JPS63224160A - Secondary battery - Google Patents

Abstract

PURPOSE:To obtain the battery in the caption with high energydensity, low self-discharging, high charging/discharging efficiency and long cycle lifetime by specifying each density of LiPF6 in electrolyte in case of completion of discharging and charging. CONSTITUTION:In a secondary battery comprising a positive plate employing a compound of polyaniline system and electrolyte made from a mixed solvent of LiPF6, propylene carbonate (PC) and 1,2-dimethoxyethane (DME), the quantity of electrolyte and the density of LiPF6 are controlled that the density of LiPF6 is more than 3 mol/l, preferably more than 3.5 mol/l when discharging is completed and is less than 1.5 mol/l, preferably less than 10 mol/l when charging is completed. Therefore, the secondary battery with high energy-density, high charging/discharging-efficiency, long cycle lifetime, low selfdischarging ratio and good flatness of a voltage on discharging can be obtained.

Description

[Detailed description of the invention] C. Industrial application field] The present invention has high energy density, low self-discharge,
The present invention relates to a secondary battery with a long cycle life and good charge/discharge efficiency (Coulomb efficiency).

[Prior Art] So-called polymer batteries, in which a polymer compound having a conjugated double bond in the main chain is used as an electrode, are expected to be used as high energy density secondary batteries.

Many reports have already been made regarding polymer batteries, for example, P. J. Nigley et al., Journal of the Chemical Society, Chemical Communication, 1979, p. 594 CP, J.
Nigrey et al., J.C.S., Chem.

Coa+mun, 1979.594),
Journal Electrochemical Society, 1
981, p. 1651 (J, Electroche
m, Soc, 1981.16513, and
JP 56-138489, JP 57-121188, JP 59-3870, JP 59-3872, JP 59-
No. 3873, No. 59-196568, No. 59-196
No. 573, No. 59-203368, No. 59-2033
Publications such as No. 89 can be mentioned as part of this.

In addition, there has already been a proposal to use polyaniline obtained by electrolytic oxidation polymerization of aniline as an electrode for aqueous or non-aqueous batteries [I. G. Matsuku Diarmid et al., Polymer Preprints, Vol. 25] , number 2. Page 248 (i984') < A, G,
MacDiarmid et al, Polyme
rPreprints, 25. No, 2.248
(i984)>, Sasaki et al., Abstracts of the 50th Annual Conference of the Electrochemical Society, 123 (i983), Abstracts of the 51st Annual Conference of the Electrochemical Society, 228 (i98, 4))
.

[Problems to be Solved by the Invention] However, polymer batteries using conventionally known polymers as electrodes have problems such as (i) high energy density, (i1) low self-discharge, (iii) commercial/discharge efficiency, and (iV) It has not been possible to obtain a product that satisfies long cycle life at the same time.

As a result of various studies on electrode materials that simultaneously satisfy the above four battery performances, the present inventors found that a polyaniline compound was used for the positive electrode, and the electrolyte was LiPF6, propylene carbonate (PC), and 1,2-dimethoxyethane. (
In a secondary battery made of a mixed solvent of DME), we discovered that the battery performance was improved depending on the Li PF6 concentration during charging and discharging.

The present invention was developed based on the above discovery, and an object of the present invention is to provide a secondary battery that satisfies the above four battery performances at the same time.

[Means for Solving the Problems] The present invention has been made to achieve the above object, and the gist thereof is that the positive electrode is made of a polyaniline compound, the negative electrode is made of (i) an alkali metal, (i1) an alkali metal alloy, (ill) a conductive polymer, or (iv) a complex of a conductive polymer and an alkali metal or an alkali metal alloy, and the electrolyte is a combination of Lt PF6, propylene carbonate, and 1,2- In a secondary battery made of a mixed solvent of dimethoxyethane, the concentration of LiPF6 in the electrolyte is 3 mo(i/(i) or more at the end of discharging, and 1 mo(i/(i) at the end of charging.
．． The secondary battery has a resistance of 5 moΩ/ρ or less.

[Specific structure and operation of the invention] The present invention will be explained in detail below.

The polyaniline compound used in the positive electrode of the secondary battery of the present invention is obtained by oxidative polymerization or oxidative copolymerization of at least one aniline compound selected from the following general formulas (i) and (2).

[However, in the formula, R1 and R2 are an alkyl group having 5 or less carbon atoms or an alkoxy group having 5 or less carbon atoms, and X and Y are 0
, 1 or 2. ] Examples of the aniline compound represented by the general formula (i) or (2) include aniline, 2-methyl-aniline,
2,5-dimethylaniline, 2-methoxyaniline,
Examples include 2,5-dimethoxy-aniline, 0-phenylenediamine, 3-methyl-1,2-diamino-benzene, and the like. Among these, aniline and 0-phenylenediamine are preferred, and aniline is particularly preferred.

The above polyaniline compound can be produced by either electrochemical polymerization or chemical polymerization.

When electrochemical polymerization is used, the polymerization of aniline compounds is carried out by anodic oxidation, for example, 0
．． Current densities of 1 to 20 mA/cJ are used, often 1
A voltage of ~300 volts is applied. The polymerization is preferably carried out in the presence of an auxiliary liquid in which the aniline compound is soluble;
Water or polar organic solvents can be used for this purpose. When using a water-miscible solvent, a small amount of water may be added.

Suitable organic solvents are alcohols, ethers such as dioxane or tetrahydrofuran, acetone or acetonitrile, benzonitrile, dimethylformamide or N-methylpyrrolidone.

Polymerization is carried out in the presence of a supporting electrolyte. This includes BF4''-, As F4-'' as anions.

ASF +, 5bF6-, sbcΩ-, PF6-.

cpo +, H8O+, So, and taste.

These salts have cations such as protons (H),
Contains quaternary ammonium ions, lithium ions, sodium ions, or potassium ions. The use of compounds of this type is known and is not the subject of the present invention. These compounds are usually used in an amount such that the polyaniline compound contains 10 to 100 mol% of anions.

To produce polyaniline compounds by chemical methods, for example, aniline compounds can be polymerized in aqueous solution with strong acids, such as hydrochloric acid, and inorganic peroxides, such as potassium persulfate. According to this method, a polyaniline compound is obtained in the form of a fine powder. Since a salt is present in these methods, the polyaniline compound is a complex compound with the corresponding anion. The complexed polyaniline compound obtained by polymerization is preliminarily treated with ammonia,
It is preferable to undope it by treating it with an alkali such as KOH or NaOH.

Further, other methods for dedoping or deprotonation include a heat treatment method at 100 to 300° C. or an electrochemical method. Further, in order to remove low molecular weight portions before or after the alkali treatment, it is preferable to perform washing or extraction with an organic solvent, but this treatment may be omitted. A dedoped or deprotonated polyaniline compound, for example polyaniline, contains a large amount of the emeraldine structure of the following formula (3).

It is more preferable to use a dedoped or deprotonated polyaniline compound that has been further reduced with a reducing agent such as hydrazine, phenylhydrazine, or titanium trichloride. The reduced polyaniline compound, taking polyaniline as an example, contains a large amount of the leucoemeraldine structure of the following formula (4).

It is more preferable to use a dedoped or deprotonated polyaniline compound that has been complexed again with a protic acid.

The emeraldine structure of formula (3) may be oxidized with an oxidizing agent to convert it to the nigraniline structure (5) or pernigraniline structure (6), and then complexed with a protonic acid.

(The following is a blank space) The method of complexing is not particularly limited, but usually a method is used in which an acidic aqueous solution containing an anion and having a pH of 3 or less is brought into contact.

As a complexing agent, hydrogen halides such as HCl, HF, HBr, protonic acids of halides of group Ha elements such as HB F4, protonic acids of halides of group Va elements such as HPF6, HC, Q O4 Examples include perchloric acid, H2SO4, HNO3, etc., but there are no particular limitations as long as the protonic acid complexes the polyaniline compound. Among these protonic acids, HBF, H
PF6.

HCΩO is preferred, with HBF and HPF6 being particularly preferred. The anions of these protonic acids may be different from the anions in the electrolyte of the secondary battery of the present invention, but it is more preferable that they be the same.

Any of the alkali treatment, organic solvent washing, reduction treatment, oxidation, and protonic acid complexing treatment may be performed either before or after molding the polyaniline compound into an electrode.

Molded bodies that can be used as electrodes can be obtained by various methods. For example, in the case of anodic oxidation of an aniline compound, the polyaniline compound is complexed with an anion and takes the shape of the anode used.If the anode is flat, the polyaniline compound is A layer is formed. When using a method for producing a polyaniline compound fine powder, this fine powder can be compression molded into a molded body by a known method under pressure and heat. Temperature and 10~10,000k
A pressure of g/(J) is used. According to this known method for producing anionic complexed polyaniline compounds, shaped bodies of any shape can be obtained.

That is, for example, a thin film, a plate or a three-dimensional shaped molding is used.

The negative electrode used in the secondary battery of the present invention is (i) an alkali metal, (ii) an alkali metal alloy, (iii) a conductive polymer, or (iv) a composite of an alkali metal or an alkali metal alloy and a conductive polymer. It is.

(i) Examples of alkali metals include Li, Na, etc. (i1) Examples of alkali metal alloys include Li/Na.
AΩ alloy, Li/Hg alloy, Li/Zn alloy, Li/C
d alloy, Li/Sn alloy, L1/pb alloy, and alloys of three or more metals containing alkali metals used in these alloys, such as Li/AI/Mg, Li/Aρ/S, Li/AN/Pb , Li/Aρ/Zn, Li/A
Examples include R/Hg.

These alloys may be manufactured by either an electrochemical method or a chemical method, but those alloyed electrochemically are more preferable.

Examples of the conductive polymer (iii) include polypyrrole, polypyrrole derivatives, polythiophene, polythiophene derivatives, polyquinoline, polyacene, polyparaphenylene, polyparaphenylene derivatives, polyacetylene, and the like. Furthermore, (iv) as a complex of an alkali metal or an alkali metal alloy and a conductive polymer, L
Examples include composites of the i/A, 9 alloy and the various conductive polymers described above, such as polyparaphenylene or polyacetylene. Among these, preferred are, for example, polyacetylene, polyparaphenylene, L1 metal, Li
/AΩ alloy, Li /A,Q /Mg alloy, Li /
Examples include composites of A and Q alloys and polyacene or polyparaphenylene. The complex herein refers to a homogeneous mixture of an alkali metal or an alkali metal alloy and a conductive polymer, a laminate, and a modified product in which a base component is modified with another component.

The polyaniline compound, conductive polymer, and interlayer compound used in the electrode of the secondary battery of the present invention may include other suitable conductive materials such as carbon black, acetylene black, metal, etc., as is well known to those skilled in the art. Powder, metal fiber, carbon fiber, etc. may be mixed.

In addition, polyethylene, modified polyethylene, polypropylene, polytetrafluoroethylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EP
It may be reinforced with thermoplastic resin such as DM.

The electrolyte used in the secondary battery of the present invention uses LiPF6 as a supporting electrolyte and a mixed solvent of PC and DME as a solvent, and the concentration of noble and LiPF6 in the electrolyte is determined by the concentration of LiPF6 at the end of discharge. The concentration is 30] oΩ/Ω or more, preferably 3.5 moΩ/ρ or more, and the concentration of LiP Fe at the end of charging is 1.5 man / (l or less, preferably 1.0 mail /Ω or less). However, the concentration unit here is m
of) /Ω means ll1oΩ/Ω-solvent. P
The mixing ratio of C and DME is not particularly limited, but usually PC
is 10 to 90% by volume, DME is 90 to 10% by volume, preferably 30 to 70% by volume of PC, and 70 to 30% by volume of DME.
It is volume %.

By using the supporting electrolyte and mixed solvent within the above range, the amount of electrolyte can be significantly reduced, the energy density of the battery can be significantly increased, and this is very useful industrially.

In the secondary battery of the present invention, the amount of dopant doped into the polyaniline compound is 1 N atom in the oxidized polymer.
0.2 to 1.5 mol per atom, preferably 0
．． It is 2 to 1.5 moles.

The amount of doping can be freely controlled by measuring the amount of electricity flowing during electrolysis. The doping can be carried out either under constant current, constant voltage or under varying conditions of current and voltage.

In the present invention, if necessary, a porous membrane made of synthetic resin such as polyethylene or polypropylene or natural fiber paper may be used as the diaphragm.

In addition, some of the electrodes used in the secondary battery of the present invention may react with oxygen or water and reduce the performance of the battery, so the battery should be sealed and substantially oxygen-free and water-free. It is desirable that the condition is as follows.

[Examples] Hereinafter, the present invention will be explained in more detail by showing Examples and Comparative Examples.

Example 1 <Production of polyaniline electrode> 400 ml of pre-deoxidized distilled water and 42% by weight HBF
100 ml of the aqueous solution of No. 4 was placed in a three-necked IIl flask, and nitrogen gas was bubbled through it for about 1 hour while stirring. Thereafter, the inside of the system was made into a nitrogen gas atmosphere, a thermometer and a condenser were attached, and then the flask was cooled with water and ice to bring the solution temperature to 15°C. To this was added 20 g of aniline. After the monomers have dissolved, add 22 g of ammonium persulfate.
was added all at once, and the mixture was reacted for 5 hours while stirring and keeping the internal temperature below 25°C. After the reaction is complete, what is the greenish brown reaction solution?
Filtration and vacuum drying yielded 15 g of dark green product.

100 cc of acetone was added to 1 g of this product, and after stirring at room temperature for 3 hours, the slurry liquid was filtered to recover solid content. Next, 100 cc of acetone was newly added and the same operation as above was repeated. This operation.

After repeating the process three times, the coloring of the furnace liquid almost disappeared. The obtained polyaniline was treated with an ammonia aqueous solution to obtain a polyaniline powder having an emeraldine structure of the formula (3) described above. To this polyaniline powder, 10% by weight of polytetrafluoroethylene and 10% by weight of carbon black were added, and the mixture was press-molded at room temperature at a pressure of 500 kg/cJ to produce an electrode.

<Production of film-like acetylene polymer> 1.7 ml of titanium tetrabutoxide was added to a glass reaction vessel with an internal volume of 500 ml under a nitrogen atmosphere.
A catalyst solution was prepared by dissolving in 30 ml of anisole and then adding 2.7 ml of triethylaluminum with stirring.

This reaction solution was cooled with liquid nitrogen, and the nitrogen gas in the system was evacuated using a vacuum pump. Next, this reaction solution was diluted with
It was cooled to 8° C. and purified acetylene gas at a pressure of 1 atmosphere was bubbled through while the catalyst solution remained stationary.

Polymerization immediately occurred on the surface of the catalyst solution, producing a film-like acetylene bulk polymer. Thirty minutes after the introduction of acetylene, the acetylene gas in the reaction vessel system was exhausted to stop the polymerization.

After removing the catalyst solution with a syringe under nitrogen atmosphere, -78
While keeping the temperature at ℃, the tube was washed 5 times with 100 ml of produced toluene. The film-like acetylene polymer swollen with toluene was a uniform film-like swollen product in which fibrils were tightly intertwined. Next, this swollen product was vacuum-dried to obtain a reddish-purple film with a metallic luster, a thickness of 180 μm, and a cis content of 98%. In addition, the height density of this film-like acetylene polymer is 0.30 g/cc, and its electrical conductivity (DC four-terminal method) is 3.2 × 10 at 20°C.
-9Ω-1·cm-1.

Battery experiment〉 Polyaniline electrode (diameter 20 mm) obtained by the above method
A battery was constructed using a disk-shaped object (disc-shaped object) and a disk-shaped object with a diameter of 20 mm cut out from the film-like acetylene polymer as active materials of a positive electrode and a negative electrode, respectively.

FIG. 1 is a schematic cross-sectional view of a battery cell for measuring the characteristics of a secondary battery, which is a specific example of the present invention. In the figure, 1 is a platinum lead wire for the negative electrode, and 2 is a platinum wire mesh current collector for the negative electrode with a diameter of 20 mm and 580 mesh. body, 3 is a disc-shaped negative electrode with a diameter of 20 mm, 4 is a diameter of 20 m
5 is a circular porous polypropylene diaphragm with a thickness sufficient to be impregnated with electrolyte, 5 is a disk-shaped positive electrode with a diameter of 20 mm, 6 is a platinum wire mesh current collector for the positive electrode with a diameter of 20 mm and 80 meshes, 7 8 indicates a positive electrode lead wire, and 8 indicates a screw-type polytetrafluoroethylene container.

First, the platinum wire mesh current collector 6 for the positive electrode is placed in the lower part of the concave portion of the container 8, and then the positive electrode 5 is stacked on the platinum wire mesh current collector 6 for the positive electrode, and the porous polypropylene diaphragm 4 is placed on top of the platinum wire mesh current collector 6 for the positive electrode. After stacking and sufficiently impregnating the electrolyte solution, the negative electrode 3 was stacked, and the platinum wire mesh current collector 2 for the negative electrode was further placed on top of the negative electrode 3, and the container 8 was tightened to produce a battery.

The electrolyte was propylene carbonate and 1,2-dimethoxyethane (volume ratio: 1), which had been distilled and dehydrated according to a conventional method.
= 4 moI of Lt PF6 dissolved in a mixed solvent of 1)/
(0.7 cc of l solution was used.

Using the battery thus prepared, the doping amount of the positive electrode and negative electrode was 45 moN% and 6 moN%, respectively, under constant current (2.5 mA/cJ) in an argon atmosphere.
The battery was charged by flowing an amount of electricity corresponding to moD%. The concentration of L iP Fe in the electrolyte at the end of charging is 0.7m6N
/D. Immediately after charging is completed, turn the device under constant current (2,
5mA/cj) until the battery voltage reaches 0. lOV
When the charge/discharge rate reached 50%, a repeated charge/discharge test was conducted under the same conditions as above, and the number of charge/discharge cycles (cycle life) was 648 times until the charge/discharge efficiency decreased to 50%. Recorded.

The energy density at the fifth repetition was 110 W-hr/dazzle per total weight of the electrode active material and electrolyte, and the highest light/discharge efficiency was 100%. Also, when left charged for 75 hours, the self-discharge rate was 1.9%.
Met.

Comparative Example 1 4 mol/1 L used in the battery experiment of Example 1
A battery test was conducted under the same conditions as in the example except that 1 mo1/l electrolyte was used instead of the I P Fe / P C + D M E electrolyte. As a result, the cycle life is 65 times, and the energy density is 110 W-hr/kg.
The maximum light/discharge efficiency is 80% and the self-discharge rate is 21.3.
%Met.

Comparative Example 2 4 mol/(l of Li PF6 used in the battery experiment)
A battery test was conducted under exactly the same conditions as in Example 1, except that 1.5 ml of the /PC+DME electrolyte was used. The concentration of LiPF6 at the end of charging was 2.0 moO/fl. As a result, the cycle life was 615 times, and the energy density was
At 96W-hr/kg, the highest light/discharge efficiency is 100%,
The self-discharge rate was 6.9%.

Example 2 The polyaniline powder having an emeraldine structure obtained in Example 1 was reduced by immersing it in an aqueous hydrazine solution to obtain the formula (4).
) with the structure of leucoemeraldine. To this leucoemeraldine, 10% by weight of polytetrafluoroethylene and 10% by weight of carbon black were added, and the mixture was pressure-molded at room temperature at a pressure of 500 kg/cJ to produce an electrode.

This electrode is used as a positive electrode, and Li −AI = 94:6 as a negative electrode.
(Weight ratio) Using an alloy, L i P of 4.5 mo1/R
Fe/! ' C+ D M E (P C:
A battery experiment was conducted in exactly the same manner as in Example 1, except that 0.6 ml of DME = 60:40 volume ratio) was used. The concentration of Li PF6 at the end of charging is 0.80moD
/Ω. This battery had a cycle life of 789 cycles, an energy density of 135 W-hr/kg, a maximum light/discharge efficiency of 100%, and a self-discharge rate of 2.5%.

Example 3 The polyaniline powder with the emeraldine structure obtained in Example 1 was immersed in an aqueous solution of HBF4 at pH=1 to form HBF4.
It was complexed (protonated) with

Example 2 except that the obtained complexed polyaniline was used as the positive electrode.
A battery experiment was conducted in exactly the same manner.

As a result, the cycle life was 737 cycles, the energy density was 130 W-hr/ ) cg, the highest light/discharge efficiency was 100%, and the self-discharge rate was 4.3%.

Example 4 Acetylene high polymer and Aρ instead of acetylene high polymer
A battery test was conducted in exactly the same manner as in Example 1, except that a 1:1 (weight ratio) composite was used. As a result, the cycle life was 737 times, and the energy density was 113 W-h.
r/kg, the highest light/discharge efficiency was 100%, and the self-discharge rate was 4.6%.

The results of Examples 1 to 4 and Comparative Examples 1 and 2 are summarized in Table 1.

(Left below) [Effects of the invention] The secondary battery of the present invention has high energy density, high charge/discharge efficiency, long cycle life, low self-discharge rate, and flatness of voltage during discharge. In good condition. Furthermore, the secondary battery of the present invention is lightweight, compact, and has a high energy density, so it is suitable for use in portable devices, electric vehicles, gasoline vehicles, and power storage batteries.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a battery cell for measuring characteristics of a secondary battery, which is a specific example of the present invention. 1... Platinum lead wire for negative electrode 2... Platinum wire mesh current collector for negative electrode 3... Negative electrode 4... Porous polypropylene diaphragm 5... Positive electrode 6... Platinum wire mesh collection for positive electrode Electric body 7...Positive lead wire

Claims (1)

[Claims] 1. The positive electrode is a polyaniline compound, and the negative electrode is (i) an alkali metal, (ii) an alkali metal alloy, (iii) a conductive polymer, or (iv) a composite of a conductive polymer and an alkali metal or an alkali metal alloy. A substance selected from
In a secondary battery in which the electrolytic solution is composed of LiPF and a mixed solvent of propylene carbonate and 1,2-dimethoxyethane, the concentration of LiPF_6 in the electrolytic solution is 3 mol/l or more at the end of discharging and 1.5 mol at the end of charging. /
1. A secondary battery characterized in that it is less than l.