Patent Application
20230216021
The present invention relates to sintered body electrodes, battery members using the same, sintered body electrode and battery member manufacturing methods, alkali-ion conductive solid electrolyte precursor solutions, alkali-ion conductive solid electrolyte precursors, and alkali-ion conductive solid electrolytes.
Lithium-ion secondary batteries have secured their place as high-capacity and light-weight power sources essential for mobile devices, electric vehicles, and so on. However, current lithium-ion secondary batteries employ as their electrolytes, mainly, combustible organic electrolytic solutions, which raises concerns about the risk of burning or explosion. As a solution to this problem, developments of lithium-ion all-solid-state batteries using a solid electrolyte instead of an organic electrolytic solution have been promoted. However, because, as for lithium, there are concerns about such issues as global rise in raw and processed material costs, studies have recently been conducted on sodium-ion all-solid-state batteries as alternatives to lithium-ion all-solid-state batteries.
Patent Literature 1 below discloses an example of a sodium battery. This sodium battery includes a positive electrode, a negative electrode, and a sulfide-based solid electrolyte. Metal sulfide or sodium metal oxide is used as the positive electrode. Sodium metal or sodium alloy is used as the negative electrode.
However, the sodium battery as described in Patent Literature 1 has difficulty in sufficiently increasing the safety because the sodium metal used as the negative electrode easily reacts with water.
In addition, many of conventional all-solid-state sodium batteries operate at a relatively high temperature, for example, 60° C. or higher and, therefore, have a problem of difficulty in sufficiently operating at low temperatures.
An object of the present invention is to provide a sintered body electrode, a battery member, sintered body electrode and battery member manufacturing methods, a solid electrolyte precursor solution, a solid electrolyte precursor, and a solid electrolyte all of which can increase the safety and operate a battery at low temperatures.
A sintered body electrode according to the present invention contains: a carbon electrode material made of graphite or hard carbon; and an alkali-ion conductive solid electrolyte.
The alkali-ion conductive solid electrolyte preferably has a sodium-ion conductivity.
The alkali-ion conductive solid electrolyte is preferably made of an oxide.
Preferably, the sintered body electrode according to the present invention contains a mixture phase of the carbon electrode material and the alkali-ion conductive solid electrolyte and the mixture phase is formed of particles having an average particle diameter of 10 μm or less.
Preferably, the carbon electrode material is a particulate carbon electrode material and the particulate carbon electrode material is coated with a coating layer made of the alkali-ion conductive solid electrolyte.
Preferably, the carbon electrode material is a particulate carbon electrode material and the particulate carbon electrode material is coated with a coating layer made of: a carbon electrode material different from the particulate carbon electrode material; and the alkali-ion conductive solid electrolyte.
Preferably, the alkali-ion conductive solid electrolyte is NASICON crystals and contains at least one of: a first compound represented by a general formula Na1+xZr2P3-xSixO12 (0≤x≤3); and a second compound in which a part of the Zr in the first compound is substituted with at least one element selected from the group consisting of Ca, Mg, Ba, Sr, Al, Nb, Ta, In, Ga, and group III elements.
The alkali-ion conductive solid electrolyte preferably contains at least one type of crystals of β-alumina crystals and β″-alumina crystals.
The alkali-ion conductive solid electrolyte preferably contains a crystalline phase represented by a general formula Li7La3Zr2O12, Li7La3Zr2-xMxO12 (where M represents at least one selected from Nb, Ga, and Ta and 0<x<2) or Li7-3xAlxLa3Zr2O12 (0<x<2.3).
The sintered body electrode according to the present invention preferably contains at least one carbon-based conductive agent in an amount of 0% by weight to 20% by weight selected from carbon black, acetylene black, Ketjenblack, carbon nanotube, and a vapor-grown carbon fiber (VGCF) conductive agent.
The sintered body electrode according to the present invention is preferably a negative electrode.
The sintered body electrode according to the present invention is preferably capable of absorbing and releasing alkali ions at 30° C. after being thermally treated in an inert atmosphere at 500° C.
The sintered body electrode according to the present invention is preferably capable of being reversibly charged and discharged with a charge/discharge efficiency of 90% or more during charge and discharge at a cut-off voltage of 9 V to 0.001 V.
A battery member according to the present invention includes: a solid electrolyte layer; and the above-described sintered body electrode layered on the solid electrolyte layer.
The solid electrolyte layer preferably has a thickness of 5 nm to 1 mm.
A battery according to the present invention includes the above-described battery member.
A method for manufacturing a sintered body electrode according to the present invention includes: a mixing step of mixing an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor to obtain a mixture of the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor, the carbon electrode material precursor being a precursor of a carbon electrode material made of graphite or hard carbon; the step of, after the mixing step, forming an electrode forming material layer containing the mixture; and the step of firing the electrode forming material layer.
Preferably, the electrode forming material layer is made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor and, in the step of firing the electrode forming material layer, an alkali-ion conductive solid electrolyte and the carbon electrode material are concurrently obtained.
It is preferred that, in the step of forming an electrode forming material layer, a first firing step of firing the mixture to obtain a carbon electrode material is performed and the electrode forming material layer made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte precursor and the carbon electrode material is then formed, and, in the step of firing the electrode forming material layer, an alkali-ion conductive solid electrolyte is obtained from the alkali-ion conductive solid electrolyte precursor.
Preferably, the method further includes a third firing step of, after the mixing step, firing the mixture to concurrently obtain an alkali-ion conductive solid electrolyte and a carbon electrode material, and, in the step of forming an electrode forming material layer, the electrode forming material layer made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte and the carbon electrode material is formed.
A method for manufacturing a sintered body electrode according to another aspect of the present invention includes: a mixing step of mixing an alkali-ion conductive solid electrolyte precursor and a particulate carbon electrode material made of graphite or hard carbon to obtain a mixture of the alkali-ion conductive solid electrolyte precursor and the particulate carbon electrode material; the step of, after the mixing step, forming an electrode forming material layer made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte precursor and the particulate carbon electrode material; and the step of firing the electrode forming material layer to obtain an alkali-ion conductive solid electrolyte from the alkali-ion conductive solid electrolyte precursor and thus obtain the particulate carbon electrode material coated with a coating layer made of the alkali-ion conductive solid electrolyte.
A method for manufacturing a sintered body electrode according to still another aspect of the present invention includes: a mixing step of mixing an alkali-ion conductive solid electrolyte precursor, a carbon electrode material precursor, and a particulate carbon electrode material made of graphite or hard carbon to obtain a mixture of the alkali-ion conductive solid electrolyte precursor, the carbon electrode material precursor, and the particulate carbon electrode material, the carbon electrode material precursor being a precursor of a carbon electrode material made of graphite or hard carbon; the step of, after the mixing step, forming an electrode forming material layer made of a paste or a powder compact each containing the mixture; and the step of firing the electrode forming material layer to obtain an alkali-ion conductive solid electrolyte and a carbon electrode material from the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor, respectively, and thus obtain the particulate carbon electrode material coated with a coating layer made of the alkali-ion conductive solid electrolyte and the carbon electrode material.
A method for manufacturing a battery member according to the present invention is a method for manufacturing a battery member including a laminate of a sintered body electrode and a solid electrolyte layer and includes: a mixing step of mixing an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor to obtain a mixture of the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor, the carbon electrode material precursor being a precursor of a carbon electrode material made of graphite or hard carbon; the step of, after the mixing step, forming an electrode forming material layer containing the mixture; the step of obtaining a sintered body electrode by firing the electrode forming material layer; and the step of obtaining a laminate of the sintered body electrode and a solid electrolyte layer.
Preferably, the electrode forming material layer is made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor and the electrode forming material layer is fired to concurrently obtain an alkali-ion conductive solid electrolyte and a carbon electrode material.
It is preferred that, in the step of forming an electrode forming material layer, a first firing step of firing the mixture to obtain a carbon electrode material is performed and the electrode forming material layer made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte precursor and the carbon electrode material is formed, and the step of obtaining a sintered body electrode is a second firing step of firing the electrode forming material layer to obtain an alkali-ion conductive solid electrolyte.
It is preferred that: the method further includes, after the mixing step, a third firing step of firing the mixture to concurrently obtain an alkali-ion conductive solid electrolyte and a carbon electrode material; in the step of forming an electrode forming material layer, the electrode forming material layer made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte and the carbon electrode material is formed; and the step of obtaining a sintered body electrode is a fourth firing step of firing the electrode forming material layer.
A method for manufacturing a battery member according to another aspect of the present invention is a method for manufacturing a battery member including a laminate of a sintered body electrode and a solid electrolyte layer and includes: a mixing step of mixing an alkali-ion conductive solid electrolyte precursor and a particulate carbon electrode material made of graphite or hard carbon to obtain a mixture of the alkali-ion conductive solid electrolyte precursor and the particulate carbon electrode material; the step of, after the mixing step, forming an electrode forming material layer made of a paste or a powder compact each containing the alkali-ion conductive solid electrolyte precursor and the particulate carbon electrode material; the step of obtaining a sintered body electrode by firing the electrode forming material layer to obtain an alkali-ion conductive solid electrolyte from the alkali-ion conductive solid electrolyte precursor and obtain the particulate carbon electrode material coated with a coating layer made of the alkali-ion conductive solid electrolyte; and the step of obtaining a laminate of the sintered body electrode and a solid electrolyte layer.
Preferably, the method further includes a layering step of layering the solid electrolyte layer and the electrode forming material layer and the step of obtaining a sintered body electrode is performed after the layering step.
Preferably, the method further includes a layering step of layering a solid electrolyte forming material layer made of a paste or a powder compact each containing a solid electrolyte precursor and the electrode forming material layer, and, after the layering step, the electrode forming material layer and the solid electrolyte forming material layer are fired to concurrently obtain the sintered body electrode and the solid electrolyte layer.
An alkali-ion conductive solid electrolyte precursor solution according to the present invention contains an alkali metal element, a transition metal element, and carbonate ions.
The carbonate ions are preferably coordinated to the transition metal element.
The transition metal element is preferably at least one selected from the group consisting of group III elements and group IV elements.
The alkali-ion conductive solid electrolyte precursor solution according to the present invention preferably has a pH of 7 or more.
The alkali-ion conductive solid electrolyte precursor solution preferably contains NR4+ (where Rs are each independently a substituent of at least one selected from the group consisting of H, CH3, C2H5, and CH2CH2OH) as counterions to the carbonate ions.
The alkali-ion conductive solid electrolyte precursor solution according to the present invention is preferably a precursor solution of a solid electrolyte made of NASICON crystals.
The alkali-ion conductive solid electrolyte precursor solution according to the present invention is preferably a precursor solution of a sodium-ion conductive solid electrolyte.
An alkali-ion conductive solid electrolyte precursor according to the present invention is made of a gelled product or dried product of the above-described alkali-ion conductive solid electrolyte precursor solution.
An alkali-ion conductive solid electrolyte according to the present invention is made of a sintered body of the above-described alkali-ion conductive solid electrolyte precursor.
The present invention enables provision of a sintered body electrode, a battery member, sintered body electrode and battery member manufacturing methods, a solid electrolyte precursor solution, a solid electrolyte precursor, and a solid electrolyte all of which can increase the safety and operate a battery at low temperatures.
Hereinafter, a description will be given of preferred embodiments. However, the following embodiments are merely illustrative and the present invention is not intended to be limited to the following embodiments. Throughout the drawings, members having substantially the same functions may be referred to by the same reference characters.
[Battery Member]
A battery member 1 includes a solid electrolyte layer 2, a sintered body electrode 3 according to one embodiment of the present invention, and a current collector 4. The solid electrolyte layer 2 has an alkali-ion conductivity. More specifically, the solid electrolyte layer 2 has a sodium-ion conductivity in this embodiment. Alternatively, the solid electrolyte layer 2 may have a lithium-ion conductivity. The solid electrolyte layer 2 is preferably as thin as possible for the purpose of increasing the energy density and its specific thickness is preferably 1 mm or less, more preferably 500 μm or less, and still more preferably 100 μm or less. The lower limit of the thickness is not particularly limited, but is, actually, preferably not less than 5 nm in order to ensure its mechanical strength and separator function.
The solid electrolyte layer 2 has a first principal surface 2a and a second principal surface 2b. The first principal surface 2a and the second principal surface 2b are opposed to each other. The sintered body electrode 3 is layered on the first principal surface 2a of the solid electrolyte layer 2. The current collector 4 is layered over the sintered body electrode 3. The current collector 4 is made of an appropriate thin metal film. The battery member 1 need not necessarily include the current collector 4. In the embodiments described hereinafter, the current collector 4 may not be shown in the figures.
In this embodiment, the sintered body electrode 3 is a negative electrode. When a positive electrode is layered on the second principal surface 2b of the solid electrolyte layer 2, an all-solid-state battery can be obtained.
The sintered body electrode 3 contains a carbon electrode material and an alkali-ion conductive solid electrolyte. The carbon electrode material is made of graphite or hard carbon. The alkali-ion conductive solid electrolyte has a sodium-ion conductivity in this embodiment. Alternatively, the alkali-ion conductive solid electrolyte may have a lithium-ion conductivity.
The sintered body electrode 3 contains a mixture phase 5 of the carbon electrode material and the alkali-ion conductive solid electrolyte. The mixture phase 5 is in particulate form. The particles in the mixture phase 5 are bound together by sintering.
Referring back to
The battery member 1 includes the sintered body electrode 3 according to the present invention containing: a carbon electrode material made of graphite or hard carbon; and an alkali-ion conductive solid electrolyte. The sintered body electrode 3 has a small reactivity to water, unlike an electrode made of a sodium metal. In addition, the sintered body electrode 3 can be used in an all-solid-state battery, need not any organic electrolyte, and, therefore, has a smaller risk of firing. Hence, the safety can be increased. Furthermore, with the use of the battery member 1, the battery can be operated at low temperatures. The details of these effects will be described hereinafter with reference to a manufacturing method according to a first embodiment of the present invention and examples using this method. Herein, the embodiments of the present invention will be described by giving the battery members and manufacturing methods their respective sequential numbers. Specifically, a description will be given below of respective battery members according to first to third embodiments of the present invention and respective battery member manufacturing methods or sintered body electrode manufacturing methods according to first to thirteenth embodiments of the present invention.
[Manufacturing Method]
In obtaining the paste 13A, an alkali-ion conductive solid electrolyte precursor is prepared. However, in this stage, an alkali-ion conductive solid electrolyte precursor solution is preferably prepared. Specific examples of the alkali-ion conductive solid electrolyte precursor and its solution will be described later. A carbon electrode material precursor (a precursor of a carbon electrode material made of graphite or hard carbon) is also prepared. As the carbon electrode material precursor, an appropriate sugar, biomass, polymer or the like can be used.
Next, the alkali-ion conductive solid electrolyte precursor solution and the carbon electrode material precursor are mixed and the mixture is then dried. Thus, a mixture of an alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor is obtained. Next, a powder obtained by grinding the mixture is mixed with a conductive agent 6 and a binder in an organic solvent. As the organic solvent, for example, N-methylpyrrolidone can be used. Thus, a paste 13A is obtained.
On the other hand, the solid electrolyte layer 2 can be obtained by mixing raw material powders, forming the mixed raw material powders into a shape, and then firing them. For example, the solid electrolyte layer 2 can be obtained by making the raw material powders into a slurry, forming the slurry into a green sheet, and then firing the green sheet. Alternatively, the solid electrolyte layer 2 may be obtained by the sol-gel method.
Next, as shown in
Thus, an alkali-ion conductive solid electrolyte and a carbon electrode material are concurrently obtained and, as a result, a mixture phase 5 of the alkali-ion conductive solid electrolyte and the carbon electrode material is obtained. In this manner, as shown in
Next, a current collector 4 is formed on the sintered body electrode 3. The method for forming the current collector 4 is not particularly limited and examples include physical vapor deposition methods, such as evaporation coating and sputtering, and chemical vapor deposition methods, such as thermal CVD, MOCVD, and plasma CVD. However, the current collector 4 need not necessarily be formed.
In the manner as thus far described, a battery member 1 can be obtained. The binder is decomposed by the firing. Therefore, the sintered body electrode 3 in the battery member 1 contains no binder. Here, specific examples of materials for the components of the battery member 1 will be described.
Carbon Electrode Material Precursor
In using a sugar as the carbon electrode material precursor, examples thereof include sucrose, cellulose, D-glucose, and sucrose. In using biomass as the carbon electrode material precursor, examples thereof include cornstalk, sorghum stalk, pine cone, mangosteen, argan nut shell, chaff, dandelion, corn straw core, ramie fiber, cotton, kelp, and coconut meat skin. In using a polymer as the carbon electrode material precursor, examples thereof include PAN (polyacrylonitrile), pitch, PVC (polyvinyl chloride) nanofiber, polyaniline, sodium polyacrylate, tire (polymer for tire), and phosphorous-doped PAN.
Alkali-Ion Conductive Solid Electrolyte in Sintered Body Electrode 3
The alkali-ion conductive solid electrolyte is preferably made of an oxide. An alkali-ion conductive solid electrolyte made of an oxide is stable to the atmosphere and, therefore, can increase the safety of the battery. Generally, an alkali-ion conductive solid electrolyte made of an oxide is a hard material having a high Young's modulus, is difficult to soften and flow by thermal treatment, and is therefore difficult to densify by cold pressing or firing. However, the manufacturing method according to this embodiment enables provision of a dense sintered body.
Examples of the alkali-ion conductive solid electrolyte include beta-alumina crystals and NASICON crystals both of which have excellent sodium ion conductivity. Beta-alumina includes two types of crystals: β-alumina (theoretical composition formula: Na2O·11Al2O3) and β″-alumina (theoretical composition formula: Na2O·5.3Al2O3). β″-alumina is a metastable material and is therefore generally used in a state in which Li2O or MgO is added as a stabilizing agent thereto. β″-alumina has a higher sodium-ion conductivity than β-alumina. Therefore, β″-alumina alone or a mixture of β″-alumina and β-alumina is preferably used and Li2O-stabilized β″-alumina (Na1.7Li0.3Al10.7O17) or MgO-stabilized β″-alumina ((Al10.32Mg0.68O16)(Na1.68O)) is more preferably used.
Examples of the NASICON crystals include compounds represented by a general formula Na1-xX2P3-xSixO12 (where X represents at least one transition metal element selected from group IV elements and 0≤x≤3). Particularly, the NASICON crystals preferably contain at least one of a first compound and a second compound both described below. The first compound is a compound represented by a general formula Na1-xZr2P3-xSixO12 (where 0≤x≤3). The second compound is a compound in which a part of Zr in the first compound is substituted with at least one element selected from the group consisting of Ca, Mg, Ba, Sr, Al, Nb, Ta, In, Ga, and group III elements. An example of the group III element is at least one selected from the group consisting of Sc, Y, and La.
Examples of the first compound and the second compound include Na3Zr2Si2PO12, Na3Zr1.6Ti0.4Si2PO12, and Na3Zr1.88Y0.12Si2PO12. Other examples of the NASICON crystal include Na3.2Zr1.3Si2.2P0.7O10.5, Na3Hf2Si2PO12, Na3.4Zr0.9Hf1.4Al0.6Si1.2P1.8O12, Na3Zr1.7Nb0.24Si2PO12, Na3.6Ti0.2Y0.7Si2.8O9, Na3.12Zr1.88Y0.12Si2PO12, Na3.6Zr0.13Yb1.67Si0.11P2.9O12, and Na3.12Zr1.88Y0.12Si2PO12.
Other than those above, examples of the alkali-ion conductive solid electrolyte include crystalline phases represented by a general formula Na5XSi4O12. X is at least one selected from group III transition metal elements, more specifically, rare earth elements. Rare earth elements include, in addition to Dy, Gd, Y, and Sm, Sc, La, Ce, Pr, Nd, Pm, Eu, Tb, Ho, Er, Tm, Yb, and Lu. Pr, Nd, Sm, Gd, Dy or Y is preferably used and Y, Sm, Dy or Gd is more preferably used. Alternatively, a part of Si may be substituted with P.
The alkali-ion conductive solid electrolyte may be a crystalline phase represented by a general formula Li7La3Zr2O12, Li7La3Zr2-xMxO12 (where M represents at least one selected from Nb, Ga, and Ta and 0<x<2) or Li7-3xAlxLa3Zr2O12 (0<x<2.3).
Alkali-Ion Conductive Solid Electrolyte Precursor and Solution Thereof
When the alkali-ion conductive solid electrolyte is beta-alumina, an alkali-ion conductive solid electrolyte precursor can be obtained, for example, by mixing aluminum nitrate, sodium nitrate, and lithium nitrate. In doing so, the ratio among these materials is adjusted to give a desired composition ratio of the alkali-ion conductive solid electrolyte.
When the alkali-ion conductive solid electrolyte is NASICON crystals or Na5XSi4O12 crystals, an example of an alkali-ion conductive solid electrolyte precursor solution is a solution containing an alkali metal element and a transition metal element both forming the alkali-ion conductive solid electrolyte, and carbonate ions. In the solution, the alkali metal element is contained in the form of alkali ions and the transition metal element is contained in the form of transition metal ions. The alkali-ion conductive solid electrolyte precursor is made of, for example, a gelled product or dried product of the alkali-ion conductive solid electrolyte precursor solution. Furthermore, the alkali-ion conductive solid electrolyte is made of a sintered body of the alkali-ion conductive solid electrolyte precursor.
The alkali metal element in the alkali-ion conductive solid electrolyte precursor or the solution of the alkali-ion conductive solid electrolyte precursor is, for example, at least one selected from the group consisting of Li, Na, and K. The transition metal element is, for example, at least one selected from the group consisting of group III elements and group IV elements. The transition metal element is preferably Ti, Zr, Hf, Sc, Y, La, Sm, Dy or Gd, more preferably Zr, Hf, Sc, Y, La, Sm, Dy or Gd, still more preferably Zr, Hf, Sc, Y, La or Sm, and particularly preferably Zr, Hf, Y, La or Sm. Other than these transition metal elements, the alkali-ion conductive solid electrolyte precursor or the solution thereof may include at least one selected from the group consisting of Ca, Mg, Ba, Sr, Al, Nb, Ta, In, and Ga. In the alkali-ion conductive solid electrolyte precursor solution, carbonate ions may be contained as a carbonate (a carbonate of a transition metal) or a mixture of carbonate ions and a carbonate. In these cases, the alkali-ion conductive solid electrolyte precursor solution is suitable, for example, as a precursor solution of a sodium-ion conductive solid electrolyte.
As the alkali-ion conductive solid electrolyte precursor solution, a solution containing nitrate ions instead of carbonate ions may be used. However, the alkali-ion conductive solid electrolyte precursor solution is preferably a solution containing carbonate ions for the following reasons.
When a solution containing nitrate ions is used as the alkali-ion conductive solid electrolyte precursor solution, there is a tendency that components in the solution heterogeneously precipitate during mixing or drying of the solution and, thus, a heterogeneous phase causing a decrease in ionic conductivity after firing is formed. Furthermore, the weight reduction due to decomposition of nitrate ions in the firing process is significant, which makes it difficult to form a homogeneous thin film layer. In addition, the production cost of facilities and so on for processing corrosive gas, such as NOx, generating in the firing process may increase. Furthermore, the solution containing nitrate ions is highly acidic and, therefore, requires high-level chemical durability of production facilities. Also in this respect, the production cost may increase.
On the other hand, when a solution containing carbonate ions is used as the alkali-ion conductive solid electrolyte precursor solution, a transition metal element in a transition metal oxide, such as ZrO2 or Y2O3, normally dissolvable in an acidic region only is dissolved in the solution by being coordinated by carbonate ions to form a complex, which enables preparation of a metallic salt solution having neutrality to weak basicity (pH 7 or more, preferably 7.5 or more, more preferably 8 or more, still more preferably 8.5 or more, and particularly preferably 9 or more). In this case, not only an alkali metal component forming part of the alkali-ion conductive solid electrolyte can be dissolved as a carbonate or a hydroxide in the solution, but also a Si component forming another part of the alkali-ion conductive solid electrolyte can be added as liquid glass (sodium silicate: Na2O·nSiO2). Therefore, an alkali-ion conductive solid electrolyte precursor solution can be easily prepared.
In the alkali-ion conductive solid electrolyte precursor solution, carbonate ions are preferably coordinated bidentately to the transition metal element. In this case, the transition metal element can be stably present in the solution.
The alkali-ion conductive solid electrolyte precursor solution preferably contains NR4+ (where Rs are each independently a substituent of at least one selected from the group consisting of H, CH3, C2H5, and CH2CH2OH) as counterions to the carbonate ions. By doing so, the transition metal element can be stably present in the solution.
The alkali-ion conductive solid electrolyte precursor solution can be obtained, for example, by mixing liquid glass (sodium silicate), tripolyphosphoric acid, and zirconium ammonium carbonate aqueous solution.
Conductive Agent 6
As the conductive agent 6, for example, a conductive carbon can be used. Examples of the conductive carbon include acetylene black, carbon black, Ketjenblack, carbon nanotube, and a vapor-grown carbon fiber (VGCF) conductive agent. The conductive agent 6 is preferably a carbon-based conductive agent made of any of the materials as just described.
Binder
The binder is a material for binding raw materials (raw material powders) together. Examples of the binder include: cellulose derivatives, such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, hydroxypropyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose, or water-soluble polymers, such as polyvinyl alcohol; thermosetting resins, such as thermosetting polyimide, phenolic resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, and polyurethane; polycarbonate-based resins, such as polypropylene carbonate; polyvinylidene fluoride; polyacrylic acid; sodium polyacrylate; polyacrylonitrile; polyethylene oxide; and butyral resin.
Solid Electrolyte Layer 2
A solid electrolyte of the same type as the alkali-ion conductive solid electrolyte in the sintered body electrode 3 can be used.
Current Collector 4
The material for the current collector 4 is not particularly limited, but metallic materials, such as aluminum, nickel, titanium, silver, copper, stainless steel, tungsten or an alloy of any of them, can be used. These metallic materials may be used singly or in combination of two or more of them. The alloy of any of them means an alloy containing at least one of the above metals.
Hereinafter, the details of the effects of the present invention will be described by comparison between a working example and a comparative example.
<Preparation of Alkali-Ion Conductive Solid Electrolyte Precursor>
Liquid glass (sodium silicate: Na2O·nSiO2), zirconium ammonium carbonate aqueous solution ((NH4)2Zr(OH)2(CO3)2), and sodium tripolyphosphate (Na5P3O10) were weighed 25 g in total to provide NASICON crystals having a composition ratio of Na3Zr2Si2PO12. These materials were added to 150 g of pure water, followed by stirring with a hot stirrer at 50° C. for 24 hours. Thus, an alkali-ion conductive solid electrolyte precursor solution (pH=9.7) was obtained. Next, this solution was allowed to stand overnight in a thermostat bath at approximately 5° C., thus turning it into a gel. In this manner, an alkali-ion conductive solid electrolyte precursor was prepared.
<Production of Mixture of Alkali-Ion Conductive Solid Electrolyte Precursor and Carbon Electrode Material Precursor>
Sucrose being a carbon electrode material precursor and serving as a source of hard carbon and the alkali-ion conductive solid electrolyte precursor were mixed for an hour in a stirrer to give a weight ratio of 4:1, thus obtaining a mixture. Next, the mixture was dried for 12 hours in a thermostat bath at 60° C., then vacuum dried at 100° C. for six hours, and then ground into powdered form in an agate mortar.
<Production of Electrode Paste>
A powder of the mixture of the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor and a conductive agent (acetylene black) were weighed to give a weight ratio of 19:1. A PPC (polypropylene carbonate) binder was added to these materials to have an external ratio of 15% by weight and all components were mixed in a N-methylpyrrolidone solvent with a planetary centrifugal mixer, thus obtaining an electrode paste.
<Production of Battery Member>
A solid electrolyte layer of Na3Zr2Si2PO12 having a thickness of 500 μm was separately prepared. The electrode paste was applied to a thickness of 70 μm on the first principal surface of the solid electrolyte layer and dried in a drier at 50° C., thus forming an electrode forming material layer. After the drying, the electrode forming material layer on the solid electrolyte layer was fired at 1000° C. for two hours in a nitrogen atmosphere (N2: 99.9999%) to precipitate a mixture phase of an alkali-ion conductive solid electrolyte having a composition of Na3Zr2Si2PO12 and a carbon electrode material made of hard carbon, thus obtaining a sintered body electrode. Next, a current collector was formed on the sintered body electrode by sputtering. The current collector was formed of an aluminum thin film. In the manner as thus far described, a battery member was obtained. The sintered body electrode in this example is a negative electrode.
<Production of Test Battery>
Metal sodium was attached as a counterelectrode to the second principal surface of the solid electrolyte layer in a glove box, thus producing a test battery.
A test battery was produced in the same manner as in Example 1 except that the negative electrode was made of a mixture of hard carbon and a PEO—(polyethylene oxide)-based polymer solid electrolyte (a mixture of PEO and NaPF6 at a weight ratio of 9:1).
<Charge and Discharge Test>
Each of the test batteries underwent a charge and discharge test in a thermostat bath at 30° C. Specifically, the charge capacity and the discharge capacity of the test battery were measured by subjecting it to charging (insertion of sodium ions) at a cut-off voltage of 0.001 V and subjecting it to discharging (extraction of sodium ions) at a cut-off voltage of 2.5 V. In doing so, in Example 1, charging and discharging were conducted by assuming (the weight of the produced negative electrode, i.e., the above-described sintered body electrode)×300 mAh/g as an actual capacity and setting a current value to give a C-rate of 0.1. Also at 60° C., the charge capacity and discharge capacity were measured in the same manner as described above.
As shown in
Unlike the above, as shown in
Next, a description will be given of the details of the effects of the present invention in relation to the alkali-ion conductive solid electrolyte precursor solution with reference to a working example and a reference example.
An alkali-ion conductive solid electrolyte precursor solution was obtained in the same manner as in Example 1. This solution was allowed to stand overnight in a thermostat bath at approximately 5° C. to turn it into a gel, thus obtaining an alkali-ion conductive solid electrolyte precursor.
The obtained alkali-ion conductive solid electrolyte precursor was dried for 12 hours in a thermostat bath at 60° C. and then vacuum dried at 100° C. for six hours. When the alkali-ion conductive solid electrolyte precursor after the drying was analyzed by XRD, it was found that, as shown in the relevant XRD chart in
The alkali-ion conductive solid electrolyte precursor after the drying was fired at 1000° C. for three hours, thus obtaining an alkali-ion conductive solid electrolyte. When the obtained alkali-ion conductive solid electrolyte was analyzed by XRD, it was confirmed that, as shown in
For the measurement of the ionic conductivity, a gold electrode was formed as an ion blocking electrode on a surface of the alkali-ion conductive solid electrolyte, the alkali-ion conductive solid electrolyte was then measured in a frequency range of 1 to 107 Hz by the AC impedance method to obtain a Cole-Cole plot, and resistance values were determined from the Cole-Cole plot. The ionic conductivity was calculated from the obtained resistance values. The measurement by the AC impedance method was conducted at 20° C.
An alkali-ion conductive solid electrolyte precursor was obtained in the same manner as in Example 2 except that a zirconium nitrate aqueous solution (ZrO(NO3)2) was used instead of the zirconium ammonium carbonate aqueous solution.
When the obtained alkali-ion conductive solid electrolyte precursor was dried in the same manner as in Example 2 and the alkali-ion conductive solid electrolyte precursor after the drying was analyzed by XRD (X-ray diffraction), it was found that, as shown in
The alkali-ion conductive solid electrolyte precursor after the drying was fired at 1000° C. for three hours, thus obtaining an alkali-ion conductive solid electrolyte. When the obtained alkali-ion conductive solid electrolyte was analyzed by XRD, it was confirmed that, as shown in
The above-described method for manufacturing a battery member 1 according to the first embodiment includes a heating step at approximately 1000° C. Therefore, the sintered body electrode 3 is difficult to decompose even if it is thermally treated again. For example, after being thermally treated in an inert atmosphere at 500° C., the sintered body electrode 3 can absorb and release alkali ions at 30° C. Thus, the thermal resistance can be effectively increased. In contrast, if a general electrode containing a binder as a solid electrolyte is thermally treated in an inert atmosphere at 500° C., the binder is decomposed to lose the function of the solid electrolyte, which makes it impossible for the battery to absorb and release alkali ions at 30° C. It is also found that the sintered body electrode 3 according to the present invention is difficult to decompose even if a voltage of about 8 V to 9 V is applied thereto. For example,
Here, in the example described above, water was used as a solvent in mixing the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor. Particularly, sugar, such as sucrose, has a high solubility in water. Therefore, in mixing the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor, the homogeneity of the mixture can be effectively increased. In the battery member according to this embodiment, before the alkali-ion conductive solid electrolyte and the carbon electrode material are obtained, their precursors are homogeneously mixed. Therefore, the contact area between them can be effectively large, which enables high output and rapid charge and discharge.
Hereinafter, other examples of a method for manufacturing a battery member will be described.
[Manufacturing Method]
A description will be given below of respective battery member manufacturing methods or sintered body electrode manufacturing methods according to second to ninth embodiments of the present invention.
In obtaining the paste 13B, a mixture powder of an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor is obtained in the same manner as in the manufacturing method according to the first embodiment. Next, the mixture powder is fired in an N2 atmosphere at not lower than 200° C. and not higher than 800° C. Alternatively, the upper limit of the temperature may not be higher than 500° C. in consideration of the firing temperature during a second firing step to be described hereinafter. Thus, a carbon electrode material is obtained from the carbon electrode material precursor. This step is a first firing step. By the first firing step, a mixture powder of the alkali-ion conductive solid electrolyte precursor and the carbon electrode material is obtained. If the firing temperature is too low, the carbon electrode material precursor is less likely to change into a carbon electrode material. On the other hand, if the firing temperature is too high, the alkali-ion conductive solid electrolyte precursor tends to change into an alkali-ion conductive solid electrolyte.
Next, the mixture powder is ground and mixed with a conductive agent 6 and a binder in an organic solvent, thus obtaining a paste 13B. Next, as shown in
In the first embodiment shown in
Unlike the above, in this embodiment, the first firing step is performed before the step of forming an electrode forming material layer, i.e., the step of forming a paste 13B. Thus, before the formation of the paste 13B, the reaction for obtaining a carbon electrode material from a carbon electrode material precursor is performed. Therefore, the amount of decomposing components in the second firing step after the formation of the paste 13B is small. As a result, the difference in thickness between the paste 13B and the sintered body electrode 3 is small. Hence, the thickness of the sintered body electrode 3 can be easily controlled. In addition, even when the thickness of the paste 13B is large, the sintered body electrode 3 obtained after the firing is less likely to cause inconveniences, such as cracks. As a result, the thickness of the sintered body electrode 3 can be easily increased and, therefore, the capacity can be easily increased. However, in the first embodiment, the number of times of firing step for obtaining a sintered body electrode 3 is only one, which simplifies the process.
In obtaining the paste 13C, a mixture powder of an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor is obtained in the same manner as in the manufacturing method according to the first embodiment. Next, the mixture powder is fired, in an N2 atmosphere, at over 500° C. and not higher than 1150° C. (preferably, over 800° C. and not higher than 1100° C.) Thus, an alkali-ion conductive solid electrolyte and a carbon electrode material are concurrently obtained. This step is a third firing step. By the third firing step, a mixture powder of the alkali-ion conductive solid electrolyte and the carbon electrode material is obtained. If the firing temperature is too low, the mixture powder of the alkali-ion conductive solid electrolyte and the carbon electrode material is difficult to obtain. On the other hand, if the firing temperature is too high, the alkaline component evaporates from the alkali-ion conductive solid electrolyte precursor, which may make it difficult to obtain an alkali-ion conductive solid electrolyte having a desired composition.
Next, the mixture powder is ground and mixed with a conductive agent 6 and a binder in an organic solvent, thus obtaining a paste 13C. Next, as shown in
In this embodiment, the third firing step is performed before the step of forming a paste 13C. Thus, before the formation of the paste 13C, both a reaction of changing from the alkali-ion conductive solid electrolyte precursor to the alkali-ion conductive solid electrolyte and a reaction of changing from the carbon electrode material precursor to the carbon electrode material occur. Therefore, the amount of decomposing components in the fourth firing step after the formation of the paste 13C is smaller. As a result, the difference in thickness between the paste 13C and the sintered body electrode 3 is smaller. Hence, the thickness of the sintered body electrode 3 can be more easily controlled. In addition, the thickness of the sintered body electrode 3 can be more easily increased and, therefore, the capacity can be more easily increased. However, in the second embodiment, the battery member 1 can be manufactured at a lower temperature than in the third embodiment.
In obtaining the powder compact 23A, a mixture powder of an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor is obtained in the same manner as in the manufacturing method according to the first embodiment. Next, the mixture powder and the conductive agent 6 are mixed and the mixture is then pressed into a shape, thus obtaining a powder compact 23A of the alkali-ion conductive solid electrolyte precursor, the carbon electrode material precursor, and the conductive agent 6. In the pressing, for example, a uniaxial pressing may be used. The conductive agent 6 need not necessarily be added.
On the other hand, the paste 22 can be obtained by adding mixed raw material powders into an organic solvent. Next, as shown in
In this embodiment, since the solid electrolyte layer 2 and the sintered body electrode 3 are concurrently obtained, the productivity can be increased. In addition, since the paste 22 is used for the production of the solid electrolyte layer 2, the solid electrolyte layer 2 can be easily reduced in thickness. Modifications of this embodiment will be described below.
In the battery member 1 produced in the fourth embodiment, as shown in
(Modification 2 of Fourth Embodiment)
In obtaining the powder compact 23B, a mixture powder of an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor is obtained in the same manner as in the manufacturing method according to the first embodiment. Next, the mixture powder is fired in an N2 atmosphere at not lower than 200° C. and not higher than 800° C. Alternatively, the upper limit of the temperature may not be higher than 500° C. in consideration of the firing temperature during a second firing step to be described hereinafter. This step is the same first firing step as in the second embodiment. Specifically, in this step, a mixture powder of the alkali-ion conductive solid electrolyte precursor and a carbon electrode material is obtained. If the firing temperature is too low, the carbon electrode material precursor is less likely to change into a carbon electrode material. On the other hand, if the firing temperature is too high, the alkali-ion conductive solid electrolyte precursor tends to change into an alkali-ion conductive solid electrolyte. Next, the mixture powder and the conductive agent 6 are mixed and the mixture is then pressed into a shape, thus obtaining a powder compact 23B.
On the other hand, as shown in
In obtaining the powder compact 23C, a mixture powder of an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor is obtained in the same manner as in the manufacturing method according to the first embodiment. Next, the mixture powder is fired, in an N2 atmosphere, at over 500° C. and not higher than 1150° C. (preferably, over 800° C. and not higher than 1100° C.) Thus, an alkali-ion conductive solid electrolyte and a carbon electrode material are concurrently obtained. This step is the same third firing step as in the third embodiment. By the third firing step, a mixture powder of the alkali-ion conductive solid electrolyte and the carbon electrode material is obtained. If the firing temperature is too low, the mixture powder of the alkali-ion conductive solid electrolyte and the carbon electrode material is difficult to obtain. On the other hand, if the firing temperature is too high, the alkaline component evaporates from the alkali-ion conductive solid electrolyte precursor, which may make it difficult to obtain an alkali-ion conductive solid electrolyte having a desired composition. Next, the mixture powder and the conductive agent 6 are mixed and the mixture is then pressed into a shape, thus obtaining a powder compact 23C.
On the other hand, as shown in
In this embodiment, since the solid electrolyte layer 2 and the sintered body electrode 3 are concurrently obtained, the productivity can be increased. In addition, like the third embodiment, the thickness of the sintered body electrode 3 can be more easily controlled. Furthermore, the thickness of the sintered body electrode 3 can be more easily increased and, therefore, the capacity can be more easily increased.
Meanwhile, the sintered body electrode 3 according to the one embodiment of the present invention can be used independently. Examples of a method for manufacturing the sintered body electrode 3 will be described below.
Next, the powder compact 23B is fired, in an N2 atmosphere, at over 500° C. and not higher than 1300° C. (preferably, over 800° C. and not higher than 1150° C.) Thus, an alkali-ion conductive solid electrolyte is obtained from the alkali-ion conductive solid electrolyte precursor and, as a result, a mixture phase 5 of the alkali-ion conductive solid electrolyte and the carbon electrode material is obtained. This step is the same second firing step as in the fifth embodiment. In the second firing step, firing is performed at a higher temperature than in the first firing step. In this manner, a sintered body electrode 3 is obtained as shown in
Next, the powder compact 23C is fired, in an N2 atmosphere, at not lower than 600° C. and not higher than 1300° C. (preferably, not lower than 900° C. and not higher than 1250° C.) This step is the same fourth firing step as in the sixth embodiment. In the fourth firing step, firing is performed at a higher temperature than in the third firing step. In this manner, a sintered body electrode 3 is obtained as shown in
[Battery Member]
The sintered body electrode 33 includes a particulate carbon electrode material 38 and a coating layer 39. The D50 of the particulate carbon electrode material 38 is 1 μm. The particulate carbon electrode material 38 is made of graphite or hard carbon. In the particulate carbon electrode material 38, the D50 is preferably 50 μm or less and more preferably 10 μm or less. Thus, the denseness of the sintered body electrode 33 can be increased. The lower limit of the D50 of the particular carbon electrode material 38 is not particularly limited, but is, for example, 10 nm, 0.1 μm, 0.3 μm, 0.5 μm or 0.6 μm.
As shown in
The sintered body electrode 33 preferably contains a conductive agent 6. When the sintered body electrode 33 contains the conductive agent 6, conductive paths are formed inside, which enables reduction of the internal resistance of the sintered body electrode 33. However, the sintered body electrode 33 need not necessary contain the conductive agent 6. The sintered body electrode 33 contains no binder.
The battery member 31 according to this embodiment, like the battery member 1 according to the first embodiment, can increase the safety and also can increase the thermal resistance and voltage resistance. In addition, in the battery member 31 according to this embodiment, the sintered body electrode 33 can be easily increased in thickness (increased in the amount thereof supported) by appropriately controlling the amount of the particulate carbon electrode material 38. Furthermore, the performance can be easily controlled by selecting the type of the particulate carbon electrode material 38 used. The sintered body electrode 33 according to the one embodiment of the present invention may be used independently.
Hereinafter, a description will be given of examples of a method for manufacturing the battery member 31 according to this embodiment and an example of a method for manufacturing the sintered body electrode 33.
[Manufacturing Method]
A description will be given below of respective battery member manufacturing methods or sintered body electrode manufacturing method according to tenth to twelfth embodiments of the present invention.
In obtaining the paste 43, an alkali-ion conductive solid electrolyte precursor of the same type as in the manufacturing method according to the first embodiment is prepared. In addition, a particulate carbon electrode material 38 is prepared. Next, the alkali-ion conductive solid electrolyte precursor and the particulate carbon electrode material 38 are mixed and the mixture is then dried. Thus, a mixture powder of the alkali-ion conductive solid electrolyte precursor and the particulate carbon electrode material 38 is obtained. Next, the mixture powder is added into an organic solvent and the mixture is further mixed with a conductive agent 6 and a binder. As the organic solvent, for example, N-methylpyrrolidone can be used. Thus, a paste 43 is obtained. However, the conductive agent 6 need not necessarily be added.
Next, as shown in
In obtaining the powder compact 53, a mixture powder of an alkali-ion conductive solid electrolyte precursor and a particulate carbon electrode material 38 is obtained in the same manner as in the manufacturing method according to the tenth embodiment. Next, the mixture powder and a conductive agent 6 are mixed and the mixture is then pressed into a shape, thus obtaining a powder compact 53.
On the other hand, the paste 22 can be obtained by adding mixed raw material powders into an organic solvent. Next, as shown in
Alternatively, the paste 22 may be applied to the powder compact 53, like the example shown in
Alternatively, a sintered body electrode 33 may be obtained by applying a paste 43 serving as an electrode forming material layer and being of the same type as in the tenth embodiment shown in
[Battery Member]
The coating layer 49 contains a carbon electrode material and an alkali-ion conductive solid electrolyte. The carbon electrode material is a material, separate from the particulate carbon electrode material 38, contained in the sintered body electrode 73 and is made of graphite or hard carbon. The alkali-ion conductive solid electrolyte has a sodium-ion conductivity in this embodiment. Alternatively, the alkali-ion conductive solid electrolyte may have a lithium-ion conductivity. The coating layer 49 contains a mixture phase of the carbon electrode material and the alkali-ion conductive solid electrolyte. The mixture phase is in particulate form. The particles in the mixture phase are bound together by sintering. The particles of the particulate carbon electrode material 38 are bonded together through the coating layer 49. Furthermore, the sintered body electrode 73 is bonded to the solid electrolyte layer 2 by the coating layer 49.
The battery member 41 according to this embodiment, like the battery member 1 according to the first embodiment, can increase the safety and also can increase the thermal resistance and voltage resistance. In addition, in the battery member 41 according to this embodiment, the sintered body electrode 73 can be easily increased in thickness (increased in the amount thereof supported) by appropriately controlling the amount of the particulate carbon electrode material 38. Furthermore, as shown in Example 3 to be described hereinafter, the battery member 41 according to this embodiment has a feature of an excellent first charge/discharge efficiency (irreversible capacity).
[Manufacturing Method]
A description will be given below of a method for manufacturing a battery member according to a thirteenth embodiment of the present invention.
In obtaining the paste 83, an alkali-ion conductive solid electrolyte precursor and a carbon electrode material precursor, both of which are of the same type as in the manufacturing method according to the first embodiment, are prepared. In addition, a particulate carbon electrode material 38 is prepared. Next, the alkali-ion conductive solid electrolyte precursor, the carbon electrode material precursor, and the particulate carbon electrode material 38 are mixed and the mixture is then dried. Thus, a mixture powder of the alkali-ion conductive solid electrolyte precursor, the carbon electrode material precursor, and the particulate carbon electrode material 38 is obtained. Next, the mixture powder is added into an organic solvent and the mixture is further mixed with a conductive agent 6 and a binder. As the organic solvent, for example, N-methylpyrrolidone can be used. Thus, a paste 83 is obtained. However, the conductive agent 6 need not necessarily be added.
Next, as shown in
Alternatively, like the eleventh embodiment shown in
Furthermore, like the twelfth embodiment shown in
Working examples of the battery member according to the third embodiment will be described below.
Liquid glass (sodium silicate), zirconium ammonium carbonate aqueous solution, and sodium tripolyphosphate were weighed 25 g in total to provide NASICON crystals having a composition ratio of Na3Zr2Si2PO12. These materials were added to 150 g of pure water, followed by stirring with a hot stirrer at 50° C. for 24 hours. Thus, an alkali-ion conductive solid electrolyte precursor solution was obtained. Next, this solution was allowed to stand overnight in a thermostat bath at approximately 5° C., thus turning it into a gel. In this manner, an alkali-ion conductive solid electrolyte precursor was prepared.
<Production of Mixture of Alkali-Ion Conductive Solid Electrolyte Precursor and Carbon Electrode Material Precursor>
Sucrose being a carbon electrode material precursor and serving as a source of hard carbon and the alkali-ion conductive solid electrolyte precursor were mixed for an hour in a stirrer to give a weight ratio of 4:1, thus obtaining a mixture. Next, the mixture was dried for 12 hours in a thermostat bath at 60° C., then vacuum dried at 100° C. for six hours, and then ground into powdered form in an agate mortar.
<Production of Electrode Paste>
A powder of the mixture of the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor, hard carbon powder (average particle diameter D50=1 μm), and a conductive agent (acetylene black) were weighed to give a weight ratio of 57:40:3. A PPC (polypropylene carbonate) binder was added to these materials to have an external ratio of 15% by weight and all components were mixed in a N-methylpyrrolidone solvent with a planetary centrifugal mixer, thus obtaining an electrode paste.
<Production of Battery Member>
A solid electrolyte layer of Na3Zr2Si2PO12 having a thickness of 500 μm was separately prepared. The electrode paste was applied to a thickness of 70 μm on the first principal surface of the solid electrolyte layer and dried in a drier at 50° C. After the drying, the electrode paste on the solid electrolyte layer was fired at 1000° C. for two hours in a nitrogen atmosphere (N2: 99.9999%), thus obtaining a sintered body electrode in which the hard carbon powder was coated with a coating layer. The coating layer was formed by precipitating a mixture phase of an alkali-ion conductive solid electrolyte having a composition of Na3Zr2Si2PO12 and a carbon electrode material made of hard carbon. Next, a current collector was formed on the sintered body electrode by sputtering. The current collector was formed of an aluminum thin film. In the manner as thus far described, a battery member was obtained. The sintered body electrode in this example is a negative electrode.
<Production of Test Battery>
Metal sodium was attached as a counterelectrode to the second principal surface of the solid electrolyte layer in a glove box, thus producing a test battery.
<Charge and Discharge Test>
The test battery underwent a charge and discharge test in a thermostat bath at 60° C. Specifically, the charge capacity and the discharge capacity of the test battery were measured by subjecting it to charging (insertion of sodium ions) at a cut-off voltage of 0.001 V and subjecting it to discharging (extraction of sodium ions) at a cut-off voltage of 2.5 V. In doing so, in Example 3, charging and discharging were conducted by assuming (the weight of the produced negative electrode, i.e., the above-described sintered body electrode)×300 mAh/g as an actual capacity and setting a current value to give a C-rate of 0.1. The results of the charge and discharge test are shown in
As shown in
The foregoing description has dealt with embodiments in which a carbon electrode material made of graphite or hard carbon is used as an active material. Although the carbon electrode material made of graphite or hard carbon is a material used mainly as a negative-electrode active material, the present invention can also be applied to the case where a positive-electrode active material is used instead of the carbon electrode material. For example, in the battery member according to the second embodiment of the present invention shown in
<Preparation of Alkali-Ion Conductive Solid Electrolyte Precursor>
Lithium acetate dihydrate CH3COOLi·2H2O, lanthanum acetate 1.5-hydrate La(CH3COO)3·1.5H2O, and a zirconium (IV) propoxide solution Zr(OCH2CH2CH3)4 were weighed 25 g in total to provide crystals having a composition ratio of Li7La3Zr2O12. These materials were added to 150 g of pure water, followed by stirring with a hot stirrer at 50° C. for 24 hours. Thus, an alkali-ion conductive solid electrolyte precursor solution was obtained. Next, this solution was allowed to stand overnight in a thermostat bath at approximately 5° C., thus turning it into a gel. In this manner, an alkali-ion conductive solid electrolyte precursor was prepared.
<Production of Mixture of Alkali-Ion Conductive Solid Electrolyte Precursor and Carbon Electrode Material Precursor>
Using sucrose being a carbon electrode material precursor and serving as a source of hard carbon and the alkali-ion conductive solid electrolyte precursor obtained in the above manner, a mixture powder of the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor was obtained in the same manner as in Example 1.
<Production of Electrode Paste>
Using the obtained mixture powder of the alkali-ion conductive solid electrolyte precursor and the carbon electrode material precursor, an electrode paste was obtained in the same manner as in Example 1.
<Production of Battery Member>
A solid electrolyte layer of Li7La3Zr2O12 having a thickness of 500 μm was separately prepared. The electrode paste was applied to a thickness of 70 μm on the first principal surface of the solid electrolyte layer and dried in a drier at 50° C., thus forming an electrode forming material layer. After the drying, the electrode forming material layer on the solid electrolyte layer was fired at 1000° C. for two hours in a nitrogen atmosphere (N2: 99.9999%) to precipitate a mixture phase of an alkali-ion conductive solid electrolyte having a composition of Li7La3Zr2O12 and a carbon electrode material made of hard carbon, thus obtaining a sintered body electrode. Next, a current collector was formed on the sintered body electrode by sputtering. The current collector was formed of a copper thin film. In the manner as thus far described, a battery member was obtained. The sintered body electrode in this example is a negative electrode.
<Production of Test Battery>
Metal lithium was attached as a counterelectrode to the second principal surface of the solid electrolyte layer in a glove box, thus producing a test battery.
<Charge and Discharge Test>
The test battery underwent a charge and discharge test in a thermostat bath at 60° C. Specifically, the charge capacity and the discharge capacity of the test battery were measured by subjecting it to charging (insertion of lithium ions) at a cut-off voltage of 0.001 V and subjecting it to discharging (extraction of lithium ions) at a cut-off voltage of 1.5 V. In doing so, charging and discharging were conducted by assuming (the weight of the produced negative electrode, i.e., the above-described sintered body electrode)×400 mAh/g as an actual capacity and setting a current value to give a C-rate of 0.1. As a result, the charge capacity was 419 mAh/g, the discharge capacity was 314 mAh/g, and the first charge/discharge efficiency was 74.9%.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-118624 | Jul 2020 | JP | national |
| 2020-168411 | Oct 2020 | JP | national |
| 2020-183728 | Nov 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/025210 | 7/2/2021 | WO |
