Solid-state secondary battery, modified polyglycolic acid used in solid-state secondary battery, and manufacturing method

Abstract

[Problem] To provide a solid-state secondary battery that can be semi-permanently used and can be easily carried. [Solution] A metal carbon fiber is used as a current collector of a positive electrode. This secondary battery uses, as an active material for a positive electrode and a negative electrode thereof, a modified polyglycolic acid obtained by adding a vanadium compound to a glycolic acid oligomer and irradiating the result with microwaves to bond the vanadium to the glycolic acid oligomer. The molecular weight of the glycolic acid oligomer is 5,000-10,000, and preferably 6,000-8,000. The addition amount of the vanadium compound is 1-10 wt.%, and preferably 4-6 wt.%. The vanadium compound is a vanadic acid amine obtained by electrolyzing an aqueous ammonium vanadate solution.

Description

Solid-state secondary battery, modified polyglycolic acid for use in solid-state secondary battery, and manufacturing method

[0001] The present invention relates to a solid secondary battery, a modified polyglycolic acid used in the solid secondary battery, a method for producing the same, and an apparatus for producing the same.

[0002] In the technical field of secondary batteries, Patent Document 1 discloses an electrolyte reflux battery using redox flow. The electrolyte reflux battery disclosed in Patent Document 1 is configured to perform charging and discharging by utilizing changes in the valence of a positive electrode active material and a negative electrode active material, using, for example, vanadium-based metal ions with valences ranging from divalent to pentavalent as the positive electrode active material and the negative electrode active material, and circulating the active material and electrolyte using a pump.

[0003] Polyglycolic acid (PGA) is an environmentally friendly biodegradable plastic made from glycolic acid, and because of its excellent biocompatibility, it is used for surgical sutures, medical materials, etc. Patent Document 2 discloses a technique for using polyglycolic acid as a surgical fiber. Patent Document 3 discloses a technique for using polyglycolic acid to produce composite molded products by reducing its melt viscosity.

[0004] Patent Document 4 proposes a secondary battery using modified polyglycolic acid as the active material for the positive and negative electrodes, in which vanadium is bonded to glycolic acid oligomer by adding a vanadium compound to the glycolic acid oligomer and irradiating the glycolic acid oligomer with microwaves. Patent Document 5 discloses a method and an apparatus for producing the modified polyglycolic acid.

[0005] Japanese Patent Application Laid-Open No. 2007-305501 Japanese Patent Application Laid-Open No. 2005-516100 Japanese Patent Application Laid-Open No. 2010-215782 Japanese Patent No. 6704544 Japanese Patent No. 6712004

[0006] The technologies described in Patent Documents 1, 2, and 3 have the problem that the battery itself becomes large due to the tanks for storing the active material and electrolyte and the pumps for circulating them, making it difficult to carry. Furthermore, although the electrolyte in a redox flow battery is unlikely to change, there is a risk that the electrolyte may deteriorate depending on the installation conditions of the battery, and it may not be possible to use the battery semi-permanently.

[0007] Patent Document 4 proposes using polyglycolic acid as a secondary battery active material, but copper plate was used as the positive electrode current collector. Therefore, an adhesive was required to apply the polyglycolic acid to the copper plate, which reduced the performance of the secondary battery. Another problem was that the adhesive froze at temperatures between -5 and -20 degrees Celsius, impeding battery function. The object of the present invention is to provide a technology that solves the above-mentioned problems and to provide a material suitable for use as a positive electrode current collector.

[0008] In order to achieve the above object, the present invention provides a solid secondary battery, wherein the positive electrode current collector is a metal carbon fiber, the negative electrode current collector is an aluminum plate or a zinc plate, and the positive and negative electrode active materials are modified polyglycolic acid obtained by adding a vanadium compound to a glycolic acid oligomer and irradiating the glycolic acid oligomer with microwaves to bond vanadium to the glycolic acid oligomer, characterized in that the positive electrode is formed by coating the surface of a metal carbon fiber current collector for the positive electrode with the modified polyglycolic acid, and the negative electrode is formed by coating the surface of an aluminum or zinc plate current collector for the negative electrode with the modified polyglycolic acid. The metal carbon fiber used as the current collector is fibrous and has a diameter of 5 μm or less, and is preferably coated with a metal alloy and plastic.

[0009] In order to achieve the above object, the secondary battery according to the present invention is a solid secondary battery that uses, as a positive electrode, a first modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid, the surface of which is coated with metal carbon fiber as a current collector, and as a negative electrode, a second modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid, and an aluminum plate or zinc plate as a current collector.

[0010] Furthermore, to achieve the above object, the present invention provides a solid secondary battery in which the positive electrode active material is a third modified polyglycolic acid having a structure in which vanadium having a valence of five is bonded to polyglycolic acid, and the negative electrode active material is a fourth modified polyglycolic acid having a structure in which vanadium having a valence of two is bonded to polyglycolic acid. Furthermore, to achieve the above object, the present invention provides a secondary battery in which, during discharge, the positive electrode active material is a first modified polyglycolic acid having a structure in which vanadium having a valence of four is bonded to polyglycolic acid, and the negative electrode active material is a second modified polyglycolic acid having a structure in which vanadium having a valence of three is bonded to polyglycolic acid, and during charge, the positive electrode active material is a third modified polyglycolic acid having a structure in which vanadium having a valence of five is bonded to polyglycolic acid, and the negative electrode active material is a fourth modified polyglycolic acid having a structure in which vanadium having a valence of two is bonded to polyglycolic acid.

[0011] In order to achieve the above object, the method for manufacturing a secondary battery according to the present invention includes: a positive electrode production step of applying a modified polyglycolic acid containing equal amounts of a first modified polyglycolic acid having a structure in which vanadium having a tetravalent valence is bonded to polyglycolic acid and a second modified polyglycolic acid having a structure in which vanadium having a trivalent valence is bonded to polyglycolic acid to a current collector that will serve as a positive electrode; a negative electrode production step of applying the modified polyglycolic acid to a current collector that will serve as a negative electrode; a laminating step of bonding the positive electrode and the negative electrode together with the modified polyglycolic acid sandwiched between them; and an initialization step of applying a constant voltage between the positive electrode and the negative electrode, wherein the laminating step includes a step of sandwiching a separator made of cellulose acetate between the modified polyglycolic acid of the positive electrode and the modified polyglycolic acid of the negative electrode to separate the positive electrode and the negative electrode.

[0012] According to the present invention, a solid secondary battery that can be used semi-permanently and is easily portable can be provided. In addition, by using a metal carbon fiber as the positive electrode current collector, a solid secondary battery that can be manufactured inexpensively and has high capacity can be provided.

[0013] 1 is a diagram showing an outline of a manufacturing procedure for modified polyglycolic acid according to the first embodiment; FIG. 2 is a diagram showing an outline of a manufacturing procedure for glycolic acid according to the first embodiment; FIG. 3 is a diagram showing an outline of a manufacturing procedure for amine vanadate according to the first embodiment; FIG. 4 is a diagram showing the configuration of a secondary battery using modified polyglycolic acid according to the second embodiment; FIG. 5 is a diagram showing an outline of a procedure for initializing a secondary battery according to the second embodiment; FIG. 6 is a diagram showing an outline of a procedure for charging and discharging a secondary battery according to the second embodiment; FIG. 7 is a diagram showing the configuration of an apparatus for manufacturing modified polyglycolic acid according to the first embodiment; FIG. 8 is a flowchart showing the manufacturing process for modified polyglycolic acid according to the first embodiment; FIG. 9 is a graph showing current-potential characteristics, which are test results for the oxidation number of vanadium in the modified polyglycolic acid manufactured by the first embodiment; FIG. 10 is a diagram showing a manufacturing procedure for glycolic acid oligomer according to the first embodiment; FIG. 11 is a diagram showing the configuration of an apparatus for manufacturing amine vanadate according to the first embodiment; FIG. 12 is a flowchart showing the manufacturing process for amine vanadate according to the first embodiment; FIG. 13 is a flowchart showing the manufacturing process for a secondary battery using modified polyglycolic acid according to the second embodiment; FIG. 14 is a flowchart showing the initial charging process for a secondary battery using modified polyglycolic acid according to the second embodiment; FIG. 15 is a diagram illustrating a prototype battery of a secondary battery using modified polyglycolic acid according to the second embodiment and its test state; FIG. 16 is a diagram showing the initial charge characteristics during initialization of a secondary battery according to the second embodiment. 1 is a diagram showing the discharge characteristics during discharge of a secondary battery according to Example 2. FIG. 2 is a diagram showing another example using modified polyglycolic acid. FIG. 3 is a diagram explaining a prototype solid secondary battery using modified polyglycolic acid with a metal carbon fiber current collector.

[0014] Hereinafter, embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the components described in the following embodiments are merely examples and are not intended to limit the technical scope of the present invention.

[0015] [First Embodiment] First, as the first embodiment, modified polyglycolic acid will be described. Note that "modified polyglycolic acid" is polyglycolic acid produced from glycolic acid as a source, which has been further chemically treated. In other words, it can be positioned as a vanadium-polyglycolic acid complex having a structure in which vanadium is bonded to polyglycolic acid in which multiple glycolic acid molecules are bonded.

[0016] The present inventors have been conducting research into ways to enhance the durability and functionality of polyglycolic acid as an industrial material while maintaining its biodegradability. During this research, they developed a method for producing modified polyglycolic acid with excellent electrical properties, which led to the present invention. The present invention relates to a method and apparatus for producing modified polyglycolic acid, which incorporates vanadium element into the polyglycolic acid molecule and is oxidized and reduced by an external electric field. This method and apparatus provide electronic and battery materials with unprecedented properties.

[0017] <Structure of Modified Polyglycolic Acid> The modified polyglycolic acid according to this embodiment contains equal amounts of modified polyglycolic acid having a structure in which vanadium having a valence of tetravalent is bonded to polyglycolic acid and modified polyglycolic acid having a structure in which vanadium having a valence of trivalent is bonded to polyglycolic acid. The structure is shown in the following chemical formula (1). Note that, within chemical formula (1), the modified polyglycolic acid having a structure in which vanadium having a valence of tetravalent is bonded will be referred to separately as chemical formula (8) in [Chemical Formula 8], and the modified polyglycolic acid having a structure in which vanadium having a valence of trivalent is bonded will be referred to separately as chemical formula (9) in [Chemical Formula 9].

[0018] Thus, when the modified polyglycolic acid according to this embodiment is used as an active material for a secondary battery, for example, a material containing a substance that serves as both a positive electrode active material and a negative electrode active material can be produced without separately producing the active materials. By electrically initializing this manufactured material, it can be used as an electronic material with various properties, including secondary batteries. The preferred molecular weight range for the modified polyglycolic acid of chemical formula (1) when used in a secondary battery is approximately 5,000 to 7,000 in number average molecular weight. This is because the modified polyglycolic acid must have a relatively low molecular weight, allowing the hydrogen atoms that serve as carriers to migrate.

[0019] <Outline of the method for producing modified polyglycolic acid> Figure 1 is a diagram showing an outline of the method for producing modified polyglycolic acid according to this embodiment. Note that "glycolic acid oligomer" refers to a relatively low molecular weight polyglycolic acid having a molecular weight of 5,000 or more and 10,000 or less.

[0020] The present inventors have found that polyglycolic acid with a large molecular weight is not necessary to produce modified polyglycolic acid, and that polyglycolic acid with a relatively small molecular weight (so-called glycolic acid oligomer) tends to be easier to produce. As a result, they have established the technology of the present embodiment for producing modified polyglycolic acid in a complete process from acetic acid, which is the initial raw material.

[0021] Step S101: Glycolic acid 101, the raw material, is heated and dehydrated in a polymerization vessel to undergo controlled dehydration polycondensation to obtain glycolic acid oligomer 102. The molecular weight of glycolic acid oligomer 102 is preferably 5,000 to 10,000, and more preferably 6,000 to 8,000. This step is represented by the following chemical formula (2).

[0022] The reason for using glycolic acid oligomer 102 as an intermediate material is to facilitate the bonding of vanadium to polyglycolic acid, as described below. The production of glycolic acid oligomer 102 (S101) is achieved by the following process: Glycolic acid is heated to approximately 175°C to 185°C at atmospheric pressure, and the resulting water is distilled off. Subsequently, the pressure is reduced and the resulting mixture is maintained at that temperature for a predetermined time to obtain glycolic acid oligomer (low-molecular-weight PGA). However, this process requires a long time and results in a variable molecular weight (degree of polymerization). Therefore, in this embodiment, concentrated glycolic acid containing some glycolide is first produced. Then, rather than purifying the resulting concentrated glycolic acid, dehydration polycondensation is performed as is (still containing glycolide), thereby shortening the production time and producing glycolic acid oligomer with a molecular weight (degree of polymerization) within a consistent range. If only purified glycolide is used for ring-opening polymerization, a high molecular weight polyglycolic acid (molecular weight >10,000 or 20,000) will be obtained, which is disadvantageous for producing the modified polyglycolic acid of this example.

[0023] Step S103: An additive containing a transition metal is added to the obtained glycolic acid oligomer 102. As the additive containing a transition metal, amine vanadate (NH2VO2) is used.

[0024] Step S105: Microwave irradiation is performed on glycolic acid oligomer 102 to which a transition metal-containing additive (1 wt% to 10 wt%, preferably 4 wt% to 6 wt% of amine vanadate, a vanadium compound) has been added, to bond vanadium (i.e., substitute oxygen for the double bond of vanadium), thereby producing modified polyglycolic acid 103. This step is shown in the following chemical formula (3).

[0025] The resulting modified polyglycolic acid 103 contains approximately equal amounts of modified polyglycolic acid 131 bonded to tetravalent vanadium (V+IV) and modified polyglycolic acid 132 bonded to trivalent vanadium (V+III), as shown in chemical formula (1). While FIG. 1 shows the steps for producing glycolic acid oligomer 102, modified polyglycolic acid 103 of this embodiment can be produced by any method as long as glycolic acid oligomer 102 having the above molecular weight is provided as a raw material. In other words, the method for producing glycolic acid oligomer 102 is not limited.

[0026] In this way, in producing the modified polyglycolic acid 103, the modified polyglycolic acid 131 to which tetravalent vanadium (V+IV) is bonded and the modified polyglycolic acid 132 to which trivalent vanadium (V+III) is bonded can be produced simultaneously without producing them separately.

[0027] <Outline of Method for Producing Glycolic Acid> FIG. 2 is a diagram showing an outline of a method for producing glycolic acid, which is a source of modified polyglycolic acid, in the first embodiment.

[0028] Step S201: Acetic anhydride is aerated with hypochlorous acid to produce chloroacetic acid and water. The produced water is discharged by vacuum distillation. This reaction is shown in the following chemical formula (4).

[0029] Step S203: Sodium hydroxide is added to chloroacetic acid to produce glycolic acid and sodium chloride. The salt produced is removed using an electrodialysis device. The glycolic acid produced is then treated with an ion exchange resin to remove residual salt using an electrodialysis device. This glycolic acid can be used to produce glycolic acid oligomers. This reaction is shown in the following chemical formula (5).

[0030] By subjecting the salt produced in step S203 to diaphragm-free electrolysis, hypochlorous acid to be aerated in step S201 is produced at the positive electrode, and sodium hydroxide to be added in step S203 is produced at the negative electrode, so that the materials used are recycled. This process is shown in the following chemical formula (6).

[0031] The method for producing glycolic acid is not limited to the method shown in FIG. 2, and other methods may be used.

[0032] <Outline of Method for Producing Amine Vanadate> Fig. 3 is a diagram showing an outline of a method for producing amine vanadate used as an additive in the vanadium bonding step (i.e., the step of substituting oxygen for the double bond of vanadium) in producing a modified polyglycolic acid from a glycolic acid oligomer in the first embodiment. The reaction for producing amine vanadate from an aqueous ammonium vanadate solution is shown in the following chemical formula (7).

[0033]

[0034] Amine vanadate (NHVO) is produced by electrolyzing an ammonium vanadate (NHVO) solution without a diaphragm (formula 301 in FIG. 3). However, as shown in FIG. 3, if the electrolysis current is excessively large during electrolysis without a diaphragm, vanadium nitrite (V(NO)) is produced (formula 302 in FIG. 3) or vanadium nitrate (V(NO)) is produced (formula 303 in FIG. 3), making it unusable as an additive in this embodiment. Therefore, the electrolysis current must be controlled so that amine vanadate is produced.

[0035] The inventors conducted experiments using various electrolysis currents and found that the electrolysis current is preferably 3 to 5 times the limiting current of the diaphragm-less electrolysis device, and that if it is greater than this, vanadium nitrite or vanadium nitrate will be produced rather than amine vanadate. For example, when the limiting current of the diaphragm-less electrolysis device is 5 mA / cm2, the electrolysis current is preferably 20 mA / cm2, and if the electrolysis current exceeds 30 mA / cm2, sufficient amine vanadate cannot be produced. Note that the vanadium nitrite and vanadium nitrate produced by formulas 302 and 303 in Figure 3 are both nitrate compounds and cannot be used as additives for producing modified polyglycolic acid from glycolic acid oligomer.

[0036] According to this embodiment, a polyglycolic acid-based material that can serve as the active material for secondary batteries can be provided. Also, a method for producing modified polyglycolic acid that has the durability and functionality required for industrial materials and excellent electrical characteristics can be provided. That is, a method for producing modified polyglycolic acid in which a transition metal element is incorporated into the polyglycolic acid molecule and the modified polyglycolic acid is oxidized and reduced by an external electric field can provide electronic materials and battery materials with unprecedented properties. Furthermore, a production apparatus for producing modified polyglycolic acid by the method for producing modified polyglycolic acid according to this embodiment is also provided.

[0037] Second Embodiment Next, as the second embodiment, a secondary battery using the modified polyglycolic acid produced in the first embodiment will be described. The modified polyglycolic acid produced in the first embodiment contains equal amounts of modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid and modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid. Therefore, even if the modified polyglycolic acid produced is used as an active material, it will not function as a secondary battery as is. That is, it is necessary to separate the positive electrode, in which the modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid, from the negative electrode, in which the modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid, as the active material. This process is hereinafter referred to as initialization.

[0038] Furthermore, upon charging after initialization, the modified polyglycolic acid with tetravalent (V+IV) vanadium bonded, which is the active material of the positive electrode, becomes modified polyglycolic acid with pentavalent (V+V) vanadium bonded. Meanwhile, the modified polyglycolic acid with trivalent (V+III) vanadium bonded, which is the active material of the negative electrode, becomes modified polyglycolic acid with divalent (V+II) vanadium bonded. Subsequently, upon discharging, the modified polyglycolic acid with pentavalent (V+V) vanadium bonded, which is the active material of the positive electrode, returns to modified polyglycolic acid with tetravalent (V+IV) vanadium bonded. Meanwhile, the modified polyglycolic acid with divalent (V+II) vanadium bonded, which is the active material of the negative electrode, returns to modified polyglycolic acid with trivalent (V+III) vanadium bonded. From then on, this charging and discharging cycle is repeated stably.

[0039] <Configuration of Secondary Battery Using Modified Polyglycolic Acid> Fig. 4 is a diagram showing the configuration of a secondary battery using modified polyglycolic acid according to this embodiment. In Fig. 4, the left drawing shows a secondary battery 401 when assembled (original), the middle drawing shows a secondary battery 402 after initial charging, and the right drawing shows a secondary battery 403 during discharge.

[0040] The secondary battery 401 contains, as an active material, modified polyglycolic acid 103, which contains equal amounts of modified polyglycolic acid having a structure in which vanadium having a valence of tetravalent is bonded to polyglycolic acid and modified polyglycolic acid having a structure in which vanadium having a valence of trivalent is bonded to polyglycolic acid. The modified polyglycolic acid 103 is applied to both a positive electrode current collector 411 and a negative electrode current collector 412, and they are pressed together with a separator 413 sandwiched between them. However, the secondary battery can be used satisfactorily without the separator 413.

[0041] In this embodiment, metal carbon fiber is preferably used as the material for the positive electrode current collector 411, and aluminum or zinc is preferably used as the material for the negative electrode current collector 412. Any conductive material may be used, and there are no particular limitations. The same conductive material may also be used for both the positive and negative electrodes. Cellulose acetate is used as the separator 413. Preferably, the separator 413 has an acetylation ratio between cellulose diacetate and cellulose triacetate. However, the separator 413 is not limited to cellulose acetate, and any material that can prevent compatibility between the positive electrode active material and the negative electrode active material and has a high molecular mesh may be used. The metal carbon fiber used as the current collector is preferably fibrous with a diameter of 5 μm or less and coated with a metal alloy and plastic.

[0042] The secondary battery 402 is in a state after initial charging, with the positive electrode current collector 411 side being modified polyglycolic acid 421 bonded with pentavalent vanadium, and the negative electrode current collector 412 side being modified polyglycolic acid 422 bonded with divalent vanadium.

[0043] The secondary battery 403 is in a discharging state, with the positive electrode current collector 411 side being modified polyglycolic acid 431 with tetravalent vanadium bonded thereto, and the negative electrode current collector 412 side being modified polyglycolic acid 432 with trivalent vanadium bonded thereto.

[0044] Thereafter, charging and discharging are repeated between the charged state of the secondary battery 402 and the discharged state of the secondary battery 403 .

[0045] (Outline of Initialization Procedure) Fig. 5 is a diagram showing an outline of the initialization procedure for the secondary battery according to the second embodiment. Note that Fig. 5 shows the change in one molecule of the modified polyglycolic acid, but in the secondary battery, this process is carried out for the entire molecule.

[0046] Modified polyglycolic acid 103, which contains approximately equal amounts of modified polyglycolic acid 131 bonded with tetravalent vanadium and modified polyglycolic acid 132 bonded with trivalent vanadium, is initialized by applying a DC power supply of, for example, 2 V between the two electrodes. Then, in the modified polyglycolic acid 103 at the positive electrode, the trivalent modified polyglycolic acid 132 is converted to tetravalent modified polyglycolic acid 131, and after initialization is complete, most of the modified polyglycolic acid 501 at the positive electrode becomes tetravalent modified polyglycolic acid 131. On the other hand, in the modified polyglycolic acid 103 at the negative electrode, the tetravalent modified polyglycolic acid 131 is converted to trivalent modified polyglycolic acid 132, and after initialization is complete, most of the modified polyglycolic acid 501 at the negative electrode becomes trivalent modified polyglycolic acid 132.

[0047] In this way, the positive and negative electrodes of the secondary battery, which were not electrically determined at the time of manufacture, become electrically determined. This state is similar to the state of the modified polyglycolic acid of the positive and negative electrodes after discharge. However, in this example, the initialization is performed as a series of initial charges, and the secondary battery transitions to the charging state shown in Figure 6 through this state.

[0048] (Outline of charge / discharge procedure) Fig. 6 is a diagram showing an outline of the charge / discharge procedure of the secondary battery according to the second embodiment. Note that Fig. 5 shows the change in one molecule of the modified polyglycolic acid, but in the secondary battery, this process is carried out on the entire molecule.

[0049] The modified polyglycolic acid 421 of the charged positive electrode and the modified polyglycolic acid 422 of the charged negative electrode are structural formulas of the modified polyglycolic acid when they reach the charged state during initial charging via the changes shown in Figure 5. That is, the modified polyglycolic acid 421 of the positive electrode is a modified polyglycolic acid bonded with pentavalent vanadium, and the modified polyglycolic acid 422 of the negative electrode is a modified polyglycolic acid bonded with divalent vanadium.

[0050] On the other hand, the modified polyglycolic acid 431 of the discharged positive electrode and the modified polyglycolic acid 432 of the discharged negative electrode have structural formulas corresponding to the initialized state in Fig. 5. That is, the modified polyglycolic acid 431 of the positive electrode is a modified polyglycolic acid bonded with tetravalent vanadium, and the modified polyglycolic acid 432 of the negative electrode is a modified polyglycolic acid bonded with trivalent vanadium.

[0051] As shown in Figure 6, this change in vanadium valence occurs when hydrogen atoms bonded to vanadium act as carriers and hop to the vanadium in the nearby counter electrode of the modified polyglycolic acid. The structure of the modified polyglycolic acid of this embodiment facilitates the movement of vanadium, capturing and releasing hydrogen atoms. Although the amount of current flowing is small due to the hopping of hydrogen atoms, the presence of vanadium in the modified polyglycolic acid corresponds to the number of polymerizations (10 moles or more per liter), making it possible to store a large amount of electricity. Furthermore, because the vanadium is double-bonded to the carbon, there is no change in the basic structure, making the active material stable.

[0052] Furthermore, the carriers in secondary batteries are hydrogen atoms or hydrogen ions, and it was found that the distance between the positive and negative electrodes must be large enough to allow hydrogen molecules to move during charging and discharging. It was also found that the molecular weight of the modified polyglycolic acid must be low enough to allow hydrogen atoms to move. Experiments showed that a distance between the electrodes of 30 to 10 μm is desirable, and that a molecular weight of the modified polyglycolic acid of 5,000 to 10,000 works well.

[0053] According to this embodiment, a secondary battery that can be used semi-permanently and is easily portable can be provided. In other words, because no electrolyte is used, tanks for storing the active material and electrolyte, and pumps for circulating them, are not required. Furthermore, even if the battery is small, it can store a large amount of electricity because the modified polyglycolic acid contains vanadium corresponding to the polymerization number. Furthermore, because the vanadium is double-bonded to the carbon, there is no change in the basic structure, making it stable as an active material.

[0054] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the configuration and details of the present invention that are understandable to those skilled in the art within the technical scope of the present invention. Furthermore, any combination of the separate features included in each embodiment is also included in the technical scope of the present invention.

[0055] [First Example] As a first example, an example of the production of modified polyglycolic acid according to the embodiment will be described.

[0056] <Apparatus for Producing Modified Polyglycolic Acid> FIG. 7 is a diagram showing the configuration of an apparatus 700 for producing modified polyglycolic acid according to this example.

[0057] The production apparatus 700 for modified polyglycolic acid includes a pressure-resistant vessel consisting of a reaction vessel 701 and a lid 702, a stirring device 704, a pressure reducing device (vacuum pump) 713, and a microwave irradiation device (microwave oscillator) 705. The production apparatus 700 for modified polyglycolic acid further includes a temperature adjusting device (heat transfer oil supplying section) 714, a control device 720, an exhaust condensing device (heat exchanger) 707, and a condensed water storage device 708.

[0058] Glycolic acid is introduced into the pressure vessel as a raw material, and the resulting modified polyglycolic acid is extracted. The agitator 704 agitates the contents of the pressure vessel. The pressure-reducing device (vacuum pump) 713 creates a negative pressure inside the pressure vessel. The microwave irradiator (microwave generator) 705 irradiates the contents with microwaves. A glass plate 706 is attached to the waveguide from the microwave irradiator 705 to maintain the pressure inside the pressure vessel. The temperature regulator (heat transfer oil supply unit) 714 adjusts the temperature of the contents using a medium heating method using heat transfer oil 703. The controller 720 monitors and controls the temperature of the contents, the pressure inside the pressure vessel, and the agitation rotation speed of the agitator 704. The exhaust condenser (heat exchanger) 707 exchanges heat with the exhaust from the pressure vessel following the intake air from the pressure-reducing device 713 to produce condensed water. The condensed water storage device 708 separates and stores the condensed water and discharges it to the outside.

[0059] The pressure vessel has a raw material inlet 710 through which glycolic acid (GA) is introduced, and a catalyst and additive inlet 712 through which a catalyst used in producing glycolic acid oligomers and a vanadium compound as an additive used in producing modified polyglycolic acid are introduced. The pressure vessel also has an outlet 711 through which modified polyglycolic acid (GPA) is removed, and a nitrogen gas aeration port 709 through which nitrogen gas is introduced to prevent contamination inside the pressure vessel. The pressure vessel also has an internal viewing window for monitoring the state of the contents of the pressure vessel, and an internal light for illuminating the inside of the pressure vessel, both of which are not shown.

[0060] The control device 720 includes a content temperature control unit 721 that monitors the temperature of the contents and adjusts the heat transfer oil 703 via the heat transfer oil supply unit 714 to control the contents to an appropriate temperature corresponding to the production process. The control device 720 also includes an internal pressure control unit 722 that monitors the pressure inside the pressure-resistant vessel and controls the pressure inside the pressure-resistant vessel via the pressure reducing device 713. The control device 720 also includes a content agitation control unit 723 that appropriately agitates the contents using the agitator 704 in accordance with the production process. The control device 720 also includes a processing time control unit 724 that controls each processing time corresponding to the production process of modified polyglycolic acid. While four control units 721-724 are illustrated in FIG. 7, other control units may be added. Alternatively, any of the control units 721-724 of the control device 720 may be manually controlled by an operator. The control device 720 may further display statuses and perform operation inputs via an external computer 730. The control device 720 and the external computer 730 may be integrated.

[0061] (Production of Modified Polyglycolic Acid) Fig. 8A is a flowchart showing the steps of producing modified polyglycolic acid according to this example using the above-described modified polyglycolic acid production apparatus 700. Fig. 8A also shows a temperature profile 800 of the contents according to the steps of producing modified polyglycolic acid. The step numbers in the temperature profile 800 correspond to the step numbers in the flowchart.

[0062] Step S801 (feeding glycolic acid): Glycolic acid is fed through the raw material feed port 710 in the pressure-resistant vessel of the production apparatus 700 for modified polyglycolic acid.

[0063] Step S803 (heat dehydration): The raw glycolic acid that was added contains approximately 10% water (concentration is 90%), so it is dehydrated and concentrated in a reduced pressure environment. Nitrogen gas is passed through the pressure vessel, which is adjusted to 180°C and dehydrated for 1-2 hours. The dehydration status is estimated from the amount of condensed water discharged from the heat exchanger.

[0064] Step S805 (cooling): The temperature of the contents is lowered to 60° C. This is because adding a catalyst at a high temperature causes a rapid reaction and partial oxidation, which is undesirable.

[0065] Step S807 (Add catalyst): Add the catalyst. The catalyst used was a mixture of equal amounts of tin octoate and dodecyl alcohol (polymerization initiator). The amount added is preferably 0.2 wt% of the content. It is not recommended to add the entire amount of catalyst at once, so add it little by little in several batches. Once the entire amount has been added, continue stirring the contents for 1 to 2 hours.

[0066] Step S809 (dehydration condensation polymerization): Set the temperature to 170°C, and once the contents reach the set temperature, polymerize for 6 to 8 hours. During this time, maintain a nitrogen flow rate of 10 liters per minute and an internal pressure of 0.1 Atm. The progress of polymerization is determined by measuring the number average molecular weight of the contents. When the number average molecular weight reaches between 5,000 and 10,000, the polymerization is terminated. After that, it is recommended to set the temperature to 220°C and continue for 1 to 2 hours to evaporate any unreacted material and remove it from the system.

[0067] The above steps S803 to S809 correspond to step 101 (dehydration polycondensation) in Fig. 1. That is, in this example, the aim was to produce glycolic acid oligomers having uniform molecular weights in as short a time as possible.

[0068] Step S811 (cooling): The temperature of the contents is lowered to 30°C.

[0069] Step S813 (additive addition): Additive (amine vanadate: 1 to 10% of the content) is added through the catalyst and additive inlet 712. The additive is not added all at once, but is added little by little in several batches.

[0070] The above steps S811 and S813 correspond to step 103 (addition of amine vanadate) in FIG.

[0071] Step S815 (Vanadium Bonding by Microwaves): After the entire amount of additive (amine vanadate) has been added, the temperature of the contents is raised to 170°C, and the microwave irradiation device (microwave generator) 705 is activated. The irradiation time is 2 to 4 hours. This microwave bonding aims to bond amine vanadate to a predetermined position (oxygen double bond) of the glycolic acid oligomer molecule. In other words, vanadium is substituted for the double-bonded oxygen. This reaction can also be achieved by irradiation with radiation such as gamma rays, but this is not common and is difficult to achieve by methods other than bonding (i.e., substitution) by microwave irradiation. The microwave output is 0.1 to 1 kW per 10 kg of contents. Note that microwaves are introduced into the container through a waveguide fitted with a glass plate 706, as shown in Figure 7. The glass plate 706 is used to maintain the pressure inside the pressure-resistant container. Nitrogen gas is circulated through the waveguide to prevent contamination.

[0072] Step S105 (termination operation, removal of modified PGA): Since the production of modified polyglycolic acid is completed, the temperature of the contents is lowered to 120° C. or less, and the contents are then removed from the removal port 711. This is because removing the contents at a high temperature is undesirable, as it increases the risk of burns and may cause the modified polyglycolic acid to oxidize.

[0073] The temperature and other conditions used in the manufacturing process for producing modified polyglycolic acid using glycolic acid as a raw material are merely examples, and production is possible within the following ranges. For example, the dehydration process involves heating to 105-110°C at atmospheric pressure to evaporate water. The dehydration process is then carried out for approximately two hours at 170-180°C in a reduced-pressure environment (approximately 1 / 10 atmosphere). If the temperature is too high, the contents will evaporate, resulting in poor yield. Furthermore, temperatures below 160°C require additional dehydration time. Furthermore, since a high temperature when mixing the catalyst (vanadate amide) can result in partial reaction and undesirable results, the mixture is mixed at approximately 40-70°C. In this example, the mixture is stirred at 60°C for approximately two hours. The temperature for dehydration condensation polymerization is determined based on the degree of vacuum, but is generally set to 160-170°C to avoid unnecessary evaporation of the contents. The vessel is continuously stirred for 15-20 hours under a reduced-pressure environment (approximately 1 / 10 atmosphere) while nitrogen gas is introduced. Once the number-average molecular weight of the contents reaches 3,000 or more, the temperature of the contents is raised to 170-190°C, and at the same time the pressure inside the container is reduced to about 1 / 15 atmospheres. If the temperature is not raised here, the material will not develop a high molecular weight and will remain in the oligomer state. To create a polymer product to be used as a biodegradable plastic (resin), the temperature is raised to around 200°C and polymerization continues, but when it is used as a battery material, the material does not polymerize and the process ends in the oligomer state. In the heating process to evaporate unreacted materials, the temperature is temporarily raised to 220-250°C, but there is no problem if this step is omitted.

[0074] Furthermore, when adding the additive (amine vanadate), the temperature of the contents is lowered to below 120°C to prevent a sudden reaction. In this example, the temperature is set to 90°C. Furthermore, during the bonding process using microwave irradiation, the temperature of the irradiated area is slightly higher than that of other areas. This occurs because the additive absorbs electromagnetic waves and becomes hot, creating a temperature difference with the glycolic acid oligomer resin backbone molecules, causing vanadium to bond to the hydrogen bonding sites. When measured with a fiber optic thermometer, the temperature difference is generally around 50–100°C. In other words, the vanadium atoms in the additive molecules are activated and replace the hydrogen in the polyglycolic acid molecules. This reaction does not occur if the microwave output is too high or too low. For this reason, the temperature of the contents is adjusted to between 160–180°C, and the microwave output is set to around 10 kg / kW.

[0075] Modified polyglycolic acid was produced by the modified polyglycolic acid production process according to this example, using modified polyglycolic acid production apparatus 700. The produced modified polyglycolic acid contains equal amounts of modified polyglycolic acid having a structure in which vanadium having a valence of tetravalent is bonded to polyglycolic acid and modified polyglycolic acid having a structure in which vanadium having a valence of trivalent is bonded to polyglycolic acid. In the produced modified polyglycolic acid, the oxygen atom double-bonded to the carbon chain of polyglycolic acid is substituted with a tetravalent vanadium atom or a trivalent vanadium atom.

[0076] (Verification of the valence of vanadium in modified polyglycolic acid) The oxidation number of vanadium contained in the modified polyglycolic acid was tested by the following procedure to verify the valence of vanadium in the modified polyglycolic acid produced in this example.

[0077] (1) The sample (modified PGA) is applied to a 20 μm layer on a well-polished copper plate (3 mm thick). The temperature of the sample when applied is 130°C, and the copper plate is also preheated to 130°C. (2) The copper plate with the sample applied is allowed to cool naturally. (3) Graphite cut to the same size as the copper plate is placed on the applied surface and pressed against it. With the graphite still pressed against it, the sample is slowly heated to 90°C, and then allowed to cool naturally. (4) CV measurements are performed using the copper plate and graphite as electrodes.

[0078] The test conditions were as follows: Positive electrode: graphite Negative electrode: copper plate Sweep voltage: 0 to 2 V Step voltage: 10 mV Step time: 0.1 sec

[0079] FIG. 8B shows a graph 810 of current-potential characteristics, which is a test result of the oxidation number of vanadium in the modified polyglycolic acid produced according to this example.

[0080] 8B , when the modified polyglycolic acid having tetravalent vanadium bonded thereto and the modified polyglycolic acid having trivalent vanadium bonded thereto are contained in approximately equal amounts, the CV measurement results in a current-potential curve 811 as shown by the solid line. On the other hand, when the amount of the modified polyglycolic acid having trivalent vanadium bonded thereto is greater than the amount of the modified polyglycolic acid having tetravalent vanadium bonded thereto, the CV measurement results in a current-potential curve 812 as shown by the dashed line. When the amount of the modified polyglycolic acid having tetravalent vanadium bonded thereto is greater than the amount of the modified polyglycolic acid having trivalent vanadium bonded thereto, the CV measurement results in a current-potential curve 813 as shown by the dashed line.

[0081] In this example, the microwave irradiation time was controlled to adjust the current-potential curve to 811. As a result, it was possible to obtain a modified polyglycolic acid containing approximately equal amounts of modified polyglycolic acid bonded with tetravalent vanadium and modified polyglycolic acid bonded with trivalent vanadium.

[0082] (Procedure for Producing Glycolic Acid Oligomer) Figure 9 is a diagram showing in detail the procedure for producing a glycolic acid oligomer according to this example. Figure 9 corresponds to step S101 (dehydration condensation polymerization) in Figure 1. In Figure 9, the same steps as in Figure 8 are assigned the same step numbers.

[0083] Step S803 (heat dehydration): The raw material glycolic acid is heat dehydrated in a pressure vessel for polymerization to obtain concentrated glycolic acid and glycolide 911, which is a glycolic acid dimer. Hereinafter, this product will be referred to as concentrated glycolic acid 901.

[0084] Step S809 (dehydration polycondensation): A catalyst is added to concentrated glycolic acid 901 containing glycolide 911, and dehydration polycondensation is carried out under a reduced pressure environment while monitoring the number average molecular weight, to obtain glycolic acid oligomer 102. Tin octoate is suitable as the catalyst, and dodecyl alcohol is used as the polymerization initiator.

[0085] (Apparatus for Producing Amine Vanadate) Fig. 10A is a diagram showing the configuration of an apparatus 1000 for producing amine vanadate according to this embodiment. The apparatus 1000 for producing amine vanadate is a diaphragm-less electrolysis apparatus for electrolyzing the contents, and can also be used in the step of producing hypochlorous acid and sodium hydroxide from brine by diaphragm-less electrolysis in the glycolic acid production step shown in Fig. 2.

[0086] The apparatus 1000 for producing amine vanadate comprises a vessel consisting of a reaction vessel 1001 and a lid 1002, a stirrer 1003, two electrode terminals 1004 and 1005, two electrodes 1006 and 1007, and a control device 1010. Ammonium vanadate is introduced into the vessel as a raw material, and the produced amine manadate is extracted. The two electrodes 1006 and 1007 are preferably titanium electrodes coated with platinum (Pt).

[0087] The control device 1010 has an electrolysis power supply unit 1011, an electrolysis mode setting unit 1012, an electrolysis current detection unit 1013, and an electrolysis voltage detection unit 1014. When the electrolysis mode setting unit 1012 has set the constant voltage mode, the electrolysis power supply unit 1011 adjusts the voltage between the two electrodes 1006 and 1007 to a constant voltage. On the other hand, when the electrolysis mode setting unit 1012 has set the constant current mode, the electrolysis power supply unit 1011 adjusts the current between the two electrodes 1006 and 1007 to a constant current, and determines the end of electrolysis based on a detection signal of a predetermined electrolysis voltage threshold (1.5 V) from the electrolysis voltage detection unit 1014. The electrolysis mode setting unit 1012 initially sets the constant voltage mode, and when the electrolysis current detection unit 1013 detects that the predetermined electrolysis current (20 mA / cm2) has been reached, it switches from the constant voltage mode to the constant current mode. The electrolysis current detection unit 1013 detects and monitors the electrolysis current, and notifies the electrolysis mode setting unit 1012 when the electrolysis current reaches a predetermined electrolysis current (20 mA / cm2) in the constant voltage mode. The electrolysis voltage detection unit 1014 detects and monitors the electrolysis voltage, and notifies the electrolysis mode setting unit 1012 of the end of electrolysis when the electrolysis voltage drops to a predetermined electrolysis voltage threshold (1.5 V) in the constant current mode.

[0088] (Amine vanadate production process) FIG. 10B is a flowchart showing an amine vanadate production process according to this example using the amine vanadate production apparatus 1000.

[0089] Step S1001 (initial setting): 500 ml of water is poured into the reaction vessel 1001 of the manufacturing apparatus 1000. Then, the agitator 1003 is activated, and a DC voltage of 12 V is applied between the two electrodes 1006 and 1007. The current application mode is set to the constant voltage mode.

[0090] Step S1003 (adding ammonium vanadate): 0.1 mol (approximately 11.7 g) of ammonium vanadate is measured and added little by little so as not to accumulate at the bottom of the reaction vessel 1001. It is confirmed that the electrolysis current increases slightly and the color of the solution inside the reaction vessel 1001 changes slightly to yellow.

[0091] Step S1005 (monitoring and adjusting electrolysis current): Electrolysis is performed slowly within a range of approximately 3 to 5 times (15 mA / cm2 to 25 mA / cm2) the limiting current of the manufacturing equipment 1000 (5 mA / cm2 in this example). Care must be taken because excessive electrolysis current (>30 mA / cm2) can produce nitrate and nitrite compounds. This reaction has already been described with reference to FIG. 3.

[0092] Step S1007 (determination of electrolysis current): It is determined whether the electrolysis current has reached 20 mA / cm 2 .

[0093] Step S1009 (constant current mode): When the electrolysis current reaches 20 mA / cm 2 , the current application mode is set to the constant current mode.

[0094] Step S1011 (monitoring and determining electrolysis voltage): Determine whether the electrolysis voltage has dropped to 1.5V.

[0095] Step S1013 (end of electrolysis): When the electrolysis voltage drops to 1.5 V, the electrolysis is ended. The color of the solution inside the reaction vessel 1001 becomes transparent yellow-orange. The produced amine vanadate, which is the content, is sealed and stored in a cool, dark place.

[0096] By this production process, amine vanadate, which is an essential additive for producing modified polyglycolic acid from glycolic acid oligomer, could be stably produced.

[0097] The modified polyglycolic acid of this example was produced by carrying out the above production steps. The produced modified polyglycolic acid contained equal amounts of modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid and modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid.

[0098] The process shown in this example made it possible to stably obtain each material, product, and manufactured item in a simple manner.

[0099] Second Example As a second example, an example of manufacturing a secondary battery using the modified polyglycolic acid manufactured in the first example will be described.

[0100] <Manufacturing Process of Secondary Battery Using Modified Polyglycolic Acid> Fig. 11A is a flowchart showing the manufacturing process of a secondary battery using modified polyglycolic acid according to this example. Hereinafter, the manufacturing process of the secondary battery will be described with reference to Fig. 4 mentioned above.

[0101] Step S1101 (Coating of Modified Polyglycolic Acid): Modified polyglycolic acid 103 is coated on two current collectors 411 and 412. The modified polyglycolic acid 103 produced in the first embodiment is coated to a thickness of 20 μm on each of the two current collectors: a 20 μm-thick metal carbon fiber for the positive electrode and a 20 μm-thick aluminum plate (or zinc plate) for the negative electrode. In other words, positive and negative electrodes are produced. Here, "metal carbon fiber" refers collectively to a porous structure formed by mixing metal waste, such as aluminum scrap or iron scrap, with carbon. There are several manufacturing methods, including impregnating carbon fiber bundles in a metal melt, forming a sintered structure, and forming a nonwoven fabric. Regardless of the manufacturing method, any structure containing carbon and voids, which is made from scrap metal, is sufficient. Because it can be produced from recycled metal scrap, it is low cost. The metal carbon fiber used as the current collector is preferably a fibrous material with a diameter of 5 μm or less, coated with a metal alloy and plastic. When the same conductor is used as the current collector, which one becomes the positive electrode and which becomes the negative electrode is determined by the voltage fluctuation during initialization.

[0102] Step S1103 (attaching of current collectors): The two electrodes coated with the modified polyglycolic acid 103 are attached together with a separator 413 made of cellulose acetate having a thickness of 10 μm sandwiched therebetween.

[0103] Step S1105 (pressure welding): The two current collectors 411 and 412 are heated to 90° C. and pressed together until the distance between them becomes 10 μm or more and 30 μm or less.

[0104] This process provided an as-assembled (original) secondary battery 401. This secondary battery 401 is a battery containing only the stable, unpolarized modified polyglycolic acid 103, and therefore its performance does not deteriorate even after long-term storage. An initial charging process can be carried out before use.

[0105] <Initial Charging Process of Secondary Battery Using Modified Polyglycolic Acid> FIG. 11B is a flowchart showing the initial charging process of a secondary battery using modified polyglycolic acid according to this example.

[0106] Step S1107 (initial charging starts): Initial charging is performed by applying a constant voltage of 2 V between the two current collectors 411 and 412. A slight current flow was observed, which increased with the passage of time.

[0107] Step S1109 (end of initial charging): The current peaked at about 5 mA and decreased, and the initial charging was terminated when it reached 0.01 mA. The release voltage at this time was 1.4 V, which was confirmed to be equal to the oxidation-reduction potential of vanadium.

[0108] This step provides a secondary battery 402 after initialization charging, i.e., a secondary battery 402 for which the initialization step and charging step have been completed. This secondary battery 402 is a battery that has already completed the charging step and has been subjected to a charging test, and it is possible to provide a secondary battery 402 with few defects.

[0109] (Prototype Secondary Battery and Testing Conditions) FIG. 11C is a diagram illustrating a prototype secondary battery 1100 using modified polyglycolic acid according to this example and its testing conditions.

[0110] A prototype secondary battery 1100 was manufactured as follows. First, two electrodes 1101 and 1102 measuring 40 x 50 mm were cut from a 0.1 mm thick aluminum sheet. One of the electrodes, 1102, was attached to an acrylic plate 1104. Then, modified polyglycolic acid 1103 was applied as an active material to each of the two electrodes 1101 and 1102, and the two electrodes were attached together with a cellulose acetate sheet (separator: not shown) sandwiched between them.

[0111] A 2.5 V DC current was applied between the two electrodes of prototype battery 1100 for 5 minutes to initialize it, and then it was charged at 2 V for 10 minutes. After leaving it for 30 minutes, the no-load voltage was measured with voltmeter 1120. The no-load voltage was 1.45 V (see 1121). When discharged at a constant current with a 100 mA electronic load, the electromotive force was 1.25 V, and when discharged until the terminal voltage reached 0.7 V, the duration was approximately 15 minutes. The discharge capacity of this prototype battery 1100 was calculated as follows: 0.1 (A) × 15 (min) ÷ 60 (min) = 0.025 Ah (= 25 mAh).

[0112] (Initial Charging Characteristics During Initialization of Secondary Battery) Fig. 12 is a diagram showing initial charging characteristics 1200 during initialization of the secondary battery according to this example. The initial charging characteristics 1200 are characteristics obtained when the secondary battery 401 in Fig. 4 is initially charged to the secondary battery 402 according to Fig. 11B. The current flow was observed when a 2 V DC power supply was connected to the electrode pair.

[0113] At first, there was a valence change from tetravalent vanadium to trivalent vanadium on the positive electrode side and from trivalent vanadium to tetravalent vanadium on the negative electrode side near separator 413, and almost no current flowed. Gradually, valence changes began to occur near current collectors 411 and 412, which were farther from separator 413, and a slight current was observed that gradually increased over time.

[0114] Then, as the initialization period shifted to charging, the valence of the tetravalent vanadium on the positive electrode changed to pentavalent vanadium, and the valence of the trivalent vanadium on the negative electrode changed to divalent vanadium, causing the current to peak at about 5 mA and then decrease. The initial charge was terminated when the positive electrode became pentavalent vanadium and the negative electrode became divalent vanadium, dropping to 0.01 mA. The release voltage at this time was 1.4 V, which was confirmed to be equal to the redox potential of vanadium.

[0115] The initialization time in the initial charge characteristics in Figure 12 refers to the time required for all tetravalent and trivalent vanadium in the modified polyglycolic acid to be converted to tetravalent vanadium on the positive electrode side through initialization. It also refers to the time required for all tetravalent and trivalent vanadium in the modified polyglycolic acid to be converted to trivalent vanadium on the negative electrode side through initialization. The battery will not function unless this reaction is completed. The secondary battery prototyped in this example required an initialization time of about 1.5 times the charging time, but once initialized, there is no initialization time from the next time onwards, so the charging time is shorter.

[0116] 13 is a diagram showing a discharge characteristic 1300 when the secondary battery according to this example is discharged. The discharge characteristic 1300 is a characteristic when discharging from the secondary battery 402 to the secondary battery 403 in FIG.

[0117] An electronic load was connected to the positive and negative electrodes, and the cut-off voltage for terminating discharge was set to 0.5 V. When the battery was discharged at 10 mA, a discharge output of 1 mAh per cm2 of electrode area was obtained.

[0118] The battery function was not lost and it could be recharged even when the terminal voltage fell below 0.1 V as the discharge progressed. Furthermore, no significant change in characteristics was observed even after repeated charge and discharge cycles, demonstrating that the modified polyglycolic acid of this example can be used as an active material for secondary batteries.

[0119] More specifically, the discharge characteristics were as follows: The no-load electromotive force of the prototype battery immediately after the initial charge was 1.4 V, and after leaving it for one hour, it was 1.35 V. The voltage was 1.3 V when a 10 mA electronic load was connected. A constant-current discharge test was performed with the final voltage set to 0.5 V, resulting in approximately 10 hours of discharge. A 10 Ω resistor was then connected, and the time it took for the voltage to drop to 0.1 V was measured, which was approximately one hour. Furthermore, it took approximately eight hours for the terminal voltage to reach 1 V, which is considered to be the usable life of the prototype battery. Based on these results, the current capacity per cm2 when discharged to 0.5 V was 1 mAh, and the current capacity per cm2 when discharged to 1 V was 0.8 mAh.

[0120] This example offers the following noteworthy advantages: There is no need to worry about overdischarge. That is, charging and discharging are possible even when the terminal voltage drops to 0.1 V. Constant-voltage charging is sufficient. Current limiting is not required as long as the voltage is within the range (1.5 to 2 V) where the molecular structure of the modified polyglycolic acid is not destroyed. Initialization takes some time, but after that, the battery can be charged at a faster rate than conventional lithium-ion batteries. Because charging and discharging occur through the oxidation-reduction of the active material, modified polyglycolic acid, the battery's electrical performance is less dependent on the electrode material. Oxidation and hydroxylation do not occur at the electrodes. Therefore, a high-current, relatively lightweight battery can be provided. Because raw materials are inexpensive and the manufacturing process does not require a drying chamber (drying is not a requirement) or a sophisticated clean room, it can be manufactured inexpensively. Because the manufacturing process for modified polyglycolic acid is consistent and simple, production that would take several days with other manufacturing processes can be completed in approximately one day. The main raw material is an environmentally friendly, biodegradable plastic, which is harmless to living organisms.・The material itself is flame-resistant, and there is no risk of toxic gas generation or explosion. ・No toxic chemicals are used in manufacturing.

[0121] 14 shows another embodiment using modified polyglycolic acid, which is applied to a memory 1400.

[0122] As shown in FIG. 14 , the modified polyglycolic acid 1403 of this example is printed in a slit pattern on the positive electrode 1401 and the negative electrode 1402. The matrix in which the electrodes 1401 and 1402 are attached perpendicularly can function as a memory. That is, by applying a predetermined voltage to the positive electrode address 1411 and the negative electrode address 1421 to perform initialization, the contact portion separates into tetravalent and trivalent vanadium and becomes a memory element, while the other portion becomes an inactive portion with equal amounts of tetravalent and trivalent vanadium. The matrix then functions as a memory using the positive electrode address 1411 and the negative electrode address 1421. The memory of this example can handle large currents and can be used in a variety of applications.

[0123] The fact that the modified polyglycolic acid of this example is produced as an active material containing approximately equal amounts of tetravalent vanadium and trivalent vanadium makes it possible to apply the same to various fields by utilizing the initialization process, and thus provides significant advantages.

[0124] Figure 15 illustrates a prototype solid-state secondary battery using modified polyglycolic acid and metallic carbon fiber as the positive electrode current collector. A 40 x 50 mm electrode was cut from a 0.1 mm thick aluminum sheet and attached to an acrylic plate as the negative electrode current collector. The negative electrode 1502 is an extended portion of the aluminum sheet. The positive electrode current collector 1503 is a 40 x 50 mm sheet made of metallic carbon fiber. A copper plate 1501 is attached to the current collector 1503 to form the positive electrode. The aluminum sheet serving as the negative electrode current collector and the metallic carbon fiber current collector for the positive electrode were coated with modified polyglycolic acid as the active material and then bonded together with a cellulose acetate sheet (separator: not shown). A direct current of 2.5 V was applied between the two electrodes for 5 minutes to initialize them, and then they were charged at 2 V for 10 minutes. After leaving them for 30 minutes, the no-load voltage was measured with a voltmeter. The no-load voltage was 1.45 V. The electromotive force when discharged at a constant current of 100 mA with an electronic load was 1.25 V, and the battery lasted approximately 15 minutes when discharged to a terminal voltage of 0.7 V. The discharge capacity of this prototype battery was calculated as follows: 0.1 (A) × 15 (min) ÷ 60 (min) = 0.025 Ah (= 25 mAh). The advantages of using metal carbon fiber include: first, the porous structure of the metal carbon fiber allows for a large contact area with the active material, modified polyglycolic acid; second, the low cost of metal carbon fiber makes it cost-effective; and third, it is easy to bond with modified polyglycolic acid, eliminating the problem of adhesive freezing.

Claims

1. A solid secondary battery comprising: a positive electrode current collector which is a metal carbon fiber; and a negative electrode current collector which is an aluminum or zinc plate; and a modified polyglycolic acid, as an active material for the positive and negative electrodes, which is formed by adding a vanadium compound to a glycolic acid oligomer and irradiating the resulting mixture with microwaves to bond vanadium to the glycolic acid oligomer; wherein the positive electrode is formed by coating the surface of a metal carbon fiber current collector for the positive electrode with the modified polyglycolic acid; and the negative electrode is formed by coating the surface of an aluminum or zinc plate for the negative electrode with the modified polyglycolic acid.

2. The solid secondary battery according to claim 1, wherein the molecular weight of the glycolic acid oligomer is 5,000 or more and 10,000 or less.

3. The solid secondary battery according to claim 1 or 2, wherein the vanadium compound is added in an amount of 1 wt % or more and 10 wt % or less.

4. The solid secondary battery according to any one of claims 1 to 3, wherein the vanadium compound is amine vanadate obtained by electrolyzing an aqueous solution of ammonium vanadate.

5. A solid-state secondary battery comprising: a positive electrode in which a first modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid is applied to the surface of a metal carbon fiber current collector; and a negative electrode in which a second modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid is applied to the surface of an aluminum or zinc plate current collector.

6. The solid secondary battery according to claim 5, wherein in the first modified polyglycolic acid, oxygen atoms double-bonded to the carbon chain of the polyglycolic acid are replaced with tetravalent vanadium atoms and oxygen atoms, and in the second modified polyglycolic acid, oxygen atoms double-bonded to the carbon chain of the polyglycolic acid are replaced with trivalent vanadium atoms and hydrogen atoms.

7. A solid secondary battery according to claim 5 or 6, wherein the first modified polyglycolic acid is represented by the following chemical formula (8), and the second modified polyglycolic acid is represented by the following chemical formula (9).

8. A solid secondary battery comprising: a positive electrode in which a third modified polyglycolic acid having a structure in which vanadium having a valence of five is bonded to polyglycolic acid is applied to the surface of a metal carbon fiber current collector; and a negative electrode in which a fourth modified polyglycolic acid having a structure in which vanadium having a valence of two is bonded to polyglycolic acid is applied to the surface of an aluminum or zinc plate current collector.

9. A secondary battery as described in claim 8, wherein the third modified polyglycolic acid has oxygen atoms double-bonded to the carbon chain of the polyglycolic acid substituted with pentavalent vanadium atoms and oxygen atoms, and the fourth modified polyglycolic acid has oxygen atoms double-bonded to the carbon chain of the polyglycolic acid substituted with divalent vanadium atoms and hydrogen atoms.

10. A secondary battery as described in claim 8 or claim 9, wherein the third modified polyglycolic acid is represented by the following chemical formula (10), and the fourth modified polyglycolic acid is represented by the following chemical formula (11).

11. A solid secondary battery characterized in that the positive electrode is a metal carbon fiber current collector having a surface coated with both a first modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid which becomes an active material during discharge, and a third modified polyglycolic acid having a structure in which vanadium having a valence of 5 is bonded to polyglycolic acid which becomes an active material during charge, and the negative electrode is an aluminum or zinc plate having a surface coated with both a second modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid which becomes an active material during discharge, and a fourth modified polyglycolic acid having a structure in which vanadium having a valence of 2 is bonded to polyglycolic acid which becomes an active material during charge.

12. The solid secondary battery according to any one of claims 1 to 11, further comprising a separator made of cellulose acetate for separating the positive electrode and the negative electrode.

13. The solid secondary battery according to any one of claims 1 to 13, wherein the distance between the current collector in the positive electrode and the current collector in the negative electrode is 10 μm or more and 30 μm or less.

14. A method for manufacturing a solid secondary battery, comprising: a positive electrode production step of applying a modified polyglycolic acid containing equal amounts of a first modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid and a second modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid to a metal carbon fiber that is a current collector that will become a positive electrode; a negative electrode production step of applying the modified polyglycolic acid to an aluminum plate or zinc plate that is a current collector that will become a negative electrode; a lamination step of bonding the positive electrode and the negative electrode together with the modified polyglycolic acid sandwiched therebetween; and an initialization step of applying a constant voltage between the positive electrode and the negative electrode, wherein the lamination step includes a step of sandwiching a separator made of cellulose acetate between the modified polyglycolic acid of the positive electrode and the modified polyglycolic acid of the negative electrode to separate the positive electrode and the negative electrode.

15. A method for producing a solid secondary battery as described in claim 14, wherein in the initialization step, a constant voltage is applied between the positive electrode and the negative electrode until the second modified polyglycolic acid of the positive electrode is changed to the first modified polyglycolic acid and the first modified polyglycolic acid of the negative electrode is changed to the second modified polyglycolic acid.

16. A method for producing a solid secondary battery as described in claim 14 or 15, wherein in the positive electrode production step and the negative electrode production step, the modified polyglycolic acid is applied to a thickness of 20 μm, and in the lamination step, the modified polyglycolic acid between the positive electrode and the negative electrode is pressed while being heated, so that the distance between the positive electrode current collector and the negative electrode current collector is 10 μm or more and 30 μm or less.

17. A method for producing a solid secondary battery, wherein the positive electrode is formed by adding a vanadium compound to a glycolic acid oligomer and irradiating the surface of a metal carbon fiber current collector for the positive electrode with microwaves to coat the surface with a modified polyglycolic acid in which vanadium is bonded to the glycolic acid oligomer, and the negative electrode is formed by coating the surface of an aluminum plate or zinc plate for the negative electrode current collector with the modified polyglycolic acid, wherein, in producing the modified polyglycolic acid, the vanadium compound is amine vanadate obtained by electrolyzing an aqueous solution of ammonium vanadate.

18. The method for producing a solid secondary battery according to claim 17, wherein the molecular weight of the glycolic acid oligomer is 5,000 or more and 10,000 or less.

19. The method for producing a solid secondary battery according to claim 18, wherein the molecular weight of the glycolic acid oligomer is 6,000 or more and 8,000 or less.

20. A method for producing a solid secondary battery according to any one of claims 17 to 19, wherein the amount of the amine vanadate added is 1 wt % or more and 10 wt % or less.

21. The method for producing a solid secondary battery according to claim 20, wherein the amount of the amine vanadate added is 4 wt % or more and 6 wt % or less.

22. The method for producing a solid secondary battery according to any one of claims 17 to 21, wherein the glycolic acid oligomer is produced by heating and dehydrating glycolic acid in a reduced pressure environment.

23. A method for producing a solid secondary battery as described in claim 22, wherein the glycolic acid oligomer is produced by heating and dehydrating the glycolic acid in a reduced pressure environment to obtain concentrated glycolic acid containing glycolide, adding tin octoate as a catalyst to the concentrated glycolic acid, and subjecting the resulting mixture to dehydration and condensation polymerization while monitoring the molecular weight.

24. The positive electrode is formed by adding a vanadium compound to a glycolic acid oligomer and irradiating the surface of a metal carbon fiber current collector for the positive electrode with microwaves to coat the surface with a modified polyglycolic acid in which vanadium is bonded to the glycolic acid oligomer, and the negative electrode is formed by coating the surface of an aluminum plate or zinc plate for the negative electrode with the modified polyglycolic acid. The modified polyglycolic acid for use in a solid secondary battery is characterized in that the modified polyglycolic acid contains equal amounts of a first modified polyglycolic acid having a structure in which vanadium having a valence of 4 is bonded to polyglycolic acid, and a second modified polyglycolic acid having a structure in which vanadium having a valence of 3 is bonded to polyglycolic acid.

25. The modified polyglycolic acid according to claim 24, characterized in that in the first modified polyglycolic acid, oxygen atoms double-bonded to the carbon chain of the polyglycolic acid are replaced with tetravalent vanadium atoms and oxygen atoms, and in the second modified polyglycolic acid, oxygen atoms double-bonded to the carbon chain of the polyglycolic acid are replaced with trivalent vanadium atoms and hydrogen atoms.

26. The modified polyglycolic acid according to claim 25, wherein the first modified polyglycolic acid is represented by the following chemical formula (8), and the second modified polyglycolic acid is represented by the following chemical formula (9).

Images