JPS63289765A - Nonaqueous secondary battery - Google Patents

Abstract

PURPOSE:To improve local discharge and a cycle life by using poly aniline containing BF4 in a specified ratio for an active material of a positive electrode. CONSTITUTION:Poly aniline is used for an active material of a positive electrode. In this case the poly aniline contains BF4 of 15 to 30 wt.%. By using the poly aniline as described above for an active material of a positive electrode, local discharge is repressed and a long lived secondary battery is obtained. When the content of BF4 is less than 15 wt.% or more than 30 wt.%, discharge capacity and capacity retention are lowered, so that the purpose is not attained. As for an active material of a negative electrode a combination of Li-Al containing Li of 25 to 65 atomic % is preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a nonaqueous secondary battery equipped with a positive electrode, a negative electrode, and a nonaqueous electrolyte. By using the present invention, it relates to a non-aqueous secondary battery that has less self-discharge, a longer cycle life, and a larger discharge capacity.

In recent years, conductive polymer substances such as polyaniline, polypyrrole, and polyacetylene have attracted attention as battery electrode materials, and various secondary batteries using these conductive polymer substances have been developed. Proposed.

In particular, secondary batteries using polyaniline as an electrode active material have been actively researched because they can have high energy density.

However, batteries using a conductive polymer material as a positive electrode active material generally suffer from many self-discharges and unstable cycle life.

As a practical secondary battery, further improvements are desired.

This point is also the same for secondary batteries using polyaniline.
Conventionally, when polyaniline is used as a positive electrode active material in a secondary battery, polyaniline obtained by adopting a specific manufacturing method or manufacturing condition to improve the performance of the secondary battery is used as the positive electrode active material, or Conventionally, polyaniline has been produced by electrolytic polymerization or chemical polymerization, but among the polyanilines produced in this way, polyanilines with specific properties are used as positive electrode active materials. Although various proposals have been made for this purpose, there is a need for a secondary battery using polyaniline that further reduces self-discharge, extends cycle life, and improves practicality.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a highly practical secondary battery using polyaniline, which has excellent performance such as large capacity, low self-discharge, and long cycle life. do.

Means and Function for Solving the Problems The present inventors have conducted extensive studies to achieve the above object, and as a result, have developed polyaniline having specific physical properties, namely BF.
When polyaniline whose content of 4 is controlled in the range of 15 to 30% by weight is used as a positive electrode active material, a high-performance secondary battery with surprisingly little self-discharge, long cycle life, and large capacity can be created. We found that it is possible to obtain

That is, as mentioned above, polyaniline with various properties has been proposed for use as a positive electrode active material in secondary batteries, but until now little consideration has been given to the composition or amount of impurities of the polyaniline positive RI film itself. Although there are some proposals for controlling the water content in polyaniline films, according to the studies of the present inventors, polyaniline used as a positive electrode active material of secondary batteries contains BF4. Moreover, within a specific range, i.e. 15 to 30% by weight.
BF containing 15 to 30% by weight is surprisingly preferable due to its properties of battery performance, especially suppressing self-discharge and extending cycle life.
It has been found that the cycle characteristics of a secondary battery can be significantly improved by using polyaniline containing the above range as a positive electrode active material. In this case, such polyaniline is used as a positive electrode active material, and a lithium alloy, especially a lithium-aluminum alloy containing 25 to 65 at% lithium, is combined as a negative electrode active material, and LiBF4 is preferably added as an electrolyte, preferably 1 mol. /l 3 moles/
When using a propylene carbonate-dimethoxyethane mixed solvent (volume ratio 35-65:65-35) dissolved at a concentration of 1 or less, a lithium non-aqueous secondary battery with better cycle characteristics and higher practicality can be obtained. This knowledge led to the present invention.

Therefore, the present invention provides a nonaqueous secondary battery equipped with a positive electrode, a negative electrode, and a nonaqueous electrolyte, in which the positive electrode active material contains 15 to 30%
Provided is a non-aqueous secondary battery characterized by using polyaniline containing BF4 in a weight percent.

The present invention will be explained in more detail below.

The secondary battery according to the present invention uses polyaniline as the positive electrode active material as described above, and in this case, BF4 is contained in the polyaniline in an amount of 15 to 30% by weight.
, more preferably 17 to 25% by weight of polyaniline. By using such polyaniline as a positive electrode active material, self-discharge is suppressed and a secondary battery with a long cycle life can be obtained. In contrast, those with a BF4 content of less than 15% by weight and those with a BF4 content of less than 15% by weight
If the content is higher than 0% by weight, the discharge capacity and capacity retention rate will be low, and therefore the object of the present invention cannot be achieved.

Note that BF4 contained in polyaniline may be contained as an ion and/or molecule, and may also be contained in any form such as an acid (HB F4) or a salt (LiBF4, etc.).

Here, there is no particular restriction on the method for producing polyaniline whose BF4 content should be controlled, but there is an electrolytic polymerization method in which polyaniline is electrodeposited from an acidic aqueous solution containing an aniline monomer, and an acidic aqueous solution containing an aniline monomer and a catalyst added. A chemical polymerization method in which polyaniline is obtained by chemically oxidatively polymerizing an aniline monomer is preferably employed, and a polyaniline film obtained by the former electrolytic polymerization method is particularly preferably used.

In addition, as the acid used for preparing the above acidic aqueous solution,
Although not necessarily limited to, HCQ, H2SO
, , HBF, , H(do4, etc.), and one or more of these are used. Among these, HBF is preferably used. Also, the concentration of the acid is 0.1 to 3 mol/ 2. It is particularly preferable that the concentration of the aniline monomer in the acidic aqueous solution is 0.05 to 4 mol/12, particularly 0.25 to 1.5 mol/l. In this acidic aqueous solution,
In addition to the above components, a soluble salt for adjusting pH may be appropriately included.

When polyaniline is obtained by electrolytic polymerization using the above acidic aqueous solution, there are no restrictions on the electrodes (working electrode and counter electrode).

As a working electrode, platinum, stainless steel, carbon,
pbo, etc., and these are used in appropriate shapes such as plate-like, foil-like, mesh-like, punched-like shapes, etc. Among these, mesh-like stainless steel is preferable.

In addition, as a counter electrode, platinum, stainless steel, carbon, PbO□, etc. are used in the shape of a plate, mesh, punched metal, etc., and many of these can be used in combination, but among these, punching metal A shaped stainless steel plate is preferably used.

The electrolytic polymerization method may be either a potential regulation method or a current regulation method. When performing electrolytic polymerization using the current regulation method, there are two methods: constant current regulation method that continues to apply current at a constant value, step current regulation method that changes the current value over time, continuous current regulation method that increases or decreases the current over time, and current value regulation method. A regulation method such as a cyclic current regulation method that changes the current in a cyclical manner can be adopted. The conditions for electrolytic polymerization are appropriately selected, and normal conditions can be used, but the temperature of the polymerization solution is -11.
The temperature is preferably 0 to 15°C, particularly -5 to 9°C.

In addition, when a chemical polymerization method is adopted, the above-mentioned acidic aqueous solution containing a catalyst is used, but any catalyst can be used as long as it promotes the reaction. For example, Na2S20s t (NH,)2S20
．． , FeCQ3, etc. can be added. This chemical polymerization method can be carried out by a conventional method, but the temperature of the polymerization solution is preferably 30° C. or higher.

In the present invention, the BF4 content of the polyaniline obtained as described above is controlled within the range of 15 to 30% by weight, but the method of controlling is not particularly limited.

It is selected according to the content, and if polyaniline is manufactured from an acidic aqueous solution containing HBF4, the resulting polyaniline will contain BF4, so a method of washing polyaniline using ion-exchanged water is generally recommended. Furthermore, when polyaniline is produced from an acidic aqueous solution containing an acid other than HBF4, the resulting polyaniline does not contain BF4, so methods such as immersion or washing in a solution containing BF4 are recommended. In this case, even if polyaniline contains BF4 in advance but the amount is less than the above range, a method of immersing or washing in a solution containing BF4 is similarly adopted.

Here, when washing or soaking polyaniline,
Not only insufficient washing and immersion, but also excessive washing and immersion should be avoided.
The cleaning/immersion means and methods also need to be controlled under controlled conditions. In addition, BF in polyaniline to be controlled,
If the amount is large, it is washed with ion-exchanged water or the like, but the washing may be carried out so that BF, -i in the polyaniline falls within the above range. In addition, polyaniline that does not contain BF4 or has a low content is immersed or washed in a solution containing BF as described above, but solutions containing BF such as HBF, LiBF4, etc. in ion-exchange water or an appropriate organic solvent can be used. 0.001 to 2 mol/l, especially 0.001 to 2 mol/l of borofluoride salt.
A solution of 0.01 to 1 mol/l is preferably used.

The secondary battery of the present invention uses the polyaniline described above as a positive electrode active material, but in this case, the negative electrode active material is appropriately selected, and any material conventionally used as a negative electrode active material may be used. . However, a lithium alloy is preferable as the negative electrode active material, and by combining the polyaniline and lithium alloy according to the present invention, a lithium secondary battery with excellent battery performance and high practicality can be obtained.

The lithium alloy is made by heating and melting lithium in an alloy of one or more metals such as aluminum, silver, lead, tin, bismuth, antimony, indium, and cadmium that can be alloyed with lithium in a vacuum or an inert gas atmosphere. Manufactured by a method of homogeneously mixing, cooling and solidifying to form an alloy.

Any material produced by a method of electrochemically introducing lithium can be used. There are no particular restrictions on the synthetic composition of the lithium alloy, the amount of negative electrode active material, etc., but the types of lithium alloys include the above-mentioned Li-AQ gold alloy LL-
AM-In alloy, Li-AQ-Bi gold alloy are suitable;
In particular, it is preferable to use a lithium-aluminum alloy containing 25 to 65 atom % of lithium from the viewpoint of stabilizing cycle life and improving battery life.

Further, the electrolyte of the non-aqueous electrolyte constituting the secondary battery of the present invention is a compound consisting of a combination of an anion and a cation, and an example of the anion is PFG-.

Halide anions of group VA elements such as SbF, -, AsFG-, 5bc4-, halide anions of group IIIA elements such as B F, -, AQCQ, -, I-(I
, -), halogen anions such as Br-, CQ-, Cl
Perchlorate anion such as 204, HF, -.

CF3 S Oz-, S CN-, O knee, HS O4
- etc. can be mentioned. In addition, as a cation, L
Examples include alkali metal ions such as "i", Na÷, and +.Specifically, examples include LiPF, Li5bF,
G, LiAsF, , LiCQO, , LiI +LiBr
, LiCQ.

NaP F, , Na5bF, , NaAsF, , NaCl
10, NaI, KP Fs.

KSbF,,KAsF,,K(j20.,LiB F4
．． LiAflCQ4. LiHF2゜Li5CN, KSC
N, Li5O3CF3, etc. can be mentioned.

Although not limited to these, lithium salts, especially LiCQO4, L
iB F4. LiPF, , LiAsFG, etc.
Among these, it is preferable to dissolve LiBF in a solvent at a concentration of more than 1 mol/12 and less than 3 mol/l.

The above-mentioned electrolyte is usually used in a state dissolved in a solvent, and in this case, the solvent is not particularly limited, but a relatively polar solvent is preferably used. Specifically, propylene carbonate, ethylene carbonate, benzonitrile, and acetonitrile.

Tetrahydrofuran, 2-methyltetrahydrofuran,
γ-butyrolactone, dioxolane, methylene chloride, triethyl phosphate, triethyl phosphite,
Dimethyl sulfate, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, dimethoxyethane, polyethylene glycol, sulfolane,
One or a mixture of two or more of dichloroethane, chlorobenzene, nitrobenzene and the like can be mentioned.

Among these, especially ethylene carbonate.

A mixed solvent consisting of one solvent or a mixture of two or more solvents selected from propylene carbonate, dimethoxyethane, tetrahydrofuran, and γ-butyrolactone, especially propylene carbonate and dimethoxyethane in a volume ratio of 35:65 to 65: It is preferable to mix the electrolyte at a ratio of 35 to 35.
From the viewpoint of battery performance, it is particularly preferable to use a mixed solvent containing 65% by volume of propylene carbonate and the remainder being dimethoxyethane, in which more than 1 mol/l and less than 3 mol/l of LiBF is dissolved as described above. .

The battery of the present invention is manufactured as a coin-shaped, box-shaped, or cylindrical battery, and is usually constructed by interposing an electrolyte between positive and negative electrodes housed in an outer can, but in this case, if necessary, A porous membrane made of synthetic resin such as polyethylene or polypropylene, natural fiber, or the like can be used as a separator between the positive and negative electrodes.

As described in detail, the non-aqueous secondary battery of the present invention contains 15 to 30% by weight of BF as a positive electrode active material.

By using polyaniline containing polyaniline, self-discharge is small, cycle life is long, and discharge capacity is large. Therefore, it is suitable for use in a variety of applications such as automobiles, airplanes, portable machines, and electric vehicles. It is something that

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

A working electrode made of stainless steel mesh was placed horizontally in an acidic aqueous solution containing 1 mol/M of χ1 pentaaniline monomer and 2 mol/l of HBF, and a punched stainless steel metal was used as the counter electrode. Electrolytic polymerization was carried out at a current flow rate of 60 C/d while maintaining the temperature at ℃.
Polyaniline was electrodeposited.

The obtained polyaniline membrane was taken out along with the stainless steel mesh, and 12 cc/aJ of ion-exchanged water at 30°C was added.
The excess BF4 was extracted and removed by passing through a polyaniline membrane at a ratio of .

After vacuum drying this polyaniline membrane for 72 hours, 50 m
g was weighed out, and 50 c of a 0.2 mol/l hydrazine aqueous solution was added.
BF4 in polyaniline was completely extracted by immersing it in water for 48 hours. After adjusting the pH of this extract to 7 with dilute sulfuric acid, the BF4 concentration was measured by the BF4 ion electrode method.

From the obtained measurement values, the BF contained in the original polyaniline
When J was calculated, it was 23% by weight.

Next, the above-mentioned polyaniline was cut into pieces of 15 mmφ together with the stainless steel mesh, and this was used as a positive electrode. A lithium-aluminum alloy (lithium content: 50 at%) was used as a negative electrode, and propylene carbonate and dimethoxyethane were used as an electrolyte. They were mixed at a volume ratio of 50:50 and LiBF4 was dissolved therein at a concentration of 3 mol/l to produce a coin-shaped secondary battery. Note that a laminated film of a polypropylene nonwoven fabric and a porous membrane was used as the separator.

This battery was charged to 3.3V with a constant current of 0.5 mA, and then further charged with a constant voltage of 3.3V for 3 hours.

Then immediately at 0.5 mA for 2. When discharged to Ov, the discharge capacity was 4.9 mAh.

In addition, a battery charged under the same conditions was held at 60°C for 1 week, and then charged at 0.5 mA for 2.5 mA. When discharged to Ov, the discharge capacity was 4.2mAh, and the capacity retention rate was 8.
It was 6%.

Polyaniline, which had been electrolytically polymerized in the same manner as in the example, was washed in the same manner as in the example, using a 0.5 mol/l aqueous sodium hydroxide solution instead of ion-exchanged water.

The amount of BF4 in the polyaniline after washing was measured in the same manner as in the example, and was found to be 14% by weight.

Next, using this polyaniline, a coin-shaped secondary battery similar to that in the example was produced, and its performance was evaluated.
The discharge capacity after holding at 0° C. for one week was 2.7 mAh, and the capacity retention rate was 76%.

Comparative Example 2 Polyaniline electrolytically polymerized in the same manner as in Example was washed with a 1 mol/l HBF4 aqueous solution.

The amount of BF in this polyaniline was measured in the same manner as in the example, and was found to be 33% by weight.

Next, using this polyaniline, a coin-shaped secondary battery similar to that in the example was produced, and its performance was evaluated.
Discharge capacity after holding at 0℃ for 1 week is 3.0 mA h
, the capacity retention rate was 72%.

Claims (1)

[Claims] 1. In a nonaqueous secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, 15 to 30% by weight of BF_ as a positive electrode active material.
A non-aqueous secondary battery characterized by using polyaniline containing 4. 2. The non-aqueous secondary battery according to claim 1, which uses a lithium-aluminum alloy containing 25 to 65 atom % of lithium as a negative electrode active material. 3. As an electrolytic solution, LiBF_4 of more than 1 mol/l and less than 3 mol/l is dissolved in a mixed solvent containing 35 to 65% by volume of propylene carbonate and the remainder being dimethoxyethane. The non-aqueous secondary battery according to item 1 or 2.