Air battery

Abstract

To provide an air battery which has high capacity and is excellent in cyclic performance.SOLUTION: An air battery comprises: a negative electrode; an air electrode to which oxygen is supplied; a solid electrolyte layer located between the negative electrode and the air electrode; an aqueous electrolyte layer located between the solid electrolyte layer and the air electrode; and a proton conductive layer located between the aqueous electrolyte layer and the air electrode. The aqueous electrolyte layer contains an aqueous electrolyte containing a polyvalent acid having two or more carboxyl groups, an electrolytic salt, and water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to an air battery.

Background Art

[0002] In recent years, the market for portable information devices such as mobile phones and email terminals has been expanding rapidly. As these devices become smaller and lighter, there is a growing demand for a power source that is also small and light. Currently, lithium-ion secondary batteries with high energy density are mainly used in these portable devices, but there is a further demand for higher capacity.

[0003] An air battery that uses oxygen in the air as a positive electrode active material does not require the built-in active material in the positive electrode, so it is expected to have a higher capacity per unit volume and weight. For example, a lithium-air battery is known as a lithium secondary battery that uses metallic lithium as the negative electrode active material and oxygen as the positive electrode active material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide an air battery having a high capacity and excellent cycle performance.

Means for Solving the Problems

[0007] According to an embodiment, there is provided an air battery including a negative electrode, an air electrode to which oxygen is supplied, a solid electrolyte layer positioned between the negative electrode and the air electrode, an aqueous electrolyte layer positioned between the solid electrolyte layer and the air electrode, and a proton conduction layer positioned between the aqueous electrolyte layer and the air electrode. The aqueous electrolyte layer contains an aqueous electrolyte including a polyvalent acid having two or more carboxyl groups, an electrolyte salt, and water. The air electrode does not contain a metal, a metal oxide, or a complex that exhibits catalytic activity.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0009] Lithium-air batteries are expected to be next-generation high-capacity batteries because of their high energy density per unit weight. However, in conventional lithium-air batteries, discharge products with low solubility precipitate as solids during discharge. The clogging of the pores in the positive electrode by the discharge products and the poisoning of the catalyst contained in the positive electrode reduce the capacity and cycle performance. For example, in a non-aqueous lithium-air battery operating under acidic conditions, Li2O2 precipitates in the non-aqueous electrolyte during discharge. In an aqueous lithium-air battery operating under non-acidic conditions, for example, LiOH is generated during discharge. As the discharge progresses, the concentration of LiOH in the aqueous electrolyte increases, and the basicity of the electrolyte increases. The capacity obtained until the dissolution limit of LiOH in the electrolyte is reached in an aqueous air battery is about 143 mAh / mL.

[0010] The above problems can be solved by using an aqueous solution containing a polyvalent carboxylic acid such as citric acid as the liquid electrolyte to improve the solubility of the discharge products. The capacity obtained until the dissolution limit of lithium citrate is reached is 285 mAh / mL, and the use of citric acid can improve the capacity by nearly twice. However, polyvalent carboxylic acids are decomposed on the positive electrode (air electrode) within the voltage range in which the air battery operates. Due to the decomposition of polyvalent carboxylic acids, there is a limit to the improvement of cycle performance.

[0011] Embodiments will be described below with reference to the drawings. In the embodiments, the same reference numerals are assigned to common configurations, and redundant descriptions are omitted. Each drawing is a schematic diagram for facilitating the explanation and understanding of the embodiments, and there are some differences in the shape, dimensions, ratio, etc. from the actual device, but these can be appropriately designed and changed in consideration of the following description and known techniques.

[0012] The air battery according to the embodiment includes a negative electrode, an air electrode (positive electrode) to which oxygen is supplied, a solid electrolyte layer, an aqueous electrolyte layer containing an aqueous electrolyte, and a proton conduction layer. The solid electrolyte layer is located between the negative electrode and the air electrode. The aqueous electrolyte layer is located between the solid electrolyte layer and the air electrode and contains an aqueous electrolyte. The aqueous electrolyte contains a polyvalent acid having two or more carboxyl groups, an electrolyte salt, and water. The proton conduction layer is located between the aqueous electrolyte layer and the air electrode.

[0013] Salts of polyvalent acids having two or more carboxyl groups have high solubility in water. Therefore, by using such a polyvalent acid, solid precipitation of discharge products such as LiOH can be suppressed, and since the salts of the polyvalent acid itself are less likely to precipitate, the discharge capacity can be greatly improved. As a specific example of the polyvalent acid, citric acid can be mentioned. Citric acid is a polyvalent acid having two or more carboxyl groups.

[0014] The polyvalent acid (RH) can be dissolved in the aqueous electrolyte in a state of being dissociated into protons (H + ) and anions (R - ) in an aqueous solvent. Also, protons can be generated by the reaction between carrier ions (cations such as Li + ) supplied from the negative electrode during discharge of the air battery and the polyvalent acid. The protons can reach the air electrode through the proton conduction layer. During discharge of the air battery, oxygen supplied from the outside of the battery to the air electrode side passes through the proton conduction layer and is supplied together with the protons supplied from the negative electrode via the external circuit (and load) and electrons (e -) It is reduced at the air electrode by a reduction reaction with []. Also, protons generated by the electrolysis of water at the air electrode during charging can be supplied to the aqueous electrolyte layer through the proton conduction layer. The proton conduction layer exhibits selective conductivity with respect to protons. Specifically, the anions of polyvalent acids cannot pass through the proton conduction layer. Since the polyvalent acid anions do not reach the air electrode, the decomposition of anions on the air electrode is prevented. That is, the air battery according to the embodiment includes a proton conduction layer located between the aqueous electrolyte layer and the air electrode, thereby suppressing the decomposition of polyvalent acids. Therefore, such an air battery can exhibit excellent cycle performance.

[0015] The negative electrode can contain a negative electrode active material. The negative electrode active material includes, for example, an alkali metal such as lithium (Li), an alkaline earth metal, or an alloy containing these metal elements. Also, the negative electrode active material can include, for example, other metals such as aluminum and zinc or alloys containing these metal elements. Alternatively, the negative electrode active material includes, for example, a material into which the above metal elements are inserted and removed.

[0016] In a specific example of the air battery, the negative electrode active material includes one or more selected from the group consisting of lithium metal, lithium alloy, and a material into which lithium is inserted and removed. That is, such an air battery can be a lithium-air battery. Cations of alkali metals and alkaline earth metals such as lithium contained in the negative electrode active material act as carrier ions that move between the negative electrode and the air electrode during the charge and discharge of the air battery. Lithium ions (Li + ) Specific examples of carrier ions other than [] include sodium ions (Na+), potassium ions (K + ), cesium ions (Cs + ), calcium ions (Ca 2+ ), magnesium ions (Mg 2+ ), aluminum ions (Al 3+ ), and zinc ions (Zn 2+ ). That is, the air battery according to the embodiment is not limited to a lithium-air battery and can be, for example, other air batteries such as sodium-air batteries or metal-air batteries.

[0017] The solid electrolyte layer is located between the negative electrode and the air electrode, more specifically, between the negative electrode and the aqueous electrolyte layer. The solid electrolyte layer functions as a separator that electrically insulates the air electrode and the negative electrode without hindering the movement of carrier ions (such as Li) from the negative electrode to the air electrode. The solid electrolyte layer may have, for example, ion conductivity. Further, when an active material highly reactive with water, such as metallic lithium, is used for the negative electrode, the solid electrolyte layer can block the negative electrode from the aqueous electrolyte.

[0018] Such an air battery may further include an intermediate layer located between the negative electrode and the solid electrolyte layer. When the negative electrode and the solid electrolyte layer come into contact, a reaction that causes deterioration of the solid electrolyte may occur. By providing the intermediate layer, the reaction between the negative electrode and the solid electrolyte layer can be prevented. The intermediate layer may contain a non-aqueous electrolyte as a negative electrode side electrolyte.

[0019] The negative electrode, the solid electrolyte layer, the aqueous electrolyte layer, the proton conduction layer, the air electrode, and any intermediate layer may constitute an electrode group. The air battery may include an exterior member that houses the electrode group.

[0020] In addition, such an air battery may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the air electrode (positive electrode).

[0021] Moreover, the air battery may further include an air diffusion layer that functions as a supply path for air containing oxygen from the outside of the exterior member to the air electrode. The air diffusion layer may be provided between the exterior member and the air electrode. Alternatively, a part of the exterior member may constitute the air diffusion layer.

[0022] An overview of an example of the air battery according to the embodiment is shown in FIG. 1. FIG. 1 is a conceptual diagram showing an example of the air battery according to the embodiment. Further, FIG. 1 shows the operation of the air battery during discharge.

[0023] The illustrated air battery 1 has an electrode group 2 including a negative electrode 3, an intermediate layer 4, a solid electrolyte layer 5, an aqueous electrolyte layer 6, a proton conduction layer 7, and an air electrode 8. In the electrode group 2, these negative electrodes 3 and the like are arranged in the above order.

[0024] In the illustrated example, the negative electrode 3 contains a metal or alloy containing lithium, or a material capable of inserting and extracting lithium (lithium ions) as a negative electrode active material. Further, the aqueous electrolyte layer 6 contains an aqueous electrolyte containing a polyvalent acid (RH) and an electrolyte salt as solutes. In the illustrated example, the aqueous electrolyte layer 6 contains, for example, a lithium salt as the electrolyte salt. That is, the exemplified air battery 1 is an aqueous lithium-air battery or a lithium-ion air battery. The polyvalent acid is dissolved in the water contained in the aqueous electrolyte as a solvent, and can be contained in the aqueous electrolyte in a state of being dissociated into protons (H + ) and anions (R - ). Also, the lithium salt contained as the electrolyte salt can also be in a state of being dissolved in water and dissociated into lithium ions (Li + ) and counter anions.

[0025] The aqueous electrolyte contained in the aqueous electrolyte layer 6 is in acidic conditions (pH < 7) at least when the air battery 1 is charged. In such an aqueous air battery 1 having an aqueous electrolyte under acidic conditions, the reactions on the air electrode 8 side (positive electrode reaction) and the negative electrode 3 side during charge and discharge are as follows. During discharge of the air battery 1, each electrode reaction proceeds in the right direction, and during charging, each electrode reaction proceeds in the left direction.

[0026]

Chemical formula

[0027] An example of the operation of the air battery 1 during discharge will be described. When oxygen (O2) can be supplied from the outside to the air electrode 8 and the negative electrode 3 and the air electrode 8 are electrically connected by an external circuit (not shown) and the electrical circuit is closed, the air battery 1 can be discharged.

[0028] Lithium ions (Li + ) are supplied from the negative electrode 3 to the aqueous electrolyte layer 6 through the intermediate layer 4 and the solid electrolyte layer 5. Also, electrons (e - ) are supplied from the negative electrode 3 to the air electrode 8 via an external circuit (and load) (not shown). For example, Li ions and electrons can be generated by dissociation of Li atoms of lithium metal contained as a negative electrode active material in the negative electrode 3. Alternatively, Li ions and electrons can be extracted by a desorption reaction from the negative electrode active material.

[0029] Oxygen (O2) is supplied to the air electrode 8 from the outside, and protons (H + ) are selectively supplied from the aqueous electrolyte layer 6 to the air electrode 8 through the proton conduction layer 7. Also, as described above, electrons (e - ) are supplied to the air electrode 8 via the external circuit. The reaction on the air electrode side proceeds at the air electrode 8, and oxygen is reduced to generate water (H2O). The generated water can move from the air electrode 8 to the aqueous electrolyte layer 6.

[0030] As described above, since protons derived from the polyvalent acid can pass through the proton conduction layer 7 and move from the aqueous electrolyte layer 6 to the air electrode 8, they can participate in the discharge reaction at the air electrode 8. On the other hand, since the polyvalent acid anion (R - ) is blocked by the proton conduction layer 7, the decomposition reaction of the polyvalent acid at the air electrode 8 accompanying charge and discharge of the air battery 1 can be suppressed.

[0031] Since the solubility of the polyvalent acid in the aqueous electrolyte is high, the lithium salt of the polyvalent acid, which is a discharge product shown in the negative electrode side reaction, tends to remain dissolved in the polyvalent acid anion and lithium ions in the aqueous electrolyte layer 6. That is, it is difficult for the discharge product to precipitate as a solid in the aqueous electrolyte layer 6. Therefore, the capacity of the air battery 1 can be increased. Also, since it is difficult for the discharge product to precipitate even when the concentration of the discharge product increases, a high capacity can be exhibited even if the volume of the aqueous electrolyte layer 6 is reduced, and the energy density can be improved. Furthermore, due to the high solubility of the discharge product, it is possible to avoid a performance degradation that may occur by separating the aqueous electrolyte layer 6 and the air electrode 8 by the proton conduction layer 7.

[0032] Since the air battery can exhibit a high energy density, it can be suitably used as a lightweight and compact power source. The applications of the air battery are not limited to the conventionally known applications, and for example, electric aircraft can be mentioned. Electric aircraft include unmanned aircraft such as drones.

[0033] The intermediate layer 4 prevents the reduction reaction of the solid electrolyte included in the solid electrolyte layer 5 by the negative electrode active material by separating the negative electrode 3 and the solid electrolyte layer 5. When the material constituting the solid electrolyte layer 5 has high reduction resistance, the intermediate layer 4 may be omitted.

[0034] The intermediate layer 4 prevents the contact between the negative electrode 3 and the solid electrolyte layer 5, but does not inhibit the movement of carrier ions such as lithium ions. For example, the intermediate layer 4 may have lithium ion conductivity. According to one aspect, the intermediate layer 4 may contain a non-aqueous electrolyte. Details of the non-aqueous electrolyte will be described later.

[0035] According to another aspect, the intermediate layer 4 may include a plurality of sub-layers. An example of the air battery 1 including such an intermediate layer is shown in FIG. 2. In the example of FIG. 2, the aspect of the intermediate layer 4 is different from the example of FIG. 1. Since other details are the same, the description is omitted.

[0036] In the air battery 1 of FIG. 2, the intermediate layer 4 includes a non-aqueous electrolyte layer 4a and a metal oxide layer 4b. The non-aqueous electrolyte layer 4a and the metal oxide layer 4b are disposed on the negative electrode 3 side and the solid electrolyte layer 5 side, respectively. By including the intermediate layer 4 having such a configuration, the reaction between the negative electrode active material such as lithium metal and the solid electrolyte can be better suppressed, leading to an improvement in cycle performance.

[0037] In the above example, an example of a lithium-air battery using an aqueous electrolyte was described. However, the air battery according to the embodiment is not limited to a lithium-air battery. For example, sodium ions, potassium ions, cesium ions, calcium ions, magnesium ions, and aluminum ions can be used instead of lithium ions as carrier ions. That is, the air battery according to the embodiment can be, for example, an aqueous electrolyte air battery that includes sodium, potassium, cesium, calcium, magnesium, or aluminum as a negative electrode active material and includes an aqueous electrolyte in which sodium ions, potassium ions, cesium ions, calcium ions, magnesium ions, or aluminum ions are dissolved in an aqueous solution, respectively, as an electrolyte salt.

[0038] Next, the negative electrode, air electrode, solid electrolyte layer, aqueous electrolyte layer, proton conduction layer, intermediate layer, exterior member, positive electrode terminal, and positive electrode terminal will be described in detail.

[0039] 1) Negative electrode The negative electrode can include a negative electrode active material. The negative electrode can include a negative electrode active material layer containing a negative electrode active material. The negative electrode can further include a negative electrode current collector that supports the negative electrode active material layer. The negative electrode can be composed of the negative electrode active material layer.

[0040] As the negative electrode active material, for example, metals and alloys capable of occluding and releasing carrier ions such as lithium ions can be used. Specific examples include materials used for electrodes in lithium batteries such as lithium metal and lithium alloys. In addition, aluminum metal, zinc metal, aluminum alloys, and zinc alloys can be cited as examples of the negative electrode active material. Further, as other examples of the negative electrode active material, materials capable of insertion and desorption (intercalation) of carrier ions can be cited. Specific examples include metal oxides, metal sulfides, metal nitrides, alkali metal-containing composite oxides, alkaline earth metal-containing composite oxides, carbonaceous materials into which carrier ions are inserted and desorbed, and the like. For example, materials commonly used as electrode active materials in secondary batteries such as lithium ion batteries or sodium ion batteries can be used as the negative electrode active material of an air battery. One of the above metals, alloys, metal compounds, composite oxides, and carbonaceous materials may be used as the negative electrode active material, or two or more thereof may be combined and used as the negative electrode active material.

[0041] Examples of alloys include, for example, aluminum alloys, tin alloys, lead alloys, and silicon alloys. Specific examples include lithium alloys such as lithium aluminum alloy, lithium tin alloy, lithium lead alloy, and lithium silicon alloy.

[0042] Examples of metal oxides include, for example, tin oxide, silicon oxide, lithium-containing titanium oxide, titanium oxide, niobium oxide, tungsten oxide, and the like. The metal oxide as the negative electrode active material may be referred to as the first metal oxide.

[0043] Examples of metal sulfides include, for example, tin sulfide, titanium sulfide, and the like.

[0044] Examples of metal nitrides include, for example, lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride.

[0045] Examples of carbonaceous materials capable of inserting and extracting lithium ions include graphite materials or carbonaceous materials such as graphite, coke, carbon fiber, spherical carbon, etc., thermosetting resins, isotropic pitch, mesophase pitch, mesophase pitch-based carbon fiber, mesophase microspheres, etc., and graphite materials or carbonaceous materials obtained by heat-treating them at 500°C to 3000°C.

[0046] A binder can be contained in the negative electrode active material layer together with the negative electrode active material. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), etc. can be used. One of these can be used as the binder, or two or more of them can be combined and used as the binder.

[0047] The mixing ratio of the negative electrode active material and the binder in the negative electrode active material layer is preferably in the range of 80% by mass or more and 98% by mass or less of the negative electrode active material and 2% by mass or more and 20% by mass or less of the binder.

[0048] As the negative electrode current collector, a conductive substrate with a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed of, for example, copper, stainless steel, or nickel. For the conductive substrate with a porous structure, for example, mesh, punched metal, expanded metal, etc. can be used. Or, after supporting the negative electrode active material layer on a metal foil, a metal foil with through holes opened therein can be used as the conductive substrate with a porous structure. The negative electrode current collector may be omitted.

[0049] The negative electrode can be produced, for example, as follows. The negative electrode active material and the binder are kneaded in the presence of a solvent, the obtained suspension is applied to the current collector, and dried. Then, the obtained laminate is subjected to a single press or a multi-stage press of 2 to 5 times at a desired pressure to produce the negative electrode.

[0050] Also, if the above-mentioned metals or alloys are used as the negative electrode active material, since these metal-based materials can be processed into a sheet shape even alone, the negative electrode active material layer can be formed without using a binder. Further, the negative electrode active material layer formed of these metal-based materials can be directly connected to the negative electrode terminal without passing through the negative electrode current collector.

[0051] 2) Air electrode The air electrode (positive electrode) can include an oxygen reaction layer (positive electrode reaction layer). The air electrode can further include a positive electrode current collector that supports the oxygen reaction layer. The air electrode can be composed of the oxygen reaction layer. The air electrode uses oxygen supplied from outside the battery to the oxygen reaction layer as the active material.

[0052] The oxygen reaction layer includes a conductive material and has a structure showing gas diffusibility. For example, as the oxygen reaction layer, a sheet material containing carbon fibers such as carbon paper, carbon cloth, and carbon non-woven fabric can be used. Alternatively, a porous material formed of a metal such as stainless steel, nickel, aluminum, and iron can be used as the oxygen reaction layer. In addition, a layer-shaped porous body can be formed using a conductive material and used as the oxygen reaction layer. The oxygen reaction layer formed of a conductive material may contain a binder.

[0053] The conductive material formed in a layer shape and used for the oxygen reaction layer can be used without particular limitation as long as it has conductivity. As the conductive material, those that do not dissolve in the aqueous electrolyte and are not easily oxidized by oxygen are preferable. Specifically, carbonaceous substances, conductive ceramics, metals, etc. can be mentioned. Examples of carbonaceous substances include natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotube, ketjen black, acetylene black, carbon black, furnace black, activated carbon, activated carbon fiber, and charcoal. Examples of conductive ceramics include oxides of metals such as In and Sn, and carbides such as SiC. Examples of metals include metals such as Al and Ti, and alloys such as SUS.

[0054] The oxygen reaction layer may further include a catalyst that reduces the oxidation-reduction and generation overvoltage of oxygen to promote the oxidation-reduction and generation reaction of oxygen. The catalyst can be supported, for example, on the outer surface or the inner wall surface of the pores of the porous material constituting the oxygen reaction layer. Alternatively, the catalyst can be supported, for example, on the surface of the conductive material included in the oxygen reaction layer.

[0055] The catalyst can be selected, for example, from metals, metal oxides, complexes, etc. that exhibit catalytic activity and have been conventionally used as the positive electrode catalyst for air batteries or the positive electrode catalyst for fuel cells and water electrolysis. As the metal that exhibits catalytic activity, at least one selected from the group consisting of Au, Pt, Pd, Ir, Ru, and Ag is preferable. As the metal oxide that exhibits catalytic activity, an oxide containing at least one metal selected from the group consisting of Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Sn, Co, Rh, Ni, Cu, Ag, In, Sn, La, and Ce is preferable. The metal oxide used as the catalyst for the air electrode may be referred to as the second metal oxide. As the complex that exhibits catalytic activity, a complex having at least one metal selected from the group consisting of Fe, Ni, and Co as the central metal and having a planar tetradentate ligand such as phthalocyanine, porphyrin, and salen is preferable.

[0056] Sheet materials containing carbon fibers such as carbon paper and porous metal materials themselves have both physical strength and conductivity. Therefore, the current collector can be omitted, and the oxygen reaction layer using these materials can be used alone as the air electrode.

[0057] The binder can maintain the shape of a conductive material such as a carbonaceous material in layers and can be adhered to the current collector. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), etc. can be used.

[0058] The blending ratios of the conductive material and the binder in the oxygen reaction layer are preferably in the range of 70% by mass or more and 98% by mass or less for the conductive material and 2% by mass or more and 30% by mass or less for the binder.

[0059] When a catalyst is included, the blending ratios of the catalyst, the conductive material, and the binder in the oxygen reaction layer are preferably in the range of 1% by mass or more and 20% by mass or less for the catalyst, 1% by mass or more and 90% by mass or less for the conductive material, and 1% by mass or more and 30% by mass or less for the binder.

[0060] Water or an aqueous solvent can be retained in the oxygen reaction layer. Part of the water and the aqueous solvent contained in the aqueous electrolyte can penetrate from the aqueous electrolyte layer through the proton conduction layer to the oxygen reaction layer. Also, the water generated during the discharge reaction can be contained in the oxygen reaction layer.

[0061] Also, the thickness of the oxygen reaction layer (excluding the current collector) is preferably in the range of 2 μm or more and 600 μm or less.

[0062] As the positive electrode current collector, it is preferable to use a porous conductive substrate in order to allow oxygen to diffuse rapidly. Specific examples include mesh, punched metal, and expanded metal. Examples of the material of the conductive substrate include stainless steel, nickel, aluminum, iron, titanium, and the like. Note that the surface of the current collector may be coated with an oxidation-resistant metal or alloy in order to suppress oxidation.

[0063] The oxygen reaction layer can be formed, for example, by mixing a conductive material such as a carbonaceous material and a binder, rolling this mixture into a film shape to form a film, and drying it.

[0064] Alternatively, the air electrode can also be produced as follows. A conductive material such as a carbonaceous material and a binder are mixed in a solvent, this is applied to a current collector, and dried. Then, the obtained laminate is rolled to obtain an air electrode.

[0065] 3) Solid electrolyte layer The solid electrolyte layer contains a material having ion conductivity for carrier ions such as lithium ions that do not dissolve and swell in the aqueous electrolyte. The solid electrolyte layer is preferably non-porous and selectively permeable to carrier ions. From the viewpoint of suppressing the deterioration of the negative electrode, it is more desirable to use a solid electrolyte layer that does not permeate water.

[0066] As the material having ion conductivity, for example, one or more solid electrolytes selected from the group consisting of a composite of an organic polymer and an electrolyte salt, an oxide, and a sulfide can be used. Since these materials exhibit ion conductivity in the solid state, a solid electrolyte layer that is non-porous and selectively permeable to carrier ions can be realized.

[0067] The organic polymer is used together with the electrolyte salt. Specifically, examples of the organic polymer include a polyethylene oxide-containing polymer and a polyvinyl-containing polymer. The polyethylene oxide-containing polymer contains polyethylene oxide as the main chain and may be partially branched. It is preferable that the terminals of the polyethylene oxide are protected by ether or ester bonds of hydroxyl groups. The polyvinyl-containing polymer contains a polyvinyl chain as the main chain, and the side chains branched from the main chain preferably contain a functional group containing an ester bond or a carbonate ester bond. In particular, the polyethylene oxide-containing polymer is desirable because it is excellent in the hopping conductivity of lithium ions. The organic polymer may contain a small amount of plasticizer such as dibutyl phthalate.

[0068] As the electrolyte salt used together with the organic polymer, for example, an electrolyte salt (supporting electrolyte) that can be used in secondary batteries such as lithium-ion secondary batteries and sodium-ion secondary batteries can be used. Specifically, the electrolyte salt that can be contained in the aqueous electrolyte described later can be used.

[0069] Examples of the oxide include oxide glass and oxide crystal. Unlike organic polymers, both exhibit ionic conductivity even when not used in combination with an electrolyte salt. Examples of the oxide glass include oxides containing one or more elements selected from the group consisting of B, Si, and P and Li, and specifically, Li4SiO4-Li3BO3-based oxides. Examples of the oxide crystal include oxides containing one or more elements selected from the group consisting of Al, Ti, P, La, N, Si, In, and Nb and Li.

[0070] As the oxide-based solid electrolyte, it is preferable to use a lithium phosphate solid electrolyte having a NASICON-type structure and represented by the general formula LiMe2(PO4)3. Me in the above general formula is preferably at least one element selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), and aluminum (Al). More preferably, the element Me contains any one of Ge, Zr, and Ti and Al.

[0071] Specific examples of the lithium phosphate solid electrolyte having a NASICON-type structure include LATP (Li 1+x+y Al x Ti 2-x Si y PO 12 ; 0 < x ≦ 2, 0 ≦ y < 3), Li 1+z+y Al z Ge 2-z Si y PO 12 represented by 0 ≦ z ≦ 2 and 0 ≦ y < 3, Li 1+z Al z Zr 2-z (PO4)3 represented by 0 ≦ z ≦ 2, and compounds represented by Li 1+2w Ca w Zr 1-w (PO4)3 represented by 0 ≦ w < 1.

[0072] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, Li a PO b Nc An amorphous LIPON compound represented by 2.6 ≦ a ≦ 3.5, 1.9 ≦ b ≦ 3.8, and 0.1 ≦ c ≦ 1.3 (for example, Li 2.9 PO 3.3 N 0.46 ); Li of garnet-type structure 5+d X d La 3-d Mα2O 12 A compound represented by X is one or more selected from the group consisting of Ca, Sr, and Ba, Mα is one or more selected from the group consisting of Nb and Ta, and 0 ≦ d ≦ 0.5; Li3Mβ 2-d L2O 12 A compound represented by Mγ is one or more selected from the group consisting of Ta and Nb, L may contain Zr, and 0 ≦ d ≦ 0.5; Li 7-3d Al d La3Zr3O 12 A compound represented by 0 ≦ d ≦ 0.5; and Li 5+e La3Mγ 2-e Zr e O 12 A LLZ compound represented by Mγ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ e ≦ 2 (for example, Li7La3Zr2O 12 ) can be mentioned.

[0073] In addition, as the solid electrolyte, a sodium-containing solid electrolyte may be used. The sodium-containing solid electrolyte has excellent ionic conductivity of sodium ions. Examples of the sodium-containing solid electrolyte include β-alumina, sodium phosphorus sulfide, sodium phosphorus oxide, and Na3Zr2Si2PO 12 and the like. The sodium ion-containing solid electrolyte is preferably in the form of glass ceramics.

[0074] Examples of sulfides include sulfide glass and sulfide crystals. Unlike organic polymers, both exhibit ionic conductivity even when not used in combination with an electrolyte salt. Specific examples include Li3PS4, Li4SiS4, LiGeS4 - Li3PS4, LiS - SiS2 systems, SiS - P2S5 systems, LiS - B2S3 systems, Li2S - SiS2 - Li4SiO4 systems, etc. Among them, Li2S - P2S5, Li 3.25 Ge 0.25 P 0.75 S4, etc. have high ionic conductivity and are preferred.

[0075] For the solid electrolyte layer, one of the above solid electrolytes may be used, or two or more of the above solid electrolytes may be used.

[0076] The solid electrolyte layer may be a solid electrolyte composite membrane containing a solid electrolyte. The solid electrolyte composite membrane is, for example, formed by shaping particles of a solid electrolyte into a film using a polymer binder. The solid electrolyte composite membrane may further include a porous self - supporting membrane that supports a film containing a solid electrolyte and a polymer binder. The porous self - supporting membrane includes, for example, self - supporting membranes made of polyolefins such as polyethylene (PE) or polypropylene (PP), or cellulose.

[0077] Examples of polymer binders include polyvinyl - based, polyether - based, polyester - based, polyamine - based, polyethylene - based, silicone - based, and polysulfide - based.

[0078] As described above, oxide - based and sulfide - based solid electrolytes exhibit conductivity for carrier ions even without an electrolyte salt. An electrolyte salt may also be added to the solid electrolyte layer using these oxides or sulfides. When the solid electrolyte layer contains an electrolyte salt, for example, the alkali metal ion conductivity of the solid electrolyte layer can be further enhanced.

[0079] The solid electrolyte layer may have a thickness of, for example, 100 μm or less. Also, the thickness of the solid electrolyte layer may be, for example, 20 μm or more.

[0080] 4) Aqueous electrolyte layer The aqueous electrolyte layer is located between the solid electrolyte layer and the proton conduction layer and contains an aqueous electrolyte.

[0081] The aqueous electrolyte layer can further include a porous body that holds the aqueous electrolyte. As the porous body, for example, a porous film containing polyethylene (PE), polypropylene (PP), or polyvinylidene fluoride (PVdF), a cellulose non-woven fabric, a synthetic resin non-woven fabric, a glass fiber non-woven fabric, etc. can be used.

[0082] The porosity of the porous body is preferably in the range of 30% or more and 90% or less. When the porosity is 30% or more, high electrolyte retention can be exhibited. When the porosity is 90% or less, high strength can be obtained. A more preferable range of the porosity is 35% or more and 60% or less.

[0083] The aqueous electrolyte can be, for example, a liquid aqueous electrolyte containing a polyvalent acid, an aqueous solvent, and an electrolyte salt. The electrolyte may be a gel-like aqueous electrolyte in which a liquid aqueous electrolyte and a polymer material are combined.

[0084] The liquid aqueous electrolyte is prepared, for example, by dissolving a polyvalent acid at a concentration of 1 mol / L to 14 mol / L and an electrolyte salt at a concentration of 0.1 mol / L to 14 mol / L in an aqueous solvent.

[0085] The polyvalent acid contained in the aqueous electrolyte has two or more carboxyl groups like citric acid. Such polyvalent acids are not limited to citric acid. Examples of polyvalent acids having two or more carboxyl groups include citric acid, maleic acid, and phthalic acid.

[0086] An aqueous solvent is a solvent containing water and can consist of water alone or water and a solvent other than water. Examples of solvents other than water include water-soluble organic solvents. Examples of water-soluble organic solvents include γ-butyrolactone, acetonitrile, alcohols, N-methylpyrrolidone (NMP), dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran. One solvent other than water may be included in the aqueous solvent, or two or more solvents other than water may be combined. In the aqueous solvent, it is desirable that the content of the solvent other than water be 20% by mass or less.

[0087] Examples of electrolyte salts that can be included in the aqueous electrolyte include lithium salts and sodium salts. Here, the electrolyte salt to be included in the aqueous electrolyte may be referred to as the first electrolyte salt. The lithium salt as the first electrolyte salt may be referred to as the first lithium salt, and the sodium salt as the first electrolyte salt may be referred to as the second sodium salt, respectively.

[0088] Examples of the first lithium salt include LiCl, LiBr, LiOH, Li2SO4, LiNO3, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI: LiN(SO2CF3)2), lithium bis(fluorosulfonyl)imide (LiFSI: LiN(SO2F)2), and lithium bisoxalate borate (LiBOB: LiB[(OCO)2]2). One of the above lithium salts may be used as the first electrolyte salt, or two or more of the above lithium salts may be combined and used.

[0089] Examples of the first sodium salt include NaCl, Na2SO4, NaOH, NaNO3, and NaTFSA (sodium trifluoromethanesulfonylamide). One of the above sodium salts may be used as the first electrolyte salt, or two or more of the above sodium salts may be combined and used.

[0090] Further, one or more of the above-mentioned first lithium salts and first sodium salts may be combined and included in the aqueous electrolyte as the first electrolyte salt. The first electrolyte salt may also include electrolyte salts other than lithium salts and sodium salts. Appropriate electrolyte salts can be selected according to the carrier ions.

[0091] Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), and the like. The content of the polymer material in the electrolyte is, for example, in the range of 0.5% by mass or more and 10% by mass or less.

[0092] The aqueous electrolyte layer may have a thickness of, for example, 250 μm or more and 1000 μm or less. In a system where discharge products precipitate as solids, a larger thickness and volume of the member that houses the electrolyte on the air electrode side can secure a space for accommodating the discharge products, thus increasing the discharge capacity. However, from the perspective of reducing the weight and size of the battery, it is desirable to reduce the volume occupied by the electrolyte. In the air battery according to the embodiment, since the aqueous electrolyte contains the above-mentioned polyvalent acid, discharge products are less likely to precipitate. Therefore, a high capacity can be exhibited even if the aqueous electrolyte layer is made thin.

[0093] The fact that water is contained in the aqueous electrolyte can be confirmed by GC-MS (Gas Chromatography - Mass Spectrometry) measurement. Also, the salt concentration and water content in the aqueous electrolyte can be measured by, for example, ICP (Inductively Coupled Plasma) emission analysis. By weighing a specified amount of the aqueous electrolyte and calculating the contained salt concentration, the molar concentration (mol / L) can be calculated. Also, by measuring the specific gravity of the aqueous electrolyte, the number of moles of the solute and solvent can be calculated.

[0094] Regarding the polyvalent acid contained in the aqueous electrolyte, for example, qualitative analysis can be performed by proton nuclear magnetic resonance ( 1 1H-NMR) for measurement. Also, quantitative analysis of the polyvalent acid can be performed by capillary electrophoresis.

[0095] 5) Proton conduction layer The proton conduction layer selectively conducts protons between the aqueous electrolyte layer and the air electrode. The proton conduction layer blocks the movement of polyvalent acid anions from the aqueous electrolyte to the air electrode.

[0096] The proton conduction layer is formed, for example, using a fluororesin having a sulfonic acid group (such as Nafion (registered trademark; DuPont) and Flemion (registered trademark; Asahi Kasei)), or a material having proton conductivity such as tungstic acid or phosphotungstic acid.

[0097] In addition to the above proton conductive material, the proton conduction layer may further contain a binder. As the binder, the above-described binders that can be included in the air electrode or the negative electrode can be used.

[0098] Water or an aqueous solvent can be retained in the proton conduction layer. A part of the water and the aqueous solvent contained in the aqueous electrolyte can penetrate from the aqueous electrolyte layer into the proton conduction layer. Also, water generated during the discharge reaction at the air electrode can be supplied to the proton conduction layer.

[0099] The proton conduction layer may have a thickness of, for example, 100 μm or less.

[0100] 6) Intermediate layer When oxides and / or sulfides are used for the solid electrolyte layer, those oxides and / or sulfides may be inferior in reduction resistance. In such a case, it is preferable to provide an intermediate layer between the negative electrode and the solid electrolyte layer to prevent the reaction between the negative electrode and the solid electrolyte layer. By providing the above intermediate layer, the negative electrode and the solid electrolyte layer are prevented from coming into contact. Therefore, it is possible to avoid the reduction decomposition of the oxides and / or sulfides contained in the solid electrolyte layer due to contact with the negative electrode and the deterioration of the solid electrolyte layer.

[0101] As the intermediate layer, for example, a porous material such as a porous membrane or a non-woven fabric can be provided. As the porous membrane or non-woven fabric, those that can be used as a separator for a lithium-ion secondary battery, such as a porous polyethylene membrane, a porous polypropylene (PP) membrane, and a cellulose non-woven fabric, can be used. The porous membrane or non-woven fabric may be impregnated with a non-aqueous electrolyte.

[0102] Also, as the intermediate layer, for example, a metal oxide layer can be provided. For the metal oxide layer, for example, metal oxides such as aluminum oxide, silicon oxide, and zinc oxide can be used. When using a metal oxide insoluble in the non-aqueous electrolyte, the non-aqueous electrolyte may be included in the intermediate layer together with the metal oxide. The metal oxide used in the intermediate layer may be referred to as a third metal oxide.

[0103] As the intermediate layer, a non-aqueous electrolyte layer containing a non-aqueous electrolyte and a metal oxide layer may be used in combination. In this case, it is desirable to arrange the non-aqueous electrolyte layer on the negative electrode side and the metal oxide layer on the solid electrolyte layer side, respectively. As the non-aqueous electrolyte layer, for example, those obtained by impregnating the above-mentioned porous membrane or non-woven fabric with a non-aqueous electrolyte, and non-aqueous electrolyte layers formed of a gel-like non-aqueous electrolyte can be used.

[0104] When the oxide and / or sulfide contained in the solid electrolyte layer is excellent in reduction resistance, it is preferable to omit the intermediate layer from the viewpoint of improving the volume energy density. Note that organic polymers tend to be excellent in reduction resistance.

[0105] As the non-aqueous electrolyte, for example, a liquid non-aqueous electrolyte or a gel-like non-aqueous electrolyte can be used. The liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less. Here, the electrolyte salt contained in the non-aqueous electrolyte may be referred to as a second electrolyte salt.

[0106] Examples of the second electrolyte salt include lithium salts (second lithium salts) such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2), and mixtures thereof. Among the second lithium salts, LiPF6, LiBF4, LiCF3SO3, and LiN(CF3SO2)2 are particularly preferred.

[0107] The second electrolyte salt can also include electrolyte salts other than lithium salts. Appropriate electrolyte salts can be selected according to the carrier ions.

[0108] Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as a mixed solvent.

[0109] The gel-like non-aqueous electrolyte is prepared by compounding a liquid non-aqueous electrolyte and a polymer material. Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0110] 7) Outer packaging member As the outer packaging member, for example, a container made of a laminate film or a metal container can be used.

[0111] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0112] As the laminate film, a multilayer film including a plurality of resin layers and a metal layer interposed between these resin layers is used. The resin layer contains, for example, polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or an aluminum alloy foil for weight reduction. The laminate film can be formed into the shape of the outer packaging member by sealing by heat fusion.

[0113] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0114] The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, its content is preferably 100 mass ppm or less. In a battery equipped with such a metal container, it is possible to dramatically improve the long-term reliability and heat dissipation performance in a high-temperature environment.

[0115] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), square, cylindrical, coin-shaped, button-shaped, sheet-shaped, laminated, etc. The exterior member can be appropriately selected according to the battery dimensions and the use of the battery.

[0116] 8) Negative electrode terminal The negative electrode terminal can be formed from a material that is electrically stable and has conductivity in the potential range in which the occlusion-discharge reaction or insertion-desorption reaction of carrier ions by the negative electrode active material proceeds. Specifically, examples of the material for the negative electrode terminal include copper, nickel, stainless steel or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce the contact resistance with the negative electrode current collector.

[0117] 9) Positive electrode terminal The positive electrode terminal can be formed from a material that is electrically stable and has conductivity in the potential range in which the oxidation-reduction reaction of oxygen proceeds. Examples of the material for the positive electrode terminal include copper, nickel, stainless steel or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce the contact resistance with the positive electrode current collector.

[0118] Referring to FIGS. 3 and 4, an example of the structure of the air battery according to the embodiment will be described. FIG. 3 is a perspective view schematically showing an example of the air battery according to the embodiment. FIG. 4 is a schematic cross-sectional view taken along line IV-IV of FIG. 3.

[0119] The air battery 1 shown in FIGS. 3 and 4 includes an exterior member 10 made of a laminate film and an electrode group 2 housed in the exterior member 10. The exterior member 10 is formed by heat-sealing a laminate film into a bag shape using its thermoplastic resin layer. The electrode group 2 includes a negative electrode 3 having a structure in which a negative electrode active material layer 3b is supported on a negative electrode current collector 3a made of, for example, a porous conductive substrate, an air electrode 8 having a structure in which an oxygen reaction layer 8b is supported on a positive electrode current collector 8a made of, for example, a porous conductive substrate, and a solid electrolyte layer 5, an aqueous electrolyte layer 6, and a proton conduction layer 7 disposed between the negative electrode 3 and the air electrode 8. The solid electrolyte layer 5, the aqueous electrolyte layer 6, and the proton conduction layer 7 are arranged in this order from the negative electrode 3 side to the air electrode 8 side. In the illustrated example, an intermediate layer 4 for preventing the reaction between the negative electrode 3 and the solid electrolyte layer 5 is further provided between the negative electrode 3 and the solid electrolyte layer 5. Also, in the illustrated example, a seal member 12 for preventing the leakage of moisture contained in the aqueous electrolyte layer 6 and contact with the negative electrode 3 is provided.

[0120] A plurality of air holes 11 for taking in air are opened on the main surface of the exterior member 10 on the air electrode 8 side.

[0121] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material layer 3b provided on the negative electrode current collector 3a. The negative electrode current collector 3a can also be omitted. The air electrode 8 (positive electrode) includes a positive electrode current collector a and an oxygen reaction layer 8b provided on the positive electrode current collector 8a. The positive electrode current collector 8a can also be omitted.

[0122] One end of the negative electrode terminal 13 is electrically connected to the negative electrode current collector 3a, and the other end protrudes outside the exterior member 10. One end of the positive electrode terminal 14 is electrically connected to the positive electrode current collector 8a, and the other end protrudes outside the exterior member 10.

[0123] Furthermore, although not shown in this figure, a sealing tape for closing the air holes 11 is arranged on the outer surface of the exterior member 10 when the battery is not in use.

[0124] In the air battery having the configuration as described above, air is supplied into the exterior member 10 from the air holes 11. The supplied air is further supplied to the oxygen reaction layer 8b of the air electrode 8, and a discharge reaction occurs with protons (H + ) supplied from the aqueous electrolyte layer 6.

[0125] In the above-described FIGS. 1 to 4, an example in which an air electrode is provided only on one side of the electrode group 2 has been described. Although not illustrated, it is also possible to use both sides of the electrode group as the positive electrode.

[0126] The air battery according to the above embodiment includes a negative electrode, an air electrode to which oxygen is supplied, a solid electrolyte layer between the negative electrode and the air electrode, an aqueous electrolyte layer between the solid electrolyte layer and the air electrode, and a proton conduction layer between the aqueous electrolyte layer and the air electrode. The aqueous electrolyte layer contains an aqueous electrolyte containing the above-described polyvalent acid containing an anion highly soluble in water, an electrolyte salt, and water. Such an air battery has a high capacity and excellent cycle performance.

Example

[0127] Examples will be described below, but the embodiments are not limited to the examples listed below as long as they do not exceed the gist of the present invention.

[0128] (Example 1) An aluminum-containing laminate film containing a thermoplastic resin layer made of polypropylene and an aluminum layer was prepared. The aluminum-containing laminate film was formed into a cup shape with a lid. Five air holes with a diameter of 2 mm were opened in the lid portion, which is the surface facing the air electrode. The battery container thus produced was prepared as an exterior member. At this time, the polypropylene layer was made to be the inner surface of the battery container. Next, a sealing tape was attached to the outer surface of the lid portion to close the air holes.

[0129] A nickel mesh with one end of the negative electrode terminal electrically connected was prepared as the negative electrode current collector. A metallic lithium foil was pressure-bonded to this negative electrode current collector as the negative electrode active material layer. Thus, a negative electrode was prepared.

[0130] Oxide crystal solid electrolyte LATP (Li 1.5 Al 0.5 Ti 1.5 (PO4)3) particles, polyvinyl butyral (PVB) resin, and NMP were mixed to obtain a mixed solution. The mass ratio of LATP particles to polyvinyl butyral resin was 9:1. The solid content concentration in the mixed solution was 60% by mass.

[0131] Next, this mixed solution was subjected to ball mill mixing to obtain a slurry. Then, this slurry was coated on one main surface of a porous PP film with a thickness of 25 μm by the doctor blade method, and the coating film was dried to form a solid electrolyte layer. The film thickness of the solid electrolyte layer formed on the PP film was approximately 20 μm.

[0132] A non-aqueous electrolyte was prepared as follows. 50% by volume of ethylene carbonate and 50% by volume of propylene carbonate were mixed to prepare a non-aqueous solvent. A liquid non-aqueous electrolyte was prepared by dissolving LiCl as an electrolyte salt in the obtained non-aqueous solvent at a concentration of 1.0 mol / L.

[0133] The liquid non-aqueous electrolyte was dropped onto the surface of the PP film to impregnate the film with the non-aqueous electrolyte. Thus, an intermediate layer containing the PP film and the non-aqueous electrolyte was obtained.

[0134] A composite of the solid electrolyte layer and the intermediate layer was laminated on the negative electrode such that the intermediate layer faced the surface of the metallic lithium foil (negative electrode active material layer) of the negative electrode. This laminate was housed in the cup portion of the battery container. At this time, the tip of the negative electrode terminal was extended outside the cup portion.

[0135] An aqueous electrolyte was prepared as follows. Citric acid was dissolved in water at a concentration of 3M and LiCl at a concentration of 1M to obtain an aqueous solution.

[0136] A glass fiber filter paper with a thickness of 1 mm was placed on the solid electrolyte layer of the laminate stored in the cup portion of the battery container, and a frame-shaped seal member was installed around it. By pouring and impregnating the above aqueous solution adjusted as an aqueous electrolyte into the glass fiber filter paper, an aqueous electrolyte layer was obtained.

[0137] As the proton conduction layer, a proton exchange membrane made of Nafion (registered trademark) was prepared.

[0138] A nickel mesh with one end of the positive electrode terminal electrically connected was prepared as the positive electrode current collector. Carbon paper was pressure-bonded to this positive electrode current collector as the oxygen reaction layer. Thus, an air electrode (positive electrode) was prepared.

[0139] The aqueous electrolyte layer was covered with the proton conduction layer, and the positive electrode was stacked thereon so that the carbon paper was in contact with the proton conduction layer. At this time, the tip of the positive electrode terminal was extended outside the cup portion. The cup portion of the battery container was closed with a lid portion, and the battery container was sealed to manufacture an air battery.

[0140] (Example 2) An air battery was fabricated in the same procedure as in Example 1, except that 1.5 M of 1,2,3 - propanetricarboxylic acid was used in the aqueous electrolyte on the air electrode side instead of citric acid.

[0141] (Example 3) An air battery was fabricated in the same procedure as in Example 1, except that 3 M of maleic acid was used in the aqueous electrolyte on the air electrode side instead of citric acid.

[0142] (Comparative Example 1) An air battery was manufactured in the same procedure as in Example 1, except that the proton conduction layer was omitted.

[0143] (Comparative Example 2) An air battery was produced in the same manner as in Example 1, except that the composition of the aqueous electrolyte on the air electrode side was changed as follows: Instead of 3 M citric acid and 1 M LiCl, 12 M LiCl and 1 M LiOH were dissolved in water to obtain an aqueous solution.

[0144] The capacity of each of the air batteries manufactured as described above was evaluated as follows. 2 Each battery was continuously discharged to 2.0 V at a constant current rate of 0.01 mA per charge, followed by a constant voltage discharge at 2.0 V, and the initial discharge capacity was measured. However, the upper limit of discharge capacity was limited to 40.0 mAh, and discharge was stopped when the discharge capacity reached 40.0 mAh. The results are shown in Table 1 below. Table 1 also lists the solutes added to the aqueous electrolyte for each battery, their concentrations, and the material of the proton exchange membrane. The solutes in the aqueous electrolyte were polyvalent acids and electrolyte salts.

[0145] [Table 1]

[0146] As shown in Table 1, the batteries manufactured in Examples 1, 2, and 3 and Comparative Example 1 continued to discharge up to the capacity limit of 40.0 mAh. In contrast, the battery manufactured in Comparative Example 2 stopped operating before reaching the capacity limit, achieving only a discharge capacity of 17.8 mAh. In Example 1 and Comparative Example 2, the aqueous electrolyte contained citric acid, which prevented the precipitation of LiOH, a discharge product, and prevented battery operation from being hindered by solid precipitation. In Comparative Example 2, the precipitation of LiOH hindered battery operation, causing the battery to stop midway through discharge.

[0147] The lifespan performance of the air batteries produced in Example 1 and Comparative Example 1 was evaluated as follows. First, the batteries were discharged under the same conditions as in the capacity evaluation above, except that discharge was stopped when the discharge capacity reached 8 mAh, and the initial discharge capacity was measured. The batteries were charged and then discharged again, and the discharge capacity at that time was measured. The results are shown in Figures 5 and 6, respectively.

[0148] FIG. 5 is a graph showing the first discharge curve and the second discharge curve of the air battery according to Example 1. The solid line 101 in FIG. 5 shows the first discharge curve in Example 1, and the broken line 102 shows the discharge curve at the time of the second discharge after recharge in Example 1. FIG. 6 is a graph showing the first discharge curve and the second discharge curve of the air battery according to Comparative Example 1. The solid line 201 in FIG. 6 shows the first discharge curve in Comparative Example 1, and the broken line 202 shows the discharge curve at the time of the second discharge after recharge in Comparative Example 1.

[0149] As shown in FIG. 6, in Comparative Example 1, a significant decrease in the battery voltage was observed during the second discharge compared to the first discharge. The decrease in voltage at the end of discharge was particularly significant. In contrast, in Example 1, almost no difference was observed in the voltage change between the first discharge and the second discharge. That is, the air battery manufactured in Example 1 had better cycle life performance than the air battery of Comparative Example 1 and higher capacity than the air battery of Comparative Example 2. In Example 1, since Nafion (registered trademark) was provided as a proton conduction layer between the aqueous electrolyte layer and the air electrode, the movement of citrate anions ([C6H7O7] - ) in the aqueous electrolyte to the air electrode (carbon paper) was prevented, and the decomposition of citrate anions on the air electrode was suppressed. In contrast, in Comparative Example 1, since it did not contain a proton conduction layer, citrate anions were decomposed on the air electrode during charge and discharge, resulting in deterioration of the battery performance.

[0150] According to one or more of the embodiments and examples described above, there is provided an air battery including a negative electrode, an air electrode to which oxygen is supplied, a solid electrolyte layer, an aqueous electrolyte layer including an aqueous electrolyte, and a proton conduction layer. The solid electrolyte layer is located between the negative electrode and the air electrode. The aqueous electrolyte layer is located between the solid electrolyte layer and the air electrode. The proton conduction layer is located between the aqueous electrolyte layer and the air electrode. The aqueous electrolyte includes a polyvalent acid having two or more carboxyl groups, an electrolyte salt, and water. The air battery exhibits high capacity and excellent cycle life performance.

[0151] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalent scope thereof. The invention described in the original claims of the present application is appended below. [1] A negative electrode, an air electrode to which oxygen is supplied, a solid electrolyte layer positioned between the negative electrode and the air electrode, an aqueous electrolyte layer positioned between the solid electrolyte layer and the air electrode and containing an aqueous electrolyte containing a polyvalent acid having two or more carboxyl groups, an electrolyte salt, and water, and a proton conduction layer positioned between the aqueous electrolyte layer and the air electrode to provide an air battery. [2] The air battery according to [1], wherein the negative electrode contains one or more negative electrode active materials selected from the group consisting of lithium metal, a lithium alloy, and a material into which lithium is inserted and removed. [3] The air battery according to [1] or [2], further comprising an intermediate layer positioned between the negative electrode and the solid electrolyte layer. [4] The air battery according to [3], wherein the intermediate layer contains a non-aqueous electrolyte. [5] The air battery according to [3] or [4], wherein the intermediate layer contains a metal oxide. [6] The air battery according to [3], wherein the intermediate layer includes a non-aqueous electrolyte layer disposed on the negative electrode side and a metal oxide layer disposed on the solid electrolyte layer side.

Description of Reference Numerals

[0152] 1... Air battery, 2... Electrode group, 3... Negative electrode, 3a... Negative electrode current collector, 3b... Negative electrode active material layer, 4... Intermediate layer, 4a... Non-aqueous electrolyte layer, 4b... Metal oxide layer, 5... Solid electrolyte layer, 6... Aqueous electrolyte layer, 7... Proton conduction layer, 8... Air electrode, 8a... Positive electrode current collector, 8b... Oxygen reaction layer, 10... Exterior member, 11... Air hole, 12... Seal member, 13... Negative electrode terminal, 14... Positive electrode terminal.

Claims

1. a negative electrode, an air electrode to which oxygen is supplied, a solid electrolyte layer positioned between the negative electrode and the air electrode, an aqueous electrolyte layer positioned between the solid electrolyte layer and the air electrode and containing an aqueous electrolyte containing a polyvalent acid having two or more carboxyl groups, an electrolyte salt, and water, a proton conduction layer positioned between the aqueous electrolyte layer and the air electrode and comprising, the air electrode does not contain a metal, metal oxide, and complex exhibiting catalytic activity, an air battery.

2. The air battery according to claim 1, wherein the negative electrode contains one or more negative electrode active materials selected from the group consisting of lithium metal, lithium alloy, and a material into which lithium is inserted and desorbed.

3. The air battery according to claim 1 or 2, further comprising an intermediate layer positioned between the negative electrode and the solid electrolyte layer.

4. The air battery according to claim 3, wherein the intermediate layer contains a non-aqueous electrolyte.

5. The air battery according to claim 3 or 4, wherein the intermediate layer contains a metal oxide.

6. The air battery according to claim 3, wherein the intermediate layer includes a non-aqueous electrolyte layer disposed on the negative electrode side and a metal oxide layer disposed on the solid electrolyte layer side.

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