JP2021128848A - Electrode active substance, power storage device, and method for manufacturing electrode active substance - Google Patents

Abstract

To provide a novel electrode active substance which enables the further enhancement in charge/discharge characteristic, a power storage device and a method for manufacturing such an electrode active substance.SOLUTION: A power storage device comprises a positive electrode, a negative electrode, and an ion conductive medium for carrier ion conduction. An electrode active substance included in the negative electrode is a mixed salt structure which includes: an organic skeleton layer containing all of aromatic dicarboxylic acid anions of three kinds of structures of Ph, Bph and Naph; and an alkali metal element layer in which an alkali metal element is coordinated to oxygen included in carboxylic acid of the organic skeleton layer to form a skeleton. Supposing that Ph included in the mixed salt structure is Xp pt.mass, and Bph is Xb pt.mass, and Naph is Xn(Xp+Xb+Xn=1) pt.mass, they may be arranged to satisfy: 0.01≤Xp≤0.3; 0.01≤Xb≤0.34; and 0.36≤Xn≤0.98.SELECTED DRAWING: Figure 4

Description

This specification discloses an electrode active material, a power storage device, and a method for producing the electrode active material.

Conventionally, as a power storage device such as a lithium ion secondary battery, an alkali metal element is coordinated with an organic skeleton layer containing an aromatic compound which is a dicarboxylic acid anion having an aromatic ring structure and oxygen contained in the carboxylic acid anion. A layered structure having an alkali metal element layer forming a skeleton is proposed as a negative electrode active material (see, for example, Patent Document 1). Although the layered structure as the negative electrode active material does not have conductivity, it is difficult to dissolve in a non-aqueous electrolyte solution, and by maintaining the crystal structure, the stability of charge / discharge cycle characteristics can be further enhanced.

Japanese Unexamined Patent Publication No. 2012-221754

However, in the above-mentioned power storage device of Patent Document 1, although the stability of the cycle characteristics can be further improved, it has been required to further improve the charge / discharge characteristics such as the battery capacity, the discharge potential and the polarization in the charge / discharge. ..

The present disclosure has been made in view of such problems, and an object of the present disclosure is to provide a novel electrode active material, a power storage device, and a method for producing an electrode active material, which can further improve charge / discharge characteristics. ..

As a result of diligent research to achieve the above-mentioned object, it is assumed that the present inventors prepare a structure within a predetermined compounding ratio range using a preparation solution containing three kinds of aromatic dicarboxylic acid metal salts. It has been found that a novel electrode active material capable of further improving charge / discharge characteristics can be produced, and the present disclosure has been completed.

That is, the electrode active material disclosed in the present specification is
An electrode active material for power storage devices
An organic skeleton layer containing all of the aromatic dicarboxylic acid anions having three types of structures represented by the formulas (1) to (3) and an alkali metal in the oxygen contained in the carboxylic acid of the organic skeleton layer. It is a mixed salt structure including an alkali metal element layer in which elements are coordinated to form a skeleton.
Pearson phase relationship between the electrode active material and a single layered structure represented by the formulas (4) to (6) when the XRD spectrum is measured in the range of 2θ of 5 ° or more and 60 ° or less using CuKα rays. When the numbers are Rp in the formula (4), Rb in the formula (5), and Rn in the formula (6), 0.38 ≦ Rp ≦ 0.49, 0.37 ≦ Rb ≦ 0.56, 0.75 By satisfying all of ≦ Rn ≦ 0.90 and occluding and releasing alkali metal ions, electric energy is stored and output.

Alternatively, the electrode active material disclosed herein is:
An electrode active material for power storage devices
An organic skeleton layer containing all of the aromatic dicarboxylic acid anions having three types of structures represented by the formulas (1) to (3) and an alkali metal in the oxygen contained in the carboxylic acid of the organic skeleton layer. It is a mixed salt structure including an alkali metal element layer in which elements are coordinated to form a skeleton.
0.01 when the mass part of the formula (4) contained in the mixed salt structure is Xp, the mass part of the formula (5) is Xb, and the mass part of the formula (6) is Xn (Xp + Xb + Xn = 1). Whether ≤Xp≤0.3, 0.01≤Xb≤0.34, 0.36≤Xn≤0.98 are satisfied.
Alternatively, electric energy is stored and output by satisfying the mathematical formula (1) and storing and releasing alkali metal ions.

The power storage device disclosed in this specification is
The negative electrode containing the above-mentioned electrode active material and the negative electrode
Positive electrode A positive electrode containing an active material and a positive electrode
An ion conduction medium that is interposed between the positive electrode and the negative electrode and conducts carrier ions,
It is equipped with.

The method for producing the electrode active material disclosed in the present specification is as follows.
Using a prepared solution prepared by dissolving an aromatic dicarboxylic acid anion having three types of structures represented by the formulas (1) to (3) and an alkali metal cation, the aromatic dicarboxylic acid anion is contained. A precipitation step of precipitating a mixed salt structure including an organic skeleton layer and an alkali metal element layer in which an alkali metal element coordinates with oxygen contained in the carboxylic acid anion of the organic skeleton layer to form a skeleton is included.
In the precipitation step, when the mass part of the formula (4) is Xp, the mass part of the formula (5) is Xb, and the mass part of the formula (6) is Xn (Xp + Xb + Xn = 1) as the raw material of the mixed salt structure. , 0.01 ≦ Xp ≦ 0.3, 0.01 ≦ Xb ≦ 0.34, 0.36 ≦ Xn ≦ 0.98.

In the present disclosure, it is possible to provide a novel electrode active material, a power storage device, and a method for producing the electrode active material, which can further improve the charge / discharge characteristics. In this method for producing an electrode active material, a power storage device, and an electrode active material, a mixed salt structure having a novel structure can be prepared by using a prepared solution in which a plurality of types of aromatic dicarboxylic acid anions are appropriately mixed. Further, in a specific compounding region, due to the synergistic effect of the three kinds of aromatic dicarboxylic acid alkali metal salts contained therein, more suitable charge / discharge characteristics such as capacity, discharge potential, and polarization are exhibited as compared with those of each of them alone. It is presumed to be.

Explanatory drawing of the compound structure of the layered structure of each aromatic dicarboxylic acid dilithium. Three-component composition diagram of each aromatic dicarboxylic acid dilithium structure. Three-component composition diagram of each aromatic dicarboxylic acid dilithium structure. The schematic diagram which shows an example of the power storage device 20. XRD pattern of each experimental example. Results of examination of the presence or absence of alcohol and the heating temperature. Charge / discharge measurement results of Experimental Example 13. Three-component composition distribution map including the measurement results of each experimental example. FIG. 5 is a relationship diagram showing the degree of similarity between the XRD spectrum and the X20 spectrum, which are the sum of Ph, Naph, and Bph at each ratio in the three-component composition diagram.

(Electrode active material)
The electrode active material disclosed in the present specification is an electrode active material for a power storage device. The electrode active material stores and outputs electrical energy by occluding and releasing alkali metal ions, which are carriers. Examples of the alkali metal ion as a carrier include one or more of Li ion, Na ion, K ion and the like. This electrode active material comprises an organic skeleton layer containing three kinds of aromatic dicarboxylic acid anions and an alkali metal element layer in which an alkali metal element coordinates with oxygen contained in the carboxylic acid of the organic skeleton layer to form a skeleton. It is a mixed salt structure provided. In this mixed salt structure, electric energy is stored and output by occluding and releasing alkali metal ions.

This electrode active material is used for an organic skeleton layer containing all of aromatic dicarboxylic acid anions having three types of structures represented by the formulas (1) to (3), Ph, Bph, and Naph, and the carboxylic acid of the organic skeleton layer. It is a mixed salt structure including an alkali metal element layer in which an alkali metal element is coordinated with the contained oxygen to form a skeleton. The aromatic dicarboxylic acid anion includes a terephthalic acid anion (formula (1): Ph), a 4,4'-biphenyldicarboxylic acid anion (formula (2): Bph), and a 2,6-naphthalenedicarboxylic acid anion (formula (3)). ): Naph). This mixed salt structure includes the structure of the layered structure represented by the formulas (4) to (6). In formulas (4) to (6), A is an alkali metal. These aromatic compounds may have substituents and heteroatoms in this structure. Specifically, instead of the hydrogen of the aromatic compound, a halogen, a chain or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group and an acyl group. , An amide group or a hydroxyl group may be used as a substituent, or a structure in which nitrogen, sulfur or oxygen is introduced instead of the carbon of the aromatic compound may be used.

Examples of the alkali metal contained in the alkali metal element layer include lithium, sodium and potassium, of which lithium is preferable. The metal ions that are carriers of the power storage device and are occluded and released in the electrode active material by charging and discharging may be of a different type from the alkali metal element contained in the alkali metal element layer, or may be of the same type. Also, for example, it can be any one or more of Li, Na, K and the like. Further, since the alkali metal element contained in the alkali metal element layer forms the skeleton of the mixed salt structure, it is presumed that the alkali metal element is not involved in the ion movement accompanying charge / discharge, that is, it is not occluded and released during charge / discharge. NS. Those While functioning as a site, the alkali metal element layer which functions as a storage site for metal ions functioning as carriers (alkali metal ion adsorption site) ^- in the energy storage mechanism, the organic skeleton layer of mixed salt structure redox (e) it is conceivable that.

Here, an example of a layered structure composed of a single aromatic dicarboxylic acid dilithium alkali metal salt will be described. FIG. 1 is an explanatory diagram of the compound structure of each aromatic dicarboxylic acid dilithium alkali metal salt, FIG. 1A is dilithium terephthalate, FIG. 1B is dilithium 4,4'-biphenyldicarboxylic acid, and FIG. 1C is 2,6-. Dilithium naphthalenedicarboxylic acid. FIG. 1 shows the lattice constant of each layered structure and the crystal structure from the ac plane and the bc plane. In dilithium terephthalate, dilithium 4,4'-biphenyldicarboxylic acid and dilithium 2,6-naphthalenedicarboxylic acid, the lattice constant of each crystal is the a-axis corresponding to the length of the aromatic skeleton that can be confirmed from the a-c plane. Is changed, whereas the lattice constant of the bc plane is almost the same. Therefore, by synthesizing a layered structure from a prepared solution in which two or more kinds of aromatic dicarboxylic acids and an alkali metal are dissolved, an organic-inorganic laminated structure of each compound observed from the ab plane is formed. While forming an organic layer packed by the π stacking interaction of each organic skeleton on the bc plane, it is possible to form a crystal sharing an inorganic layer portion composed _{of a LiO 4 tetrahedron of dilithium carboxylate.} It is presumed to be.

In the compounding ratio contained in the mixed salt structure, the electrode active material has a mass portion of Ph (formula (4)) of Xp, a mass portion of Bph (formula (5)) of Xb, and Naph (formula (6)). When the mass part of is Xn, Xp + Xb + Xn = 1 is satisfied, and 0.01 ≦ Xp ≦ 0.3, 0.01 ≦ Xb ≦ 0.34, and 0.36 ≦ Xn ≦ 0.98 are satisfied. good. FIG. 2 is a three-component composition diagram of each aromatic dicarboxylic acid dilithium structure. The range specified here corresponds to the range of the alternate long and short dash line in FIG. When the compounding ratio satisfies any of these ranges, the charge / discharge characteristics can be further improved by the synergistic effect of the three kinds of aromatic dicarboxylic acid salts. At this time, it is more preferable that the mixed salt structure satisfies 0.01 ≦ Xp ≦ 0.20, 0.05 ≦ Xb ≦ 0.30, 0.60 ≦ Xn ≦ 0.80. This defined range corresponds to the range of the dotted line in FIG. When the compounding ratio satisfies all of these, the charge / discharge characteristics can be further improved.

Further, in the compounding ratio contained in the mixed salt structure, the electrode active material has a mass portion of Ph (formula (4)) of Xp, a mass portion of Bph (formula (5)) of Xb, and Naph (formula (6)). )) When the mass part of) is Xn (Xp + Xb + Xn = 1), the equation (1) may be satisfied. FIG. 3 is a three-component composition diagram of each aromatic dicarboxylic acid dilithium structure. The range defined by the mathematical formula (1) corresponds to the range of the alternate long and short dash line in FIG. When the compounding ratio satisfies this formula (1), the charge / discharge characteristics can be further improved by the synergistic effect of the three kinds of aromatic dicarboxylic acid salts. Further, at this time, it is preferable that the mixed salt structure satisfies the mathematical formula (2). The range defined by the mathematical formula (2) corresponds to the range of the dotted line in FIG. When the compounding ratio satisfies the formula (2), the charge / discharge characteristics can be further improved. Further, it is more preferable that the mixed salt structure satisfies the formulas (3) to (5). The range defined by the formulas (3) to (5) corresponds to the range shaded by the solid line in FIG. When the compounding ratio satisfies the formulas (3) to (5), the charge / discharge characteristics can be improved most.

This electrode active material uses CuKα rays to obtain an XRD spectrum of this mixed salt structure and a single layered structure represented by the formulas (4) to (6) in a range of 2θ of 5 ° or more and 60 ° or less. When the Pearson correlation coefficient at the time of measurement is Rp in equation (4), Rb in equation (5), and Rn in equation (6), 0.38 ≦ Rp ≦ 0.49, 0.37 ≦ Rb ≦ Both 0.56 and 0.75 ≦ Rn ≦ 0.90 may be satisfied. When the Pearson correlation coefficient satisfies all of these, the charge / discharge characteristics can be further improved by the synergistic effect of the three kinds of aromatic dicarboxylic acid salts. Here, the Pearson correlation coefficient will be described. The Pearson correlation coefficient is a coefficient representing the similarity between two active materials and can be obtained from the XRD spectrum. This Pearson correlation coefficient shall be obtained using all the spectral values in the range where 2θ is 5 to 60 °. When the XRD spectra of the active material X and the active material Y are xi and yi, respectively, the Pearson correlation coefficient R (X, Y) is defined by the equation (6). R (X, Y) takes a value between -1 and 1, and can be used as an index showing the similarity between the XRD spectra of X and Y. If there is a perfect positive correlation between the two, then R = 1, if there is a perfect negative correlation, then R = -1, and if there is no correlation, then R = 0. There is a correlation between the Pearson correlation coefficient of the XRD spectrum and the battery characteristics of the active material. The Pearson correlation coefficient that compares the XRD spectrum of Ph alone with respect to the XRD spectrum of the active material in which Ph, Naph, and Bph are mixed in an arbitrary ratio is Rp, and the Pearson correlation coefficient that compares the XRD spectrum of Naph alone is Rn. The Pearson correlation coefficient comparing the XRD spectrum of Bph alone can be used as Rb, and the Pearson correlation coefficient between the single layered structure of Ph, Naph, and Bph and the mixed salt structure can be used as an index. ..

(Manufacturing method of electrode active material)
The method for producing an electrode active material of the present disclosure is the above-mentioned method for producing an electrode active material for a power storage device. This production method may include a solution preparation step and a precipitation step. The solution preparation step may be omitted as the preparation solution is prepared separately.

In the solution preparation step, a preparation solution in which three kinds of aromatic dicarboxylic acids (Ph, Bph, Naph) and an alkali metal cation are dissolved is prepared. The solvent of this preparation solution is not particularly limited, but may be an aqueous solvent or an organic solvent, but water is preferable. Examples of the organic solvent include alcohols such as methanol and ethanol. Alcohol is not considered to affect the structure of the mixed salt structure even if it is not contained in the solvent. Therefore, it is not necessary to use alcohol as a solvent in this step. In this step, it is preferable to prepare a preparation solution in which the total concentration of the aromatic dicarboxylic acid anion is 0.1 mol / L or more, more preferably 0.2 mol / L or more. Further, in this step, it is preferable to prepare a preparation solution in which the concentration of the aromatic dicarboxylic acid anion is 5 mol / L or less. In such a concentration range, it is easier to carry out the precipitation step of the next step. In this step, it is preferable to prepare a preparation solution containing one or more alkali metal cations among lithium, sodium and potassium. In this step, for example, it is preferable to obtain a prepared solution having a molar ratio B / A of more than 2.0, which is the number of moles B (mol) of the alkali metal cation with respect to the number A (mol) of the aromatic dicarboxylic acid anion. It is more preferable to obtain a preparation solution having a B / A of 2.2 or more. By making the alkali metal cation excessive in this way, the resistance of the electrode for the power storage device can be further reduced, which is preferable. This molar ratio B / A may be 2.5 or more. Further, the molar ratio B / A may be 3.0 or less.

Further, in this step, Ph, Naph, and Bph may be blended in the blending ratio shown in the above-mentioned electrode active material. For example, when the mass part of Ph is Xp, the mass part of Bph is Xb, and the mass part of Naph is Xn, Xp + Xb + Xn = 1 is satisfied, and 0.01 ≦ Xp ≦ 0.3 and 0.01 ≦ Xb ≦ 0. It may satisfy .34 and 0.36 ≦ Xn ≦ 0.98. Further, the blending ratio of the raw materials more preferably satisfies the ranges of 0.01 ≦ Xp ≦ 0.20, 0.05 ≦ Xb ≦ 0.30, and 0.60 ≦ Xn ≦ 0.80. Alternatively, it may have the above-mentioned mathematical formula (1), may satisfy the mathematical formula (2), or may satisfy any of the mathematical formulas (3) to (5).

In the precipitation step, the prepared solution prepared in the above solution preparation step is used, and the alkali metal element is coordinated with the organic skeleton layer containing three kinds of aromatic dicarboxylic acid anions and the oxygen contained in the carboxylic acid anion of the organic skeleton layer. A mixed salt structure including an alkali metal element layer forming a skeleton is precipitated. In this step, the mixed salt structure may be precipitated by a solution mixing method in which the prepared solution is stirred and then the solvent is removed. Further, the mixed salt structure may be precipitated by a spray drying method in which the prepared solution is spray-dried using a spray-drying device. This method is preferable because the mixed salt structure can be precipitated in a shorter time. The spray drying may be performed by a spray dryer. The spray drying conditions may be appropriately adjusted depending on, for example, the scale of the apparatus and the amount of the electrode active material to be produced. In this step, the drying temperature may be, for example, heated to room temperature or higher, for example, 40 ° C. or higher, preferably the boiling point of the solvent or higher, and preferably 100 ° C. or higher and 330 ° C. or lower. At 100 ° C. or higher, the solvent can be sufficiently removed, and at 330 ° C. or lower, energy consumption can be further reduced, which is preferable. The drying temperature is more preferably 150 ° C. or higher, more preferably 180 ° C. or higher, and may be 200 ° C. or higher.

(Power storage device)
The power storage device disclosed in the present specification includes a negative electrode containing the above-mentioned electrode active material, a positive electrode containing the positive electrode active material, and an ion conduction medium that is interposed between the positive electrode and the negative electrode and conducts carrier ions. There is. This power storage device may be, for example, an electric double layer capacitor, a hybrid capacitor, a pseudo electric double layer capacitor, a lithium ion secondary battery, or the like. The positive electrode may contain a positive electrode active material that occludes and releases carrier ions. The negative electrode may contain the above-mentioned electrode active material that occludes and releases alkali metal ions as carriers. Further, the ion conduction medium conducts carrier ions (either cations or anions). Here, a power storage device in which the carrier of the negative electrode is lithium ion will be mainly described.

The negative electrode contains the above-mentioned electrode active material. Since the potential of the above-mentioned electrode active material is about 1.0 to 1.5 V based on the lithium metal, it is preferable to use the negative electrode active material. For the negative electrode, the above-mentioned electrode active material, conductive material, and binder are mixed, and an appropriate solvent is added to form a paste-like negative electrode mixture, which is applied and dried on the surface of the current collector, and if necessary. It may be formed by compression in order to increase the electrode density. In this negative electrode, it is preferable that the electrode active material is contained as much as possible, and for example, it may be contained in the negative electrode mixture in the range of 60% by mass or more and 95% by mass or less. Conductive materials include, for example, graphite such as natural graphite (scaly graphite, scaly graphite) and artificial graphite, acetylene black, carbon black, Ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, etc.). One type or a mixture of two or more types such as silver, gold, etc. can be used. Among these, carbon black and acetylene black are preferable as the conductive material from the viewpoint of electron conductivity and coatability. The binder plays a role of binding the active material particles and the conductive material particles, and is, for example, a fluororesin such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, or polypropylene. Thermoplastic resins such as polyethylene, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Further, an aqueous dispersion of cellulose-based binder or styrene-butadiene rubber (SBR), which is an aqueous binder, can also be used. Examples of the coating method include roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater and the like, and any of these can be used to obtain an arbitrary thickness and shape. As the current collector, aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass and the like can be used. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous body, foam, and fiber group forming body. As the thickness of the current collector, for example, one having a thickness of 1 to 500 μm is used.

As the positive electrode, a known positive electrode used for a capacitor, a lithium ion capacitor, or the like may be used. The positive electrode may contain, for example, a carbon material as the positive electrode active material. The carbon material is not particularly limited, but for example, activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, etc. Examples include polyacenes. Of these, activated carbons showing a high specific surface area are preferable. Activated carbon as a carbon material preferably has a specific surface area of 1000 m ² / g or more, and more preferably 1500 m ² / g or more. When the specific surface area is 1000 m ² / g or more, the discharge capacity can be further increased. The specific surface area of this activated carbon ^{is preferably 3000 m 2} / g or less, and ^{more preferably 2000 m 2} / g or less, from the viewpoint of ease of production. It is considered that at the positive electrode, at least one of the anion and the cation contained in the ion conduction medium is adsorbed and desorbed to store electricity, but further, at least one of the anion and the cation contained in the ion conduction medium is inserted and desorbed. It may be used to store electricity.

Alternatively, the positive electrode may be a positive electrode used in a general lithium ion secondary battery. In this case, as the positive electrode active material, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used. Specifically, _{transition metal sulfides such as TiS 2} , TiS ₃ , MoS ₃ , and FeS _2, and the basic composition formula is Li _(1-x) MnO ₂ (0≤x≤1, etc., the same applies hereinafter) and Li _{(1). -x)} Lithium-manganese composite oxide with Mn ₂ O _{4, etc., Lithium cobalt composite oxide with basic composition formula as Li (1-x)} CoO _2, etc., basic composition formula as Li _(1-x) NiO _2, etc. Li _(1-x) Ni _a Co _b Mn _c O ₂ (a + b + c = 1) and Li _(1-x) Ni _a Co _b Mn _c O ₄ (a + b + c = 2) ) Etc., a lithium nickel cobalt manganese composite oxide having a basic composition formula of LiV ₂ O ₃ or the like, a transition metal oxide having a basic composition formula of V ₂ O _{5 or the like can be used.} .. Further, the positive electrode active material may be lithium iron phosphate or the like. Of these, lithium transition metal composite oxides, such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiV ₂ O ₃ , are preferred. The "basic composition formula" means that other elements may be contained.

For the positive electrode, for example, the above-mentioned positive electrode active material, the conductive material, and the binder are mixed, and an appropriate solvent is added to form a paste-like positive electrode mixture, which is applied to the surface of the current collector, dried, and required. Therefore, it may be formed by compression in order to increase the electrode density. As the conductive material, the binder, the solvent, and the current collector used for the positive electrode, for example, those exemplified for the negative electrode can be appropriately used.

In this power storage device, the ion conduction medium may be, for example, a non-aqueous electrolyte solution containing a supporting salt and an organic solvent. As the supporting salt, for example, when the carrier is lithium ion, a known lithium salt may be contained. As the lithium salt, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, Li (CF 3 SO 2) 2 N, LiN (C 2 F 5 SO 2) 2 and the like, Ya Among LiPF ₆ LiBF _{4 and the} like are preferable. The concentration of this supporting salt in the non-aqueous electrolyte solution is preferably 0.1 mol / L or more and 5 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less. When the concentration at which the supporting salt is dissolved is 0.1 mol / L or more, a sufficient current density can be obtained, and when it is 5 mol / L or less, the electrolytic solution can be made more stable. Further, a flame retardant such as phosphorus or halogen may be added to this non-aqueous electrolytic solution. As the organic solvent, for example, an aprotic organic solvent can be used. Examples of such an organic solvent include cyclic carbonates, chain carbonates, cyclic esters, cyclic ethers, chain ethers and the like. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and the like. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like. Examples of the cyclic ester carbonate include gamma-butyrolactone and gamma-valerolactone. Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran and the like. Examples of the chain ether include dimethoxyethane and ethylene glycol dimethyl ether. These may be used alone or in combination of two or more. In addition, as the non-aqueous electrolyte solution, a nitrile solvent such as acetonitrile or propylnitrile, an ionic liquid, a gel electrolyte, or the like may be used.

This power storage device may include a separator between the positive electrode and the negative electrode. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the power storage device, and is, for example, a polymer non-woven fabric such as a polypropylene non-woven fabric or a polyphenylene sulfide non-woven fabric, or an olefin resin such as polyethylene or polypropylene. Examples include microporous films. These may be used alone or in combination.

The shape of the power storage device is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Further, it may be applied to a large-sized vehicle used for an electric vehicle or the like. FIG. 4 is a schematic view showing an example of the power storage device 20. The power storage device 20 has a cup-shaped battery case 21, a positive electrode 22 having a positive electrode active material and provided at the lower part of the battery case 21, and a negative electrode active material with respect to the positive electrode 22 via a separator 24. A negative electrode 23 provided at a facing position, a gasket 25 formed of an insulating material, and a sealing plate 26 disposed in the opening of the battery case 21 and sealing the battery case 21 via the gasket 25 are provided. There is. In the power storage device 20, the space between the positive electrode 22 and the negative electrode 23 is filled with the ion conductive medium 27. Further, the negative electrode 23 has a mixed salt structure containing three kinds of aromatic dicarboxylic acid anions (Ph, Bph, Naph) as the negative electrode active material.

The charge / discharge characteristics can be further improved by the electrode active material, the power storage device, and the method for producing the electrode active material described in detail above. In this method for producing an electrode active material, a power storage device, and an electrode active material, a mixed salt structure having a novel structure can be prepared by using a prepared solution in which a plurality of types of aromatic dicarboxylic acid anions are appropriately mixed. Further, in a specific compounding region, due to the synergistic effect of the three kinds of aromatic dicarboxylic acid alkali metal salts contained therein, more suitable charge / discharge characteristics such as capacity, discharge potential, and polarization are exhibited as compared with those of each of them alone. It is presumed to be.

It goes without saying that the present disclosure is not limited to the above-described embodiment, and can be implemented in various embodiments as long as it belongs to the technical scope of the present disclosure.

Hereinafter, an example in which the electrode active material and the power storage device are specifically implemented will be described as experimental examples. Experimental examples 25, 26, 45 to 48 correspond to the examples of the present disclosure, and the others correspond to comparative examples.

[Experimental Example 1]
(Synthesis of active material)
A mixture of 0.2 mol / L terephthalic acid, 2,6-naphthalenedicarboxylic acid, and 4,4'-biphenyldicarboxylic acid in an aqueous solution of 0.44 mol / L lithium hydroxide dissolved in ion-exchanged water was prepared. Let the solutions be A (Ph), B (Naph), and C (Bph), respectively. Further, methanol is used as a solution D (Meth). The raw material ratio is adjusted so that the total mass of the solutions A, B, C, and D is 5 g, the solution is injected and mixed, and then the temperature is raised at 10 ° C./min in a tubular furnace with a nitrogen gas atmosphere, and then 220 ° C. The material obtained by heating in 1 hour was used as an active material. Specifically, three kinds of reference materials, 100% by mass Ph (Experimental Examples 9 and 10), 100% by mass Naph (Experimental Examples 11 and 12), and 100% by mass Bph (Experimental Examples 13 and 14). And 23 kinds (X1 to X23) in which solutions A, B, C and D were mixed at an appropriate ratio were designated as Experimental Examples 1 to 52. The blending amounts of Experimental Examples 1 to 52 were as shown in Tables 1 and 2.

(X-ray diffraction measurement)
X-ray diffraction measurement of the mixed salt structure of Experimental Examples 1 to 52 was performed. The measurement was carried out using CuKα rays (wavelength 1.54051 Å) as radiation and using an X-ray diffractometer (Ultima IV manufactured by Rigaku). For the measurement, a graphite single crystal monochromator was used to monochromate the X-rays, the applied voltage was set to 40 kV, the current was set to 30 mA, and the scanning speed was 5 ° / min in 0.02 ° increments, 2θ = 5 °. It was performed in an angle range of ~ 60 °. In addition, the Pearson correlation coefficient of the XRD spectrum between the synthesized active materials was evaluated using all the spectral values in the range of 2θ of 5 to 60 °. Here, when the XRD spectra of the active material X and the active material Y are xi and yi, respectively, the Pearson correlation coefficient R (X, Y) is defined by the mathematical formula (6). R (X, Y) takes a value between -1 and 1, and can be used as an index showing the similarity between the XRD spectra of X and Y. If there is a perfect positive correlation between the two, then R = 1, if there is a perfect negative correlation, then R = -1, and if there is no correlation, then R = 0. As a result of analyzing the Pearson correlation coefficient of the XRD spectrum and the battery characteristics of the active material, it became clear that there is a correlation between the two. Therefore, the Pearson correlation coefficient obtained by comparing the XRD spectrum of Ph alone with respect to the XRD spectrum of the active material in which Ph, Naph and Bph are mixed in an arbitrary ratio is set as Rp, and the Pearson correlation coefficient comparing the XRD spectrum of Naph alone is used. Is Rn, the Pearson correlation coefficient comparing the XRD spectrum of Bph alone is Rb, and the Pearson correlation coefficient between Ph, Naph, Bph and each active material is used as an index.

(Results of XRD spectrum examination)
FIG. 5 is an XRD spectrum of the active material of each experimental example. Tables 1 and 2 show the sample name, the mixing ratio (parts by mass) of the raw materials, the amount of active substance A (g), the current density I (mA / g) with respect to the amount of unit active material, and the Pearson correlation coefficients Rp, Rn, Rb. Was summarized. For example, X20 is not simply a combination of Ph, Naph, and Bph XRD patterns in composition ratio, and it is considered that a compound different from the three materials is formed. For example, the XRD spectrum is systematically changed with respect to the input ratio of the raw material so that Rn is high when Naph is high as a raw material and Rn is low when Naph is low, and the structure determines the characteristics. It turned out to be the main factor. The same tendency was observed for Bph and Ph.

In order to confirm the effect of methanol, the characteristics of materials having the same Ph: Naph: Bph ratio but different amounts of methanol were compared. FIG. 6 shows the results of examining the presence / absence of alcohol (FIG. 6A) and the heating temperature (FIG. 6B). In the evaluated material composition, X6 (0% by mass Meth), X9 (20% by mass Meth), X11 (0% by mass Meth), X14 (20% by mass Meth), X21 (0% by mass Meth), and X23. (20% by mass Meth) corresponds to such data. It was clarified that the XRD spectra were almost the same regardless of the presence or absence of methanol (see FIG. 6A), and it was confirmed that the presence or absence of methanol did not affect the structural change. Therefore, it was concluded that the main factor governing the tendency of the characteristics is the crystal structure determined by the ratio of Ph: Naph: Bph. However, in all of these samples, in the charge / discharge test described later, 20% by mass Meth showed lower average potential and polarization, and there was a tendency that the characteristics improved when methanol was added. .. The active material was synthesized under heating conditions of 180 ° C. to 330 ° C., but as shown in FIG. 6B, the change in the XRD spectrum does not depend on the heating conditions, and the structure can be used regardless of the heating conditions. It was confirmed that almost the same thing was synthesized.

(Creation of test cell, characterization)
Using the powder obtained in the synthesis experiment as an active material, the amount of the active material was fixed at 0.6 g to prepare a mixture slurry, and an electrode was prepared using the mixture slurry. The active material, carbon black as a conductive material (Tokai Carbon, TB5500), polyvinyl alcohol as a binder (PVA; T-330, Mitsubishi Chemical), and a styrene-butadiene copolymer as a binder. (SBR; TRD 2001 manufactured by JSR) was set to a molar ratio of 85:15: 3: 4.5. First, the active material, carbon black, and PVA binder were mixed well in a mortar, 0.9 to 1.5 g of ion-exchanged water was added, and the mixture was stirred with a stirrer. Then, SBR was added and the mixture was stirred again. The slurry obtained in each process was applied to a copper foil and vacuum dried at 120 ° C. for 8 hours. The prepared electrode was cut to a diameter of 16 mm, attached to a tom cell, and the battery characteristics (capacity, average potential, polarization) were evaluated. Metallic Li was used as the counter electrode, and 1 mol / L LiPF ₆ dissolved in a non-aqueous solvent was used as the electrolytic solution. As the non-aqueous solvent, a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 30:40:30 was used. The amount of the electrolytic solution was 100 to 200 μL.

(Evaluation of charge / discharge characteristics)
After charging and discharging for 2 cycles at C / 10, 2 cycles were charged and discharged at C / 5, 2 cycles at C / 3, and 2 cycles at C / 2. The lower limit of the voltage was 500 mV and the upper limit was 1500 mV, and the charge / discharge characteristics were evaluated between them. When the mixed salt structure is used as an active material, the theoretical volumes of Ph and Naph are 279.4 mAh / g and 221.6 mAh / g, respectively. Therefore, the theoretical volumes are set by the mixing ratio (mass ratio) and C / 10 I decided the conditions such as. Two cycles of charging and discharging were performed under each condition, and the capacitance, average potential, and polarization were evaluated. FIG. 7 shows the results of evaluation of charge / discharge characteristics using an active material prepared from 100% by mass Bph (Experimental Examples 13 and 14) using a tom cell. In FIG. 7, C / H (H = 2,3,5,10) is set under the condition that "the current is fixed so as to fully charge 200.0 mAh / g, which is the theoretical capacity of Bph in H time". This is the result of measurement. Further, as shown in FIG. 7, using the second charge capacity C'2nd, power capacity W'2nd, discharge capacity C2nd, and power capacity W2nd in each step, the capacity is C2nd and the average potential Vave is Vave. = (W2nd / C2nd + W'2nd / C'2nd) / 2, and the polarization Vpol was evaluated by Vpol = (W2nd / C2nd-W'2nd / C'2nd) / 2. This time, two electrodes were prepared for each composition in order to confirm individual differences, and a total of 26 active materials were evaluated.

(Results and discussion)
The measurement results of the capacitance C2nd of each electrode, the average voltage Vave, and the polarization Vpol of each electrode are summarized in Tables 3 and 4. As shown in Tables 3 and 4, Ph having a large theoretical capacity had a small capacity when actually charged and discharged, and had a high average voltage and polarization. On the other hand, Naph had the largest volume and less polarization among the raw materials. In addition, Bph tended to have a low average potential. And, in particular, in the material composition of the experimental example, X16 (Ph: Naph: Bph: Meth = 0.7: 3.6: 0.4: 0.3), X17 (Ph: Naph: Bph: Meth = 0.7: 3.1: 1.2: 0) and X20. When (Ph: Naph: Bph: Meth = 0.1: 3.8: 1.1: 0) is viewed as the average value of the two electrodes, the 6 items in Tables 3 and 4 show better capacitance C2nd and average voltage Vave than Naph. , It became clear that it shows a polarized Vpol. In such a compounding ratio, it was presumed that, for example, there was a synergistic effect of the three kinds of aromatic dicarboxylic acid alkali metal salts contained therein.

(Correlation between material composition and properties)
Assuming that the masses of the aqueous solutions of Ph, Naph and Bph at the time of producing each active material are Wp, Wn and Wb (g), respectively, the raw material ratios Xp, Xn and Xb of Ph, Naph and Bph can be defined by the following. .. Xp = Wp / (Wp + Wn + Wb), Xn = Wn / (Wp + Wn + Wb), Xb = Wb / (Wp + Wn + Wb). This ratio can be defined independently of the presence / absence of the Meth aqueous solution, and Xp + Xn + Xb = 1. FIG. 8 shows a three-component composition distribution diagram of raw material ratios in mass of Ph, Naph, and Bph including the measurement results of each experimental example. Each white circle ○ is the raw material ratio of the active material evaluated, and the active material (X16, X17, X20) located at the apex of the triangle indicated by the black circle ● has a better capacity, average potential, and average potential than Naph alone. It shows polarization. Therefore, it was expected that charge / discharge characteristics exceeding those of the raw materials could be obtained within the range of the blended ratio shown by the alternate long and short dash line or the dotted line shown in the figure. Further, it was assumed that the active material having the raw material ratio located in the region within the solid triangular line has particularly better characteristics than Naph. Table 5 shows the composition ratios of Ph, Naph, and Bph of the electrode materials of X16, X17, and X20. From the above results, among those containing Ph, Naph and Bph, the compounding ratios Xp, Xn and Xb of Ph, Naph and Bph are 0.01 ≦ Xp ≦ 0.3 and 0.01 ≦ Xb ≦ 0.34. It was presumed that the active material satisfying the conditions of 0.36 ≦ Xn ≦ 0.98 simultaneously exhibited better charge / discharge characteristics. Further, the optimum electrode material is an active material in which the compounding ratios Xp, Xn, and Xb simultaneously satisfy the conditions of Xp≤-0.0575Xb + 0.1538, Xp≥6.0Xb-1.3, and Xp≥-0.9555Xb + 0.2302. It was speculated that it would be. Further, considering the Pearson correlation coefficients Rp, Rb, and Rn, the optimum XRD spectrum for improving the charge / discharge characteristics includes the electrode materials of X16, X17, and X20, 0.38 ≦ Rp ≦ 0. It was presumed that all the conditions of 49, 0.37 ≦ Rb ≦ 0.56, 0.75 ≦ Rn ≦ 0.90 were satisfied.

(Examination of compounding ratio of unknown sample based on Pearson correlation coefficient)
The raw material ratio of the active material is important information that describes the characteristics of the material and is one of the effective means for identifying the material. Therefore, a method for determining the compounding ratio of the aromatic dicarboxylic acid salt in the active material was examined using the Pearson correlation coefficient as an index as the similarity of the XRD spectrum. The raw material ratio is inferred using three XRD spectra of Ph, Naph, and Bph. As an example, a contour diagram of the Pearson correlation coefficient between the spectrum obtained by adding the three XRDs Ph, Naph, and Bph and the spectrum of X20 was created. FIG. 9 is a relationship diagram showing the degree of similarity between the XRD spectrum and the X20 spectrum, which are the sum of Ph, Naph, and Bph at each ratio in the three-component composition diagram. The higher the correlation coefficient, the more similar the spectra are, and X20 is estimated to be the raw material ratio in the vicinity. The black circles ● in the figure are the actual compounding ratios of X20, and it was found that they are on the highest contour line of 0.84. Since the XRD spectrum is important as the structure of the structure (iMOF) with respect to the battery characteristics, for example, if the correlation coefficient is in the range of the contour diagram of 0.84, the battery characteristics are close to X20. You might also say that. Similarly, if the range of the optimum raw material ratio shown in FIG. 8 and the range of the raw material ratio shown in FIG. 9 partially overlap, it can be said that the battery characteristics close to the optimum raw material ratio can be obtained. Therefore, as the range of the compounding ratio, the XRD spectrum of the mixed salt layered structure (iMOF) is measured, and the correlation coefficient shown in FIG. 9 is evaluated using the three XRD spectra of Ph, Naph, and Bph to obtain the maximum. When the contour map is output and the range of the optimum raw material ratio and the maximum contour map overlap, the optimum raw material ratio range can be determined by regarding it as the optimum raw material ratio. However, the maximum contour map shall be less than -0.2 with respect to the maximum value. This is because if it is −0.2 or more, the maximum contour map becomes wide and the composition range cannot be limited.

It should be noted that the present disclosure is not limited to the above-described examples, and it goes without saying that the present disclosure can be carried out in various aspects as long as it belongs to the technical scope of the present disclosure.

The present disclosure is available to the battery industry.

20 power storage device, 21 battery case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 ion conducting medium.

Claims (10)

An electrode active material for power storage devices
An organic skeleton layer containing all of the aromatic dicarboxylic acid anions having three types of structures represented by the formulas (1) to (3) and an alkali metal in the oxygen contained in the carboxylic acid of the organic skeleton layer. It is a mixed salt structure including an alkali metal element layer in which elements are coordinated to form a skeleton.
Pearson phase relationship between the electrode active material and a single layered structure represented by the formulas (4) to (6) when the XRD spectrum is measured in the range of 2θ of 5 ° or more and 60 ° or less using CuKα rays. When the numbers are Rp in the formula (4), Rb in the formula (5), and Rn in the formula (6), 0.38 ≦ Rp ≦ 0.49, 0.37 ≦ Rb ≦ 0.56, 0.75 By satisfying all of ≤Rn≤0.90 and storing and releasing alkali metal ions, electrical energy is stored and output.
Electrode active material.

When the mass part of the formula (4) is Xp, the mass part of the formula (5) is Xb, and the mass part of the formula (6) is Xn (Xp + Xb + Xn = 1), 0.01 ≦ Xp ≦ 0. 3. Whether 0.01 ≤ Xb ≤ 0.34, 0.36 ≤ Xn ≤ 0.98 is satisfied.
Alternatively, the electrode active material according to claim 1, which satisfies the formula (1).

An electrode active material for power storage devices
An organic skeleton layer containing all of the aromatic dicarboxylic acid anions having three types of structures represented by the formulas (1) to (3) and an alkali metal in the oxygen contained in the carboxylic acid of the organic skeleton layer. It is a mixed salt structure including an alkali metal element layer in which elements are coordinated to form a skeleton.
0.01 when the mass part of the formula (4) contained in the mixed salt structure is Xp, the mass part of the formula (5) is Xb, and the mass part of the formula (6) is Xn (Xp + Xb + Xn = 1). Whether ≤Xp≤0.3, 0.01≤Xb≤0.34, 0.36≤Xn≤0.98 are satisfied.
Alternatively, by satisfying the mathematical formula (1) and storing and releasing alkali metal ions, electric energy is stored and output.
Electrode active material.

The electrode active material according to claim 2 or 3, wherein the mixed salt structure satisfies 0.01 ≦ Xp ≦ 0.20, 0.05 ≦ Xb ≦ 0.30, 0.60 ≦ Xn ≦ 0.80. .. The electrode active material according to any one of claims 2 to 4, wherein the mixed salt structure satisfies the formula (2).

The electrode active material according to any one of claims 2 to 5, wherein the mixed salt structure satisfies the formulas (3) to (5).

A negative electrode containing the electrode active material according to any one of claims 1 to 6 and a negative electrode.
Positive electrode A positive electrode containing an active material and a positive electrode
An ion conduction medium that is interposed between the positive electrode and the negative electrode and conducts carrier ions,
Power storage device equipped with. A method for manufacturing electrode active materials for power storage devices.
Using a prepared solution prepared by dissolving an aromatic dicarboxylic acid anion having three types of structures represented by the formulas (1) to (3) and an alkali metal cation, the aromatic dicarboxylic acid anion is contained. A precipitation step of precipitating a mixed salt structure including an organic skeleton layer and an alkali metal element layer in which an alkali metal element coordinates with oxygen contained in the carboxylic acid anion of the organic skeleton layer to form a skeleton is included.
In the precipitation step, when the mass part of the formula (4) is Xp, the mass part of the formula (5) is Xb, and the mass part of the formula (6) is Xn (Xp + Xb + Xn = 1) as the raw material of the mixed salt structure. A method for producing an electrode active material, which is blended in a range satisfying 0.01 ≦ Xp ≦ 0.3, 0.01 ≦ Xb ≦ 0.34, and 0.36 ≦ Xn ≦ 0.98.

The electrode according to claim 8, wherein in the precipitation step, the raw materials are blended so as to satisfy 0.01 ≦ Xp ≦ 0.20, 0.05 ≦ Xb ≦ 0.30, and 0.60 ≦ Xn ≦ 0.80. Method of manufacturing active material. The method for producing an electrode active material according to claim 8 or 9, wherein in the precipitation step, the raw material is dissolved in water and alcohol is not added.

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