JP2002313307A - Separator for use in battery and battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for use in a battery capable of preventing inflammation of the battery due to overcharge and having a favorable separator characteristic on a secondary battery such as a lithium secondary battery and the battery using it. SOLUTION: This separator for use in the battery is constituted by forming a thin film of a ferrocene derivative of expressions (1)-(5) on one side of both sides of a polyolefine fine porous film. (R<1> -)(R<2> -)(R<3> -)C-CH5 H4 -Fe-C5 H5 (1) R<4> -C5 H4 -Fe-C5 H5 (2) R<5> -(C=O)-C5 H4 -Fe-C5 H5 (3) R<6> -NH-(C=O)-C5 H4 -Fe-C5 H5 (4) (R<7> -)(R<6> -)P-C5 H4 -Fe-C5 H4 -P(-R<9> )(-R<10> ) (5) (where R<1> -R<3> , R<5> , R<6> are an alkyl group, R<4> is an alkenyl group and R<7> -R<10> are an aryl group or an alkyl group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator and a battery using the same, and more particularly, to a battery separator having good separator characteristics and capable of preventing ignition of the battery due to overcharge. And a battery using the same.

[0002]

2. Description of the Related Art In recent years, non-aqueous secondary batteries, particularly lithium secondary batteries, have been attracting attention as batteries for responding to cordless electronic equipment due to their high energy density, high electromotive force and low self-discharge. Is taking a bath.

A positive electrode material and a negative electrode in a non-aqueous secondary battery
The material is usually the electrode material itself, that is, the gold as the current collector.
The active material is supported on the surface of the metal foil. For example,
As a negative electrode material for lithium secondary batteries, copper foil, lithium
Simple particles, alloy particles of lithium and aluminum,
Adsorb lithium ions such as carbon and graphite.
Or particles of material to be absorbed, doping with lithium ions
Of conductive polymer material attached as active material
Things are known. In addition, as the positive electrode material, aluminum
For example, (CF)_nFluoride represented by the composition formula
Graphite particles, LiCoO₂, LiMn₂O₄, LiNiO
₂, MnO₂, V₂O₅, CuO, Ag ₂CrO₄Such
Metal oxide particles, metal sulfide particles such as CuS
What is attached as quality is known.

In a lithium secondary battery, ethylene carbonate, propylene carbonate, acetonitrile, γ-butyrolactone, diethyl carbonate,
An organic solvent such as 2-dimethoxyethane, tetrahydrofuran, ethyl methyl carbonate, dimethyl carbonate, or the like may be added to LiPF ₆ , LiCF ₃ SO ₃ , LiClO ₄ ,
LiBF ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Li [C
(C ₂ F ₅ ) ₃ PF ₃ ] or the like is used as an electrolyte.

Further, as a separator used in a non-aqueous electrolyte battery such as a lithium secondary battery, a porous body made of a polyolefin such as polypropylene or polyethylene is often used. For example, as a separator for a non-aqueous electrolyte battery, JP-A-6-325747 discloses a microporous membrane made of a high-molecular-weight polyethylene having an intrinsic viscosity (η) of 5 dl / g or more. As a battery separator for a lithium primary / secondary battery or the like, Japanese Patent Application Laid-Open No. 6-163023 discloses a microporous porous membrane made of a mixture of polyethylene and ethylene-propylene rubber.

[0006] By the way, since a charged battery is in a state of high energy, there is a danger that heat or fire may occur if the battery is not in a normal state. For example, in a lithium secondary battery, the battery temperature rises for some reason. Then, there is a risk of thermal runaway in which the battery self-heats and the battery temperature further rises. In order to prevent this, efforts to reduce the cause of self-heating of the battery are required.
One of the causes of self-heating of a battery is, for example, a reaction between an electrolytic solution and a positive electrode. Basically, in a battery system, an electrolytic solution having a decomposition potential higher than the potential of the positive electrode is selected, so that the reaction between the electrolytic solution and the positive electrode does not occur in a normal state. However, when the potential of the positive electrode is forcibly increased as in the case of overcharging, an oxidation reaction of the electrolytic solution accompanied by heat generation, that is, self-heating of the battery occurs, and there is a possibility that smoke or ignition may occur. As described above, if the lithium secondary battery is used improperly, it may be in a dangerous state such as heat generation, smoking, and ignition.

[0007] As described above, the lithium secondary battery has a problem such as ignition when overcharged. for that reason,
Attempts have been made to add a compound that produces a redox shuttle reaction to the electrolyte to prevent ignition, but such electrolytes have the problem of poor storage stability.
In WO 98/32184, the porous base material is selected from organic silicon compounds, organic titanium compounds, organic aluminum compounds, organic zirconium compounds, and organic zirconaluminate compounds in order to prevent ignition of the battery. There has been proposed a separator for a non-aqueous electrolyte battery to which an organometallic compound is attached. However, despite these proposals, there are still no electrolytes or separators that do not generate sufficient self-heating of the battery during overcharge, ie, do not cause battery ignition.

Therefore, development of a battery separator which has good separator physical properties, suppresses the heat generation of the electrodes, reduces the cause of self-heating of the battery, and prevents the ignition of the battery, and a battery using the same has been desired. ing.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a secondary battery such as a lithium secondary battery which is capable of preventing the battery from being ignited due to overcharging. An object of the present invention is to provide a battery separator having separator characteristics and a battery using the same.

[0010]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by forming a thin film of a specific ferrocene derivative on one or both surfaces of a polyolefin microporous film. The present inventors have found that, when the battery is overcharged, heat generation of the electrodes can be suppressed and ignition of the battery can be prevented, and the present invention has been completed.

That is, according to the first aspect of the present invention,
A battery separator is provided in which a thin film made of at least one ferrocene derivative selected from compounds represented by the following general formulas (1) to (5) is formed on one or both surfaces of a polyolefin microporous membrane. ^{(R 1 -) (R 2} -) (R 3 -) C-C 5 H 4 -Fe-C 5 H 5 (1) R 4 -C 5 H 4 -Fe-C 5 H 5 (2) R 5 _{- (C = O) -C 5} H 4 -Fe-C 5 H 5 (3) R 6 -NH- (C = O) -C 5 H 4 -Fe-C 5 H 5 (4) (R 7 - _{^{) (R 8 -) P-}} C 5 H 4 -Fe-C 5 H 4 -P (-R 9) (- R 10) (5) ( ^wherein, R 1, ^{R 2} and ^{R 3} is an alkyl group Wherein R ⁴ represents an alkenyl group, R ⁵ represents an alkyl group, R ⁶ represents an alkyl group, and R ⁷ , R ⁸ , R ⁹ and R ¹⁰ represent , An aryl group or an alkyl group, which may be the same or different.)

According to the second aspect of the present invention, at least one ferrocene derivative selected from the compounds represented by the above general formulas (1) to (5) is provided on one or both surfaces of the microporous polyolefin membrane. A method for producing a battery separator according to a first aspect of the present invention, which comprises applying a solution to be contained, followed by heating and drying.

Further, according to a third aspect of the present invention, there is provided a battery using the battery separator according to the first aspect.

As described above, the present invention relates to a battery separator in which a thin film of a specific ferrocene derivative is formed on at least one surface of a polyolefin microporous film, and a method for producing the same. Include the following: (1) The method for producing a battery separator according to the second aspect of the present invention, wherein the method of forming the ferrocene derivative thin film is a coating type coating. (2) The method for producing a battery separator according to the above (1), wherein the application type coating is a microgravure coating. (3) In the second aspect of the present invention, the solvent for the solution of the ferrocene derivative is at least one solvent selected from toluene, methylene chloride, carbon tetrachloride or xylene, and the method for producing a battery separator is characterized in that: Method. (4) The battery separator according to the first aspect of the present invention, wherein the ferrocene derivative is vinyl ferrocene. (5) The battery separator according to the first aspect of the present invention, wherein the ferrocene derivative is butyryl ferrocene. (6) The battery separator according to the first aspect of the present invention, wherein the ferrocene derivative is N-methylferrocenecarboxamide. (7) The battery separator according to the first aspect of the present invention, wherein the thin film is formed by coating using a microgravure coater method. (8) The battery separator according to the first aspect of the present invention, wherein the thin film is formed on the surface of the polyolefin microporous film on the positive electrode side. (9) The battery separator according to the first aspect of the present invention, wherein the amount of the thin film attached to the microporous polyolefin membrane is 0.01 to 1 g / m ² . (10) In the first invention of the present invention, the thickness of the thin film is
A battery separator having a thickness of 0.001 to 0.5 μm. (11) A lithium secondary battery using the battery separator according to the first invention of the present invention.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The battery separator of the present invention and a battery using the same will be described in detail below for each item.

1. Polyolefin microporous membrane Used as the base material of the battery separator of the present invention, as the polyolefin used in the polyolefin microporous membrane, ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like Polymerized crystalline homopolymers or copolymers may be mentioned. Among these, from the viewpoints of microporous formability and mechanical strength,
High molecular weight polyethylene, especially high density ultra high molecular weight polyethylene, is preferred.

The method for producing the microporous polyolefin membrane is not limited. For example, the weight average molecular weight is 5 × 10 ^{5 to} 2.5 × 10 ⁶ and the weight average molecular weight / number average molecular weight is less than 10. 5 to 50% by weight of polyolefin
And preparing a solution consisting of 95 to 50% by weight of a solvent, extruding the solution from a die, cooling to form a gel-like composition,
It is preferable to use a microporous polyolefin membrane produced by stretching the gel composition at a temperature equal to or lower than the melting point of the polyolefin + 10 ° C. and then removing the residual solvent.

The microporous polyolefin membrane used in the present invention generally has a porosity of 30 to 95%, a film thickness of 25 μm, an air permeability of 2,000 seconds / 100 cc or less, an average through-hole diameter of 0.005 to 1 μm, and a tensile strength. A microporous membrane having mechanical properties of a breaking strength of 80 MPa or more and a piercing strength of 3000 mN (306 gf) or more is preferable.

The thickness of the microporous polyolefin membrane is appropriately selected, but is usually about 0.1 to 50 μm, preferably about 1 to 25 μm. If the thickness is less than 0.1 μm,
It is difficult to put into practical use due to insufficient mechanical strength of the membrane.
If it exceeds 0 μm, the effective resistance becomes too large, which is not preferable.

2. On one or both sides of the polyolefin microporous membrane of the present invention,
The compounds forming the thin film are represented by the following general formulas (1) to (5)
At least one ferrocene derivative selected from the compounds represented by These particular ferrocene derivatives are
The potential at which a redox shuttle reaction can occur is high. In other ferrocene derivatives, for example,
n-Butylferrocene has a low potential for causing a redox shuttle reaction and is not used in the present invention. here,
The redox shuttle reaction refers to a reversible oxidation-reduction reaction. When the above specific ferrocene compound exceeds a certain potential, it is oxidized on the positive electrode, and is then reduced on the negative electrode to return to the original ferrocene compound, and this can be repeated.

(R ^1- ) (R ^2- ) (R ^3- ) CC ₅ H ₄ —Fe—C ₅ H ₅ (1) R ⁴ —C ₅ H ₄ —Fe—C ₅ H ₅ (2 _{^{) R 5 - (C = O}} ) -C 5 H 4 -Fe-C 5 H 5 (3) R 6 -NH- (C = O) -C 5 H 4 -Fe-C 5 H 5 (4) ( ^{R 7 -) (R 8 -} ) P-C 5 H 4 -Fe-C 5 H 4 -P (-R 9) (- R 10) (5) ( ^wherein, R 1, ^{R 2} and ^{R 3} R ⁴ represents an alkenyl group; R ⁵ represents an alkyl group; R ⁶ represents an alkyl group; R ⁷ , R ⁸ , R ⁹ and R ¹⁰ represents an aryl group or an alkyl group, and may be the same or different.)

The ferrocene derivative represented by the above general formula (1) used in the present invention has a specific compound name, for example, te wherein R ¹ , R ² and R ³ are each a methyl group.
rt-butylferrocene and the like, and R ¹ , R ² and R ³ are preferably an alkyl group having 1 to 5 carbon atoms.

Further, ferrocene derivatives represented by the general formula (2) is a specific compound names, for example, vinyl ferrocene can be mentioned R ⁴ is a vinyl group, R ⁴
Is preferably a vinyl group or an allyl group.

Further, the ferrocene derivative represented by the above general formula (3) has a specific compound name such as R ⁵
Are methyl groups, butyrylferrocene wherein R ⁵ is a propyl group, and the like, and R ⁵ is preferably an alkyl group having 1 to 5 carbon atoms.

Further, ferrocene derivatives represented by the general formula (4) is a specific compound names, for example, R ⁶ and N- methyl ferrocene carboxamide with a methyl group, and examples R ⁶ is It is preferably an alkyl group having 1 to 5 carbon atoms.

Further, the ferrocene derivative represented by the above general formula (5) has a specific compound name, for example,
R ^{7, R} 8, ^{R 9} and ^{R 10} are like 1,1'-bis (diphenylphosphine) ferrocene is respectively a phenyl ^group, as R ^7, R 8, ^{R 9} and ^{R 10,}
It is preferably a phenyl group or an alkyl group having 1 to 5 carbon atoms.

3. Thin film forming method The battery separator of the present invention is to form a thin film of the specific ferrocene derivative according to the present invention on one or both surfaces of a polyolefin microporous film, but the thin film forming method is not particularly limited. A method known to those skilled in the art, for example, a method of applying a solution containing a specific ferrocene derivative to at least one surface of the polyolefin microporous membrane, followed by heating and drying to form a ferrocene derivative thin film. Can be taken. As a preferred method of forming a thin film, the thin film is formed by using a coating solution containing a specific ferrocene derivative. Coating liquid is a conventional casting or coating method, for example, roll coater, air knife coater, blade coater, rod coater, bar coater, comma coater, gravure coater, silk screen coater, die coater,
It is cast or applied to at least one surface of the microporous polyolefin membrane by a microgravure coater (coating) method or the like. That is, the thin film is formed by applying a coating solution containing a specific ferrocene derivative to at least one surface of the polyolefin microporous film and drying. Further, a thin film may be formed by using dipping, PVD, CVD, or the like.

The content of the specific ferrocene derivative in the coating solution is appropriately adjusted depending on the coating method and the thickness of the thin film to be formed, but is usually 1 to 10% by weight. Examples of the solvent for the coating solution include toluene, methylene chloride, carbon tetrachloride, xylene, methyl alcohol, and ethyl alcohol.By using such a highly soluble solvent for the coating solution, The content of remaining impurities can also be reduced, and deterioration of battery characteristics can be suppressed. Furthermore, the coating film obtained by coating is usually dried by heat treatment, and the heat treatment temperature is in the range of 60 to 90 ° C., and the heat treatment time is preferably in the range of 1 to 10 minutes.

The adhesion amount of the thin film formed on at least one surface of the microporous polyolefin membrane in this manner varies depending on the pore size and the porosity of the polyolefin microporous membrane, but is usually 0.01 to 1 g / g. a m ^2. The amount of adhesion is 0.
If less than 01G / m ^2, the effect of preventing the ignition of the battery due to overcharging are reduced, whereas, if it exceeds 1 g / m ^2, inhibiting the ionic conductivity of the electrolyte. Further, the thickness of the thin film is usually in the range of 0.001 to 0.5 μm.
In the battery separator of the present invention, a thin film formed on the positive electrode side surface of a polyolefin microporous film may be used by a microgravure coater method in order to suppress an increase in the potential of the positive electrode during overcharge. preferable.

4. Battery The battery separator on which the thin film of the present invention is formed is a secondary battery such as a nickel-hydrogen battery, a nickel-cadmium battery, a nickel-zinc battery, a silver-zinc battery, a lithium secondary battery, and a lithium polymer secondary battery. Is preferably used as a separator of a lithium secondary battery.

[0031]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The methods for evaluating the physical properties of the battery separator and the methods for evaluating the battery characteristics are shown below.

(1) Air permeability: Measured according to JIS P8117. (Unit: sec / 100cc)

(2) Piercing strength: A needle having a diameter of 1 mm and a tip radius of 0.5 mm was pierced into the polyolefin microporous membrane at 2 mm / sec, and the load at the time of breaking was measured. (Unit: mN)

(3) Residue Amount: The battery separator after the formation of the thin film was extracted with chloroform at 60 ° C. for 1 hour, and the weight% of the extract relative to the separator was defined as “residue amount”. (Unit: wt%)

(4) Redox shuttle potential: The potential at which the Redox shuttle reaction starts was measured by cyclic voltammetry evaluation using a three-electrode cell. The measurement conditions are as follows. Triode cell: working electrode (Pt) / separator / counter electrode (Li), reference electrode is lithium. -Cyclic voltammetry device-Electrolyte: A solution in which an equal volume of an organic solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) is mixed and LiPF ₆ is used as an electrolyte at a concentration of 1.0 mol / l.

(5) Overcharge characteristics: rated capacity of battery (14
(0 mAh / g), and the voltage at that time was measured. The measurement conditions are as follows. · Seikyokuhan battery having the structure: cathode / separator / lithium metal & positive electrode: LiCoO ₂ (85 wt%) + PVDF (5 wt%) + acetylene black (10 wt%) Electrolytic solution: ethylene carbonate (EC) and diethyl carbonate ( DEC) in which an equal volume of mixed organic solvent contains LiPF ₆ as an electrolyte at a concentration of 1.0 mol / l.・ Coin type simulation cell ・ Constant current charging: 0.1mA / cm ²

Example 1 A microporous polyolefin (polyethylene) film having a thickness of 20 μm was coated on one surface with the general formula (2)
Vinyl ferrocene as a specific ferrocene derivative, and a 5% by weight toluene solution of the vinyl ferrocene was used as a coating solution by a microgravure coater method.
The coating was performed at a line speed of 10 m / min using a 0-mesh microgravure roll. Then, at 60 ° C,
By drying at a line speed of 10 m / min for 1 minute, a thin film of vinyl ferrocene was formed on the microporous polyethylene film. The attached amount of the thin film was 0.2 g / m ² , and the thickness was 0.15 μm. Using the separator on which the thin film was formed, evaluation of physical properties of the separator (air permeability, piercing strength) and evaluation of battery characteristics (Redox shuttle potential, overcharge characteristics) were performed. Table 1 shows the results.

Example 2 A butyrylferrocene thin film was formed on a microporous polyethylene film in the same manner as in Example 1, except that butyrylferrocene of the general formula (3) was used as a specific ferrocene derivative. . Using the separator on which the thin film was formed, the physical properties of the separator (air permeability, piercing strength, residual amount) and the battery characteristics (Redox shuttle potential, overcharge characteristics) were evaluated. Table 1 shows the results.

Example 3 A microporous polyethylene membrane was prepared in the same manner as in Example 1 except that butyrylferrocene of the general formula (3) was used as a specific ferrocene derivative and carbon tetrachloride was used as a solvent. Then, a butyrylferrocene thin film was formed. Using the separator on which the thin film was formed, the physical properties of the separator (air permeability, piercing strength, residual amount) and the battery characteristics (Redox shuttle potential, overcharge characteristics) were evaluated. Table 1 shows the results.

Example 4 N-methyl ferrocene carboxy was formed on a polyethylene microporous membrane in the same manner as in Example 1 except that N-methyl ferrocene carboxamide of the general formula (4) was used as a specific ferrocene derivative. An amide thin film was formed. Using the separator on which the thin film was formed, the physical properties of the separator (air permeability, piercing strength) and the battery characteristics (Redox shuttle potential, overcharge characteristics) were evaluated. Table 1 shows the results.

Comparative Example 1 n-butylferrocene was formed on a polyethylene microporous membrane in the same manner as in Example 1 except that n-butylferrocene was used as a ferrocene derivative which did not correspond to the specific ferrocene derivative according to the present invention. Was formed. Using the separator on which the thin film was formed, the physical properties of the separator (air permeability, piercing strength) and the battery characteristics (Redox shuttle potential, overcharge characteristics) were evaluated. Table 1 shows the results.

[Comparative Example 2] Using a microporous polyethylene membrane having a thickness of 20 µm and using a separator not formed with a ferrocene derivative thin film, evaluation of the separator physical properties (air permeability, puncture strength, residual amount) Battery characteristics evaluation (overcharge characteristics) was performed. Table 1 shows the results.

[0043]

[Table 1]

As is clear from Table 1 above, Example 1
The separators obtained in ~ 4 have excellent separator properties,
It is good, and also in the battery characteristics evaluation using the separator, the Redox shuttle potential is high (4.0 to 4.0).
1V) and excellent overcharge characteristics. On the other hand, in the separator of Comparative Example 1 using n-butylferrocene without using a specific ferrocene derivative, the Redox shuttle potential does not increase so much in battery characteristics evaluation. Further, the separator of Comparative Example 2 in which the thin film of the ferrocene derivative was not formed had a relatively large amount of residue, and was in an overcharged state even in the evaluation of battery characteristics, which was worse than the separators of Examples 1 to 4.

[0045]

According to the separator of the present invention, in a secondary battery such as a lithium secondary battery, ignition of the battery due to overcharge can be prevented, and the content of impurities remaining in the separator is reduced. Deterioration of battery characteristics is suppressed, and excellent separator characteristics are obtained. Therefore, it is useful as a battery separator and a battery using the same.

Continued on the front page (72) Inventor Kotaro Takita 4-16-24 Okamura, Isogo-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Koichi Kono 3-29-10-404 Mihara, Asaka-shi, Saitama 4F074 AA16 CC10Z CE38 CE88 DA49 5H021 BB01 BB12 BB13 CC04 CC08 EE01 EE04 HH10 5H029 AJ01 AJ12 AK01 AK02 AK03 AK05 AL07 AL08 AL12 AM02 AM03 AM05 AM07 BJ03 EJ04 EJ12 HJ12

Claims (3)

[Claims] 1. A battery separator in which a thin film comprising at least one ferrocene derivative selected from compounds represented by the following general formulas (1) to (5) is formed on one or both surfaces of a microporous polyolefin membrane. ^{(R 1 -) (R 2} -) (R 3 -) C-C 5 H 4 -Fe-C 5 H 5 (1) R 4 -C 5 H 4 -Fe-C 5 H 5 (2) R 5 _{- (C = O) -C 5} H 4 -Fe-C 5 H 5 (3) R 6 -NH- (C = O) -C 5 H 4 -Fe-C 5 H 5 (4) (R 7 - _{^{) (R 8 -) P-}} C 5 H 4 -Fe-C 5 H 4 -P (-R 9) (- R 10) (5) ( ^wherein, R 1, ^{R 2} and ^{R 3} is an alkyl group Wherein R ⁴ represents an alkenyl group, R ⁵ represents an alkyl group, R ⁶ represents an alkyl group, and R ⁷ , R ⁸ , R ⁹ and R ¹⁰ represent , An aryl group or an alkyl group, which may be the same or different.) 2. A solution containing at least one ferrocene derivative selected from the compounds represented by the following general formulas (1) to (5) is applied to one or both surfaces of the microporous polyolefin membrane, and then heated and dried. The method for producing a battery separator according to claim 1, wherein: ^{(R 1 -) (R 2} -) (R 3 -) C-C 5 H 4 -Fe-C 5 H 5 (1) R 4 -C 5 H 4 -Fe-C 5 H 5 (2) R 5 _{- (C = O) -C 5} H 4 -Fe-C 5 H 5 (3) R 6 -NH- (C = O) -C 5 H 4 -Fe-C 5 H 5 (4) (R 7 - _{^{) (R 8 -) P-}} C 5 H 4 -Fe-C 5 H 4 -P (-R 9) (- R 10) (5) ( ^wherein, R 1 ^{to R 10} are as defined above) 3. A battery using the battery separator according to claim 1.