JP6922209B2 - Power storage device - Google Patents

Description

The present disclosure, which is the invention disclosed in the present specification, relates to a power storage device.

Conventionally, as a power storage device such as a lithium ion secondary battery or a lithium ion capacitor, a device in which graphite is used as a negative electrode and lithium hexafluorophosphate is dissolved as a supporting salt in a non-aqueous electrolyte solution is known. Further, in such a power storage device, lithium tetrafluoroborate may be mentioned as a supporting salt, but when the supporting salt is changed from lithium hexafluorophosphate to lithium tetrafluoroborate, the resistance of the negative electrode increases. In general, lithium tetrafluoroborate was considered to have high resistance (see, for example, Non-Patent Document 1 and FIG. 8). FIG. 8 is an explanatory diagram of the impedance behavior of the graphite negative electrode using _{LiPF 6} and LiBF _{4 as supporting salts.}

Further, as the negative electrode for a lithium secondary battery, an alkali metal element is coordinated with an organic skeleton layer containing an aromatic compound which is a dicarboxylic acid anion having two or more aromatic ring structures 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

J. Electrochem.Soc., 2016,163, A1686-A1692

However, in the above-mentioned power storage device of Patent Document 1, although the stability of the charge / discharge cycle characteristics can be further improved, the negative electrode resistance may be high, and it has been required to further reduce this resistance.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a power storage device capable of further reducing the resistance of a negative electrode using a layered structure as a negative electrode active material.

As a result of diligent research to achieve the above-mentioned object, the present inventors have found that in the negative electrode containing the layered structure of the aromatic dicarboxylic acid metal salt, particularly the layered structure having the organic skeleton layer of the biphenyldicarboxylic acid anion. It has been found that the combination with the supporting salt of lithium tetrafluoroborate can specifically significantly reduce the negative electrode resistance, and the present invention has been completed.

That is, the power storage device disclosed in this specification is
With the positive electrode
A negative electrode having a layered structure of an aromatic dicarboxylic acid metal salt containing a biphenyldicarboxylic acid anion as a negative electrode active material, and a negative electrode.
An ionic conduction medium containing lithium tetrafluoroborate and conducting lithium ions,
It is equipped with.

In the power storage device disclosed in the present specification, the resistance of the negative electrode can be further reduced. The reason why such an effect is obtained is presumed as follows. For example, if a layered structure containing a biphenyldicarboxylic acid anion and lithium tetrafluoroborate are contained in the power storage device, the charge transfer reaction at the interface between the electrode and the ionic conduction medium is smoothly performed, so that the negative electrode resistance Is presumed to decrease.

The schematic diagram which shows an example of the power storage device 20. Charge / discharge curves of Experimental Examples 1 to 6 and Reference Examples 1 and 2. A differential curve obtained from the charge / discharge curves of Experimental Examples 1 to 6. Explanatory drawing of polarization obtained from the charge / discharge differential curve of Experimental Example 1. The relationship diagram between the ratio (mol%) of LiBF _{4 and the IV resistance value (Ω).} Charge / discharge cycle characteristic evaluation results of Experimental Examples 1 to 5. Charge / discharge cycle characteristic evaluation result of Experimental Example 6. Explanatory drawing of impedance behavior of graphite negative electrode using _{LiPF 6} and LiBF ₄ as supporting salts.

The power storage device disclosed in the present specification includes a positive electrode, a negative electrode, and an ionic conduction medium. The positive electrode may contain a positive electrode active material that occludes and releases lithium ions. The negative electrode contains a layered structure that occludes and releases lithium ions, which are carriers, as a negative electrode active material. This negative electrode active material is a layered structure of an aromatic dicarboxylic acid metal salt containing a biphenyldicarboxylic acid anion. Further, the ion conduction medium is interposed between the positive electrode and the negative electrode to conduct lithium ions. This ionic conduction medium contains lithium tetrafluoroborate (LiBF ₄ ). 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 battery, or the like. The metal ion that is the carrier is a Li ion. Here, for convenience of explanation, a lithium ion capacitor in which lithium ions are occluded and discharged into a layered structure by charging and discharging will be mainly described below.

In the power storage device of the present disclosure, a known positive electrode used for a capacitor, a lithium ion capacitor, or the like may be used as the positive electrode. 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, coke, glassy carbons, graphites, graphitizable carbons, thermally decomposed carbons, carbon fibers, carbon nanotubes, etc. Examples include graphite. 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 non-aqueous electrolyte solution is adsorbed and desorbed to store electricity, but further, at least one of the anion and the cation contained in the non-aqueous electrolyte solution is inserted. It may be desorbed and stored.

Alternatively, the positive electrode may be a positive electrode used in a general lithium ion 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. A lithium nickel 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.} 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. 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 a foil shape, a film shape, a sheet shape, a net shape, a punched or expanded body, a lath body, a porous body, a foam body, and a fiber group forming body. As the thickness of the current collector, for example, one having a thickness of 1 to 500 μm is used.

In this power storage device, the negative electrode includes a layered structure as a negative electrode active material. This layered structure has an organic skeleton layer containing an aromatic compound which is a biphenyldicarboxylic acid anion, and an alkali metal element layer in which an alkali metal element coordinates with oxygen contained in the carboxylic acid anion to form a skeleton. May be. The alkali metal contained in the alkali metal element layer can be, for example, any one or more of Li, Na, K and the like, but Li is preferable. Since the alkali metal element contained in this alkali metal element layer forms the skeleton of the layered structure, it is presumed that the alkali metal element is not involved in the ion transfer associated with charging / discharging, that is, it is not occluded and released during charging / discharging.

It is structurally stable that this layered structure is formed in layers by the π-electron interaction of aromatic compounds and has a monoclinic crystal structure belonging to _{the space group P2 1 / c.} Yes, preferred. This layered structure contains an aromatic compound represented by the following formula (1). Further, it is structurally stable that this layered structure has a structure of the formula (2) in which four oxygens of different dicarboxylic acid anions and an alkali metal element form a four-coordination. preferable. However, in this formula (2), R has an aromatic ring structure of a biphenyldicarboxylic acid. Further, A is an alkali metal element. In the energy storage mechanism, organic framework layer of the layered structure redox (e ^-) while functioning as a site, the alkali metal element layer and functions as a storage site for the metal ion is a carrier (alkali metal ion adsorption site) Conceivable.

For the negative electrode, for example, a layered structure which is a negative electrode active material and other materials are mixed, and an appropriate solvent is added to form a paste-like negative electrode mixture, which is applied to the surface of the current collector, dried, and required. It may be formed by compression in order to increase the electrode density. As the conductive material, the binder, and the like used for the negative electrode, those exemplified for the positive electrode can be used. Further, the negative electrode is assumed to be a negative electrode mixture containing a layered structure and a conductive material, which is formed on a current collector and then fired in an inert atmosphere in a temperature range of 250 ° C. or higher and 450 ° C. or lower. May be good. By doing so, the crystal structure can be made more suitable, the π-electron interaction of the aromatic compound is enhanced, the transfer of electrons is facilitated, and the charge / discharge characteristics can be further enhanced.

In this power storage device, the ion conducting medium may be, for example, a non-aqueous electrolyte solution containing a supporting salt (supporting electrolyte) and an organic solvent. The ionic conduction medium contains lithium tetrafluoroborate (LiBF ₄ ) as a supporting salt. The ion conduction medium preferably contains lithium tetrafluoroborate in a range of 20 mol% or more and 100 mol% or less of the total supporting salt. In this range, the resistance of the negative electrode can be reduced more effectively. As the supporting salt, a known lithium salt may be contained in addition to _{LiBF 4.} Examples of this lithium salt include LiPF ₆ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiN (C ₂ F ₅ SO ₂ ) _{2, and the} like, of which LiPF ₆ is preferable. At this time, the ion conduction medium _{preferably contains LiPF 6} in the range of 0 mol% or more and 20 mol% or less. In this range, the resistance of the negative electrode can be reduced more effectively. In addition, it is possible to suppress a decrease in charge / discharge cycle characteristics, such as suppressing a decrease in the capacity retention rate during the charge / discharge cycle. The ion conduction medium contains a non-aqueous electrolyte solution, and _{preferably contains a supporting salt containing LiBF 4} in the range of 1.0 mol / L or more and 1.5 mol / L or less, and 1.0 mol / L or more and 1.2 mol / L. It is more preferably in the following range. 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. 1 is a schematic view showing an example of the power storage device 20 of the above-described embodiment. 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. The energy storage device 20 is filled with an ionic conduction medium 27 containing lithium tetrafluoroborate in the space between the positive electrode 22 and the negative electrode 23. Further, the negative electrode 23 has a layered structure of an aromatic dicarboxylic acid metal salt containing a biphenyldicarboxylic acid anion as a negative electrode active material.

In the power storage device described in detail above, the resistance of the negative electrode can be further reduced. The reason why such an effect is obtained is presumed as follows. For example, if a layered structure containing a biphenyldicarboxylic acid anion and lithium tetrafluoroborate are contained in the power storage device, the charge transfer reaction at the interface between the electrode and the ionic conduction medium is smoothly performed, so that the negative electrode resistance Is presumed to decrease.

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

Hereinafter, an example in which the power storage device is specifically implemented will be described as an experimental example. In this embodiment, a bipolar cell in which the counter electrode is a lithium metal is examined, but if the counter electrode is a positive electrode containing an arbitrary positive electrode active material, it can operate as a power storage device.

[Experimental Example 1]
(Synthesis of layered structure of dilithium 4,4'-biphenyldicarboxylic acid)
A layered structure (formula (3)) having a structure of dilithium 4,4'-biphenyldicarboxylic acid was synthesized. As the dilithium 4,4'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid and lithium hydroxide monohydrate (LiOH · H ₂ O) were used as starting materials. First, methanol was added to lithium hydroxide monohydrate and stirred. After dissolving lithium hydroxide monohydrate, 4,4'-biphenyldicarboxylic acid was added, and the mixture was stirred for 1 hour. After stirring, the solvent was removed, and the mixture was dried under vacuum at 150 ° C. for 16 hours to obtain a white powder sample.

(Preparation of negative electrode)
The obtained powder sample was 79% by mass, carbon black (TB5500 manufactured by Tokai Carbon) was 14% by mass as a particulate carbon conductive material, and polyvinyl alcohol (PVA, Gosenex T-330 manufactured by Nippon Synthetic Chemical Co., Ltd.), which was a water-soluble polymer, was 2 .8% by mass and 4.2% by mass of a styrene-butadiene copolymer (SBR, BM-400B manufactured by Nippon Zeon) were mixed, and an appropriate amount of water was added and dispersed as a dispersant to obtain a slurry-like mixture. This slurry-like mixture is uniformly applied to a 10 μm-thick copper foil current collector so that the amount of the dilithium 4,4'-biphenyldicarboxylic acid dilithium active material per unit area is 3 mg / cm ^2, and the coating sheet is dried by heating. Was produced. Then, the coating sheet was pressure-pressed ^{and punched into an area of 2 cm 2} to prepare a disk-shaped electrode.

(Preparation of bipolar evaluation cell)
_{Lithium tetrafluoroborate (LiBF 4} ) was added to a non-aqueous solvent in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 30:40:30 so as to be 1.10 mol / L. A water electrolyte was prepared. A separator (manufactured by Toray Tonen) impregnated with the non-aqueous electrolytic solution between both electrodes is provided with the prepared dilithium 4,4′-biphenyldicarboxylic acid negative electrode as the working electrode and the lithium metal foil (thickness 300 μm) as the counter electrode. A bipolar evaluation cell of Experimental Example 1 was prepared by sandwiching it.

[Experimental Examples 2 to 6]
In the non-aqueous electrolytic solution, LiBF ₄ was added to 0.825 mol / L and lithium hexafluorophosphate (LiPF ₆ ) was added so as to be 0.275 mol / L to prepare a non-aqueous electrolytic solution. The cell prepared in the same manner was used as a bipolar evaluation cell of Experimental Example 2. Further, _{a non-aqueous electrolytic solution prepared by adding LiBF 4} to 0.550 mol / L and LiPF ₆ to 0.550 mol / L was prepared in the same manner as in Experimental Example 1 in Experimental Example 3-2. It was used as a polar evaluation cell. Further, _{a non-aqueous electrolytic solution was prepared by adding LiBF 4} to 0.275 mol / L and LiPF ₆ to 0.825 mol / L, and the same preparation as in Experimental Example 1 was prepared in Experimental Example 4-2. It was used as a polar evaluation cell. Further, _{a non-aqueous electrolytic solution prepared by adding LiBF 4} to 0.110 mol / L and LiPF ₆ to 0.990 mol / L was prepared in the same manner as in Experimental Example 1 in Experimental Example 5-2. It was used as a polar evaluation cell. Further, a _{cell prepared in the same manner as in Experimental Example 1 except that LiPF 6} was added so as to be 1.10 mol / L to prepare a non-aqueous electrolytic solution was used as a bipolar evaluation cell of Experimental Example 6.

[Reference Examples 1 and 2]
(Synthesis of layered structure of dilithium 2,6-naphthalenedicarboxylic acid)
For the synthesis of dilithium 2,6-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and lithium hydroxide monohydrate (LiOH · H ₂ O) were used as starting materials. Methanol (100 mL) was added to lithium hydroxide monohydrate (0.556 g), and the mixture was stirred. After dissolving lithium hydroxide monohydrate, 2,6-naphthalenedicarboxylic acid (1.0 g) was added and stirred for 1 hour. After stirring, the solvent was removed, and the mixture was dried under vacuum at 150 ° C. for 16 hours to obtain a white powder sample of dilithium 2,6-naphthalenedicarboxylic acid (formula (4) below).

A bipolar evaluation cell of Reference Example 1 was prepared in the same manner as in Experimental Example 1 except that dilithium 2,6-naphthalenedicarboxylic acid was used as a negative electrode instead of dilithium 4,4'-biphenyldicarboxylic acid. Further, a product prepared in the same manner as in Experimental Example 6 except that dilithium 2,6-naphthalenedicarboxylic acid was used as a negative electrode instead of dilithium 4,4'-biphenyldicarboxylic acid was used as the bipolar evaluation cell of Reference Example 2. bottom.

(Evaluation of charge / discharge characteristics)
The capacity obtained by reducing the prepared bipolar evaluation cell to 0.5 V at 0.1 mA under a temperature environment of 20 ° C. was defined as the discharge capacity. Further, the capacity oxidized to 1.5 V at 0.1 mA thereafter was defined as the charge capacity. The number of measurement cells n = 2. FIG. 2 is a charge / discharge curve of Experimental Examples 1 to 6 and Reference Examples 1 and 2. Further, using the obtained charge / discharge curve, the differential value of the charge / discharge curve was calculated with respect to the potential difference to obtain the differential curve. FIG. 3 is a differential curve obtained from the charge / discharge curves of Experimental Examples 1 to 6. The charge / discharge polarization was read from the peaks of the two different internal resistance differential curves on this differential curve, and the IV resistance was calculated in consideration of the applied current. FIG. 4 is an explanatory diagram of polarization obtained from the charge / discharge differential curve of Experimental Example 1. For the IV resistance, the charge / discharge curve of the first cycle was used. Further, using the prepared bipolar evaluation cell, a continuous charge / discharge test of 10 cycles was performed under the above conditions under 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 10 cycles. And said.

(Results and discussion)
Table 1 summarizes the details of the prepared bipolar evaluation cell, the average IV resistance (Ω), and the capacity retention rate (%). FIG. 5 is a diagram showing the relationship between the ratio (mol%) of _{LiBF 4} and LiPF _{6 and the IV resistance (Ω).} FIG. 6 shows the charge / discharge cycle characteristic evaluation results of Experimental Examples 1 to 5, and FIG. 7 shows the charge / discharge cycle characteristic evaluation results of Experimental Example 6. As shown in Table 1 and FIG. 5, when the negative electrode active material and a layered structure containing a biphenyl dicarboxylic acid anion, tetrafluoroborate as a supporting salt in a non-aqueous electrolyte anions BF ₄ ^- the containing 20～100Mol% In Experimental Examples 1 to 4, it was found that the IV resistance was reduced by 50% to 60% as compared with Experimental Example 6 containing 100 mol% of _{hexafluorophosphate anion PF 6} ^−. Further, as shown in Reference Examples 1 and 2, it was found that when the negative electrode active material was a layered structure containing a naphthalene dicarboxylic acid anion, the large effect as in Experimental Examples 1 to 4 could not be obtained. As for the capacity retention rate, as shown in Tables 1, 6 and 7, all of them showed high values in Experimental Examples 1 to 6, so that _{both LiBF 4} and LiPF ₆ have high charge / discharge stability. I understood.

Regarding the supporting salt, as described in Non-Patent Document 1, it is known that in the graphite negative electrode, the negative _{electrode resistance is lower when LiPF 6} is used, and the negative electrode resistance is higher when LiBF ₄ is used (Fig.). 8). However, the results of this experiment revealed that the combination of the negative electrode active material of the layered structure containing the biphenyldicarboxylic acid anion and _{the supporting salt of LiBF 4} can specifically reduce the negative electrode resistance. rice field.

The present invention is available in 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 (5)

With the positive electrode
A negative electrode having a layered structure of an aromatic dicarboxylic acid metal salt containing a biphenyldicarboxylic acid anion as a negative electrode active material, and a negative electrode.
An ionic conduction medium containing lithium tetrafluoroborate and conducting lithium ions,
With
The ion conduction medium contains a supporting salt and contains the lithium tetrafluoroborate in the range of 50 mol% or more and 100 mol% or less of the total supporting salt.
Power storage device. The power storage device according to claim 1 , wherein the ion conduction medium contains a supporting salt and contains lithium hexafluorophosphate in the range of 0 mol% or more and 20 mol% or less of the entire supporting salt. With the positive electrode
A negative electrode having a layered structure of an aromatic dicarboxylic acid metal salt containing a biphenyldicarboxylic acid anion as a negative electrode active material, and a negative electrode.
An ionic conduction medium containing lithium tetrafluoroborate and conducting lithium ions,
With
The ion conduction medium contains a non-aqueous electrolyte solution and contains the supporting salt containing lithium tetrafluoroborate in the range of 1.1 mol / L or more and 1.5 mol / L or less.
Power storage device. With the positive electrode
A negative electrode having a layered structure of an aromatic dicarboxylic acid metal salt containing a biphenyldicarboxylic acid anion as a negative electrode active material, and a negative electrode.
An ionic conduction medium containing lithium tetrafluoroborate and conducting lithium ions,
With
The ionic conduction medium contains an organic solvent, and the ethylene carbonate in the organic solvent is 30% by volume or less.
Power storage device. The power storage device according to any one of claims 1 to 4, wherein the negative electrode has the layered structure represented by the following formula (1) as a negative electrode active material.

Images