JP4755765B2 - Battery separator and battery using the same - Google Patents

Description

【００４８】
【発明の効果】
本発明は、電解液の分解および該分解生成物による電極表面上への膜生成を抑制し、負極の不可逆容量を低減させ、基本電池特性および充放電サイクル特性を向上させた電池を構成し得る電池用セパレータであって、かつ、セパレータ中に残存する不純物含有量も低減されており電池特性の劣化が抑制された電池用セパレータおよびそれを用いた電池を提供するものであり、その工業的価値は極めて大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery separator and a battery using the same, and more particularly, to a battery separator capable of constituting a battery with reduced basic capacity characteristics and charge / discharge cycle characteristics by reducing the irreversible capacity of a negative electrode and using the same. Related to the battery.
[0002]
[Prior art]
In recent years, non-aqueous secondary batteries, particularly lithium secondary batteries, are attracting attention as batteries for dealing with the cordlessness of electronic devices because of their high energy density, high electromotive force, and low self-discharge.
[0003]
The positive electrode material and the negative electrode material in the non-aqueous secondary battery are usually configured by supporting an active material on the surface of a metal foil as a current collector, that is, a current collector. For example, as a negative electrode material for a lithium secondary battery, copper foil is doped with lithium simple particles, alloy particles of lithium and aluminum, particles of materials that adsorb or absorb lithium ions such as carbon and graphite, and lithium ions. A material in which conductive polymer material particles are attached as an active material is known. Moreover, as a positive electrode material, for example, fluorinated graphite particles represented by a composition formula of (CF) _n , LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , MnO ₂ , V ₂ O ₅ , CuO, and Ag _{2 on} an aluminum foil. Known are metal oxide particles such as CrO ₄ and metal sulfide particles such as CuS attached as active materials.
[0004]
In the lithium secondary battery, LiPF ₆ , LiCF ₃ SO is used in an organic solvent such as ethylene carbonate, propylene carbonate, acetonitrile, γ-butyrolactone, diethyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, ethylmethyl carbonate, dimethyl carbonate, and the like. 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 a non-aqueous electrolyte solution.
[0005]
A secondary battery such as the above lithium secondary battery has advantages such as high energy density, high electromotive force, and low self-discharge as described above, but on the other hand, due to the difference between discharge capacity and charge capacity. There is a disadvantage that a certain irreversible capacity is large. The cause of the large irreversible capacity of the negative electrode is thought to be due to the decomposition of the electrolyte and the formation of a film on the electrode surface by the decomposition product. That is, for example, in a lithium secondary battery, lithium contained in the electrolyte is deposited as a film on the surface of the negative electrode due to decomposition of the electrolytic solution, thereby reducing the number of lithium ions responsible for charge and discharge, and thus increasing the irreversible capacity. It is thought to do.
In order to solve such a problem, attempts have been made to add a compound to the electrolytic solution to suppress the decomposition of the electrolyte, but such an electrolytic solution has a new problem of poor storage stability.
[0006]
Therefore, for a battery that can constitute a battery that suppresses decomposition of the electrolytic solution and film formation on the electrode surface by the decomposition product, reduces the irreversible capacity of the negative electrode, and improves basic battery characteristics and charge / discharge cycle characteristics Development of a separator and a battery using the separator is eagerly desired.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a battery separator and a battery using the same that can constitute a battery having improved basic battery characteristics and charge / discharge cycle characteristics in a secondary battery such as a lithium secondary battery. .
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have formed basic battery characteristics and charge / discharge cycles by forming a thin film containing a specific compound on one side or both sides of a polyolefin microporous membrane. The present inventors have found that a battery separator capable of constituting a battery with improved characteristics and a battery using the same can be obtained, and the present invention has been completed.
[0009]
That is, according to the first invention of the present invention, the sulfide compound represented by the following general formula (1), the polysulfide compound represented by the following general formula (2), the following general formula on one or both surfaces of the polyolefin microporous membrane There is provided a battery separator in which a thin film of at least one compound selected from the group consisting of a sulfone compound, a sulfur-containing cyclic compound and a crown ether compound represented by (3) is formed.
R ¹ —S—R ² Formula (1)
(In the formula, R ¹ and R ² represent hydrocarbon residues, which may be the same or different.)
R ³ —Sx—R ⁴ general formula (2)
(Wherein R ³ and R ⁴ represent hydrocarbon residues, which may be the same or different, and x represents an integer of 2 to 5)
R ⁵ —SO ₂ —R ⁶ general formula (3)
(Wherein R ⁵ and R ⁶ represent a hydrocarbon residue and may be the same or different.)
[0010]
Moreover, according to the 2nd invention of this invention, the battery using the separator for batteries in the 1st invention is provided.
[0011]
Preferred embodiments of the present invention are shown below.
(A) The battery separator, wherein the sulfide compound is methyl sulfide and / or ethyl sulfide.
(B) The battery separator, wherein the polysulfide compound is di (tert-nonyl) sulfide and / or di (tert-dodecyl) sulfide.
(C) The battery separator, wherein the sulfone compound is vinyl sulfone.
(D) The battery separator, wherein the sulfur-containing cyclic compound is 2-methylthiophene, 1,3,5-trithiane, ethylene trithiocarbonate and / or vinylene trithiocarbonate.
(E) The battery separator, wherein the crown ether compound is 12-crown-4, 15-crown-5 and / or 18-crown-6.
(F) The battery separator, wherein the thin film is formed by coating by a micro gravure coater method.
(G) The battery separator, wherein the thin film is formed on a surface of the polyolefin microporous film on the negative electrode side.
(H) The battery separator, wherein the amount of the thin film attached to the polyolefin microporous film is 0.01 to 1 g / m ² .
(Li) The battery separator, wherein the thin film has a thickness of 0.001 to 0.5 μm.
(Nu) A lithium secondary battery using the battery separator.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the battery separator of the present invention and the battery using the same will be described in detail for each item.
[0013]
1. Polyolefin microporous membrane The polyolefin used in the polyolefin microporous membrane used as the base material of the battery separator of the present invention includes ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. Polymerized crystalline homopolymer or copolymer can be mentioned. Among these, high molecular weight polyethylene, particularly high-density ultrahigh molecular weight polyethylene is preferable from the viewpoints of microporosity and mechanical strength.
[0014]
The method for producing the polyolefin microporous membrane is not limited, but, for example, polyolefin 5 having a weight average molecular weight of 5 × 10 ^{5 to} 2.5 × 10 ⁶ and a weight average molecular weight / number average molecular weight of less than 10. A solution composed of ˜50% by weight and a solvent of 95% to 50% by weight is prepared. The solution is extruded from a die and cooled to form a gel-like composition. The gel-like composition is melted at a polyolefin melting point + 10 ° C. or lower. It is preferable to use a polyolefin microporous membrane produced by stretching at a temperature and then removing the residual solvent.
[0015]
The polyolefin microporous membrane used in the present invention usually has a porosity of 30 to 95%, a film thickness of 25 μm, an air permeability of 2000 sec / 100 cc or less, an average through-hole diameter of 0.005 to 1 μm, and a tensile breaking strength. A microporous membrane having mechanical properties of 80 MPa or more and a puncture strength of 3000 mN or more is preferable.
[0016]
In addition, although the thickness of the polyolefin microporous film is appropriately selected, it 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 it to practical use due to insufficient mechanical strength of the film, and if it exceeds 50 μm, the effective resistance becomes too large.
[0017]
2. Thin Film Forming Compound The compound that forms a thin film on one or both surfaces of the polyolefin microporous film of the present invention is at least one compound selected from the following sulfur compounds and / or crown ether compounds.
(I) Sulfur Compound (i) Sulfide Compound The sulfide compound used in the present invention is represented by the following general formula (1).
R ¹ —S—R ² Formula (1)
(In the formula, R ¹ and R ² represent hydrocarbon residues, which may be the same or different.)
The hydrocarbon residue is preferably an alkyl group, particularly preferably an alkyl group having 1 to 5 carbon atoms.
[0018]
Specific examples of the sulfide compound include methyl sulfide, ethyl sulfide, methyl ethyl sulfide, propyl sulfide, and ethyl propyl sulfide. Among these, methyl sulfide and ethyl sulfide are preferable.
[0019]
(Ii) Polysulfide compound The polysulfide compound used in the present invention is represented by the following general formula (2).
R ³ —Sx—R ⁴ general formula (2)
(Wherein R ³ and R ⁴ represent hydrocarbon residues, which may be the same or different, and x represents an integer of 2 to 5)
The hydrocarbon residue of R ³ and R ⁴ is preferably an alkyl group, and particularly preferably a tertiary alkyl group having 3 to 12 carbon atoms. X is preferably 2.
[0020]
As the polysulfide compound, di (tert-nonyl) sulfide and di (tert-dodecyl) sulfide are preferable.
[0021]
(Iii) Sulfone Compound The sulfone compound used in the present invention is represented by the following general formula (3).
R ⁵ —SO ₂ —R ⁶ general formula (3)
(Wherein R ⁵ and R ⁶ represent a hydrocarbon residue and may be the same or different.)
The hydrocarbon residue of R ⁵ and R ⁶ is preferably an alkyl group, a vinyl group, and an allyl group, and particularly preferably an alkyl group having 1 to 5 carbon atoms and a vinyl group.
[0022]
Specific examples of the sulfone compound include methyl sulfone, ethyl sulfone methyl ethyl sulfone, propyl sulfone, vinyl sulfone, allyl sulfone, and propenyl sulfone. Among these, vinyl sulfone is preferable.
[0023]
(Iv) Sulfur-containing cyclic compound Specific examples of the sulfur-containing cyclic compound used in the present invention include 1,3,5-trithiane, lenthionine, hexathiepan, 2-methylthiophene, 3-methylthiophene, ethylene trithiocarbonate, Although vinylene trithiocarbonate etc. are mentioned, Among these, 1,3,5-trithiane, 2-methylthiophene, ethylene trithiocarbonate, and vinylene trithiocarbonate are preferable.
[0024]
(II) Crown ether compound Specific examples of the crown ether compound used in the present invention include 12-crown-4, 15-crown-5, 18-crown-6, 24-crown-8, and dibenzo-18-crown. -6, dibenzo-24-crown-8, dicyclohexyl-24-crown-8 and the like. Among them, 12-crown-4, 15-crown-5, 18-crown-6 are preferable.
[0025]
3. Thin Film Formation Method The battery separator of the present invention is produced by forming a thin film on one or both surfaces of the polyolefin microporous film with a coating solution containing the sulfur compound and / or crown ether compound of the present invention. The coating solution is applied by a conventional casting or coating method, such as a roll coater, air knife coater, blade coater, rod coater, bar coater, comma coater, gravure coater, silk screen coater, die coater, micro gravure coater method, etc. It is cast or applied to at least one surface of the polyolefin microporous membrane. That is, the thin film is formed by applying a coating solution containing the above compound to at least one surface of the polyolefin microporous membrane and drying.
Further, a thin film may be formed using dipping, PVD, CVD, or the like.
[0026]
Moreover, although content of the said compound in a coating liquid is suitably adjusted with the coating method and the thickness of the thin film which should be formed, it is 1 to 10 weight% normally. Examples of the solvent for the coating solution include toluene, methylene chloride, propylene carbonate, xylene, methyl alcohol, and ethyl alcohol. Furthermore, although the coating film obtained by application | coating is normally dried by heat processing, it is preferable that this heat processing temperature is the range of 60-90 degreeC, and the heat processing time is the range of 1-10 minutes.
[0027]
The amount of the thin film formed on at least one surface of the polyolefin microporous membrane in this way varies depending on the pore size and porosity of the polyolefin microporous membrane, but is usually 0.01 to 1 g / m ² . is there. When the amount deposited is less than 0.01 g / ^{m 2,} the effect of reducing the irreversible capacity is reduced, whereas, if it exceeds 1 g / ^{m 2,} inhibiting the ionic conductivity of the electrolyte. The thickness of the thin film is usually in the range of 0.001 to 0.5 μm.
The battery separator of the present invention preferably uses a thin film formed on the negative electrode side surface of the polyolefin microporous membrane by the microgravure coater method.
Furthermore, since the battery separator of the present invention uses a highly soluble solvent as a coating solution when the thin film is applied, the content of impurities remaining in the separator can be reduced, and thus the battery characteristics are deteriorated. It also has the advantage that it can be suppressed.
[0028]
4). Battery The battery separator formed with the thin film of the present invention 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, or a lithium polymer secondary battery. The separator is preferably used as a separator for lithium secondary batteries.
[0029]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In addition, the measuring method of the used battery separator physical property and the evaluation method of battery characteristics are shown below.
[0030]
(1) Air permeability: Measured according to JIS P8117. (Unit: sec / 100cc)
[0031]
(2) Puncture strength: A polyolefin microporous membrane was pierced with a needle having a diameter of 1 mm and a tip radius of 0.5 mm at 2 mm / sec, and the load at the time of breaking was measured. (Unit: mN)
[0032]
(3) Residue amount: The battery separator after forming the thin film was extracted with chloroform at 60 ° C. for 1 hour, and the weight% of the extract with respect to the separator was defined as “residue amount”. (Unit:% by weight)
[0033]
(4) Initial irreversibility: a negative electrode half-cell having a negative electrode / separator / lithium metal as its negative electrode is made of a material comprising 90% by weight of graphite and 10% by weight of polyvinylidene difluoride (PVDF) as the negative electrode. did. The electrolytic solution used was an equal volume mixed organic solvent of ethylene carbonate (EC) and diethyl carbonate (DEC), and LiPF ₆ as an electrolyte having a concentration of 1.0 mol / l.
The negative electrode half-cell was charged and discharged once, and the initial irreversibility (%) was calculated based on the following formula.
Initial irreversibility (%) = (discharge capacity−charge capacity) / discharge capacity
Example 1
On one side of a 20 μm thick polyethylene microporous membrane having the air permeability and puncture strength shown in Table 1, a 170 wt. Coating was performed using a gravure roll at a line speed of 10 m / min. Thereafter, an ethyl sulfide thin film was formed on the polyethylene microporous film by drying at 60 ° C. for 2 minutes at a line speed of 10 m / min.
The adhesion 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, the amount of residue and the initial irreversibility as battery characteristics were measured.
The results are shown in Table 1.
[0035]
Example 2
Except that the solvent of the coating solution was changed to methylene chloride, an ethyl sulfide thin film was formed in the same manner as in Example 1, and the amount of residual separator and initial irreversibility as battery characteristics were measured.
The results are shown in Table 1.
[0036]
Example 3
Except that a 5% by weight toluene solution of di (tert-dodecyl) sulfide was used as a coating solution on one side of a 20 μm thick polyethylene microporous membrane having the air permeability and pin puncture strength shown in Table 1. A thin film was formed in the same manner as in Example 1, and the initial irreversibility, which is a battery characteristic, was measured.
The results are shown in Table 1.
[0037]
Example 4
A thin film was formed in the same manner as in Example 3 except that di (tert-nonyl) sulfide was used instead of di (tert-dodecyl) sulfide, and the initial irreversibility as battery characteristics was measured.
The results are shown in Table 1.
[0038]
Example 5
A thin film was formed in the same manner as in Example 1 except that vinyl sulfone was used instead of ethyl sulfide, and the initial irreversibility, which is a battery characteristic, was measured.
The results are shown in Table 1.
[0039]
Example 6
A thin film was formed in the same manner as in Example 1 except that 2-methylthiophene was used in place of ethyl sulfide, and the initial irreversibility as battery characteristics was measured.
The results are shown in Table 1.
[0040]
Example 7
A thin film was formed in the same manner as in Example 3 except that 1,3,5-trithiane was used in place of di (tert-dodecyl) sulfide, and the initial irreversibility as battery characteristics was measured. .
The results are shown in Table 1.
[0041]
Example 8
A thin film was formed in the same manner as in Example 3 except that ethylene trithiocarbonate was used in place of di (tert-dodecyl) sulfide, and the initial irreversibility as battery characteristics was measured.
The results are shown in Table 1.
[0042]
Example 9
A thin film was formed in the same manner as in Example 3 except that vinylene trithiocarbonate was used instead of di (tert-dodecyl) sulfide, and the initial irreversibility, which is a battery characteristic, was measured.
The results are shown in Table 1.
[0043]
Example 10
Example except that a 5% by weight propylene carbonate solution of 12-crown-4 was used as a coating solution on one side of a 20 μm thick polyethylene microporous membrane having the air permeability and puncture strength shown in Table 1. A thin film was formed in the same manner as in Example 1, and the initial irreversibility, which is battery characteristics, was measured.
The results are shown in Table 1.
[0044]
Example 11
A thin film was formed in the same manner as in Example 10 except that 15-crown-5 was used in place of 12-crown-4, and the initial irreversibility as battery characteristics was measured.
The results are shown in Table 1.
[0045]
Example 12
A thin film was formed in the same manner as in Example 10 except that 18-crown-6 was used instead of 12-crown-4, and the initial irreversibility, which is battery characteristics, was measured.
The results are shown in Table 1.
[0046]
Comparative Example 1
Using a polyethylene microporous membrane having a gas permeability and pin puncture strength shown in Table 1 and having a thickness of 20 μm, the amount of separator remaining and initial irreversibility as battery characteristics were measured.
The results are shown in Table 1.
[0047]
[Table 1]

[0048]
【The invention's effect】
INDUSTRIAL APPLICABILITY The present invention can constitute a battery that suppresses decomposition of the electrolytic solution and film formation on the electrode surface by the decomposition product, reduces the irreversible capacity of the negative electrode, and improves basic battery characteristics and charge / discharge cycle characteristics. The present invention provides a battery separator and a battery separator using the battery separator, in which the content of impurities remaining in the separator is reduced and the deterioration of battery characteristics is suppressed, and its industrial value. Is extremely large.

Claims (7)

On one or both sides of a polyolefin microporous membrane, a sulfide compound represented by the following general formula (1), a polysulfide compound represented by the following general formula (2), a sulfone compound represented by the following general formula (3), a sulfur-containing cyclic compound And a separator for a battery, wherein a thin film of at least one compound selected from the group consisting of a crown ether compound and a crown ether compound is formed.
R ¹ —S—R ² Formula (1)
(In the formula, R ¹ and R ² represent hydrocarbon residues, which may be the same or different.)
R ³ —Sx—R ⁴ general formula (2)
(Wherein R ³ and R ⁴ represent hydrocarbon residues, which may be the same or different, and x represents an integer of 2 to 5)
R ⁵ —SO ₂ —R ⁶ general formula (3)
(Wherein R ⁵ and R ⁶ represent a hydrocarbon residue and may be the same or different.) The battery separator according to claim 1, wherein the sulfide compound is methyl sulfide and / or ethyl sulfide. The battery separator according to claim 1, wherein the polysulfide compound is di (tert-nonyl) sulfide and / or di (tert-dodecyl) sulfide. The battery separator according to claim 1, wherein the sulfone compound is vinyl sulfone. 2. The battery separator according to claim 1, wherein the sulfur-containing cyclic compound is 2-methylthiophene, 1,3,5-trithiane, ethylene trithiocarbonate and / or vinylene trithiocarbonate. The battery separator according to claim 1, wherein the crown ether compound is 12-crown-4, 15-crown-5 and / or 18-crown-6. A battery comprising the battery separator according to any one of claims 1 to 6 .