JP4343819B2 - Redox-active polymer, electrode using the same, and non-aqueous battery - Google Patents

Description

  The present invention relates to a redox active polymer, an electrode using the same, and a non-aqueous battery.

  In recent years, the demand for batteries with high energy density has increased. As one of such batteries, a lithium battery having a high voltage of a single battery can be given. According to the lithium battery, a high voltage of 3 V or higher can be obtained by using a non-aqueous electrolyte, but the capacity per weight of the electrode material of each of the positive and negative electrodes is, for example, that of cobalt lithium oxide used for the positive electrode As in the case of 140 to 150 mAh / g, it is not always sufficient.

  Therefore, various electrode materials that can increase the capacity per weight for each of the positive and negative electrodes have been studied. Among these, metal oxides such as manganese, iron, and niobium have been studied for the positive electrode. However, it is difficult to obtain a large capacity because all of them are heavy and have a small number of reaction electrons.

  In addition, since the weight is small, the use of a conductive polymer such as polyaniline as a positive electrode material has also been studied. However, the number of reaction electrons per unit molecular weight of polyaniline is 0.5, and the capacity per weight is 145 mAh / g. It is before and after and does not greatly exceed the lithium cobaltate.

  On the other hand, it is known that an organic sulfur polymer compound is used as a positive electrode material as a redox-active polymer having a high capacity and a high energy density (see Patent Document 1, Non-Patent Documents 1 and 2).

  The organic sulfur polymer compound has an S—S bond in the main chain and is represented by R—S—S—R. The organic sulfur polymer compound is reversible in that the SS bond is cleaved to form an organic thiolate (R-SH) in the reduced state, and the SS bond is regenerated by the organic thiolate bond in the oxidized state. A typical redox reaction is performed. Therefore, when the organic sulfur polymer compound is used as a positive electrode material, it can be charged and discharged using the oxidation-reduction reaction.

  However, the organic sulfur polymer compound has a problem that the reaction rate is slow because of a large difference in oxidation-reduction potential, and a high temperature of 100 ° C. or higher is required to operate as a battery. In addition, when the organic sulfur polymer compound is reduced to become an organic thiolate, the molecular weight is small, so that the organic sulfur polymer compound is dissolved in the electrolytic solution and diffuses outside the electrode, which tends to cause capacity deterioration.

  In order to solve the problem in the organic sulfur polymer compound, a redox reaction is performed by providing a pair of S atoms at adjacent positions in the molecule and cleaving and reforming SS bonds between adjacent S atoms. There has been proposed a redox-active polymer adapted to perform (see, for example, Patent Document 2).

However, the redox-active polymer does not have a sufficient capacity per weight, and the capacity tends to decrease when the charge / discharge cycle is repeated, and a further excellent redox-active polymer is desired. .
US Pat. No. 4,833,048 JP 2001-72865 A J. Electrochem. Soc., Vol 136, p.661-664 (1989) J. Electrochem. Soc., Vol 136, p. 2570-2575 (1989)

  An object of the present invention is to provide an oxidation-reduction active polymer that can solve such disadvantages, can be operated at a low temperature, can obtain a large capacity, and hardly deteriorates even after repeated charge and discharge cycles. To do.

  Another object of the present invention is to provide an electrode using the redox-active polymer and a nonaqueous solution battery using the electrode as a positive electrode.

In order to achieve this object, the redox active polymer of the present invention is a copolymer of a dithiobiurea derivative and an aromatic compound having two or more isothiocyanate groups, and in the reduced state, the general formula (1) It is characterized by having a structure represented by the general formula (2) in an oxidized state.

  In the present specification, the dithiobiurea derivative may be dithiobiurea itself or a compound in which a lower alkyl group having 1 to 3 carbon atoms is bonded to at least one S atom of dithiobiurea. The aromatic compound may be a hydrocarbon-based aromatic compound such as benzene or naphthalene, or a heterocyclic compound having aromaticity.

  In the oxidation-reduction active polymer of the present invention, an oxidation-reduction reaction can be performed by S—S bond cleavage and reformation between adjacent S atoms of a dithiobiurea derivative. Therefore, according to the oxidation-reduction active polymer of the present invention, the oxidation-reduction reaction can be performed at a low temperature of about room temperature, and a large capacity per weight can be obtained. In addition, according to the redox active polymer, the SS bond is provided in the side chain of the repeating unit and forms a bond in the molecule. Therefore, even if the SS bond is cleaved by reduction, the low molecular weight Therefore, the deterioration of the capacity due to the diffusion outside the electrode can be prevented, and the deterioration due to the repeated charge / discharge cycle can be reduced.

Comprising a structure represented by the general formula (1) in its original state changed, as the redox-active polymer comprising a structure represented by the general formula (2) oxidation state, for example, 2,5-Jichiobiurea -S, A redox-active polymer having a structure represented by the general formula (3), which is obtained by copolymerizing S′-alkyl ether and phenylene-1,4-diisothiocyanate, can be exemplified.

In the general formula (3), R ² is a protecting group for the S atom of the dithiobiurea derivative, and a benzyl group may be used in place of the lower alkyl group. As the redox active polymer using a benzyl group as the protecting group, for example, 2,5-dithiobiurea-S, S′-benzyl ether and phenylene-1,4-diisothiocyanate are copolymerized, A redox active polymer having a structure represented by the general formula (4) can be mentioned.

  The electrode of the present invention is characterized by containing the redox active polymer as an electrode material. The non-aqueous battery of the present invention comprises a positive electrode, an electrolyte, and a negative electrode, and the positive electrode is oxidized. It is characterized by comprising an electrode containing a reducing active polymer as an electrode material.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a graph showing changes over time in battery terminal voltage during charge / discharge of a non-aqueous battery using an electrode made of a redox active polymer according to the first embodiment of the present invention as a positive electrode.

  Next, a first embodiment of the present invention will be described.

  In this embodiment, first, 150 mg of 2,5-dithiobiurea (manufactured by Sigma-Aldrich) is dissolved in a mixed solvent obtained by mixing 4 ml of N-methyl-2-pyrrolidone and 4 ml of ethanol, and 270 mg of benzyl chloride is added to the resulting solution. Was dripped. The obtained solution was heated to reflux for 30 minutes and cooled to room temperature, and then an alkaline solution in which 80 mg of sodium hydroxide was dissolved in 10 ml of distilled water was added to the reaction solution. Next, 40 ml of ether was added to the reaction solution, and the ether layer was extracted. After adding 150 mg of anhydrous magnesium sulfate to the obtained ether solution and stirring for 2 hours, the ether solution was filtered and the filtrate was distilled to obtain 325 mg of 2,5-dithiobiurea-S, S′-benzyl ether. . The reaction is shown in the following formula (5).

  Next, 320 mg of 2,5-dithiobiurea-S, S′-benzyl ether was dissolved in a mixed solvent of 10 ml of dried tetrahydrofuran (dry THF) and 10 ml of dried benzene (dry benzene). -A dithiobiurea-S, S'-benzyl ether solution was prepared. Next, a solution obtained by dissolving phenylene-1,4-diisothiocyanate (manufactured by Sigma Aldrich) in a mixed solvent of 5 ml of dry THF and 5 ml of dry benzene in the 2,5-dithiobiurea-S, S′-benzyl ether solution. And heated to reflux for 3 days. The obtained reaction solution was filtered, and the solid on the filter paper was washed with acetone to obtain 87 mg of S-benzylated dithiobiuret polymer. The reaction is shown in the following formula (6). The S-benzylated dithiobiuret polymer is represented by A in the following formula (6).

  Next, the S-benzylated dithiobiuret polymer A was pulverized and classified to obtain about 75 mg of powder having a particle size of 10 to 30 μm. Next, when the conductivity was confirmed using a part of the powder, it was found that the S-benzylated dithiobiuret polymer A was not electrically conductive and was an electrically insulating substance.

  Next, 20 mg of acetylene black as a conductive additive and 10 mg of polytetrafluoroethylene (PTFE) as a binder were added to 70 mg of the powder, and mixed well in a very small V mixer. Next, a sheet-like body having a thickness of about 0.5 mm was formed using a mixture of the powder, acetylene black, and PTFE, which was sufficiently stirred in an automatic mortar. Next, a disk having a diameter of 14 mm was punched from the sheet-like body, superimposed on a pure titanium net having a diameter of 14 mm, and integrated by forming a pressure with a hydraulic press to form an electrode. The weight of the electrode minus the weight of the pure titanium net was 36 mg. The positive electrode was vacuum-dried at 80 ° C. for 16 hours, and then stored in a glove box having a dew point of −80 ° C. or lower in which argon gas was circulated.

Next, the electrode is used as a working electrode, and a 20 mm × 20 mm pure titanium net is superimposed on a 20 mm × 20 mm lithium foil having a purity of 99.99% and a thickness of 0.2 mm, and is pressed with a hydraulic press. The two electrodes formed integrally with each other were used as a counter electrode and a reference electrode, respectively, and the working electrode, the counter electrode, and the reference electrode were immersed in an electrolyte contained in a beaker. As the electrolytic solution, 100 ml of a 1 mol / l solution in which LiClO ₄ was dissolved in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 1: 1 (volume ratio) was used. The working electrode was electrochemically oxidized at 0.1 mA for 55 hours. The voltage between the reference electrode and the working electrode was 1.85 V at the start and 4.23 V at the end. As a result, the S-benzylated dithiobiuret polymer A constituting the working electrode was electrochemically oxidized, and a 1,2,4-dithiazoline polymer B was obtained as shown in the following formula (7). .

Next, the working electrode was used as a positive electrode, and a battery was prepared using components of a commercially available coin-type cell (CR2032). A disk made of lithium foil having a purity of 99.99%, a thickness of 0.2 mm, and a diameter of 15.3 mm was used as the negative electrode, and a disk made of polyolefin resin having a thickness of 30 μm and a diameter of 20 mm was vacuum-dried at 60 ° C. for 24 hours. Then, what was stored in the said glove box was made into the separator. In addition, as the electrolytic solution, a solution having a concentration of 1 mol / l obtained by dissolving LiClO ₄ in a solvent in which ethylene carbonate and diethyl carbonate were mixed at 1: 1 (volume ratio) was used, and 600 μl of the LiClO ₄ solution was placed on the separator. The solution was injected to assemble a non-aqueous battery.

  Next, the non-aqueous battery was allowed to stand for 24 hours, and then charged and discharged repeatedly at an ambient temperature of 25 ± 2 ° C. to evaluate the performance of the battery. The open circuit voltage before charging / discharging was 4.0V.

  The first discharge had a constant current of 0.2 mA, a final voltage of 2.0 V, and a discharge capacity of 5.0 mAh. The next charging was performed at a constant current of 0.2 mA up to a final voltage of 4.2 V, and then at a constant voltage of 4.2 V until the charging current reached 0.02 mA. The charge capacity was 5.1 mAh.

  The second discharge was performed under the same conditions as the first discharge, the discharge capacity was 4.8 mAh, and the average discharge voltage was 2.67V. The results are shown in FIG.

  Further, in the non-aqueous battery, the discharge capacity at the 20th cycle was 4.3 mAh, and no significant decrease in capacity was observed with respect to the initial discharge capacity.

  When calculated from this result, it is apparent that the electrode material made of the redox active polymer of the present embodiment has a capacity of about 290 mAh / g or more in the initial stage.

  In the embodiment, the positive electrode is formed by using acetylene black as a conductive additive and polyvinylidene fluoride as a binder together with the polymer compound for electrode material. However, other carbon materials, metal powders, conductive polymers, etc. may be used as the conductive aid, and any polymer may be used as the binder as long as it is a polymer that is normally used for electrode preparation. Also good.

  In addition to the acetylene black, examples of the carbon material include ketjen black, graphite, and scaly graphite. Examples of the metal powder include powders of nickel, titanium, silver, and the like. Examples of the conductive polymer include polyaniline, polypyrrole, and polyacetylene.

  On the other hand, examples of the polymer used for the binder include polytetrafluoroethylene (PTFE) in addition to the polyvinylidene fluoride.

  Next, a second embodiment of the present invention will be described.

  In this embodiment, first, 0.45 g of the S-benzylated dithiobiuret polymer A represented by the above formula (6), which is sufficiently pulverized in an agate mortar, 0.45 g of acetylene black and polyfluoride as a binder. Add 0.1 g of vinylidene powder and mix well, then add 2.5-2.6 g of N-methyl-2-pyrrolidone (NMP) little by little and mix well to obtain a kneaded product with a viscosity that is easy to apply. It was.

  Next, the kneaded material was applied to a 20 μm thick aluminum foil in a uniform thickness and then dried to form a sheet-like body composed of the kneaded material and the aluminum foil. The drying was performed in a constant temperature bath at a temperature of 80 ° C. for 4 hours, followed by further drying at a temperature of 110 ° C. for 2 hours. Next, the said sheet-like body was pressurized with the roller, and the total thickness of the said aluminum foil and the said kneaded material was 70 micrometers.

  Next, a disk having a diameter of 14 mm was punched from the sheet-like body to form an electrode. Next, after the electrode was vacuum-dried at 80 ° C. for 16 hours, it was transferred into a glove box having a dew point of −80 ° C. or less in which argon gas was circulated, and the weight was measured, and the weight of the aluminum foil was subtracted. The weight of the electrode was 9 mg.

Next, the electrode was used as a positive electrode, and a battery was created in the glove box using components of a commercially available coin-type cell (CR2032). In the battery, a disk made of lithium foil having a purity of 99.99%, a thickness of 0.2 mm, and a diameter of 15.3 mm was used as the negative electrode, and a disk made of polyolefin resin having a thickness of 20 μm and a diameter of 20 mm was used at 60 ° C. What was stored in the glove box after vacuum drying for a time was used as a separator. As the electrolytic solution, a solution having a concentration of 1 mol / l obtained by dissolving LiClO ₄ in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a ratio of 1: 1 (volume ratio) is used, and 200 μl of the electrolytic solution is poured onto the separator. After the electrolyte was sufficiently permeated into the separator, the battery was assembled to obtain a non-aqueous battery.

  Next, the non-aqueous battery was allowed to stand at room temperature (25 ° C.) for 24 hours, and then charged and discharged repeatedly at the same room temperature to evaluate the performance of the battery. The charging was performed at a constant current of 0.1 mA until the voltage reached 4.20 V, and thereafter, the charging current was decreased at a constant voltage of 4.20 V to 0.01 mA. The discharge was performed at a constant current of 0.1 mA until the voltage dropped to 2.0V.

  Table 1 shows the discharge capacity (mAh / g) per weight in the first cycle, the third cycle, the 10th cycle, and the 20th cycle when charging and discharging are repeated 20 times under the above conditions.

  Next, a comparative example of the present invention will be described.

  In this comparative example, first, 406 mg of N, N′-1,4-phenylenebisthiourea-S, S′-benzyl ether was dissolved in a mixed solvent of 10 ml of dry THF and 10 ml of dry benzene, and N, N′-1, A 4-phenylenebisthiourea-S, S′-benzyl ether solution was prepared. Next, 200 mg of phenylene-1,4-diisothiocyanate is dissolved in a mixed solvent of 5 ml of dry THF and 5 ml of dry benzene in the N, N′-1,4-phenylenebisthiourea-S, S′-benzyl ether solution. Was added and heated to reflux for 3 days. The obtained reaction solution was filtered, and the solid on the filter paper was washed with acetone to obtain 100 mg of S-benzylated poly (1-phenyl 2,4-dithiobiuret). The reaction is shown in the following formula (8). The S-benzylated poly (1-phenyl 2,4-dithiobiuret) is represented by C in the following formula (8).

  Next, an electrode was formed in the same manner as in the second embodiment except that S-benzylated poly (1-phenyl 2,4-dithiobiuret) C represented by the formula (8) was used. Next, when the weight of the electrode was measured in exactly the same manner as in the second embodiment, the weight of the electrode minus the weight of the aluminum foil was 10 mg.

  Next, a nonaqueous solution battery was obtained in exactly the same manner as in the second embodiment except that the electrode obtained in this comparative example was used as a positive electrode. Next, the performance of the non-aqueous battery was evaluated in the same manner as in the second embodiment. Table 1 shows the discharge capacity (mAh / g) per weight of the first cycle, the third cycle, the 10th cycle, and the 20th cycle when the charge / discharge cycle is repeated 20 times.

  From Table 1, according to the battery of the second embodiment of the present invention, even after 20 cycles of charge and discharge, the discharge capacity is larger than that of the battery of the comparative example, and the redox active polymer is hardly deteriorated. it is obvious.

The graph which shows the time-dependent change of the battery terminal voltage at the time of charging / discharging of the nonaqueous solution type | system | group battery which used the electrode which consists of a high molecular compound for electrode materials of one Embodiment of this invention for the positive electrode.

Explanation of symbols

  No sign.

Claims (5)

A copolymer of a dithiobiurea derivative and an aromatic compound having two or more isothiocyanate groups,
An oxidation-reduction active polymer comprising a structure represented by the general formula (1) in a reduced state and a structure represented by the general formula (2) in an oxidized state.

A 2,5-dithiobiurea-S, S′-alkyl ether and a phenylene-1,4-diisothiocyanate are copolymerized to have a structure represented by the general formula (3). 1 Symbol placement redox-active polymer of claim.

2,5-dithiobiurea-S, S′-benzyl ether and phenylene-1,4-diisothiocyanate are copolymerized to have a structure represented by the general formula (4) 1 Symbol placement redox-active polymer of claim.

A copolymer of a dithiobiurea derivative and an aromatic compound having two or more isothiocyanate groups,
An electrode comprising a redox active polymer having a structure represented by the general formula (1) in a reduced state and having a structure represented by the general formula (2) in an oxidized state as an electrode material.

A copolymer of a dithiobiurea derivative and an aromatic compound having two or more isothiocyanate groups,
It comprises an electrode comprising a redox-active polymer having a structure represented by general formula (1) in the reduced state and having a structure represented by general formula (2) in the oxidized state as an electrode material. Non-aqueous battery.

Images