JP2020129532A - Power storage element - Google Patents

Abstract

To provide a power storage element with high temperature stability, high capacity, high cycle stability, and excellent capacity appearance rate at low temperature.SOLUTION: A power storage element includes a positive electrode containing a positive electrode active material capable of occluding or releasing anions, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte, and the positive electrode active material contains porous carbon having pores of a three-dimensional network structure, a solvent of the non-aqueous electrolyte is an ionic liquid, the ionic radius of the anion of the ionic liquid is 2.7 Å or more, and the anion of the electrolyte salt of the non-aqueous electrolyte and the anion of the ionic liquid are the same.SELECTED DRAWING: None

Description

The present invention relates to a power storage element.

In recent years, the characteristics of power storage elements with high energy density have been improved and become popular with the miniaturization and high performance of mobile devices, and the development of power storage elements with larger capacity and superior safety has been promoted. It has also started to be installed in etc.

Electric double-layer capacitors and lithium-ion capacitors have been put on the market as one of the power storage devices having such a high energy density and suitable for rapid charge/discharge. However, these capacitors do not sufficiently meet the demand for energy density of the storage element, and further higher capacity is required.
Therefore, a conductive polymer, a carbon material or the like is used for the positive electrode, a negative electrode such as carbon and a non-aqueous electrolytic solution prepared by dissolving a lithium salt in a non-aqueous solvent, and during charging, anions in the non-aqueous electrolytic solution are A so-called dual intercalation type in which cations are inserted into the negative electrode and cations are inserted into the negative electrode during discharge and the anions and cations inserted into the positive electrode and the negative electrode are desorbed into the non-aqueous electrolyte. Practical application of the electric storage element is expected.

As the positive electrode active material capable of occluding and releasing anions in the electricity storage device, for example, graphite is used to occlude or release anions between layers (see, for example, Patent Documents 1 and 2), and alkali activated software. Those utilizing physical occlusion or release of anions to carbon (see, for example, Patent Document 3), and storage and release of anions on the surface of a carbon material having a surface area enlarged by forming voids by roughening treatment. Those to be used (for example, refer to Patent Document 4) have been proposed.

In recent years, further enhancement of performance has been demanded for in-vehicle electric storage elements, and in addition to the above-mentioned high energy density, long life, high temperature support and high safety are required. However, since an electric storage element generally uses an organic solvent that is easily decomposed by heat and has high flammability as an electrolyte solvent, it is not possible to solve the problem of high temperature and safety among the above performances.
In order to solve this point, the present applicant has previously used porous carbon in which pores having a three-dimensional network structure are formed as the positive electrode active material, and the non-aqueous electrolytic solution is a non-aqueous solvent or electrolyte. A non-aqueous power storage element containing a salt and an ionic liquid has been proposed (for example, see Patent Document 5).

It is an object of the present invention to provide a power storage element having high temperature stability, high capacity, high cycle stability, and an excellent capacity appearance rate at low temperatures.

An electricity storage device of the present invention as a means for solving the above-mentioned problems is an electricity storage device having a positive electrode containing a positive electrode active material capable of occluding or releasing anions, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte solution. The positive electrode active material contains porous carbon having pores having a three-dimensional network structure, the solvent of the non-aqueous electrolyte is an ionic liquid, and the ionic radius of the anion of the ionic liquid is 2.7Å. As described above, the anion of the electrolyte salt of the non-aqueous electrolyte is common to the anion of the ionic liquid.

According to the present invention, it is an object of the present invention to provide a power storage element having high temperature stability, high capacity, high cycle stability, and excellent capacity appearance rate at low temperatures.

FIG. 1 is a schematic cross-sectional view showing an example of porous carbon as a positive electrode active material used in the present invention. FIG. 2 is a schematic diagram showing an example of the electricity storage device of the present invention. FIG. 3 is a schematic view showing another example of the electricity storage device of the present invention.

(Storage element)
An electricity storage device of the present invention is an electricity storage device having a positive electrode containing a positive electrode active material capable of occluding or releasing anions, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte, wherein the positive electrode active material is a tertiary An electrolyte of the non-aqueous electrolyte, which contains porous carbon having pores of an original network structure, a solvent of the non-aqueous electrolyte is an ionic liquid, and an anion radius of anions of the ionic liquid is 2.7 Å or more. The anion of the salt and the anion of the ionic liquid are the same, and further have other members as necessary.

In the electricity storage device of the present invention, when a highly graphitized artificial graphite or natural graphite material is used for the conventional positive electrode active material, the graphite crystal collapses when anions are electrochemically occluded in the graphite material. This is based on the finding that the capacity for reversible occlusion or release of anions is reduced by repeating charge/discharge for (cleavage). This is remarkable when an electrolyte salt having a large anion ionic radius is used.
In addition, the electrolytic solution using the conventional ionic liquid is less than the thermal stability and safety such as the capacity decreases at low temperature and the problem of long-term stability of life, compared with the electrolytic solution using the conventional organic solvent. Performance will be significantly reduced. Further, in order to mitigate the influence on such performance, in the conventional technique described in Patent Document 5, a non-aqueous electrolytic solution containing a non-aqueous solvent, an electrolyte salt and an ionic liquid is used, but high temperature resistance However, there is a problem that the problem of flammability and decrease in capacity appearance rate at low temperature cannot be solved.

Therefore, in the present invention, high temperature resistance and flame retardancy can be obtained by using the ionic liquid as the solvent of the non-aqueous electrolyte. In addition, by making the anion of the ionic liquid the same as the anion of the electrolyte salt, it is possible to suppress phenomena such as precipitation and local crystallization due to the presence of another kind of salt, thereby suppressing the decrease in capacity at low temperatures. .. Furthermore, since the positive electrode active material uses porous carbon having pores of a three-dimensional network structure, collapse (cleavage) of the positive electrode active material does not occur even after repeated storage and release of anions having a large ionic radius. The capacity does not decrease even after repeated charging and discharging. Therefore, even when using a non-aqueous electrolyte solution in which the anion of the ionic liquid is the same as the anion of the electrolyte salt and the ionic radius is 2.7 Å or more, a stable capacity for a long period of time is maintained against repeated charging and discharging. Can be maintained over.

<Positive electrode>
The positive electrode is not particularly limited as long as it contains a positive electrode active material capable of absorbing or releasing anions, and can be appropriately selected according to the purpose. For example, a positive electrode material having a positive electrode active material on a positive electrode current collector. And a positive electrode provided with.
The above-mentioned occlusion of anions in the positive electrode active material means a state in which the chemical state of the positive electrode active material or the anions is changed and the anions are stably retained in the positive electrode active material. The occlusion of anions in the positive electrode active material during charging can be confirmed, for example, by a nuclear magnetic resonance (NMR: Nuclear Magnetic Resonance) method. If the electrolyte used contains an anion having an NMR-measurable nuclide, the presence state of the anion in the electrode can be observed using the liquid NMR technique. Generally, when ions are present in a limited space such as pores of the active material and the active material and the ions are in contact with each other, the chemical state of the ion changes due to the interaction with the active material. , The chemical shift of the liquid NMR of the ion changes, and the signal of the ion existing in the pore can be detected. Therefore, for example, when an electrolytic solution having an anion containing a fluorine atom is used, by obtaining the ¹⁹ F-liquid NMR spectrum of the charged positive electrode, the chemical shift of the peak attributed to the anion is in the uncharged state. If it changes from the chemical shift of the peak attributed to the anion contained in the electrolytic solution, it can be confirmed that the storage of the anion in the positive electrode active material is exhibited.
The shape of the positive electrode is appropriately selected depending on the intended purpose without any limitation, and examples thereof include a flat plate shape.

-Cathode material-
The positive electrode material is not particularly limited and may be appropriately selected depending on the intended purpose. For example, it contains at least a positive electrode active material, and further contains a conductive aid, a binder, a thickener and the like as necessary.

--- Positive electrode active material ---
As the positive electrode active material, it is preferable to use porous carbon having pores having a three-dimensional network structure and porous carbon having pores having a continuous three-dimensional network structure.
The porous carbon "has pores forming a three-dimensional network structure" means that the surface and the inside of the porous carbon particles have a plurality of pores, and adjacent pores are connected to each other. And three-dimensionally connected to each other, and a communication hole having an opening is formed on the surface. The dual intercalation type electricity storage device can obtain a high energy density by inserting a part of anions into the crystal part in the carbon skeleton. On the other hand, carbon is expanded due to the insertion of anions into the crystal part, which causes cleavage of the crystal part and desorption of the positive electrode active material from the electrode, which deteriorates the cycle life.
Having the pores of the three-dimensional network structure means that the pores are arranged around the carbon crystal part, and the expansion of the crystal part in which an anion is inserted is relaxed by the contraction of the surrounding pores. And long cycle life is possible.

As a method of confirming that the porous carbon has pores forming a three-dimensional network structure, for example, a method of observing using SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope), or the like, etc. Is mentioned.
The cross section of the porous carbon having the “pores forming the three-dimensional network structure” can be shown as the schematic cross-sectional view of FIG. 1 produced based on a photograph by TEM. In FIG. 1, 101 indicates pores and 100 indicates carbon particles.

In the porous carbon, mesopores are essential, but micropores are not essential. Therefore, although micropores may or may not be present, organic substances as the source of porous carbon usually release volatiles during carbonization and thus carbonize, and thus usually the traces of release. However, since micropores are left as it is, it is difficult to obtain a product having no micropores. In contrast, mesopores are usually formed intentionally. For example, after reinforcing material of acid (alkali)-soluble metal, metal oxide, metal salt, or metal-containing organic material and carbon material or organic material as a raw material thereof are molded together, the reinforcing material part is treated with acid (alkali). In many cases, the traces of dissolved and removed are mesopores.

Here, in the present specification, those having a pore size of less than 2 nm are referred to as micropores, and those having a pore size of 2 nm or more and 50 nm or less are referred to as mesopores. Since the size of the anion of the electrolyte salt is 6.5 Å or more, that is, 0.65 nm or more, it is hard to say that the micropores make a significant contribution to the migration of ions. Therefore, mesopores are important for the smooth migration of ions. Incidentally, the pore size in activated carbon, which is the same porous carbon, is said to be about 1 nm on average, and in the case of activated carbon, it is regarded as one of all adsorptions accompanied by exotherm (decrease in enthalpy) without exception.
The mesopores of the above size preferably have a three-dimensional network structure. If the holes have a three-dimensional mesh structure, ions move smoothly.

The porous carbon preferably has crystallinity.
As the crystallinity of the porous carbon, it is not necessary that all of the carbonaceous matter has a crystal structure having crystallinity, and an amorphous structure having no crystallinity may be present in a part thereof. , All may have an amorphous structure.
The term “having crystallinity” means a state (graphite layer) in which hexagonal plate-shaped single crystals in which carbons are bonded by sp2 hybrid orbital are formed in a layer. As a method of confirming that the porous carbon has crystallinity, for example, a method of observing a layered structure of graphite using TEM, a method of confirming a spectrum peak by X-ray diffraction, and a Raman spectrum Examples include a method of confirming using analysis.
The crystal part of the layered structure can be confirmed using, for example, TEM (JEM-2100, manufactured by JEOL Ltd.). In the TEM image, a crystal part having a layered structure derived from the graphite layer can be confirmed in at least a part of the carbon part (carbonaceous wall) forming the mesopore. The crystals having the layered structure are oriented so as to surround the mesopores.
The diffraction peak can be confirmed using, for example, an X-ray diffractometer (X'pert PRO, manufactured by Malvern Panoramic Co., Ltd.). In the X-ray diffraction spectrum, when a copper tube is used, it is preferable to confirm that it has a diffraction peak in the region of Bragg angle 2θ of 25.00 or more and 27.00 or less, and in the region of the Bragg angle 2θ. It is more preferable to confirm that it has two diffraction peaks.
When the crystallinity of the porous carbon is confirmed by Raman spectroscopic analysis, the graphitization degree (ratio of amorphous carbon in the positive electrode active material) can also be indicated. Specifically, the ratio of the peak intensity at 1,360 cm ⁻¹ and the peak intensity at 1,580 cm ⁻¹ in the Raman spectrum (1,360 cm ⁻¹ /1,580 cm ⁻¹ ) (hereinafter, “graphitization degree Rh It may be referred to as “”). The degree of graphitization Rh of the porous carbon is preferably 0.9 or more and 1.6 or less, and more preferably 1.0 or more and 1.3 or less.
The graphitization degree Rh can be confirmed using, for example, a microscopic laser Raman spectroscope (Nanofinder 30, manufactured by Tokyo Instruments Co., Ltd.).

The electricity storage device of the present invention is charged and discharged using occlusion or release of anions in the positive electrode active material, but at that time, some anions are inserted into or removed from the crystalline layers of the porous carbon. It has a high energy density. At this time, it can be confirmed that a part of the crystal layer in the positive electrode carbon expands between layers due to the anion insertion, so that the crystal state varies depending on the presence or absence of the anion insertion.
The variation in the crystalline state can be confirmed by, for example, an increase in the peak half width at 1,580 cm ⁻¹ by Raman spectroscopy or an increase in the diffraction peak half width at the Bragg angle 2θ by in-situ X-ray diffraction.

There is no particular limitation on such porous carbon, and appropriately manufactured carbon may be used, or a commercially available product may be used.
Examples of the commercially available product include Knobel (registered trademark) (manufactured by Toyo Tanso Co., Ltd.).

The BET specific surface area of the porous carbon is preferably 50 m ² /g or more and 2,000 m ² /g or less, more preferably 300 m ² /g or more and 1,800 m ² /g or less, and 500 m ² /g or more and 1,500 m. ² /g or less is more preferable. When the BET specific surface area is 50 m ² /g or more, a sufficient amount of pores are formed and ions are sufficiently occluded, so that the capacity can be increased. Further, when the BET specific surface area is 2,000 m ² /g or less, mesopores are sufficiently formed and the occlusion of ions is not hindered, so that the capacity can be increased.
The BET specific surface area can be obtained, for example, from the result of analysis of the adsorption isotherm by using an automatic specific surface area/pore distribution measuring device (TriStarII3020, manufactured by Shimadzu Corporation) and analyzing using the BET method.

The pore volume of the porous carbon is preferably 0.2 mL/g or more and 2.3 mL/g or less, and more preferably 0.2 mL/g or more and 1.7 mL/g or less. When the pore volume is 0.2 mL/g or more, it is rare that the mesopores become independent pores, the migration of anions is not hindered, and a large discharge capacity can be obtained. On the other hand, if the pore volume of the porous carbon is 2.3 mL/g or less, the carbon structure is not bulky and the energy density as an electrode is increased, so that the discharge capacity per unit volume can be increased. Further, it is advantageous in that the carbonaceous wall forming the pores does not become thin and the shape of the carbonaceous wall can be maintained even after repeated storage and release of anions, and the charge/discharge characteristics are improved. ..
The pore volume of the porous carbon is obtained, for example, from an analysis result obtained by obtaining an adsorption isotherm using an automatic specific surface area/pore distribution measuring device (TriStarII3020, manufactured by Shimadzu Corporation) and analyzing it using the BET method. be able to.
The micropore volume of the porous carbon is preferably 1.0 mL/g or less, and more preferably 0.1 mL/g or more and 0.6 mL/g or less. When the micropore volume is larger than 1.0 mL/g, the storage and release of anions are inhibited, and the capacity appearance rate at low temperature is impaired.
For the micropore volume of the porous carbon, for example, an adsorption isotherm is obtained using an automatic specific surface area/pore distribution measuring device (TriStarII3020, manufactured by Shimadzu Corporation), and the analysis result using the t-plot method is used. You can ask.

The mesopore content of the porous carbon is preferably 15% or more and 80% or less, more preferably 25% or more and 70% or less, and further preferably 35% or more and 60% or less.
The mesopore content can be calculated, for example, from the adsorption isotherm, and the adsorption isotherm is prepared by measuring the adsorption amount of gas molecules when the material is kept at a constant temperature and the pressure is changed. For example, it can be measured by an automatic specific surface area/pore distribution measuring device (TriStarII3020, manufactured by Shimadzu Corporation).
The adsorption amount of gas molecules at the relative pressure (p/p ₀ ) of 0.3 or less of the adsorption isotherm is the adsorption amount of gas molecules due to the micropores, and the relative pressure of 0.3 or more and 0.96 or less is due to the mesopores. The mesopore content rate can be calculated from the following Equation 1 since the gas molecule adsorption amount is

[Formula 1]

The porous carbon preferably has a particle shape.
The median diameter of the porous carbon is preferably 0.3 μm or more and 20 μm or less, more preferably 0.4 μm or more and 10 μm or less, and further preferably 0.5 μm or more and 5 μm or less.
The median diameter can be measured using, for example, a laser diffraction/scattering particle size distribution device (LA-960, manufactured by Horiba, Ltd.).
The bulk density of the porous carbon is preferably 0.1 g/cc or more and 1.0 g/cc or less, and more preferably 0.1 g/cc or more and 0.6 g/cc or less.
When the bulk density is 0.1 g/cc or more, the thickness of the carbonaceous wall forming the pores is appropriate, a good pore structure can be obtained, and the electrode density can be increased when formed into an electrode. Therefore, the discharge capacity per unit volume can be increased.
On the other hand, when the bulk density is more than 1.0 g/cc, the formation of mesopores becomes insufficient and the abundance ratio of independent mesopores increases, so that the storage amount of anions decreases and a large discharge capacity is obtained. You will not be able to get it.
The bulk density can be measured by, for example, a multifunctional powder physical property measuring device (Multitester MT-1001K, manufactured by Seishin Enterprise Co., Ltd.).
The true density is preferably 1.0 g/cc or more. If the true density is less than 1.0 g/cc, it is difficult to secure a specific surface area, and the shape of the carbonaceous wall may not be maintained. The true density can be measured by, for example, a dry automatic densitometer (Acupic II1340, manufactured by Shimadzu Corporation).

The electrical resistivity of the porous carbon is preferably 1.0 Ω·cm or less, more preferably 1.0×10 ⁻¹ Ω·cm or less.
When the electrical resistivity is 1.0 Ω·cm or less, the electrical conductivity in the electrode is good, and high output characteristics can be obtained.
The smaller the electric resistivity, the more preferable, but it is not necessarily 1.0×10 ⁻¹ Ω·cm or less, and if the electric resistivity is 1.0 Ω·cm or less, the conductive path in the electrode is sufficient. Can be formed.
The electrical resistivity can be measured, for example, by a powder resistance measuring system (MCP-PD51 type, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

The ignition residue of the porous carbon is preferably 0.1% or more and 10% or less. The above-mentioned porous carbon having an ignition residue of less than 0.1% is poor in mass productivity, while on the other hand, if the ignition residue is more than 10%, a side reaction occurs due to charging/discharging, which increases the resistance of the storage element. Will end up. The ignition residue can be confirmed, for example, based on JIS K 1474-2014, by heating the porous carbon in an electric furnace and from the rate of mass change before and after heating.
The oxidation consumption temperature of the porous carbon is preferably 300° C. or higher, more preferably 500° C. or higher, even more preferably 600° C. or higher. The oxidation consumption temperature is, for example, TG-DTA (Thermo plus EVO2, manufactured by Rigaku Co., Ltd.). It can be confirmed from the intersection with the extension line.

The method for producing the porous carbon is not particularly limited and may be appropriately selected depending on the purpose. For example, a reinforcing material having a three-dimensional network structure and an organic material as a porous carbon forming source are molded. And carbonized, and then the muscle material is dissolved with an acid or an alkali. In this case, the traces of the dissolution of the muscular material form a plurality of mesopores forming a three-dimensional network structure, which can be intentionally formed.
The muscle material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include metals, metal oxides, metal salts, and metal-containing organic substances. Among these, acid- or alkali-soluble ones are preferable.
The organic substance is not particularly limited as long as it can be carbonized, and can be appropriately selected according to the purpose. In addition, since the organic substance releases a volatile substance at the time of carbonization, micropores are formed as an emission trace, and thus it is difficult to manufacture porous carbon having no micropores at all.

---Binder and thickener---
The binder and the thickener are not particularly limited as long as they are a solvent or an electrolytic solution used during electrode production, and a material that is stable against an applied potential, and can be appropriately selected according to the purpose. Fluorinated binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, acrylate latex, carboxymethyl cellulose (CMC) , Methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyacrylic acid, polyvinyl alcohol, alginic acid, oxidized starch, starch phosphate, casein and the like. These may be used alone or in combination of two or more. Among these, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), acrylate latex, and carboxymethyl cellulose (CMC) are preferable.

---Conductive agent---
In the present invention, the conductive aid means a conductive material that is dispersed in the electrodes and used to reduce the resistance of the electrodes, plays a role of assisting the conductivity between the electrode materials, and forms a conductive network. It has a function and is added as needed.
Examples of the conductive aid include metal materials such as copper and aluminum, and carbonaceous materials such as carbon black, acetylene black, and carbon nanotubes. These may be used alone or in combination of two or more.

-Positive electrode current collector-
The material, shape, size and structure of the positive electrode current collector are not particularly limited and can be appropriately selected according to the purpose.
The material of the positive electrode current collector is formed of a conductive material, and is not particularly limited as long as it is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Examples include stainless steel, nickel, aluminum, titanium and tantalum. Among these, stainless steel and aluminum are particularly preferable.
The shape of the positive electrode current collector is not particularly limited and may be appropriately selected depending on the purpose.
The size of the positive electrode current collector is not particularly limited as long as it is a size that can be used for a power storage element, and can be appropriately selected according to the purpose.

<Method for producing positive electrode>
The positive electrode, the positive electrode active material, if necessary, the binder, the thickener, the conductive aid, a positive electrode material in the form of a slurry by adding a solvent or the like, is applied on the positive electrode current collector, It can be manufactured by drying. The solvent is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include aqueous solvents and organic solvents. Examples of the aqueous solvent include water and alcohol. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP) and toluene.
The positive electrode active material may be roll-formed as it is to form a sheet electrode, or compression-molded to form a pellet electrode.

<Negative electrode>
The negative electrode is not particularly limited as long as it contains a negative electrode active material, and can be appropriately selected according to the purpose, and examples thereof include a negative electrode including a negative electrode material having a negative electrode active material on a negative electrode current collector. To be
The shape of the negative electrode is appropriately selected depending on the intended purpose without any limitation, and examples thereof include a flat plate shape.

-Negative electrode material-
The negative electrode material contains at least a negative electrode active material, and further contains a conductive auxiliary agent, a binder, a thickener, etc., if necessary.

---Negative electrode active material---
The negative electrode active material is not particularly limited as long as it can occlude and release cations in a non-aqueous solvent system, and can be appropriately selected according to the purpose. For example, lithium ions as cations can be occluded and released. Carbonaceous materials, metal oxides, metals or metal alloys capable of alloying with lithium, compound alloy compounds of lithium and alloys containing metals capable of alloying with lithium and lithium, lithium metal nitride, elemental silicon, silicon compounds And so on.

The carbonaceous material is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include graphite and organic pyrolysates under various pyrolysis conditions.
Examples of the graphite include graphite such as coke, artificial graphite, and natural graphite. Of these, artificial graphite and natural graphite are preferable.
Examples of the metal oxides include antimony tin oxide and silicon monoxide.
Examples of the metal or metal alloy include lithium, aluminum, tin, silicon, zinc, and the like.
Examples of the composite alloy compound with lithium include lithium titanate and the like.
Examples of the lithium metal nitride include lithium cobalt nitride and the like.
Examples of the silicon compound include transition metal-silicon compounds such as silicon oxide, silicon nitride, silicon carbide, nickel silicide, and cobalt silicide. The elemental silicon and silicon compound may be coated or compounded with conductive carbon.
The negative electrode active material may be used alone or in combination of two or more. Among these, the carbonaceous material and lithium titanate are preferable from the viewpoint of safety and cost.

---Binder and thickener---
The binder and the thickener are not particularly limited as long as they are a solvent or an electrolytic solution used during electrode production, and a material that is stable against an applied potential, and can be appropriately selected according to the purpose. Fluorinated binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, acrylate latex, carboxymethyl cellulose (CMC) , Methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyacrylic acid, polyvinyl alcohol, alginic acid, oxidized starch, starch phosphate, casein and the like. These may be used alone or in combination of two or more. Among these, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) are preferable.

---Conductive agent---
Examples of the conductive aid include metal materials such as copper and aluminum, and carbonaceous materials such as carbon black, acetylene black, and carbon nanotubes. These may be used alone or in combination of two or more.

-Negative electrode current collector-
The material, shape, size and structure of the negative electrode current collector are not particularly limited and can be appropriately selected according to the purpose.
The material of the negative electrode current collector is formed of a conductive material and is not particularly limited as long as it is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Examples include steel, nickel, aluminum and copper. Among these, stainless steel, copper and aluminum are particularly preferable.
The shape of the negative electrode current collector is not particularly limited and may be appropriately selected depending on the purpose.
The size of the negative electrode current collector is not particularly limited as long as it is a size that can be used for a power storage element, and can be appropriately selected according to the purpose.

<Method for producing negative electrode>
The negative electrode, a negative electrode material in the form of a slurry by adding the binder and thickener, the conductive auxiliary agent, a solvent and the like to the negative electrode active material, if necessary, is applied on the negative electrode current collector, and dried. Can be manufactured. As the solvent, the same solvent as used in the method for producing the positive electrode can be used.
Further, the negative electrode active material to which the binder, the thickening agent, the conductive auxiliary agent and the like are added is directly roll-formed into a sheet electrode, or compression-molded into a pellet electrode, or a method such as vapor deposition, sputtering or plating. Then, a thin film of the negative electrode active material may be formed on the negative electrode current collector.
After manufacturing the negative electrode, cations may be doped. Since the negative electrode potential can be lowered by doping with cations, the charge potential of the power storage element can be increased, and accordingly, the energy density can be improved.

<Non-aqueous electrolyte>
The non-aqueous electrolytic solution is an electrolytic solution obtained by using an ionic liquid as a solvent and dissolving an electrolyte salt in the solvent.

-Cation that constitutes ionic liquid-
As the cation that constitutes the ionic liquid, any cation that can form an ionic liquid when combined with an anion can be used without problems. Representative cations capable of forming an ionic liquid include cations having a basic skeleton such as pyrrolidinium-based and imidazolinium-based. Among these, it is preferable that the side chain is formed of a straight-chain alkane from the viewpoint of difficulty in precipitation of a solid salt when forming an ionic liquid.
Examples of the cation constituting the ionic liquid include 1-methyl-1-propyl-pyrrolidinium, 1-butyl-1-methyl-pyrrolidinium, 1-ethyl-3-butylimidazolium, 1-ethyl-3-methylimidazolium. , 1-butyl-2,3-dimethylimidazolium and the like. These may be used alone or in combination of two or more. Among these, 1-methyl-1-propyl-pyrrolidinium is particularly preferable.

-Anion that constitutes ionic liquid-
The anion that constitutes the ionic liquid must have an ionic radius of 2.7 Å or more and be capable of forming an ionic liquid with the cation.
Examples of the anion constituting the ionic liquid include bis(trifluoromethylsulfonyl)imide anion, nonafluoro-1-butanesulfonic acid anion, tris(trifluoromethylsulfonyl)methide anion, and bis(fluorosulfonyl)imide anion. .. These may be used alone or in combination of two or more. Among these, bis(fluorosulfonyl)imide anion is preferable from the viewpoint of thermal stability and electric conductivity.
The ionic radius of the anion constituting the ionic liquid is 2.7 Å or more, preferably 3.5 Å or more, and more preferably 3.5 Å or more and 5 Å or less. When the ionic radius of the anion is 2.7 Å or more, there is an advantage that a high capacity can be obtained by increasing the number of effective ion migration paths that can be secured when the pretreatment is performed.

-Electrolyte salt-
As the anion of the electrolyte salt, the same anion and lithium ion salt as the anion selected for the ionic liquid is used from the viewpoint of thermal stability and electric conductivity. That is, the ionic radius of the anion of the electrolyte salt is 2.7 Å or more, preferably 3.5 Å or more, and more preferably 3.5 Å or more and 5 Å or less.
Examples of anions having an ionic radius of 2.7 Å or more include bis(trifluoromethylsulfonyl)imide anion (ionic radius 4.7 Å), nonafluoro-1-butane sulfonate anion (ionic radius 3.35 Å), tris(tri The same kind of anion as the above ionic liquid such as fluoromethylsulfonyl)methide anion (ionic radius 3.8Å) and bis(fluorosulfonyl)imide anion (ionic radius 3.5Å) can be mentioned. Among these, bis(fluorosulfonyl)imide anion is preferable.

The concentration of the electrolyte salt is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.5 mol/L or more and 5 mol/L or less in the non-aqueous solvent, and the capacity and the output of the storage element. From the viewpoint of compatibility of both, 1 mol/L or more and 3 mol/L or less are more preferable.

<Separator>
The separator is provided between the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode.
The material, shape, size and structure of the separator are not particularly limited and may be appropriately selected depending on the purpose.
Examples of the material of the separator include kraft paper, vinylon mixed paper, paper such as synthetic pulp mixed paper, cellophane, polyethylene graft film, polyolefin nonwoven fabric such as polypropylene meltblown nonwoven fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, and micropore film. Can be mentioned.
Among these, those having a porosity of 50% or more are preferable from the viewpoint of retaining an electrolytic solution. A non-woven fabric having a higher porosity is preferable as a shape than a thin film type having micropores (micropores).
The average thickness of the separator is appropriately selected depending on the intended purpose without any limitation, but it is preferably 20 μm or more and 100 μm or less. When the average thickness is 20 μm or more, the amount of the electrolytic solution retained becomes good, and when it is 100 μm or less, the energy density can be appropriately maintained.
The size of the separator is not particularly limited as long as it is a size that can be used for a power storage element, and can be appropriately selected according to the purpose.
The structure of the separator may be a single layer structure or a laminated structure.

<Method of manufacturing storage element>
The electricity storage device of the present invention is manufactured by assembling the positive electrode, the negative electrode, the nonaqueous electrolytic solution, and the separator used as necessary into an appropriate shape. Furthermore, it is possible to use other constituent members such as an outer can, if necessary. The method for assembling the electricity storage device is not particularly limited, and can be appropriately selected from the commonly used methods.

The shape of the electricity storage device of the present invention is not particularly limited, and can be appropriately selected from various commonly used shapes according to the application. As the shape, for example, a cylinder type in which a sheet electrode and a separator are formed in a spiral shape, a laminate type in which a sheet electrode and a separator are laminated on a plane and sealed with a laminate, and a cylinder type of an inside-out structure in which a pellet electrode and a separator are combined. , A coin type in which a pellet electrode and a separator are laminated.

<Pretreatment>
The pretreatment in the present invention is a treatment to be performed after the device is manufactured and before being put into actual use, in addition to a treatment such as aging for giving general property stabilization, and the presence of anions having a large ionic radius. Under this condition, a charge/discharge is once performed in a wide charge/discharge range, or the charge/discharge is stored in a high temperature environment for a certain period of time to secure a migration path of ions and promote an increase in effective capacity. This is not limited to only the examples illustrated in the text and the conditions shown in the claims. As an example, the charge and discharge with a specified current value is repeated in a specified voltage range under a specified temperature, after charging to a constant voltage under a specified temperature, the voltage is maintained for a certain period of time, This refers to processing such as applying a voltage that exceeds the operating voltage at a specified temperature, or leaving it at a specified temperature without applying a load such as a voltage.

Here, an example of the power storage element of the present invention is shown in FIG. The electricity storage device 10 shown in FIG. 2 has a separator 3 that holds a nonaqueous electrolytic solution containing a positive electrode 1, a negative electrode 2, a solvent that is an ionic liquid, and an electrolyte salt in which an ionic radius of anions is 2.7 Å or more. And an outer can 4, a positive electrode lead wire 6, and a negative electrode lead wire 5, and other members if necessary. Specific examples of the electricity storage device 10 include a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte capacitor.

FIG. 3 is a schematic diagram for explaining the basic configuration of the storage element 10 in an easy-to-understand manner.
The positive electrode 11 is, for example, a positive electrode current collector 20 made of aluminum, a porous carbon 21 fixed on the positive electrode current collector 20 and having pores of a three-dimensional network structure as a positive electrode active material, and a porous carbon 21. It has a binder 22 that holds them together, a conductive aid 23 represented by black circles that provides a conductive path between the porous carbons 21, and the like.
The negative electrode 12 includes, for example, a negative electrode current collector 24 made of copper, a negative electrode active material 25 made of a carbonaceous material or the like fixed on the negative electrode current collector 24, a binder 22 that holds the negative electrode active materials 25 together, and a negative electrode. It has a conductive aid 23 and the like indicated by black circles for providing a conductive path between the active materials 25.
A separator 13 is arranged between the positive electrode 11 and the negative electrode 12, and a non-aqueous electrolytic solution 26 containing a solvent which is an ionic liquid and an electrolyte salt having an ionic radius of anion of 2.7 Å or more is arranged. There is. Reference numeral 27 indicates an ion. Charge/discharge is performed by occluding or releasing ions in the pores of porous carbon having pores of a three-dimensional network structure.
For example, when lithium bis(fluorosulfonyl)imide is used as the electrolyte salt in which the ionic radius of the anion is 2.7 Å or more, the charge/discharge reaction of the electricity storage device is performed from the non-aqueous electrolyte to the three-dimensional network structure of the positive electrode. The bis(fluorosulfonyl)imide anion is occluded in the pores of the porous carbon having the pores, and the lithium cation is occluded in the carbon material of the negative electrode, whereby charging is performed. The sulfonyl)imide anion releases lithium cations from the negative electrode to the non-aqueous electrolytic solution, so that discharging is performed.

<Use>
The use of the electricity storage device of the present invention is not particularly limited and can be used for various purposes, for example, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a mobile phone, a mobile fax, a mobile copy, a mobile printer. , Headphone stereo, video movie, LCD TV, handy cleaner, portable CD, mini disk, transceiver, electronic organizer, calculator, memory card, portable tape recorder, radio, motor, lighting equipment, toys, game equipment, clock, strobe, camera , Power supplies for electric bicycles, electric tools, etc., backup power supplies, etc.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
Described below are the methods for measuring the state of pore formation of carbon used as the positive electrode active material (porosity, three-dimensional network structure), BET specific surface area, mesopore content, pore volume, and graphitization degree. To do.

<Pore formation state (porous, three-dimensional network structure)>
The presence or absence of porosity and a three-dimensional network structure was observed with a transmission electron microscope (JEM-2100, manufactured by JEOL Ltd.).

<BET specific surface area and pore volume>
After measuring the adsorption isotherm by an automatic specific surface area/pore distribution measuring device (TriStarII3020, manufactured by Shimadzu Corporation), the BET specific surface area was determined by the BET (Brunauer, Emmett, Teller) method. Further, the pore volume was determined from the adsorption isotherm by the BJH (Barrett, Joyner, Hallender) method.

<Mesopore content>
After measuring the adsorption isotherm by an automatic specific surface area/pore distribution measuring device (TriStarII3020, manufactured by Shimadzu Corporation), the mesopore content rate in the pores was calculated by the following mathematical formula 1. The amount of gas molecules adsorbed at a relative pressure (p/p ₀ ) of 0.3 or less of the adsorption isotherm is the amount of gas molecules adsorbed due to micropores, and the relative pressure of 0.3 or more and 0.96 or less is mesopores. It is the amount of gas molecules adsorbed due to.
[Formula 1]

<Graphization degree Rh>
The graphitization degree Rh was measured using a microscopic laser Raman spectroscope (Nanofinder 30, manufactured by Tokyo Instruments Co., Ltd.).

(Example 1)
<Production of positive electrode>
Porous carbon (Knobel, manufactured by Toyo Tanso Co., Ltd.) was used as a positive electrode active material, acetylene black (Denka black powder, manufactured by Denka Co., Ltd.) as a conduction aid, and acrylate latex (TRD202A, manufactured by JSR Co., Ltd.) as a binder , And carboxymethyl cellulose (Daicel 1270, manufactured by Daicel Chemical Industries, Ltd.) as a thickener so that the mass ratio of the solid content is 100:7.5:3.0:7.6, and water is added. And adjusted to an appropriate viscosity to obtain a slurry. Next, using a comma coater, the slurry was applied on both sides of an aluminum foil having a thickness of 20 μm and dried to prepare an electrode.
The average weight of the positive electrode active material in the positive electrode film after drying was 2.8 mg/cm ² . This was punched so that the coated surface had a length of 40 mm and a width of 25 mm, and a current collector was taken out from the coated surface for current extraction. A lead tab (PLUS LEAD, manufactured by Sumitomo Electric Wire Co., Ltd.) was welded to the current extraction portion to obtain a positive electrode.
The porous carbon (Kunobel, manufactured by Toyo Tanso Co., Ltd.) has a BET specific surface area of 1,000 m ² /g, a pore volume of 0.6 mL/g, a mesopore content of 44%, and a median diameter of 0. It has a diameter of 4 μm and has continuous pores having a three-dimensional network structure.

<Production of negative electrode>
Graphite (MAGD, manufactured by Hitachi Chemical Co., Ltd.) as a negative electrode active material, acetylene black (Denka black powder, manufactured by Denka Co., Ltd.) as a conduction aid, and polyvinylidene fluoride (PVDF) (BM-400B, Nippon Zeon Co., Ltd.) as a binder. (Manufactured by the company) were mixed so that the mass ratio of the solid content was 100:3.0:5.0, respectively, and N-methylpyrrolidone (NMP) was added to adjust the viscosity to an appropriate level to obtain a slurry. Next, using a comma coater, the slurry was applied on both sides of a copper foil having a thickness of 8 μm and dried to prepare an electrode.
The average basis weight of the active material in the electrode film after drying was 11.4 mg/cm ² . This was punched so that the coated surface had a length of 43 mm and a width of 28 mm, and a current collector was taken out from the coated surface for current extraction. A lead tab (MINUS LEAD, manufactured by Sumitomo Electric Wire Co., Ltd.) was welded to the current extraction part to obtain a negative electrode.

<Non-aqueous electrolyte>
A mixed solution of 1-methyl-1-propyl-pyrrolidinium bis(fluorosulfonyl)imide, which is an ionic liquid containing lithium bis(fluorosulfonyl)imide as an electrolyte salt of 2 mol/L, was used as a non-aqueous electrolyte. ..

<Separator>
As the separator, a cellulose separator (TDZ3540, manufactured by Nippon Koshigyo Kogyo Co., Ltd.) punched into a length of 45 mm and a width of 30 mm was used.

The above two positive electrodes, three negative electrodes and 12 separators were dried under reduced pressure at 150°C. The subsequent work was carried out in a dry argon glove box.

<Negative electrode pre-doping>
In the electricity storage device, in order to supply a sufficient amount of lithium ions for charging/discharging, a pre-doping process of previously occluding lithium on the negative electrode side was performed. As a method of pre-doping, one sheet of the above negative electrode is taken, both sides thereof are sandwiched by the above separators, and a lithium metal having a thickness of 2 mm cut out in a length of 45 mm and a width of 30 mm is arranged on both sides thereof, and then the above non-aqueous electrolysis is carried out. The solution was impregnated and left standing for 24 hours with the lithium metal and the negative electrode short-circuited. Through the above steps, the negative electrode active material was pre-doped with lithium.

<Assembly of storage element>
After removing the metallic lithium and the separator from the negative electrode for which pre-doping is completed, using the above two positive electrodes, three negative electrodes, and six separators, these are laminated with separator-negative electrode-separator-positive electrode-separator, by repeating the following, An internal element was produced.
After that, the internal element is heated to 150° C. under reduced pressure and dried for 20 hours, and then the metal lithium foil and the copper foil are punched out so that the pressure-bonding surface has a length of 43 mm and a width of 28 mm, and pressure-bonded so that there is no deviation. It was a lithium electrode. The laminated body and the lithium electrode were fixed so as not to be displaced, impregnated with a non-aqueous electrolyte, and then sealed using an aluminum laminate film (manufactured by Showa Denko Packaging Co., Ltd.) as an exterior material to form a storage element. It was made. The negative electrode was doped with lithium ions by short-circuiting the negative electrode and the lithium electrode. After that, the lithium electrode was taken out and the exterior material was fused again to manufacture a power storage element. All of these assembly operations were performed in a dry argon glove box.

<Evaluation of power storage element>
The obtained electricity storage device of Example 1 was held in a constant temperature bath, and various tests shown below were carried out using an automatic battery evaluation device (1024B-7V0.1A-4, manufactured by Electrofield Corporation).

-Pretreatment-
As a pretreatment for the first charge and discharge, constant current charging was performed at 60° C. at a charge and discharge rate of 1 C as a current value up to 4.4 V as a charge end voltage. Then, after maintaining a constant voltage at 4.4 V for 1 hour, constant current discharge was performed up to 2.2 V as a discharge end voltage at a charge/discharge rate of 0.2 C, and this charge/discharge cycle was repeated twice. went.
Note that the 1 C-converted current value refers to a current value at which a storage element having a capacity of a nominal capacity value is discharged at a constant current and the discharge ends in 1 hour.

-Measurement of discharge capacity-
Next, after the above-mentioned pretreatment, constant current charging was performed at room temperature (25° C.) to a charge end rate of 4.2 V at a charge/discharge rate of 0.2 C. Then, at a current value converted into a charge/discharge rate of 0.2 C, constant current discharge was performed up to a discharge end voltage of 2.2 V, and the discharge capacity was measured. The results are shown in Table 3.
The discharge capacity is a conversion value (unit: mAh/g) per 1 g of porous carbon as the positive electrode active material.

-Measurement of low temperature characteristics-
Next, the temperature of the constant temperature bath was set to −20° C., and the storage element was left standing until the temperature became stable, and then the capacity was measured under the same conditions as the measurement of the discharge capacity except for the temperature. Then, the discharge capacity measured at −20° C. was divided by the discharge capacity measured at room temperature (25° C.) to calculate the appearance rate of the capacity at −20° C., which was used as an index of low temperature characteristics. The results are shown in Table 3.

-Measurement of high temperature stability-
Next, the temperature of the constant temperature bath was set to 25° C., and the storage element was allowed to stand until the temperature became stable, and then constant current charging was performed up to 4.2 V as a charge end voltage at a charge/discharge rate of 1 C. Then, after maintaining a constant voltage at 4.2V for 30 minutes, constant current discharge was performed up to 2.2V as a discharge end voltage at a charge/discharge rate of 1C. In the charging/discharging at this time, from the point where the discharge curve was linearly stable immediately after maintaining the constant voltage for 30 minutes, the straight line was extended to the discharge start time, and the intersection was taken as the voltage drop due to the discharge. Based on this value, the DC resistance (DC-IR) of the storage element was calculated.
After that, the temperature was set to 80° C., the storage element was left standing until the temperature became stable, and then the battery was charged to 4.0 V as a charge end voltage at a current value of a charge/discharge rate of 0.2 C. Thereafter, the constant voltage was maintained for 100 hours while maintaining the temperature and the voltage.
Then, the constant temperature bath was returned to 25° C., and DC-IR measurement was performed by the same method as the discharge capacity measurement. From the obtained results, the rate of increase of the resistance value after the high temperature test with respect to the resistance value before the high temperature test was calculated and used as an index of stability under high temperature. The results are shown in Table 3.

-Evaluation of cycle stability-
Next, the temperature of the constant temperature bath is set to room temperature (25° C.), and the storage element is left to stand until the temperature stabilizes, and then charged and discharged at a rate of 10 C, a charge end voltage of 4.2 V, and a discharge end voltage of 2.2 V. A discharge test was carried out, and the discharge capacity was measured after 1,000 cycles had elapsed. From the obtained measurement results, the discharge capacity after the cycle was divided by the initial discharge capacity was taken as the capacity retention rate and used as an index of cycle stability. The results are shown in Table 3.

(Examples 2 to 4)
Electric storage elements of Examples 2 to 4 were produced in the same manner as in Example 1 except that the compositions of the non-aqueous electrolyte solutions were changed to those shown in Table 2-1. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Examples 5 to 8)
Electric storage elements of Examples 5 to 8 were produced in the same manner as in Example 1 except that the concentration of the electrolyte salt was changed to the value shown in Table 2-1. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Examples 9 to 12)
Example 1 Example 1 was repeated except that the BET specific surface area of the porous carbon (Knobel, manufactured by Toyo Tanso Co., Ltd.) used as the positive electrode active material was changed to the value shown in Table 1. 9-12 storage elements were produced. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Examples 13 to 16)
Example 1 Example 1 was repeated except that the pore volume of porous carbon (Knobel, manufactured by Toyo Tanso Co., Ltd.) used as the positive electrode active material was changed to the value shown in Table 1. 13 to 16 storage elements were produced. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Examples 17 to 20)
Example 1 was carried out in the same manner as in Example 1 except that the mesopore content of the porous carbon (Knobel, manufactured by Toyo Tanso Co., Ltd.) used as the positive electrode active material was changed to the value shown in Table 1. The electricity storage devices of Examples 17 to 20 were produced. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Examples 21 to 24)
Example 1 was carried out in the same manner as in Example 1 except that the mesopore content of the porous carbon (Knobel, manufactured by Toyo Tanso Co., Ltd.) used as the positive electrode active material was changed to the value shown in Table 1. Examples 21 to 24 were produced. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Examples 25 to 28)
Example 1 was carried out in the same manner as in Example 1 except that the graphitization degree Rh of the porous carbon (Knobel, manufactured by Toyo Tanso Co., Ltd.) used as the positive electrode active material was changed to the value shown in Table 1. Examples 25 to 28 were produced. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Example 29)
Example 29 was produced in the same manner as in Example 1 except that the element prepared in Example 1 was not subjected to pretreatment before measurement. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Examples 30 to 31)
Examples 30 to 31 were produced in the same manner as in Example 1 except that the electrolyte salt concentration was changed to the value shown in Table 2-2. With respect to each of the manufactured power storage elements, the power storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Comparative Example 1)
Comparison was performed in the same manner as in Example 1 except that the carbon material used for the positive electrode active material was changed to graphite (KS-6, manufactured by Imerys Graphite & Carbon Co., Ltd.) having no pore structure in Example 1. The electricity storage device of Example 1 was produced. With respect to the manufactured storage element, the storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Comparative example 2)
In Example 1, except that the carbon material used for the positive electrode active material was changed to activated carbon (YP-50F, manufactured by Kuraray Co., Ltd.) having a pore structure but not a communicating pore structure, the same as in Example 1. Thus, the electricity storage device of Comparative Example 2 was produced. With respect to the manufactured storage element, the storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Comparative example 3)
A storage element of Comparative Example 3 was produced in the same manner as in Example 1 except that the electrolytic solution in Example 1 was changed to the organic solvent-based electrolytic solution shown in Table 2-2. With respect to the manufactured storage element, the storage element was evaluated in the same manner as in Example 1. The results are shown in Table 3. However, only for the high temperature stability measurement, gas generation was very large at the time of standing for 24 hours after the start of the test, and there was a risk of bursting, so the application of voltage was stopped at this time.

(Comparative example 4)
A power storage device of Comparative Example 4 was produced in the same manner as in Example 1, except that the ionic liquid used in the electrolytic solution and the anionic species of the electrolyte salt were changed to tetrafluoroborate ions. With respect to the manufactured electricity storage device, the electricity storage device was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Comparative example 5)
Storage of Comparative Example 5 in the same manner as in Example 1 except that the anionic species of the ionic liquid used in the electrolytic solution and the anionic species of the electrolyte salt were changed to anions different from those shown in Table 2-2. A device was produced. With respect to the manufactured electricity storage device, the electricity storage device was evaluated in the same manner as in Example 1. The results are shown in Table 3.

(Comparative example 6)
A power storage device of Comparative Example 6 was produced in the same manner as in Example 1 except that the electrolytic solution in Example 1 was changed to the organic electrolytic solution shown in Table 2-2 to which 10% by mass of the ionic liquid was added. did. With respect to the manufactured electricity storage device, the electricity storage device was evaluated in the same manner as in Example 1. The results are shown in Table 3.

From the results of Table 3, it can be seen that Examples 1 to 4 have high temperature stability, high capacity, high cycle stability, and high capacity appearance rate at low temperatures, as compared with Comparative Examples 1 to 6. This is because the requirements of the present invention shown below are satisfied.
(1) Since it uses an ionic liquid, it has high stability to high temperatures.
(2) Since the positive electrode active material uses porous carbon having pores having a three-dimensional network structure, it is possible to absorb the influence of volume expansion due to intercalation of anions having a large ionic radius, and exfoliation of the active material. It does not easily crack or crack, and has high cycle stability.
(3) By using an anion having an ionic radius of 2.7 Å or more as the anion species and performing pretreatment, the effective capacity increase is promoted by ensuring the ion migration path.
(4) By using a common anion species as the anion species of the ionic liquid and the electrolyte salt, local precipitation or crystallization due to the presence of different kinds of ions does not occur, so the capacity appearance rate at low temperature Is high.

Further, looking at Examples 5 to 8, as compared with Example 1, Example 5 having an electrolyte salt concentration of less than 0.5 mol/L has a slightly lower capacity, and the electrolyte salt concentration is 5.0 mol/L. In Example 8 having L or more, the capacity appearance rate at a slightly low temperature is low. From this, it is understood that the optimum electrolyte salt concentration is in the range of 0.5 mol/L or more and 5.0 mol/L or less.
Further, looking at Examples 9 to 12, as compared with Example 1, Example 9 in which the BET specific surface area of the carbon material is less than 50 m ² /g has a slightly lower discharge capacity and also 2,000 m ² /g. Example 12 above that has reduced cycle stability. From this, the BET specific surface area of carbon used for the positive electrode is preferably in the range of 50 m ² /g or more and 2,000 m ² /g or less.
Further, looking at Examples 13 to 16, in comparison with Example 1, Example 13 in which the pore volume of the carbon material is less than 0.2 mL/g has a low discharge capacity and 2.3 mL/g. In Example 16, which exceeds the above, the cycle stability is deteriorated. From this, the pore volume of the carbon material used for the positive electrode is preferably in the range of 0.2 mL/g or more and 2.3 mL/g or less.
Further, looking at Examples 17 to 20, in comparison with Example 1, Example 17 in which the mesopore content of the carbon material is less than 25% has low cycle stability and exceeds 80%. Initial capacity is slightly reduced. From this, the mesopore content of the carbon material used for the positive electrode is preferably in the range of 25% to 80%.
In Examples 17 to 20, as compared with Example 1, in Example 20 in which the micropore volume of the carbon material is larger than 1.0 mL/g, the low-temperature capacity appearance rate decreases and the DC-IR increase rate after high-temperature loading increases. .. From this, the micropore volume of the carbon material used for the positive electrode is preferably within the range of 1.0 mL/g or less.
Further, looking at Examples 21 to 24, compared with Example 1, Example 21 in which the mesopore content of the carbon material is less than 15% has low cycle stability and exceeds 80%. Initial capacity is slightly reduced. From this, the mesopore content of the carbon material used for the positive electrode is preferably in the range of 15 to 80%.
In Examples 25 to 28, the low-temperature capacity appearance rate was lower in Example 25 in which the graphitization degree Rh of the carbon material was smaller than 0.9, and the initial capacity was higher in Example 28 than 1.6. It is falling. From this, the graphitization degree Rh of the carbon material used for the positive electrode is preferably in the range of 0.9 to 1.6.
Further, looking at Example 29, as compared with Example 1, under the condition that the pretreatment is not performed before the measurement, the initial capacity and the low-temperature capacity appearance rate are slightly lowered. Therefore, it is desirable to carry out the pretreatment.

Looking at the results in Table 3 focusing on the comparative example, it can be seen that the electricity storage device manufactured in Comparative Example 1 has lower initial capacity and cycle stability as compared with Example 1. Since this does not have a pore structure, there is no pore volume that increases due to pretreatment, and the effect of volume expansion during anion intercalation accompanying cycle application cannot be absorbed, and the active material This is due to the occurrence of peeling and cracking.
Further, it can be seen that the electricity storage device manufactured in Comparative Example 2 has lower cycle stability as compared with Example 1. This is because it has a pore structure, but it does not have a continuous pore structure, so the effect of volume expansion during anion intercalation accompanying cycle application could not be absorbed, and peeling or cracking of the active material occurred. Due to.
In addition, the electricity storage device manufactured in Comparative Example 3 generated much more gas than in Example 1 during the test at a high temperature. This is because the mixed solvent of ethylene carbonate and ethyl methyl carbonate was used for the electrolytic solution, so that the decomposition reaction of the solvent occurred at high temperature and the decomposed component of the solvent was gasified.
In addition, the electricity storage device manufactured in Comparative Example 4 has a lower initial capacity and a lower capacity appearance rate at low temperatures than in Example 1. This is because the ionic radius of the anionic species used in the ionic liquid and the electrolyte salt is 2.7 Å or less. That is, for the initial capacity, the effect of capacity activation by pretreatment cannot be obtained because the ionic radius is too small, and for the capacity appearance rate at low temperature, crystallization occurs at low temperature because the ionic radius is small. This is because it has become easier.
Further, the electricity storage device manufactured in Comparative Example 5 has a lower capacity appearance rate at low temperatures than in Example 1. This is because the anion species used in the ionic liquid and the anion species used in the electrolyte salt are different from each other, which facilitates crystallization at low temperature.
In addition, in the electricity storage device manufactured in Comparative Example 6, the increase rate of DC-IR after applying the high temperature load was significantly larger than that in Example 1. This is because even if 10% by mass of the ionic liquid is added, the basic solvent is an organic solvent system, so that the decomposition reaction of the organic solvent cannot be completely prevented under the condition of high temperature load. Due to.

As described above, by using the technique described in the present invention, it has a wide operating temperature range having stability at high temperature and high capacity appearance rate at low temperature, and has high cycle stability. In addition, an element having high capacitance can be manufactured.

Aspects of the present invention are as follows, for example.
<1> An electricity storage device comprising a positive electrode containing a positive electrode active material capable of occluding and releasing anions, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte,
The positive electrode active material contains porous carbon having pores of a three-dimensional network structure,
The solvent of the non-aqueous electrolyte is an ionic liquid, the ionic radius of the anion of the ionic liquid is 2.7 Å or more, and the anion of the electrolyte salt of the non-aqueous electrolyte is common to the anion of the ionic liquid. It is an electric storage element characterized by being present.
<2> At least the electrolyte salt is selected from lithium bis(trifluoromethylsulfonyl)imide, lithium nonafluoro-1-butanesulfonate, lithium tris(trifluoromethylsulfonyl)methide, and lithium bis(fluorosulfonyl)imide. The electricity storage device according to <1>, which is one type.
<3> The electricity storage device according to any one of <1> to <2>, wherein the electrolyte salt is lithium bis(trifluoromethylsulfonyl)imide.
<4> The electricity storage device according to any one of <1> to <3>, wherein the content of the electrolyte salt in the entire electrolytic solution is 0.5 mol/L or more and 5 mol/L or less.
<5> The electricity storage device according to any one of <1> to <4>, in which the electricity storage device is pretreated before use.
<6> The electricity storage device according to any one of <1> to <5>, wherein the BET specific surface area of the porous carbon is 50 m ² /g or more and 2,000 m ² /g or less.
<7> The electricity storage device according to any one of <1> to <6>, wherein the porous carbon has a pore volume of 0.2 mL/g or more and 2.3 mL/g or less.
<8> The electricity storage device according to any one of <1> to <7>, wherein the porous carbon has micropores, and the micropore volume of the porous carbon is 1.0 mL/g or less. ..
<9> Any one of <1> to <8>, wherein the pores of the three-dimensional network structure in the porous carbon include mesopores, and the mesopore content of the porous carbon is 15% or more and 80% or less. The electric storage device according to 1.
<10> The electricity storage device according to any one of <1> to <9>, wherein the degree of graphitization of the porous carbon is 0.9 or more and 1.6 or less.

According to the electricity storage device described in any one of the above items <1> to <10>, various problems in the related art can be solved and the object of the present invention can be achieved.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Outer can 5 Negative electrode lead wire 6 Positive electrode lead wire 10 Storage element

Patent No. 4569126 Patent No. 4314087 Patent No. 5399185 JP2012-195563A Japanese Unexamined Patent Publication No. 2018-152519

Claims (10)

A power storage device comprising a positive electrode containing a positive electrode active material capable of occluding or releasing anions, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte solution,
The positive electrode active material contains porous carbon having pores of a three-dimensional network structure,
The solvent of the non-aqueous electrolyte is an ionic liquid, the ionic radius of the anion of the ionic liquid is 2.7 Å or more, and the anion of the electrolyte salt of the non-aqueous electrolyte is common to the anion of the ionic liquid. An electric storage element characterized by being present. The electrolyte salt is at least one selected from lithium bis(trifluoromethylsulfonyl)imide, lithium nonafluoro-1-butanesulfonate, lithium tris(trifluoromethylsulfonyl)methide, and lithium bis(fluorosulfonyl)imide. The electric storage element according to claim 1. The electricity storage device according to claim 1, wherein the electrolyte salt is lithium bis(trifluoromethylsulfonyl)imide. The electricity storage device according to claim 1, wherein the content of the electrolyte salt in the entire electrolytic solution is 0.5 mol/L or more and 5 mol/L or less. The power storage element according to claim 1, wherein the power storage element is subjected to pretreatment before use. The electricity storage device according to claim 1, wherein the BET specific surface area of the porous carbon is 50 m ² /g or more and 2,000 m ² /g or less. 7. The electricity storage device according to claim 1, wherein the pore volume of the porous carbon is 0.2 mL/g or more and 2.3 mL/g or less. The electricity storage device according to claim 1, wherein the porous carbon has micropores, and the micropore volume of the porous carbon is 1.0 mL/g or less. 9. The electricity storage device according to claim 1, wherein the pores of the three-dimensional network structure in the porous carbon include mesopores, and the mesopore content of the porous carbon is 15% or more and 80% or less. The electricity storage device according to claim 1, wherein the degree of graphitization of the porous carbon is 0.9 or more and 1.6 or less.