JP7181709B2 - storage device - Google Patents

Description

The invention disclosed herein relates to an electricity storage device.

Conventionally, a layered structure having an organic skeleton layer containing an aromatic dicarboxylic acid anion and an alkali metal element layer forming a skeleton by coordinating an alkali metal element to oxygen contained in the carboxylic acid of the organic skeleton layer is used for power storage. It has been proposed to use it for the negative electrode of a device (for example, Patent Documents 1 and 2). Such a negative electrode has a charge/discharge potential higher than that of a graphite negative electrode, and therefore has the advantage that deposition of lithium metal is less likely to occur. In addition, in an electric storage device using such a negative electrode, it has been proposed to reduce the internal resistance by using a non-aqueous electrolyte containing more than 0.5% by mass of an additive such as lithium bisoxalate borate (LiBOB). (Patent Document 3).

JP 2017-22186 A JP 2017-191864 A JP 2016-219204 A

However, in the electricity storage devices of Patent Documents 1 to 3, the charging/discharging capacity is sometimes small and the coulombic efficiency is low. Therefore, it has been desired to provide an electricity storage device that uses a layered structure as an electrode active material and has a large charge/discharge capacity and a good coulomb efficiency.

The present disclosure has been made in view of such problems, and the main purpose is to provide an electricity storage device that uses a layered structure as an electrode active material and has a large charge-discharge capacity and good coulomb efficiency. do.

As a result of intensive research to achieve the above-mentioned object, the present inventors have found an electrode containing a layered structure of a metal salt of an aromatic dicarboxylic acid obtained by spray drying, and a predetermined compound of less than 1.0% by mass. and a non-aqueous electrolyte containing in the range of Then, the inventors have found that an electricity storage device having a large charge/discharge capacity and a good coulomb efficiency can be obtained by using such an electrode and a non-aqueous electrolyte, and have completed the present invention.

That is, the electricity storage device of the present disclosure is
A strip of a layered structure comprising an organic skeleton layer containing an aromatic dicarboxylic acid anion and an alkali metal element layer forming a skeleton by coordinating an alkali metal element to oxygen contained in the carboxylic acid of the organic skeleton layer is used as an electrode. an electrode comprising as a substance;
A non-aqueous electrolyte containing a compound represented by the general formula (1) in a range of less than 1.0% by mass and conducting carrier ions;
is provided.

（但し、Ｍは、遷移元素、周期表の１３族、１４族又は１５族元素を表す；Ａ^a+は金属イオンプロトン又はオニウムイオン、ａは１～３の整数、ｐはｂ／ａ；ｂは１～３の整数、ｍは１～４の整数、ｎは０～８の整数、ｑは０又は１を表す；Ｒ¹は、炭素数１～１０のアルキレン、炭素数１～１０のハロゲン化アルキレン、炭素数６～２０のアリーレン又は炭素数６～２０のハロゲン化アリーレン（これらのアルキレン及びアリーレンはその構造中に置換基、ヘテロ原子を持っていてもよく、またｑが１でｍが２～４のときにはｍ個のＲ¹はそれぞれが結合していてもよい）を表す；Ｒ²は、ハロゲン、炭素数１～１０のアルキル、炭素数１～１０のハロゲン化アルキル、炭素数６～２０のアリール、炭素数６～２０のハロゲン化アリール（これらのアルキル及びアリールはその構造中に置換基、ヘテロ原子を持っていてもよく、またｎが２～８のときにはｎ個のＲ²はそれぞれが結合して環を形成してもよい）又は－Ｘ³Ｒ³を表す；Ｘ¹，Ｘ²及びＸ³は、それぞれが独立でＯ，Ｓ又はＮＲ⁴を表す；Ｒ³及びＲ⁴は、それぞれが独立で水素、炭素数１～１０のアルキル、炭素数１～１０のハロゲン化アルキル、炭素数６～２０のアリール、炭素数６～２０のハロゲン化アリール（これらのアルキル及びアリールはその構造中に置換基、ヘテロ原子を持っていてもよく、Ｒ³又はＲ⁴は複数個存在する場合にはそれぞれが結合して環を形成してもよい）を表す）

(where M represents a transition element, a group 13, 14 or 15 element of the periodic table; A ^{a +} is a metal ion proton or onium ion, a is an integer of 1 to 3, p is b/a; b is an integer of 1 to 3, m is an integer of 1 to 4, n is an integer of 0 to 8, q is 0 or 1; R ¹ is alkylene having 1 to 10 carbon atoms, halogenated Alkylene, arylene having 6 to 20 carbon atoms or arylene halide having 6 to 20 carbon atoms (these alkylene and arylene may have substituents and heteroatoms in their structures, and q is 1 and m is 2 R ² represents halogen, alkyl having 1 to ¹⁰ carbon atoms, halogenated alkyl having 1 to 10 carbon atoms, 6 to 20 aryl, halogenated aryl having 6 to 20 carbon atoms (these alkyl and aryl may have substituents and heteroatoms in their structures, and when n is 2 to 8, n R ² each may combine to form a ring) or -X ³ R ³ ; X ¹ , X ² and X ³ each independently represent O, S or NR ⁴ ; R ³ and R ⁴ are each independently hydrogen, alkyl having 1 to 10 carbon atoms, alkyl halide having 1 to 10 carbon atoms, aryl having 6 to 20 carbon atoms, aryl halide having 6 to 20 carbon atoms (these alkyl and aryl are It may have substituents and heteroatoms in its structure, and when there are a plurality of R ³ or R ⁴ , each may combine to form a ring)).

In the electricity storage device of the present disclosure, an electricity storage device that uses a layered structure as an electrode active material and has a large charge/discharge capacity and a good coulomb efficiency can be provided.

FIG. 2 is a schematic diagram showing an example of an electricity storage device 20; Explanatory drawing of the active material and electrode produced by the solvent drying method and the spray-drying method. Explanatory drawing of the coating on the electrode and the electrode produced by the solvent drying method and the spray drying method. SEM photograph of Reference Example 1. SEM photograph of Reference Example 5. XRD measurement results of the electrode active materials of Reference Examples 1, 2, 5, 6 and 9. XRD measurement results of the electrode active materials of Reference Examples 3, 4, 7, 8 and 9. SEM photographs of electrode surfaces of Reference Examples 1 to 9. Oxygen distribution maps of electrode cross sections of Reference Examples 1, 2, and 9. XRD measurement results of the electrodes of Reference Examples 1 to 9. 3 shows charge-discharge curves in charge-discharge cycles of Reference Examples 1 to 9. FIG. Evaluation results of discharge capacity of Reference Examples 1 to 9. Differential curves obtained from charge/discharge curves of Reference Examples 1 to 9. Evaluation results of IV resistance of Reference Examples 1 to 9. FIG. 4 is a relational diagram between peak intensity ratios P(300)/P(111), P(300)/P(011) and IV resistance. FIG. 4 is a relational diagram between peak intensity ratios P(100)/P(111), P(100)/P(011) and IV resistance. FIG. 4 is a relational diagram between the peak intensity ratio P(100)/P(300) and the IV resistance; Explanatory drawing of crystal planes (011), (111), (100), and (300) of a layered structure. 4 is a graph showing changes in discharge capacity of Examples 1 to 3 and Comparative Example 1; 4 is a graph showing changes in coulombic efficiency of Examples 1 to 3 and Comparative Example 1; 5 is a graph showing the relationship between the amount of LiBOB added and the initial capacity; 4 is a graph showing the relationship between the amount of LiBOB added and the discharge capacity and coulomb efficiency. 1 shows charge-discharge curves at the first cycle discharge of Examples 1 to 3 and Comparative Examples 1 to 3. FIG. Graphs plotting changes in current with respect to potential changes in Examples 1 to 3 and Comparative Examples 1 to 3. FIG.

The electricity storage device of the present disclosure includes an electrode containing flakes of a predetermined layered structure as an electrode active material, a non-aqueous electrolyte containing a compound represented by general formula (1) in a range of less than 1.0% by mass, It has This electric storage device may be, for example, an electric double layer capacitor, a hybrid capacitor, a pseudo electric double layer capacitor, or a secondary battery (lithium ion battery, etc.). In this electricity storage device, the above-described electrodes may be used as either positive or negative electrodes, but are preferably used as negative electrodes because the potential of the electrode active material is about 0.5 to 1.0 V relative to lithium metal. An electricity storage device using the above-described electrode as a negative electrode will be mainly described below.

In this electricity storage device, the non-aqueous electrolyte is interposed between the positive electrode and the negative electrode and conducts carrier ions. The carrier ions are preferably metal ions, more preferably alkali metal ions, and more preferably one or more of Li ions, Na ions and K ions. The non-aqueous electrolyte contains less than 1.0% by mass of the compound represented by the general formula (1). In the general formula (1), M is a transition element, group 13, group 14 or group 15 element of the periodic table, among which Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb is preferred, and Al, B or P is more preferred. When M is Al, B or P, the anion contained in the compound can be synthesized relatively easily, and the production cost can be suppressed. The anion has a valence b of 1 to 3, preferably 1. If the valence b is greater than 3, the salt of the compound tends to be difficult to dissolve in the mixed organic solvent, which is not preferred. Constants m and n are values related to the number of ligands and are determined depending on the type of M. m is an integer of 1 to 4, and n is an integer of 0 to 8. The constant q is 0 or 1. When q is 0, the chelate ring is a five-membered ring.

Here, R ¹ represents alkylene having 1 to 10 carbon atoms, alkylene halide having 1 to 10 carbon atoms, arylene having 6 to 20 carbon atoms or halogenated arylene having 6 to 20 carbon atoms. These alkylene and arylene may have substituents and heteroatoms in their structures. Specifically, instead of hydrogen on alkylene and arylene, halogen, linear or cyclic alkyl group, aryl group, alkenyl group, alkoxy group, aryloxy group, sulfonyl group, amino group, cyano group, carbonyl group, acyl It may have a group, an amide group, or a hydroxyl group as a substituent, or may have a structure in which nitrogen, sulfur, or oxygen is introduced in place of the carbon on the alkylene or arylene. Also, when q is 1 and m is 2 to 4, each of m R ¹ may be bonded. Examples of such may include ligands such as ethylenediaminetetraacetic acid.

R ² is halogen, alkyl having 1 to 10 carbon atoms, alkyl halide having 1 to 10 carbon atoms, aryl having 6 to 20 carbon atoms, aryl halide having 6 to 20 carbon atoms or —X ³ R ³ (X ³ , R ³ will be described later). Alkyl and aryl here may have substituents and heteroatoms in their structures, similarly to R ¹ , and when n is 2 to 8, n R ² are each bonded to form a ring. may form As R ² , an electron-withdrawing group is preferred, and a fluorine atom is particularly preferred. This is because, in the case of a fluorine atom, the solubility and dissociation degree of the salt of the anion compound are improved, and accordingly the ionic conductivity is improved. Moreover, it is because the oxidation resistance is improved, thereby suppressing the occurrence of side reactions.

X ¹ , X ² and X ³ each independently represent O, S or NR ⁴ . That is, the ligand will be attached to M through these heteroatoms.

R ³ and R ⁴ each independently represents hydrogen, alkyl having 1 to 10 carbon atoms, alkyl halide having 1 to 10 carbon atoms, aryl having 6 to 20 carbon atoms, or aryl halide having 6 to 20 carbon atoms. . These alkyls and aryls may also have substituents and heteroatoms in their structures, like R ¹ . Also, when there are a plurality of R ³ or R ⁴ , they may combine to form a ring.

In the cation (A ^a+ ) of the compound represented by formula (1), a is 1 to 3 and p is b/a. Examples of such cations include lithium, sodium, potassium, magnesium, calcium, barium, cesium, rubidium, silver, zinc, copper, cobalt, iron, nickel, manganese, titanium, lead, chromium, vanadium, ruthenium, yttrium, lanthanides, In addition to cations such as actinides, ammonium cations such as tetraalkylammonium (alkyl is methyl, ethyl, butyl, etc.), triethylammonium, pyridinium, imidazolium, etc., protons, and the like can be used. Of these, lithium cations, sodium cations and potassium cations are preferred. In particular, compounds containing lithium or potassium are preferred because they are easily dissolved in non-aqueous solvents. This cation may be of the same type as the carrier ion.

The compound represented by general formula (1) preferably contains one or more anions of PTFO, PFO, PO, BFO and BOB represented by formulas (2) to (6). The reason is that a stable SEI is easily formed on the surface of the negative electrode active material. The compound represented by the general formula (1) is more preferably a compound containing lithium or potassium as cations and PFO or BOB as anions. Among them, lithium bisoxalate borate (LiBOB) containing lithium as a cation and BOB as an anion is more preferable. In such a case, the internal resistance can be further reduced, and the cycle characteristics can be further improved.

As a method for synthesizing such a compound, for example, in the case of PFO, after reacting LiPF ₆ with 4 times the mole of lithium alkoxide in a non-aqueous solvent, oxalic acid is added to obtain the alkoxide bound to phosphorus. is replaced with oxalic acid. In the case of BOB, LiBF ₄ is reacted with 4 times the molar amount of lithium alkoxide in a non-aqueous solvent, and then oxalic acid is added to replace the alkoxide bound to boron with oxalic acid. etc. In these cases, the compound represented by general formula (1) can be obtained as an anion lithium salt.

It is believed that all or part of the compound (for example, anion) decomposes and coats the surface of the negative electrode active material to form a film when the electricity storage device is charged at least once. This coating can be detected by, for example, X-ray photoelectron spectroscopy (XPS), IR analysis, or the like.

The non-aqueous electrolyte contains the compound represented by the general formula (1) less than 1.0% by mass with respect to the non-aqueous solvent in which the supporting salt is dissolved, that is, the total amount of the supporting salt and the non-aqueous solvent. Including in the range of If this compound is contained in a range of less than 1.0% by mass, it is believed that a thin and stable film is formed on the electrode surface. The content of this compound is preferably 0.1% by mass or more and 0.5% by mass or less, more preferably 0.2% by mass or more and 0.5% by mass or less.

Examples of non-aqueous solvents include carbonates, esters, ethers, nitriles, furans, sulfolanes and dioxolanes, and these can be used alone or in combination. Specifically, the carbonates include cyclic carbonates such as ethylene carbonate, propylene carbonate and vinylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di- Chain carbonates such as i-propyl carbonate and t-butyl-i-propyl carbonate, cyclic esters such as γ-butyl lactone and γ-valerolactone, chain esters such as methyl formate and ethyl acetate, dimethoxyethane, ethers such as ethoxymethoxyethane; nitriles such as acetonitrile and benzonitrile; furans such as tetrahydrofuran and methyltetrahydrofuran; sulfolane such as sulfolane and tetramethylsulfolane; mentioned. Among these, a combination of cyclic carbonates and chain carbonates is preferred. According to this combination, not only is the cycle characteristic, which represents the characteristics of the storage device in repeated charging and discharging, excellent, but also the viscosity of the non-aqueous electrolyte, the resulting electrical capacity of the storage device, and the output of the storage device are well balanced. can be taken. Cyclic carbonates have a relatively high dielectric constant and are thought to increase the dielectric constant of the non-aqueous electrolyte, while chain carbonates are thought to reduce the viscosity of the non-aqueous electrolyte.

Examples of supporting salts include _LiPF6 , _{LiBF4 ,} LiAsF6, _LiCF3SO3 , LiN( _{CF3SO2 ) 2} , LiC( _{CF3SO2 ) 3 ,} LiSbF6, _{LiSiF6 , LiAlF4} , LiSCN, LiClO ₄ , LiCl, LiF, LiBr, LiI, LiAlCl ₄ and the like. Among them, from the group consisting of inorganic salts such as _LiPF6 , _LiBF4 , _{LiAsF6 and LiSbF6} , and organic _salts such as _LiCF3SO3 , LiN( _{CF3SO2 ) 2} and LiC( _CF3SO2 ) ₃ From the viewpoint of electrical properties, it is preferable to use one selected salt or a combination of two or more selected salts. Among them, LiPF ₆ is preferred. The supporting salt does not include the compound represented by general formula (1). The concentration of the supporting salt in the non-aqueous solvent in which the supporting salt is dissolved is preferably 0.1 mol/L or more and 5 mol/L or less, more preferably 0.5 mol/L or more and 2 mol/L or less. At 0.1 mol/L or more, a sufficient current density can be obtained, and at 5 mol/L or less, the non-aqueous electrolyte can be more stabilized. Further, a phosphorus-based or halogen-based flame retardant may be added to this non-aqueous non-aqueous electrolytic solution.

In this electricity storage device, the negative electrode includes a strip of a predetermined layered structure as a negative electrode active material. The negative electrode may store and release carrier ions.

The negative electrode active material is a layered structure comprising an organic skeleton layer containing an aromatic dicarboxylic acid anion and an alkali metal element layer in which an alkali metal element is coordinated with oxygen contained in the carboxylic acid of the organic skeleton layer to form a skeleton. Contains flakes. The negative electrode active material may have a hollow spherical structure formed by enclosing a collection of flakes of the layered structure (see FIG. 2 below), or may have a flake structure obtained by pulverizing it. may have. In this negative electrode active material, the hollow spherical structure may have a structure in which flakes of the layered structure irregularly extend from the center toward the outer periphery. Alternatively, the hollow spherical structure may have a structure in which flakes of the layered structure are irregularly directed from the outer periphery toward the center. A negative electrode active material having such a hollow spherical structure can be obtained by spray-drying a solution containing an aromatic dicarboxylic acid anion and an alkali metal cation. The hollow spherical structure may have a diameter of 10 μm or less. The hollow spherical structure may have a diameter of 0.1 μm or more. Hollow particles of the layered structure obtained by the spray-drying method are obtained in the range of 0.1 μm or more and 10 μm or less. The thickness of flakes in the hollow spherical structure or flake-like structure is, for example, 1 nm or more and 100 nm or less, preferably 1 nm or more and 20 nm or less.

This layered structure may have an organic skeleton layer to which one or more aromatic ring structures are connected. This layered structure is structurally stable if it has a monoclinic crystal structure that is formed in layers by the π-electron interaction of the aromatic compound and belongs to the space group P2 ₁ /c. Yes and preferred. This layered structure may have a structure represented by one or more of formulas (7) to (9). However, in the formulas (7) to (9), a is an integer of 1 or more and 5 or less, and b is an integer of 0 or more and 3 or less. It may have atoms. Specifically, instead of hydrogen of the aromatic compound, halogen, chain or cyclic alkyl group, aryl group, alkenyl group, alkoxy group, aryloxy group, sulfonyl group, amino group, cyano group, carbonyl group, acyl group , an amide group, or a hydroxyl group as a substituent, or a structure in which nitrogen, sulfur, or oxygen is introduced instead of the carbon of the aromatic compound. More specifically, this layered structure may be an aromatic compound represented by formulas (10) to (12). In formulas (7) to (12), A is an alkali metal. Further, the layered structure is structurally stable and preferably has a structure of formula (13) in which four oxygen atoms of different dicarboxylate anions and an alkali metal element form four-coordination. . However, in this formula (13), R has 1 or 2 or more aromatic ring structures, and 2 or more of a plurality of R may be the same, or 1 or more may be different. Also, A is an alkali metal. In this way, it is preferable to have a structure in which the organic skeleton layers are bonded by the alkali metal element.

In this layered structure, when the organic skeleton layer has two or more aromatic ring structures, for example, it may be an aromatic polycyclic compound in which two or more aromatic rings are bonded, such as biphenyl, or two aromatic rings such as naphthalene, anthracene, and pyrene. A condensed polycyclic compound in which the above aromatic rings are condensed may be used. This aromatic ring may be a five-membered ring, a six-membered ring, or an eight-membered ring, preferably a six-membered ring. Also, the number of aromatic rings is preferably 2 or more and 5 or less. When the number of aromatic rings is 2 or more, a layered structure is likely to be formed, and when the number of aromatic rings is 5 or less, the energy density can be further increased. This organic skeleton layer may have a structure in which one or more carboxyanions are bound to an aromatic ring. The organic skeleton layer preferably contains an aromatic compound in which one and the other of the dicarboxylate anions are bonded to the diagonal positions of the aromatic ring structure. The diagonal position where the carboxylic acid is bonded may be the farthest position from the bonding position of one carboxylic acid to the bonding position of the other carboxylic acid. is mentioned.

The alkali metal contained in the alkali metal element layer can be, for example, any one or more of Li, Na and K, and Li is preferable. It should be noted that the metal ions that are carriers of the electric storage device and that are occluded and released by the layered structure due to charging and discharging may be different from or the same as the alkali metal element contained in the alkali metal element layer. , Li, Na, K, and the like. Further, since the alkali metal element contained in the alkali metal element layer forms the skeleton of the layered structure, it is presumed that it does not participate in ion migration accompanying charging and discharging, that is, it does not occlude and release during charging and discharging. . In the energy storage mechanism, the organic skeleton layer of the layered structure functions as a redox (e ⁻ ) site, while the alkali metal element layer functions as a metal ion absorption site (alkali metal ion absorption site) as a carrier. Conceivable. This layered structure is preferably one or more of, for example, 2,6-naphthalenedicarboxylic acid alkali metal salt, 4,4'-biphenyldicarboxylic acid alkali metal salt and terephthalic acid alkali metal salt.

This negative electrode active material may be obtained through a step of spray-drying a solution prepared by dissolving an aromatic dicarboxylic acid anion and an alkali metal cation using a spray-drying apparatus. This negative electrode active material can be obtained, for example, by the method for producing a negative electrode active material described below. This manufacturing method may include a solution preparation step and a precipitation step. Note that the solution preparation step may be omitted as the prepared solution is prepared separately.

In the solution preparation step, a preparation solution is prepared by dissolving the aromatic dicarboxylate anion and the alkali metal cation. The solvent for this prepared solution is not particularly limited, and may be an aqueous solvent or an organic solvent, preferably water. In this step, it is preferable to prepare a prepared solution having an aromatic dicarboxylate anion concentration of 0.1 mol/L or more, more preferably 0.2 mol/L or more. Moreover, in this step, it is preferable to prepare a prepared solution having an aromatic dicarboxylate anion concentration of 5 mol/L or less. In such a concentration range, it is easier to carry out the next step of spray drying. Alternatively, in this step, it is preferable to prepare a prepared solution having an aromatic dicarboxylate anion concentration of 0.1 mol % or more. In such a concentration range, it is easier to carry out the next step of spray drying. In this step, a preparation solution having a concentration of aromatic dicarboxylate anion of 0.4 mol % or less may be prepared. Also, in this step, an aromatic dicarboxylic acid anion having an organic skeleton obtained by extending a benzene ring, naphthalene, biphenyl, naphthalene skeleton or biphenyl skeleton may be used. Further, in this step, it is preferred 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 in which the molar ratio B/A, which is the number of moles B (mol) of the alkali metal cation to the number of moles A (mol) of the aromatic dicarboxylate anion, is 2.0 or more. , the molar ratio B/A is more preferably 2.2 or more. By setting the alkali metal cation to an equivalent amount or an excess amount in this way, the resistance of the negative electrode can be further reduced, which is preferable. This molar ratio B/A may be 2.5 or more. Also, this molar ratio B/A may be 3.0 or less, or may be 2.5 or less.

In the deposition step, the prepared solution is spray-dried using a spray-drying apparatus to deposit a negative electrode active material having a hollow spherical structure formed by enclosing a set of flakes of the layered structure. This layered structure is the one described in the above negative electrode active material. and an alkali metal element layer forming a skeleton. In this precipitation step, the adjusted solution prepared in the solution preparing step is used. Spray drying may be carried out using a spray dryer. The spray-drying conditions may be appropriately adjusted according to, for example, the scale of the apparatus and the amount of the negative electrode active material to be produced. The drying temperature is preferably in the range of, for example, 100° C. or higher and 200° C. or lower. At 100° C. or higher, the solvent can be sufficiently removed, and at 200° C. or lower, energy consumption can be further reduced, which is preferable. The drying temperature is more preferably 120°C or higher, and more preferably 180°C or lower. The amount of liquid to be supplied may be in the range of, for example, 0.1 L/h or more and 2 L/h or less, depending on the scale of production. In addition, the size of the nozzle for spraying the prepared solution may be, for example, a range of 0.5 mm or more and 5 mm or less in diameter, although it depends on the scale of production. When the layered structure is produced by spray drying in this manner, the negative electrode active material having the above-described hollow spherical structure including the layered structure is obtained. The negative electrode active material having a hollow spherical structure may be used as it is, or may be pulverized into flakes for use.

The negative electrode is obtained by mixing the layered structure, which is the negative electrode active material, the conductive material, and the binder, and adding an appropriate solvent to make a paste-like negative electrode mixture, which is applied to the surface of the current collector and dried. However, if necessary, it may be formed by compression to increase the electrode density. In this negative electrode, the negative electrode active material is preferably contained as much as possible. Conductive materials include, for example, graphite such as natural graphite (flaky graphite, flaky graphite) and artificial graphite, acetylene black, carbon black, ketjen black, carbon whisker, needle coke, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.), or a mixture of two or more thereof can be used. Among these, carbon black and acetylene black are preferable as the conductive material from the viewpoint of electronic conductivity and coatability. The binder plays a role of binding the active material particles and the conductive material particles, and examples thereof include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing resin such as fluororubber, 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. Cellulose-based or styrene-butadiene rubber (SBR) aqueous dispersions, which are water-based binders, can also be used. Application methods include, for example, roller coating such as applicator roll, screen coating, doctor blade method, spin coating, and bar coater, and any thickness and shape can be obtained using any of these methods. As the current collector, aluminum, titanium, stainless steel, nickel, iron, calcined carbon, conductive polymer, conductive glass, or the like can be used. Examples of the shape of the current collector include foil, film, sheet, net, punched or expanded, lath, porous, foam, and fiber group formations. The current collector used has a thickness of, for example, 1 to 500 μm.

This negative electrode preferably exhibits a peak intensity ratio P(300)/P(111) of (300) to the peak intensity of (111) of 2.0 or more when the electrode is subjected to X-ray diffraction measurement. That is, the peak intensity of (300) may be twice or more the peak intensity of (111). This intensity ratio is more preferably 2.5 or more, and even more preferably 3.0 or more. Also, this intensity ratio may be 5.0 or less. Within this range, the layer spacing of the layered structure is good, and the negative electrode resistance can be further reduced. In addition, when the electrode is subjected to X-ray diffraction measurement, the peak intensity ratio P (300) / P (011) of (300) to the peak intensity of (011) in X-ray diffraction measurement is 2.0 or more. is preferably shown. That is, the peak intensity of (300) may be twice or more the peak intensity of (011). This intensity ratio is more preferably 2.5 or more, and even more preferably 3.0 or more. Also, this intensity ratio may be 5.0 or less. Within this range, the layer spacing of the layered structure is good, and the negative electrode resistance can be further reduced. In addition, when the electrode is subjected to X-ray diffraction measurement, the negative electrode has a peak intensity ratio P (100) / P (111) of (100) to the peak intensity of (111) in X-ray diffraction measurement of 6.0 or more. is preferably shown. That is, the peak intensity of (100) may be six times or more the peak intensity of (111). This intensity ratio is more preferably 6.5 or more, and even more preferably 6.6 or more. Also, this intensity ratio may be 10.0 or less. Within this range, the layer spacing of the layered structure is good, and the negative electrode resistance can be further reduced. In addition, the negative electrode preferably exhibits a peak intensity ratio P(100)/P(011) of (100) to the peak intensity of (011) of 5.0 or more when the electrode is subjected to X-ray diffraction measurement. That is, the peak intensity of (100) may be five times or more the peak intensity of (011). This intensity ratio is more preferably 6.0 or more, and even more preferably 6.5 or more. Also, this intensity ratio may be 10.0 or less. Within this range, the layer spacing of the layered structure is good, and the negative electrode resistance can be further reduced. In addition, the negative electrode preferably exhibits a peak intensity ratio P(100)/P(300) of (100) to the peak intensity of (300) of 1.5 or more when the electrode is subjected to X-ray diffraction measurement. That is, the peak intensity of (100) may be one or more times the peak intensity of (300). This intensity ratio is more preferably 1.8 or more, and even more preferably 2.0 or more. Also, this intensity ratio may be 5.0 or less. Within this range, the layer spacing of the layered structure is good, and the negative electrode resistance can be further reduced. In addition, when the negative electrode is subjected to X-ray diffraction measurement, it is found that small flakes of the active material present inside the negative electrode are oriented in a specific manner, and the peak intensity corresponding to the n00 plane is showing a tendency to increase. Also, this negative electrode may have a smooth surface when observed with a scanning electron microscope. Since this negative electrode active material can be easily pulverized to form a negative electrode in which flakes are highly dispersed, the surface of the negative electrode becomes smoother.

In this electricity storage device, the positive electrode may store and release carrier ions. In this electricity storage device, the positive electrode may be a known positive electrode used in capacitors, lithium ion capacitors, and the like. The positive electrode may contain, for example, a carbon material as a positive electrode active material. Examples of carbon materials include, but are not limited to, activated carbons, cokes, vitreous carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Among these, activated carbons exhibiting a high specific surface area are preferred. Activated carbon as the carbon material preferably has a specific surface area of 1000 m ² /g or more, 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, more preferably 2000 m ² /g or less, for ease of production. The positive electrode is considered to store electricity by adsorbing/desorbing at least one of the anions and cations contained in the non-aqueous electrolyte. It may be desorbed and stored.

Alternatively, the positive electrode may be a positive electrode used in common lithium ion batteries. In this case, a sulfide containing a transition metal element, an oxide containing lithium and a transition metal element, or the like can be used as the positive electrode active material. Specifically, transition metal sulfides such as TiS ₂ , TiS ₃ , MoS ₃ and FeS ₂ , and basic compositional formulas of Li _(1-x) MnO ₂ (0<x<1, etc., the same applies hereinafter) and Li _{(1 -x)} Lithium-manganese composite oxides such as Mn ₂ O ₄ , Lithium-cobalt composite oxides such as Li _(1-x) CoO ₂ with a basic composition formula, Li _(1-x) NiO ₂ with a basic composition formula, etc. a lithium-nickel composite oxide having a basic composition formula of Li _(1-x) Ni _a Co _b Mn _c O ₂ (a+b+c=1) or the like, a basic composition formula of LiV ₂ O ₃ Lithium vanadium composite oxides such as V ₂ O 5 , transition metal oxides having a basic composition formula such as V 2 O ₅ , and the like can be used. Also, the positive electrode active material may be lithium iron phosphate or the like. Among these, transition metal composite oxides of lithium such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ and LiV ₂ O ₃ are preferred. It should be noted that the “basic composition formula” means that other elements may be included.

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

This electricity 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 electric storage device. Examples include microporous films. These may be used alone or in combination.

The shape of the electricity storage device is not particularly limited, and examples thereof include coin-shaped, button-shaped, sheet-shaped, laminated, cylindrical, flat, and rectangular shapes. Also, it may be applied to a large-sized one used for an electric vehicle or the like. FIG. 1 is a schematic diagram showing an example of an electricity storage device 20. As shown in FIG. The power storage device 20 has a cup-shaped case 21 , a positive electrode 22 having a positive electrode active material and provided at the bottom of the case 21 , and a negative electrode active material and facing the positive electrode 22 with a separator 24 interposed therebetween. a gasket 25 made of an insulating material; and a sealing plate 26 disposed in the opening of the case 21 and sealing the case 21 via the gasket 25 . In this electricity storage device 20 , a space between a positive electrode 22 and a negative electrode 23 is filled with a non-aqueous electrolyte 27 . The non-aqueous electrolyte 27 contains less than 1.0% by mass of the compound represented by the general formula (1). Moreover, the negative electrode 23 has the above-described layered structure as a negative electrode active material.

In the electricity storage device described in detail above, an electricity storage device that uses the layered structure as an electrode active material and has a large charge/discharge capacity and a good coulomb efficiency can be provided. The reason why such an effect is obtained is presumed as follows. FIG. 2 is an illustration of active materials and electrodes prepared by the conventional solvent drying method (a) and the spray drying method of the present disclosure (b). For example, in the conventional solvent-drying method, an aromatic dicarboxylic acid and an alkali metal are dissolved, and the solvent is removed by drying the solvent to obtain a layered structure of dialkali metal salt of an aromatic dicarboxylic acid. When an electrode is produced using this active material, the active material exists as secondary aggregates inside the electrode, and as a result, the active material inside the aggregates and the electrolyte do not form a sufficient interface and function effectively. Reducing the reaction interface increases the internal resistance. On the other hand, in the present disclosure, active material particles are produced by a spray drying method using a spray dryer using a solution in which an aromatic dicarboxylic acid and an alkali metal are dissolved. As shown in FIG. 2, the electrode active material 10 produced by this method becomes hollow particles 11 containing flake-like layered structures 12, which are easily pulverized, suppress aggregation of the layered structures, and The particles can form very highly dispersed structures inside the electrode. Therefore, it is presumed that the internal resistance can be reduced. In addition, when a conventional electrode active material having large particles of secondary aggregation is used, the electrode structure has a small interface for receiving metal ions (for example, lithium ions) inside the electrode, so that a sufficient discharge capacity cannot be obtained. On the other hand, when a flake of this layered structure is used as an electrode, the electrode structure has many interfaces for accepting metal ions, and more of the existing electrode active material functions, so that a larger discharge capacity can be obtained.

Further, by using a non-aqueous electrolyte containing less than 1.0% by mass of the compound represented by the general formula (1), a stable film is formed on the electrode surface, and the charge-discharge reaction on the electrode surface is smooth. It is presumed that the internal resistance can be reduced because the In addition, it is believed that this film prevents leakage current and side reactions with the electrolyte that occur during charging and discharging, thereby reducing irreversible capacity during charging and discharging, improving coulombic efficiency, and increasing cycle life. By the way, a layered structure such as dilithium aromatic carboxylate has a high charge/discharge potential of about 0.5 to 1.0 V (vs. Li/Li ⁺ ). Sufficient reductive decomposition of the electrolytic solution, which occurs on graphite with a discharge potential of about 0.1 V (vs. Li/Li ⁺ ), does not occur, and a stable film (SEI film) cannot be formed on the electrode surface. Therefore, a compound (such as LiBOB) represented by the general formula (1) that causes reductive decomposition at about 1.0 V (vs. Li/Li ⁺ ) higher than the charge/discharge potential of the layered structure to form a film on the electrode is used. By using it, it is thought that a good coating can be formed.

FIG. 3 shows an illustration of an electrode and a coating on the electrode prepared by the conventional solvent drying method (a) and the spray drying method of the present disclosure (b). The electrode using the active material produced by the spray-drying method of the present disclosure has a smoother electrode surface than the electrode produced using the active material produced by the conventional solvent drying method. There is no unevenness and the surface area is small. For this reason, it is presumed that a thin, uniform and stable film can be formed, and the layer that becomes a resistance component of the charge/discharge reaction can be reduced. Moreover, since the amount of the compound represented by the general formula (1) can be reduced, the cost can be reduced. When the content of the compound represented by formula (1) is 1% by mass or more, the initial capacity is significantly reduced. It is presumed that this is because the film on the electrode surface is too thick and the effect of the film resistance exceeds the effect of the film described above.

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

An example in which the electricity storage device of the present disclosure was specifically manufactured will be described below as an example. In this example, a bipolar cell using lithium metal as the counter electrode was examined, but if the counter electrode is a positive electrode containing any positive electrode active material, it can operate as an electricity storage device.

1. Preparation of electricity storage device [Example 1]
(Electrode active material: Synthesis of layered structure of dilithium 4,4′-biphenyldicarboxylate)
For the synthesis of dilithium 4,4'-biphenyldicarboxylate, 4,4'-biphenyldicarboxylic acid and lithium hydroxide monohydrate (LiOH.H ₂ O) were used as starting materials. An aqueous solution was prepared by adding lithium hydroxide to water and stirring so that the concentration became 0.44 mol/L. Then, the molar ratio B/A, which is the ratio of the number of moles B (mol) of lithium hydroxide to the number of moles A (mol) of 4,4′-biphenyldicarboxylic acid, is 2.2, that is, 4, An aqueous solution was adjusted so that 4′-biphenyldicarboxylic acid was 0.20 mol/L. The prepared aqueous solution was spray-dried using a spray dryer (Mini Spray Dryer B-290, manufactured by Nippon Buchi) to precipitate dilithium 4,4′-biphenyldicarboxylate. The nozzle diameter of the spray dryer used was 1.4 mm, the spray amount of the solution was 0.4 L/hour, and the drying temperature was 150° C. to synthesize lithium 4,4′-biphenyldicarboxylate.

(Electrode: Preparation of dilithium 4,4'-biphenyldicarboxylate electrode)
85 parts by mass of dilithium 4,4'-biphenyldicarboxylate prepared by the above method, 15 parts by mass of carbon black (Tokai Carbon, TB5500) as a particulate carbon conductive material, and sodium carboxymethyl cellulose (Daicel, 1120) as a water-based binder. and 3 parts by mass of a styrene-butadiene copolymer (JSR, TRD102A), which is a rubber-based binder, were mixed at a ratio of 4.5 parts by mass, and an appropriate amount of water was added as a dispersant and dispersed to obtain a slurry-like mixture. . This slurry mixture was evenly applied to a copper foil current collector having a thickness of 10 μm so that the dilithium 4,4′-biphenyldicarboxylate active material per unit area was 3.0 mg/cm ² . It was dried by heating to prepare a coated sheet. Thereafter, the coated sheet was press-pressed and punched into a 2 cm ² area to prepare a disk-shaped electrode.

(Preparation of non-aqueous electrolyte)
Lithium hexafluorophosphate as a supporting electrolyte was added to a non-aqueous solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 30:40:30. It was dissolved to 0 mol/L. 0.1% by mass of lithium bisoxalate borate (LiBOB) was added thereto to prepare a non-aqueous electrolyte.

(Energy storage device: fabrication of bipolar evaluation cell)
The 4,4′-biphenyldicarboxylate dilithium electrode prepared by the above method is used as the working electrode, and the lithium metal foil (thickness 200 μm) is used as the counter electrode, and the non-aqueous electrolyte is impregnated between both electrodes. A bipolar evaluation cell was prepared by sandwiching a separator (Celgard 2500 manufactured by Polypore).

[Examples 2 and 3]
Example 2 was the same as Example 1, except that 0.2% by mass of LiBOB was added in the preparation of the non-aqueous electrolyte. Example 3 was the same as Example 1, except that 0.5% by mass of LiBOB was added in the preparation of the non-aqueous electrolyte.

[Comparative Examples 1 to 4]
Comparative Example 1 was the same as Example 1 except that LiBOB was not added in the preparation of the non-aqueous electrolyte. Comparative Examples 2 to 4 were prepared in the same manner as in Example 1, except that 1.0% by mass, 2.0% by mass, and 5.0% by mass of LiBOB were added in the preparation of the non-aqueous electrolyte.

[Reference Examples 1 and 2]
(Electrode: preparation of dilithium 4,4'-biphenyldicarboxylate electrode) in slurry form, polyvinyl alcohol (Gosenex, T-330, Nippon Synthetic Chemical Industry) is used as a water-based binder, and a styrene-butadiene copolymer is used as a rubber-based binder. (Nippon Zeon, BM-400B), the same as Comparative Example 1 was used as Reference Example 1. Reference Example 2 was the same as Reference Example 1, except that after synthesizing dilithium 4,4'-biphenyldicarboxylate with a spray dryer, vacuum drying was performed at 120°C.

[Reference Examples 3 and 4]
Reference Example 3 was the same as Reference Example 1 except that an aqueous solution was prepared with a molar ratio of lithium hydroxide to 4,4'-biphenyldicarboxylic acid of 2.5 and synthesized using a spray dryer. Reference Example 4 was the same as Reference Example 3, except that after synthesizing dilithium 4,4'-biphenyldicarboxylate with a spray dryer, vacuum drying was performed at 120°C.

[Reference Examples 5 to 8]
Reference Example 5 was the same as Reference 1 except that a non-aqueous electrolytic solution prepared by adding lithium tetrafluoroborate to the supporting electrolyte so as to have a concentration of 1.1 mol/L was used. Reference Example 6 was the same as Reference Example 2, except that a non-aqueous electrolytic solution prepared by adding lithium tetrafluoroborate to the supporting electrolyte in an amount of 1.1 mol/L was used. Reference Example 7 was the same as Reference Example 3, except that a non-aqueous electrolytic solution prepared by adding lithium tetrafluoroborate to the supporting electrolyte in an amount of 1.1 mol/L was used. Reference Example 8 was the same as Reference Example 4, except that a non-aqueous electrolytic solution prepared by adding lithium tetrafluoroborate to the supporting electrolyte to a concentration of 1.1 mol/L was used.

[Reference Example 9]
Using 4,4′-biphenyldicarboxylic acid and lithium hydroxide monohydrate (LiOH.H ₂ O) as starting materials, methanol (100 mL) was added to lithium hydroxide monohydrate (0.556 g) and stirred. After that, 1.0 g of 4,4'-biphenyldicarboxylic acid was added and stirred for 1 hour. Then, after stirring, the solvent was removed and the mixture was dried at 150° C. under vacuum for 16 hours to obtain a white powder sample of lithium 4,4′-biphenyldicarboxylate. Reference Example 9 was the same as Reference Example 1 except that this was used.

2. Experiment (SEM observation)
The electrode active materials of Reference Examples 1 and 9 were observed with a scanning electron microscope (SEM). The electrode active material of Reference Example 1 is the same as the electrode active materials of Examples 1-3 and Comparative Examples 1-4. SEM observation was performed using a scanning electron microscope (Quanta200FEG manufactured by FEI Japan) under conditions of 1,000 to 50,000 magnifications. Further, the elemental distribution (oxygen distribution mapping) of the cut surface of the electrode was examined using an electron beam microanalyzer (JXA-8500F manufactured by JEOL).

(X-ray diffraction measurement)
The electrode active materials and electrodes of Reference Examples 1 to 9 were subjected to X-ray diffraction measurement. The measurement was performed using a CuKα ray (wavelength: 1.54051 Å) as radiation and an X-ray diffractometer (Ultima IV manufactured by Rigaku). In addition, the measurement was performed using a graphite single crystal monochromator for monochromatic X-rays, setting the applied voltage to 40 kV, current to 30 mA, scanning speed of 5°/min, and 2θ=5° for the electrode active material. 60°, and 2θ = 5° to 30° for the electrodes.

(Evaluation of charge/discharge characteristics)
The capacity obtained by reducing the bipolar evaluation cells of Reference Examples 1 to 9 to 0.5 V at 0.1 mA in a temperature environment of 20° C. was taken as the discharge capacity. Further, the capacity oxidized to 1.5 V at 0.1 mA was taken as the charge capacity. Using the obtained charge/discharge curve, the differential value of the charge/discharge curve was calculated with respect to the potential difference to obtain a differential curve. Also, the charge/discharge polarization was calculated from the peak difference between the two different internal resistance differential curves in this differential curve, and the IV resistance was calculated in consideration of the applied current. For the IV resistance, the charge/discharge curve of the second cycle was used. In addition, using the bipolar evaluation cell produced above, a continuous charge-discharge test was performed for 10 cycles under the above conditions in a temperature environment of 20° C., and the capacity retention rate was examined. The first charge capacity of this charge-discharge operation is Q _(1st) , the tenth charge capacity is Q _(10th) , and Q _(10th) / Q _(1st) × 100 is the capacity retention rate after charge-discharge cycles (% ).

Using the bipolar evaluation cells of Examples 1 to 3 and Comparative Examples 1 to 4, charge and discharge were performed at a current density d corresponding to 1/10 C, and charge and discharge capacity and coulombic efficiency were evaluated. Specifically, the capacity obtained by reducing the bipolar evaluation cell to 0.5 V at 0.1 mA in a temperature environment of 20° C. was taken as the discharge capacity. Further, the capacity oxidized to 1.5 V at 0.1 mA was taken as the charge capacity. Coulomb efficiency was defined as charge capacity/discharge capacity. A continuous charging/discharging test of 10 cycles was performed under the above conditions, and changes in coulombic efficiency were examined.

(Results and discussion 1)
First, using Reference Examples 1 to 9, active materials were examined. Table 1 shows the production method of Reference Examples 1 to 9, the Li composition, the presence or absence of drying of the active material, the supporting salt of the secondary battery, the IV resistance, the specific resistance based on Reference Example 5, the maximum discharge capacity, and the charge-discharge cycle. The capacity retention rate is collectively shown. 4 is an SEM photograph of Reference Example 1. FIG. 5 is an SEM photograph of Reference Example 9. FIG. As shown in FIG. 5, the electrode active material of the layered structure produced by the conventional solvent-drying method was in a state in which particles of 1 μm were aggregated. On the other hand, as shown in FIG. 4, it was found that the electrode active material of the layered structure of the reference example produced by the spray drying method has hollow particles with a size of 10 μm or less. In addition, when the particles whose insides are exposed are magnified, it is found that this electrode active material has a hollow spherical structure formed by enclosing a collection of flakes of a layered structure with a thickness of several nanometers. In addition, it was found that this electrode active material has a structure in which flakes of the layered structure irregularly extend from the center toward the outer periphery (same as a structure in which flakes irregularly extend from the outer periphery toward the center).

6 shows the XRD measurement results of the electrode active materials of Reference Examples 1, 2, 5, 6 and 9. FIG. 7 shows the XRD measurement results of the electrode active materials of Reference Examples 3, 4, 7, 8 and 9. FIG. As shown in FIG. 6, in Reference Example 1, which is an active material prepared by a spray drying method using an aqueous solution in which the molar ratio of lithium hydroxide to 4,4'-biphenyldicarboxylic acid is 2.2, Reference Example 9 and It showed an XRD pattern considered to have a crystal structure different from that of Reference Example 2 after drying. On the other hand, in Reference Example 2 in which the active material particles of Reference Example 1 were vacuum-dried at 120° C., a peak appeared at the same 2θ position as in the conventional production method. Therefore, it was found that Reference Example 1 had the same crystal structure as the conventional one when dried. Further, as shown in FIG. 7, in Reference Example 3 in which the molar ratio of lithium hydroxide to 4,4'-biphenyldicarboxylic acid was 2.5, and in Reference Example 4 in which it was vacuum-dried at 120° C., Results similar to those of Reference Example 2 were shown.

FIG. 8 is SEM photographs of the surfaces of the electrodes of Reference Examples 1 to 9. FIG. 8(a) is Reference Examples 1 and 5, FIG. 8(b) is Reference Examples 2 and 6, and FIG. 8(c) is Reference Example. 3 and 7, FIG. 8(d) are reference examples 4 and 8, and FIG. 8(e) is reference example 9. As shown in FIG. 8, when an electrode was produced using the active material of Reference Example 5, it was found that the unevenness of the surface was large. This is because, as shown in FIG. 2, the layered structure produced by the solvent drying method is an aggregate of large particles, and the large particles are formed as they are on the current collector when forming an electrode. It was speculated that this was because On the other hand, it was found that the electrodes using the active materials of Reference Examples 1 and 2 produced by the spray drying method had smooth surfaces. This is because, as shown in FIG. 2, the hollow particles of the flake-like layered structure are very fragile, and are likely to be crushed and highly dispersed when formed on the current collector as an electrode mixture. It was speculated that

FIG. 9 is an oxygen distribution map of the cross section of the electrode of Reference Examples 1, 2, and 9 by electron probe microanalyzer analysis. (c) is Reference Example 9. Oxygen in the electrode mixture is contained in the carboxylic acid of the layered structure, and the distribution of oxygen indicates the distribution of the layered structure. As shown in FIG. 9, from the cross-sectional observation of the produced electrode, it was found that in the electrode produced using the active material of Reference Example 1, the oxygen concentration was high on the outer peripheral side of the large block-shaped portion (see the dotted line in the figure). It was found that the aggregated state of the layered structure formed at the time of fabrication remained. On the other hand, it was found that the electrodes of Reference Examples 1 to 8 using the active material produced by the spray drying method formed a state in which the active material was uniformly dispersed. From this, when an electrode is produced using an active material produced by the solvent drying method, the active material is present inside the electrode without being crushed due to the strong cohesive force of the active material, whereas the spray drying method It was inferred that the layered structure having a hollow spherical structure formed by aggregation of flakes produced by the method was easily crushed during electrode fabrication, and that small flakes were uniformly dispersed inside the electrode.

FIG. 10 shows the XRD measurement results of the electrodes of Reference Examples 1-9. As shown in FIG. 10, in the electrodes of Reference Examples 1 to 8, which are the active materials prepared by the spray drying method, the 2θ position was the same as that of the conventional solvent drying method, regardless of whether or not the active material was vacuum dried at 120 ° C. A peak appeared at . It is considered that this is because vacuum drying is performed at 120° C. after electrode preparation, and that the same effect as 120° C. vacuum drying of the active material is brought about. The peak intensity corresponding to the n00 plane tended to increase in the electrode prepared by the spray drying method. This indicates a specific orientation of small flakes of active material present inside the electrode. In particular, in the electrodes of Reference Examples 1 to 8, the peak intensity of (300) is more than twice the peak intensity of (111) and (011) in X-ray diffraction measurement, and the peak intensity of (100) is ( 111) and (011) at least five times the peak intensity.

FIG. 11 shows charge-discharge curves in charge-discharge cycles of Reference Examples 1-9. FIG. 12 shows the evaluation results of the discharge capacities of Reference Examples 1-9. As shown in FIG. 11, it was found that the electrodes of Reference Examples 1 to 8, which are active materials produced by the spray drying method, exhibit reversible charge-discharge curves. Then, as shown in FIG. 12 and Table 1, it was found that the reversible charge/discharge capacity also increased. Since the electrode structure is such that the active material is uniformly dispersed in the form of small flakes inside the electrode, the interface that is effectively used for charge/discharge increases, resulting in improved utilization efficiency and increased charge/discharge capacity. inferred.

Also, the IV resistance was obtained from the differential curve of the charge/discharge curve. FIG. 13 shows differential curves obtained from the charge/discharge curves of Reference Examples 1-9. FIG. 14 shows evaluation results of IV resistance of Reference Examples 1-9. When dQ/dV was calculated from the charge/discharge curve results, it was found that the peak potential difference was smaller in the electrode using the active material produced by the spray drying method. In addition, as shown in FIG. 14, it was found that the electrode using the active material produced by the spray drying method has a lower IV resistance than the electrode using the active material produced by the conventional solvent drying method. . It is presumed that this is because the electrode structure in which the active material is uniformly dispersed in the form of small flakes inside the electrode increases the number of interfaces that are effectively used for charging and discharging, and as a result, the resistance is lowered.

Also, the relationship between the peak intensity ratio by XRD measurement and the IV resistance was examined. FIG. 15 shows the peak intensity ratio P(300)/P(111) of (300) to the peak intensity of (111) in the X-ray diffraction measurement, and the peak intensity ratio P of (300) to the peak intensity of (011) FIG. 4 is a relational diagram between (300)/P(011) and IV resistance. FIG. 16 shows the peak intensity ratio of (100) to the peak intensity of (111) in X-ray diffraction measurement P(100)/P(111), and the peak intensity ratio of (100) to the peak intensity of (011) P FIG. 4 is a relationship diagram between (100)/P(011) and IV resistance. FIG. 17 is a relational diagram between the peak intensity ratio P(100)/P(300) of (100) to the peak intensity of (300) in X-ray diffraction measurement and the IV resistance. FIG. 18 is an explanatory diagram of the crystal planes (011), (111), (100), and (300) of the layered structure. Table 2 summarizes the peak intensity ratios and IV resistance values of Reference Examples 1 to 4 and 9. As shown in FIGS. 15 to 17, the IV resistance tended to decrease as the peak intensity ratio increased. Also, it was found that the peak intensity ratio P(300)/P(111) and the peak intensity ratio P(300)/P(011) are preferably 2.0 or more. Also, it was found that the peak intensity ratio P(100)/P(111) is preferably 6.0 or more, and the peak intensity ratio P(100)/P(011) is preferably 5.0 or more. Also, it was found that the peak intensity ratio P(100)/P(300) is preferably 1.5 or more. As shown in FIG. 18, (100) and (300) reflect the crystal planes of the alkali metal element layer of the layered structure, and (011) and (111) represent the crystal planes of the organic skeleton layer. It is a reflection. Therefore, in this electrode, it was found that a higher peak intensity of the crystal plane of the alkali metal element layer is preferable for further improving the characteristics of the electricity storage device, such as further reducing the IV resistance.

From the above, the electrode material using the above-mentioned active material produced by the proposed spray drying method has an electrode structure in which the active material is uniformly dispersed inside the electrode at the time of electrode production, and an electrochemically active interface is formed. It has been found that forming a large number of layers significantly reduces the electrode resistance and improves the utilization factor.

(Results and discussion 2)
Next, using Examples 1-3 and Comparative Examples 1-4, non-aqueous electrolytes are examined. The active materials used in Examples 1 to 3 and Comparative Examples 1 to 4 are the same as those used in Reference Examples 1 and 5. Table 3 shows the addition ratio of LiBOB in Examples 1 to 3 and Comparative Examples 1 to 4, the discharge capacity at the 3rd cycle, and the coulombic efficiency at the 3rd cycle. 19 is a graph showing changes in discharge capacity during 10 cycles of Examples 1 to 3 and Comparative Example 1. FIG. FIG. 20 is a graph showing changes in coulombic efficiency during 10 cycles of Examples 1 to 3 and Comparative Example 1; FIG. 21 is a graph showing the relationship between the amount of LiBOB added and the initial capacity. FIG. 22 is a graph showing the relationship between the amount of LiBOB added in Examples 1 to 3 and Comparative Example 1 and the discharge capacity and coulombic efficiency.

In Examples 1 to 3 in which LiBOB was added in the range of 0.1 mass % or more and less than 1 mass %, the initial capacity of the negative electrode increased (Fig. 19) and the coulombic efficiency during charging and discharging also increased (Fig. 20). On the other hand, in Comparative Examples 2 to 4 in which 1% by mass or more of LiBOB was added, the initial capacity decreased rapidly, and the electrode performance decreased (FIG. 21). found to be favorable. Among them, the coulombic efficiency was particularly high in Examples 2 and 3 (Fig. 23), so it was found that the addition amount is more preferably 0.2% by mass or more and 0.5% by mass or less.

It is speculated that the reason why such an effect was obtained is that LiBOB decomposed at a potential higher than that at which Li begins to be absorbed into dilithium biphenyldicarboxylate, forming a suitable film on the electrode surface. This point will be described below. FIG. 23 shows charge/discharge curves of Examples 1 to 3 and Comparative Examples 1 to 3 during the first cycle of discharge (Li absorption reaction to dilithium biphenyldicarboxylate). FIG. 24 is a graph plotting changes in current amount with respect to potential changes in Examples 1-3 and Comparative Examples 1-3. From FIG. 24, it can be seen at which potential the decomposition current and the reaction current flow.

From the charge/discharge curves in FIG. 23, it can be seen that Examples 1 to 3 and Comparative Example 1 initially exhibit a discharge capacity of 300 mAhg ⁻¹ . On the other hand, in Comparative Examples 2 and 3 in which 1% by mass or more of LiBOB was added, the discharge capacity decreased to about 150 mAhg ⁻¹ . It was presumed that this was because the amount of LiBOB added was too large, so that a thick film was formed on the electrode surface, and the electrode resistance increased, resulting in a decrease in charge/discharge capacity.

Regarding this point, it was inferred from FIG. 24 that the LiBOB decomposition reaction and the electrolytic solution decomposition reaction were suppressed. That is, in Comparative Example 1 in which LiBOB was not added, a decomposition current corresponding to decomposition of the electrolyte flowed in the range of 0.7 to 1.3 V based on Li. Li absorption into dilithium biphenyldicarboxylate occurred around 7V. On the other hand, in Examples 1 to 3 and Comparative Examples 2 and 3 in which LiBOB was added, a current peak appeared at 1.7 V based on Li (FIG. 24). Since the peak at 1.7 V increased as the amount of LiBOB added increased, it was presumed that LiBOB was reductively decomposed on the electrode surface. In Examples 1 to 3, the 0.7-1.3 V peak corresponding to the decomposition of the electrolytic solution is reduced compared to Comparative Example 1, and LiBOB decomposes on the electrode surface to form a stable film, It was inferred that the decomposition of the electrolytic solution was suppressed.

From the above, it is speculated that by adding LiBOB in a range of less than 1% by mass, a stable SEI film is formed on the electrode surface, the decomposition of the electrolyte is suppressed, side reactions are prevented, and the coulombic efficiency is improved. rice field. In addition, it was speculated that the same results as in the case of using LiBOB would be obtained when the compound represented by the general formula (1) capable of forming a film like LiBOB is used.

INDUSTRIAL APPLICABILITY The present invention can be used in fields such as the battery industry.

10 electrode active material, 11 hollow particles, 12 layered structure, 20 electricity storage device, 21 case, 22 positive electrode, 23 negative electrode, 24 separator, 25 gasket, 26 sealing plate, 27 non-aqueous electrolyte.

Claims (7)

A strip of a layered structure comprising an organic skeleton layer containing an aromatic dicarboxylic acid anion and an alkali metal element layer forming a skeleton by coordinating an alkali metal element to oxygen contained in the carboxylic acid of the organic skeleton layer is used as an electrode. an electrode comprising as a substance;
A non-aqueous electrolyte containing a compound represented by the general formula (1) in a range of 0.5% by mass or less and conducting carrier ions;
A power storage device.

(where M represents a transition element, a group 13, 14 or 15 element of the periodic table; A ^{a +} is a metal ion proton or onium ion, a is an integer of 1 to 3, p is b/a; b is an integer of 1 to 3, m is an integer of 1 to 4, n is an integer of 0 to 8, q is 0 or 1; R ¹ is alkylene having 1 to 10 carbon atoms, halogenated Alkylene, arylene having 6 to 20 carbon atoms or arylene halide having 6 to 20 carbon atoms (these alkylene and arylene may have substituents and heteroatoms in their structures, and q is 1 and m is 2 R ² represents halogen, alkyl having 1 to ¹⁰ carbon atoms, halogenated alkyl having 1 to 10 carbon atoms, 6 to 20 aryl, halogenated aryl having 6 to 20 carbon atoms (these alkyl and aryl may have substituents and heteroatoms in their structures, and when n is 2 to 8, n R ² each may combine to form a ring) or -X ³ R ³ ; X ¹ , X ² and X ³ each independently represent O, S or NR ⁴ ; R ³ and R ⁴ are each independently hydrogen, alkyl having 1 to 10 carbon atoms, alkyl halide having 1 to 10 carbon atoms, aryl having 6 to 20 carbon atoms, aryl halide having 6 to 20 carbon atoms (these alkyl and aryl are It may have substituents and heteroatoms in its structure, and when there are a plurality of R ³ or R ⁴ , each may combine to form a ring)). The electricity storage device according to claim 1, wherein the compound represented by the general formula ( 1 ) is a bisoxalate borate salt. The electrode active material satisfies at least one of having a hollow spherical structure formed by enclosing a collection of flakes of the layered structure, or having a flake-like structure obtained by crushing the hollow spherical structure. The electricity storage device according to claim 1 or 2 . The electricity storage device according to any one of claims 1 to 3 , wherein the electrode satisfies one or more of the following (1) to (5).
(1) The peak intensity ratio P(300)/P(111) of (300) to the peak intensity of (111) in X-ray diffraction measurement is 2.0 or more.
(2) The peak intensity ratio P(300)/P(011) of (300) to the peak intensity of (011) in X-ray diffraction measurement is 2.0 or more.
(3) The peak intensity ratio P(100)/P(111) of (100) to the peak intensity of (111) in X-ray diffraction measurement is 6.0 or more.
(4) The peak intensity ratio P(100)/P(011) of (100) to the peak intensity of (011) in X-ray diffraction measurement is 5.0 or more.
(5) The peak intensity ratio P(100)/P(300) of (100) to the peak intensity of (300) in X-ray diffraction measurement is 1.5 or more. The electricity storage device according to any one of claims 1 to 4, wherein the electrode active material has a structure represented by one or more of formulas (2) to ( 4 ).

The electricity storage device according to any one of claims 1 to 5 , wherein the electrode is a negative electrode. 7. Any one of claims 1 to 6 , wherein the electrode active material is obtained through a step of spray-drying a solution prepared by dissolving an aromatic dicarboxylate anion and an alkali metal cation using a spray-drying apparatus. 6. The electricity storage device according to the item.

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