JP2574730B2 - Organic electrolyte battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an organic electrolyte battery, and more particularly, to a negative electrode comprising an insoluble and infusible substrate having a polyacene skeleton structure and a thermosetting resin. The present invention relates to an organic electrolyte battery using a molded article to be formed or a heat-treated product of the molded article carrying lithium.

(Prior Art) In recent years, batteries using a conductive polymer, a transition metal oxide or activated carbon as a positive electrode have been proposed. When lithium is used as the negative electrode of these batteries, it has a high voltage,
A secondary battery for an energy source having a large capacity and a high energy density can be obtained. However, when a battery using lithium for such a negative electrode is put into practical use, there is a problem that a charge / discharge cycle command is reduced due to generation of dendrite. Dendrite is a dendritic or moss-like lithium crystal generated on the surface of a lithium negative electrode during charging. The dendrite grows with the repetition of charge and discharge, and eventually the two electrodes are short-circuited, resulting in a long cycle life. Therefore, it is important to suppress the generation of the dentite when the battery is put to practical use.

In recent years, research on lithium batteries in which lithium is supported on a carbon material such as graphite and a conductive polymer such as polyacetylene and polyparaphenylene has been advanced. However, although the generation of dendrites is extremely small, there is a problem that a change in the structure is large with respect to lithium in / out, and the cycle characteristics are deteriorated.

In general, a battery electrode is obtained by kneading an active material in the form of a powder or the like with a thermoplastic resin binder such as a polytetrafluoroethylene binder, polyethylene, or polypropylene, and press-molding, thereby improving productivity and dimensional stability. From the viewpoint of, it is preferably used.

However, when lithium is supported on a molded product obtained by molding an insoluble and infusible substrate containing a polyacene-based skeleton structure such as a powder, the electrode is remarkably loosened, and the battery characteristics, particularly rapid discharge characteristics and cycle characteristics, are deteriorated. The problem remained.

(Problems to be Solved by the Invention) The present inventors have made intensive studies in view of the above problems and completed the present invention. An object of the present invention is to provide a secondary battery that can be charged and discharged for a long time.

Another object of the present invention is to provide a secondary battery having good rapid discharge characteristics.

Still another object of the present invention is to provide a secondary battery which is easy to manufacture.

(Means for Solving the Problems) An object of the present invention is to provide an organic electrolyte battery including a positive electrode, a negative electrode, and an electrolytic solution containing a solution in which a lithium salt is dissolved in an aprotic organic solvent. , A heat-treated product of an aromatic condensation polymer comprising hydrogen and oxygen, wherein the aromatic condensation polymer is (a) a condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde, and (b) a phenolic hydroxyl group. An aromatic hydrocarbon compound having no phenolic hydroxyl group, an aldehyde condensate, and (c) a furan resin, and the heat-treated product has an atomic ratio of hydrogen atom / carbon atom of 0.50. Lithium is added to a molded product containing a thermosetting resin or an insoluble infusible substrate containing a polyacene-based skeleton structure of It is achieved by an organic electrolyte battery characterized by using those obtained by supporting at least 3% Le percentage.

The insoluble and infusible substrate containing a polyacene-based skeleton structure (hereinafter referred to as PAS) according to the present invention is obtained by using an aromatic condensation polymer described in Japanese Patent Application Laid-Open No. 59-3806 filed by the applicant of the present application. It is obtained by heat treatment under specific conditions.

PAS with specific surface area by BET method of 600m ² / g or more
Can be obtained by the method described in JP-A-60-170163 filed by the applicant of the present application.

Specifically, when a high specific surface area is not required, the aromatic condensation polymer used in the present invention includes (a) an aromatic hydrocarbon compound having a phenolic hydroxyl group, such as a phenol-formaldehyde resin, and an aldehyde. Condensate, (b) xylene-modified phenol, formaldehyde resin (phenol partially substituted with xylene)
Examples of suitable compounds include aromatic hydrocarbon compounds having a phenolic hydroxyl group, aromatic hydrocarbon compounds having no phenolic hydroxyl group, condensates of aldehydes, and (c) furan resins.

The aromatic condensation polymer is placed in a non-oxidizing atmosphere (including a vacuum state) at a temperature of 400 ° C. to 1000 ° C., preferably 600 ° C.
PAS can be obtained by gradually heating to a suitable temperature of 800C to 800C to obtain a heat-treated product having an atomic ratio of hydrogen atoms / carbon atoms (hereinafter referred to as H / C) of 0.50 to 0.05, preferably 0.35 to 0.10. 6
In the case of PAS having a specific surface area of at least 00 m ² / g by the BET method,
An inorganic salt such as zinc chloride or sodium phosphate is mixed with the aromatic condensation polymer. The amount to be mixed varies depending on the type of the inorganic salt and the shape and performance of the target electrode, but is preferably 10/1 to 1/7 by weight.

The mixture of the inorganic salt and the aromatic condensation polymer thus obtained varies depending on the composition of the polymer, the kind of the inorganic salt, etc., but is usually at a temperature of 50 to 180 ° C., and is cured by heating for 2 to 90 minutes, thus. The obtained cured product is then heated in a non-oxidizing atmosphere at a temperature of 350 to 800 ° C., preferably 400 ° C.
The resulting heat-treated body is sufficiently washed with water or diluted hydrochloric acid to remove the inorganic salts contained in the heat-treated body. Thereafter, when this is dried, 600 m ^{2 of} H / C = 0.50-0.05, preferably 0.35-0.10 is obtained.
PAS having a specific surface area of at least / g is obtained.

In the PAS used in the present invention, the position of the main peak in X-ray diffraction (CuKα ray) is generated at 24 ° or less at 2θ and at 2θ.
Those showing a broad peak between 41 ° and 46 ° C. are preferred.

In the present invention, PAS is an absorbance ratio (D) represented by the following equation, which is determined from an infrared absorption spectrum: D = D _2900-2940 / D _{1560-1640 In the} equation, D _2900-2940 is 29 in the infrared absorption spectrum.
Absorbance determined from the maximum absorption peak in the range of 00 to 2940 Kaiser, D _{1560 to 1640} in the infrared absorption spectrum
The absorbance determined from the maximum absorption peak in the range of 1560 to 1640 Kaiser is preferably 0.5 or less, particularly preferably 0.3 or less. (Note that the method of calculating the absorbance ratio (D) is described in detail in JP-A-59-3806.
This is described in Japanese Patent Application Publication No. PAS suggests that the aromatic polycyclic structure is moderately developed and that the average distance of the planar polyacene skeleton structure is relatively large, so that PAS can stably support lithium.

When the average distance is small, that is, as the graphite crystal approaches the graphite crystal, the structure of the base is easily changed when lithium is supported or when lithium is taken in and out (during charging and discharging), and the cycle characteristics deteriorate.

Further, when the aromatic polycyclic structure is not developed, lithium cannot be stably supported, and a battery manufactured using such a negative electrode in which lithium is supported on PAS has a large self-discharge.

The PAS in the present invention is manufactured in the form of powder, short fiber or the like or manufactured in an appropriate shape so as to be easily molded, and is used in the form of powder or short fiber.

In the present invention, a molded article containing at least PAS carrying lithium and a thermosetting resin can be roughly divided into the following two methods.

The first method is to knead PAS in the form of powder, short fiber, etc. that is easy to mix with an initial condensate of a thermosetting resin, if necessary, by adding a solvent such as methanol, toluene, or water, and then kneading at 50 ° C.
The second method is to use the PAS in the above-mentioned form generally for battery electrodes such as polytetrafluoroethylene, polyethylene, and polypropylene. This method involves mixing with a binder or kneading and molding as necessary, followed by impregnating the molded body with a solution of an initial condensate of a thermosetting resin, followed by drying and curing by heating or the like.

Examples of the thermosetting resin in the present invention include resins capable of firmly adhering PAS powder or the like and suppressing loosening of the electrode, such as phenol resin, melamine resin, and furan resin. The molded body thus obtained can be optionally used after heat treatment in an inert atmosphere (including vacuum).

For example, when a phenolic resin is used as a thermosetting resin, a large amount of hydroxyl groups, carbonyl groups, and the like that easily react with lithium are present, and extra lithium is required when lithium is supported. It is advantageous to keep the groups reduced. Heating temperature is 15
The temperature is 0 ° C. or higher, preferably 250 ° C. to 500 ° C., and as the temperature increases, the electrode strength decreases, and it becomes difficult to obtain the original effects of the present invention.

The proportion of the thermosetting resin in the above molded product depends on the PAS shape, PAS
Is determined by the specific surface area, the amount of other kinds of binders, the amount of lithium to be supported, and the like. Preferably, the proportion in the electrode is 1% or more and 70% or less, more preferably 5% by weight.
Not less than 50%. If it is less than 1%, the effect of suppressing the loosening of the electrode is small, and if it is more than 70%, the amount of PAS is naturally reduced, so that sufficient lithium cannot be carried and the battery capacity is reduced.

The negative electrode applied to the organic electrolyte of the present invention is obtained by supporting lithium on a molded article containing PAS and a thermosetting resin obtained by the above-described method or a heat-treated product of the molded article.

The method for supporting lithium may be appropriately selected from known methods such as an electrolytic method, a gas phase method, a liquid phase method, and an ion implantation method. For example, when lithium is supported by the electrolytic method, the PAS molded body is immersed as a working electrode in an electrolytic solution containing lithium ions, and a current is applied or a voltage is applied between the counter electrode in the same electrolytic solution. I do.

Further, it can also be supported by a method in which an appropriate amount of lithium foil is brought into direct contact with the above-mentioned molded body.

When using the gas phase method, for example, to the vapor of lithium,
Expose the PAS compact. When the liquid phase method is used, for example, a complex containing lithium ions is reacted with an insoluble and infusible substrate. Examples of the complex used in this reaction include, but are not limited to, an alkali metal naphthalene complex and an alkoxide.

The amount of thylium supported on the PAS by the above method is 3% or more, preferably 10% or more, expressed as a molar percentage (percentage of the number of lithium to one carbon atom of the PAS). The amount of lithium depends on the specific surface area of the PAS, and the potential of the PAS compact supporting lithium is Li / Li ⁺
It is desirable to carry lithium so that the voltage becomes 1.0 to 0 V with respect to that of lithium. When the amount of lithium is small, the capacity of the battery of the present invention decreases, and when the amount is large, excess lithium is undesirably deposited on the surface of the PAS molded body.

When lithium is supported on a PAS compact obtained by molding the above PAS powder or the like by a conventionally known method, the electrode has a large slack, and the battery has a larger slack than when a plate or film PAS is used as the lithium carrier. The internal resistance increased, rapid discharge became difficult, and sufficient cycle characteristics could not be obtained.

In particular, when a PAS having a high comparative example surface area is used, the amount of lithium to be supported is increased, so that the electrode is easily loosened in the conventional method, and the effect of the present invention is clearly exhibited. Ie 60
It has been confirmed that PAS having a specific surface area of 0 m ² / g or more by the BET method can reduce the internal resistance of the battery because the diffusion rate of Li in the substrate is fast, but there is a problem in the molding method and it can not be used practically However, by using the method of the present invention, a high-performance battery can be obtained.

Furthermore, since a thermosetting resin is used as a main binder in the present invention, water which is a main cause of deterioration of a lithium-based battery can be removed in a short time at a high temperature of, for example, 300 ° C. or more. is there.

An aprotic organic solvent is used as a solvent constituting the electrolytic solution used in the present invention. Examples of the aprotic organic solvent include, for example, ethylene carbonate, propylene carbonate, γ-butyrolactone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolan, methylene chloride, sulfolane, or a mixture of these aprotic organic solvents. Any of a mixture of more than one species may be used.

The electrolyte to be mixed or dissolved in a single solvent may be any electrolyte that can generate lithium ions. Such electrolytes include, for example, LiI, LiClO ₄ , LiAs
F ₆ , LiBF ₄ or LiHF ₂ .

The electrolyte and the solvent are mixed in a sufficiently dehydrated state to form an electrolyte. The concentration of the electrolyte in the electrolyte should be at least 0.1 mol / or more to reduce the internal resistance due to the electrolyte. Is desirable, usually 0.2-1.
More preferably, it is 5 mol /.

As the positive electrode of the organic electrolyte battery of the present invention, for example, a conductive polymer, a metal oxide, a metal sulfide, activated carbon, or the like, which can be electrochemically doped and undoped, which will be described later, can be used.

Examples of conductive polymers that can be electrochemically doped and undoped include polyacetylene, polythiophene, polyaniline, and polyacene-based organic semiconductors that are heat-treated aromatic condensation polymers. When used as an electrode material, stability and moldability are extremely important in practical use, and from this viewpoint, a polymer of a polyacene-based organic semiconductor and an aniline is particularly preferable.

Metal oxides which can be preferably used as the positive electrode include lithium ions which can be reversibly brought in and out by intercalation or deintercalation (referred to as doping or undoping in the present invention), for example, vanadium, chromium, manganese, molybdenum. And oxides of transition metals such as bismuth.

For example _{V 2 O 5, V 6 O} 15, Cr 3 O 8, MnO 2, using _{MoO 3, Cu 2 V 2 O} 7 one or more of the like. The structure of these transition metal oxides may be in a crystalline state or in an amorphous state by heat treatment or the like.

Examples of metal sulfides that can be preferably used as the positive electrode include TiS ₂ , MoS ₂ , and MoS ₃ . The structure of these metal sulfides may be in a crystalline state or an amorphous state.

The most preferred of the positive electrodes is a polyacene-based organic semiconductor (Japanese Patent Application Laid-Open No. 60-170163). The semiconductor is particularly excellent in stability, and it is possible to produce a high-voltage battery having a voltage of 4.0 V by using the semiconductor as a positive electrode. This makes it possible to produce a battery with excellent performance.

As a current collector for extracting a current to the outside of the battery, a conductive material having corrosion resistance to a doping material and an electrolytic solution, for example, carbon, near white, nickel, stainless steel, or the like can be used.

Next, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a basic configuration diagram of a battery according to the present invention. In FIG. 1, (1) is a positive electrode, and (2) is a negative electrode.
(3) and (3 ') are current collectors, which are connected to each electrode and the external terminals (7) and (7') so as not to cause a voltage drop. (4) is an electrolytic solution in which the above-mentioned compound capable of generating ions that can be doped is dissolved in an aprotic organic solvent. The electrolyte is usually liquid, but may be used in a gel or solid state to prevent liquid leakage. (5) is a separator arranged for the purpose of preventing contact between the positive and negative electrodes and holding the electrolytic solution.

The separator is a non-electron-conductive porous body having continuous pores that are durable with respect to an electrolyte or an electrode material, and the electrolyte or an electrode active material such as a doping agent or an alkali metal. A cloth, nonwoven cloth or porous body made of glass fiber, polyethylene or polypropylene is used. The thickness of the separator is preferably thinner to reduce the internal resistance of the battery, but the amount of retained electrolyte,
Determined in consideration of distribution, strength, and the like. The positive and negative electrodes and the separator are fixed in the battery case (6) so that there is no practical problem. The shape, size, and the like of the electrode are appropriately determined depending on the shape and performance of the intended battery.

(Effect of the Invention) The organic electrolyte battery of the present invention uses, as a negative electrode, a material obtained by bonding an insoluble and infusible substrate containing a polyacene-based skeleton structure supporting lithium with a thermosetting resin.
It is a secondary battery with excellent rapid discharge characteristics and long-term cycle characteristics.

 Hereinafter, the present invention will be described specifically with reference to examples.

Examples (1) PAS production method 1 Novolak type phenolic resin placed in silicon electric furnace and placed in a nitrogen atmosphere at 650 ° C (PAS1-1) and 800 ° C (PAS1-
Heat treatment was performed at a heating rate of 10 ° C./hour until 2) and pulverized by a disk mill to obtain a PAS powder.

(2) PAS Production Method 2 An aqueous solution in which a water-soluble resol (about 60% concentration), zinc chloride and water were mixed at a weight ratio of 10: 25: 4 was formed on a glass plate with a film applicator. Next, a glass plate is placed on the aqueous solution to prevent water from evaporating.
It was cured by heating at a temperature of 100 ° C. for 1 hour.

The phenol resin film was placed in a siliconite electric furnace and heated at a rate of 10 ° C./hour under a nitrogen stream to 550 ° C. (P
AS2-1), heat treatment was performed up to 750 ° C (PAS2-2).

Next, the heat-treated product was washed with dilute hydrochloric acid, washed with water, and then dried to obtain a PAS film having a high specific surface area.
By grinding this PAS film with a disc mill,
AS powder was obtained.

(PAS Production Method 3 Positive Electrode) An aqueous solution in which a water-soluble resol (about 60% concentration), zinc chloride and water were mixed at a weight ratio of 10: 25: 4 was formed on a glass plate with a film applicator. Next, cover the aqueous solution with the film with glass so that water does not evaporate.
The composition was cured by heating at a temperature of 0 ° C. for 1 hour.

The phenol resin film was placed in a siliconite electric furnace and heated at a rate of 40 ° C./hour under a nitrogen stream to 500 ° C.
The heat treatment was performed until. Next, the heat-treated product was washed with diluted hydrochloric acid, washed with water, and then dried to obtain an insoluble and infusible substrate.

Powder 100 obtained by pulverizing the insoluble infusible substrate with a disc mill
Parts, acetylene black 15 parts, ethylene tetrafluoride powder 10
After sufficiently kneading the part, it was formed into a film of about 500 μ using a roller.

(PAS3) (Negative electrode production method 1) 40 parts of a methanol solution (about 65% concentration) of a resol type phenolic resin precondensate is sufficiently mixed with 100 parts of each powder of PAS1-1 and PAS1-2. The mixture at 150 ° C
About 500μ by applying pressure at 50kg / cm ² for 15 minutes under heating
m.

The molded body was used as a working electrode, lithium metal was used as a counter electrode and a reference electrode, and LiCl was added to sufficiently dehydrated propylene carbonate.
An electrochemical cell was assembled using a 1 mol / solution of O ₄ dissolved therein as an electrolyte. By applying a voltage of 0.2 V to lithium for 12 hours, lithium was supported on the insoluble and infusible substrate. The amount of lithium carried is expressed as a percentage of the number of lithium per carbon atom of PAS. 37% of lithium was carried on the PAS1-1 molded body and 31% of lithium was carried on the PAS1-2 molded body (negative electrodes No. 1 and No. 2, respectively).

(Negative electrode production method 2) 10 parts of polytetrafluoroethylene powder was thoroughly mixed and kneaded with 100 parts of each powder of PAS1-2 and PAS2-2, and then formed into a film of about 500μ using a roller. did.
Subsequently, the molded body is immersed in a methanol solution (10%, 20%, 30%, 45% concentration) of a resol type phenol resin precondensate,
The phenol resin was impregnated. The impregnated film was dried at 100 ° C. for 24 hours and then heat-treated at 250 ° C. for 4 hours in a nitrogen atmosphere.

A 300μ Li metal foil (lithium carrying amount of about 80
%) And left in a 1 mol / LiClO ₄ -propylene carbonate solution for 48 hours, the Li metal foil completely disappeared, and all of the Li could be carried on the PAS compact.

The phenolic resin content in the molded article was calculated from the weight before the phenolic resin impregnation and the weight after the impregnation drying and curing.

(Preparation of battery) PAS3 was used as the positive electrode, and the first
The batteries were assembled as shown.

A stainless steel wire mesh was used as a current collector, and a felt made of glass fiber was used as a separator. A battery was assembled using a 1 mol / LiClO ₄ -propylene carbonate solution as an electrolyte.

(Measurement of Cycle Characteristics) A voltage of 4.0 V was applied to the battery from an external power supply for about 1 hour to perform charging, and then discharged to 2.0 V at a current density of 1 mA / cm ² to obtain an initial capacity. The charge / discharge cycle was further repeated, and the number of times that the capacity reached 80% of the initial capacity was measured.

(Measurement of rapid discharge characteristics) The charging method is 5 mA / cm
^The battery was discharged at a current density of ² until the voltage reached 2.0 V, and was compared with the capacity at the time of 1 mA / cm ² discharge. The result is (capacity at 5 mA / cm ² ) / (1 mA / c
shown by the m capacity of ² o'clock).

Table 1 shows the physical properties of PAS, Table 2 shows the physical properties of the negative electrode obtained by the negative electrode production method 2, and Table 3 shows the test results of the present invention.

Comparative Example 1 After mixing and kneading 10 parts (per weight) of polytetrafluoroethylene (PTFE) powder with each powder of PAS1-1, PAS1-2, PAS2-1 and PAS2-2, 500 μm Into a film. Lithium was supported by the method in Production Method 2 of the negative electrode without impregnating the phenol resin. However, for PAS1-1 and PAS1-2, a 150 μm (about 40% lithium carrying amount) lithium foil was used.

A battery was assembled in the same manner as in the example, and cycle characteristics and rapid discharge characteristics were measured.

 The results are summarized in Table 4.

[Brief description of the drawings]

FIG. 1 is a basic structural view of a battery according to the present invention, and (1)
Is a positive electrode, (2) a negative electrode, (3) and (3 ') are current collectors,
(4) is an electrolyte, (5) is a separator, (6) is a battery case, (7) and (7 ') are external terminals.

Claims (1)

(57) [Claims] 1. An organic electrolyte battery comprising a positive electrode, a negative electrode, and an electrolytic solution containing a solution in which a lithium salt is dissolved in an aprotic organic solvent, a heat treatment of an aromatic condensation polymer comprising carbon, hydrogen and oxygen as a negative electrode. Wherein the aromatic condensation polymer is (a) a condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde,
(B) an aromatic hydrocarbon compound having a phenolic hydroxyl group, an aromatic hydrocarbon compound having no phenolic hydroxyl group and a condensate of an aldehyde and (c) a furan resin, and a hydrogen atom / carbon of the heat-treated product. Lithium is added in a molar percentage of 3% or more to a molded article containing an insoluble infusible substrate containing a polyacene-based skeleton structure having an atomic ratio of 0.50 to 0.05 and a thermosetting resin or a heat-treated product of the molded article. An organic electrolyte battery characterized by using a supported one.