JP2006127890A - Separator for electrochemical element and electrochemical element comprising it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for an electrochemical element and an electrochemical element comprising it excellent in liquid-retaining properties and moisture-releasing properties of electrolyte solution. <P>SOLUTION: The separator for an electrochemical element has a moisture-absorbing/releasing coefficient MR of 10 or more as expressed in formula; MR=(M<SB>1</SB>)-(M<SB>2</SB>) (1), where M<SB>1</SB>denotes a moisture-absorbing ratio (%) after a sample is left to stand for 360 minutes at 35°C under a 95% RH atmosphere, and M<SB>2</SB>denotes a moisture-absorbing ratio (%) after the sample is left to stand for 90 minutes at 20°C under a 65% RH atmosphere. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a separator for an electrochemical element (primary battery, secondary battery, electrolytic capacitor, electric double layer capacitor, etc.) and an electrochemical element comprising the same. More particularly, the present invention relates to an electrochemical element separator and an electrochemical element comprising the same, which are excellent in electrolyte retention and moisture release.

The most important characteristic required for separators used in electrochemical elements such as primary batteries, secondary batteries, electrolytic capacitors, and electric double layer capacitors is retention of electrolyte.
When the retention of the electrolytic solution is low, the internal resistance of the electrochemical element increases, and as a result, problems such as insufficient capacity of the electrochemical element, voltage reduction, and shortening of the lifetime occur.

  In addition, in an electrochemical element such as a primary battery, a secondary battery, an electrolytic capacitor, or an electric double layer capacitor, when an organic electrolytic solution or a non-aqueous gel electrolyte is used as the electrolytic solution or gel electrolyte, there is little water in the system. However, if it is included, problems such as a decrease in capacity and a shortened service life will occur, so great care has been taken not to mix moisture as much as possible, and there is a tendency to increase the drying temperature to increase the drying efficiency. Therefore, the separator is also required to have heat resistance.

  In order to solve these problems, at least one part contains at least one type of organic fiber fibrillated to a fiber diameter of 1 μm or less, and at least one type of organic fiber that is not fibrillated and has a fineness of 0.5 dtex or less The separator for electrochemical elements which consists of a wet nonwoven fabric formed by this is proposed (refer patent document 1).

However, in this method, it is necessary to prepare at least two types of constituent fibers in order to achieve both electrolytic solution retention and heat resistance, and it is very difficult to uniformly mix the two types of constituent fibers. In addition, there is a problem that the production efficiency of the wet nonwoven fabric is inferior, and it is necessary to take two steps of a process for manufacturing a fiber constituting the nonwoven fabric and a process for manufacturing the nonwoven fabric, resulting in poor production efficiency.
International Publication No. 01/0935050 Pamphlet

  An object of the present invention is to provide a separator for an electrochemical element and an electrochemical element comprising the same, which are excellent in liquid retention and moisture release of an electrolytic solution.

  In the above prior art, the present inventors need to increase the drying temperature in order to remove water in the drying process of the separator when it is incorporated into an electrochemical element, because the moisture releasing performance of the separator is inferior. In particular, as a result of further intensive studies, the present invention has been completed.

That is, the object of the present invention is to
The separator for electrochemical devices whose moisture absorption-release coefficient MR represented by following formula (1) is 10 or more.
MR = (M ₁ ) − (M ₂ ) (1)
Here, M ₁ is the moisture absorption rate (%) after leaving the sample in a 95% RH atmosphere at 35 ° C. for 360 minutes, and M ₂ is the sample being left in a 65% RH atmosphere at 20 ° C. for 90 minutes. It represents the subsequent moisture absorption rate (%).

  Still another object of the present invention is achieved by an electrochemical element comprising a negative electrode, a positive electrode, a separator and an electrolyte, wherein the separator according to claim 1 is used as the separator.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for electrochemical elements excellent in the liquid retention property and moisture release of an electrolyte solution, and an electrochemical element consisting thereof can be provided.

Hereinafter, the present invention will be described in detail.
The separator for electrochemical devices of the present invention needs to have a moisture absorption / release coefficient MR of 10 or more. When the MR is 10 or more, when incorporated in an electrochemical device, moisture can be efficiently removed even at low temperatures in the drying step, and the electrolyte can be sufficiently retained.

  Any one may be used as long as it has such characteristics, and the main repeating unit is alkylene terephthalate, and the organic sulfonic acid metal salt (A) represented by the following formula (I) and the following formula (II) Use of a polyester polymer copolymerized with the polyalkylene glycol (B) shown is preferable because the effects of the present application are remarkably exhibited.

  Here, the polyester having an alkylene terephthalate unit as a “main” repeating unit is a repeating unit other than an alkylene terephthalate unit, based on all repeating units constituting the polyester, 20 mol% or less, preferably 15 mol% or less, Particularly preferably, it means that it may be contained as a copolymer component of 10 mol% or less. In addition, as a glycol component of an alkylene terephthalate unit, a C2-C4 alkylene glycol is preferable, and ethylene glycol, trimethylene glycol, tetramethylene glycol etc. can be illustrated.

  Examples of the bifunctional carboxylic acid component other than terephthalic acid that can be copolymerized include isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, β-hydroxyethoxybenzoic acid, P-oxybenzoic acid, and adipic acid. And aromatic, alicyclic and aliphatic bifunctional carboxylic acids such as sebacic acid and 1,4-cyclohexanedicarboxylic acid.

  Examples of diol components other than alkylene glycol that can be copolymerized include, for example, aliphatic, alicyclic, and aromatic diol compounds such as cyclohexane-1,4-dimethanol, neopentyl glycol, bisphenol A, and bisphenol S. Can be mentioned.

  Furthermore, as long as the achievement of the object of the present invention is not substantially impaired, a tricarboxylic acid or more polycarboxylic acid such as trimellitic acid or pyromellitic acid, glycerin, trimethylolpropane, pentaerythritol, etc. A trifunctional or higher functional polyol may be used as a copolymerization component.

The component (A) copolymerized with the polyester is an organic sulfonic acid metal salt represented by the formula (I), wherein R ¹ is an aromatic hydrocarbon group or an aliphatic hydrocarbon group, and X ¹ is an ester. A formable functional group, X ² is an ester-forming functional group or a hydrogen atom. The ester-forming functional group here is a functional group that can be reacted and bonded to the polyester via an ester bond, and is generally a hydroxyl group, a carboxyl group, or an ester thereof. M is an alkali metal such as Na, K or Li, or an alkaline earth metal such as Mg or Ca, and Na or K is particularly preferable. Such an organic sulfonic acid metal salt can be used alone or as a mixture of two or more thereof, and preferred specific examples thereof include 5-dimethylsulfoisophthalate dimethyl, 5-potassium sulfoisophthalate dimethyl, 5-lithium sulfoisophthalate. Dimethyl acid, 5-sodium sulfoisophthalic acid bis (β-hydroxyethyl) ester, 5-potassium sulfoisophthalic acid bis (β-hydroxyethyl) ester, 5-lithium sulfoisophthalic acid bis (β-hydroxyethyl) ester, etc. be able to.

  The copolymerization amount of the organic sulfonic acid metal salt to the polyester is preferably 0.1 to 30 mol%, particularly 0.1 to 10 mol%, based on all dicarboxylic acid components constituting the polyester. Is preferred.

  Next, the polyalkylene glycol as the component (B) represented by the above formula (II) is copolymerized for the purpose of improving the moisture absorption / release performance of the polyester, but based on all dicarboxylic acid components constituting the polyester, The copolymerization is preferably 0.1 to 60% by weight, particularly preferably 0.2 to 15% by weight.

  Examples of such polyalkylene glycols include triethylene glycol, tetraethylene glycol, tripropylene glycol, polyethylene glycol (molecular weight 1000, 2000, 4000, 8000, 20000, 50000), and the like, particularly those having a molecular weight of 1000 to 8000. Polyethylene glycol is preferred.

Next, it is preferable to mix | blend the organic carboxylic acid metal salt as a component (C) shown by following formula (III) in the said copolyester.

  Examples of the organic carboxylic acid metal salt include sodium benzoate, potassium benzoate, magnesium benzoate, lithium benzoate, zinc benzoate, sodium toluate, potassium toluate, lithium toluate and the like. Among these, sodium benzoate, potassium benzoate, and magnesium benzoate are particularly preferable, and the organic carboxylic acid metal salt may be used alone or in combination of two or more. Moreover, it is preferable to mix | blend the compounding quantity of this organic carboxylic acid metal salt so that it may occupy 0.01 to 5 weight% in a polyester composition, More preferably, it is 0.05 to 3 weight%.

  The intrinsic viscosity of the polymer is usually in the range of 0.2 to 1.5, particularly preferably in the range of 0.4 to 1.0. When the intrinsic viscosity is less than 0.2, the physical properties are likely to be lowered. On the other hand, when the intrinsic viscosity is more than 1.5, the productivity is deteriorated and the moldability is easily lowered.

  In addition, the polymer of the present invention may be blended with other polymers as long as the object of the present invention is achieved. Examples of the polymer that may be blended include the polymers of the present invention having different intrinsic viscosities, etc. Polyester, polyamide, acrylic (methyl methacrylate), and the like.

Next, the method for producing the polymer will be described below by taking polyester having ethylene terephthalate units as the main repeating unit as an example.
First, dimethyl terephthalate and ethylene glycol are transesterified in the presence of a transesterification catalyst, terephthalic acid and ethylene glycol are directly esterified, or terephthalic acid and ethylene oxide are reacted. Bis (β-hydroxyethyl) terephthalate and / or its oligomer, and then melt polycondensation under high temperature and reduced pressure in the presence of a polycondensation catalyst and a stabilizer to obtain polyethylene terephthalate. This is achieved by adding the following components (I), (II) and optionally (III) into the reaction system at any stage before the synthesis of the polyester is completed. Preferably, the components (I) and (II) are used before the formation of bis (β-hydroxyethyl) terephthalate and / or its oligomer, and during the polycondensation reaction when component (III) is added. It is preferable to add.

Any catalyst can be used for these reactions as required, and among them, as the catalyst used for the transesterification reaction, alkaline earth metal salts such as magnesium and calcium, titanium, zinc, manganese, etc. These metal compounds are preferably used, and germanium compounds, antimony compounds, titanium compounds, cobalt compounds, and tin compounds are preferably used as the polycondensation catalyst.
The amount of the catalyst used is not particularly limited as long as it is a necessary amount for proceeding the transesterification reaction and polycondensation reaction, and a plurality of catalysts can be used in combination.

  In addition, as stabilizers, phosphate esters such as trimethyl phosphate, triethyl phosphate and triphenyl phosphate, phosphites such as triphenyl phosphate and trisdodecyl phosphate, methyl acid phosphate, dibutyl phosphate, monobutyl phosphate It is preferable to use a phosphorus compound such as acidic phosphoric acid ester, phosphoric acid, phosphorous acid, hypophosphorous acid, or polyphosphoric acid.

  The transesterification reaction catalyst can be supplied at the initial stage of the transesterification reaction in addition to the preparation of the raw material. The stabilizer can be supplied before the beginning of the polycondensation reaction, but it is preferably added at the end of the transesterification reaction. Furthermore, the polycondensation catalyst can be supplied by the early stage of the polycondensation reaction step.

  The reaction temperature during the transesterification reaction is usually 200 to 260 ° C., and the reaction pressure is normal pressure to 0.3 MPa. The reaction temperature during polycondensation is usually 250 to 300 ° C., and the reaction pressure is usually 50 to 200 Pa. Such a transesterification reaction and polycondensation reaction may be performed in one stage or in multiple stages.

The above polymer is then fiberized by a conventional method to form a nonwoven fabric or formed into a film shape.
Here, as a nonwoven fabric, what was manufactured by the conventionally well-known arbitrary methods including the electrospin method is mentioned, Among these, the nonwoven fabric obtained by the melt blow method is illustrated preferably.

In the melt-blowing method, a molten polymer is usually discharged from a plurality of spinning holes arranged side by side in the width direction of the die such as a T-die, and at the same time, a high-temperature and high-speed gas flow is generated from slits provided adjacent to both sides of the die. This is a method for obtaining a sheet-like material by depositing ultrafine fibers formed by thinning a polymer discharged by jetting on a moving air-permeable collecting surface.
In this method, a fine fiber can be easily obtained, and a molten polymer can be directly formed into a sheet, so that a nonwoven fabric can be most suitably obtained.

  Further, the spinning conditions will be described in detail. The polymer melt viscosity is preferably 100 poise or more and 3000 poise or less, and more preferably 500 poise or more and 2000 poise or less. If the melt viscosity is too low, yarn breakage tends to occur, and polymer balls tend to be generated at the same time, and the uniformity of the fiber diameter also deteriorates. On the other hand, if the melt viscosity is too high, it is difficult to reduce the fiber diameter.

  The spinning temperature of the polymer is preferably the melting point of the polymer + [10 ° C. or higher and 100 ° C. or lower], and it is preferable to lower the viscosity at a temperature as high as possible within the range where the polymer is not thermally decomposed and the process condition is stable. If the temperature is too high, the melt viscosity becomes high, which is not preferable. If the temperature is too high, thermal decomposition tends to occur, and long-term operation stability decreases.

The high-temperature and high-pressure gas that pulls and thins the discharged polymer is preferably air or water vapor. If the temperature of the traction gas is too far from the spinning temperature of the polymer, the temperature of the discharged polymer will be affected. Therefore, the [polymer spinning (melting) temperature −10 ° C.] or higher and the [polymer melting point + 100 ° C.] or lower [Spinning temperature of polymer + (10 to 50 ° C.)] is preferable. Moreover, what is necessary is just to determine a gas flow rate suitably with the target fiber diameter, discharge amount, and an adhesion state. At this time, although depending on the ejection slit width of the gas flow, a preferable flow rate is 0.01 to 0.2 Nm ³ / min per 1 cm of the base width. If the flow rate is less than 0.01 Nm ³ / min, the thinning does not proceed sufficiently, and the resulting non-woven fabric spots also increase. On the other hand, if the flow rate exceeds 0.2 Nm ³ / min, depending on the slit width and discharge amount, The fiber breakage is excessive and undesirable.

  The fiber group discharged from the spinning hole and drawn and refined by the high-temperature and high-pressure gas is deposited on a collecting surface such as a net having suction, and is obtained as a sheet-like material, that is, a nonwoven fabric. In this case, the distance between the lower surface of the base and the collecting surface is preferably lower than the position where the fibers are solidified, so that the fibers do not adhere more than necessary and the nonwoven fabric texture does not become hard. However, if the collecting surface is located too low, the fiber flow is disturbed by the jet gas flow or the accompanying flow, and the fibers are entangled in a bundle to cause a non-woven fabric spot. A preferable distance between the lower surface of the base and the collecting surface is 10 to 80 cm.

  The nonwoven fabric is preferably used in which the fibers are fused to each other at at least one location, and the thickness of the nonwoven fabric is 0.1 μm to 1000 μm. Furthermore, the range of preferable thickness is 0.5 micrometer-500 micrometers, Most preferably, it is 1-250 micrometers.

  On the other hand, the film shape may be formed by melt-forming or solution-casting the polymer. Specifically, the film is formed by extrusion from a casting die such as an I die or T die through an extruder such as a ruder. A method for forming a product or the above-described polymer may be dissolved in a solvent and cast on a plate, and then the solvent may be evaporated and dried.

Moreover, the film obtained as needed may be stretched, and may be further subjected to heat treatment with or without applying any tension after stretching.
The thickness of the film is preferably 0.1 to 500 μm.

The electrochemical element of the present invention includes a negative electrode, a positive electrode, a separator, and an electrolyte, and the separator uses the separator according to claim 1 of the present invention.
Here, as the electrolyte, the negative electrode, and the positive electrode, any of those that can be normally used in conventional electrochemical devices can be used.

There is no limitation in particular as a manufacturing method of the electrochemical element of this invention, All well-known methods are employable.
Specifically, a method is generally used in which a joined body in which a positive electrode and a negative electrode are joined via a separator of the present invention is placed in an exterior, an electrolyte is injected, and then sealed.
The shape of the electrochemical element thus obtained is not particularly limited, and may be any shape such as a cylindrical shape, a flat shape such as a square shape, and a button shape.

Further, if necessary, the separator of the present invention can be used by laminating, laminating, etc., with a film-like porous material such as a microporous membrane and a nonwoven fabric as a support. It can be set as the separator which has intensity | strength. In this case, the separator of the present invention may be laminated only on one side of the support, but lamination on both sides of the support is also preferably performed. Moreover, an electrode can also be used as a support body of a separator as it is.
Examples of the exterior include, but are not limited to, a steel can, a pack made of aluminum, and a pack made of an aluminum laminate film.

  Hereinafter, an example is given and the composition and effect of the present invention are explained in detail. In addition, the physical property in an Example is measured with the following method.

(1) Moisture absorption / release coefficient MR
After measuring the moisture absorption M ₁ (%) after leaving the nonwoven fabric in a 95% RH atmosphere at 35 ° C. for 360 minutes, the moisture absorption M after leaving the sample in a 65% RH atmosphere at 20 ° C. for 90 minutes. ₂ (%) is measured, and the moisture absorption / release coefficient MR is calculated by the following formula (1).
MR = (M ₁ ) − (M ₂ ) (1)
Here, M ₁ is the moisture absorption rate (%) after leaving the sample in a 95% RH atmosphere at 35 ° C. for 360 minutes, and M ₂ is the sample being left in a 65% RH atmosphere at 20 ° C. for 90 minutes. It represents the subsequent moisture absorption rate (%).

(2) Retainability of electrolyte solution The mass of a sample cut to a size of 15 cm x 10 cm was measured, and then immersed in the electrolyte solution for 1 minute, and then the sample was taken out and suspended with tweezers. When the electrolytic solution stopped dripping, the mass of the sample was measured, and the electrolytic solution retention rate (%) with respect to the weight of the separator was determined from the mass difference before and after the immersion. The electrolyte prepared by the operation of Reference Example 3 was used.

(3) Liquid absorption speed of electrolyte solution The height of the electrolyte solution sucked into the sample when the sample cut to a size of 20 mm in width and 150 mm in length is hung and the lower end 10 mm is immersed in the electrolyte solution for 1 minute. Measurement was made to be the liquid absorption speed (mm / min) of the electrolytic solution. The electrolytic solution prepared by the operation of Reference Example 3 was used.

[Example 1]
(A) Production of polymer 90 parts by weight of dimethyl terephthalate, 68 parts by weight of tetramethylene glycol, 20 parts by weight of ethylene glycol, 16 parts by weight of 5-sodium sulfoisophthalic acid (component (A)) and polyethylene glycol (molecular weight: 4000) ) 106 parts by weight (component (B)) was used as a transesterification reaction catalyst, manganese acetate tetrahydrate, and by-produced methanol was distilled out of the system to carry out the transesterification reaction.

Furthermore, after adding germanium dioxide as a polymerization catalyst, a transesterification reaction was carried out while heating to 285 ° C., and when methanol was almost completely distilled off, orthophosphoric acid as a stabilizer and benzoic acid as a crystallization accelerator. 1% by weight of sodium acid (component (C)) was added to complete the transesterification reaction.
Next, the reaction product was subjected to a polycondensation reaction under high temperature and high vacuum to obtain a polyester polymer having an intrinsic viscosity of 0.82, a terminal carboxyl group concentration of 45 eq / ton, and a melt viscosity of 180 Pa · S.

(B) Production of nonwoven fabric as separator The polyester polymer was dried at 130 ° C. for 23 hours, melted at 260 ° C. by a melt blow method, and then discharged at a pack temperature of 245 ° C., a pack pressure of 7.1 MPa, and hot air of 185 ° C. After stretching and thinning, the particles were collected on a collection net provided 20 cm below the base. The moisture absorption after the polyester fibers constituting the obtained nonwoven fabric were allowed to stand at 35 ° C. for 360 minutes in a 95% RH atmosphere was 36%. Moreover, the moisture absorption / release coefficient MR of the obtained nonwoven fabric was 24. Moreover, the retention property of electrolyte solution was 200%, and the liquid absorption rate of electrolyte solution was 20 mm / min. The nonwoven fabric had a thickness of 201 μm.

[Comparative Example 1]
In Example 1, except having not added polyethyleneglycol, it implemented like Example 1 and obtained the nonwoven fabric.
The moisture absorption after the polyester fibers constituting the obtained nonwoven fabric were allowed to stand at 35 ° C. for 360 minutes in a 95% RH atmosphere was 1.5%. Moreover, the moisture absorption / release coefficient MR of the obtained nonwoven fabric was 0.3. Further, the retention of the electrolytic solution was 40%, and the liquid absorption rate of the electrolytic solution was 15 mm / min. The nonwoven fabric had a thickness of 200 μm.

[Reference Example 1] Preparation of electrode (positive electrode):
The lithium cobalt oxide (LiCoO ₂ manufactured by Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by mass, acetylene black 4.5 parts by mass, and 6% by mass PVdF N- A positive electrode paste was prepared using a methyl-pyrrolidone (NMP) solution. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.

[Reference Example 2] Preparation of electrode (negative electrode):
As a negative electrode active material, an NMP solution of 6% by mass of PVdF was used so that 87 parts by mass of mesophase carbon microbeads (manufactured by Osaka Gas Chemical Co., Ltd.), 3 parts by mass of acetylene black, and 10 parts by mass of PVdF were dried. A negative electrode paste was prepared. The obtained paste was applied to a 18 μm thick copper foil, dried and pressed to obtain a 90 μm thick negative electrode.

[Reference Example 3] Preparation of electrolyte solution:
The electrolytic solution was prepared by dissolving lithium hexafluorophosphate at a concentration of 1M in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a weight ratio of 3: 7.

[Example 2]
When a lithium ion secondary battery was manufactured using the separator manufactured by the operation of Example 1, the electrode prepared in the above reference example, and the electrolytic solution, the battery operated well.
Similarly, when a nickel-metal hydride battery and an electric double layer capacitor were manufactured using the separator manufactured by the operation of Example 1, both worked well.

Claims (8)

The separator for electrochemical devices whose moisture absorption-release coefficient MR represented by following formula (1) is 10 or more.
MR = (M ₁ ) − (M ₂ ) (1)
Here, M ₁ is the moisture absorption rate (%) after leaving the sample in a 95% RH atmosphere at 35 ° C. for 360 minutes, and M ₂ is the sample being left in a 65% RH atmosphere at 20 ° C. for 90 minutes. It represents the subsequent moisture absorption rate (%). It is formed from a polyester polymer in which an alkylene terephthalate is a main repeating unit and an organic sulfonic acid metal salt (A) represented by the following formula (I) and a polyalkylene glycol (B) represented by the following formula (II) are copolymerized. The separator according to claim 1.

The separator of Claim 2 formed from the polymer by which the organic carboxylic acid metal salt (C) shown by following formula (III) is further mix | blended with the said polymer.

  The separator according to claim 2 or 3, wherein the polymer according to claim 2 or 3 has a fiber shape.   The separator according to claim 4, wherein the polymer according to claim 2 or 3 is in the form of a nonwoven fabric.   The separator according to claim 5, wherein the nonwoven fabric according to claim 2 or 3 is produced by a melt blow method.   The separator according to claim 2 or 3, wherein the polymer according to claim 2 or 3 is in the form of a film.   An electrochemical element comprising a negative electrode, a positive electrode, a separator and an electrolyte, wherein the separator according to claim 1 is used as the separator.