JP5153101B2 - Separator and manufacturing method thereof - Google Patents

Description

  The present invention relates to a fabric separator made of thermoplastic fibers containing a large amount of inorganic powder and a method for producing the same, and is suitably used in the field of separators for capacitors such as batteries or capacitors.

In capacitors such as batteries or capacitors, short-circuiting between both electrodes is prevented by placing a separator as an electrical insulator between the positive electrode and the negative electrode. Conventionally, separators using capacitors such as paper, non-woven fabric, glass fiber, and porous membrane are known. As separators, ion permeability and electronic insulation are required to function without problems during the use of capacitors for a long period of time, and in addition, those that satisfy the capacity and cost of the capacitors have been selected.
For example, a lithium ion battery has a basic structure in which lithium cobaltate is used for a positive electrode, a graphite-based carbon electrode is used for a negative electrode, and a polyethylene porous film is disposed between both electrodes as a separator, and this basic structure is wound or stacked. It is known that a laminated body is formed, inserted into a metal can body or a film packaging body, injected with an organic electrolyte, and sealed to form a battery.

In general, an insulating organic substance, an insulating inorganic substance, or the like is used as an electronic nonconductor that provides insulation, which is a necessary condition of the separator. In the case of a lead storage battery, a glass fabric or a porous sheet obtained by mixing polyethylene and inorganic powder is used as a separator in dilute sulfuric acid electrolyte.
In a nickel cadmium battery, a polyamide nonwoven fabric that is excellent in insulation and ion permeability is generally used as a separator in an alkaline electrolyte using a caustic potash aqueous solution as an electrolyte. As described above, the separator is required to be electrochemically stable because the material and shape used depend on the type of electrode and the type of electrolyte.

Lithium-ion batteries, which are world-class for mobile communication devices and have proven to be compact and lightweight, are being considered for larger driving power sources for automobiles based on their track record. Safety measures are also important because the number of batteries used per unit increases.
Lithium ion batteries use a lithium compound as an electrode active material and a flammable organic solvent as an electrolyte, and are concerned about heat generation due to some factors, and are required to have a high safety function. As a safety problem of a battery using a flammable organic solvent as an electrolytic solution, battery heat generation due to a short circuit or the like can be mentioned. For example, when a battery circuit is short-circuited, that is, a state called a battery external short circuit, a large current flows and the battery itself generates heat due to the internal resistance of the battery, or the positive electrode due to some reason inside the battery. A case where the negative electrode is short-circuited, that is, when heat is generated due to a short-circuit inside the battery, can be mentioned. For these battery heat generation, safety measures have been taken assuming various causes.

For example, the PTC element that detects heat transmitted to the battery can due to the heat generated by the battery and shuts off the battery circuit when the temperature rises above the set value, or the safety valve provided in the can is activated to increase the pressure inside the battery due to heat generation. ing. In addition, even if the circuit outside the battery is shut off when the internal short circuit occurs, the internal battery circuit cannot be shut off, and there is a possibility that thermal escape will occur, but as a safety measure at this time, the separator characteristics will greatly contribute. .
Currently, a separator of a lithium ion battery generally uses a microporous membrane made of polyolefin in order to satisfy the required basic performance of electron non-conductivity, ion permeability, and electrochemical stability in an electrolytic solution. In other words, when the temperature rises above the melting point of the separator due to the heat generation of the battery, the porous part for allowing ion permeation provided in the separator is blocked by melting and prevents ion permeation, and the current is stopped accordingly. A function as a battery is safely stopped by a so-called shutdown function.

In order to give such a safety function to the separator, a thermoplastic resin porous film that melts at a low temperature is necessary, and a polyolefin microporous film is often used. For example, a polyethylene microporous membrane “Hypore” (registered trademark) sold by Asahi Kasei Chemicals Corporation is an example.
In this way, batteries using flammable organic electrolytes typified by lithium-ion batteries have various safety measures including other safety devices. However, with the advancement of batteries, further improvement in performance is required. It has been.

  Battery heat generation is not only caused by its own reaction heat, but also becomes dangerous when heated from the outside.For example, when dropped in heated oil, the ambient atmosphere becomes abnormally high, and the internal temperature of the lithium ion battery becomes the separator melting temperature. Assuming that the above is the case, the shutdown function of the separator works first and the function as a battery is lost. After that, when the external heating continues and the internal temperature of the battery rises, the nonporous film-like separator may be damaged by heat shrinkage or fluidization, or the pressure that is applied between the positive and negative electrodes, that is, during winding The separator softened by the pressure of the electrode due to the tension of the battery or the increase in the electrode volume due to battery charging / discharging, etc., is pressed, the electrodes are brought into contact with each other and short-circuited.

When the battery is in some thermal abnormal state, it has a design philosophy that various protection measures work on the battery power system and the safety as a whole is ensured, but in the case of a large battery for automobiles, Compared to mobile applications, the capacity is high, and higher technology is required for the safety of the battery itself.Especially, the distance between the electrodes is maintained even when the battery is abnormally heated internally or abnormally heated from the outside. The separator is required to have a strong electronic insulating property that does not sag and short-circuit. The adoption of large batteries for driving automobiles has attracted attention as an environmental measure to reduce CO ₂ , and hybrid electric vehicles combining reciprocating engines and nickel metal hydride batteries have already been put into practical use.

  Nickel metal hydride batteries use a caustic potash solution as the electrolyte, and there is no risk of ignition when overheated. Since both the positive and negative electrodes are sintered metals, electrode active materials are almost eliminated and electrode products are generated. No. Therefore, the separator hardly requires the filter effect of these fallen products and products, and rather, hydrophilic performance is required with a gap that does not crush between the hard electrode active materials and does not prevent ion permeation. A sulfonated nonwoven fabric made of polypropylene suitable for the function is used as a separator.

On the other hand, lithium ion batteries have begun to attract attention in order to increase the energy efficiency of hybrid electric vehicles, but improvement of thermal stability is a major issue. If this problem is overcome, it is considered that the use of large-sized lithium ion batteries will start rapidly not only in hybrid type with reciprocating engines but also in fuel cell hybrid type vehicles and pure type electric vehicles.
The thermal stability of the lithium ion battery is to ensure high safety even when the battery is placed in an abnormally high temperature atmosphere, and improving the function of the separator is one of the countermeasures. is there.

In order to ensure safety inside the battery in the separator, not only does the separator close to the melting point of the separator, for example, a polyethylene microporous film, the microporous film closes at around 130 ° C. and becomes a film, preventing the permeation of ions. Even when the battery temperature rises, a new technique is required such that a nonporous polyethylene microporous membrane separator in the form of a film covers the electrode while preventing the short circuit while keeping the film shape firmly.
It is considered effective to maintain the distance between the electrodes with an insulating inorganic material that does not melt by heat in order to completely maintain the electronic insulation, that is, the function expected of the separator in such a battery overheated state.
In order to use an insulating inorganic substance as a separator, considering a winding process at the time of battery production, etc., use a nonwoven fabric that is a flexible fabric structure because flexibility is required on the separator structure, A method is conceivable in which insulating inorganic powder is filled in the gaps between the fibers forming the nonwoven fabric and heated and fixed.

For example, a lithium ion battery separator having excellent heat resistance, in which powder silica, which is an insulating inorganic powder, is fixed and held between coating fibers on a non-woven fabric made of polyester resin. When this separator is used, even when the lithium ion battery becomes abnormally high for some reason, the distance between the electrodes is maintained because the polyester resin with high heat resistance is used, and the battery becomes hotter. Even when the polyester fiber is softened, the distance between the electrodes is maintained by the powder silica interposed in the fiber gap, so that a short circuit is prevented and it is effective for ensuring safety at high temperatures.
However, when producing a lithium ion battery, a considerable tension is applied in the process of winding the electrode and the separator, and the separator is pulled and wound at a high speed. As a result, powder silica falls off due to friction, and the expected heat resistance function of the separator is not perfect.

  In addition, the high-melting integrity battery separator for a lithium ion battery described in Patent Document 1 is formed by adhering a thermoplastic resin microporous membrane having a low-temperature shutdown characteristic and a non-woven flat sheet, that is, a non-woven fabric. It is also possible to perform coating or surface treatment. Further, the high melt integrity battery separator focuses on the method of bonding the microporous membrane and the non-woven flat sheet, i.e., non-woven fabric, as the non-woven fabric, thermoplastic polymer having high temperature melt integrity, cellulose derivative and / or A battery separator made of a polymer selected from the group consisting of ceramics is described.

Therefore, the invention described in Patent Document 1 shares the function by giving the microporous membrane a low-temperature shutdown characteristic and heat resistance of the nonwoven fabric to prevent contact between the positive electrode and the negative electrode at high temperatures. is there.
JP 2005-38854 A

  The present invention provides a fabric separator that can be used effectively for many types of batteries and capacitors, and in particular, can improve safety during overheating of a large-sized lithium ion battery represented by a power source for driving an automobile, and a method for manufacturing the same. The purpose is to do.

In order to solve the above problems, the present inventors have intensively studied and completed a fabric separator having high thermal stability required for many batteries and capacitors, particularly large batteries.
That is, the present invention is as follows.
(1) From a fabric comprising inorganic powder in an amount of 40% by mass to 95 % by mass, a polyolefin resin having a viscosity average molecular weight (Mv) of 3 million or more, and a fiber having a porosity of 20% or more The separator for lithium ion batteries characterized by becoming.
(2) an inorganic powder containing 95 mass% or less than 40 wt%, viscosity-average molecular weight (Mv) 300 million in consists more polyolefin resin, and a porosity of the fabric comprised of fibers at least 20% A separator for a lithium ion battery , wherein a thermoplastic resin porous film having a shutdown effect is laminated on at least one surface of the separator.
(3) Lithium-ion battery using the separators described in the above (1) or (2).
( 4 ) Viscosity average molecular weight (Mv) 3 million or more polyolefin resin, inorganic powder , obtained by extracting the solvent after passing through a step of forming a mixture containing the polyolefin resin solvent into a fiber using a hot melt extrusion apparatus A method for producing a fabric , wherein fibers containing 40% by mass or more and 95% by mass or less of inorganic powder and having a porosity of 20% or more are formed into a fabric by a nonwoven fabric manufacturing method.

  According to the fabric-like separator of the present invention, it is possible to give a battery or a capacitor higher safety, and it may occur not only at the time of higher temperature but also at the time of current interruption by preventing ion permeation when the condenser is abnormally overheated. It is possible to prevent dielectric breakdown of a separator and to prevent thermal escape due to an electrode short circuit.

The separator of the present invention is made of a fabric made of thermoplastic fibers (hereinafter simply referred to as “fibers of the present invention”) containing inorganic powder in an amount of 40% by mass to 95% by mass. The separator of the present invention is constituted by the fibers by softening and melting the fibers even when the battery is heated due to a short circuit or the like and becomes overheated, and even near the melting temperature of the thermoplastic resin. The voids are reduced, the permeability of ions contained in the electrolytic solution is reduced, and it becomes difficult for current to flow. As a result, heat generation can be suppressed by eliminating the battery function.
Also, when the ion permeation could not be completely prevented even by softening and melting of the separator or when the battery temperature continued to rise due to some cause of overheating of the battery, such as external heating, for example, the polyethylene resin used as the thermoplastic resin Although there is a concern that a short circuit may occur without resisting the pressure between the two electrodes, the separator of the present invention is made of an insulating inorganic powder contained in a large amount in the fiber even when such a severe state is shifted. The distance between the two poles is maintained to prevent a short circuit, and then another battery safety mechanism is activated, and the battery can be proposed as a battery separator having an epoch-making safety function capable of reaching the end of safety.

  Furthermore, in the separator of the present invention, since the inorganic powder is contained in the fiber, when the separator travels in a processing operation such as a winding process at the time of battery creation, due to external force due to bending by a guide or rubbing at high speed travel Dropping can be reduced, and as a result, the insulation between the two electrodes can be maintained at a high temperature even in a high temperature state.

As the inorganic powder used in the present invention, many things such as metal powder, alloy powder, non-metal powder such as carbon and ceramics can be used, and among them, when insulating inorganic powder is used The separator is more preferable because it can be a high-performance capacitor separator. Insulating inorganic powders include Li ₂ O, BeO, B ₂ O ₃ , Na ₂ O, MgO, Al ₂ O ₃ , SiO ₂ , P ₂ O ₅ , CaO, Cr ₂ O ₃ , Fe ₂ O ₃ , Oxides such as ZnO, ZrO ₂ and TiO ₂ , nitrides such as zeolite, BN, AlN, Si ₃ O ₄ and Ba ₃ N ₂ , carbonates such as SiC, ZrSiO ₄ , MgCO ₃ and CaCO ₃ , CaSO ₄ sulfate salts such as BaSO _4, steatite (MgO · SiO _2), forsterite (2MgO ₂ · SiO _2), a ceramic such as cordierite _{(2MgO 2 · 2Al 2 O 3} · 5SiO 2) can be used. In this case, the larger the volume occupancy ratio of the insulating inorganic powder in the fiber is to keep the distance between the electrodes at a high temperature, that is, to make it difficult to short-circuit, the insulating inorganic powder should have a low density, for example, In particular, the use of oxides such as silica, aluminum oxide, and magnesium oxide is more preferable.

The mixing ratio of the inorganic powder and the thermoplastic resin in the fiber can be determined by the following method. When the crucible is put in an electric furnace in advance and air-baked at 900 ° C. for 1 hour, taken out from the electric furnace, cooled in a desiccator for about 1 hour and then weighed with an electronic balance, and the weight difference between the crucibles becomes 0.0010 g or less. Is the constant weight W1 (g) of the crucible. Next, about 5 g of fiber was weighed to 4 decimal places with an electronic balance to make W2 (g), put into a constant crucible, immediately placed in an electric furnace and heated at 800 ° C. for 1 hour to incinerate the thermoplastic resin. The crucible is taken out, placed in a desiccator, cooled for about 1 hour, and weighed with an electronic balance to obtain W3 (g).
The mass% of the inorganic powder in the fiber is obtained by the following formula (1).
Inorganic powder mass% = [(W3-W1) / W2] X100 Formula (1)

  The amount of the inorganic powder contained in the fiber is 40% by mass or more and 95% by mass or less, but preferably 70% by mass or more and 95% by mass or less in order to exhibit the properties of the inorganic powder, and 40% by mass from the viewpoint of fiber strength. % To 80% by mass is more preferable. In particular, in the case of an inorganic powder having a small specific gravity such as silica, 80% by mass or less is preferable for manufacturing reasons.

Since the separator of the present invention uses thermoplastic fibers containing a high concentration of inorganic powder, it can prevent shrinkage due to heat. This is because the shrinkage action of the thermoplastic resin constituting the fibers is hindered by a large amount of inorganic powder as a support, and there is almost no thermal shrinkage as compared with the fabric separator made of only the thermoplastic resin. For this reason, when the capacitor separator using the fabric separator of the present invention is used for a battery or a capacitor, the separator does not thermally contract even when these capacitors are overheated, and the positive / negative generated frequently. Since the short circuit phenomenon by the end surface of an electrode does not occur, it can contribute to higher safety.
In addition, the separator of the present invention can be used as a material for a stable substrate that prevents thermal shrinkage, and can mix and stably maintain a high concentration of inorganic powder. By selecting the characteristics, it can be effectively used for applications having thermal conductivity, electrical conductivity, ion adsorption or catalytic action.

  The thermoplastic resin constituting the fiber of the present invention can be used as long as there is no problem with the electrolytic solution used in individual capacitors and the electrical stability. For example, polyethylene, polypropylene, polystyrene AS resin, ABS resin, polyvinyl chloride, polyvinylidene chloride, polymethyl methacrylate, polyester resin, polyamide resin, polycarbonate resin, ethylene vinyl alcohol copolymer, polyacetal resin, polyether ether ketone resin, polytetrafluoroethylene and polyfluoride Examples thereof include a fluororesin such as vinylidene, and these resins may be used alone or in combination. When the separator of the present invention is used in a lithium ion battery which is an important battery as a mobile power source or a high capacity power source, the fiber is more preferably made of a polyolefin resin.

The fiber of the present invention preferably has a porosity of 20% or more, more preferably 30% or more, and still more preferably 40% or more. The porosity of the fiber can be calculated from the ratio of the fiber density calculated based on the weight ratio of the thermoplastic resin and the inorganic powder contained in the fiber and the measured fiber density. That is, the porosity D% is obtained by the following formula (2).
Porosity D (%) = 100 * [A− (B + C)] / A Formula (2)
In the above formula (2), A represents the volume of the fiber, B represents the volume of the inorganic powder in the fiber, and C represents the volume of the resin in the fiber, which are determined as follows.
Fiber volume A [cm ³ ] = fiber length (A) [cm] * fiber area (B) [cm ² ]
Inorganic powder volume B (cm ³ ) in fiber = inorganic powder weight b (g) ^* / inorganic powder density (g / cm ³ )
Inorganic powder weight b ^* is based on ash measurement
Resin volume in fiber C (cm ³ ) = (fiber weight a−inorganic powder weight b) (g) / resin density (g / cm ³ )
When fibers having a porous structure with a high porosity are used, the electrolyte solution penetrates into the pores of the fiber and is also retained between the fabric structures composed of the fibers, thereby maintaining more electrolyte solution for a long period of time. This is preferable because the battery characteristics can be greatly improved.

The fiber diameter of the present invention is not particularly limited, but is preferably 1 μm or more and 10 μm or less in order to obtain a uniform and high-strength fabric.
The basis weight of the fabric of the present invention can be appropriately selected depending on the use, but from the viewpoint of prevention of short circuit at high temperature, it is 20 g / m ² or more, in particular, the content of inorganic powder in the fiber is 40 mass% or more and 90 mass%. The fabric weight per unit area is 20 g / m ² or more, further 30 g / m ² or more, and the content of the inorganic powder in the fiber may be 40% by mass or more and 80% by mass or less. preferable. Here, the basis weight represents the fabric of the present invention in terms of weight per unit area, and the measurement method depends on the conditions of JIS-K7100.

That is, A (m ² ) obtained by allowing the fabric to stand under a constant temperature and humidity condition for a predetermined time and then measuring the area, and then the weight B (g) obtained by measuring the weight of the sample with an electronic balance. From the following equation (3)
Weight per unit area C g / m ² = B / A Formula (2)

The fabric of the present invention may contain other fibers, preferably thermoplastic fibers, in addition to the inorganic powder-containing fibers as long as the object of the present invention is not impaired. As resin which comprises such a thermoplastic fiber, the thing similar to the thermoplastic resin which comprises the said inorganic powder containing fiber can be used.
In the separator of the present invention, a thermoplastic resin porous membrane or a thermoplastic fiber fabric can be laminated on the above fabric. The thermoplastic resin porous membrane refers to a film-like one having a porous structure by a stretching method, a phase separation method, a mixed extraction method, a sintering method, etc. using a thermoplastic resin. This refers to a fiber that is extruded by melt spinning or the like using a plastic resin.
The thermoplastic resin constituting the thermoplastic resin porous membrane or thermoplastic fiber is low density polyethylene, linear low density polyethylene, high density polyethylene, ultra high density polyethylene, etc. from the viewpoint of processability, cost, and environmental safety. Polyolefin resins such as polyethylene, copolymers of ethylene / propylene, ethylene / vinyl acetate, polypropylene, cyclic polyolefin / copolymers, and the like are preferable. The laminated separator can be obtained, for example, by laminating a thermoplastic resin porous membrane or a thermoplastic fiber cloth on at least one surface of the cloth and integrating them by means of a thermocompression bonding method, an ultrasonic bonding method, an adhesive method, or the like. It is done.

  When the storage battery separator integrated in this way is used as, for example, a lithium ion battery separator, it is possible to more reliably prevent ion permeation at around 130 ° C. in the early stage of temperature rise. That is, when the lithium ion battery is exposed to the melting point of the thermoplastic resin porous membrane or more, the thermoplastic resin porous membrane melts into a non-porous film, and exhibits a shutdown effect that is a safety mechanism currently used. At the same time, it is easily bonded to the softened fibers constituting the cloth-like separator and contributes to more completely closing the gaps between the fibers narrowed by overheating, thereby preventing the permeation of ions more completely.

  For example, a polyethylene resin is used as a thermoplastic resin constituting a fabric, a polyethylene porous membrane is used as a thermoplastic resin porous membrane laminated on the fabric, and a separator for a battery unit is formed by integrating both of them into a lithium ion battery. When the battery is overheated, the polyethylene porous membrane is first softened and melted around 130 ° C., which is the melting point temperature, to become non-porous to form a film, and at the same time, the fibers constituting the separator are softened and melted. The effect | action which fills a space | gap between gaps is produced and safety | security can be improved also when using a thermoplastic resin fiber similarly.

  Further, a fabric A made of fibers formed by mixing insulating inorganic powder and polyethylene resin, and a cloth B made of fibers not containing inorganic powder but using only polyethylene resin as a thermoplastic resin, are A / B. / A laminate, molded into a fabric by thermocompression bonding, etc., and used as a separator for a lithium ion battery, the battery becomes overheated and the thermoplastic resin fibers in the intermediate layer under conditions above the polyethylene resin melting temperature B softens and melts to form a film in the same manner as the porous film and becomes non-porous, while the fabric A softens and ion permeability can be completely prevented. Thereafter, even when the temperature rises due to some reason, the fabric A has the insulating inorganic powder, so that the short circuit between the electrodes can be prevented.

Although there is no restriction | limiting in particular in the thickness of the separator of this invention, For example, they are 10 micrometers or more and 100 micrometers or less.
The separator of the present invention, for example, after a step of forming a mixture containing 5 to 60 parts by mass of a thermoplastic resin and 40 to 95 parts by mass of an inorganic powder into a fibrous form such as a melt extrusion method, It is obtained by a method including a step of forming a fabric from fibers.
In order to obtain a separator in which a very large amount of inorganic powder is mixed, it is preferable that a thermoplastic resin solvent be included in the mixture. This is because when the solvent is contained, a large amount of inorganic powder can be mixed to form a fiber. Specific examples of the solvent for the thermoplastic resin include a poor solvent in which the thermoplastic resin dissolves at a high temperature. From the viewpoint of operability, cost, and imparting porosity to fibers, liquid paraffin, DOP, decalin, and the like. Is preferred. The amount of the solvent is not particularly limited, but when the mixture of the thermoplastic resin and the inorganic powder is 100 parts by mass, it is 200 parts by mass or more and 800 parts by mass or less, and further 300 parts by mass or more and 600 parts by mass or less. It is preferable that

  Moreover, in order to make the fiber obtained by using the polyethylene resin as the thermoplastic resin thin and high in strength, it is preferable that the polyethylene resin used has a large molecular weight, and the viscosity average molecular weight Mv is 3 million or more. More preferably, it is appropriate to use Mv 6 million or more. For this reason, it is desirable to use a polyethylene resin having a molecular weight as large as possible in order to obtain a fiber having a higher strength and containing more inorganic powder.

  The separator of the present invention is subjected to a step of forming a mixture containing a thermoplastic resin and an inorganic powder, or a mixture containing a thermoplastic resin solvent into a fiber shape by a hot melt extrusion apparatus or the like, and then adding a solvent as necessary. A process of forming fibers obtained by volatilization or extraction into a fabric, that is, a method of forming into a fabric by a woven or non-woven fabric manufacturing method, or a fabric obtained by extruding fibers obtained by extrusion into a fiber into a fabric or the like After forming into a shape, it is obtained through a method of volatilizing or extracting the solvent.

  In the manufacturing method of this invention, the porosity of a fiber can be adjusted by adjusting the solvent and inorganic powder to be used. For example, when the solvent for forming pores in the fiber is liquid paraffin that is relatively non-volatile even by heat, a mixture containing a thermoplastic resin, an inorganic powder, and a solvent for the thermoplastic resin is subjected to hot melt extrusion. When the solvent is retained in the pores of the fiber formed by phase separation due to temperature drop when extruded from the device, and the solvent remains clogged even after the fiber cools, and the solvent is extracted with the solvent Have fine pores throughout the fiber. Moreover, when the insulating inorganic powder to be used is a porous body, it becomes a fiber having more porosity.

Also, when the thermoplastic resin solvent is volatile, such as decalin, when the mixture containing the thermoplastic resin, the inorganic powder and the thermoplastic resin solvent is extruded into a fiber from a hot melt extruder, the temperature decreases. Vaporization occurs almost immediately after the phase separation in the molten state of the thermoplastic resin, and voids are not formed in the fibers, and the amount of inorganic powder occupying the volume of the fibers can be increased, so the porosity can be easily controlled. Therefore, it is preferable.
The optimum shape of the fabric-formed body obtained by the present invention varies depending on the intended use. For example, in order to obtain a capacitor separator by a nonwoven fabric manufacturing method, the gap formed between fibers when the basis weight is small, that is, the pore diameter is large and the variation is also large. growing. In addition, the thickness of the fibers to be formed is also important, and if the fabric weight is the same, it is possible to reduce the hole diameter and variation by forming the thin fibers as much as possible, but there are problems in strength and productivity.

Therefore, when forming a fabric by a nonwoven fabric manufacturing method, a layer in which a part of the cross-sectional direction is deposited with as thin fibers as possible is formed to reduce the pore diameter, and the other layer is formed with relatively thick high-strength fibers. Creating layers, that is, forming multiple layers and integrating them is also an effective means for function sharing.
In order to obtain a capacitor separator by the method of the present invention, for example, a polyethylene resin containing an ultra-high molecular weight as a thermoplastic resin, hydrophobic SiO ₂ as an insulating inorganic powder, and liquid paraffin are uniformly mixed as a raw material, Introduced into a hot extruder and extruded as fibers from a number of spinning nozzles in a high-temperature melted state, after being shaken down on a belt-like conveyor, pressurized between superheated rolls to fuse the fibers into a fabric. Then, it introduce | transduces into the solvent bath which dissolves the liquid paraffin which is a solvent of polyethylene, and a solvent is dried, and the fabric-like separator of this invention is obtained.
Similarly, after becoming a fiber, a thermoplastic resin solvent such as liquid paraffin is extracted, then formed into a cloth shape, and formed into a fabric separator by thermal fusion, fiber entanglement with an adhesive or fluid, and the like. Can be used as a separator.

The separator manufacturing method of the present invention has an excellent effect compared to the conventional separator manufacturing method. For example, a lithium-ion battery separator is required to have a porous body that is thinner and higher in strength and has fine pores as long as there is no problem in battery performance. In the case of porous membrane separators, increasing the strength is generally done by selecting the resin composition or physically pulling it and molecular orientation, that is, stretching, but stretching the membrane is an area expansion and is practical for high stretching. In addition to its limitations, the equipment is expensive and unrealistic.
In addition, when producing a porous film containing inorganic powder at a high concentration with respect to the thermoplastic resin, the high concentration of the inorganic powder prevents the stretching along with the stretching, ie, the thickness of the membrane decreases. In addition to being difficult, the membrane may be broken due to inorganic powder and the productivity of the porous membrane is not excellent. On the other hand, the production method of the present invention can produce a large amount of fine and strong fibers because the molecules are highly aligned by high speed and high stretch by the spinning method. Since such a fiber-like separator is formed by such fibers, there is an advantage that the strength per unit area is much higher than that of a microporous membrane made of the same thermoplastic resin. When obtaining a separator for a capacitor by the nonwoven fabric production method, the biggest drawback is that the pore diameter of the formed pore is large and the pore diameter variation is large, and this is considered to be because the fiber is thicker than the porous membrane.

As a solution to this, it is preferable to reduce the dispersion by increasing the number of fiber laminations by reducing the fiber diameter, for example, a nonwoven fabric manufacturing method such as a melt blow method or a high-strength fiber, a flash spinning method, or the like. And a spunbond combination are also effective, or even after forming the nonwoven fabric, a method of crushing the fibers by heat-bonding with a heat roller or the like can obtain a uniform high-strength nonwoven fabric with small inter-fiber gaps, that is, pore diameter and hole diameter variation. By utilizing this technique, a battery separator that is an epoch-making fabric separator can be obtained.
In addition, a method of cutting a spun fiber into a short fiber, dispersing in water or the like to obtain a non-woven fabric by a method such as papermaking, the fiber dispersibility is improved, variation is small, and the pore diameter is uniform. This is one of the preferred methods for obtaining the fabric.

  Such a method according to the present invention makes it possible to produce a lithium ion battery separator that requires the most uniform, small pore diameter and thin film as a capacitor separator, and confirms the operation of the shutdown function in an abnormally high temperature test of the battery. Even when the temperature was raised, it was proved that the battery was stable until another safety device worked, and the object of the present invention was achieved.

The present invention also includes a lithium ion battery using the above-described battery separator. Such a lithium ion battery can be manufactured by the following method, for example. Separator and strip positive electrode of the present invention (lithium cobalt composite oxide LiCoO ₂ as an active material, flake graphite as a conductive agent, acetylene black, and polyvinylidene fluoride (PVDF) as a binder are dispersed in N-methylpyrrolidone (NMP). Obtained by coating the both sides of the aluminum foil with a slurry prepared) and a strip-shaped negative electrode (artificial graphite as an active material, ammonium salt of carboxymethyl cellulose and a styrene-butadiene copolymer latex as a binder are dispersed in purified water) Obtained by applying a slurry prepared on both sides of the copper foil, etc.), and then winding the strip-shaped negative electrode, separator, strip-shaped positive electrode, separator in the order of a plurality of times in a spiral shape, Electrode plate lamination by pressing The to produce. The produced electrode plate laminate is housed in an aluminum container, the aluminum lead led out from the positive electrode current collector is connected to the container wall, and the nickel lead led out from the negative electrode current collector is connected to the container lid terminal portion. Further, the non-aqueous electrolyte described above is injected into the container and sealed.

The present invention will be specifically described by the following description, but the present invention is not limited thereto. Unless otherwise specified, parts and% are based on mass. Moreover, the measuring method used by this invention was based on the following method.
(1) Gurley air permeability Measured according to JIS P-8117 using a Gurley type densometer (manufactured by Toyo Seiki).
(2) Thickness An average value measured at three points with a minute thickness gauge (“KBM thickness gauge” manufactured by Toyo Seiki Co., Ltd.) was used. The constant side pressure was 63.7 ± 7.5 kPa, the measurement terminal diameter was 5 ± 0.05 mm, and measured at 23 ± 3 ° C. atmosphere.
(3) Average pore diameter The average pore diameter was measured by a mercury porosimeter method using a measuring device “Shimadzu Autopore” (trademark, manufactured by Shimadzu Corporation), and the mode diameter was defined as the average pore diameter.

[Example 1]
Mv 6 million powdered polyethylene “Hi-Zex Million 630M” (trademark, manufactured by Mitsui Chemicals), powdered SiO ₂ “Nipseal LP” (trademark, manufactured by Tosoh Silica), and liquid paraffin “Molesco White p-260” (trademark, Matsumura) Made by Petroleum Laboratories Co., Ltd.) were weighed 32 parts, 8 parts, and 160 parts, respectively, and A composition, and 28 parts, 12 parts, and 140 parts were weighed, and B composition, 24 parts, 16 parts, 120 Partly weighed C composition, 16 parts, 24 parts, and 100 parts weighed D composition. According to these compositions, powdered polyethylene and powdered SiO ₂ are first mixed in a mixer and then mixed uniformly, then a predetermined amount of liquid paraffin Is added to the extruder and fed to an extruder, heated to 200 ° C. to be mixed and melted, and the fibers from the spout attached to the extruder outlet. Created extrusion, winding the composition A at the bobbin, B, C, and four fabric samples made of D to. These four types of fibers are extracted with a liquid paraffin solvent at 25 ° C., dried, individually cut to about 2 cm, layered in a cotton form with a card, pressed with a heating roll, and made into a very thin film as a fabric. A fabric having a basis weight of 30 g / m ² was produced.

The obtained fabric-like sample was placed on a copper plate, a nickel metal rod having a diameter of 2 cm and a weight of 200 g was placed on the sample, left in an atmosphere of 150 ° C. for 10 minutes, and then taken out. The presence or absence of energization was confirmed by applying a voltage of. As a result, it was confirmed that the A composition and the B composition were energized. This suggests that a separator that requires insulation at least in a high-temperature state needs to have a powdered SiO ₂ content in the fibers forming the fabric of 40 % by mass or more.

[Example 2]
It is considered that the fiber characteristics are influenced by the molecular weight of the thermoplastic resin used when the thermoplastic resin is made into a fiber shape by containing inorganic powder at a high concentration. In this example, a polyethylene resin is used as the thermoplastic resin, and the relationship with the fiber physical properties is examined using materials having different viscosity average molecular weights.
Mv 3.3 million powdered polyethylene “Sunfine UH900” (trademark, manufactured by Asahi Kasei Chemicals), powdered SiO ₂ (same example 1), and liquid paraffin (same example 1) were weighed as 15 parts, 25 parts, and 80 parts, respectively. Those having E composition, and those having 12 parts, 28 parts, and 80 parts, respectively, were F compositions. Similarly, powdered polyethylene (same example 1) with Mv 6 million (same example 1), powdered SiO ₂ (same example 1), liquid paraffin (same example 1) as weighed 15 parts, 25 parts and 80 parts, respectively, G composition, 12 Parts, 28 parts, and 80 parts were designated as H composition. Those having these compositions were melt-extruded in the same manner as in the operation method described in Example 1 to obtain a fibrous material, wound around a bobbin, and extracted with a liquid paraffin solvent to obtain a fiber sample.
What was obtained as a fiber sample had G and H compositions, but the fibers of E composition were weak and could not be completely wound on a bobbin, and those of F composition could not be molded as fibers. As a result, it was proved that increasing the molecular weight of polyethylene contained a large amount of inorganic powder and improved fiber strength.

[Example 3]
Since the increase in the concentration of the inorganic powder content decreases the strength of the fibers formed by the decrease in the amount of the thermoplastic resin, it becomes difficult to form a fabric. The present embodiment is performed in order to grasp the limit amount. Ultra-high molecular weight polyethylene capable of obtaining high strength, that is, 12 parts by weight and 28 parts by weight of powdered polyethylene having Mv 6 million (same Example 1), powdered SiO ₂ (same Example 1) and liquid paraffin (same Example 1), respectively. 80 parts weighed are I composition, 10 parts, 30 parts, 80 parts are weighed J composition, 8 parts, 32 parts, 80 parts are weighed K composition, 4 parts, 36 parts, 80 parts a material obtained by parts weighed and L composition, like "Hizex Million 630M" (manufactured by TM Toho Zinc Co., Ltd.) powder SiO ₂ (the first embodiment) than the specific gravity larger powder ZnO of "Ginrei A90-1", liquid paraffin (same embodiment What weighed 10 parts, 30 parts and 80 parts of Example 1) as M composition, and similarly weighed 8 parts, 32 parts and 80 parts, and weighed N parts, 4 parts, 36 parts and 80 parts. O composition, 2 , 38 parts of a material obtained by weighing 80 parts is P composition. These were melt-extruded in the same manner as in the operation method described in Example 1 to obtain a fibrous material, wound around a bobbin and extracted with a liquid paraffin solvent to obtain a fiber sample.
As a result, the I, J, M, N, and O compositions were normally made into long fibers and could be wound with a bobbin, but the L composition was completely impossible to obtain a fibrous form. Also. Although the K and P compositions are fibrous, they are very fragile and often cut, but they could be formed as short fibers and laminated to form a fabric.

From this example and Example 2, when powdered SiO ₂ having a low specific gravity is used as an inorganic powder in powdered polyethylene, the inorganic powder concentration is 80 % by mass or less, and powdered ZnO having a large specific gravity is 95 % by mass. The following is preferable, and it has been confirmed that the higher the specific gravity of the inorganic powder, the higher the content concentration can be, and it has been found that 75 % by mass or less of the inorganic powder is desirable in order to obtain fibers stably.

[Example 4]
Mv 6 million powdered polyethylene (same example 1) 8 parts, powdery SiO ₂ (same example 1) 32 parts, liquid paraffin (same example 1) 140 parts were weighed to obtain powdered polyethylene and powdered SiO ₂ After mixing in a mixer and uniformly dispersing, a predetermined amount of liquid paraffin added and further stirred and mixed is sent to an extruder and heated to 200 ° C. to be in a mixed molten state from a T-die die nozzle. At the same time as extrusion, high-temperature air was jetted from both sides of the spinneret to obtain ultrafine fibers in which inorganic powder was dispersed at a high concentration by a so-called melt blow method. The ultrafine fibers were collected on a wire mesh belt to form a fiber deposit, and then pressed between heated rolls to form a nonwoven fabric. Then, it extracted through the bath of 25 degreeC containing the solvent which melt | dissolves a liquid paraffin, and was able to obtain the separator for electrical storage devices of this invention after drying.
The obtained capacitor separator according to the present invention was a nonwoven fabric having a porosity of 52%, a thickness of 42 μm, and a basis weight of 35 g / m ² made of fibers of ultrahigh molecular weight polyethylene 20 % by mass and SiO ₂ 80 % by mass . . This separator is placed on a copper plate, and a nickel metal rod with a diameter of 2 cm and a weight of 200 g is placed on the separator, left in an atmosphere at 150 ° C. for 10 minutes, and then taken out and a voltage of 50 V is applied between the two metals. However, the current did not flow and the separator was visually observed, but the separator was not cut and the shrinkage was hardly observed, and it was confirmed that the gap was maintained between the metal plate and the metal rod even when left at a high temperature.

[Comparative Example 1]
As a result of conducting an experiment by heat-treating a polyethylene microporous membrane having a thickness of 45 μm and a porosity of 41% under the same conditions as in Example 1, it was confirmed that a current flows between both metals, and shrinkage and thinning were remarkable. The through-holes were partially visible, and it was confirmed that the capacitor separator according to the present invention was excellent.

[Example 5]
Mv 6 million powdered polyethylene (same example 1) 18 parts, powdered SiO ₂ (same example 1) 22 parts, liquid paraffin (same example 1) 240 parts in the same operation as example 3 Fabric A was made by laminating the obtained fibers of 45 % by mass of ultrahigh molecular weight polyethylene and 55 % by mass of SiO ₂ , followed by powder of Mv 700,000 “Sunfine UH650” (trademark, manufactured by Asahi Kasei Chemicals). 40 % by mass of polyethylene and 60 % by mass of liquid paraffin (Example 1) are mixed and fed to a melt extruder, heated to 200 ° C. to be in a mixed molten state, extruded at the same time as the silica-mixed fiber, and simultaneously spun. Fabric B is formed on fabric A by blowing a fiber by hot blown air from both sides of the mouth, and then fabric A is again formed on fabric B in the same manner as A / B / A fabric A was obtained and rolled in a hot roll to obtain a separator having a thickness of 44 μm, a porosity of 41%, and a basis weight of 36 g / m ² .

The separator thus obtained was tested at a high temperature to confirm the shutdown effect.
That is, the air permeability of the separator of the present invention processed in this state was 57 seconds / 100 cc by the Gurley method, but this separator was wound around a copper tube and left at 140 ° C. for 10 minutes, and then taken out in the same manner. It was 5650 seconds / 100cc when measured, and the shutdown effect in a high temperature state was confirmed.

[Example 6]
Mv 2 million powdered polyethylene “Sunfine UH850” (trademark, manufactured by Asahi Kasei Chemicals) 20 % by mass and liquid paraffin (Example 1) 80 % by mass are mixed and sent to a melt extruder, heated to 200 ° C. and melted. Then, after extruding from a T-shaped die, longitudinally and transversely stretching, and then extracting liquid paraffin with a solvent at 25 ° C., a porous film having a film thickness of 20 μm and an average pore diameter of 0.06 μm was obtained with the silica-containing nonwoven fabric obtained in Example 4. A partial separator was bonded with a hot-melt adhesive to form a composite separator, which was heat treated by placing it in an oven at 140 ° C. for 5 minutes, and then taken out and tested for a shutdown effect due to a change in air permeability. As a result, the Gurley air permeability before the heat treatment was 210 seconds / 100 cc, but after the heat treatment was 10,000 seconds / 100 cc or more, and a complete shutdown effect was seen. The insulation effect in the high temperature state of Example 3 was low at low temperatures. A shutdown effect could be added.

Since the separator of the present invention can hold a large amount of inorganic powder, an electromagnetic wave absorber, a heat transfer / heat dissipation structure, an electrode structure, a dimensional stability support, an adsorption structure, a catalyst structure, a filter medium, and a capacitor separator However, it is particularly preferable to use it for a capacitor separator from the viewpoint of being a thin film and requiring heat resistance. The separator for a battery of the present invention has a stable performance especially at a high temperature as a separator for lithium ion battery, a separator for electric double layer capacitor, or a separator for other organic solvent battery, which is particularly expected as an energy source for driving an automobile. It can be suitably used as a high safety separator.
Furthermore, in addition to containing a high concentration of inorganic powder in the fiber, when the fiber having a porous structure with a high porosity is formed in a fabric shape, the electrolyte solution penetrates into the pores of the fiber, In addition, it is also retained between fabrics composed of the fibers, and more electrolyte can be maintained for a long period of time, so that battery characteristics can be greatly improved. In particular, it is particularly effective for applications that require a large amount of ions dissolved in the electrolyte.

It is the schematic showing the cross-sectional view of one horizontal direction of the inorganic powder containing thermoplastic fiber (an example) of this invention. It is the schematic showing the fabric (an example) of this invention. It is the schematic showing the cross-sectional structure at the time of heating the fabric (an example) of this invention, and it. It is the schematic showing the cross-sectional structure at the time of heating the fabric (an example) of this invention comprised from the inorganic powder containing thermoplastic fiber and thermoplastic fiber. It is the schematic showing the cross-sectional structure at the time of heating the structure (an example) which bonded the thermoplastic resin porous film to the fabric of this invention, and the structure.

Explanation of symbols

1 Inorganic powder 2 Thermoplastic resin 3 Hole 4 Fiber (thermoplastic resin + inorganic powder)
5 Fiber (thermoplastic resin)
6 Porous membrane 7 Melted porous membrane

Claims (4)

It is made of a fabric comprising inorganic powder in an amount of 40% by mass to 95 % by mass, a polyolefin resin having a viscosity average molecular weight (Mv) of 3 million or more, and a fiber having a porosity of 20% or more. A lithium ion battery separator. At least one surface on a fabric comprising inorganic powder in an amount of 40% to 95% by mass, a polyolefin resin having a viscosity average molecular weight (Mv) of 3 million or more, and a porosity of 20% or more. A separator for a lithium ion battery , wherein a thermoplastic porous film having a shutdown effect is laminated on the separator. Lithium-ion batteries using the separators of claim 1 or 2. The viscosity-average molecular weight (Mv) 300 10,000 or more of the polyolefin resin, inorganic powder, the mixture containing the solvent of the polyolefin resin through the steps of forming a fibrous thermally melt extrusion apparatus, the inorganic powder obtained by extracting the solvent A method for producing a fabric , wherein fibers containing 40% by mass or more and 95% by mass or less of a body and having a porosity of 20% or more are formed into a fabric by a nonwoven fabric manufacturing method.

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