JPS61225761A - Organic electrolyte battery - Google Patents

Abstract

PURPOSE:To obtain an organic electrolyte battery having high capacity by using porous activated carbon having through pores as positive and negative electrodes and a solution containing a compound which produces as ion to be doped in electrode by electrolysis as electrolyte. CONSTITUTION:A film- or plate-form porous activated carbon, having through pores of a mean pore size of 10mum or less and a specific area measured by BET method of 600m<2>/g, produced from phenol resin is used in a positive electrode 1 and negative electrode 2, or in the positive electrode 1 and an alkali metal is used in the negative electrode 2. An electrolyte 4 is prepared by dissolving a compound such as LiI which produces an ion to be doped in the electrodes 1, 2 by electrolysis in an aprotic solvent, and an organic electrolyte battery is formed. Therefore, a secondary battery having high capacity, compact and thin size is economically obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to organic electrolyte batteries. More specifically, it relates to an organic electrolyte battery in which a porous activated carbon having micro-interconnected pores is used as a positive electrode and/or a negative electrode, and an electrolyte is a solution in which a compound capable of producing doped ions is dissolved in an aprotic organic solvent.

[Conventional technology]

In recent years, electronic devices have become smaller, thinner, and lighter.
There is a great demand for weight reduction. Currently, silver oxide batteries are widely used as small, high-performance batteries, and lithium batteries have been developed and put into practical use as thin dry batteries and small, lightweight, high-performance batteries. However, since these batteries are primary batteries, they cannot be used for long periods of time by being repeatedly charged and discharged. On the other hand, although nickel-cadmium batteries have been put into practical use as high-performance secondary batteries, they are still unsatisfactory in terms of miniaturization, thinning, and weight reduction.

Furthermore, as a high-capacity secondary battery, cylindrical lead-acid batteries have conventionally been used in various industrial fields, but the biggest drawback of this battery is that it is heavy. This is fateful since lead peroxide and lead are used as electrodes. In recent years, attempts have been made to reduce the weight and improve the performance of batteries for electric vehicles, but they have not been put to practical use. However, there is a strong demand for a large capacity and lightweight secondary battery as a storage battery.

As mentioned above, each of the batteries currently in practical use has advantages and disadvantages, and each is used differently depending on its purpose.
There is a great need for smaller, thinner, and lighter batteries. As a battery that attempts to meet these needs,
BACKGROUND ART Recently, batteries have been researched and proposed in which thin film polyacetylene, which is an organic semiconductor, is doped with an electron-donating substance or an electron-accepting substance as an electrode active material.

Although this battery has high performance as a secondary battery and has the potential to be made thinner and lighter, it has a major drawback.

The reason is that polyacetylene, which is an organic semiconductor, is an extremely unstable substance and is easily oxidized by oxygen in the air and deteriorated by heat. Therefore, battery manufacturing must be carried out in an inert gas atmosphere, and there are also restrictions on manufacturing polyacetylene into a shape suitable for one pole.

Furthermore, Japanese Patent Application Laid-Open No. 58-35881 discloses that at least one electrode has 1. Electrochemical cells using carbon fibers having a specific surface area of OOO to 10,000 m/I have been proposed. According to the detailed description in the publication, the carbon fibers have a diameter of 10 to 20 μm, and the electrodes are formed from such carbon fibers in the form of a sheet, for example.

[Problem that the invention seeks to solve]

An object of the present invention is to provide an organic electrolyte battery.

Another object of the present invention is to provide a high-capacity organic electrolyte battery using porous activated carbon as an electrode, which has a large electrode surface area in contact with an electrolyte solution.

Still another object of the present invention is to provide an organic electrolyte battery that is an economical secondary battery that can be made smaller, thinner, lighter, and easier to manufacture.

Still another object of the present invention is to provide a secondary battery with a high electromotive voltage and excellent charge efficiency over a long period of time.

Further objects and advantages of the present invention will become apparent from the description below.

[Means and effects for solving the problems] According to the present invention, such objects and advantages of the present invention are as follows: (A) A BET method having continuous pores with an average pore diameter of 10 μm or less and at least 600 vL'/I. (7?) Porous activated carbon having a specific surface area value of This is achieved by an organic electrolyte battery characterized by the following.

The porous activated carbon used as an electrode in the present invention can be manufactured from a phenol resin, for example, in the following manner.

An initial condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group or an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aromatic hydrocarbon compound having no phenolic hydroxyl group and aldehydes is prepared, and this initial condensate and Prepare an aqueous solution containing an inorganic salt, pour this aqueous solution into a suitable mold, and then heat the aqueous solution while suppressing the evaporation of water to shape it into a shape such as a plate, a film, or a cylinder in the mold. After curing and conversion, the obtained cured product is fired in a non-oxidizing atmosphere, and then the obtained fired product is washed to remove inorganic salts contained in the fired product, and if necessary, dried. do.

In the present invention, the phenolic resin is a condensate of an aromatic hydrocarbon compound having a phenolic acid group and an aldehyde. As such aromatic hydrocarbon compounds, so-called phenols such as phenol, cresol, and xylenol are suitable, but are not limited thereto. For example, in the following formula, X and y are each independently 0.1 or ll1
It can be methylene bis phenols represented by 2, or it can also be hydrocarbon biphenyls or hydroxynaphthalenes.

Among these, phenols, particularly phenol, are practically preferred.

The phenolic resin in the present invention further includes a modified aromatic polymer in which a part of the aromatic hydrocarbon compound having a phenolic hydroxyl group is replaced with an aromatic hydrocarbon compound not having a phenolic hydroxyl group, such as xylene, toluene, etc., such as phenol. A modified aromatic polymer which is a condensation product of xylene and formaldehyde can also be used.

Further, as the aldehyde, not only formaldehyde but also other aldehydes such as acetaldehyde and furfural can be used, but formaldehyde is preferred. The phenol-formaldehyde condensate may be a novolac type, a resol type, or a composite thereof.

The above-mentioned inorganic salts used together with the initial mesh are pore-forming agents that are removed in a later step and used to provide communicating pores to the activated carbon, such as zinc chloride, tin chloride, sodium chloride,
These include sodium phosphate, thorium hydroxide, and thorium sulfide. Among these, zinc chloride is particularly preferably used. The inorganic salt can be used in an amount of, for example, 2.5 to 10 times the weight of the initial mesh. If the amount is less than the lower limit, it is difficult to obtain porous activated carbon having communicating pores, and if the amount is more than the upper limit, the mechanical strength of the porous activated carbon tends to decrease, which is not desirable. The aqueous solution of the initial wire mesh and the inorganic salt may be prepared using, for example, water in an amount of 0.1 to 1 times the weight of the inorganic salt, although it varies depending on the type of inorganic salt used.

The initial mesh of phenolic resin and the aqueous μ solution of inorganic salt are
For example, by adding a zinc chloride aqueous solution to a water-soluble resol and then stirring, a homogeneous solution can be prepared, or by mixing a methanol solution of the resol and a zinc chloride aqueous solution, a highly viscous slurry can be prepared. It can also be prepared. At this time, other additives such as hardened phenol resin powder or fibers, cellulose fine particles, etc. may be mixed into the aqueous solution. Further, as mentioned above, an organic solvent such as methanol, ethanol, or acetone may be added for uniform mixing. Thus, for example 10
An aqueous solution having a viscosity of 0,000 to 100 poise is poured into a suitable mold and heated to a temperature of, for example, 50 to 200°C. During this heating, it is important to suppress evaporation of water in the aqueous solution. That is, it is thought that the initial mesh is heated in an aqueous solution, gradually hardens, and grows into a six-dimensional network structure while separating from inorganic salt water such as zinc chloride.

By firing the obtained cured body in a non-oxidizing atmosphere, the cured body can be converted into carbon. Firing is usually carried out until a temperature of 800° C. or higher is reached. The preferred rate of temperature increase during firing varies somewhat depending on the phenolic resin used or its shape, but generally it is possible to set a relatively high rate of temperature increase from room temperature to a temperature of about 300°C, for example, 100°C. A rate of °C/hour is also possible. When the temperature reaches 300℃ or more,
Thermal decomposition of the resin begins and gases such as water vapor (H* 0 ), hydrogen, methane, and carbon oxide begin to be generated.
After reaching 300°C, it is advantageous to raise the temperature at a sufficiently slow rate. Examples of the non-oxidizing atmosphere include nitrogen, argon, helium, neon, carbon dioxide, etc., with nitrogen being preferably used. Such a non-oxidizing atmosphere may be stationary or flowing.

Inorganic salts contained in the fired body can be removed by thoroughly washing the fired body with water, dilute hydrochloric acid, or the like. After removing the inorganic salt, if necessary, drying is performed to obtain porous activated carbon with developed communicating pores.

The porous activated carbon thus obtained has excellent mechanical strength and chemical resistance, and can be formed into any shape such as a film, a plate, or a cylinder, making it suitable as an electrode material.

The porous activated carbon used in the present invention has a three-dimensional network structure of carbon parts or communicating pores, so that it has communicating pores that allow fluid to easily enter and exit fine parts. The average pore size is 10 μm or less, which is fine, and it is a sharp porous material with uniform pore size, that is, a pore size distribution. For example, in the above manufacturing method, by selecting the composition of the uncured phenolic resin aqueous solution containing metal chloride or the thermosetting conditions, the average pore size can be made from extremely fine porous materials with an average pore size of 0.03 to 0.1 μm. Since it is possible to obtain a porous body with a pore diameter of about 10 μm, it is possible to use it depending on the specifications of the battery.

Further, the porous activated carbon of the present invention has a specific surface area value of at least 600 m/g by the BET method. Specific surface area is 600rr
? When a battery is constructed using porous activated carbon with a porous activated carbon of less than /11 as an electrode, it is not preferable because, for example, it is necessary to increase the charging voltage during charging, resulting in a decrease in energy efficiency, etc., and also causing deterioration of the electrolyte.

The apparent density (bulk density) of the porous activated carbon used in the present invention is usually 0.2 to Q, 6.9/i. In other words,
The porous activated carbon used in the present invention includes porous bodies with relatively high porosity to porous bodies with relatively low porosity. The mechanical strength of porous materials varies depending on the density, but
For example, even a porous material having a diameter of 0.211/- has a strength necessary for practical use.

As described above, the organic electrolyte battery of the present invention uses the above-mentioned porous activated carbon as a positive electrode and/or negative electrode, and contains a solution in which a compound capable of producing ions that can be doped into the electrode by electrolysis is dissolved in an aprotic organic solvent. This is an organic secondary battery that uses an electrolyte.

↓ Compounds that can generate ions to be doped into the electrode include, for example, alkali metal or tetraargylammonium halide perchlorates, hexafluorophosphates,
Examples include hexafluoroarsenate, tetrafluoroborate, and the like.

Specifically, Lil.

MalSNB41. LiCIO4, LiAsF6, Li
BF, , KPF6, HapF6, (n-C4H,)
4NCIO,, (C4H9), NCI O4, (Cg
Hs)4N B'4, (n-C,B,) 4NBF4,
(n-C4H9)4NAsF6, (n-C4H9)4
Examples include NpF. or Li HF.

An aprotic organic solvent is used as the solvent for dissolving the compound. For example, ethylene carbonate, propylene carbonate, r-butyrolactone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, dimethoxyethane, tetrahydroctane, methylene chloride or sulfolane or mixtures thereof are selected.

The degree of immersion of the compound in the electrolytic solution is set to at least 1 mole of CL/1 or more in order to reduce the internal resistance due to the electrolytic solution. It is preferable to use electrochemical doping of a doping agent to 0.2 to 1.5 mole carbon and electrochemical and-doping.

That is, energy can be stored by electrochemical doping of the porous activated carbon with a doping agent, or can be extracted externally as electrical energy by electrochemical doping, which is released to the outside, or can be extracted internally. is stored in

Batteries according to the invention are divided into two types.

The first type is a battery that uses porous activated carbon for both the positive and negative electrodes, and the second type is an electrode that uses porous activated carbon for the positive electrode and an alkali metal or alkaline earth metal for the negative electrode. Examples of alkali metals and alkaline earth metals include cesium, rubidium, potassium, sodium, lithium, barium, strontium, and calcium. Of these, lithium is most preferred. These metals can be used alone or as an alloy.

The shape of the electrode made of porous activated carbon placed inside the battery,
The size can be chosen arbitrarily depending on the type of battery desired, but since the battery reaction is an electrochemical reaction on the surface of the electrode, it is advantageous to make the surface area of the electrode as large as possible. be. In addition, porous activated carbon or porous activated carbon doped with a doping agent can be used as a current collector for extracting current from the substrate to the outside of the stain pond. Conductive materials such as carbon, platinum, nickel, stainless steel, etc. can also be used.

Next, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 is a basic configuration diagram of a battery according to the present invention.

First, a first type of battery according to the present invention, that is, a battery using porous activated carbon for both the positive and negative electrodes will be described. In Figure 1, 1 is the positive electrode, which is porous activated carbon in the form of a film or plate, and 2 is the negative electrode, which is porous activated carbon which is also in the form of a film or plate. be. These may or may not be doped with a doping agent. After assembling the battery, a doping agent is doped by applying stain pressure from an external power source. For example, when undoped porous activated carbon is used for both electrodes, the electromotive force of the battery after assembly is Ov, and stain pressure is applied from an external power source to dope the doping agent to both electrodes. As a result, the battery has an electromotive force. Reference numerals 3 and 3' denote current collectors for supplying current for electrochemical doping, that is, charging, from which current is taken out from each electrode to the outside, and each electrode and external terminal 7.7 are ’ is connected so as not to cause a voltage drop. Reference numeral 4 denotes an electrolytic solution in which the aforementioned metal compound capable of producing ions that can be doped into both positive and negative electrodes is dissolved in an aprotic organic solvent. The electrolyte is usually in liquid form, but it can also be used in gel or solid form to prevent leakage. A separator 5 is arranged for the purpose of preventing contact between the positive and negative electrodes and retaining the electrolyte. The ceno-arm plate is a porous material with no electronic conductivity and has continuous pores that enhances its durability against electrolytes, doping agents, and electrode active materials such as alkali metals, and is usually made of glass fiber, polyethylene, polynolopyrene, etc. Cloth, nonwoven fabric, or porous material is used. The thickness of the separator is preferably thin in order to reduce the internal resistance of the battery, but it is determined by taking into consideration the amount of electrolyte retained, flowability, strength, etc. . The positive and negative electrodes and the separator are fixed in the battery case 6 so as not to cause any practical problems.

The shape, size, etc. of the electrode are determined as appropriate depending on the shape and performance of the intended battery. For example, to manufacture thin batteries,
Film-shaped electrodes are suitable, and large-capacity batteries can be produced by laminating a large number of film-shaped or plate-shaped electrodes, with both positive and negative electrodes alternately stacked.

Next, a second type of battery according to the present invention, that is, a case where porous activated carbon is used for the positive electrode and an alkali metal or alkaline earth metal is used for the negative electrode, will be described. To explain with reference to FIG. 1, this second type of battery differs from the first type only in that the negative electrode 2 is made of an alkali metal or alkaline earth metal. 7 has the same meaning for the first type of battery.

For this second type of battery, the doping mechanism, ie the operating mechanism of the battery, can be further divided into two mechanisms. In the first mechanism, porous activated carbon is doped with an electron-accepting doping agent, which corresponds to charging, and undoping corresponds to discharging. For example, as an electrode,
Doped porous activated carbon and lithium as electrolyte
When porous activated carbon is doped with CtO,- ions by applying stain pressure to the iC10° power supply, the electromotive force is 55%.
〜4.5■. In the second mechanism, doping porous activated carbon with an electron-donating doping agent corresponds to discharging, and undoping corresponds to charging.

For example, in the battery configuration described above, the electromotive voltage after battery assembly is approximately 3V, and if porous activated carbon is doped with lithium ions by discharging a current to the outside, the electromotive force #: t 1.0 to 2.5Y However, when the stain pressure is applied by an external power source and the lithium ions are and-pumped, the electromotive force becomes approximately 3y again.

Doping or undoping may be carried out under a constant current, a constant voltage, or under conditions where the current and voltage are varied, but the amount of doping agent doped into the porous activated carbon is determined by the amount of doping agent per carbon atom of the activated carbon. The percentage of the number of ions to be doped with respect to the total number of ions is preferably 05 to 10%.

The battery of the present invention using porous activated carbon as an electrode is a secondary battery that can be repeatedly charged and discharged, and its electromotive voltage varies depending on the configuration of the battery, but the first type has a voltage of 1 to 3 V, and the second type has a voltage of 1 to 3 V. When the first type is used, the voltage is 3.5 to 4.5V, and when the second type is used, the voltage is about 3V. In addition, the battery of the present invention has a particularly high energy density per weight, and if an appropriate amount of doping is performed, the energy density will be approximately 300F based on the weight of porous activated carbon.
It has a value of H7k&. Regarding power density, although there are differences depending on the structure of the battery, it has a much higher power density than a lead-acid battery. Furthermore, when the porous activated carbon of the present invention is used as an electrode, it is possible to produce a secondary battery that has a low internal resistance, can be repeatedly charged and discharged, and does not exhibit deterioration in battery performance over a long period of time.

The secondary battery of the present invention uses porous activated carbon with a fine structure compared to conventional secondary batteries using activated carbon fibers, so it is easier for electrolyte to penetrate, and doping at the interface is prevented. Because it is carried out smoothly, it is a high-performance secondary battery with high capacity and high output. It is also a secondary battery that can be made smaller, thinner, and lighter, and its performance will not deteriorate over a long period of time.

Hereinafter, the present invention will be specifically explained with reference to Examples.

In addition, in this specification, the average pore diameter of the communicating pores is measured and defined as follows.

An electron micrograph is taken of the sample at a magnification of, for example, 1,000 to 10,000 times. If an arbitrary straight line is drawn on this photograph and the number of holes that intersect with the straight line is n, then the average pore diameter (
The force is calculated using the following formula.

Σ1t i=1 d= − Here, li is the sum of the lengths of the straight lines cut by the intersecting holes, and the outside is the number of holes that intersect the straight lines, provided that n is 10 The value shall be greater than or equal to the value.

Example 1 An aqueous solution containing water-soluble resol (approximately 60% concentration)/zinc chloride/water mixed in a weight ratio of 10/25/4 was formed into a film on a glass plate using a film applicator. Next, a glass plate was placed over the formed aqueous solution to prevent moisture from evaporating, and then heated at a temperature of about 100° C. for 1 hour to cure it.

The phenolic resin composite was heated in a silicone electric furnace at 90°C.
It was fired to 0°C. Next, the heat-treated film was washed with dilute hydrochloric acid, then water, and dried.

The film thus obtained has a thickness of approximately 200 μm.
The apparent density was approximately 0.3 Ji'/CrI. It also had excellent mechanical strength, which was hard to believe for activated carbon, and even had some flexibility. Next, the specific surface area value was measured using the BET method and was found to be 1800 m/Ji'
This was an extremely high value.

Next, an electron microscope photograph of a cross section of the film was taken in order to observe the pore state of the film-like activated carbon.

Shown in Figure 2. As is clear from the figure, it had a three-dimensional network structure with fine communicating holes of less than 10 μm, and the thickness of the pillars was extremely thin, less than 10 μm.

Next, LiBF is added to sufficiently dehydrated glopylene carbonate.
A battery was assembled as shown in FIG. 1, using a 1.0 mol/l solution of , as an electrolyte, lithium metal as a negative electrode, and the porous activated carbon film described above as a positive electrode. A stainless steel mesh was used as the current collector, and felt made of glass fiber was used as the separator. This example is a battery that utilizes the second type of first mechanism of the present invention.

That is, doping porous activated carbon with BF4- ions, which are electron-accepting doping agents, corresponds to charging, and carrying out AND-2 corresponds to discharging.

Further, the doping amount is expressed by the number of doped ions per carbon atom in the activated carbon, but in the present invention, the number of doped ions is determined from the value of the current flowing through the circuit.

The voltage immediately after assembling the battery was 3.0 ■.

Next, a voltage was applied externally to the battery, and the porous activated carbon was doped with BF, ``'' ions at a constant current for 3.5 hours so that the doping amount per hour was 1%. The open circuit voltage was 4.4 V.Next, a constant current was applied to the circuit so that the amount of and-ping per hour was 1%, and the and-ping of BF4'' ions was carried out, and the open circuit voltage was 50 V. The continuation continues until V. The value of the and-doping amount for the doping amount in this test is 80
%Met.

Example 2 This example relates to the first type of battery according to the present invention, that is, a secondary battery using molded bodies made of porous activated carbon for the positive and negative electrodes.

The porous activated carbon film obtained in Example 1 was used as a positive electrode and a negative electrode, and (CvHs)4NCtO, 1 was used as an electrolyte.
A battery was constructed using a mol/737' propylene carbonate solution and subjected to charge/discharge tests.

The voltage immediately after the battery was assembled was Ov. Next, a voltage was applied from an external power supply to charge the battery by doping the positive electrode with CtO, - ions and the negative electrode with (CvHs)+N+ ions. The charging speed is 1 doping amount per hour.
% for 3 hours. The open circuit voltage at this time is 3. It was OV.

Next, CtO4- ions and (('!
H5) It was a bumpy straight line that performs and-pumping of 4A'+ ions, and the battery had characteristics similar to a capacitor.

Considering this battery as a capacitor, its capacitance was calculated to be 25 F/i per electrode weight. (F
: Farad) Comparative Example 1 A plain woven fabric of Kynol fiber (woven fabric of phenolic resin fiber manufactured by Nippon Kynol Co., Ltd.) was fired in a silicone electric furnace to 900°C in a non-oxidizing atmosphere, carbonized, and then heated in an electric furnace at the same temperature. Steam was blown into the container and activated for about 1 hour. The specific surface area value of the obtained activated carbon fabric by the EET method was 1600 m''/I. The fiber diameter was about 15 μm, and the mechanical strength of the fabric was almost the same.

Next, a battery was assembled with the same configuration as in Example 2 using the activated carbon fabric as a positive electrode and a negative electrode, and a charge/discharge test was conducted under the same conditions. Considering the battery as a capacitor, the capacitance was calculated to be 16 F/I per electrode weight.

[Brief explanation of drawings]

FIG. 1 shows the basic configuration of a battery according to the present invention. 1 is a positive electrode, 2 is a negative electrode, 3 is a current collector, 4 is an electrolytic solution, 5 is a celltor, 6 is a battery case, and 7 is an external terminal. FIG. 2 is an electron micrograph of a cross section of the porous activated carbon film of the present invention. In the photograph, the length of the bar shown at the bottom right is 5 μm.

Claims (1)

[Claims] 1. (A) A porous activated carbon having continuous pores with an average pore diameter of 10 μm or less and exhibiting a specific surface area value by the BET method of at least 600 m^2/g is used as a positive electrode or a negative electrode, (B ) An organic electrolyte battery characterized in that the electrolyte is a solution in which a compound capable of producing ions that can be doped into the electrode by electrolysis is dissolved in an aprotic organic solvent. 2. The average pore diameter of the continuous pores of the porous activated carbon is 0.2~
The organic electrolyte battery according to claim 1, which has a thickness of 10 μm. 3. The organic electrolyte battery according to claim 1, wherein the communicating pores of the porous activated carbon exist in a three-dimensional network. 4. The bulk density of the porous activated carbon is 0.2 to 0.6 g/c
The organic electrolyte battery according to claim 1, wherein m^2. 5. The organic electrolyte battery according to claim 1, wherein the porous activated carbon is in the form of a film or a plate. 6. The organic electrolyte battery according to claim 1, wherein the porous activated carbon is the positive electrode, and the alkali metal or alkaline earth metal is the negative electrode. 7. The organic electrolyte battery according to claim 1, wherein the negative electrode is an alkali metal, and the alkali metal is lithium or a lithium alloy. 8. The organic electrolyte battery according to claim 1, wherein porous activated carbon constitutes a positive electrode and a negative electrode. 9. A compound that can generate ions that can be doped is L
iI, NaI, NH_4I, LiUO_4, LiAsF
_6, LiBF_4, KPF_6, NaPF_6(C_
2H_5)_4NClO_4, (n-C_4H_9)_
4, NClO(C_2H_5)_4NBF_4, (n-
C_4H_9)_4NBF_4, (n-C_4H_9)
_4NAsF_6, (n-C_4H_9)_4PF_6
or LiHF_2, the organic electrolyte battery according to claim 1. 10, the aprotic organic solvent is ethylene carbonate,
The organic electrolyte battery according to claim 1, which is propylene carbonate, r-butyrolactone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, dimethoxyethane, tetrahydrofuran, methylene chloride, or sulfolane.