Electrode manufacturing method, power storage device manufacturing method, pre-doping method, and power storage device

Abstract

To further increase the reversible capacity of a power storage device.SOLUTION: Provided is a manufacturing method of a power storage device electrode, which includes a doping step of bringing an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more on lithium reference into contact with a dope solution containing metal ions and an aromatic hydrocarbon compound in a reduction state, and pre-doping the initial electrode with the metal ions to obtain a doped electrode.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing an electrode, a method for manufacturing an electricity storage device, a pre-doping method, an electrode, and an electricity storage device. [Background technology]

[0002] Previously, positive electrodes suitable for increasing the capacity of power storage devices have been investigated (for example, Non-Patent Document 1). This document describes that when a lithium composite oxide with a composition of (1-α)LiMnO2·αLi3PO4, which is obtained by mixing layered LiMnO2 and Li3PO4 by mechanical milling, is used as a positive electrode, Mn 3+ / Mn 4+ It is said to exhibit a high capacity that exceeds the theoretical capacity based on the oxidation-reduction of [Prior art documents] [Patent documents]

[0003] [Non-Patent Document 1] M. Sawamura, et al., ACS Cent. Sci. 2020, 6, 2326-2338 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Non-Patent Document 1, although the discharge capacity can be increased, the initial discharge capacity is lower than the subsequent initial charge capacity, and therefore, depending on the negative electrode combined, the irreversible capacity increases due to a shortage of lithium ions as a carrier, and the discharge capacity that should have been obtained may not be obtained. For this reason, there has been a demand for further increasing the reversible capacity of electricity storage devices.

[0005] The present disclosure has been made to solve such problems, and a main object of the present disclosure is to further increase the reversible capacity of an electricity storage device. [Means for solving the problem]

[0006] As a result of intensive research to achieve the above-mentioned object, the inventors have found that the reversible capacity of an electricity storage device can be further increased by contacting an electrode (also referred to as an initial electrode) with a predetermined dope solution and then using it as a positive electrode of the electricity storage device, and have thus completed the present disclosure.

[0007] That is, the method for producing an electrode according to the present disclosure includes the steps of: A method for manufacturing an electrode of an electricity storage device, comprising: a doping step of contacting an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium potential with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions to pre-dope the initial electrode with the metal ions to obtain a doped electrode; It is something.

[0008] The method for manufacturing an electricity storage device according to the present disclosure includes: a cell fabrication step in which the electrode manufactured by the above-described electrode manufacturing method is used as a positive electrode, and an ion-conductive medium that conducts the metal ions is placed between the positive electrode and a negative electrode containing a negative electrode active material; It includes:

[0009] The pre-doping method of the present disclosure includes: A method for pre-doping an electrode, comprising: a doping step of contacting an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium potential with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions to pre-dope the initial electrode with the metal ions; It is something.

[0010] The electrode of the present disclosure comprises: An electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium reference potential, a peak of an aromatic hydrocarbon compound different from a peak of the active material appears in the infrared absorption (IR) spectrum of the electrode; The active material contains metal ions in an excess amount intercalated in a reduced state. It is something.

[0011] The electricity storage device of the present disclosure includes: An electricity storage device comprising: a positive electrode that is an electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium reference potential; a negative electrode that contains a negative electrode active material; and an ion-conductive medium that is interposed between the positive electrode and the negative electrode and conducts metal ions, a peak of an aromatic hydrocarbon compound different from a peak of the active material appears in the infrared absorption (IR) spectrum of the electrode; When the electricity storage device is completely discharged, the active material is in a reduced state in which the metal ions are excessively inserted. It is something. [Effects of the Invention]

[0012] The electrode manufacturing method, electricity storage device manufacturing method, pre-doping method, electrode, and electricity storage device disclosed herein can further increase the reversible capacity of the electricity storage device. The reason for this effect is presumed to be as follows. For example, a doping solution containing a reduced aromatic hydrocarbon compound and metal ions can act on a specific electrode simply by contacting the electrode with the electrode, pre-doping the electrode with metal ions. It is presumed that using an electrode pre-doped with metal ions in this way as the positive electrode of an electricity storage device can resolve the shortage of metal ions necessary for the discharge reaction, allowing the discharge reaction to proceed sufficiently, thereby further increasing the reversible capacity. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic diagram showing an example of an electricity storage device 20. [Figure 2] Charge / discharge curves of half cells of Experimental Examples 1 to 6. [Figure 3] Charge and discharge curves of full cells for experimental examples 3, 5, and 6. [Figure 4] IR spectra of the doped positive electrodes of Experimental Examples 3 and 6. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present disclosure relates to a power storage device and an electrode of the power storage device. The power storage device includes a positive electrode, a negative electrode, and an ion conductive medium. The positive electrode contains a positive electrode active material that occludes and releases metal ions as carriers. The negative electrode contains a negative electrode active material, and may contain a negative electrode active material that occludes and releases metal ions as carriers. The ion conductive medium is interposed between the positive electrode and the negative electrode and conducts metal ions as carriers. Examples of the metal ions as carriers include alkali metal ions such as Li, Na, and K, and Group 2 ions (alkaline earth metal ions) such as Mg, Ca, and Sr. Among these, lithium ions are preferable. The power storage device may be, for example, an electric double layer capacitor, a hybrid capacitor, a pseudo electric double layer capacitor, a metal ion secondary battery such as a lithium ion secondary battery, an air battery, or the like. Here, for the sake of convenience of explanation, the lithium ion secondary battery in which the metal ions as carriers are Li ions will be mainly described below.

[0015] [Method for manufacturing electrode] The method for manufacturing an electrode of the present disclosure may include, for example, an initial electrode manufacturing step of manufacturing an initial electrode which is an electrode before pre-doping metal ions, and a pre-doping step of pre-doping the initial electrode with metal ions. The metal ions to be pre-doped may be of the same type as the metal ions that are carriers of the power storage device, and may be, for example, lithium ions. The initial electrode manufacturing step may be omitted.

[0016] (Initial electrode manufacturing step) In this step, an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more, preferably 2.5 V or more with respect to the lithium reference potential is manufactured. This initial electrode may be a known positive electrode used in a general lithium ion battery or the like. The active material may be, for example, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like. Specifically, transition metal sulfides such as TiS2, TiS3, MoS3, FeS2, the basic composition formula of Li (1-x) MnO2 (0 < x < 1 etc., the same below) or Li (1-x)A lithium manganese composite oxide such as Mn2O4, with a basic composition formula of Li (1-x) A lithium cobalt composite oxide such as CoO2, with a basic composition formula of Li (1-x) A lithium nickel composite oxide such as NiO2, a lithium vanadium composite oxide with a basic composition formula such as LiV2O3, and a transition metal oxide with a basic composition formula such as V2O5 can be used. Note that the "basic composition formula" means that other elements may be included. Alternatively, this initial electrode may be a known positive electrode used in a general capacitor or the like. The active material may be, for example, carbon materials such as activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, polyacenes

[0017] The active material may have an initial oxidation capacity smaller than its subsequent initial reduction capacity. That is, this active material is used after being initially charged when used in a positive electrode, and the initial charging capacity may be smaller than its subsequent initial discharging capacity. Examples of such active materials include lithium manganese composite oxides, iron oxides, and vanadium oxides. The lithium manganese composite oxide may have a spinel structure or a random rock salt structure. The lithium manganese composite oxide may, for example, contain phosphorus, may contain a halogen such as fluorine, or may contain sulfur. The lithium manganese composite oxide may, for example, have a basic composition formula Li a P x Mn y O 2-z A z (where A is one or more of F, Cl, Br, I, and S, and satisfies 0 < a < 2, 0 ≤ x ≤ 0.09, 0 < y < 1, 0 ≤ z < 2).) It may also be represented as such. The basic composition formula Li a P x Mn y O 2-z A zIn this case, x may satisfy 0.02 ≦ x ≦ 0.08, and z may satisfy 0 < z < 0.5. The active material may be in a state containing lithium in the initial electrode, or may be one that can contain an excessive amount of lithium by reduction. The active material may be unstable in air when it contains an excessive amount of lithium by reduction (for example, Li2Mn2O4, etc.). Although the manufacturing process becomes complicated when synthesizing an active material in an unstable state in air and manufacturing an electrode using it, in the present disclosure, since an electrode containing such an active material can be manufactured simply by bringing the electrode into contact with the doping solution, the significance of applying the technology of the present disclosure is high. The active material may have multiple redox potentials, and in the initial electrode, it may be in a state with a potential higher than the lowest redox potential.

[0018] In this process, for example, the active material, conductive material, and binder may be mixed, and an appropriate solvent may be added to form a paste-like electrode mixture. This paste may then be applied to the surface of a current collector, dried, and compressed, as necessary, to increase electrode density to form an initial electrode. Examples of the conductive material include graphite, such as natural graphite (scale graphite or flake graphite) or artificial graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.), or mixtures of two or more of these. Examples of the binder include fluorine-containing resins, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber; thermoplastic resins, such as polypropylene and polyethylene; ethylene propylene diene monomer (EPDM) rubber; sulfonated EPDM rubber; and natural butyl rubber (NBR), either alone or in combination. The binder may be, for example, a water-based binder such as cellulose-based carboxymethyl cellulose (CMC), styrene-butadiene copolymer (SBR), or an aqueous dispersion of polyvinyl alcohol, which may be used alone or as a mixture of two or more. Examples of methods for applying the electrode composite include roller coating (e.g., applicator roll), screen coating, doctor blade coating, spin coating, and bar coating, and any of these can be used to form a desired thickness and shape. Examples of current collectors that can be used include aluminum, copper, titanium, stainless steel, nickel, iron, baked carbon, conductive polymers, and conductive glass. Examples of current collector shapes include foil, film, and sheet. The thickness of the current collector is, for example, 1 to 500 μm.

[0019] (Pre-doping process) In this step, the initial electrode is pre-doped with metal ions by contacting the initial electrode with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions. In this step, the initial electrode may be immersed in the doping solution or the doping solution may be injected into the initial electrode.

[0020] The dope solution used in this step may contain one or more aromatic hydrocarbon compounds selected from the compounds of the following formulas (1) and (2). Specifically, the aromatic hydrocarbon compound is preferably one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, and chrysene. The aromatic hydrocarbon compound may be biphenyl, ortho-terphenyl, or para-terphenyl. This dope solution may be obtained by one or more of the following formulas (3) and (4). That is, a dope solution containing a reduced aromatic hydrocarbon compound and metal ions may be prepared by reacting an aromatic hydrocarbon compound with a metal. More specifically, as shown in the following formulas (5) to (7), one of naphthalene, diphenyl, and terphenyl may be reacted with Li metal in a tetrahydrofuran (THF) solvent. In this way, a dope solution containing a reduced aromatic hydrocarbon compound and metal ions can be prepared. The concentration of the reduced aromatic hydrocarbon compound in the doping solution is preferably, for example, 0.1 mol / L to 3 mol / L, and may be 0.5 mol / L to 2 mol / L. The same applies to the concentration of the metal ions in the doping solution. The higher these concentrations are, the more reliably the pre-doping of the metal ions can be performed.

[0021] [ka]

[0022] [ka]

[0023] [ka]

[0024] The dope solution may contain an allenide solution containing a reduced aromatic hydrocarbon compound and metal ions, and an electrolyte. Adding the electrolyte to the allenide solution weakens the reducing power of the dope solution, thereby suppressing deterioration of the binder contained in the electrode. For example, fluorine-based polymers such as fluorine-containing resins used as binders may be carbonized by the allenide solution, resulting in a decrease in binding strength. However, adding the electrolyte to the allenide solution can suppress this decrease in binding strength. The allenide solution is, for example, dark green, while the dope solution obtained by adding the electrolyte to the allenide solution is, for example, brown. The difference in color is presumably due to the difference in reducing power. The dope solution may contain 10% to 70% by volume of electrolyte, 20% to 60% by volume, or 30% to 50% by volume. The allenide solution may be used as the dope solution in its undiluted form.

[0025] The arenide solution may be prepared by reacting an aromatic hydrocarbon compound with lithium metal in a solvent, as shown in the above formulas (5) to (7). The solvent for the arenide solution may be an ether-based compound. The ether-based compound may be, for example, a cyclic ether-based compound or a chain ether-based compound. Examples of the ether-based compound include one or more of tetrahydrofuran (THF), dioxolane, dioxane, diethyl ether (DEE), dimethoxyethane (G1), diglyme (G2), triglyme (G3), and tetraglyme (G4). Among these, THF is preferred.

[0026] The electrolyte solution contains a solvent different from the solvent of the arenide solution, and may be the same as or different from the ion-conducting medium of the electricity storage device. The solvent of the electrolyte solution may be a compound other than an ether-based compound, such as a carbonate-based compound, a nitrile-based compound, or a sulfolane-based compound. Among these, carbonate-based compounds are preferred. Examples of the carbonate-based compound include one or more of cyclic carbonate compounds such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), butylene carbonate, and chloroethylene carbonate, and chain carbonate compounds such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate. The supporting salt of the electrolyte may be any salt different from the solute of the arenide solution. Examples of such salts include inorganic salts such as LiPF6 and LiBF4, and imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). These supporting salts may be used alone or in combination. The concentration of the supporting salt in the electrolyte may be 0.1 to 2.0 M or 0.8 to 1.2 M. The dope solution may contain the arenide solution and a solvent for the electrolyte, and the supporting salt may be omitted. In this case, the ratio of the solvent in the electrolyte may be 10 to 70% by volume, 20 to 60% by volume, or 30 to 50% by volume.

[0027] In this step, the initial electrode is brought into contact with the doping solution. The temperature may be, for example, in the range of 0°C to 80°C, 10°C to 60°C, or 20°C to 40°C. This temperature is preferably near room temperature (20°C to 25°C). The time for which the initial electrode is brought into contact with the doping solution may be, for example, 12 hours or less, 6 hours or less, or 2 hours or less, from the viewpoint of shortening the processing time. The contact time may be 1 minute or more, 5 minutes or more, or 30 minutes or more, from the viewpoint of sufficient pre-doping of the metal ions. In this step, the amount of metal ions pre-doped into the initial electrode can be adjusted by appropriately changing the concentration of the doping solution, the pre-doping temperature, the pre-doping time, etc., depending on, for example, the size of the initial electrode and the amount of active material. Among these, the pre-doping amount can be adjusted relatively easily by adjusting the time for which the doping solution is brought into contact with the initial electrode. The doped electrode, which is the electrode after pre-doping, may be washed and dried as necessary. For washing, a solvent for the arene solution, a solvent for the electrolyte solution, or a combination of these may be used. In this process, simply by contacting the initial electrode containing the active material with the pre-doping solution, a chemical reaction occurs between the doping solution and the active material, allowing metal ions to be pre-doped into the initial electrode easily. In this process, only this electrode can be easily charged without using a metal lithium electrode or the like.

[0028] [electrode] The electrode of the present disclosure contains an active material having a redox potential of 2 V or more relative to lithium. This electrode may be an electrode (doped electrode) manufactured by the above-mentioned electrode manufacturing method. In this electrode, each of the components described in the electrode manufacturing method may be appropriately adopted. In this electrode, due to the aromatic hydrocarbon compound in a reduced state contained in the dope solution, a peak of the aromatic hydrocarbon compound different from the peak of the active material appears in the infrared absorption (IR) spectrum of the electrode. In the IR spectrum of this electrode, for example, a peak at 705 cm -1 More than 725cm -1 The following range and 760cm -1 More than 780cm -1A peak may appear in at least one of the following ranges, preferably both. Furthermore, this electrode is pre-doped with metal ions, and the active material is contained in a reduced state in which metal ions are inserted in excess. In this doped electrode, the active material may have a multi-stage redox potential, or may be contained in a state of a low potential below the lowest redox potential. The active material may have a composition that is unstable in air (e.g., Li2Mn2O4, etc.). When an active material with a composition that is unstable in air is synthesized and used to manufacture an electrode, the manufacturing process becomes complicated. However, in the present disclosure, an electrode containing an active material with such a composition can be manufactured simply by contacting the electrode with a doping solution, and therefore, the application of the technology of the present disclosure is highly significant. Specifically, the active material may be, for example, Li2Mn2O4 or Li 1.20 Mn 0.84 P 0.04 It may also be O2.

[0029] [Method of manufacturing an electricity storage device] The method for manufacturing an electricity storage device according to the present disclosure includes a cell manufacturing step of manufacturing a cell using, as a positive electrode, an electrode (doped electrode) manufactured by the above-described electrode manufacturing method.

[0030] (Cell manufacturing process) In this process, the doped electrode is used as a positive electrode, and an ion-conductive medium that conducts metal ions is inserted between the positive electrode and a negative electrode having a negative electrode active material. The positive electrode and the negative electrode may be disposed in a cell case. In this case, a separator may be disposed between the positive electrode and the negative electrode.

[0031] The negative electrode may be a known negative electrode used in lithium-ion secondary batteries, capacitors, etc. The negative electrode may be formed, for example, by closely adhering a negative electrode active material to a current collector. Alternatively, the negative electrode may be formed, for example, by mixing a negative electrode active material, a binder, and optionally a conductive material, adding an appropriate solvent to form a paste-like negative electrode mixture, applying it to the surface of a current collector, drying it, and compressing it as needed to increase electrode density. Examples of negative electrode active materials include inorganic compounds such as lithium, lithium alloys, and tin compounds; carbon materials capable of absorbing and releasing lithium ions; composite oxides containing multiple elements; and conductive polymers. Examples of carbon materials include cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, and carbon fibers. Examples of composite oxides include lithium-titanium composite oxides and lithium-vanadium composite oxides. Among these, carbon materials are preferred as negative electrode active materials from the standpoint of safety. When used in the cell fabrication process, the negative electrode active material preferably does not contain lithium, which serves as a carrier. In an energy storage device using a negative electrode active material that does not contain a carrier metal, when combined with a positive electrode whose initial discharge capacity is greater than its initial charge capacity, lithium ions, which acts as a carrier, are likely to be insufficient. Therefore, the application of the technology of the present disclosure is highly significant. From this perspective, carbon materials are suitable as negative electrode active materials. The conductive materials, binders, solvents, etc. used in the negative electrode can be those exemplified in the electrode (positive electrode) manufacturing method. For the negative electrode current collector, copper, nickel, stainless steel, titanium, aluminum, calcined carbon, conductive polymers, conductive glass, Al-Cd alloys, etc. can be used. For the purpose of improving adhesion, conductivity, and reduction resistance, copper or other materials whose surfaces have been treated with carbon, nickel, titanium, silver, etc. can also be used. The surfaces of these materials can also be oxidized. The shape of the current collector can be the same as that of the positive electrode.

[0032] The ion-conducting medium may be, for example, a non-aqueous electrolyte solution containing a supporting salt (supporting electrolyte) and an organic solvent. Examples of the supporting salt include the supporting salt of the electrolyte solution described in the pre-doping process. The concentration of the supporting salt is preferably 0.1 to 2.0 M, more preferably 0.8 to 1.2 M. Examples of the organic solvent that can be used include aprotic organic solvents. Examples of such organic solvents include carbonate-based compounds, nitrile-based compounds, sulfolane-based compounds, and ether-based compounds described in the pre-doping process. These may be used alone or in combination. In addition, nitrile-based solvents such as acetonitrile and propylnitrile, ionic liquids, gel electrolytes, etc. may also be used as the non-aqueous electrolyte solution. Alternatively, examples of the ion-conducting medium that can be used include solid ion-conducting polymers, polymer gels composed of polymers and supporting salts, inorganic solid electrolytes, mixed materials of organic polymer electrolytes and inorganic solid electrolytes, and inorganic solid powders bound by an organic binder.

[0033] The separator may have any composition that can withstand the range of use of the electricity storage device, and examples thereof include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and microporous films of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination.

[0034] [Energy storage devices] The electricity storage device of the present disclosure includes a positive electrode that is an electrode containing an active material, a negative electrode that contains a negative electrode active material, and an ion-conductive medium that is interposed between the positive electrode and the negative electrode and conducts metal ions. This electricity storage device may be an electricity storage device manufactured by the above-mentioned electricity storage device manufacturing method. In this electricity storage device, each of the components described in the electricity storage device manufacturing method may be appropriately adopted. In this electricity storage device, due to the reduced aromatic hydrocarbon compound contained in the dope solution, a peak of the aromatic hydrocarbon compound that is different from the peak of the active material appears in the infrared absorption (IR) spectrum of the electrode. This peak is preferably different from the peak of the component that constitutes the ion-conductive medium. In this electricity storage device, for example, a peak at 705 cm -1 More than 725cm -1 The following range and 760cm -1 More than 780cm -1 The active material may have a peak in at least one of the following ranges, preferably in both: When the power storage device is fully discharged, the active material is in a reduced state in which an excess of metal ions is inserted; and since the power storage device has electrodes pre-doped with metal ions, the active material is in a reduced state in which an excess of metal ions is inserted not only when the power storage device is fully discharged but also before use. The active material may have a multi-stage oxidation-reduction potential, and may be in a state of a low potential equal to or lower than the lowest oxidation-reduction potential before use or when the power storage device is fully discharged.

[0035] The shape of this electricity storage device is not particularly limited, and examples thereof include coin-type, button-type, sheet-type, laminated-type, cylindrical, flat, and rectangular types. The device may also be applied to large devices used in electric vehicles and the like. FIG. 1 is a schematic diagram showing an example of an electricity storage device 20 according to the above-described embodiment. The electricity storage device 20 includes a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material and disposed at the bottom of the battery case 21, a negative electrode 23 having a negative electrode active material and disposed opposite the positive electrode 22 with a separator 24 interposed therebetween, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed at the opening of the battery case 21 and sealing the battery case 21 via the gasket 25. In the electricity storage device 20, the space between the positive electrode 22 and the negative electrode 23 is filled with an ion-conducting medium 27 containing an alkali metal salt (lithium salt) dissolved therein. The positive electrode 22 is pre-doped with lithium ions in a pre-doping process.

[0036] The electrode manufacturing method, electricity storage device manufacturing method, electrode, and electricity storage device described above in detail can further increase the reversible capacity of the electricity storage device. For example, the reversible capacity can be increased by about 1.2 to 2.5 times compared to when pre-doping is not performed. The reason for this effect is presumed to be as follows. For example, a doping solution containing a reduced aromatic hydrocarbon compound and metal ions acts on a predetermined electrode simply by contacting the electrode with the electrode, thereby pre-doping the electrode with metal ions. It is presumed that using an electrode pre-doped with metal ions in this way as the positive electrode of an electricity storage device can eliminate the shortage of metal ions necessary for the discharge reaction, allowing the discharge reaction to proceed sufficiently, and further increasing the reversible capacity.

[0037] In addition, Mn-based positive electrodes such as LiMn2O4 with a spinel structure have a larger initial discharge capacity than the initial charge capacity. When using lithium metal as the negative electrode, the initial charge capacity of LiMn2O4 is approximately 140 mAh / g, while the initial discharge capacity is 280 mAh / g. During the initial charge, LiMn2O4 is converted from LiMn2O4 to Li + +Mn2O4+e -The reaction proceeds, while the reaction proceeds at around 4V during the first discharge. + +Mn2O4+e - → In addition to LiMn2O4, LiMn2O4+Li at around 2.8V + +e - → As the Li2Mn2O4 reaction progresses, the initial discharge capacity is greater than the initial charge capacity. However, because Li2Mn2O4 is unstable in air, when synthesized LiMn2O4 is used as a positive electrode, a capacity of only 140 mAh / g was achieved. However, in this disclosure, by using a chemical doping method using a metal arenide such as lithium naphthalenide to introduce carrier metal ions into the positive electrode during electrode fabrication, it is inferred that the maximum capacity that the positive electrode can exhibit can be utilized. From the above, it is inferred that the technology disclosed herein is highly significant when applied to Mn-based positive electrodes such as lithium manganese composite oxides.

[0038] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0039] For example, in the above-described embodiment, an electrode manufacturing method including a metal ion pre-doping step has been described, but it may also be a method for pre-doping an electrode. That is, in this electrode pre-doping method, an initial electrode containing an active material having a redox potential of 2 V or more relative to a lithium reference potential is contacted with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions, thereby pre-doping the initial electrode with metal ions. In this pre-doping method, if the aspect described in the above-described embodiment is adopted, the same effect as that can be obtained.

[0040] The present disclosure may be any of the following [1] to

[13] . [1] A method for manufacturing an electrode of an electricity storage device, comprising: a doping step of contacting an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium potential with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions to pre-dope the initial electrode with the metal ions to obtain a doped electrode; Electrode manufacturing method. [2] The active material has an initial oxidation capacity greater than a subsequent initial reduction capacity. [1] A method for manufacturing the electrode described in [1]. [3] the dope solution includes an arenide solution containing the aromatic hydrocarbon compound in a reduced state and the metal ions, and an electrolyte solution; A method for producing the electrode according to [1] or [2]. [4] The active material is a lithium manganese composite oxide. The method for producing an electrode according to any one of [1] to [3]. [5] The dope solution has a ratio of the electrolyte solution of 30% by volume or more and 50% by volume or less. [3] A method for manufacturing an electrode according to the present invention. [6] The solvent of the arenide solution is an ether-based compound. A method for producing the electrode according to [3] or [4]. [7] The solvent of the electrolyte solution is a carbonate-based compound. The method for producing an electrode according to any one of [3] to [5]. [8] The aromatic hydrocarbon compound is one or more of the compounds of formula (1) and formula (2). The method for producing an electrode according to any one of [1] to [7]. [C1] [9] a cell fabrication step in which the electrode manufactured by the electrode manufacturing method according to any one of [1] to [8] is used as a positive electrode, and an ion-conductive medium that conducts the metal ions is placed between the positive electrode and a negative electrode containing a negative electrode active material; A method for manufacturing an electricity storage device comprising:

[10] The negative electrode active material is a carbon material. [9] A method for manufacturing the electricity storage device according to [9].

[11] A method for pre-doping an electrode, comprising: a doping step of contacting an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium potential with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions to pre-dope the initial electrode with the metal ions; Pre-dope method.

[12] An electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium reference potential, a peak of an aromatic hydrocarbon compound different from a peak of the active material appears in the infrared absorption (IR) spectrum of the electrode; The active material contains metal ions in an excess amount intercalated in a reduced state. electrode.

[13] An electricity storage device comprising: a positive electrode that is an electrode containing a substance having an active oxidation-reduction potential of 2 V or more relative to a lithium reference potential; a negative electrode that contains a negative electrode active material; and an ion-conductive medium that is interposed between the positive electrode and the negative electrode and conducts metal ions, a peak of an aromatic hydrocarbon compound different from a peak of the active material appears in the infrared absorption (IR) spectrum of the electrode; When the electricity storage device is completely discharged, the active material is in a reduced state in which the metal ions are excessively inserted. Energy storage device. [Example]

[0041] Specific examples of fabricating electrodes and electricity storage devices will be described below as experimental examples, with Experimental Examples 1 to 5 corresponding to working examples and Experimental Example 6 corresponding to a comparative example.

[0042] [Experimental Example 1] First, we synthesized a phosphorus-containing lithium manganese composite oxide (LMPO) as a positive electrode active material. Specifically, the raw materials, disordered rock salt LiMnO2, LiF, and Li3PO4, were mixed in an agate pot in an appropriate ratio, and then sealed in a zirconia pot together with zirconia balls. The mixture was then ground in a planetary ball mill at 600 rpm for 36 hours to produce Li 0.90 Mn 0.84 P 0.04 LMPO represented by O2 was obtained. The obtained LMPO had a disordered rock salt structure. 70% by mass of the obtained positive electrode active material, 25% by mass of Ketjen black (ECP-600 manufactured by Mitsubishi Chemical) as a conductive material, and 5% by mass of polytetrafluoroethylene (F-104 manufactured by Daikin Industries) as a binder were mixed and crushed in a mixer to prepare a positive electrode composite by dry processing. The obtained positive electrode composite was formed into a circular pellet with a diameter of 10 mm, placed on a circular aluminum expanded metal with a diameter of 15 mm, and pressed to obtain initial positive electrode A (initial electrode). Furthermore, 80% by mass of the above-mentioned positive electrode active material, 10% by mass of acetylene black (TB5500 manufactured by Tokai Carbon Co., Ltd.) as a conductive material, and 5% by mass of polyvinylidene fluoride as a binder were mixed together, and the mixture was made into a paste using N-methylpyrrolidone (NMP) as a solvent. This was then coated onto aluminum foil with a gap of 50 μm and dried at 150° C. to obtain an initial positive electrode B (initial electrode).

[0043] In a glove box under an Ar atmosphere, naphthalene was dissolved in tetrahydrofuran (THF) solvent to a concentration of 1.0 mol / L, followed by the addition of 1.0 mol / L lithium metal and stirring to prepare a dark green lithium naphthalenide solution in THF. LiPF6 was also dissolved in an electrolyte solvent consisting of 30 vol% ethylene carbonate (EC), 40 vol% dimethyl carbonate (DMC), and 30 vol% ethyl methyl carbonate (EMC) to a concentration of 1 mol / L to prepare the electrolyte. The electrolyte was then mixed at a ratio of 50 vol% to 50 vol% to obtain a brown doped solution.

[0044] The initial positive electrodes A and B were immersed in the doping solution for 10 minutes to obtain doped positive electrodes A and B (doped electrodes). After that, the doped positive electrodes A and B were collected and washed twice with THF. Then, coin cells were fabricated in a glove box without air exposure. The active material composition of the doped positive electrodes A and B was Li 1.20 Mn 0.84 P 0.04 The estimated value was O2. Two coin cells were fabricated: a half cell using doped positive electrode A and metallic Li as the counter electrode, and a full cell using doped positive electrode B and a graphite-based negative electrode as the counter electrode. The graphite-based negative electrode of the full cell was made by mixing 98% by mass of coated spherical natural graphite and 2% by mass of binder, forming a slurry using N-methylpyrrolidone (NMP) as the solvent, coating the mixture on copper foil with a 50 μm gap, and drying overnight at 120 °C. These coin cells used an electrolyte prepared similarly to the electrolyte in the doped solution as the ion-conducting medium.

[0045] Constant current charging and discharging was carried out for each of the half-cell and full-cell described above. Constant current charging and discharging started with charging, and the potential range was 4.8 to 1.5 V relative to the lithium potential, and the current value was 20 mA / g.

[0046] [Experimental Examples 2-6] Experimental Example 2 was carried out in the same manner as Experimental Example 1, except that the immersion time in the dope solution was 20 minutes. Experimental Example 3 was carried out in the same manner as Experimental Example 1, except that the immersion time in the dope solution was 30 minutes. Experimental Example 4 was carried out in the same manner as Experimental Example 1, except that the immersion time in the dope solution was 60 minutes. Experimental Example 5 was carried out in the same manner as Experimental Example 1, except that the immersion time in the dope solution was 90 minutes. Experimental Example 6 was carried out in the same manner as Experimental Example 1, except that the immersion in the dope solution was omitted.

[0047] [Experimental Results] Figure 2 shows the charge / discharge curves of the half-cells of Experimental Examples 1 to 6. Table 1 also summarizes the open circuit voltage (OCV) [V] before the start of charge / discharge, the initial charge capacity [mAh / g], the initial discharge capacity [mAh / g], and the initial charge / discharge efficiency [%], which were obtained from Figure 2. The initial charge / discharge efficiency was calculated using the formula: initial charge / discharge efficiency [%] = initial discharge capacity [mAh / g] / initial charge capacity [mAh / g] × 100.

[0048] [Table 1]

[0049] In the half cell of Experimental Example 6 in which pre-doping was not performed, the open circuit voltage before the start of charge and discharge was as high as 3.17 V. On the other hand, in the half cells of Experimental Examples 1 to 5 in which pre-doping was performed, the open circuit voltage before the start of charge and discharge decreased as the pre-doping time was increased, and in Experimental Example 5 in which pre-doping was performed for 90 minutes, it decreased to 2.45 V. This is equivalent to the situation in which the positive electrode was discharged using Li as the counter electrode, and it was inferred that this indicates that Li was introduced into the positive electrode by pre-doping.

[0050] The half-cell of Experimental Example 6, which was not pre-doped, exhibited high capacities, with an initial charge capacity of 254 mAh / g and an initial discharge capacity of 346 mAh / g. When the positive electrode of Experimental Example 6 (i.e., the initial electrode) is combined with a graphite negative electrode or the like to form a full cell, considering that the charge / discharge efficiency of the graphite negative electrode is approximately 100 to 90%, it is necessary to adjust the charge / discharge conditions so that the initial discharge capacity is approximately 100 to 90% of the initial charge capacity. As a result, it is presumed that the high discharge capacity of the positive electrode of Experimental Example 6 cannot be fully utilized. On the other hand, the half-cells of Experimental Examples 1 to 5, which were pre-doped, had discharge capacities equivalent to those of the half-cell of Experimental Example 6, and the initial discharge capacity was 100 to 90% or close to this value of the initial charge capacity, so that the high discharge capacity could be fully utilized, and it is presumed that a high reversible capacity can be realized.

[0051] Figure 3 shows the charge / discharge curves of the full cells of Experimental Examples 3, 5, and 6. As shown in Figure 3, Experimental Examples 3 and 5, in which pre-doping was performed, had a higher reversible capacity than Experimental Example 6, in which pre-doping was omitted, and the same results as those inferred from the half-cell were obtained. From this, it was inferred that in Experimental Examples 1 to 5, chemical Li pre-doping eliminated the difference in the initial charge / discharge efficiency with the graphite negative electrode, and brought about the effect of maximizing the discharge capacity of the positive electrode.

[0052] Figure 4 shows the IR spectra of the doped positive electrodes (washed twice with THF) of Experimental Examples 3 and 6. The IR spectra were measured using an infrared spectrometer (NICOLET IS20 manufactured by Thermo) by the reflection method. For reference, Figure 4 also shows the IR spectrum of naphthalene. As shown in Figure 4, in Experimental Example 3, where pre-doping was performed using a doping solution containing lithium naphthalenide, a peak (770 cm) derived from naphthalene was observed, which was not observed in Experimental Example 6, where pre-doping was omitted. -1 Nearby peaks and 715cm -1 A shoulder peak near the peak was observed. This indicates that whether pre-doping was performed using a doping solution containing an arene such as naphthalenide can be determined by whether arenes are observed in the IR spectrum. It is also inferred that whether pre-doping with metal ions such as lithium ions was performed can be determined from the amount of metal (e.g., Li amount) in the positive electrode when the energy storage device was fully discharged. Specifically, it was inferred that if the device was in a reduced state in which an excess of metal (e.g., Li) was inserted relative to the composition, it could be determined that pre-doping with metal ions was performed. [Industrial Applicability]

[0053] The present disclosure is applicable to the battery industry. [Explanation of symbols]

[0054] 20 non-aqueous secondary battery, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 ion conductive medium.

Claims

1. A method for manufacturing an electrode of an electricity storage device, comprising: a doping step of contacting an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium potential with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions to pre-dope the initial electrode with the metal ions to obtain a doped electrode; Electrode manufacturing method.

2. The active material has an initial oxidation capacity greater than a subsequent initial reduction capacity. A method for manufacturing the electrode according to claim 1 .

3. the dope solution includes an arenide solution containing the aromatic hydrocarbon compound in a reduced state and the metal ions, and an electrolyte solution; The method for producing the electrode according to claim 1 or 2.

4. The active material is a lithium manganese composite oxide. The method for producing the electrode according to claim 1 or 2.

5. The method for manufacturing an electrode according to claim 3, wherein the doping solution has one or more of the following characteristics (a) to (c): (a) The dope solution contains the electrolyte at a ratio of 30% by volume to 50% by volume. (b) The solvent of the arenide solution is an ether-based compound. (c) The solvent of the electrolyte is a carbonate-based compound.

6. The method for producing an electrode according to claim 1 or 2, wherein the aromatic hydrocarbon compound is one or more of compounds represented by formula (1) and formula (2). 【Chemical 1】

7. a cell fabrication step of using the electrode manufactured by the electrode manufacturing method according to claim 1 or 2 as a positive electrode and inserting an ion-conductive medium that conducts the metal ions between the positive electrode and a negative electrode containing a negative electrode active material; A method for manufacturing an electricity storage device comprising:

8. A method for pre-doping an electrode, comprising: a doping step of contacting an initial electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium potential with a doping solution containing a reduced aromatic hydrocarbon compound and metal ions to pre-dope the initial electrode with the metal ions; Pre-dope method.

9. An electricity storage device comprising: a positive electrode that is an electrode containing an active material having an oxidation-reduction potential of 2 V or more relative to a lithium reference potential; a negative electrode that contains a negative electrode active material; and an ion-conductive medium that is interposed between the positive electrode and the negative electrode and conducts metal ions, a peak of an aromatic hydrocarbon compound different from a peak of the active material appears in the infrared absorption (IR) spectrum of the electrode; When the electricity storage device is completely discharged, the active material is in a reduced state in which the metal ions are excessively inserted. Energy storage device.

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