JPH11162441A - Separator for battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator with long life and high fineness by forming aggregation parts of silica family compound particles in pores of net structure parts comprising a polyethylene porous structure having the specified porosity, and continuing the gaps formed between the aggregated particles to openings on the surface of the porous structure through the net structure parts so that an electrolyte can be permeated. SOLUTION: A porous structure 1 constituting a separator consists mainly of a polyethylene net structure 2 having a porosity of 20-70% as a whole, silica family compound particles 4 are aggregated in pores 3, and gaps formed between the particles 4 continue to openings formed on the surface of the porous structure 1 through the net structure 2. The particles 4 are aggregated in the pores 3 of the polyethylene net structure 2, and the gaps formed between the particles 4 become the flow path of an electrolyte, the polyethylene does not directly expose to the electrolyte, the polyethylene is prevented from deterioration, and the life of the separator can be lengthened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator.

[0002]

2. Description of the Related Art A battery separator is provided to prevent a short circuit between a positive electrode and a negative electrode and to keep the interval between the electrodes constant, so that an electrolyte can flow smoothly between the two electrodes. In this case, a structure made of a porous structure is used. Currently, there are various porous structures,
In batteries, there are compounds with strong oxidizing power,
It is necessary to select a material having acid resistance as a material for the separator. As such a material, a ceramic material is typical as a material having acid resistance, but there is a problem that the mass is large and the material is easily cracked. Therefore, an inexpensive plastic material having good moldability is used as an alternative. Of these plastic materials, polyethylene and fluororesins are not as acid resistant as ceramic materials, but can withstand use in batteries, so porous structures using these polymer materials have been proposed. I have. Above all, polyethylene is inexpensive and easier to mold than a fluororesin, and therefore a porous structure made of polyethylene is mainly used as a battery separator.

The battery separator is made of polyethylene 1
30 to 500 parts by weight of a liquid compound selected from a plasticizer such as paraffin or dioctyl phthalate (DOP) and 20 to 200 parts by weight of a silicon oxide-based compound powder for imparting hydrophilicity to 00 parts by weight 130 to 25 parts
After mixing and molding in a temperature range of 0 ° C., the mixture is immersed in an organic solvent to extract a liquid compound.
It is a porous structure of 0 to 70%. According to a schematic diagram obtained by observing the cross section of this porous structure with an electron microscope, the one using paraffin as the plasticizer has a mesh-like cross-sectional structure having closed voids 13 as shown in FIG. The one using dioctyl phthalate as the agent has a sectional structure having a tomographic void 23 as shown in FIG. Polyethylenes 12 and 22 have randomly formed voids 13 and 23
To form a mesh-like porous structure, and voids 13 and 23
Inside, primary particles 14, 24 of silica as a powder of a silicon oxide-based compound are agglomerated. The silica primary particles 14, 24 and polyethylene 1 in the voids 13, 23
The gap between the first and second substrates 22 and 22 forms a structure that serves as a flow path for the electrolytic solution.

The mechanism for forming this structure is that polyethylene and the liquid compound are compatible with each other at the time of mixing and molding, and secondary or tertiary silica particles (so-called aggregated particles) that are aggregated at the time of mixing and molding. ) Is crushed, and if the liquid compound is lost by the above extraction, a gap is formed due to the lack of affinity between polyethylene and silica.

[0005]

The above-mentioned conventional battery separator has a disadvantage that its life is short because polyethylene, which is a polymer material, is attacked and deteriorated by an electrolytic solution. In other words, the conventional separator, as described above,
Since the gap between the silica and the polymer material has a structure in which the electrolyte flows, the polyethylene constituting the skeleton is easily exposed to the electrolyte and deteriorates. Therefore, in order to prolong the life by delaying the deterioration due to the electrolyte, a structure in which polyethylene is not exposed in the flow path of the electrolyte has been desired.

Further, in the conventional separator, the size of the gap, which is the flow path of the electrolytic solution, is several hundred nm, and it has been desired to introduce a prescription for making the flow path of the electrolytic solution more highly minute and taking measures. Therefore, the present invention provides a battery having a structure in which polyethylene, which is a polymer material, is not exposed in an electrolyte solution flow path, and has a longer life with a highly fine electrolyte solution flow path (electrolyte). It is an object of the present invention to provide a novel battery separator which is highly refined and a method for manufacturing the same.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found a battery separator which is practically desirable, and have completed the present invention. That is, the invention according to claim 1 has a total porosity of 20%.
About 70% of a porous structure, having aggregated portions of silicon oxide-based compound particles in the voids of the network structure portion made of polyethylene, and the gaps between the aggregated particles are formed through the network structure portion. Communicating with the opening formed on the surface of the porous structure,
This is a battery separator (hereinafter, abbreviated as “separator”) having a structure through which an electrolyte passes through the passage. In other words, since the secondary particles or tertiary particles of silica as the silicon oxide-based compound are dispersed without being pulverized,
Polyethylene that forms the skeleton is covered by silica and the exposed area in the void is reduced, so that the life is extended,
In addition, the gap between the primary particles can be highly refined to about several tens of nm.

[0008] The invention described in claim 2 is the first invention.
Wherein the silicon oxide compound particles have a flow start temperature or a freezing point of 1
A liquid compound having a decomposition point and a boiling point of not less than 0 ° C. and a melting point of not less than 150 ° C. and incompatible with polyethylene (hereinafter, referred to as “polyethylene”);
Abbreviated as liquid agent. ), The mixture is subjected to a crush prevention treatment, then mixed with polyethylene, molded at a temperature of 200 ° C. or lower, and finally the liquid agent is extracted and removed. In other words, when agglomerated particles of a silicon oxide-based compound such as silica are dispersed in a polymer material, the agglomerated particles are pulverized to the level of primary particles by shearing during processing. The knowledge that, if a liquid agent is included in the particles, the liquid agent can be protected, and if a liquid agent that is incompatible with the polymer material is selected, the liquid agent is not lost from the aggregated particles and the protective action continues. It was made based on it.

Next, the invention according to claim 3 is based on claim 2
In a preferred embodiment of the method for producing a separator according to the present invention, the silicon oxide-based compound is equivalent to 10 to 100 volumes with respect to 100 volumes of polyethylene, and the liquid agent 25 is equivalent to 100 volumes of silicon oxide-based compound and polyethylene in total.
It is a method of blending up to 230 volumes. The invention described in claim 4 is a preferred embodiment of the method for producing a separator according to claim 2 or 3, wherein a polyester-based oligomer is used as a liquid agent.
Furthermore, the invention according to claim 5 is another preferred embodiment of the method for producing a separator according to claim 2 or 3, wherein the liquid agent is polyethylene glycol having a molecular weight of 700 or less, and the liquid agent is based on 100 parts by weight of the polyethylene glycol. To add a surfactant or an alkyl silane compound to 0.1.
This is a method in which 1 to 3.0 parts by weight is added.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the separator of the present invention will be described in detail. FIG. 1 is a schematic explanatory view showing a porous structure used in the present invention. As shown in this figure, the porous structure 1 constituting the separator has a total porosity of 20 to 70% mainly composed of polyethylene 2 having a network structure, and the silicon oxide compound Are agglomerated, and the gap between these particles 4 is connected to the opening formed on the surface of the porous structure 1 via the network structure. In particular, agglomerated particles are formed in the voids 3 of the polyethylene 2 and the gaps between the particles form a flow path for the electrolytic solution, so that the polyethylene is not directly exposed. Can be measured.

Next, the silicon oxide-based compound, liquid agent and polyethylene used in the production of the separator of the present invention will be described. Examples of the silicon oxide-based compound used in the present invention include silica, glass (powder), quartz (powder) and the like, and mainly silica is used, including synthetic silica such as wet silica or dry silica, Fine powder of natural silica such as silica sand may be used. Among them, synthetic silica composed of fine powder that easily aggregates is suitable, but wet silica having particularly high cohesiveness is preferably used. In this synthetic silica, usually, individual particles of several tens nm to several hundreds nm, that is, primary particles are aggregated to form aggregated particles of secondary particles or tertiary particles of approximately several μm. The aggregated particles have a gap of about several tens nm, and the present invention is characterized in that the gap is used as a solvent flow path. The particle size of the primary particles of this silica is 1 μm.
If it exceeds m, it is not preferable because the gap to be formed is not complicated, and the particle size is desirably small. However, the primary particle of the wet silica preferably has an average particle size of about several tens nm to 100 nm.

The liquid agent used in the present invention is a material to be added for delaying the pulverization of the aggregated silica particles due to shearing during mixing and molding, that is, for the purpose of preventing crushing. Extract and remove with. This liquid material has a flow start temperature or freezing point of 10 ° C. or less,
It is selected from those having a decomposition point and a boiling point of 150 ° C. or higher and having no compatibility with polyethylene. The former “flow starting temperature or freezing point is 10 ° C. or less” is a condition for preventing inconvenience such that a liquid material is easily broken when solidified when stored in a state of a semi-finished product before extraction. In other words, the semi-finished product before extraction is in a state in which the liquid agent is blended, but when it is solidified, it tends to break. The flow start temperature or freezing point of the liquid agent in the present invention must be 10 ° C or lower, and preferably 0 ° C or lower. The latter "having a decomposition point and a boiling point of 1
“50 ° C. or higher” is a condition for matching with the thermal characteristics such as the molding temperature of polyethylene. Considering the effect on the working environment due to the volatilization during mixing with polyethylene performed under heating, the lower the volatility, the better the decomposition point and boiling point in the present invention are 180 ° C or more. Also,
The fact that the liquid agent is not compatible with the polyethylene means that the selected liquid agent and polyethylene do not become one phase even if they are mixed at room temperature or high temperature. Is not taken into account. The liquid agent in the present invention is not particularly limited as long as it is incompatible with polyethylene, and may be one type or a mixture of two or more different types.

Examples of the liquid agent for satisfying the above selection criterion include a single molecule having a high polarity and an oligomer. Among them, it is particularly preferable to use a polyester oligomer and a polyethylene glycol. The reason for this is that if a single molecule liquid such as a phthalate plasticizer or an adipic ester plasticizer is used, it will not be compatible with polyethylene, so it will not evaporate and will be volatilized without loss of porosity. This is because the use of the oligomer reduces the volatility, so that such a problem hardly occurs. Among the above oligomers, polyester oligomers are particularly inexpensive, and are effective in reducing the production cost.

The polyester oligomer used in the present invention includes a sebacic polyester, an adipic polyester, a phthalic polyester and the like having a molecular weight of 10 ² to 10 ² .
And those in the range of 10 ⁴ . At present, polyester-based oligomers are used as plasticizers for polyvinyl chloride and various rubbers, and those having various viscosities depending on the molecular weight of the polyester are used. In the present invention, the solubility parameter (hereinafter referred to as S
P value) is about 8.5 to 10.0, and is excellent in wettability with polyethylene (SP value is about 8.0).
However, since this oligomer and polyethylene are incompatible even at high temperatures, they are suitable as a liquid agent in the present invention. In addition, these polyester-based oligomers all have a flow onset temperature of −5 ° C. or lower and a decomposition point of more than 220 ° C., and therefore are suitable as the liquid agent of the present invention also in terms of thermal properties. In the present invention, the polyester-based oligomer includes:
There is no particular limitation on the type, and one type or a mixture of many types may be used.

[0015] On the other hand, polyethylene glycol is water-soluble and biodegradable, and can use water without using an organic solvent as an extraction means. Is excellent. This polyethylene glycol preferably has a molecular weight of 700 or less, and if the molecular weight exceeds 700, the flow start temperature exceeds room temperature, and is not suitable as a liquid agent in the present invention. Also,
Those having a molecular weight of 300 have the highest decomposition point of 186 ° C., and when the molecular weight exceeds 300, the decomposition point gradually decreases. This decomposition point can be raised by about 20 to 30 ° C. by adding an antioxidant such as methyl ether of hydroxyquinone or hydroxyanisole, and this formula may be introduced in the present invention.

Further, polyethylene glycol has an SP value of about 11.0 and is very difficult to mix with polyethylene. Therefore, anionic surfactants such as fatty acid soaps and metal salts of alkylbenzene sulfonic acids, and ether type ,
Addition of a nonionic surfactant such as an alkylphenol type, a cationic surfactant such as a methyl type or a benzyl type, or an alkyl-based silane compound facilitates mixing. It is important to add a surfactant or an alkyl silane compound. If the amount of the surfactant or the alkyl-based silane compound is less than 0.1 part by weight with respect to 100 parts by weight of polyethylene glycol, mixing cannot be performed easily. Therefore, the content is disadvantageous in terms of cost, so the range is preferably 0.1 to 3 parts by weight, more preferably 1 part by weight.

The treatment for preventing crushing of the silicon oxide-based compound, particularly silica, in the present invention includes a method of impregnating aggregated particles of silica with a liquid agent and a method of coating aggregated particles of silica with a liquid agent. Is appropriately selected in accordance with the viscosity of the polymer. The former impregnation methods are dioctyl phthalate (DOP) and diisononyl phthalate (DIN).
P), polyethylene glycol and the like having a viscosity of 10 poise or less are suitable, and the mixing is performed with a liquid agent having an oil absorption of silica (weight at which the silica powder per unit weight absorbs the liquid agent to be mixed). . For the latter coating method, a liquid material having a high viscosity of 50 poise or more such as adipic acid polyester having a high molecular weight is suitable, and a liquid material having an oil absorption of silica or more is mixed.

As the polymer material used in the present invention, polyethylene suitable as a separator has been conventionally used.
Examples of the polyethylene include low-density polyethylene, high-density polyethylene (including ultrahigh-molecular-weight polyethylene having a molecular weight of 500,000 or more), and linear low-density polyethylene. Such polyethylene can be freely selected from the viewpoint of processability, physical properties, and the like, but high-density polyethylene having excellent bromine resistance is desirable. Further, in the present invention, one kind of the above-mentioned polyethylene or a mixture of many kinds thereof may be used.

Next, the compounding amount of the silicon oxide-based compound, silica, polyethylene and the liquid agent used in the present invention is preferably in the range of 10 to 100 volumes of silica, more preferably in the range of 30 to 100 volumes, for 100 volumes of polyethylene. 7
A range equivalent to 0 volumes is preferable. If the blending amount of the silica is less than 10 volumes, the separator becomes non-hydrophilic, and if it exceeds 100 volumes, mixing becomes difficult, and the physical properties deteriorate. The amount of the liquid agent is one of the requirements for determining the pore diameter and porosity of the separator, and the amount of the agent is preferably in the range of 25 to 230 volumes corresponding to a total of 100 volumes of silica and polyethylene. . This range is about 20-70 when the liquid is extracted.
% Of the liquid material for forming the porous structure having a porosity of%. If this value is less than 25 volumes, the flow path of the electrolytic solution inside the separator will not be in communication. Conversely, if it exceeds 230 volumes, it will be difficult to mix and the physical properties will be reduced. In a range of about 230 volumes, preferably in a range of about 40 to 185 volumes (the amount of the liquid agent for forming a porous structure having a porosity of about 30 to 65% when the liquid agent is extracted). is there.

In the separator of the present invention, a porous structure can be obtained by forming a matrix composed of polyethylene, silica as a silicon oxide-based compound and a liquid agent and then extracting the liquid agent in the matrix with a solvent.
The manufacturing process is as follows. The first step is a step for obtaining silica impregnated or coated with the liquid agent. Such silica is obtained by mixing with a liquid agent using a kneading device such as a kneader or a stirrer. In this step, kneading conditions such as a kneading apparatus and a temperature are not particularly limited and can be freely selected. However, a device using a roll is unsuitable because a shear force acts on the material to be kneaded, and secondary or tertiary particles formed by agglomeration of primary particles of silica are pulverized. Even for devices that do not work, it is undesirable to knead for a long time.

As described above, the mixing ratio of the silica and the liquid agent depends on the type of the liquid agent to be kneaded, particularly the viscosity, and thus the oil absorption varies depending on the viscosity. Therefore, whether the liquid agent is impregnated or coated is determined. The mixing ratio of the solution and the liquid agent may be appropriately determined depending on the convenience of the subsequent steps. When the polyethylene to be used is a powder, in the mixing step, the three components of polyethylene, silica and the liquid agent can be simultaneously mixed.

The second step is a step of obtaining a matrix consisting of polyethylene, silica and a liquid agent.
This matrix can be obtained by kneading using a kneader such as a kneader, an extruder, or a two-roll mill under a temperature condition not lower than the melting point or softening point of polyethylene. At this time, if a kneading machine such as extrusion or two rolls is used, molding can be performed simultaneously with kneading.

The third step is a molding step in which the mixture is processed into a flat sheet, a sheet having irregularities, or a molded article having a predetermined shape. In this step, molding is performed simultaneously with kneading in the second step,
If a desired shape is obtained, it may be omitted. In this step, processing such as embossing, pressing, and rolling is performed. The method for forming the separator of the present invention is not particularly limited, and may be appropriately selected according to the application. In addition, a glass net, a frame, or the like may be integrated and strengthened.

The fourth step is a step of extracting a liquid preparation, which is essentially carried out by immersion in a solvent. In this case, in order to extract a liquid agent other than polyethylene glycol, toluene, hexane, xylene, various alcohols, rubber volatile oil, and the like can be mentioned. An appropriate selection may be made in consideration of the above.
On the other hand, in order to extract polyethylene glycol, extraction with water is good in terms of workability, but extraction with water may be performed more quickly.

In the present invention, there is no particular limitation on the extraction method, and the extraction may be performed by a commonly used method. In addition, although drying is required after the extraction, a means of natural drying or a means of forced drying by heating or blowing may be used. Further, post-processing such as cutting and drilling may be optionally performed as necessary.

[0026]

Next, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1, Comparative Example 1 Using a pressure kneader at room temperature,
The average particle size of the primary particles is 16 nm, and the average particle size of the aggregated particles is 9
μm wet silica particles: Nip Seal LP (trade name, manufactured by Nippon Silica Industry Co., Ltd.) was mixed with each of the five types of liquid agents shown in Table 1 and subjected to a crush prevention treatment. Next, polyethylene: HIZEX 5000S (trade name, manufactured by Mitsui Petrochemical Industry Co., Ltd.) using two rolls whose temperature was controlled to about 160 ° C.
When the above kneaded material was mixed and dispersed in 100 parts by weight, five types of white sheet materials shown in Table 1 each having a thickness of about 1 mm were obtained. In addition, 3 which shows incompatibility with the above polyethylene
The liquids of the species (Sample Nos. 1-1, 1-2, and 1-3) were selected according to the prescription of the present invention. 1-
The liquid preparation of 5) was selected according to a conventional formulation, and these were used as comparative examples. In this sheet-like material, silica is equivalent to about 50 volumes with respect to 100 volumes of polyethylene. If the total of both is equivalent to 100 volumes, the liquid agent is equivalent to about 120 volumes, and about 55% of the liquid agent is extracted. The composition is such that a porous body having a porosity can be obtained. When a test on the life of the separator was performed by the following evaluation method, the results were as shown in Table 2. When the state of the cross section was observed with an electron microscope, Nos. 1-1, 1-2, and 1-3 have fine structures as shown in FIG. No. 1-4 is a fine structure as shown in FIG. 1-5 had a fine structure as shown in FIG.

<Test on the Life of the Separator> As a condition for accelerated deterioration, the separator was exposed to H ₂ SO ₄ (conk) at room temperature for one week, and the physical properties at the initial stage and after the exposure were compared and evaluated. The evaluation of the physical properties was made based on the tensile strength at break and elongation. Change rate of physical property [%] = 100− (initial physical property ÷ physical property after accelerated deterioration) × 100

[0028]

[Table 1]

[0029]

[Table 2]

As is evident from the results, the separator according to the present invention was able to delay the deterioration due to the electrolytic solution and achieve a long life, and exhibited a remarkable improvement in miniaturization.

Example 2 Using a pressure kneader at room temperature, polyethylene glycol: PEG having a molecular weight of 300
# 300 (trade name, manufactured by NOF Corporation), 100 parts by weight, primary particles having an average particle size of 16 nm, and aggregate particles having an average particle size of 9
μm wet silica particles: Nip Seal LP (same as above) 50
Alkylbenzenesulfonic acid-based (ABS-based) surfactant: Oarai A (Nippon Oil & Fat Co., trade name), nonionic surfactant: Nonion S-220 (Nippon Oil & Fat Co., product; Name), higher alkyl silane: KBM
-6000 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) was obtained to obtain a kneaded product having the compounding composition shown in Table 3.

[0032]

[Table 3]

Next, using the two rolls of the above seven kinds of kneaded material, the temperature of which was adjusted to about 160 ° C., using polyethylene: HIZEX 5000S (same as above) 100
Kneaded with parts by weight. At this time, No. 2-4, 2-5,
When kneaded, Nos. 2-6 and 2-7 lost unity and could not be formed into sheets. 2-1, 2-2, 2-3
From this, a white sheet having a thickness of about 1 mm could be obtained. No. The sheet material obtained from 2-1 2-2, 2-3 is immersed in purified water treated with an ion-exchange filter for 3 hours, taken out, allowed to stand at room temperature for 24 hours, and further heated with a hot air dryer. To obtain a white opaque sheet. Observation of the cross section of this sheet-like material with an electron microscope revealed that the sheet had a structure having a solvent flow path composed of aggregated silica particles as shown in FIG.

[0034]

According to the separator of the present invention, it is possible to provide a novel separator which has a long service life and a high degree of miniaturization in a battery.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing a porous structure used in the present invention.

FIG. 2 is an explanatory view schematically showing a porous structure conventionally used.

FIG. 3 is an explanatory view schematically showing another porous structure conventionally used.

[Explanation of Signs] 1 ... porous structure 2, 12, 22 ... polyethylene 3, 13, 23 ... void 4, 14, 24 ... particles

Claims (5)

[Claims] 1. A porous structure having an overall porosity of 20 to 70%, wherein silicon oxide-based compound particles have agglomerated portions in voids of a network structure portion made of polyethylene. Wherein the gap communicates with the opening formed on the surface of the porous structure through the mesh structure, and the electrolyte permeates through the passage. 2. A method for preventing crushing by mixing a liquid compound having a flow start temperature or a freezing point of 10 ° C. or lower, a decomposition point and a boiling point of 150 ° C. or higher, and incompatible with polyethylene, to silicon oxide-based compound particles. A method for producing a battery separator, comprising: subjecting the mixture to polyethylene, molding the mixture at a temperature of 200 ° C. or lower, and finally extracting and removing the liquid compound. 3. With respect to 100 volumes of polyethylene,
3. The battery separator according to claim 2, wherein the amount of the silicon oxide-based compound is from 10 to 100 volumes, and the amount of the liquid compound is from 25 to 230 volumes based on the total of 100 volumes of the silicon oxide-based compound and the polyethylene. Manufacturing method. 4. The method for producing a battery separator according to claim 2, wherein the liquid compound is a polyester oligomer. 5. The liquid compound is polyethylene glycol having a molecular weight of 700 or less, and 0.1 to 3.0 parts by weight of a surfactant or an alkyl silane compound is added to 100 parts by weight of the polyethylene glycol. A method for producing the battery separator according to claim 2 or 3.