Biodegradable electronic materials and secondary batteries, energy storage units, and large-scale energy storage devices using the same

Abstract

To provide a novel electronic material excellent in biodegradability, capable of performing charge / discharge operation only by applying an external electric field, and a secondary battery using the same.SOLUTION: A biodegradable electronic material includes a solid charge storage layer formed by coating one surface of a current collector with an organometallic complex formed by bonding transition metals exhibiting a plurality of oxidation numbers to a biodegradable organic polymer. Due to a change in the direction of the electric field applied to the solid charge storage layer through the current collector, electrons are absorbed and emitted between the solid charge storage layer and the current collector, thereby performing charging and discharging.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a novel biodegradable electronic material having excellent biodegradability, a secondary battery using the same, a power storage unit using the secondary battery, and a large-scale power storage device.

Background Art

[0002] Currently, the mainstream lithium-ion battery has advantages such as being small in size, having a high nominal voltage, a long service life, a long number of charge-discharge cycles, and a high energy density compared to secondary batteries such as lead-acid batteries, nickel-metal hydride batteries, and alkaline storage batteries. However, since it uses an electrolyte solution, it cannot be discarded as an organic substance as it is. In addition, it is difficult to withstand high temperatures and has a risk of explosion, so it has a disadvantage of poor safety. Therefore, recently, a biodegradable secondary battery that can be disposed of as organic waste after use, excluding metal parts such as electrodes, has been desired and developed. As prior arts related to such secondary batteries, there are the following Patent Documents 1 and 2. Here, Patent Documents 1 and 2 propose a method of using biodegradable polylactic acid or polyglycolic acid as a base material, binding vanadium to this base material to produce positive and negative electrode active materials, and a secondary battery using the same.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] This invention is the result of the inventors' diligent analysis and study of organometallic complexes with excellent biodegradability, and proposes a novel biodegradable electronic material and a secondary battery using this biodegradable electronic material. The inventors investigated various aspects of secondary batteries that do not use liquid electrolytes and can replace lithium batteries. As a result, they selected PLGA as an organic polymer obtained by polymerizing organic molecules with the same molecular structure. By bonding specific transition metals exhibiting multiple oxidation states to this PLGA to form an organometallic complex, when a current collector plate is attached to the organometallic complex and a unidirectional electric field is applied, the organometallic complex releases electrons to the current collector plate and stores energy. Conversely, when the direction of the electric field is reversed, the organometallic complex absorbs electrons and discharges. Based on these findings, the inventors arrived at the present invention. [Means for solving the problem]

[0005] Therefore, the biodegradable electronic material proposed as the first part of the present invention comprises a current collector plate and a solid charge storage layer formed by coating one side of the current collector plate with an organometallic complex composed of PLGA with an oxidation state of 3 or higher and a transition metal of group 3 to group 7. By changing the direction of the electric field applied to this solid charge storage layer through the current collector plate, electrons are absorbed and released between the solid charge storage layer and the current collector plate, thereby storing and discharging electrons. Furthermore, the second invention proposes a secondary battery constructed primarily from the biodegradable electronic material of the first invention, and the third invention proposes an energy storage unit and a large-scale energy storage device utilizing the secondary battery of the second invention. [Effects of the Invention]

[0006] The first aspect of this invention allows it to be used as a main component of a rechargeable battery with excellent biodegradability. Furthermore, since organometallic complexes are manufactured as thermoplastic powders, they can be heated to form a paste which can then be applied to current collector plates to form a solid charge storage layer. Therefore, by using printing technology to coat the current collector plate, a solid charge storage layer can be formed in film form, and high-speed work is also possible. Furthermore, the material itself is flame-retardant, can be used semi-permanently, and does not pose a risk of generating toxic gases or explosions. The production of organometallic complexes does not require a highly cleanroom, resulting in significantly lower manufacturing costs and the absence of toxic chemicals. Furthermore, since it can store electric charge and maintain that state without consuming power, it can also be used as a memory element in backup memory devices. Furthermore, by joining another current collector plate to the opposite side of a current collector plate coated with a solid charge storage layer, a structure similar to a capacitor is created, while exhibiting different properties from a capacitor. Therefore, it can be used as an electronic device with properties intermediate between a capacitor and a battery. The second invention constructs a secondary battery by interposing a set of biodegradable electronic materials, as described in the first invention, with an insulating separator in between, and providing positive and negative electrode terminals for each. As a result, oxidation and OH formation do not occur at the electrodes, and a relatively lightweight battery capable of handling high current can be provided. Furthermore, after use, the battery can be converted into a biodegradable secondary battery that does not cause environmental problems if the metal parts such as the positive and negative electrode terminals are removed and it is buried in the soil. This secondary battery allows for the curvature of the current collector plate and the shaping of the solid charge storage layer to conform to the shape of the current collector plate. Furthermore, it can be manufactured using mold molding, enabling the production of large secondary batteries with curved designs tailored to specific applications. This rechargeable battery has excellent high-temperature characteristics (it can operate even at ambient temperatures of 85°C and can be stored at temperatures above 100°C), and its charge and discharge can be easily controlled. Furthermore, since the organic polymer used as a base material for secondary batteries is in powder form, encapsulating it in a film allows for the manufacture of thin, easily portable products with freely adjustable shapes. The third invention is a package of the secondary battery which is the second invention. Energy storage unit Large-scale energy storage devices can be provided. These large-scale energy storage devices connect multiple energy storage units in series and parallel. emergency power supply It can also be used suitably in large mobile machinery and plants. [Brief explanation of the drawing]

[0007] [Figure 1] It is an explanatory diagram showing an example of the biodegradable electronic material of the first invention. [Figure 2] (a) and (b) are explanatory diagrams of the power storage and discharge operations of the biodegradable electronic material of the present invention. [Figure 3] It is an exploded perspective view of the secondary battery which is the second invention. [Figure 4] It is an explanatory diagram of the appearance in which the secondary battery is enclosed in an insulating film. [Figure 5] (a) and (b) are explanatory diagrams of the charging and discharging operations of the secondary battery. [Figure 6] It is a diagram showing the change in the oxidation number of vanadium in the organometallic complex during charging and discharging. [Figure 7] It is a cross-sectional view of an example of the secondary battery. [Figure 8] It is a cross-sectional view of another example of the secondary battery. [Figure 9] It is an explanatory diagram of a power storage unit that houses multiple secondary batteries as a package. [Figure 10] It is an explanatory diagram of a large-scale power storage device in which multiple power storage units are arranged and fixed in a rack.

Mode for Carrying Out the Invention

[0008] Hereinafter, desirable examples of the present invention will be described. First, the biodegradable electronic material, which is the first invention, will be described. As shown in FIG. 1, the biodegradable electronic material A is a structure in which a solid charge accumulation layer 2 is coated on a current collector plate 1. The current collector plate 1 is composed of a metal such as copper or aluminum or a conductor such as carbon. On the other hand, as will be described later, one solid charge accumulation layer 2 is a biodegradable electronic material formed by bonding a transition metal having a plurality of oxidation numbers to a PLGA organic polymer. When bonding the transition metal, microwave irradiation is preferably used in a vacuum environment or for direct heating without unevenness.

[0009] Next, an organic polymer that can be used as a base material for the biodegradable electronic material A will be described. In the present invention, PLGA used as an organic polymer shows its molecular structure in Chemical Formula 1. These polymers can be produced from bio-products such as lactic acid and acetic acid, or organic waste, rather than fossil fuels, and thus become environmentally friendly electronic materials that contribute to carbon neutrality. The transition metal elements that are bonded to PLGA to form an organometallic complex are selected from Groups 3 to 7 such as titanium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, and manganese, which exhibit multiple oxidation numbers. The organometallic complex formed by bonding can be produced as powders at the micron level or the nanolevel. Therefore, if this is heated to a paste state and coated on a current collector plate, a solid charge storage layer can be easily produced. In the examples of this specification, vanadium of Group 5 is used for explanation to facilitate understanding. Chemical Formula 2 shows the molecular structure of the PLGA organometallic complex, where R is a transition metal element. The inventors have found that the biodegradable electronic material using PLGA thus formed as an organic polymer can easily absorb and release electrons in the solid charge storage layer only by applying an electric field from the outside, enabling charge storage and discharge. This fact is the discovery that when an electric field is applied from the outside to the solid charge storage layer connected to the current collector plate, electron transfer can occur between the current collector plate and the solid charge storage layer to enable charge storage and discharge. Looking at this microscopically, it is推测 that electron transfer occurs within and between the molecules of the organometallic complex using PLGA, and further between the current collector plate, for charge storage or discharge. [Chemical Formula] [Chemical Formula]

[0010] The basic principle in the biodegradable electronic material A is shown in Figs. 2(a) and (b). When an electric field E1 is applied from the current collector plate 1 towards the solid charge storage layer 2, electrons e move from the solid charge storage layer 2 towards the current collector plate 1. These electrons e are released from the transition metal elements bonded to the organometallic complex of the solid charge storage layer 2. As a result, the valence of the transition metal element V becomes higher than before the application of the electric field E1, indicating that it has been oxidized. In other words, this movement of electrons e causes the solid charge storage layer 2 to enter a state where its electron density decreases, that is, a charged state. In contrast, when an electric field E2 is applied from the solid charge storage layer 2 towards the current collector plate 1, electrons e move from the current collector plate 1 to the solid charge storage layer 2. These electrons e are absorbed by the transition metal element V. As a result, the valence of the transition metal element V becomes lower than before the application of the electric field E2, meaning it is reduced. In other words, this movement of electrons e causes the solid charge storage layer 2 to enter a discharge state (a state with increased electron density). The electron movement described above occurs within the range of changeable valence of the transition metal element V. For example, in the case of vanadium, a group 5 element, the changeable valence is between 2 and 5. Therefore, it can be inferred that a maximum of 3 electrons move per element of vanadium, resulting in charging and discharging.

[0011] On the other hand, in organometallic complexes using PLGA as the substrate for organic polymers, the change in the element bonded to the transition metal element whose valence changes is only minor, such as changing from hydrogen to oxygen (or vice versa), and this exchange is reversible. In particular, since PLGA, which serves as the substrate for organometallic complexes, has a double bond between carbon and the transition metal element, the basic structure hardly changes. Therefore, this biodegradable electronic material, and the secondary batteries that use it as a component, hardly degrade even after repeated charging and discharging, resulting in a very long lifespan.

[0012] Next, we will explain a method for producing organometallic complexes using PLGA as a substrate. In short, a PLGA organometallic complex of a predetermined molecular weight can be produced by copolymerizing PLA and PGA in a known ratio, for example, 1:1, to obtain a relatively low molecular weight PLGA, mixing it with an additive containing a transition metal element, and then polymerizing it further using microwaves. Performing the polymerization under vacuum conditions using microwave irradiation allows for rapid and accurate polymerization.

[0013] Generally, the higher the PGA ratio of PLGA, the more easily it degrades. However, as an exception, the highest degradation rate is achieved when the PGA to PLA ratio is 50:50. Furthermore, the degree of crystallinity changes depending on the ratio, so when used as a material for secondary batteries, it has the advantage of easily controlling the biodegradability and physical strength of the battery.

[0014] Next, the secondary battery of the present invention will be described. As shown in Figure 3, secondary battery B has a basic structure in which two biodegradable electronic materials A1 and A2 are aligned with an insulating separator 3 in between, so that the positive and negative current collector plates 11 and 21 are on the outside, and a positive terminal 11a is provided on one current collector plate 11 and a negative terminal 21a is provided on the other current collector plate 21. This can be easily manufactured by thermocompressing the aforementioned biodegradable electronic materials A1 and A2 and the insulating separator 3. To protect the whole, as shown in Figure 4, the entire thing is sealed with an insulating film 4 so that only the positive terminal 11a and negative terminal 21a are exposed. The positive terminal 11a is connected to the positive terminal of the charging device, and the negative terminal 21a is connected to the negative terminal of the charging device to perform charging. Once charging is complete, the charging device is removed, a load is connected, and the battery can be used. When the battery discharges, it can be charged in the same manner, and by repeating the discharge and charging process, it can be used many times. Here, the positive terminal 11a and the negative terminal 21a are thin plates made of common metals such as copper and aluminum, and the type of metal is not particularly limited. Furthermore, the solid charge storage layer 2 that constitutes the biodegradable electronic materials A1 and A2 uses the same organometallic complex. The insulating separator 3 only needs to exhibit insulating properties and be chemically stable; its type is not particularly limited. For example, paper, resin, glass, etc., can be used.

[0015] Next, we will explain the charging and discharging operation of secondary battery B. The following describes a secondary battery that uses vanadium as the transition metal element in an organometallic complex. The inventors have confirmed that in secondary battery B using vanadium, the oxidation state of vanadium in the solid charge storage layers 12 and 22 on the positive and negative electrode sides is stable in a tetravalent, trivalent, or mixed state when not charged. (Charging operation → Fully charged) The operation during charging is shown in Figure 5(a). When the charging device 7 is connected to the secondary battery B, charging begins, and the positive electrode side releases electrons during charging (the current flows in the reverse direction). Specifically, as charging progresses, electrons are released from the solid charge storage layer 12 and move to the current collector plate 11, so the valence of vanadium in the solid charge storage layer 12 increases from 4 (or 3), and in a fully charged state, the amount of vanadium with the maximum valence of 5 increases and stabilizes. In contrast, the other negative electrode side performs electron absorption. Specifically, as charging progresses, electrons move from the current collector plate 21 and are absorbed by the solid charge storage layer 22. As a result, the valence of vanadium in the solid charge storage layer 22 decreases from 3 (or 4), and in the fully charged state, the amount of vanadium with the minimum valence of 2 increases and stabilizes. During charging, secondary battery B generates an electromotive force, and the charging device 7 forces a current to flow against this force, thus accumulating energy. When a load 8 is connected to the charged secondary battery B, the electromotive force causes a current to flow, resulting in a discharge state. (Operation during discharge → complete discharge) The operation during discharge is shown in Figure 5(b). During discharge, the positive electrode side performs electron absorption. Specifically, as the discharge progresses, electrons move from the current collector plate 11 and are absorbed by the solid charge storage layer 12. As a result, the valence of vanadium in the solid charge storage layer 12 decreases from valence 5, and in the state of complete discharge, the valence increases to 4 (or valence 3) and stabilizes. In contrast, the other negative electrode side undergoes electron emission. Specifically, as the discharge progresses, electrons are emitted from the solid charge storage layer 22 and move to the current collector plate 21. As a result, the valence of the vanadium in the solid charge storage layer 22 increases from valence 2, and stabilizes at valence 3 (or valence 4) in the state of complete discharge. During discharge, secondary battery B forces current to flow through load 8 due to its electromotive force, gradually releasing energy until it reaches a point where it is no longer possible to supply current, resulting in complete discharge.

[0016] Figure 6 shows the change in the oxidation state of vanadium within the organometallic complex of a solid charge storage layer using vanadium as the transition metal element. Considering this change in the oxidation state of vanadium, in the state immediately after manufacturing a secondary battery, both the positive and negative solid charge storage layers contain a mixture of vanadium with oxidation states of 3 and 4. Although this ratio depends on the manufacturing conditions, the presence of a mixture of oxidation states 3 and 4 means that the equilibrium oxidation state of vanadium is between 3 and 4. Then, when the secondary battery is charged from this state, electrons are released on the positive electrode side, causing the oxidation state of vanadium to increase. When fully charged, the amount of vanadium with an oxidation state of 5 increases, and the average oxidation state becomes 5. In contrast, on the negative electrode side, electrons are absorbed, causing the oxidation state of vanadium to decrease. When fully charged, the amount of vanadium with an oxidation state of 2 increases, resulting in an average oxidation state of 2. Then, the oxidation state of vanadium, which has changed as described above on both the positive and negative electrodes due to full charging, changes again on both the positive and negative electrodes when the discharge process begins, and returns to its state immediately after manufacturing once completely discharged. In this invention, the solid charge storage layer performs charging and discharging operations by releasing and absorbing electrons between the current collector plate and the organometallic complex based on the principle described above. Therefore, if the oxidation state of vanadium is initialized to the state of the organometallic complex after manufacturing on both the positive and negative electrode sides during complete discharge when no electromotive force is generated, then during full charging, the oxidation state of vanadium in the organometallic complexes on both the positive and negative electrode sides changes to the maximum (pentavalent) and minimum (divalent), respectively, enabling stable charging and discharging operations.

[0017] During the initialized charging process, a positive potential is applied to the positive electrode and a negative potential is applied to the negative electrode simultaneously. This causes a charging current to flow through the secondary battery, changing the oxidation state of the metal elements in the positive electrode's charge storage layer from 4 to 5, and the oxidation state of the metal elements in the negative electrode's charge storage layer from 3 to 2. Charging should be terminated (fully charged) when the oxidation state of all metal elements in the positive electrode's charge storage layer reaches 5 and the oxidation state of all metal elements in the negative electrode's charge storage layer reaches 2.

[0018] After charging, a rechargeable battery generates an electromotive force with the positive electrode having a positive potential and the negative electrode having a negative potential. When the rechargeable battery is connected to a load, a discharge current flows from the positive electrode to the negative electrode. Consequently, the oxidation number of the metal elements in the charge storage layer on the positive electrode side returns from 5 to 4, and the oxidation number of the metal elements in the charge storage layer on the negative electrode side returns from 2 to 3. Furthermore, even if a rechargeable battery is completely discharged, the basic structure of the molecules within the charge storage layer remains unchanged, so its performance does not degrade. Therefore, it can be used for a long time.

[0019] Figures 7 and 8 are cross-sectional views of a secondary battery. The secondary battery B shown in Figure 7 is a single-layer film-type secondary battery, similar to the secondary battery shown in Figure 3, while the secondary battery B shown in Figure 8 is a double-layer film-type secondary battery with B1 and B2 connected in series. In this way, secondary battery B can be made into single, double, or even multi-layer structures, and the electromotive force can be freely set by connecting them in series or parallel. Double and multi-layer structures can be manufactured in the same way as single-layer structures.

[0020] Furthermore, even if the current collector plates 11 and 21 of secondary battery B are curved, the solid charge storage layers 12 and 22 can be shaped to conform to the current collector plates 11 and 21. Mold molding is also possible, allowing for the manufacture of large, curved secondary batteries tailored to specific applications. This secondary battery B has excellent high-temperature characteristics (it can operate even at ambient temperatures of 85°C and can be stored at temperatures above 100°C), and its charge and discharge can be easily controlled.

[0021] Figure 9 is a transmission perspective view of a storage unit in which the secondary battery B is packaged, and Figure 10 is a perspective view of a large-scale storage device formed by assembling these storage units.

[0022] The energy storage unit C consists of stacked secondary batteries B, arranged in series or parallel and housed in an insulating case 4. The insulating case 4 is provided with an anode terminal 51 and a cathode terminal 52. Such an energy storage unit can be used as a replacement for existing standard general-purpose storage batteries if the size, arrangement, electromotive force, etc., of the insulating case 4, anode terminal 51, and cathode terminal 52 are matched.

[0023] The large-scale energy storage device D consists of multiple energy storage units C arranged and fixed in a rack 6. These energy storage units C can be freely combined and connected in series or parallel, making the large-scale energy storage device D suitable for use as an emergency power source, for large mobile machinery, and in plants.

Claims

1. The current collector plate and a solid charge accumulation layer are provided, which is formed by coating one side of the current collector plate with an organometallic complex composed of an organic polymer of PLGA (polylactic acid / glycolic acid copolymer) to which transition metals of group 3 to group 7 exhibiting an oxidation state of 3 or higher are bonded. This biodegradable electronic material is configured to store and discharge electrons between the solid charge storage layer and the current collector by changing the direction of the electric field applied to the solid charge storage layer through the current collector.

2. Prepare two sheets of the biodegradable electronic material described in claim 1, and align the current collector plates of the two biodegradable electronic materials with an insulating separator in between, A secondary battery having a structure in which a positive terminal is provided on one side of the current collector plate and a negative terminal is provided on the other side of the current collector plate.

3. A secondary battery having a structure in which multiple secondary batteries according to Claim 2 are stacked and connected in series or in parallel.

4. In claim 2 A curved secondary battery comprising a curved current collector plate and a solid charge storage layer shaped to conform to the current collector plate.

5. A power storage unit comprising a secondary battery as described in claim 2 housed in an insulating case, with anode and cathode terminals provided in the insulating case.

6. A large-scale energy storage device comprising multiple energy storage units as described in claim 5, arranged and fixed in a rack.

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