JP7796377B2 - All-solid-state battery and method for manufacturing same - Google Patents

Description

One embodiment of the present invention relates to an all-solid-state battery and a method for manufacturing the same. For example, one embodiment of the present invention relates to an all-solid-state battery having a geopolymer as an electrolyte and a method for manufacturing the same.

Geopolymers are amorphous condensation polymers formed by the reaction of an alkaline silica solution with alumina-silica powder. They have attracted attention in recent years as structural materials that exhibit superior properties different from those of concrete, which is made from cement. Geopolymers are also known to function as electrolytes in all-solid-state batteries (see non-patent literature 1 and 2).

Chaoli, Meng, et al., "Battery in the form of a cement-matrix composite," Cement & Concrete Composite, Elsevier (USA), 2010, Vol. 32, pp. 829-839 M. Surfi, et al., "Inherent multifunctional geopolymer cementitious composite as an electrical energy storage and self-sensing structural material," Composite Structures, Elsevier (USA), 2018, Vol. 201, pp. 766-778

An object of one embodiment of the present invention is to provide an all-solid-state battery having a novel structure and a method for manufacturing the same. Alternatively, an object of one embodiment of the present invention is to provide an all-solid-state battery containing a geopolymer as an electrolyte and a method for manufacturing the same. Alternatively, an object of one embodiment of the present invention is to provide an all-solid-state battery containing a geopolymer as an electrolyte and having excellent charge/discharge characteristics and a method for manufacturing the same.

One embodiment of the present invention is an all-solid-state battery. The all-solid-state battery includes a solid electrolyte containing a geopolymer and an additive, a positive electrode partially embedded in the solid electrolyte, and a negative electrode partially embedded in the solid electrolyte. The additive is a metal ion or a material that can be ionized to provide a cation.

One embodiment of the present invention is a method for fabricating an all-solid-state battery. The method includes mixing an alkaline solution, a filler, and an additive to form a flowable mixture, inserting a positive electrode and a negative electrode into the mixture, and solidifying the mixture. The additive is a metal ion or a material that can be ionized to provide a cation. The filler includes alumina and silica. The alkaline solution is selected from an aqueous solution of an alkali metal silicate and an aqueous solution of an alkali metal hydroxide.

FIG. 1 is a schematic perspective view of an all-solid-state battery according to an embodiment of the present invention. 1A and 1B are schematic top and end views of an all-solid-state battery according to an embodiment of the present invention; 1A and 1B are schematic top and end views of an all-solid-state battery according to an embodiment of the present invention; 1 is a flowchart showing a method for producing an all-solid-state battery according to an embodiment of the present invention. 1 shows discharge characteristics of all-solid-state batteries of Examples and Comparative Examples.

Each embodiment of the present invention will be described below with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the invention, and should not be construed as being limited to the description of the embodiments exemplified below.

In order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but this is merely an example and does not limit the interpretation of the present invention. In this specification and each drawing, elements with the same function as those explained in the previous drawings may be given the same reference numerals, and duplicate explanations may be omitted.

Hereinafter, the expression "a structure exposed from another structure" means a state in which a portion of a structure is not covered by another structure, and also includes a state in which this portion not covered by another structure is covered by yet another structure.

1. Structure of All-Solid-State Battery A schematic perspective view of an all-solid-state battery 100 according to an embodiment of the present invention is shown in Fig. 1. As shown in Fig. 1, the all-solid-state battery 100 includes an electrolyte 102, and a positive electrode 104 and a negative electrode 106 that are in contact with or partially inserted into the electrolyte 102.

The electrolyte 102 is a solid-state electrolyte containing a geopolymer and exhibiting complete or substantial lack of fluidity. Here, geopolymer is an amorphous polycondensation product formed by the reaction of an alkali silica solution with alumina-silica powder. Therefore, the electrolyte 102 contains at least one of fine particles containing silicon oxide, fine particles containing aluminum oxide, and fine particles containing silicon oxide and aluminum oxide. The electrolyte 102 may further contain fine particles containing an oxide of an alkali metal, Group 2 metal, or transition metal, such as iron oxide, calcium oxide, magnesium oxide, sodium oxide, or potassium oxide. Furthermore, the electrolyte 102 has silicon-oxygen-aluminum (Si-O-Al) bonds, and may further contain silicon-oxygen-silicon (Si-O-Si) bonds, silicon-oxygen-metal-oxygen-silicon (Si-O-M-O-Si) bonds, or silicon-oxygen-metal-oxygen-aluminum (Si-O-M-O-Al) bonds. The fine particles are fixed by the amorphous inorganic material formed by the above bonds. Here, M is a metal selected from alkali metals such as lithium, sodium, potassium, and cesium, Group 2 metals such as magnesium and calcium, and transition metals such as cobalt, copper, and iron.

The electrolyte 102 further contains, as an additive, a material that exists as a metal ion in the electrolyte 102 or that ionizes to provide a cation. Examples of metal ions include ions of alkali metals or Group 2 elements. The material that provides the cation can be selected from transition metals, for example. Examples of transition metals include scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. Preferred transition metals are, for example, iron, cobalt, and copper.

The material that provides the cations may be a carbon material. The carbon material may be electrically conductive. Here, the carbon material is a material substantially composed of ^sp2 carbon atoms, and examples thereof include carbon nanotubes, graphene, and fullerenes. The carbon nanotubes may be single-walled or multi-walled carbon nanotubes. There are no limitations on the diameter or length of the carbon nanotubes. Furthermore, one or both ends of the carbon nanotube may be capped, or one or both ends may be open. Alternatively, the carbon nanotube may contain other molecules or ions, such as peapods, or may have a molecularly modified surface. When graphene is used as the carbon material, it may be an independent single-layer graphene, or an oligographene in which multiple graphenes are stacked, or graphite. Furthermore, graphene oxide, in which part of the basic skeleton is oxidized, may be used. When fullerene is used as the carbon material, not only _C60 and _C70 but also _C74 , _C76 , _C78 , etc. may be used. Further, fullerenes containing metal ions such as scandium, lanthanum, and cerium may be used, or fullerenes in which some of the carbon atoms are modified and which have functional groups such as ester groups may be used.

The size and shape of the electrolyte 102 may be selected arbitrarily. For example, the electrolyte 102 may have a rectangular parallelepiped or cubic shape as shown in FIG. 1, or, although not shown, may have a cylindrical, elliptical cylinder, spherical, hemispherical, plate-like (film-like), rod-like, or other shape. Alternatively, the electrolyte 102 may be part of a structural material containing a geopolymer. That is, the electrolyte 102 may be part of a structure containing a geopolymer, such as a bridge, building, road, tunnel, or dam.

The positive electrode 104 and the negative electrode 106 are electrodes that each contain a metal such as copper, nickel, aluminum, zinc, palladium, silver, chromium, or manganese. The metal materials contained in the positive electrode 104 and the negative electrode 106 are different from each other. The positive electrode 104 and the negative electrode 106 may be configured so that the metal with the smaller ionization tendency is contained in the positive electrode 104.

The shape and size of the positive electrode 104 and the negative electrode 106 can also be selected arbitrarily. For example, the positive electrode 104 and the negative electrode 106 may have a plate (film), rod, or wire shape. If they are plate-shaped, the positive electrode 104 and the negative electrode 106 may have a mesh-like form.

The distance between the positive electrode 104 and the negative electrode 106 can also be selected arbitrarily, taking into consideration the power required by the load connected to the positive electrode 104 and the negative electrode 106. For example, the distance can be selected from the range of 0.1 mm to 5 m, 1 mm to 5 m, 1 mm to 3 mm, 20 mm to 1 m, or 50 mm to 0.5 m.

The arrangement of the positive electrode 104 and the negative electrode 106 may also be determined arbitrarily. As shown in Figure 1, the length of each of the portions where the positive electrode 104 and the negative electrode 106 are embedded in the electrolyte 102 (length in the z direction in Figure 1) may be the same as, longer than, or shorter than the height (length in the z direction) of the electrolyte 102.

One of the factors that influences the energy density, which is one of the characteristics of the all-solid-state battery 100, is the contact area between the electrolyte 102 and the portions of the cathode 104 and anode 106 embedded in the electrolyte 102. Therefore, to increase the contact area, the cathode 104 and anode 106 may have a folded structure within the electrolyte 102, as shown in the schematic top view of FIG. 2(A) and the schematic end view (FIG. 2(B)) along the dashed line A-A' in FIG. 2(A). Alternatively, the cathode 104 and anode 106 may have a spiral shape within the electrolyte 102, as shown in the schematic top view of FIG. 3(A) and the schematic end view (FIG. 3(B)) along the dashed line B-B' in FIG. 3(A). In these arrangements, one straight line passing through the electrolyte 102 passes through the cathode 104 at least multiple times and through the anode 106 multiple times. Furthermore, a portion of the positive electrode 104 and another portion thereof sandwich a portion of the negative electrode 106, and similarly, a portion of the negative electrode 106 and another portion thereof sandwich a portion of the positive electrode 104. By adopting such an arrangement, the energy density of the all-solid-state battery 100 can be improved.

Geopolymers are known to function as battery electrolytes. However, the performance of batteries using geopolymers as electrolytes is extremely poor and has not yet reached a practical level. In contrast, as shown in the examples, adding the above-mentioned additives to the electrolyte 102 significantly improves battery performance, providing an all-solid-state battery with excellent charge-discharge characteristics. Therefore, embodiments of the present invention make it possible to use structural materials containing geopolymers as a source of electrical energy.

In addition, because the all-solid-state battery 100 also functions as a rechargeable secondary battery, electrical energy obtained from, for example, a solar cell can be stored in the structural material containing the geopolymer itself. This eliminates the need to provide a separate battery for storing electrical energy, making it possible to store electrical energy at low cost.

2. Method for Producing All-Solid-State Battery An example of a method for producing the all-solid-state battery 100 will be described with reference to the flowchart of FIG.

First, the raw materials for the electrolyte 102, namely, the alkaline solution, filler, and the additives mentioned above, are mixed to prepare a fluid mixture (precursor). The temperature during mixing may be, for example, room temperature (20°C to 25°C), but there are no restrictions. For example, the temperature during mixing may be selected from the range of -20°C to 40°C, 0°C to 35°C, or 15°C to 30°C. During mixing, water may be added as needed, taking into account the strength required for the electrolyte 102.

Examples of alkaline solutions include alkali silicate solutions and aqueous solutions of alkali metal hydroxides. An example of an alkali silicate solution is so-called water glass. Therefore, specific examples of alkali silicate solutions include aqueous solutions of silicates of alkali metals such as sodium and potassium. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. The concentration of the aqueous alkali metal hydroxide solution may be selected from the range of, for example, 5% by mass or more and 30% by mass or less, or 10% by mass or more and 20% by mass or less.

Any material containing aluminum oxide and silicon oxide can be used as a filler. Typical examples include fly ash, slag (also known as iron ore slag or steel slag), sewage sludge, silica fume, rice husk ash, general incineration ash, metakaolin, and clay. Fly ash, also known as coal ash, is the residue from burning coal at coal-fired power plants. Slag is the residue produced when silicon oxide and aluminum oxide contained in ore melt with ash from coke during the refining of metals from ores such as iron ore. Silica fume is dust obtained when collecting dust generated during the production of silicon metal and electrofused zirconia, and contains high-purity silicon oxide. General incineration ash is the residue from burning waste in a waste incinerator. Metakaolin is a material obtained by heating the clay mineral kaolinite at around 700°C to amorphousize it.

The composition of the alkaline solution and filler can be determined as appropriate, but the alkaline solution may be 20% by mass or more and 50% by mass or less, or 30% by mass or more and 50% by mass or less, relative to the total amount of alkaline solution and filler. Meanwhile, the filler may be 50% by mass or more and 80% by mass or less, or 50% by mass or more and 70% by mass or less, relative to the total amount of the mixture. The amount of additive added may be, for example, 0.001% by mass or more and 10% by mass or less, 0.01% by mass or more and 10% by mass or less, or 0.1% by mass or more and 10% by mass or less.

When forming the mixture, aggregates (fine aggregate, coarse aggregate) such as sand, gravel, and crushed stone used in mortar and concrete may be added separately.

The resulting mixture, in a fluid state, is poured into a container or formwork of the desired shape. The material used for the container or formwork can be any material, including metal materials such as iron, stainless steel, and aluminum, wood, resin materials, and glass. If a formwork is used, rebar can be placed inside the formwork.

Then, while the mixture is still fluid, the positive electrode 104 and the negative electrode 106 are placed. The positive electrode 104 and the negative electrode 106 may each be placed so that a portion thereof is embedded in the electrolyte 102 and another portion thereof is exposed from the electrolyte 102. Alternatively, the positive electrode 104 and the negative electrode 106 may be placed on the surface of the mixture.

In addition, the positive electrode 104 and negative electrode 106 may be placed in a container or mold, and then the mixture may be prepared and poured into the container or mold.

The mixture is then left to stand (cured) to solidify. The solidification temperature can also be set as desired, within the ranges of -20°C to 100°C, 0°C to 60°C, or 20°C to 50°C. The solidification rate can be increased by solidifying at a temperature higher than room temperature, for example, 40°C to 100°C. The solidification time depends on the solidification temperature and the composition of the mixture, but can be appropriately selected from the ranges of, for example, 3 hours to 1 week, 3 hours to 3 days, or 3 hours to 24 hours.

Through the above steps, an all-solid-state battery 100 is produced. The all-solid-state battery 100 may be used while placed in a container or mold, or may be used with the container or mold removed.

As described above, in this method, fillers that can be used include fly ash, slag also known as iron and steel slag, sewage sludge, silica fume, rice husk ash, general incineration ash, metakaolin, and clay. Because these fillers are types of industrial waste, the method for producing the all-solid-state battery 100 according to the embodiment of the present invention can also be positioned as a tool for effectively utilizing industrial waste.

Below, we will explain the results of fabricating an all-solid-state battery 100 using carbon nanotubes as an additive.

1. Preparation of an All-Solid-State Battery: 27% by weight of silica gel, 30% by weight of potassium oxide, and 43% by weight of distilled water were mixed at room temperature to obtain a potassium silicate solution. The resulting potassium silicate solution was added to commercially available fly ash, specified in JIS Type 2, primarily composed of silica gel and alumina, and mixed. Commercially available carbon nanotubes were then added to obtain a mixture. The potassium silicate solution was used at 60% by weight of the fly ash, and the carbon nanotubes were used at 0.01% by weight of the total amount of the potassium silicate solution and fly ash. The resulting mixture was poured into a 50 mm x 50 mm x 50 mm plastic prismatic container. A 50 mm x 60 mm mesh copper plate was inserted into the mixture as the positive electrode 104, and a 50 mm x 60 mm mesh aluminum plate was inserted into the container as the negative electrode 106. The positive electrode 104 and negative electrode 106 were spaced 10 mm apart, with approximately 10 mm of the electrode exposed from the surface of the mixture. Thereafter, the mixture was allowed to stand in a constant temperature room at 50° C. for 6 hours to solidify, thereby obtaining an all-solid-state battery 100.

As a comparative example, an all-solid-state battery that did not contain carbon nanotubes was fabricated using the same method and conditions as in the example.

2. Evaluation A load (300 mΩ to 400 mΩ) was placed between the positive electrode 104 and the negative electrode 106, and the change in voltage between the positive electrode 104 and the negative electrode 106 over time was measured using a voltmeter connected in parallel to the load. The results are shown in FIG. 5. As can be seen from FIG. 5, the voltage of the all-solid-state battery of the comparative example dropped rapidly from an initial voltage of 2.0 V, reaching nearly 0 V after about two hours, and it was confirmed that the battery function was lost. In contrast, the all-solid-state battery 100 of the example had a high initial voltage (3.7 V), and although the voltage dropped rapidly thereafter, it was found that a voltage of approximately 1.8 V could be maintained for 45 hours or more. From this, it can be said that the addition of a small amount of additive can maintain the discharge characteristics of a battery for a long period of time.

After the discharge experiment described above was completed, a reverse voltage of 14 V was applied between the positive electrode 104 and the negative electrode 106 to the all-solid-state battery of the example, and charging was performed for 5 or 15 minutes, and then a discharge experiment was performed again. As a result, it was confirmed that results similar to those shown in Figure 5 were obtained, regardless of the charging time. This demonstrates that the all-solid-state battery according to the embodiment of the present invention functions as a rechargeable secondary battery.

As described above, it has been confirmed that by using a geopolymer containing metal ions or a material that ionizes to provide cations as an electrolyte, it is possible to provide an all-solid-state secondary battery that exhibits excellent discharge characteristics over a long period of time. This indicates that structural materials containing geopolymers can also be used as secondary batteries, suggesting that a new type of infrastructure may be possible through this invention.

The above-described embodiments of the present invention can be implemented in any suitable combination, provided they are not mutually inconsistent. Any product in which a person skilled in the art appropriately adds, deletes, or modifies components based on each embodiment is also included within the scope of the present invention, as long as it maintains the essence of the present invention.

Even if there are other effects and advantages different from those provided by the above-described embodiments, those that are clear from the description in this specification or that would be easily predicted by a person skilled in the art are naturally understood to be provided by the present invention.

100: All-solid-state battery, 102: Electrolyte, 104: Cathode, 106: Anode

Claims (6)

solid electrolytes containing geopolymers and additives;
a positive electrode partially embedded in the solid electrolyte; and a negative electrode partially embedded in the solid electrolyte,
The all-solid-state battery, wherein the additive is a carbon nanotube . The all-solid-state battery described in claim 1, wherein the composition of the additive in the solid electrolyte is 0.001% by weight or more and 10% by weight or less. The all-solid-state battery described in claim 1, wherein the geopolymer has an amorphous structure and contains an aluminosilicate having Si-O-Al bonds. The all-solid-state battery described in claim 1, wherein the positive electrode and the negative electrode contain different metals. mixing an aqueous alkali metal silicate solution, a filler, and an additive to form a flowable mixture;
inserting a positive electrode and a negative electrode into the mixture; and solidifying the mixture.
the additive is carbon nanotubes ,
The method for producing an all-solid-state battery, wherein the filler includes alumina and silica. The method according to claim 5 , wherein the composition of the additive in the mixture is 0.001% by weight or more and 10% by weight or less.