JP7007830B2 - Solvent for electrolyte - Google Patents

Description

The present invention relates to a solvent for an electrolytic solution and the like.

Various solvents are known as a solvent constituting the electrolytic solution (solvent for the electrolytic solution).
For example, in Patent Document 1 (Japanese Unexamined Patent Publication No. 2012-18916), as an organic solvent constituting an electrolytic solution containing a specific non-aqueous electrolyte, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, γ-butyrolactone, γ -Valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrachloride, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, ethyl carbonate Methyl, diethyl carbonate, acetonitrile, glutaronitrile, adiponitrile, methoxynitrile, 3-methoxypropionitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N'-dimethylimidazolidinone , Nitromethane, nitroethane, sulfolane, dimethylsulfoxide, trimethyl phosphate and the like can be used.

Japanese Unexamined Patent Publication No. 2012-18916 (Claims, paragraph [0029])

An object of the present invention is to provide a novel solvent for an electrolytic solution.

As described above, various solvents are known as solvents constituting the electrolytic solution.

Under these circumstances, the present inventor pays particular attention to propylene carbonate among the solvents, and the solvent containing propylene carbonate may inevitably contain hydroxyacetone due to decomposition of propylene carbonate or the like. In addition, the solvent containing hydroxyacetone may cause performance deterioration of electrochemical devices (electric double layer capacitors, etc.) such as an increase in resistance (particularly initial resistance). It has been found that a fixed amount of hydroxyacetone can suppress the degree of such performance deterioration within a sufficiently small range and can be used without any problem in practical use, and further diligent studies have been carried out to complete the present invention. ..

The relationship between hydroxyacetone and the performance of electrochemical devices has not been known at all.

That is, the present invention includes the following contents.
[1]
A solvent for an electrolytic solution containing propylene carbonate, wherein the content ratio (content) of hydroxyacetone is 4000 ppm or less on a mass basis.
[2]
The solvent according to [1], wherein the content ratio of hydroxyacetone is 2000 ppm or less on a mass basis.
[3]
The solvent according to [1] or [2], wherein the content ratio of hydroxyacetone is 10 ppm or more on a mass basis.
[4]
The solvent according to any one of [1] to [3], wherein the content ratio of hydroxyacetone is 50 to 1500 ppm on a mass basis.
[5]
The solvent according to any one of [1] to [4], wherein the ratio of propylene carbonate to the total solvent is 20% by mass or more.
[6]
An electrolytic solution containing the solvent according to any one of [1] to [5].
[7]
The electrolytic solution according to [6], wherein the content ratio of hydroxyacetone is 4000 ppm or less on a mass basis.
[8]
The electrolytic solution according to [6] or [7], which contains a quaternary ammonium salt as an electrolyte.
[9]
Quaternary ammonium salts are derived from N-ethyl-N-methylpyrrolidinium tetrafluoroborate, spiro (1,1) -bipyrrolidinium tetrafluoroborate, triethylmethylammonium tetrafluoroborate and diethyldimethylammonium tetrafluoroborate. The electrolytic solution according to [8], which is at least one selected.
[10]
An electrochemical device comprising the electrolytic solution according to any one of [6] to [9].
[11]
The electrochemical device according to [10], which is an electric double layer capacitor.
[12]
A method for suppressing or reducing an increase in (initial) resistance of an electrochemical device provided with an electrolytic solution containing propylene carbonate as a solvent, wherein the content ratio of hydroxyacetone in the solvent and / or the electrolytic solution is 4000 ppm on a mass basis. How to do the following.
[13]
The resistance (initial resistance) increase rate is set to 20% or less based on the resistance value (initial resistance value) when the content ratio of hydroxyacetone in the solvent and / or the electrolytic solution is 0 ppm on a mass basis [12]. The method described.

In the present invention, it is possible to provide a novel solvent suitable for an electrolytic solution or the like. Although such a solvent contains propylene carbonate, the content ratio of hydroxyacetone is set to a predetermined ratio.
Then, according to such a solvent, an electrolytic solution having a small resistance (particularly the initial resistance) (or an electrolytic solution whose resistance does not easily increase) can be efficiently formed. In particular, even if a high voltage is applied and used, it is easy to suppress an increase in resistance, which is suitable.

FIG. 1 is a front view of a laminated electric double layer capacitor. FIG. 2 is an internal configuration diagram of a laminated electric double layer capacitor.

Hereinafter, the present invention will be described in detail.

[solvent]
The solvent contains propylene carbonate and may be suitably used for an electrolytic solution (or a solvent constituting the electrolytic solution).

Such a solvent may contain at least propylene carbonate as a solvent component, may be composed of only propylene carbonate, or may contain propylene carbonate and another solvent.

The other solvent is not particularly limited, and is, for example, a carbonate-based solvent other than propylene carbonate [for example, a cyclic carbonate (for example, an alkylene carbonate such as ethylene carbonate or butylene carbonate, an alkenylene carbonate such as vinylene carbonate), a chain carbonate (for example, for example). , Dialkyl carbonate such as dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate)], ether solvent [eg, chain ether (eg, 1,2-dimethoxyethane), cyclic ether (eg, tetrahydrofuran, 2-methyltetrachloride), etc. , 1,3-Dioxolane, 4-Methyl-1,3-Dioxolan, etc.], Ester-based solvents [For example, chain esters (eg, alkanoic acid alkyl esters such as methyl acetate, methyl propionate, ethyl propionate) , Lactones or cyclic esters (eg, γ-butyrolactone, β-butyrolactone, γ-valerolactone)], nitrile solvents [eg, mononitriles (eg, acetonitrile, methoxynitrile, 3-methoxypropionitrile, etc.), dinitriles, etc. (Eg, glutaronitrile, adiponitrile, etc.)], amide solvents [eg, chain amides (eg, dimethylformamide, etc.), cyclic amides or lactams (eg, N-methylpyrrolidinone), etc.], nitro solvents (eg, N-methylpyrrolidinone), etc. , Nitromethane, nitroethane, etc.), sulfur-based solvents (eg, sulfolane, ethylmethylsulfolane, dimethylsulfoxide, etc.), phosphorus-based solvents (eg, phosphate esters such as trimethyl phosphate), and other non-aqueous solvents.

Other solvents may be used alone or in combination of two or more.

When the other solvent is contained, the content ratio of the other solvent to the whole solvent is, for example, 90% by mass or less (for example, 0.01 to 85% by mass) and 80% by mass or less (for example, 0.1 to 75% by mass). ), 70% by mass or less (for example, 1 to 65% by mass), 60% by mass or less, 50% by mass or less, and the like.

The content ratio of propylene carbonate to the whole solvent may be, for example, 10% by mass or more, preferably 20% by mass or more, more preferably 25% by mass or more, and 30% by mass or more, 40% by mass or more, 50% by mass. As mentioned above, it may be 60% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more.

The solvent does not have to contain (substantially) hydroxyacetone, and may contain hydroxyacetone as long as it is in a predetermined range or amount.

The content ratio (concentration) of hydroxyacetone in the solvent can be generally selected from the range of 4000 ppm or less (for example, 3500 ppm or less) on a mass basis, and is 3000 ppm or less (for example, 2500 ppm or less), preferably 2000 ppm or less, and more preferably 1500 ppm. It may be about 1350 ppm or less (for example, 1400 ppm or less), and may be 1350 ppm or less, 1300 ppm or less, 1200 ppm or less, 1000 ppm or less, 800 ppm or less, 700 ppm or less, 600 ppm or less, 500 ppm or less, and the like.

The lower limit of the content ratio of hydroxyacetone is not particularly limited, and may be 0 ppm (or detection limit) on a mass basis with respect to the entire solvent, and may be a finite value (for example, 1 ppm, 2 ppm, 3 ppm, 5 ppm, 7 ppm). It may be 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, etc.).

In the present invention, low resistance (initial resistance) can be realized without strictly removing hydroxyacetone.

The reason why hydroxyacetone is contained in propylene carbonate is not clear, but it is assumed that it is derived from propylene carbonate or propylene glycol which is considered to be a decomposition product thereof.

The method for adjusting the content ratio (concentration) of hydroxyacetone is not particularly limited, and the propylene carbonate containing hydroxyacetone may be adjusted by performing a conventional purification method (for example, extraction, distillation, etc.). ..

Further, the propylene carbonate containing hydroxyacetone may be prepared by purifying until the hydroxyacetone concentration reaches a desired concentration, or by adding hydroxyacetone until the desired concentration is reached.

As mentioned above, hydroxyacetone may be derived from propylene glycol. Therefore, the ratio of propylene glycol in the solvent may be a predetermined ratio.

For example, the content ratio (concentration) of propylene glycol in the solvent can be generally selected from the range of 3000 ppm or less (for example, 2500 ppm or less) on a mass basis, and is 500 ppm or less, preferably 200 ppm or less, and more preferably about 100 ppm or less. May be.

The lower limit of the content ratio of propylene glycol is not particularly limited and may be 0 ppm (or detection limit) on a mass basis, and may be a finite value (for example, 1 ppm, 2 ppm, 3 ppm, 5 ppm, 7 ppm, 10 ppm, 15 ppm, 20 ppm). Etc.).

The concentration of propylene glycol can also be adjusted by a conventional method.

The solvent (solvent for electrolytic solution) may be usually a non-aqueous solvent (organic solvent).

[Electrolytic solution]
The solvent of the present invention can be used for an electrolytic solution (or a solvent for forming an electrolytic solution) as described above. Therefore, the present invention includes an electrolytic solution containing the solvent.

That is, the electrolytic solution contains the solvent as a solvent component.

Such an electrolytic solution usually contains the solvent and an electrolyte. The electrolyte is not particularly limited as long as it functions as an electrolyte. Specific examples of the electrolyte include a quaternary ammonium salt (a compound having a quaternary ammonium cation (unit)) and the like.

The quaternary ammonium salt may be a compound represented by the following formula (I).
Q ⁺ X ^-... (I)
(In the formula, Q ⁺ is a quaternary ammonium cation (unit)), and X ^- represents an anion. )

As a quaternary ammonium cation (for example, Q ⁺ in the above formula (I)), any tertiary amine is quaternized with a hydrocarbon group (for example, an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, etc.). Is used.
Further, a hydroxyl group, an amino group, a nitro group, a cyano group, a carbonyl group, an ether group, an aldehyde group and the like may be bonded to the hydrocarbon moiety (hydrocarbon group) forming the quaternary ammonium cation.

Typical quaternary ammonium cation units include, for example, chain ammonium units {eg, alkylammonium [eg, tetraalkylammonium (eg, tetramethylammonium, tetraethylammonium, triethylmethylammonium, trimethylpropylmethylammonium, dimethyldiethyl). Tetra C _1-6 alkylammonium such as ammonium, ethyltrimethylammonium, tetrabutylammonium), alkylalkoxyalkylammonium (eg, N, N, N-trimethyl-N-methoxymethylammonium, N-ethyl-N, N-dimethyl) -Tri C _1-6 alkyl mono C _1-4 alkoxy C _1-6 alkyl ammonium such as N-methoxymethylammonium], alkyl aralkylammonium (eg C _1-6 alkyl-C _1- such as benzyltrimethylammonium) ₄ Alkyl C _6-10 arylammonium), etc.}, Cyclic ammonium units [eg, imidazole-based cations (eg, N, N'-dimethylimidazolium, N-ethyl-N'-methylimidazolium, 1,2,3- N, N'-di C _1-6 alkyl imidazolium such as trimethyl imidazolium, 1,3-dimethyl-2-phenyl imidazolium), pyridine-based cations (eg, NC _1-6 such as N-ethylpyridinium) Alkylpyridinium), pyrrolidine-based cations, piperidine-based cations, etc.] and the like.

Examples of the pyrrolidine-based cation (unit) include N, N-dialkylpyrrolidinium (eg, N, N-dimethylpyrrolidinium, N, N-diethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium). , N, N-diC _1-6 alkylpyrrolidinium such as N-methyl-N-propylpyrrolidinium, N-butyl-N-methylpyrrolidinium, N-ethyl-N-propylpyrrolidinium), N-alkyl-N-alkoxyalkylpyrrolidinium (eg, N-methyl-N-methoxymethylpyrrolidinium, N-methyl-N-ethoxymethylpyrrolidinium, N-ethyl-N-methoxymethylpyrrolidinium, NC _1-6 alkyl-NC _1-4 alkoxyC _1-6 alkylpyrrolidinium such as N-ethyl-N-ethoxymethylpyrrolidinium), N, N-bis (alkoxyalkyl) pyrrolidinium (eg , N-C _1-6 alkyl-NC _1-4 alkoxy C _1-6 alkyl pyrrolidinium such as N-methyl-N-methoxyethyl pyrrolidinium, N-ethyl-N-methoxyethyl pyrrolidinium) , N, N-di (alkoxyalkyl) pyrrolidinium (N, N-bismethoxymethylpyrrolidinium, N-methoxymethyl-N-methoxyethylpyrrolidinium, N-methoxymethyl-N-ethoxymethylpyrrolidinium, N , N-bisethoxymethylpyrrolidinium, N, N-bismethoxyethylpyrrolidinium, etc. NC _1-4 alkoxy C _1-6 alkyl-NC _1-4 alkoxy C _1-6 alkyl pyrrolidinium ), Spiro (1,1) -bipyrrolidinium (1,1'-spiro-bispyrrolidinium) and the like.

Examples of the piperidin-based cation (unit) include N, N-dialkylpiperidinium (eg, N, N-dimethylpiperidinium, N-methyl-N-ethylpiperidinium, N-methyl-N-propylpi). N, N-diC _1-6 alkyl piperidinium such as peridinium, N-ethyl-N-propyl piperidinium), N-alkyl-N-alkoxyalkyl piperidinium (eg, N-methyl-N-) NC _1-6 alkyl such as methoxymethylpiperidinium, N-methyl-N-ethoxymethylpiperidinium, N-ethyl-N-methoxymethylpiperidinium, N-ethyl-N-ethoxymethylpiperidinium -NC _1-4 alkoxy C _1-6 alkyl piperidinium), N, N-bis (alkoxyalkyl) piperidinium (eg, N-methyl-N-methoxyethyl piperidinium, N-ethyl-N-methoxy) NC _1-4 alkoxy C _1-6 alkyl-NC _1-4 alkoxy C _1-6 alkyl piperidinium such as ethyl piperidinium), N, N-bis (methoxymethyl) piperidinium, N-methoxy NC ₁ such as Methyl-N-methoxyethyl piperidinium, N-methoxymethyl-N-ethoxymethylpiperidinium, N, N-bis (ethoxymethyl) piperidinium, N, N-bis (methoxyethyl) piperidinium _-4 alkoxy C _1-6 alkyl-NC _1-4 alkoxy C _1-6 alkyl piperidinium) and the like.

The compound (or electrolyte) having a quaternary ammonium cation unit is not particularly limited in the content form in the electrolytic solution as long as it has a quaternary ammonium cation unit, but for example, a salt is added together with an anion (counter anion). It may be formed and contained. In the composition, the salt may be ionized.

Specific anions (for example, X ⁻ in the above formula (I)) include, for example, halogens (or halide ions, chlorine, bromine, iodine or ions thereof, etc.), fluorine-containing anions [tetrafluoroborate ion (tetrafluoroborate ion (). BF _4- ⁾ , Hexafluorophosphate ion (PF _6- ⁾ , Hexafluoroantimonic acid (SbF _6- ⁾ , CF ₃ CO _2- ^, CF ₃ SO _3- ^, N (FSO ₂ ) _2- ^, N (CF ₃ ) SO ₂ ) _2- ^, N (CF ₃ CF ₂ SO ₂ ) _2- , N (FSO ₂ ) (CF ₃ SO ₂ ) ^- , N (CF ₃ SO ₂ ) ^- , C (CF ₃ CF ₂ SO ₂ ) ^- , C ( CF ₃ SO ₂ ) _3- ^, N (CF ₃ SO ₂ ) (CF ₃ CO) ^- , CF ₃ BF _3- ^, C ₂ F ₅ BF _3- ^, (CF ₃ ) ₂ BF _2- ^, (CF ₃ ) ( C ₂ F ₅ ) BF _2- ^, (C ₂ F ₅ ) ₂ BF _2- ^, (CF ₃ ) ₃ BF- ^, etc.], Inorganic acid anions (phosphate ion, borate ion, perchlorate ion, etc.), Organic acids [eg, monocarboxylic acids (eg, aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid, stearic acid, acrylic acid, oleic acid; aromatic monocarboxylic acids such as benzoic acid and salicylic acid), polycarboxylic acids. (For example, aliphatic polycarboxylic acids such as oxalic acid, malonic acid and maleic acid; aromatic polycarboxylic acids such as phthalic acid and terephthalic acid)] and the like.

Among these anions, BF _4- ^, PF _6- ^, AsF _6- ^, SbF _6- ^, N (CF ₃ SO ₃ ) _2- ^, RfSO _3- ^[ In the formula, Rf is a fluoroalkyl group (eg, trifluoromethyl). Fluoro C _1-8 alkyl group such as a group)] and the like are preferable, and _BF4 ⁻ may be particularly preferable.

The quaternary ammonium salt may be a salt of the quaternary ammonium cation and the anion, and includes any combination thereof. For example, among the quaternary ammonium salts, the tetrafluoroborate ( _BF4- ) salt includes N ^- ethyl-N-methylpyrrolidinium tetrafluoroborate and spiro (1,1) -bipyrrolidinium tetrafluoroborate. , Triethylmethylammonium tetrafluoroborate, diethyldimethylammonium tetrafluoroborate and the like.

The electrolyte may be used alone or in combination of two or more.

As the electrolyte, a commercially available product may be used, or an electrolyte produced according to a known method (for example, the method described in Japanese Patent Publication No. 08-31401) may be used.

In the electrolytic solution, the content ratio (concentration) of the electrolyte is not particularly limited, but may be, for example, about 0.1 to 3.0 mol / L, preferably about 0.5 to 2.5 mol / L.
Further, the concentration of the electrolyte is about 0.1 to 70% by weight, preferably about 1 to 50% by weight, and more preferably about 10 to 30% by weight with respect to the total amount of the electrolytic solution.
At such a concentration, sufficient conductivity can be easily obtained, and salt precipitation is unlikely to occur even at low temperatures, which is suitable.

The content ratio (concentration) of hydroxyacetone in the electrolytic solution can also be selected from the same range as the above (concentration in the solvent), for example, from the range of 4000 ppm or less (for example, 3500 ppm or less) on a mass basis. It may be about 3000 ppm or less (for example, 2500 ppm or less), preferably 2000 ppm or less, more preferably 1500 ppm or less (for example, 1400 ppm or less), 1350 ppm or less, 1300 ppm or less, 1200 ppm or less, 1000 ppm or less, 800 ppm or less, 700 ppm or less, It can also be 600 ppm or less, 500 ppm or less, and the like.

The lower limit of the content ratio of hydroxyacetone in the electrolytic solution is not particularly limited, and may be 0 ppm (or the detection limit) on a mass basis with respect to the entire electrolytic solution, and may be a finite value (for example, 1 ppm, 2 ppm, 3 ppm). , 5 ppm, 7 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, etc.).

The method for adjusting the hydroxyacetone concentration in the electrolytic solution is not particularly limited, and may be adjusted by, for example, the amount of hydroxyacetone in the propylene carbonate used, or the electrolytic solution may be adjusted by adding hydroxyacetone to the electrolytic solution. You may adjust.

The electrolytic solution may contain a substance other than the electrolyte and the solvent, such as lithium salts such as LiBF ₄ and LiPF ₆ , as long as the effects of the present invention are exhibited.

[Electrochemical device]
The present invention also includes an electrochemical device equipped with (used) the above-mentioned electrolytic solution.
The electrochemical device is not particularly limited, and examples thereof include an electric double layer capacitor, a lithium ion capacitor, a lithium ion battery, a solar cell, a fuel cell, and the like, and an electric double layer capacitor, a lithium ion capacitor, and a lithium ion are preferable. Batteries and the like can be mentioned.

The electrochemical device may be any as long as it uses the solvent as the solvent or the electrolytic solution as the electrolytic solution, and the production method thereof is not particularly limited, and conventionally known methods can be used. The method for manufacturing an electrochemical device has been well established in the past, and the present invention may follow it. For example, the electrochemical device includes the methods described in Japanese Patent No. 5430464, Japanese Patent No. 5063172, Japanese Patent No. 543909, Japanese Patent Application Laid-Open No. 2012-18916, Japanese Patent Application Laid-Open No. 8-107048, Japanese Patent Application Laid-Open No. 2013-20835, and the like. Can be manufactured according to.

(Electric double layer capacitor)
When an electric double layer capacitor is manufactured as an electrochemical device, an example of the electric double layer capacitor may be a laminated type. However, the shape of the electric double layer capacitor is not limited to the laminated type, and it is a laminated type in which electrodes are laminated and stored in a can body, a wound type in which electrodes are wound and stored, or an insulating type. It may be a coin type made of a metal can electrically insulated by a gasket. Hereinafter, the structure of the laminated electric double layer capacitor will be described as an example.

1 and 2 are drawings showing a laminated electric double layer capacitor. In the capacitor, the capacitor electrode 3 and the aluminum tab 1 are adhered to each other, and the two electrodes 3 are arranged so as to face each other via the separator 4 and are housed in the laminate 2. The electrode is composed of a polar electrode portion made of a carbon material such as activated carbon and a current collector portion. The laminated container body 2 is sealed by thermocompression bonding to prevent moisture and air from entering from the outside of the container.

The polar electrode material preferably has a large specific surface area and high electrical conductivity, and needs to be electrochemically stable with respect to the electrolytic solution within the range of the applied voltage to be used. Examples of such a material include a carbon material, a metal oxide material, a conductive polymer material, and the like. Considering the cost, the polarizable electrode material is preferably a carbon material.
As the carbon material, an activated carbon material is preferable, and specific examples thereof include shavings activated carbon, sardine activated carbon, pitch coke activated carbon, phenol resin activated carbon, polyacrylonitrile activated carbon, cellulose activated carbon and the like.
Examples of the metal oxide-based material include ruthenium oxide, manganese oxide, cobalt oxide and the like. Examples of the conductive polymer material include a polyaniline membrane, a polypyrrole membrane, a polythiophene membrane, a poly (3,4-ethylenedioxythiophene) membrane and the like.

The electrode can be obtained according to a known technique. For example, the polar electrode material is kneaded with a binder such as PTFE (polytetrafluoroethylene) and pressure-molded with a conductive adhesive such as an aluminum foil. It is bound to a current collector, or the above polar electrode material is mixed with a thickener such as CMC (carboxymethyl cellulose) or an organic solvent such as pyrrolidone together with a binder to form a paste, such as an aluminum foil. It can be obtained by drying after coating on the current collector.

The separator preferably has high electronic insulation, excellent wettability of the electrolytic solution, and high ion permeability, and needs to be electrochemically stable within the applied voltage range. The material of the separator is not particularly limited, but a paper machine made of rayon, Manila hemp or the like; a polyolefin-based porous film; a polyethylene non-woven fabric; a polypropylene non-woven fabric or the like is preferably used.

(Lithium ion capacitor)
A lithium-ion capacitor as an electrochemical device is, for example, a capacitor in which an electrode facing each other across a separator and an electrolytic solution are housed in a container. Examples thereof include an electrode which is a carbon material that can be separated and contacted and which has occluded lithium in advance, and whose electrolytic solution is a non-aqueous electrolytic solution.
Two types of electrodes are used for lithium ion capacitors, and each polarizable electrode is composed of a carbon material that can occlude and desorb lithium in an ionized state, which serves as a negative electrode and one of which is polarizable. The electrode can adsorb anions to the activated carbon, which becomes the positive electrode. The positive electrode is preferably composed of activated carbon and a conductive agent that imparts electron conductivity.

Examples of the activated carbon that can be used for the positive electrode include coconut-based activated carbon and petroleum coke-based activated carbon as the carbon material constituting the electrode.
Examples of the conductive agent that imparts electron conductivity include highly conductive carbon black, acetylene black, natural graphite, artificial graphite, and the like. The amount of these conductive agents used may be 1 to 50% by weight of the activated carbon.

Carbon materials that can be stored and desorbed in the ionized state of lithium, which are the main constituent materials of the negative electrode, include natural graphite, artificial graphite, graphitized mesophase carbon globules, graphitized mesophase carbon fibers, graphite whiskers, and graphitized carbon. Examples thereof include pyrolysis products of fibers, furfuryl alcohol resin, pyrolysis products of novolak resin, and pyrolysis products of condensed polycyclic hydrocarbon compounds such as pitch and coke.

Electrodes can be obtained according to known techniques. For example, the positive electrode can be obtained by kneading the activated carbon powder, a conductive agent, a binder such as polytetrafluoroethylene in the presence of alcohol, forming a sheet, and then drying to obtain a polar electrode on the positive electrode side.
Further, among the electrodes, the negative electrode mainly composed of a carbonaceous material in which lithium is occluded in advance in a carbon material that can be occluded and desorbed in the ionized state of lithium is preferably a carbon material that can be occluded in the ionized state of lithium. Consists of a binder. This negative electrode can be formed by, for example, the following method.

A carbon material powder that can be occluded in an ionized state of lithium and a binder are kneaded in the presence of alcohol, molded into a sheet, and dried to obtain a negative electrode. Next, this negative electrode may be bonded to a current collector using a conductive adhesive or the like, the lithium foil may be sealed in a container in a state of being in contact with the negative electrode, and then heated to store lithium in a carbon material. The amount of the binder used may be 0.5 to 20% by weight.

The separator preferably has high insulating properties, excellent wettability of the electrolytic solution, and high ion permeability, and preferably electrochemically stable. The material is not particularly limited, but cellulose (paper), polyolefin-based porous film, and the like are suitable.

When the electrolytic solution of the present invention is used in the lithium ion capacitor produced as described above, a lithium salt such as LiBF ₄ or LiPF ₆ can be added to the electrolytic solution. These lithium salts are preferably added to an electrolytic solution containing the compound represented by the above formula (1) so as to have a concentration of 0.1 to 2.5 mol / L, and more preferably 0.2 to 2. It is more preferable to add it to 0 mol / L.

(Lithium-ion battery)
A lithium ion battery as an electrochemical device is a secondary battery in which the capacity of the negative electrode is represented by the capacity component of the storage and winding of lithium, which is an electrode reactant, and is a separator inside a metal or film-like exterior member. The non-aqueous electrolyte solution or the non-aqueous electrolyte is provided together with the positive electrode and the negative electrode opposed to each other, and for example, the wound electrode body to which the positive electrode lead and the negative electrode lead are attached is inside the film-shaped exterior member. Examples include those having a configuration stored in.

For the positive electrode, a positive electrode mixture is prepared by mixing a positive electrode active material, a binder, and a conductive agent, and a slurry dispersed in a solvent such as N-methyl-2-pyrrolidone is applied to a positive electrode current collector and dried. It can be produced by compression molding.
The positive electrode active material is composed of one or more positive electrode materials capable of occluding and winding lithium, which is an electrode reactant, and includes lithium composite oxides, lithium phosphorus oxides, lithium sulfides, and lithium. Examples thereof include lithium-containing compounds such as intercalating compounds.

Examples of the binder include synthetic rubbers such as styrene-butadiene rubber, fluororubber, and ethylene propylene diene rubber; and polymer materials such as polyvinylidene fluoride.
Examples of the conductive agent include carbon materials such as graphite and carbon black, and one or a mixture of two or more of these may be used.

For the negative electrode, a negative electrode mixture is prepared by mixing a negative electrode active material and a binder, and a slurry dispersed in a solvent such as N-methyl-2-pyrrolidone is applied to the negative electrode current collector and dried. , Can be manufactured by compression molding.
Examples of the negative electrode active material include a negative electrode material capable of occluding and winding lithium, which is an electrode reactant, and containing at least one of a metal element and a semi-metal element as a constituent element. Examples of such a material include lithium metal, and a material that forms an alloy with these may be used.
As the binder, the one shown in the case of the positive electrode can be used.

The produced positive electrode and negative electrode are piled up via a separator and wound to form a wound electrode body, which is housed inside the exterior member. Subsequently, after injecting the electrolytic solution into the inside of the exterior member, the opening of the exterior member is sealed to form a battery.
Examples of the separator include a porous membrane made of a synthetic resin such as polytetrafluoroethylene, polypropylene, and polyethylene, a porous membrane made of ceramic, and the like.

In the lithium ion battery produced as described above, when the electrolytic solution of the present invention is used, a lithium ion battery obtained by adding a lithium salt such as LiBF ₄ or LiPF ₆ to the electrolytic solution can be used. These lithium salts are preferably added to the electrolytic solution in an amount of 0.1 to 2.5 mol / L, more preferably 0.2 to 2.0 mol / L.

The electrochemical device of the present invention contains the solvent. That is, the electrochemical device of the present invention contains propylene carbonate as a solvent, but by setting hydroxyacetone at the predetermined concentration, an increase in resistance (particularly initial resistance) can be suppressed or reduced.

Therefore, the present invention is a method for suppressing or reducing an increase in resistance (particularly initial resistance) of an electrochemical device provided with an electrolytic solution containing propylene carbonate as a solvent, and hydroxy in the solvent and / or the electrolytic solution. It includes a method of reducing the content ratio of acetone to 3000 ppm or less on a mass basis.

In such a method, for example, the resistance (particularly the initial resistance) increases based on the resistance value (particularly the initial resistance value) when the content ratio of hydroxyacetone in the solvent and / or the electrolytic solution is 0 ppm on a mass basis. The rate is 20% or less (for example, 18% or less), preferably 15% or less (for example, 12% or less), more preferably 10% or less (for example, 8% or less), and particularly 5% or less (for example, 4%). It may be 3% or less, 2% or less, 1% or less, or the like.

As described above, the electrochemical device (or electrolytic solution) of the present invention can make it difficult for the resistance to increase, but in particular, even when a high voltage is applied, such an increase in resistance can be efficiently suppressed. Can be done.
The applied voltage of the electrochemical device [or the electrolytic solution (when using)] is, for example, 2.0 to 3.5 V, preferably 2.3 to 3.2 V, and more preferably 2.5 to 3.0 V. It may be, and in particular, it may be a high voltage (for example, 2.5 V or more, 2.7 V or more, 2.8 V or more).

The present invention will be specifically described with reference to the following Examples and Comparative Examples, but the present invention is not limited thereto.

The content ratio of hydroxyacetone was measured by gas chromatography.
The gas chromatography analysis conditions are shown below.
Column: Agilent DB-624
Introductory part: 230 ° C, split ratio 20: 1
Flow rate: He 130 kPa Constant column temperature Condition: 100 ° C. After holding for 5 minutes, raise the temperature to 230 ° C. at 10 ° C./min. Hold at 230 ° C for 22 minutes.
Detector: FID 250 ° C
H2 flow rate: 30 mL / min
Air flow rate: 400 mL / min

(Example 1)
A commercially available propylene carbonate (manufactured by Kishida Chemical Co., Ltd.) was purified as follows.
Using a lab precision distillation apparatus filled with sluzer lab packing (24 mm x 400 mm), the product was fully refluxed for 1 hour, then the initial distillate was cut at a reflux ratio of 5 to 20%, and then up to 80% was purified as the main distillate. Propylene carbonate was obtained.

When the purified propylene carbonate was analyzed, the content ratio of hydroxyacetone was 0 ppm (undetected) on a mass basis, and the content ratio of propylene glycol was 0 ppm (undetected) on a mass basis.

An electrolytic solution was prepared by dissolving N-ethyl-N-methylpyrrolidinium tetrafluoroborate in the purified propylene carbonate so as to be 1.5 mol / L.

An element (3 cm x 5 cm: 5 laminated sheets) was prepared using the following materials, vacuum dried at 150 ° C. for 15 hours, and then impregnated with the obtained electrolytic solution (electrolyte solution amount 0.097 cc / F). To prepare a laminated cell.
-Electrode: Sheet electrode manufactured by Japan Gore-Tex Co., Ltd.-Electrolytic paper: TF4050 manufactured by Nippon Kodoshi Paper Industry Co., Ltd.

The prepared cell was subjected to aging treatment for 24 hours in a state where 2.7 V was applied at room temperature, and then the initial resistance (resistance after aging and before actual use) was measured. The internal resistance was measured by the AC two-terminal method at a frequency of 1 kHz.

(Example 2)
Hydroxyacetone was added to the purified propylene carbonate obtained in Example 1 to obtain a propylene carbonate containing 67 ppm of hydroxyacetone.

Then, the initial resistance was measured in the same manner as in Example 1 except that the obtained propylene carbonate containing 67 ppm of hydroxyacetone was used.
The concentration of hydroxyacetone in the electrolytic solution is 50 ppm on a mass basis.

(Example 3)
Hydroxyacetone was added to the purified propylene carbonate obtained in Example 1 to obtain a propylene carbonate containing 133 ppm of hydroxyacetone.

Then, the initial resistance was measured in the same manner as in Example 1 except that the obtained propylene carbonate containing 133 ppm of hydroxyacetone was used.
The concentration of hydroxyacetone in the electrolytic solution is 100 ppm on a mass basis.

(Example 4)
Hydroxyacetone was added to the purified propylene carbonate obtained in Example 1 to obtain a propylene carbonate containing 267 ppm of hydroxyacetone.

Then, the initial resistance was measured in the same manner as in Example 1 except that the obtained propylene carbonate containing 267 ppm of hydroxyacetone was used.
The concentration of hydroxyacetone in the electrolytic solution was 200 ppm on a mass basis.

(Example 5)
Hydroxyacetone was added to the purified propylene carbonate obtained in Example 1 to obtain a propylene carbonate containing 667 ppm of hydroxyacetone.

Then, the initial resistance was measured in the same manner as in Example 1 except that the obtained propylene carbonate containing 667 ppm of hydroxyacetone was used.
The concentration of hydroxyacetone in the electrolytic solution was 500 ppm on a mass basis.

(Example 6)
Hydroxyacetone was added to the purified propylene carbonate obtained in Example 1 to obtain a propylene carbonate containing 1333 ppm of hydroxyacetone.

Then, the initial resistance was measured in the same manner as in Example 1 except that the obtained propylene carbonate containing 1333 ppm of hydroxyacetone was used.
The concentration of hydroxyacetone in the electrolytic solution was 1000 ppm on a mass basis.

(Reference example 1)
Hydroxyacetone was added to the purified propylene carbonate obtained in Example 1 to obtain a propylene carbonate containing 6667 ppm of hydroxyacetone.
Then, the initial resistance was measured in the same manner as in Example 1 except that the obtained propylene carbonate containing 6667 ppm of hydroxyacetone was used.
The concentration of hydroxyacetone in the electrolytic solution was 5000 ppm on a mass basis.

From the initial resistance obtained in Example 1 and the initial resistance obtained in Examples 2 to 6 or Reference Example 1, the initial resistance based on the initial resistance obtained in Example 1 based on the following formula is used as a reference. The rate of increase was calculated.

Initial resistance increase rate (%) = [(R1-R0) ÷ R0] × 100
(In the formula, R0 indicates the initial resistance value obtained in Example 1, and R1 indicates the initial resistance value obtained in Examples 2 to 6 or Reference Example 1.)

These results are summarized in the table below.

According to the present invention, it is possible to provide a novel solvent for an electrolytic solution containing propylene carbonate.

1 Aluminum tab 2 Laminate 3 Electrode 4 Separator

Claims (13)

A solvent for an electrolytic solution containing propylene carbonate, which contains a solvent having a hydroxyacetone content of 10 to 4000 ppm on a mass basis and a quaternary ammonium salt as an electrolyte. The electrolytic solution according to claim 1, wherein the content ratio of hydroxyacetone is 3000 ppm or less on a mass basis. The electrolytic solution according to claim 1 or 2, wherein the content ratio of hydroxyacetone is 2000 ppm or less on a mass basis. The electrolytic solution according to any one of claims 1 to 3, wherein the content ratio of hydroxyacetone is 20 ppm or more on a mass basis. The electrolytic solution according to any one of claims 1 to 4, wherein the content ratio of hydroxyacetone is 30 ppm or more on a mass basis. The electrolytic solution according to any one of claims 1 to 5, wherein the content ratio of hydroxyacetone is 50 to 1500 ppm on a mass basis. The electrolytic solution according to any one of claims 1 to 6, wherein the ratio of propylene carbonate to the total solvent is 20% by mass or more. Quaternary ammonium salts are derived from N-ethyl-N-methylpyrrolidinium tetrafluoroborate, spiro (1,1) -bipyrrolidinium tetrafluoroborate, triethylmethylammonium tetrafluoroborate and diethyldimethylammonium tetrafluoroborate. The electrolytic solution according to any one of claims 1 to 7, which is at least one selected. An electrochemical device comprising the electrolytic solution according to any one of claims 1 to 8. The electrochemical device according to claim 9, which is an electric double layer capacitor. A method for suppressing or reducing an increase in resistance of an electrochemical device provided with an electrolytic solution containing propylene carbonate as a solvent and a quaternary ammonium salt as an electrolyte, wherein the hydroxyacetone in the solvent and / or the electrolytic solution is used. A method for setting the content ratio to 10 to 4000 pp m on a mass basis. The method according to claim 11, wherein the resistance increase rate is set to 20% or less based on the resistance value when the content ratio of hydroxyacetone in the solvent and / or the electrolytic solution is 0 ppm on a mass basis. A solvent for an electrolytic solution containing propylene carbonate, wherein the content ratio of hydroxyacetone is 10 to 4000 ppm on a mass basis.

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