JP2015153700A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device which is high in voltage and capacity, and superior in rate characteristic.SOLUTION: A power storage device comprises: an electrode group including a positive electrode having a positive electrode active material and a positive electrode collector holding the positive electrode active material, a negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material, and a separator interposed between the positive and negative electrodes; a nonaqueous electrolyte having lithium ion conductivity; and a case which encloses the electrode group and the nonaqueous electrolyte. The nonaqueous electrolyte includes an ionic liquid containing a first salt of lithium ions and first anions. The positive electrode active material includes a material capable of reversibly supporting the first anions. The negative electrode active material includes a material capable of reversibly supporting the lithium ions. With the power storage device discharged, the percentage of the lithium ions to cations included in the nonaqueous electrolyte is 20 mol% or more.

Description

  The present invention relates to an electricity storage device, and more particularly, to an electricity storage device having high voltage, high capacity, and excellent rate characteristics.

  Amid the close-up of environmental issues, systems for converting clean energy such as sunlight and wind power into electric power and storing it as electric energy are being actively developed. As such an electricity storage device, a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery and a capacitor such as a lithium ion capacitor are known.

  Among power storage devices, non-aqueous electrolyte secondary batteries and capacitors using dual carbon cells are known. Patent Document 1 proposes a battery using dual carbon cells (hereinafter referred to as a dual carbon battery). A dual carbon battery uses a carbon material as both a positive electrode active material and a negative electrode active material. In the case of a lithium ion secondary battery, during charging, anions contained in the non-aqueous electrolyte are inserted into the carbon material that is the positive electrode active material, and lithium ions are inserted into the carbon material that is the negative electrode active material. During discharge, the inserted anions and lithium ions are desorbed from the respective carbon materials into the non-aqueous electrolyte.

  Non-Patent Document 1 reports that an intercalation compound is formed by inserting an anion in an ionic liquid into graphite in a positive electrode.

International Publication No. 2013/035361 Pamphlet

Journal of The Electrochemical Society, 160 (11) A1979-A1991 (2013)

  In a dual carbon battery or the like, the capacity depends on the concentration of lithium ions and anions contained in the nonaqueous electrolyte. Therefore, in patent document 1, the density | concentration of a lithium ion and an anion is improved by using the organic solvent containing lithium salt as a nonaqueous electrolyte, and also making a solid lithium salt contain in the inside of a battery. However, in this method, since lithium salt is deposited inside the battery during discharge, there is a concern that the performance of the battery may be affected. Furthermore, since an organic solvent is used, it is difficult to obtain a high voltage.

  Non-patent document 1 only reports on a cell in which metallic lithium and graphite are combined.

  A first aspect of the present invention includes a positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material, a negative electrode active material and a negative electrode having a negative electrode current collector holding the negative electrode active material, and An electrode group including a separator interposed between a positive electrode and the negative electrode, a non-aqueous electrolyte having lithium ion conductivity, and a case containing the electrode group and the non-aqueous electrolyte, and the non-aqueous electrolyte The electrolyte includes an ionic liquid including a first salt of lithium ions and a first anion, the positive electrode active material includes a material capable of reversibly supporting the first anion, and the negative electrode active material includes: Including a material capable of reversibly supporting the lithium ions, and in a discharged state, the proportion of the lithium ions in the cations contained in the non-aqueous electrolyte is 20 mol% or more. About the power storage device.

The second aspect of the present invention comprises said power storage device, a charge control device that controls the charging current I _in the electric storage device, and a discharge control device for controlling the discharge current I _out of the electric storage device, and The charge control device relates to a charge / discharge system that controls the end-of-charge voltage of the power storage device to be 5.0 V or higher.

  The electricity storage device of the present invention has a high voltage and a high capacity, and is excellent in rate characteristics.

1 is a longitudinal sectional view schematically showing an electricity storage device according to an embodiment of the present invention. It is a schematic diagram which shows an example of the structure of a part of frame | skeleton of a positive electrode electrical power collector. It is a cross-sectional schematic diagram which shows the state which filled the positive electrode current collector with the positive electrode current collector. It is a block diagram which shows the outline | summary of the charging / discharging system which concerns on one Embodiment of this invention.

[Description of Embodiment of the Invention]
First, the contents of the embodiments of the invention will be listed and described.
A first aspect of the present invention is (1) a positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material, a negative electrode active material, and a negative electrode having a negative electrode current collector holding the negative electrode active material, And an electrode group comprising a separator interposed between the positive electrode and the negative electrode, a non-aqueous electrolyte having lithium ion conductivity, and a case containing the electrode group and the non-aqueous electrolyte, The non-aqueous electrolyte includes an ionic liquid containing a first salt of lithium ions and a first anion, and the positive electrode active material includes a material capable of occluding and releasing the first anion, and the negative electrode active material Includes a material capable of reversibly supporting the lithium ions, and in a discharged state, the proportion of the lithium ions in the cations contained in the non-aqueous electrolyte is 20 mol% or less. In which, on the power storage device. Thereby, an electricity storage device having a high voltage and a high capacity and excellent rate characteristics can be obtained.

  (2) It is preferable that content of the ionic liquid in the non-aqueous electrolyte is 80% by mass or more. This is because further improvement in voltage, capacity, and rate characteristics can be expected.

  (3) It is preferable that the ionic liquid further includes a second salt of an organic cation and a second anion, and the first anion and the second anion are each independently a polyatomic anion. This is because a further improvement in voltage and capacity can be expected.

  (4) It is preferable that the positive electrode active material includes a carbon material having a graphite structure, and the first anion and the second anion both include a bis (fluorosulfonyl) amide anion. This is because the rate characteristics can be further improved.

  (5) The positive electrode current collector is a first metal porous body having a three-dimensional network structure, and the negative electrode current collector is a second metal porous body having a three-dimensional network structure. preferable. This is because the rate characteristics can be further improved.

(6) the second aspect of the present invention includes the electricity storage device, a charge control device that controls the charging current I _in the electric storage device, and a discharge control device for controlling the discharge current I _out of the electric storage device, the And the charge control device relates to a charge / discharge system that controls the end-of-charge voltage of the power storage device to be 5.0 V or more. Thereby, a high voltage electrical storage device can be obtained.

[Details of the embodiment of the invention]
Embodiments of the present invention will be specifically described below. In addition, this invention is not limited to the following content, but is shown by the claim, and it is intended that all the changes within the meaning and range equivalent to a claim are included.

[Nonaqueous electrolyte]
The nonaqueous electrolyte has lithium ion conductivity and contains an ionic liquid containing a first salt of lithium ions and a first anion. Here, the ionic liquid is synonymous with a molten salt (molten salt) and is a liquid substance composed of a cation and an anion.

  The lithium ion concentration is 20 mol% or more with respect to the total of cations contained in the nonaqueous electrolyte in the discharged state. When the lithium ion concentration is 20 mol% or more, a high capacity can be achieved even when charging / discharging at a high rate. In particular, in an electricity storage device in which lithium ions are occluded (or adsorbed) in the negative electrode active material during charging and the first anion is occluded in the positive electrode active material (hereinafter sometimes referred to as a dual ion electricity storage device or a dual ion battery). The concentration of lithium ions contained in the non-aqueous electrolyte greatly affects the capacity. Therefore, an ionic liquid that can increase the lithium ion concentration has a high effect of improving capacity. In addition, a discharge state means the state discharged to the discharge end voltage.

  The lithium ion concentration is preferably 25 mol% or more, more preferably 30 mol% or more, based on the total number of cations contained in the nonaqueous electrolyte. The lithium ion concentration is preferably 60 mol% or less, more preferably 50 mol% or less, and particularly preferably 45 mol% or less with respect to the total number of cations contained in the nonaqueous electrolyte. . Such a non-aqueous electrolyte has a relatively low viscosity, and it is easy to achieve a high capacity even when charging / discharging at a higher rate of current. The preferable upper limit and the lower limit of the lithium ion concentration can be arbitrarily combined to set a preferable range.

  The content of the ionic liquid in the nonaqueous electrolyte is preferably 80% by mass or more. When the content of the ionic liquid is within this range, an even higher voltage electricity storage device can be obtained. Moreover, heat resistance and nonflammability can be further improved. The ionic liquid may contain a second salt of an organic cation and a second anion in addition to the first salt.

  Although the ionic liquid may occupy 100% by mass of the nonaqueous electrolyte, the additive may contain an organic solvent at a rate of 10% by mass or less, preferably 8% by mass or less. As an organic solvent, a carbonate compound is preferable. Examples of the carbonate compound include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chain carbonates such as diethyl carbonate (DEC) and dimethyl carbonate (DMC), and fluorine-containing carbonate compounds such as fluoroethylene carbonate. It is done.

The first anion and the second anion are preferably each independently a polyatomic anion. A polyatomic anion is an anion composed of two or more atoms. For example, anion of fluorine-containing acid [anion of fluorine-containing phosphate such as hexafluorophosphate ion (PF ₆ ⁻ ); anion of fluorine-containing boric acid such as tetrafluoroborate ion (BF ₄ ⁻ )], chlorine-containing Anion of acid [perchlorate ion (ClO ₄ ⁻ ) and the like], Anion of oxygen acid having an oxalate group [Oxalatoborate ion such as bis (oxalato) borate ion (B (C ₂ O ₄ ) ₂ ⁻ ); Tris; (Oxalato) phosphate ions (Oxalatoborate ions such as P (C ₂ O ₄ ) ₃ ⁻ )], fluoroalkanesulfonic acid anions [trifluoromethanesulfonic acid ions (CF ₃ SO ₃ ⁻ ) etc.], fluorine-containing amides And anions. The first anion and the second anion may be the same or different.

  Among these, the first anion and the second anion preferably both contain a fluorine-containing amide anion, and more preferably contain a fluorine-containing bis (sulfonyl) amide anion. This is because a non-aqueous electrolyte having high heat resistance and high ion conductivity can be obtained. The fluorine-containing bis (sulfonyl) amide anion is an anion having a structure having a bis (sulfonyl) amide skeleton and a fluorine atom in the sulfonyl group.

As the fluorine-containing bis (sulfonyl) amide anion, bis (fluorosulfonyl) amide anion (FSA ⁻ : bis (fluorosulfonyl) amide anion)); bis (trifluoromethylsulfonyl) amide anion (TFSA ⁻ : bis (trifluoromethylsulfonyl) amide anion) ), Bis (pentafluoroethylsulfonyl) amide anion, bis (perfluoroalkylsulfonyl) amide anion (PFSA ⁻ : bis (perfluoroalkylsulfonyl) amide anion) such as (fluorosulfonyl) (trifluoromethylsulfonyl) amide anion, etc. . Of these, FSA ^- is preferable. These anions can be used singly or in combination of two or more.

  That is, each of the first salt and the second salt may be a single salt or a combination of a plurality of types of salts. In addition to the first salt and the second salt, the nonaqueous electrolyte may contain a salt of a metal cation other than lithium ions such as sodium, potassium, rubidium, and cesium and an anion.

  Examples of organic cations include nitrogen-containing cations; sulfur-containing cations; phosphorus-containing cations. Nitrogen-containing cations include cations derived from aliphatic amines, alicyclic amines, and aromatic amines (for example, quaternary ammonium cations), and organic cations having nitrogen-containing heterocycles (that is, cyclic amines). Examples thereof include derived cations).

Examples of the quaternary ammonium cation include tetramethylammonium cation, ethyltrimethylammonium cation, hexyltrimethylammonium cation, tetraethylammonium cation (TEA ⁺ : tetraethylammonium cation), and methyltriethylammonium cation (TEMA ⁺ : methyltriethylammonium cation). An alkyl ammonium cation (tetra C _1-10 alkyl ammonium cation etc.) etc. can be illustrated.

Examples of the sulfur-containing cation include tertiary sulfonium cations such as trialkylsulfonium cations such as trimethylsulfonium cation, trihexylsulfonium cation, and dibutylethylsulfonium cation (for example, tri-C _1-10 alkylsulfonium cation). .

Phosphorus-containing cations include quaternary phosphonium cations, for example, tetraalkylphosphonium cations such as tetramethylphosphonium cation, tetraethylphosphonium cation, tetraoctylphosphonium cation (for example, tetra C _1-10 alkylphosphonium cation); triethyl (methoxymethyl) ) Alkyl (alkoxyalkyl) phosphonium cations such as phosphonium cation, diethylmethyl (methoxymethyl) phosphonium cation, trihexyl (methoxyethyl) phosphonium cation (for example, tri-C _1-10 alkyl (C _1-5 alkoxy C _1-5 alkyl)) Phosphonium cation, etc.). In the alkyl (alkoxyalkyl) phosphonium cation, the total number of alkyl groups and alkoxyalkyl groups bonded to the phosphorus atom is 4, and the number of alkoxyalkyl groups is preferably 1 or 2.

  In addition, as for carbon number of the alkyl group couple | bonded with the nitrogen atom of the quaternary ammonium cation, the sulfur atom of the tertiary sulfonium cation, or the phosphorus atom of the quaternary phosphonium cation, 1-8 are preferable, and 1-4 are further 1, 2, or 3 is particularly preferable.

  Here, the organic cation is preferably an organic cation having a nitrogen-containing heterocycle. An ionic liquid having an organic cation having a nitrogen-containing heterocycle is promising as a molten salt electrolyte because of its high heat resistance and low viscosity. Examples of the nitrogen-containing heterocyclic skeleton of the organic cation include pyrrolidine, imidazoline, imidazole, pyridine, piperidine and the like, 5- to 8-membered heterocycles having 1 or 2 nitrogen atoms as ring constituent atoms; Examples thereof include 5- to 8-membered heterocycles having 1 or 2 nitrogen atoms and other heteroatoms (oxygen atoms, sulfur atoms, etc.).

  Note that the nitrogen atom which is a constituent atom of the ring may have an organic group such as an alkyl group as a substituent. Examples of the alkyl group include alkyl groups having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, and an isopropyl group. 1-8 are preferable, as for carbon number of an alkyl group, 1-4 are more preferable, and it is especially preferable that it is 1, 2 or 3.

  Among organic cations having a nitrogen-containing heterocycle, organic cations having a pyrrolidine skeleton are particularly promising as nonaqueous electrolytes because of their high heat resistance and low production costs. The organic cation having a pyrrolidine skeleton preferably has two of the above alkyl groups on one nitrogen atom constituting the pyrrolidine ring. The organic cation having a pyridine skeleton preferably has one alkyl group on one nitrogen atom constituting the pyridine ring. In addition, the organic cation having an imidazoline skeleton preferably has one of the above alkyl groups on each of two nitrogen atoms constituting the imidazoline ring.

Specific examples of the organic cation having a pyrrolidine skeleton include 1,1-dimethylpyrrolidinium cation, 1,1-diethylpyrrolidinium cation, 1-ethyl-1-methylpyrrolidinium cation, 1-methyl-1- Propylpyrrolidinium cation (P13 ⁺ : 1-methyl-1-propylpyrrolidinium cation), 1-methyl-1-butylpyrrolidinium cation (MBPY ⁺ : 1-butyl-1-methylpyrrolidinium cation), 1-ethyl-1- And propylpyrrolidinium cation. Of these, pyrrolidinium cations having a methyl group and an alkyl group having 2 to 4 carbon atoms, such as P13 ⁺ and MBPY ^+, are preferable because of particularly high electrochemical stability.

  Specific examples of the organic cation having a pyridine skeleton include 1-alkylpyridinium cations such as 1-methylpyridinium cation, 1-ethylpyridinium cation, and 1-propylpyridinium cation. Of these, pyridinium cations having an alkyl group having 1 to 4 carbon atoms are preferred.

Specific examples of the organic cation having an imidazole skeleton include 1,3-dimethylimidazolium cation, 1-ethyl-3-methylimidazolium cation (EMI ⁺ : 1-ethyl-3-methylimidazolium cation), and 1-methyl-3. -Propylimidazolium cation, 1-butyl-3-methylimidazolium cation (BMI ⁺ : 1-buthyl-3-methylimidazolium cation), 1-ethyl-3-propylimidazolium cation, 1-butyl-3-ethylimidazolium And cations. Of these, an imidazolium cation having a methyl group such as EMI ⁺ or BMI ⁺ and an alkyl group having 2 to 4 carbon atoms is preferable.

As a specific example of the combination of the first salt and the second salt,
(I) a first salt of lithium ions and FSA ⁻ (Li · FSA), and a second salt of P13 ⁺ and FSA ⁻ (P13 · FSA),
(Ii) a first salt of lithium ions and TFSA ⁻ (Li · TFSA), and a second salt of P13 ⁺ and TFSA ⁻ (P13 · TFSA),
(Iii) a first salt of lithium ion and FSA ⁻ (Li · FSA), and a second salt of EMI ⁺ and FSA ⁻ (EMI · FSA),
(Iv) A first salt of lithium ion and TFSA ⁻ (Li · TFSA), a second salt of EMI ⁺ and TFSA ⁻ (EMI · TFSA), and the like.

[Positive electrode active material]
The positive electrode active material exchanges electrons with the first anion (Faraday reaction). Therefore, the positive electrode active material may be any material that can occlude and release the first anion. In addition, when the ionic liquid contains the second salt, electrons are exchanged between the first anion and / or the second anion and the positive electrode active material. Therefore, the positive electrode active material may be a material that can occlude and release the second anion. Examples of such a material include a carbon material. Examples of the carbon material include graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), graphite (carbon materials having a graphite-type crystal structure such as artificial graphite and natural graphite), and the like. These carbon materials can be used singly or in combination of two or more. Of the carbon materials, graphite is particularly preferable in that the movement of the first anion is easier.

Examples of graphite include natural graphite (such as flake graphite), artificial graphite, and graphitized mesocarbon microspheres. Graphite is a layered structure in which planar six-membered rings of carbon are two-dimensionally connected, and has a hexagonal crystal structure. The first anion (and / or the second anion) can easily move between the layers of graphite, and forms an intercalation compound with graphite. The average particle size of graphite (particle size D _{50 at} 50% cumulative volume of volume particle size distribution, the same shall apply hereinafter) may be, for example, 3 to 20 μm, and 3 to 15 μm, particularly 5 to 15 μm. From the viewpoint of enhancing the filling property of the positive electrode active material and suppressing side reactions with the electrolyte (ionic liquid).

[Positive electrode current collector]
As the positive electrode current collector, a metal foil, a non-woven fabric made of metal fibers, a porous metal sheet, or the like is used. The metal constituting the positive electrode current collector is preferably aluminum or an aluminum alloy because it is stable at the positive electrode potential, but is not particularly limited. When using an aluminum alloy, it is preferable that metal components (for example, Fe, Si, Ni, Mn, etc.) other than aluminum are 0.5 mass% or less. The thickness of the metal foil serving as the positive electrode current collector is, for example, 10 to 50 μm, and the thickness of the metal fiber nonwoven fabric or the metal porous sheet is, for example, 100 to 600 μm. Among them, the positive electrode current collector is preferably a porous body of a first metal having a three-dimensional network structure in terms of filling property, retainability, and current collecting property of the positive electrode active material. It is preferable that aluminum is included. As a commercially available aluminum porous body, “Aluminum Celmet” (registered trademark) manufactured by Sumitomo Electric Industries, Ltd. can be used.

  For example, a porous body containing aluminum can be obtained by forming a coating layer of aluminum or an aluminum alloy on the surface of a foamed resin or a nonwoven fabric serving as a base material and then removing the base material. The foamed resin is not particularly limited as long as it is a porous resin molded body. Examples of the resin molding include urethane foam (polyurethane foam) and foamed styrene (polystyrene foam). In particular, urethane foam is preferable in terms of high porosity, high cell diameter uniformity, and excellent thermal decomposability. When urethane foam is used, a porous body containing aluminum that is less likely to cause variations in thickness and has excellent surface flatness can be obtained.

The first metal porous body will be described in detail below.
The first metal porous body preferably has a three-dimensional network structure and a hollow skeleton. Since the skeleton has a cavity inside, the first metal porous body is extremely lightweight while having a bulky three-dimensional structure. Such a first metal porous body is formed by plating a resin porous body having continuous voids with the metal constituting the current collector, and further decomposing or dissolving the internal resin by heat treatment or the like. it can. A three-dimensional network skeleton is formed by the plating process, and the inside of the skeleton can be made hollow by decomposition and dissolution of the resin.

  The plating process is not limited as long as a metal layer functioning as a current collector can be formed on the surface of the resin porous body (including the surface in the continuous void). For example, a known plating process such as electrolytic plating or molten salt plating is used. Etc. can be adopted. By the plating process, a three-dimensional network metal porous body corresponding to the shape of the resin porous body is formed. In addition, when performing a plating process by the electrolytic plating method, it is desirable to form a conductive layer prior to electrolytic plating. The conductive layer may be formed on the surface of the resin porous body by electroless plating, vapor deposition, sputtering, or by applying a conductive agent. The resin porous body is immersed in a dispersion containing the conductive agent. May be formed.

After the plating treatment, the resin porous body is removed by heating, whereby a cavity 102a (see FIG. 3) is formed inside the skeleton of the first metal porous body to become hollow. The width w _f of the cavity 102a inside the skeleton is an average value, for example, 0.5 to 5 μm, preferably 1 to 4 μm or 2 to 3 μm. The resin porous body can be removed by performing a heat treatment while appropriately applying a voltage as necessary. Alternatively, the plated porous body may be immersed in a molten salt plating bath, and heat treatment may be performed while applying a voltage.

  The first metal porous body has a three-dimensional network structure corresponding to the shape of the resin foam. A schematic diagram of the skeleton of the first metal porous body is shown in FIG. The first metal porous body has a plurality of cellular holes 101 surrounded by a metal skeleton 102, and a substantially polygonal opening (or window) 103 is formed between the adjacent holes 101. Yes. The openings 103 communicate with each other between the adjacent holes 101, whereby the current collector has a continuous gap. The shape of the opening 103 (or window) is not particularly limited, and is, for example, a substantially polygonal shape (such as a substantially triangular shape, a substantially square shape, a substantially pentagonal shape, and / or a substantially hexagonal shape). The substantially polygonal shape is used in the meaning including a polygon and a shape similar to the polygon (for example, a shape in which the corners of the polygon are rounded or a shape in which the sides of the polygon are curved).

The specific surface area (BET specific surface area) of the first metal porous body is, for example, 100 to 700 cm ² / g, preferably 150 to 650 cm ² / g, and more preferably 200 to 600 cm ² / g. The porosity of a 1st metal porous body is 40-99 volume%, for example, Preferably it is 60-98 volume%, More preferably, it is 80-98 volume%. Moreover, the average hole diameter (average diameter of the cell-shaped void | holes connected mutually) in a three-dimensional network structure is 50-1000 micrometers, for example, Preferably it is 100-900 micrometers, More preferably, it is 350-900 micrometers. However, the average pore diameter is smaller than the thickness of the metal porous body (or electrode). Note that the skeleton of the first metal porous body is deformed by rolling, and the porosity and the average pore diameter are changed. The ranges of the porosity and the average pore diameter are the porosity and the average pore diameter of the metal porous body before rolling (before filling the mixture).

  A positive electrode current collector including the first metal porous body is filled with a positive electrode mixture including a positive electrode active material, thereby forming a positive electrode. FIG. 3 is a schematic cross-sectional view showing a state in which the positive electrode mixture is filled in the voids of the first metal porous body in FIG. 2. The cellular holes 101 are filled with the positive electrode mixture 104 and adhere to the surface of the metal skeleton 102 to form a positive electrode mixture layer. Since the positive electrode mixture 104 adheres in a layered manner over a wide area including the surface in the void, the porosity can be increased while a large amount of the positive electrode active material is held in the first metal porous body. Therefore, the contact area between the nonaqueous electrolyte and the positive electrode active material is increased, and the positive electrode active material can be effectively used. Therefore, a high capacity can be obtained even in charge / discharge at a high rate. Further, in the dual ion power storage device, the amount of non-aqueous electrolyte is reduced during charging. Since the first metal porous body having a high porosity can hold the nonaqueous electrolyte therein, it can be expected to have a higher capacity without being drained.

The thickness w _m of the mixture layer formed by filling the mixture in the cellular pores of the first metal porous body is, for example, 10 to 500 μm, preferably 40 to 250 μm, and more preferably 100 to 100 μm. 200 μm. The thickness w _m of the mixture layer may be 5 to 40% of the average pore diameter of the cell-like pores so that voids can be secured inside the mixture layer formed in the cell-like pores. Preferably, it is more preferable that it is 10 to 30%.

[Negative electrode active material]
The negative electrode active material may be any material that can reversibly carry lithium ions. Examples of such materials include carbon materials, lithium-containing titanium compounds, silicon oxides, silicon alloys, zinc, zinc alloys, tin oxides, and tin alloys. The thickness of the negative electrode active material layer is preferably 0.05 to 1 μm, for example. In addition, it is preferable that metal components (for example, Fe, Ni, Si, Mn, etc.) other than zinc or tin in a zinc alloy or a tin alloy shall be 0.5 mass% or less.

  Examples of the carbon material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), and the like. These carbonaceous materials can be used singly or in combination of two or more. Among these, graphite and / or hard carbon are preferable from the viewpoint of thermal stability and electrochemical stability. The average particle diameter of the carbon material may be, for example, 3 to 20 μm, and 3 to 15 μm, particularly 5 to 15 μm, improves the filling property of the negative electrode active material in the negative electrode, and the electrolyte (ionic liquid). This is desirable from the viewpoint of suppressing side reactions.

  Examples of graphite include those exemplified as the positive electrode active material. Lithium ions can easily move between the layers of graphite and are reversibly inserted into and desorbed from the graphite.

  Hard carbon is a carbon material that does not develop a graphite structure even when heated in an inert atmosphere. Fine graphite crystals are arranged in random directions, and nano-order voids are formed between crystal layers. A material having

As the lithium-containing titanium compound, lithium titanate is preferable. Specifically, it is preferable to use at least one selected from the group consisting of Li ₂ Ti ₃ O ₇ and Li ₄ Ti ₅ O ₁₂ . Moreover, you may substitute a part of Ti or Na of lithium titanate with another element. For example, Li _2-x M ⁵ _x Ti _3-y M ⁶ _y O ₇ (0 ≦ x ≦ 3/2, 0 ≦ y ≦ 8/3, M ⁵ and M ⁶ are each independently of Ti and Na A metal element, for example, at least one selected from the group consisting of Ni, Co, Mn, Fe, Al and Cr), Li _4-x M ⁷ _x Ti _5-y M ⁸ _y O ₁₂ ( 0 ≦ x ≦ 11/3, 0 ≦ y ≦ 14/3, M ⁷ and M ⁸ are each independently a metal element other than Ti and Na, for example, from Ni, Co, Mn, Fe, Al and Cr It is also possible to use at least one selected from the group consisting of A lithium-containing titanium compound may be used individually by 1 type, and may be used in combination of multiple types. The lithium-containing titanium compound may be used in combination with non-graphitizable carbon. M ⁵ and M ⁷ are Na sites, and M ⁶ and M ⁸ are elements occupying Ti sites.

[Negative electrode current collector]
As the negative electrode current collector, a metal foil, a non-woven fabric made of metal fibers, a porous metal sheet, or the like is used. As the metal, a metal that is not alloyed with lithium can be used. Of these, copper, copper alloy, nickel, nickel alloy, and the like are preferable because they are stable at the negative electrode potential. The copper alloy preferably contains less than 50% by mass of elements other than copper, and the nickel alloy preferably contains less than 50% by mass of elements other than nickel. The thickness of the metal foil serving as the negative electrode current collector is, for example, 10 to 50 μm, and the thickness of the metal fiber nonwoven fabric or the metal porous body sheet is, for example, 100 to 600 μm. Among these, the negative electrode current collector is preferably a porous body of a second metal having a three-dimensional network structure in terms of the filling property, retention property, and current collecting property of the negative electrode active material. Copper or nickel is preferred.

  Examples of the second metal porous body include those having the same structure as the first metal porous body. The negative electrode mixture layer can also have the same structure as the positive electrode mixture layer. In addition, as a 2nd metal porous body marketed, the product made from Sumitomo Electric Industries, Ltd. which is a copper porous body (porous body containing copper or a copper alloy) and a nickel porous body (porous body containing nickel or a nickel alloy) is used. Copper or nickel "Celmet" (registered trademark) can be used.

[Positive electrode]
The positive electrode includes a positive electrode current collector and a positive electrode active material layer held by the positive electrode current collector. The thickness of the positive electrode is preferably 50 to 600 μm. If the thickness of the positive electrode is within this range, a non-aqueous electrolyte can be retained inside the positive electrode, so that a higher capacity can be expected. The positive electrode active material layer includes a positive electrode active material as an essential component, and may include a binder or the like as an optional component.

  The binder serves to bind the positive electrode active materials to each other and fix the positive electrode active material to the positive electrode current collector. As the binder, fluorine resin, polyamide, polyimide, polyamideimide, carboxymethyl cellulose (CMC), or the like can be used. As the fluororesin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, or the like can be used. The amount of the binder is preferably 1 to 10 parts by mass and more preferably 3 to 5 parts by mass per 100 parts by mass of the positive electrode active material.

[Negative electrode]
The negative electrode includes a negative electrode current collector and a negative electrode active material layer held by the negative electrode current collector. The thickness of the negative electrode is preferably 50 to 600 μm. If the thickness of the negative electrode is within this range, a non-aqueous electrolyte can be retained inside the negative electrode, so that a higher capacity can be expected. The negative electrode active material layer includes a negative electrode active material as an essential component, and may include a binder or the like as an optional component. As the binder used for the negative electrode, the materials exemplified as components of the positive electrode can be used. The amount of the binder is preferably 1 to 10 parts by mass and more preferably 3 to 5 parts by mass per 100 parts by mass of the negative electrode active material.

[Separator]
A separator can be disposed between the positive electrode and the negative electrode. The separator material may be selected in consideration of the operating temperature of the battery. From the viewpoint of suppressing side reactions with the non-aqueous electrolyte, polyolefin, glass fiber, silica-containing polyolefin, fluororesin, alumina, polyphenylene sulfite It is preferable to use (PPS) or the like. Among these, the microporous membrane made of polyolefin is thin and effective in preventing a short circuit. A glass fiber nonwoven fabric is preferable in that it is inexpensive and has high heat resistance. Silica-containing polyolefin and alumina are preferable in terms of excellent heat resistance. Moreover, a fluororesin and PPS are preferable in terms of heat resistance and corrosion resistance.

  The thickness of the separator is preferably 10 μm to 500 μm, more preferably 20 to 50 μm. If the thickness is within this range, an internal short circuit can be effectively prevented, and the volume occupancy of the separator in the electrode group can be kept low, so that a high capacity density can be obtained.

[Electrode group]
The electricity storage device is used in a state where the electrode group including the positive electrode, the negative electrode, and the separator and the nonaqueous electrolyte are accommodated in a case. The electrode group is formed by laminating or winding a positive electrode and a negative electrode with a separator interposed therebetween. At this time, a metal case is used, and one of the positive electrode and the negative electrode is electrically connected to the case, whereby a part of the case can be used as the first external terminal. On the other hand, the other of the positive electrode and the negative electrode is connected to the second external terminal led out of the case in a state insulated from the case, using a lead piece or the like.

[Power storage device]
Next, the structure of the electricity storage device according to one embodiment of the present invention will be described. However, the structure of the electricity storage device according to the present invention is not limited to the following structure.
FIG. 1 is a longitudinal sectional view schematically showing a configuration of an electricity storage device according to an embodiment of the present invention.

  The power storage device is not particularly limited. For example, a capacitor such as a lithium ion capacitor, a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery, and the like can be exemplified.

  The electricity storage device 100 includes a stacked electrode group 11, an electrolyte (not shown), and a rectangular aluminum case 10 that accommodates these. The case 10 includes a bottomed container body 12 having an upper opening and a lid 13 that closes the upper opening. When assembling the power storage device 100, first, the electrode group 11 is configured and inserted into the container body 12 of the case 10.

  Thereafter, a step of injecting a nonaqueous electrolyte into the container body 12 and impregnating the nonaqueous electrolyte into the gaps of the separator 1, the positive electrode 2 and the negative electrode 3 constituting the electrode group 11 is performed. Alternatively, the non-aqueous electrolyte may be impregnated with the electrode group, and then the electrode group including the non-aqueous electrolyte may be accommodated in the container body 12.

  An external positive terminal (not shown) penetrating the sealing plate 13 is provided near one side of the lid 13, and an external negative terminal 15 penetrating the sealing plate 13 is positioned near the other side of the sealing plate 13. Is provided. Each terminal is preferably insulated from the case. In the center of the sealing plate 13, a safety valve 16 is provided for releasing the gas generated inside when the internal pressure of the case 10 rises.

  The stacked electrode group 11 is composed of a plurality of positive electrodes 2, a plurality of negative electrodes 3, and a plurality of separators 1 interposed between them, each having a rectangular sheet shape. In FIG. 1, the separator 1 is formed in a bag shape so as to surround the positive electrode 2, but the form of the separator is not particularly limited. The plurality of positive electrodes 2 and the plurality of negative electrodes 3 are alternately arranged in the stacking direction in the electrode group 11.

  A positive electrode lead piece 2 c may be formed at one end of each positive electrode 2. The plurality of positive electrodes 2 are connected in parallel by bundling the positive electrode lead pieces 2 c of the plurality of positive electrodes 2 and connecting them to the external positive terminal 14 provided on the lid portion 13 of the case 10. Similarly, a negative electrode lead piece 3 c may be formed at one end of each negative electrode 3. A plurality of negative electrodes 3 are connected in parallel by bundling the negative electrode lead pieces 3 c of the plurality of negative electrodes 3 and connecting them to the external negative terminal 15 provided on the lid portion 13 of the case 10. The bundle of the positive electrode lead pieces 2c and the bundle of the negative electrode lead pieces 3c are desirably arranged on the left and right sides of one end face of the electrode group 11 so as to avoid mutual contact.

  Both the external positive terminal 14 and the external negative terminal 15 are columnar, and at least a portion exposed to the outside has a screw groove. A nut 7 is fitted in the screw groove of each terminal, and the nut 7 is fixed to the lid portion 13 by rotating the nut 7. A flange portion 8 is provided in a portion of each terminal accommodated in the case, and the flange portion 8 is fixed to the inner surface of the lid portion 13 via a washer 9 by the rotation of the nut 7.

[Charging / Discharging System]
Charging / discharging of an electrical storage device can be performed by a charging / discharging system as shown in FIG. 4, for example. Discharge system includes power storage device 100, the charging current I _in charge control device for controlling the discharge control device for controlling the discharge current I _out of the (charging circuit) 101 and the power storage device 100 (discharging circuit) 102 of the electric storage device 100 And a control unit 103 provided. The power storage device 100 is used as a power source for the external load 105. The charging control device 101 sets a charging current I _in supplied from the power source 104. Moreover, the charge control apparatus 101 controls the charge termination voltage of the power storage device to be 5.0 V or higher. According to this system, since the nonaqueous electrolyte contains lithium ions at a high concentration, a high-capacity, high-voltage electricity storage device can be obtained. Moreover, a large capacity can be obtained even when charging at high rate charge / discharge, for example, at 2C or higher (specifically, 2 to 10C). Note that charging / discharging at the rate “N” C means charging / discharging a battery having a nominal capacity at a current value at which charging / discharging is completed in “1 / N” time after rated charging / discharging.

[Appendix]
Regarding the above embodiment, the following additional notes are disclosed.
A positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material;
A negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material; and
An electrode group comprising a separator interposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte having lithium ion conductivity;
Containing the electrode group and the non-aqueous electrolyte, and
The non-aqueous electrolyte comprises an ionic liquid comprising a first salt of lithium ions and a first anion and a second salt of an organic cation and a second anion;
The positive electrode active material includes a material capable of occluding and releasing the first anion and / or the second anion,
The negative electrode active material includes a material capable of reversibly supporting the lithium ions,
The electrical storage device whose ratio of the said lithium ion to the cation contained in the said nonaqueous electrolyte is 20 mol% or more in a discharge state.
Thereby, an electricity storage device having a high voltage and a high capacity and excellent rate characteristics can be obtained.

[Example]
Next, based on an Example, this invention is demonstrated more concretely. However, the following examples do not limit the present invention.

Example 1
A dual ion battery was prepared according to the following procedure.
(1) Production of positive electrode (a) Production of positive electrode current collector Thermosetting polyurethane foam (porosity: 95 vol%, surface 1 inch (= 2.54 cm) Number of pores (cells) per length: About 50, 100 mm long × 30 mm wide × 1.1 mm thick) were prepared.

  The foam is immersed in a conductive suspension containing graphite, carbon black (average particle size 0.5 μm), a resin binder, a penetrating agent, and an antifoaming agent, and then dried. A conductive layer was formed on the surface. The total content of graphite and carbon black in the suspension was 25% by mass.

The foam having the conductive layer formed on the surface was immersed in a molten salt aluminum plating bath, and a direct current having a current density of 3.6 A / dm ² was applied for 90 minutes to form an aluminum layer. The mass of the aluminum layer per apparent area of the foam was 150 g / m ² . The molten salt aluminum plating bath contained 33 mol% 1-ethyl-3-methylimidazolium chloride and 67 mol% aluminum chloride, and the temperature was 40 ° C.

The foam with the aluminum layer formed on the surface was immersed in a lithium chloride-potassium chloride eutectic molten salt at 500 ° C., and a negative potential of −1 V was applied for 30 minutes to decompose the foam. The obtained aluminum porous body was taken out from the molten salt, cooled, washed with water, and dried to obtain a positive electrode current collector. The obtained positive electrode current collector has a three-dimensional network-like porous structure in which the pores communicate with each other, reflecting the pore shape of the foam, has a porosity of 95%, and an average pore diameter of 550 μm. Yes, the BET specific surface area (BET specific surface area) was 350 cm ² / g, and the thickness was 1100 μm. In addition, the three-dimensional network-like aluminum skeleton had inside it a cavity formed by removing the foam. In this way, a positive electrode current collector was obtained.

(B) Production of positive electrode 90 parts by mass of graphite powder (positive electrode active material) having an average particle diameter of about 3 μm and 10 parts by mass of PVDF (binder) were dispersed in N-methyl-2-pyrrolidone (NMP) to produce a positive electrode A slurry was prepared. The obtained positive electrode mixture slurry was filled in the current collector obtained in the step (a) and dried at 100 ° C. for 30 minutes. The dried product was rolled using a pair of rolls to produce a positive electrode having a thickness of 500 μm.

(2) Production of negative electrode (a) Production of negative electrode current collector By using the same method as for the positive electrode, a foam having a conductive layer formed on the surface was immersed in a copper sulfate plating bath as a work piece to obtain a cathode current density of 2A. A Cu layer was formed on the surface by applying a direct current of / dm ² . The mass of the copper layer per apparent area of the foam was 300 g / m ² . The copper sulfate plating bath contained 250 g / L copper sulfate, 50 g / L sulfuric acid, and 30 g / L copper chloride, and the temperature was 30 ° C.

The foam with the Cu layer formed on the surface is heat-treated at 700 ° C. in an air atmosphere to decompose the foam, and then fired in a hydrogen atmosphere to remove the oxide film formed on the surface. As a result, a copper porous body (negative electrode current collector) was obtained. The obtained negative electrode current collector has a three-dimensional network-like porous structure in which pores communicate with each other, reflecting the pore shape of the foam, has a porosity of 97%, and an average pore diameter of 550 μm. Yes, the BET specific surface area was 200 cm ² / g, and the thickness was 1100 μm. In addition, the three-dimensional network copper skeleton had inside it a cavity formed by removing the foam.

(B) Production of Negative Electrode 90 parts by mass of graphite powder having an average particle diameter of about 3 μm and 10 parts by mass of PVDF (binder) were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a negative electrode slurry.
The obtained negative electrode mixture slurry was filled in the current collector obtained in the step (a) and dried at 100 ° C. for 30 minutes. The dried product was rolled using a pair of rolls to produce a negative electrode having a thickness of 400 μm.

(3) Adjustment of nonaqueous electrolyte Li * FSA and P13 * FSA were mixed so that the lithium ion density | concentration to all the cations might be 20 mol%, and the nonaqueous electrolyte was prepared.

(4) Preparation of Separator A polyolefin microporous membrane separator having a thickness of 50 μm (average pore diameter 0.1 μm, porosity 70%) was cut into a size of 110 × 110 mm to prepare 22 separators.

(5) Production of Lithium Ion Secondary Battery The positive electrode obtained in the above (1) was cut into a rectangle of size 100 × 100 mm to prepare 10 positive electrodes. However, a lead piece for current collection was formed at one end of one side of the positive electrode. Further, the negative electrode obtained in the above (2) was cut into a rectangle of size 105 × 105 mm to prepare 11 negative electrodes. However, a current collecting lead piece was formed at one end of one side of the negative electrode.

  Next, the positive electrode, the negative electrode, and the separator were sufficiently dried by heating at 90 ° C. or higher under a reduced pressure of 0.3 Pa. Thereafter, a separator is interposed between the positive electrode and the negative electrode, the positive electrode lead pieces and the negative electrode lead pieces overlap each other, and the bundle of the positive electrode lead pieces and the bundle of the negative electrode lead pieces are arranged at the left and right target positions. Thus, an electrode group was prepared. Then, the same separator was also arranged outside both ends of the electrode group. The obtained laminate was housed in a rectangular aluminum case (inner dimensions: 110 mm × 110 mm × 10.5 mm) together with a non-aqueous electrolyte to complete a dual ion battery A having a nominal capacity of 1.8 Ah.

Example 2
A dual ion battery B was produced in the same manner as in Example 1 except that the positive electrode and the negative electrode produced as described below were used.

(Preparation of positive electrode)
90 parts by mass of graphite powder (positive electrode active material) having an average particle size of about 3 μm and 10 parts by mass of PVDF (binder) were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode paste. The obtained positive electrode paste was applied to both surfaces of an aluminum foil having a thickness of 20 μm, sufficiently dried, and rolled to prepare a positive electrode having a total thickness of 120 μm having a positive electrode mixture layer having a thickness of 50 μm on both surfaces. The obtained positive electrode was cut into a rectangle of size 100 × 100 mm to prepare 10 positive electrodes.

(Preparation of negative electrode)
A negative electrode paste was prepared by dispersing 90 parts by mass of graphite powder having an average particle size of about 3 μm and 10 parts by mass of PVDF (binder) in N-methyl-2-pyrrolidone (NMP). The obtained negative electrode paste was applied to both sides of an aluminum foil having a thickness of 20 μm, sufficiently dried, and rolled to produce a negative electrode having a total thickness of 100 μm having a negative electrode mixture layer having a thickness of 40 μm on both sides. The obtained negative electrode was cut into a rectangle having a size of 105 × 105 mm to prepare 11 negative electrodes. Note that two of the 11 negative electrodes were electrodes having a negative electrode active material layer only on one side.

Example 3
A dual ion battery C was produced in the same manner as in Example 1 except that an electrolyte in which Li · FSA and P13 · FSA were mixed so that the lithium ion concentration in all cations was 50 mol% was used.

<< Comparative Example 1 >>
Except that Li · FSA was blended in a solvent composed of EC (50% by mass) and DEC (50% by mass) as an electrolyte so that the lithium ion concentration would be 1 mol / L, the same as in Example 2. Thus, a dual ion battery D was produced.

<< Comparative Example 2 >>
A dual ion battery E was produced in the same manner as in Example 2 except that LiPF ₆ was blended so that the lithium ion concentration was 2.5 mol / L.

<< Comparative Example 3 >>
A dual ion battery F was produced in the same manner as in Example 2 except that the electrolyte was prepared by mixing Li · FSA and P13 · FSA so that the lithium ion concentration in all cations was 10 mol%. did.

[Evaluation 1]
Each of the dual ion batteries A to F was heated in a temperature-controlled room until reaching 60 ° C., and charging and discharging were performed with the following conditions (1) and (2) as one cycle in a state where the temperature was stable. Table 1 shows the discharge capacity of each dual ion battery.

(1) Charging to 0.5V with a charging current of 0.5C (2) Discharging to 0.5V with a discharging current of 0.5C

  Moreover, it evaluated similarly to the evaluation 1 by setting discharge current to 5C and 10C. The results are also shown in Table 1.

  In the batteries A to C, a large discharge capacity was obtained even when discharging at a high rate. In particular, the batteries A and C using a metal porous body as a current collector showed excellent discharge capacity.

  The electricity storage device according to the present invention is excellent as a rate characteristic in high rate charge / discharge and has a high voltage, so that it is useful as a power source for various applications.

  1: separator, 2: positive electrode, 2c: positive electrode lead piece, 3: negative electrode, 3c: negative electrode lead piece, 7: nut, 8: collar, 9: washer, 10: case, 11: electrode group, 12: container body , 13: lid, 14: external positive terminal, 15: external negative terminal, 16: safety valve, 100: power storage device, 102: charge control device, 103: discharge control device, 103: control unit, 104: power supply device, 105 : External load

The quaternary ammonium cations such as tetramethyl ammonium cation, trimethyl ammonium cation, hexyl trimethyl ammonium cation, tetraethylammonium cation (TEA ^+: tetraethylammonium cation), preparative Riechiru methyl ammonium cation ^{(TEMA +: t riethyl methyl ammonium} cation And tetraalkylammonium cations (such as tetra-C _1-10 alkylammonium cations).

Specific examples of the organic cation having a pyrrolidine skeleton include 1,1-dimethylpyrrolidinium cation, 1,1-diethylpyrrolidinium cation, 1-ethyl-1-methylpyrrolidinium cation, 1-methyl-1- propyl pyrrolidinium cation ^{(P13 +: 1-methyl-} 1-propylpyrrolidinium cation), 1- methyl-1-butyl pyrrolidinium cation ^{(MBPY +: 1- methyl -1- butyl} pyrrolidinium cation), 1- ethyl -1 -Propylpyrrolidinium cation and the like. Of these, pyrrolidinium cations having a methyl group and an alkyl group having 2 to 4 carbon atoms, such as P13 ⁺ and MBPY ^+, are preferable because of particularly high electrochemical stability.

[Charging / Discharging System]
Charging / discharging of an electrical storage device can be performed by a charging / discharging system as shown in FIG. 4, for example. The charge / discharge system includes a power storage device 100, a charge control device (charging circuit) 200 that controls the charging current I _in of the power storage device 100, and a discharge control device (discharge circuit) 2 that controls the discharge current I _out of the power storage device 100. 02 and the control unit 2 03 with a, comprises a.
Electricity storage device 100 is used as the power supply of the external load 2 05. Charging control device 2 01 sets the charging current I _in supplied from the power supply 2 04. The charging control unit 2 01 is controlled so that the charge voltage of the electric storage device becomes equal to or greater than 5.0V. According to this system, since the nonaqueous electrolyte contains lithium ions at a high concentration, a high-capacity, high-voltage electricity storage device can be obtained. Moreover, a large capacity can be obtained even when charging at high rate charge / discharge, for example, at 2C or higher (specifically, 2 to 10C). Note that charging / discharging at the rate “N” C means charging / discharging a battery having a nominal capacity at a current value at which charging / discharging is completed in “1 / N” time after rated charging / discharging.

1: separator, 2: positive electrode, 2c: positive electrode lead piece, 3: negative electrode, 3c: negative electrode lead piece, 7: nut, 8: collar, 9: washer, 10: case, 11: electrode group, 12: container body , 13: Lid, 14: External positive terminal, 15: External negative terminal, 16: Safety valve, 100: Power storage device, 101: Hole, 102: Metal frame, 102a: Cavity, 103: Opening, 104: Positive electrode combination agent, 201: charging control device (charging circuit), 2 0 2: discharge control device (discharge circuit), 2 03: control unit, 2 04: power supplies, 2 05: external load

Claims (6)

A positive electrode having a positive electrode active material and a positive electrode current collector holding the positive electrode active material;
A negative electrode having a negative electrode active material and a negative electrode current collector holding the negative electrode active material; and
An electrode group comprising a separator interposed between the positive electrode and the negative electrode;
A non-aqueous electrolyte having lithium ion conductivity;
Containing the electrode group and the non-aqueous electrolyte, and
The non-aqueous electrolyte includes an ionic liquid containing a first salt of lithium ions and a first anion;
The positive electrode active material includes a material that can occlude and release the first anion,
The negative electrode active material includes a material capable of reversibly supporting the lithium ions,
The electrical storage device whose ratio of the said lithium ion to the cation contained in the said nonaqueous electrolyte is 20 mol% or more in a discharge state.   The electricity storage device according to claim 1, wherein the content of the ionic liquid in the nonaqueous electrolyte is 80% by mass or more. The ionic liquid further comprises a second salt of an organic cation and a second anion;
The electricity storage device according to claim 1 or 2, wherein the first anion and the second anion are each independently a polyatomic anion. The positive electrode active material includes a carbon material having a graphite structure,
The electricity storage device according to claim 3, wherein each of the first anion and the second anion includes a bis (fluorosulfonyl) amide anion. The positive electrode current collector is a first metal porous body having a three-dimensional network structure;
The electricity storage device according to any one of claims 1 to 4, wherein the negative electrode current collector is a second metal porous body having a three-dimensional network structure. The electricity storage device according to claim 1;
A charge control device for controlling a charge current I _in of the power storage device;
A discharge control device for controlling the discharge current I _out of the electricity storage device,
The charge control device is a charge / discharge system that controls a charge end voltage of the power storage device to be 5.0 V or more.

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