reason why such an effect is obtained is not clear, but is presumed as follows. For example, since elemental sulfur is bonded to polycyclic aromatics, the shuttle effect, which is a problem when using sulfur alone, can be prevented, and repeated charging / discharging in a state where capacity reduction and charge / discharge efficiency decrease are further suppressed. It can be carried out. This polycyclic aromatic compound having a thiophene structure has electronic conductivity and contributes to the redox electron transport of sulfur element. Polycyclic aromatic compounds have a structure in which molecules are stacked due to intermolecular interactions such as van der Waals force and π-π interaction. When the distance is increased, it is presumed that a large capacitance like an electric double layer capacitor or Li intercalation is expressed. For this reason, when sulfur is immobilized, only one-electron redox can occur, and lowering the capacity becomes a problem. However, in the present invention, it accompanies redox of sulfur bonded to a polycyclic aromatic compound. In addition to the capacity, it is surmised that the capacity could be greatly improved by a novel mechanism that has not been heretofore, in which the increase or decrease in the electrostatic capacity of the polycyclic aromatic compound due to sulfur redox is superimposed. Since the electrode active material of the present invention superimposes the capacitance of the aromatic compound on the sulfur redox capacity, it is not possible to superimpose the capacitance if the sulfur content is too high, and if it is too low, the sulfur The redox capacity of becomes too small. For this reason, it is considered that the effect of further improving the cycle characteristics and capacity is remarkably exhibited when the sulfur content is more than 38 wt% and not more than 70 wt%.

Explanatory drawing of the evaluation cell 10. FIG. The figure which shows the charging / discharging behavior of Example 1. The Raman spectrum of Examples 1-4 and the comparative example 2. FIG. Cyclic voltammetry of Example 1. Cyclic voltammetry of Comparative Example 4.

  The electricity storage device of the present invention uses, as an electrode active material, a polycyclic aromatic compound having carbon and sulfur as main components and a sulfur content of more than 38% by weight and 70% by weight or less and having a thiophene structure in the skeleton. ing. In this polycyclic aromatic compound, the sulfur content is more than 38% by weight and 70% by weight or less, and the sulfur content is more preferably 45% by weight or more and 65% by weight or less, and 50% by weight. More preferably, it is 60 weight% or less. If the sulfur content exceeds 38% by weight, the capacity of the battery can be further increased, and if it is 70% by weight or less, less excess sulfur is preferable. More preferably, sulfur is contained in the skeleton of the polycyclic aromatic compound or bonded to the polycyclic aromatic compound.

This polycyclic aromatic compound contains a thiophene structure in the skeleton, but considering the high conductivity, a structure in which aromatic rings are continuously connected is desirable, and in order to utilize capacitance, A larger area is desirable. This polycyclic aromatic compound preferably has a polythienoacene structure represented by the following formula (1), in which sulfur is contained in a cyclic structure and a thiophene structure is developed in a uniaxial direction. In this case, since sulfur is bonded to the ring structure, it is easy to suppress the shuttle effect that is a problem when using sulfur alone, and it is easier to suppress the decrease in capacity and the decrease in charge / discharge efficiency. Further, since the area is relatively large, the capacitance can be further increased. The Porichienoasen is whether it has the structure, in the Raman spectrum can be identified from the presence of weak peaks around the main peak and 1250 cm ^-1 in the vicinity of 1450 cm ^-1 (Reference: J.Phys.Chem.A, 110, 5058 (2006)). In this polythienoacene structure, the ratio of sulfur to carbon is 1: 2, and sulfur can be immobilized more efficiently.

  In this polycyclic aromatic compound, the element ratio S / C between sulfur and carbon is preferably 0.40 or more and 0.70 or less, more preferably 0.45 or more and 0.65 or less, and 0 More preferably, it is in the vicinity of .50. When the element ratio S / C is in the range of 0.40 or more and 0.70 or less, the abundance of the structure of the polycyclic aromatic compound is appropriate and the sulfur is sufficiently immobilized, and the capacitance between the polycyclic aromatic compounds is sufficient. Is easy to use. In particular, when the element ratio S / C is 0.50, there is a high possibility of a polythienoacene structure, and in addition to sulfur oxidation-reduction, it has a capacitance, and the capacity can be further increased.

  In the polycyclic aromatic compound, the total content of carbon and sulfur is preferably 85% by weight or more, and more preferably 90% by weight or more. It can be said that it is desirable that the content of nitrogen and oxygen is small in addition to the elements of carbon and sulfur. This is because nitrogen and oxygen have fewer arms that can be bonded than carbon and sulfur.

  In the electricity storage device of the present invention, it is preferable to perform an aging treatment in the range of 0.5 V or less on the basis of the Li potential in the initial charge / discharge to the electrode provided with the active material. In this way, the capacity can be further increased.

  Although the electricity storage device of the present invention is not particularly limited, lithium is interposed between the positive electrode having the above-mentioned polycyclic aromatic compound as a positive electrode active material, the negative electrode having a negative electrode active material, and the positive electrode and the negative electrode. An ion conducting medium that conducts ions.

  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 the above-described polycyclic aromatic compound bonded with sulfur.

  In the electricity storage device of the present invention, the negative electrode is prepared by, for example, mixing a negative electrode active material, a conductive material, and a binder, and adding a suitable solvent to form a paste-like negative electrode material on the surface of the current collector. However, it may be compressed to increase the electrode density as necessary. The negative electrode active material preferably contains a metal or metal ion. The negative electrode active material may include a material that absorbs and releases lithium. Here, examples of the material that occludes and releases lithium include metal oxides, metal sulfides, metal nitrides, and carbonaceous substances that occlude and release lithium, in addition to metal lithium and lithium alloys. Examples of the lithium alloy include alloys of lithium with aluminum, silicon, tin, magnesium, indium, calcium, and the like. Examples of the metal oxide include tin oxide, silicon oxide, lithium titanium oxide, niobium oxide, and tungsten oxide. Examples of the metal sulfide include tin sulfide and titanium sulfide. Examples of the metal nitride include lithium nitride. Examples of the carbonaceous material that occludes and releases lithium include graphite, coke, mesophase pitch-based carbon fiber, spherical carbon, and resin-fired carbon. For this negative electrode, a current collector, a conductive material, and a binder can be used as appropriate as in the case of the positive electrode.

  In the electricity storage device of the present invention, the conductive material used for the positive electrode and the negative electrode is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance. For example, natural graphite (scale graphite, flake graphite) or artificial Graphite such as graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, or a mixture of one or more of metals (copper, nickel, aluminum, silver, gold, etc.) Can be used. Among these, carbon black, ketjen black, and acetylene black are preferable as the conductive material 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. 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 active material, the conductive material, and the binder include ethanol, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, and N, N-dimethylamino. Organic solvents such as propylamine, 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. The thickness of the current collector is, for example, 1 to 500 μm.

In the electricity storage device of the present invention, the ion conductive medium may be a solution in which a supporting salt is dissolved in a solvent. The supporting salt is not particularly limited as long as it is a lithium salt used for a normal lithium secondary battery. For example, lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), Li (C ₂ F ₅ SO ₂ ) Known supporting salts such as ₂ N, LiPF ₆ , LiClO ₄ , and LiBF ₄ can be used. These may be used alone or in combination. The solvent of the ion conductive medium is not particularly limited, but carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC), ethers such as dimethoxyethane (DME), triglyme and tetraglyme, Cyclic ethers such as dioxolane (DOL) and tetrahydrofuran and mixtures thereof are preferred. Alternatively, ionic liquids such as 1-methyl-3-propylimidazolium bis (trifluorosulfonyl) imide and 1-ethyl-3-butylimidazolium tetrafluoroborate can be used. The ion conductive medium may be gelled by adding an electrolyte containing a supporting salt to a polymer such as polyvinylidene fluoride, polyethylene oxide, polyethylene glycol, polyacrylonitrile, or a saccharide such as an amino acid derivative or a sorbitol derivative. .

  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. Can be 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 cell type, a wound battery type, a laminate 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.

  Next, the manufacturing method of an electrode active material is demonstrated. This electrode active material contains the above-mentioned polycyclic aromatic compound to which sulfur is bonded. The production method for producing the electrode active material of the present invention comprises mixing at least one of an aliphatic polymer compound having a linear structure and a polymer compound having a thiophene structure with sulfur, heating the mixture in an inert atmosphere, and surplus The production | generation process which produces | generates the polycyclic aromatic compound which has a thiophene structure in frame | skeleton by performing the process which removes sulfur of this is included.

  Examples of the polymer compound used as a raw material in the generation step include an aliphatic polymer compound having a linear structure and a polymer compound having a thiophene structure. Examples of the aliphatic polymer compound having a linear structure include polyethylene. Examples of the polymer compound having a thiophene structure include polythiophene. In this production step, excess sulfur is removed by heating the conjugate obtained by mixing the polymer compound and sulfur in an inert atmosphere at a temperature not lower than the boiling point of sulfur in the inert atmosphere. It is good also as what to do. In the heating for generating the combined product, the reaction may be performed at a temperature equal to or higher than the melting point of sulfur, for example, at a high temperature of 300 ° C. to form a carbon-sulfur bond while removing hydrogen sulfide. Moreover, in the heating which removes surplus sulfur, it is good also as what removes by heating to 450 degreeC or more vicinity of the boiling point of sulfur, volatilizing surplus sulfur. Examples of the inert atmosphere include a nitrogen atmosphere, a helium atmosphere, and an argon atmosphere. Moreover, in a production | generation process, it is good also as what heats to produce | generate the polycyclic aromatic compound whose sulfur content exceeds 38 weight% and is 70 weight% or less. Alternatively, in the production step, surplus sulfur is obtained by mixing the above conjugate with a good sulfur solvent such as carbon disulfide so that the sulfur content is more than 38% by weight and 70% by weight or less. It is good also as what removes. Thus, a sulfur-bonded polycyclic aromatic compound as an electrode active material can be obtained.

  Here, the capacity development mechanism of the electrode active material of the electricity storage device of the present invention will be considered. The polycyclic aromatic compound, which is the electrode active material of the present invention, is considered to have a structure in which molecules are stacked due to intermolecular interactions such as van der Waals force and π-π interaction. In this state, although the specific surface area is small, for example, when the intermolecular distance increases due to sulfur becoming an anion, for example, the solvent and Li ions can enter the interlayer, and the capacitance as a capacitor increases significantly. Conceivable. And since this electrostatic capacitance is superimposed on the discharge capacity due to oxidation and reduction of sulfur, it is presumed that a large capacity appears. In addition, the oxidation-reduction potential of sulfur is around 2V with respect to the Li electrode, whereas that of carbon is slightly over 3V. Therefore, when the capacitance increases at a stretch in the vicinity of 2V, a capacity corresponding to the voltage difference between the open circuit voltage of 3V or more and the reduction potential of sulfur of about 2V is immediately developed in the vicinity of 2V. Battery-like constant voltage discharge (charge that is negatively charged as a capacitor) occurs. The reverse phenomenon occurs reversibly during charging. Therefore, the electricity storage device of the present invention can express much larger capacity than the capacity expected from the sulfur content, and is considered to be an epoch-making electricity storage device with an unprecedented mechanism.

  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]
In an eggplant-shaped flask, 2.4 g of polyethylene (manufactured by Aldrich) and 17 g of sulfur powder (75 μm or less, 99.99%, high-purity chemical) were added, and the temperature was raised to 300 ° C. over 4 hours while stirring. . Heating at 300 ° C. for 7 hours gave 9.1 g of a black solid. From the change in weight, 74% by weight of the sulfur component remained. This black solid was ball milled to obtain black powder PES300. 0.3 g of this powder was placed in a test tube, heated to 450 ° C. in a tube furnace in a nitrogen atmosphere, and maintained for 3 hours. After cooling to room temperature, black powder PES300-450 was obtained (polymer-sulfur composite). 70% by weight of this PES300-450, 20% by weight of carbon (LCP ECP600JD), 10% by weight of polytetrafluoroethylene (PTFE) as a binder, kneaded well in a mortar until it becomes a bowl, sheet-like Molded into. A 12 mm diameter circular shape was cut out and vacuum dried to obtain a positive electrode material. Using this positive electrode material, Li metal as a negative electrode, porous polyethylene as a separator, and electrolyte (1M-LiPF ₆ ethylene carbonate EC + diethyl carbonate DEC (volume ratio 3: 7)), the evaluation cell of FIG. Was made. The obtained evaluation cell was defined as Example 1. Note that a Li plate having a thickness of 0.4 mm and a diameter of 18 mm was used for Li, and the weight of the positive electrode material was 3 mg and the electrode area was 1.3 cm ² .

  1A and 1B are explanatory views of the evaluation cell 10, FIG. 1A is a cross-sectional view before the evaluation cell 10 is assembled, and FIG. 1B is a cross-sectional view after the evaluation cell 10 is assembled. An evaluation cell 10 was produced in a glove box under an argon atmosphere. In assembling the evaluation cell 10, first, a negative electrode 16 and a polyethylene separator 18 (a microporous polyethylene film, a microporous polyethylene film, a cavity 14 provided in the center of the upper surface of a stainless steel cylindrical substrate 12 with a thread groove engraved on the outer peripheral surface thereof. Tonen Chemical Co., Ltd.) and the positive electrode 20 were laminated in this order while injecting an appropriate amount of a non-aqueous electrolyte into the cavity 14. Further, an insulating ring 29 made of polypropylene is inserted, and then a conductive column 24 fixed in a liquid-tight manner in the hole of the insulating ring 22 is disposed on the positive electrode 20, and a conductive cup-shaped lid 26 is formed on the cylinder. Screwed into the substrate 12. Further, an insulating resin ring 27 is disposed 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, the solid electrolyte membrane 18, and the positive electrode 20 were pressed and adhered. Thus, the evaluation cell 10 was produced. 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 this evaluation cell 10, the lid 26, the pressure bolt 25, and the cylindrical base 12 are integrated with the negative electrode 16, so that the whole becomes 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. The evaluation cell thus obtained was named Example 1.

(Elemental analysis)
Elemental analysis was performed on the obtained sample. The elemental analysis of CHN was performed by a combustion method using a fully automatic elemental analyzer (manufactured by Elemental Co., VarioEL). The sulfur was analyzed by flask combustion-ion chromatography. As a system for sulfur analysis, DX320 manufactured by Dionex was used, the column was IonPacAS12A, and the mobile phase was Na ₂ CO ₃ (2.7 mmol / L) / NaHCO ₃ (0.3 mmol / L).

(Raman spectrum analysis)
Raman spectroscopic measurement was performed on the obtained sample. The Raman spectrum analysis was measured using a laser Raman spectroscopy system (manufactured by JASCO Corporation, NRS-3300). Raman spectroscopic measurement was performed with excitation light having a wavelength of 532 nm. The Raman spectra of Examples 1 to 4 and Comparative Example 2 are shown in FIG.

(Evaluation of electrochemical properties)
The electrochemical characteristics of the obtained evaluation cell were evaluated. In the evaluation of electrochemical characteristics, the capacity per unit weight of the polymer-sulfur composite material (mAh / g), the charge / discharge efficiency (%), the capacity per unit weight of sulfur (mAh / g-S), the 50th cycle The capacity (mAh / g) was examined. First, the evaluation cell was installed in a constant temperature bath at 25 ° C., and constant current charging / discharging at 0.5 mA was performed twice in the region from 3.0 V to 0.5 V as initial aging at this temperature. Thereafter, as a charge / discharge test, a constant current charge / discharge of 0.5 mA was performed in a region of 1.0 V to 3.0 V. A cycle test in which this constant current charging / discharging was repeated 50 cycles was performed, and the capacity per unit weight (mAh / g) of the composite material at the first, fifth and 50th cycles was determined. Each voltage value (V) shown here is a value based on the Li potential. Further, using the charge capacity and discharge capacity at the fifth cycle, the discharge capacity was divided by the charge capacity and multiplied by 100 to obtain the charge / discharge efficiency, and the capacity per unit weight of sulfur was calculated.

[Example 2]
A black powder PES300S450 was obtained in the same manner as in Example 1, except that 0.5 g of sulfur was mixed with 0.25 g of the black solid (PES300) obtained in the intermediate step of Example 1 above. It was. Using this sample, an evaluation cell obtained through the same steps as in Example 1 was defined as Example 2. Evaluation was performed in the same manner as in Example 1.

[Example 3]
A black powder PES300 was obtained through the same process as in Example 1 except that 0.25 g of the black solid (PES300) obtained in the intermediate process of Example 1 was heat-treated at 300 ° C. for 6 hours in a nitrogen atmosphere. I got -300. The weight of the obtained black powder was 0.18 g. Using this sample, an evaluation cell obtained through the same steps as in Example 1 was defined as Example 3. Evaluation was performed in the same manner as in Example 1.

[Example 4]
To 1 g of polythiophene (manufactured by Aldrich), 5 g of sulfur powder (75 μm or less, 99.99%, manufactured by High Purity Chemical) was added and mixed well. The test tube was placed in a tubular furnace in a nitrogen stream and heated to 300 ° C. over 1 hour. After heating for 3 hours, the temperature was raised to 450 ° C. over 30 minutes and allowed to stand for 3 hours to obtain black powder PTS450. Using this sample, an evaluation cell obtained through the same steps as in Example 1 was defined as Example 3. Evaluation was performed in the same manner as in Example 1.

[Comparative Example 1]
According to Example 1 of JP2003-123758, HCBS200 was synthesized as follows. Under an Ar atmosphere, 50 ml of a 1: 1 ethanol / water mixed solvent was added to 21.6 g of sodium sulfide nonahydrate and dissolved by stirring for 1 hour. Thereto, 12.8 g of sulfur was added and stirred to obtain a brown liquid. The mixture was heated to 50 ° C., stirred for 1 hour, and concentrated in vacuo. To this, 135 ml of dimethylformamide was added, and 7.75 g of hexachlorobutadiene was added thereto. After standing overnight, water was added to cause precipitation, and the solid content was collected by filtration. Washing with acetone gave a pink solid. This was heat-dried at 200 ° C. and ball milled to obtain HCBS200. Using this sample, an evaluation cell obtained through the same steps as in Example 1 was defined as Comparative Example 1. Evaluation was performed in the same manner as in Example 1.

[Comparative Example 2]
The evaluation cell obtained through the same steps as in Example 1 using the PES300 produced in Example 1 as it was, that is, using a sample in excess of sulfur, was referred to as Comparative Example 2. Evaluation was performed in the same manner as in Example 1.

[Comparative Example 3]
SSPYS450 was obtained in the same manner as in Example 1 except that polypyrrole (manufactured by SSPY) was used as the polymer. Using this sample, an evaluation cell obtained through the same steps as in Example 1 was defined as Comparative Example 3. Evaluation was performed in the same manner as in Example 1.

[Comparative Example 4]
50% by weight of sulfur, 10% by weight of PTFE, 40% by weight of carbon (ECP600JD manufactured by Lion Corporation) were obtained, and ECPS of 50% was obtained as a positive electrode material. An evaluation cell obtained through the same steps as in Example 1 using this sample was referred to as Comparative Example 4. Regarding the evaluation, since the electrolyte solution (EC + DEC) does not operate when sulfur alone is contained, the electrolyte solution of Comparative Example 4 is 1M-LiTFSI ( Evaluation was carried out in the same manner as in Example 1, except that the liquid was dimethoxyethane + dioxolane (volume ratio 9/1) of lithium bistrifluoromethanesulfonic acid imide).

  Table 1 summarizes the evaluation results of the capacities and charge / discharge efficiencies of Examples 1 to 3 and Comparative Examples 1 to 4. FIG. 2 shows the charge / discharge behavior of Example 1, which is a representative example. In general charge and discharge of sulfur alone, it is known that the plateau region where the voltage shows a substantially constant value with respect to the capacity change has two-stage characteristics depending on the oxidation state of sulfur. In No. 1, this plateau region has one stage, which is excellent in voltage stability. Although omitted here, the waveform was almost the same as in Example 1 although the capacity was different in other Examples.

FIG. 3 shows Raman spectra of Examples 1 to 4 and Comparative Example 2 as representative examples. In Examples 1 to 4, in the vicinity of 1450 cm ^-1 and a weak peak near the main peak and 1250 cm ^-1 was observed, was inferred to have a Porichienoasen structure. Further, according to the value of the element ratio S / C in Table 1, in Examples 1, 2, and 4, it was about 0.5, which was assumed to be a polythienoacene structure. Moreover, although Example 3 is the same processing temperature of 300 degreeC as the comparative example 2, processing time is as long as 6 hours and the sulfur component is fully removed. For this reason, in Example 3, the element ratio S / C value showed a relatively high value of 0.64, but it was very similar to the Raman spectrum of Examples 1, 2, and 4, and the polythienoacene structure was used as the main skeleton. It was inferred. On the other hand, in Comparative Example 2, although the attribution of the spectrum is not clear, there is a peak that is not seen in Examples 1 to 4, and the sulfur content is as high as 74% by weight, so that part of the thiophene skeleton is formed. However, it was inferred that the structure contained a polysulfide bond. Therefore, it was found that it is important to remove the sulfur component, which can be said to be excessive, by heat treatment.

  As shown in Table 1, those having a polycyclic aromatic compound having sulfur in the skeleton shown in Examples 1 to 4 showed high capacity, and the charge / discharge efficiency was also 100%. Looking at the capacity per sulfur, it exceeds the theoretical capacity of monovalent sulfur of 862 mAh / g, and it is clear that a large capacity is obtained by superimposing electrostatic capacity on the redox capacity of sulfur. It became. 4 and 5, as a representative example, PES300-450 of Example 1 and ECPS 50% of Comparative Example 4 are 2.2V to 3V after charging to 3V, or 1V to 2V after discharging to 2.5 to 3V, 1V. The cyclic voltammetry measured in the region of is shown. If these are compared, the change of the electrostatic capacitance as a capacitor after charge and after discharge will be understood. In Comparative Example 4 (ECPS 50%) using conventional sulfur alone, the capacitor components in both regions are almost the same and small, whereas in Example 1 (PES300-450), in the 1-2 V region after discharge. It can be seen that the capacitor component is very large and the capacitance is 9 times as large as the 2.2-3 V region after charging. This is a new phenomenon that has not been reported so far, and as a result, an extremely high performance active material has been realized. The capacitor component is presumed to be charge accumulation due to capacitance in the polycyclic aromatic moiety, and the development of its skeleton is considered to be important. Naturally, the sulfur concentration also has an effect, and when the sulfur concentration is 30% by weight or less as in Comparative Example 3, the capacity is low. On the contrary, in Comparative Example 1 in which the sulfur concentration is 80% by weight or more, the capacity is small, and the dissolution of the sulfur component occurs, so the charge / discharge efficiency is low. In Comparative Example 2 having a sulfur concentration of 74% by weight, although the capacity was large, the fifth decay was large and the charge / discharge efficiency was considerably low. In Comparative Example 2, it was presumed that the polythienoacene structure was not developed, and polysulfide ions were generated from the contained polysulfide structure by charge and discharge, and this was self-discharged by the shuttle effect, so that the charge efficiency was lowered. From the above results, it was found that the sulfur concentration is more than 38% by weight and 70% by weight or less, more preferably 45% by weight or more and 65% by weight or less.

  The present invention can be used in the industrial field related to batteries.

10 Evaluation Cell, 12 Cylindrical Base, 14 Cavity, 16 Negative Electrode, 18 Separator, 20 Positive Electrode, 22 Ring, 24 Column, 25 Pressure Bolt, 25a Through Hole, 26 Lid, 26a Opening, 27 Insulating Resin Ring, 28 Packing, 29 Insulation ring.

Claims (6)

An electricity storage device using a polycyclic aromatic compound having carbon and sulfur as main components and a sulfur content of 45 wt% or more and 65 wt% or less and having a thiophene structure in a skeleton as an electrode active material.   The electricity storage device according to claim 1, wherein the polycyclic aromatic compound has a polythienoacene structure containing sulfur. The electricity storage device according to claim 1 or 2, wherein the polycyclic aromatic compound has an element ratio S / C of sulfur to carbon of 0.45 or more and 0.65 or less. A manufacturing method for manufacturing an electrode active material used for an electrode of an electricity storage device,
By mixing at least one of an aliphatic polymer compound having a straight chain structure and a polymer compound having a thiophene structure with sulfur, heating in an inert atmosphere, and removing excess sulfur, the inside of the skeleton A production step of producing a polycyclic aromatic compound having a thiophene structure in
A method for producing an electrode active material comprising:   In the production step, excess sulfur is removed by heating the conjugate obtained by mixing the polymer compound and sulfur and heating in an inert atmosphere at a temperature equal to or higher than the boiling point of sulfur in the inert atmosphere. The manufacturing method of the electrode active material of Claim 4.   6. The method for producing an electrode active material according to claim 4, wherein in the generation step, heating is performed so as to generate a polycyclic aromatic compound having a sulfur content of more than 38 wt% and 70 wt% or less.

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